U.S. patent application number 09/918469 was filed with the patent office on 2002-02-07 for organic electroluminescence display device and producing method thereof.
Invention is credited to Codama, Mitsufumi, Tanaka, Masaru.
Application Number | 20020014836 09/918469 |
Document ID | / |
Family ID | 26477903 |
Filed Date | 2002-02-07 |
United States Patent
Application |
20020014836 |
Kind Code |
A1 |
Codama, Mitsufumi ; et
al. |
February 7, 2002 |
ORGANIC ELECTROLUMINESCENCE DISPLAY DEVICE AND PRODUCING METHOD
THEREOF
Abstract
In manufacturing of an organic electroluminescence (EL) display
device, after first electrodes are formed on a substrate,
insulating films are formed on the first electrodes except regions
corresponding to light emitting portions. Spacers are formed on the
insulating films, and overhanging portions are formed so as to
overhang the spacers. Thus, element isolating structure portions
for isolating organic EL elements are formed. Then, organic EL
films, second electrodes, and protecting films are sequentially
formed between the spacers. In the thus formed light emitting
portions of the organic EL display device, the bending angle of a
bending portion of a pattern of the element isolating structure
portion is larger than 90.degree..
Inventors: |
Codama, Mitsufumi; (Tokyo,
JP) ; Tanaka, Masaru; (Tokyo, JP) |
Correspondence
Address: |
ARMSTRONG,WESTERMAN, HATTORI,
MCLELAND & NAUGHTON, LLP
1725 K STREET, NW, SUITE 1000
WASHINGTON
DC
20006
US
|
Family ID: |
26477903 |
Appl. No.: |
09/918469 |
Filed: |
August 1, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09918469 |
Aug 1, 2001 |
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09653379 |
Sep 1, 2000 |
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6290563 |
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09653379 |
Sep 1, 2000 |
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09274021 |
Mar 22, 1999 |
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6147442 |
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09274021 |
Mar 22, 1999 |
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08834733 |
Apr 3, 1997 |
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6037712 |
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Current U.S.
Class: |
313/504 ;
313/506 |
Current CPC
Class: |
H01L 27/3239 20130101;
H01L 27/3237 20130101; Y10S 428/917 20130101; H01L 27/3283
20130101; H01L 51/5212 20130101; H01L 51/5253 20130101 |
Class at
Publication: |
313/504 ;
313/506 |
International
Class: |
H01J 001/88; H01J
001/62 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 10, 1996 |
JP |
8-147313 |
Dec 6, 1996 |
JP |
8-327045 |
Claims
What is claimed is:
1. An organic electroluminescence display device comprising: a
first electrode which is transparent and formed on a substrate; an
insulating film selectively formed on the first electrode; a
plurality of spacers formed on the insulating film; an overhanging
film which is formed on each spacer and has a width wider than that
of each spacer; an organic electroluminescence film formed on the
first electrode and between adjacent spacers; and a second
electrode formed on the organic electroluminescence film.
2. The device of claim 1 wherein the spacers comprise a metal.
3. The device of claim 2 further comprising a protecting film which
includes at least one selected from the group having a metal and an
insulating film and covers the second electrode.
4. The device of claim 3 wherein an undercut length of the spacers
is determined so that the protecting film including a metal is not
in contact with a side surface of the spacers.
5. A method for producing an organic electroluminescence display
device, comprising the steps of: forming a first electrode which is
transparent on a substrate; selectively forming an insulating film
on the first electrode; forming a spacer film on the insulating
film; selectively forming a photosensitive film on the spacer film;
forming a plurality of spacers by overetching the spacer film, so
that the photosensitive film overhangs each spacer; forming an
organic electroluminescence film on the first electrode and between
adjacent spacers; and forming a second electrode on the organic
electroluminescence film.
6. The method of claim 5 wherein the spacers comprise a metal.
7. The method of claim 6 further comprising the step of forming a
protecting film which includes at least one selected from the group
having a metal and an insulating film and covers the second
electrode.
8. The method of claim 7 wherein the spacer film is overetched by
an undercut length that the protecting film including a metal is
not in contact with a side surface of the spacers.
9. The method of claim 8 further comprising the step of removing
the photosensitive film which overhangs the spacers.
10. The method of claim 7 wherein the organic electroluminescence
film, the second electrode and the protecting film are formed
without exposing to an air.
11. The method of claim 9 further comprising the step of removing
the spacers after the photosensitive film removing step.
12. An organic electroluminescence display device comprising: a
plurality of organic electroluminescence elements; and an element
isolating structure portion which is formed between adjacent
organic electroluminescence elements and has an overhanging
portion, wherein a bending portion of the element isolating
structure portion has a bending angle larger than 90.degree..
13. The device of claim 12 wherein the element isolating structure
portion further comprises a spacer which is formed under the
overhanging portion and includes a metal.
14. An organic electroluminescence display device comprising: a
plurality of organic electroluminescence elements; and an element
isolating structure portion which is formed between adjacent
organic electroluminescence elements and has an overhanging
portion, wherein a bending portion of the element isolating
structure portion is formed by an arc having a radius of curvature
of 5 .mu.m or more.
15. The device of claim 14 wherein the element isolating structure
portion further comprises a spacer which is formed under the
overhanging portion and includes a metal.
16. A method for producing an organic electroluminescence display
device having an element isolating structure portion formed between
adjacent organic electroluminescence elements, a bending portion of
the element isolating structure portion having a bending angle
larger than 90.degree., the method comprising the steps of: forming
a first electrode which is transparent on a substrate; selectively
forming an insulating film on the first electrode; forming a spacer
film on the insulating film; selectively forming a photosensitive
film on the spacer film; forming a plurality of spacers overhung by
the photosensitive film by overetching the spacer film, to obtain
the element isolating structure portion; forming an organic
electroluminescence film on the first electrode and between
adjacent spacers; and forming a second electrode on the organic
electroluminescence film.
17. The method of claim 16 wherein the spacers comprise a
metal.
18. The method of claim 17 further comprising the step of forming a
protecting film which includes at least one selected from the group
having a metal and an insulating film and covers the second
electrode.
19. The method of claim 18 wherein the spacer film is overetched by
an undercut length that the protecting film including a metal is
not in contact with a side surface of the spacers.
20. The method of claim 19 further comprising the step of removing
the photosensitive film which overhangs the spacers.
21. The method of claim 20 further comprising the step of removing
the spacers after the photosensitive film removing step.
22. The method of claim 18 wherein the organic electroluminescence
film, the second electrode and the protecting film are formed
without exposing to an air.
23. An organic electroluminescence display device comprising: a
first electrode which is transparent and formed on a substrate; an
insulating film selectively formed on the first electrode; a
plurality of first spacers formed on the insulating film; a
plurality of second spacers formed on the first spacers; an
overhanging film which is formed on each second spacer and has a
width wider than that of each first spacer; an organic
electroluminescence film formed on the first electrode and between
adjacent first spacers; and a second electrode formed on the
organic electroluminescence film.
24. The device of claim 23 wherein the first spacers comprise a
metal.
25. The device of claim 23 wherein each second spacer supports the
overhanging film and includes a harder film than the overhanging
film.
26. A method for producing an organic electroluminescence display
device, comprising the steps of: forming a first electrode which is
transparent on a substrate; selectively forming an insulating film
on the first electrode; forming a spacer film having a plurality of
layers on the insulating film; selectively forming a photosensitive
film on the spacer film; forming a plurality of spacers by
overetching one layer of the spacer film which is not in contact
with the photosensitive film, so that the photosensitive film
overhangs each spacer; forming an organic electroluminescence film
on the first electrode and between adjacent spacers; and forming a
second electrode on the organic electroluminescence film.
27. The method of claim 26 wherein the spacers comprise a
metal.
28. The method of claim 26 wherein another layer of the spacer film
which is in contact with the photosensitive film supports the
photosensitive film and includes a harder film than the
photosensitive film.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an organic
electroluminescence display device which is used as a display
device or a light source and which can be formed by a process
including photolithography with easy isolation of organic
electroluminescence elements, and also relates to a producing
method of the above organic electroluminescence display device.
[0003] 2. Description of the Related Art
[0004] At present, liquid crystal display devices are used as thin
flat panel displays which are currently the main stream of the
technical field of display devices. However, organic
electroluminescence (hereinafter referred to "organic EL") display
devices using organic EL elements are superior to liquid crystal
display devices in the following points:
[0005] (1) Having a wide viewing angle because the organic EL
elements emit light by themselves.
[0006] (2) Allowing easy manufacture of a thin display device of
about 2-3 mm in thickness.
[0007] (3) Capable of providing a natural emission color because of
no need for using any polarizing plate.
[0008] (4) Capable of clear display because of a wide light and
shade dynamic range.
[0009] (5) Allowing organic EL elements to operate in a wide
temperature range.
[0010] (6) Easily enabling dynamic image display because the
response speed of the organic EL elements is three orders or more
higher than that of liquid crystal elements.
[0011] In spite of the above advantages, the organic EL display
devices have the following problems in manufacture. For example,
organic layers constituting the organic EL elements and electrodes
containing a metal having a small work function which is usually
used as a cathode to inject electrons into the organic layers are
easily deteriorated by water and oxygen. Further, the organic
layers are easily dissolved by a solvent and are not resistant to
heat.
[0012] In a manufacturing method using water, organic solvents, and
heat, it is difficult to isolate or divide elements after the
formation of organic layers and an electrode containing a metal
having a small work function. Therefore, when it is intended to
form an organic EL display device in the same class as liquid
crystal display devices currently implemented, the matured
semiconductor manufacturing technology and liquid crystal display
device manufacturing technology cannot be applied as they are to
isolate small organic EL elements.
[0013] In the above circumstance, a method has been proposed in
which walls higher than films constituting organic EL films are
formed between display line electrodes to be isolated, and
materials for forming the organic EL films are vacuum-evaporated in
a direction not perpendicular to the substrate surface (i.e.,
evaporated obliquely). This method utilizes the fact that the
materials for forming the organic EL films are not formed in the
portions shielded by the high walls. (Refer to U.S. Pat. Nos.
5,276,380 and 5,294,869.)
[0014] In the above method, it is very important that the
directions in which atoms or molecules travel from the evaporation
source to the substrate be aligned. As shown in FIG. 8, in an
ordinary evaporation method, an evaporation material is vaporized
to assume concentric spheres with an evaporation source 101 in
which the evaporation material is set as the center, and then
attaches to a substrate 100. The incident angle of the evaporation
material with respect to the substrate 100 varies with the position
on the substrate 100, and the thickness of a resulting film formed
on the substrate 100 varies in response to the distance from the
evaporation source 101.
[0015] Therefore, it is difficult for the above method to isolate
the display line electrodes in a stable manner, and to form the
films uniformly over the entire substrate surface. Although the
above method could manufacture small-size display devices, in order
to apply the above method to medium-size or large-size substrates
of the 10-inch class or larger, for example, the distance between
the substrate 100 and the evaporation source 101 should be set
sufficiently long. In this case, the size of the evaporation
apparatus becomes impractical.
[0016] Even if such a large evaporation apparatus is produced, a
large amount of organic EL material does not reach the substrate
surface, and thus is consumed in vain without being formed on the
substrate, resulting in a major factor of cost increase.
[0017] In general, a substrate is rotated or a plurality of
evaporation sources are used to evaporate a thin film uniformly on
the substrate. These methods are actually employed in semiconductor
device manufacturing processes and liquid crystal device
manufacturing processes. However, if the above method of forming
high walls is applied to these methods, the element isolation
cannot be attained any more.
[0018] In the conventional method, the organic EL films and the
metal electrodes having a small work function are necessarily
exposed unless protecting layers are consecutively formed in the
same direction. Thus, it is difficult to completely eliminate the
influences of water, oxygen, etc. It is impossible to perform
photolithography having a process using an organic solvent or water
after formation of the organic EL films.
SUMMARY OF THE INVENTION
[0019] An object of the present invention is to provide a highly
reliable organic EL display device and a producing method thereof
by making the element isolation easier irrespective of the manner
of evaporating an organic EL material, enabling the use of a
large-size substrate, and completely covering organic EL layers and
metal electrodes having a small work function by forming films that
are stable with respect to water, oxygen, and organic solvents
without exposing those to the air, i.e., in a vacuum.
[0020] According to the present invention, there is provided an
organic electroluminescence display device comprising: a first
electrode which is transparent and formed on a substrate; an
insulating film selectively formed on the first electrode; a
plurality of spacers formed on the insulating film; an overhanging
film which is formed on each spacer and has a width wider than that
of each spacer; an organic electroluminescence film formed on the
first electrode and between adjacent spacers; and a second
electrode formed on the organic electroluminescence film.
[0021] According to the present invention, there is provided a
method for producing an organic electroluminescence display device,
comprising the steps of: forming a first electrode which is
transparent on a substrate; selectively forming an insulating film
on the first electrode; forming a spacer film on the insulating
film; selectively forming a photosensitive film on the spacer film;
forming a plurality of spacers by overetching the spacer film, so
that the photosensitive film overhangs each spacer; forming an
organic electroluminescence film on the first electrode and between
adjacent spacers; and forming a second electrode on the organic
electroluminescence film.
[0022] According to the present invention, there is provided an
organic electroluminescence display device comprising: a plurality
of organic electroluminescence elements; and an element isolating
structure portion which is formed between adjacent organic
electroluminescence elements and has an overhanging portion,
wherein a bending portion of the element isolating structure
portion has a bending angle larger than 90.degree..
[0023] According to the present invention, there is provided an
organic electroluminescence display device comprising: a plurality
of organic electroluminescence elements; and an element isolating
structure portion which is formed between adjacent organic
electroluminescence elements and has an overhanging portion,
wherein a bending portion of the element isolating structure
portion is formed by an arc having a radius of curvature of 5
.mu.m.
[0024] According to the present invention, there is provided a
method for producing an organic electroluminescence display device
having an element isolating structure portion formed between
adjacent organic electroluminescence elements, a bending portion of
the element isolating structure portion having a bending angle
larger than 90.degree., the method comprising the steps of: forming
a first electrode which is transparent on a substrate; selectively
forming an insulating film on the first electrode; forming a spacer
film on the insulating film; selectively forming a photosensitive
film on the spacer film; forming a plurality of spacers overhung by
the photosensitive film by overetching the spacer film, to obtain
the element isolating structure portion; forming an organic
electroluminescence film on the first electrode and between
adjacent spacers; and forming a second electrode on the organic
electroluminescence film.
[0025] According to the present invention, there is provided an
organic electroluminescence display device comprising: a first
electrode which is transparent and formed on a substrate; an
insulating film selectively formed on the first electrode; a
plurality of first spacers formed on the insulating film; a
plurality of second spacers formed on the first spacers; an
overhanging film which is formed on each second spacer and has a
width wider than that of each first spacer; an organic
electroluminescence film formed on the first electrode and between
adjacent first spacers; and a second electrode formed on the
organic electroluminescence film.
[0026] According to the present invention, there is provided a
method for producing an organic electroluminescence display device,
comprising the steps of: forming a first electrode which is
transparent on a substrate; selectively forming an insulating film
on the first electrode; forming a spacer film having a plurality of
layers on the insulating film; selectively forming a photosensitive
film on the spacer film;forming a plurality of spacers by
overetching one layer of the spacer film which is not in contact
with the photosensitive film, so that the photosensitive film
overhangs each spacer; forming an organic electroluminescence film
on the first electrode and between adjacent spacers; and forming a
second electrode on the organic electroluminescence film.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIGS. 1A and 1B show the structure of an organic
electroluminescence (EL) elements according to a first embodiment
of the invention;
[0028] FIG. 2 is a diagram explaining rotary evaporation;
[0029] FIGS. 3A-3J and 4A-4C show a manufacturing process of the
organic EL element according to the first embodiment of the
invention;
[0030] FIGS. 5A-5E and 7A-7B show a manufacturing process of
organic EL elements according to a second embodiment of the
invention;
[0031] FIG. 6 is a plan view of a color filter portion of an
organic EL display device according to the second embodiment of the
invention;
[0032] FIG. 8 is a diagram explaining an ordinary evaporation
method;
[0033] FIGS. 9A and 9B are a plan pattern view and a sectional view
of light emitting portions of an organic EL display device
according to a third embodiment of the invention;
[0034] FIGS. 10A and 10B are a plan pattern view and a sectional
view of light emitting portions of an organic EL display device
according to a fourth embodiment of the invention;
[0035] FIGS. 11A-11C are plan pattern views of a display portion of
an organic EL display device according to a fifth embodiment of the
invention;
[0036] FIGS. 12A-12H are plan pattern views and sectional views of
a bar graph portion of the display portion of the organic EL
display device according to the fifth embodiment of the
invention;
[0037] FIGS. 13A-13C and 14A-14C are plan pattern views and
sectional views of a light emitting portion of an organic EL
display device having element isolating structure portions
according to the invention;
[0038] FIG. 15 shows the chemical structural formula of
N,N'-bis(m-methyl
phenyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine;
[0039] FIG. 16 shows the chemical structural formula of
tris(8-hydroxyquinoline) aluminium;
[0040] FIG. 17 shows the chemical structural formula of
poly(tiophene-2,5-diyl);
[0041] FIG. 18 shows the chemical structural formula of
rubrene;
[0042] FIG. 19 shows the chemical structural formula of
4,4'-bis[(1, 2,2'-trisphenyl)ethenyl]-biphenyl; and
[0043] FIG. 20 shows an organic EL element according to the
invention with a harder film which is used as a support film.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0044] Embodiments of the present invention will be hereinafter
described in detail with reference to the accompanying
drawings.
Embodiment 1
[0045] FIGS. 1A and 1B show the structure of organic
electroluminescence (EL) elements according to a first embodiment
of the invention. As shown in FIG. 1A, a first transparent
electrode 2 (for example, an indium tin oxide (ITO) film) is formed
on an insulating transparent substrate 1 in a desired pattern
shape. Then, an insulating film (for example, a polyimide film or
an SiO.sub.2 film) is formed on the first transparent electrode 2.
Organic EL films and second electrodes contacting with the organic
EL films will be formed later to constitute a light emitting
portion. A portion of the insulating film located on the display
surface side of the light emitting portion is removed.
[0046] Next, a spacer film (for example, a polyimide film)
constituted of at least one layer is formed. After photosensitive
films (photosensitive resin films) such as resists are formed
between electrodes to be isolated, photosensitive films 5 on
remaining insulating films 3 are left by photolithography.
Subsequently, the exposed portions of the spacer film are removed
by etching. At this time, the portions of the spacer film under the
photosensitive films 5 are also removed to form sufficiently long
undercut regions. As a result, with respect to the spacers 4 formed
by undercutting, the photosensitive films 5 assumes eaves, hat, or
cap-shaped structure, or an overhanging structure in general terms.
Thus, element isolating structure portions can be formed.
[0047] By forming the element isolating structure portions, when
organic EL films 6 which control light emission and carriers and
second electrodes 7 directly contacting with the organic EL films 6
are formed by evaporation, as shown in FIG. 1B, the elements can
always be isolated irrespective of the positional relationship
between the evaporation source and the substrate and the method for
improving the uniformity of the films. Thus, a method that regards,
as most important, improving the uniformity of the organic EL films
6 formed, such as a rotary method in the case of evaporation, can
be selected.
[0048] After the organic EL films 6 and the second electrodes 7
directly contacting with the organic EL films 6 are formed in the
above manner, metal films 8 made of a stable metal that is hardly
affected by water, oxygen, or organic solvents are formed as
protecting films for the second electrodes 7. When the organic EL
films 6 and the second electrodes 7 are formed by evaporation, the
metal films 8 are formed by a method (for example, sputtering) that
provides resulting films with better step coverage than
evaporation.
[0049] The protecting film may be any of a metal film of a stable
metal such as aluminum (Al), an insulating film such as an
SiO.sub.2 film, and a combination of an Al film and a second
protecting film 9 such as an SiO.sub.2 film formed thereon (see
FIG. 1B). The second protecting film 9 protects the organic EL film
6, the second electrode 7, the metal film 8, and other films.
[0050] It is desirable to form the protecting film subsequently to
the formation of the organic EL film 6 and the second electrode 7
without being exposed to the air, i.e., with maintaining a vacuum
state. For example, the protecting film may be formed by
evaporation in a low vacuum or sputtering. A film having good step
coverage can be formed by rotating the substrate 1 while it is
considerably inclined from the direction of vaporization from an
evaporation source 10 as shown in FIG. 2.
[0051] Thus, the structure of FIG. 1B is obtained in which even the
end portions of the organic EL films 6 and the second electrodes 7
are not exposed by forming the metal films 8 as the protecting
films or the metal films 8 and the second protecting films formed
thereon so that they are also formed in the above undercut regions.
Since the organic EL films 6 are completely enclosed by the first
transparent electrodes 2, the insulating films 3, and the metal
films 8 (and the protecting films 9), the organic EL elements can
resist through a process using water or an organic solvent, such as
photolithography that is performed in forming lead out electrodes
for the metal electrodes 8.
[0052] It is apparent from the above description that it becomes
possible to cause the organic EL elements to emit light uniformly,
to manufacture a highly reliable organic EL flat panel display at a
stable yield, and to increase the flexibility of the manufacturing
process of an organic EL flat panel display.
[0053] The first embodiment of the invention will be described in
more detail. FIGS. 3A-3J and 4A-4C show a manufacturing process of
the organic EL elements according to the first embodiment of the
invention. This process is directed to a case of manufacturing a
2-row/16-column dot matrix type display device in which the 1-dot
pixel size is 0.4 mm.times.0.6 mm and the character display area is
5.times.8 dots.
[0054] An inexpensive soda glass substrate, which is used in
amorphous silicon (a-Si) solar cells, super twisted nematic (STN)
liquid crystal display devices, etc., is used as the substrate of
the organic EL display device. The entire surface of the glass
substrate is coated with silica (SiO.sub.2). The silica coating
prevents sodium elution from the glass substrate when it is heated,
protects the soda glass substrate which is not resistant to acids
and alkalis, and improves the flatness of the glass substrate
surface. For example, the silica coating is performed by immersing
the glass substrate in a SiO.sub.2 solution or by spin on glass
(SOG) coating for the glass substrate.
[0055] Next, an ITO film which is a transparent conductive film as
a first electrode is formed at a thickness of about 1,500 angstrom
by sputtering on the glass substrate. The use of the ITO film is
due to the fact that it exhibits superior characteristics to films
made of other materials when it is used as a transparent conductive
film. However, a transparent electrode of a ZnO film, an SnO.sub.2
film, or the like may be used if it has transmittance and
resistivity, for example, that will not cause any problem during
use. When the ITO film is formed over a large area, sputtering is
advantageous in uniformity and film quality of a resulting film as
well as productivity. However, the ITO film need not always be
formed by sputtering, and may be formed by evaporation, for
example.
[0056] As shown in FIGS. 3A and 3F, after the ITO film is formed on
the silica-coated substrate 1 (the silica coating film is not
shown), a resist pattern (not shown) is formed on the ITO film by
photolithography. After unnecessary portions of the ITO film are
removed by etching to form the ITO film into a desired electrode
pattern, the resist pattern is removed. As shown in FIG. 3A in
enlarged form, it is desired that the ends of the ITO films 2 be
tapered. This is to prevent, in the step portions of the ITO films
2, step disconnection of organic films and second electrodes to be
evaporated in later processes, to thereby improve the yield and
life of the organic EL elements. It is desired that the taper angle
be 45.degree. or less. Incidentally, FIGS. 3F-3J are plan views of
element patterns, and FIGS. 3A-3E are sectional-views taken along
dot-chain lines A-A', B-B', C-C', D-D', and E-E' in FIGS. 3F-3J,
respectively.
[0057] Steps having a small taper angle can be formed by wet
etching or dry etching. For example, in wet etching, since the
etching proceeds isotropically, a taper angle of about 45.degree.
can naturally obtained if the overetching time is not set too long.
Also, in dry etching, a taper angle of 20.degree. to 30.degree. can
easily be obtained by utilizing retreat of a resist due to the
etching, that is, by selecting etching conditions such as a dry
etching gas, high frequency (e.g., RF) power and a gas pressure so
that a taper angle of the resist is transferred. The etching gas
for this purpose includes gases of hydrogen halides such as
hydrogen chloride and hydrogen iodide, a bromine gas, and a
methanol gas.
[0058] Films for disposing spacers to be formed in a later process
are formed on the ITO films 2. Any insulating film may be used as
such films. The films may be formed by various methods: forming
inorganic thin films such as SiO.sub.2 films or SiN.sub.x films by
sputtering or vacuum evaporation, forming SiO.sub.2 films by SOG
coating, and applying resist, polyimide, acrylic resin or the like.
Since it is necessary to expose a portion of the ITO films 2 formed
under the insulating film, the insulating film needs to be
patterned without damaging the ITO films 2. Although there is no
limitation on the thickness of the insulating films, when an
inorganic thin film is used, the manufacturing cost can be reduced
by decreasing the thickness thereof.
[0059] It is desirable that the ends of the insulating films 3
formed above the ITO film 2 be also tapered. The taper angle should
be about 60.degree. or less, preferably 45.degree. or less. When
SiO.sub.2 films are formed as the insulating films 3, a taper angle
of 45.degree. can be obtained by wet etching if the overetching
time is not set too long. To make the taper angle even smaller, dry
etching is suitable as in the case of forming the ITO films 2. A
carbon fluoride type etching gas such as CF.sub.4+O.sub.2 is
generally used.
[0060] In this embodiment, polyimide is used to form the insulating
films 3. Non-photosensitive polyimide to be prepared is diluted to
about 5% with N-methyl pyrrolidone (NMP) or .gamma.-butyrolactone.
Such polyimide is applied by spin coating and then prebaked at
145.degree. C. for one hour. After a positive resist is applied,
patterning is performed to form a structure shown in FIGS. 3B and
3G.
[0061] Exposed portions of the resist and corresponding portions of
the polyimide film are removed sequentially with an aqueous
solution of tetra methyl ammonium hydroxide (TMAH) having a
concentration of about 2.38%. The TMAH is a developer for the
resist. Further, only the remaining portions of the resist are
removed by ethanol, to form desired insulating films. Although the
above description is directed to the case of using
non-photosensitive polyimide, photosensitive polyimide may also be
used. In this case, no resist is needed.
[0062] The polyimide insulating films 3 thus obtained are
completely cured at about 350.degree. C. to prevent them from being
affected by a chemical solution. Since the insulating films 3
contract in this process, their steps come to be tapered.
[0063] When the step shape of the ITO films 2 is hard to control in
the above manner, the photomask may be so designed that the
insulating films 3 formed in this process also cover the step
portions of the ITO films 2.
[0064] Subsequently, a spacer film to be used as spacers 4 (see
FIG. 1A) is formed. Because of their purpose, the spacers 4 may be
either a conductor or an insulator, and have either a single layer
or a multilayer structure. However, when the spacers 4 are a
conductor, there is a possibility that metal films formed in a
later process cause a short circuit or a current leak between
adjacent display lines via a spacer. This problem may be-solved by
making the undercut amount in etching the spacer film sufficiently
large.
[0065] The spacer made of a metal has the following advantages. (1)
Since the spacer is sufficiently strong and malleable, the elements
that are easily rendered faulty due to the existence of dust can
sufficiently be cleaned with ultrasonic waves, for example. (2)
Since the spacer is more resistant to heat than a resist etc.,
dehydration can be effected by heat treatment. (3) Since the spacer
is hardly charged, particles are less likely to attach to the
spacer. (4) When a short circuit occurs in an element circuit due
to dust, the spacer can be burnt off.
[0066] It is necessary to select an etching material for the spacer
film which neither etches nor affects the ITO films 2 that are in
contact with the spacer film in etching the spacer film. Also,
since the spacer film is used to form the spacers 4, it should be
so formed as to be thicker than a total thickness of all of the
organic EL film 6, the second electrode 7, the metal film 8, the
protecting film 9, and other films, as shown in FIG. 1B. Thus, it
is desirable that the spacer film be made of a material which
allows easy formation of a thick spacer film. As such a material
film, an SOG film and a resin film are used. When the spacer film
is made of a metal material, a laminate structure of a Cr film, a
Ti film, a TiN film, or other film as an etching barrier film for
the ITO films 2 and an Al film or other film which has a high
formation rate may be formed. The etching barrier film is not
limited to a metal material.
[0067] When the spacer film is made of polyimide, polyimide whose
concentration has adjusted to 15% is spin-coated at a thickness of
2 .mu.m, and then prebaked at 145.degree. C. for one hour to form a
spacer film 4' (see FIGS. 3C and 3H). The thickness of the spacer
film 4' can be adjusted by the polyimide concentration and the
rotational speed of the spin coater.
[0068] After the formation of the spacer film 4', a positive resist
is applied. When the thickness of the positive resist is 1 .mu.m or
more, desirably 2 .mu.m or more, a highly viscous resist is used or
the rotational speed of the spin coater is set low.
[0069] Since the positive resist is relatively fragile, the method
of forming a thick resist is used in this embodiment. However, as
shown in FIG. 20, no such method is needed if a harder film (a
second spacer) 64 is formed under the resist 65 to support the
resist 65. The use of the harder film 64 as a support film has
another advantage that heat treatment for eliminating water can be
performed in a later process. Conversely, if heat treatment is
performed without forming the support film, the resist becomes
likely to be deformed and undercut regions may be broken. Note that
in FIG. 20, numeral 60 is a substrate, 61 is an ITO film, 62 is an
insulating film, and 63 is a spacer (a first spacer).
[0070] A conductor such as Cr, Ti, TiN, W, Mo, Ta, ITO, SnO.sub.2
or ZnO, an inorganic insulator such as SiN.sub.x, SiO.sub.2,
diamond like carbon (DLC), Al.sub.2O.sub.3, Ta.sub.2O.sub.5, or
glass, a semiconductor such as Si or SiC, or other materials can be
used to form the harder film 64.
[0071] The harder film 64 can be formed by sputtering, vacuum
evaporation, plating, plasma chemical vapor deposition (CVD),
thermal CVD or the like. In the spacer formed by a thin film having
a plurality of layers, when one layer which is in contact with a
photosensitive material constituting the resist is not overetched,
it can be used as the support film for the photosensitive material.
The photosensitive material can be removed, and in this case a
substrate can be baked at a heat resistant temperature of the
photosensitive material or a higher temperature. Thus, it is
advantages in the case that dehydration process for a substrate can
be performed.
[0072] As described above, by applying the-positive resist and then
performing exposure and development to form a desired photopattern,
cap-shaped (an overhanging structure in general) photosensitive
films (photosensitive resin films) 5 are formed as shown in FIGS.
3D and 3I. The portions of the polyimide spacer films 4 which are
exposed when the positive resist is developed are subsequently
removed by using the developer, to form spacers 4 as shown in FIGS.
3E and 3J.
[0073] The development time is determined in accordance with the
undercut amount (i.e., undercut length) of the polyimide spacer
film 4'. The undercut amount is greatly influenced by the polyimide
prebaking temperature and time. In particular, the prebaking
temperature needs to be controlled so as to make the thickness of
the spacer film 4' uniform over the entire substrate surface. In
this embodiment, the development time is so controlled that the
undercut length becomes about 4 .mu.m. Thus, a structure shown in
FIG. 3E is formed. Note that in FIG. 1A, an undercut length 39 is a
length from the side surface of the spacer 4 to the lower edge of
the photosensitive film 5.
[0074] A structure shown in FIG. 4A is formed by consecutively
evaporating, without exposure to the air, i.e., in a vacuum,
N,N'-bis(m-methyl phenyl)-N,N'-diphenyl-1,1'-biphenyl-4,4'-diamine
(hereinafter referred to TPD; see FIG. 15) as a hole injection
layer/hole transport layer of the organic EL film 6,
tris(8-hydroxyquinoline) aluminum (hereinafter referred to
Alq.sub.3; see FIG. 16) as a light emitting layer/electron
transport layer of the organic EL film 6, and an Mg/Ag alloy
(weight ratio: 10:1) film as the second electrode 7. The thickness
of each of the TPD layer and the Alq.sub.3 layer constituting the
organic EL film 6 is 500 angstrom and the thickness of the Mg/Ag
alloy film constituting the second electrode 7 is 2,000
angstrom.
[0075] In the invention, the constituent films of the organic EL
element and the order of laying those films are not limited to
those of this embodiment. The hole injection layer, the light
emitting layer, and the second electrode may be made of materials
other than the above ones. A hole injection layer, an electron
transport layer, an electron injection layer, and other layers may
additionally be formed to provide multilayer structures.
[0076] In order to form the organic EL films 6, the second
electrodes 7, and other layers only on the light emitting portion
(i.e., display screen portion), the evaporation is performed by
using a metal mask that is mounted on a substrate holder of an
evaporation apparatus.
[0077] As shown in FIGS. 4A and 4B, after the formation of the
organic EL films 6 and the second electrodes 7, the substrate is
transferred without exposing to the air, i.e., in a vacuum, to a
vacuum chamber capable of film formation by sputtering, so that the
metal films 8 such as Al films are formed by sputtering. In this
process, it is important that the metal films 8 be formed by a
method that can provide superior step coverage to the method by
which the organic EL films 6 having organic EL layers are formed.
In this manner, the Al films are also formed in the undercut
regions, so that the organic EL films 6 which are not resistant to
water and oxygen are completely shielded from the air.
[0078] The above process provides a notable advantage that the
organic El, films 6 can be shielded from an organic solvent used in
etching, as well as from water and oxygen. In the conventional
structure, the entire organic EL film is removed by an organic
solvent that has soaked into it from an exposed portion of the film
at an end portion of the pattern, for example. Thus, once the
organic EL film is formed, it is prohibited to be in contact with
any organic solvent, which restrict the kinds of usable
manufacturing processes. In contrast, the invention allows use of a
variety of manufacturing processes.
[0079] To further improve the resistance to water and an organic
solvent, the protecting films 9 such as SiO.sub.2 films may be
formed as shown in FIG. 4B after the metal films 8 made of a stable
metal such as aluminum are formed.
[0080] In this embodiment, Al films are formed at a sputtering
pressure of 8.times.10.sup.-3 torr. The sputtering pressure is
desired to be as high as possible. This is because if the
sputtering pressure is higher, Al atoms emitted from the Al target
to various directions more likely collide with argon atoms and are
scattered, so as to go into the undercut regions more likely,
whereby the organic EL films 6 are sufficiently covered with the Al
films. That is, the mean free path of Al atoms should be shorter
than the distance between the target and the substrate. On the
other hand, if the sputtering pressure is high, the formation rate
decreases due to a reduction in the voltage applied to the target
and the scattering of Al atoms. Thus, the sputtering pressure is
determined by a balance between the productivity and the step
coverage.
[0081] Although in this embodiment the metal films 8 of a stable
metal such as aluminum are formed by sputtering, the invention is
not limited to such a case. For example, similar advantages are
obtained by methods capable of providing good step coverage such as
a method in which evaporation is performed in a low vacuum with
introduction of an inert gas, plasma CVD, and photo-assisted CVD.
The same methods apply to the formation of the SiO films as the
protecting films 9.
[0082] By the way, when lead out Al electrode pads (not shown) are
formed to connect a control integrated circuit (IC) to the metal
films 8 which are in contact with the second electrodes 7, the lead
out Al electrode pads are arranged at side portions of the display
portion so as not to cause defect portions on the display portion.
To prevent the constituent films of the organic EL elements and the
SiO.sub.2 films from being formed below and above the Al electrode
pads, respectively, the Al electrode pads are shielded by the metal
masks in forming the constituent films of the organic EL elements 6
and the SiO.sub.2 protecting films. This is to improve the
adhesiveness between the Al electrode pads and the substrate and to
prevent insulating films from being formed on the Al electrode
pads. In plasma CVD and photo-assisted CVD which are much superior
in coverage performance, the SiO.sub.2 films may be formed on the
Al electrode pads even if the metal masks are used. In such a case,
connection holes reaching the Al electrode pads may be formed by
photolithography.
[0083] When insulating films such as SiO.sub.2 films are formed as
the protecting films 9 in the final process, even if the resist
films, i.e., the photosensitive films 5 are broken by mechanical
pressure, the respective display lines would be still covered with
the protecting films 9. Thus, if only the resist in the vicinity of
the Al electrode pads on which no insulating film is formed is
wiped off by using a solvent, failures such as a short circuit via
constituent films of the organic EL elements will not occur without
removing the constituent films remaining on the resist in the
vicinity of the display lines. The elimination of the process of
removing the cap-shaped resist remaining over the entire substrate
surface is advantageous in the manufacturing cost.
[0084] To provide more reliable organic EL elements by protecting
the organic EL films from physical contact, pollution, etc., it is
desirable to attach a glass substrate or the like to the organic EL
elements from above (i.e., from the opposite side of a display
surface). However, in such a case, a solvent contained in an
adhesive dissolve the resist films, i.e., the cap-shaped
photosensitive films (photosensitive resin films) to possibly cause
a short circuit between adjacent organic EL elements if insulating
films as the protecting films are not formed in the final process.
Thus, when the glass substrate or the like for protection is
attached to the organic EL elements from above, it is desirable to
remove in advance the constituent films of the organic EL elements
and Al films remaining on the photosensitive resin films. These
films can easily be removed by immersing them in a chemical
solution that can dissolve the photosensitive resin films or the
spacers. A structure shown in FIG. 4C can be formed by removing
only the photosensitive resin films by using an alcohol such as
ethanol or isopropyl alcohol, an ester such as butyl acetate or
ethyl acetate, or an organic solvent such as acetone or xylene.
[0085] Both the spacers 4 and the photosensitive resin films can be
removed by using a resist removing solution such as NMP,
.gamma.-butyrolactone, or type number MS-2001 of Fuji Hant Co.,
Ltd. which is on the market. In this case, the thin films formed on
the photosensitive resin films are lifted off. By removing also the
spacers 4, the thin films on the photosensitive resin films 5 can
easily be lifted off. Thus, this process is easy on
manufacture.
[0086] If the spacers 4 are left as shown in FIG. 4C, they can be
used as posts. That is, when the substrate for protection is
attached as described above, since it is not in contact with the
organic EL elements because of the existence of the spacers 4,
physical influences of the substrate on the organic EL elements can
be lowered and it is advantageous on the prolongation of the life
of the organic EL elements.
[0087] In this manner, the manufacturing process and the structure
of the organic EL elements may be determined in accordance with the
purpose of manufacturing the organic EL display device, that is,
depending on which of the manufacturing cost and the life is
important.
[0088] In this embodiment, only the photosensitive resin films 5
are removed and the spacers 4 are left as shown in FIG. 4C. Also,
to further improve the water resistance, carbon fluoride polymer
films (not shown) are formed on the protecting films 9 by plasma
CVD. Film forming gases of CF.sub.4 and CHF.sub.3 to be used are
decomposed at a gas pressure of 100 m torr to form the carbon
fluoride polymer films. Since plasma CVD provides better coverage
performance than sputtering, it is difficult to lift off the
photosensitive resin films 5 on the spacers 4 once the carbon
fluoride polymer films are formed.
[0089] The portions of the carbon fluoride polymer films formed on
the Al electrode pads are removed by photolithography using enzyme
plasma, and then the resist is removed. Thus, a desired organic EL
display device is completed.
[0090] In the organic EL display device thus manufactured which is
superior in the resistance to water and an organic solvent, the
display lines are independent of each other and the organic EL
films are completely covered with the stable thin films. Thus, it
has been confirmed that the organic EL display device of this
embodiment is as reliable as organic EL display devices constituted
of conventional organic EL elements which operate in a vacuum or a
dried nitrogen atmosphere.
Embodiment 2
[0091] FIGS. 5A-5E and 7A-7B show a manufacturing process of an
organic EL display device according to a second embodiment of the
invention. The second embodiment is directed to the process of
manufacturing a simple matrix (multiplex) type display device in
which one pixel size is 330 .mu.m.times.110 .mu.m, the number of
pixels is 320.times.240.times.3 (RGB) dots, and color filters are
provided. In comparison with the first embodiment, in this
embodiment, a higher resolution display device is manufactured and
color filters are formed in advance.
[0092] FIG. 6 is a plan view of a color filter portion of the
organic EL display device according to the second embodiment of the
invention, in which the top-right block and the bottom blocks are
drawn in white to describe dimensions of color filters. One pixel
has a size of 330 .mu.m.times.110 .mu.m. A TiN film and an Al film
are shown as connecting portions C to ITO films which portions have
a size of 30 .mu.m.times.30 .mu.m and a line L having a width of 10
.mu.m. FIGS. 5A-5E and 7A-7B are sectional views taken along a dot
line A-A' in FIG. 6.
[0093] As the resolution increases, the electric resistance of
transparent conductive films such as ITO films more likely causes a
problem. To solve this problem, the Al films, whose resistivity is
about {fraction (1/100)} of that of the transparent conductive
films, are used to form a laminate structure with the transparent
conductive films, to thereby reduce the resistance value. Since
direct contact between the Al film and the transparent conductive
film causes a large contact resistance, it may be better to form a
TiN film, a Cr film, or other film between those films.
[0094] An Al film of about 1.5 .mu.m in thickness is formed on a
transparent substrate (not shown) such as a glass substrate by
sputtering. Immediately thereafter, a TiN film of about 300
angstrom in thickness is formed thereon by sputtering. Thus, a
laminate film of the Al film and the TiN film is formed. If the Al
film and the TiN film are formed in succession without being
exposed to the air, i.e., in a vacuum, a native oxide film can be
prevented from being formed on a surface of the Al film, so that
good contact is obtained between the Al film and the TiN film.
Instead of the Al film, an Al alloy film containing an element
other than aluminum may be used. To prevent uneven portions
(hillocks) from being formed on the surface of the Al film due to
crystal growth of aluminum in a later heat treatment process, it is
in many cases desirable to use an Al alloy film containing scandium
(Sc) or the like.
[0095] The laminate film of the Al film and the TiN film is then
patterned by photolithography to obtain Al films 11 and TiN films
12 formed thereon as shown in FIG. 5A. To obtain a high throughput
and a good processed shape, the TiN film and the Al film are etched
at the same time by dry etching.
[0096] The dry etching is reactive ion etching (RIE) in which the
electric power is 2,000 W, the gas pressure is 100 m torr, and
etching gases are Cl.sub.2 and BCl.sub.3. After the etching, ashing
is performed without exposure to the air, i.e., in a vacuum. This
is to prevent corrosion of aluminum after the dry etching, which is
called "after-corrosion." Wet etching may be performed because a
poor processed shape does not cause any serious problems.
[0097] To form color filters, a pigment dispersion type color
filter application/formation process is performed which is most
commonly employed as a coloring manner for liquid crystal displays.
Application conditions for forming RGB (red, green, blue) filters
at a thickness of 1.0-2.5 .mu.m are determined. In FIG. 5B, red
filters 13, green filters 14, and blue filters 15 are patterned to
expose the surfaces of the TiN films 12.
[0098] For example, the application/formation process of the red
filters 13 is as follows. After a red filter solution is applied by
spin coating at 1,000 rpm (revolutions per minute) for about 5
seconds, prebaking is performed at 100.degree. C. for 3 minutes.
Then, a photomask is positioned by using an exposing apparatus, and
ultraviolet light of 20 mW/cm.sup.2 is irradiated for 30 seconds.
Subsequently, development is performed with an about 0.1% TMAH
aqueous solution. The development time is about one minute.
Further, thermal curing is performed at 220.degree. C. for one hour
so that the red filters 13 thus formed will not be dissolved by
filter solutions of the other colors (green and blue) to be applied
in the later processes.
[0099] Because of the use of different pigments, the conditions for
forming the green filters 14 and the blue filters 15 are somewhat
different from those for forming the red filters 13. However, the
green filters 14 and the blue filters 15 may be formed sequentially
by approximately the same processes as the processes for forming
the red filters 13. Thus, the red filters 13, the green filters 14,
and the blue filters 15 are formed as shown in FIG. 5B.
[0100] Although this embodiment relates to the case of forming only
the color filters because it can be manufactured relatively easily,
the invention is not limited to such a case. For example,
fluorescence conversion filters may be used to output green light
and red light through color conversion, to provide more intense
light. Further, a laminate structure of color filters and
fluorescence conversion filters may be formed to prevent reduction
in brightness while improving the purity of colors.
[0101] In order to improve the flatness of the forming surface of
an ITO film to be formed in a later process, an overcoat material
such as polyimide or acrylic resin is applied to the red filters
13, the green filters 14, and the blue filters 15, and then
patterning is performed to expose the surfaces of the TiN films 12.
Also, thermal curing is performed at about 220.degree. C. for one
hour, to form overcoat layers 16 as shown in FIG. 5C.
[0102] After the formation of the overcoat layers 16, an ITO film
as a transparent conductive film is formed at a thickness of about
1,400 angstrom by sputtering. Further, a resist pattern is formed
by photolithography, and then the ITO film is etched with dilute
hydrochloric acid. The resist is removed to form an ITO film 17
(see FIG. 15D). Therefore, a pattern in which the transparent
conductive film and the Al film wiring that is formed to reduce the
resistance are connected to each other is formed to constitute a
display line (column line).
[0103] An SiO.sub.2 film as an insulating film is formed on the
patterned ITO film 17 by sputtering, and then patterned to remain
in the regions other than the regions where light emitting portions
are seen from the side of the glass substrate (not shown), so that
SiO.sub.2 films 18 are formed (see FIG. 5E). By the structure in
which the ITO film 17 is covered with the SiO.sub.2 films 18,
useless light emission in the regions not seen from the glass
substrate side can be avoided. In addition, since holes or grooves
are necessarily formed in these regions, an organic EL film such as
a light emitting layer evaporated on an inclined portion may be
rendered thin, to possibly form a current leak path. Thus, the
formation of the insulating film is desirable.
[0104] Although in this embodiment an SiO.sub.2 film is used as the
insulating film, the invention is not limited to such a case. Since
what is needed is insulation, not only an inorganic insulating film
such as an SiO.sub.2 film and an SiN.sub.x film but also resin such
as polyimide, acrylic resin, and epoxy resin may be used. In
patterning the insulating film, if a mask pattern is formed such
that insulating films are left also in the regions where spacers
are to be formed, a process for forming insulating films under a
spacer film can be omitted.
[0105] After the patterning of the SiO.sub.2 films 18, resist films
20 having a cap-shaped structure (overhanging structure in general)
are formed on spacers 19 by processes similar to the processes of
FIGS. 3C-3E with a polyimide film used as a spacer film (see FIG.
7A).
[0106] For a color display, light emitting elements are constructed
by forming the following materials on the structure of FIG. 7A. In
this embodiment, organic EL materials are used which emit white
light.
[0107] To form a yellow light emission organic EL film,
polythiophene (see FIG. 17) is evaporated at a thickness of 100
angstrom as a hole injection layer, and then TPD doped with rubrene
(see FIG. 18) at 1 weight % is coevaporated at a thickness of 500
angstrom as a hole transport layer/yellow light emission layer. It
is preferable that the concentration of rubrene be in a range of
0.1 to 10 weight %, in this range high efficiency light emission is
attained. The rubrene concentration, which may be determined in
accordance with the color balance of light emission colors, depends
on the light intensity and the wavelength spectrum of a blue light
emission layer to be formed in a later process. To form a blue
light emission organic EL film, 4,4'-bis [(1, 2,
2-trisphenyl)ethenyl]-biphenyl (see FIG. 19) is evaporated at a
thickness of 500 angstrom as a blue light emission layer, and then
Alq.sub.3 is evaporated at 100 angstrom as an electron transport
layer. They are evaporated in succession without being exposed to
the air, i.e., in a vacuum. Thus, organic EL films 21 are
formed.
[0108] Further, an Mg/Ag alloy (weight ratio: 10:1) film is
evaporated at a thickness of 2,000 angstrom as second electrodes 22
without being exposed to the air, i.e., in a vacuum. Then, Al films
23 and SiO.sub.2 protecting films 24 are formed in succession by
sputtering in the same manner as in the processes of FIGS. 4B and
4C.
[0109] Finally, the resist films 20, the various thin films formed
thereon, and the spacers 19 are removed by a removing solution, to
provide a desired simple matrix organic EL display device as shown
in FIG. 7B.
[0110] According to this embodiment, since the evaporation method
can be one in which the uniformity of films are regarded as
important, the yield can be increased and the light emission
characteristic can be made uniform.
[0111] Conventionally, a material not resistant to water or oxygen
is necessarily exposed to the air even temporarily, which decreases
the reliability of organic EL elements thereby. In contrast, the
invention can provide organic EL elements with very high
reliability because the organic EL film can be completely covered
with a material that is stable with respect to water and oxygen on
each display line (pixel line).
[0112] Numerical values used in the invention are merely examples
and the invention is not limited to those values.
[0113] According to the invention, the overhanging portions wider
than the spacers can easily be formed by overetching. By the
existence of the overhanging portions, the organic EL elements can
be isolated easily.
[0114] According to the invention, since only the overhanging
portions formed on the spacers can be removed, a sealing glass
substrate or the like for sealing the entire device can easily be
provided over the organic EL elements.
[0115] According to the invention, since not only the overhanging
portions but also the spacers can be removed, even an adhesive
containing a solvent capable of dissolving a resist or the like can
be used as the adhesive for adhering a sealing glass substrate or
the like to the device. This allows selection of an adhesive from a
wide variety of and various kinds of adhesives.
[0116] Further, according to the invention, the protecting films
constructed by at least one of an insulating film and a metal film
which is stable with respect to oxygen, water and organic solvents
can be formed on the second electrodes by using a method that can
provide better step coverage than methods for forming the organic
films and the second electrodes. This allows photolithography to be
conducted thereafter. Thus, the embodiment enables manufacture of
an organic EL display device having very high reliability and a
long life.
Embodiment 3
[0117] FIGS. 13A-13C and 14A-14C are plan pattern views and
sectional views of a light emitting portion of an organic EL
display device having element isolating structure portions formed
therein according to the invention. If the element isolating
structure portions as shown in FIG. 1A are formed straight, the
element isolation can be effected with a very high yield. However,
in FIG. 13B that is a sectional view taken along a dot chain line
B-B' in FIG. 13A, the undercut length tends to be short in a region
inside a portion of an element isolating structure portion 121
where it is bent at 90.degree. or less or a region inside its
curved portion having a small curvature. As a result, there may
occur a case that the light emitting portion and the element
isolating structure portion are short-circuited with each other via
a metal film 116 made of a stable metal that is hardly affected by
water, oxygen, and organic solvents. This will cause a reduction in
yield.
[0118] That is, in the case wherein light emitting portions 120a
and 120b are isolated from each other by the element isolating
structure portion 121 having an overhanging structure of FIG. 13A,
if the bending portions have an angle of 90.degree. or less, the
undercut length becomes very short in the regions inside the
bending portions as indicated by a dot line in the enlarged part of
FIG. 13A. As a result, when an organic EL film 114, a second
electrode 115, a metal film 116, and other films are formed in each
of the light emitting portions 120a and 120b, the metal film 116 is
formed also on the side surface of a spacer 112 in the undercut
region where the undercut length is very short as shown in FIG.
13B. In this manner, the metal film 116 formed above a resist 113
and the light emitting portion 120a and 120b are connected to each
other.
[0119] The short circuit may also occur in a region inside a curved
bending portion of the element isolating structure portion which
has a radius of curvature of 5 .mu.m or less.
[0120] When the element isolating structure portion 121 is formed
straight as in a portion indicated by a dot chain line A-A' in FIG.
13A, the undercut length of the spacer 112 is proper as shown in
FIG. 13C that is a sectional view taken along line A-A' in FIG.
13A. Since the metal film 116 is not formed on the side surface of
the spacer 112 so as to assume a thick film, the metal films 116
formed above and below the resist 113 are not short-circuited with
each other.
[0121] Conversely, in a region outside a bending portion
(90.degree. or less) of the element isolating structure portion 121
(see FIG. 14A), an undercut region 117 becomes extremely long as
shown in FIG. 14B that is a sectional view taken along a dot chain
line B-B' in FIG. 14A. As a result, when the overhanging body of
the element isolating structure portion 121 is constituted only of
a resist 113, the overhanging body likely hangs down as shown in
FIG. 14C. This may cause a short circuit between the metal films
116 which are formed on the light emitting portion and the outside
portion of the element isolating structure portion 121 when the
metal films 116 are formed.
[0122] To reduce the number of lead out electrodes of a display
device having complicated patterns, it is necessary to form element
isolating structure portions that meander. It is desired to
increase the yield in forming those element isolating structure
portions.
[0123] When a bending portion of the element isolating structure
portion has an angle of 90.degree. or less or it is curved at a
small radius of curvature of 5 .mu.m or less, the reason why the
undercut length varies with the shape of the plan pattern is
considered non-uniformity in the degree of the action that an
etching chemical goes around to act on the spacer film. Thus, in a
region where the undercut length tends to be short, it is expected
that the non-uniformity can be avoided by employing a plan pattern
that allows an etching chemical to go around more easily.
[0124] It has been confirmed that a marked increase in yield can be
obtained by forming a photomask pattern that is free of a portion
where the element isolating structure portion is bent at a small
angle of 90.degree. or less as a simplest but effective method for
attaining a plan pattern that allows an etching chemical to go
around more easily in undercutting the spacer film.
[0125] Although a pattern bending angle larger than 90.degree. is
effective, the bending angle should be 100.degree. or more and,
more desirably, 135.degree. or more. In experiments, portions
having a bending angle of 135.degree. show a difference in undercut
length of only 30% as compared to straight portions. That is, it
has been confirmed that the undercut length decreases by 30% in
regions inside such bending portions from that of the straight
portions, and that it increases by 30% in regions outside the
bending portions.
[0126] When an organic EL display device having the element
isolating structure portions on a substrate is manufactured by
using the above described pattern, no short circuit is observed in
the bending portions. A similar increase in yield is obtained by
forming circular arc patterns having radii of curvature that are
larger than 5 .mu.m.
[0127] The third embodiment of the invention will be described in a
more specific manner with reference to FIGS. 9A and 9B, which are
plan pattern views and sectional views of light emitting portions
of an organic EL display device according to the third embodiment
of the invention. In FIG. 9A, an element isolating structure
portion 31 isolates light emitting portions 32a and 32b constituted
of organic EL films and other films. The element isolating
structure portion 31 is composed of a resist 33 and a spacer 34,
and regions inside its bending portions are bent at an angle of
135.degree..
[0128] In FIG. 9B that is a sectional view taken along a dot chain
line A-A' in FIG. 9A, the regions inside and outside the spacer 34
which are formed under the resist 33 have sufficiently long
undercut lengths of about 3 .mu.m and about 4 .mu.m, respectively.
Thus, no short circuit occurs when a metal wiring film is formed on
this structure.
[0129] As described above, according to the invention, a flat panel
display using organic EL elements which can be manufactured at a
stable, high yield and enables various lighting patterns is
obtained.
Embodiment 4
[0130] FIGS. 10A and 10B are plan pattern views and sectional views
of light emitting portions of an organic EL display device
according to the fourth embodiment of the invention. In FIG. 10A,
an element isolating structure portion 31' isolates light emitting
portions 32a' and 32b' constituted of organic EL films and other
films. The element isolating structure portion 31' is composed of a
resist 33' and a spacer 34', and regions inside its bending
portions assume circular arcs having a radius of 10 .mu.m.
[0131] In FIG. 10B that is a sectional view taken along a dot chain
line A-A' in FIG. 10A, the regions inside and outside the spacer
34' formed under the resist 33' have sufficiently long undercut
lengths of about 3 .mu.m and about 4 .mu.m, respectively. Thus, no
short circuit occurs when a metal wiring film is formed on this
structure.
Embodiment 5
[0132] FIGS. 11A-11C are plan pattern views of a display portion of
an organic EL display device according to a fifth embodiment of the
invention, and FIGS. 12A-12H are plan pattern views and sectional
views of a bar graph portion of the display portion of the above
organic EL display device. The fifth embodiment is directed to a
case of manufacturing a 2-digit digital counter with a bar
graph.
[0133] FIG. 11A is a view of a 2-digit digital counter as viewed
from the organic EL film side (i.e., the bask side) rather than
from the transparent substrate side (i.e., the display side), and
is hence a mirror image of an ordinary view as viewed from the
display side. FIG. 11A also shows light emitting regions as viewed
from the organic EL film side.
[0134] FIG. 11B shows a relationship between the pattern of ITO
films (indicated by dot lines) formed on a substrate 40 and
openings (where the ITO films are exposed; indicated by solid
lines) that are obtained by partially removing an insulating film
formed on the ITO films.
[0135] FIG. 11C shows element isolating structure portions 41a and
41b, an area E where organic EL films and second electrode portions
are formed, and an area S where metal wirings made of a stable
metal hardly affected by water, oxygen, and organic solvents and
protecting films are formed. The element isolating structure
portion 41a isolates the bar graph from the numeral displaying
portion as well as isolates the bar graph into two sections. The
element isolating structure portion 41b encloses the numeral
display portion.
[0136] After the openings (indicated by solid lines) are formed by
partially removing the insulating film formed on the pattern of the
ITO films (indicated by dot lines) as shown in FIG. 11B, the
element isolating structure portions 41a and 41b are formed as
shown in FIG. 11C. As described later, the element isolating
structure portions 41a and 41b are formed with a pattern in which
every bending portion has a bending angle of 135.degree.. The
element isolating structure portion 41a includes a slant straight
portion 41a' formed at the center of the 2-figure bar graph.
[0137] After the element isolating structure portions 41a and 41b
are formed, organic EL films and second electrodes containing a
metal having a small work function are formed by evaporation in the
area E indicated by the dot chain line, and metal films and
protection films are formed in the area S indicated by the two-dot
chain line (see FIG. 11C). At this time, a common electrode C1 is
connected to the metal film of the element isolating structure
portion 41a-1 located on the right side of the slant straight
portion 41a', and a common electrode C2 is connected to the metal
electrode of the element isolating structure portion 41a-2 located
on the left side of the slant straight portions 41a'. A common
electrode C3 is connected to the metal electrode of the element
isolating structure portion 41b.
[0138] A manufacturing process of the bar graph will be described
with reference to FIGS. 12A-12H. FIGS. 12A-12D are plan views of
the bar graph pattern, and FIGS. 12E-12H are sectional views taken
along dot chain lines A-A', B-B', C-C', and D-D' in FIGS. 12A-12D,
respectively.
[0139] An inexpensive soda glass substrate is used as a substrate
40 for an organic EL display device. A silica coating is performed
for the entire surface of the substrate 40. The silica coating
prevents sodium from being eluted from the glass substrate when it
is heated, protects the soda glass substrate that is not resistant
to acids and alkalis, and improves the flatness of the glass
substrate surface.
[0140] Next, an ITO film which is a transparent conductive film as
a first electrode is formed at a thickness of 1,000 angstrom on the
glass substrate 40 by sputtering. The use of the ITO film is due to
the fact that it exhibits superior characteristics to films made of
other materials when used as a transparent conductive film.
However, a transparent electrode of a ZnO film, SnO.sub.2 film, or
the like may also be used if it has transmittance and resistivity,
for example, that will not cause any problem during use. When the
ITO film is formed over a large area, sputtering is advantageous in
uniformity and film quality of a resulting film as well as
productivity. The ITO film need not always be formed by sputtering,
and may be formed by evaporation, for example.
[0141] After a resist pattern is formed on the formed ITO film by
photolithography, unnecessary portions of the ITO film are removed
by etching and then the resist is removed, to leave a desired
electrode pattern of the ITO film 41 (see FIGS. 12A and 12E).
[0142] Next, a film for determining the light emitting regions is
formed on the ITO film 41. Any insulating film may be used as this
film. The film may be formed by various methods: forming an
inorganic thin film such as an SiO.sub.2 film or an SiN.sub.x film
by sputtering or vacuum evaporation, forming an SiO.sub.2 film by
SOG coating, and applying resist, polyimide, acrylic resin, or the
like. Since it is necessary to expose a portion of the ITO films 41
formed under the insulating film, the insulating film needs to be
patterned without damaging the ITO film 41. Although there is no
limitation on the thickness of the insulating film, when an
inorganic thin film is used, the manufacturing cost can be reduced
by decreasing the thickness thereof.
[0143] In this embodiment, polyimide is used to form the insulating
film. Non-photosensitive polyimide to be prepared is diluted to
about 5% with NMP or .gamma.-butyrolactone. Such polyimide is
applied by spin coating, and then prebaked at 145.degree. C. for
one hour. After a positive resist is applied, patterning is
performed (see FIGS. 12B and 12F).
[0144] Exposed portions of the resist and corresponding portions of
the polyimide film are removed sequentially-with an aqueous
solution of TMAH having a concentration of about 2.38%. TMAH is a
developer for the resist. Further, only the remaining portions of
the resist are removed by ethanol, to form a desired insulating
film 42. Although the above description is directed to the case of
using non-photosensitive polyimide, photosensitive polyimide may
also be used. In this case, no resist is needed.
[0145] The polyimide insulating film 42 thus obtained is completely
cured at a temperature not higher than 350.degree. C. so as not to
be affected by chemical solutions to be used in later process.
Since the insulating film 42 contract at this time, the steps are
tapered. Thus, a pattern for exposing only the light emitting
portions and connecting portions to external circuits is obtained
(see FIG. 12B)
[0146] Subsequently, a spacer film to be used as a spacer 43 is
formed (see FIG. 12G). Because of their purpose, the spacer 43 may
be either a conductor or an insulator, and have-either a single
layer or multilayer structure. However, when the spacer 43 is a
conductor, there is a possibility that metal films formed in a
later process cause a short circuit or a current leak between
adjacent display lines via a spacer 43. This problem may be solved
by making the undercut amount in etching the spacer film
sufficiently large.
[0147] As described above, the spacer made of a metal has the
following advantages. (1) Since the spacer is sufficiently strong
and malleable, the elements that are easily rendered faulty due to
the existence of dust can sufficiently be cleaned with ultrasonic
waves, for example. (2) Since the spacer is more resistant to heat
than a resist etc., dehydration can be effected by heat treatment.
(3) Since the spacer is hardly charged, particles are less likely
to attach to the spacer. (4) When a short circuit occurs in an
element circuit due to dust, the spacer can be burnt off.
[0148] It is necessary to select an etching material for the spacer
film which neither etches nor affects the ITO film 41 that are in
contact with the spacer film in etching the spacer film. Also,
since the spacer film is used to form the spacer 43, it should be
so formed as to be thicker than all of an organic EL film, a second
electrode, a protecting film, and other films. Thus, it is
desirable that the spacer film be made of a material which allows
easy formation of a thick spacer film. Examples of such a film are
an SOG film and a resin film. When the spacer film is made of a
metal material, a laminate structure of a Cr film, a Ti film, a TiN
film, or other film as an etching barrier film formed on the ITO
film 41 to prevent their etching and an Al film or other film which
has a high formation rate may be formed. The etching barrier film
is not limited to a metal material.
[0149] When polyimide is used to form the spacer 43, polyimide
whose concentration has been adjusted to 15% is spin-coated at a
thickness of 2 .mu.m, and then prebaked at 145.degree. C. for one
hour. The thickness of polyimide can be adjusted by the
concentration of the solution to be applied by spin coating and the
rotational speed of the spin coater. The polyimide film can be made
thicker by increasing the concentration or decreasing the
rotational speed.
[0150] Subsequently, a positive resist is applied to the prebaked
polyimide film. When the thickness of the positive resist is not
less than 1 .mu.m, desirably not less than 2 .mu.m, a highly
viscous resist is used or the rotational speed of the spin coater
is set low.
[0151] Since the positive resist is relatively fragile, the method
of forming a thick resist is employed in this embodiment. However,
no such method is needed if a harder film is formed and then a
resist is applied thereon, i.e., if a harder film is formed under
the resist to support the resist, as described above. That is, it
is not necessary to increase a thickness of the resist. The use of
the harder film such as a support film has another advantage that a
dehydration treatment by heating for eliminating water absorbed on
the substrate surface can be performed in a later process.
Conversely, if a heat treatment is performed without formation of
the support film, the resist becomes likely to be deformed and
undercut regions may be broken. Further, if the support film is
made even stronger, since the overhanging portions remain even
after removal of the resist, dehydration by heating the substrate
to a temperature no lower than the maximum heat resistant
temperature of the resist can be performed. Thus, as described
above, the structure as shown in FIG. 20 can be also formed so that
the harder film 64 as the support film supports the resist 65 as a
photosensitive material.
[0152] Exposure and development are performed to form a desired
photolithography pattern of the element isolating structure portion
41a. Portions of the polyimide film which are exposed by this
resist development are also removed subsequently to the removal of
the resist.
[0153] As shown in FIG. 12C, even in bending portions of the
pattern which may be given an angle of 90.degree., the number of
bending portions is increased to provide larger bending angle. That
is, the patterning is so made that the bending portions have a
bending angle of 135.degree..
[0154] The undercut amount of the polyimide film formed under the
resist is determined based on the development time. The undercut
amount is also greatly influenced by the polyimide prebaking
temperature and time. In particular, it is necessary to control the
prebaking temperature so that the film quality of the polyimide
film be uniform over the entire substrate surface. In this
embodiment, the development time is so determined that the undercut
length becomes about 4 .mu.m. In this manner, as shown in FIG. 12G,
an element isolating structure portion having the polyimide spacer
43 and a resist 44 is formed similar to that of FIG. 1A.
[0155] Next, TPD as a hole injection layer/hole transport layer of
an organic EL film, Alq.sub.3 as a light emitting layer/electron
transport layer of the organic EL film, and an Mg/Ag alloy (weight
ratio: 10:1) film as a second electrode are consecutively
evaporated in a consecutive evaporation chambers without being
exposed to the air, i.e., in a vacuum. The thickness of each of the
TPD layer and the Alq.sub.3 layer is set at 500 angstrom and the
thickness of the Mg/Ag alloy layer is set at 2,000 angstrom.
[0156] In the invention, the constituent films of the organic EL
element and the order of laying those films are not limited to
those of this embodiment. The hole injection layer, the light
emitting layer, and the second electrode may be made of materials
other than the above ones. A hole injection layer, an electron
transport layer, an electron injection layer, and other layers may
additionally be formed to provide laminate structures. Further, the
thicknesses of the respective films are not limited to those of the
embodiment. That is, the invention is applicable irrespective of
the kinds of film forming materials and the structure of the
films.
[0157] The respective films of TPD, Alq.sub.3, and the second
electrode are formed only in the area E by using a metal mask
provided in the evaporation apparatus. In FIGS. 12D and 12H, an
organic EL constituent film 45 including the organic light emitting
layer includes organic films such as TPD and Alq.sub.3 and the
second electrode.
[0158] After the evaporation of TPD serving as the hole injection
layer/hole transport layer, Alq.sub.3 serving as the light emitting
layer/electron transport layer, and the second electrode, a TiN
film and an Al film are formed in succession by sputtering without
being exposed to the air, i.e., in a vacuum, to form a metal wiring
film 46 (see FIG. 12H). The TiN film is formed between the Al film
and the patterned ITO film as the connection electrode terminal to
improve the contact performance between those films.
[0159] The metal wiring film 46 is formed via the metal mask. The
opening size of the metal mask is so designed that the metal wiring
film is not formed on the portions where lead out wirings for the
ITO film located outside the area enclosed by the two dot chain
line (see FIG. 11C) are connected to external circuits. Thus, the
metal wiring film 46 is formed only in the area S enclosed by the
two dot chain line in FIG. 11C.
[0160] The resulting digital counter with the bar graph is divided
by the element isolating structure portions 41a-1, 41a-2, and 42a.
The three second electrodes are provided therein (see FIG. 11C).
The common electrode C3 for numeral display is always grounded
electrically. The common electrodes C1 and C2 are supplied with a
voltage having an operation frequency of 60 Hz and a duty ratio of
1/2; that is, they are supplied with the grounding voltage and the
same voltage as the first electrode alternately.
[0161] When the common electrode is not divided, the number of
electrode terminals connected to the bar graph portion is the same
as the number of electrode terminals connected to the numeral
display portion, i.e., 10. In this case, the common electrode is
shared by the bar graph portion and the numeral display portion. On
the other hand, if the common electrode is divided, the number of
total terminals can be made 7:5 terminals that are connected to the
first electrodes plus 2 terminals for the common electrodes C1 and
C2. As such, the invention is effective in dividing common
electrodes of various shapes with a high yield.
[0162] Although this embodiment is directed to the case where the
bending portions of the plan pattern of the element isolating
structure portions have an angle larger than 90.degree., the same
advantages can be obtained even in a case where the bending
portions of the plan pattern are so formed as to assume circular
arcs having a radius of curvature larger than 5 .mu.m.
[0163] As described above, by etching the spacer film so that the
undercut length does not have a large variation (the uniformity of
the undercut length is improved) in the regions inside and outside
the bending portions of the plan pattern of the element isolating
structure portions, overhanging portions are overhang by a
sufficient amount in the above inside and outside regions. Thus,
organic EL elements can be isolated certainly.
[0164] The invention provides the following superior
advantages:
[0165] (1) Since the bending portions of the plan pattern of the
element isolating structure portions having an overhanging
structure have angles larger than 90.degree., the yield of element
isolation can be increased remarkably. If the angles of the bending
portions are made 135.degree. or more, the element isolating
structure portions can be formed while a short circuit is
completely avoided in the bending portions.
[0166] (2) Since the bending portions of the plan pattern of the
element isolating structure portions are formed by circular arcs
having radii of curvature larger than 5 .mu.m, the yield of element
isolation can be increased remarkably. If the radii of curvature of
the circular arcs of the bending portions are 10 .mu.m or more, the
element isolating structure portions can be formed while a short
circuit is completely avoided in the bending portions.
[0167] (3) Since the uniformity of the undercuts of the element
isolating structure portions are greatly improved, an organic EL
display device can be manufactured at a high yield. Further, since
the second electrodes of various shapes which are isolated
electrically can be formed, an organic EL display device of the
invention can be applied to products of various kinds of display
method.
* * * * *