U.S. patent application number 16/460001 was filed with the patent office on 2019-12-26 for display device.
The applicant listed for this patent is SEMICONDUCTOR ENERGY LABORATORY CO., LTD.. Invention is credited to Hisao IKEDA, Fumito ISAKA, Shunpei YAMAZAKI.
Application Number | 20190391427 16/460001 |
Document ID | / |
Family ID | 61069178 |
Filed Date | 2019-12-26 |
View All Diagrams
United States Patent
Application |
20190391427 |
Kind Code |
A1 |
IKEDA; Hisao ; et
al. |
December 26, 2019 |
DISPLAY DEVICE
Abstract
To display a high-quality video regardless of a usage
environment. To provide a display device which is lightweight and
less likely to be broken. To reduce power consumption of the
display device. The display device includes a first display
element, a first transistor connected to the first display element,
a second display element, and a second transistor connected to the
second display element. The first display element is a reflective
display element. The first display element and the first transistor
are bonded to the second display element and the second transistor
with an adhesive layer. Light from the second display element is
extracted to the display surface on the first display element side.
The light is condensed or guided by a light-condensing means or a
light-guiding means provided in a path of the light from the second
display element to the display surface.
Inventors: |
IKEDA; Hisao; (Zama, JP)
; ISAKA; Fumito; (Zama, JP) ; YAMAZAKI;
Shunpei; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SEMICONDUCTOR ENERGY LABORATORY CO., LTD. |
Atsugi-shi |
|
JP |
|
|
Family ID: |
61069178 |
Appl. No.: |
16/460001 |
Filed: |
July 2, 2019 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
15666701 |
Aug 2, 2017 |
10345670 |
|
|
16460001 |
|
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
G02F 2001/133541
20130101; G02F 2202/28 20130101; H01L 2227/323 20130101; H01L
27/3232 20130101; G02F 2001/133616 20130101; G02F 1/133345
20130101; H01L 27/322 20130101; H01L 2227/326 20130101; G02F
1/133528 20130101; H01L 29/66969 20130101; H01L 27/1225 20130101;
G02F 2001/133567 20130101; G02F 1/1368 20130101; H01L 51/5271
20130101; H01L 27/3267 20130101; G02F 2203/02 20130101; H01L
2251/303 20130101; H01L 27/3262 20130101; G02F 2201/44 20130101;
H01L 2251/301 20130101; H01L 29/7869 20130101; G02F 1/133526
20130101; G02F 1/133305 20130101; H01L 27/3248 20130101; H01L
51/5275 20130101; H01L 27/3251 20130101; G02F 1/1333 20130101; G02F
2001/133618 20130101 |
International
Class: |
G02F 1/1368 20060101
G02F001/1368; H01L 51/52 20060101 H01L051/52; H01L 29/786 20060101
H01L029/786; H01L 27/32 20060101 H01L027/32; G02F 1/1333 20060101
G02F001/1333; G02F 1/1335 20060101 G02F001/1335 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 5, 2016 |
JP |
2016-154189 |
Claims
1. (canceled)
2. A display device comprising: a first substrate; a first
transistor over the first substrate; a light-emitting element over
the first substrate, the light-emitting element being electrically
connected to the first transistor; a light-condensing means over
the light-emitting element; and a liquid crystal element over the
light-condensing means, the liquid crystal element comprising a
pixel electrode comprising a first conductive layer and a second
conductive layer, wherein the first conductive layer is configured
to reflect visible light, and wherein the second conductive layer
is configured to transmit visible light.
3. The display device according to claim 2, wherein the
light-condensing means has a tapered shape.
4. The display device according to claim 2, further comprising a
coloring layer in contact with a bottom surface of the
light-condensing means.
5. The display device according to claim 2, further comprising a
second substrate over the liquid crystal element, wherein light
from the light-emitting element is extracted outside of the display
device through the second substrate.
6. The display device according to claim 2, wherein the first
transistor comprises a channel formation region comprising an oxide
semiconductor.
7. The display device according to claim 2, further comprising a
second transistor electrically connected to the liquid crystal
element.
8. A display device comprising: a first substrate; a first
transistor over the first substrate; a light-emitting element over
the first substrate, the light-emitting element being electrically
connected to the first transistor; a first insulating layer over
the light-emitting element; a second insulating layer covering a
side surface of the first insulating layer; and a liquid crystal
element over the first insulating layer, the liquid crystal element
comprising a pixel electrode comprising a first conductive layer
and a second conductive layer, wherein a refractive index of the
first insulating layer is higher than a refractive index of the
second insulating layer, wherein the first conductive layer is
configured to reflect visible light, and wherein the second
conductive layer is configured to transmit visible light.
9. The display device according to claim 8, wherein the first
insulating layer comprises SiC, TiO.sub.2, ZnS, CeO.sub.2, or an
indium tin oxide, and wherein the second insulating layer comprises
silicon oxide, CaF.sub.2, MgF.sub.2, acrylic, or a fluorine
resin.
10. The display device according to claim 8, wherein the first
insulating layer has a tapered shape.
11. The display device according to claim 8, further comprising a
coloring layer in contact with a bottom surface of the first
insulating layer.
12. The display device according to claim 8, further comprising a
second substrate over the liquid crystal element, wherein light
from the light-emitting element is extracted outside of the display
device through the second substrate.
13. The display device according to claim 8, wherein the first
transistor comprises a channel formation region comprising an oxide
semiconductor.
14. The display device according to claim 8, further comprising a
second transistor electrically connected to the liquid crystal
element.
15. A display device comprising: a first substrate; a first
transistor over the first substrate; a light-emitting element over
the first substrate, the light-emitting element being electrically
connected to the first transistor; an insulating layer over the
light-emitting element; a metal film covering a side surface of the
insulating layer; and a liquid crystal element over the insulating
layer, the liquid crystal element comprising a pixel electrode
comprising a first conductive layer and a second conductive layer,
wherein the first conductive layer is configured to reflect visible
light, and wherein the second conductive layer is configured to
transmit visible light.
16. The display device according to claim 15, wherein the
insulating layer has a tapered shape.
17. The display device according to claim 15, further comprising a
coloring layer in contact with a bottom surface of the insulating
layer.
18. The display device according to claim 15, further comprising a
second substrate over the liquid crystal element, wherein light
from the light-emitting element is extracted outside of the display
device through the second substrate.
19. The display device according to claim 15, wherein the first
transistor comprises a channel formation regions comprising an
oxide semiconductor.
20. The display device according to claim 15, further comprising: a
second transistor electrically connected to the liquid crystal
element.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 15/666,701, filed Aug. 2, 2017, now allowed, which claims the
benefit of a foreign priority application filed in Japan as Serial
No. 2016-154189 on Aug. 5, 2016, both of which are incorporated by
reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0002] One embodiment of the present invention relates to a display
device.
[0003] Note that one embodiment of the present invention is not
limited to the above technical field. Examples of the technical
field of one embodiment of the present invention disclosed in this
specification and the like include a semiconductor device, a
display device, a light-emitting device, a power storage device, a
memory device, an electronic device, a lighting device, an input
device, an input/output device, a method for driving any of them,
and a method for manufacturing any of them.
[0004] Note that in this specification and the like, a
semiconductor device generally means a device that can function by
utilizing semiconductor characteristics. A transistor, a
semiconductor circuit, an arithmetic device, a memory device, and
the like are each an embodiment of the semiconductor device. In
addition, an imaging device, an electro-optical device, a power
generation device (e.g., a thin film solar cell and an organic thin
film solar cell), and an electronic device may each include a
semiconductor device.
2. Description of the Related Art
[0005] An example of a display device is a liquid crystal display
device provided with a liquid crystal element. For example, an
active matrix liquid crystal display device, in which pixel
electrodes are arranged in a matrix and transistors are used as
switching elements connected to respective pixel electrodes, has
attracted attention.
[0006] For example, an active matrix liquid crystal display device
including transistors, in which metal oxide is used for a channel
formation region, as switching elements connected to respective
pixel electrodes is already known (Patent Documents 1 and 2).
[0007] It is known that an active matrix liquid crystal display
device is classified into two major types: transmissive type and
reflective type.
[0008] In a transmissive liquid crystal display device, a backlight
such as a cold cathode fluorescent lamp or a light-emitting diode
(LED) is used, and optical modulation action of liquid crystal is
utilized to select one of the two states in each pixel: a state
where light from the backlight passes through liquid crystal to be
output to the outside of the liquid crystal display device and a
state where light is not output to the outside of the liquid
crystal display device, whereby a bright or dark image is
displayed. Furthermore, those images are combined to display an
image.
[0009] In a reflective liquid crystal display device, a state in
which external light, that is, incident light is reflected at a
pixel electrode and output to the outside of the liquid crystal
display device or a state in which incident light is not output to
the outside of the liquid crystal display device is selected, in
each pixel, using optical modulation action of liquid crystal,
whereby bright and dark images are displayed. Furthermore, those
images are combined to display an image. Compared to the
transmissive liquid crystal display device, the reflective liquid
crystal display device has the advantage of low power consumption
since the backlight is not used.
REFERENCES
Patent Documents
[0010] [Patent Document 1] Japanese Published Patent Application
No. 2007-123861
[0011] [Patent Document 2] Japanese Published Patent Application
No. 2007-096055
SUMMARY OF THE INVENTION
[0012] Electronic devices that include a display device need to
reduce the power consumption. In particular, a display device in
electronic devices that use a battery as a power source, such as
mobile phones, smartphones, tablet terminals, smart watches, or
laptop personal computers, accounts for a large percentage of power
consumption; thus, the display device is required to reduce the
power consumption.
[0013] Portable electronic devices are required to have high
visibility both in an environment where external light illuminance
is high and in an environment where external light illuminance is
low.
[0014] When a portable electronic device is dropped or put in a
trouser pocket or the like, its display device might be cracked in
some cases. For this reason, there is a demand for lightweight,
non-breakable display devices for use in electronic devices.
[0015] An object of one embodiment of the present invention is to
reduce power consumption of a display device and to increase
display quality of the display device. Another object of one
embodiment of the present invention is to reduce power consumption
of a display device and display a high-quality video regardless of
a usage environment. Another object of one embodiment of the
present invention is to provide a lightweight and non-breakable
display device. Another object of one embodiment of the present
invention is to provide a flexible display device.
[0016] An object of one embodiment of the present invention is to
provide a method for manufacturing a display device with high
productivity.
[0017] One embodiment of the present invention is a display device
including a first display element, a first transistor electrically
connected to the first display element, a second display element, a
second transistor electrically connected to the second display
element, and a light-condensing means or a light-guiding means. The
first display element is a reflective display element. The first
display element and the first transistor are bonded to the second
display element and the second transistor with an adhesive layer.
The first transistor is positioned between the first display
element and the adhesive layer, and the second display element is
positioned between the second transistor and the adhesive layer. A
display surface is positioned on the side of the first display
element opposite to the side on which the first transistor is
positioned. The second display element emits light to the display
surface side through the adhesive layer and the first display
element, and the first display element reflects light to the
display surface side. The light from the second display element is
condensed or guided between the adhesive layer and the first
display element by the light-condensing means or the light-guiding
means.
[0018] The light-condensing means or the light-guiding means
includes a first insulating layer including a low refractive index
material and a second insulating layer including a high refractive
index material. Light from the light-emitting element is condensed
by utilizing total reflection at a boundary between the first
insulating layer and the second insulating layer.
[0019] According to another embodiment of the present invention,
the light-condensing means or the light-guiding means includes a
first insulating layer and a metal film. Light from the
light-emitting element is condensed or guided by utilizing
reflection on a metal film surface.
[0020] The first transistor and the second transistor each
preferably include an oxide semiconductor in a channel.
[0021] According to one embodiment of the present invention, power
consumption of a display device can be reduced and display quality
of the display device can be improved owing to displaying a bright
image. A display device that displays a high-quality video
regardless of a usage environment can be provided. A lightweight
and non-breakable display device can be provided. A flexible
display device can be provided. A method for manufacturing a
display element with high productivity can be provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] FIGS. 1A and 1B illustrate structural examples of a display
device of Embodiment.
[0023] FIGS. 2A and 2B illustrate structure examples of a display
device of Embodiment.
[0024] FIGS. 3A to 3E illustrate a method for manufacturing a
display device of Embodiment.
[0025] FIGS. 4A to 4F illustrate a method for manufacturing a
display device of Embodiment.
[0026] FIGS. 5A to 5C illustrate a method for manufacturing a
display device of Embodiment.
[0027] FIGS. 6A to 6C illustrate a method for manufacturing a
display device of Embodiment.
[0028] FIGS. 7A and 7B illustrate a method for manufacturing a
display device of Embodiment.
[0029] FIGS. 8A to 8D illustrate a method for manufacturing a
display device of Embodiment.
[0030] FIGS. 9A and 9B illustrate a method for manufacturing a
display device of Embodiment.
[0031] FIGS. 10A and 10B illustrate a method for manufacturing a
display device of Embodiment.
[0032] FIGS. 11A to 11D illustrate a method for manufacturing a
display device of Embodiment.
[0033] FIG. 12 illustrates a structural example of a display device
of Embodiment.
[0034] FIGS. 13A to 13E illustrate a method for manufacturing a
display device of Embodiment.
[0035] FIG. 14 illustrates a structural example of a display device
of Embodiment.
[0036] FIGS. 15A to 15E illustrate structure examples of a display
device of Embodiment.
[0037] FIGS. 16A and 16B illustrate structure examples of a display
device of Embodiment.
[0038] FIGS. 17A, 17B1, and 17B2 illustrate structure examples of a
display device of Embodiment.
[0039] FIG. 18 is a circuit diagram of a display device of
Embodiment.
[0040] FIGS. 19A and 19B are circuit diagrams of a display device
of Embodiment.
[0041] FIG. 20 illustrates a structure example of a display device
of Embodiment.
[0042] FIG. 21 illustrates a structure example of a display device
of Embodiment.
[0043] FIG. 22 illustrates a structure example of a display device
of Embodiment.
[0044] FIG. 23 illustrates a structure example of a display device
of Embodiment.
[0045] FIG. 24 illustrates a structure example of a display module
of Embodiment.
[0046] FIGS. 25A to 25D illustrate electronic devices of
Embodiment.
DETAILED DESCRIPTION OF THE INVENTION
[0047] Embodiments will be described in detail with reference to
the drawings. Note that the present invention is not limited to the
following description, and it will be 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. Therefore, the present invention should not be construed
as being limited to the description in the following
embodiments.
[0048] 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. Furthermore, the same
hatch pattern is used for portions having similar functions, and
the portions are not especially denoted by reference numerals in
some cases.
[0049] Note that in each drawing described in this specification,
the size, the layer thickness, or the region of each component is
exaggerated for clarity in some cases. Therefore, embodiments of
the present invention are not limited to such a scale.
[0050] Note that ordinal numbers such as "first" and "second" in
this specification and the like are used in order to avoid
confusion among components, and the terms do not limit the
components numerically.
[0051] A transistor is a kind of semiconductor elements and can
achieve amplification of current or voltage, switching operation
for controlling conduction or non-conduction, or the like. A
transistor in this specification includes, in its category, an
insulated-gate field-effect transistor (IGFET) and a thin film
transistor (TFT).
Embodiment 1
[0052] In this embodiment, a display device of one embodiment of
the present invention and a manufacturing method thereof will be
described.
[0053] A display device of one embodiment of the present invention
has a structure where light-emitting elements and reflective liquid
crystal elements are stacked. The reflective liquid crystal
elements can produce gray levels by controlling the amount of
reflected light. The light-emitting elements can produce gray
levels by controlling the amount of light emission.
[0054] A microelectromechanical systems (MEMS) shutter element, an
optical interference type MEMS element, a display element to which
a microcapsule method, an electrophoretic method, an electrowetting
method, an Electronic Liquid Powder (registered trademark) method,
or the like is applied, or the like can be used as a reflective
display element other than a liquid crystal element. As a
light-emitting display element, a self-luminous light-emitting
element such as an organic light-emitting diode (OLED), a
light-emitting diode (LED), or a quantum-dot light-emitting diode
(QLED) can be used.
[0055] The display device can perform display by using only
reflected light, display by using only light emitted from the
light-emitting elements, and display by using both reflected light
and light emitted from the light-emitting elements, for
example.
[0056] In the display device, the reflective liquid crystal element
is provided on the viewing side (display surface side) and the
light-emitting element is provided on the side opposite to the
viewing side. The light-emitting element can emit light to the
viewing side through a region not overlapping with a reflective
electrode in the liquid crystal element (e.g., an opening in the
reflective electrode).
[0057] As the display device, an active-matrix display device in
which a light-emitting element and a reflective liquid crystal
element are each electrically connected to a transistor can be
used.
[0058] The display device includes a first element layer including
a first transistor electrically connected to the light-emitting
element; a second element layer including the light-emitting
element; a third element layer including a second transistor
electrically connected to the liquid crystal element; and a fourth
element layer including the liquid crystal element. In the display
device, the first element layer, the second element layer, the
third element layer, and the fourth element layer are stacked in
this order from the side opposite to the viewing side.
[0059] Here, resin layers (a first resin layer and a second resin
layer) are preferably provided on the viewing side of the fourth
element layer and the side opposite to the viewing side of the
first element layer, respectively. Thus, the display device can be
extremely lightweight and less likely to be broken.
[0060] The first resin layer and the second resin layer
(hereinafter also collectively referred to as a resin layer) have a
feature of being extremely thin. Specifically, it is preferable
that each of the resin layers have a thickness of 0.1 .mu.m or more
and 3 .mu.m or less. Thus, even a structure where two display
panels are stacked can have a small thickness. Furthermore, light
absorption due to the resin layer positioned in the path of light
emitted from the light-emitting element can be reduced, so that
light can be extracted with higher efficiency and the power
consumption can be reduced.
[0061] The resin layer can be formed in the following manner, for
example. A thermosetting resin material with a low viscosity is
applied to a support substrate and cured by heat treatment to form
the resin layer. Then, the element layers are formed over the resin
layer. Then, the resin layer and the support substrate are
separated from each other, whereby one surface of the resin layer
is exposed.
[0062] As a method of reducing adhesion between the support
substrate and the resin layer to separate the support substrate and
the resin layer from each other, laser light irradiation is given.
For example, it is preferable to perform the irradiation by
scanning using linear laser light. By the method, the process time
of the case of using a large support substrate can be shortened. As
the laser light, excimer laser light with a wavelength of 308 nm
can be suitably used.
[0063] A thermosetting polyimide is a typical example of a material
that can be used for the resin layer. It is particularly preferable
to use a photosensitive polyimide. A photosensitive polyimide is a
material that is suitably used for formation of a planarization
film or the like of the display panel, and therefore, the formation
apparatus and the material can be shared. Thus, there is no need to
prepare another apparatus and another material to obtain the
structure of one embodiment of the present invention.
[0064] Furthermore, the resin layer that is formed using a
photosensitive resin material can be processed by light exposure
and development treatment. For example, an opening can be formed
and an unnecessary portion can be removed. Moreover, by optimizing
a light exposure method or light exposure conditions, an uneven
shape can be formed in a surface of the resin layer. For example,
an exposure technique using a half-tone mask or a gray-tone mask or
a multiple exposure technique may be used.
[0065] Note that a non-photosensitive resin material may be used.
In that case, a method of forming an opening or an uneven shape
using a resist mask or a hard mask that is formed over the resin
layer can be used.
[0066] In this case, part of the resin layer that is positioned in
the path of light emitted from the light-emitting element is
preferably removed. That is, an opening overlapping with the
light-emitting element is provided in the first resin layer. Thus,
a reduction in color reproducibility and light extraction
efficiency that is caused by absorption of part of light emitted
from the light-emitting element by the resin layer can be
inhibited.
[0067] A light-condensing means or a light-guiding means is
provided between the light-emitting element in the second element
layer and the liquid crystal element in the fourth element layer
and in the path of light from the light-emitting element. By the
light-condensing means or the light-guiding means, light from the
light-emitting element can be efficiently condensed or guided, so
that a large amount of light can be extracted from a finite
light-transmitting region in the display device.
[0068] As in the display devices illustrated in FIGS. 1A and 1B in
the present invention, when a surface (display surface) of the
display device through which light from the light-emitting element
120 is extracted is apart from the light-emitting element 120 that
is a light-emitting source, the light from the light-emitting
element 120 might be trapped and absorbed by layers therebetween.
Specifically, the light from the light-emitting element 120 is
trapped between a light-emitting element in a second element layer
200a and a liquid crystal element in a fourth element layer 200b.
Thus, the amount of the light from the light-emitting element 120
which is extracted through the display surface of the display
device is reduced. However, light which is conventionally trapped
and absorbed can be collected by the light-condensing means 500
(also referred to as a light-guiding means 500), and the light from
the light-emitting element 120 can be guided to and extracted from
the finite light-transmitting region in the display device.
[0069] The resin layer may be provided with a depressed portion so
that a portion of the resin layer that is positioned in the path of
light emitted from the light-emitting element is thinner than the
other portion. That is, the resin layer may have a structure where
two portions with different thicknesses are included and the
portion with a smaller thickness overlaps with the light-emitting
element. Even with such a structure, absorption of light from the
light-emitting element by the resin layer can also be reduced.
[0070] In particular, an opening overlapping with the
light-emitting element is preferably provided in the resin layer on
the viewing side of the fourth element layer. Thus, color
reproducibility and light extraction efficiency can be further
increased. Furthermore, it is preferable that part of the resin
layer in the path of light from the reflective liquid crystal
element be removed and an opening overlapping with the reflective
liquid crystal element be provided. This can increase the
reflectivity of the reflective liquid crystal element. Coloring
light reflected by the reflective liquid crystal element owing to
passing through the resin layer can be prevented.
[0071] As a method for forming an opening in the resin layer, the
following method can be used, for example. That is, a thin part is
formed in a portion where the opening of the resin layer is to be
formed, and the support substrate and the resin layer are separated
from each other by the above-described method. Then, plasma
treatment or the like is performed on a separated surface of the
resin layer to reduce the thickness of the resin layer, whereby the
opening can be formed in the thin part of the resin layer.
[0072] As another example, the following method can be used. That
is, a light absorption layer is formed over the support substrate,
the resin layer having the opening is formed over the light
absorption layer, and a light-transmitting layer covering the
opening is formed.
[0073] The light absorption layer is a layer that emits a gas such
as hydrogen or oxygen by absorbing light and being heated. By
performing light irradiation from the support substrate side to
make the light absorption layer emit a gas, adhesion at the
interface between the light absorption layer and the support
substrate or between the light absorption layer and the
light-transmitting layer can be reduced to cause separation, or the
light absorption layer itself can be broken to cause
separation.
[0074] It is preferable that the first transistor and the second
transistor each include an oxide semiconductor as a semiconductor
where a channel is formed. An oxide semiconductor can achieve high
on-state current and high reliability even when the highest
temperature in the manufacturing process of the transistor is
reduced (e.g., 400.degree. C. or lower, preferably 350.degree. C.
or lower). Furthermore, in the case of using an oxide
semiconductor, high heat resistance is not required for a material
of the resin layer positioned on the surface side on which the
transistor is formed; thus, the material of the resin layer can be
selected from a wider range of alternatives. For example, the
material can be the same as a resin material of the planarization
film.
[0075] In the case of using an oxide semiconductor, a special
material having high heat resistance is not required for the resin
layer, and the resin layer is not necessarily formed thick. Thus,
the proportion of the cost of the resin layer in the cost of the
whole display panel can be reduced.
[0076] An oxide semiconductor has a wide band gap (e.g., 2.5 eV or
more, or 3.0 eV or more) and transmits light. Thus, even when an
oxide semiconductor is irradiated with laser light in a step of
separating the support substrate and the resin layer, the laser
light is hardly absorbed, so that the electrical characteristics
can be less affected. Therefore, the resin layer can be thin as
described above.
[0077] In one embodiment of the present invention, a display device
excellent in productivity can be obtained by using both a resin
layer that is formed thin using a photosensitive resin material
with a low viscosity typified by a photosensitive polyimide and an
oxide semiconductor with which a transistor having excellent
electrical characteristics can be obtained even at a low
temperature.
[0078] Needless to say, as the semiconductors where the channels of
the first and second transistors are formed, a semiconductor such
as polysilicon, amorphous silicon, single crystal silicon, or an
organic semiconductor may be used other than an oxide
semiconductor.
[0079] Oxide semiconductors (also simply referred to as OS) are
classified as a metal oxide in this specification and the like. A
metal oxide refers to an oxide of metal in a broad sense. Metal
oxides are classified into an oxide insulator, an oxide conductor
(including a transparent oxide conductor), an oxide semiconductor,
and the like. That is to say, a metal oxide that has at least one
of an amplifying function, a rectifying function, and a switching
function can be called a metal oxide semiconductor, or OS for
short. In addition, an OS FET is a transistor including a metal
oxide or an oxide semiconductor.
[0080] An oxide semiconductor may have a c-axis aligned crystal
(CAAC) structure. A CAAC-OS film is subjected to structural
analysis with an X-ray diffraction (XRD) apparatus. For example,
when the CAAC-OS film including an InGaZnO.sub.4 crystal is
analyzed by an out-of-plane method, a peak appears frequently when
the diffraction angle (2.theta.) is around 31.degree.. This peak is
derived from the (009) plane of the InGaZnO.sub.4 crystal, which
indicates that crystals in the CAAC-OS film have c-axis alignment,
and that the c-axes are aligned in a direction substantially
perpendicular to the formation surface or the top surface of the
CAAC-OS film.
[0081] In the CAAC-OS film having c-axis alignment, while the
directions of a-axes and b-axes are irregularly oriented between
crystal parts, the c-axes are aligned in a direction parallel to a
normal vector of a formation surface or a normal vector of a top
surface. Thus, in a cross-sectional TEM image of the CAAC-OS film,
each metal atom layer arranged in a layered manner corresponds to a
plane parallel to the a-b plane of the crystal.
[0082] The oxide semiconductor may have a function or material
composition of a cloud-aligned composite (CAC). A CAC-OS or a CAC
metal oxide has a conducting function in a part of the material and
has an insulating function in another part of the material; as a
whole, the CAC-OS or the CAC metal oxide has a function of a
semiconductor. In the case where the CAC-OS or the CAC metal oxide
is used in a semiconductor layer of a transistor, the conducting
function is to allow electrons (or holes) serving as carriers to
flow, and the insulating function is to not allow electrons serving
as carriers to flow. By the complementary action of the conducting
function and the insulating function, the CAC-OS or the CAC metal
oxide can have a switching function (on/off function). In the
CAC-OS or the CAC metal oxide, separation of the functions can
maximize each function.
[0083] In this specification and the like, the CAC-OS or the CAC
metal oxide includes conductive regions having the above conducting
function and insulating regions having the above insulating
function. In the CAC-OS or the CAC metal oxide, the conductive
regions and the insulating regions each have a size greater than or
equal to 0.5 nm and less than or equal to 10 nm, preferably greater
than or equal to 0.5 nm and less than or equal to 3 nm and are
dispersed in the oxide semiconductor material, in some cases. In
some cases, the conductive regions and the insulating regions in
the material are separated at the nanoparticle level. In some
cases, the conductive regions and the insulating regions are
unevenly distributed in the material. The conductive regions are
observed to be coupled in a cloud-like manner with their boundaries
blurred, in some cases.
[0084] In other words, the CAC-OS or the CAC metal oxide can be
called a matrix composite or a metal matrix composite.
[0085] Next, a pixel structure is described. The display device can
include first pixels each including a light-emitting element and a
first transistor and second pixels each including a liquid crystal
element and a second transistor. The first pixels and the second
pixels are arranged in a matrix to form a display portion. In
addition, the display device preferably includes a first driver
portion for driving the first pixels and a second driver portion
for driving the second pixels.
[0086] The first pixels and the second pixels are preferably
arranged in a display region with the same pitch. Furthermore, the
first pixels and the second pixels are preferably mixed in the
display region of the display device. Accordingly, as described
later, an image displayed by a plurality of first pixels, an image
displayed by a plurality of second pixels, and an image displayed
by both the plurality of first pixels and the plurality of second
pixels can be displayed in the same display region.
[0087] The first pixel is preferably formed of one pixel that emits
white (W) light, for example. The second pixel preferably includes
subpixels that emit light of three colors of red (R), green (G),
and blue (B), for example. In addition, a subpixel that emits white
(W) light or yellow (Y) light may be included. By arranging such
first pixels and second pixels with the same pitch, the area of the
first pixels can be increased and the aperture ratio of the first
pixels can be increased.
[0088] Note that the first pixel may include subpixels that emit
light of three colors of red (R), green (G), and blue (B), and may
further include a subpixel that emits white (W) light or yellow (Y)
light.
[0089] In one embodiment of the present invention, switching
between a first mode in which an image is displayed by the first
pixels, a second mode in which an image is displayed by the second
pixels, and a third mode in which an image is displayed by the
first pixels and the second pixels can be performed.
[0090] Since display can be performed using only reflected light in
the first mode, a light source is unnecessary. Thus, the first mode
is a driving mode with extremely low power consumption. The first
mode is effective in the case where, for example, external light
has sufficiently high illuminance and is white light or light near
white light. The first mode is a display mode suitable for
displaying text information of a book or a document, for
example.
[0091] Since display can be performed using light from the light
source in the second mode, an extremely vivid image with extremely
high color reproducibility can be displayed regardless of the
illuminance and chromaticity of external light. For example, the
second mode is effective in the case where the illuminance of
external light is extremely low, such as during the nighttime or in
a dark room. When a bright image is displayed under weak external
light, a user may feel that the image is too bright. To prevent
this, an image with reduced luminance is preferably displayed in
the second mode. In that case, not only a reduction in brightness
but also low power consumption can be achieved. The second mode is
a mode suitable for displaying a vivid image and a smooth moving
image, for example.
[0092] In the third mode, display can be performed using both light
from the light source and reflected light. Specifically, the
display device is driven so that light from the first pixel and
light from the second pixel adjacent to the first pixel are mixed
to express one color. A vivider image with higher color
reproducibility than that in the first mode can be displayed and
power consumption can be lower than that in the second mode. For
example, the third mode is effective when the illuminance of
external light is relatively low, such as under indoor illumination
or in the morning or evening, or when the external light does not
represent a white chromaticity.
[0093] Next, transistors that can be used in the display device are
described. The first transistor and the second transistor have
either the same structure or different structures.
[0094] As a structure of the transistor, a bottom-gate structure is
given, for example. A transistor having a bottom-gate structure
includes a gate electrode below a semiconductor layer (on the
formation surface side). A source electrode and a drain electrode
are provided in contact with a top surface and a side end portion
of the semiconductor layer, for example.
[0095] As another structure of the transistor, a top-gate structure
is given, for example. A transistor having a top-gate structure
includes a gate electrode above a semiconductor layer (on the side
opposite to the formation surface side). A first source electrode
and a first drain electrode are provided over an insulating layer
covering part of a top surface and a side end portion of the
semiconductor layer and are electrically connected to the
semiconductor layer through openings provided in the insulating
layer, for example.
[0096] The transistor preferably includes a first gate electrode
and a second gate electrode that face each other with the
semiconductor layer provided therebetween.
[0097] Here, the reflective electrode in the reflective liquid
crystal element also functions as a pixel electrode and is
electrically connected to the second transistor. The reflective
electrode has a uniformly flat surface on the viewing side.
Furthermore, the reflective electrode is electrically connected to
one of a source and a drain of the second transistor on a rear
surface side (the side opposite to the viewing side) of the flat
portion of the reflective electrode. Thus, a depressed portion is
not formed on a surface on the viewing side of the reflective
electrode, so that the aperture ratio of the display portion can be
increased.
[0098] An insulating layer is provided to cover the reflective
electrode, and the second transistor is provided on a surface of
the insulating layer opposite to a surface over which the
reflective electrode is formed. That is, the reflective electrode
is provided on the rear surface side (formation surface side) of
the second transistor with the insulating layer located
therebetween. The one of the source and the drain of the second
transistor is electrically connected to the reflective electrode
through an opening in the insulating layer.
[0099] A third resin layer is preferably provided on the viewing
side of the reflective electrode. Such a structure can be formed in
such a manner that the reflective electrode and the second
transistor are formed over the third resin layer that is formed
over the support substrate and separation is caused at an interface
between the support substrate and the third resin layer. In that
case, since the third resin layer is located between the reflective
electrode and the liquid crystal, the third resin layer is
preferably used as an alignment film.
[0100] As the light-emitting element, a top-emission light-emitting
element which emits light to the side opposite to the formation
surface side can be suitably used. The first transistor and the
light-emitting element are stacked in this order from the side
opposite to the viewing side.
[0101] The display device of one embodiment of the present
invention has a structure in which the first transistor and the
second transistor are provided to face each other in the vertical
direction. In other words, it can be expressed that the direction
in which a plurality of films included in the first transistor are
stacked and the direction in which a plurality of films included in
the second transistor are stacked are opposite.
[0102] A more specific example of the display device of one
embodiment of the present invention is described below with
reference to drawings.
[0103] Note that the expressions indicating directions such as
"over" and "under" are basically used to correspond to the
directions of drawings. However, in some cases, the direction
indicating "over" or "under" in the specification does not
correspond to the direction in the drawings for the purpose of
simplicity or the like. For example, when a stacked order
(formation order) of a stacked body or the like is described, even
in the case where a surface on which the stacked body is provided
(e.g., a formation surface, a support surface, an attachment
surface, or a planarization surface) is positioned above the
stacked body in the drawings, the direction and the opposite
direction are referred to as "under" and "over", respectively, in
some cases.
Structure Example 1
[0104] FIG. 1A is a schematic cross-sectional view of a display
device 10. The display device 10 includes an element layer 100a,
the element layer 200a, an element layer 100b, and the element
layer 200b which are stacked in this order. The display device 10
includes a substrate 11 on the rear side (the side opposite to the
viewing side) and a substrate 12 on the front side (the viewing
side). A resin layer 101 is provided between the substrate 11 and
the element layer 100a, and a resin layer 202 is provided between
the substrate 12 and the element layer 200b. The resin layer 101
and the substrate 11 are bonded to each other with an adhesive
layer 51. The resin layer 202 and the substrate 12 are bonded to
each other with an adhesive layer 52.
[0105] The element layer 100a includes a transistor 110 over the
resin layer 101. The element layer 200a includes the light-emitting
element 120 electrically connected to the transistor 110. The
element layer 100b includes a transistor 210. The element layer
200b includes a liquid crystal element 220 electrically connected
to the transistor 210.
[0106] An opening is provided in the resin layer 202. A region 31
in FIG. 1A is a region overlapping with the light-emitting element
120 and is also a region overlapping with the opening in the resin
layer 202. In addition, the region 31 is a region overlapping with
an opening in a light-blocking layer 153.
[0107] The element layer 100b includes the light-condensing means
500. With the light-condensing means 500, light from the
light-emitting element 120 can be efficiently extracted through a
display surface. The light-condensing means 500 in FIG. 1A utilizes
total reflection at a boundary surface between a low refractive
index material and a high refractive index material. Specifically,
the light-condensing means 500 includes an insulating layer 521
using a high refractive index material having a light-transmitting
property and an insulating layer 520 using a low refractive index
material having a light-transmitting property. In the case where
incident light enters at an angle larger than or equal to the
critical angle at the boundary surface between the insulating layer
521 and the insulating layer 520, total reflection occurs at the
boundary surface. Therefore, light absorbed and trapped by the
insulating layer 234 in a structure without a light-condensing
means can be condensed and guided to the display surface by
providing the light-condensing means 500.
[0108] For the insulating layer 521 using a high refractive index
material having a light-transmitting property, SiC, TiO.sub.2, ZnS,
CeO.sub.2, indium tin oxide, polycarbonate, or a polyester resin
can be used, for example. For the insulating layer 520 using a low
refractive index material having a light-transmitting property,
silicon oxide, CaF.sub.2, MgF.sub.2, acrylic, or a fluorine resin
can be used, for example.
[0109] Reflection of light by a metal film 522 may be used as
another mode of the light-condensing means 500, which is
illustrated in FIG. 1B. Specifically, the light-condensing means
500 is formed in the following manner: an opening is provided in
the insulating layer 234; and the metal film 522 is provided in the
opening so that light from the light-emitting element 120 is
reflected by the metal film 522. With such a structure, light
conventionally absorbed by the insulating layer 234 can be
reflected by the metal film 522 and can be condensed and guided to
the display surface.
[0110] Note that a surface of the metal film 522 may be covered
with a light-transmitting insulating layer or a light-transmitting
semiconductor film in order to improve reflectance of the metal
film 522. The surface of the metal film 522 covered with the
insulating layer or the semiconductor film corresponds to a surface
from which light from the light-emitting element 120 is
reflected.
[0111] The metal film 522 is preferably formed using a highly
reflective material. For the metal film 522, aluminum, silver, an
alloy containing any of these metal materials, or the like can be
used. Furthermore, a metal material such as gold, platinum, nickel,
tungsten, chromium, molybdenum, iron, cobalt, copper, or palladium
or an alloy containing any of these metal materials can be used.
Furthermore, lanthanum, neodymium, germanium, or the like may be
added to the metal material or the alloy. Furthermore, an alloy
containing aluminum (an aluminum alloy) such as an alloy of
aluminum and titanium, an alloy of aluminum and nickel, an alloy of
aluminum and neodymium, or an alloy of aluminum, nickel, and
lanthanum (Al--Ni--La); or an alloy containing silver such as an
alloy of silver and copper, an alloy of silver, palladium, and
copper (also referred to as Ag--Pd--Cu or APC), or an alloy of
silver and magnesium may be used. An alloy containing silver and
copper is preferable because of its high heat resistance.
Furthermore, when a metal film or a metal oxide film is stacked in
contact with an aluminum film or an aluminum alloy film, oxidation
can be suppressed. Examples of a material for the metal film or the
metal oxide film include titanium and titanium oxide.
[0112] The structure illustrated in FIG. 1B is the same as that
illustrated in FIG. 1A except for the structure of the
light-condensing means 500.
[0113] Although not illustrated, the area of a top surface of the
light-condensing means 500 in FIG. 1A may be substantially the same
as or larger than the area of the opening in the light-blocking
layer 153. Specifically, the area of a surface of the insulating
layer 521, which is in contact with the coloring layer 152, may be
substantially the same as or larger than the area of the opening in
the light-blocking layer 153. Thus, light emitted from the
light-emitting element 120 and transmitted through the opening in
the light-blocking layer 153 can be efficiently condensed by the
light-condensing means 500 and extracted to the viewing side of the
display device.
[0114] The above description of FIG. 1A can be applied to FIG. 1B.
The area of a surface of an insulator 523, which is in contact with
the coloring layer 152, may be substantially the same as or larger
than the area of the opening in the light-blocking layer 153. Thus,
light emitted from the light-emitting element 120 can be condensed
and guided efficiently and extracted to the viewing side of the
display device.
[0115] FIGS. 2A and 2B illustrate a light-condensing means having
another structure. In FIGS. 2A and 2B, the cross section of the
light-condensing means 500 has a tapered shape which gradually
becomes narrower from the light-emitting element 120 toward the
display surface. In FIG. 2A, the insulating layer 521 has a tapered
shape which gradually becomes narrower from the light-emitting
element 120 toward the display surface, and the insulating layer
520 covers a side surface of the insulating layer 521. In FIG. 2B,
the insulator 523 of the light-condensing means 500 has a tapered
shape which gradually becomes narrower from the light-emitting
element 120 toward the display surface, and the metal film 522
covers a side surface of the insulator 523. Light is normally
diffused in all directions. When the light-condensing means 500 has
a tapered shape, a larger amount of light can be extracted to the
viewing side of the display device.
[0116] FIGS. 16A and 16B illustrate light-condensing means having
other structures. The light-condensing means 500 in FIGS. 16A and
16B each include the insulating layer 521 using a high refractive
index material, the insulating layer 520 using a low refractive
index material, and a metal film 528 covering an outer surface of
the insulating layer 520. The metal film 528 can be formed using
the same material as the metal film 522 in FIG. 1B.
[0117] In the light-condensing means in FIG. 1A which utilizes
total reflection, total reflection occurs in the case where the
incident angle of incident light to the boundary surface between
the insulating layer 520 and the insulating layer 521 is larger
than or equal to the critical angle. However, in the case where the
incident angle of incident light is smaller than the critical
angle, the light enters the insulating layer 520 without reflection
at the boundary surface. Meanwhile, the metal film has high light
reflectance with respect to incident light. The light-condensing
means having the structure in FIG. 16A can condense more light to
the display surface because even light incident on the insulating
layer 520 at an incident angle smaller than the critical angle is
reflected by the metal film 528.
[0118] FIG. 16B illustrates a structure in which the
light-condensing means 500 in FIG. 16A has a tapered shape. For
advantageous effects of the tapered shape, those of the
light-condensing means in FIGS. 2A and 2B can be referred to.
[Element Layer 100a and Element Layer 200a]
[0119] Over the resin layer 101, the transistor 110, the
light-emitting element 120, an insulating layer 131, an insulating
layer 132, an insulating layer 133, an insulating layer 134, an
insulating layer 135, and the like are provided.
[0120] The transistor 110 includes a conductive layer 111 serving
as a gate electrode, part of the insulating layer 132 serving as a
gate insulating layer, a semiconductor layer 112, a conductive
layer 113a serving as one of a source electrode and a drain
electrode, and a conductive layer 113b serving as the other of the
source electrode and the drain electrode.
[0121] The semiconductor layer 112 preferably includes an oxide
semiconductor.
[0122] The insulating layer 133 and the insulating layer 134 cover
the transistor 110. The insulating layer 134 serves as a
planarization layer.
[0123] The light-emitting element 120 includes a conductive layer
121, an EL layer 122, and a conductive layer 123 that are stacked.
The conductive layer 121 has a function of reflecting visible
light, and the conductive layer 123 has a function of transmitting
visible light. Therefore, the light-emitting element 120 is a
light-emitting element having a top-emission structure which emits
light to the side opposite to the formation surface side.
[0124] The conductive layer 121 is electrically connected to the
conductive layer 113b through an opening provided in the insulating
layer 134 and the insulating layer 133. The insulating layer 135
covers an end portion of the conductive layer 121 and is provided
with an opening to expose part of a surface of the conductive layer
121. The EL layer 122 and the conductive layer 123 are provided in
this order to cover the insulating layer 135 and the exposed
portion of the conductive layer 121.
[0125] The light-emitting element 120 is sealed with an adhesive
layer 151. Furthermore, the element layer 200a and the element
layer 100b are bonded to each other with the adhesive layer
151.
[0126] Here, a stacked structure including the insulating layer
131, the insulating layer 132, the insulating layer 133, the
insulating layer 134, and the transistor 110 is referred to as the
element layer 100a. A stacked structure including the insulating
layer 135 and the light-emitting element 120 is referred to as the
element layer 200a. Note that the element layer 200a may include
the coloring layer 152 and the light-blocking layer 153 which are
described later.
[Element Layer 100b and Element Layer 200b]
[0127] An insulating layer 204, the liquid crystal element 220, a
resin layer 201, the transistor 210, an insulating layer 231, an
insulating layer 232, an insulating layer 233, the insulating layer
234, and the like are provided on the side opposite to the viewing
side of the resin layer 202. The light-condensing means 500 is
provided in the same layer as the insulating layer 234.
[0128] The liquid crystal element 220 includes a conductive layer
221a, a conductive layer 221b, a liquid crystal 222, and a
conductive layer 223. The liquid crystal 222 is sandwiched between
the conductive layer 221b and the conductive layer 223. The
conductive layer 221a and the conductive layer 221b are provided in
contact with each other and function as a pixel electrode. The
conductive layer 221a has a function of reflecting visible light
and functions as a reflective electrode. The conductive layer 221b
has a function of transmitting visible light. Therefore, the liquid
crystal element 220 is a reflective liquid crystal element.
[0129] The periphery of the liquid crystal 222 is sealed with an
adhesive layer in a region which is not illustrated. An alignment
film 224 is provided between the conductive layer 223 and the
liquid crystal 222. The resin layer 201 is provided between the
conductive layer 221b and the liquid crystal 222. The resin layer
201 functions as an alignment film.
[0130] The insulating layer 231 is provided to cover the conductive
layer 221a. For the transistor 210, a surface of the insulating
layer 231 that is opposite to the conductive layer 221a serves as a
formation surface.
[0131] The transistor 210 includes a conductive layer 211 serving
as a gate electrode, part of the insulating layer 232 serving as a
gate insulating layer, a semiconductor layer 212, a conductive
layer 213a serving as one of a source electrode and a drain
electrode, and a conductive layer 213b serving as the other of the
source electrode and the drain electrode.
[0132] The semiconductor layer 212 preferably includes an oxide
semiconductor.
[0133] The insulating layer 233 and the insulating layer 234 are
provided to cover the transistor 210. The insulating layer 234
serves as a planarization layer. The light-condensing means 500 is
provided in part of the insulating layer 234. The light-condensing
means 500 in FIG. 1A consists of the insulating layer 521 formed
using a high refractive index material having a light-transmitting
property and the insulating layer 520 formed using a low refractive
index material having a light-transmitting property. In the
light-condensing means 500 in FIG. 1B, an opening is provided in
part of the insulating layer 234 and the metal film 522 is provided
in the opening. The insulator 523 provided on an inner side of the
metal film 522 and the insulating layer 234 may be formed using the
same material or different materials.
[0134] The conductive layer 213b is electrically connected to the
conductive layer 221a through an opening provided in the insulating
layer 232 and the insulating layer 231. Since a surface of the
conductive layer 221a that is on the viewing side is flat in a
portion where the conductive layer 221a and the conductive layer
213b are connected to each other, the portion can also function as
part of the liquid crystal element 220; thus, the aperture ratio
can be increased.
[0135] The resin layer 201 functioning as an alignment film is
provided to cover the conductive layer 221b. The resin layer 201
supports the conductive layer 221b and the like.
[0136] The conductive layer 223 and the alignment film 224 are
stacked on the resin layer 201 side of the resin layer 202. The
insulating layer 204 is provided between the resin layer 202 and
the conductive layer 223. Note that a coloring layer for coloring
light reflected by the liquid crystal element 220 may be provided
between the conductive layer 223 and the substrate 12. A
light-blocking layer for inhibiting mixture of colors between
adjacent pixels may be provided.
[0137] The insulating layer 204 covers the opening of the resin
layer 202. A portion of the insulating layer 204 that overlaps with
the opening of the resin layer 202 is in contact with the adhesive
layer 52.
[0138] The coloring layer 152 and the light-blocking layer 153 are
provided on a surface of the insulating layer 234 which is on the
substrate 11 side. The coloring layer 152 is provided to overlap
with the light-emitting element 120. The light-blocking layer 153
includes an opening in a portion overlapping with the
light-emitting element 120.
[0139] Here, a stacked structure including the insulating layer
231, the insulating layer 232, the insulating layer 233, the
insulating layer 234, and the transistor 210 is referred to as the
element layer 100b. A stacked structure including the conductive
layer 221a, the conductive layer 221b, the resin layer 201, the
liquid crystal 222, the alignment film 224, the conductive layer
223, and the insulating layer 204 is referred to as the element
layer 200b.
[Display Device 10]
[0140] The display device 10 includes a portion where the
light-emitting element 120 does not overlap with the conductive
layer 221a serving as the reflective electrode of the liquid
crystal element 220 when seen from above. Thus, light 21 that is
colored by the coloring layer 152 is emitted from the
light-emitting element 120 to the viewing side as shown in FIGS. 1A
and 1B. Furthermore, reflected light 22 that is external light
reflected by the conductive layer 221a is extracted from the liquid
crystal element 220 through the liquid crystal 222.
[0141] The light 21 emitted from the light-emitting element 120 is
emitted to the viewing side through the opening of the resin layer
202. Since the resin layer 202 is not provided in the path of the
light 21, even in the case where the resin layer 202 absorbs part
of visible light, high light extraction efficiency and high color
reproducibility can be obtained.
[0142] Part of the light 21 emitted from the light-emitting element
120 is emitted to the viewing side through the light-condensing
means 500. Therefore, light absorbed and trapped by the insulating
layer 234 in a conventional structure in which a light-condensing
means is not provided can be condensed to the viewing side with the
structures illustrated in FIGS. 1A and 1B and FIGS. 2A and 2B.
[0143] The conductive layer 221b is also provided in a portion
overlapping with the light-emitting element 120. Since the
conductive layer 221b transmits visible light, the light 21 can
pass through the conductive layer 221b even when the conductive
layer 221b is positioned in the path of the light 21. When the
conductive layer 221b is provided in a larger area than an area
where the conductive layer 221a is provided, the liquid crystal 222
in a region outside the region where the conductive layer 221a is
provided can also be aligned by application of an electric field.
Therefore, the area of a region of the liquid crystal 222 where
defective alignment occurs can be reduced, so that the aperture
ratio can be increased. The conductive layer 221b preferably has a
transmittance in the entire range of visible light (e.g., in the
wavelength range of 400 nm to 750 nm) of 60% or more, further
preferably 70% or more, still further preferably 80% or more.
[0144] The conductive layer 221b is provided to both ends in FIGS.
1A and 1B and the like; however, in practice, the conductive layer
221b is provided to have an island shape in each pixel and is
electrically insulated from those in adjacent pixels.
[0145] The conductive layer 221b is not necessarily provided in the
case where the aperture ratio is little influenced by defective
alignment, e.g., the case where the distance between adjacent
pixels is sufficiently long or the case where the conductive layer
221a has a sufficiently large area.
[0146] As illustrated in FIGS. 1A and 1B, in the element layers
100a and 200a, the conductive layer 121 serving as a reflective
electrode of the light-emitting element 120 is positioned closer to
the viewing side than the transistor 110 is. Therefore, the
transistor 110 can be provided to overlap with the light-emitting
element 120, which enables high integration and high aperture ratio
of the pixels.
[0147] Similarly, in the element layers 100b and 200b, the
conductive layer 221a serving as the reflective electrode of the
liquid crystal element 220 is positioned on the viewing side of the
transistor 210. Therefore, the transistor 210 can be provided to
overlap with the liquid crystal element 220, which enables high
integration and high aperture ratio of the pixels.
[0148] The display device 10 has a structure in which the
transistor 210 and the transistor 110 are stacked to face each
other. In other words, the transistor 210 and the transistor 110
are vertically inverted relative to each other.
[0149] The substrate 12 preferably serves as a polarizing plate or
a circular polarizing plate. A polarizing plate or a circular
polarizing plate may be located outward from the substrate 12.
[0150] In the above-described structure of the display device 10, a
coloring layer is provided not to overlap with the liquid crystal
element 220, but a coloring layer may be provided on the resin
layer 202 side of the liquid crystal element 220.
[0151] As the substrate 11 and the substrate 12, a glass substrate
or the like may be used, and a material containing a resin is
preferably used. The use of a resin material reduces the weight of
the display device 10 as compared with the case where glass or the
like is used, even when the thickness is the same. A material which
is thin enough to have flexibility (including a glass substrate and
the like) is preferably used because the display device can be
further reduced in weight. Furthermore, when a resin material is
used, the display device can have higher impact resistance; thus, a
non-breakable display device can be achieved.
[0152] Since the substrate 11 is located on the side opposite to
the viewing side, the substrate 11 does not necessarily transmit
visible light. Therefore, a metal material can also be used. A
metal material, which has high thermal conductivity, can suppress a
local temperature rise in the display device 10 because it can
easily conduct heat to the whole substrate.
[0153] The above is the description of the structure example.
Example of Manufacturing Method
[0154] An example of a method of manufacturing the display devices
10 illustrated in FIGS. 1A and 1B is described below with reference
to drawings.
[0155] Note that thin films included in the display device (e.g.,
insulating films, semiconductor films, or conductive films) can be
formed by any of a sputtering method, a chemical vapor deposition
(CVD) method, a vacuum evaporation method, a pulsed laser
deposition (PLD) method, an atomic layer deposition (ALD) method,
and the like. As the CVD method, a plasma-enhanced chemical vapor
deposition (PECVD) method or a thermal CVD method may be used. As
the thermal CVD method, for example, a metal organic chemical vapor
deposition (MOCVD) method may be used.
[0156] Alternatively, thin films included in the display device
(e.g., insulating films, semiconductor films, or conductive films)
can be formed by a method such as spin coating, dipping, spray
coating, ink-jetting, dispensing, screen printing, or offset
printing, or with a tool (equipment) such as a doctor knife, a slit
coater, a roll coater, a curtain coater, or a knife coater.
[0157] When thin films included in the display device are
processed, a photolithography method or the like can be used for
the processing. Alternatively, island-shaped thin films may be
formed by a film formation method using a blocking mask. A
nanoimprinting method, a sandblasting method, a lift-off method, or
the like may be used for the processing of thin films. Examples of
the photolithography method include a method in which a
photosensitive resist material is applied on a thin film to be
processed, the material is exposed to light using a photomask and
developed to form a resist mask, the thin film is processed by
etching or the like, and the resist mask is removed, and a method
in which a photosensitive thin film is formed and then exposed to
light and developed to be processed into a desired shape.
[0158] As light used for exposure in a photolithography method, for
example, light with an i-line (wavelength: 365 nm), light with a
g-line (wavelength: 436 nm), light with an h-line (wavelength: 405
nm), or light in which the i-line, the g-line, and the h-line are
mixed can be used. Alternatively, ultraviolet light, KrF laser
light, ArF laser light, or the like can be used. Light exposure may
be performed by liquid immersion exposure technique. As the light
for the exposure, extreme ultra-violet light (EUV) or X-rays may be
used. Instead of the light for the exposure, an electron beam can
be used. It is preferable to use EUV, X-rays, or an electron beam
because extremely minute processing can be performed. Note that in
the case of performing exposure by scanning with light or a beam
such as an electron beam, a photomask is not needed.
[0159] For etching of thin films, a dry etching method, a wet
etching method, a sandblast method, or the like can be used.
[0160] First, a method for forming the element layers 100a and 200a
will be described.
[Preparation of Support Substrate]
[0161] First, a support substrate 61 is prepared. For the support
substrate 61, a material having stiffness high enough to facilitate
the transfer and having resistance to heat applied in the
manufacturing process can be used. For example, a material such as
glass, quartz, ceramics, sapphire, an organic resin, a
semiconductor, a metal, or an alloy can be used. As the glass, for
example, alkali-free glass, barium borosilicate glass, or
aluminoborosilicate glass can be used.
[Formation of Resin Layer]
[0162] Next, the resin layer 101 is formed over the support
substrate 61 (FIG. 3A). The resin layer 101 is formed to perform
separation of the support substrate 61 in a later step. Note that
another method may be used to perform separation of the support
substrate 61. For example, a stack of inorganic films including a
tungsten film and a silicon oxide film is provided over the support
substrate 61, and the support substrate 61 can be separated by
applying physical force to the stack. Alternatively, over the
support substrate 61, a separation layer is formed using a material
from which hydrogen or oxygen is released by heating and is
irradiated with light, so that the support substrate 61 can be
separated. As the material from which hydrogen or oxygen is
released, hydrogenated amorphous silicon, silicon oxide, silicon
oxynitride, aluminum oxide, or the like can be used. In the case
where the separation is performed using the stack of inorganic
films or the material from which hydrogen or oxygen is released,
the resin layer 101 need not be formed.
[0163] First, a material to be the resin layer 101 is applied on
the support substrate 61. For the application, a spin coating
method is preferred because the resin layer 101 can be thinly and
uniformly formed over a large substrate.
[0164] Alternatively, the resin layer 101 can be formed by dipping,
spray coating, ink-jetting, dispensing, screen printing, or offset
printing, or with a doctor knife, a slit coater, a roll coater, a
curtain coater, or a knife coater, for example.
[0165] The material contains a polymerizable monomer exhibiting a
thermosetting property (also referred to as a thermopolymerization
property) in which case polymerization proceeds by heat.
Furthermore, the material is preferably photosensitive. In
addition, the material contains a solvent for adjusting the
viscosity.
[0166] The material preferably contains a polymerizable monomer
that becomes a polyimide resin, an acrylic resin, an epoxy resin, a
polyamide resin, a polyimide amide resin, a siloxane resin, a
benzocyclobutene-based resin, or a phenol resin after
polymerization. That is, the formed resin layer 101 contains any of
these resin materials. In particular, it is preferable that the
material include a polymerizable monomer containing an imide bond
and then a resin typified by a polyimide resin be used for the
resin layer 101 because heat resistance and weather resistance can
be improved.
[0167] The viscosity of the material used for the application is
greater than or equal to 5 cP and less than 500 cP, preferably
greater than or equal to 5 cP and less than 100 cP, more preferably
greater than or equal to 10 cP and less than or equal to 50 cP. The
lower the viscosity of the material is, the easier the application
becomes. Furthermore, the lower the viscosity of the material is,
the more the entry of bubbles can be suppressed, leading to a film
with good quality. Lower viscosity of the material allows
application for a thin and uniform film, whereby the resin layer
101 can be thinner.
[0168] Then, heat treatment (postbake treatment) is performed to
polymerize the applied material, whereby the resin layer 101 is
formed. The temperature at this heating is preferably higher than
the highest temperature in the process for forming the transistor
110 to be performed later. The temperature is, for example, higher
than or equal to 300.degree. C. and lower than or equal to
600.degree. C., preferably higher than or equal to 350.degree. C.
and lower than or equal to 550.degree. C., more preferably higher
than or equal to 400.degree. C. and lower than or equal to
500.degree. C., and is typically 450.degree. C. For the formation
of the resin layer 101, heating at such a temperature is performed
in a state where the surface of the resin layer 101 is exposed, so
that a gas that can be released from the resin layer 101 can be
removed. Thus, release of the gas in the process for forming the
transistor 110 can be suppressed.
[0169] The thickness of the resin layer 101 is preferably greater
than or equal to 0.01 .mu.m and less than 10 .mu.m, further
preferably greater than or equal to 0.1 .mu.m and less than or
equal to 3 .mu.m, still further preferably greater than or equal to
0.5 .mu.m and less than or equal to 1 .mu.m. The use of a low
viscosity solvent facilitates the formation of the thin and uniform
resin layer 101.
[0170] The thermal expansion coefficient of the resin layer 101 is
preferably greater than or equal to 0.1 ppm/.degree. C. and less
than or equal to 20 ppm/.degree. C., more preferably greater than
or equal to 0.1 ppm/.degree. C. and less than or equal to 10
ppm/.degree. C. The lower the thermal expansion coefficient of the
resin layer 101 is, the more the breakage of the transistor or the
like by stress caused by expansion or contraction due to heating
can be suppressed.
[0171] In the case where an oxide semiconductor film is used as the
semiconductor layer 112 in the transistor 110, the semiconductor
layer 112 can be formed at a low temperature, so that the resin
layer 101 does not need high heat resistance. Thus, the cost of the
material can be reduced. The heat resistance of the resin layer 101
and the like can be evaluated by, for example, weight loss
percentage due to heating, specifically 5% weight loss temperature.
The 5% weight loss temperature of the resin layer 101 and the like
is lower than or equal to 450.degree. C., preferably lower than or
equal to 400.degree. C., further preferably lower than 400.degree.
C., still further preferably lower than 350.degree. C. In addition,
the highest temperature in the process for forming the transistor
110 and the like is preferably lower than or equal to 350.degree.
C.
[Formation of Insulating Layer 131]
[0172] The insulating layer 131 is formed over the resin layer 101
(FIG. 3B).
[0173] The insulating layer 131 can be used as a barrier layer that
prevents impurities contained in the resin layer 101 from diffusing
into a transistor or a light-emitting element to be formed later.
Therefore, a material having a high barrier property is preferably
used for the insulating layer 131.
[0174] As the material having a high barrier property, an inorganic
insulating material such as a silicon nitride film, a silicon
oxynitride film, a silicon oxide film, a silicon nitride oxide
film, an aluminum oxide film, or an aluminum nitride film can be
used. Two or more of these insulating films may be stacked. In
particular, a structure in which a silicon nitride film and a
silicon oxide film are stacked on the resin layer 101 side is
preferably employed.
[0175] In the case where the resin layer 101 has an uneven surface,
the insulating layer 131 preferably covers the unevenness. The
insulating layer 131 may function as a planarization layer that
fills the unevenness. It is preferable to use a stack including an
organic insulating material and an inorganic insulating material
for the insulating layer 131, for example. The organic insulating
material can be an organic resin such as 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.
[0176] The insulating layer 131 is preferably formed at a
temperature higher than or equal to room temperature and lower than
or equal to 400.degree. C., further preferably higher than or equal
to 100.degree. C. and lower than or equal to 350.degree. C., still
further preferably higher than or equal to 150.degree. C. and lower
than or equal to 300.degree. C.
[Formation of Transistor]
[0177] Next, as illustrated in FIG. 3C, the transistor 110 is
formed over the insulating layer 131. Here, an example where a
bottom-gate transistor is formed as an example of the transistor
110 will be described.
[0178] The conductive layer 111 is formed over the insulating layer
131. The conductive layer 111 can be formed in the following
manner: a conductive film is formed; a resist mask is formed; the
conductive film is etched; and the resist mask is removed.
[0179] Next, the insulating layer 132 is formed. For the insulating
layer 132, the description of the inorganic insulating film that
can be used as the insulating layer 131 can be referred to.
[0180] Then, the semiconductor layer 112 is formed. The
semiconductor layer 112 can be formed in the following manner: a
semiconductor film is formed; a resist mask is formed; the
semiconductor film is etched; and the resist mask is removed.
[0181] The semiconductor film is formed at a substrate temperature
higher than or equal to room temperature and lower than or equal to
300.degree. C., preferably higher than or equal to room temperature
and lower than or equal to 220.degree. C., further preferably
higher than or equal to room temperature and lower than or equal to
200.degree. C., still further preferably higher than or equal to
room temperature and lower than or equal to 170.degree. C. Here,
"the substrate temperature for the film formation is room
temperature" means that the substrate is not heated, and includes
the case where the substrate temperature is higher than the room
temperature because the substrate receives energy in the film
formation. The room temperature has a range of, for example, higher
than or equal to 10.degree. C. and lower than or equal to
30.degree. C., and is typically 25.degree. C.
[0182] It is preferable to use an oxide semiconductor for the
semiconductor film. In particular, an oxide semiconductor having a
wider band gap than silicon is preferably used. A semiconductor
material having a wider band gap and a lower carrier density than
silicon is preferably used because off-state current of the
transistor can be reduced.
[0183] It is preferable to use a material having a band gap of
greater than or equal to 2.5 eV, preferably greater than or equal
to 2.8 eV, more preferably greater than or equal to 3.0 eV as the
oxide semiconductor. With use of such an oxide semiconductor, in
light (e.g., laser light) irradiation in the separation process to
be described later, the light passes through the semiconductor film
and thus electrical characteristics of the transistor are less
likely to be adversely affected.
[0184] In particular, the semiconductor film used for one
embodiment of the present invention is preferably formed under an
atmosphere that contains one or both of an inert gas (e.g., Ar) and
an oxygen gas by a sputtering method.
[0185] The substrate temperature for the film formation is
preferably higher than or equal to room temperature and lower than
or equal to 200.degree. C., more preferably higher than or equal to
room temperature and lower than or equal to 170.degree. C. A high
substrate temperature results in a larger number of crystal parts
with orientation, which electrically stabilize the semiconductor
film. A transistor including such a semiconductor film can have
high electrical stability. Alternatively, film formation at a low
substrate temperature or film formation without substrate heating
can make a semiconductor film have a low proportion of crystal
parts with orientation and high carrier mobility. A transistor
including such a semiconductor film can have high field-effect
mobility.
[0186] The oxygen flow rate ratio (partial pressure of oxygen)
during the film formation is preferably higher than or equal to 0%
and lower than 100%, further preferably higher than or equal to 0%
and lower than or equal to 50%, still further preferably higher
than or equal to 0% and lower than or equal to 33%, and yet still
further preferably higher than or equal to 0% and lower than or
equal to 15%. A low oxygen flow rate can result in a semiconductor
film with high carrier mobility, leading to a transistor with high
field-effect mobility. Meanwhile, a high oxygen flow rate can
result in a semiconductor film with high crystallinity, which
electrically stabilizes the semiconductor film.
[0187] Setting the substrate temperature and the oxygen flow rate
during the film formation within the above ranges can result in a
semiconductor film containing both crystal parts with orientation
and crystal parts with no orientation. Furthermore, the proportions
of crystal parts with orientation and crystal parts with no
orientation can be adjusted by optimization of the substrate
temperature and the oxygen flow rate within the above ranges.
[0188] An oxide target that can be used for forming the
semiconductor film is not limited to an In--Ga--Zn-based oxide; for
example, an In-M-Zn-based oxide (M represents one or more of Al,
Ga, Si, B, Y, Ti, Fe, Ni, Ge, Zr, Mo, La, Ce, Nd, Hf, Ta, W, Mg, V,
Be, and Cu) can be used.
[0189] When a semiconductor film containing crystal parts is formed
using a sputtering target containing a polycrystalline oxide having
a plurality of crystal grains, a semiconductor film with
crystallinity can be obtained easier than the case of using a
sputtering target not containing a polycrystalline oxide.
[0190] In particular, a transistor including a semiconductor film
that contains both crystal parts with orientation in a thickness
direction (also referred to as a film surface direction, or a
direction perpendicular to a formation surface or surface of a
film) and randomly aligned crystal parts with no such orientation
can have more stable electrical characteristics and a smaller
channel length, for example. On the other hand, a transistor
including a semiconductor film that contains only crystal parts
with no orientation can have high field-effect mobility. Note that
as described later, a reduction in oxygen vacancies in an oxide
semiconductor can achieve a transistor with high field-effect
mobility and high stability of electrical characteristics.
[0191] The semiconductor layer 112 can be formed at a significantly
low temperature. Therefore, the resin layer 101 can be formed
thin.
[0192] Then, the conductive layer 113a and the conductive layer
113b are formed. The conductive layers 113a and 113b can be formed
in the following manner: a conductive film is formed; a resist mask
is formed; the conductive film is etched; and the resist mask is
removed.
[0193] Note that during the processing of the conductive layers
113a and 113b, the semiconductor layer 112 might be partly etched
to be thin in a region not covered with the resist mask. An oxide
semiconductor film containing crystal parts with orientation is
preferable for the semiconductor layer 112 because the unintended
etching can be prevented.
[0194] In the above manner, the transistor 110 can be fabricated.
The transistor 110 contains an oxide semiconductor in the
semiconductor layer 112 where a channel is formed.
[0195] In the transistor 110, part of the conductive layer 111
functions as a gate, part of the insulating layer 132 functions as
a gate insulating layer, and the conductive layer 113a and the
conductive layer 113b function as a source and a drain.
[Formation of Insulating Layer 133]
[0196] Next, the insulating layer 133 that covers the transistor
110 is formed. The insulating layer 133 can be formed in a manner
similar to that of the insulating layer 132.
[0197] The insulating layer 133 is preferably formed at a
temperature higher than or equal to room temperature and lower than
or equal to 400.degree. C., further preferably higher than or equal
to 100.degree. C. and lower than or equal to 350.degree. C., still
further preferably higher than or equal to 150.degree. C. and lower
than or equal to 300.degree. C. Higher temperatures can provide the
insulating film with higher density and a higher barrier
property.
[0198] It is preferable to use an oxide insulating film, such as a
silicon oxide film or a silicon oxynitride film, formed at a low
temperature in the above range under an atmosphere containing
oxygen for the insulating layer 133. An insulating film with low
oxygen diffusibility and low oxygen permeability, such as a silicon
nitride film, is preferably stacked over the silicon oxide film or
the silicon oxynitride film. The oxide insulating film formed at
low temperatures under an atmosphere containing oxygen can easily
release a large amount of oxygen by heating. When a stack including
such an oxide insulating film that releases oxygen and an
insulating film with low oxygen diffusibility and low oxygen
permeability is heated, oxygen can be supplied to the semiconductor
layer 112. As a result, oxygen vacancies in the semiconductor layer
112 can be filled and defects at the interface between the
semiconductor layer 112 and the insulating layer 133 can be
repaired, leading to a reduction in defect levels. Accordingly, an
extremely highly reliable semiconductor device can be
fabricated.
[0199] Through the above steps, the transistor 110 and the
insulating layer 133 covering the transistor 110 can be formed over
the flexible resin layer 101. If the resin layer 101 and the
support substrate 61 are separated from each other at this stage by
a method described later, a flexible device including no display
element can be fabricated. Forming the transistor 110 or forming a
capacitor, a resistor, a wiring, and the like in addition to the
transistor 110 can provide a flexible device including a
semiconductor circuit, for example.
[Formation of Insulating Layer 134]
[0200] Then, the insulating layer 134 is formed over the insulating
layer 133. The display element is formed on the insulating layer
134 in a later step; thus, the insulating layer 134 preferably
functions as a planarization layer. For the insulating layer 134,
the description of the organic insulating film or the inorganic
insulating film that can be used for the insulating layer 131 can
be referred to.
[0201] For the insulating layer 134, as well as for the resin layer
101, a photosensitive and thermosetting resin material is
preferably used. In particular, the same material is preferably
used for the insulating layer 134 and the resin layer 101. In that
case, the insulating layer 134 can be formed using the same
material and apparatus as the resin layer 101.
[0202] The thickness of the insulating layer 134, as well as the
thickness of the resin layer 101, is preferably greater than or
equal to 0.01 .mu.m and less than 10 .mu.m, further preferably
greater than or equal to 0.1 .mu.m and less than or equal to 3
.mu.m, still further preferably greater than or equal to 0.5 .mu.m
and less than or equal to 1 .mu.m. The use of a low viscosity
solvent facilitates the formation of the thin and uniform
insulating layer 134.
[Formation of Light-Emitting Element 120]
[0203] Next, an opening that reaches the conductive layer 113b and
the like is formed in the insulating layer 134 and the insulating
layer 133.
[0204] After that, the conductive layer 121 is formed. Part of the
conductive layer 121 functions as a pixel electrode. The conductive
layer 121 can be formed in the following manner: a conductive film
is formed; a resist mask is formed; the conductive film is etched;
and the resist mask is removed.
[0205] Subsequently, the insulating layer 135 that covers an end
portion of the conductive layer 121 is formed as illustrated in
FIG. 3D. For the insulating layer 135, the description of the
organic insulating film or the inorganic insulating film that can
be used for the insulating layer 131 can be referred to.
[0206] For the insulating layer 135, as well as for the resin layer
101, a photosensitive and thermosetting resin material is
preferably used. In particular, the same material is preferably
used for the insulating layer 135 and the resin layer 101. In that
case, the insulating layer 135 can be formed using the same
material and apparatus as the resin layer 101.
[0207] The thickness of the insulating layer 135, as well as the
thickness of the resin layer 101, is preferably greater than or
equal to 0.01 .mu.m and less than 10 .mu.m, further preferably
greater than or equal to 0.1 .mu.m and less than or equal to 3
.mu.m, still further preferably greater than or equal to 0.5 .mu.m
and less than or equal to 1 .mu.m. The use of a low viscosity
solvent facilitates the formation of the thin and uniform
insulating layer 135.
[0208] Next, the EL layer 122 and the conductive layer 123 are
formed as illustrated in FIG. 3E.
[0209] The EL layer 122 can be formed by an evaporation method, a
coating method, a printing method, a discharge method, or the like.
In the case where the EL layer 122 is formed for each individual
pixel, an evaporation method using a shadow mask such as a metal
mask, an ink-jet method, or the like can be used. In the case of
sharing the EL layer 122 by some pixels, an evaporation method not
using a metal mask can be used. Here, an example where the EL layer
122 is formed by an evaporation method without using a metal mask
is described.
[0210] The conductive layer 123 can be formed by an evaporation
method, a sputtering method, or the like.
[0211] In the above manner, the light-emitting element 120 can be
completed. In the light-emitting element 120, the conductive layer
121 part of which functions as a pixel electrode, the EL layer 122,
and the conductive layer 123 part of which functions as a common
electrode are stacked.
[0212] Note that an insulating layer serving as a barrier layer
against impurities such as water may be formed to cover the
conductive layer 123.
[0213] In the case where an inorganic insulating film is used as
the insulating layer, the inorganic insulating film can be suitably
formed by a sputtering method, a plasma CVD method, an ALD method,
or a vapor deposition method, for example. An organic insulating
film is preferably formed between the inorganic insulating film and
the light-emitting element 120, specifically, between the inorganic
insulating film and the conductive layer 123 so that the
light-emitting element 120 is prevented from being damaged when the
inorganic insulating film is formed. The organic insulating film
may be thin (e.g., with a thickness of 100 nm or less), and can be
formed by a vapor deposition method, for example.
[0214] Through the above steps, the element layers 100a and 200a
can be formed. At the point of FIG. 3E, the element layers 100a and
200a are supported by the support substrate 61.
[0215] Next, a method for forming the element layer 100b will be
described.
[Formation of Resin Layer 201]
[0216] A support substrate 63 is prepared and the resin layer 201
is formed over the support substrate 63 (FIG. 4A). The description
of the support substrate 61 can be referred to for the support
substrate 63. The description of the method and the material for
forming the resin layer 101 can be referred to for those for
forming the resin layer 201. As in the case of the resin layer 101,
a separation method without the resin layer 201 may be employed. In
that case, as in the method for separating the support substrate
61, a stack structure of inorganic films or a separation layer
using a material from which hydrogen or oxygen is released by
heating may be used.
[0217] An insulating layer serving as a barrier film may be formed
over the resin layer 201. The description of the method and the
material for forming the insulating layer 131 can be referred to
for those for forming the insulating layer.
[Formation of Conductive Layer 221b and Conductive Layer 221a]
[0218] Next, the conductive layer 221b and the conductive layer
221a are stacked (FIG. 4B).
[0219] The conductive layer 221b is formed in the following manner:
a conductive film to be the conductive layer 221b is formed; a
resist mask is formed; the conductive film is etched; and the
resist mask is removed. Subsequently, the conductive layer 221a is
formed in the following manner: a conductive film to be the
conductive layer 221a is formed; a resist mask is formed; the
conductive film is etched; and the resist mask is removed.
[0220] Alternatively, the conductive film to be the conductive
layer 221b and the conductive film to be the conductive layer 221a
may be successively formed first, the conductive film to be the
conductive layer 221a may be processed, and then, the conductive
film to be the conductive layer 221b may be processed. In that
case, resist masks may be separately formed and processed; however,
an exposure technique using a multi-tone mask such as a half-tone
mask or a gray-tone mask or a multiple exposure technique using two
or more photomasks is preferably used, which leads to a reduction
in steps.
[Formation of Insulating Layer 231]
[0221] Next, the insulating layer 231 is formed to cover the
conductive layer 221a, the conductive layer 221b, and the resin
layer 201 (FIG. 4C). The description of the method and the material
for forming the insulating layer 131 can be referred to for those
for forming the insulating layer 231.
[Formation of Transistor 210]
[0222] Next, as illustrated in FIG. 4D, the transistor 210 is
formed over the insulating layer 231.
[0223] First, the conductive layer 211 is formed over the
insulating layer 231, the insulating layer 232 is formed to cover
the conductive layer 211 and the insulating layer 231, and the
semiconductor layer 212 is formed over the insulating layer 232.
The conductive layer 211, the insulating layer 232, and the
semiconductor layer 212 can be formed by methods similar to those
for forming the conductive layer 111, the insulating layer 132, and
the semiconductor layer 112, respectively.
[0224] Next, an opening that reaches the conductive layer 221a is
formed in the insulating layer 232 and the insulating layer
231.
[0225] Then, the conductive layer 213a and the conductive layer
213b are formed. The conductive layer 213a and the conductive layer
213b can be formed by a method similar to that for forming the
conductive layer 113a and the conductive layer 113b.
[0226] Here, the conductive layer 213b is formed to fill the
opening in the insulating layers 231 and 232, so that the
conductive layer 213b and the conductive layer 221a are
electrically connected to each other.
[0227] Through the above process, the transistor 210 can be
formed.
[0228] The transistor 210 contains an oxide semiconductor in the
semiconductor layer 212 where a channel is formed. In the
transistor 210, part of the conductive layer 211 functions as a
gate, part of the insulating layer 232 functions as a gate
insulating layer, and the conductive layer 213a and the conductive
layer 213b function as a source and a drain.
[Formation of Insulating Layer 233, Insulating Layer 234,
Light-Condensing Means 500]
[0229] Next, the insulating layer 233 and the insulating layer 234
are formed in this order to cover the transistor 210. The
insulating layer 233 and the insulating layer 234 can be formed by
methods similar to those for forming the insulating layer 133 and
the insulating layer 134, respectively.
[0230] Then, an opening reaching the insulating layer 233 is formed
in the insulating layer 234. In the case where the insulating layer
521 using a high refractive index material having a
light-transmitting property and the insulating layer 234 having a
light-transmitting property may be formed using the same material,
the opening is provided only in a portion where the insulating
layer 520 is to be formed. After that, the insulating layer 520
illustrated in FIG. 1A is formed using a low refractive index
material. The insulating layer 520 is formed to fill the opening in
the insulating layer 234. The insulating layer 520 is formed using
a material having a refractive index lower than that of the
insulating layer 521 (insulating layer 234) (FIG. 4E).
[0231] In the case where not the insulating layer 234 but another
insulating layer is used as the insulating layer 521 formed using a
high refractive index material having a light-transmitting
property, an opening with the same size as the light-condensing
means 500 to be formed later is formed in the insulating layer 234.
Then, the insulating layer 520 and the insulating layer 521 are
formed.
[0232] The opening in the insulating layer 234 is filled with the
insulating layer 521 and the insulating layer 520, and then, if
needed, planarization treatment may be performed so that the
surface of the insulating layer 234 and the surface of the
light-condensing means 500 are in the same plane.
[0233] For the insulating layer 521 using a high refractive index
material having a light-transmitting property, SiC, TiO.sub.2, ZnS,
CeO.sub.2, indium tin oxide, polycarbonate, or a polyester resin
can be used, for example. For the insulating layer 520 using a low
refractive index material having a light-transmitting property,
silicon oxide, CaF.sub.2, MgF.sub.2, acrylic, or a fluorine resin
can be used, for example.
[0234] FIGS. 4A to 4F illustrate an example of the light-condensing
means 500 in FIG. 1A that includes the insulating layer 521 using a
high refractive index material having a light-transmitting property
and the insulating layer 520 using a low refractive index material
having a light-transmitting property, and the light-condensing
means 500 in FIG. 1B can be formed in a similar manner. In that
case, after the insulating layer 234 is formed, an opening is
formed in a portion where the metal film 522 is to be formed in
FIG. 1B, and the metal film 522 is formed to fill the opening.
Therefore, the insulating layer 234 and the insulator 523 are
formed using the same material in FIG. 1B. Needless to say, the
insulating layer 234 and the insulator 523 may be formed using
different materials. An unnecessary portion of the metal film may
be removed by etching.
[0235] In the case where the light-condensing means 500 has a
tapered shape as illustrated in FIGS. 2A and 2B, an opening is
formed in the insulating layer 234 so that the top surface
(coloring layer 152 side) has a larger area than that of the bottom
surface (insulating layer 233 side). The opening is filled with a
low refractive index material, an opening having a tapered shape is
formed in the low refractive index material, and then, the opening
is filled with a high refractive index material. In such a manner,
the light-condensing means 500 in FIG. 2A can be formed. The order
and method for forming the insulating layer 520 and the insulating
layer 521 in the opening in the insulating layer 234 are not
limited to those described above, and may be selected from existing
deposition methods and etching methods as appropriate.
[0236] Also in the case of the light-condensing means 500
illustrated in FIG. 2B, the opening is formed in the insulating
layer 234 so that the top surface (coloring layer 152 side) has a
larger area than that of the bottom surface (insulating layer 233
side). The opening is filled with a metal film, an opening having a
tapered shape is formed in the metal film, and then, the opening is
filled with an insulator. In such a manner, the light-condensing
means 500 in FIG. 2B can be formed. The order and method for
forming the insulator 523 and the metal film 522 in the opening in
the insulating layer 234 are not limited to those described above,
and may be selected from the existing deposition methods and
etching methods as appropriate.
[0237] Also in the case of the light-condensing means in FIGS. 16A
and 16B, an opening is formed in the insulating layer 234, the
metal film 528 and the insulating layer 520 are formed, and the
insulating layer 521 may be further formed if needed.
[0238] Through the above steps, the element layer 100b can be
formed. At the point of FIG. 4E, the element layer 100b is
supported by the support substrate 63.
[Formation of Coloring Layer 152 and Light-Blocking Layer 153]
[0239] Next, the light-blocking layer 153 and the coloring layer
152 are formed over the insulating layer 234 (FIG. 4F).
[0240] For the light-blocking layer 153, a metal material or a
resin material can be used, for example. In the case where a metal
material is employed, the light-blocking layer 153 can be formed in
such a manner that a conductive film is formed and an unnecessary
portion is removed by a photolithography method or the like. In the
case where a metal material or a photosensitive resin material
containing pigment or dye is used, the light-blocking layer 153 can
be formed by a photolithography method or the like. The
light-blocking layer 153 may include an opening overlapping with
the light-condensing means 500.
[0241] For the coloring layer 152, a photosensitive material can be
used. The coloring layer 152 formed with a photosensitive material
can be processed into an island-like shape by a photolithography
method or the like.
[0242] In that case, the light-blocking layer 153 includes an
opening overlapping with the coloring layer 152.
[0243] The light-blocking layer 153 is preferably provided to cover
the transistor 210. Specifically, in the case where the transistor
210 is a bottom-gate transistor, external light and light from the
light-emitting element 120 are prevented from reaching the
semiconductor layer 212 by the light-blocking layer 153, so that
the reliability can be improved.
[0244] In the case where the light-condensing means 500 includes
the metal film 522 in FIG. 1B, the metal film 522 and the
light-blocking layer 153 can be formed using the same material.
After an opening for providing the metal film 522 is formed in the
insulating layer 234, a conductive layer is formed to cover the top
surface of the insulating layer 234 and fill the opening. By
removing only a portion of the conductive layer that overlaps with
the insulator 523 in FIG. 1B, the metal film 522 and the
light-blocking layer 153 can be formed at the same time. In that
case, the metal film 522 and the light-blocking layer 153 are
integrated.
[Bonding]
[0245] Next, as illustrated in FIG. 5A, the support substrate 61
and the support substrate 63 are bonded to each other with the
adhesive layer 151 so that the element layer 100a and the element
layer 100b face each other. Then, the adhesive layer 151 is cured.
Thus, the light-emitting element 120 can be sealed by the adhesive
layer 151.
[0246] A curable material is preferably used for the adhesive layer
151. For example, a photocurable resin, a reactive curable resin,
or a thermosetting resin can be used. In particular, a resin
material without a solvent is preferably used.
[0247] When misalignment of the support substrate 61 and the
support substrate 63 occurs, light from the light-emitting element
120 is blocked by a light-blocking member in the element layer 100b
or the like, the light-blocking layer 153, or the like in some
cases. Therefore, it is preferable that each of the support
substrates 63 and 61 be provided with an alignment marker.
[Separation of Support Substrate 61]
[0248] Next, as illustrated in FIG. 5B, the resin layer 101 is
irradiated with light 70 through the support substrate 61 from the
support substrate 61 side.
[0249] Laser light is suitable for the light 70. In particular,
linear laser is preferable.
[0250] Note that a flash lamp or the like may be used as long as
the resin layer 101 can be irradiated with light whose energy is as
high as that of laser light.
[0251] As the light 70, light having a wavelength by which at least
part of the light 70 is transmitted through the support substrate
61 and absorbed by the resin layer 101 is preferably used. In
particular, it is preferable to use light with a wavelength range
from visible light to ultraviolet light as the light 70. For
example, light having a wavelength of greater than or equal to 200
nm and less than or equal to 400 nm, preferably greater than or
equal to 250 nm and less than or equal to 350 nm, is used. In
particular, an excimer laser having a wavelength of 308 nm is
preferably used because the productivity is increased. The excimer
laser is preferable because the excimer laser can be used also for
laser crystallization of LTPS, so that the existing LTPS production
line device can be used and newly capital investment is not
necessary. Alternatively, a solid-state UV laser (also referred to
as a semiconductor UV laser), such as a UV laser having a
wavelength of 355 nm which is the third harmonic of an Nd:YAG
laser, may be used. As a laser, a CW (continuous wave) laser or a
pulsed laser may be used. As the pulsed laser, a short time pulsed
laser such as a nanosecond laser, a picosecond laser, or a
femtosecond laser, or a longer time pulsed laser (for example,
shorter than or equal to several hundreds of hertz) can be
used.
[0252] In the case where a linear laser light is used as the light
70, scanning is performed with the light 70 and a region to be
peeled is entirely irradiated with the light 70 by relatively
moving the support substrate 61 and a light source. At this step,
when irradiation is performed on the entire surface where the resin
layer 101 is provided, the resin layer 101 can be peeled entirely
and it is not necessary to cut the peripheral portion of the
support substrate 61 by scribing or the like in a subsequent
separation step. Alternatively, it is preferable that the
peripheral portion of the region where the resin layer 101 is
provided have a region not irradiated with the light 70 because the
adhesion of the region remains strong and separation of the resin
layer 101 and the support substrate 61 can be suppressed at the
irradiation with the light 70.
[0253] By the irradiation with the light 70, the vicinity of the
surface of the resin layer 101 on the support substrate 61 side or
part of the inside of the resin layer 101 is improved and the
adhesion between the support substrate 61 and the resin layer 101
is reduced and a state where separation is easily performed can be
formed.
[0254] Next, the support substrate 61 and the resin layer 101 are
separated (FIG. 5C).
[0255] Separation can be performed by applying pulling force in the
perpendicular direction to the support substrate 61 while the
support substrate 63 is fixed to a stage. For example, the support
substrate 61 can be separated by adsorbing part of the top surface
of the support substrate 61 and pulling it upward. The stage may
have any structure as long as the support substrate 63 can be
fixed. For example, the stage may have an adsorption mechanism
capable of vacuum adsorption, electrostatic adsorption, or the like
or a mechanism physically fastening the support substrate 63.
Alternatively, separation may be performed by applying pulling
force in the perpendicular direction to the support substrate 63
while the support substrate 61 is fixed to the stage.
[0256] Alternatively, separation may be performed by pressing a
drum-shaped member with an adhesive surface against the top surface
of the support substrate 61 or 63 and rotating the member. At this
time, the stage may be moved in the peeling direction.
[0257] In the case where the region not irradiated with the light
70 is provided in the peripheral portion of the resin layer 101, a
notch may be formed in part of the resin layer 101 irradiated with
the light 70 to serve as a trigger for peeling. The notch can be
formed with a sharp edged tool or a needle-like member or can be
formed by cutting the support substrate 61 and the resin layer 101
at the same time by scribing or the like.
[0258] Depending on the condition of the irradiation with the light
70, separation (fracture) occurs inside the resin layer 101 and
part of the resin layer 101 remains on the support substrate 61
side in some cases. FIG. 5C illustrates a case in which fracture
occurs inside the resin layer 101 and a resin layer 101a which is
part of the resin layer 101 remains on the support substrate 61
side.
[0259] Also in the case where part of the surface of the resin
layer 101 is melted, part of the resin layer 101 sometimes remains
on the support substrate 61 side in a similar manner. In the case
where separation is performed at the interface between the support
substrate 61 and the resin layer 101, part of the resin layer 101
sometimes does not remain on the support substrate 61 side.
[0260] The thickness of the resin layer 101a remaining on the
support substrate 61 side can be less than or equal to 100 nm,
specifically approximately greater than or equal to 40 nm and less
than or equal to 70 nm. The support substrate 61 can be reused by
removing the remaining resin layer 101a. For example, in the case
where glass is used for the support substrate 61 and a polyimide
resin is used for the resin layer 101, the remaining resin layer
101a can be removed by ashing treatment or with fuming nitric acid
or the like.
[Bonding of Substrate 11]
[0261] Next, as illustrated in FIG. 6A, the resin layer 101 and the
substrate 11 are bonded to each other with the adhesive layer
51.
[0262] The description of the adhesive layer 151 can be referred to
for the adhesive layer 51.
[0263] When a resin material is used for the substrate 11 and the
substrate 12 to be described later, the display device can be
reduced in weight as compared with the case where glass or the like
is used for the substrate 11 and the substrate 12 with the same
thicknesses. A material which is thin enough to have flexibility is
preferably used because the display device can be further reduced
in weight. Furthermore, when a resin material is used, the display
device can have higher impact resistance; thus, a non-breakable
display device can be achieved.
[0264] Since the substrate 11 is located on the side opposite to
the viewing side, the substrate 11 does not necessarily transmit
visible light. Therefore, a metal material can also be used. A
metal material, which has high thermal conductivity, can suppress a
local temperature rise in the display device because it can easily
conduct heat to the whole substrate.
[0265] Next, a method for forming the element layer 200b will be
described.
[Separation of Support Substrate 63]
[0266] Next, the resin layer 201 is irradiated with the light 70
through the support substrate 63 from the support substrate 63 side
(FIG. 6B). The above description can be referred to for the
irradiation method of the light 70.
[0267] After that, as illustrated in FIG. 6C, the support substrate
63 and the resin layer 201 are separated. FIG. 6C illustrates an
example in which fracture occurs inside the resin layer 201 and a
resin layer 201a which is part of the resin layer 201 remains on
the support substrate 63 side.
[Thinning of Resin Layer 201]
[0268] Next, part of the resin layer 201 is removed to thin the
resin layer 201. The thinned resin layer 201 can be thinner than
the resin layer 101, for example. Specifically, the thinned resin
layer 201 preferably has a thickness of greater than or equal to 1
nm and less than 3 .mu.m, further preferably greater than or equal
to 5 nm and less than or equal to 1 .mu.m, still further preferably
greater than or equal to 10 nm and less than or equal to 200
nm.
[0269] The thinning method is not particularly limited as long as
the resin layer 201 can be etched; plasma treatment, a dry etching
method, a wet etching method, or the like can be used. Especially,
a dry etching method is preferable because high uniformity can be
obtained. It is particularly preferable that plasma treatment in an
environment containing oxygen (also referred to as ashing
treatment) be employed because the resin layer 201 contains an
organic substance. In the case where a wet etching method is
employed, a diluted etchant or the like is preferably used to
prevent the resin layer 201 from being completely removed.
Alternatively, a method without thinning may be employed; for
example, the resin layer 201 is formed thin by sufficiently
diluting a material for forming a thin film to be the resin layer
201 with a solvent to have low viscosity.
[0270] FIG. 7A illustrates a state where the top surface of the
resin layer 201 is irradiated with plasma 80, so that part of the
upper portion of the resin layer 201 is etched to be thinned.
[Rubbing Treatment]
[0271] Next, rubbing treatment is performed on the top surface of
the resin layer 201. Thus, the resin layer 201 can be used as an
alignment film.
[0272] FIG. 7B illustrates a state where the rubbing treatment is
performed. As illustrated in FIG. 7B, uniaxial alignment can be
performed on the resin layer 201 by sliding the substrate 11 as
shown by an arrow of a dashed-dotted line in the drawing in a state
where a rotating rubbing roller 85 is pressed against the resin
layer 201.
[0273] The example where the resin layer 201 is thinned and used as
an alignment film is shown here, and the planarity of a surface of
the resin layer 201 might be lowered in thinning treatment. In that
case, a resin or the like to be an alignment film may be formed
after the resin layer 201 is completely removed in a step of
thinning the resin layer 201. Furthermore, the resin or the like is
subjected to rubbing treatment, so that the alignment film can be
formed.
[0274] Although not illustrated here, it is preferable that the
substrate 11 side be fixed to another support substrate to
facilitate transfer in subsequent steps after bonding of the
substrate 11. For example, the substrate 11 and the support
substrate can be fixed with a viscous material, a double-sided
tape, a silicone sheet, a water-soluble adhesive, or the like.
Similarly, it is preferable that the substrate 11 side be fixed to
another support substrate also in subsequent steps after bonding of
the support substrate 64 described later.
[Formation of Light Absorption Layer 103]
[0275] Next, the support substrate 64 is prepared. For the support
substrate 64, the description of the support substrate 61 can be
referred to.
[0276] A light absorption layer 103 is formed over the support
substrate 64 (FIG. 8A). The light absorption layer 103 releases
hydrogen, oxygen, or the like by absorbing light 70 and generating
heat in a light 70 irradiation step to be performed later.
[0277] As the light absorption layer 103, for example, a
hydrogenated amorphous silicon (a-Si:H) film from which hydrogen is
released by heating can be used. The hydrogenated amorphous silicon
film can be formed by, for example, a plasma CVD method using a
deposition gas containing SiH.sub.4. Furthermore, after the
deposition, heat treatment may be performed under an atmosphere
containing hydrogen in order that the light absorption layer 103
contains a larger amount of hydrogen.
[0278] Alternatively, as the light absorption layer 103, an oxide
film from which oxygen is released by heating can be used. In
particular, an oxide semiconductor film or an oxide conductor film
is preferred because they have a narrower band gap and are more
likely to absorb light than an insulating film such as a silicon
oxide film. Note that the oxide conductor film can be formed by
increasing defect states or impurity states in the oxide
semiconductor film. In the case where an oxide semiconductor is
used for the light absorption layer 103, the above-described method
for forming the semiconductor layer 112 and a material to be
described later which can be used for the semiconductor layer can
be employed. The oxide film can be formed by a plasma CVD method, a
sputtering method, or the like under an atmosphere containing
oxygen, for example. In particular, in the case where an oxide
semiconductor film is used, a sputtering method under an atmosphere
containing oxygen is preferred. Furthermore, after the deposition,
heat treatment may be performed under an atmosphere containing
oxygen in order that the light absorption layer 103 contains a
larger amount of oxygen.
[0279] Alternatively, the oxide film that can be used as the light
absorption layer 103 may be an oxide insulating film. For example,
a silicon oxide film, a silicon oxynitride film, an aluminum oxide
film, or a silicon oxynitride film can be used. For example, such
an oxide insulating film is formed under an atmosphere containing
oxygen at a low temperature (e.g., lower than or equal to
250.degree. C., preferably lower than or equal to 220.degree. C.),
whereby an oxide insulating film containing excess oxygen can be
formed. This oxide insulating film can be formed by, for example, a
sputtering method or a plasma CVD method.
[Formation of Resin Layer 202]
[0280] Next, the resin layer 202 having an opening is formed over
the light absorption layer 103 (FIG. 8B). The description of the
method and the material for forming the resin layer 101 can be
referred to for those for forming the resin layer 202 except for
the opening of the resin layer 202. A stack of the light absorption
layer 103 and the resin layer 202 is formed to separate the support
substrate 64; however, another separation method may be employed.
For example, the support substrate 64 can be separated in the
following manner: a stack of inorganic films including a tungsten
film and a silicon oxide film is provided over the support
substrate 64; and physical force is applied to the stack. In that
case, the formation steps of the light absorption layer 103 and the
resin layer 202 and the irradiation step with the light 70 become
unnecessary. The insulating layer 204, the conductive layer 223,
and the alignment film 224 are formed in this order after the stack
of inorganic films is provided over the support substrate 64.
[0281] In order to form the resin layer 202, first, a
photosensitive material is applied on the light absorption layer
103 to form a thin film, and pre-baking is performed. Next, the
material is exposed to light with use of a photomask, and then
developed, whereby the resin layer 202 having an opening can be
formed. After that, post-baking is performed to sufficiently
polymerize the material and remove a gas in the film.
[Formation of Insulating Layer 204]
[0282] Next, the insulating layer 204 is formed to cover the resin
layer 202 and the opening of the resin layer 202 (FIG. 8C). Part of
the insulating layer 204 is in contact with the light absorption
layer 103. The insulating layer 204 can be used as a barrier layer
that prevents impurities contained in the resin layer 202 from
diffusing into a transistor, a liquid crystal element, or the like
to be formed later. Thus, a material having a high barrier property
is preferably used for the insulating layer 204.
[0283] The description of the method and the material for forming
the insulating layer 131 can be referred to for those for forming
the insulating layer 204.
[Formation of Conductive Layer 223]
[0284] Next, the conductive layer 223 is formed over the insulating
layer 204. The conductive layer 223 can be formed using a material
that transmits visible light. The conductive layer 223 can be
formed by forming a conductive film. Note that the conductive layer
223 may be formed by, for example, a sputtering method using a
shadow mask such as a metal mask such that the conductive layer 223
is not provided in the peripheral portion of the resin layer 202.
Alternatively, the conductive layer 223 may be formed in such a
manner that a conductive film is formed and then an unnecessary
portion of the conductive film is removed by etching using a
photolithography method or the like.
[Formation of Alignment Film 224]
[0285] Next, the alignment film 224 is formed over the conductive
layer 223 (FIG. 8D). The alignment film 224 can be formed in the
following manner: a thin film is formed using a resin or the like
and then, rubbing treatment is performed.
[Bonding of Substrate 11 and Support Substrate 64]
[0286] Next, as illustrated in FIG. 9A, the substrate 11 and the
support substrate 64 are bonded to each other with the liquid
crystal 222 interposed therebetween. In that case, the substrate 11
and the support substrate 64 are bonded so that the opening of the
resin layer 202 and the light-emitting element 120 overlap with
each other. Furthermore, the substrate 11 and the support substrate
64 are bonded so that the opening of the resin layer 202 overlaps
with the opening of the light-blocking layer 153 and the coloring
layer 152.
[0287] In addition, the resin layer 201 and the resin layer 202 are
bonded with an adhesive layer (not illustrated) in the peripheral
portion.
[0288] Next, an adhesive layer (not illustrated) for bonding the
resin layer 201 and the resin layer 202 is formed on one or both of
the resin layer 201 and the resin layer 202. The adhesive layer is
formed to surround a region where a pixel is provided. The adhesive
layer can be formed by a screen printing method, a dispensing
method, or the like. For the adhesive layer, a thermosetting resin,
an ultraviolet curable resin, or the like can be used.
Alternatively, a resin which is cured when heated after pre-cured
by ultraviolet light or the like may be used. Alternatively, a
thermosetting and ultraviolet curable resin or the like may be used
as the adhesive layer.
[0289] Next, the liquid crystal 222 is dropped in a region
surrounded by the adhesive layer by a dispensing method or the
like. Then, the substrate 11 and the support substrate 64 are
bonded to each other such that the liquid crystal 222 is interposed
therebetween, and the adhesive layer is cured. The bonding is
preferably performed in a reduced-pressure atmosphere because air
bubbles and the like can be prevented from entering between the
substrate 11 and the support substrate 64.
[0290] In addition, after the liquid crystal 222 is dropped, a
particulate gap spacer may be dispersed in a region where the pixel
is provided or outside the region, or the liquid crystal 222
containing the gap spacer may be dropped. The liquid crystal 222
may be injected in a reduced-pressure atmosphere through a space
provided in the adhesive layer after the substrate 11 and the
support substrate 64 are bonded to each other.
[0291] Through the above steps, the liquid crystal element 220 and
the element layer 200b can be formed at the same time. At this
time, the support substrate 64 and the light absorption layer 103
are provided on the display surface side.
[Separation of Support Substrate 64]
[0292] Next, as illustrated in FIG. 9B, the light absorption layer
103 is irradiated with the light 70 through the support substrate
64 from the support substrate 64. The above description can be
referred to for the irradiation method of the light 70.
[0293] Here, as the light 70, light having a wavelength by which at
least part of the light 70 is transmitted through the support
substrate 61 and absorbed by the light absorption layer 103 is
selected.
[0294] By the irradiation with the light 70, the light absorption
layer 103 is heated and hydrogen, oxygen, or the like is released
from the light absorption layer 103. At this time, hydrogen,
oxygen, or the like is released in a gaseous state. The released
gas remains near the interface between the light absorption layer
103 and the resin layer 202 or near the interface between the light
absorption layer 103 and the support substrate 64; thus, the force
of peeling them occurs. Consequently, adhesion between the light
absorption layer 103 and the resin layer 202 or adhesion between
the light absorption layer 103 and the support substrate 64 is
reduced and a state where peeling is easily performed can be
formed.
[0295] Part of the gas released from the light absorption layer 103
remains in the light absorption layer 103 in some cases. Therefore,
in some cases, the light absorption layer 103 is embrittled and
separation is likely to occur inside the light absorption layer
103.
[0296] Moreover, in the case where a film releasing oxygen is used
as the light absorption layer 103, part of the resin layer 202 is
oxidized and embrittled in some cases by oxygen released from the
light absorption layer 103. Accordingly, a state where peeling is
easily performed can be formed at the interface between the resin
layer 202 and the light absorption layer 103.
[0297] Also in a region overlapping with the opening of the resin
layer 202, adhesion at the interface between the light absorption
layer 103 and the insulating layer 204 or adhesion at the interface
between the light absorption layer 103 and the support substrate 64
is reduced and a state where peeling is easily performed is formed
for the same reason as above. In some cases, the light absorption
layer 103 is embrittled and a state where separation is likely to
occur.
[0298] In contrast, the region not irradiated with the light 70
still has high adhesion.
[0299] Here, in the case where an oxide semiconductor film is used
for each of the light absorption layer 103 and the semiconductor
layer 212 of the transistor 210, light having a wavelength which
can be absorbed by the oxide semiconductor film is used as the
light 70. However, the conductive layer 221a serving as a
reflective electrode is provided between the light absorption layer
103 and the semiconductor layer 212. Therefore, even when part of
the light 70 is not absorbed by the light absorption layer 103 and
is transmitted, the part of the light 70 is absorbed or reflected
by the conductive layer 221a and reaching of the light to the
semiconductor layer 112 is suppressed. Even when the light 70
passes through the conductive layer 221a, the light can be
reflected or absorbed by the conductive layer 211 because the
conductive layer 211 serving as a gate electrode is provided
between the conductive layer 221a and the semiconductor layer 212
in the case where the transistor 210 has a bottom-gate structure.
Consequently, the electrical characteristics of the transistor 210
are hardly changed.
[0300] Next, the support substrate 64 and the resin layer 202 are
separated (FIG. 10A). The above description can be referred to for
the separation. FIG. 10A illustrates an example in which separation
occurs at the interface between the light absorption layer 103 and
the resin layer 202 and the interface between the light absorption
layer 103 and the insulating layer 204.
[0301] Part of the light absorption layer 103 remains on surfaces
of the resin layer 202 and the insulating layer 204 in some cases.
For example, this example corresponds to the case where separation
(fracture) occurs inside the light absorption layer 103. In the
case where separation occurs at the interface between the light
absorption layer 103 and the support substrate 64, the light
absorption layer 103 entirely remains on the resin layer 202 and
the insulating layer 204 in some cases.
[0302] The light absorption layer is preferably removed when partly
remaining in this manner. Although the remaining light absorption
layer can be removed by a dry etching method, a wet etching method,
a sandblast method, or the like, it is particularly preferable to
employ a dry etching method. Note that in removing the remaining
light absorption layer, part of the resin layer 202 and part of the
insulating layer 204 are thinned by etching in some cases. The
remaining light absorption layer may remain in the case where the
light absorption layer 103 is formed using a light-transmitting
material or the case where the remaining light absorption layer is
thin enough to transmit light.
[Bonding of Substrate 12]
[0303] Next, the resin layer 202 and the substrate 12 are bonded to
each other with the adhesive layer 52 (FIG. 10B). The description
of the adhesive layer 151 can be referred to for the adhesive layer
52.
[0304] Since the substrate 12 is located on the viewing side, a
material that transmits visible light can be used.
[0305] Through the above steps, the display devices 10 illustrated
in FIGS. 1A and 1B, FIGS. 2A and 2B, and FIGS. 16A and 16B can be
manufactured.
[0306] In the display device 10 manufactured according to this
embodiment, light from the light-emitting element 120 can be
efficiently extracted to the display surface by the
light-condensing means 500, a bright image can be displayed, and
the display device can have higher display quality. In particular,
the display quality can be improved in the second mode or the third
mode in which an image is displayed using the light-emitting
element 120. Furthermore, when resin substrates are used as the
substrates 11 and 12, the display device 10 which is lightweight,
is not easily broken, and is bendable can be provided.
[0307] Since display can be performed using light of the
light-emitting element 120 that is the light source in the second
mode, an extremely vivid image with extremely high color
reproducibility can be displayed regardless of the illuminance and
chromaticity of external light. For example, the second mode is
effective in the case where the illuminance of external light is
extremely low, such as during the nighttime or in a dark room. When
a bright image is displayed under weak external light, a user may
feel that the image is too bright. To prevent this, an image with
reduced luminance is preferably displayed in the second mode. In
that case, not only a reduction in brightness but also low power
consumption can be achieved. The second mode is a mode suitable for
displaying a vivid image and a smooth moving image, for example.
Thus, by providing the light-condensing means 500, a bright image
can be displayed in the second mode without change in power
consumption. In other words, an image with conventional brightness
can be displayed with less power consumption. Furthermore, since an
image with conventional brightness can be displayed with a small
current value. The application of load to the light-emitting
element 120 can be suppressed, which enables a longer lifetime of
the light-emitting element 120.
[0308] In the third mode, display can be performed using both light
of the light-emitting element 120 that is the light source and
reflected light. Specifically, the display device is driven so that
light emitted from the light-emitting element 120 and light
transmitted through the liquid crystal element 220 are mixed to
express one color. A vivider image with higher color
reproducibility than that in the first mode can be displayed and
power consumption can be lower than that in the second mode. For
example, the third mode is effective when the illuminance of
external light is relatively low, such as under indoor illumination
or in the morning or evening, or when the external light does not
represent a white chromaticity.
[0309] By providing the light-condensing means 500, a large amount
of light from the light-emitting element 120 can be extracted also
in the third mode; thus, display with low power consumption and
improved display quality can be performed regardless of a usage
environment.
Embodiment 2
[0310] In this embodiment, a display device including a
light-condensing means which has a structure different from the
structures illustrated in FIGS. 1A and 1B, and a manufacturing
method thereof will be described. In this embodiment, the
description in Embodiment 1 can be referred to for the description
of portions denoted by the same reference numerals as those in
Embodiment 1.
[0311] FIGS. 11A to 11D correspond to FIGS. 4A to 4F in Embodiment
1 and illustrate steps of forming the element layer 100b. The steps
similar to those in FIGS. 4A to 4C in Embodiment 1 are performed to
obtain a structure in FIG. 11A.
[0312] After the insulating layer 231 is formed, an insulator 524
is formed over the insulating layer 231. Then, the insulating layer
232 is formed over the conductive layer 211 and the insulator 524,
and the transistor 210 is formed in a manner similar to that
illustrated in FIG. 4D in Embodiment 1 (FIG. 11B). The formation
order of the conductive layer 211 serving as a gate electrode of
the transistor 210 and the insulator 524 may be reversed.
[0313] The insulator 524 is formed using a high refractive index
material having a light-transmitting property, and the insulating
layer 232 is formed using a low refractive index material having a
light-transmitting property. Examples of the high refractive index
material having a light-transmitting property include SiC,
TiO.sub.2, ZnS, CeO.sub.2, indium tin oxide, polycarbonate, and a
polyester resin. Examples of the low refractive index material
having a light-transmitting property include silicon oxide,
CaF.sub.2, MgF.sub.2, acrylic, and a fluorine resin.
[0314] Next, the insulating layer 233 and the insulating layer 234
are formed in this order to cover the transistor 210 and the
insulating layer 232. The insulating layer 233 and the insulating
layer 234 can be formed by methods similar to those for forming the
insulating layer 133 and the insulating layer 134 in Embodiment 1,
respectively (FIG. 11C).
[0315] After the insulating layer 234 is formed, the insulating
layer 234, the insulating layer 233, the insulating layer 232, and
the insulator 524 are etched back. A top surface of the insulator
524 is exposed by the etching back process. The etching back
process can also serve as a planarization process.
[0316] Next, the light-blocking layer 153 and the coloring layer
152 are formed over the insulating layer 234 and the insulator 524
(FIG. 11D).
[0317] Then, steps similar to those in FIG. 5A to FIG. 10B in
Embodiment 1 are carried out, so that the display device 10
illustrated in FIG. 12 can be obtained. In the display device in
FIG. 12, total reflection occurs at a boundary between the
insulator 524 and the insulating layer 232, and the
light-condensing means 500 utilizing total reflection of light is
provided.
[0318] Although the insulator 524 is formed between the insulating
layer 231 and the insulating layer 232 in this embodiment, the
insulator 524 may be formed between the insulating layer 232 and
the insulating layer 233. Alternatively, the insulator 524 may be
formed between the insulating layer 233 and the insulating layer
234. Further alternatively, the insulator 524 may be formed between
the conductive layer 221b and the insulating layer 231.
[0319] In other words, the light-condensing means 500 including the
insulator 524 and any one of the insulating layer 231, the
insulating layer 232, the insulating layer 233, and the insulating
layer 234 may be provided in the path of the light emitted from the
light-emitting element 120 through the opening of the
light-blocking layer 153. When total reflection occurs at a
boundary between the insulator 524 and the insulating layer (any
one of the insulating layers 231, 232, 233, and 234) covering a
side surface of the insulator 524, the light 21 can be efficiently
condensed and guided to the display surface of the display device.
Thus, a bright image can be displayed and the display quality of
the display device can be improved.
[0320] By providing a metal film on a side surface of the insulator
524 in FIG. 11B, a light-condensing means utilizing reflection on
the metal surface may be formed. In that case, after the insulator
524 is formed, a conductive film to be the conductive layer 211 is
formed over the insulator 524. At the same time as etching for
forming the conductive layer 211, a metal film covering the side
surface of the insulator 524 is formed. After that, a step of
forming the insulating layer 232 and subsequent steps are performed
in a manner similar to that in FIGS. 11B to 11D. Needless to say,
the side surface of the insulator 524 may be covered with a metal
film using a material different from that of the conductive layer
211.
[0321] A light-condensing means in which light that is not totally
reflected and passes through the boundary between the insulator 524
and the insulating layer (any one of the insulating layers 231,
232, 233, and 234) covering the side surface of the insulator 524
is reflected by a metal film may be provided. In that case, as in
the structures illustrated in FIGS. 16A and 16B, the metal film is
provided on an outer surface of the insulating layer covering the
side surface of the insulator 524. With such structures, light
whose incident angle is smaller than the critical angle is
reflected by the metal film, so that light can be condensed to the
display surface.
[0322] Next, a display device including a light-condensing means
having another structure and a manufacturing method thereof will be
described. Steps similar to those up to and including the step in
FIG. 4D in Embodiment 1 are performed to obtain a state illustrated
in FIG. 13A.
[0323] Next, the insulating layer 233 and the insulating layer 234
are formed in this order to cover the transistor 210 (FIG. 13B).
The insulating layer 233 and the insulating layer 234 can be formed
by methods similar to those for forming the insulating layer 133
and the insulating layer 134 in Embodiment 1, respectively.
[0324] Next, the light-blocking layer 153 and the coloring layer
152 are formed over the insulating layer 234 (FIG. 13C).
[0325] Next, an insulating layer is formed over the light-blocking
layer 153 and the coloring layer 152. An opening reaching the
coloring layer 152 and the light-blocking layer 153 is formed in
the insulating layer. The opening may be formed along a peripheral
edge of the coloring layer 152. By forming the opening, the
insulating layer 525 and the insulator 527 are obtained (FIG. 13D).
After that, an insulator 526 is formed to fill the opening (FIG.
13E). The insulator 527 is formed using a high refractive index
material having a light-transmitting property, and the insulator
526 is formed using a low refractive index material having a
light-transmitting property. As the high refractive index material
and the low refractive index material, materials similar to those
of the insulating layer 521 and the insulating layer 520 in
Embodiment 1 can be used.
[0326] Through the above steps, the light-condensing means 500
including the insulator 526 using a low refractive index material
and the insulator 527 using a high refractive index material is
formed.
[0327] The light-condensing means 500 utilizing reflection on metal
as in FIG. 1B is formed in the following manner: the opening is
formed in the insulating layer so that the insulating layer 525 and
the insulator 527 are obtained; and a metal film is formed in the
opening.
[0328] The light-condensing means illustrated in FIGS. 16A and 16B
may be formed by providing a metal film between the insulating
layer 525 and the insulator 526. With such structures, light
entering the insulator 526 can be reflected by the metal film and
condensed on the display surface side.
[0329] After that, steps similar to those in FIG. 5A to FIG. 10B in
Embodiment 1 are performed to obtain the display device 10
illustrated in FIG. 14. In the display device in FIG. 14, the
light-condensing means 500 is formed in a newly provided layer
between the coloring layer 152 and the adhesive layer 151 instead
of the insulating layer in the element layer 100b. The
light-condensing means 500 in FIG. 14 utilizes total reflection of
light at the boundary between the insulator 526 and the insulator
527. The light-condensing means 500 including a metal film instead
of the insulator 526 and utilizing reflection on metal may be
formed.
[0330] As in FIGS. 2A and 2B in Embodiment 1, the insulator 526 and
the insulator 527 may have a tapered shape which gradually becomes
narrower from the element layer 200a toward the element layer 100b.
A metal film having a tapered shape may be used instead of the
insulator 526. With the tapered shape, light can be condensed more
efficiently, and a large amount of light can be extracted through
the opening in the resin layer 202.
Embodiment 3
[0331] The display devices 10 exemplified in Embodiments 1 and 2
each show an example of using bottom-gate transistors as the
transistor 110 and the transistor 210.
[0332] In each of the transistors 110 in Embodiments 1 and 2, the
conductive layer 111 functioning as a gate electrode is located
closer to the formation surface (the resin layer 101 side) than the
semiconductor layer 112. The insulating layer 132 serving as a gate
insulating layer covers the conductive layer 111. The semiconductor
layer 112 covers the conductive layer 111. A region of the
semiconductor layer 112 that overlaps with the conductive layer 111
corresponds to a channel formation region. The conductive layers
113a and 113b are provided in contact with the top surface and side
end portions of the semiconductor layer 112.
[0333] Note that in the transistor 110 shown as an example, the
width of the semiconductor layer 112 is wider than that of the
conductive layer 111. In such a structure, the semiconductor layer
112 is located between the conductive layer 111 and each of the
conductive layers 113a and 113b. Thus, the parasitic capacitance
between the conductive layer 111 and each of the conductive layers
113a and 113b can be reduced.
[0334] The transistor 110 is a channel-etched transistor and can be
suitably used for a high-resolution display device because the
occupation area of the transistor can be reduced comparatively
easily.
[0335] The transistor 210 and the transistor 110 have common
characteristics.
[0336] A structure example of a transistor that can be used for the
transistor 110 and the transistor 210 will be described.
[0337] A transistor 110a illustrated in FIG. 15A is different from
the transistor 110 in that the transistor 110a includes a
conductive layer 114 and an insulating layer 136. The conductive
layer 114 is provided over the insulating layer 133 and includes a
region overlapping with the semiconductor layer 112. The insulating
layer 136 covers the conductive layer 114 and the insulating layer
133.
[0338] The conductive layer 114 is located to face the conductive
layer 111 with the semiconductor layer 112 interposed therebetween.
In the case where the conductive layer 111 is used as a first gate
electrode, the conductive layer 114 can function as a second gate
electrode. By supplying the same potential to the conductive layer
111 and the conductive layer 114, the on-state current of the
transistor 110a can be increased. By supplying a potential for
controlling the threshold voltage to one of the conductive layer
111 and the conductive layer 114 and a potential for driving to the
other, the threshold voltage of the transistor 110a can be
controlled.
[0339] A conductive material including an oxide is preferably used
for the conductive layer 114. In that case, a conductive film to be
the conductive layer 114 is formed in an atmosphere containing
oxygen, whereby oxygen can be supplied to the insulating layer 133.
The proportion of an oxygen gas in a film formation gas is
preferably higher than or equal to 90% and lower than or equal to
100%. Oxygen supplied to the insulating layer 133 is supplied to
the semiconductor layer 112 by heat treatment to be performed
later, so that oxygen vacancies in the semiconductor layer 112 can
be reduced.
[0340] It is particularly preferable to use, as the conductive
layer 114, an oxide semiconductor whose resistance is reduced. In
this case, the insulating layer 136 is preferably formed using an
insulating film that releases hydrogen, for example, a silicon
nitride film. Hydrogen is supplied to the conductive layer 114
during the formation of the insulating layer 136 or by heat
treatment to be performed after that, whereby the electrical
resistance of the conductive layer 114 can be reduced
effectively.
[0341] A transistor 110b illustrated in FIG. 15B is a top-gate
transistor.
[0342] In the transistor 110b, the conductive layer 111 functioning
as a gate electrode is provided over the semiconductor layer 112
(provided on the side opposite to the formation surface side). The
semiconductor layer 112 is formed over the insulating layer 131.
The insulating layer 132 and the conductive layer 111 are stacked
over the semiconductor layer 112. The insulating layer 133 covers
the top surface and the side end portions of the semiconductor
layer 112, side surfaces of the insulating layer 132, and the
conductive layer 111. The conductive layers 113a and 113b are
provided over the insulating layer 133. The conductive layers 113a
and 113b are electrically connected to the top surface of the
semiconductor layer 112 through openings provided in the insulating
layer 133.
[0343] Note that although the insulating layer 132 is not present
in a portion that does not overlap with the conductive layer 111 in
the example, the insulating layer 132 may be provided in a portion
covering the top surface and the side end portion of the
semiconductor layer 112.
[0344] In the transistor 110b, the physical distance between the
conductive layer 111 and the conductive layer 113a or 113b can be
easily increased, so that the parasitic capacitance therebetween
can be reduced.
[0345] A transistor 110c illustrated in FIG. 15C is different from
the transistor 110b in that the transistor 110c includes a
conductive layer 115 and an insulating layer 137. The conductive
layer 115 is provided over the insulating layer 131 and includes a
region overlapping with the semiconductor layer 112. The insulating
layer 137 covers the conductive layer 115 and the insulating layer
131.
[0346] The conductive layer 115 functions as a second gate
electrode like the conductive layer 114. Thus, the on-state current
can be increased and the threshold voltage can be controlled, for
example.
[0347] FIG. 15D illustrates a stacked-layer structure of the
transistor 110 and a transistor 110d. The transistor 110d is a
transistor including a pair of gate electrodes.
[0348] The transistor 110d includes part of the conductive layer
113b serving as a first gate electrode, part of the insulating
layer 133 serving as a first gate insulating layer, a semiconductor
layer 112a, a conductive layer 113c serving as one of a source
electrode and a drain electrode, a conductive layer 113d serving as
the other of the source electrode and the drain electrode, part of
the insulating layer 136 serving as a second gate insulating layer,
and a conductive layer 114a serving as a second gate electrode.
[0349] Such a structure is particularly suitable to the first
element layer 100a. That is, it is preferable to use the transistor
110 as a transistor (also referred to as a switching transistor or
a selection transistor) for controlling whether a pixel is selected
or not, and to use the transistor 110d as a transistor (also
referred to as a driving transistor) for controlling current
flowing to the light-emitting element 120.
[0350] In the structure illustrated in FIG. 15D, the conductive
layer 114a is electrically connected to the conductive layer 113c
through an opening formed in the insulating layer 136. The
conductive layer 121 is electrically connected to the conductive
layer 114a through an opening provided in the insulating layer 134.
Here, the capacitance (also referred to as gate capacitance)
between the conductive layer 114a and the semiconductor layer 112a
can be utilized as a storage capacitor of a pixel.
[0351] As illustrated in FIG. 15E, a conductive layer 114b
functioning as an electrode for connecting the conductive layer
113c and the conductive layer 121 and the conductive layer 114a
functioning as a second gate electrode of the transistor 110d may
be separately formed. Here, since the conductive layer 114a is not
connected to the conductive layer 113c, for example, a potential
for controlling a threshold voltage of the transistor 110d may be
supplied to the conductive layer 114a, or the conductive layer 114a
and the conductive layer 113b functioning as a first gate electrode
may be electrically connected to each other and supplied with the
same potential.
[0352] Instead of the transistors 110 illustrated in FIGS. 1A and
1B and the like, the transistor 110a, the transistor 110b, the
transistor 110c, the transistor 110d, or the like can be used.
Furthermore, instead of the transistors 210, the transistor 110a,
the transistor 110b, the transistor 110c, the transistor 110d, or
the like can be used.
[0353] In the display device 10, the transistor included in the
element layer 100a and the transistor included in the element layer
100b may be different from each other. For example, a transistor
including two gate electrodes, e.g., the transistor 110a, the
transistor 110c, or the transistor 110d, can be used as the
transistor that is electrically connected to the light-emitting
element 120 because a comparatively large amount of current needs
to be fed to the transistor, and the transistor 110 or the like can
be suitably used as the other transistor to reduce the occupation
area of the transistor.
[0354] The above is the description of the transistor.
[0355] At least part of this embodiment can be implemented in
appropriate combination with any of the other embodiments described
in this specification.
Embodiment 4
[0356] In this embodiment, a specific example of a display device
of one embodiment of the present invention will be described. A
display device described below includes both a reflective liquid
crystal element and a light-emitting element. The display device
can perform display in a transmission mode and in a reflection
mode.
Structure Example
[0357] FIG. 17A is a block diagram illustrating an example of the
structure of a display device 400. The display device 400 includes
a plurality of pixels 410 that are arranged in a matrix in a
display portion 362. The display device 400 also includes a circuit
GD and a circuit SD. In addition, the display device 400 includes a
plurality of wirings G1, a plurality of wirings G2, a plurality of
wirings ANO, and a plurality of wirings CSCOM, which are
electrically connected to the circuit GD and the plurality of
pixels 410 arranged in a direction R. Moreover, the display device
400 includes a plurality of wirings S1 and a plurality of wirings
S2, which are electrically connected to the circuit SD and the
plurality of pixels 410 arranged in a direction C.
[0358] Although the configuration including one circuit GD and one
circuit SD is illustrated here for simplicity, the circuit GD and
the circuit SD for driving the liquid crystal element and those for
driving the light-emitting element may be provided separately.
Specifically, the element layers 100a and 100b exemplified in
Embodiment 1 may each include a circuit GD and a circuit SD.
[0359] The pixel 410 includes a reflective liquid crystal element
and a light-emitting element. In the pixel 410, the liquid crystal
element and the light-emitting element partly overlap with each
other.
[0360] FIG. 17B1 illustrates a structure example of a conductive
layer 311b included in the pixel 410. The conductive layer 311b
serves as a reflective electrode of the liquid crystal element in
the pixel 410. The conductive layer 311b includes an opening
451.
[0361] In FIG. 17B1, a light-emitting element 360 in a region
overlapping with the conductive layer 311b is shown by a dashed
line. The light-emitting element 360 overlaps with the opening 451
included in the conductive layer 311b. Thus, light from the
light-emitting element 360 is emitted to the display surface side
through the opening 451. Therefore, the light-condensing means
described in Embodiments 1 and 2 are provided to overlap with the
opening 451 or the light-emitting element 360 in FIGS. 17B1 and
17B2. The light-condensing means may have a top surface larger than
the opening 451. With such a structure, light from the
light-emitting element 360 can be condensed more efficiently by the
light-condensing means and extracted through the opening 451.
[0362] In FIG. 17B1, the pixels 410 adjacent in the direction R
correspond to different emission colors. As illustrated in FIG.
17B1, the openings 451 are preferably provided in different
positions in the conductive layers 311b so as not to be aligned in
the two pixels adjacent to each other in the direction R. This
allows the two adjacent light-emitting elements 360 to be apart
from each other, thereby preventing light emitted from the
light-emitting element 360 from entering a coloring layer in the
adjacent pixel 410 (such a phenomenon is also referred to as
"crosstalk"). Furthermore, since the two adjacent light-emitting
elements 360 can be arranged apart from each other, a
high-resolution display device can be obtained even when EL layers
of the light-emitting elements 360 are separately formed with a
shadow mask or the like.
[0363] Alternatively, arrangement illustrated in FIG. 17B2 may be
employed.
[0364] The opening 451 may have a polygonal shape, a quadrangular
shape, an elliptical shape, a circular shape, a cross-like shape, a
stripe shape, a slit-like shape, or a checkered pattern, for
example. The opening 451 may be close to the adjacent pixel.
Preferably, the opening 451 is provided close to another pixel that
emits light of the same color, in which case crosstalk can be
suppressed.
[0365] The top surface of the light-condensing means described in
Embodiments 1 and 2 may have a similar shape to the shape of the
opening 451. For example, when the opening 451 has a polygonal
shape, the top surface of the light-condensing means has a
polygonal shape, and when the opening 451 has a cross-like shape,
the top surface of the light-condensing means has a cross-like
shape. The area of the top surface of the light-condensing means is
the same as or larger than the area of the opening 451. Thus, light
from the light-emitting element 360 can be condensed more
efficiently by the light-condensing means and extracted through the
opening 451. Furthermore, the light-condensing means may be
provided across adjacent pixels.
Circuit Configuration Example
[0366] FIG. 18 is a circuit diagram illustrating a configuration
example of the pixel 410. FIG. 18 shows two adjacent pixels
410.
[0367] The pixel 410 includes a switch SW1, a capacitor C1, a
liquid crystal element 340, a switch SW2, a transistor M, a
capacitor C2, the light-emitting element 360, and the like. The
pixel 410 is electrically connected to the wiring G1, the wiring
G2, the wiring ANO, the wiring CSCOM, the wiring S1, and the wiring
S2. FIG. 18 also illustrates a wiring VCOM1 electrically connected
to the liquid crystal element 340 and a wiring VCOM2 electrically
connected to the light-emitting element 360.
[0368] FIG. 18 illustrates an example in which a transistor is used
as each of the switches SW1 and SW2. The switch SW1 is electrically
connected to the liquid crystal element 340 and corresponds to the
transistor 210 in Embodiments 1 and 2. The transistor M is
electrically connected to the light-emitting element 360 and
corresponds to the transistor 110 in Embodiments 1 and 2.
[0369] A gate of the switch SW1 is connected to the wiring G1. One
of a source and a drain of the switch SW1 is connected to the
wiring S1, and the other of the source and the drain is connected
to one electrode of the capacitor C1 and one electrode of the
liquid crystal element 340. The other electrode of the capacitor C1
is connected to the wiring CSCOM. The other electrode of the liquid
crystal element 340 is connected to the wiring VCOM1.
[0370] A gate of the switch SW2 is connected to the wiring G2. One
of a source and a drain of the switch SW2 is connected to the
wiring S2, and the other of the source and the drain is connected
to one electrode of the capacitor C2 and a gate of the transistor
M. The other electrode of the capacitor C2 is connected to one of a
source and a drain of the transistor M and the wiring ANO. The
other of the source and the drain of the transistor M is connected
to one electrode of the light-emitting element 360. The other
electrode of the light-emitting element 360 is connected to the
wiring VCOM2.
[0371] FIG. 18 illustrates an example in which the transistor M
includes two gates between which a semiconductor is provided and
which are connected to each other. This structure can increase the
amount of current flowing through the transistor M. As a specific
structure of the transistor M including two gates, the structure
illustrated in FIG. 15A or FIG. 15C in Embodiment 3 can be
employed, for example.
[0372] The wiring G1 can be supplied with a signal for changing the
on/off state of the switch SW1. A predetermined potential can be
supplied to the wiring VCOM1. The wiring S1 can be supplied with a
signal for changing the orientation of a liquid crystal of the
liquid crystal element 340. A predetermined potential can be
supplied to the wiring CSCOM.
[0373] The wiring G2 can be supplied with a signal for changing the
on/off state of the switch SW2. The wiring VCOM2 and the wiring ANO
can be supplied with potentials having a difference large enough to
make the light-emitting element 360 emit light. The wiring S2 can
be supplied with a signal for changing the conduction state of the
transistor M.
[0374] In the pixel 410 of FIG. 18, for example, an image can be
displayed in the reflective mode by driving the pixel with the
signals supplied to the wiring G1 and the wiring S1 and utilizing
the optical modulation of the liquid crystal element 340. In the
case where an image is displayed in the transmissive mode, the
pixel is driven with the signals supplied to the wiring G2 and the
wiring S2 and the light-emitting element 360 emits light. In the
case where both modes are performed at the same time, the pixel can
be driven with the signals supplied to the wiring G1, the wiring
G2, the wiring S1, and the wiring S2.
[0375] Although FIG. 18 illustrates the example in which one pixel
410 includes one liquid crystal element 340 and one light-emitting
element 360, one embodiment of the present invention is not limited
to this example. FIG. 19A illustrates an example in which one pixel
410 includes one liquid crystal element 340 and four light-emitting
elements 360 (light-emitting elements 360r, 360g, 360b, and 360w).
The pixel 410 illustrated in FIG. 19A differs from that in FIG. 18
in being capable of performing full-color display by one pixel.
[0376] In addition to the example in FIG. 18, a wiring G3 and a
wiring S3 are connected to the pixel 410 in FIG. 19A.
[0377] In the example illustrated in FIG. 19A, light-emitting
elements which exhibit red (R), green (G), blue (B), and white (W)
can be used as the four light-emitting elements 360, for example. A
reflective liquid crystal element which exhibits white light can be
used as the liquid crystal element 340. This enables white display
with high reflectance in the reflective mode. This also enables
display with excellent color-rendering properties and low power
consumption in the transmissive mode.
[0378] FIG. 19B illustrates a configuration example of the pixel
410. The pixel 410 includes the light-emitting element 360w which
overlaps with the opening 451 in the conductive layer 311b and the
light-emitting elements 360r, 360g, and 360b which are located near
the conductive layer 311b. It is preferable that the light-emitting
elements 360r, 360g, and 360b have substantially the same
light-emitting area.
[0379] In FIG. 19B, the light-condensing means described in
Embodiments 1 and 2 is provided to overlap with the opening 451 or
the light-emitting element 360w.
Structure Example of Display Device
[0380] FIG. 20 is a schematic perspective view illustrating a
display device 300 of one embodiment of the present invention. In
the display device 300, a substrate 351 and a substrate 361 are
bonded to each other. In FIG. 20, the substrate 361 is shown by a
dashed line.
[0381] The display device 300 includes the display portion 362, a
circuit portion 364, a wiring 365, a circuit portion 366, a wiring
367, and the like. The substrate 351 is provided with the circuit
portion 364, the wiring 365, the circuit portion 366, the wiring
367, the conductive layer 311b functioning as a reflective
electrode of a liquid crystal element, and the like. In FIG. 20, an
IC 373, an FPC 372, an IC 375, and an FPC 374 are mounted on the
substrate 351. Thus, the structure illustrated in FIG. 20 can be
referred to as a display module including the display device 300,
the IC 373, the FPC 372, the IC 375, and the FPC 374.
[0382] For the circuit portion 364, a circuit functioning as a scan
line driver circuit can be used, for example.
[0383] The wiring 365 has a function of supplying signals and
electric power to the display portion and the circuit portion 364.
The signals and electric power are input to the wiring 365 from the
outside through the FPC 372 or from the IC 373.
[0384] FIG. 20 shows an example in which the IC 373 is provided on
the substrate 351 by a chip on glass (COG) method or the like. As
the IC 373, an IC functioning as a scan line driver circuit, a
signal line driver circuit, or the like can be used. Note that it
is possible that the IC 373 is not provided, for example, when the
display device 300 includes circuits functioning as a scan line
driver circuit and a signal line driver circuit and when the
circuits functioning as a scan line driver circuit and a signal
line driver circuit are provided outside and signals for driving
the display device 300 are input through the FPC 372.
Alternatively, the IC 373 may be mounted on the FPC 372 by a chip
on film (COF) method or the like.
[0385] FIG. 20 is an enlarged view of part of the display portion
362. Conductive layers 311b included in a plurality of display
elements are arranged in a matrix in the display portion 362. The
conductive layer 311b has a function of reflecting visible light
and serves as a reflective electrode of the liquid crystal element
340 described later.
[0386] As illustrated in FIG. 20, the conductive layer 311b has an
opening in the central portion. The light-emitting element 360 is
positioned closer to the substrate 351 than the conductive layer
311b. Accordingly, part of the light-emitting element 360 can be
exposed through the opening in the conductive layer 311b in FIG.
20. Light is emitted from the light-emitting element 360 to the
substrate 361 side through the opening in the conductive layer
311b. Light from the light-emitting element 360 can be condensed
more efficiently by the light-condensing means in Embodiments 1 and
2 and extracted through the opening in the conductive layer
311b.
Cross-Sectional Structure Examples
[0387] FIG. 21 illustrates an example of cross sections of part of
a region including the FPC 372, part of a region including the
circuit portion 364, part of a region including the display portion
362, part of a region including the circuit portion 366, and part
of a region including the FPC 374 of the display device 300
illustrated in FIG. 20.
[0388] The display device illustrated in FIG. 21 has a structure in
which the element layer 100a, the element layer 200a, the element
layer 100b, and the element layer 200b are stacked in this order
from the substrate 351 side. The resin layer 101 is positioned
between the element layer 100a and the substrate 351. The resin
layer 202 is positioned between the element layer 200b and the
substrate 361. The resin layer 101 and the substrate 351 are bonded
to each other with the adhesive layer 51. The resin layer 202 and
the substrate 361 are bonded to each other with the adhesive layer
52.
[Element Layer 100a and Element Layer 200a]
[0389] The element layer 100a includes, over the resin layer 101,
an insulating layer 478, a plurality of transistors, a capacitor
405, the wiring 365, an insulating layer 411, an insulating layer
412, an insulating layer 413, an insulating layer 414, and the
like. The element layer 200a includes an insulating layer 415, the
light-emitting element 360, a spacer 416, a coloring layer 425, a
light-blocking layer 426, and the like. The coloring layer 425 and
the light-blocking layer 426 are provided on the insulating layer
514 (described later) side, and the insulating layer 514 is bonded
to the resin layer 101 side with an adhesive layer 417.
[0390] The circuit portion 364 includes a transistor 401. The
display portion 362 includes a transistor 402, a transistor 403,
and the capacitor 405.
[0391] Each of the transistors includes a gate, the insulating
layer 411, a semiconductor layer, a source, and a drain. The gate
and the semiconductor layer overlap with each other with the
insulating layer 411 provided therebetween. Part of the insulating
layer 411 functions as a gate insulating layer, and another part of
the insulating layer 411 functions as a dielectric of the capacitor
405. A conductive layer that functions as the source or the drain
of the transistor 402 also functions as one electrode of the
capacitor 405.
[0392] The transistors illustrated in FIG. 21 have bottom-gate
structures. The transistor structures may be different between the
circuit portion 364 and the display portion 362. The circuit
portion 364 and the display portion 362 may each include a
plurality of kinds of transistors.
[0393] The capacitor 405 includes a pair of electrodes and the
dielectric therebetween. The capacitor 405 includes a conductive
layer that is formed using the same material and the same process
as the gates of the transistors 402 and 403, and a conductive layer
that is formed using the same material and the same process as the
sources and the drains of the transistors 402 and 403.
[0394] The insulating layer 412, the insulating layer 413, and the
insulating layer 414 are each provided to cover the transistors and
the like. There is no particular limitation on the number of the
insulating layers covering the transistors and the like. The
insulating layer 414 functions as a planarization layer. It is
preferred that at least one of the insulating layer 412, the
insulating layer 413, and the insulating layer 414 be formed using
a material inhibiting diffusion of impurities such as water and
hydrogen. Diffusion of impurities from the outside into the
transistors can be effectively inhibited, leading to improved
reliability of the display device.
[0395] In the case of using an organic material for the insulating
layer 414, impurities such as moisture might enter the
light-emitting element 360 or the like from the outside of the
display device through the insulating layer 414 exposed at an end
portion of the display device. Deterioration of the light-emitting
element 360 due to the entry of impurities can lead to
deterioration of the display device. For this reason, the
insulating layer 414 is preferably not positioned at the end
portion of the display device, as illustrated in FIG. 21. Since an
insulating layer formed using an organic material is not positioned
at the end portion of the display device in the structure of FIG.
21, entry of impurities into the light-emitting element 360 can be
inhibited.
[0396] The light-emitting element 360 includes a conductive layer
421, an EL layer 422, and a conductive layer 423. The
light-emitting element 360 may include an optical adjustment layer
424. The light-emitting element 360 has a top-emission structure
with which light is emitted to the conductive layer 423 side.
[0397] The transistors, the capacitor, the wiring, and the like are
positioned so as to overlap with a light-emitting region of the
light-emitting element 360; accordingly, the aperture ratio of the
display portion 362 can be increased.
[0398] One of the conductive layer 421 and the conductive layer 423
functions as an anode and the other functions as a cathode. When a
voltage higher than the threshold voltage of the light-emitting
element 360 is applied between the conductive layer 421 and the
conductive layer 423, holes are injected to the EL layer 422 from
the anode side and electrons are injected to the EL layer 422 from
the cathode side. The injected electrons and holes are recombined
in the EL layer 422 and a light-emitting substance contained in the
EL layer 422 emits light.
[0399] The conductive layer 421 is electrically connected to the
source or the drain of the transistor 403 directly or through a
conductive layer. The conductive layer 421 functioning as a pixel
electrode is provided for each light-emitting element 360. Two
adjacent conductive layers 421 are electrically insulated from each
other by the insulating layer 415.
[0400] The EL layer 422 contains a light-emitting substance.
[0401] The conductive layer 423 functioning as a common electrode
is shared by a plurality of light-emitting elements 360. A fixed
potential is supplied to the conductive layer 423.
[0402] The light-emitting element 360 overlaps with the coloring
layer 425 with the adhesive layer 417 provided therebetween. The
spacer 416 overlaps with the light-blocking layer 426 with the
adhesive layer 417 provided therebetween. Although FIG. 21
illustrates the case where a space is provided between the
conductive layer 423 and the light-blocking layer 426, the
conductive layer 423 and the light-blocking layer 426 may be in
contact with each other. Although the spacer 416 is provided on the
substrate 351 side in the structure illustrated in FIG. 21, the
spacer 416 may be provided on the substrate 361 side (e.g., in a
position closer to the substrate 361 than that of the
light-blocking layer 426).
[0403] Owing to the combination of a color filter (the coloring
layer 425) and a microcavity structure (the optical adjustment
layer 424), light with high color purity can be extracted from the
display device. The thickness of the optical adjustment layer 424
is varied depending on the color of the pixel.
[0404] The coloring layer 425 is a coloring layer that transmits
light in a specific wavelength range. For example, a color filter
for transmitting light in a red, green, blue, or yellow wavelength
range can be used.
[0405] Note that one embodiment of the present invention is not
limited to a color filter method, and a separate coloring method, a
color conversion method, a quantum dot method, and the like may be
employed.
[0406] The light-blocking layer 426 is provided between the
adjacent coloring layers 425. The light-blocking layer 426 blocks
light emitted from the adjacent light-emitting element 360 to
inhibit color mixture between the adjacent light-emitting elements
360. Here, the coloring layer 425 is provided such that its end
portion overlaps with the light-blocking layer 426, whereby light
leakage can be reduced. For the light-blocking layer 426, a
material that blocks light emitted from the light-emitting element
360 can be used. Note that it is preferable to provide the
light-blocking layer 426 in a region other than the display portion
362, such as the circuit portion 364, in which case undesired
leakage of guided light or the like can be inhibited.
[0407] The insulating layer 478 is formed on a surface of the resin
layer 101. The insulating layer 513 and the like are formed on the
substrate 361 side of the light-emitting element 360. The
insulating layer 478 and the insulating layer 513 are preferably
highly resistant to moisture. The light-emitting element 360, the
transistors, and the like are preferably provided between a pair of
insulating layers which are highly resistant to moisture, in which
case impurities such as water can be prevented from entering these
elements, leading to an increase in the reliability of the display
device. Note that an insulating film which is highly resistant to
moisture may be provided to cover the coloring layer 425 and the
light-blocking layer 426.
[0408] Examples of the insulating film highly resistant to moisture
include a film containing nitrogen and silicon (e.g., a silicon
nitride film and a silicon nitride oxide film) and a film
containing nitrogen and aluminum (e.g., an aluminum nitride film).
Alternatively, a silicon oxide film, a silicon oxynitride film, an
aluminum oxide film, or the like may be used.
[0409] For example, the moisture vapor transmission rate of the
insulating film highly resistant to moisture is lower than or equal
to 1.times.10.sup.-5 [g/(m.sup.2day)], preferably lower than or
equal to 1.times.10.sup.-6 [g/(m.sup.2day)], further preferably
lower than or equal to 1.times.10.sup.-7 [g/(m.sup.2day)], still
further preferably lower than or equal to 1.times.10.sup.-8
[g/(m.sup.2day)].
[0410] A connection portion 406 includes the wiring 365. The wiring
365 can be formed using the same material and the same process as
those of the sources and the drains of the transistors, for
example. The connection portion 406 is electrically connected to an
external input terminal through which a signal and a potential from
the outside are transmitted to the circuit portion 364. Here, an
example in which the FPC 372 is provided as the external input
terminal is described. The FPC 372 is electrically connected to the
connection portion 406 through a connection layer 419.
[0411] The connection layer 419 can be formed using any of various
kinds of anisotropic conductive films (ACF), anisotropic conductive
pastes (ACP), and the like.
[0412] The above is the description of the element layers 100a and
200a.
[Element Layer 100b and Element Layer 200b]
[0413] The element layer 100b and the element layer 200b are
stacked with the insulating layer 510 provided therebetween. The
element layers 100b and 200b can be referred to as a reflective
liquid crystal display device employing a vertical electric field
mode.
[0414] The element layer 100b includes a plurality of transistors,
a capacitor (not illustrated), the wiring 367, an insulating layer
511, an insulating layer 512, the insulating layer 513, the
insulating layer 514, the light-condensing means 500, and the like
that are positioned closer to the substrate 351 than the insulating
layer 510 is. The element layer 200b includes the liquid crystal
element 340, the resin layer 201, an alignment film 564, an
adhesive layer 517, an insulating layer 576, and the like that are
positioned closer to the substrate 361 than the insulating layer
510 is. Furthermore, the resin layer 202 is provided between the
element layer 200b and the adhesive layer 52.
[0415] Light from the light-emitting element 360 can be efficiently
condensed by the light-condensing means 500 and extracted to the
display surface side of the substrate 361. The light-condensing
means 500 is provided to overlap with an opening in the
light-blocking layer 426. The light-condensing means 500 can have
any one of the structures described in Embodiments 1 and 2.
[0416] The resin layers 201 and 202 are bonded to each other with
the adhesive layer 517. Liquid crystal 563 is sealed in a region
surrounded by the resin layer 201, the resin layer 202, and the
adhesive layer 517. The polarizing plate 599 is positioned on an
outer surface of the substrate 361.
[0417] An opening overlapping with the liquid crystal element 340
and the light-emitting element 360 is formed in the resin layer
202. The opening in the resin layer 202 and the light-condensing
means 500 preferably overlap with each other because light
condensed by the light-condensing means can be extracted to the
display surface side without being absorbed by the resin layer
202.
[0418] The liquid crystal element 340 includes the conductive layer
311b, a conductive layer 561, a conductive layer 562, and the
liquid crystal 563. The conductive layer 311b and the conductive
layer 561 are electrically connected to each other and function as
a pixel electrode. The conductive layer 562 functions as a common
electrode. Alignment of the liquid crystal 563 can be controlled
with an electric field generated between the conductive layer 561
and the conductive layer 562. The resin layer 201 functioning as an
alignment film is provided between the liquid crystal 563 and the
conductive layer 561. The alignment film 564 is provided between
the liquid crystal 563 and the conductive layer 562.
[0419] The conductive layer 561 and the conductive layer 311b are
stacked, and the insulating layer 510 is provided to cover the
conductive layer 561 and the conductive layer 311b. A surface of
the insulating layer 510 on the substrate 361 side and a surface of
the conductive layer 561 on the substrate 361 side are positioned
at substantially the same level. The resin layer 201 is provided on
surfaces of the insulating layer 510 and the conductive layer 561
on the substrate 361 side. The conductive layer 311b has a function
of reflecting visible light and serves as a reflective electrode.
The conductive layer 561 has a function of transmitting visible
light.
[0420] The conductive layer 561 is provided to extend beyond the
conductive layer 311b in a plan view. Part of the conductive layer
561 overlaps with the light-emitting element 360. Light from the
light-emitting element 360 passes through a portion of the
conductive layer 561 that does not overlap with the conductive
layer 311b serving as the reflective electrode. In other words,
light from the light-emitting element 360 passes through the
opening in the conductive layer 311b serving as the reflective
electrode. The light-condensing means 500 is provided in the path
of the light from the light-emitting element 360. The
light-condensing means 500 overlaps with the opening in the
conductive layer 311b. The light-condensing means 500 also overlaps
with the conductive layer 561.
[0421] The insulating layer 576, the conductive layer 562, the
alignment film 564, and the like are provided to cover the resin
layer 202.
[0422] A transistor 501, a transistor 503, a capacitor (not
illustrated), the wiring 367, and the like are provided on the
substrate 351 side of the insulating layer 510. Insulating layers,
e.g., the insulating layer 511, the insulating layer 512, the
insulating layer 513, and the insulating layer 514, are provided on
the substrate 351 side of the insulating layer 510. The coloring
layer 425 and the light-blocking layer 426 are provided on the
substrate 351 side of the insulating layer 514.
[0423] One of a source and a drain of the transistor 503 is
electrically connected to the conductive layer 311b through an
opening in the insulating layer 510. FIG. 21 shows an example where
the one of the source and the drain of the transistor 503 is
electrically connected to the conductive layer 311b through a
conductive layer formed by processing the same conductive film as a
gate electrode of the transistor 503.
[0424] As illustrated in FIG. 21, the conductive layer 311b can
have a flat surface on the viewing side even in a contact portion
with the one of the source and the drain of the transistor 503.
Thus, the contact portion also contributes to display, so that the
aperture ratio can be increased.
[0425] Note that a portion of the conductive layer functioning as
the source or the drain of the transistor 503 which is not
electrically connected to the conductive layer 311b may function as
part of a signal line. The conductive layer functioning as the gate
of the transistor 503 may function as part of a scan line.
[0426] FIG. 21 illustrates a structure without a coloring layer as
an example of the display portion 362. Thus, the liquid crystal
element 340 is an element that performs monochrome display.
[0427] FIG. 21 illustrates an example of the circuit portion 366 in
which the transistor 501 is provided.
[0428] A material inhibiting diffusion of impurities such as water
and hydrogen is preferably used for at least one of the insulating
layers 512 and 513 which cover the transistors.
[0429] Since a reflective liquid crystal display device is used
here, a conductive material that reflects visible light is used for
the conductive layer 311b and a conductive material that transmits
visible light is used for the conductive layer 562.
[0430] As the polarizing plate 599, a linear polarizing plate or a
circularly polarizing plate can be used. An example of a circularly
polarizing plate is a stack including a linear polarizing plate and
a quarter-wave retardation plate. Such a structure can reduce
reflection of external light. The cell gap, alignment, drive
voltage, and the like of the liquid crystal element 340 are
controlled in accordance with the kind of the polarizing plate 599
so that desirable contrast is obtained.
[0431] The connection portion 506 is provided in a region near an
end portion of the resin layer 201. A conductive layer 581
functioning as a terminal is provided in the connection portion
506. The conductive layer 581 is electrically connected to the
wiring 367 through the opening in the insulating layer 510. The
conductive layer 581 is provided to expose its top surface and is
electrically connected to the FPC 374 through a connection layer
519. In the example shown in FIG. 21, part of the wiring 367, a
conductive layer obtained by processing the same conductive film as
a gate electrode of the transistor, a conductive layer obtained by
processing the same conductive film as the conductive layer 311b,
and the conductive layer 581 obtained by processing the same
conductive film as the conductive layer 561 are stacked to form the
connection portion 506.
[0432] The top surface of the conductive layer 581 projects above
the top surface of the resin layer 201. The conductive layer 581
having such a structure can be formed in the following manner: an
opening is formed in the resin layer 201; the conductive layer 581
is formed to fill the opening; the resin layer 201 and the support
substrate are separated from each other; and the resin layer 201 is
thinned. When the top surface of the conductive layer 581 projects,
the exposed surface area is increased, so that adhesion with the
connection layer 519 can be enhanced.
[0433] The conductive layer 562 is electrically connected to a
conductive layer on the resin layer 201 side through a connector
543 in a portion close to an end portion of the resin layer 202.
Thus, a potential or a signal can be supplied from the FPC 374, an
IC, or the like placed on the resin layer 201 side to the
conductive layer 562.
[0434] As the connector 543, a conductive particle can be used, for
example. As the conductive particle, a particle of an organic
resin, silica, or the like coated with a metal material can be
used. It is preferable to use nickel or gold as the metal material
because contact resistance can be decreased. It is also preferable
to use a particle coated with layers of two or more kinds of metal
materials, such as a particle coated with nickel and further with
gold. As the connector 543, a material capable of elastic
deformation or plastic deformation is preferably used. As
illustrated in FIG. 21, the connector 543, which is the conductive
particle, has a shape that is vertically crushed in some cases.
With the crushed shape, the contact area between the connector 543
and a conductive layer electrically connected to the connector 543
can be increased, thereby reducing contact resistance and
suppressing the generation of problems such as disconnection.
[0435] The connector 543 is preferably provided so as to be covered
with the adhesive layer 517. For example, the connectors 543 are
dispersed in the adhesive layer 517 before curing of the adhesive
layer 517.
[0436] Note that the conductive layer 581, the conductive layer
311b, the conductive layer 561, and the like are positioned on the
formation surface side of the transistor 503 and the like.
Therefore, these conductive layers can also be referred to as rear
electrodes.
[0437] The above is the description of the element layers 100b and
200b.
[Components]
[0438] The above components will be described below.
[Substrate]
[0439] A material having a flat surface can be used as the
substrate included in the display panel. The substrate on the side
from which light from the display element is extracted is formed
using a material transmitting the light. For example, a material
such as glass, quartz, ceramics, sapphire, or an organic resin can
be used.
[0440] The weight and thickness of the display panel can be reduced
by using a thin substrate. A flexible display panel can be obtained
by using a substrate that is thin enough to have flexibility.
[0441] Since the substrate through which light is not extracted
does not need to have a light-transmitting property, a metal
substrate or the like can be used, other than the above-mentioned
substrates. A metal substrate, which has high thermal conductivity,
is preferable because it can easily conduct heat to the whole
substrate and accordingly can prevent a local temperature rise in
the display panel. To obtain flexibility and bendability, the
thickness of a metal substrate is preferably greater than or equal
to 10 .mu.m and less than or equal to 400 .mu.m, more preferably
greater than or equal to 20 .mu.m and less than or equal to 50
.mu.m.
[0442] Although there is no particular limitation on a material of
a metal substrate, it is favorable to use, for example, a metal
such as aluminum, copper, and nickel, an aluminum alloy, or an
alloy such as stainless steel.
[0443] It is possible to use a substrate subjected to insulation
treatment, e.g., a metal substrate whose surface is oxidized or
provided with an insulating film. The insulating film may be formed
by, for example, a coating method such as a spin-coating method or
a dipping method, an electrodeposition method, an evaporation
method, or a sputtering method. An oxide film may be formed on the
substrate surface by exposure to or heating in an oxygen atmosphere
or by an anodic oxidation method or the like.
[0444] Examples of the material that has flexibility and transmits
visible light include glass which is thin enough to have
flexibility, polyester resins such as polyethylene terephthalate
(PET) and polyethylene naphthalate (PEN), a polyacrylonitrile
resin, a polyimide resin, a polymethyl methacrylate resin, a
polycarbonate (PC) resin, a polyethersulfone (PES) resin, a
polyamide resin, a cycloolefin resin, a polystyrene resin, a
polyamide imide resin, a polyvinyl chloride resin, and a
polytetrafluoroethylene (PTFE) resin. It is particularly preferable
to use a material with a low thermal expansion coefficient, for
example, a material with a thermal expansion coefficient lower than
or equal to 30.times.10.sup.-6/K, such as a polyamide imide resin,
a polyimide resin, or PET. A substrate in which a glass fiber is
impregnated with an organic resin or a substrate whose thermal
expansion coefficient is reduced by mixing an inorganic filler with
an organic resin can also be used. A substrate using such a
material is lightweight, and thus a display panel using this
substrate can also be lightweight.
[0445] In the case where a fibrous body is included in the above
material, a high-strength fiber of an organic compound or an
inorganic compound is used as the fibrous body. The high-strength
fiber is specifically a fiber with a high tensile elastic modulus
or a fiber with a high Young's modulus. Typical examples thereof
include a polyvinyl alcohol-based fiber, a polyester-based fiber, a
polyamide-based fiber, a polyethylene-based fiber, an aramid-based
fiber, a polyparaphenylene benzobisoxazole fiber, a glass fiber,
and a carbon fiber. As the glass fiber, a glass fiber using E
glass, S glass, D glass, Q glass, or the like can be used. These
fibers may be used in a state of a woven or nonwoven fabric, and a
structure body in which this fibrous body is impregnated with a
resin and the resin is cured may be used as the flexible substrate.
The structure body including the fibrous body and the resin is
preferably used as the flexible substrate, in which case the
reliability against bending or breaking due to local pressure can
be increased.
[0446] Alternatively, glass, metal, or the like that is thin enough
to have flexibility can be used as the substrate. Alternatively, a
composite material where glass and a resin material are bonded to
each other with an adhesive layer may be used. When a glass layer
is used, a barrier property against water and oxygen can be
improved and thus a highly reliable display panel can be
provided.
[0447] A hard coat layer (e.g., a silicon nitride layer and an
aluminum oxide layer) by which a surface of a display panel is
protected from damage, a layer (e.g., an aramid resin layer) that
can disperse pressure, or the like may be stacked over the flexible
substrate. Furthermore, to suppress a decrease in lifetime of the
display element due to moisture and the like, an insulating film
with low water permeability may be stacked over the flexible
substrate. For example, an inorganic insulating material such as
silicon nitride, silicon oxynitride, silicon nitride oxide,
aluminum oxide, or aluminum nitride can be used.
[Transistor]
[0448] The transistor includes a conductive layer serving as a gate
electrode, a semiconductor layer, a conductive layer serving as a
source electrode, a conductive layer serving as a drain electrode,
and an insulating layer serving as a gate insulating layer. In the
above, a bottom-gate transistor is used.
[0449] Note that there is no particular limitation on the structure
of the transistor included in the display device of one embodiment
of the present invention. For example, a planar transistor, a
staggered transistor, or an inverted staggered transistor can be
used. A top-gate transistor or a bottom-gate transistor may be
used. Gate electrodes may be provided above and below a
channel.
[0450] There is no particular limitation on the crystallinity of a
semiconductor material used for the transistors, and an amorphous
semiconductor or a semiconductor having crystallinity (a
microcrystalline semiconductor, a polycrystalline semiconductor, a
single crystal semiconductor, or a semiconductor partly including
crystal regions) may be used. It is preferred that a semiconductor
having crystallinity be used, in which case deterioration of the
transistor characteristics can be suppressed.
[0451] As the semiconductor material used for the transistor, an
oxide semiconductor can be used. Typically, an oxide semiconductor
containing indium can be used.
[0452] In particular, a semiconductor material having a wider band
gap and a lower carrier density than silicon is preferably used
because off-state current of the transistor can be reduced.
[0453] In a transistor with an oxide semiconductor whose band gap
is larger than the band gap of silicon, charges stored in a
capacitor that is connected in series to the transistor can be held
for a long time, owing to the low off-state current of the
transistor. When such a transistor is used for a pixel, operation
of a driver circuit can be stopped while a gray scale of each pixel
is maintained. As a result, a display device with extremely low
power consumption is obtained.
[0454] The semiconductor layer preferably includes, for example, a
film represented by an In-M-Zn-based oxide that contains at least
indium, zinc, and M (a metal such as aluminum, titanium, gallium,
germanium, yttrium, zirconium, lanthanum, cerium, tin, neodymium,
or hafnium). In order to reduce variations in electrical
characteristics of the transistor including the oxide
semiconductor, the oxide semiconductor preferably contains a
stabilizer in addition to In, Zn, and M.
[0455] As examples of the stabilizer, in addition to the above
metals that can be used as M, lanthanoid such as praseodymium,
samarium, europium, gadolinium, terbium, dysprosium, holmium,
erbium, thulium, ytterbium, or lutetium can be given.
[0456] As an oxide semiconductor included in the semiconductor
layer, any of the following can be used, for example: an
In--Ga--Zn-based oxide, an In--Al--Zn-based oxide, an
In--Sn--Zn-based oxide, an In--Hf--Zn-based oxide, an
In--La--Zn-based oxide, an In--Ce--Zn-based oxide, an
In--Pr--Zn-based oxide, an In--Nd--Zn-based oxide, an
In--Sm--Zn-based oxide, an In--Eu--Zn-based oxide, an
In--Gd--Zn-based oxide, an In--Tb--Zn-based oxide, an
In--Dy--Zn-based oxide, an In--Ho--Zn-based oxide, an
In--Er--Zn-based oxide, an In--Tm--Zn-based oxide, an
In--Yb--Zn-based oxide, an In--Lu--Zn-based oxide, an
In--Sn--Ga--Zn-based oxide, an In--Hf--Ga--Zn-based oxide, an
In--Al--Ga--Zn-based oxide, an In--Sn--Al--Zn-based oxide, an
In--Sn--Hf--Zn-based oxide, and an In--Hf--Al--Zn-based oxide.
[0457] Note that here, an "In--Ga--Zn-based oxide" means an oxide
containing In, Ga, and Zn as its main components and there is no
limitation on the ratio of In:Ga:Zn. Furthermore, a metal element
in addition to In, Ga, and Zn may be contained.
[0458] The semiconductor layer and the conductive layer may include
the same metal elements contained in the above oxides. The use of
the same metal elements for the semiconductor layer and the
conductive layer can reduce the manufacturing cost. For example,
the use of metal oxide targets with the same metal composition can
reduce the manufacturing cost. In addition, the same etching gas or
the same etchant can be used in processing the semiconductor layer
and the conductive layer. Note that even when the semiconductor
layer and the conductive layer include the same metal elements,
they have different compositions in some cases. For example, a
metal element in a film is released during the manufacturing
process of the transistor and the capacitor, which might result in
different metal compositions.
[0459] The energy gap of the oxide semiconductor included in the
semiconductor layer is preferably 2 eV or more, further preferably
2.5 eV or more, still further preferably 3 eV or more. The use of
such an oxide semiconductor having a wide energy gap leads to a
reduction in off-state current of a transistor.
[0460] In the case where the oxide semiconductor contained in the
semiconductor layer is an In-M-Zn-based oxide, it is preferable
that the atomic ratio of metal elements of a sputtering target used
to deposit a film of the In-M-Zn oxide satisfy In.gtoreq.M and
Zn.gtoreq.M. The atomic ratio of metal elements in such a
sputtering target is preferably, for example, In:M:Zn=1:1:1,
In:M:Zn=1:1:1.2, In:M:Zn=3:1:2, In:M:Zn=4:2:3, In:M:Zn=4:2:4.1,
In:M:Zn=5:1:6, In:M:Zn=5:1:7, or In:M:Zn=5:1:8. Note that the
atomic ratio of metal elements in the formed semiconductor layer
varies from the above atomic ratios of metal elements of the
sputtering targets in a range of .+-.40%.
[0461] The bottom-gate transistor described in this embodiment is
preferable because the number of manufacturing steps can be
reduced. When an oxide semiconductor, which can be formed at a
lower temperature than polycrystalline silicon, is used, materials
with low heat resistance can be used for a wiring, an electrode, or
a substrate below the semiconductor layer, so that the range of
choices of materials can be widened. For example, an extremely
large glass substrate can be favorably used.
[Conductive Layer]
[0462] As materials for the gates, the source, and the drain of a
transistor, and the conductive layers serving as the wirings and
electrodes included in the display device, any of metals such as
aluminum, titanium, chromium, nickel, copper, yttrium, zirconium,
molybdenum, silver, tantalum, and tungsten, or an alloy containing
any of these metals as its main component can be used. A
single-layer structure or a layered structure including a film
containing any of these materials can be used. For example, the
following structures can be given: a single-layer structure of an
aluminum film containing silicon, a two-layer structure in which an
aluminum film is stacked over a titanium film, a two-layer
structure in which an aluminum film is stacked over a tungsten
film, a two-layer structure in which a copper film is stacked over
a copper-magnesium-aluminum alloy film, a two-layer structure in
which a copper film is stacked over a titanium film, a two-layer
structure in which a copper film is stacked over a tungsten film, a
three-layer structure in which a titanium film or a titanium
nitride film, an aluminum film or a copper film, and a titanium
film or a titanium nitride film are stacked in this order, and a
three-layer structure in which a molybdenum film or a molybdenum
nitride film, an aluminum film or a copper film, and a molybdenum
film or a molybdenum nitride film are stacked in this order. Note
that an oxide such as indium oxide, tin oxide, or zinc oxide may be
used. Copper containing manganese is preferably used because
controllability of a shape by etching is increased.
[0463] A conductive material that transmits visible light or a
conductive material that reflects visible light can be used for a
conductive layer (a conductive layer serving as a pixel electrode
or a common electrode) in a display element (a liquid crystal
element, a light-emitting element, or another display element).
[0464] For example, a material containing one of indium, zinc, and
tin is preferably used as the conductive material that transmits
visible light. Specifically, indium oxide, indium tin oxide, indium
zinc oxide, indium oxide containing tungsten oxide, indium zinc
oxide containing tungsten oxide, indium oxide containing titanium
oxide, indium tin oxide containing titanium oxide, indium tin oxide
containing silicon oxide, zinc oxide, and zinc oxide containing
gallium are given, for example. Alternatively, a film of a metal
material such as gold, silver, platinum, magnesium, nickel,
tungsten, chromium, molybdenum, iron, cobalt, copper, palladium, or
titanium; an alloy containing any of these metal materials; or a
nitride of any of these metal materials (e.g., titanium nitride)
can be formed thin so as to have a light-transmitting property.
Alternatively, a stacked film of any of the above materials can be
used for the conductive layer. For example, a stacked film of
indium tin oxide and an alloy of silver and magnesium is preferably
used, in which case conductivity can be increased. Note that a film
including graphene can be used as well. The film including graphene
can be formed, for example, by reducing a film containing graphene
oxide.
[0465] Examples of a conductive material that reflects visible
light include aluminum, silver, and an alloy containing any of
these metal materials. Furthermore, a metal material such as gold,
platinum, nickel, tungsten, chromium, molybdenum, iron, cobalt,
copper, or palladium or an alloy containing any of these metal
materials can be used. Furthermore, lanthanum, neodymium,
germanium, or the like may be added to the metal material or the
alloy. Furthermore, an alloy containing aluminum (an aluminum
alloy) such as an alloy of aluminum and titanium, an alloy of
aluminum and nickel, an alloy of aluminum and neodymium, or an
alloy of aluminum, nickel, and lanthanum (Al--Ni--La); or an alloy
containing silver such as an alloy of silver and copper, an alloy
of silver, palladium, and copper (also referred to as Ag--Pd--Cu or
APC), or an alloy of silver and magnesium may be used. An alloy
containing silver and copper is preferable because of its high heat
resistance. Furthermore, when a metal film or a metal oxide film is
stacked in contact with an aluminum film or an aluminum alloy film,
oxidation can be suppressed. Examples of a material for the metal
film or the metal oxide film include titanium and titanium oxide.
Alternatively, the above conductive film that transmits visible
light and a film containing a metal material may be stacked. For
example, a stack of silver and indium tin oxide, a stack of indium
tin oxide and an alloy of silver and magnesium, or the like can be
used.
[0466] The conductive layers may each be formed by an evaporation
method or a sputtering method. Alternatively, a discharging method
such as an inkjet method, a printing method such as a screen
printing method, or a plating method may be used.
[Insulating Layer]
[0467] As an insulating material that can be used for the
insulating layers, polyimide, acrylic, epoxy, a silicone resin, or
an inorganic insulating material such as silicon oxide, silicon
oxynitride, silicon nitride oxide, silicon nitride, or aluminum
oxide can be used.
[0468] The light-emitting element is preferably provided between a
pair of insulating films with low water permeability, in which case
entry of impurities such as water into the light-emitting element
can be inhibited. Thus, a decrease in device reliability can be
suppressed.
[0469] As an insulating film with low water permeability, a film
containing nitrogen and silicon, such as a silicon nitride film or
a silicon nitride oxide film, a film containing nitrogen and
aluminum, such as an aluminum nitride film, or the like can be
used. Alternatively, a silicon oxide film, a silicon oxynitride
film, an aluminum oxide film, or the like may be used.
[0470] For example, the amount of water vapor transmission of the
insulating film with low water permeability is lower than or equal
to 1.times.10.sup.-5 [g/(m.sup.2day)], preferably lower than or
equal to 1.times.10.sup.-6 [g/(m.sup.2day)], further preferably
lower than or equal to 1.times.10.sup.-7 [g/(m.sup.2day)], still
further preferably lower than or equal to 1.times.10.sup.-8
[g/(m.sup.2day)].
[Display Element]
[0471] As a display element included in the first pixel located on
the display surface side, an element which performs display by
reflecting external light can be used. Such an element does not
include a light source and thus power consumption in display can be
significantly reduced. As a typical example of the display element
included in the first pixel, a reflective liquid crystal element
can be given. Alternatively, as the display element included in the
first pixel, an element using a microcapsule method, an
electrophoretic method, an electrowetting method, an Electronic
Liquid Powder (registered trademark) method, or the like can be
used, other than a microelectromechanical systems (MEMS) shutter
element or an optical interference type MEMS element.
[0472] As a display element included in the second pixel located on
the side opposite to the display surface side, an element which
includes a light source and performs display using light from the
light source can be used. Since the luminance and the chromaticity
of light emitted from such a pixel are not affected by external
light, an image with high color reproducibility (a wide color
gamut) and a high contrast, i.e., a clear image can be displayed.
As the display element included in the second pixel, a
self-luminous light-emitting element such as an organic
light-emitting diode (OLED), a light-emitting diode (LED), or a
quantum-dot light-emitting diode (QLED) can be used. Alternatively,
a combination of a backlight as a light source and a transmissive
liquid crystal element which controls the amount of transmitted
light emitted from a backlight may be used as the display element
included in the second pixel.
[Liquid Crystal Element]
[0473] The liquid crystal element can employ, for example, a
vertical alignment (VA) mode. Examples of the vertical alignment
mode include a multi-domain vertical alignment (MVA) mode, a
patterned vertical alignment (PVA) mode, and an advanced super view
(ASV) mode.
[0474] The liquid crystal element can employ a variety of modes;
for example, other than the VA mode, a twisted nematic (TN) mode,
an in-plane switching (IPS) 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, or an antiferroelectric liquid crystal
(AFLC) mode can be used.
[0475] The liquid crystal element controls transmission or
non-transmission of light utilizing an optical modulation action of
liquid crystal. Note that the optical modulation action of liquid
crystal is controlled by an electric field applied to the liquid
crystal (including a horizontal electric field, a vertical electric
field, and an oblique electric field). As the liquid crystal used
for the liquid crystal element, thermotropic liquid crystal,
low-molecular liquid crystal, high-molecular liquid crystal,
polymer dispersed liquid crystal (PDLC), 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.
[0476] As the liquid crystal material, either a positive liquid
crystal or a negative liquid crystal may be used, and an
appropriate liquid crystal material can be used depending on the
mode or design to be used.
[0477] An alignment film can be provided to adjust the alignment of
liquid crystal. In the case where a horizontal electric field mode
is employed, liquid crystal exhibiting a blue phase for which an
alignment film is unnecessary may be used. A blue phase is one of
liquid crystal phases, which is generated just before a cholesteric
phase changes into an isotropic phase while temperature of
cholesteric liquid crystal is increased. Since the blue phase
appears only in a narrow temperature range, a liquid crystal
composition in which several weight percent or more of a chiral
material is mixed is used for the liquid crystal layer in order to
improve the temperature range. The liquid crystal composition which
includes liquid crystal exhibiting a blue phase and a chiral
material has a short response time and has optical isotropy. In
addition, the liquid crystal composition which includes liquid
crystal exhibiting a blue phase and a chiral material does not need
alignment treatment and has a small viewing angle dependence. An
alignment film is not necessarily provided and rubbing treatment is
thus not necessary; accordingly, electrostatic discharge damage
caused by the rubbing treatment can be prevented and defects and
damage of the liquid crystal display device in the manufacturing
process can be reduced.
[0478] In one embodiment of the present invention, in particular,
the reflective liquid crystal element can be used. In the
reflective liquid crystal element, an electrode on the viewing side
can be formed using a conductive material that transmits visible
light and an electrode on the side opposite to the viewing side can
be formed using a conductive material that reflects visible
light.
[0479] In the case where a reflective liquid crystal element is
used, a polarizing plate is provided on the display surface side.
In addition, a light diffusion plate is preferably provided on the
display surface side to improve visibility.
[Light-Emitting Element]
[0480] As the light-emitting element, a self-luminous element can
be used, and an element whose luminance is controlled by current or
voltage is included in the category of the light-emitting element.
For example, an LED, a QLED, an organic EL element, or an inorganic
EL element can be used.
[0481] In one embodiment of the present invention, in particular,
the light-emitting element preferably has a top emission structure.
The conductive material that transmits visible light is used for
the electrode through which light is extracted. The conductive
material that reflects visible light is preferably used for the
electrode through which light is not extracted.
[0482] The EL layer includes at least a light-emitting layer. In
addition to the light-emitting layer, the EL layer may further
include one or more layers containing any of a substance with a
high hole-injection property, a substance with a high
hole-transport property, a hole-blocking material, a substance with
a high electron-transport property, a substance with a high
electron-injection property, a substance with a bipolar property (a
substance with a high electron- and hole-transport property), and
the like.
[0483] For the EL layer, either a low-molecular compound or a
high-molecular compound can be used, and an inorganic compound may
also be used. Each of the layers included in the EL layer can be
formed by any of the following methods: an evaporation method
(including a vacuum evaporation method), a transfer method, a
printing method, an inkjet method, a coating method, and the
like.
[0484] When a voltage higher than the threshold voltage of the
light-emitting element is applied between a cathode and an anode,
holes are injected to the EL layer from the anode side and
electrons are injected to the EL layer from the cathode side. The
injected electrons and holes are recombined in the EL layer and a
light-emitting substance contained in the EL layer emits light.
[0485] In the case where a light-emitting element emitting white
light is used as the light-emitting element, the EL layer
preferably contains two or more kinds of light-emitting substances.
For example, the two or more kinds of light-emitting substances are
selected so as to emit light of complementary colors to obtain
white light emission. Specifically, it is preferable to contain two
or more selected from light-emitting substances that emit light of
red (R), green (G), blue (B), yellow (Y), orange (O), and the like
and light-emitting substances that emit light containing two or
more of spectral components of R, G, and B. The light-emitting
element preferably emits light with a spectrum having two or more
peaks in the wavelength range of a visible light region (e.g.,
greater than or equal to 350 nm and less than or equal to 750 nm).
An emission spectrum of a material that emits light having a peak
in a yellow wavelength range preferably includes spectral
components also in green and red wavelength ranges.
[0486] A light-emitting layer containing a light-emitting material
that emits light of one color and a light-emitting layer containing
a light-emitting material that emits light of another color are
preferably stacked in the EL layer. For example, the plurality of
light-emitting layers in the EL layer may be stacked in contact
with each other or may be stacked with a region not including any
light-emitting material therebetween. For example, between a
fluorescent layer and a phosphorescent layer, a region containing
the same material as one in the fluorescent layer or the
phosphorescent layer (for example, a host material or an assist
material) and no light-emitting material may be provided. This
facilitates the manufacture of the light-emitting element and
reduces the drive voltage.
[0487] The light-emitting element may be a single element including
one EL layer or a tandem element in which a plurality of EL layers
are stacked with a charge generation layer therebetween.
[0488] Note that the aforementioned light-emitting layer and layers
containing a substance with a high hole-injection property, a
substance with a high hole-transport property, a substance with a
high electron-transport property, a substance with a high
electron-injection property, a substance with a bipolar property,
and the like may include an inorganic compound such as a quantum
dot or a high molecular compound (e.g., an oligomer, a dendrimer,
and a polymer). For example, when used for the light-emitting
layer, the quantum dot can function as a light-emitting
material.
[0489] The quantum dot may be a colloidal quantum dot, an alloyed
quantum dot, a core-shell quantum dot, a core quantum dot, or the
like. A quantum dot containing elements belonging to Groups 12 and
16, elements belonging to Groups 13 and 15, or elements belonging
to Groups 14 and 16 may be used. Alternatively, a quantum dot
containing an element such as cadmium, selenium, zinc, sulfur,
phosphorus, indium, tellurium, lead, gallium, arsenic, or aluminum
may be used.
[0490] The above-described materials can be used as the conductive
material that transmits visible light and the conductive material
that reflects visible light, which can be used for the electrodes
of the light-emitting element.
[Adhesive Layer]
[0491] As the adhesive layer, any of a variety of curable
adhesives, e.g., a photo-curable adhesive such as an ultraviolet
curable adhesive, a reactive curable adhesive, a thermosetting
curable adhesive, and an anaerobic adhesive can be used. Examples
of these adhesives include 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,
and an ethylene vinyl acetate (EVA) resin. In particular, a
material with low moisture permeability, such as an epoxy resin, is
preferred. Alternatively, a two-component-mixture-type resin may be
used. Still alternatively, an adhesive sheet or the like may be
used.
[0492] Furthermore, the resin may include a drying agent. For
example, a substance that adsorbs moisture by chemical adsorption,
such as oxide of an alkaline earth metal (e.g., calcium oxide or
barium oxide), can be used. Alternatively, a substance that adsorbs
moisture by physical adsorption, such as zeolite or silica gel, may
be used. The drying agent is preferably included because it can
inhibit entry of impurities such as moisture into an element,
leading to an improvement in the reliability of the display
panel.
[0493] In addition, a filler with a high refractive index or a
light-scattering member may be mixed into the resin, in which case
light extraction efficiency can be improved. For example, titanium
oxide, barium oxide, zeolite, or zirconium can be used.
[Connection Layer]
[0494] As a connection layer, an anisotropic conductive film (ACF),
an anisotropic conductive paste (ACP), or the like can be used.
[Coloring Layer]
[0495] Examples of materials that can be used for the coloring
layer include a metal material, a resin material, and a resin
material containing a pigment or dye.
[Light-Blocking Layer]
[0496] Examples of a material that can be used for the
light-blocking layer include carbon black, titanium black, a metal,
a metal oxide, and a composite oxide containing a solid solution of
a plurality of metal oxides. The light-blocking layer may be a film
containing a resin material or a thin film of an inorganic material
such as a metal. Stacked films containing the material of the
coloring layer can also be used for the light-blocking layer. For
example, a stacked-layer structure of a film containing a material
of a coloring layer which transmits light of a certain color and a
film containing a material of a coloring layer which transmits
light of another color can be employed. It is preferred that the
coloring layer and the light-blocking layer be formed using the
same material because the same manufacturing apparatus can be used
and the process can be simplified.
[0497] The above is the description of each of the components.
Modification Example
[0498] Structure examples which partly differ from the display
device described in the above cross-sectional structure example
will be described below. Note that the description of the portions
already described above is omitted and only different portions are
described.
Modification Example 1 of Cross-Sectional Structure Example
[0499] FIG. 22 is different from FIG. 21 in the structures of
transistors and the resin layer 202 and in that a coloring layer
565, a light-blocking layer 566, and an insulating layer 567 are
provided.
[0500] The transistors 401, 403, and 501 illustrated in FIG. 22
each include a second gate electrode. In this manner, a transistor
including a pair of gates is preferably used as each of the
transistors provided in the circuit portion 364 and the circuit
portion 366, the transistor that controls current flowing to the
light-emitting element 360, and the like.
[0501] In the resin layer 202, an opening overlapping with the
liquid crystal element 340 and an opening overlapping with the
light-emitting element 360 are separately formed, whereby the
reflectance of the liquid crystal element 340 can be increased.
[0502] The light-blocking layer 566 and the coloring layer 565 are
provided on a surface of the insulating layer 576 on the liquid
crystal element 340 side. The coloring layer 565 is provided so as
to overlap with the liquid crystal element 340. Thus, the element
layer 200b can perform color display. The light-blocking layer 566
has an opening overlapping with the liquid crystal element 340 and
an opening overlapping with the light-emitting element 360. This
allows fabrication of a display device that suppresses mixing of
colors between adjacent pixels and thus has high color
reproducibility.
Modification Example 2 of Cross-Sectional Structure Example
[0503] FIG. 23 illustrates an example in which a top-gate
transistor is used as each transistor. The use of a top-gate
transistor can reduce parasitic capacitance, leading to an increase
in the frame frequency of display. Furthermore, a top-gate
transistor can favorably be used for a large display panel with a
size of 8 inches or more, for example.
[0504] FIG. 23 shows an example where a top-gate transistor
including a second gate electrode is used as the transistors 401,
402, 403, and 501.
[0505] The transistors on the element layer 100a side include a
conductive layer 491 over the insulating layer 478. An insulating
layer 418 is provided to cover the conductive layer 491. The
transistors on the element layer 100b side include a conductive
layer 591 over the insulating layer 510. An insulating layer 578 is
provided to cover the conductive layer 591.
[0506] The above is the description of the modification
examples.
[0507] At least part of this embodiment can be implemented in
appropriate combination with any of the other embodiments described
in this specification.
Embodiment 5
[0508] In this embodiment, a display module that can be fabricated
using one embodiment of the present invention will be
described.
[0509] In a display module 8000 in FIG. 24, a touch panel 8004
connected to an FPC 8003, a display panel 8006 connected to an FPC
8005, a frame 8009, a printed circuit board 8010, and a battery
8011 are provided between an upper cover 8001 and a lower cover
8002.
[0510] The display device fabricated using one embodiment of the
present invention can be used for, for example, the display panel
8006.
[0511] The shapes and sizes of the upper cover 8001 and the lower
cover 8002 can be changed as appropriate in accordance with the
sizes of the touch panel 8004 and the display panel 8006.
[0512] The touch panel 8004 can be a resistive touch panel or a
capacitive touch panel and may be formed to overlap with the
display panel 8006. Instead of providing the touch panel 8004, the
display panel 8006 can have a touch panel function.
[0513] The frame 8009 protects the display panel 8006 and functions
as an electromagnetic shield for blocking electromagnetic waves
generated by the operation of the printed circuit board 8010. The
frame 8009 may also function as a radiator plate.
[0514] The printed circuit board 8010 has a power supply circuit
and a signal processing circuit for outputting a video signal and a
clock signal. As a power source for supplying power to the power
supply circuit, an external commercial power source or a power
source using the battery 8011 provided separately may be used. The
battery 8011 can be omitted in the case of using a commercial power
source.
[0515] The display module 8000 may be additionally provided with a
member such as a polarizing plate, a retardation plate, or a prism
sheet.
[0516] At least part of this embodiment can be implemented in
appropriate combination with any of the other embodiments described
in this specification.
Embodiment 6
[0517] In this embodiment, electronic devices to which the display
device of one embodiment of the present invention can be applied
will be described.
[0518] The display device of one embodiment of the present
invention can achieve high visibility regardless of the intensity
of external light. For this reason, the display device can be used
for portable electronic devices, wearable electronic devices
(wearable devices), e-book readers, and the like.
[0519] FIGS. 25A and 25B illustrate an example of a portable
information terminal 800. The portable information terminal 800
includes a housing 801, a housing 802, a display portion 803, a
display portion 804, and a hinge 805, for example.
[0520] The housing 801 and the housing 802 are joined together with
the hinge 805. The portable information terminal 800 can be changed
from a folded state illustrated in FIG. 25A to an opened state
illustrated in