U.S. patent application number 09/901097 was filed with the patent office on 2002-09-26 for method of manufacturing organic el element, organic el element, and organic el display device.
This patent application is currently assigned to Seiko Epson Corporation. Invention is credited to Kanbe, Sadao, Kiguchi, Hiroshi, Miyashita, Satoru, Shimoda, Tatsuya.
Application Number | 20020136823 09/901097 |
Document ID | / |
Family ID | 18046006 |
Filed Date | 2002-09-26 |
United States Patent
Application |
20020136823 |
Kind Code |
A1 |
Miyashita, Satoru ; et
al. |
September 26, 2002 |
Method of manufacturing organic EL element, organic EL element, and
organic EL display device
Abstract
A method of manufacturing an organic EL element according to the
present invention comprises the steps of forming pixel electrodes
(801), (802), (803) on a transparent substrate (804) and forming on
the pixel electrodes by patterning luminescent layers (806), (807),
(808) made of an organic compound by means of an ink-jet method.
According to this method, it is possible to carry out a high
precise patterning easily and in a short time, thereby enabling to
carry out optimization for a film design and luminescent
characteristic easily as well as making it easy to adjust a
luminous efficiency.
Inventors: |
Miyashita, Satoru;
(Suwa-shi, JP) ; Kiguchi, Hiroshi; (Suwa-shi,
JP) ; Shimoda, Tatsuya; (Suwa-shi, JP) ;
Kanbe, Sadao; (Suwa-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 19928
ALEXANDRIA
VA
22320
US
|
Assignee: |
Seiko Epson Corporation
Tokyo
JP
|
Family ID: |
18046006 |
Appl. No.: |
09/901097 |
Filed: |
July 10, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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09901097 |
Jul 10, 2001 |
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09101083 |
Jul 8, 1998 |
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09101083 |
Jul 8, 1998 |
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PCT/JP97/04283 |
Nov 25, 1997 |
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Current U.S.
Class: |
427/66 ; 347/100;
427/157; 427/256; 428/917; 438/29; 438/99 |
Current CPC
Class: |
H01L 51/5246 20130101;
H01L 27/3281 20130101; H01L 27/3211 20130101; Y10S 428/917
20130101; H01L 51/5253 20130101; H01L 27/3244 20130101; H01L
27/3283 20130101; H01L 51/5284 20130101; H05B 33/10 20130101; H01L
27/3218 20130101; H01L 51/56 20130101; Y10T 428/24868 20150115;
Y10T 428/31855 20150401; H01L 51/001 20130101; C09K 2323/00
20200801; H01L 51/0005 20130101 |
Class at
Publication: |
427/66 ; 427/157;
427/256; 428/917; 438/29; 438/99; 347/100 |
International
Class: |
H05B 033/10; B05D
005/06 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 25, 1996 |
JP |
8-313828 |
Claims
What is claimed is:
1. A method of manufacturing an organic EL element, comprising the
steps of: forming pixel electrodes on a transparent substrate;
forming on said pixel electrodes by patterning at least one
luminescent layer having a certain color and made of an organic
compound; and forming a counter electrode opposing the pixel
electrodes, wherein the formation of the luminescent layer is
performed by means of an ink-jet method.
2. The method of manufacturing an organic EL element as claimed in
claim 1, wherein the organic compound is a polymer organic
compound.
3. The method of manufacturing an organic EL element as claimed in
claim 2, wherein the polymer organic compound is a hole injection
and transfer type material.
4. The method of manufacturing an organic EL element as claimed in
claim 2 or 3, wherein the polymer organic compound is a
polyparaphenylene vinylene or its derivative or a copolymer which
contains at least either one of these compounds.
5. The method of manufacturing an organic EL element as claimed in
any one of claims 1 to 4, wherein said at least one luminescent
layer comprises three luminescent layers having diff erent three
colors, and at least two luminescent layers in the three
luminescent layers are formed by patterning by means of an ink-jet
method.
6. The method of manufacturing an organic EL element as claimed in
claim 5, wherein said three colors include red, green and blue, and
the red luminescent layer and the green luminescent layer are
formed by patterning by means of an ink-jet method.
7. The method of manufacturing an organic EL element as claimed in
claim 6, wherein the blue luminescent layer is formed by a vacuum
deposition method.
8. The method of manufacturing an organic EL element as claimed in
claim 7, wherein the blue luminescent layer is made of an electron
injection and transfer type material.
9. The method of manufacturing an organic EL element as claimed in
any one of claims 1 to 8, wherein said at least one luminescent
layer is laminated with a hole injection and transfer layer.
10. The method of manufacturing an organic EL element as claimed in
any one of claims 1 to 9, further comprising the step of forming a
protective film on the counter electrode.
11. The method of manufacturing an organic EL element as claimed in
any one of claims 1 to 10, further comprising the step of forming
on said transparent substrate electrodes for driving the respective
pixels.
12. The method of manufacturing an organic EL element as claimed in
any one of claims 1 to 11, wherein said pixel electrodes are
transparent pixel electrodes.
13. An organic EL element, comprising: a transparent substrate;
pixel electrodes provided on the transparent substrate; at least
one luminescent layer having a certain color and made of an organic
compound, said luminescent layer being patterned on the pixel
electrodes by an ink-jet system; and a counter electrode formed on
the luminescent layer.
14. The organic EL element, as claimed in claim 13, wherein the
organic compound is a polymer organic compound.
15. The organic EL element as claimed in claim 14, wherein the
polymer organic compound is a hole injection and transfer type
material.
16. The organic EL element as claimed in claim 14 or 15, wherein
the polymer organic compound is a polyparaphenylene vinylene or its
derivative or a copolymer which contains at least either one of
these compounds.
17. The organic EL element as claimed in any one of claims 13 to
16, wherein said at least one luminescent layer comprises three
luminescent layers having different three colors, and at least two
luminescent layers in the three luminescent layers are formed by
patterning by means of an ink-jet method.
18. The organic EL element as claimed in claim 17, wherein said
three colors include red, green and blue, and the red luminescent
layer and the green luminescent layer are patterned by means of an
ink-jet method.
19. The organic EL element as claimed in any one of claims 13 to
18, wherein the blue luminescent layer is formed by a vacuum
deposition method.
20. The organic EL element as claimed in claim 19, wherein the blue
luminescent layer is made of an electron injection and transfer
type material.
21. The organic EL element as claimed in any one of claims 13 to
20, wherein said at least one luminescent layer is laminated with
an electron injection and transfer type material.
22. The organic EL element as claimed in any one of claims 13 to
31, further comprising a protective film formed on the counter
electrode.
23. The organic EL element as claimed in any one of claims 13 to
22, wherein said pixel electrodes are transparent pixel
electrodes.
24. An organic EL display device comprising the organic EL element
as claimed in any one of claims 13 to 23.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a method of manufacturing
an organic electroluminescent (EL) element, an organic EL element,
and an organic EL display device.
BACKGROUND ART
[0002] An organic EL element is an element which has a
configuration in which a thin film containing a fluorescent organic
compound is held between a cathode and an anode. In the organic EL
element, electrons and holes are injected from the respective
electrodes into the thin film to generate excitons through the
recombimation of the electrons and holes. The organic EL element
produces luminescence by utilizing emission of light (fluorescence
or phosphorescence) at the deactivation of the excitons.
[0003] The features of the organic EL element is that it is
possible to obtain a high intensity surface luminescence on the
order of 100 to 100,000 cd/m.sup.2 at a low voltage of less than
10V, and that it is possible to produce luminescence of from blue
to red by the selection of the kind of fluorescent material.
[0004] The organic EL element is drawing attraction as a device for
realizing a large area full color display element at a low cost
(see, Technical Reports of the Society of Electronic Information
and Communications, Vol. 89, No. 106, 1989, p. 49). According to
the report, bright luminescence of blue, green and red were
obtained by forming a luminescent layer using an organic
luminescent material which emits strong fluorescence. This fact is
considered to mean that it is possible to realize a high brightness
full color display by using an organic coloring matter which emits
strong fluorescence in a thin film state and has less pin hole
defects.
[0005] In addition, in Japanese Laid-Open Publication No. Hei
5-78655, there is proposed to use an organic luminescent layer
containing a luminescent material which is formed of a mixture of
an organic charging material and an organic luminescent material,
thereby obtaining a high brightness full color element by
preventing quenching due to higher concentration as well as
expanding the latitude in the selection of the luminescent
material.
[0006] Further, in Appl. Phys. Lett. Vol. 64, 1994, p. 815, it is
reported that a white luminescence was obtained by using polyvinyl
carbazole (PVK) as a luminescent material and doping it with
coloring matters corresponding to three primary colors R, G and B.
However, in neither of the above references, the configuration or
the method of manufacture of an actual full color display panel is
not shown.
[0007] In the organic thin film EL elements using the organic
luminescent materials described above, in order to realize a full
color display device, it is necessary to arrange organic
luminescent layers which emit any one of the three primary colors
for the respective pixels. However, there is a problem in that a
polymer or precursor that forms the organic luminescent layer lacks
a sufficient resistance to a patterning process such as
photolithography, so that it is very difficult to carry out
patterning with highly precision.
[0008] Further, when several organic layers are to be formed by a
vacuum deposition method, it takes a long time. Therefore, such a
method cannot be said to be an efficient method of manufacturing
the element.
SUMMAY OF THE INVENTION
[0009] It is an object of the present invention to provide a method
of manufacturing an organic EL element which makes it possible to
carry out patterning easily and precisely, can attain optimization
of a film design in a simple manner, and has excellent luminescence
characteristics, as well as to provide an organic EL element and an
organic EL display device.
[0010] In order to achieve the above object, the manufacturing
method of an organic EL element according to the present invention
comprises the steps of forming pixel electrodes on a transparent
substrate, forming on the pixel electrodes by patterning at least
one luminescent layer having a certain color and made of an organic
compound, and forming a counter electrode opposing the pixel
electrodes, wherein the formation of the luminescent layers is
performed by means of an ink-jet method.
[0011] In the present invention, it is preferable that the organic
compound is a polymer organic compound. In this case, it is
preferable that the polymer organic compound is a hole injection
and transfer type material. Preferably, such a polymer organic
compound is a polyparaphenylene vinylene or its derivative or a
copolymer which contains at least either one of these
compounds.
[0012] In this connection, when an organic luminescent material
itself is not a hole injection and transfer type material, as is
the case in the above-mentioned polymer organic compound, it is
possible to add a hole injection and transfer type material to the
luminescent layer in addition to the luminescent material.
[0013] Further, it is also preferred that the at least one
luminescent layer comprises three layers having different colors,
in which the at least two colors out of the luminescent layers of
three colors are patterned by means of an ink-jet method. The three
colors are red, green and blue, and it is preferable that the red
luminescent layer and the green luminescent layer are patterned by
means of an ink-jet method. In this case, it is more preferable
that the blue luminescent layer is formed by a vacuum deposition
method. Further, it is preferable that the blue luminescent layer
is made of an electron injection and transfer type material, such
as an aluminum quinolinol complex.
[0014] In the manufacturing method for the organic EL element
according to the present invention, it is preferable that at least
one luminescent layer is laminated with a hole injection and
transfer layer, and it is also preferable that a protective film is
formed on the counter electrode.
[0015] In the manufacturing method for the organic EL element of
the present invention, it is preferable that the transparent
substrate is provided with thin film transistors for driving
respective pixels.
[0016] Further, it is preferable that the pixel electrodes are
formed into a transparent pixel electrode.
[0017] Furthermore, the organic EL element of the present invention
is provided with a transparent substrate, pixel electrodes formed
on the transparent substrate, at least one luminescent layers
having a certain color and made of an organic compound, the
luminescent layer being patterned on the pixel electrodes by an
ink-jet method, and a counter electrode formed on the luminescent
layer.
[0018] It is preferable that the organic compound is a polymer
organic compound, and it is more preferable that the polymer
organic compound is a hole injection and transfer type
material.
[0019] Moreover, it is preferable that the polymer organic compound
is a polyparaphenylene vinylene or its derivative or a copolymer
containing at least one of them.
[0020] It is preferred that the at least luminescent layer includes
three layers having different three colors, and it is preferable
that two layers thereof in the luminescent layers of three colors
are patterned by an ink-jet method. The three colors are red, green
and blue, and it is more preferable that the red luminescent layer
and the green luminescent layer are separately patterned by an
ink-jet method. In this case, it is more preferable that the blue
luminescent layer is formed by a vacuum deposition method.
[0021] It is preferable that the blue luminescent layer is made of
an electron injection and transfer material. As for such a blue
luminescent layer, a layer containing an aluminum quinolynol
complex can be mentioned.
[0022] Moreover, it is preferable that at least one luminescent
layer is laminated with a hole injection and transfer type layer,
and it is more preferable that a protective film is formed on the
cathode.
[0023] Furthermore, it is preferable that the pixel electrodes are
formed into a transparent pixel electrode.
[0024] Moreover, the organic EL display device according to the
present invention is characterized in that it includes the organic
EL element described in the above.
BRIEF DESCRIPTION OF THE DRAWINGS
[0025] FIG. 1 is a sectional view which shows a first embodiment of
a manufacturing method for an organic EL element according to the
present invention.
[0026] FIG. 2 is a sectional view which shows a second embodiment
of a manufacturing method for an organic EL element according to
the preset invention.
[0027] FIG. 3 is a sectional view which shows a third embodiment of
a manufacturing method for an organic EL element according to the
present invention.
[0028] FIG. 4 is a sectional view which shows a fourth embodiment
of a manufacturing method for an organic EL element according to
the present invention.
[0029] FIG. 5 is a sectional view which shows a fifth embodiment of
a manufacturing method for an organic EL element according to the
preset invention.
[0030] FIG. 6 is a sectional view which shows an example of the
organic EL element according to the present invention.
[0031] FIG. 7 is a sectional view which shows an example of an
organic EL display device using the organic EL element according to
the present invention.
[0032] FIG. 8 is a diagram which shows an example of an active
matrix type organic EL display device using the organic EL element
according to the present invention.
[0033] FIG. 9 is a sectional view which shows an example of a
manufacturing method of the active matrix type organic EL display
device.
[0034] FIG. 10 is a perspective view which shows an example of a
configuration of a head for an ink-jet method which is used in the
manufacturing method of the organic EL element according to the
present invention.
[0035] FIG. 11 is a sectional view of the nozzle part of the head
for an ink-jet method which is used in the manufacturing method of
the organic EL element according to the present invention.
[0036] FIG. 12 is a diagram which shows another embodiment of an
organic EL display device according to the present invention.
[0037] FIG. 13 is a schematic perspective view of an organic EL
display device according to the present invention.
[0038] FIG. 14 is a diagram which shows an example of the waveform
of the driving voltage applied to the electrodes.
[0039] FIG. 15 is a partial sectional view which shows another
embodiment of an organic EL element according to the present
invention.
PREFERRED EMBODIMENTS OF THE INVENTION
[0040] In the following, the manufacturing method of the organic EL
element and the organic EL element according to the present
invention will be described in detail based on the preferred
embodiments shown in the accompanying drawings.
[0041] FIG. 1 shows a first embodiment of the manufacturing method
of the organic EL element according to the present invention. This
figure shows the manufacturing method of a full color organic EL
element with three colors. As shown in the figure, this invention
is directed to a method of manufacturing an organic EL element
which comprises a step of forming pixel electrodes 101, 102 and 103
on a transparent substrate (transparent support) 104, a step of
patterning luminescent layers 106 and 107 which are made of organic
compounds on the respective pixel electrodes, and a step of forming
a cathode 113, wherein the method is characterized in that the
formation of the luminescent layers is carried out by means of an
ink-jet method.
[0042] The transparent substrate 104 functions not only as a
support but also as a surface through which light is taken out.
Accordingly, the material for the transparent substrate 104 is
selected by taking the light-permeability, thermal stability and
the like into consideration. As for examples of the material to be
used for the transparent substrate, glass, transparent plastic or
the like can be mentioned, and among these materials, a substrate
made of glass is particularly preferable in view of its excellent
heat resistance.
[0043] In more details, the first, pixel electrodes 101, 102 and
103 are formed on the transparent substrate 104. As for examples of
methods of forming these pixel electrodes, photolithography, vacuum
deposition method, sputtering method and pyrosol method can be
mentioned. Among these methods, the photolithography is
particularly preferable. As for these pixel electrodes, it is
preferred that they are formed into transparent pixel electrodes.
As for the materials constituting the transparent pixel electrodes,
a tin oxide film, an ITO (indium tin oxide) film and a composite
oxide film of indium oxide and zinc oxide can be mentioned.
[0044] Next, partitioning walls (banks) 105 are formed to fill the
spaces between the pixel electrodes.
[0045] In this way, it is possible to improve the contrast, to
prevent mixing of colors of the luminescent materials, and to
prevent light from leaking between the pixels.
[0046] As for the materials constituting the banks 105, no
particular limitation is imposed, if they have a resistance to the
solvent for the EL material. For example, organic material such as
acrylic resin, epoxy resin, photosensitive polyimide and the like;
and inorganic material such as liquid glass and the like can be
mentioned. In this regard, it is to be noted that the banks 105 may
be formed into a black resist which is formed by mixing carbon
black and the like into the above-mentioned material.
[0047] As for examples of the forming method for the banks 105,
photolithography and the like can be mentioned.
[0048] Further, organic luminescent layers are formed respectively
on the pixel electrodes according to a predetermined pattern. In
this case, it is preferable to provide organic luminescent layers
with three color types. In this connection, it is preferred that at
least one layer among these organic luminescent layers is formed by
an ink-jet method.
[0049] In the embodiment shown in FIG. 1, a red luminescent layer
106 and a green luminescent layer 107 are formed on the pixel
electrodes 101 and 102, respectively, by the ink-jet method.
[0050] In the above descriptions, the term "ink-jet method" is used
to mean a method of forming a pixel of one of the three primary
colors including red, green and blue or a pixel of at least one
color which is intermediate between the primary colors by
dissolving or dispersing a luminescent material in a solvent to
obtain a discharge liquid and then discharging the discharge liquid
from a head 110 of an ink-jet device 109.
[0051] According to such an ink-jet method, it is possible to carry
out fine patterning in a simple manner and in a short time.
Further, it is also possible to control easily and freely the
luminescent characteristics such as color balance and brightness
(luminance) by adjusting the thickness of the layer through
adjustment of the discharge amount of the ink or by adjusting the
ink concentration.
[0052] When the organic luminescent materials are conjugated
polymer precursors described later, the luminescent layers are
formed by discharging the luminescent materials by the ink-jet
method to carry out patterning, and then conjugating (to form a
film) the precursor components by heating or irradiation with light
or the like.
[0053] Next, as shown in FIG. 1, a blue luminescent layer 108 is
formed on the red luminescent layer 106, the green luminescent
layer 107 and the pixel electrode 103. In this way, it is possible
not only to form layers having the three primary colors including
red, green and blue, but also to bury the level differences between
the banks 105 and each of the red luminescent layer 106 and the
green luminescent layer 107 so as to be flattened.
[0054] No particular limitation is imposed upon the forming method
for the blue luminescent layer 108, and it is possible to form the
layer using the general film forming method known as deposition
method or wet method, for instance, or using the ink-jet
method.
[0055] Further, the blue luminescent layer 108 can be formed of an
electron injection and transfer material such as aluminum
quinolynol complex. In this case, it is possible to promote the
injection and transfer of the carriers so as to improve the
luminous efficiency. Furthermore, when such a blue luminescent
layer 108 is laminated with red and green luminescent layers formed
of a hole injection and transfer material described later, it is
also possible to inject and transfer the electrons and the holes
from the respective electrodes into these laminated luminescent
layers with appropriate balance, thereby enabling to improve the
luminous efficiency.
[0056] Moreover, when such a blue luminescent layer 108 is
laminated with the red and green luminescent layers made of a hole
injection and transfer type material, the function of hole
injection and transfer and the function of electron injection and
transfer can be assigned separately to different layers, so that
optimum design can be selected for the respective materials. No
particular limitation is imposed upon the forming method of such an
electron injection and transfer layer, and it is possible to form
the layer by using, for example, the general film forming method
known as deposition method or wet method or the ink-jet method.
[0057] In this connection, as for an organic compound which can
form an electron injection and transfer layer, oxadiazole
derivative such as PBD, OXD-8 and the like, DSA, aluminum
quinolinol complex, Bebq, triazole derivative, azomethine complex,
porphine complex, benzoxadiazol and the like can be mentioned. In
this case, an electron injection and transfer layer can be formed
from just one of these materials, or formed by mixing or laminating
one of or two or more of them. In addition, the electron injection
and transfer layer may be formed by doping a fluorescence dye
described later to the organic compound described. Further, the
electron injection and transfer layer itself may have a function of
luminescence.
[0058] As described above, in this embodiment, organic luminescent
layers for two colors are formed by the ink-jet method while the
layer for the remaining one color is formed by a different method.
Therefore, according to this embodiment, even when a luminescent
material which is not so suited for the ink-jet method is used, a
full color organic EL element can be formed by using such a
material in a combination with other organic luminescent materials
that are suited for the ink-jet method, so that the latitude in the
design for the EL element will be expanded.
[0059] As for examples of the forming method for the luminescent
layer other than the ink-jet method, photolithography method,
vacuum deposition method, printing method, transfer method, dipping
method, spin coating method, casting method, capillary method, roll
coating method, bar coating method and the like can be
mentioned.
[0060] Finally, a cathode (a counter electrode) 113 is formed,
thereby the organic EL element of the present invention is
completed. In this case, it is preferred that the cathode 113 is
formed into a metallic thin film electrode, and as for examples of
the metal for forming the cathode, Mg, Ag, Al, Li and the like can
be mentioned. In addition, a material having small work function
can be used for the material for the cathode 113, and for example,
alkali metal, alkali earth metal such as Ca and the like, and
alloys containing these metals can be used. Such a cathode 113 may
be formed using a deposition method, a sputtering method or the
like.
[0061] The organic EL element of the present invention is
manufactured through the processes described in the above. Namely,
as shown in FIG. 1, the pixel electrodes 101 and 102 are provided
on the transparent substrate 104, the red luminescent layer 106 and
the green luminescent layer 107 which are made of organic compounds
are then formed on the pixel electrodes 101 and 102, respectively,
by patterning by using the ink-jet method, and then the blue
luminescent layer 108 is formed on the luminescent layers 106 and
107 and the pixel electrode 103 by the vacuum deposition method.
Thereafter, the cathode 113 is formed on top of the blue
luminescent layer 108, thereby the organic EL element according to
the present invention is completed.
[0062] Further, as shown in FIG. 6, a protective film 415 may be
formed on top of a cathode 413. By forming such a protective film
415, it becomes possible to prevent deterioration, damage, peeling
and the like from occurring in the cathode 413 and in the
luminescent layers 406, 407 and 408.
[0063] As for materials for constructing the protective film 415,
epoxy resin, acrylic resin, liquid glass and the like can be
mentioned. Further, as for examples of the forming method for the
protective film 415, spin coating method, casting method, dipping
method, bar coating method, roll coating method, capillary method
and the like can be mentioned.
[0064] In this embodiment, it is preferable that these luminescent
layers are formed of an organic compound, and it is more preferable
that these luminescent layers are formed of a polymer organic
compound. By providing such luminescent layers that are formed of
the organic compound, it is possible to obtain high brightness
surface luminescence at low voltages. Further, since luminescent
materials can be selected from wide range of field, a rational
design for the luminescent element becomes possible.
[0065] In particular, polymer organic compounds have an excellent
film formation property, and the luminescent layers composed of
polymer organic compounds have an extremely good durability.
Further, these polymer organic compounds have a band gap in the
visible region and a relatively high electrical conductivity. Among
such polymer organic compounds, a conjugated polymer can exhibit
such properties prominently.
[0066] As for materials for the organic luminescent layers, polymer
organic compound itself, precursor of conjugated organic polymer
compound which is to be conjugated (to form a film) by heating or
the like, and other materials are used.
[0067] When a precursor prior to conjugation (to form a film) is
used as a luminescent material, the viscosity or the like of a
discharge liquid used for the ink-jet system can be adjusted
easily, so that the patterning is carried out precisely and the
luminescence characteristics and the film properties of the
luminescent layer can be controlled easily.
[0068] It is preferred that the polymer organic compound forming
the luminescent layers is a hole injection and transfer material.
In this way, it is possible to promote the injection and transfer
of the carriers and thereby to improve the luminous efficiency.
[0069] As for examples of an organic compound which can form the
luminescent layers, polyalkylthiophene such as PPV
(poly(para-phenylene vinylene)) or its derivative, PTV
(poly(2,5-thienylene vinylene)) and the like; polyallylene vinylene
such as PFV (poly(2,5-furylene vinylene)) polyparaphenylene,
polyalkylfluorene and the like; pyrazoline dimer; quinolizine
carboxylic acid; benzopyrylium perchlorate; benzopyranoquinolizine;
rubrene; phenanthroline europium complex and the like can be
mentioned. In this case, just one of them or a mixture of two or
more of them can be selectively used.
[0070] Among these organic compounds, PPV which is a conjugated
organic polymer compound or its derivative is preferable. The
precursor prior to conjugation (to form a film) of PPV or its
derivative is soluble to water or organic solvent, so that they are
suitable for pattern formation by the ink-jet method. Further, it
is possible to obtain a thin layer which has high optical quality
and excellent durability, since it is a polymer. Furthermore, PPV
or its derivative possesses a strong fluorescence, and since it is
a conductive polymer in which .pi.-electron of double bond is
delocalized on the polymer chain, a thin film of PPV also functions
as a hole injection and transfer layer, which makes it possible to
obtain an organic EL element having high performance.
[0071] Furthermore, the composition for an organic EL element in a
case where a polymer organic compound is used for the material for
the luminescent layers may include at least one kind of fluorescent
dye in it. By including such fluorescent dye way, it becomes
possible to change the luminous property of the luminescent layer.
Therefore, the addition of the fluorescent dye is effective as a
means, for example, for improving the luminous efficiency of the
luminescent layer or for changing the maximum wavelength of light
absorption (emitted color) of the luminescent layers.
[0072] Namely, a fluorescent dye can be utilized not only as a
material for the luminescent layers but also as a material for the
coloring matter which has the luminescence function itself. For
example, almost all of the energy of the excitons which are
generated by the recombination of carriers on the molecules of a
conjugated organic polymer compound such as PPV can be transferred
onto the molecules of the fluorescent dye. In this case, the
current quantum efficiency of the EL element is also increased,
because the luminescence arises only from the molecules of the
fluorescent dye which have a high fluorescence quantum efficiency.
Accordingly, by the addition of a fluorescent dye into the
composition for the organic EL element, the luminescence spectrum
of the luminescent layer becomes at the same time the spectrum of
the fluorescent dye, whereby this method becomes also an effective
means for changing the emitted color.
[0073] In this connection, it should be noted that what is meant
here by the current quantum efficiency is a scale for considering
the luminescence performance according to the luminescence
function, and it is defined by the following expression.
.eta..sub.E =energy of emitted photon/input electrical energy.
[0074] The changes in the maximum wavelength of light absorption
induced by the doping of a fluorescent dye make it possible, for
example, to emit the three primary colors of red, green and blue,
thereby enabling to obtain a full color display device.
[0075] Further, the doping of the fluorescent dye makes it possible
to improve extremely the luminous efficiency of the EL element.
[0076] As for a fluorescent dye used for the red luminescent layer,
laser dye DCM, rhodamine or a rhodamine derivative, perylene and
the like can be used. These fluorescent dyes are soluble to
solvents because they are low molecules, and have a high
compatibility with PPV or the like, so that a luminescent layer
with a good uniformity and good stability can be formed easily. As
for examples of the rhodamine derivative fluorescent dyes,
rhodamine B, rhodamine B base, rhodamine 6G, rhodamine 101
perchlorate can be mentioned. In this case, a mixture of two or
more of them can be selectively used.
[0077] Further, as for a fluorescent dye used in the green
luminescent layer, quinacridone, rubrene, DCJT and their
derivatives can be mentioned. Since these fluorescent dyes are low
molecules in the same manner as the fluorescent dyes to be used in
the above-mentioned red luminescent layer, they are soluble to
solvents and have a high compatibility with PPV or the like, so
that the luminescent layer can be formed easily.
[0078] As for the fluorescent dye used in the blue luminescent
layer, distyrylbiphenyl and its derivative can be mentioned. These
fluorescent dyes are soluble to aqueous solutions in the same
manner as the above-mentioned fluorescent dyes for the red
luminescent layer, and have high compatibility with PPV or the
like, so that the luminescent layer can be formed easily.
[0079] In addition, as for other fluorescent dyes that can be used
in the blue luminescent layer, coumarin; and coumarin derivatives
such as coumarin-1, coumarin-6, coumarin-7, coumarin 120, coumarin
138, coumarin 152, coumarin 153, coumarin 311, coumarin 314,
coumarin 334, coumarin 337, coumarin 343 and the like can be
mentioned.
[0080] Moreover, as for other luminescent materials that can be
used in the blue luminescent layer, tetraphenylbutadiene (TPB) or
TPB derivative, DPVBi and the like can be mentioned. Since these
luminescent materials are also low molecules in the same manner as
the fluorescent dyes for the red luminescent layer, they are
soluble to solvents, and have high compatibility with PPV or the
like, so that the luminescent layer can be formed easily.
[0081] These fluorescent dyes and luminescent materials as
described above can be selectively used as a just one of them or as
a mixture of two or more of them.
[0082] The structure of a head of the ink-jet system used in the
manufacturing method of the organic EL element according to the
present invention is shown in FIG. 10 and FIG. 11.
[0083] The head 10 for the ink-jet system is provided with, for
example, a stainless steel nozzle plate 11 and a vibration plate
13, and they are coupled via partitioning members (reservoir
plates) 15.
[0084] Between the nozzle plate 11 and the vibration plate 13, a
liquid storage 21 and a plurality of spaces 19 are formed by means
of the reservoir plates 15. The inside of the respective spaces 19
and the liquid storage 21 are filled with the composition according
to the present invention, and the spaces 19 communicate with the
liquid storage 21 through supply ports 23.
[0085] Further, a nozzle hole 25 is provided in the nozzle plate 11
for discharging the composition in a jet-form from the spaces 19.
In the meantime, a hole 27 is formed in the vibration plate 13 for
supplying the composition to the liquid storage 21.
[0086] Further, on a surface of the vibration plate 13 which is
opposite to the other surface that faces with the spaces 19,
piezoelectric elements 29 are attached at positions corresponding
to the positions of the respective spaces 19.
[0087] Each of the piezoelectric elements 29 is positioned between
a pair of electrodes 31. The piezoelectric element 29 is adapted to
bend so as to protrude outward when energized, and at the same
time, the vibration plate 13 to which the piezoelectric element 29
is attached is also bent outward together with the piezoelectric
element 29. In this way, the volume of the space 19 is increased.
With this result, a quantity of the composition corresponding to
the increased volume flows into the space 19 from the liquid
storage 21 through the supply port 23.
[0088] Next, when the piezoelectric element is de-energized, both
the piezoelectric element 29 and the vibration plate 13 return to
their original shapes. In this way, the space 19 also returns to
its original volume, so that the pressure exerted to the
composition within the space 19 goes up, whereby the composition is
jetted out from the nozzle hole 25 toward the substrate.
[0089] In this connection, a water repellent layer 26 is formed at
the peripheral part of the nozzle hole 25 in order to prevent the
bend of the jetted direction of the composition and the clogging of
the hole from occurring.
[0090] Namely, a water repellent layer 26 formed of, for example, a
Ni-tetrafluoroethylene eutectoid plated layer is provided in the
peripheral part of the nozzle hole 25 as shown in FIG. 11.
[0091] Using the head with the above construction, it is possible
to form respective organic luminescent layers by discharging the
compositions corresponding to, for example, the three primary
colors red, blue, and green according to a predetermined pattern,
thereby enabling to form the pixels.
[0092] In the manufacturing method of the organic EL element
according to the present invention, compositions with the following
characteristics can be used as organic luminescent materials for
the ink-jet method.
[0093] It is preferable that the compositions have a contact angle
of 30 to 170 degrees, and more preferably, 35 to 65 degrees, with
respect to the material constituting the nozzle surface 251 of the
nozzle provided in the head for the ink-jet system for discharging
the composition. When the composition has the contact angle given
in this range, it is possible to carry out a precise patterning by
suppressing the bend in the jetted direction of the
composition.
[0094] Namely, if the contact angle is less than 30 degrees,
wettability of the composition with respect to the material
constituting the nozzle surface increases, so that there is a case
that the composition attaches asymmetrically to the periphery of
the nozzle hole at the time of discharging the composition. In this
case, an attraction acts between the composition attached to the
nozzle hole and the composition to be discharged. This causes the
discharge of the composition by a non-uniform force, which gives
rise to a situation so-called "bend in the jetted direction" in
which the composition is unable to reach the target position, and
also to an increase in the occurrence frequency of the bend in the
jetted direction. Meantime, if the contact angle exceeds 170
degrees, the interaction between the composition and the nozzle
hole becomes a minimum and the shape of the meniscus at the tip of
the nozzle is unstable, so that the control of the amount and the
timings of discharge of the composition tends to be difficult.
[0095] In the above descriptions, what is meant here by the bend in
the jetted direction refers to a situation in which, when the
composition is discharged from the nozzle, the point of impact of a
dot deviates from the target position by more than 50 .mu.m.
Further, the occurrence frequency of the bend in the jetted
direction is defined as the time until the bend in the jetted
direction occurs after a continuous discharge of the composition is
started at the frequency of 7200 Hz. The bend in the jetted
direction is generated principally by such causes as the
nonuniformity in the wettability of the nozzle hole and the
clogging of the nozzle hole by the attachment of solid components
of the composition. Such bend in the jetted direction can be
eliminated by cleaning the head. In this connection, more frequent
head cleaning is required for more frequency of occurrence of the
bend in the jetted direction, and such a composition that arises
the higher occurrence frequency can be said to a composition that
deteriorates the manufacturing efficiency of the EL element by the
ink-jet method. On the practical level, an occurrence frequency of
the bend in the jetted direction is required to be more than 1000
seconds.
[0096] By preventing such bend in the jetted direction from
occurring, it becomes possible to carry out a highly fine
patterning with high precision.
[0097] Further, it is preferable that the viscosity of the
composition is 1 to 20 cp, and more preferably 2 to 4 cp. If the
viscosity of the composition is less than 1 cp, the contents of the
precursor and the fluorescent dye in the material are too small, so
that the luminescent layer which is formed cannot exhibit
luminescence power sufficiently. On the other hand, if it exceeds
20 cp, it is impossible to discharge the composition smoothly from
the nozzle, and it becomes difficult to carry out patterning unless
otherwise such a change in the specification as the enlargement of
the diameter of the nozzle hole is introduced. In addition, when
the viscosity of the composition is high, precipitation of the
solid components in the composition tends to occur, thus leading to
an increased occurrence frequency of clogging of the nozzle
hole.
[0098] Furthermore, it is preferable that the composition has the
surface tension of 20 to 70 dyne/cm, and more preferably 25 to 40
dyne/cm. By restricting the surface tension to such a range, it is
possible to suppress the bend in the jetted direction and suppress
the occurrence frequency of the bend in the jetted direction to a
low level, in the same manner as the case of the above-mentioned
contact angle. If the surface tension is less than 20 dyne/cm, the
wettability of the composition with respect to the material
constituting the nozzle surface increases, which results in the
occurrence of the bend in the jetted direction, and an increase in
the occurrence frequency of the bend in the jetted direction,
similar to the case of the contact angle. On the other hand, if it
exceeds 70 dyne/cm, the shape of the meniscus at the tip of the
nozzle is not stable, which results in the difficulty in the
control of the amount and the timings of discharge of the
composition.
[0099] Further, as for the composition of the organic luminescent
material suitable for the manufacturing method of the organic EL
element of this invention, it needs to satisfy the condition on the
numerical range for at least one of the characteristics including
the contact angle, the viscosity and the surface tension described
above. In this connection, a composition which satisfies the
conditions for the arbitrary combination of two characteristics is
more preferable, and a composition which satisfies the conditions
for all the characteristics is most preferable.
[0100] FIG. 2 shows a second embodiment of the manufacturing method
of the organic EL element according to the present invention.
[0101] In this second embodiment, after formation of pixel
electrodes 201, 202 and 203 and banks 205 on a transparent
substrate 204, a red luminescent layer 206 and a green luminescent
layer 207 are formed by using an ink-jet method in the same manner
as the first embodiment.
[0102] This second embodiment is different from the first
embodiment in the point that a hole injection and transfer layer
208 is formed on the pixel electrode 203 and then a blue
luminescent layer 210 is laminated on the layer 208. By the
lamination of the hole injection and transfer layer 208 with the
blue luminescent layer, it becomes possible to promote the
injection and transfer of the holes from the electrode to improve
the luminous efficiency as mentioned above.
[0103] Thus, in the manufacturing method for the organic EL element
according to the present invention, it is preferable to laminate a
hole injection and transfer layer with at least one luminescent
layer with a certain color. In this way, it is possible to improve
the luminous efficiency and to improve the stability of the thin
film element itself.
[0104] In this case, at the vicinity of the interface between the
luminescent layer and the hole injection and transfer layer which
are laminated with each other, a part of the materials contained in
either of layers may exist in the state of mutual impregnation and
diffusing into the other layer.
[0105] It is preferable that the hole injection and transfer layer
208 is a non-luminescent layer. With this arrangement, it is
possible to make a region of the blue luminescent layer 210
positioned above the pixel electrode 203 to be a luminescent
portion, thereby enabling to fabricate a full color organic EL
element more easily.
[0106] No particular limitation is imposed upon the forming method
for such a hole injection and transfer layer 208, but for example,
it is possible to form the layer by using the ink-jet method. In
this way, it becomes possible to arrange the hole injection and
transfer layer 208 precisely with a predetermined pattern.
[0107] As for examples of the material constituting the hole
injection and transfer layer 208, aromatic diamine based compound
such as TPD; MTDATA; quinacridone; bisstil anthracene derivative;
PVK (polyvinyl carbazole); phthalocyanine based complex such as
copper phthalocyanine; porphin based compound; NPD; TAD;
polyaniline; and the like can be mentioned. Among these materials,
PVK is particuraly preferred. By using PVK, it becomes possible to
form a non- luminescent hole injection and transfer layer.
[0108] Further, the organic EL element according to the present
invention can be obtained by forming a blue luminescent layer 210
and a cathode 211 in the same way as the first embodiment. The
materials constituting the blue luminescent layer 210 and the
cathode 211 and the manufacturing method thereof are the same as
those of the first embodiment.
[0109] FIG. 3 shows a third embodiment of the manufacturing method
for the organic EL element according to the present invention.
[0110] In this third embodiment, after the formation of pixel
electrodes 301, 302 and 303 and banks 305 on a transparent
substrate 304, a red luminescent layer 306 and a green luminescent
layer 307 are formed in the same manner as the first
embodiment.
[0111] Next, a hole injection and transfer layer 308 is formed on
the entire surface of the red luminescent layer 306, the green
luminescent layer 307 and the pixel electrode 303. By laminating
the hole injection and transfer layer 308 with the luminescent
layers 306 and 307 in this way, it is possible to promote the
injection and the transfer of the holes from the electrodes to
improve the luminescence efficiency, as described in the above.
[0112] Further, by the same reason as in the above, it is
preferable that the hole injection and transfer layer 308 is formed
into a non-luminescent layer.
[0113] No particular limitation is imposed upon the forming method
for the hole injection and transfer layer 308, and for example,
ink-jet method, vacuum deposition method, dipping method, spin
coating method, casting method, capillary method, roll coating
method, bar coating method and the like can be mentioned. In this
embodiment, it is to be noted that the hole injection and transfer
layer can be formed using the vacuum deposition method. In this
connection, as for the material constituting the hole injection and
transfer layer 308, the same materials as those mentioned in the
second embodiment can be used.
[0114] Further, by forming a blue luminescent layer 309 and a
cathode 311 on the hole injection and transfer layer 308, the
organic EL element according to the present invention can be
obtained. The constituent material and the forming method of the
cathode 311 are the same as those of the above-mentioned
embodiments.
[0115] FIG. 4 shows a fourth embodiment of the manufacturing method
for the organic EL element according to the present invention.
[0116] In this fourth embodiment, after the formation of pixel
electrodes 801, 802 and 803 and banks 805 on a transparent
substrate 804 in the same way as the first embodiment, luminescent
layers 806, 807 and 808 are patterned on the pixel electrodes 801,
802 and 803, respectively, by the ink-jet method. In this way, the
amount of the material to be discharged for the respective
luminescent layers, the number of times of the discharge and the
formation pattern of the luminescent layers, for example, can be
adjusted easily and handily, so that the luminescent
characteristics and film thickness and the like of the respective
luminescent layers can be controlled easily.
[0117] In addition, an electron injection and transfer layer 811 is
formed on the luminescent layers 806, 807 and 808. The electron
injection and transfer layer 811 facilitates the injection of the
electrons from the cathode, and contributes to the prevention of
electrode extinction by keeping the luminescent portions away from
the cathode to establish a better contact with the cathode. As for
the electron injection and transfer layer 811, aluminum quinolynol
complex to which the doping is not carried out can be used. This
electron injection and transfer layer 811 can be formed by means of
a vacuum deposition method.
[0118] In this connection, the forming method for the electron
injection and transfer layer 811 is not limited to this method, and
for example, the ink-jet method, vacuum deposition method, dipping
method, spin coating method, casting method, capillary method, roll
coating method, bar coating method or the like can be used.
[0119] Further, the organic EL element according to the present
invention can be obtained by forming a cathode 813 on top of it.
The constituent material and the formation method of the cathode
813 are the same as those of the above-mentioned embodiments.
[0120] FIG. 5 shows a fifth embodiment of the manufacturing method
of the organic EL element according to the present invention.
[0121] In this fifth embodiment, pixel electrodes 801, 802 and 803
are first formed on a transparent substrate 804 in the same manner
as the first embodiment. Then, a hole injection and transfer layer
815 which is for example made of PVK is formed on the entire
surfaces of the pixel electrodes by means of, for example, a spin
coating method. Accordingly, since the hole injection and transfer
layer 815 in this embodiment can be formed by means of coating
without need of patterning, it is possible to increase
manufacturing efficiency.
[0122] No particular limitation is imposed upon the forming method
for the hole injection and transfer layer 815, and for example,
ink-jet method, vacuum deposition method, dipping method, spin
coating method, casting method, capillary method, roll coating
method, bar coating method and the like can be used.
[0123] Further, from the same reason described above with reference
to the other embodiments, it is preferred that the hold injection
and transfer layer 815 is formed into a non-luminescent layer.
[0124] On top of the hole injection and transfer layer 815,
luminescent layers 806, 807 and 808 are formed. In this regard, it
is preferred that among these luminescent layers, at least one
luminescent layer for a certain color is formed by pattering using
the ink-jet method carried by the ink-jet device 809.
[0125] Then, by forming a cathode 813 on top of the luminescent
layers, an organic EL element according to the present invention
can be obtained. The structural material for the cathode 813 and
the manufacturing method thereof are the same as those of the other
embodiment described above.
[0126] According to this fifth embodiment, no bank is formed.
However, by using this manufacturing method, the coating of the
luminescent layers for the primary colors R, G and B can be carried
out correctly and preciously, thus leading to improvement of
manufacturing efficiency. In this regard, it is to be noted that
the manufacturing method of this embodiment can be also applied to
the case where banks are provided to form respective pixels like
the previous embodiments.
[0127] The organic EL element of the present invention can be
manufactured according to the manufacturing methods described above
with reference to the embodiments. However, the present invention
is not limited to the structures provided by these methods, and the
following structures can be adopted, for instance.
[0128] FIG. 15 is a partial cross-sectional view which shows other
embodiment of an organic EL element according to the present
invention.
[0129] The organic EL element of this embodiment has a construction
in which a reflection layer 62, a transparent conductive film (ITO
film) 63, a hole injection and transfer layer 64, an organic
luminescent layer 65, a metal layer 66 and a transparent conductive
layer (ITO film) 67 are laminated on a transparent substrate 61 in
this order. Hereinbelow, the materials and the manufacturing
methods of the respective layers (films) are described, in which a
description is made only for the differences from the previous
embodiments and the common explanation is omitted.
[0130] In the organic EL element according to this embodiment, on
the transparent substrate 61, the reflection layer 62 which is made
from a metal thin film such as Al is provided directly.
[0131] The metal layer 66 which is laminated onto the luminescent
layer 65 as a cathode is extremely thin (approximate to 10 to 50
.ANG.), so that the metal layer has a light permeability so as to
pass emitted light from the luminescent layer 65 therethrough. On
the other hand, since the metal layer is extremely thin, its value
of resistance is high and therefore its conductivity is
insufficient. Therefore, the metal layer can not sufficiently
exhibit function as the cathode. For this reason, the transparent
conductive film (ITO film) 67 is laminated onto the metal layer 66.
In this connection, it is to be noted that such a metal layer 66
can be made from Al--Li alloy or the like for example, and it can
be formed using the vacuum deposition method, sputtering method or
the like.
[0132] By using the above described construction, light which is
converted in the luminescent layer 65 from a current which has been
injected from the electrodes is transmitted in the direction
indicated by the arrow in the drawing. With this result, it becomes
possible to take out the light without passing through the
transparent substrate 61, so that a display with a higher
brightness becomes possible.
[0133] FIG. 7 is an illustration which shows an embodiment of an
organic EL display device according to the present invention.
[0134] In this embodiment, a bus line (gate line) 511 made of Al is
formed on a glass plate 501 by means of a photolithography
patterning method, and a thin film transistor (not shown in the
drawing) is formed thereon to constitute the ITO transparent pixel
electrode 504 and the like. Then, as is the same manner as the
first embodiment, a red luminescent layer 502 and a green
luminescent layer 503 are formed by means of the ink-jet method,
and then a blue luminescent layer 505 is formed by means of the
vacuum deposition method. Thereafter, a cathode 506 is formed by
means of the vacuum deposition method, thereby constructing the
organic EL element same as the first embodiment described
above.
[0135] In addition, a protective base material 507 is stuck onto
the transparent substrate 501 in a fixed manner by means of a
peripheral seal 509.
[0136] Next, this assembly is placed in an inert gas atmosphere
such as argon gas or the like, and thereby introducing the inert
gas inside thereof from a seal opening 513 and then the seal
opening 513 is sealed with a seal member 508. By filing the inside
of the assembly with the inert gas 51 and then sealing it, as
described above, it becomes possible to protect the organic EL
element from external contamination such as moisture or
environmental changes, thereby enabling to maintain the luminescent
characteristics of the organic EL display device. In this case, it
is preferred that the seal member 508 is formed form a material
through which the inert gas 512 does not penetrate.
[0137] A silver paste 510 has a function that realizes a contact
between the cathode 506 and the gate line 511 on the element.
[0138] Gate lines 511 are provided to control ON and OFF of the
thin film transistors (TFT), which are provided in the respective
display pixels, in each line of the pixels in order to select
pixels to be displayed. Upon writing, potential of the gate line
for one line of pixels is turned into a selected level, thereby
bringing the TFTs on this line into a conductive state. At this
time, by supplying picture signals for the corresponding pixels
from the source electrode wires of the respective lines (not shown
in the drawing), the voltages of the picture signals are applied to
the pixel electrodes through the TFTs, thereby enabling to charge
the potentials to the pixels to a level of a signal voltage and
then discharge them.
[0139] FIG. 8 is an illustration which shows other embodiment of an
active matrix type organic EL display device using the organic EL
element according to the present invention. This organic EL display
device of this embodiment includes an pixel arrangement comprised
of a plurality of luminescent pixels which are arranged in a matrix
form and which are formed into any one of R, G and B luminescent
elements.
[0140] As shown in this figure, on the substrate (not shown), there
are provided signal lines (signal electrodes) 601 and gate lines
(gate electrodes) 602 which are arranged in a matrix form so as to
be orthogonal to each other. Further, in each of the pixels, a thin
film transistor (TFT) 604 which is connected to both the signal
line 601 and the gate line 602 is provided, and a luminescent layer
605, 606 which is formed of the organic EL element and connected to
the TFT is laminated on the TFT. In this case, at least one
luminescent layer for any one of colors R, G, B is formed by means
of the ink-jet method.
[0141] FIG. 9 is a sectional view which shows one example of the
manufacturing method of the active matrix type organic EL display
device according to the present invention.
[0142] First, on a transparent substrate 904, predetermined thin
film transistors 915 as well as gate lines and signal lines (not
shown) and the like are formed. Next, on respective pixel
electrodes (ITO) 901, 902, 903 which are respectively provided with
prescribed functional elements such as the thin film transistors
915, hole injection and transfer layers 911 are formed so as to
cover the respective pixel electrodes. As for the hole injection
and transfer type material, the same materials that are discussed
in this specification with reference to the previous embodiments
can be used. Further, the method of forming the hole injection and
transfer layer 911 is not limited to a specific method, and it is
possible to form the layer by means of any method described
above.
[0143] Further, respective luminescent layers 906 (red), 907
(green) and 908 (blue) are formed by patterning. In the formation
of these luminescent layers, at least one layer for one color is
formed by the ink-jet method using an ink-jet device 910.
[0144] Finally, a reflection electrode 913 is formed, thereby
completing the organic EL display device according to the present
invention. As for the reflection electrode 913, Mg--Ag electrode
having a thickness of about 0.1 to 0.2 .mu.m or the like is formed,
for instance.
[0145] In the above-mentioned embodiment concerning the active
matrix type organic EL display device according to the present
invention, a thin film transistor is used as a switching element,
but the present invention is not limited thereto. Other switching
elements and two-terminal element such as MIM can be used. Further,
the display device may be configured into a passive drive type or a
static drive type (static image, segment display).
[0146] Furthermore, the number of the switching element is not
limited to one per one pixel. A plurality of switching elements may
be provided per one pixel.
[0147] FIG. 12 shows an embodiment of an organic EL display device
in which a plurality of switching elements are provided per one
pixel. In this embodiment, a switching type thin film transistor
142 carries out a role that transmits the potential at a signal
electrode 132 to a current thin film transistor 143 in response to
the potential at a scanning electrode 131, and the current thin
film transistor 143 carries out a role that controls electrical
connection between the common electrode 133 and the pixel electrode
141.
[0148] Next, referring to the drawings, a description is made with
regard to an embodiment of a passive matrix type (simple matrix
type) organic EL display device using the organic EL element
according to the present invention.
[0149] FIG. 13 is a perspective view which roughly shows a
structure of the organic EL display device according to the present
invention.
[0150] As shown in the drawings, in the organic EL display device
of this embodiment, a scanning electrode 53 and a signal electrode
54 which are formed into an elongated strip, respectively, are
arranged outside the organic EL element 52 so that scanning lines
extending from the scanning electrode 53 and the signal lines
extending from the signal electrode 54 are orthogonal to each other
through the organic EL element.
[0151] Such a passive matrix type display device is driven by
selecting scanning lines of the scanning electrode 53 in a pulsed
manner in a sequential order while a voltage is applied to signal
lines of the signal electrode 54 corresponding to pixels to be
displayed on the scanning line. Such selection of the lines is
carried out by a controller 55.
[0152] In this connection, it should be noted that in a case of the
passive drive type display device, it is necessary that a cathode
is patterned so as to be separate forms to correspond to each of
lines. For example, when a thin cathode having a thickness of about
0.2 .mu.m is formed according to the third embodiment, such
separate forms of the cathode can be automatically obtained since
the cathode is separated by the banks.
[0153] Such a cathode is formed by the patter formation performed
by a masking deposition method or a laser cutting method, for
instance.
[0154] FIG. 14 is a diagram which shows one example of wave forms
of driving voltages applied to the scanning electrode 13 and signal
electrode 14, respectively. The wave forms shown in the drawing are
determined so as to be able to apply a voltage Vs which is
sufficient to luminescence to selected pixels. Further, the
brightness of a pixel to be displayed is controlled through the
width of the pulse from the signal electrode 14 that has been
determined so as to meet with a gray scale of the brightness to be
displayed. On the other hand, a voltage Vn which is lower than a
luminescent threshold voltage is applied to respective non-selected
pixels.
[0155] In FIG. 14, Tf shows a scanning timing. In this case, the
scanning signal is driven by a pulse having a duty ration of 1/100.
In this connection, it has been confirmed that the luminescence of
the blue luminescent layer 808 of the organic EL display device
comprised of the organic EL elements of the fourth embodiment was a
brightness of 100 cd/m2 at a driving voltage of 20V.
EXAMPLES
[0156] <Manufacturing of Organic EL Elements>
EXAMPLE 1
[0157] As shown in FIG. 1, on the glass substrate 104, ITO
transparent pixel electrodes 101, 102 and 103 were formed by means
of photolithography so as to form a pattern having a pitch of 100
.mu.m and a thickness of 0.1 .mu.m.
[0158] Then, the spaces between the ITO transparent pixel
electrodes were buried, and then banks 105 which act not only as a
light cut-off layer but also an ink drop preventing wall were
formed by photolithography. In this case, the banks 105 were
designed so as to have a width of 20 .mu.m and a thickness of 2.0
.mu.m.
[0159] Further, after the pattern formation with red and green
luminescent materials shown in Table 1 and Table 2 which were
jetted from the head 110 of the ink-jet device 109, they were
undergone heat treatment under a nitrogen atmosphere for hours to
polymerize the precursors in the compositions of the materials,
thereby forming luminescent layers 106 (red) and 107 (green).
[0160] Then, by carrying out a vacuum deposition of aluminum
quinolynol complex to which perylene condensed aromatic was added
as a dopant, a blue luminescent layer 108 of the electron injection
and transfer type having a thickness of 0.1 .mu.m was formed.
[0161] At the last, a Mg--Ag electrode 113 having a thickness of
0.8 .mu.m was formed as a cathode using a vacuum deposition method
to obtain an organic EL element.
EXAMPLE 2
[0162] In the same manner as Example 1, ITO transparent pixel
electrodes 201, 202, 203 were formed on a glass substrate 204 as
shown in FIG. 2. Thereafter, the spaces between the ITO transparent
pixel electrodes were buried and then resists (partitioning walls)
205 made of a light-sensitive polyimide and functioning not only as
a light cut off layer but also an ink drop preventing wall were
formed.
[0163] Then, after coating and pattern formation of read and green
luminescent materials shown in Table 1 and Table 2, respectively,
by using an ink-jet device 209 in the same way as the Example 1,
they were undergone heat treatment under a nitrogen atmosphere for
four hours to polymerize the precursors in the compositions of the
materials, thereby forming luminescent layers 206 (red) and 207
(green).
[0164] Next, a hole injection and transfer layer made of polyvinyl
carbazole (PVK) was patterned on the transparent pixel electrode
203 by means of the ink-jet device 209. Then, a blue luminescent
layer 210 was formed by coating the pyrazoline dimer on top of the
hole injection and transfer layer.
[0165] Finally, an Al--Li electrode 211 having the thickness of 0.8
.mu.m was formed as the cathode by the deposition method, and
thereby the organic EL element was manufactured.
EXAMPLE 3
[0166] First, ITO transparent pixel electrodes 801, 802 and 803 and
banks 805 were formed on a glass substrate 804 as shown in FIG. 4
in the same way as Example 1.
[0167] Next, an organic hole injection and transfer type material
was mixed in the luminescent materials shown in Table 1 and Table 2
to form luminescent layers 806 (red), 807 (green) and 808 (blue) by
using an ink-jet device 809.
[0168] Next, the vacuum deposition was carried out using the
aluminum quinolynol complex to which the doping was not carried out
to form an electron injection and transfer layer 811 having the
thickness of 0.1.mu.m.
[0169] Finally, an Al--Li electrode 813 having the thickness of 0.2
.mu.m was formed as the cathode by the deposition method, and
thereby the organic EL element was manufactured.
EXAMPLE 4
[0170] In the same way as Example 1, ITO transparent pixel
electrodes 301, 302 and 303 and banks 305 were formed on a glass
substrate 304 as shown in FIG. 3.
[0171] Next, after coating and pattern formation with red and green
luminescent materials shown in Table 1 and Table 2, respectively,
by using an ink-jet device 310 in the same way as Example 1, they
were undergone heat treatment under a nitrogen atmosphere for four
hours to polymerize the precursors in the compositions of the
materials, thereby forming luminescent layers 306 (red) and 307
(green).
[0172] Next, a hole injection and transfer layer 308 made of
polyvinyl carbazole (PVK) was formed on the entire surfaces of the
luminescent layers 306, 307 and the transparent electrode 303 by
means of the coating method.
[0173] Then, a blue luminescent layer 309 made of a distyryl
derivative was formed on the hole injection and transfer layer 308
by means of the vacuum deposition method.
[0174] Finally, an Al--Li electrode 311 having the thickness of 0.8
.mu.m was formed as the cathode by the deposition method, and
thereby the organic EL element was manufactured. In this case, as
described above, the cathode 311 was automatically separated and
then insulated by the formation of the banks 304, the cathode was
brought into a condition that is was patterned so as to correspond
to the respective pixels 301, 302 and 303.
EXAMPLE 5
[0175] First, in the same way as Example 1, ITO transparent
electrodes 801, 802 and 803 and banks 805 were formed on a glass
substrate 804 as shown in FIG. 4.
[0176] Then, after coating and pattern formation with the red,
green and blue luminescent materials by discharging polymeric
organic luminescent materials shown in Table 1 and Table 2,
respectively, using the ink-jet device 809, they were undergone
heat treatment under a nitrogen atmosphere at 150.degree. C. for
four hours to polymerize the precursors in the compositions of the
materials, thereby forming luminescent layers 806 (red), 807
(green) and 808 (blue).
[0177] Next, the vacuum deposition was carried with the aluminum
quinolynol complex to which the doping was not carried out to form
the electron transfer layer 811 having the thickness of 0.19
.mu.m.
[0178] Finally, an Al--Li electrode 812 having the thickness of 0.8
.mu.m was formed as the cathode by the vacuum deposition, so that
the organic EL element was manufactured.
[0179] <Evaluation of the Luminescence Characteristics and the
Film Characteristics of the Luminescent Layers>
[0180] The luminescence characteristics and the film
characteristics of the luminescent layers of the organic EL
elements which were manufactured in Examples 1 to 5 described above
were evaluated according to the following methods.
[0181] 1. Luminescence Starting Voltage
[0182] A prescribed voltage was applied to the element, and the
applied voltage at which a luminance of 1 cd/m.sup.2 is observed
was defined as the luminescence starting voltage [Vth].
[0183] 2. Luminescence Life
[0184] The initial luminance after applying a stabilization
treatment was set to 100%, and the changes in the luminance of the
EL element were measured when subjecting it to continuous
luminescence through supply of a constant current of standard
waveform, wherein the luminescence life is defined as the time
until the luminance drops to 50% of the initial luminance.
[0185] In this case, the drive conditions for this experiment were
set at 40.degree. C. for room temperature, 23% for humidity and 20
mA/cm.sup.2 for current density.
[0186] 3. Luminance (Brightness)
[0187] The luminance was measured, in which the current was set to
20 mA/cm.sup.2.
[0188] 4. Wavelength at Maximum Absorption
[0189] The wavelength at maximum absorption for each luminescent
layer was measured.
[0190] 5. Stability in Film Formation
[0191] After heating the luminescent layer at 200.degree. C. for 60
minutes, conditions for occurrence of defects such as cracks and
deformation in the respective luminescent layers were observed by a
microscope.
[0192] The results of the evaluation were classified according to
the following marks.
[0193] .circleincircle. . . . Extremely favorable
[0194] .largecircle. . . . Favorable
[0195] X . . . Unsatisfactory
[0196] The results of the evaluation are shown in Table 3 and Table
4.
[0197] As indicated in Table 3 and Table 4, the luminescent layers
in Examples 1 to 5 have excellent luminescence characteristics and
excellent film characteristics. In particular, when the luminescent
layers were formed of polymer organic compounds, no defects were
observed in the luminescent layers, and extremely favorable thin
films were obtained.
[0198] In the above, the compositions for the organic EL elements
and the manufacturing methods for the organic EL elements according
to the present invention have been described according to the
embodiments that are illustrated. However, the present invention is
not limited to these embodiments, and for example, there may be
inserted in the manufacturing processes for providing any
intermediate functional layers between the respective layers.
Further, the fluorescent dyes which are added for changing the
luminescence characteristics are not limited to those described
above.
[0199] Further, a layer made of, for example, 1,2,4-triazole
derivative (TAZ) may be provided as a buffer layer between the
respective layers, thereby enabling to more improve the luminance,
luminescence life and the like.
[0200] Furthermore, the manufacturing method for the organic EL
elements according to the present invention may include a further
process in which surface treatment such as plasma, UV treatment,
coupling or the like are applied to the surface of the resin
resists, the pixel electrodes and the underlying layers in order to
facilitate the sticking of the EL materials. Moreover, it is
possible to apply the manufacturing method for the organic EL
element of the present invention to the manufacturing method for
the inorganic EL element.
[0201] The organic EL display device according to the present
invention may be applied to the low information field, such as
segment display and still image display of whole surface
simultaneous luminescence, for example, display of pictures,
characters, labels, or may be utilized as a light source having
point, line, or surface shape.
INDUSTRIAL UTILIZATION
[0202] As described in the above, according to the manufacturing
method of the organic EL element of the present invention, it is
possible to explore rational design of the EL luminescent elements
through a wide ranging selection of the luminescent materials. For
example, through arbitrary combinations of the luminescent
materials and fluorescent dyes, it is possible to obtain wide
variety of display lights.
[0203] Further, by using the organic luminescent materials, it is
possible to obtain the diversified designs of the EL element having
high luminance and long life.
[0204] Furthermore, by carrying out the pattern forming and
arrangement of the luminescent layer for at least one color, the
hole injection and transfer layer and the electron injection and
transfer layer by means of the ink-jet method, it is possible to
set arbitrarily and precisely the size and the pattern of the
luminescent elements.
[0205] When a precursor, which can be conjugated (form a film) by
thermosetting is used as a luminescent material, the latitude in
the setting of conditions such as viscosity can be expanded, and
the adjustment of the conditions suitable as a discharge liquid for
the ink-jet method can be facilitated.
[0206] Further, according to the manufacturing method for the
organic EL element of the present invention, conditions such as the
film thickness, the number of dots and the like can be adjusted
arbitrarily, so that it is possible to control readily the
luminescence characteristics of the luminescent layers.
[0207] Furthermore, according to the ink-jet method, it is possible
to move freely the head on the transparent substrate, thereby
enabling to form an element with an arbitrary size without
restricting the dimensions of the substrate. Moreover, since
required amounts of materials can be arranged at required
locations, it is possible to maximally exclude the uselessness of
waste liquid or the like. In this way, manufacturing of a full
color display device with large screen size becomes possible at a
low cost.
1TABLE 1 Luminescent Layer Red Green Blue Layer between Layers
Example 1 Luminescent CN-PPV Precursor PPV Precursor Aluminum
Quinolinol -- Material Complex Forming Method Ink-Jet System
Ink-Jet System Vacuum Deposition Method Example 2 Luminescent
CN-PPV Precursor PPV Precursor Pyrazoline Dimer PVK Material (Hole
Injection Layer) Forming Method Ink-Jet System Ink-Jet System
Coating Method Ink-Jet System Example 3 Luminescent
2-13',4'-dihydroxyphenyl 2,3,6,7-tetrahydro-11-
2,3,6,7-tetrahydro-9- -- Material -3,5,7-trihydroxy-1-
oxo-1H,5H,11H- (1) methyl-11-oxo-1H,5H,11H- benzopyrylium
benzopyrano [6,7,8-ij]- (1) benzopyrano [6,7,8-ij] perchlorate
quinolizine-10- -quinolizine carboxylic acid 1,1-bis- (4-N,
N-ditolyl) 1,1-bis- (4-N, N-ditolyl Tris (8-hydroxyquinolinol)
aminophenyl) cyclohexane aminophenyl) cyclohexane aluminum (Hole
Injection Layer (Hole injection layer (Hole injection layer
Material) Material) Material) Forming Method Ink-Jet System Ink-Jet
System Ink-Jet System Example 4 Luminescent CN-PPV Precursor PPV
Precursor Distyryl Derivative PVK Material (Hole Injection Layer)
Forming Method Ink-Jet System Ink-Jet System Coating method Vacuum
Deposition Method Example 5 Luminescent PPV Precursor PPV Precursor
PPV Precursor -- Material Rhodamine B -- Distyrlbiphenyl
(Fluorescent Dye) (Fluorescent Dye) Forming Method Ink-Jet System
Ink-Jet System Ink-Jet System
[0208]
2TABLE 2 Physical Properties of Composition Viscosity Surface
Tension for EL Element [cp] [dyne/cm] Contact Angle [.degree.]
Example 1 Red 3.77 32.9 54.4 Green 3.72 32.8 59.0 Blue -- -- --
Example 2 Red 3.70 32.6 55.6 Green 7.73 33.1 59.8 Blue 3.88 33.3
60.0 Example 3 Red 4.85 27.8 47.8 Green 5.31 25.6 45.6 Blue 4.52
28.2 40.3 Example 4 Red 3.78 33.5 60.1 Green 3.75 32.1 59.7 Blue --
-- -- Example 5 Red 3.80 33.1 55.0 Green 3.75 32.9 59.1 Blue 3.91
33.2 60.2
[0209]
3 TABLE 3 Luminescence Wavelength Starting at Maximum Voltage [Vhd
th] Luminescence Life [hr] Luminance [cd/m.sup.2] Absorption [nm] R
G B R G B R G B R G B Example 1 2.0 2.2 3.1 8000 8000 8000 210 230
200 600 500 400 Example 2 1.7 1.8 3.2 10000 10000 9000 230 230 180
600 500 410 Example 3 4.0 3.5 3.8 4000 5000 4000 150 180 100 580
510 420 Example 4 1.7 1.8 2.2 10000 10000 10000 250 250 200 600 530
480 Example 5 3.0 3.2 5.0 5000 5000 5000 200 200 200 590 530
420
[0210]
4 TABLE 4 Stability in Film Formation R G B Example 1
.circleincircle. .circleincircle. .circleincircle. Example 2
.circleincircle. .circleincircle. .circleincircle. Example 3
.largecircle. .largecircle. .largecircle. Example 4
.circleincircle. .circleincircle. .circleincircle. Example 5
.circleincircle. .circleincircle. .circleincircle.
* * * * *