U.S. patent application number 15/290052 was filed with the patent office on 2017-02-02 for display panel, data processor, and method for manufacturing display panel.
The applicant listed for this patent is Semiconductor Energy Laboratory Co., Ltd.. Invention is credited to Yoshiharu HIRAKATA, Koji KUSUNOKI, Shunpei YAMAZAKI.
Application Number | 20170033172 15/290052 |
Document ID | / |
Family ID | 57112215 |
Filed Date | 2017-02-02 |
United States Patent
Application |
20170033172 |
Kind Code |
A1 |
YAMAZAKI; Shunpei ; et
al. |
February 2, 2017 |
DISPLAY PANEL, DATA PROCESSOR, AND METHOD FOR MANUFACTURING DISPLAY
PANEL
Abstract
Provided is a novel display panel that is highly convenient or
reliable, a novel data processor that is highly convenient or
reliable, or a method for manufacturing a novel display panel that
is highly convenient or reliable. The display panel includes a
pixel and a terminal electrically connected to the pixel. The pixel
includes a first insulating film, a first contact portion in a
first opening provided in the first insulating film, a pixel
circuit electrically connected to the first contact portion, a
second contact portion electrically connected to the pixel circuit,
a first display element electrically connected to the first contact
portion, and a second display element electrically connected to the
second contact portion. The first insulating film includes a region
lying between the first display element and the second display
element. The terminal includes a surface at which contact with
other component can be made.
Inventors: |
YAMAZAKI; Shunpei; (Tokyo,
JP) ; KUSUNOKI; Koji; (Kawasaki, JP) ;
HIRAKATA; Yoshiharu; (Ebina, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Semiconductor Energy Laboratory Co., Ltd. |
Atsugi-shi |
|
JP |
|
|
Family ID: |
57112215 |
Appl. No.: |
15/290052 |
Filed: |
October 11, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
15092221 |
Apr 6, 2016 |
|
|
|
15290052 |
|
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02F 1/133512 20130101;
G02F 2001/136222 20130101; G06F 3/0416 20130101; G02F 1/13452
20130101; G02F 2001/13398 20130101; G06F 3/03547 20130101; G09G
2380/02 20130101; G02F 1/1339 20130101; G02F 1/1362 20130101; G09G
3/2003 20130101; G02F 1/133514 20130101; G02F 1/133555 20130101;
G02F 1/134309 20130101; G02F 1/13338 20130101; G09G 3/2007
20130101; G02F 1/133345 20130101; H01L 27/3267 20130101; G02F
1/133553 20130101; G09G 2330/021 20130101; G02F 1/134336 20130101;
G02F 1/136227 20130101; G09G 3/3677 20130101; G09G 3/3233 20130101;
G02F 2001/134345 20130101; G02F 1/1368 20130101; G02F 1/1337
20130101; H01L 27/3232 20130101; G02F 1/136286 20130101; G09G
3/3648 20130101; G02F 1/1334 20130101; G06F 3/04164 20190501; G09G
2310/08 20130101; G06F 2203/04103 20130101; G09G 2300/023 20130101;
G09G 2320/0247 20130101; G02F 1/13624 20130101; G02F 2201/44
20130101; G06F 2203/04102 20130101; G02F 1/13394 20130101; H01L
2227/323 20130101; G02F 1/133305 20130101 |
International
Class: |
H01L 27/32 20060101
H01L027/32; G02F 1/1368 20060101 G02F001/1368; G02F 1/1345 20060101
G02F001/1345; G02F 1/1333 20060101 G02F001/1333; G02F 1/1335
20060101 G02F001/1335 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 13, 2015 |
JP |
2015-081519 |
Jun 8, 2015 |
JP |
2015-115638 |
Jul 30, 2015 |
JP |
2015-150202 |
Claims
1. A method for manufacturing an electronic device comprising the
steps of: forming a first conductive film over a substrate; forming
an insulating film over the first conductive film; forming an
opening in the insulating film that reaches the first conductive
film; forming a second conductive film over the insulating film and
electrically connected to the first conductive film through the
opening; separating the substrate from the first conductive film;
and exposing the first conductive film by separating the
substrate.
2. The method for manufacturing the electronic device according to
claim 1, further comprising a step of forming a third conductive
film, wherein the first conductive film is located between the
insulating film and the third conductive film, and wherein the
third conductive film is in contact with the first conductive
film.
3. The method for manufacturing the electronic device according to
claim 1, further comprising a step of forming a terminal, wherein
the conductive film is located between the insulating film and the
terminal, and wherein the terminal is in contact with the first
conductive film.
4. The method for manufacturing the electronic device according to
claim 1, wherein a laser is used for separating the substrate.
5. A method for manufacturing an electronic device comprising the
steps of: forming a film comprising a resin over a substrate;
forming a first conductive film over the film comprising the resin;
forming an insulating film over the first conductive film; forming
an opening in the insulating film that reaches the first conductive
film; forming a second conductive film over the insulating film and
electrically connected to the first conductive film through the
opening; separating the substrate from the film comprising the
resin; and exposing the first conductive film by removing the film
comprising the resin.
6. The method for manufacturing the electronic device according to
claim 5, wherein a laser is used for separating the substrate.
7. A method for manufacturing a display device comprising the steps
of: forming a reflective film over a substrate; forming an
insulating film over the reflective film; forming an opening in the
insulating film that reaches the reflective film; forming a
conductive film over the insulating film and electrically connected
to the reflective film; forming a pixel circuit electrically
connected to the conductive film; forming a first display element
electrically connected to the pixel circuit; separating the
substrate from the reflective film; and forming a second display
element comprising the reflective film, wherein the insulating film
is located between the first display element and the second display
element.
8. The method for manufacturing the display device according to
claim 7, wherein a laser is used for separating the substrate.
9. The method for manufacturing the display device according to
claim 7, wherein the first display element is an organic EL
element, and wherein the second display element is a reflective
liquid crystal element.
10. The method for manufacturing the display device according to
claim 7, wherein the pixel circuit comprises a first transistor
electrically connected to the first display element, and a second
transistor electrically connected to the second display
element.
11. The method for manufacturing the display device according to
claim 10, wherein each of the first transistor and the second
transistor comprises a channel formation region comprising a metal
oxide.
12. A method for manufacturing a display device comprising the
steps of: forming a film comprising a resin over a substrate;
forming a reflective film over the film comprising the resin;
forming an insulating film over the reflective film; forming an
opening in the insulating film that reaches the reflective film;
forming a conductive film over the insulating film and electrically
connected to the reflective film; forming a pixel circuit
electrically connected to the conductive film; forming a first
display element electrically connected to the pixel circuit;
separating the substrate from the film comprising the resin;
exposing the reflective film by removing the film comprising the
resin; and forming a second display element comprising the
reflective film after exposing the reflective film, wherein the
insulating film is located between the first display element and
the second display element.
13. The method for manufacturing the display device according to
claim 12, wherein a laser is used for separating the substrate.
14. The method for manufacturing the display device according to
claim 12, wherein the first display element is an organic EL
element, and wherein the second display element is a reflective
liquid crystal element.
15. The method for manufacturing the display device according to
claim 12, wherein the pixel circuit comprises a first transistor
electrically connected to the first display element, and a second
transistor electrically connected to the second display
element.
16. The method for manufacturing the display device according to
claim 12, wherein each of the first transistor and the second
transistor comprises a channel formation region comprising a metal
oxide.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 15/092,221, filed Apr. 6, 2016, now pending, which claims the
benefit of foreign priority applications filed in Japan as Serial
No. 2015-081519 on Apr. 13, 2015, Serial No. 2015-115638 on Jun. 8,
2015, and Serial No. 2015-150202 on Jul. 30, 2015, all of which are
incorporated by reference.
TECHNICAL FIELD
[0002] One embodiment of the present invention relates to a display
panel, a data processor, a method for manufacturing a display
panel, or a semiconductor device.
[0003] Note that one embodiment of the present invention is not
limited to the above technical field. The technical field of one
embodiment of the invention disclosed in this specification and the
like relates to an object, a method, or a manufacturing method.
Another embodiment of the present invention relates to a process, a
machine, manufacture, or a composition of matter. Specifically,
examples of the technical field of one embodiment of the present
invention disclosed in this specification include a semiconductor
device, a display device, a light-emitting device, a power storage
device, a memory device, a method for driving any of them, and a
method for manufacturing any of them.
BACKGROUND ART
[0004] A liquid crystal display device in which a light-condensing
means and a pixel electrode are provided on one side of a substrate
and a region transmitting visible light in the pixel electrode is
provided to overlap with an optical axis of the light-condensing
means is known. In addition, a liquid crystal display device which
uses an anisotropic light-condensing means having a
light-condensing direction X and a non-light-condensing direction
Y, where the non-light-condensing direction Y corresponds to a
longitudinal direction of a region transmitting visible light in
the pixel electrode is known (Patent Document 1).
REFERENCE
Patent Document
[0005] [Patent Document 1] Japanese Published Patent Application
No. 2011-191750
DISCLOSURE OF INVENTION
[0006] One object of one embodiment of the present invention is to
provide a novel display panel that is highly convenient or
reliable. Another object of one embodiment of the present invention
is to provide a novel data processor that is highly convenient or
reliable. Another object of one embodiment of the present invention
is to provide a method for manufacturing a novel display panel that
is highly convenient or reliable. Another object of one embodiment
of the present invention is to provide a novel display panel, a
novel data processor, a method for manufacturing a novel display
panel, or a novel semiconductor device.
[0007] The descriptions of these objects do not disturb the
existence of other objects. Note that one embodiment of the present
invention does not necessarily achieve all the objects. Other
objects will be apparent from and can be derived from the
descriptions of the specification, the drawings, the claims, and
the like.
Means for Solving the Problems
[0008] (1) One embodiment of the present invention is a display
panel including a pixel and a terminal.
[0009] The pixel includes a first insulating film, a first contact
in a first opening provided in the first insulating film, a pixel
circuit electrically connected to the first contact, a second
contact electrically connected to the pixel circuit, a first
display element electrically connected to the first contact, and a
second display element electrically connected to the second
contact.
[0010] The first insulating film includes a region lying between
the first display element and the second display element. The first
display element includes a reflective film. The reflective film
reflects incident light and includes a second opening. The first
display element is configured to control the intensity of the
reflected light.
[0011] The second display element includes a region overlapping
with the second opening. The region overlapping with the second
opening emits light toward the second opening.
[0012] The terminal is electrically connected to the pixel circuit
and includes a surface at which contact with other component can be
made.
[0013] (2) One embodiment of the present invention is the display
panel in which the pixel circuit includes a switching element.
[0014] The display panel according to one embodiment of the present
invention includes the pixel and the terminal electrically
connected to the pixel. The pixel includes the first insulating
film, the first contact in the first opening provided in the first
insulating film, the pixel circuit electrically connected to the
first contact, the second contact electrically connected to the
pixel circuit, the first display element electrically connected to
the first contact, and the second display element electrically
connected to the second contact. The first insulating film includes
the region lying between the first display element and the second
display element. The terminal includes the surface at which contact
with other component can be made.
[0015] With the structure, the first display element and the second
display element between which the first insulating film is provided
can be driven using the pixel circuit connected to the terminal,
for example. Thus, a novel display panel which is highly convenient
or reliable can be provided.
[0016] (3) One embodiment of the present invention is the display
panel in which the pixel circuit includes a transistor capable of
suppressing off-state current more than a transistor in which
amorphous silicon is used as a semiconductor.
[0017] Since the pixel circuit of the display panel according to
one embodiment of the present invention includes the transistor
capable of suppressing off-state current, the frequency of
supplying a selection signal to the pixel circuit can be reduced
while flickers with display performance is suppressed. Thus, a
novel display panel with reduced power consumption which is highly
convenient or reliable can be provided.
[0018] (4) One embodiment of the present invention is the display
panel in which the first display element includes a layer
containing a liquid crystal material and first and second
conductive films. The first and second conductive films are
provided so that the alignment of the liquid crystal material can
be controlled. The first conductive film is electrically connected
to the first contact.
[0019] (5) One embodiment of the present invention is the display
panel in which the second display element includes a third
conductive film, a fourth conductive film including a region
overlapping with the third conductive film, and a layer containing
a light-emitting organic compound between the third conductive film
and the fourth conductive film. The third conductive film is
electrically connected to the second contact and transmits
light.
[0020] In the display panel, which is one embodiment of the present
invention, a reflective liquid crystal element and an organic EL
element are used as the first display element and the second
display element, respectively.
[0021] Owing to the structure, in a bright place, external light
and the reflective liquid crystal element are utilized to perform
display, while in a dark place, light emitted from the organic EL
element is utilized to perform display. In a dim place, external
light and light emitted from the organic EL element are utilized to
perform display. Thus, a novel display panel capable of performing
display with high visibility, a novel display panel with reduced
power consumption, or a novel display panel highly convenient or
reliable can be provided.
[0022] (6) One embodiment of the present invention is the display
panel in which the first display element is configured to reflect
external light and in which the ratio of the total area of the
second opening provided in the reflective film to that of a portion
of the reflective film other than the second opening is more than
or equal to 0.052 and less than or equal to 0.6. The area of the
second opening is larger than or equal to 3 .mu.m.sup.2 and smaller
than or equal to 25 .mu.m.sup.2.
[0023] The display panel, which is one embodiment of the present
invention, includes the second element which is configured to
reflect external light and one or more of the openings. The area of
one opening is larger than or equal to 3 .mu.m.sup.2 and smaller
than or equal to 25 .mu.m.sup.2. The ratio of the total area of the
opening to that of the reflective film other than the opening is
more than or equal to 0.052 and less than or equal to 0.6
[0024] Thus, irregular alignment of the liquid crystal material can
be avoided. In a bright place, display can be performed utilizing
external light. In a dark place, display can be performed utilizing
light emitted from the organic EL element. Thus, a novel display
panel capable of performing display with high visibility, a novel
display panel with reduced power consumption, or a novel display
panel highly convenient or reliable can be provided.
[0025] (7) One embodiment of the present invention is the display
panel in which the reflective film includes a region embedded in
the first insulating film and a region not covered by the first
insulating film.
[0026] Since the display panel, which is one embodiment of the
present invention, includes the reflective film which is composed
of the exposed region and the region embedded in the first
insulating film, a step at the edge of the reflective film can be
minimized to reduce the possibility of alignment defects due to the
step. In addition, the surface serving as the contact of the
terminal can be exposed. Thus, a novel display panel which is
highly convenient or reliable can be provided.
[0027] (8) One embodiment of the present invention is the display
panel in which the surface at which contact with other component
can be made faces the same direction as a surface of the reflective
film which reflects external light used for performing display. The
terminal includes a region embedded in the first insulating film
and a region not covered by the second insulating film.
[0028] The display panel according to one embodiment of the present
invention includes the terminal including the region embedded in
the first insulating film and the region not covered by the second
insulating film. Accordingly, the surface of the terminal at which
contact with other component can be made can be exposed. Thus, such
a novel display panel which is highly convenient or reliable can be
provided.
[0029] (9) One embodiment of the present invention is the display
panel in which the pixel includes a second insulating film. The
second insulating film includes a region that is provided such that
the reflective film is sandwiched between the region and the first
insulating film, and a region that covers the reflective film.
[0030] (10) One embodiment of the present invention is a data
processor including an arithmetic device and an input/output
device.
[0031] The arithmetic device is configured to receive positional
information and to supply image information and control
information.
[0032] The input/output device is configured to supply the
positional information and to receive the image information and the
control information. The input/output device includes a display
portion that displays the image information and an input portion
that supplies the positional information.
[0033] The display portion includes the above-mentioned display
panel. The input portion is configured to detect the position of a
pointer and to supply the positional information based on the
position.
[0034] The arithmetic device is configured to determine the moving
speed of the pointer in accordance with the positional information
and to determine the contrast or brightness of the image
information in accordance with the moving speed of the pointer.
[0035] The data processor of one embodiment of the present
invention includes the input/output device that supplies the
positional information and receives the image information and the
arithmetic device. The arithmetic device receives the positional
information and supplies the image information and determines the
contrast or brightness of the image information in accordance with
the moving speed of the pointer. With the structure, eyestrain on a
user which might be caused by scrolling the image information can
be reduced, that is, eye-friendly display can be achieved. Thus, a
novel data processor that is highly convenient or reliable can be
provided.
[0036] (11) One embodiment of the present invention is the data
processor in which the input portion includes at least one of a
keyboard, a hardware button, a pointing device, a touch sensor, an
illuminance sensor, an imaging device, an audio input device, a
viewpoint input device, and a pose detection device.
[0037] Thus, power consumption can be reduced and excellent
visibility can be ensured even in a bright place. Thus, a novel
data processor that is highly convenient or reliable can be
provided.
[0038] (12) One embodiment of the present invention is a
manufacturing method of the display panel including the following
11 steps.
[0039] A step 1 is for forming the first insulating film over a
substrate for use in manufacturing processes.
[0040] A step 2 is for forming the reflective film and the
terminal.
[0041] A step 3 is for forming the second insulating film covering
the reflective film and the terminal.
[0042] A step 4 is for forming the first contact electrically
connected to the reflective film and the third contact electrically
connected to the terminal.
[0043] A step 5 is for forming the pixel circuit electrically
connected to the first contact and the third contact.
[0044] A step 6 is for forming the second contact electrically
connected to the pixel circuit.
[0045] A step 7 is for forming the second display element
electrically connected to the second contact.
[0046] A step 8 is for stacking a substrate.
[0047] A step 9 is for separating the substrate for use in
manufacturing processes.
[0048] A step 10 is for removing the first insulating film to
expose the reflective film and the terminal.
[0049] A step 11 is for forming the first display element.
[0050] The manufacturing method of the display panel, which is one
embodiment of the present invention, includes the step for
separating the substrate for use in manufacturing processes and the
step for removing the first insulating film to expose the
reflective film and the terminal. Accordingly, a step at the edge
of the reflective film can be minimized to reduce the possibility
of alignment defects due to the step. In addition, the surface of
the terminal at which contact with other components is made can be
exposed. A manufacturing method of a novel display panel that is
highly convenient or reliable can be thus provided.
[0051] Although the block diagram attached to this specification
shows components classified by their functions in independent
blocks, it is difficult to classify actual components according to
their functions completely and it is possible for one component to
have a plurality of functions.
[0052] In this specification, the terms "source" and "drain" of a
transistor interchange with each other depending on the polarity of
the transistor or the levels of potentials applied to the
terminals. In general, in an n-channel transistor, a terminal to
which a lower potential is applied is called a source, and a
terminal to which a higher potential is applied is called a drain.
Further, in a p-channel transistor, a terminal to which a lower
potential is applied is called a drain, and a terminal to which a
higher potential is applied is called a source. In this
specification, although connection relation of the transistor is
described assuming that the source and the drain are fixed in some
cases for convenience, actually, the names of the source and the
drain interchange with each other depending on the relation of the
potentials.
[0053] Note that in this specification, a "source" of a transistor
means a source region that is part of a semiconductor film
functioning as an active layer or a source electrode connected to
the semiconductor film. Similarly, a "drain" of the transistor
means a drain region that is part of the semiconductor film or a
drain electrode connected to the semiconductor film. A "gate" means
a gate electrode.
[0054] Note that in this specification, a state in which
transistors are connected to each other in series means, for
example, a state in which only one of a source and a drain of a
first transistor is connected to only one of a source and a drain
of a second transistor. In addition, a state in which transistors
are connected parallel to each other means a state in which one of
a source and a drain of a first transistor is connected to one of a
source and a drain of a second transistor and the other of the
source and the drain of the first transistor is connected to the
other of the source and the drain of the second transistor.
[0055] In this specification, the term "connection" means
electrical connection and corresponds to a state where current,
voltage, or a potential can be supplied or transmitted.
Accordingly, a connection state means not only a state of direct
connection but also a state of indirect connection through a
circuit element such as a wiring, a resistor, a diode, or a
transistor that allows current, voltage, or a potential to be
supplied or transmitted.
[0056] In this specification, even when different components are
connected to each other in a circuit diagram, there is actually a
case where one conductive film has functions of a plurality of
components such as a case where part of a wiring serves as an
electrode. The term "connection" also means such a case where one
conductive film has functions of a plurality of components.
[0057] In addition, in this specification, one of a first electrode
and a second electrode of a transistor refers to a source electrode
and the other refers to a drain electrode.
[0058] One embodiment of the present invention provides a novel
display panel that is highly convenient or reliable, a novel
information processing device that is highly convenient or
reliable, a method for manufacturing a novel display panel that is
highly convenient or reliable, a novel display panel, a novel
information processing device, a method for manufacturing a display
panel, or a novel semiconductor device.
[0059] Note that the description of these effects does not disturb
the existence of other effects. One embodiment of the present
invention does not necessarily achieve all the effects listed
above. Other effects will be apparent from and can be derived from
the description of the specification, the drawings, the claims, and
the like.
BRIEF DESCRIPTION OF DRAWINGS
[0060] FIGS. 1A to 1C are top views and a circuit diagram
illustrating the structure of a display panel according to one
embodiment of the present invention.
[0061] FIGS. 2A to 2C are cross-sectional views illustrating the
structure of a display panel according to one embodiment of the
present invention.
[0062] FIGS. 3A and 3B are cross-sectional views illustrating the
structure of a terminal of a display panel according to one
embodiment of the present invention.
[0063] FIGS. 4A and 4B are cross-sectional views illustrating the
structure of a terminal of a display panel according to one
embodiment of the present invention.
[0064] FIG. 5 is a cross-sectional view illustrating the structure
of a terminal of a display panel according to one embodiment of the
present invention.
[0065] FIGS. 6A and 6B are top views illustrating the structure of
a pixel according to one embodiment of the present invention.
[0066] FIG. 7 is a cross-sectional view illustrating the structure
of a display panel according to one embodiment of the present
invention.
[0067] FIGS. 8A to 8C are cross-sectional views illustrating the
structure of a display panel according to one embodiment of the
present invention.
[0068] FIGS. 9A to 9D are circuit diagrams illustrating the
structure of a display portion according to one embodiment of the
present invention.
[0069] FIG. 10 is a cross-sectional view illustrating the structure
of a display panel according to one embodiment of the present
invention.
[0070] FIG. 11 is a cross-sectional view illustrating the structure
of a display panel according to one embodiment of the present
invention.
[0071] FIG. 12 is a flow chart illustrating a method for
manufacturing a display panel according to one embodiment of the
present invention.
[0072] FIG. 13 illustrates a method for manufacturing a display
panel according to one embodiment of the present invention.
[0073] FIG. 14 illustrates a method for manufacturing a display
panel according to one embodiment of the present invention.
[0074] FIG. 15 illustrates a method for manufacturing a display
panel according to one embodiment of the present invention.
[0075] FIG. 16 illustrates a method for manufacturing a display
panel according to one embodiment of the present invention.
[0076] FIG. 17 illustrates a method for manufacturing a display
panel according to one embodiment of the present invention.
[0077] FIG. 18 illustrates a method for manufacturing a display
panel according to one embodiment of the present invention.
[0078] FIG. 19 illustrates a method for manufacturing a display
panel according to one embodiment of the present invention.
[0079] FIGS. 20A to 20D illustrate the structure of a transistor
according to one embodiment of the present invention.
[0080] FIGS. 21A to 21C illustrate the structure of a transistor
according to one embodiment of the present invention.
[0081] FIG. 22 illustrates the structure of an input/output device
according to one embodiment of the present invention.
[0082] FIGS. 23A and 23B are a block diagram and a projection view
illustrating the structure of an information processor according to
one embodiment of the present invention.
[0083] FIGS. 24A to 24C are block diagrams and a circuit diagram
illustrating the structure of a display portion according to one
embodiment of the present invention.
[0084] FIGS. 25A and 25B are flow charts illustrating a program
according to one embodiment of the present invention.
[0085] FIG. 26 schematically illustrates image information
according to one embodiment of the present invention.
[0086] FIGS. 27A to 27C are a cross-sectional view and circuit
diagrams illustrating the structure of a semiconductor device
according to one embodiment of the present invention.
[0087] FIG. 28 is a block diagram illustrating the structure of a
CPU according to one embodiment of the present invention.
[0088] FIG. 29 is a circuit diagram illustrating the structure of a
storage element according to one embodiment of the present
invention.
[0089] FIGS. 30A to 30H illustrate the structures of electronic
devices according to one embodiment of the present invention.
[0090] FIGS. 31A1 to 31C are images for showing the display quality
of a display panel according to one example of the present
invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0091] The display panel according to one embodiment of the present
invention includes the pixel and the terminal electrically
connected to the pixel. The pixel includes the second insulating
film, the first contact in the opening provided in the second
insulating film, the pixel circuit electrically connected to the
first contact, the second contact electrically connected to the
pixel circuit, the first display element electrically connected to
the first contact, and the second display element electrically
connected to the second contact. The second insulating film
includes the region lying between the first display element and the
second display element. The terminal includes the surface at which
contact with other component can be made.
[0092] With the structure, the first display element and the second
display element between which the second insulating film is
provided can be driven using the pixel circuit connected to the
terminal, for example. Thus, a novel display panel which is highly
convenient or reliable can be provided.
[0093] Embodiments will be described in detail with reference to
drawings. Note that the present invention is not limited to the
description below, and it is easily understood by those skilled in
the art that various changes and modifications can be made without
departing from the spirit and scope of the present invention.
Accordingly, the present invention should not be interpreted as
being limited to the content of the embodiments below. Note that in
the structures of the invention described below, the same portions
or portions having similar functions are denoted by the same
reference numerals in different drawings, and description of such
portions is not repeated.
Embodiment 1
[0094] In this embodiment, the structure of a display panel of one
embodiment of the present invention will be described with
reference to FIGS. 1A to 1C and FIGS. 2A to 2C.
[0095] FIGS. 1A to 1C illustrate the structure of the display panel
of one embodiment of the present invention. FIG. 1A is a top or
bottom view of a display panel 700, 700B, or 700C of one embodiment
of the present invention. FIG. 1B is a top view of a pixel 702(i,j)
illustrated in FIG. 1B. Note that in this specification, an
integral variable of 1 or more may be used for reference numerals.
For example, "(p)" where p is an integral variable of 1 or more may
be used for part of a reference numeral that specifies any one of
components (p components in maximum). For another example, "(m, n)"
where m and n are each an integral variable of 1 or more may be
used for part of a reference numeral that specifies any one of
components (m.times.n components in maximum).
[0096] FIGS. 2A to 2C illustrate the structure of the display panel
of one embodiment of the present invention. FIG. 2A is a
cross-sectional view of the display panel 700 taken along the
section lines X1-X2, X3-X4, and X5-X6 in FIG. 1A. FIG. 2B is a
cross-sectional view of a transistor M in FIG. 2A. FIG. 2C is a
cross-sectional view of a transistor MD in FIG. 2A.
<Structure Example 1 of Display Panel>
[0097] The display panel 700 described in this embodiment includes
the pixel 702(i,j) and a substrate 770 (see FIG. 1A).
[0098] The substrate 770 includes a region overlapping with the
pixel 702(i,j) (see FIG. 2A).
[0099] The pixel 702(i,j) includes a first display element 750, a
second display element 550 having a region overlapping with the
first display element 750, and a functional layer 520 between the
first display element 750 and the second display element 550.
[0100] The functional layer 520 includes a first contact 704C
electrically connected to the first display element 750, a second
contact 504C electrically connected to the second display element
550, and a pixel circuit 730(i,j) electrically connected to the
first contact 704C and the second contact 504C (see FIG. 1C and
FIG. 2A).
[0101] The first display element 750 includes a reflective film
reflecting incident light and has a function of controlling the
ratio of reflection to incident light. For example, a first
conductive film 751 can serve as the reflective film (see FIG.
2A).
[0102] The reflective film includes an opening 751H. The second
display element 550 has a region overlapping with the opening 751H.
In the case of using the first conductive film 751 as the
reflective film, the first conductive film 751 has the opening
751H.
[0103] The region of the second display element 550 overlapping
with the opening 751H has a function of emitting light toward the
opening 751H. Note that light emitted from the second display
element 550 is extracted from a display surface of the display
panel 700 through the opening 751H.
[0104] The pixel circuit 730(i,j) of the display panel 700 includes
a switching element, such as a switch SW1 or a switch SW2 (see FIG.
1C).
[0105] The display panel 700 includes the first display element
750, the second display element 550 having the region overlapping
with the first display element 750, the first contact 704C
electrically connected to the first display element 750, the second
contact 504C electrically connected to the second display element
550, and the pixel circuit 730(i,j) electrically connected to the
first contact 704C and the second contact 504C.
[0106] With the structure, the first and second display elements
can be driven by the pixel circuit which can be formed in the same
process and can be included in the functional layer. Thus, a novel
display panel which is highly convenient or reliable can be
provided.
[0107] The pixel circuit 730(i,j) of the display panel 700 also
includes a transistor that can be used as a switch and can suppress
off-state current more than a transistor including an amorphous
silicon as a semiconductor (see FIG. 1C).
[0108] Since the pixel circuit 730(i,j) of the display panel 700
includes such a transistor capable of suppressing off-state
current, the frequency of supplying a selection signal to the pixel
circuit can be reduced while suppressing flickers with display.
Thus, a novel display panel with reduced power consumption and
which is highly convenient or reliable can be provided.
[0109] The first display element 750 of the display panel 700
includes a layer 753 containing a liquid crystal material, the
first conductive film 751, and the second conductive film 752. The
first conductive film 751 and the second conductive film 752 are
provided to control the alignment of the liquid crystal material.
Electrical connection with the first conductive film 751 is made at
the first contact 704C.
[0110] The second display element 550 of the display panel 700
includes a third conductive film 551, a fourth conductive film 552
having a region overlapping with the third conductive film 551, and
a layer 553 containing a light-emitting organic compound between
the third conductive film 551 and the fourth conductive film 552.
The third conductive film 551 is electrically connected to the
second contact 504C and transmits light.
[0111] The display panel 700 includes a reflective liquid crystal
element and an organic EL element which are respectively used as
the first display element 750 and the second display element
550.
[0112] Owing to the structure, in a bright place, external light
and the reflective liquid crystal element are utilized to perform
display, while in a dark place, light emitted from the organic EL
element is utilized to perform display. Thus, a novel display panel
highly convenient or reliable can be provided.
[0113] The second display element 550 preferably has a function of
reflecting external light. For example, a material reflecting
visible light can be used for the fourth conductive film 552.
[0114] The ratio of the total area of openings including the
opening 751H in the reflective film to that of a portion of the
reflective film other than the openings is more than or equal to
0.052 and less than or equal to 0.6. The area of one opening 751H
is larger than or equal to 3 .mu.m.sup.2 and smaller than or equal
to 25 .mu.m.sup.2. Note that in the case of using the first
conductive film 751 as the reflective film, the ratio of the total
area of openings including the opening 751H in the first conductive
film 751 to that of a portion of the first conductive film 751
other than the openings is more than or equal to 0.052 and less
than or equal to 0.6 (see FIG. 1B).
[0115] When the area of a pixel is assumed to be 1, the area of the
reflective film can be more than or equal to 0.5 and less than or
equal to 0.95 of the area of the pixel. Furthermore, the area of
the opening 751H can be more than or equal to 0.052 and less than
or equal to 0.3 of the area of the pixel.
[0116] Owing to the structure, in a bright place, external light
and the reflective liquid crystal element are utilized to perform
display, while in a dark place, light emitted from the organic EL
element is utilized to perform display. In a dim place, external
light and light emitted from the organic EL element are utilized to
perform display. In addition, the size of the opening is small
enough to perform display while avoiding irregular alignment of
liquid crystal elements. Thus, a novel display panel highly
convenient or reliable can be provided.
[0117] The pixel 702(i,j) of the display panel 700 includes an
insulating film 501A covering the first conductive film 751 and an
insulating film 501B between the first conductive film 751 and the
pixel circuit 730(i,j).
[0118] The first conductive film 751 is provided between the
insulating film 501A and the insulating film 501B and is embedded
in the insulating film 501B.
[0119] Since the display panel 700 includes the first conductive
film 751 embedded in the insulating film 501B, a step at the edge
of the first conductive film can be minimized to reduce the
possibility of alignment defects due to the step. Thus, a novel
display panel highly convenient or reliable can be provided.
[0120] Note that the display panel 700 can include one or a
plurality of pixels. For example, n pixels 702(i,j) can be arranged
in a row direction and m pixels 702(i,j) can be arranged in a
column direction which intersects with the row direction. Note that
i is an integer greater than or equal to 1 and less than or equal
to m, j is an integer greater than or equal to 1 and less than or
equal to n, and each of m and n is an integer greater than or equal
to 1.
[0121] In addition, the display panel 700 can include scan lines
G1(i) and G2(i) electrically connected to pixels 702(i,1) to
702(i,n) arranged in the row direction (see FIG. 1C).
[0122] In addition, the display panel 700 can include a signal line
S(j) electrically connected to pixels 702(1,j) to 702(m,j) arranged
in the column direction.
[0123] In addition, the pixel 702(i,j) of the display panel 700
includes a coloring film CF1 having a region overlapping with the
first display element 750, a light blocking film BM having an
opening in a region overlapping with the first display element 750,
and an insulating film 771 between the coloring film CF1 or the
blocking film BM and the layer 753 containing a liquid crystal
material (see FIG. 2A). Owing to the insulating film 771,
unevenness due to the thickness of the coloring film CF1 can be
avoided. Alternatively, impurities can be prevented from being
diffused from the light blocking film BM, the coloring film CF1, or
the like to the layer 753 containing a liquid crystal material
[0124] The display panel 700 includes an alignment film AF2 between
the substrate 770 and the layer 753 containing a liquid crystal
material and an alignment film AF1 between the layer 753 containing
a liquid crystal material and the insulating film 501A.
[0125] In the display panel 700, the layer 753 containing a liquid
crystal material is surrounded by the substrate 770, the insulating
film 501A, and a sealant 705. The sealant 705 has a function of
bonding the substrate 770 and the insulating film 501A.
[0126] The display panel 700 includes a structure KB1 for the space
between the substrate 770 and the insulating film 501A.
[0127] The display panel 700 includes an optical film 770P having a
region overlapping with the pixel 702(i,j). In the display panel
700, the substrate 770 is provided between the optical film 770P
and the layer 753 containing a liquid crystal material.
[0128] The display panel 700 includes the functional layer 520. The
functional layer 520 includes the insulating film 501A, the
insulating film 501B, an insulating film 501C, an insulating film
521B, an insulating film 521A, and an insulating film 528.
[0129] The insulating film 501B and the insulating film 501C each
have an opening where the first contact 704C is provided. Although
the insulating film 501C is stacked over the insulating film 501B
in this embodiment, the insulating film 501C may be omitted.
[0130] The insulating film 521B has a region overlapping with the
insulating film 501C.
[0131] The insulating film 521A lies between the insulating film
501C and the insulating film 521B.
[0132] The insulating film 521A has an opening where the second
contact 504C is provided.
[0133] The insulating film 528 has an opening where the second
display element 550 is provided.
[0134] In the display panel 700, a coloring film CF2 lies between
the second display element 550 and the opening 751H in the
reflective film.
[0135] The display panel 700 includes a substrate 570 having a
region overlapping with the functional layer 520, and a bonding
layer 505 bonding the functional layer 520 and the substrate
570.
[0136] In the display panel 700, the second display element 550
lies between the functional layer 520 and the substrate 570.
[0137] The display panel 700 includes a structure KB2 between the
functional layer 520 and the substrate 570 to provide a space
therebetween.
[0138] The display panel 700 includes a driver circuit GD. The
driver circuit GD includes the transistor MD, for example (see FIG.
1A and FIG. 2A). The driver circuit GD has a function of supplying
a selection signal to the scan line G1(i) or the scan line G2(i),
for example.
[0139] The display panel 700 includes a wiring 511 and a terminal
519 which are electrically connected to the pixel circuit 730(i,j).
The display panel 700 can include a wiring ANO, a wiring VCOM1, and
a wiring VCOM2 (see FIG. 1C and FIG. 2A).
[0140] Note that a flexible printed circuit board FPC1 can be
electrically connected to the terminal 519 using a conductive
material film ACF1. For example, the display panel 700 can be
electrically connected to a driver circuit SD using the conductive
material film ACF1.
[0141] The display panel 700 can include a terminal 719 (see FIG.
4A). The terminal 719 is electrically connected to the second
conductive film 752, for example. Note that a flexible printed
circuit board FPC2 can be electrically connected to the terminal
719 using a conductive material film ACF2. Note that a material of
the terminal 519 can be used for the terminal 719 and a material of
the conductive material film ACF1 can be used for the conductive
material film ACF2.
[0142] The display panel 700 can include a conductive member
electrically connecting the second conductive film 752 and the
terminal 519 (see FIG. 4B or FIG. 5). For example, a conductive
particle can be used as the conductive member.
[0143] Note that the driver circuit SD supplies an image signal in
accordance with image information.
[0144] Components of the display panel 700 will be described below.
Note that the components cannot be clearly distinguished and one
unit serves as another unit or include part of another unit in some
cases.
[0145] For example, in the case where a conductive film reflecting
visible light is used as the first conductive film 751, the first
conductive film 751 can be used as a reflective film: the first
conductive film 751 serves as the reflective film, and the
reflective film serves as the first conductive film 751.
<Structure>
[0146] The display panel 700 includes the substrate 570, the
substrate 770, the wiring 511, and the terminal 519.
[0147] The display panel 700 includes the sealant 705, the bonding
layer 505, the structure KB1, and the structure KB2.
[0148] The display panel 700 includes the pixel 702(i,j), the first
display element 750, and the second display element 550.
[0149] The display panel 700 includes the first conductive film
751, the second conductive film 752, the layer 753 containing a
liquid crystal material, the opening 751H, and the reflective
film.
[0150] The display panel 700 includes the third conductive film
551, the fourth conductive film 552, and the layer 553 containing a
light-emitting organic compound.
[0151] The display panel 700 includes the functional layer 520, the
pixel circuit 730(i,j), the first contact 704C, and the second
contact 504C.
[0152] The display panel 700 includes the switching element, the
transistor M, the transistor MD, the insulating film 501A, the
insulating film 501B, the insulating film 501C, the insulating film
521A, the insulating film 521B, and the insulating film 528.
[0153] The display panel 700 includes the coloring film CF1, the
coloring film CF2, the light-blocking film BM, the insulating film
771, the alignment film AF1, the alignment film AF2, and the
optical film 770P.
[0154] The display panel 700 includes the driver circuit GD and the
driver circuit SD.
<<Substrate 570>>
[0155] The substrate 570 can be formed using a material having heat
resistance high enough to withstand heat treatment in the
manufacturing process.
[0156] For example, a large-sized glass substrate having any of the
following sizes can be used as the substrate 570: the 6th
generation (1500 mm.times.1850 mm), the 7th generation (1870
mm.times.2200 mm), the 8th generation (2200 mm.times.2400 mm), the
9th generation (2400 mm.times.2800 mm), and the 10th generation
(2950 mm.times.3400 mm). Thus, a large-sized display device can be
manufactured.
[0157] For the substrate 570, an organic material, an inorganic
material, a composite material of an organic material and an
inorganic material, or the like can be used. For example, an
inorganic material such as glass, ceramic, or a metal can be used
for the substrate 570.
[0158] Specifically, non-alkali glass, soda-lime glass, potash
glass, crystal glass, quartz, sapphire, or the like can be used for
the substrate 570. Specifically, a material containing an inorganic
oxide, an inorganic nitride, an inorganic oxynitride, or the like
can be used for the substrate 570. For example, a material
containing silicon oxide, silicon nitride, silicon oxynitride,
aluminum oxide, or the like can be used for the substrate 570.
Stainless steel, aluminum, or the like can be used for the
substrate 570.
[0159] For example, a single crystal semiconductor substrate or a
polycrystalline semiconductor substrate of silicon or silicon
carbide, a compound semiconductor substrate of silicon germanium,
or an SOI substrate can be used as the substrate 570. Thus, a
semiconductor element can be formed over the substrate 570.
[0160] For example, a composite material, such as a resin film to
which a metal plate, a thin glass plate, or an inorganic film is
bonded can be used for the substrate 570. For example, a composite
material formed by dispersing a fibrous or particulate metal,
glass, inorganic material, or the like into a resin film can be
used for the substrate 570. For example, a composite material
formed by dispersing a fibrous or particulate resin, organic
material, or the like into an inorganic material can be used for
the substrate 570.
[0161] A single-layer material or a stacked-layer material in which
a plurality of layers are stacked can be used for the substrate
570. For example, a stacked-layer material in which a base, an
insulating film that prevents diffusion of impurities contained in
the base, and the like are stacked can be used for the substrate
570. Specifically, a stacked-layer material in which glass and one
or a plurality of films that prevent diffusion of impurities
contained in the glass and that are selected from a silicon oxide
layer, a silicon nitride layer, a silicon oxynitride layer, and the
like are stacked can be used for the substrate 570. Alternatively,
a stacked-layer material in which a resin and a film for preventing
diffusion of impurities that penetrate the resin, such as a silicon
oxide film, a silicon nitride film, and a silicon oxynitride film
are stacked can be used for the substrate 570.
[0162] Specifically, a material including polyester, polyolefin,
polyamide (e.g., nylon or aramid), polyimide, polycarbonate, an
acrylic resin, a urethane resin, an epoxy resin, a resin having a
siloxane bond, such as a silicone resin, or the like can be used
for the substrate 570.
[0163] Alternatively, a film, a plate, a stacked body, or the like
which contains any one or more of the resins can be used for the
substrate 570.
[0164] Specifically, polyethylene terephthalate (PET), polyethylene
naphthalate (PEN), polyethersulfone (PES), acrylic, or the like can
be used for the substrate 570.
[0165] Alternatively, paper, wood, or the like can be used for the
substrate 570.
[0166] For example, a flexible substrate can be used as the
substrate 570.
[0167] Note that a transistor, a capacitor, or the like can be
directly formed on the substrate. Alternatively, a transistor, a
capacitor, or the like can be formed over a substrate for use in
manufacturing processes having heat resistance and can be
transferred to another substrate, in which case heat treatment
temperature in the process for fabricating the substrate 570
included in the display panel of one embodiment of the present
invention can be reduced, for example. Thus, a transistor, a
capacitor, or the like can be formed over a flexible substrate.
<<Substrate 770>>
[0168] A light-transmitting material can be used for the substrate
770. For example, a material that can be used for the substrate 570
can be used for the substrate 770.
<<Wiring 511 and Terminal 519>>
[0169] A conductive material can be used for the wiring 511 or the
terminal 519.
[0170] For example, an inorganic conductive material, an organic
conductive material, or the like can be used for the wiring 511 or
the terminal 519.
[0171] Specifically, the wiring 511 or the terminal 519 can be
formed of a metal, conductive ceramic, or the like. For example, a
metal element selected from aluminum, gold, platinum, silver,
copper, chromium, tantalum, titanium, molybdenum, tungsten, nickel,
iron, cobalt, palladium, and manganese can be used for the wiring
511 or the terminal 519. Alternatively, an alloy including any of
the above-described metal elements, or the like can be used for
wiring 511 or the terminal 519. In particular, an alloy of copper
and manganese is preferably used in microfabrication using wet
etching.
[0172] Specifically, the following structures can be used for the
wiring 511 or the terminal 519: a two-layer structure in which a
titanium film is stacked over an aluminum film, a two-layer
structure in which a titanium film is stacked over a titanium
nitride film, a two-layer structure in which a tungsten film is
stacked over a titanium nitride film, a two-layer structure in
which a tungsten film is stacked over a tantalum nitride film or a
tungsten nitride film, a three-layer structure in which a titanium
film, an aluminum film, and a titanium film are stacked in this
order, or the like.
[0173] For example, a conductive oxide, such as indium oxide,
indium tin oxide, indium zinc oxide, zinc oxide, or zinc oxide to
which gallium is added, can be used for the wiring 511 or the
terminal 519.
[0174] Specifically, a film containing graphene or graphite can be
used for the wiring 511 or the terminal 519.
[0175] For example, a film containing graphene formed by reducing a
film containing graphene oxide can be used. Specifically, the
reduction can be performed by applying heat, using a reducing
agent, or the like.
[0176] A conductive high molecule compound can be used for the
wiring 511 or the terminal 519.
<<First Contact 704C and Second Contact 504C>>
[0177] The first contact 704C or the second contact 504C can be
formed using a conductive material. For example, the materials of
the wiring 511 or the terminal 519 can be used.
<<Bonding Layer 505 and Sealant 705>>
[0178] An inorganic material, an organic material, a composite
material of an inorganic material and an organic material, or the
like can be used for the bonding layer 505 or the sealant 705.
[0179] For example, an organic material, such as a resin having
thermal fusibility or a curable resin, can be used for the bonding
layer 505 or the sealant 705.
[0180] For example, an organic material, such as a reactive curable
adhesive, a light curable adhesive, a thermosetting adhesive,
and/or an anaerobic adhesive, can be used for the bonding layer 505
or the sealant 705.
[0181] Specifically, an adhesive containing an epoxy resin, an
acrylic resin, a silicone resin, a phenol resin, a polyimide resin,
an imide resin, a polyvinyl chloride (PVC) resin, a polyvinyl
butyral (PVB) resin, or an ethylene vinyl acetate (EVA) resin, or
the like can be used for the bonding layer 505 or the sealant
705.
<<Structures KB1 and KB2>>
[0182] The structures KB1 and KB2 can be formed using an organic
material, an inorganic material, a composite material of an organic
material and an inorganic material, or the like. Accordingly, a
predetermined space can be provided between components between
which the structure KB1 or KB2 is provided.
[0183] Specifically, for structures KB1 and KB2, polyester,
polyolefin, polyamide, polyimide, polycarbonate, polysiloxane, an
acrylic resin, or the like, or a composite material of a plurality
of kinds of resins selected from these can be used. A
photosensitive material can be used.
<<Pixel 702(i,j)>>
[0184] The pixel 702(i,j) can include the first display element
750, the second display element 550, and the functional layer
520.
[0185] The pixel 702(i,j) can include the coloring film CF1, the
light-blocking film BM, the insulating film 771, the alignment film
AF1, the alignment film AF2, and the coloring film CF2.
<<First Display Element 750>>
[0186] For example, a display element having a function of
controlling transmission or reflection of light can be used as the
first display element 750. For example, a combined structure of a
polarizing plate and a liquid crystal element or a MEMS shutter
display element can be used. The use of a reflective display
element can reduce power consumption of a display panel.
Specifically, a reflective liquid crystal display element can be
used as the first display element 750.
[0187] Specifically, a liquid crystal element that can be driven by
any of the following driving methods can be used: an in-plane
switching (IPS) mode, a twisted nematic (TN) mode, a fringe field
switching (FFS) mode, an axially symmetric aligned micro-cell (ASM)
mode, an optically compensated birefringence (OCB) mode, a
ferroelectric liquid crystal (FLC) mode, an antiferroelectric
liquid crystal (AFLC) mode, and the like.
[0188] In addition, a liquid crystal element that can be driven by,
for example, a vertical alignment (VA) mode such as a multi-domain
vertical alignment (MVA) mode, a patterned vertical alignment (PVA)
mode, an electrically controlled birefringence (ECB) mode, a
continuous pinwheel alignment (CPA) mode, or an advanced super view
(ASV) mode can be used.
[0189] For example, thermotropic liquid crystal, low-molecular
liquid crystal, high-molecular liquid crystal, polymer dispersed
liquid crystal, ferroelectric liquid crystal, or anti-ferroelectric
liquid crystal can be used. These liquid crystal materials exhibit
a cholesteric phase, a smectic phase, a cubic phase, a chiral
nematic phase, an isotropic phase, or the like depending on
conditions. Alternatively, a liquid crystal material which exhibits
a blue phase can be used.
[0190] For example, the liquid crystal element 750 can include the
layer 753 containing a liquid crystal material, the first
conductive film 751, and the second conductive film 752. The first
conductive film 751 and the second conductive film 752 are disposed
to apply an electric field for controlling the alignment of the
liquid crystal material.
[0191] The first conductive film 751 or the second conductive film
752 can be formed using a conductive material.
[0192] For example, the material of the wiring 511 can be used for
the first conductive film 751 or the second conductive film
752.
<<Reflective Film>>
[0193] The reflective film can be formed of a material reflecting
light which passes through the layer 753 containing a liquid
crystal material, in which case the first display element 750 can
be a reflective liquid crystal element.
[0194] Alternatively, a material or the like with an uneven surface
can be used for the reflective film, in which case incident light
is reflected in various directions to display white.
[0195] Note that the first conductive film 751 formed using a
material reflecting visible light can be used as the reflective
film.
[0196] Other structures may be used as the reflective film without
limitation to the first conductive film 751. For example, a
reflective film containing a material reflecting visible light may
be provided between the layer 753 containing a liquid crystal
material and the first conductive film 751. Alternatively, the
first conductive film 751 formed using a light-transmitting and
conductive material may be provided between a reflective film
containing a material reflecting visible light and the layer 753
containing a liquid crystal material.
[0197] Note that the second conductive film 752 can be formed using
the conductive material transmitting visible light.
[0198] For example, a conductive oxide or a conductive oxide
containing indium can be used for the second conductive film 752.
Alternatively, a metal film thin enough to transmit light can be
used as the second conductive film 752.
[0199] Specifically, indium oxide, indium tin oxide, indium zinc
oxide, zinc oxide, zinc oxide to which gallium is added, or the
like can be used for the second conductive film 752.
<<Opening 751H>>
[0200] The ratio of the total area of the opening 751H in the
reflective film in one pixel to that of a portion of the reflective
film other than the opening is preferably more than or equal to
0.052 and less than or equal to 0.6. If the ratio of the total area
of the opening 751H is too large, display performed using the first
display element 750 is dark. If the ratio of the total area of the
opening 751H is too small, display performed using the second
display element 550 is dark.
[0201] In the case where the first conductive film 751 is used as
the reflective film, the area of one opening 751H is larger than or
equal to 3 .mu.m.sup.2 and smaller than or equal to 25 .mu.m.sup.2.
If the area of the opening 751H in the first conductive film 751 is
too large, electric field is not uniformly applied to the layer 753
containing a liquid crystal material, which lowers the display
performance of the first display element 750. If the area of the
opening 751H in the first conductive film 751 is too small, light
emitted from the second display element 550 is not efficiently
extracted for display.
[0202] The opening 751H may have a polygonal shape, a quadrangular
shape, an elliptical shape, a circular shape, a cross shape, a
stripe shape, a slit-like shape, or a checkered pattern, for
example (see FIG. 1B and FIG. 6A). The opening 751H may be close to
the next pixel (see FIG. 6B). The opening 751H is provided close to
preferably a pixel emitting light of the same color, in which case
an undesired phenomenon in which light emitted from the second
display element 550 enters a coloring film of the adjacent pixel,
which is called cross talk, can be suppressed.
[0203] Note that the opening 751H is preferably not provided in a
region overlapping with a seam between the coloring films CF1
transmitting different colors, in which case light emitted from the
second display element 550 is less likely to reach a coloring film
of the adjacent pixel. As a result, a display panel with high color
reproducibility can be produced.
<<Second display element 550>>
[0204] A light-emitting element, for example, can be used as the
second display element 550. Specifically, an organic
electroluminescence element, an inorganic electroluminescence
element, a light-emitting diode, or the like can be used for the
second display element 550.
[0205] For example, a stack formed to emit white light can be used
as the layer 553 containing a light-emitting organic material.
Specifically, a stack of a layer containing a light-emitting
organic material containing a fluorescent material that emits blue
light, a layer containing a material that is other than a
fluorescent material and that emits green light and/or red light,
or a layer containing a material that is other than a fluorescent
material and that emits yellow light can be used as the layer 553
containing a light-emitting organic material.
[0206] For example, a material used for the wiring 511 can be used
for the third conductive film 551 or the fourth conductive film
552.
[0207] For example, a conductive material that transmits visible
light can be used for the third conductive film 551.
[0208] For example, a conductive material that transmits visible
light can be used for the fourth conductive film 552.
[0209] Specifically, conductive oxide, indium-containing conductive
oxide, indium oxide, indium tin oxide, indium zinc oxide, zinc
oxide, zinc oxide to which gallium is added, or the like can be
used for the third conductive film 551.
[0210] Alternatively, a metal film that is thin enough to transmit
light can be used as the third conductive film 551.
<<Functional Layer 520>>
[0211] The functional layer 520 includes the pixel circuit
730(i,j), the first contact 704C, and the second contact 504C. The
functional layer 520 includes the insulating film 501A, the
insulating film 501B, the insulating film 501C, the insulating film
521A, the insulating film 521B, or the insulating film 528.
<<Pixel circuit 730(i,j)>>
[0212] A circuit electrically connected to the scan line G1(i), the
scan line G2(j), the signal line S(j), the wiring ANO, the wiring
VCOM1, and the wiring VCOM2 can be used as the pixel circuit
730(i,j) (see FIG. 1C).
[0213] Specifically, the pixel circuit 730(i,j) can include the
switch SW1, the capacitor C1, the switch SW2, the capacitor C2, and
the transistor M.
[0214] The switch SW1 includes a control electrode and a first
electrode which are electrically connected to the scan line G1(i)
and the signal line S(j), respectively. Note that the switch SW1
may be a transistor.
[0215] The capacitor C1 includes a first electrode and a second
electrode which are electrically connected to a second electrode of
the switch SW1 and the wiring VCOM1, respectively.
[0216] Note that the first conductive film 751 and the second
conductive film 752 of the first display element 750 can be
electrically connected to the second electrode of the switch SW1
and the wiring VCOM1, respectively.
[0217] The switch SW2 includes a control electrode and a first
electrode which are electrically connected to the scan line G2(i)
and the signal line S(j), respectively. Note that the switch SW2
may be a transistor.
[0218] The transistor M includes a gate electrode and a first
electrode which are electrically connected to a second electrode of
the switch SW2 and the wiring ANO, respectively.
[0219] The capacitor C2 includes a first electrode and a second
electrode which are electrically connected to the second electrode
of the switch SW2 and a second electrode of the transistor M,
respectively.
[0220] Note that the third conductive film 551 and the fourth
conductive film 552 of the second display element 550 can be
electrically connected to the second electrode of the transistor M
and the wiring VCOM2, respectively.
<<Transistor M>>
[0221] The transistor M includes the semiconductor film 508 and the
conductive film 504 which includes a region overlapping with the
semiconductor film 508 (see FIG. 2B). The transistor M includes the
conductive film 512A, the conductive film 512B, and the insulating
film 506 between the semiconductor film 508 and the conductive film
504.
[0222] Note that the conductive film 504 serves as a gate
electrode, and the insulating film 506 serves as a gate insulating
film. The conductive film 512A has one of a function as a source
electrode and a function as a drain electrode, and the conductive
film 512B has the other.
[0223] Note that the functional layer 520 can include the
insulating film 516 and the insulating film 518 which cover the
transistor M, thereby suppressing impurity diffusion to the
transistor M.
[0224] As the transistor M, a bottom-gate transistor, a top-gate
transistor, or the like can be used.
[0225] For example, a transistor including a semiconductor
containing an element of Group 4 can be used. Specifically, a
semiconductor containing silicon can be used for a semiconductor
film. For example, single crystal silicon, polysilicon,
microcrystalline silicon, amorphous silicon, or the like can be
used for the semiconductor films of the transistors.
[0226] For example, a transistor including an oxide semiconductor
can be used. Specifically, an oxide semiconductor containing indium
or an oxide semiconductor containing indium, gallium, and zinc can
be used for a semiconductor film.
[0227] For example, a transistor having a lower leakage current in
an off state than a transistor that uses amorphous silicon for a
semiconductor film can be used. Specifically, a transistor that
uses an oxide semiconductor for a semiconductor film can be
used.
[0228] A pixel circuit in the transistor that uses an oxide
semiconductor for the semiconductor film can hold an image signal
for a longer time than a pixel circuit in a transistor that uses
amorphous silicon for a semiconductor film. Specifically, the
selection signal can be supplied at a frequency of lower than 30
Hz, preferably lower than 1 Hz, more preferably less than once per
minute while flickering is suppressed. Consequently, eyestrain on a
user of the information processing device can be reduced, and power
consumption for driving can be reduced.
[0229] Alternatively, for example, a transistor including a
compound semiconductor can be used. Specifically, a semiconductor
containing gallium arsenide can be used for a semiconductor
film.
[0230] For example, a transistor including an organic semiconductor
can be used. Specifically, an organic semiconductor containing any
of polyacenes and graphene can be used for the semiconductor
film.
<<Switches SW1 and SW2>>
[0231] A transistor can serve as the switches SW1 and SW2.
[0232] For example, a transistor which can be fabricated in the
same process as the transistor M can be used as the switches SW1
and SW2.
<<Insulating film 501A>>
[0233] The insulating film 501A can be formed using an inorganic
oxide film, an inorganic nitride film, an inorganic oxynitride
film, or a material stacking any of these films. Specifically, the
insulating film 501A can be formed using silicon oxide, silicon
nitride, silicon oxynitride, aluminum oxide, or a material stacking
a plurality of them.
[0234] Specifically, a film containing a stacked-layer material of
a 600-nm-thick silicon oxynitride film and a 200-nm-thick silicon
nitride film can be used as the insulating film 501A.
[0235] Specifically, a film containing a stacked-layer material of
a 600-nm-thick silicon oxynitride film, a 200-nm-thick silicon
nitride film, a 200-nm-thick silicon oxynitride film, a
140-nm-thick silicon nitride oxide film, and a 100-nm-thick silicon
oxynitride film stacked in this order can be used as the insulating
film 501A.
[0236] Alternatively, the insulating film 501A can be formed using
a material containing resin, such as polyimide.
[0237] An insulating film is formed over a substrate for use in
manufacturing processes and is separated from the substrate to be
used as the insulating film 501A. In that case, the thickness of
the insulating film 501A can be 5 .mu.m or less, preferably 1.5
.mu.m or less, further preferably 1 .mu.m or less.
<<Insulating Film 501B and Insulating Film 501C>>
[0238] For example, an insulating inorganic material, an insulating
organic material, or an insulating composite material containing an
inorganic material and an organic material can be used for the
insulating film 501B and the insulating film 501C.
[0239] Specifically, an inorganic oxide film, an inorganic nitride
film, an inorganic oxynitride film, or a material stacking any of
these films can be used for the insulating film 501B and the
insulating film 501C. For example, a silicon oxide film, a silicon
nitride film, an aluminum oxide film, a silicon oxynitride film, or
a material stacking any of these films can be used for the
insulating film 501B and the insulating film 501C.
[0240] For example, the material which can be used for the
insulating film 501A can be used for the insulating film 501C.
[0241] Specifically, for the insulating film 501B and the
insulating film 501C, polyester, polyolefin, polyamide, polyimide,
polycarbonate, polysiloxane, an acrylic resin, and the like, or a
stacked material of or a composite material of a plurality of kinds
of resins selected from these can be used. Alternatively, a
photosensitive material can be used.
<<Insulating films 521A, 521B, and 528>>
[0242] The materials which can be used for the insulating film 501B
or the insulating film 501C can be used for the insulating film
521A, 521B, or 528.
[0243] Thus, steps due to components overlapping with the
insulating film 521A, for example, can be covered so that a flat
surface can be formed. The insulating film 521B provided between a
plurality of wirings can prevent short circuit of the plurality of
wirings. The insulating film 528 having an opening which overlaps
with the third conductive film 551 can prevent short circuit
between the third conductive film 551 and the fourth conductive
film which can occur at the edges of the third conductive film
551.
<<Coloring films CF1 and CF2>>
[0244] The coloring film CF1 can be formed using a material
transmitting light of a predetermined color, and can thus be used
as a color filter or the like.
[0245] For example, the coloring film CF1 can be formed using a
material transmitting light of blue, green, red, yellow, or
white.
[0246] The coloring film CF2 can be formed using, for example, the
material of the coloring film CF1, specifically, a material
transmitting light passing through the coloring film CF1. In that
case, part of light emitted from the second display element 550
that passes through the coloring film CF2, the opening 751H, and
the coloring film CF1 can be extracted to the outside of the
display panel. Note that a material having a function of converting
the emitted light to a predetermined color light can be used for
the color film CF2. Specifically, quantum dots can be used for the
color film CF2. Thus, display with high color purity can be
achieved.
<<Light-Blocking Film BM>>
[0247] A material that prevents light transmission can be used for
the light-blocking film BM, in which case the light-blocking film
BM serves as a black matrix, for example.
<<Insulating Film 771>>
[0248] The insulating film 771 can be formed of polyimide, epoxy
resin, acrylic resin, or the like.
<<Alignment Films AF1 and AF2>>
[0249] The alignment films AF1 and AF2 can be formed of a material
containing polyimide or the like, such as a material formed to have
a predetermined alignment by a rubbing process or an optical
alignment process.
<<Optical Film 770P>>
[0250] For example, a polarizing plate, a retardation plate, a
diffusing film, an anti-reflective film, a condensing film, or the
like can be used as the optical film 770P. Alternatively, a
polarizing plate containing a dichromatic pigment can be used for
the optical film 770P.
[0251] Alternatively, an antistatic film preventing the attachment
of a foreign substance, a water repellent film suppressing the
attachment of stain, a hard coat film suppressing a scratch in use,
or the like can be used for the optical film 770P.
<<Driver Circuit GD>>
[0252] Any of a variety of sequential circuits, such as a shift
register, can be used as the driver circuit GD. For example, the
transistor MD, a capacitor, and the like can be used in the driver
circuit GD. Specifically, a transistor including a semiconductor
film that can be formed at the same step as the transistor M can be
used.
[0253] As the transistor MD, a transistor different from the
transistor M can be used, such as a transistor including the
conductive film 524. The semiconductor film 508 is provided between
the conductive films 524 and 504. The insulating film 516 is
provided between the conductive film 524 and the semiconductor film
508. The insulating film 506 is provided between the semiconductor
film 508 and the conductive film 504. For example, the conductive
film 524 is electrically connected to a wiring supplying the same
potential as that supplied to the conductive film 504.
[0254] Note that the transistor MD can have the same structure as
the transistor M.
<<Driver Circuit SD>>
[0255] For example, an integrated circuit can be used in the driver
circuit SD. Specifically, an integrated circuit formed over a
silicon substrate can be used.
[0256] For example, a chip on glass (COG) method can be used to
mount the driver circuit SD on a pad provided over the insulating
film 501C. Specifically, a conductive material film can be used to
mount the integrated circuit on the pad. Note that the pad is
electrically connected to the pixel circuit 730(i,j).
<Structure Example 2 of Display Panel>
[0257] Another structure of the display panel of one embodiment of
the present invention will be described with reference to FIGS. 3A
and 3B.
[0258] FIG. 3A is a cross-sectional view illustrating
cross-sectional structures of the display panel 700B of one
embodiment of the present invention taken along the section lines
X1-X2, X3-X4, and X5-X6 in FIG. 1A. FIG. 3B is a cross-sectional
view illustrating the transistor MB or the transistor MDB in FIG.
3A.
[0259] Structures different from those in the display device
described in Structure example 1 will be described in detail below,
and the above description is referred to for the other similar
structures.
[0260] Specifically, the display panel 700B in FIGS. 3A and 3B is
different from the display panel 700 in FIGS. 2A to 2C in that the
coloring film CF2 is omitted, that the second display element 550B
emitting light of blue, green, red, or the like, that top gate
transistors MB and MDB are provided, that a terminal 519B
electrically connected to the wiring 511 using a through electrode
is provided, and that an insulating film 570B is provided instead
of the substrate 570.
<<Second Display Element 550B>>
[0261] In one pixel (also referred to as sub-pixel), the second
display element 550B that emits light of a color different from
that emitted from the second display element provided in another
sub-pixel is used. For example, the second display element 550B
that emits blue light is used in one pixel, and the second display
element that emits green light or red light is used in another
pixel.
[0262] Specifically, an organic EL element including a layer 553B
containing a light-emitting organic compound that emits blue light
is used in the second display element 550B. An organic EL element
including a layer containing a light-emitting organic compound that
emits green light or red light is used in another pixel.
[0263] Note that an evaporation method, an ink-jet method, or a
printing method using a shadow mask can be employed to form the
layer containing a light-emitting organic compound. In that case,
in one pixel, the layer containing a light-emitting organic
compound that emits light of a color different from that emitted
from the second display element provided in another pixel can be
used.
[0264] Note that the second display element 550B may have a concave
shape, and emitted light may be gathered into the opening 751H.
Thus, a region having a light-emitting function of the second
display element 550B can be widened to a region not overlapping
with the opening 751H. For example, the area of the region not
overlapping with the opening 751H can be 20% or more of the area of
a region overlapping with the opening 751H. Accordingly, the
density of current flowing through the second display element 550B
can be reduced, and for example, heat generation can be suppressed.
Furthermore, reliability can be improved. Furthermore, the area of
the opening 751H can be reduced.
<<Transistor MB>>
[0265] The transistor MB includes the conductive film 504 having a
region overlapping with an insulating film 501C and the
semiconductor film 508 having a region provided between the
insulating film 501C and the conductive film 504. Note that the
conductive film 504 functions as a gate electrode (see FIG.
3B).
[0266] The semiconductor film 508 is consisted of a first region
508A, a second region 508B, and a third region 508C. The first
region 508A and the second region 508B do not overlap with the
conductive film 504. The third region 508C is positioned between
the first region 508A and the second region 508B and overlaps with
the conductive film 504.
[0267] The transistor MB includes an insulating film 506 between
the third region 508C and the conductive film 504. Note that the
insulating film 506 functions as a gate insulating film.
[0268] The first region 508A and the second region 508B have a
lower resistance than the third region 508C, and function as a
source region and a drain region.
[0269] Note that, for example, a method for controlling the
resistivity of the oxide semiconductor film to be described later
can be used as a method for forming the first region 508A and the
second region 508B in the semiconductor film 508. Specifically,
plasma treatment using a gas containing a rare gas can be used. For
example, when the conductive film 504 is used as a mask, the shape
of part of the third region 508C can be the same as the shape of an
end portion of the conductive film 704.
[0270] The transistor MB includes the conductive films 512A and
512B which are in contact with the first region 508A and the second
region 508B, respectively. The conductive film 512A serves as one
of the source electrode and drain electrode, and the conductive
film 512B serves as the other thereof.
[0271] The transistor which can be formed in the same process as
the transistor MB can be used as the transistor MDB or the switch
SW1.
<<Terminal 519B>>
[0272] A conductive film formed in the opening in the insulating
films 501A, 501B, and 501C can be used for the through electrode.
Thus, the terminal 519B can be provided on the side of the
insulating film 501A, 501B, or 501C opposite to the side where the
pixel circuit is provided. That is, the insulating film 501A, 501B,
and 501C can be provided between the pixel circuit and the terminal
519B.
<<Insulating Film 570B>>
[0273] As the insulating film 570B, an insulating film having a
thickness of more than or equal to 50 nm and less than 10 .mu.m,
preferably more than or equal to 100 nm and less than 5 .mu.m, can
be used, for example. Specifically, such an insulating film may be
formed on a substrate for use in manufacturing processes and be
transferred therefrom to a different substrate. The thickness of
the display panel 700B can thus be small.
[0274] Specifically, a film containing a stacked-layer material of
a 600-nm-thick silicon oxynitride film and a 200-nm-thick silicon
nitride film can be used as the insulating film 570B.
[0275] Specifically, a film containing a stacked-layer material of
a 600-nm-thick silicon oxynitride film, a 200-nm-thick silicon
nitride film, a 200-nm-thick silicon oxynitride film, a
140-nm-thick silicon nitride oxide film, and a 100-nm-thick silicon
oxynitride film stacked in this order can be used as the insulating
film 570B.
<Structure Example 3 of Display Panel>
[0276] Another structure of a display panel of one embodiment of
the present invention will be described with reference to FIG.
7.
[0277] FIG. 7 is a cross-sectional view illustrating
cross-sectional structures of a display panel 700C of one
embodiment of the present invention taken along the section lines
X1-X2, X3-X4, and X5-X6 in FIG. 1.
[0278] Structures different from those in the display device
described in Structure example 1 will be described in detail below,
and the above description is referred to for the other similar
structures.
[0279] Specifically, the display panel in FIG. 7 is different from
that in FIGS. 2A to 2C in that the coloring films CF1 and CF2 are
omitted, the second display element 550B emits light of blue,
green, red, or the like, that a fourth insulating film 501D is
provided between the insulating film 501A and the insulating film
501B, that a second conductive film 752C instead of the second
conductive film 752 is provided between the insulating film 501A
and the fourth insulating film 501D, and that the second conductive
film 752C has a comb-like shape.
[0280] With such a structure, the first conductive film 751 and the
second conductive film 752C can apply a horizontal electric field
in the thickness direction of the layer 753 containing a liquid
crystal material; thus, the first display element 750 can be driven
in an FFS mode.
<<Fourth Insulating Film 501D>>
[0281] The fourth insulating film 501D can be formed using any of
the materials which can be used for the insulating film 501A and
the insulating film 501B.
<Method for Controlling Resistivity of Oxide Semiconductor
Film>
[0282] The method for controlling the resistivity of an oxide
semiconductor film will be described.
[0283] An oxide semiconductor film with a certain resistivity can
be used for the semiconductor film 508, the conductive film 524,
the first region 508A, or the second region 508B.
[0284] For example, a method for controlling the concentration of
impurities such as hydrogen and water contained in the oxide
semiconductor and/or the oxygen vacancies in the film can be used
as the method for controlling the resistivity of an oxide
semiconductor film.
[0285] Specifically, plasma treatment can be used as a method for
increasing or decreasing the concentration of impurities such as
hydrogen and water and/or the oxygen vacancies in the film.
[0286] Specifically, plasma treatment using a gas containing one or
more kinds selected from a rare gas (He, Ne, Ar, Kr, Xe), hydrogen,
boron, phosphorus, and nitrogen can be employed. For example,
plasma treatment in an Ar atmosphere, plasma treatment in a mixed
gas atmosphere of Ar and hydrogen, plasma treatment in an ammonia
atmosphere, plasma treatment in a mixed gas atmosphere of Ar and
ammonia, or plasma treatment in a nitrogen atmosphere can be
employed. Thus, the oxide semiconductor film can have a high
carrier density and a low resistivity.
[0287] Alternatively, hydrogen, boron, phosphorus, or nitrogen is
added to the oxide semiconductor film by an ion implantation
method, an ion doping method, a plasma immersion ion implantation
method, or the like, so that the oxide semiconductor film can have
a low resistivity.
[0288] Alternatively, an insulating film containing hydrogen is
formed in contact with the oxide semiconductor film, and the
hydrogen is diffused from the insulating film to the oxide
semiconductor film, so that the oxide semiconductor film can have a
high carrier density and a low resistivity.
[0289] For example, an insulating film with a hydrogen
concentration of greater than or equal to 1.times.10.sup.2
atoms/cm.sup.3 is formed in contact with the oxide semiconductor
film, in that case hydrogen can be effectively supplied to the
oxide semiconductor film. Specifically, a silicon nitride film can
be used as the insulating film formed in contact with the oxide
semiconductor film.
[0290] Hydrogen contained in the oxide semiconductor film reacts
with oxygen bonded to a metal atom to be water, and an oxygen
vacancy is formed in a lattice from which oxygen is released (or a
portion from which oxygen is released). Due to entry of hydrogen
into the oxygen vacancy, an electron serving as a carrier is
generated in some cases. Furthermore, bonding of part of hydrogen
to oxygen bonded to a metal atom causes generation of an electron
serving as a carrier in some cases. Thus, the oxide semiconductor
film can have a high carrier density and a low resistivity.
[0291] Specifically, an oxide semiconductor with a hydrogen
concentration measured by secondary ion mass spectrometry (SIMS) of
greater than or equal to 8.times.10.sup.19 atoms/cm.sup.3,
preferably greater than or equal to 1.times.10.sup.2
atoms/cm.sup.3, more preferably greater than or equal to
5.times.10.sup.2 atoms/cm.sup.3 can be suitably used for the
conductive film 524, the first region 508A, or the second region
508B.
[0292] On the other hand, an oxide semiconductor with a high
resistivity can be used for a semiconductor film where a channel of
a transistor is formed.
[0293] For example, an insulating film containing oxygen, in other
words, an insulating film capable of releasing oxygen, is formed in
contact with an oxide semiconductor film, and the oxygen is
supplied from the insulating film to the oxide semiconductor film,
so that oxygen vacancies in the film or at the interface can be
filled. Thus, the oxide semiconductor film can have a high
resistivity.
[0294] For example, a silicon oxide film or a silicon oxynitride
film can be used as the insulating film capable of releasing
oxygen.
[0295] The oxide semiconductor film in which oxygen vacancies are
filled and the hydrogen concentration is reduced can be referred to
as a highly purified intrinsic or substantially highly purified
intrinsic oxide semiconductor film. The term "substantially
intrinsic" refers to the state in which an oxide semiconductor film
has a carrier density lower than 8.times.10.sup.11/cm.sup.3,
preferably lower than 1.times.10.sup.11/cm.sup.3, further
preferably lower than 1.times.10.sup.10/cm.sup.3. A highly purified
intrinsic or substantially highly purified intrinsic oxide
semiconductor film has few carrier generation sources and thus can
have a low carrier density. The highly purified intrinsic or
substantially highly purified intrinsic oxide semiconductor film
has a low density of defect states and accordingly can have a low
density of trap states.
[0296] Furthermore, a transistor including the highly purified
intrinsic or substantially highly purified intrinsic oxide
semiconductor film has an extremely low off-state current; even
when an element has a channel width of 1.times.10.sup.6 .mu.m and a
channel length L of 10 .mu.m, the off-state current can be lower
than or equal to the measurement limit of a semiconductor parameter
analyzer, that is, lower than or equal to 1.times.10.sup.-13 A, at
a voltage (drain voltage) between a source electrode and a drain
electrode of from 1 V to 10 V.
[0297] The transistor in which a channel region is formed in the
oxide semiconductor film that is a highly purified intrinsic or
substantially highly purified intrinsic oxide semiconductor film
can have a small change in electrical characteristics and high
reliability.
[0298] Specifically, an oxide semiconductor has a hydrogen
concentration which is measured by secondary ion mass spectrometry
(SIMS) of lower than or equal to 2.times.10.sup.2 atoms/cm.sup.3,
preferably lower than or equal to 5.times.10.sup.19 atoms/cm.sup.3,
more preferably lower than or equal to 1.times.10.sup.19
atoms/cm.sup.3, more preferably lower than 5.times.10.sup.1s
atoms/cm.sup.3, more preferably lower than or equal to
1.times.10.sup.1' atoms/cm.sup.3, more preferably lower than or
equal to 5.times.10.sup.17 atoms/cm.sup.3, more preferably lower
than or equal to 1.times.10.sup.16 atoms/cm.sup.3 can be favorably
used for a semiconductor film where a channel of a transistor is
formed.
[0299] An oxide semiconductor film that has a higher hydrogen
concentration and/or a larger number of oxygen vacancies and that
has a lower resistivity than the semiconductor film 508 is used as
the conductive film 524.
[0300] The hydrogen concentration in the conductive film 524 is
twice or more, preferably ten times or more that in the
semiconductor film 508.
[0301] The resistivity of the conductive film 524 is greater than
or equal to 1.times.10.sup.-8 times and less than 1.times.10.sup.-1
times that of the semiconductor film 508.
[0302] Specifically, the resistivity of the conductive film 524 is
higher than or equal to 1.times.10.sup.-3 .OMEGA.cm and lower than
1.times.10.sup.4 .OMEGA.cm, preferably higher than or equal to
1.times.10.sup.-3 .OMEGA.cm and lower than 1.times.10.sup.-1
.OMEGA.cm.
[0303] This embodiment can be combined with any of the other
embodiments in this specification as appropriate.
Embodiment 2
[0304] In this embodiment, the structure of a display panel of one
embodiment of the present invention will be described with
reference to FIGS. 1A to 1C and FIGS. 8A and 8B.
[0305] FIGS. 1A and 1C illustrate the structure of a display panel
of one embodiment of the present invention. FIGS. 1A and 1B are top
views of a display panel 700D of one embodiment of the present
invention and the pixel 702(i,j) in FIG. 1A, respectively.
[0306] FIGS. 8A to 8C illustrate the structure of the display panel
of one embodiment of the present invention. FIG. 8A is a
cross-sectional view of the display panel 700D taken along the
section lines X1-X2, X3-X4, and X5-X6 in FIG. 1A. FIG. 8B is a
cross-sectional view of the transistor M in FIG. 8A. FIG. 8C is a
cross-sectional view of the transistor MD in FIG. 8A.
<Structure Example 1 of Display Panel>
[0307] The display panel 700D described in this embodiment includes
the pixel 702(i,j) and a terminal 519D(1) (see FIG. 1A).
[0308] The pixel 702(i,j) includes the insulating film 501B, a
first contact 591 in an opening provided in the insulating film
501B, the pixel circuit 730(i,j) electrically connected to the
first contact 591, a second contact 592 electrically connected to
the pixel circuit 730(i,j), the first display element 750
electrically connected to the first contact 591, and the second
display element 550 electrically connected to the second contact
592 (see FIG. 1C and FIG. 8A).
[0309] The insulating film 501B includes a region lying between the
first display element 750 and the second display element 550.
[0310] The first display element 750 includes a reflective film
which reflects incident light and has the opening 751H. The first
display element 750 is configured to control the intensity of the
reflected light. Note that the first conductive film 751 can be
used as the reflective film.
[0311] The region of the second display element 550 overlapping
with the opening 751H has a function of emitting light toward the
opening 751H.
[0312] The terminal 519D(1) is electrically connected to the pixel
circuit 730(i,j) and has a surface at which contact with other
component can be made. The surface at which contact with other
component can be made faces the same direction as a surface of the
reflective film which reflects external light used for performing
display.
[0313] The pixel circuit 730(i,j) of the display panel 700D
includes a switching element, such as the switch SW1 or SW2 (see
FIG. 1C).
[0314] The display panel 700D according to one embodiment of the
present invention includes the pixel 702(i,j) and the terminal
519D(i,j) electrically connected to the pixel. The pixel 702(i,j)
includes the insulating film 501B, the first contact 591 in the
opening provided in the insulating film 501B, the pixel circuit
electrically connected to the first contact 591, the second contact
592 electrically connected to the pixel circuit 730(i,j), the first
display element 750 electrically connected to the first contact
591, and the second display element 550 electrically connected to
the second contact 592. The insulating film 501B includes the
region lying between the first display element 750 and the second
display element 550. The terminal 519D(i,j) includes the surface at
which contact with other component can be made. The surface at
which contact with other component can be made faces the same
direction as a surface of the reflective film which reflects
external light used for performing display.
[0315] With the structure, the first display element and the second
display element between which the second insulating film is
provided can be driven using the pixel circuit connected to the
terminal, for example. Thus, a novel display panel which is highly
convenient or reliable can be provided.
[0316] The pixel circuit 730(i,j) of the display panel 700D also
includes a transistor that can be used as a switch and can suppress
off-state current more than a transistor including an amorphous
silicon as a semiconductor (see FIG. 1C).
[0317] Since the pixel circuit 730(i,j) of the display panel 700D
includes such a transistor capable of suppressing off-state
current, the frequency of supplying a selection signal to the pixel
circuit can be reduced while suppressing flickers with display.
Thus, a novel display panel with reduced power consumption and
which is highly convenient or reliable can be provided.
[0318] The first display element 750 of the display panel 700D
includes a layer 753 containing a liquid crystal material, the
first conductive film 751, and the second conductive film 752. The
first conductive film 751 and the second conductive film 752 are
provided to control the alignment of the liquid crystal material.
Electrical connection with the first conductive film 751 is made at
the first contact 591 (see FIG. 8A).
[0319] The second display element 550D of the display panel 700
includes a third conductive film 551, a fourth conductive film 552
having a region overlapping with the third conductive film 551, and
a layer 553 containing a light-emitting organic compound between
the third conductive film 551 and the fourth conductive film 552.
The third conductive film 551 is electrically connected to the
second contact 592 and transmits light.
[0320] The display panel 700D includes a reflective liquid crystal
element and an organic EL element which are respectively used as
the first display element 750 and the second display element
550.
[0321] Owing to the structure, in a bright place, external light
and the reflective liquid crystal element are utilized to perform
display, while in a dark place, light emitted from the organic EL
element is utilized to perform display. Thus, a novel display panel
highly convenient or reliable can be provided. Thus, a novel
display panel capable of performing display with high visibility, a
novel display panel with reduced power consumption, or a novel
display panel highly convenient or reliable can be provided.
[0322] The second display element 550 preferably has a function of
reflecting external light. For example, a material reflecting
visible light can be used for the fourth conductive film 552.
[0323] The ratio of the total area of one or a plurality of
openings including the opening 751H in the reflective film to that
of a portion of the reflective film other than the openings is more
than or equal to 0.052 and less than or equal to 0.6. The area of
one opening 751H is larger than or equal to 3 .mu.m.sup.2 and
smaller than or equal to 25 .mu.m.sup.2. Note that in the case of
using the first conductive film 751 as the reflective film, the
ratio of the total area of openings including the opening 751H in
the first conductive film 751 to that of a portion of the first
conductive film 751 other than the openings is more than or equal
to 0.052 and less than or equal to 0.6 (see FIG. 1B).
[0324] When the area of a pixel is assumed to be 1, the area of the
reflective film can be more than or equal to 0.5 and less than or
equal to 0.95 of the area of the pixel. Furthermore, the area of
the opening 751H can be more than or equal to 0.052 and less than
or equal to 0.3 of the area of the pixel.
[0325] Owing to the structure, irregular alignment of the liquid
crystal material can be avoided. In addition, in a bright place,
external light and the reflective liquid crystal element are
utilized to perform display, while in a dark place, light emitted
from the organic EL element is utilized to perform display. Thus, a
novel display panel highly convenient or reliable can be
provided.
[0326] The reflective film of the display panel 700D includes a
region embedded in the insulating film 501B and a region not
covered by the insulating film 501B. For example, in the case where
the first conductive film 751 is used as the reflective film, a
region embedded in the insulating film 501B is provided on the side
surface of the first conductive film 751 and the surface thereof in
contact with the first contact 591.
[0327] The terminal 519D(1) includes a region embedded in the
insulating film 501B and a region not covered by the insulating
film 501B.
[0328] Thus, a step at the edge of the first conductive film can be
minimized to reduce the possibility of alignment defects due to the
step. Thus, a novel display panel highly convenient or reliable can
be provided.
[0329] Note that the display panel 700D can include one or a
plurality of pixels. For example, n pixels 702(i,j) can be arranged
in a row direction and m pixels 702(i,j) can be arranged in a
column direction which intersects with the row direction. Note that
i is an integer greater than or equal to 1 and less than or equal
to m, j is an integer greater than or equal to 1 and less than or
equal to n, and each of m and n is an integer greater than or equal
to 1.
[0330] In addition, the display panel 700D can include scan lines
G1(i) and G2(i) electrically connected to pixels 702(i,1) to
702(i,n) arranged in the row direction (see FIG. 1C).
[0331] In addition, the display panel 700D can include a signal
line S(O) electrically connected to pixels 702(1,j) to 702(m,j)
arranged in the column direction.
[0332] In addition, the pixel 702(i,j) of the display panel 700
includes a coloring film CF1 having a region overlapping with the
first display element 750, a light blocking film BM having an
opening in a region overlapping with the first display element 750,
and an insulating film 771 between the coloring film CF1 or the
blocking film BM and the layer 753 containing a liquid crystal
material (see FIG. 8A). Owing to the insulating film 771,
unevenness due to the thickness of the coloring film CF1 can be
avoided. Alternatively, impurities can be prevented from being
diffused from the light blocking film BM, the coloring film CF1, or
the like to the layer 753 containing a liquid crystal material
[0333] The display panel 700D includes an alignment film AF2
between the substrate 770 and the layer 753 containing a liquid
crystal material and an alignment film AF1 between the layer 753
containing a liquid crystal material and the insulating film
501B.
[0334] In the display panel 700D, the layer 753 containing a liquid
crystal material is surrounded by the substrate 770, the insulating
film 501B, and a sealant 705. The sealant 705 has a function of
bonding the substrate 770 and the insulating film 501B.
[0335] The display panel 700D includes a structure KB1 for the
space between the substrate 770 and the insulating film 501B.
[0336] The display panel 700D includes an optical film 770P having
a region overlapping with the pixel 702(i,j). In the display panel
700D, the substrate 770 is provided between the optical film 770P
and the layer 753 containing a liquid crystal material.
[0337] The display panel 700D includes the functional layer 520D.
The functional layer 520D includes the insulating film 501B, the
insulating film 501C, the insulating film 521A, the insulating film
521B, and the insulating film 528.
[0338] The insulating film 501B and the insulating film 501C each
have an opening where the first contact 591 is provided and an
opening where the third contact 593 is provided. Although the
insulating film 501C is stacked over the insulating film 501B in
this embodiment, the insulating film 501C may be omitted.
[0339] The insulating film 521B has a region overlapping with the
insulating film 501B.
[0340] The insulating film 521A lies between the insulating film
501B and the insulating film 521B.
[0341] The insulating film 521A has an opening where the second
contact 592 is provided.
[0342] The insulating film 528 has an opening where the second
display element 550 is provided.
[0343] In the display panel 700D, a coloring film CF2 lies between
the second display element 550 and the opening 751H in the
reflective film.
[0344] The display panel 700D includes a substrate 570 having a
region overlapping with the functional layer 520D, and a bonding
layer 505 bonding the functional layer 520D and the substrate
570.
[0345] In the display panel 700D, the second display element 550
lies between the functional layer 520D and the substrate 570.
[0346] The display panel 700D includes a structure KB2 between the
functional layer 520D and the substrate 570 to provide a space
therebetween.
[0347] The display panel 700D includes a driver circuit GD. The
driver circuit GD includes the transistor MD, for example (see FIG.
1A and FIG. 8A). The driver circuit GD has a function of supplying
a selection signal to the scan line G (i) or the scan line G2(i),
for example.
[0348] The display panel 700D includes a wiring 511 and a terminal
519D(1) which are electrically connected to the pixel circuit
730(i,j). The display panel 700D can include a wiring ANO, a wiring
VCOM1, and a wiring VCOM2 (see FIG. 1C and FIG. 8A).
[0349] Note that a flexible printed circuit board FPC1 can be
electrically connected to the terminal 519D(1) using a conductive
material film ACF1. For example, the display panel 700D can be
electrically connected to a driver circuit SD using the conductive
material film ACF1.
[0350] The display panel 700D can include the terminal 519D(2). The
terminal 519D(2) is electrically connected to a terminal which can
be formed in the same process for forming the pixel circuit
730(i,j) or the terminal 519D(1). One surface of the terminal
519D(2) is contact with other component and faces the same
direction as a surface of the reflective film which reflects
external light used for performing display. Note that the terminal
519D(2) can be electrically connected to the second conductive film
752 using the conductive member CP, for example.
[0351] Note that the driver circuit SD supplies an image signal in
accordance with image information.
[0352] Components of the display panel 700D will be described
below. Note that the components cannot be clearly distinguished and
one unit serves as another unit or include part of another unit in
some cases.
[0353] For example, in the case where a conductive film reflecting
visible light is used as the first conductive film 751, the first
conductive film 751 can be used as a reflective film: the first
conductive film 751 serves as the reflective film, and the
reflective film serves as the first conductive film 751.
<Structure>
[0354] The display panel 700D includes the substrate 570, the
substrate 770, the wiring 511, and the terminals 519D(1) and
519D(2) (see FIG. 8A).
[0355] The display panel 700D includes the sealant 705, the bonding
layer 505, the structure KB1, and the structure KB2.
[0356] The display panel 700D includes the pixel 702(i,j), the
first display element 750, and the second display element 550.
[0357] The display panel 700D includes the first conductive film
751, the second conductive film 752, the layer 753 containing a
liquid crystal material, the opening 751H, and the reflective
film.
[0358] The display panel 700D includes the third conductive film
551, the fourth conductive film 552, and the layer 553 containing a
light-emitting organic compound.
[0359] The display panel 700D includes the functional layer 520D,
the pixel circuit 730(i,j), the first contact 591, the second
contact 592, or the third contact 593 (see FIG. 8A and FIG.
1C).
[0360] The display panel 700D includes the switching element SW1,
the switching element SW2, the transistor M, the transistor MD, the
insulating film 501B, the insulating film 501C, the insulating film
521A, the insulating film 521B, and the insulating film 528.
[0361] The display panel 700D includes the coloring film CF1, the
coloring film CF2, the light-blocking film BM, the insulating film
771, the alignment film AF1, the alignment film AF2, and the
optical film 770P.
[0362] The display panel 700D includes the driver circuit GD and
the driver circuit SD.
<<Substrate 570>>
[0363] The substrate 570 can be formed using a material having heat
resistance high enough to withstand heat treatment in the
manufacturing process. For example, a material similar to the
material which can be used for the substrate 570 and is described
in Embodiment 1 can be used.
<<Substrate 770>>
[0364] A light-transmitting material can be used for the substrate
770. For example, a material that can be used for the substrate 570
can be used for the substrate 770.
<<Wiring 511, Terminal 519D(1), and Terminal
519D(2)>>
[0365] A conductive material can be used for the wiring 511, the
terminal 519D(1), or the terminal 519D(2). For example, a material
similar to the material which can be used for the wiring 511 or 519
in Embodiment 1 can be used.
<<First Contact 591, Second Contact 592, and Third Contact
593>>
[0366] A conductive material can be used for the first contact 592
or the second contact 592. For example, a material similar to the
material which can be used for the wiring 511 or the terminal
519D(1) or 519D(2) can be used.
<<Bonding Layer 505 and Sealant 705>>
[0367] An inorganic material, an organic material, a composite
material of an inorganic material and an organic material, or the
like can be used for the bonding layer 505 or the sealant 705. For
example, a material similar to the material of the bonding layer
505 or the sealant 705 described in Embodiment 1 can be used.
<<Structures KB1 and KB2>>
[0368] The structures KB1 and KB2 can be formed using an organic
material, an inorganic material, a composite material of an organic
material and an inorganic material, or the like. Accordingly, a
predetermined space can be provided between components between
which the structure KB1 or KB2 is provided. For example, a material
similar to the material which can be used for the structure KB1 or
KB2 and is described in Embodiment 1 can be used.
<<Pixel 702(i,j)>>
[0369] The pixel 702(i,j) can include the first display element
750, the second display element 550, and the functional layer
520D.
[0370] The pixel 702(i,j) can include the coloring film CF1, the
light-blocking film BM, the insulating film 771, the alignment film
AF1, the alignment film AF2, and the coloring film CF2.
<<First Display Element 750>>
[0371] For example, a display element having a function of
controlling transmission or reflection of light can be used as the
first display element 750. For example, a combined structure of a
polarizing plate and a liquid crystal element or a MEMS shutter
display element can be used. The use of a reflective display
element can reduce power consumption of a display panel.
Specifically, a reflective liquid crystal display element can be
used as the first display element 750. For example, a material
similar to the material which can be used for the first display
element 750 and is described in Embodiment 1 can be used.
<<Reflective Film>>
[0372] The reflective film can be formed of a material reflecting
light which passes through the layer 753 containing a liquid
crystal material, in which case the first display element 750 can
be a reflective liquid crystal element. For example, a material
similar to the material which can be used for the reflective film
and is described in Embodiment 1 can be used.
<<Opening 751H>>
[0373] For example, the opening described in Embodiment 1 can be
used as the opening.
<<Second Display Element 550>>
[0374] A light-emitting element, for example, can be used as the
second display element 550. Specifically, an organic
electroluminescence element, an inorganic electroluminescence
element, a light-emitting diode, or the like can be used for the
second display element 550.
[0375] For example, a stack formed to emit white light can be used
as the layer 553 containing a light-emitting organic material.
Specifically, a stack of a layer containing a light-emitting
organic material containing a fluorescent material that emits blue
light, a layer containing a material that is other than a
fluorescent material and that emits green light and/or red light,
or a layer containing a material that is other than a fluorescent
material and that emits yellow light can be used as the layer 553
containing a light-emitting organic material.
[0376] For example, a material used for the wiring 511 can be used
for the third conductive film 551 or the fourth conductive film
552.
[0377] For example, a conductive material that transmits visible
light can be used for the third conductive film 551.
[0378] For example, a conductive material that transmits visible
light can be used for the fourth conductive film 552.
[0379] Specifically, conductive oxide, indium-containing conductive
oxide, indium oxide, indium tin oxide, indium zinc oxide, zinc
oxide, zinc oxide to which gallium is added, or the like can be
used for the third conductive film 551.
[0380] Alternatively, a metal film that is thin enough to transmit
light can be used as the third conductive film 551.
<<Functional Layer 520D>>
[0381] The functional layer 520D includes the pixel circuit
730(i,j), the first contact 591, the second contact 592, and the
third contact 593. The functional layer 520D includes the
insulating film 501A, the insulating film 501B, the insulating film
501C, the insulating film 521A, the insulating film 521B, and the
insulating film 528.
<<Pixel circuit 730(i,j)>>
[0382] For example, a structure similar to the structure which can
be used for the pixel circuit 730(i,j) and is described in
Embodiment 1 can be used.
<<Transistor M>>
[0383] The transistor M includes the semiconductor film 508 and the
conductive film 504 which includes a region overlapping with the
semiconductor film 508 (see FIG. 8B). The transistor M includes the
conductive film 512A, the conductive film 512B, and the insulating
film 506 between the semiconductor film 508 and the conductive film
504. For example, a structure similar to the structure which can be
used for the transistor M and is described in Embodiment 1 can be
used.
<<Switches SW1 and SW2>>
[0384] A transistor can serve as the switch SW1 or SW2.
[0385] For example, a transistor which can be fabricated in the
same process as the transistor M can be used as the switch SW1 or
SW2.
<<Insulating Film 501B and Insulating Film 501C>>
[0386] Although the insulating film 501C is stacked over the
insulating film 501B in this embodiment, the insulating film 501C
may be omitted. For example, a material similar to the material
which can be used for the insulating film 501B or the insulating
film 501C and is described in Embodiment 1 can be used.
<<Insulating films 521A, 521B, and 528>>
[0387] For example, a material similar to the material which can be
used for the insulating film 521A, 521B, or 528 and is described in
Embodiment 1 can be used.
<<Coloring Film CF1 and CF2>>
[0388] For example, a material similar to the material which can be
used for the coloring film CF1 or CF2 and is described in
Embodiment 1 can be used.
<<Light-Blocking Film BM>>
[0389] A material that prevents light transmission can be used for
the light-blocking film BM, in which case the light-blocking film
BM serves as a black matrix, for example.
<<Insulating film 771>>
[0390] The insulating film 771 can be formed of polyimide, epoxy
resin, acrylic resin, or the like.
<<Alignment Films AF1 and AF2>>
[0391] The alignment films AF1 and AF2 can be formed of a material
containing polyimide or the like, such as a material formed to have
a predetermined alignment by a rubbing process or an optical
alignment process.
<<Optical Film 770P>>
[0392] For example, a material similar to the material which can be
used for the optical film 770P and is described in Embodiment 1 can
be used.
<<Driver Circuit GD>>
[0393] For example, a structure similar to the structure which can
be used for the driver circuit GD and is described in Embodiment 1
can be used.
<<Driver Circuit SD>>
[0394] For example, an integrated circuit can be used in the driver
circuit SD. Specifically, an integrated circuit formed over a
silicon substrate can be used.
[0395] For example, a chip on glass (COG) method can be used to
mount the driver circuit SD on a pad provided over the insulating
film 501C. Specifically, a conductive material film can be used to
mount the integrated circuit on the pad. Note that the pad is
electrically connected to the pixel circuit 730(i,j).
<Structure Example 2 of Display Panel>
[0396] Another structure of a display panel of one embodiment of
the present invention will be described with reference to FIGS. 9A
to 9D.
[0397] FIGS. 9A to 9D illustrate structures of a pixel circuit
which can be used for the display panel of one embodiment of the
present invention. The pixel circuit shown in FIGS. 9A to 9D can be
used instead of the pixel circuit 730(i,j) in FIG. 1C.
[0398] Note that the pixel circuit 730(i,j) in FIG. 9A is different
from the pixel circuit 730(i,j) in FIG. 1C in that it is
electrically connected to signal lines S1(j) and S2(j).
[0399] The pixel circuit 730(i,j) shown in FIG. 9B is different
from the pixel circuit 730(i,j) shown in FIG. 1C in that it is
electrically connected to the signal lines S1(j) and S2(j) and that
the control electrodes of the switches SW1 and SW2 are electrically
connected to the scan line G1(i).
[0400] The pixel circuit 730(i,j) shown in FIG. 9C is different
from the pixel circuit 730(i,j) shown in FIG. 1C in that the second
electrode of the capacitor C1 is electrically connected to a wiring
CS. Note that a wiring other than the wiring VCOM1 can be used as
the wiring CS.
[0401] The pixel circuit 730(i,j) shown in FIG. 9D is different
from the pixel circuit 730(i,j) shown in FIG. 9A in that the second
electrode of the capacitor C2 is electrically connected to the
wiring ANO and that the second electrode of the transistor M is
electrically connected to the wiring ANO. Note that for example,
the transistor M can have a structure similar to the transistor MD
including the conductive film 524.
<Structure Example 3 of Display Panel>
[0402] Another structure of the display panel of one embodiment of
the present invention will be described with reference to FIG.
10.
[0403] FIG. 10 illustrates the structure of the display panel of
one embodiment of the present invention. FIG. 10 is a
cross-sectional view of a display panel 700E, which is one
embodiment of the present invention, taken along the section lines
X1-X2, X3-X4, and X5-X6 in FIG. 1A.
[0404] Note that the display panel 700E shown in FIG. 10 is
different from the display panel 700D shown in FIG. 8A in that the
first conductive film 751 and the second conductive film 752
include a region embedded in the insulating film 501B and a region
exposed from the insulating film 501B and that the second contact
592 and the third conductive film 551 contain the same conductive
material.
[0405] Specifically, the first display element 750 of the display
panel 700E includes a liquid crystal display element driven in an
IPS mode or the like.
<Structure Example 4 of Display Panel>
[0406] Another structure of the display panel of one embodiment of
the present invention will be described with reference to FIG.
11.
[0407] FIG. 11 illustrates a structure of the display panel of one
embodiment of the present invention. FIG. 11 is a cross-sectional
view of the display panel 700E, which is one embodiment of the
present invention, taken along the section lines X1-X2, X3-X4, and
X5-X6 in FIG. 1A.
[0408] Note that the display panel 700F in FIG. 11 is different
from the display panel 700D in FIG. 8A in that a layer 753T
containing electronic ink is provided instead of the layer 753
containing a liquid crystal material, that a first transparent
conductive film 751T is provided instead of the first conductive
film 751 having the opening 751H, and that a transparent structure
KB3 lies in a region overlapping with the second display element
550.
[0409] Specifically, the layer 753T containing electronic ink of
the display panel 700F contains rewritable electronic ink, such as
electrophoretic ink. By electrical control of the electronic ink,
rewriting and erasing can be performed.
[0410] This embodiment can be combined with any of the other
embodiments in this specification as appropriate.
Embodiment 3
[0411] In this embodiment, a method for manufacturing a display
panel of one embodiment of the present invention will be described
with reference to FIGS. 12 to 19.
[0412] FIG. 12 is a flow chart illustrating a method for
manufacturing a display panel 700D of one embodiment of the present
invention. FIGS. 13 to 19 are cross-sectional views of the display
panel 700D in the manufacturing steps taken along the section lines
X1-X2, X3-X4, and X5-X6 of FIG. 1A.
<Method for Manufacturing Display Panel>
[0413] The method for manufacturing the display panel 700D
described in this embodiment is composed of the following 11
steps.
<Step 1>
[0414] In a step 1, the insulating film 501A is formed over a
substrate for use in manufacturing processes (see U1 in FIG. 12).
For example, the insulating film 501A is formed so that a
separation film 510W is provided between the insulating film 501A
and a substrate 510.
[0415] The substrate for use in manufacturing processes can
include, for example, the substrate 510 and the separation film
510W having a region overlapping with the substrate 510.
[0416] The substrate 510 can be formed using a material having heat
resistance high enough to withstand heat treatment in the
manufacturing process.
[0417] For example, a large-sized glass substrate having any of the
following sizes can be used: the 6th generation (1500 mm.times.1850
mm), the 7th generation (1870 mm.times.2200 mm), the 8th generation
(2200 mm.times.2400 mm), the 9th generation (2400 mm.times.2800
mm), and the 10th generation (2950 mm.times.3400 mm). Thus, a
large-sized LCD can be used as the substrate 510, and a large-sized
display device can be manufactured.
[0418] For the substrate 510, an organic material, an inorganic
material, a composite material of an organic material and an
inorganic material, or the like can be used. For example, an
inorganic material such as glass, ceramic, or metal can be used for
the substrate 510.
[0419] Specifically, non-alkali glass, soda-lime glass, potash
glass, crystal glass quartz, sapphire, or the like can be used for
the substrate 510. Specifically, an inorganic oxide, an inorganic
nitride, an inorganic oxynitride, or the like can be used for the
substrate 510. For example, a silicon oxide film, a silicon nitride
film, a silicon oxynitride film, or an aluminum oxide film can be
used for the substrate 510. Stainless steel, aluminum, or the like
can be used for the substrate 510.
[0420] For example, an organic material such as a resin, a resin
film, or plastic can be used for the substrate 510. Specifically, a
resin film or resin plate of polyester, polyolefin, polyamide,
polyimide, polycarbonate, an acrylic resin, or the like can be used
for the substrate 510.
[0421] For example, a composite material such as a resin film to
which a metal plate, a thin glass plate, or a film of an inorganic
material is attached can be used for the substrate 510. For
example, a composite material formed by dispersing a fibrous or
particulate metal, glass, inorganic material, or the like into a
resin film can be used as the substrate 510. For example, a
composite material formed by dispersing a fibrous or particulate
resin, organic material, or the like into an inorganic material can
be used as the substrate 510.
[0422] A single-layer material or a stacked-layer material in which
a plurality of layers are stacked can be used for the substrate
510. For example, a stacked-layer material in which a base, an
insulating film that prevents diffusion of impurities contained in
the base, and the like are stacked can be used for the substrate
510.
[0423] For example, the separation film 510W can be formed using a
material that allows the insulating film 501A to be separated from
the substrate 510 in the step 9.
[0424] Note that the separation film 510W can remain on the
substrate 510 side after the insulating film 501A is separated from
the substrate 510. Alternatively, the separation film 510W can be
separated together with the insulating film 501A from the substrate
510.
[0425] Specifically, the separation film 510W can remain on the
substrate 510 side after the insulating film 501A can be separated
from the substrate 510 in the case where the substrate 510, the
separation film 501W, and the insulating film 501A are formed using
a non-alkali glass substrate, a film containing tungsten or the
like, and a film containing inorganic oxide or inorganic
oxynitride, respectively.
[0426] The separation film 510W can be separated together with the
insulating film 501A from the substrate 510 when the substrate 510,
the separation film 510W, and the insulating film 501A are formed
using a non-alkali glass substrate, a film containing polyimide,
and a film containing various materials, respectively.
[0427] For example, the insulating film 501A is formed on the
separation film 510W by a chemical vapor deposition method, a
sputtering method, a coating method, or the like. Then, unnecessary
portions are removed by a photolithography process, or the like so
that the insulating film 501A is completed.
[0428] Note that it is preferable that the insulating film 501A be
larger than the separation film 510W so that the peripheral portion
of the insulating film 501A is in contact with the substrate 510,
in which case occurrence of unintended separation of the insulating
film 501A from the substrate for use in manufacturing processes can
be reduced.
[0429] Specifically, a 0.7-mm-thick glass plate is used as the
substrate 510, and a stacked-layer material of a 200-nm-thick
silicon oxynitride film and a 30-nm-thick tungsten film stacked in
this order from the substrate 510 side is used for the separation
film 510W. In addition, a film including a stacked-layer material
in which a 600-nm-thick silicon oxynitride film and a 200-nm-thick
silicon nitride film are stacked in this order from the separation
film 510W side can be used as the insulating film 501A. Note that a
silicon oxynitride film refers to a film that includes more oxygen
than nitrogen, and a silicon nitride oxide film refers to a film
that includes more nitrogen than oxygen.
[0430] Specifically, instead of the insulating film 501A, a film
including a stacked-layer material of a 600-nm-thick silicon
oxynitride film, a 200-nm-thick silicon nitride film, a
200-nm-thick silicon oxynitride film, a 140-nm-thick silicon
nitride oxide film, and a 100-nm-thick silicon oxynitride film
stacked in this order from the separation film 510W side can be
used.
<<Step 2>>
[0431] In a step 2, a reflective film and terminals are formed (see
U2 in FIG. 12). Note that the first conductive film 751 serves as
the reflective film in an example of this embodiment.
[0432] The reflective film includes the opening 751H. The terminals
include the terminals 519D(1) and 519D(2).
[0433] A film containing a conductive material is formed on the
insulating film 501A by a chemical vapor deposition method, a
sputtering method, a coating method, or the like. Then, unnecessary
portions are removed by a photolithography process, so that the
first conductive film 751 used as the reflective film and the
terminals 519D(1) and 519D(2) are completed.
<<Step 3>>
[0434] In a step 3, the insulating film 501B covering the
reflective film and the terminal is formed (see U3 in FIG. 12).
Note that the insulating film 501C having a region overlapping with
the insulating film 501B may be formed successively after the
insulating film 501B is formed.
[0435] The insulating film 501B and the insulating film 501C have
openings.
[0436] A film suppressing impurity diffusion is formed to cover the
reflective film and the terminal by a chemical vapor deposition
method, a sputtering method, a coating method, or the like.
[0437] Then, an opening reaching the first conductive film 751 and
an opening reaching the terminal 519D(1) are formed by a
photolithography process or the like, so that the insulating film
501B and the insulating film 501C are completed.
<<Step 4>>
[0438] In a step 4, the first contact 591 and the third contact 593
are formed (see U4 in FIG. 12 and FIG. 13). The reflective film is
electrically connected to the first contact 591. The terminal
519D(1) is electrically connected to the third contact 593. Note
that the conductive film 504 serving as a gate electrode of the
transistor M, the transistor MD, or the transistor which can be
used as the switch SW1 may be formed together with the first
contact 591 and the terminal 519D.
[0439] A film containing a conductive material is formed to be in
contact with the insulating film 501C, the opening reaching the
first conductive film 751, and the opening reaching the terminal
519D(1) by a chemical vapor deposition method, a sputtering method,
a coating method, or the like.
[0440] Then, unnecessary portions are removed by a photolithography
process or the like, so that the first contact 591, the third
contact 593, and the conductive film 504 are completed.
<<Step 5>>
[0441] In a step 5, a pixel circuit electrically connected to the
first contact 591 and the third contact 593 is formed (see U5 in
FIG. 12).
[0442] A film containing a conductive material, a film containing
an insulating material, a film containing a semiconductor material,
and the like are formed by a chemical vapor deposition method, a
sputtering method, or the like. Then, unnecessary portions of the
films are removed by a photolithography method or the like. With
combination of a deposition method and a photolithography method or
the like, the pixel circuit including the transistor M, the
transistor MD, and the transistor or the like serving as the switch
SW1 is completed.
[0443] Next, the insulating films 516 and 518 protecting elements,
such as transistors, of the pixel circuit are formed. Furthermore,
the conductive film 524 serving as a second gate electrode is
formed between the insulating films 516 and 518.
[0444] Then, the coloring film CF2 is formed.
[0445] Then, the insulating film 521A is formed. An opening
reaching the pixel circuit is formed in the insulating films 516,
518, and 521A.
<<Step 6>>
[0446] In a step 6, the second contact 592 electrically connected
to the pixel circuit is formed (see U6 in FIG. 12 and FIG. 14).
Note that a wiring may be formed together with the second contact
592.
[0447] For example, a film containing a conductive material is
formed by a chemical vapor deposition method, a sputtering method,
a coating method, or the like.
[0448] Then, unnecessary portions of the films are removed by a
photolithography method or the like to form the second contact
592.
<<Step 7>>
[0449] In a step 7, the second display element 550 electrically
connected to the second contact 592 is formed (see U7 in FIG. 12
and FIG. 15).
[0450] For example, the insulating film 521B is formed between the
second contact 592 and the second display element 550.
[0451] Next, to form the third conductive film 551 electrically
connected to the second contact 592, a film containing a conductive
material is formed by a chemical vapor deposition method, a
sputtering method, or the like. Then, unnecessary portions are
removed by a photolithography method, so that the third conductive
film 551 is finished.
[0452] Next, the insulating film 528 having an opening in a region
overlapping with the third conductive film 551 is formed. Note that
the ends of the third conductive film 551 are covered by the
insulating film 528. For example, a photosensitive polymer film is
formed by a coating method or the like, and its unnecessary
portions are removed by a photolithography method or the like, so
that the insulating film 528 is finished.
[0453] Then, the structure KB2 in contact with the insulating film
528 is formed by a method similar to that of the insulating film
528, for example.
[0454] Then, the layer 553 containing a light-emitting organic
compound is formed to cover the third conductive film 551 exposed
in the opening of the insulating film 528. An evaporation method, a
printing method, an ink-jet method, or the like using a shadow mask
can be used.
[0455] Then, the fourth conductive film 552 is formed such that the
layer 553 containing a light-emitting organic compound is provided
between the third conductive film 551 and the fourth conductive
film 552. Specifically, an evaporation method, a sputtering method,
or the like using a shadow mask can be used. Note that the fourth
conductive film 552 is electrically connected to the wiring
511.
<<Step 8>>
[0456] In a step 8, the substrate 570 is stacked (see U8 in FIG. 12
and FIG. 16).
[0457] A fluid resin or the like is applied to form the bonding
layer 505. Specifically, a coating method, a printing method, an
ink-jet method, or the like can be used. Alternatively, a
sheet-like fluid resin or the like is bonded to form the bonding
layer 505.
[0458] Then, the functional layer 520D and the substrate 570 are
bonded using the bonding layer 505.
<<Step 9>>
[0459] In a step 9, the substrate 510 for use in manufacturing
processes is separated (see U9 in FIG. 12 and FIG. 17).
[0460] For example, part of the separation film 510W can be removed
from the insulating film 501A by sticking a sharp tip into the
separation film 510W from the substrate 510 for use in
manufacturing processes, or by a method using a laser or the like
(e.g., a laser ablation method), thereby forming a separation
starting point.
[0461] Then, the substrate 510 for use in manufacturing processes
is gradually separated from the separation starting point.
[0462] Note that the separation may be performed while the vicinity
of the interface between the separation film 510W and the
insulating film 501A is irradiated with ions to remove static
electricity. Specifically, the ions may be generated by an ionizer.
Alternatively, a liquid may be ejected and sprayed by a nozzle to
the interface between the separation film 510W and the insulating
film 501A. For example, as the liquid to be injected or the liquid
to be sprayed, water, a polar solvent, a liquid which dissolves the
separation film 510W, or the like can be used. By injecting such a
liquid, influence of static electricity and the like accompanying
the separation can be reduced.
[0463] Particularly in the case where a film containing tungsten
oxide is used for the separation film 510W, the substrate 510 is
separated while a water-containing liquid is injected or sprayed,
which leads to a reduction in stress with separation.
<<Step 10>>
[0464] In a step 10, the insulating film 501A is removed to expose
the reflective film and the terminal (see U10 in FIG. 12 and FIG.
18).
[0465] The insulating film 501A can be removed by etching, chemical
mechanical polishing, or the like, such as wet etching or dry
etching.
<<Step 11>>
[0466] In a step 11, the first display element is formed (see U11
in FIG. 12 and FIG. 19).
[0467] A counter substrate is prepared. Specifically, the substrate
770 including the light blocking film BM, the coloring film CF1,
the insulating film 771, the second conductive film 752, the
structure KB1, and the alignment film AF2 is prepared as the
counter substrate.
[0468] Then, the alignment film AF1 including a region overlapping
with the insulating film 501B and the first conductive film 751 is
formed using a printing method, a rubbing method, and the like.
[0469] The sealant 705 is formed. Specifically, a fluid resin is
applied to form a frame-like shape using a dispensing method, a
printing method, or the like. Note that a material containing the
conductive member CP is applied to a region of the sealant 705
overlapping with the terminal 519D(2).
[0470] Then, a liquid crystal material is dropped in the region
surrounded by the sealant 705 using a dispensing method.
[0471] Then, the substrate 770 is bonded to the insulating film
501B using the sealant 705. Note that the structure KB1 is provided
between the insulating film 501B and the substrate 770 to
electrically connect the terminal 519D(2) and the second conductive
film 752 using the conductive member CP.
[0472] The manufacturing method of the display panel 700D in this
embodiment includes the step for separating the substrate 510 for
use in manufacturing processes and the step for removing the
insulating film 501A to expose the reflective film and the
terminal. Accordingly, a step at the edge of the reflective film
can be minimized to reduce the possibility of alignment defects due
to the step. In addition, the surface of the terminal at which
contact with other components is made can be exposed. A
manufacturing method of a novel display panel that is highly
convenient or reliable can be thus provided.
[0473] This embodiment can be combined with any of the other
embodiments in this specification as appropriate.
Embodiment 4
[0474] In this embodiment, the structure of a transistor which can
be used for the display panel of one embodiment of the present
invention will be described with reference to FIGS. 20A to 20C.
<Structural Example of Semiconductor Device>
[0475] FIG. 20A is a top view of the transistor 100. FIG. 20B is a
cross-sectional view taken along the section line X1-X2 in FIG.
20A, and FIG. 20C is a cross-sectional view taken along the section
line Y1-Y2 in FIG. 20A. Note that in FIG. 20A, some components of
the transistor 100 (e.g., an insulating film serving as a gate
insulating film) are not illustrated to avoid complexity. In some
cases, the direction of the section line Y1-Y2 is referred to as a
channel length direction and the direction of the section line
X1-X2 is referred to as a channel width direction. As in FIG. 20A,
some components might not be illustrated in some top views of
transistors described below.
[0476] Note that the transistor 100 can be used in the display
panel described in Embodiment 1 or 2.
[0477] For example, when the transistor 100 is used as the
transistor M, a substrate 102, a conductive film 104, a stacked
film of an insulating film 106 and an insulating film 107, an oxide
semiconductor film 108, a conductive film 112a, a conductive film
112b, a stacked film of an insulating film 114 and an insulating
film 116, and an insulating film 118 can be referred to as the
insulating film 501C, the conductive film 504, the insulating film
506, the semiconductor film 508, the conductive film 512A, the
conductive film 512B, an insulating film 516, and the insulating
film 518, respectively.
[0478] The transistor 100 includes a conductive film 104
functioning as a gate electrode over a substrate 102, an insulating
film 106 over the substrate 102 and the conductive film 104, an
insulating film 107 over the insulating film 106, an oxide
semiconductor film 108 over the insulating film 107, and conductive
films 112a and 112b functioning as source and drain electrodes
electrically connected to the oxide semiconductor film 108. Over
the transistor 100, specifically, over the conductive films 112a
and 112b and the oxide semiconductor film 108, insulating films
114, 116, and 118 are provided. The insulating films 114, 116, and
118 function as protective insulating films for the transistor
100.
[0479] The oxide semiconductor film 108 includes a first oxide
semiconductor film 108a on the conductive film 104 side and a
second oxide semiconductor film 108b over the first oxide
semiconductor film 108a. Furthermore, the insulating films 106 and
107 function as gate insulating films of the transistor 100.
[0480] An In-M oxide (M is Ti, Ga, Sn, Y, Zr, La, Ce, Nd, or Hf) or
an In-M-Zn oxide can be used for the oxide semiconductor film 108.
It is particularly preferable to use an In-M-Zn oxide for the
semiconductor film 108.
[0481] The first oxide semiconductor film 108a includes a first
region in which the atomic proportion of In is larger than the
atomic proportion of M. The second oxide semiconductor film 108b
includes a second region in which the atomic proportion of In is
smaller than that in the first oxide semiconductor film 108a. The
second region include a portion thinner than the first region.
[0482] The first oxide semiconductor film 108a including the first
region in which the atomic proportion of In is larger than that of
M can increase the field-effect mobility (also simply referred to
as mobility or .mu.FE) of the transistor 100. Specifically, the
field-effect mobility of the transistor 100 can exceed 10
cm.sup.2/Vs.
[0483] For example, the use of the transistor with high
field-effect mobility for a gate driver that generates a gate
signal (specifically, a demultiplexer connected to an output
terminal of a shift register included in a gate driver) allows a
semiconductor device or a display device to have a narrow
frame.
[0484] On the other hand, the first oxide semiconductor film 108a
including the first region in which the atomic proportion of In is
larger than that of M makes it easier to change electrical
characteristics of the transistor 100 in light irradiation.
However, in the semiconductor device of one embodiment of the
present invention, the second oxide semiconductor film 108b is
formed over the first oxide semiconductor film 108a. In addition,
the thickness of a portion including a channel region and the
vicinity of the channel region in the second oxide semiconductor
film 108b is smaller than the thickness of the first oxide
semiconductor film 108a.
[0485] Furthermore, the second oxide semiconductor film 108b
includes the second region in which the atomic proportion of In is
smaller than the first oxide semiconductor film 108a and thus has
larger Eg than that of the first oxide semiconductor film 108a. For
this reason, the oxide semiconductor film 108 which is a layered
structure of the first oxide semiconductor film 108a and the second
oxide semiconductor film 108b has high resistance to a negative
bias stress test with light irradiation.
[0486] The amount of light absorbed by the oxide semiconductor film
108 can be reduced during light irradiation. As a result, the
change in electrical characteristics of the transistor 100 due to
light irradiation can be reduced. In the semiconductor device of
one embodiment of the present invention, the insulating film 114 or
the insulating film 116 includes excess oxygen. This structure can
further reduce the change in electrical characteristics of the
transistor 100 due to light irradiation.
[0487] Here, the oxide semiconductor film 108 is described in
detail with reference to FIG. 20B.
[0488] FIG. 20B is a cross-sectional enlarged view of the oxide
semiconductor film 108 and the vicinity thereof in the transistor
100 illustrated in FIG. 20C.
[0489] In FIG. 20B, t1, t2-1, and t2-2 denote a thickness of the
oxide semiconductor film 108a, one thickness of the oxide
semiconductor film 108b, and the other thickness the oxide
semiconductor film 108b, respectively. The oxide semiconductor film
108b over the oxide semiconductor film 108a prevents the oxide
semiconductor film 108a from being exposed to an etching gas, an
etchant, or the like when the conductive films 112a and 112b are
formed. This is why the oxide semiconductor film 108a is not or is
hardly reduced in thickness. In contrast, in the oxide
semiconductor film 108b, a portion not overlapping with the
conductive films 112a and 112b is etched by formation of the
conductive films 112a and 112b, so that a depression is formed in
the etched region. In other words, a thickness of the oxide
semiconductor film 108b in a region overlapping with the conductive
films 112a and 112b is t2-1, and a thickness of the oxide
semiconductor film 108b in a region not overlapping with the
conductive films 112a and 112b is t2-2.
[0490] As for the relationships between the thicknesses of the
oxide semiconductor film 108a and the oxide semiconductor film
108b, t2-1>t1>t2-2 is preferable. A transistor with the
thickness relationships can have high field-effect mobility and
less variation in threshold voltage in light irradiation.
[0491] When oxygen vacancy is formed in the oxide semiconductor
film 108 included in the transistor 100, electrons serving as
carriers are generated; as a result, the transistor 100 tends to be
normally-on. Therefore, for stable transistor characteristics, it
is important to reduce oxygen vacancy in the oxide semiconductor
film 108 particularly oxygen vacancy in the oxide semiconductor
film 108a. In the structure of the transistor of one embodiment of
the present invention, excess oxygen is introduced into an
insulating film over the oxide semiconductor film 108, here, the
insulating film 114 and/or the insulating film 116 over the oxide
semiconductor film 108, whereby oxygen is moved from the insulating
film 114 and/or the insulating film 116 to the oxide semiconductor
film 108 to fill oxygen vacancy in the oxide semiconductor film 108
particularly in the oxide semiconductor film 108a.
[0492] It is preferable that the insulating films 114 and 116 each
include a region (oxygen excess region) including oxygen in excess
of that in the stoichiometric composition. In other words, the
insulating films 114 and 116 are insulating films capable of
releasing oxygen. Note that the oxygen excess region is formed in
the insulating films 114 and 116 in such a manner that oxygen is
introduced into the insulating films 114 and 116 after the
deposition, for example. As a method for introducing oxygen, an ion
implantation method, an ion doping method, a plasma immersion ion
implantation method, plasma treatment, or the like may be
employed.
[0493] In order to fill oxygen vacancy in the oxide semiconductor
film 108a, the thickness of the portion including the channel
region and the vicinity of the channel region in the oxide
semiconductor film 108b is preferably small, and t2-2<t1 is
preferably satisfied. For example, the thickness of the portion
including the channel region and the vicinity of the channel region
in the oxide semiconductor film 108b is preferably more than or
equal to 1 nm and less than or equal to 20 nm, more preferably more
than or equal to 3 nm and less than or equal to 10 nm.
[0494] Other constituent elements of the semiconductor device of
this embodiment are described below in detail.
<<Substrate>>
[0495] There is no particular limitation on the property of a
material and the like of the substrate 102 as long as the material
has heat resistance enough to withstand at least heat treatment to
be performed later. For example, a glass substrate, a ceramic
substrate, a quartz substrate, or a sapphire substrate may be used
as the substrate 102.
[0496] Alternatively, a single crystal semiconductor substrate or a
polycrystalline semiconductor substrate of silicon or silicon
carbide, a compound semiconductor substrate of silicon germanium,
an SOI substrate, or the like can be used as the substrate 102.
[0497] Alternatively, any of these substrates provided with a
semiconductor element, an insulating film, or the like may be used
as the substrate 102.
[0498] In the case where a glass substrate is used as the substrate
102, a large substrate having any of the following sizes can be
used: the 6th generation (1500 mm.times.1850 mm), the 7th
generation (1870 mm.times.2200 mm), the 8th generation (2200
mm.times.2400 mm), the 9th generation (2400 mm.times.2800 mm), and
the 10th generation (2950 mm.times.3400 mm). Thus, a large display
device can be manufactured.
[0499] Alternatively, a flexible substrate may be used as the
substrate 102, and the transistor 100 may be provided directly on
the flexible substrate. Alternatively, a separation layer may be
provided between the substrate 102 and the transistor 100. The
separation layer can be used when part or the whole of a
semiconductor device formed over the separation layer is separated
from the substrate 102 and transferred onto another substrate. In
such a case, the transistor 100 can be transferred to a substrate
having low heat resistance or a flexible substrate as well.
<<Conductive Film Functioning as Gate Electrode and Source
and Drain Electrodes>>
[0500] The conductive film 104 functioning as a gate electrode and
the conductive films 112a and 112b functioning as a source
electrode and a drain electrode, respectively, can each be formed
using a metal element selected from chromium (Cr), copper (Cu),
aluminum (Al), gold (Au), silver (Ag), zinc (Zn), molybdenum (Mo),
tantalum (Ta), titanium (Ti), tungsten (W), manganese (Mn), nickel
(Ni), iron (Fe), and cobalt (Co); an alloy including any of these
metal element as its component; an alloy including a combination of
any of these metal elements; or the like.
[0501] Furthermore, the conductive films 104, 112a, and 112b may
have a single-layer structure or a stacked-layer structure of two
or more layers. For example, a single-layer structure of an
aluminum film including silicon, a two-layer structure in which a
titanium film is stacked over an aluminum film, a two-layer
structure in which a titanium film is stacked over a titanium
nitride film, a two-layer structure in which a tungsten film is
stacked over a titanium nitride film, a two-layer structure in
which a tungsten film is stacked over a tantalum nitride film or a
tungsten nitride film, and a three-layer structure in which a
titanium film, an aluminum film, and a titanium film are stacked in
this order can be given. Alternatively, an alloy film or a nitride
film in which aluminum and one or more elements selected from
titanium, tantalum, tungsten, molybdenum, chromium, neodymium, and
scandium are combined may be used.
[0502] The conductive films 104, 112a, and 112b can be formed using
a light-transmitting conductive material such as indium tin oxide,
indium oxide including tungsten oxide, indium zinc oxide including
tungsten oxide, indium oxide including titanium oxide, indium tin
oxide including titanium oxide, indium zinc oxide, or indium tin
oxide to which silicon oxide is added.
[0503] A Cu--X alloy film (X is Mn, Ni, Cr, Fe, Co, Mo, Ta, or Ti)
may be used for the conductive films 104, 112a, and 112b. Use of a
Cu--X alloy film enables the manufacturing cost to be reduced
because wet etching process can be used in the processing.
<<Insulating Film Functioning as Gate Insulating
Film>>
[0504] As each of the insulating films 106 and 107 functioning as
gate insulating films of the transistor 100, an insulating film
including at least one of the following films formed by a plasma
enhanced chemical vapor deposition (PECVD) method, a sputtering
method, or the like can be used: a silicon oxide film, a silicon
oxynitride film, a silicon nitride oxide film, a silicon nitride
film, an aluminum oxide film, a hafnium oxide film, an yttrium
oxide film, a zirconium oxide film, a gallium oxide film, a
tantalum oxide film, a magnesium oxide film, a lanthanum oxide
film, a cerium oxide film, and a neodymium oxide film. Note that
instead of a stacked-layer structure of the insulating films 106
and 107, an insulating film of a single layer formed using a
material selected from the above or an insulating film of three or
more layers may be used.
[0505] The insulating film 106 has a function as a blocking film
which inhibits penetration of oxygen. For example, in the case
where excess oxygen is supplied to the insulating film 107, the
insulating film 114, the insulating film 116, and/or the oxide
semiconductor film 108, the insulating film 106 can inhibit
penetration of oxygen.
[0506] Note that the insulating film 107 that is in contact with
the oxide semiconductor film 108 functioning as a channel region of
the transistor 100 is preferably an oxide insulating film and
preferably includes a region including oxygen in excess of the
stoichiometric composition (oxygen-excess region). In other words,
the insulating film 107 is an insulating film capable of releasing
oxygen. In order to provide the oxygen excess region in the
insulating film 107, the insulating film 107 is formed in an oxygen
atmosphere, for example. Alternatively, the oxygen excess region
may be formed by introduction of oxygen into the insulating film
107 after the deposition. As a method for introducing oxygen, an
ion implantation method, an ion doping method, a plasma immersion
ion implantation method, plasma treatment, or the like may be
employed.
[0507] In the case where hafnium oxide is used for the insulating
film 107, the following effect is attained. Hafnium oxide has a
higher dielectric constant than silicon oxide and silicon
oxynitride. Therefore, by using hafnium oxide, the thickness of the
insulating film 107 can be made large as compared with the case
where silicon oxide is used; thus, leakage current due to tunnel
current can be low. That is, it is possible to provide a transistor
with a low off-state current. Moreover, hafnium oxide with a
crystalline structure has higher dielectric constant than hafnium
oxide with an amorphous structure. Therefore, it is preferable to
use hafnium oxide with a crystalline structure in order to provide
a transistor with a low off-state current. Examples of the
crystalline structure include a monoclinic crystal structure and a
cubic crystal structure. Note that one embodiment of the present
invention is not limited thereto.
[0508] In this embodiment, a silicon nitride film is formed as the
insulating film 106, and a silicon oxide film is formed as the
insulating film 107. The silicon nitride film has a higher
dielectric constant than a silicon oxide film and needs a larger
thickness for capacitance equivalent to that of the silicon oxide
film. Thus, when the silicon nitride film is included in the gate
insulating film of the transistor 100, the physical thickness of
the insulating film can be increased. This makes it possible to
reduce a decrease in withstand voltage of the transistor 100 and
furthermore to increase the withstand voltage, thereby reducing
electrostatic discharge damage to the transistor 100.
<<Oxide Semiconductor Film>>
[0509] The oxide semiconductor film 108 can be formed using the
materials described above.
[0510] In the case where the oxide semiconductor film 108 includes
In-M-Zn oxide, it is preferable that the atomic ratio of metal
elements of a sputtering target used for forming the In-M-Zn oxide
satisfy In.gtoreq.M and Zn.gtoreq.M. As the atomic ratio of metal
elements of such a sputtering target, In:M:Zn=1:1:1,
In:M:Zn=1:1:1.2, In:M:Zn=2:1:3, In:M:Zn=3:1:2, and In:M:Zn=4:2:4.1
are preferable.
[0511] In the case where the oxide semiconductor film 108 is formed
of In-M-Zn oxide, it is preferable to use a target including
polycrystalline In-M-Zn oxide as the sputtering target. The use of
the target including polycrystalline In-M-Zn oxide facilitates
formation of the oxide semiconductor film 108 having crystallinity.
Note that the atomic ratios of metal elements in the formed oxide
semiconductor film 108 vary from the above atomic ratio of metal
elements of the sputtering target within a range of .+-.40% as an
error. For example, when a sputtering target with an atomic ratio
of In to Ga and Zn of 4:2:4.1 is used, the atomic ratio of In to Ga
and Zn in the oxide semiconductor film 108 may be 4:2:3 or in the
vicinity of 4:2:3.
[0512] The oxide semiconductor film 108a can be formed using the
sputtering target having an atomic ratio of In:M:Zn=2:1:3,
In:M:Zn=3:1:2, or In:M:Zn=4:2:4.1. The oxide semiconductor film
108b can be formed using the sputtering target having an atomic
ratio of In:M:Zn=1:1:1 or In:M:Zn=1:1:1.2. Note that the atomic
ratio of metal elements in a sputtering target used for forming the
oxide semiconductor film 108b does not necessarily satisfy
In.gtoreq.M and Zn.gtoreq.M, and may satisfy In.gtoreq.M and
Zn<M, such as In:M:Zn=1:3:2.
[0513] The energy gap of the oxide semiconductor film 108 is 2 eV
or more, preferably 2.5 eV or more, further preferably 3 eV or
more. The use of an oxide semiconductor having a wide energy gap
can reduce off-state current of the transistor 100. In particular,
an oxide semiconductor film having an energy gap more than or equal
to 2 eV, preferably more than or equal to 2 eV and less than or
equal to 3.0 eV is preferably used as the oxide semiconductor film
108a, and an oxide semiconductor film having an energy gap more
than or equal to 2.5 eV and less than or equal to 3.5 eV is
preferably used as the oxide semiconductor film 108b. Furthermore,
the oxide semiconductor film 108b preferably has a higher energy
gap than that of the oxide semiconductor film 108a.
[0514] Each thickness of the oxide semiconductor film 108a and the
oxide semiconductor film 108b is more than or equal to 3 nm and
less than or equal to 200 nm, preferably more than or equal to 3 nm
and less than or equal to 100 nm, more preferably more than or
equal to 3 nm and less than or equal to 50 nm. Note that the
above-described thickness relationships between them are preferably
satisfied.
[0515] An oxide semiconductor film with low carrier density is used
as the oxide semiconductor film 108b. For example, the carrier
density of the oxide semiconductor film 108b is lower than or equal
to 1.times.10.sup.17/cm.sup.3, preferably lower than or equal to
1.times.10.sup.15/cm.sup.3, further preferably lower than or equal
to 1.times.10.sup.13/cm.sup.3, still further preferably lower than
or equal to 1.times.10.sup.11/cm.sup.3.
[0516] Note that, without limitation to the compositions and
materials described above, a material with an appropriate
composition may be used depending on required semiconductor
characteristics and electrical characteristics (e.g., field-effect
mobility and threshold voltage) of a transistor. Further, in order
to obtain required semiconductor characteristics of a transistor,
it is preferable that the carrier density, the impurity
concentration, the defect density, the atomic ratio of a metal
element to oxygen, the interatomic distance, the density, and the
like of the oxide semiconductor film 108a and the oxide
semiconductor film 108b be set to be appropriate.
[0517] Note that it is preferable to use, as the oxide
semiconductor film 108a and the oxide semiconductor film 108b, an
oxide semiconductor film in which the impurity concentration is low
and the density of defect states is low, in which case the
transistor can have more excellent electrical characteristics.
Here, the state in which the impurity concentration is low and the
density of defect states is low (the amount of oxygen vacancy is
small) is referred to as "highly purified intrinsic" or
"substantially highly purified intrinsic". A highly purified
intrinsic or substantially highly purified intrinsic oxide
semiconductor film has few carrier generation sources, and thus can
have a low carrier density. Thus, a transistor in which a channel
region is formed in the oxide semiconductor film rarely has a
negative threshold voltage (is rarely normally on). A highly
purified intrinsic or substantially highly purified intrinsic oxide
semiconductor film has a low density of defect states and
accordingly has few carrier traps in some cases. Further, the
highly purified intrinsic or substantially highly purified
intrinsic oxide semiconductor film has an extremely low off-state
current; even when an element has a channel width of
1.times.10.sup.6 .mu.m and a channel length of 10 .mu.m, the
off-state current can be less than or equal to the measurement
limit of a semiconductor parameter analyzer, that is, less than or
equal to 1.times.10.sup.-13 A, at a voltage (drain voltage) between
a source electrode and a drain electrode of from 1 V to 10V.
[0518] Accordingly, the transistor in which the channel region is
formed in the highly purified intrinsic or substantially highly
purified intrinsic oxide semiconductor film can have a small change
in electrical characteristics and high reliability. Charges trapped
by the trap states in the oxide semiconductor film take a long time
to be released and may behave like fixed charges. Thus, the
transistor whose channel region is formed in the oxide
semiconductor film having a high density of trap states has
unstable electrical characteristics in some cases. As examples of
the impurities, hydrogen, nitrogen, alkali metal, alkaline earth
metal, and the like are given.
[0519] Hydrogen included in the oxide semiconductor film reacts
with oxygen bonded to a metal atom to be water, and also causes
oxygen vacancy in a lattice from which oxygen is released (or a
portion from which oxygen is released). Due to entry of hydrogen
into the oxygen vacancy, an electron serving as a carrier is
generated in some cases. Furthermore, in some cases, bonding of
part of hydrogen to oxygen bonded to a metal atom causes generation
of an electron serving as a carrier. Thus, a transistor including
an oxide semiconductor film which contains hydrogen is likely to be
normally on. Accordingly, it is preferable that hydrogen be reduced
as much as possible in the oxide semiconductor film 108.
Specifically, in the oxide semiconductor film 108, the
concentration of hydrogen which is measured by SIMS is lower than
or equal to 2.times.10.sup.20 atoms/cm.sup.3, preferably lower than
or equal to 5.times.10.sup.19 atoms/cm.sup.3, further preferably
lower than or equal to 1.times.10.sup.19 atoms/cm.sup.3, further
preferably lower than or equal to 5.times.10.sup.18 atoms/cm.sup.3,
further preferably lower than or equal to 1.times.10.sup.18
atoms/cm.sup.3, further preferably lower than or equal to
5.times.10.sup.17 atoms/cm.sup.3, and further preferably lower than
or equal to 1.times.10.sup.16 atoms/cm.sup.3.
[0520] When silicon or carbon that is one of elements belonging to
Group 14 is included in the first oxide semiconductor film 108a,
oxygen vacancy is increased in the first oxide semiconductor film
108a, and the first oxide semiconductor film 108a becomes an n-type
film. Thus, the concentration of silicon or carbon (the
concentration is measured by SIMS) in the first oxide semiconductor
film 108a or the concentration of silicon or carbon (the
concentration is measured by SIMS) in the vicinity of an interface
with the oxide semiconductor film 108a is set to be lower than or
equal to 2.times.10.sup.18 atoms/cm.sup.3, preferably lower than or
equal to 2.times.10.sup.17 atoms/cm.sup.3.
[0521] In addition, the concentration of alkali metal or alkaline
earth metal of the first oxide semiconductor film 108a, which is
measured by SIMS, is lower than or equal to 1.times.10.sup.18
atoms/cm.sup.3, preferably lower than or equal to 2.times.10.sup.16
atoms/cm.sup.3. Alkali metal and alkaline earth metal might
generate carriers when bonded to an oxide semiconductor, in which
case the off-state current of the transistor might be increased.
Therefore, it is preferable to reduce the concentration of alkali
metal or alkaline earth metal of the oxide semiconductor film
108a.
[0522] Furthermore, when including nitrogen, the oxide
semiconductor film 108a easily becomes n-type by generation of
electrons serving as carriers and an increase of carrier density.
Thus, a transistor including an oxide semiconductor film which
contains nitrogen is likely to have normally-on characteristics.
For this reason, nitrogen in the oxide semiconductor film is
preferably reduced as much as possible; the concentration of
nitrogen which is measured by SIMS is preferably set to be, for
example, lower than or equal to 5.times.10.sup.18
atoms/cm.sup.3.
[0523] Each of the first and second oxide semiconductor films 108a
and 108b may have a non-single-crystal structure, for example. The
non-single crystal structure includes a c-axis aligned crystalline
oxide semiconductor (CAAC-OS) which is described later, a
polycrystalline structure, a microcrystalline structure, or an
amorphous structure, for example. Among the non-single crystal
structure, the amorphous structure has the highest density of
defect states, whereas CAAC-OS has the lowest density of defect
states.
<<Insulating Film Functioning as Protective Insulating Film
of Transistor>>
[0524] The insulating films 114 and 116 each have a function of
supplying oxygen to the oxide semiconductor film 108. The
insulating film 118 has a function of a protective insulating film
of the transistor 100. The insulating films 114 and 116 include
oxygen. Furthermore, the insulating film 114 is an insulating film
which can transmit oxygen. The insulating film 114 also functions
as a film which relieves damage to the oxide semiconductor film 108
at the time of forming the insulating film 116 in a later step.
[0525] A silicon oxide film, a silicon oxynitride film, or the like
with a thickness greater than or equal to 5 nm and less than or
equal to 150 nm, preferably greater than or equal to 5 nm and less
than or equal to 50 nm can be used as the insulating film 114.
[0526] In addition, it is preferable that the number of defects in
the insulating film 114 be small and typically, the spin density
corresponding to a signal that appears at g=2.001 due to a dangling
bond of silicon be lower than or equal to 3.times.10.sup.17
spins/cm.sup.3 by electron spin resonance (ESR) measurement. This
is because if the density of defects in the insulating film 114 is
high, oxygen is bonded to the defects and the amount of oxygen that
transmits the insulating film 114 is decreased.
[0527] Note that all oxygen entering the insulating film 114 from
the outside does not move to the outside of the insulating film 114
and some oxygen remains in the insulating film 114. Furthermore,
movement of oxygen occurs in the insulating film 114 in some cases
in such a manner that oxygen enters the insulating film 114 and
oxygen included in the insulating film 114 moves to the outside of
the insulating film 114. When an oxide insulating film which can
transmit oxygen is formed as the insulating film 114, oxygen
released from the insulating film 116 provided over the insulating
film 114 can be moved to the oxide semiconductor film 108 through
the insulating film 114.
[0528] Note that the insulating film 114 can be formed using an
oxide insulating film having a low density of states due to
nitrogen oxide. Note that the density of states due to nitrogen
oxide can be formed between the energy of the valence band maximum
(E.sub.v.sub._.sub.os) and the energy of the conduction band
minimum (E.sub.c.sub._.sub.os) of the oxide semiconductor film. A
silicon oxynitride film that releases less nitrogen oxide, an
aluminum oxynitride film that releases less nitrogen oxide, and the
like can be used as the above oxide insulating film.
[0529] Note that a silicon oxynitride film that releases less
nitrogen oxide is a film of which the amount of released ammonia is
larger than the amount of released nitrogen oxide in TDS analysis;
the amount of released ammonia is typically greater than or equal
to 1.times.10.sup.18/cm.sup.3 and less than or equal to
5.times.10.sup.19/cm.sup.3. Note that the amount of released
ammonia is the amount of ammonia released by heat treatment with
which the surface temperature of a film becomes higher than or
equal to 50.degree. C. and lower than or equal to 650.degree. C.,
preferably higher than or equal to 50.degree. C. and lower than or
equal to 550.degree. C.
[0530] Nitrogen oxide (NO.sub.x; x is greater than 0 and less than
or equal to 2, preferably greater than or equal to 1 and less than
or equal to 2), typically NO.sub.2 or NO, forms levels in the
insulating film 114, for example. The level is positioned in the
energy gap of the oxide semiconductor film 108. Therefore, when
nitrogen oxide is diffused to the interface between the insulating
film 114 and the oxide semiconductor film 108, an electron is in
some cases trapped by the level on the insulating film 114 side. As
a result, the trapped electron remains in the vicinity of the
interface between the insulating film 114 and the oxide
semiconductor film 108; thus, the threshold voltage of the
transistor is shifted in the positive direction.
[0531] Nitrogen oxide reacts with ammonia and oxygen in heat
treatment. Since nitrogen oxide included in the insulating film 114
reacts with ammonia included in the insulating film 116 in heat
treatment, nitrogen oxide included in the insulating film 114 is
reduced. Therefore, an electron is hardly trapped at the vicinity
of the interface between the insulating film 114 and the oxide
semiconductor film 108.
[0532] By using such an oxide insulating film, the insulating film
114 can reduce the shift in the threshold voltage of the
transistor, which leads to a smaller change in the electrical
characteristics of the transistor.
[0533] Note that in an ESR spectrum at 100 K or lower of the
insulating film 114, by heat treatment of a manufacturing process
of the transistor, typically heat treatment at a temperature higher
than or equal to 300.degree. C. and lower than 350.degree. C., a
first signal that appears at a g-factor of greater than or equal to
2.037 and less than or equal to 2.039, a second signal that appears
at a g-factor of greater than or equal to 2.001 and less than or
equal to 2.003, and a third signal that appears at a g-factor of
greater than or equal to 1.964 and less than or equal to 1.966 are
observed. The split width of the first and second signals and the
split width of the second and third signals that are obtained by
ESR measurement using an X-band are each approximately 5 mT. The
sum of the spin densities of the first signal that appears at a
g-factor of greater than or equal to 2.037 and less than or equal
to 2.039, the second signal that appears at a g-factor of greater
than or equal to 2.001 and less than or equal to 2.003, and the
third signal that appears at a g-factor of greater than or equal to
1.964 and less than or equal to 1.966 is lower than
1.times.10.sup.18 spins/cm.sup.3, typically higher than or equal to
1.times.10.sup.17 spins/cm.sup.3 and lower than 1.times.10.sup.18
spins/cm.sup.3.
[0534] In the ESR spectrum at 100 K or lower, the first signal that
appears at a g-factor of greater than or equal to 2.037 and less
than or equal to 2.039, the second signal that appears at a
g-factor of greater than or equal to 2.001 and less than or equal
to 2.003, and the third signal that appears at a g-factor of
greater than or equal to 1.964 and less than or equal to 1.966
correspond to signals attributed to nitrogen oxide (NO; x is
greater than 0 and less than or equal to 2, preferably greater than
or equal to 1 and less than or equal to 2). Typical examples of
nitrogen oxide include nitrogen monoxide and nitrogen dioxide. In
other words, the lower the total spin density of the first signal
that appears at a g-factor of greater than or equal to 2.037 and
less than or equal to 2.039, the second signal that appears at a
g-factor of greater than or equal to 2.001 and less than or equal
to 2.003, and the third signal that appears at a g-factor of
greater than or equal to 1.964 and less than or equal to 1.966 is,
the lower the content of nitrogen oxide in the oxide insulating
film is.
[0535] The concentration of nitrogen of the above oxide insulating
film measured by SIMS is lower than or equal to 6.times.10.sup.20
atoms/cm.sup.3.
[0536] The above oxide insulating film is formed by a PECVD method
at a film surface temperature higher than or equal to 220.degree.
C. and lower than or equal to 350.degree. C. using silane and
dinitrogen monoxide, whereby a dense and hard film can be
formed.
[0537] The insulating film 116 is formed using an oxide insulating
film that contains oxygen in excess of that in the stoichiometric
composition. Part of oxygen is released by heating from the oxide
insulating film including oxygen in excess of that in the
stoichiometric composition. The oxide insulating film including
oxygen in excess of that in the stoichiometric composition is an
oxide insulating film of which the amount of released oxygen
converted into oxygen atoms is greater than or equal to
1.0.times.10.sup.19 atoms/cm.sup.3, preferably greater than or
equal to 3.0.times.10.sup.20 atoms/cm.sup.3 in TDS analysis. Note
that the temperature of the film surface in the TDS analysis is
preferably higher than or equal to 100.degree. C. and lower than or
equal to 700.degree. C., or higher than or equal to 100.degree. C.
and lower than or equal to 500.degree. C.
[0538] A silicon oxide film, a silicon oxynitride film, or the like
with a thickness greater than or equal to 30 nm and less than or
equal to 500 nm, preferably greater than or equal to 50 nm and less
than or equal to 400 nm can be used as the insulating film 116.
[0539] It is preferable that the number of defects in the
insulating film 116 be small, and typically the spin density
corresponding to a signal which appears at g=2.001 due to a
dangling bond of silicon be lower than 1.5.times.10.sup.18
spins/cm.sup.3, preferably lower than or equal to 1.times.10.sup.18
spins/cm.sup.3 by ESR measurement. Note that the insulating film
116 is provided more apart from the oxide semiconductor film 108
than the insulating film 114 is; thus, the insulating film 116 may
have higher density of defects than the insulating film 114.
[0540] Furthermore, the insulating films 114 and 116 can be formed
using insulating films formed of the same kinds of materials; thus,
a boundary between the insulating films 114 and 116 cannot be
clearly observed in some cases. Thus, in this embodiment, the
boundary between the insulating films 114 and 116 is shown by a
dashed line. Although a two-layer structure of the insulating films
114 and 116 is described in this embodiment, the present invention
is not limited to this. For example, a single-layer structure of
the insulating film 114 may be employed.
[0541] The insulating film 118 includes nitrogen. Alternatively,
the insulating film 118 includes nitrogen and silicon. The
insulating film 118 has a function of blocking oxygen, hydrogen,
water, alkali metal, alkaline earth metal, or the like. It is
possible to prevent outward diffusion of oxygen from the oxide
semiconductor film 108, outward diffusion of oxygen included in the
insulating films 114 and 116, and entry of hydrogen, water, or the
like into the oxide semiconductor film 108 from the outside by
providing the insulating film 118. A nitride insulating film, for
example, can be used as the insulating film 118. The nitride
insulating film is formed using silicon nitride, silicon nitride
oxide, aluminum nitride, aluminum nitride oxide, or the like. Note
that instead of the nitride insulating film having a blocking
effect against oxygen, hydrogen, water, alkali metal, alkaline
earth metal, and the like, an oxide insulating film having a
blocking effect against oxygen, hydrogen, water, and the like may
be provided. As the oxide insulating film having a blocking effect
against oxygen, hydrogen, water, and the like, an aluminum oxide
film, an aluminum oxynitride film, a gallium oxide film, a gallium
oxynitride film, an yttrium oxide film, an yttrium oxynitride film,
a hafnium oxide film, a hafnium oxynitride film, and the like can
be given.
[0542] Although the variety of films such as the conductive films,
the insulating films, and the oxide semiconductor films which are
described above can be formed by a sputtering method or a PECVD
method, such films may be formed by another method, e.g., a thermal
CVD method. Examples of the thermal CVD method include a metal
organic chemical vapor deposition (MOCVD) method and an atomic
layer deposition (ALD) method.
[0543] A thermal CVD method has an advantage that no defect due to
plasma damage is generated since it does not utilize plasma for
forming a film.
[0544] Deposition by a thermal CVD method may be performed in such
a manner that a source gas and an oxidizer are supplied to the
chamber at a time so that the pressure in a chamber is set to an
atmospheric pressure or a reduced pressure, and react with each
other in the vicinity of the substrate or over the substrate.
[0545] Deposition by an ALD method may be performed in such a
manner that the pressure in a chamber is set to an atmospheric
pressure or a reduced pressure, source gases for reaction are
sequentially introduced into the chamber, and then the sequence of
the gas introduction is repeated. For example, two or more kinds of
source gases are sequentially supplied to the chamber by switching
respective switching valves (also referred to as high-speed
valves). For example, a first source gas is introduced, an inert
gas (e.g., argon or nitrogen) or the like is introduced at the same
time as or after the introduction of the first gas so that the
source gases are not mixed, and then a second source gas is
introduced. Note that in the case where the first source gas and
the inert gas are introduced at a time, the inert gas serves as a
carrier gas, and the inert gas may also be introduced at the same
time as the introduction of the second source gas. Alternatively,
the first source gas may be exhausted by vacuum evacuation instead
of the introduction of the inert gas, and then the second source
gas may be introduced. The first source gas is adsorbed on the
surface of the substrate to form a first layer, then the second
source gas is introduced to react with the first layer, as a
result, a second layer is stacked over the first layer, so that a
thin film is formed. The sequence of the gas introduction is
repeated plural times until a desired thickness is obtained,
whereby a thin film with excellent step coverage can be formed. The
thickness of the thin film can be adjusted by the number of
repetition times of the sequence of the gas introduction;
therefore, an ALD method makes it possible to accurately adjust a
thickness and thus is suitable for manufacturing a minute FET.
[0546] The variety of films such as the conductive films, the
insulating films, the oxide semiconductor films, and the metal
oxide films in this embodiment can be formed by a thermal CVD
method such as an MOCVD method or an ALD method. For example, in
the case where an In--Ga--Zn--O film is formed, trimethylindium,
trimethylgallium, and dimethylzinc are used. Note that the chemical
formula of trimethylindium is In(CH.sub.3).sub.3. The chemical
formula of trimethylgallium is Ga(CH.sub.3).sub.3. The chemical
formula of dimethylzinc is Zn(CH.sub.3).sub.2. Without limitation
to the above combination, triethylgallium (chemical formula:
Ga(C.sub.2H.sub.5).sub.3) can be used instead of trimethylgallium
and diethylzinc (chemical formula: Zn(C.sub.2H.sub.5).sub.2) can be
used instead of dimethylzinc.
[0547] For example, in the case where a hafnium oxide film is
formed by a deposition apparatus using an ALD method, two kinds of
gases, that is, ozone (O.sub.3) as an oxidizer and a source gas
which is obtained by vaporizing liquid containing a solvent and a
hafnium precursor compound (e.g., a hafnium alkoxide or a hafnium
amide such as tetrakis(dimethylamide)hafnium (TDMAH)) are used.
Note that the chemical formula of tetrakis(dimethylamide)hafnium is
Hf[N(CH.sub.3).sub.2].sub.4. Examples of another material liquid
include tetrakis(ethylmethylamide)hafnium.
[0548] For example, in the case where an aluminum oxide film is
formed by a deposition apparatus using an ALD method, two kinds of
gases, e.g., H.sub.2O as an oxidizer and a source gas which is
obtained by vaporizing liquid containing a solvent and an aluminum
precursor compound (e.g., trimethylaluminum (TMA)) are used. Note
that the chemical formula of trimethylaluminum is
Al(CH.sub.3).sub.3. Examples of another material liquid include
tris(dimethylamide)aluminum, triisobutylaluminum, and aluminum
tris(2,2,6,6-tetramethyl-3,5-heptanedionate).
[0549] For example, in the case where a silicon oxide film is
formed by a deposition apparatus using an ALD method,
hexachlorodisilane is adsorbed on a surface where a film is to be
formed, chlorine included in the adsorbate is removed, and radicals
of an oxidizing gas (e.g., O.sub.2 or dinitrogen monoxide) are
supplied to react with the adsorbate.
[0550] For example, in the case where a tungsten film is formed
using a deposition apparatus using an ALD method, a WF.sub.6 gas
and a B.sub.2H.sub.6 gas are sequentially introduced plural times
to form an initial tungsten film, and then a WF.sub.6 gas and an
H.sub.2 gas are used, so that a tungsten film is formed. Note that
an SiH.sub.4 gas may be used instead of a B.sub.2H.sub.6 gas.
[0551] For example, in the case where an oxide semiconductor film,
e.g., an In--Ga--Zn--O film is formed using a deposition apparatus
using an ALD method, an In(CH.sub.3).sub.3 gas and an O.sub.3 gas
are sequentially introduced plural times to form an InO layer, a
GaO layer is formed using a Ga(CH.sub.3).sub.3 gas and an O.sub.3
gas, and then a ZnO layer is formed using a Zn(CH.sub.3).sub.2 gas
and an O.sub.3 gas. Note that the order of these layers is not
limited to this example. A mixed compound layer such as an
In--Ga--O layer, an In--Zn--O layer, or a Ga--Zn--O layer may be
formed by mixing these gases. Note that although an H.sub.2O gas
which is obtained by bubbling water with an inert gas such as Ar
may be used instead of an O.sub.3 gas, it is preferable to use an
O.sub.3 gas, which does not contain H. Furthermore, instead of an
In(CH.sub.3).sub.3 gas, an In(C.sub.2H.sub.5).sub.3 gas may be
used. Instead of a Ga(CH.sub.3).sub.3 gas, a
Ga(C.sub.2H.sub.5).sub.3 gas may be used. Furthermore, a
Zn(CH.sub.3).sub.2 gas may be used.
[0552] This embodiment can be combined with any of the other
embodiments in this specification as appropriate.
Embodiment 5
[0553] In this embodiment, structures of a transistor that can be
used in the display panel of one embodiment of the present
invention will be described with reference to FIGS. 21A to 21C.
<Structure Example of Semiconductor Device>
[0554] FIG. 21A is a top view of the transistor 100. FIG. 21B is a
cross-sectional view taken along the cutting plane line X1-X2 in
FIG. 10A, and FIG. 21C is a cross-sectional view taken along the
cutting plane line Y1-Y2 in FIG. 10A. Note that in FIG. 21A, some
components of the transistor 100 (e.g., an insulating film serving
as a gate insulating film) are not illustrated to avoid complexity.
Furthermore, the direction of the cutting plane line X1-X2 may be
called a channel length direction, and the direction of the cutting
plane line Y1-Y2 may be called a channel width direction. As in
FIG. 21A, some components are not illustrated in some cases in top
views of transistors described below.
[0555] The transistor 100 can be used for the display panel
described in Embodiment 1 or 2, or the like.
[0556] For example, when the transistor 100 is used as the
transistor MD, the substrate 102, the conductive film 104, a
stacked film of the insulating film 106 and the insulating film
107, the oxide semiconductor film 108, the conductive film 112a,
the conductive film 112b, a stacked film of the insulating film 114
and the insulating film 116, the insulating film 118, and a
conductive film 120b can be referred to as the insulating film
501C, the conductive film 504, the insulating film 506, the
semiconductor film 508, the conductive film 512A, the conductive
film 512B, the insulating film 516, the insulating film 518, and
the conductive film 524, respectively.
[0557] The transistor 100 includes a conductive film 104
functioning as a first gate electrode over a substrate 102, an
insulating film 106 over the substrate 102 and the conductive film
104, an insulating film 107 over the insulating film 106, an oxide
semiconductor film 108 over the insulating film 107, and conductive
films 112a and 112b functioning as source and drain electrodes
electrically connected to the oxide semiconductor film 108, the
insulating films 114 and 116 over the oxide semiconductor film 108
and the conductive films 112a and 112b, a conductive film 120a that
is over the insulating film 116 and electrically connected to the
conductive film 112b, the conductive film 120b over the insulating
film 116, and the insulating film 118 over the insulating film 116
and the conductive films 120a and 120b.
[0558] The insulating films 106 and 107 function as a first gate
insulating film of the transistor 100. The insulating films 114 and
116 function as a second gate insulating film of the transistor
100. The insulating film 118 functions as a protective insulating
film of the transistor 100. In this specification and the like, the
insulating films 106 and 107 are collectively referred to as a
first insulating film, the insulating films 114 and 116 are
collectively referred to as a second insulating film, and the
insulating film 118 is referred to as a third insulating film in
some cases.
[0559] The conductive film 120b can be used as a second gate
electrode of the transistor 100.
[0560] In the case where the transistor 100 is used in a display
panel, the conductive film 120a can be used as an electrode of a
display element, or the like.
[0561] The oxide semiconductor film 108 includes the oxide
semiconductor film 108b (on the conductive film 104 side) that
functions as a first gate electrode, and an oxide semiconductor
film 108c over the oxide semiconductor film 108b. The oxide
semiconductor films 108b and 108c contain In, M (M is Al, Ga, Y, or
Sn), and Zn.
[0562] The oxide semiconductor film 108b preferably includes a
region in which the atomic proportion of In is larger than the
atomic proportion of M, for example. The oxide semiconductor film
108c preferably includes a region in which the atomic proportion of
In is smaller than that in the oxide semiconductor film 108b.
[0563] The oxide semiconductor film 108b including the region in
which the atomic proportion of In is larger than that of M can
increase the field-effect mobility (also simply referred to as
mobility or .mu.FE) of the transistor 100. Specifically, the
field-effect mobility of the transistor 100 can exceed 10
cm.sup.2/Vs, preferably exceed 30 cm.sup.2/Vs.
[0564] For example, the use of the transistor with high
field-effect mobility for a gate driver that generates a gate
signal (specifically, a demultiplexer connected to an output
terminal of a shift register included in a gate driver) allows a
semiconductor device or a display device to have a narrow
frame.
[0565] On the other hand, the oxide semiconductor film 108b
including the region in which the atomic proportion of In is larger
than that of M makes it easier to change electrical characteristics
of the transistor 100 in light irradiation. However, in the
semiconductor device of one embodiment of the present invention,
the oxide semiconductor film 108c is formed over the oxide
semiconductor film 108b. Furthermore, the oxide semiconductor film
108c including the region in which the atomic proportion of In is
smaller than that in the oxide semiconductor film 108b has larger
Eg than the oxide semiconductor film 108b. For this reason, the
oxide semiconductor film 108 which is a layered structure of the
oxide semiconductor film 108b and the oxide semiconductor film 108c
has high resistance to a negative bias stress test with light
irradiation.
[0566] Impurities such as hydrogen or moisture entering the channel
region of the oxide semiconductor film 108, particularly the oxide
semiconductor film 108b adversely affect the transistor
characteristics and therefore cause a problem. Moreover, it is
preferable that the amount of impurities such as hydrogen or
moisture in the channel region of the oxide semiconductor film 108b
be as small as possible. Furthermore, oxygen vacancies formed in
the channel region in the oxide semiconductor film 108b adversely
affect the transistor characteristics and therefore cause a
problem. For example, oxygen vacancies formed in the channel region
in the oxide semiconductor film 108b are bonded to hydrogen to
serve as a carrier supply source. The carrier supply source
generated in the channel region in the oxide semiconductor film
108b causes a change in the electrical characteristics, typically,
shift in the threshold voltage, of the transistor 100 including the
oxide semiconductor film 108b. Therefore, it is preferable that the
amount of oxygen vacancies in the channel region of the oxide
semiconductor film 108b be as small as possible.
[0567] In view of this, one embodiment of the present invention is
a structure in which insulating films in contact with the oxide
semiconductor film 108, specifically the insulating film 107 formed
under the oxide semiconductor film 108 and the insulating films 114
and 116 formed over the oxide semiconductor film 108 include excess
oxygen. Oxygen or excess oxygen is transferred from the insulating
film 107 and the insulating films 114 and 116 to the oxide
semiconductor film 108, whereby the oxygen vacancies in the oxide
semiconductor film can be reduced. As a result, a change in
electrical characteristics of the transistor 100, particularly a
change in the transistor 100 due to light irradiation, can be
reduced.
[0568] In one embodiment of the present invention, a manufacturing
method is used in which the number of manufacturing steps is not
increased or an increase in the number of manufacturing steps is
extremely small, because the insulating film 107 and the insulating
films 114 and 116 are made to contain excess oxygen. Thus, the
transistors 100 can be manufactured with high yield.
[0569] Specifically, in a step of forming the oxide semiconductor
film 108b, the oxide semiconductor film 108b is formed by a
sputtering method in an atmosphere containing an oxygen gas,
whereby oxygen or excess oxygen is added to the insulating film 107
over which the oxide semiconductor film 108b is formed.
[0570] Furthermore, in a step of forming the conductive films 120a
and 120b, the conductive films 120a and 120b are formed by a
sputtering method in an atmosphere containing an oxygen gas,
whereby oxygen or excess oxygen is added to the insulating film 116
over which the conductive films 120a and 120b are formed. Note that
in some cases, oxygen or excess oxygen is added also to the
insulating film 114 and the oxide semiconductor film 108 under the
insulating film 116 when oxygen or excess oxygen is added to the
insulating film 116.
<Oxide Conductor>
[0571] Next, an oxide conductor is described. In a step of forming
the conductive films 120a and 120b, the conductive films 120a and
120b serve as a protective film for suppressing release of oxygen
from the insulating films 114 and 116. The conductive films 120a
and 120b serve as semiconductors before a step of forming the
insulating film 118 and serve as conductors after the step of
forming the insulating film 118.
[0572] To allow the conductive films 120a and 120b to serve as
conductors, an oxygen vacancy is formed in the conductive films
120a and 120b and hydrogen is added from the insulating film 118 to
the oxygen vacancy, whereby a donor level is formed in the vicinity
of the conduction band. As a result, the conductivity of each of
the conductive films 120a and 120b is increased, so that the oxide
semiconductor film becomes a conductor. The conductive films 120a
and 120b having become conductors can each be referred to as oxide
conductor. Oxide semiconductors generally have a visible light
transmitting property because of their large energy gap. An oxide
conductor is an oxide semiconductor having a donor level in the
vicinity of the conduction band. Therefore, the influence of
absorption due to the donor level is small in an oxide conductor,
and an oxide conductor has a visible light transmitting property
comparable to that of an oxide semiconductor.
<Components of the Semiconductor Device>
[0573] Components of the semiconductor device of this embodiment
will be described below in detail.
[0574] As materials described below, materials described in
Embodiment 4 can be used.
[0575] The material that can be used for the substrate 102
described in Embodiment 4 can be used for the substrate 102 in this
embodiment. Furthermore, the materials that can be used for the
insulating films 106 and 107 described in Embodiment 4 can be used
for the insulating films 106 and 107 in this embodiment.
[0576] In addition, the materials that can be used for the
conductive films functioning as the gate electrode, the source
electrode, and the drain electrode described in Embodiment 4 can be
used for the conductive films functioning as the first gate
electrode, the source electrode, and the drain electrode in this
embodiment.
<<Oxide Semiconductor Film>>
[0577] The oxide semiconductor film 108 can be formed using the
materials described above.
[0578] In the case where the oxide semiconductor film 108b includes
In-M-Zn oxide, it is preferable that the atomic ratio of metal
elements of a sputtering target used for forming the In-M-Zn oxide
satisfy In>M. The atomic ratio between metal elements in such a
sputtering target is, for example, In:M:Zn=2:1:3, In:M:Zn=3:1:2, or
In:M:Zn=4:2:4.1.
[0579] In the case where the oxide semiconductor film 108c is
In-M-Zn oxide, it is preferable that the atomic ratio of metal
elements of a sputtering target used for forming a film of the
In-M-Zn oxide satisfy In.ltoreq.M. The atomic ratio of metal
elements in such a sputtering target is, for example,
In:M:Zn=1:1:1, In:M:Zn=1:1:1.2, In:M:Zn=1:3:2, In:M:Zn=1:3:4,
In:M:Zn=1:3:6, or In:M:Zn=1:4:5.
[0580] In the case where the oxide semiconductor films 108b and
108c are formed of In-M-Zn oxide, it is preferable to use a target
including polycrystalline In-M-Zn oxide as the sputtering target.
The use of the target including polycrystalline In-M-Zn oxide
facilitates formation of the oxide semiconductor films 108b and
108c having crystallinity. Note that the atomic ratios of metal
elements in each of the formed oxide semiconductor films 108b and
108c vary from the above atomic ratio of metal elements of the
sputtering target within a range of .+-.40% as an error. For
example, when a sputtering target of the oxide semiconductor film
108b with an atomic ratio of In to Ga and Zn of 4:2:4.1 is used,
the atomic ratio of In to Ga and Zn in the oxide semiconductor film
108b may be 4:2:3 or in the vicinity of 4:2:3.
[0581] The energy gap of the oxide semiconductor film 108 is 2 eV
or more, preferably 2.5 eV or more, further preferably 3 eV or
more. The use of an oxide semiconductor having a wide energy gap
can reduce off-state current of the transistor 100. In particular,
an oxide semiconductor film having an energy gap more than or equal
to 2 eV, preferably more than or equal to 2 eV and less than or
equal to 3.0 eV is preferably used as the oxide semiconductor film
108b, and an oxide semiconductor film having an energy gap more
than or equal to 2.5 eV and less than or equal to 3.5 eV is
preferably used as the oxide semiconductor film 108c. Furthermore,
the oxide semiconductor film 108c preferably has a higher energy
gap than the oxide semiconductor film 108b.
[0582] Each thickness of the oxide semiconductor film 108b and the
oxide semiconductor film 108c is more than or equal to 3 nm and
less than or equal to 200 nm, preferably more than or equal to 3 nm
and less than or equal to 100 nm, more preferably more than or
equal to 3 nm and less than or equal to 50 nm.
[0583] An oxide semiconductor film with low carrier density is used
as the oxide semiconductor film 108c. For example, the carrier
density of the oxide semiconductor film 108c is lower than or equal
to 1.times.10.sup.17/cm.sup.3, preferably lower than or equal to
1.times.10.sup.15/cm.sup.3, further preferably lower than or equal
to 1.times.10.sup.13/cm.sup.3, still further preferably lower than
or equal to 1.times.10.sup.11/cm.sup.3.
[0584] Note that, without limitation to the compositions and
materials described above, a material with an appropriate
composition may be used depending on required semiconductor
characteristics and electrical characteristics (e.g., field-effect
mobility and threshold voltage) of a transistor. Further, in order
to obtain required semiconductor characteristics of a transistor,
it is preferable that the carrier density, the impurity
concentration, the defect density, the atomic ratio of a metal
element to oxygen, the interatomic distance, the density, and the
like of the oxide semiconductor film 108b and the oxide
semiconductor film 108c be set to be appropriate.
[0585] Note that it is preferable to use, as the oxide
semiconductor film 108b and the oxide semiconductor film 108c, an
oxide semiconductor film in which the impurity concentration is low
and the density of defect states is low, in which case the
transistor can have more excellent electrical characteristics.
Here, the state in which the impurity concentration is low and the
density of defect states is low (the amount of oxygen vacancy is
small) is referred to as "highly purified intrinsic" or
"substantially highly purified intrinsic". A highly purified
intrinsic or substantially highly purified intrinsic oxide
semiconductor film has few carrier generation sources, and thus can
have a low carrier density. Thus, a transistor in which a channel
region is formed in the oxide semiconductor film rarely has a
negative threshold voltage (is rarely normally on). A highly
purified intrinsic or substantially highly purified intrinsic oxide
semiconductor film has a low density of defect states and
accordingly has few carrier traps in some cases. Further, the
highly purified intrinsic or substantially highly purified
intrinsic oxide semiconductor film has an extremely low off-state
current; even when an element has a channel width of
1.times.10.sup.6 .mu.m and a channel length of 10 .mu.m, the
off-state current can be less than or equal to the measurement
limit of a semiconductor parameter analyzer, that is, less than or
equal to 1.times.10.sup.-13 A, at a voltage (drain voltage) between
a source electrode and a drain electrode of from 1 V to 10V.
[0586] Accordingly, the transistor in which the channel region is
formed in the highly purified intrinsic or substantially highly
purified intrinsic oxide semiconductor film can have a small change
in electrical characteristics and high reliability. Charges trapped
by the trap states in the oxide semiconductor film take a long time
to be released and may behave like fixed charges. Thus, the
transistor whose channel region is formed in the oxide
semiconductor film having a high density of trap states has
unstable electrical characteristics in some cases. As examples of
the impurities, hydrogen, nitrogen, alkali metal, and alkaline
earth metal are given.
[0587] Hydrogen included in the oxide semiconductor film reacts
with oxygen bonded to a metal atom to be water, and also causes
oxygen vacancy in a lattice from which oxygen is released (or a
portion from which oxygen is released). Due to entry of hydrogen
into the oxygen vacancy, an electron serving as a carrier is
generated in some cases. Furthermore, in some cases, bonding of
part of hydrogen to oxygen bonded to a metal atom causes generation
of an electron serving as a carrier. Thus, a transistor including
an oxide semiconductor film which contains hydrogen is likely to be
normally on. Accordingly, it is preferable that hydrogen be reduced
as much as possible in the oxide semiconductor film 108.
Specifically, in the oxide semiconductor film 108, the
concentration of hydrogen which is measured by SIMS is lower than
or equal to 2.times.10.sup.20 atoms/cm.sup.3, preferably lower than
or equal to 5.times.10.sup.19 atoms/cm.sup.3, further preferably
lower than or equal to 1.times.10.sup.19 atoms/cm.sup.3, further
preferably lower than or equal to 5.times.10.sup.18 atoms/cm.sup.3,
further preferably lower than or equal to 1.times.10.sup.18
atoms/cm.sup.3, further preferably lower than or equal to
5.times.10.sup.17 atoms/cm.sup.3, and further preferably lower than
or equal to 1.times.10.sup.16 atoms/cm.sup.3.
[0588] The oxide semiconductor film 108b preferably includes a
region in which hydrogen concentration is smaller than that in the
oxide semiconductor film 108c. A semiconductor device including the
oxide semiconductor film 108b having the region in which hydrogen
concentration is smaller than that in the oxide semiconductor film
108c can be increased in reliability.
[0589] When silicon or carbon that is one of elements belonging to
Group 14 is included in the oxide semiconductor film 108b, oxygen
vacancy is increased in the oxide semiconductor film 108b, and the
oxide semiconductor film 108b becomes an n-type film. Thus, the
concentration of silicon or carbon (the concentration is measured
by SIMS) in the oxide semiconductor film 108b or the concentration
of silicon or carbon (the concentration is measured by SIMS) in the
vicinity of an interface with the oxide semiconductor film 108b is
set to be lower than or equal to 2.times.10.sup.18 atoms/cm.sup.3,
preferably lower than or equal to 2.times.10.sup.17
atoms/cm.sup.3.
[0590] In addition, the concentration of alkali metal or alkaline
earth metal of the oxide semiconductor film 108b, which is measured
by SIMS, is lower than or equal to 1.times.10.sup.18
atoms/cm.sup.3, preferably lower than or equal to 2.times.10.sup.16
atoms/cm.sup.3. Alkali metal and alkaline earth metal might
generate carriers when bonded to an oxide semiconductor, in which
case the off-state current of the transistor might be increased.
Therefore, it is preferable to reduce the concentration of alkali
metal or alkaline earth metal of the oxide semiconductor film
108b.
[0591] Furthermore, when including nitrogen, the oxide
semiconductor film 108b easily becomes n-type by generation of
electrons serving as carriers and an increase of carrier density.
Thus, a transistor including an oxide semiconductor film which
contains nitrogen is likely to have normally-on characteristics.
For this reason, nitrogen in the oxide semiconductor film is
preferably reduced as much as possible; the concentration of
nitrogen which is measured by SIMS is preferably set to be, for
example, lower than or equal to 5.times.10.sup.18
atoms/cm.sup.3.
[0592] The oxide semiconductor film 108b and the oxide
semiconductor film 108c may have a non-single-crystal structure,
for example. The non-single crystal structure includes a c-axis
aligned crystalline oxide semiconductor (CAAC-OS) which is
described later, a polycrystalline structure, a microcrystalline
structure, or an amorphous structure, for example. Among the
non-single crystal structure, the amorphous structure has the
highest density of defect states, whereas CAAC-OS has the lowest
density of defect states.
<<Insulating Films Functioning as Second Gate Insulating
Film>>
[0593] The insulating films 114 and 116 function as a second gate
insulating film of the transistor 100. In addition, the insulating
films 114 and 116 each have a function of supplying oxygen to the
oxide semiconductor film 108. That is, the insulating films 114 and
116 contain oxygen. Furthermore, the insulating film 114 is an
insulating film which can transmit oxygen.
[0594] Note that the insulating film 114 also functions as a film
which relieves damage to the oxide semiconductor film 108 at the
time of forming the insulating film 116 in a later step.
[0595] For example, the insulating films 114 and 116 described in
Embodiment 4 can be used as the insulating films 114 and 116 in
this embodiment.
<<Oxide Semiconductor Film Functioning as Conductive Film,
Oxide Semiconductor Film Functioning as Second Gate
Electrode>>
[0596] The material of the oxide semiconductor film 108 described
above can be used for the conductive film 120a and the conductive
film 120b functioning as the second gate electrode.
[0597] That is, the conductive film 120a and the conductive film
120b functioning as a second gate electrode contain a metal element
which is the same as that contained in the oxide semiconductor film
108 (the oxide semiconductor film 108b and the oxide semiconductor
film 108c). For example, the conductive film 120b functioning as a
second gate electrode and the oxide semiconductor film 108 (the
oxide semiconductor film 108b and the oxide semiconductor film
108c) contain the same metal element; thus, the manufacturing cost
can be reduced.
[0598] For example, in the case where the conductive film 120a and
the conductive film 120b functioning as a second gate electrode are
each In-M-Zn oxide, the atomic ratio of metal elements in a
sputtering target used for forming the In-M-Zn oxide preferably
satisfies In.gtoreq.M. The atomic ratio of metal elements in such a
sputtering target is In:M:Zn=2:1:3, In:M:Zn=3:1:2, In:M:Zn=4:2:4.1,
or the like.
[0599] The conductive film 120a and the conductive film 120b
functioning as a second gate electrode can each have a single-layer
structure or a stacked-layer structure of two or more layers.
[0600] Note that in the case where the conductive film 120a and the
conductive film 120b each have a stacked-layer structure, the
composition of the sputtering target is not limited to that
described above.
<<Insulating Film Functioning as Protective Insulating Film
of Transistor>>
[0601] The insulating film 118 serves as a protective insulating
film of the transistor 100.
[0602] The insulating film 118 includes one or both of hydrogen and
nitrogen. Alternatively, the insulating film 118 includes nitrogen
and silicon. The insulating film 118 has a function of blocking
oxygen, hydrogen, water, alkali metal, alkaline earth metal, or the
like. It is possible to prevent outward diffusion of oxygen from
the oxide semiconductor film 108, outward diffusion of oxygen
included in the insulating films 114 and 116, and entry of
hydrogen, water, or the like into the oxide semiconductor film 108
from the outside by providing the insulating film 118.
[0603] The insulating film 118 has a function of supplying one or
both of hydrogen and nitrogen to the conductive film 120a and the
conductive film 120b functioning as a second gate electrode. The
insulating film 118 preferably includes hydrogen and has a function
of supplying the hydrogen to the conductive films 120a and 120b.
The conductive films 120a and 120b supplied with hydrogen from the
insulating film 118 function as conductors.
[0604] A nitride insulating film, for example, can be used as the
insulating film 118. The nitride insulating film is formed using
silicon nitride, silicon nitride oxide, aluminum nitride, aluminum
nitride oxide, or the like.
[0605] Although the variety of films such as the conductive films,
the insulating films, and the oxide semiconductor films which are
described above can be formed by a sputtering method or a PECVD
method, such films may be formed by another method, e.g., a thermal
CVD method. Examples of the thermal CVD method include an MOCVD
method and an ALD method. Specifically, the methods described in
Embodiment 4 can be used.
[0606] This embodiment can be combined with any of the other
embodiments in this specification as appropriate.
Embodiment 6
[0607] In this embodiment, a structure of an input/output device
which is one embodiment of the present invention will be described
with reference to FIG. 22.
[0608] FIG. 22 is an exploded view of an input/output device 800
for illustrating the components.
[0609] The input/output device 800 includes a display panel 806 and
a touch sensor 804 having a region overlapping with the display
panel 806. Note that the input/output device 800 can be referred to
as a touch panel.
[0610] The input/output device 800 is provided with a driver
circuit 810 for driving the touch sensor 804 and the display panel
806, a battery 811 for supplying power to the driver circuit 810,
and a housing where the touch sensor 804, the display panel 806,
the driver circuit 810, and the battery 811 are stored.
<<Touch Sensor 804>>
[0611] The touch sensor 804 includes a region overlapping with the
display panel 806. Note that an FPC 803 is electrically connected
to the touch sensor 804.
[0612] For the touch sensor 804, a resistive touch sensor, a
capacitive touch sensor, or a touch sensor using a photoelectric
conversion element can be used, for example.
[0613] Note that the touch sensor 804 may be used as part of the
display panel 806.
<<Display Panel 806>>
[0614] For example, the display panel described in Embodiment 1 or
2 can be used as the display panel 806. Note that an FPC 805 is
electrically connected to the display panel 806.
<<Driver Circuit 810>>
[0615] As the driver circuit 810, a power supply circuit or a
signal processing circuit can be used, for example. Power supplied
to the battery or an external commercial power supply can be
utilized.
[0616] The signal processing circuit has a function of outputting a
video signal and a clock signal.
[0617] The power supply circuit has a function of supplying
predetermined power.
<<Housing>>
[0618] An upper cover 801, a lower cover 802 which fits the upper
cover 801, and a frame 809 which is stored in a region surrounded
by the upper cover 801 and the lower cover 802 can be used for the
housing, for example.
[0619] The frame 809 has a function of protecting the display panel
806, and a function of blocking electromagnetic waves generated by
the operation of the driver circuit 810 or a function of a radiator
plate.
[0620] Metal, a resin, an elastomer, or the like can be used for
the upper cover 801, the lower cover 802, or the frame 809.
<<Battery 811>>
[0621] The battery 811 has a function of supplying power.
[0622] Note that a member such as a polarizing plate, a retardation
plate, or a prism sheet can be used for the input/output device
800.
[0623] This embodiment can be combined with any of the other
embodiments in this specification as appropriate.
Embodiment 7
[0624] In this embodiment, a structure of an information processing
device of one embodiment of the present invention will be described
with reference to FIGS. 23A and 23B, FIGS. 24A to 24D, FIGS. 25A
and 25B, and FIG. 26.
[0625] FIG. 23A is a block diagram illustrating a structure of an
information processing device 200. FIG. 23B is a projection view
illustrating an example of an external view of the information
processing device 200.
[0626] FIG. 24A is a block diagram illustrating a configuration of
a display portion 230. FIG. 24B is a block diagram illustrating a
configuration of a display portion 230B. FIG. 24C is a circuit
diagram illustrating a configuration of a pixel 232(i,j).
<Configuration Example of Information Processing Device>
[0627] The information processing device 200 described in this
embodiment includes an arithmetic device 210 and an input/output
device 220 (see FIG. 23A).
[0628] The arithmetic device 210 is configured to receive
positional information P1 and supply image information V and
control information.
[0629] The input/output device 220 is configured to supply the
positional information P1 and receive the image information V and
the control information.
[0630] The input/output device 220 includes the display portion 230
that displays the image information V and an input portion 240 that
supplies the positional information P1.
[0631] The display portion 230 includes a first display element and
a second display element overlapping with the opening in the
reflective film of the first display element. The display portion
230 further includes a first pixel circuit for driving the first
display element and a second pixel circuit for driving the second
display element.
[0632] The input portion 240 is configured to detect the position
of a pointer and supply the positional information P1 determined in
accordance with the position.
[0633] The arithmetic device 210 is configured to determine the
moving speed of the pointer in accordance with the positional
information P1.
[0634] The arithmetic device 210 is configured to determine the
contrast or brightness of the image information V in accordance
with the moving speed.
[0635] The information processing device 200 described in this
embodiment includes the input/output device 220 that supplies the
positional information P1 and receives the image information V and
the arithmetic device 210 that receives the positional information
P1 and supplies the image information V. The arithmetic device 210
is configured to determine the contrast or brightness of the image
information V in accordance with the moving speed of the positional
information P1.
[0636] With this structure, eyestrain on a user caused when the
display position of image information is moved can be reduced, that
is, eye-friendly display can be achieved. Moreover, the power
consumption can be reduced and excellent visibility can be provided
even in a bright place exposed to direct sunlight, for example.
Thus, the novel information processing device that is highly
convenient or reliable can be provided.
<Configuration>
[0637] The information processing device of one embodiment of the
present invention includes the arithmetic device 210 or the
input/output device 220.
<<Arithmetic Device 210>>
[0638] The arithmetic device 210 includes an arithmetic portion 211
and a memory portion 212. The arithmetic device 210 further
includes a transmission path 214 and an input/output interface 215
(see FIG. 23A).
<<Arithmetic Portion 211>>
[0639] The arithmetic portion 211 is configured to, for example,
execute a program. For example, a CPU described in Embodiment 8 can
be used. Thus, power consumption can be sufficiently reduced.
<<Memory Portion 212>>
[0640] The memory portion 212 is configured to, for example, store
the program executed by the arithmetic portion 211, initial
information, setting information, an image, or the like.
[0641] Specifically, a hard disk, a flash memory, a memory
including a transistor including an oxide semiconductor, or the
like can be used for the memory portion 212.
<<Input/Output Interface 215, Transmission Path
214>>
[0642] The input/output interface 215 includes a terminal or a
wiring and is configured to supply and receive information. For
example, the input/output interface 215 can be electrically
connected to the transmission path 214 and the input/output device
220.
[0643] The transmission path 214 includes a wiring and is
configured to supply and receive information. For example, the
transmission path 214 can be electrically connected to the
input/output interface 215. In addition, the transmission path 214
can be electrically connected to the arithmetic portion 211 or the
memory portion 212.
<<Input/Output Device 220>>
[0644] The input/output device 220 includes the display portion
230, the input portion 240, a sensor portion 250, or a
communication portion 290.
<<Display Portion 230>>
[0645] The display portion 230 includes a display region 231, a
driver circuit GD, and a driver circuit SD (see FIG. 24A). For
example, the display panel described in Embodiment 1 or 2 can be
used. Thus, low power consumption can be achieved.
[0646] The display region 231 includes a plurality of pixels 232(i,
1) to 232 (i, n) arranged in the row direction, a plurality of
pixels 232(1,j) to 232 (m,j) arranged in the column direction, a
scan line G(i) electrically connected to the pixels 232(i, 1) to
232 (i, n), and a signal line S(j) electrically connected to the
pixels 232(1, j) to 232 (m,j). Note that i is an integer greater
than or equal to 1 and less than or equal to m, j is an integer
greater than or equal to 1 and less than or equal to n, and each of
m and n is an integer greater than or equal to 1.
[0647] Note that the pixel 232(i,j) is electrically connected to
the scan line G1(i), the scan line G2(i,j), the signal line S(j),
the wiring ANO, the wiring VCOM1, and the wiring VCOM2 (see FIG.
24C).
[0648] Note that the scan line G1(i) includes the scan line G1(i)
and the scan line G2(i,j) (see FIGS. 24A and 24B).
[0649] The display portion can include a plurality of driver
circuits. For example, the display portion 230B can include a
driver circuit GDA and a driver circuit GDB (see FIG. 24B).
<<Driver Circuit GD>>
[0650] The driver circuit GD is configured to supply a selection
signal in accordance with the control information.
[0651] For example, the driver circuit GD is configured to supply a
selection signal to one scan line at a frequency of 30 Hz or
higher, preferably 60 Hz or higher, in accordance with the control
information. Accordingly, moving images can be smoothly
displayed.
[0652] For example, the driver circuit GD is configured to supply a
selection signal to one scan line at a frequency of lower than 30
Hz, preferably lower than 1 Hz, more preferably less than once per
minute, in accordance with the control information. Accordingly, a
still image can be displayed while flickering is suppressed.
[0653] For example, in the case where a plurality of driver
circuits is provided, the driver circuits GDA and GDB may supply
the selection signals at different frequencies. Specifically, the
selection signal can be supplied at a higher frequency to a region
on which moving images are smoothly displayed than to a region on
which a still image is displayed in a state where flickering is
suppressed.
<<Driver Circuit SD>>
[0654] The driver circuit SD is configured to supply an image
signal in accordance with the image information V.
<<Pixel 232(i,j)>>
[0655] The pixel 232(i, j) includes a first display element 235LC
and a second display element 235EL overlapping with the opening in
the reflective film of the first display element 235LC. The pixel
232(i,j) further includes a first pixel circuit for driving the
first display element 235LC and a second pixel circuit for driving
the second display element 235EL (see FIG. 24C).
<<First Display Element 235LC>>
[0656] For example, a display element having a function of
controlling light transmission can be used as the first display
element 235LC. Specifically, a polarizing plate and a liquid
crystal element, a MEMS shutter display element, or the like can be
used.
[0657] Specifically, a liquid crystal element driven in any of the
following driving modes can be used: an in-plane switching (IPS)
mode, a twisted nematic (TN) mode, a fringe field switching (FFS)
mode, an axially symmetric aligned micro-cell (ASM) mode, an
optically compensated birefringence (OCB) mode, a ferroelectric
liquid crystal (FLC) mode, an antiferroelectric liquid crystal
(AFLC) mode, and the like.
[0658] In addition, a liquid crystal element that can be driven by,
for example, a vertical alignment (VA) mode such as a multi-domain
vertical alignment (MVA) mode, a patterned vertical alignment (PVA)
mode, an electrically controlled birefringence (ECB) mode, a
continuous pinwheel alignment (CPA) mode, or an advanced super view
(ASV) mode can be used.
[0659] The first display element 235LC includes a first electrode,
a second electrode, and a liquid crystal layer. The liquid crystal
layer contains a liquid crystal material whose orientation is
controlled by voltage applied between the first electrode and the
second electrode. For example, the orientation of the liquid
crystal material can be controlled by an electric field in the
thickness direction (also referred to as the vertical direction),
the horizontal direction, or the diagonal direction of the liquid
crystal layer.
[0660] For example, thermotropic liquid crystal, low-molecular
liquid crystal, high-molecular liquid crystal, polymer dispersed
liquid crystal, ferroelectric liquid crystal, anti-ferroelectric
liquid crystal, or the like can be used. These liquid crystal
materials exhibit a cholesteric phase, a smectic phase, a cubic
phase, a chiral nematic phase, an isotropic phase, or the like
depending on conditions. Alternatively, a liquid crystal material
that exhibits a blue phase can be used.
<<Second Display Element 235EL>>
[0661] A display element having a function of emitting light, such
as an organic EL element, can be used as the second display element
235EL.
[0662] Specifically, an organic EL element which emits white light
can be used as the second display element 235EL. Alternatively, an
organic EL element which emits blue light, green light, or red
light can be used as the second display element 235EL.
<<Pixel Circuit>>
[0663] A pixel circuit including a circuit which is configured to
drive the first display element 235LC and/or the second display
element 235EL can be used.
[0664] For example, a pixel circuit which is electrically connected
to the scan line G1(i), the scan line G2(i,j), the signal line
S(j), the wiring ANO, the wiring VCOM1, and the wiring VCOM2 and
which drives a light-emitting element and an organic EL element is
described (see FIG. 24C).
[0665] Alternatively, for example, a switch, a transistor, a diode,
a resistor, a capacitor, or an inductor can be used in the pixel
circuit.
[0666] For example, one or a plurality of transistors can be used
as a switch. Alternatively, a plurality of transistors connected in
parallel, in series, or in combination of parallel connection and
series connection can be used as a switch.
[0667] For example, a capacitor may be formed by the first
electrode of the first display element 235LC and a conductive film
having a region overlapping with the first electrode.
[0668] For example, the pixel circuit includes a transistor
functioning as the switch SW1, the first display element 235LC, and
the capacitor C1. A gate electrode of the transistor is
electrically connected to the scan line G1(i), and a first
electrode of the transistor is electrically connected to the signal
line S(j). A first electrode of the first display element 235LC is
electrically connected to a second electrode of the transistor, and
a second electrode of the first display element 235LC is
electrically connected to the wiring VCOM1. A first electrode of
the capacitor C1 is electrically connected to the second electrode
of the transistor, and a second electrode of the capacitor C1 is
electrically connected to the wiring VCOM1.
[0669] The pixel circuit includes the transistor functioning as the
switch SW2. A gate electrode of the transistor is electrically
connected to the scan line G2(i), a first electrode of the
transistor is electrically connected to the signal line S(j). In
addition, the pixel circuit includes the transistor M. A gate
electrode of the transistor M is electrically connected to a second
electrode of the transistor functioning as the switch SW2. A first
electrode of the transistor M is electrically connected to the
wiring ANO. In addition, the pixel circuit includes the capacitor
C2. A first electrode of the capacitor C2 is electrically connected
to the second electrode of the transistor functioning as the switch
SW2. A second electrode of the capacitor C2 is electrically
connected to the second electrode of the transistor M. In addition,
the pixel circuit includes a second display element 235EL. A first
electrode and a second electrode of the second display element
235EL are electrically connected to the second electrode of the
transistor M and the wiring VCOM2, respectively.
<<Transistor>>
[0670] For example, a semiconductor film formed at the same step
can be used for transistors in the driver circuit and the pixel
circuit.
[0671] As the transistors in the driver circuit and the pixel
circuit, bottom-gate transistors, top-gate transistors, or the like
can be used.
[0672] For example, a manufacturing line for a bottom-gate
transistor including amorphous silicon as a semiconductor can be
easily remodeled into a manufacturing line for a bottom-gate
transistor including an oxide semiconductor as a semiconductor.
Furthermore, for example, a manufacturing line for a top-gate
transistor including polysilicon as a semiconductor can be easily
remodeled into a manufacturing line for a top-gate transistor
including an oxide semiconductor as a semiconductor.
[0673] For example, a transistor including a semiconductor
containing an element of Group 4 can be used. Specifically, a
semiconductor containing silicon can be used for a semiconductor
film. For example, single crystal silicon, polysilicon,
microcrystalline silicon, or amorphous silicon can be used for the
semiconductor of the transistor.
[0674] Note that the temperature for forming a transistor using
polysilicon in a semiconductor is lower than the temperature for
forming a transistor using single crystal silicon in a
semiconductor.
[0675] In addition, the transistor using polysilicon in a
semiconductor has higher field-effect mobility than the transistor
using amorphous silicon in a semiconductor, and therefore a pixel
including the transistor using polysilicon can have a high aperture
ratio. Moreover, pixels arranged at a high density, a gate driver
circuit, and a source driver circuit can be formed over the same
substrate. As a result, the number of components included in an
electronic device can be reduced.
[0676] In addition, the transistor using polysilicon in a
semiconductor has higher reliability than the transistor using
amorphous silicon in a semiconductor.
[0677] For example, a transistor including an oxide semiconductor
can be used. Specifically, an oxide semiconductor containing indium
or an oxide semiconductor containing indium, gallium, and zinc can
be used for a semiconductor film.
[0678] For example, a transistor having a lower leakage current in
an off state than a transistor that uses amorphous silicon for a
semiconductor film can be used. Specifically, a transistor that
uses an oxide semiconductor for a semiconductor film can be
used.
[0679] A pixel circuit in the transistor that uses an oxide
semiconductor for the semiconductor film can hold an image signal
for a longer time than a pixel circuit in a transistor that uses
amorphous silicon for a semiconductor film. Specifically, the
selection signal can be supplied at a frequency of lower than 30
Hz, preferably lower than 1 Hz, more preferably less than once per
minute while flickering is suppressed. Consequently, eyestrain on a
user of the information processing device can be reduced, and power
consumption for driving can be reduced.
[0680] Alternatively, for example, a transistor including a
compound semiconductor can be used. Specifically, a semiconductor
containing gallium arsenide can be used for a semiconductor
film.
[0681] For example, a transistor including an organic semiconductor
can be used. Specifically, an organic semiconductor containing any
of polyacenes and graphene can be used for the semiconductor
film.
<<Input Portion 240>>
[0682] A variety of human interfaces or the like can be used as the
input portion 240 (see FIG. 12A).
[0683] For example, a keyboard, a mouse, a touch sensor, a
microphone, a camera, or the like can be used as the input portion
240. Note that a touch sensor having a region overlapping with the
display portion 230 can be used. An input/output device that
includes the display portion 230 and a touch sensor having a region
overlapping with the display portion 230 can be referred to as a
touch panel.
[0684] For example, a user can make various gestures (e.g., tap,
drag, swipe, and pinch in) using his/her finger as a pointer on the
touch panel.
[0685] The arithmetic device 210, for example, analyzes information
on the position, track, or the like of the finger on the touch
panel and determines that a specific gesture is supplied when the
analysis results meet predetermined conditions. Therefore, the user
can supply a certain operation instruction associated with a
certain gesture by using the gesture.
[0686] For instance, the user can supply a "scrolling instruction"
for changing a portion where image information is displayed by
using a gesture of touching and moving his/her finger on the touch
panel.
<<Sensor Portion 250>>
[0687] The sensor portion 250 is configured to acquire information
P2 by measuring the surrounding state.
[0688] For example, a camera, an acceleration sensor, a direction
sensor, a pressure sensor, a temperature sensor, a humidity sensor,
an illuminance sensor, or a global positioning system (GPS) signal
receiving circuit can be used as the sensor portion 250.
[0689] For example, when the arithmetic device 210 determines that
the ambient light level measured by an illuminance sensor of the
sensor portion 250 is sufficiently higher than the predetermined
illuminance, image data is displayed using the first display
element 235LC. When the arithmetic device 210 determines that it is
dim, image data is displayed using the first display element 235LC
and the second display element 235EL. When the arithmetic device
210 determines that it is dark, image data is displayed using the
second display element 235EL.
[0690] Specifically, an image is displayed with a reflective
display element and/or a self-luminous display element depending on
the ambient brightness. For example, a liquid crystal element and
an organic EL element can be used as the reflective display element
and the self-luminous display element, respectively.
[0691] Thus, image information can be displayed in such a manner
that, for example, a reflective display element is used under
strong ambient light, a reflective display element and a
self-luminous display element are used in dim light, and a
self-luminous display element is used in dark light. Thus, a novel
display device with high visibility and low power consumption can
be provided. A novel data processor which is highly convenient or
reliable can be provided.
[0692] For example, a sensor measuring chromaticity of ambient
light, such as a CCD camera, can be used in the sensor portion 250,
white balance can be adjusted in accordance with the chromaticity
of ambient light measured by the sensor portion 250.
[0693] Specifically, in the first step, imbalance disruption of
white balance of ambient light is measured.
[0694] In the second step, the intensity of light of a color which
is insufficient in an image to be displayed by the first display
element using reflection of ambient light is estimated.
[0695] In the third step, ambient light is reflected by the first
display element, and light is emitted from the second display
element so that light of the insufficient color is supplemented,
whereby the image is displayed.
[0696] In this manner, display can be performed with adjusted white
balance by utilizing light reflected by the first display element
and light emitted from the second display element. Thus, a novel
data processor which can display an image with low power
consumption or with adjusted white balance and which is highly
convenient and reliable can be provided.
<<Communication Portion 290>>
[0697] The communication portion 290 is configured to supply and
acquire information to/from a network.
<<Program>>
[0698] A program of one embodiment of the present invention will be
described with reference to FIGS. 25A and 25B and FIG. 26.
[0699] FIG. 25A is a flow chart showing main processing of the
program of one embodiment of the present invention, and FIG. 25B is
a flow chart showing interrupt processing.
[0700] FIG. 26 schematically illustrates a method for displaying
image information on the display portion 230.
[0701] The program of one embodiment of the present invention has
the following steps (see FIG. 25A).
[0702] In a first step, setting is initialized (see (S1) in FIG.
25A).
[0703] For instance, predetermined image information and the second
mode can be used for the initialization.
[0704] For example, a still image can be used as the predetermined
image information. Alternatively, a mode in which the selection
signal is supplied at a frequency of lower than 30 Hz, preferably
lower than 1 Hz, more preferably less than once per minute can be
used as the second mode. For example, in the case where the time is
displayed on the data processor on the second time scale, a mode in
which the selection signal is supplied at a frequency of 1 Hz can
be used as the second mode. In the case where the time is displayed
on the data processor on the minute time scale, a mode in which the
selection signal is supplied once per minute can be used as the
second mode.
[0705] In a second step, interrupt processing is allowed (see S2 in
FIG. 25A). Note that an arithmetic device allowed to execute the
interrupt processing can perform the interrupt processing in
parallel with the main processing. The arithmetic device which has
returned from the interrupt processing to the main processing can
reflect the results of the interrupt processing in the main
processing. For example, in the case where the time is displayed on
the information processing device on the second time scale, a mode
in which the selection signal is supplied at a frequency of 1 Hz
can be used as the second mode. In the case where the time is
displayed on the information processing device on the minute time
scale, a mode in which the selection signal is supplied once per
minute can be used as the second mode.
[0706] The arithmetic device may execute the interrupt processing
when a counter has an initial value, and the counter may be set at
a value other than the initial value when the arithmetic device
returns from the interrupt processing. Thus, the interrupt
processing is ready to be executed after the program is started
up.
[0707] In a third step, image information is displayed in a mode
selected in the first step or the interrupt processing (see S3 in
FIG. 25A).
[0708] For instance, predetermined image information is displayed
in the second mode, in accordance with the initialization.
[0709] Specifically, the predetermined image information is
displayed in a mode in which the selection signal is supplied to
one scan line at a frequency of lower than 30 Hz, preferably lower
than 1 Hz, more preferably less than once per minute.
[0710] For example, the selection signal is supplied at Time T1 so
that first image information PIC1 is displayed on the display
portion 230 (see FIG. 26). At Time T2, which is, for example, one
second after Time T1, the selection signal is supplied so that the
predetermined image information is displayed.
[0711] Alternatively, in the case where a predetermined event is
not supplied in the interrupt processing, image information is
displayed in the second mode.
[0712] For example, the selection signal is supplied at Time T5 so
that fourth image information PIC4 is displayed on the display
portion 230. At Time T6, which is, for example, one second after
Time T5, the selection signal is supplied so that the same image
information is displayed. Note that the length of a period from
Time T5 to Time T6 can be equal to that of a period from Time T1 to
Time T2.
[0713] For instance, in the case where the predetermined event is
supplied in the interrupt processing, predetermined image
information is displayed in the first mode.
[0714] Specifically, in the case where an event associated with a
"page turning instruction" is supplied in the interrupt processing,
image information is switched from one to another in a mode in
which the selection signal is supplied to one scan line at a
frequency of 30 Hz or higher, preferably 60 Hz or higher.
[0715] Alternatively, in the case where an event associated with
the "scrolling instruction" is supplied in the interrupt
processing, second image information PIC2, which includes part of
the displayed first image information PIC1 and the following part,
is displayed in a mode in which the selection signal is supplied to
one scan line at a frequency of 30 Hz or higher, preferably 60 Hz
or higher.
[0716] Thus, for example, moving images in which images are
gradually switched in accordance with the "page turning
instruction" can be displayed smoothly. Alternatively, a moving
image in which an image is gradually moved in accordance with the
"scrolling instruction" can be displayed smoothly.
[0717] Specifically, the selection signal is supplied at Time T3
after the event associated with the "scrolling instruction" is
supplied so that the second image information PIC2 whose display
position and the like are changed from those of the first image
information PIC1 is displayed (see FIG. 26). The selection signal
is supplied at Time T4 so that third image information PIC3 whose
display position and the like are changed from those of the second
image information PIC2 is displayed. Note that each of a period
from Time T2 to Time T3, a period from Time T3 to Time T4, and a
period from Time T4 to Time T5 is shorter than the period from Time
T1 to Time T2.
[0718] In the fourth step, the program moves to the fifth step when
a termination instruction is supplied, and the program moves to the
third step when the termination instruction is not supplied (see S4
in FIG. 25A).
[0719] Note that in the interrupt processing, for example, the
termination instruction can be supplied.
[0720] In the fifth step, the program terminates (see S5 in FIG.
25A).
[0721] The interrupt processing includes sixth to eighth steps
described below (see FIG. 25B).
[0722] In the sixth step, the processing proceeds to the seventh
step when a predetermined event has been supplied, whereas the
processing proceeds to the eighth step when the predetermined event
has not been supplied (see S6 in FIG. 25B).
[0723] For example, whether the predetermined event is supplied in
a predetermined period or not can be a branch condition.
Specifically, the predetermined period can be longer than 0 seconds
and shorter than or equal to 5 seconds, preferably shorter than or
equal to 1 second, further preferably shorter than or equal to 0.5
seconds, still further preferably shorter than or equal to 0.1
seconds.
[0724] For example, the predetermined event can include an event
associated with the termination instruction.
[0725] In the seventh step, the mode is changed (see S7 in FIG.
25B). Specifically, the mode is changed to the second mode when the
first mode has been selected, or the mode is changed to the first
mode when the second mode has been selected.
[0726] In the eighth step, the interrupt processing terminates (see
S8 in FIG. 25B).
<<Predetermined Event>>
[0727] A variety of instructions can be associated with a variety
of events.
[0728] The following instructions can be given as examples:
"page-turning instruction" for switching displayed image
information from one to another and "scroll instruction" for moving
the display position of part of image information and displaying
another part continuing from that part.
[0729] For example, the following events can be used: events
supplied using a pointing device such as a mouse (e.g., "click" and
"drag") and events supplied to a touch panel with a finger or the
like used as a pointer (e.g., "tap", "drag", and "swipe").
[0730] For example, the position of a slide bar pointed by a
pointer, the swipe speed, and the drag speed can be used as
parameters assigned to an instruction associated with the
predetermined event.
[0731] Specifically, a parameter that determines the page-turning
speed or the like can be used to execute the "page-turning
instruction," and a parameter that determines the moving speed of
the display position or the like can be used to execute the "scroll
instruction."
[0732] For example, the display brightness, contrast, or saturation
may be changed in accordance with the page-turning speed and/or the
scroll speed.
[0733] Specifically, in the case where the page-turning speed
and/or the scroll speed are/is higher than the predetermined speed,
the display brightness may be decreased in synchronization with the
speed.
[0734] Alternatively, in the case where the page-turning speed
and/or the scroll speed are/is higher than the predetermined speed,
the contrast may be decreased in synchronization with the
speed.
[0735] For example, the speed at which user's eyes cannot follow
displayed images can be used as the predetermined speed.
[0736] The contrast can be reduced in such a manner that the gray
level of a bright region (with a high gray level) included in image
information is brought close to the gray level of a dark region
(with a low gray level) included in the image information.
[0737] Alternatively, the contrast can be reduced in such a manner
that the gray level of the dark region included in image
information is brought close to the gray level of the bright region
included in the image information.
[0738] Specifically, in the case where the page-turning speed
and/or the scroll speed are/is higher than the predetermined speed,
display may be performed such that the yellow tone is increased or
the blue tone is decreased in synchronization with the speed.
[0739] Image information may be generated based on the usage
ambience of the information processing device 200 acquired by the
sensor portion 250. For example, a color selected from user's
selections in accordance with the acquired ambient brightness or
the like can be used as the background color of the image
information (see FIG. 23B). Thus, favorable environment can be
provided for a user of the information processing device 200.
[0740] Image information may be generated in accordance with
received information distributed among a specific space using the
communication portion 290. For example, educational materials can
be distributed among a classroom and displayed to be used as a
school book. Alternatively, materials transmitted among a
conference room in a company can be received and displayed.
[0741] This embodiment can be combined with any of the other
embodiments in this specification as appropriate.
Embodiment 8
[0742] In this embodiment, a semiconductor device (memory device)
that can retain stored data even when not powered and that has an
unlimited number of write cycles, and a CPU including the
semiconductor device will be described. The CPU described in this
embodiment can be used for the information processing device
described in Embodiment 7, for example.
<Memory Device>
[0743] An example of a semiconductor device (memory device) which
can retain stored data even when not powered and which has an
unlimited number of write cycles is shown in FIGS. 27A to 27C. Note
that FIG. 27B is a circuit diagram of the structure in FIG.
27A.
[0744] The semiconductor device illustrated in FIGS. 27A and 27B
includes a transistor 3200 using a first semiconductor material, a
transistor 3300 using a second semiconductor material, and a
capacitor 3400.
[0745] The first and second semiconductor materials preferably have
different energy gaps. For example, the first semiconductor
material can be a semiconductor material other than an oxide
semiconductor (examples of such a semiconductor material include
silicon (including strained silicon), germanium, silicon germanium,
silicon carbide, gallium arsenide, aluminum gallium arsenide,
indium phosphide, gallium nitride, and an organic semiconductor),
and the second semiconductor material can be an oxide
semiconductor. A transistor using a material other than an oxide
semiconductor, such as single crystal silicon, can operate at high
speed easily. On the other hand, a transistor including an oxide
semiconductor has a low off-state current.
[0746] The transistor 3300 is a transistor in which a channel is
formed in a semiconductor layer including an oxide semiconductor.
Since the off-state current of the transistor 3300 is small, stored
data can be retained for a long period. In other words, power
consumption can be sufficiently reduced because a semiconductor
memory device in which refresh operation is unnecessary or the
frequency of refresh operation is extremely low can be
provided.
[0747] In FIG. 27B, a first wiring 3001 is electrically connected
to a source electrode of the transistor 3200. A second wiring 3002
is electrically connected to a drain electrode of the transistor
3200. A third wiring 3003 is electrically connected to one of a
source electrode and a drain electrode of the transistor 3300. A
fourth wiring 3004 is electrically connected to a gate electrode of
the transistor 3300. A gate electrode of the transistor 3200 and
the other of the source electrode and the drain electrode of the
transistor 3300 are electrically connected to one electrode of the
capacitor 3400. A fifth wiring 3005 is electrically connected to
the other electrode of the capacitor 3400.
[0748] The semiconductor device in FIG. 27A has a feature that the
potential of the gate electrode of the transistor 3200 can be
retained, and thus enables writing retaining, and reading of data
as follows.
[0749] Writing and retaining of data are described. First, the
potential of the fourth wiring 3004 is set to a potential at which
the transistor 3300 is turned on, so that the transistor 3300 is
turned on. Accordingly, the potential of the third wiring 3003 is
supplied to the gate of the transistor 3200 and the capacitor 3400.
That is, a predetermined charge is supplied to the gate electrode
of the transistor 3200 (writing). Here, one of two kinds of charges
providing different potential levels (hereinafter referred to as a
low-level charge and a high-level charge) is supplied. After that,
the potential of the fourth wiring 3004 is set to a potential at
which the transistor 3300 is turned off, so that the transistor
3300 is turned off. Thus, the charge supplied to the gate electrode
of the transistor 3200 is held (retaining).
[0750] Since the off-state current of the transistor 3300 is
extremely small, the charge of the gate electrode of the transistor
3200 is retained for a long time.
[0751] Next, reading of data is described. An appropriate potential
(a reading potential) is supplied to the fifth wiring 3005 while a
predetermined potential (a constant potential) is supplied to the
first wiring 3001, whereby the potential of the second wiring 3002
varies depending on the amount of charge retained in the gate
electrode of the transistor 3200. This is because in the case of
using an n-channel transistor as the transistor 3200, an apparent
threshold voltage V.sub.th.sub._.sub.H at the time when the
high-level charge is given to the gate electrode of the transistor
3200 is lower than an apparent threshold voltage
V.sub.th.sub._.sub.L at the time when the low-level charge is given
to the gate electrode of the transistor 3200. Here, an apparent
threshold voltage refers to the potential of the fifth wiring 3005
which is needed to turn on the transistor 3200. Thus, the potential
of the fifth wiring 3005 is set to a potential V.sub.0 which is
between V.sub.th.sub._.sub.H and V.sub.th.sub._.sub.L, whereby
charge supplied to the gate electrode of the transistor 3200 can be
determined. For example, in the case where the high-level charge is
supplied to the gate electrode of the transistor 3200 in writing
and the potential of the fifth wiring 3005 is V.sub.0
(>V.sub.th.sub._.sub.H), the transistor 3200 is turned on. On
the other hand, in the case where the low-level charge is supplied
to the gate electrode of the transistor 3200 in writing, even when
the potential of the fifth wiring 3005 is V.sub.0
(<V.sub.th.sub._.sub.L), the transistor 3200 remains off. Thus,
the data retained in the gate electrode of the transistor 3200 can
be read by determining the potential of the second wiring 3002.
[0752] Note that in the case where memory cells are arrayed, it is
necessary that data of a desired memory cell is read. For example,
the fifth wiring 3005 of memory cells from which data is not read
may be supplied with a potential at which the transistor 3200 is
turned off regardless of the potential supplied to the gate
electrode, that is, a potential lower than V.sub.th.sub._.sub.H,
whereby only data of a desired memory cell can be read.
Alternatively, the fifth wiring 3005 of the memory cells from which
data is not read may be supplied with a potential at which the
transistor 3200 is turned on regardless of the potential supplied
to the gate electrode, that is, a potential higher than
V.sub.th.sub._.sub.L, whereby only data of a desired memory cell
can be read.
[0753] The semiconductor device illustrated in FIG. 27C is
different from the semiconductor device illustrated in FIG. 27A in
that the transistor 3200 is not provided. Also in this case,
writing and retaining operation of data can be performed in a
manner similar to the semiconductor device illustrated in FIG.
27A.
[0754] Next, reading of data of the semiconductor device
illustrated in FIG. 27C is described. When the transistor 3300 is
turned on, the third wiring 3003 which is in a floating state and
the capacitor 3400 are electrically connected to each other, and
the charge is redistributed between the third wiring 3003 and the
capacitor 3400. As a result, the potential of the third wiring 3003
is changed. The amount of change in the potential of the third
wiring 3003 varies depending on the potential of the one electrode
of the capacitor 3400 (or the charge accumulated in the capacitor
3400).
[0755] For example, the potential of the third wiring 3003 after
the charge redistribution is
(C.sub.B.times.V.sub.B0+C.times.V)/(C.sub.B+C), where V is the
potential of the one electrode of the capacitor 3400, C is the
capacitance of the capacitor 3400, Ca is the capacitance component
of the third wiring 3003, and V.sub.Bo is the potential of the
third wiring 3003 before the charge redistribution. Thus, it can be
found that, assuming that the memory cell is in either of two
states in which the potential of the one electrode of the capacitor
3400 is V.sub.1 and V.sub.0 (V.sub.1>V.sub.0), the potential of
the third wiring 3003 in the case of retaining the potential
V.sub.1 (=(C.sub.B.times.V.sub.B0+C.times.V.sub.1)/(C.sub.B+C)) is
higher than the potential of the third wiring 3003 in the case of
retaining the potential V.sub.0
(=(C.sub.B.times.V.sub.B0+C.times.V.sub.0)/(C.sub.B+C)).
[0756] Then, by comparing the potential of the third wiring 3003
with a predetermined potential, data can be read.
[0757] In this case, a transistor including the first semiconductor
material may be used for a driver circuit for driving a memory
cell, and a transistor including the second semiconductor material
may be stacked over the driver circuit as the transistor 3300.
[0758] When including a transistor in which a channel formation
region is formed using an oxide semiconductor and which has an
extremely small off-state current, the semiconductor device
described in this embodiment can retain stored data for an
extremely long time. In other words, refresh operation becomes
unnecessary or the frequency of the refresh operation can be
extremely low, which leads to a sufficient reduction in power
consumption. Moreover, stored data can be retained for a long time
even when power is not supplied (note that a potential is
preferably fixed).
[0759] Furthermore, in the semiconductor device described in this
embodiment, high voltage is not needed for writing data and there
is no problem of deterioration of elements. Unlike in a
conventional nonvolatile memory, for example, it is not necessary
to inject and extract electrons into and from a floating gate;
thus, a problem such as deterioration of a gate insulating film is
not caused. That is, the semiconductor device described in this
embodiment does not have a limit on the number of times data can be
rewritten, which is a problem of a conventional nonvolatile memory,
and the reliability thereof is drastically improved. Furthermore,
data is written depending on the state of the transistor (on or
off), whereby high-speed operation can be easily achieved.
[0760] The above memory device can also be used in an LSI such as a
digital signal processor (DSP), a custom LSI, or a programmable
logic device (PLD), in addition to a central processing unit (CPU),
and a radio frequency identification (RF-ID) tag, for example.
<CPU>
[0761] A CPU including the above memory device is described
below.
[0762] FIG. 28 is a block diagram illustrating a configuration
example of the CPU including the above memory device.
[0763] The CPU illustrated in FIG. 28 includes, over a substrate
1190, an arithmetic logic unit (ALU) 1191, an ALU controller 1192,
an instruction decoder 1193, an interrupt controller 1194, a timing
controller 1195, a register 1196, a register controller 1197, a bus
interface (BUS I/F) 1198, a rewritable ROM 1199, and a ROM
interface (ROM I/F) 1189. A semiconductor substrate, an SOI
substrate, a glass substrate, or the like is used as the substrate
1190. The ROM 1199 and the ROM interface 1189 may be provided over
a separate chip. Needless to say, the CPU in FIG. 28 is just an
example in which the configuration is simplified, and an actual CPU
may have a variety of configurations depending on the application.
For example, the CPU may have the following configuration: a
structure including the CPU illustrated in FIG. 28 or an arithmetic
circuit is considered as one core; a plurality of the cores are
included; and the cores operate in parallel.
[0764] The number of bits that the CPU can process in an internal
arithmetic circuit or in a data bus can be, for example, 8, 16, 32,
or 64.
[0765] An instruction that is input to the CPU through the bus
interface 1198 is input to the instruction decoder 1193 and decoded
therein, and then, input to the ALU controller 1192, the interrupt
controller 1194, the register controller 1197, and the timing
controller 1195.
[0766] The ALU controller 1192, the interrupt controller 1194, the
register controller 1197, and the timing controller 1195 conduct
various controls in accordance with the decoded instruction.
Specifically, the ALU controller 1192 generates signals for
controlling the operation of the ALU 1191. While the CPU is
executing a program, the interrupt controller 1194 processes an
interrupt request from an external input/output device or a
peripheral circuit depending on its priority or a mask state. The
register controller 1197 generates an address of the register 1196,
and reads/writes data from/to the register 1196 depending on the
state of the CPU.
[0767] The timing controller 1195 generates signals for controlling
operation timings of the ALU 1191, the ALU controller 1192, the
instruction decoder 1193, the interrupt controller 1194, and the
register controller 1197. For example, the timing controller 1195
includes an internal clock generator for generating an internal
clock signal on the basis of a reference clock signal, and supplies
the internal clock signal to the above circuits.
[0768] In the CPU illustrated in FIG. 28, a memory cell is provided
in the register 1196.
[0769] In the CPU illustrated in FIG. 28, the register controller
1197 selects operation of retaining data in the register 1196 in
accordance with an instruction from the ALU 1191. That is, the
register controller 1197 selects whether data is retained by a
flip-flop or by a capacitor in the memory cell included in the
register 1196. When data retaining by the flip-flop is selected, a
power supply voltage is supplied to the memory cell in the register
1196. When data retaining by the capacitor is selected, the data is
rewritten in the capacitor, and supply of the power supply voltage
to the memory cell in the register 1196 can be stopped.
[0770] FIG. 29 is an example of a circuit diagram of a memory
element that can be used for the register 1196. A memory element
1200 includes a circuit 1201 in which stored data is volatile when
power supply is stopped, a circuit 1202 in which stored data is
nonvolatile even when power supply is stopped, a switch 1203, a
switch 1204, a logic element 1206, a capacitor 1207, and a circuit
1220 having a selecting function. The circuit 1202 includes a
capacitor 1208, a transistor 1209, and a transistor 1210. Note that
the memory element 1200 may further include another element such as
a diode, a resistor, or an inductor, as needed.
[0771] Here, the above-described memory device can be used as the
circuit 1202. When supply of a power supply voltage to the memory
element 1200 is stopped, a ground potential (0 V) or a potential at
which the transistor 1209 in the circuit 1202 is turned off
continues to be input to a gate of the transistor 1209. For
example, the gate of the transistor 1209 is grounded through a load
such as a resistor.
[0772] Shown here is an example in which the switch 1203 is a
transistor 1213 having one conductivity type (e.g., an n-channel
transistor) and the switch 1204 is a transistor 1214 having a
conductivity type opposite to the one conductivity type (e.g., a
p-channel transistor). A first terminal of the switch 1203
corresponds to one of a source and a drain of the transistor 1213,
a second terminal of the switch 1203 corresponds to the other of
the source and the drain of the transistor 1213, and conduction or
non-conduction between the first terminal and the second terminal
of the switch 1203 (i.e., the on/off state of the transistor 1213)
is selected by a control signal RD input to a gate of the
transistor 1213. A first terminal of the switch 1204 corresponds to
one of a source and a drain of the transistor 1214, a second
terminal of the switch 1204 corresponds to the other of the source
and the drain of the transistor 1214, and conduction or
non-conduction between the first terminal and the second terminal
of the switch 1204 (i.e., the on/off state of the transistor 1214)
is selected by the control signal RD input to a gate of the
transistor 1214.
[0773] One of a source and a drain of the transistor 1209 is
electrically connected to one of a pair of electrodes of the
capacitor 1208 and a gate of the transistor 1210. Here, the
connection portion is referred to as a node M2. One of a source and
a drain of the transistor 1210 is electrically connected to a
wiring that can supply a low power supply potential (e.g., a GND
line), and the other thereof is electrically connected to the first
terminal of the switch 1203 (the one of the source and the drain of
the transistor 1213). The second terminal of the switch 1203 (the
other of the source and the drain of the transistor 1213) is
electrically connected to the first terminal of the switch 1204
(the one of the source and the drain of the transistor 1214). The
second terminal of the switch 1204 (the other of the source and the
drain of the transistor 1214) is electrically connected to a wiring
that can supply a power supply potential VDD. The second terminal
of the switch 1203 (the other of the source and the drain of the
transistor 1213), the first terminal of the switch 1204 (the one of
the source and the drain of the transistor 1214), an input terminal
of the logic element 1206, and one of a pair of electrodes of the
capacitor 1207 are electrically connected to each other. Here, the
connection portion is referred to as a node M1. The other of the
pair of electrodes of the capacitor 1207 can be supplied with a
constant potential. For example, the other of the pair of
electrodes of the capacitor 1207 can be supplied with a low power
supply potential (e.g., GND) or a high power supply potential
(e.g., VDD). The other of the pair of electrodes of the capacitor
1207 is electrically connected to the wiring that can supply a low
power supply potential (e.g., a GND line). The other of the pair of
electrodes of the capacitor 1208 can be supplied with a constant
potential. For example, the other of the pair of electrodes of the
capacitor 1208 can be supplied with a low power supply potential
(e.g., GND) or a high power supply potential (e.g., VDD). The other
of the pair of electrodes of the capacitor 1208 is electrically
connected to the wiring that can supply a low power supply
potential (e.g., a GND line).
[0774] The capacitor 1207 and the capacitor 1208 are not
necessarily provided as long as the parasitic capacitance of the
transistor, the wiring, or the like is actively utilized.
[0775] A control signal WE is input to a first gate (first gate
electrode) of the transistor 1209. As for each of the switch 1203
and the switch 1204, a conduction state or a non-conduction state
between the first terminal and the second terminal is selected by
the control signal RD that is different from the control signal WE.
When the first terminal and the second terminal of one of the
switches are in the conduction state, the first terminal and the
second terminal of the other of the switches are in the
non-conduction state.
[0776] A signal corresponding to data retained in the circuit 1201
is input to the other of the source and the drain of the transistor
1209. FIG. 29 illustrates an example in which a signal output from
the circuit 1201 is input to the other of the source and the drain
of the transistor 1209. The logic value of a signal output from the
second terminal of the switch 1203 (the other of the source and the
drain of the transistor 1213) is inverted by the logic element
1206, and the inverted signal is input to the circuit 1201 through
the circuit 1220.
[0777] In the example of FIG. 29, a signal output from the second
terminal of the switch 1203 (the other of the source and the drain
of the transistor 1213) is input to the circuit 1201 through the
logic element 1206 and the circuit 1220; however, one embodiment of
the present invention is not limited thereto. The signal output
from the second terminal of the switch 1203 (the other of the
source and the drain of the transistor 1213) may be input to the
circuit 1201 without its logic value being inverted. For example,
in the case where the circuit 1201 includes a node in which a
signal obtained by inversion of the logic value of a signal input
from the input terminal is retained, the signal output from the
second terminal of the switch 1203 (the other of the source and the
drain of the transistor 1213) can be input to the node.
[0778] In FIG. 29, the transistors included in the memory element
1200 except for the transistor 1209 can each be a transistor in
which a channel is formed in a layer formed using a semiconductor
other than an oxide semiconductor or in the substrate 1190. For
example, the transistor can be a transistor whose channel is formed
in a silicon layer or a silicon substrate. Alternatively, a
transistor in which a channel is formed in an oxide semiconductor
film can be used for all the transistors in the memory element
1200. Further alternatively, in the memory element 1200, a
transistor in which a channel is formed in an oxide semiconductor
film can be included besides the transistor 1209, and a transistor
in which a channel is formed in a layer formed using a
semiconductor other than an oxide semiconductor or the substrate
1190 can be used for the rest of the transistors.
[0779] As the circuit 1201 in FIG. 29, for example, a flip-flop
circuit can be used. As the logic element 1206, for example, an
inverter or a clocked inverter can be used.
[0780] In a period during which the memory element 1200 is not
supplied with the power supply voltage, the semiconductor device
described in this embodiment can retain data stored in the circuit
1201 by the capacitor 1208 that is provided in the circuit
1202.
[0781] The off-state current of a transistor in which a channel is
formed in an oxide semiconductor film is extremely small. For
example, the off-state current of a transistor in which a channel
is formed in an oxide semiconductor film is significantly smaller
than that of a transistor in which a channel is formed in silicon
having crystallinity. Thus, when the transistor in which a channel
is formed in an oxide semiconductor film is used as the transistor
1209, a signal is retained in the capacitor 1208 for a long time
also in a period during which the power supply voltage is not
supplied to the memory element 1200. The memory element 1200 can
accordingly retain the stored content (data) also in a period
during which the supply of the power supply voltage is stopped.
[0782] Since the memory element performs pre-charge operation with
the switch 1203 and the switch 1204, the time required for the
circuit 1201 to retain original data again after the supply of the
power supply voltage is restarted can be shortened.
[0783] In the circuit 1202, a signal retained by the capacitor 1208
is input to the gate of the transistor 1210. Thus, after supply of
the power supply voltage to the memory element 1200 is restarted,
the signal retained by the capacitor 1208 can be converted into the
one corresponding to the state (the on state or the off state) of
the transistor 1210 to be read from the circuit 1202. Consequently,
an original signal can be accurately read even when a potential
corresponding to the signal retained by the capacitor 1208 changes
to some degree.
[0784] By using the above-described memory element 1200 in a memory
device such as a register or a cache memory included in a
processor, data in the memory device can be prevented from being
lost owing to the stop of the supply of the power supply voltage.
Furthermore, shortly after the supply of the power supply voltage
is restarted, the memory device can be returned to the same state
as that before the power supply is stopped. Thus, the power supply
can be stopped even for a short time in the processor or one or a
plurality of logic circuits included in the processor, resulting in
lower power consumption.
[0785] Although the memory element 1200 is used in a CPU in this
embodiment, the memory element 1200 can also be used in an LSI such
as a digital signal processor (DSP), a custom LSI, or a
programmable logic device (PLD), and a radio frequency
identification (RF-ID).
[0786] At least part of this embodiment can be implemented in
combination with any of the other embodiments described in this
specification as appropriate.
Embodiment 9
[0787] In this embodiment, a display module and electronic devices
which include a reflective display device of one embodiment of the
present invention will be described with reference to FIGS. 30A to
30H.
[0788] FIGS. 30A to 30G illustrate electronic devices. These
electronic devices can include a housing 5000, a display portion
5001, a speaker 5003, an LED lamp 5004, operation keys 5005
(including a power switch and an operation switch), a connection
terminal 5006, a sensor 5007 (a sensor having a function of
measuring force, displacement, position, speed, acceleration,
angular velocity, rotational frequency, distance, light, liquid,
magnetism, temperature, chemical substance, sound, time, hardness,
electric field, current, voltage, electric power, radiation, flow
rate, humidity, gradient, oscillation, odor, or infrared ray), a
microphone 5008, and the like.
[0789] FIG. 30A illustrates a mobile computer which can include a
switch 5009, an infrared port 5010, and the like in addition to the
above components. FIG. 30B illustrates a portable image reproducing
device (e.g., a DVD reproducing device) provided with a recording
medium, and the portable image reproducing device can include a
second display portion 5002, a recording medium reading portion
5011, and the like in addition to the above components. FIG. 30C
illustrates a goggle-type display which can include the second
display portion 5002, a support portion 5012, an earphone 5013, and
the like in addition to the above components. FIG. 30D illustrates
a portable game console which can include the recording medium
reading portion 5011 and the like in addition to the above
components. FIG. 30E illustrates a digital camera with a television
reception function, and the digital camera can include an antenna
5014, a shutter button 5015, an image receiving portion 5016, and
the like in addition to the above components. FIG. 30F illustrates
a portable game console which can include the second display
portion 5002, the recording medium reading portion 5011, and the
like in addition to the above components. FIG. 30G illustrates a
portable television receiver which can include a charger 5017
capable of transmitting and receiving signals, and the like in
addition to the above components.
[0790] The electronic devices in FIGS. 30A to 30G can have a
variety of functions such as a function of displaying a variety of
information (e.g., a still image, a moving image, and a text image)
on the display portion, a touch panel function, a function of
displaying a calendar, date, time, and the like, a function of
controlling processing with a variety of software (programs), a
wireless communication function, a function of being connected to a
variety of computer networks with a wireless communication
function, a function of transmitting and receiving a variety of
data with a wireless communication function, and a function of
reading out a program or data stored in a recording medium and
displaying it on the display portion. Furthermore, the electronic
device including a plurality of display portions can have a
function of displaying image information mainly on one display
portion while displaying text information mainly on another display
portion, a function of displaying a three-dimensional image by
displaying images on a plurality of display portions with a
parallax taken into account, or the like. Furthermore, the
electronic device including an image receiving portion can have a
function of shooting a still image, a function of taking moving
images, a function of automatically or manually correcting a shot
image, a function of storing a shot image in a recording medium (an
external recording medium or a recording medium incorporated in the
camera), a function of displaying a shot image on the display
portion, or the like. Note that functions of the electronic devices
in FIGS. 30A to 30G are not limited thereto, and the electronic
devices can have a variety of functions.
[0791] FIG. 30H illustrates a smart watch, which includes a housing
7302, a display panel 7304, operation buttons 7311 and 7312, a
connection terminal 7313, a band 7321, a clasp 7322, and the
like.
[0792] The display panel 7304 mounted in the housing 7302 serving
as a bezel includes a non-rectangular display region. The display
panel 7304 may have a rectangular display region. The display panel
7304 can display an icon 7305 indicating time, another icon 7306,
and the like.
[0793] The smart watch in FIG. 30H can have a variety of functions
such as a function of displaying a variety of information (e.g., a
still image, a moving image, and a text image) on the display
portion, a touch panel function, a function of displaying a
calendar, date, time, and the like, a function of controlling
processing with a variety of software (programs), a wireless
communication function, a function of being connected to a variety
of computer networks with a wireless communication function, a
function of transmitting and receiving a variety of data with a
wireless communication function, and a function of reading out a
program or data stored in a recording medium and displaying it on
the display portion.
[0794] The housing 7302 can include a speaker, a sensor (a sensor
having a function of measuring force, displacement, position,
speed, acceleration, angular velocity, rotational frequency,
distance, light, liquid, magnetism, temperature, chemical
substance, sound, time, hardness, electric field, current, voltage,
electric power, radiation, flow rate, humidity, gradient,
oscillation, odor, or infrared rays), a microphone, and the like.
Note that the smart watch can be manufactured using the
light-emitting element for the display panel 7304.
[0795] This embodiment can be combined with any of the other
embodiments in this specification as appropriate.
Example 1
[0796] In this example, a fabricated display panel of one
embodiment of the present invention will be described with
reference to FIGS. 31A1 to 31C.
[0797] FIGS. 31A to 31C are photos of the fabricated display panel
displaying images. FIGS. 31A1 to 31A3 and FIG. 31C are photos for
showing the display quality of the display panel when the first
display element was used. FIGS. 31B1 to 31B3 are photos for showing
the display quality of the display panel when the second display
element was used.
[0798] Table 1 shows the specifications of the fabricated display
panel.
TABLE-US-00001 TABLE 1 Panel size 1.55 inch Effective pixels 320
.times. RGB (H) .times. 320 (V) Pixel size 29 .mu.m (H) .times. 87
.mu.m (V) Resolution 292 ppi First display element Reflective
liquid crystal element (ECB mode) Second display element Organic EL
element (Bottom emission) Pixel circuit LCD: 1Tr + 1C EL: 2Tr + 1C
Aperture ratio LCD: 69% EL: 3.9% Scan line driver circuit
incorporated Signal line driver circuit COF
[0799] A reflective liquid crystal element of an electrically
controlled birefringence (ECB) mode was used as the first display
element included in the fabricated display panel, which is one
embodiment of the present invention. A white-light-emitting organic
EL element was used as the second display element.
[0800] The fabricated display panel included a coloring layer
having regions overlapping with the first display element and the
second display element. Full-color display was performed utilizing
light passing through the coloring layer.
<<Evaluation>>
[0801] The display panel made displays using the first display
element in a light room equipped with a fluorescent lamp (see FIGS.
31A1 to 31A3). The display panel offered good full-color display
using the reflective liquid crystal element.
[0802] In addition, using the first display element, the display
panel performed display outdoors in fine weather during the daytime
(see FIG. 31C). Even under such strong ambient light, the display
panel offered good full-color display using the reflective liquid
crystal element.
[0803] The display panel performed display in a dark place using
the second display element (see FIGS. 31B1 to 31B3). The display
panel offered good full-color display using the organic EL
element.
[0804] In this specification and the like, for example, when it is
explicitly described that X and Y are connected, the case where X
and Y are electrically connected, the case where X and Y are
functionally connected, and the case where X and Y are directly
connected are included therein. Accordingly, another element may be
interposed between elements having a connection relation shown in
drawings and texts, without limiting to a predetermined connection
relation, for example, the connection relation shown in the
drawings and the texts.
[0805] Here, X and Y each denote an object (e.g., a device, an
element, a circuit, a line, an electrode, a terminal, a conductive
film, or a layer).
[0806] For example, in the case where X and Y are directly
connected, an element that enables electrical connection between X
and Y (e.g., a switch, a transistor, a capacitor, an inductor, a
resistor, a diode, a display element, a light-emitting element, or
a load) is not connected between X and Y, and X and Y are connected
without the element that enables electrical connection between X
and Y (e.g., a switch, a transistor, a capacitor, an inductor, a
resistor, a diode, a display element, a light-emitting element, or
a load) provided therebetween.
[0807] For example, in the case where X and Y are electrically
connected, one or more elements that enable electrical connection
between X and Y (e.g., a switch, a transistor, a capacitor, an
inductor, a resistor, a diode, a display element, a light-emitting
element, or a load) can be connected between X and Y. A switch is
controlled to be on or off. That is, a switch is conducting or not
conducting (is turned on or off) to determine whether current flows
therethrough or not. Alternatively, the switch has a function of
selecting and changing a current path. Note that the case where X
and Y are electrically connected includes the case where X and Y
are directly connected.
[0808] For example, in the case where X and Y are functionally
connected, one or more circuits that enable functional connection
between X and Y (e.g., a logic circuit such as an inverter, a NAND
circuit, or a NOR circuit; a signal converter circuit such as a DA
converter circuit, an AD converter circuit, or a gamma correction
circuit; a potential level converter circuit such as a power source
circuit (e.g., a step-up circuit or a step-down circuit) or a level
shifter circuit for changing the potential level of a signal; a
voltage source; a current source; a switching circuit; an amplifier
circuit such as a circuit that can increase signal amplitude, the
amount of current, or the like, an operational amplifier, a
differential amplifier circuit, a source follower circuit, or a
buffer circuit; a signal generation circuit; a memory circuit;
and/or a control circuit) can be connected between X and Y. Note
that for example, in the case where a signal output from X is
transmitted to Y even when another circuit is interposed between X
and Y, X and Y are functionally connected. Note that the case where
X and Y are functionally connected includes the case where X and Y
are directly connected and the case where X and Y are electrically
connected.
[0809] Note that when it is explicitly described that X and Y are
electrically connected, the case where X and Y are electrically
connected (i.e., the case where X and Y are connected with another
element or another circuit provided therebetween), the case where X
and Y are functionally connected (i.e., the case where X and Y are
functionally connected with another circuit provided therebetween),
and the case where X and Y are directly connected (i.e., the case
where X and Y are connected without another element or another
circuit provided therebetween) are included therein. That is, in
this specification and the like, the explicit description "X and Y
are electrically connected" is the same as the description "X and Y
are connected".
[0810] For example, any of the following expressions can be used
for the case where a source (or a first terminal or the like) of a
transistor is electrically connected to X through (or not through)
Z1 and a drain (or a second terminal or the like) of the transistor
is electrically connected to Y through (or not through) Z2, or the
case where a source (or a first terminal or the like) of a
transistor is directly connected to one part of Z1 and another part
of Z1 is directly connected to X while a drain (or a second
terminal or the like) of the transistor is directly connected to
one part of 22 and another part of Z2 is directly connected to
Y.
[0811] Examples of the expressions include, "X, Y, a source (or a
first terminal or the like) of a transistor, and a drain (or a
second terminal or the like) of the transistor are electrically
connected to each other, and X, the source (or the first terminal
or the like) of the transistor, the drain (or the second terminal
or the like) of the transistor, and Y are electrically connected to
each other in this order", "a source (or a first terminal or the
like) of a transistor is electrically connected to X, a drain (or a
second terminal or the like) of the transistor is electrically
connected to Y, and X, the source (or the first terminal or the
like) of the transistor, the drain (or the second terminal or the
like) of the transistor, and Y are electrically connected to each
other in this order", and "X is electrically connected to Y through
a source (or a first terminal or the like) and a drain (or a second
terminal or the like) of a transistor, and X, the source (or the
first terminal or the like) of the transistor, the drain (or the
second terminal or the like) of the transistor, and Y are provided
to be connected in this order". When the connection order in a
circuit structure is defined by an expression similar to the above
examples, a source (or a first terminal or the like) and a drain
(or a second terminal or the like) of a transistor can be
distinguished from each other to specify the technical scope.
[0812] Other examples of the expressions include, "a source (or a
first terminal or the like) of a transistor is electrically
connected to X through at least a first connection path, the first
connection path does not include a second connection path, the
second connection path is a path between the source (or the first
terminal or the like) of the transistor and a drain (or a second
terminal or the like) of the transistor, Z1 is on the first
connection path, the drain (or the second terminal or the like) of
the transistor is electrically connected to Y through at least a
third connection path, the third connection path does not include
the second connection path, and Z2 is on the third connection
path". Another example of the expression is "a source (or a first
terminal or the like) of a transistor is electrically connected to
X at least with a first connection path through Z1, the first
connection path does not include a second connection path, the
second connection path includes a connection path through which the
transistor is provided, a drain (or a second terminal or the like)
of the transistor is electrically connected to Y at least with a
third connection path through 22, and the third connection path
does not include the second connection path". Still another example
of the expression is "a source (or a first terminal or the like) of
a transistor is electrically connected to X through at least Z1 on
a first electrical path, the first electrical path does not include
a second electrical path, the second electrical path is an
electrical path from the source (or the first terminal or the like)
of the transistor to a drain (or a second terminal or the like) of
the transistor, the drain (or the second terminal or the like) of
the transistor is electrically connected to Y through at least Z2
on a third electrical path, the third electrical path does not
include a fourth electrical path, and the fourth electrical path is
an electrical path from the drain (or the second terminal or the
like) of the transistor to the source (or the first terminal or the
like) of the transistor". When the connection path in a circuit
structure is defined by an expression similar to the above
examples, a source (or a first terminal or the like) and a drain
(or a second terminal or the like) of a transistor can be
distinguished from each other to specify the technical scope.
[0813] Note that these expressions are examples and there is no
limitation on the expressions. Here, X, Y, Z1, and Z2 each denote
an object (e.g., a device, an element, a circuit, a wiring, an
electrode, a terminal, a conductive film, and a layer).
[0814] Even when independent components are electrically connected
to each other in a circuit diagram, one component has functions of
a plurality of components in some cases. For example, when part of
a wiring also functions as an electrode, one conductive film
functions as the wiring and the electrode. Thus, "electrical
connection" in this specification includes in its category such a
case where one conductive film has functions of a plurality of
components.
EXPLANATION OF REFERENCE
[0815] ACF1: conductive material, ACF2: conductive material, AF1:
alignment film, AF2: alignment film, ANO: wiring, C1: capacitor,
C2: capacitor, CF1: coloring film, CF2: coloring film, CP:
conductive member, CS: wiring, G: scan line, G1: scan line, G2:
scan line, GD: driver circuit, SD: driver circuit, GDA: driver
circuit, GDB: driver circuit, KB1: structure, KB2: structure, KB3:
structure, M: transistor, MB: transistor, MD: transistor, MDB:
transistor, M1: node, M2: node, P1: positional information, P2:
information, SW1: switch, SW2: switch, T1: time, T2: time, T3:
time, T4: time, T5: time, T6: time, V: image data, V0: potential,
V1: potential, VCOM1: wiring, VCOM2: wiring, VDD: power supply
potential, FPC1: flexible printed circuit board, FPC2: flexible
printed circuit board, PIC1: image data, PIC2: image data, PIC3:
image data, PIC4: image data, 100: transistor, 102: substrate, 104:
conductive film, 106: insulating film, 107: insulating film, 108:
oxide semiconductor film, 108a: oxide semiconductor film, 108b:
oxide semiconductor film, 108c: oxide semiconductor film, 112a:
conductive film, 112b: conductive film, 114: insulating film, 116:
insulating film, 118: insulating film, 120a: conductive film, 120b:
conductive film, 150: transistor, 200: data processor, 210:
arithmetic device, 211: arithmetic portion, 212: memory portion,
214: transmission path, 215: input/output interface, 220:
input/output device, 230: display portion, 230B: display portion,
231: display region, 232: pixel, 235EL: display element, 235LC:
display element, 240: input portion, 250: sensor portion, 290:
communication portion, 501A: insulating film, 501B: insulating
film, 501C: insulating film, 501D: insulating film, 504: conductive
film, 504C: contact, 505: bonding layer, 506: insulating film, 508:
semiconductor film, 510: substrate, 510W: separation film, 511:
wiring, 512A: conductive film, 512B: conductive film, 516:
insulating film, 518: insulating film, 520: functional layer, 519:
terminal, 519B: terminal, 519D: terminal, 520D: functional layer,
521A: insulating film, 521B: insulating film, 524: conductive film,
528: insulating film, 550: display element, 550B: display element,
551: conductive film, 552: conductive film, 553: layer containing a
light-emitting organic compound, 553B: layer containing a
light-emitting organic compound, 570: substrate, 570B: insulating
film, 591: contact, 592: contact, 593: contact, 700: display panel,
700B: display panel, 700C: display panel, 700D: display panel,
700E: display panel, 700F: display panel, 702: pixel, 704:
conductive film, 704C: contact, 705: sealant, 719: terminal, 730:
pixel circuit, 750: display element, 751: conductive film, 751T:
conductive film, 751H: opening, 752: conductive film, 752C:
conductive film, 753: layer containing a liquid crystal material,
753T: layer containing electronic ink, 770: substrate, 770P:
optical film, 771: insulating film, 800: input/output device, 801:
upper cover, 802: lower cover, 803: FPC, 804: touch sensor, 805:
FPC, 806: display panel, 809: frame, 810: driver circuit, 811:
battery, 1189: ROM interface, 1190: substrate, 1191: ALU, 1192: ALU
controller, 1193: instruction decoder, 1194: interrupt controller,
1195: timing controller, 1196: register, 1197: register controller,
1198: bus interface, 1199: ROM, 1200: memory element, 1201:
circuit, 1202: circuit, 1203: switch, 1204: switch, 1206: logic
element, 1207: capacitor, 1208: capacitor, 1209: transistor, 1210:
transistor, 1213: transistor, 1214: transistor, 1220: circuit,
3001: wiring, 3002: wiring, 3003: wiring, 3004: wiring, 3005:
wiring, 3200: transistor, 3300: transistor, 3400: capacitor, 5000:
housing, 5001: display portion, 5002: display portion, 5003:
speaker, 5004: LED lamp, 5005: operation key, 5006: connection
terminal, 5007: sensor, 5008: microphone, 5009: switch, 5010:
infrared port, 5011: recording medium reading portion, 5012:
support portion, 5013: earphone, 5014: antenna, 5015: shutter
button, 5016: image receiving portion, 5017: charger, 7302:
housing, 7304: display panel, 7305: icon, 7306: icon, 7311:
operation button, 7312: operation button, 7313: connection
terminal, 7321: band, 7322: clasp.
[0816] This application is based on Japanese Patent Application
serial no. 2015-081519 filed with Japan Patent Office on Apr. 13,
2015, Japanese Patent Application serial no. 2015-115638 filed with
Japan Patent Office on Jun. 8, 2015, and Japanese Patent
Application serial no. 2015-150202 filed with Japan Patent Office
on Jul. 30, 2015, the entire contents of which are hereby
incorporated by reference.
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