U.S. patent application number 09/817674 was filed with the patent office on 2001-10-04 for light emitting device and a method of manufacturing the same.
Invention is credited to Fukunaga, Takeshi, Hiroki, Masaaki, Yamazaki, Shunpei.
Application Number | 20010026125 09/817674 |
Document ID | / |
Family ID | 18602158 |
Filed Date | 2001-10-04 |
United States Patent
Application |
20010026125 |
Kind Code |
A1 |
Yamazaki, Shunpei ; et
al. |
October 4, 2001 |
Light emitting device and a method of manufacturing the same
Abstract
To provide a light emitting device having a highly definite
pixel portion. An anode (102) and a bank (104) orthogonal to the
anode (102) are formed on an insulator (101). A portion of the bank
(104) (controlling bank 104b) is made of a metal film. By applying
a voltage thereto, an electric field is formed, and a track of an
EL material that is charged with an electric charge can be
controlled. Thus, it becomes possible to control a film deposition
position of an EL layer with precision by utilizing the above
method.
Inventors: |
Yamazaki, Shunpei;
(Kanagawa, JP) ; Hiroki, Masaaki; (Kanagawa,
JP) ; Fukunaga, Takeshi; (Kanagawa, JP) |
Correspondence
Address: |
JOHN F. HAYDEN
Fish & Richardson P.C.
601 Thirteenth Street, NW
Washington
DC
20005
US
|
Family ID: |
18602158 |
Appl. No.: |
09/817674 |
Filed: |
March 27, 2001 |
Current U.S.
Class: |
313/505 ;
313/506; 345/80; 427/66 |
Current CPC
Class: |
H01L 27/127 20130101;
H01L 27/3246 20130101; H01L 29/78627 20130101; H01L 27/1214
20130101; H01L 51/56 20130101; G09G 3/3208 20130101; H01L 27/3276
20130101; H01L 51/0011 20130101; H01L 29/78621 20130101; H01L
51/0002 20130101 |
Class at
Publication: |
313/505 ; 427/66;
313/506; 345/80 |
International
Class: |
H01J 001/62 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 27, 2000 |
JP |
2000-085910 |
Claims
What is claimed is:
1. A light emitting device comprising: at least one thin film
transistor on an insulating surface; an anode electrically
connected to said thin film transistor; a cathode provided opposite
said anode; and a luminous material provided between said anode and
said cathode, wherein said anode is surrounded by a bank, and a
portion of said bank contains a metal film.
2. A light emitting device according to claim 1, wherein said
luminous material is an EL material.
3. A light emitting device according to claim 1, wherein said metal
film has a tapered shape.
4. A light emitting device according to claim 1, wherein said light
emitting device is one selected from the group consisting of a
video camera, a digital camera, a goggle type display, car
navigation system, a note book type computer, and a mobile
telephone.
5. A light emitting device comprising: at least one thin film
transistor on an insulating surface; an anode electrically
connected to said thin film transistor; a cathode provided opposite
said anode; and a luminous material provided between said anode and
said cathode, wherein said anode is surrounded by a bank, and said
bank is formed of a lamination of an insulating film and a metal
film.
6. A light emitting device according to claim 5, wherein said
luminous material is an EL material.
7. A light emitting device according to claim 5, wherein said metal
film has a tapered shape.
8. A light emitting device according to claim 5, wherein said light
emitting device is one selected from the group consisting of a
video camera, a digital camera, a goggle type display, car
navigation system, a note book type computer, and a mobile
telephone.
9. A light emitting device comprising: at least one thin film
transistor on an insulating surface; a cathode electrically
connected to said thin film transistor; an anode provided opposite
said cathode; and a luminous material provided between said cathode
and said anode, wherein said cathode is surrounded by a bank, and a
portion of said bank contains a metal film.
10. A light emitting device according to claim 9, wherein said
luminous material is an EL material.
11. A light emitting device according to claim 9, wherein said
metal film has a tapered shape.
12. A light emitting device according to claim 9, wherein said
light emitting device is one selected from the group consisting of
a video camera, a digital camera, a goggle type display, car
navigation system, a note book type computer, and a mobile
telephone.
13. A light emitting device comprising: at least one thin film
transistor on an insulating surface; a cathode electrically
connected to said thin film transistor; an anode provided opposite
said cathode; and a luminous material provided between said cathode
and said anode, wherein said cathode is surrounded by a bank, and
said bank is formed of a lamination of an insulating film and a
metal film.
14. A light emitting device according to claim 13, wherein said
luminous material is an EL material.
15. A light emitting device according to claim 13, wherein said
metal film has a tapered shape.
16. A light emitting device according to claim 13, wherein said
light emitting device is one selected from the group consisting of
a video camera, a digital camera, a goggle type display, car
navigation system, a note book type computer, and a mobile
telephone.
17. A method of manufacturing a light emitting device, comprising
the steps of: forming at least one thin film transistor on an
insulating surface; forming a pixel electrode electrically
connected to said thin film transistor; forming a bank so as to
surround said pixel electrode; and forming an EL material over said
pixel electrode while charging a portion of said bank with a
negative or positive charge.
18. A method of manufacturing a light emitting device according to
claim 17, wherein said step of forming said EL material is
performed by an evaporation method, an ion plating method, or an
ink jet method.
19. A method of manufacturing a light emitting device according to
claim 17, wherein said light emitting device is one selected from
the group consisting of a video camera, a digital camera, a goggle
type display, car navigation system, a note book type computer, and
a mobile telephone.
20. A method of manufacturing a light emitting device, comprising
the steps of: forming at least one thin film transistor on an
insulating surface; forming a pixel electrode electrically
connected to said thin film transistor; forming a bank so as to
surround said pixel electrode; and while charging a portion of said
bank with a negative or positive charge, forming an EL material
charged to have a same polarity as said bank over said pixel
electrode
21. A method of manufacturing a light emitting device according to
claim 20, wherein said step of forming said EL material is
performed by an evaporation method, an ion plating method, or an
ink jet method.
22. A method of manufacturing a light emitting device according to
claim 20, wherein said light emitting device is one selected from
the group consisting of a video camera, a digital camera, a goggle
type display, car navigation system, a note book type computer, and
a mobile telephone.
23. A method of manufacturing a light emitting device, comprising
the steps of: forming at least one thin film transistor on an
insulating surface; forming a pixel electrode electrically
connected to said thin film transistor; forming a bank composed of
a lamination of an insulating film and a metal film so as to
surround said pixel electrode; and forming an EL material over said
pixel electrode while charging said metal film with a negative or
positive charge.
24. A method of manufacturing a light emitting device according to
claim 23, wherein said step of forming said EL material is
performed by an evaporation method, an ion plating method, or an
ink jet method.
25. A method of manufacturing a light emitting device according to
claim 23, wherein said light emitting device is one selected from
the group consisting of a video camera, a digital camera, a goggle
type display, car navigation system, a note book type computer, and
a mobile telephone.
26. A method of manufacturing a light emitting device, comprising
the steps of: forming at least one thin film transistor on an
insulating surface; forming a pixel electrode electrically
connected to said thin film transistor; forming a bank composed of
a lamination of an insulating film and a metal film so as to
surround said pixel electrode; and while charging said metal film
with a negative or positive charge, forming an EL material charged
to have a same polarity as said metal film over said pixel
electrode.
27. A method of manufacturing a light emitting device according to
claim 26, wherein said step of forming said EL material is
performed by an evaporation method, an ion plating method, or an
ink jet method.
28. A method of manufacturing a light emitting device according to
claim 26, wherein said light emitting device is one selected from
the group consisting of a video camera, a digital camera, a goggle
type display, car navigation system, a note book type computer, and
a mobile telephone.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a device having an element
that is comprised of a luminous material sandwiched between
electrodes (hereinafter referred to as luminous element)
(hereinafter the device will be referred to as light emitting
device) and to a method of manufacturing the same. In particular,
the present invention relates to a light emitting device using a
luminous element that utilizes a luminous material (hereinafter
referred to as an EL material) which provides EL (Electro
Luminescence) (hereinafter the luminous element will be referred to
as an EL element and the device will be referred to as an EL light
emitting device). It is to be noted that an organic EL display and
an organic light emitting diode (OLED) are included in the light
emitting device of the present invention.
[0003] Further, the EL materials that can be used in the present
invention include all the EL materials that luminesce by way of a
singlet excitation or a triplet excitation, or via both excitations
(fluorescence and/or phosphorescence).
[0004] 2. Description of the Related Art
[0005] The EL light emitting device is constructed of a structure
having an EL element that is composed of an anode, a cathode, and
an EL material sandwiched therebetween. By applying a voltage
between the anode and the cathode to cause a current to flow in the
EL material, the carriers are made to re-couple, whereby the EL
element emits light. In other words, the luminous element itself in
the EL light emitting device has a luminescing ability, and
therefore the EL light emitting device, unlike a liquid crystal
display device, does not need a back light. In addition, the EL
light emitting device has merits such as a wide angle of view and
is light in weight.
[0006] At this point, when film deposition is performed on the EL
material to thereby form the EL layer, various types of film
deposition methods are adopted. In particular, the evaporation
method is employed for the film deposition of a low molecular
weight type organic EL material, while the spin coating method or
the ink jet method is employed for film deposition of a high
molecular weight type organic EL material.
[0007] In any case, although there are strong points and
shortcomings in all the film deposition methods, there exist a
problem in the case of the evaporation method where the utilization
of EL material is inefficient. In the case of the evaporation
method, the EL material is formed by being vaporized through resist
heating or electron beam heating and then scattered. However, the
amount of loss due to the EL material being formed on areas other
than on the surface to be formed, such as on an evaporation mask
(shadow mask) and on the interior of the evaporation chamber, was
large. The price of the EL material in the present situation is
high, and hence, this type of problem consequently invites an
increase in the manufacturing costs.
[0008] Further, in the case of the ink jet method, the tracks of
the drops of solution containing the EL material that is discharged
from the tip end of a nozzle is difficult to control, thereby
making it difficult to accurately control the point where the drops
of solution is to be applied (the portion where the EL layer is to
be formed). If the application point is off the point, a problem in
which the drops of solution will mix into an adjacent pixel may
occur. This problem, in particular, becomes particularly a
conspicuous problem in terms of manufacturing a light emitting
device having a highly definite pixel portion.
SUMMARY OF THE INVENTION
[0009] The present invention has been made in view of the above
problem, and therefore an object of the present invention is to
provide a technique for accurately controlling a film deposition
position in forming an EL material. Another object of the present
invention is to attain a light emitting device that has a highly
definite pixel portion. A further object of the present invention
is to provide an electric appliance, which has high displaying
quality, that employs the light emitting device as its display
portion.
[0010] The present invention is characterized in that a metal film
is used for forming a portion of a bank for dividing the pixels,
and then a voltage is applied to the metal film (to make a negative
or positive charge) to form an electric field to thereby control a
track of the EL material. Therefore, in this specification,
"applying an electric field" means "controlling the direction of
the charged particles".
[0011] It is to be noted that the term "bank" throughout this
specification, indicates a lamination layer that is composed of an
insulating film and a conductive film and provided so as to
surround a pixel electrode. The bank assumes the role of dividing
the respective pixels. In addition, for the sake of convenience in
making the present invention clear, the bank is divided into parts
and classified as "a supporting bank" and "a controlling bank"
throughout this specification.
[0012] By adopting the above-mentioned structure, in film
deposition methods such as the evaporation method, the ion plating
method, or the ink jet method in which the discharged EL material
adheres to the upper part or the lower part of the surface on which
the EL material is to be formed, it is possible to accurately
control the film deposition position of the EL material. As a
result, a light emitting device having a highly definite pixel
portion can be attained.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] The above and other objects and features of the present
invention will be more apparent from the following description
taken in conjunction with the accompanying drawings:
[0014] FIGS. 1A and 1B are diagrams showing a top view structure
and a cross-sectional structure, respectively, of a light emitting
device;
[0015] FIG. 2 is a diagram for explaining a film deposition process
of an EL material;
[0016] FIG. 3 is a diagram for explaining a film deposition process
of an EL material by using the evaporation method;
[0017] FIGS. 4A and 4B are diagrams for explaining a film
deposition process of an EL material by using the ink jet
method;
[0018] FIG. 5 is a diagram for explaining a film deposition process
of an EL material by using the ion plating method;
[0019] FIG. 6 is a diagram showing a cross-sectional structure of a
pixel portion of a light emitting device;
[0020] FIGS. 7A to 7C are diagrams showing a top view structure of
a pixel portion and a circuit configuration thereof, respectively,
of a light emitting device;
[0021] FIGS. 8A to 8E are views showing a manufacturing process of
a light emitting device;
[0022] FIGS. 9A to 9D are views showing a manufacturing process of
a light emitting device;
[0023] FIGS. 10A to 10C are views showing a manufacturing process
of a light emitting device;
[0024] FIGS. 11A and 11B are views showing a structure of a
switching TFT;
[0025] FIGS. 12A and 12B are views showing a structure of a current
controlling TFT;
[0026] FIG. 13 is a drawing showing the outer appearance of a light
emitting device;
[0027] FIG. 14 is a diagram illustrating a circuit configuration of
a light emitting device;
[0028] FIGS. 15A and 15B are diagrams showing a top view structure
and a cross-sectional structure, respectively, of a light emitting
device;
[0029] FIG. 16 is a diagram for explaining a gang-printing
process;
[0030] FIGS. 17A and 17B are diagrams for explaining a
gang-printing process;
[0031] FIG. 18 is a diagram for explaining a film deposition
process of an EL material;
[0032] FIGS. 19A and 19B are diagrams for explaining a film
deposition process of an EL material;
[0033] FIGS. 20A to 20F are views showing examples of electric
appliances; and
[0034] FIGS. 21A and 21B are views showing examples of electric
appliances.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0035] A structure of the light emitting device of the present
invention will be explained with reference to FIGS. 1A and 1B. The
top view of a pixel portion of the light emitting device is shown
in FIG. 1A, and the cross-sectional view thereof taken along the
line A-A' of FIG. 1A is shown in FIG. 1B. However, the state of the
light emitting device shown here is before the sealing of a
luminous element.
[0036] In the light emitting device of the present invention, a TFT
102 is provided on an insulator 101. A glass substrate, a plastic
substrate (including a plastic film), a metal substrate, and a
ceramic substrate having an insulating film thereon may be used as
the insulator 101, or a quartz substrate may be used as it is.
[0037] A know structure of an n-channel TFT or a p-channel TFT may
be used to form the TFT (thin film transistor) 102. The structure
thereof may be a top gate structure (typically a planar type TFT)
or a bottom gate structure (typically an inverted stagger type
TFT). Further, although there is also no limit placed on the
arrangement of the TFT, typically a pixel structure disclosed in
Japanese Patent Application Laid-open No. Hei 5-107561 by the
present applicant may be adopted. Covered by an interlayer
insulating film 103, the TFT 102 is electrically connected to a
pixel electrode 104 with the interlayer insulating film 103
sandwiched therebetween. An insulating film containing silicon,
typically a silicon oxide film, a silicon nitride film, a silicon
oxynitride film, or a carbonized silicon film can be used as the
interlayer insulating film 103. Further, a resin film can be used,
or the insulating film containing the resin film and the silicon
may be combined and used.
[0038] A conductive film having a large work function is used as
the pixel electrode 104 in the embodiment mode, typically, a
transparent oxide conductive film with respect to visible radiation
is used. As the oxide conductive film, a conductive film made from
indium oxide, tin oxide, zinc oxide, or a compound composed of
these materials can be used. In addition, a film in which gallium
is doped into these oxide conductive films may be used. A bank 105
is further provided surrounding the pixel electrode 104. The bank
105 is composed of a supporting bank 105a that is made of an
insulating film, and a controlling bank 105b that is made of a
metal film formed thereon. At this point, the line width of the
controlling bank 105b is formed thinner than that of the supporting
bank 105a. It is preferable that the supporting bank 105a and the
controlling bank 105b have taper shapes. In the present invention,
even if a voltage having a polarity that is different from the
pixel electrode is applied to the controlling bank 105b, the
controlling bank 105b is charged with a negative or a positive
charge, thereby making it possible to control the trajectory of the
EL material by applying an electric field thereto.
[0039] An EL layer 106 is further provided in the pixel that is
surrounded by the bank 105, and a cathode 107 is provided so as to
cover the bank 105 and the EL layer 106.
[0040] It is to be noted that in this specification, the EL layer
denotes an insulating layer that is formed between an anode and a
cathode in an EL element. The layer thereof is formed from the
combination of various kinds of organic films or inorganic films.
Typically, the EL layer includes at least a light emitting layer,
and an EL layer in which an electron injection layer and an
electron transporting layer are combined with the light emitting
layer is used. Further, an organic EL material, an inorganic EL
material, or an EL material that is composed of a combination
thereof is used as the EL layer 106. In the case of using an
organic EL material, it is appropriate to use a low molecular
weight type material, a high molecular weight type material, or any
known material.
[0041] A conductive film having a small work function is used to
form the cathode 107. Typically, a conductive film containing an
element that belongs to Group 1 or Group 2 of the Periodic Table is
used. An alloy film containing magnesium, lithium, cesium,
beryllium, potassium, or calcium is typically used. In addition, a
bismuth film can also be used as the conductive film to form the
cathode 107.
[0042] Thus, the above pixel electrode (anode) 104, the EL layer
106 and the cathode 107 forms an EL element 100. Actually, either a
resin film as a sealing material is formed on the EL element 100 or
an airtight space is formed on top of the EL element 100 to thereby
protect the EL element 100 from the open air. These measures are
taken for the purpose of preventing, as much as possible, contact
with oxygen and moisture which causes the EL layer 106 and the
cathode 107 to oxidize thereby resulting in deterioration of the EL
element.
[0043] The light emitting device of the present invention adopting
a structure such as the one above is characterized in that in the
case of using methods such as the evaporation method, the ion
plating method, or the ink jet method in which the EL material is
film deposited by being discharged from an upper direction or a
lower direction and adhering to a surface, an electric field is
applied to the EL material by using the metal film that forms a
portion of the bank, whereby the film deposition position thereof
is controlled by this electric field.
[0044] By implementing the present invention, it becomes possible
to form the EL material while making a precise position control.
Consequently, the realization of the light emitting device having a
highly definite pixel portion can be realized.
Embodiment 1
[0045] A film deposition process of an EL layer in manufacturing a
light emitting device having the structure shown in FIGS. 1A and 1B
is explained with reference to FIG. 2. Note that reference symbols
of FIGS. 1A and 1B will be referred to in the explanation of a
portion thereof. In FIG. 2, the TFT 102 is formed on the insulator
101, and the pixel electrode (functions as an anode in Embodiment
1) 104 is formed on the interlayer insulating film 103, which is
formed covering the TFT 102. In addition, the bank 105 that is
composed of the supporting bank 105a and the controlling bank 105b
is formed so as to surround the pixel electrode 104.
[0046] Then in this state the pixel electrode 104 is first charged
with a positive charge. A positive voltage may be applied to the
pixel electrode 104, or it is possible to charge the pixel
electrode by subjecting it to an ion shower that has been
positively charged. In the case of applying a positive voltage, the
TFT 102 may be operated to thereby apply the positive voltage.
Next, the controlling bank 105b is charged with a negative charge.
It is also possible to apply a negative voltage to the controlling
bank 105b. The size of the negative voltage may be appropriately
determined by the implementor.
[0047] Under this condition, an EL material (a solution containing
an EL material is also included as an EL material in this
specification) 201 is laminated by using the evaporation method,
the ion plating method, or the ink jet method. At this point, the
present invention is characterized in that the EL material 201 is
charged so that it has the same polarity as that of the controlling
bank 105b. In other words, in the case of Embodiment 1, because the
controlling bank 105b is charged with a negative charge, the EL
material 201 is also charged with a negative charge. Thus, the EL
material 201 repels the electric field that is formed in the
periphery of the controlling bank 105b, thereby drawing a track
which avoids the controlling bank 105b.
[0048] In addition, because the pixel electrode 104 is charged with
a positive charge in Embodiment 1, it moves in a direction that
draws the negatively charged EL material 201 thereto.
[0049] Avoiding the controlling bank 105b, the EL material 201 is
thus laminated on the pixel electrode 104. Accordingly, an EL layer
202 is formed on a portion of the pixel. That is, without
particularly using such as a shadow mask, the EL material can be
intensively formed on the pixel, thereby making it possible to
drastically improve the utilization efficiency of the EL
material.
[0050] Further, the present invention may be implemented in a
highly definite pixel portion, such as a pixel portion having a
pixel pitch of several tens of .mu.m, without any problems. In the
method of using a shadow mask to laminate the EL material, the
alignment precision of the shadow mask becomes a problem, and hence
is not a suitable method for the formation of a highly definite
pixel portion. In such a case, it can be stated that the
implementation of the present invention is extremely effective.
Embodiment 2
[0051] A case of implementing the present invention when film
depositing the EL material by the evaporation method will be
explained in Embodiment 2 with reference to FIG. 3.
[0052] In FIG. 3, reference symbol 301 denotes an evaporation
chamber, and a bulkhead 302 of the evaporation chamber is connected
to a negative power source 303 that will be charged with a negative
voltage. An evaporation boat 304 is provided inside the evaporation
chamber 301, and a solid state EL material 305 is provided inside
the evaporation boat 304. The evaporation boat 304 is heated by
using power sources 307a and 307b, which are connected to a
supporting platform 306. That is, Embodiment 2 uses an evaporation
source by resist heating. Right outside a hole that is provided in
the evaporation boat 304 (a hole for the EL material that has
turned into a gaseous body to exit to the outside of the
evaporation boat), a ring-like electrode 320 is provided so as to
surround the EL material which has turned into a gaseous body
(hereinafter referred to as a gaseous EL material) coming out from
the hole. The ring-like electrode 320 is connected to a negative
power source 308. An electric field is formed in the interior of
the ring-like electrode 320 to thereby charge the gaseous EL
material with a negative charge. In other words, the gaseous EL
material spurting from the evaporation boat 304 is made to pass
through the electric field while it is scattering to thereby apply
an electric charge. At this point, because the bulkhead 302 of the
evaporation chamber is charged with a negative charge, the EL
material that will adhere to the bulkhead 302 can be suppressed to
a minimum.
[0053] Avoiding the electric fields formed by controlling banks
310, the scattered gaseous EL material 309 is thus laminated on a
pixel electrode 311. A negative power source 312 is connected to
the controlling banks 310 to thereby form the electric field. It is
to be noted that all the controlling banks not shown in the drawing
are electrically connected so that they all have an equivalent
electric potential.
[0054] Further, at this point, a positive power source 314 is
connected to a source wiring of a TFT 313 to which the pixel
electrode 311 is connected, so that a positive voltage can be
applied to the pixel electrode 311. A substrate 315 having the TFT
313 formed thereon is held by a susceptor 316. The susceptor 316
may be charged with a negative charge during film deposition.
[0055] A positive voltage is applied to the pixel electrode 311 by
operating the TFT 313, which is electrically connected, to thereby
charge it with a positive charge. In other words, Embodiment 2 is
characterized in that the EL material is laminated on the pixel
electrode under the state of operating the TFT 313. Of course, it
is not always necessary that the TFT 313 be operated.
[0056] By adopting the above structure, the utilization efficiency
of the gaseous EL material 309 that is to be evaporated is
enhanced, thereby making it possible to form a desired EL layer
with the least essential amount of EL material. Accordingly, the
consumption amount of the EL material is substantially reduced, and
hence the manufacturing cost can be reduced.
[0057] Note that although an example of using a resist heating as
the evaporation source was shown here, electron beam (EB) heating
may be used.
[0058] Further, an example of charging the gaseous EL material with
a negative charge was shown in Embodiment 2, but it may be charged
with a positive charge. In the case of charging the gaseous EL
material with a positive charge, the bulkhead 302, the evaporation
boat 304, and the controlling banks 310 may be charged with a
positive charge whereas the pixel electrode 311 may be charge with
a negative charge.
Embodiment 3
[0059] A case of implementing the present invention when performing
the application of the EL material by using the ink jet method will
be explained in Embodiment 3 with reference to FIGS. 4A and 4B. The
processes illustrated in FIGS. 4A and 4B are performed under an
inert atmosphere (under a nitrogen gas or an inert gas).
[0060] In FIG. 4A, reference symbol 401 denotes a glass substrate,
402 denotes a TFT, 403 denotes a pixel electrode functioning as an
anode, and a positive power source 404 is connected to a source
wiring of the TFT 402. Further, a negative power source 406 is
connected to a controlling bank 405 in Embodiment 3. In this case,
all the controlling banks not shown in the drawing are electrically
connected so that they all have an equivalent electric
potential.
[0061] Heads 407 to 409 of a thin film formation apparatus for
laminating the EL material through the ink jet method are arranged
above the substrate 401. A solution 410 containing an EL material
for luminescing a red color is provided in the head 407, a solution
411 containing an EL material for luminescing a green color is
provided in the head 408, and a solution 412 containing an EL
material for luminescing a blue color is provided in the head 409.
These solutions containing the EL materials are discharged from the
heads by using a piezo device. Of course, the bubble jet system may
be used.
[0062] In Embodiment 3, negative power sources 413 to 415 are
connected to each of the heads 407 to 409 to thereby charge the EL
materials 410 to 412 with a negative charge. A solution containing
the EL material discharged under this state drops along the
trajectory indicated by the dotted line and is applied on the pixel
electrode 403 exposed between the banks. That is, the solutions 410
to 412 containing the negatively charged EL material are applied
into the pixels avoiding the negatively charged controlling bank
405, as expected.
[0063] Thus, an EL layer 416 corresponding to a red color
luminescence, an EL layer 417 corresponding to a green color
luminescence, and an EL layer 418 corresponding to a blue color
luminescence are formed inside the pixel. Note that although only
three pixels are shown in the drawing, the EL layers may be formed
in one pixel at a time or may be formed in a plurality of three or
more pixels at the same time.
[0064] Shown in FIG. 4B is an example of providing an electrode in
the vicinity of the discharging exit of the heads 407 to 409 for
the purpose of charging the solutions containing the EL material.
In Embodiment 3, an extraction electrode 421, an accelerating
electrode 422, and a controlling electrode 423 are provided in the
structure. Further, each of the above electrodes are connected to a
power source 424.
[0065] The extraction electrode 421 is an electrode for forming an
electric field to extract the solutions containing the EL materials
from the heads 407 to 409. The accelerating electrode 422 is an
electrode for forming an electric field to accelerate the EL
material that has been extracted, and the controlling electrode 423
is an electrode for forming an electric field to control the
position where the EL material will finally drop. Of course, there
is no need to always used these three electrodes and there is no
need to be limited to these combinations.
[0066] In the case of the structure shown in FIG. 4B, any one of
the three electrodes is used to charge the solutions containing the
EL material with a negative charge. Therefore, without the
necessity of particularly providing a power source to the heads 407
to 409, the extracted solutions containing the EL materials
themselves can be directly charged with an electric charge. In this
case, similar to the case of FIG. 4A, a solution containing the EL
material drops along the trajectory indicated by the dotted line
and is applied on the pixel electrode 403 exposed between the
banks. That is, the negatively charged EL material 409 to 411 are
applied into the pixels avoiding the negatively charged controlling
bank 404, as expected.
[0067] By adopting a structure such as the one described above, the
possibility of the trajectory becoming off the point during the
application of the EL material by the ink jet method can be
substantially reduced, whereby it becomes possible to improve the
yield. Accordingly, the manufacturing cost can be reduced.
[0068] An example of charging the solutions containing the EL
materials with a negative charge was shown in Embodiment 3.
However, the solutions may be charged with a positive charge. In
that case, the controlling bank 405 and the solutions 410 to 412
containing the EL materials are charged with a positive charge,
whereas the pixel electrode 403 is charged with a negative
charge.
Embodiment 4
[0069] In Embodiment 5, a case of implementing the present
invention when forming the EL layer by using the ion plating method
is shown in FIG. 5.
[0070] In FIG. 5, reference symbol 501 denotes an evaporation
chamber, and a bulkhead 502 of the evaporation chamber is connected
to a positive power source 503 that will be applied with a positive
voltage. An evaporation boat 504 is provided inside the evaporation
chamber 501, and a solid state EL material 505 is provided inside
the evaporation boat 504. The evaporation boat 504 is heated by
using power sources 507a and 507b, which are connected to a
supporting platform 506. That is, Embodiment 4 uses an evaporation
source generated by resist heating.
[0071] A conductor having an antenna 508 wound into a spiral shape
is provided above the evaporation boat 504. The antenna 508 is
connected to a high frequency power source 508a and is applied with
a high frequency in high vacuum. An electric wave (typically a
microwave) can thus be generated. In Embodiment 4, the electric
wave is applied to a vaporized gaseous EL material 509 to thereby
charge it with a positive charge. At this point, plasma may be
generated between the antenna 508. The plasma may be formed by
using a noble gas such as argon gas or neon gas. Because the
bulkhead 502 of the evaporation chamber is positively charged at
this point, the EL material that will adhere to the bulkhead 502
can be suppressed to a minimum.
[0072] Avoiding the electric fields formed by controlling banks
510, the scattered gaseous EL material 509 is thus laminated on a
pixel electrode 511. A positive power source 512 is connected to
the controlling banks 510 to thereby form the electric field. It is
to be noted that all the controlling banks not shown in the drawing
are electrically connected so that they all have an equivalent
electric potential.
[0073] Further, at this point, a negative power source 514 is
connected to a source wiring of a TFT 513 to which the pixel
electrode 511 is connected, so that a negative voltage can be
applied to the pixel electrode 511. A substrate 515 having the TFT
513 formed thereon is held by a susceptor 516. The susceptor 516
may be charged with a negative charge during film deposition.
[0074] A negative voltage is applied to the pixel electrode 511 by
operating the TFT 513, which is electrically connected, to thereby
charge the pixel electrode 511 with a negative charge. In other
words, Embodiment 4 is characterized in that the EL material is
laminated on the pixel electrode under the state of operating the
TFT 513. Of course, it is not always necessary that the TFT 513 be
operated.
[0075] By adopting the above structure, the utilization efficiency
of the gaseous EL material 509 that is to be evaporated is
enhanced, thereby making it possible to form a desired EL layer
with the least essential amount of EL material. Accordingly, the
amount of EL material consumed is substantially reduced, and hence
the manufacturing cost can be reduced.
[0076] Note that although Embodiment 4 takes the method of charging
a positive charge to the gaseous EL material 509 by applying the
electric field that was formed between the electrodes 508a and
508b, the gaseous EL material 509 can be charged with a positive
charge by applying a bias voltage between the anode 511 and the
evaporation boat 504.
[0077] Further, an example of positively charging the gaseous EL
material was shown in Embodiment 4. However, the gaseous EL
material may be charged with a negative charge. In that case, the
bulkhead 502, the evaporation boat 504, and the controlling banks
510 are charged with a negative charge whereas the anode 511 is
charged with a positive charge.
Embodiment 5
[0078] Shown in FIG. 6 is a sectional view of a pixel portion of
the light emitting device according to the present invention, and
FIG. 7A is a top view of the pixel portion thereof whereas FIG. 7B
illustrates the circuit configuration of the pixel portion thereof.
Actually, plural pixels are arranged in matrix to thereby form the
pixel portion (image display portion). Therefore, common reference
symbols are used in FIG. 6 and FIGS. 7A and 7B, and both figures
may be conveniently referenced. In addition, two pixels shown in
the top view of FIG. 7A share the same structure. FIG. 7C
illustrates an enlarged cross sectional view of 80 in FIG. 7A.
Reference numerals 81 and 82 denote the supporting bank and
controlling bank, respectively.
[0079] In FIG. 6, reference symbol 11 denotes a substrate and
reference symbol 12 denotes an insulating film that serves as a
base (hereinafter referred to as a base film). Substrates usable as
the substrate 11 include a glass substrate, a glass ceramic
substrate, a quartz substrate, a silicon substrate, a ceramic
substrate, a metal substrate, and a plastic substrate.
[0080] The base film 12 is effective particularly in using a
substrate containing a movable ion or a substrate having a
conductivity. However, the base film is not necessarily provided on
a quartz substrate. An insulating film containing silicon is
suitable as the base film 12. To give heat releasing action to the
base film 12 to release heat generated from the TFT is also
effective in preventing degradation of the TFT or degradation of
the EL element. Any known material may be used to impart the heat
releasing effect to the base film.
[0081] In Embodiment 5, two TFTs are formed in each pixel.
Reference symbol 601 denotes a switching TFT that is formed of an
n-channel TFT, and reference symbol 602 denotes a current
controlling TFT that is formed of a p-channel TFT.
[0082] However, according to the present invention, the switching
TFT and the current controlling TFT are not necessarily limited to
the above combination of n-channel TFT and p-channel TFT. The
switching TFT can be formed of the p-channel TFT whereas the
current controlling TFT can be formed of the n-channel TFT, or the
n-channel TFT or the p-channel TFT may be used to form both
TFTs.
[0083] The switching TFT 601 is formed to have a source region 13,
a drain region 14, LDD regions 15a to 15d, an active layer
including a high concentration impurity region 16 and channel
forming regions 17a and 17b, a gate insulating film 18, gate
electrodes 19a and 19b, a first interlayer insulating film 20, a
source wiring 21, and a drain wiring 22.
[0084] As shown in FIG. 7A, the gate electrodes 19a and 19b
constitute the double gate structure in which a gate wiring 611
formed from a different material used for forming the gate
electrodes 19a and 19b (a material less resistive than the gate
electrodes 19a and 19b) electrically connects the gate electrode
19a to the gate electrode 19b. The structure of the gate electrodes
of course is not limited to the double gate structure, but may be
formed to have a single gate structure or a triple gate structure,
that is, the so called multi-gate structure (a structure containing
an active layer that has two or more channel forming regions
connected in series). The multi-gate structure is extremely
effective in terms of reducing an OFF current value. Therefore, the
switching element 601 of the pixel is formed to have a multi-gate
structure in the present invention to thereby realize a switching
element having a low OFF current value.
[0085] The active layer is formed of a semiconductor film
containing a crystalline structure. In other words, the active
layer may be formed of a single crystal semiconductor film or it
may be formed of a poly-crystalline semiconductor film or a
micro-crystalline semiconductor film. Further, the gate insulating
film 18 may be formed of an insulating film containing silicon. All
kinds of conductive films can be used as the gate electrodes, the
source wiring, or the drain wiring. Furthermore, the LDD regions
15a to 15d in the switching TFT 601 are formed so as not to overlap
with the gate electrodes 19a and 19b through the gate insulating
film 18 sandwiched therebetween. This structure is very effective
in lowering the OFF current value.
[0086] Note that it is even more preferable to provide an off set
region (a region which is formed from a semiconductor layer having
the same composition as the channel forming regions and to which a
gate voltage is not applied) between the channel forming regions
and the LDD regions to reduce the OFF current value. In addition,
in the case where the switching TFT 601 is a multi-gate structure
having more than two gate electrodes, then the high concentration
impurity region provided between the channel forming regions is
effective in reducing the OFF current value.
[0087] Next, the current controlling TFT 602 is formed to have a
source region 31, a drain region 32, an active layer including a
drain region 32 and a channel forming region 34, a gate insulating
film 18, a gate electrode 35, a first interlayer insulating film
20, a source wiring 36, and a drain wiring 37. It is to be noted
that the gate electrode 35 is formed having a single gate
structure, but it may take a multi-gate structure.
[0088] As shown in FIG. 7A, the drain of the switching TFT 601 is
connected to the gate of the current controlling TFT 602. To be
more specific, the gate electrode 35 of the current controlling TFT
602 is electrically connected to the drain region 14 of the
switching TFT 601 via the drain wiring 22 (may also be called a
connecting wiring). Further, the source wiring 36 is a current
supply line and is connected to a supply source of the current
flowing to the EL element.
[0089] Although the current controlling TFT 602 is an element for
controlling the amount of current injected into the EL element 603,
taking into consideration the deterioration of the EL element, it
is not preferable to cause too large a current to flow in the
current controlling TFT 602. Therefore, it is preferable that a
channel length (L) of the current controlling TFT 602 is designed
longer so that excessive current will not flow therein. Desirably,
the channel length thereof is designed so that it is between 0.5
and 2 .mu.A (preferably between 1 and 1.5 .mu.A) per pixel.
[0090] In addition, the length (width) of the LDD region that is
formed in the switching TFT 601 may be between 0.5 and 3.5 .mu.m,
typically between 2.0 and 2.5 .mu.m.
[0091] As shown in FIG. 7A, in a region denoted by the reference
symbol 50, a wiring including the gate electrode 35 of the current
controlling TFT 602 is formed to overlap with an insulating film
and the source wiring (current supply line) 36 of the current
controlling TFT 602 sandwiched therebetween. In the region denoted
by the reference symbol 50, a storage capacitor (condenser) is
formed at this point. A semiconductor film 51 that is electrically
connected to the source wiring 36, an insulating film (not shown in
the figure) formed on the same layer as the gate insulating film,
and a capacitance formed by the power source supply line 36 may be
used as the storage capacitor 50.
[0092] The storage capacitor 50 functions as a condenser for
maintaining the voltage that is applied to the gate electrode 35 of
the current controlling TFT 602.
[0093] Further, from the perspective of increasing the amount of
current that may flow, it is also effective to make the film
thickness of the active layer (particularly the channel forming
region) of the current controlling TFT 602 thicker (preferably
between 50 and 100 nm, further preferably between 60 and 80 nm).
Conversely, from the perspective of making the OFF current value
smaller in the case of the switching TFT 601, it is effective to
make the film thickness of the active layer (particularly the
channel forming region) of the switching TFT 601 thinner
(preferably between 20 and 50 nm, further preferably between 25 and
40 nm).
[0094] In the case of performing a gradation display by means of an
analog gradation system, operating the current controlling TFT 602
in a saturated region is preferable. On the other hand, in the case
of performing the gradation display by means of a digital gradation
system, it is preferable to operate the current controlling TFT 602
in a linear region.
[0095] Next, reference symbol 38 denotes a passivation film and the
film thickness thereof may be between 10 nm and 1 .mu.m (preferably
between 200 and 500 nm). As a material for forming the passivation
film 38, an insulating film containing silicon (a silicon
oxynitride film or a silicon nitride film is particularly
preferable) can be used.
[0096] A second interlayer insulating film (may also be called a
planarizing film) 39 is formed on the passivation film 38 so as to
cover each of the TFTs to thereby level out a level difference
caused by the TFTs. A preferred material for the second interlayer
insulating film 39 is an organic resin film, and a polyimide film,
a polyamide film, an acrylic resin film, a BCB (benzocyclobuten)
film, and the like, are also appropriate. Of course, an inorganic
film may be used if it can satisfactorily level out the level
difference.
[0097] It is very important to level out the level difference
caused by the TFT using the second interlayer insulating film 39.
The EL layer to be formed later is extremely thin so that the
existence of a level difference may lead to inferior light
emission. Therefore, planarization before formation of a pixel
electrode is desirable, so that the EL layer can be formed on a
surface as flat as possible.
[0098] Denoted by reference symbol 40 is a pixel electrode formed
from a transparent conductive film (corresponds to the anode of the
EL element). The pixel electrode 40 is formed by opening a contact
hole (aperture) piercing through the second interlayer insulating
film 39 and the passivation film 38, and then being brought into
connection, in the thus formed aperture portion, with the drain
wiring 37 of the current controlling TFT 602.
[0099] In Embodiment 5, a conductive film made of a compound of
indium oxide and tin oxide is used as the pixel electrode 40. In
addition, a small amount of gallium may be doped therein. A
compound of indium oxide and zinc oxide or a compound of zinc oxide
and gallium oxide may also be used.
[0100] Upon formation of the pixel electrode 40, a supporting bank
41a made of a resin film is formed, and a controlling bank 41b made
of a metal film is formed thereon. At the same time, an insulating
film 42 for filling up the contact hole of the pixel electrode 40
(hereinafter referred to as a filling-up material) is formed. In
Embodiment 5, the supporting bank 41a and the filling-up material
42 are formed from an acrylic film, and the controlling bank 41b is
formed from a tungsten film.
[0101] At this point, the supporting bank 41a and the filling-up
material 42, which are made from acrylic, are formed to a film
thickness of 300 nm or less, preferably between 100 and 200 nm. It
is preferable that the supporting bank 41a and the filling-up
material 42 are formed so that the edge portions thereof are taper
shaped. Further, the controlling bank 41b that is made from a
tungsten film is also formed so that the edge portion thereof is
preferably taper shaped.
[0102] As shown in FIG. 1A, the supporting bank 41a and the
controlling bank 41b are formed surrounding the edge portions of
the pixel electrode 40.
[0103] An EL layer 43 is formed next by using the film deposition
methods explained in FIGS. 2 to 5. It is to be noted that although
only one pixel is shown here, EL layers corresponding to each of
the colors R (red), G (green), and B (blue) are formed. In
Embodiment 5, the evaporation method illustrated in FIG. 2 is
adopted, and a low molecular weight type EL material is used as the
EL material.
[0104] Note that as the EL materials used in Embodiment 5, a
material using Alq.sub.3, as the host material and doped with a red
fluorescent pigment DCM is used for the EL layer luminescing a red
color. Further, for the EL layer luminescing a green color,
Alq.sub.3, which is an aluminum-8-hydroxyquinoline complex, is
used, and a benzoxazole complex of zinc (Zn(oxz).sub.2) is used for
the EL layer luminescing a blue color.
[0105] However, the examples of the materials mentioned above are
merely an example of EL materials usable as the EL layer of the
present invention, and that there is no need to limit the EL
material to these. That is, high molecular weight type EL materials
that are not described here may be used, and furthermore, a low
molecular weight type EL material and a high molecular weight type
material may be used together.
[0106] Thus, upon forming the EL layer 43, a cathode 44 is next
formed from a metal film. In Embodiment 5, an alloy film in which
lithium is doped into aluminum is used as the cathode 44. Note that
an insulating film may be formed on the cathode 44 as a passivation
film (not shown in the figure).
[0107] An EL element 603 that is composed of the pixel electrode
40, the EL layer 43, and the cathode 44 is thus formed. Actually,
it is desirable that the structure of the EL element is formed in a
way so that the EL element does not come into contact with the open
air. In order to prevent exposure to the open air, after forming
the EL element 603, a covering member is provided on the EL element
603 to thereby perform sealing under an inert atmosphere, or
sealing is performed by providing resin on the entire surface
thereof.
[0108] The provision of a moisture absorbent agent (typically
barium oxide) or an antioxidant in the airtight space or the resin
is also effective.
[0109] Any one of the structures of Embodiments 1 to 4 can be used
to manufacture the light emitting device of Embodiment 5.
Embodiment 6
[0110] In Embodiment 6, an explanation is made on a method of
manufacturing a pixel portion and a TFT of a driver circuit portion
simultaneously that is provided in the periphery of the pixel
portion with reference to FIGS. 8A to 10C. However, in order to
simplify the explanation, a CMOS circuit, which is the basic
circuit for the driver circuit, is shown in the figures.
[0111] First, as shown in FIG. 8A, a base film 801 is formed to a
thickness of 300 nm on a glass substrate 800. A lamination film
constituting a 100 nm thick silicon oxynitride film and a 200 nm
thick silicon oxynitride film is used as the base film 801 in
Embodiment 6. At this point, it is appropriate to set the nitrogen
concentration of the silicon oxynitride film that is in contact
with the glass substrate 800 to between 10 and 25 wt %. Of course,
an element may be directly formed on a quartz substrate without the
provision of the base film.
[0112] Next, an amorphous silicon film (not shown in the figure) is
formed to a thickness of 50 nm on the base film 801 by using a
known film deposition method. Note that the present invention is
not necessarily limited to using the amorphous silicon film, but a
semiconductor film containing an amorphous structure (including a
micro-crystalline semiconductor film) may be used. In addition, a
compound semiconductor film containing an amorphous structure such
as an amorphous silicon germanium film may also be used, and the
film thickness thereof may be between 20 and 100 nm.
[0113] The amorphous silicon film is then crystallized by a known
method to thereby form a crystalline silicon film (also referred to
as a polycrystalline silicon film or a polysilicon film) 802.
Thermal crystallization using an electric furnace, laser annealing
crystallization using a laser, and lamp annealing crystallization
using infrared light exist as known crystallization methods.
Crystallization is performed in Embodiment 6 using light from an
excimer laser which uses XeCl gas.
[0114] Note that the pulse emission type excimer laser light
processed into a linear shape is used in Embodiment 6, but a
rectangular shape may also be used, and that continuous emission
type argon laser light and continuous emission excimer type laser
light can also be used.
[0115] In Embodiment 6, although the crystalline silicon film is
used as the active layer of the TFT, it is also possible to use an
amorphous silicon film. Furthermore, it is also possible to use the
amorphous silicon to form the active layer of the switching TFT,
which requires a lowering of the OFF current value, while using the
crystalline silicon film to form the active layer of the current
controlling TFT. Carrier mobility is low in the amorphous silicon
film, and therefore it is difficult for a current to flow therein,
and as a result, it is difficult for an OFF current to flow. That
is, the merits of both the amorphous silicon film in which it is
hard to flow a current therein and the crystalline silicon film in
which it is easy to flow a current therein can be utilized
advantageously. Next, as shown in FIG. 8B, a protective film 803
made of a silicon oxide film is formed to a thickness of 130 nm on
the crystalline silicon film 802. The thickness thereof may be
chosen from within the range of 100 to 200 nm (preferably between
130 and 170 nm). Furthermore, other films may also be used provided
that they are insulating films containing silicon. The protective
film 803 is provided so that the crystalline silicon film is not
directly exposed to plasma during the doping of an impurity and to
make it possible to have delicate concentration control of the
impurity.
[0116] Resist masks 804a and 804b are then formed on the protective
film 803, and an impurity element that imparts n-type conductivity
(hereafter referred to as n-type impurity element) is doped therein
through the protective film 803. Note that elements belonging to
the Periodic Table Group 15 are generally used as the n-type
impurity element. Typically, phosphorus or arsenic can be used.
Also note that in Embodiment 6, a plasma (ion) doping method in
which phosphine (PH.sub.3) is plasma activated without separation
of mass is used, and that phosphorus is doped at a concentration of
1.times.10.sup.18 atoms/cm.sup.3. The ion implantation method, in
which separation of mass is performed, may also be used, of
course.
[0117] In an n-type impurity region 805 thus formed by this
process, the dose amount of the n-type impurity element contained
therein is regulated so that the concentration thereof is
2.times.10.sup.16 to 5.times.10.sup.19 atoms/cm.sup.3 (typically
between 5.times.10.sup.17 and 5.times.10.sup.18
atoms/cm.sup.3).
[0118] Next, as shown in FIG. 8C, the protective film 803 and the
resists 804a and 804b are removed to thereby activate the element
belonging to Periodic Table Group 15 that is doped therein. A known
activation technique may be used as the means of activation, and in
Embodiment 6, activation is conducted by irradiation of an excimer
laser light. Without being necessarily limited to the use of the
excimer laser light, a pulse emission type excimer laser and a
continuous emission type excimer laser may both, of course, be
used. The aim here is the activation of the doped impurity element,
and therefore it is preferable that irradiation is performed at an
energy level at which the crystalline silicon film does not melt.
Note that the laser irradiation may also be performed with the
protective film 803 provided thereon.
[0119] It is to be noted that during the activation of the impurity
element by laser light, activation by heat treatment may also be
performed along therewith. When activation is performed by heat
treatment, in considering the heat resistance of the substrate, it
is appropriate to perform a heat treatment on the order of 450 to
550.degree. C.
[0120] Due to this process, edge portions of the n-type impurity
region 805, that is, a boundary portion (connecting portion) and
regions existing in the periphery of the n-type impurity regions
805 and not doped with the n-type impurity element will become
distinct. This means that, at the point when the TFTs are later
completed, extremely good connecting portions can be formed between
LDD regions and channel forming regions. As shown in FIG. 8D,
unnecessary portions of the crystalline silicon film are removed
next to thereby form island-like semiconductor films (hereinafter
referred to as active layers) 806 to 809.
[0121] Then, as shown in FIG. 8E, a gate insulating film 810 is
formed covering the active layers 806 to 809. An insulating film
containing silicon and having a thickness of 10 to 200 nm,
preferably between 50 and 150 nm, may be used as the gate
insulating film 810. The film thereof may take a single layer
structure or a lamination structure. A 110 nm thick silicon
oxynitride film is used in Embodiment 6.
[0122] A 200 to 400 nm thick conductive film is formed next and
patterned, thereby forming gate electrodes 811 to 815. The edge
portions of the gate electrodes 811 to 815 may be formed into taper
shapes. Note that in Embodiment 6, the gate electrodes and lead
wirings that are electrically connected to the gate electrodes
(hereinafter referred to as gate wirings) are formed from different
materials. Specifically, a material having a lower resistance than
that of the gate electrodes is used as the gate wirings. The reason
for this resides in that a material which is capable of being
micro-processed is used as the gate electrodes, and even if the
material for the gate wirings cannot be micro-processed, materials
having lower resistance is used for the gate wirings. Of course,
the gate electrodes and the gate wirings may also be formed from
the same material.
[0123] Further, the gate electrodes may be formed from a single
layer conductive film, and if necessary, it is preferable to use a
two layer or a three layer lamination film. All known conductive
films can be used as the material for the gate electrodes. However,
as stated above, it is preferable to use a material which can be
micro-processed, specifically, a material which can be patterned to
a line width of 2 .mu.m or less.
[0124] Typically, it is possible to use a film made of an element
selected from the group consisting of tantalum (Ta), titanium (Ti),
molybdenum (Mo), tungsten (W), chromium (Cr), and silicon (Si), or
a nitride film containing the above elements (typically a tantalum
nitride film, a tungsten nitride film, or a titanium nitride film),
or an alloy film having a combination of the above elements
(typically an Mo--W alloy or an Mo--Ta alloy), or a silicide film
of the above elements (typically a tungsten suicide film or a
titanium silicide film). Of course, the films may be used as a
single layer or a laminate layer.
[0125] A lamination film that is composed of a 50 nm thick tantalum
nitride (TaN) film and a 350 nm thick tungsten (W) film is used in
Embodiment 6. These films may be formed by sputtering. Further,
when an inert gas such as Xe or Ne is added as a sputtering gas,
peeling of the films due to stress can be prevented.
[0126] At this point, a gate electrode 812 is formed so as to
overlap a portion of the n-type impurity region 805 and the gate
insulating film 810, with the gate insulating film 810 sandwiched
therebetween. This overlapping portion later becomes an LDD region
overlapping the gate electrode. Note that in a cross-sectional
view, gate electrodes 813 and 814 can be seen as two electrodes,
but they are actually electrically connected.
[0127] Next, as shown in FIG. 9A, an n-type impurity element
(phosphorus is used in Embodiment 6) is doped in a self-aligning
manner using the gate electrodes 811 to 815 as masks. The doping of
phosphorus is regulated so that it can be doped into the impurity
regions 816 to 823 thus formed at a concentration of 1/2 to
{fraction (1/10)} that of the n-type impurity region 805 (typically
between 1/3 and 1/4). To be more specific, a concentration of
1.times.10.sup.16 to 5.times.10.sup.18 atoms/cm.sup.3 (typically
3.times.10.sup.17 to 3.times.10.sup.18 atoms/cm.sup.3) is
preferable.
[0128] As shown in FIG. 9B, resist masks 824a to 824d are formed
next covering the gate electrodes and the like, and an n-type
impurity element (phosphorus is used in Embodiment 6) is doped to
thereby form impurity regions 825 to 829 containing a high
concentration of phosphorus. Ion doping using phosphine (PH.sub.3)
is also performed here, and the concentration of phosphorus in
these regions is regulated so that it is between 1.times.10.sup.20
and 1.times.10.sup.21 atoms/cm.sup.3 (typically between
2.times.10.sup.20 and 5.times.10.sup.20 atoms/cm.sup.3).
[0129] A source region or a drain region of the n-channel TFT is
formed through this process, and in the switching TFT, a portion of
the n-type impurity regions 819 to 821 formed through the process
of FIG. 9A remains. These remaining regions correspond to the LDD
regions 15a to 15d of the switching TFT 601 in FIG. 6.
[0130] Next, as shown in FIG. 9C, the resist masks 824a to 824d are
removed, and a new resist mask 832 is formed. A p-type impurity
element (boron is used in Embodiment 6) is then doped to thereby
form impurity regions 833 to 836 containing a high concentration of
boron. Boron is doped here by ion doping using diborane
(B.sub.2H.sub.6) so that the concentration thereof is
3.times.10.sup.20 to 3.times.10.sup.21 atoms/cm.sup.3 (typically
between 5.times.10.sup.20 and 1.times.10.sup.21
atoms/cm.sup.3).
[0131] Note that phosphorus has already been doped into the
impurity regions 833 to 836 at a concentration of 1.times.10.sup.20
to 1.times.10.sup.21 atoms/cm.sup.3, but boron is doped here at a
concentration of at least 3 times higher than that of phosphorus.
Therefore, the n-type impurity regions that have been formed in
advance are completely inverted to have the p-type conductivity,
thereby functioning as p-type impurity regions.
[0132] Next, after removing the resist mask 832, the n-type and
p-type impurity elements doped at respective concentrations are
activated. Furnace annealing, laser annealing, or lamp annealing
may be performed as a means of activation. Heat treatment is
performed in Embodiment 6 under a nitrogen atmosphere for 4 hours
at 550.degree. C. in an electric furnace.
[0133] It is important to remove as much oxygen as possible
contained in the atmosphere at this point. This is because even a
small trace of oxygen exists, then the exposed surface of the
electrode is oxidized, inviting an increase in resistance, and at
the same time, it becomes more difficult to make an ohmic contact
later. It is therefore preferable that the concentration of oxygen
in the processing environment in the above activation process is
set to 1 ppm or less, desirably 0.1 ppm or less.
[0134] After the activation process is completed, a gate wiring 837
is next formed to a thickness of 300 nm as shown in FIG. 9D. A
metal having aluminum (Al) or copper (Cu) as its principal
constituent (comprising 50 to 100% of the composition) may be used
as the material of the gate wiring 837. Regarding the placement of
the gate wiring 837, it is formed so that the gate wiring 611 and
the gate electrodes 19a and 19b of the switching TFT (corresponding
to gate electrodes 813 and 814 of FIG. 8E) are electrically
connected as in FIG. 7.
[0135] The wiring resistance of the gate wiring can be made
extremely small by forming such a type of structure, and therefore
a pixel display region (pixel portion) having a large surface area
can be formed. That is, the pixel structure of Embodiment 6 is
extremely effective when realizing a light emitting device having a
screen size of a 10 inch diagonal or larger (in addition, a 30 inch
or larger diagonal).
[0136] Next, as shown in FIG. 10A, a first interlayer insulating
film 838 is formed. As the first interlayer insulating film 838,
either a single layer insulating film containing silicon is used,
or a lamination film in which two or more types of insulating film
containing silicon are combined may be used. Further, it is
appropriate to set the film thickness thereof between 400 nm and
1.5 .mu.m. A structure in which an 800 nm thick silicon oxide film
is formed laminated on a 200 nm thick silicon oxynitride film is
used in Embodiment 6.
[0137] Additional heat treatment is performed under an atmosphere
containing 3% to 100% of hydrogen for 1 to 12 hours at a
temperature of between 300.degree. C. and 450.degree. C. to thereby
perform hydrogenation. This process is one for terminating the
dangling bonds in the semiconductor film caused thermally excited
hydrogen. Plasma hydrogenation (using hydrogen generated by plasma)
may be performed as another means of hydrogenation.
[0138] Note that the hydrogenation process may also be inserted
between the step of forming of the first interlayer insulating film
838. That is, hydrogenation processing such as the above may be
performed after forming the 200 nm thick silicon oxynitride film,
and then the remaining 800 nm thick silicon oxide film may be
formed.
[0139] Next, a contact hole is formed in the first interlayer
insulating film 838 and the gate insulating film 810 to thereby
form source wirings 839 to 842 and drain wirings 843 to 845. It is
to be noted that in Embodiment 6, this electrode is made of a
lamination film composed of a three layer structure in which a Ti
film having a thickness of 100 nm, an aluminum film containing Ti
and having a thickness of 300 nm, and a Ti film having a thickness
of 150 nm are formed in succession by sputtering. Of course, other
conductive films may be used.
[0140] Next, a first passivation film 846 is formed to a thickness
of 50 to 500 nm (typically between 200 and 300 nm). A 300 nm thick
silicon oxynitride film is used as the first passivation film 846
in Embodiment 6. This may also be substituted with a silicon
nitride film.
[0141] Note that it is effective to perform plasma treatment using
a gas containing hydrogen such as H.sub.2 or NH.sub.3 prior to the
formation of the silicon oxynitride film. Hydrogen excited by this
pre-process is supplied to the first interlayer insulating film
838, and the film quality of the passivation film 846 is improved
by performing heat treatment. At the same time, the hydrogen doped
into the first interlayer insulating film 838 diffuses to the lower
layer side, and therefore the active layers can be effectively
hydrogenated.
[0142] Next, as shown in FIG. 10B, a second interlayer insulating
film 847 made of an organic resin is formed. As the organic resin,
materials such as polyimide, polyamide, acrylic resin, or BCB
(benzocyclobutene) can be used. In particular, because the second
interlayer insulating film 847 is primarily used for leveling,
acrylic resin that has excellent leveling properties is preferable.
In Embodiment 6, an acrylic resin film is formed to a thickness
that is sufficient to level a step difference formed by TFTs. A
preferred film thickness thereof is between 1 to 5 .mu.m (more
preferably between 2 and 4 .mu.m).
[0143] A contact hole is formed in the second interlayer insulating
film 847 and the first passivation film 846 to thereby form a pixel
electrode 848 to be electrically connected to the drain wiring 845.
In Embodiment 6, an indium tin oxide (ITO) film is formed to a
thickness of 110 nm, and patterning is carried out to thereby form
the pixel electrode. Incidentally, as other materials, it is also
possible to use a compound in which 2 to 20% of zinc oxide (ZnO) is
mixed in indium oxide or a compound constituting zinc oxide and
gallium oxide may be used as a transparent electrode. The pixel
electrode 848 becomes the anode of the EL element.
[0144] As shown in FIG. 10C, a supporting bank 849a and a
filling-up material 850 made of resin are formed next. An acrylic
film is formed to a thickness of 500 nm, and thereafter, etching is
performed so that the film thickness thereof becomes 200 nm. Then
the acrylic film is patterned to thereby form the supporting bank
849a and the filling-up material 850 to have the shape as shown in
FIG. 10C.
[0145] A controlling bank 849b made of a metal film is further
formed on the supporting bank 849a. In Embodiment 6, a tungsten
film is used as the metal film, and it is formed into a taper shape
during etching. A technique for forming a taper shape disclosed in
Japanese Patent Application Laid-Open No. 2001-035808 by the
present applicant may be referenced.
[0146] An EL layer 851 is formed next by using the methods that
were illustrated in FIGS. 2 to 5. It is to be noted that although
only one pixel is shown here, the EL layers corresponding to each
of the colors R (red), G (green), and B (blue) are formed. As the
EL materials used in Embodiment 6, a material that uses Alq.sub.3
as the host material and doped with a red fluorescent pigment DCM
is used for the EL layer luminescing a red color. Further, for the
EL layer luminescing a green color, Alq.sub.3, which is an
aluminum-8-hydroxyquinoline complex, is used, and a benzoxazole
complex of zinc (Zn(oxz).sub.2) is used for the EL layer
luminescing a blue color. The respective EL layers are formed to a
thickness of 50 nm.
[0147] It is to be noted that in Embodiment 6 the EL layer 851 it
takes a single layer structure. However, an electron injecting
layer, an electron transporting layer, a hole transporting layer, a
hole injecting layer, an electron preventing layer, or a hole
element layer may be provided if necessary.
[0148] A cathode 852 made of an alloy film constituting aluminum
and lithium is formed by vacuum evaporation after the formation of
the EL layer 851. It is to be noted that the film thickness of the
EL layer 851 may appropriately be formed to between 30 and 100 nm
(typically between 50 and 80 nm) and the thickness of the cathode
852 to between 150 and 300 nm (typically between 200 and 250 nm).
Although Embodiment 6 shows an example of using the alloy film of
aluminum and lithium as the cathode 852 of the EL element, other
known materials may be used. Shown in FIGS. 11A and 11B here is the
cross-sectional structure of an n-channel TFT when it is used as
the switching TFT. First, in FIG. 11A, the LDD regions 15a to 15d
provided so as not to overlap with the gate electrodes 19a and 19b
through the gate insulating film 18 sandwiched therebetween. Such
structure is very effective in lowering the OFF current value.
[0149] With respect to the above structure of FIG. 11A, in the
structure thereof shown in FIG. 11B, the LDD regions 15a to 15d are
not provided. In the case of adopting the structure of FIG. 11B,
productivity can be improved because the number of processes can be
reduced when compared with case of forming the structure of FIG.
11A.
[0150] In the present invention, a TFT may take either structure
shown in FIGS. 11A and 11B as the switching TFT.
[0151] Next, in the case of using an n-channel TFT as the current
controlling TFT, the cross-sectional structure views thereof is
illustrated in FIGS. 12A and 12B. First, in the current controlling
TFT shown in FIG. 12A, the LDD region 33 is provided between the
drain region 32 and the channel forming region 34. The structure of
the current controlling TFT shown here has a region where the LDD
region 33 overlaps with the gate electrode 35 through the gate
insulating film 18 sandwiched therebetween and a region where the
LDD region 33 does not overlap with the gate electrode 35. However,
as shown in FIG. 12B, the LDD region 33 need not be provided in the
structure thereof.
[0152] The current controlling TFT supplies a current for causing
the EL element to emit light, and at the same time controls the
supply amount to enable gradation display. Thus, it is necessary to
take a countermeasure against deterioration due to the hot carrier
injection so that deterioration does not occur even if a current is
supplied.
[0153] Regarding deterioration caused by the hot carrier injection,
it is known that a structure where the LDD region overlaps with the
gate electrode is very effective. Therefore, the structure in which
the LDD region is provided overlapping with the gate electrode 35
through the gate insulating film 18 sandwiched therebetween as
shown in FIG. 12A is appropriate. However, in the structure shown
here, the LDD region is provided so as not to overlap with the gate
electrode as a countermeasure against the OFF current value.
Nevertheless, an LDD region not overlapping the gate electrode does
not have to be necessarily provided.
[0154] Further, if a voltage that is applied between the source
region and the drain region of the current controlling TFT is 10 V
or less, preferably 5 V or less, then hot carrier deterioration
cease to become a problem, whereby the LDD region need not be
provided in the structure as shown in FIG. 12B.
[0155] In the case of Embodiment 6, as shown in FIG. 10C, the
active layer of the n-channel TFT 605 contains a source region 855,
a drain region 856, an LDD region 857, and a channel forming region
858. The LDD region 857 overlaps with the gate electrode 812
through the gate insulating film 810 sandwiched therebetween.
[0156] The LDD region is formed only on the drain region side in
consideration of not to drop the operating speed. Further, it is
not necessary to pay very much attention to the OFF current value
in the n-channel TFT 605, but rather, it is better to place
importance on the operating speed. Thus, it is desirable that the
LDD region 857 is formed to completely overlap with the gate
electrode to reduce the resist component to a minimum. That is, it
is preferable to remove the so-called offset. An active matrix
substrate having a structure as shown in FIG. 10C is thus
completed. In the active matrix substrate of Embodiment 6, a TFT
having an optimum structure is not only provided in the pixel
portion but also in the driver circuit portion. Therefore, very
high reliability is attained and operating characteristics may be
improved.
[0157] First, a TFT having a structure that will decrease hot
carrier injection so as not to drop the operating speed thereof as
much as possible is used as the n-channel TFT 605 of a CMOS circuit
forming the driver circuit portion. Incidentally, the driver
circuit here includes a shift register, a buffer, a level shifter,
a sampling circuit (sample and hold circuit) and the like. In the
case of performing digital driving, a signal conversion circuit
such as a D/A converter is also included therein.
[0158] Further, after completing through FIG. 10C, actually, the
packaging (sealing) of the active matrix substrate with a covering
member such as glass, quartz, or plastic, which has airtightness
properties, is preferably performed so that the substrate is not
exposed to the open air. At that point, it is appropriate to place
a moisture absorbent agent such as barium oxide or an anti-oxidant
inside the covering member.
[0159] After enhancing the airtightness by conducting the packaging
process or the like, a connecter (flexible printed circuit: FPC)
for connecting the element formed on the insulator or a terminal
lead out from the circuit to an external signal terminal is
attached, whereby the light emitting device is completed as a
product. In this specification, the product in such a state that it
can be shipped is called an EL display device (or an EL
module).
[0160] Note that an IC using a single crystal silicon may be
provided as the driver circuit for transmitting a signal to the
pixel portion, a memory, a control circuit, a power source circuit
or the like. In this case, the IC may be connected by using a TAB
or a COG, or a method of connecting the IC that is incorporated in
a printed wiring board with a TAB tape may be adopted.
[0161] An explanation will be made here on the structure of the
light emitting device of Embodiment 6 with reference to the
perspective view of FIG. 13. The light emitting device of
Embodiment 6 is composed of a pixel portion 1302, a gate side
driver circuit 1303, and a source side driver circuit 1304 formed
on a glass substrate 1301. A switching TFT 1305 of the pixel
portion is an n-channel TFT and is arranged at an intersection
point of a gate wiring 1306 that is connected to the gate side
driver circuit 1303 and a source wiring 1307 that is connected to
the source side driver circuit 1304. Further, a drain of the
switching TFT 1305 is connected to a gate of a current controlling
TFT 1308. A reference numeral 1315 denotes a capacitor.
[0162] Further, a source side of the current controlling TFT 1308
is connected to a power supply line 1309. An EL element 1310 is
connected to a drain of the current controlling TFT 1308. Further,
a predetermined voltage is applied to the cathode of the EL element
1310.
[0163] Connecting wirings 1312 and 1313 for transmitting signals to
the driver circuit portion and a connecting wiring 1314 connected
to the power supply line 1309 are provided in an FPC 1311 serving
as an external input/output terminal.
[0164] An example of a circuit configuration of the light emitting
device shown in FIG. 13 is illustrated in FIG. 14. The light
emitting device of Embodiment 6 includes a source side driver
circuit 1401, a gate side driver circuit (A) 1407, a gate side
driver circuit (B) 1411, and a pixel portion 1406. Note that in
this specification, the term "driver circuit portion" is a generic
term including the source side driver circuit and the gate side
driver circuit.
[0165] The source side driver circuit 1401 is provided with a shift
register 1402, a level shifter 1403, a buffer 1404, and a sampling
circuit (transfer gate) 1405. Further, the gate side driver circuit
(A) 1407 is provided with a shift register 1408, a level shifter
1409, and a buffer 1410. The gate side driver circuit (B) 1411 also
takes the same structure.
[0166] Here, the shift registers 1402 and 1408 have driving
voltages of 5 to 16 V (typically 10 V), respectively, and the
structure indicated by reference symbol 605 in FIG. 10C is suitable
for the n-channel TFT that is used in a CMOS circuit for forming
the circuits.
[0167] Similar to the shift register, the CMOS circuit including
the n-channel TFT 605 of FIG. 10C is suitable for each of the level
shifters 1403 and 1409 and the buffers 1404 and 1410. Incidentally,
it is effective that the gate wiring is formed such that it takes a
multi-gate structure such as a double gate structure or a triple
gate structure in improving the reliability of each circuit.
[0168] The structure of the pixel illustrated in FIG. 6 is arranged
in the pixel portion 1406.
[0169] The foregoing structure can be easily realized by
manufacturing TFTs in accordance with the manufacturing steps shown
in FIGS. 8A to 10C. In Embodiment 6, although only the structure of
the pixel portion and the driver circuit portion is shown, it is
possible to form a logical circuit other than the driver circuit,
such as a signal dividing circuit, a D/A converter circuit, an
operational amplifier circuit, or a -correction circuit, on the
same insulator if the manufacturing steps of the circuits are
carried out in accordance with those of Embodiment 6. In addition,
it is considered that a memory portion, a microprocessor, or the
like can be formed on the same insulator.
[0170] The EL module of Embodiment 6 including the covering member
will be explained with reference to FIGS. 15A and 15B. Note that
the reference symbols used in FIGS. 13 and 14 will be referred to,
if necessary.
[0171] Shown in FIG. 15A is a top view of a state in which a
sealing structure is provided to the structure shown in FIGS. 10A
to 10C. Reference symbol 1302 denotes the pixel portion, reference
symbol 1303 denotes the gate side driver circuit, and 1304 denotes
the source side driver circuit, which are indicated by dotted
lines. The sealing structure of the present invention is a
structure which is provided to the state shown in FIG. 10 and is
composed of a filling member (not shown in the figure), a covering
member 1501, a sealing member (not shown in the figure), and a
framing member 1502.
[0172] A sectional view taken along the line A-A' of FIG. 15A is
shown here in FIG. 15B. Note that in FIGS. 15A and 15B, the same
reference symbols are used to denote the same components. As shown
in FIG. 15B, the pixel portion 1302 and the gate side driver
circuit 1303 are formed on the glass substrate 1301. The pixel
portion 1302 is composed of a plurality of pixels each including
the current controlling TFT 602 and the pixel electrode 848 that is
electrically connected to the current controlling TFT 602. The gate
side driver circuit 1303 is formed using a CMOS circuit in which
the n-channel TFT 605 and the p-channel TFT 606 are combined
complementarily.
[0173] The pixel electrode 848 functions as the anode of the EL
element. The supporting bank 849a and the controlling bank 849b are
formed in the gap between the pixel electrodes 848 to thereby form
the EL layer 851 and the cathode 852 inside of the supporting bank
849a and the controlling bank 849b. Of course, the structure of the
EL element may be inverted, and the pixel electrode may function as
the cathode.
[0174] In the case of Embodiment 6, the cathode 852 also functions
as a common wiring shared by all the pixels, and is electrically
connected to the FPC 1311 via the connecting wiring 1312.
[0175] Next, a filling member 1503 is provided so as to cover the
EL element. The filling member 1503 functions as an adhesive for
bonding the covering member 1501. As the filling member 1503, PVC
(polyvinyl chloride), epoxy resin, silicone resin, PVB (polyvinyl
butylal), or EVA (ethylenevinyl acetate) can be used. A drying
agent (not shown) placed inside the filling member 1503 keeps
moisture absorbing effect, which is preferable. At this point, the
drying agent may be an additive of the filling member or may be
sealed within the filling member.
[0176] A material made of glass, plastic, or ceramic can be used as
the covering member 1501 in Embodiment 6. Note that doping a
moisture absorbent material such as barium oxide in the filling
member 1503 in advance is effective.
[0177] Then, after bonding the covering member 1501 by using the
filling member 1503, the framing member 1502 is attached so as to
cover the sides (exposed faces) of the filling member 1503. The
framing member 1502 is bonded by using the sealing member
(functions as an adhesive) 1504. At this time, a photo curable
resin is preferably used for the sealing member 1504. However, a
thermosetting resin may also be used if the heat resistivity of the
EL layer is permitted. A desirable material of the sealing member
1504 is one which allows minimum amount of moisture and oxygen to
permeate. A drying agent may be doped into the sealing member 1504.
By sealing the EL element within the filling member 1503 using the
method as described above, the EL element is completely cut off
from external environment, and the invasion from the outside by
substances that accelerate the oxidation degradation of the EL
layer, such as moisture and oxygen, can thus be prevented.
Accordingly, an EL display device with high reliability can be
manufactured.
[0178] A polarizing plate may be provided on the display surface
(surface for observing an image) of the light emitting device shown
in Embodiment 6. The polarizing plate has the effect of suppressing
the reflection of light entered from the outside to thereby prevent
an observer from being reflected on the display surface. Generally,
a circular polarizing plate is used. However, in order to prevent
the light emitted from the EL layer from being reflected by the
polarizing plate and reversed back into the interior thereof, a
refractive index is regulated to thereby form a desirable structure
having very little interior reflection.
Embodiment 7
[0179] A case of sequentially laminating the anode, the EL layer,
and the cathode on the insulator was chiefly explained in
Embodiments 1 through 6. However, it is possible to laminate the
cathode, the EL layer, the anode, and an auxiliary wiring on the
insulator in order.
[0180] While, in the former lamination structure, light penetrating
the insulator is observed, in the latter lamination structure,
light is irradiated in the direction away from the insulator.
Embodiment 8
[0181] In Embodiment 8, an explanation is made on an example of
implementing the present invention to a case of manufacturing a
plurality of light emitting devices from one piece of substrate by
means of gang-printing. The explanation thereof is made with
reference to FIG. 16.
[0182] A plurality of light emitting devices each containing a
pixel portion 1602a and a driver circuit 1602b are formed on a
glass substrate 1601. Nine light emitting devices will be formed on
one piece of glass substrate in this embodiment. Further, the pixel
portion 1602a of each of the light emitting devices is formed of
the structure illustrate in FIG. 1, and a controlling bank 1603 is
formed in a matrix shape in each pixel portion 1602a.
[0183] A wiring (hereinafter referred to as a bank connecting
wiring) 1604 for connecting each of the controlling banks so that
all the controlling banks 1603 have equivalent electric potential
is formed in Embodiment 8. If a voltage is applied to a pad portion
1605, the applied voltage will be transmitted to all the anodes. A
characteristic of this embodiment is that the bank connecting
wiring 1604 can be used as an electrostatic countermeasure. In
other words, if all the controlling banks 1603 have equivalent
electric potential, then a large voltage will not suddenly be
applied between the wiring, whereby destruction of the substrate
can be effectively suppressed.
[0184] An enlarged view of a region 1600 surrounded by the dotted
line is shown in FIG. 17A here. As shown in FIG. 17A, the bank
connecting wiring 1604 is formed at the same time with the
controlling bank 1603 and part of the way, has a portion that is
coupled with a buffer wiring 1606. The buffer wiring 1606 is formed
simultaneously with the pixel electrode (the anode of the EL
element in this embodiment) by using an oxide conductive film.
[0185] A cross-sectional view taken along the line A-A' of FIG. 17A
is shown in FIG. 17B. Note that reference symbol 1607 denotes an
interlayer insulating film that is laminated in the process of
manufacturing a TFT.
[0186] Because a resistance value of the oxide conductive film used
as the buffer wiring 1606 is high compared with a metal film, the
buffer wiring functions one kind of resistor. Therefore, if a large
current flows in the bank connecting wiring 1604, the current is
buffered by the buffer connecting wiring, thereby making it
possible to prevent damages to the plurality of light emitting
devices.
[0187] By adopting the structure of Embodiment 8, the present
invention may be implemented even in the case of manufacturing a
plurality of light emitting devices in one time by means of the
gang-printing process without providing complicated wiring.
[0188] Further, upon completion of the light emitting device, the
substrate 1601 is cut by using a dicer or a scriber to thereby
separate each of the light emitting devices. At this point, if the
bank connecting wiring 1604 is cut, then the respective light
emitting devices become a state of being electrically independent.
It is to be noted that the structure of Embodiment 8 may be
implemented by freely combining it with any one of the structures
of Embodiments 1 to 7.
Embodiment 9
[0189] A case of using a combination of the present invention and a
shadow mask is explained in Embodiment 9 with reference to FIG. 18.
Note that the same reference symbols are used to denote components
similar to those in the structure shown in FIG. 2.
[0190] In FIG. 18, a shadow mask 1801 is further provided on a
controlling bank 105b, and the shadow mask 1801 is charged with a
negative charge. In other words, the shadow mask 1801 and the
controlling bank 105b are charged to have the same polarity.
[0191] At this point, if a distance between the respective
controlling banks 105b is denoted by X.sub.1 and a distance of an
aperture provided in the shadow mask 1801 is denoted by X.sub.2,
then it is preferable to make the relation between the two
distances to X.sub.1<X.sub.2. Thus, the EL material (or a
solution containing the EL material) 201 coming from the top of the
shadow mask 1801 will first be guided to the vicinity of the
aperture of the shadow mask 1801 by the electric field that is
generated by the shadow mask 1801. The EL material 201 will further
be guided into the pixel by the electric field formed by the
controlling bank 105b. The EL layer 202 is thus formed.
[0192] The structure of Embodiment 9 is particularly effective in
the case of separating the different kinds of EL material into
several times to thereby form the EL layers, as in the case of
forming the EL layers by separating the EL material for luminescing
a red color, the EL material for luminescing a green color, and the
EL material for luminescing a blue color.
[0193] It is to be noted that the structure of Embodiment 9 may be
implemented by freely combining it with any one of the structures
of Embodiments 1 to 8.
Embodiment 10
[0194] A case of separating an EL material for luminescing a red
color, an EL material for luminescing a green color, and an EL
material for luminescing a blue color by an electric field control
of the present invention to thereby form the EL layers without
using a shadow mask will be explained in Embodiment 10.
[0195] The concept of Embodiment 10 is shown in FIGS. 19A and 19B.
In FIGS. 19A and 19B, pixel electrodes 1901 to 1903 are formed on
an insulator (in Embodiment 10, the insulator is an interlayer
insulating film formed on an TFT) not shown in the figure.
Controlling banks 1904 are formed and processed into a matrix shape
to thereby surround the above electrodes.
[0196] In Embodiment 10, first as shown in FIG. 19A, only the pixel
electrode 1902 is charged with a positive charge and the other
pixel electrodes 1901 and 1903 are charged with a negative charge.
Further, the controlling bank 1904 is also charged with a negative
charge. The negatively charged EL material for luminescing a red
color is then formed by evaporation under this state. At this
point, on the pixel electrodes 1901 and 1903 that have been charged
with a negative charge, the EL material is repelled, whereby most
of the EL material is film deposited on the anode 1902 that has
been charged with a positive charge. An EL layer 1905 for
luminescing a red color is thus formed.
[0197] Next, as shown in FIG. 19B, only the pixel electrode 1901 is
charged with a positive charge and the other pixel electrodes 1902
and 1903 are charged with a negative charge. Further, the
controlling bank 1904 is also charged with a negative charge. The
negatively charged EL material for luminescing a green color is
then formed by evaporation under this state. At this point, on the
pixel electrodes 1902 and 1903 that have been charged with a
negative charge, the EL material is repelled, whereby most of the
EL material is film deposited on the pixel electrode 1901 that has
been charged with a positive charge. An EL layer 1906 for
luminescing a green color is thus formed.
[0198] Furthermore, although not shown in the figure, an EL layer
for luminescing a blue color is similarly formed by only charging
the pixel electrode 1903 with a positive charge and charging the
other pixel electrodes 1901 and 1902 with a negative charge to
thereby film deposit the EL material for luminescing a blue
color.
[0199] With the structure of Embodiment 10, film deposition of the
EL material can be selectively performed on the pixels without the
use of the shadow mask by controlling the EL material with the
electric field formed by the controlling bank 1904 and the electric
field formed by the pixel electrodes 1901 to 1903 to thereby
determine the track of the EL material.
[0200] It is to be noted that the structure of Embodiment 10 may be
implemented by freely combining it with any one of the structures
of Embodiments 1 to 8.
Embodiment 11
[0201] In this embodiment, an external light emitting quantum
efficiency can be remarkably improved by using an EL material by
which phosphorescence from a triplet exciton can be employed for
emitting a light. As a result, the power consumption of the EL
element can be reduced, the lifetime of the EL element can be
elongated and the weight of the EL element can be lightened.
[0202] The following is a report where the external light emitting
quantum efficiency is improved by using the triplet exciton (T.
Tsutsui, C. Adachi, S. Saito, Photochemical processes in Organized
Molecular Systems, ed. K. Honda, (Elsevier Sci. Pub., Tokyo, 1991)
p. 437).
[0203] The molecular formula of an EL material (coumarin pigment)
reported by the above article is represented as follows.
[0204] Chemical Formula 1
[0205] (M. A. Baldo, D. F. O'Brien, Y. You, A. Shoustikov, S.
Sibley, M. E. Thompson, S. R. Forrest, Nature 395 (1998) p.
151)
[0206] The molecular formula of an EL material (Pt complex)
reported by the above article is represented as follows.
[0207] Chemical Formula 2
[0208] (M. A. Baldo, S. Lamansky, P. E. Burrows, M. E. Thompson, S.
R. Forrest, Appl. Phys. Lett., 75 (1999) p. 4.)
[0209] (T. Tsutsui, M.-J. Yang, M. Yahiro, K. Nakamura, T.
Watanabe, T. Tsuji, Y. Fukuda, T. Wakimoto, S. Mayaguchi, Jpn,
Appl. Phys., 38 (12B) (1999) L1502)
[0210] The molecular formula of an EL material (Ir complex)
reported by the above article is represented as follows.
[0211] Chemical Formula 3
[0212] As described above, if phosphorescence from a triplet
exciton can be put to practical use, it can realize the external
light emitting quantum efficiency three to four times as high as
that in the case of using fluorescence from a singlet exciton in
principle. The structure according to this embodiment can be freely
implemented in combination of any structures of the first to ninth
embodiments.
Embodiment 12
[0213] The light emitting apparatus formed according to the present
invention, is a self light emitting type, therefore compared to a
liquid crystal display device, it has excellent visible properties
and is broad in an angle of visibility. Accordingly, it may be used
as a display portion of various electric devices. In such a case,
since the light emitting apparatus of this invention is a passive
type light emitting device but may have a large size screen by
decreasing the wiring resistance, it may be used in various
situations.
[0214] As other electronic equipments of the present invention
there are: a video camera; a digital camera; a goggle type display
(head mounted display); a car navigation system; a car audio
stereo; a notebook type personal computer; a game apparatus; a
portable information terminal (such as a mobile computer, a
portable telephone, a portable game machine, or an electronic
book); and an image playback device equipped with a recording
medium (specifically, device provided with a display portion which
plays back images in a recording medium such as a compact disc
player (CD), a laser disk player (LD), or a digital versatile disk
Player (DVD), and displays the images). Specific examples of those
electronic equipments are shown in FIGS. 20A to 21B.
[0215] FIG. 20A shows an EL display containing a casing 2001, a
support stand 2002, and a display portion 2003. The light emitting
device of the present invention can be used as the display portion
2003. Such an EL display is a self light emitting type so that a
back light is not necessary. Thus, the display portion can be made
thinner than that of a liquid crystal display. Note that, if a
stick driver is provided in the light emitting device used in the
display portion 2003, it is preferable that it is dividedly
provided in several tens of parts.
[0216] FIG. 20B shows a video camera, and contains a main body
2101, a display portion 2102, a sound input portion 2103, operation
switches 2104, a battery 2105, and an image receiving portion 2106.
The light emitting device of the present invention can be used as
the display portion 2102. Note that, if a stick driver is provided
in the light emitting device used in the display portion 2102, it
is preferable that it is dividedly provided in several parts.
[0217] FIG. 20C shows a digital camera, and contains a main body
2201, a display portion 2202, an eye piece portion 2203, and
operation switches 2204. The light emitting device of the present
invention can be used as the display portion 2202. Note that, if a
stick driver is provided in the light emitting device used in the
display portion 2202, it is preferable that it is dividedly
provided in several parts.
[0218] FIG. 20D is an image playback device equipped with a
recording medium (specifically, a DVD playback device), and
contains a main body 2301, a recording medium (such as a CD, LD or
DVD) 2302, operation switches 2303, a display portion (a) 2304, and
a display portion (b) 2305. The display portion (a) 2304 is mainly
used for displaying image information. The display portion (b) 2305
is mainly used for displaying character information. The light
emitting device of the present invention can be used as the display
portion (a) 2304 and as the display portion (b) 2305. Note that the
image playback device equipped with the recording medium includes
devices such as CD playback devices and game machines. Note that,
if a stick driver is provided in the light emitting device used in
the display portion (b) 2305, it is preferable that it is dividedly
provided into several tens of parts.
[0219] FIG. 20E shows a portable (mobile) computer, and contains a
main body 2401, a camera portion 2402, an image receiving portion
2403, operation switches 2404, and a memory slot 2405. The
electro-optical device of the present invention can be used as the
display portion 2402. This portable computer can record or play
back information in the recording medium which is an accumulation
of flash memory or involatile memory. Note that, if a stick driver
is provided in the light emitting device used in the display
portion 2402, it is preferable that it is dividedly provided in
several tens of parts.
[0220] FIG. 20F is a personal computer, and contains a main body
2501, a casing 2502, a display portion 2503, and a keyboard 2504.
The light emitting device of the present invention can be used as
the display portion 2503. Note that, if a stick driver is provided
in the light emitting device used in the display portion 2503, it
is preferable that it is dividedly provided in several tens of
parts.
[0221] Note that if the luminance increases in the future, then it
will become possible to use the light emitting device of the
present invention in a front type or a rear type projector by
expanding and projecting light containing output image information
with a lens or the like.
[0222] Further, the above electric devices display often
information transmitted through an electronic communication circuit
such as the Internet and CATV (cable TV), and particularly
situations of displaying moving images is increasing. The response
speed of EL materials is so high that the above electric devices
are good for display of moving image.
[0223] In addition, since the light emitting device conserves power
in the light emitting portion, it is preferable to display
information so as to make the light emitting portion as small as
possible. Consequently, when using the light emitting device in a
display portion mainly for character information, such as in a
portable information terminal, in particular a portable telephone
or a car audio stereo, it is preferable to drive the light emitting
device so as to form character information by the light emitting
portions while non-light emitting portions are set as
background.
[0224] FIG. 21A shows a portable telephone, and contains a main
body 2601, a sound output portion 2602, a sound input portion 2603,
a display portion 2604, operation switches 2605, and an antenna
2606. The light emitting device of the present invention can be
used as the display portion 2604. Note that by displaying white
color characters in a black color background, the display portion
2604 can suppress the power consumption of the portable
telephone.
[0225] FIG. 21B shows a car audio stereo, and contains a main body
2701, a display portion 2702, and operation switches 2703 and 2704.
The light emitting device of the present invention can be used as
the display portion 2702. Further, a car mounting audio stereo is
shown in this embodiment, but a fixed type audio playback device
may also be used. Note that, by displaying white color characters
in a black color background, the display portion 2704 can suppress
the power consumption. Note that, if a stick driver is provided in
the light emitting device used in the display portion 2704, it is
preferable that it is dividedly provided in several parts.
[0226] As described above, the application range of this invention
is extremely wide, and it may be used for electric devices in
various fields. Further, the electric device of this embodiment may
be obtained by using a light emitting device freely combining the
structures of the first to tenth embodiments.
[0227] By implementing the present invention, it is possible to
accurately control the film deposition position in depositing the
EL material. Therefore, the light emitting device having a highly
definite pixel portion can be manufactured. Further, because film
deposition of the EL material to the necessary portion can be given
priority, the utilization efficiency of the EL material is enhanced
and the manufacturing cost can be reduced. In addition, electric
equipment having a highly fine display portion can be attained by
employing the light emitting device of the present invention as its
display portion.
* * * * *