U.S. patent application number 10/075761 was filed with the patent office on 2002-08-15 for organic electroluminescent device with self-aligned insulating fillers and method for manufacturing the same.
This patent application is currently assigned to NEC CORPORATION. Invention is credited to Ishikawa, Hitoshi, Oda, Atsushi, Tada, Hiroshi, Toguchi, Satoru.
Application Number | 20020110703 10/075761 |
Document ID | / |
Family ID | 18901723 |
Filed Date | 2002-08-15 |
United States Patent
Application |
20020110703 |
Kind Code |
A1 |
Tada, Hiroshi ; et
al. |
August 15, 2002 |
Organic electroluminescent device with self-aligned insulating
fillers and method for manufacturing the same
Abstract
In an organic electroluminescent device, a plurality of striped
lower electrodes are formed on an insulating substrate, and a
plurality of fillers made of amorphous carbon are filled between
the lower electrodes. Organic thin film layers including an
emitting layer is formed on the fillers and the lower electrodes. A
plurality of striped upper electrodes are formed on the organic
thin film layer along a second direction different from the first
direction.
Inventors: |
Tada, Hiroshi; (Tokyo,
JP) ; Oda, Atsushi; (Tokyo, JP) ; Ishikawa,
Hitoshi; (Tokyo, JP) ; Toguchi, Satoru;
(Tokyo, JP) |
Correspondence
Address: |
SUGHRUE, MION, ZINN, MACPEAK & SEAS
2100 Pennsylvania Avenue, N.W.
Washington
DC
20037
US
|
Assignee: |
NEC CORPORATION
|
Family ID: |
18901723 |
Appl. No.: |
10/075761 |
Filed: |
February 15, 2002 |
Current U.S.
Class: |
428/690 ;
313/504; 313/505; 313/506; 427/66; 428/167; 428/179; 428/917;
430/313; 430/319 |
Current CPC
Class: |
Y10T 428/2457 20150115;
H01L 2251/5392 20130101; Y10T 428/24669 20150115; H01L 27/3281
20130101; H01L 51/56 20130101 |
Class at
Publication: |
428/690 ;
428/917; 428/167; 428/179; 313/504; 313/505; 313/506; 430/319;
430/313; 427/66 |
International
Class: |
H05B 033/12; H05B
033/10 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 15, 2001 |
JP |
2001-038808 |
Claims
1. An organic electroluminescent device comprising: an insulating
substrate; a plurality of striped lower electrodes formed on said
insulating substrate; a plurality of filters made of amorphous
carbon filled between said lower electrodes; at least one organic
thin film layer including an emitting layer formed on said fillers
and said lower electrodes; and a plurality of striped upper
electrodes formed on said organic thin film layer along a second
direction different from said first direction.
2. The organic electroluminescent device as set forth in claim 1,
wherein said lower electrodes are anodes and said upper electrodes
are cathodes.
3. The organic electroluminescent device as set forth in claim 2,
further comprising a hole-transporting layer between said lower
electrodes and said emitting layer.
4. The organic electroluminescent device as set forth in claim 2,
further comprising an electron-transporting layer between said
emitting layer and said upper electrodes.
5. The organic electroluminescent device as set forth in claim 1,
wherein said insulating substrate is transparent and said lower
electrodes comprise transparent conductive layers.
6. The organic electroluminescent device as set forth in claim 5,
wherein said transparent conductive layers comprise indium tin
oxide.
7. The organic electroluminescent device as set forth in claim 1,
wherein said first direction is approximately normal to said second
direction.
8. A method for manufacturing an organic electroluminescent device,
comprising the steps of: forming a conductive layer on an
insulating substrate; forming a photoresist pattern layer having a
plurality of striped elements on said conductive layer; etching
said conductive layer by a dry etching process using a first plasma
gas and using said photoresist pattern layer as an etching mask in
a chamber to form striped lower electrodes; depositing an
insulating layer on said photoresist pattern layer and on said
insulating substrate between said lower electrodes by a plasma
deposition process using a second plasma gas in said chamber;
performing a lift-off operation upon said photoresist pattern layer
to remove said photoresist pattern layer and a part of said
insulating layer on said photoresist pattern layer; forming at
least one organic thin film layer including an emitting layer on
said insulating layer and said lower electrodes; and forming a
plurality of striped upper electrodes on said organic thin film
layer along a second direction different from said first
direction.
9. The method as set forth in claim 8, wherein a condition for
introducing said first plasma gas is the same as a condition for
introducing said second plasma gas.
10. The method as set forth in claim 9, wherein each of said first
and second plasma gas includes hydrocarbon gas.
11. The method as set forth in claim 8, wherein a condition for
introducing said first plasma gas is different from a condition for
introducing said second plasma gas.
12. The method as set forth in claim 11, wherein said first plasma
gas includes halogen gas, and said second plasma gas includes
hydrocarbon gas.
13. The method as set forth in claim 8, wherein said lower
electrodes are anodes and said upper electrodes are cathodes.
14. The method as set forth in claim 13, further comprising a step
of forming a hole-transporting layer between said lower electrodes
and said emitting layer.
15. The method as set forth in claim 13, further comprising a step
of forming an electron-transporting layer between said emitting
layer and said upper electrodes.
16. The method as set forth in claim 8, wherein said insulating
substrate is transparent and said lower electrodes comprise
transparent conductive layers.
17. The method as set forth in claim 16, wherein said transparent
conductive layers comprise indium tin oxide.
18. The method as set forth in claim 8, wherein said first
direction is approximately normal to said second direction.
19. The method as set forth in claim 8, wherein said insulating
layer comprises amorphous carbon.
20. A method for manufacturing an organic electroluminescent
device, comprising the steps of: forming a conductive layer on an
insulating substrate; forming a photoresist pattern layer having a
plurality of striped elements on said conductive layer; etching
said conductive layer by a dry etching process using gas including
hydrocarbon gas and using said photoresist pattern layer as an
etching mask in a chamber to form striped lower electrodes, and
subsequently depositing an insulating layer on said photoresist
pattern layer and on said insulating substrate between said lower
electrodes by a plasma deposition process using said gas including
hydrocarbon gas in said chamber; performing a lift-off operation
upon said photoresist pattern layer to remove said photoresist
pattern layer and a part of said insulating layer on said
photoresist pattern layer, forming at least one organic thin film
layer including an emitting layer on said insulating layer and said
lower electrodes; and forming a plurality of striped upper
electrodes on said organic thin film layer along a second direction
different from said first direction.
21. A method for manufacturing an organic electroluminescent
device, comprising the steps of: forming a conductive layer on an
insulating substrate; forming a photoresist pattern layer having a
plurality of striped elements on said conductive layer; etching
said conductive layer by a dry etching process using a gas
including halide gas and using said photoresist pattern layer as an
etching mask in a chamber to form striped lower electrodes;
depositing an insulating layer on said photoresist pattern layer
and on said insulating substrate between said lower electrodes by a
plasma deposition process using a gas including hydrocarbon gas in
said chamber; performing a lift-off operation upon said photoresist
pattern layer to remove said photoresist pattern layer and a part
of said insulating layer on said photoresist pattern layer; forming
at least one organic thin film layer including an emitting layer on
said insulating layer and said lower electrodes; and forming a
plurality of striped upper electrodes on said organic thin film
layer along a second direction different from said first direction.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an organic
electroluminescent device and its manufacturing method.
[0003] 2. Description of the Related Art
[0004] An organic electroluminescent device is a light-emitting
device which makes use of a principle that when an electric field
is applied to the device, a fluoresent material emits light in
response to a charge recombination of holes a injected from an
anode and electrons from a cathode. Such organic electroluminescent
devices have been developed ever since C. W. Tang et al. Published
"Organic Electroluminescent Diodes", Applied physics Lett. 51(12),
pp. 913-915, Sep. 21, 1987.
[0005] Tang et al. reported an electroluminecent device of a
stacked structure using tris (8-quinolinol aluminum) in an emitting
layer and a triphenyldiamine derivative in a hole-transporting
layer. This stacked structure has advantages in that the injection
efficiency of holes into the emitting layer can be improved, that
electrons injected from a cathode can be blocked to increase the
efficiency of exciton production from charge recombination, and
that the excitons into the emitting layer can be confined. A
multi-layered structure such as a double layered structure composed
of a hole-injecting and transporting layer and an
electron-transporting and emitting layer or a triple layered
structure composed of a hole-injecting and transporting layer, an
emitting layer and an electron-injecting and transporting layer is
well known as an organic electroluminescent device. In order to
increase the recombination efficiency of injected holes and
electrons, various improvements have been introduced into the
structure and fabrication process of the multi-layered
structure.
[0006] A first prior art organic electroluminescent device is
constructed by a transparent insulating substrate, striped lower
electrodes made of indium tin oxide (IT0) formed on the transparent
insulating substrate, an emitting layer formed on the lower
electrodes, and striped upper electrodes formed on the emitting
layer. In this case, the upper electrodes are arranged along a
first direction, and the lower electrodes are arranged along a
second direction normal to the first direction. As occasion
demands, a hole-transporting layer is interposed between the lower
electrodes and the emitting layer, and an electron-transporting
layer is interposed between the emitting layer and the upper
electrodes, to enhance the injection efficiency of carriers such as
holes and electrons into the emitting layer. Note that the emitting
layer, the hole-transporting layer and the electron-transporting
layer are made of organic materials.
[0007] In the above-described first prior art organic
electroluminescent device, however, since there are steps at the
edges of the lower electrodes, the portions of the organic layers
such as the hole-transporting layer, the emitting layer and the
electron-transporting layer in proximity to the steps of the lower
electrodes become thinner. Particularly, since the emitting layer
is very thin, i.e., about 100 nm thick, when the portions of the
emitting layer in proximity to the steps of the lower electrodes
become thinner, a short-circuit would occur between the lower
electrodes and the upper electrodes through the thinner portions of
the emitting layer to damage the organic electroluminescent
device.
[0008] A second prior art organic electroluminescent device
includes an insulating pattern layer having elements filled between
the lower electrodes to substantially make the edges of the lower
electrodes smooth, thus avoiding a short-circuit between the lower
electrodes and the upper electrodes through the organic layers
including the emitting layer (see: JP-A-3-250583, JP-A-3-274694
& JP-A-4-51494).
[0009] In the above-described second prior art organic
electroluminescent device, however, since a photolithography and
etching process is required to form the insulating pattern layer,
the manufacturing cost is increased.
[0010] In a third prior art organic electroluminescent device, the
insulating layer filled between the lower electrodes is formed by
the same photoresist pattern layer for forming the lower
electrodes, to thereby decrease the manufacturing cost (see: FIG. 6
of JP-A-2000-123978). That is, first, an ITO layer is deposited on
a transparent insulating substrate. Then, a photoresist pattern
layer is formed on the ITO layer by a photolithography process, and
the ITO layer is patterned by an etching process using the
photoresist pattern layer as a mask to form lower electrodes. Then,
an insulating layer is deposited on the entire surface without
removing the photoresist pattern layer, and a so-called lift-off
operation is performed on the photoresist pattern layer, so that
the photoresist pattern layer and a part of the insulating layer on
the photoresist pattern layer are simultaneously removed. As a
result, the remainder of the insulating layer is filled as fillers
between the lower electrodes.
[0011] In the above-described third prior art organic
electroluminescent device, however, since the formation of the
lower electrodes by an etching process is carried out in a chamber
different from a chamber where the formation of the insulating
layer is carried out, the manufacturing cost is still high.
SUMMARY OF THE INVENTION
[0012] It is an object of the present invention to provide an
organic electroluminescent device and its manufacturing method
suppressing short-circuits without increasing the manufacturing
cost.
[0013] According to the present invention, in an organic
electroluminescent device, a plurality of striped lower electrodes
are formed on an insulating substrate, and a plurality of fillers
made of amorphous carbon are filled between the lower electrodes.
At least one organic thin film layer including an emitting layer is
formed on the fillers and the lower electrodes. A plurality of
striped upper electrodes are formed on the organic thin film layer
along a second direction different from the first direction.
[0014] Also, in a method for manufacturing an organic
electroluminescent device according to the present invention, a
conductive layer is formed on an insulating substrate. Then, a
photoresist pattern layer having a plurality of striped elements is
formed on the conductive layer. Then, the conductive layer is
etched by a dry etching process using a first plasma gas and using
the photoresist pattern layer as an etching mask in a chamber to
form striped lower electrodes. Then, an insulating layer is
deposited on the photoresist pattern layer and on the insulating
substrate between the lower electrodes by a plasma deposition
process using a second plasma gas in the above-mentioned chamber.
Then, a lift-off operation is performed upon the photoresist
pattern layer to remove the photoresist pattern layer and a part of
the insulating layer on the photoresist pattern layer. Then, at
least one organic thin film layer including an emitting layer is
formed on the insulating layer and the lower electrodes. Finally, a
plurality of striped upper electrodes are formed on the organic
thin film layer along a second direction different from the first
direction.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The present invention will be more clearly understood from
the description set forth below, with reference to the accompanying
drawings, wherein:
[0016] FIGS. 1A, 1B, 1C, 1D and 1E are perspective views for
explaining a first embodiment of the method for manufacturing an
organic electroluminescent device according to the present
invention;
[0017] FIGS. 2A, 2B, 2C, 2D, 2E and 2F are perspective views for
explaining a second embodiment of the method for manufacturing an
organic electroluminescent device according to the present
invention;
[0018] FIGS. 3A, 3B, 3C, 3D, 3E and 3F are diagrams showing
chemical structures of material for the hole-transporting layer of
FIGS. 1E and 2F; and
[0019] FIGS. 4A, 4B, 4C, 4D, 4E, 4F, 4G, 4H, 4I and 4J are diagrams
showing chemical structures of material the electron-transporting
layer of FIGS. 1E and 2F.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] A first embodiment of the method for manufacturing an
organic electroluminescent device according to the present
invention will now be explained with reference to FIGS. 1A, 1B, 1C,
1D and 1E.
[0021] First, referring to FIG. 1A, an about 80 nm thick ITO layer
12 is deposited on a transparent insulating substrate 11 made of
glass by a sputtering process.
[0022] Next, referring to FIG. 1B, a photoresist layer is coated on
the ITO layer 12 by a spin-coating process. Then,the photoresist
layer is patterned by a photolithography and developing process to
form a photoresist pattern layer 13 having striped elements along a
predetermined direction.
[0023] Next, referring to FIG. 1C; the transparent insulating
substrate 11 is put in a reactive ion etching (RIE) chamber, and
the ITO layer 12 is etched by an RIE process using CH.sub.4/H.sub.4
mixture gas, to form lower electrodes 12a. In this case, plasma
generating conditions such as the pressure, the flow rate and the
ratio of gas mixture are changed, so that an about 80 nm thick
amorphous carbon layer 14 is deposited simultaneously with the
etching of the ITO layer 12.
[0024] Next, referring to FIG. 1D, a so-called lift-off operation
is performed upon the photoresist pattern layer 13, so that the
photoresist pattern layer 13 and a part of the amorphous carbon
layer 14 thereon are simultaneously removed. As a result, amorphous
carbon fillers 14a are filled between the lower electrodes 12a. In
this case, as occasion demands, a flattening process such as a
chemical mechanical polishing (CMP) process is performed upon the
amorphous carbon fillers 14a. Note that the amorphous carbon
fillers 14a are 5 nm to 1 .mu.m thick, preferably, 20 to 300 nm
thick.
[0025] Finally, referring to FIG. 1E, an about 50 nm thick
hole-transporting layer 5, an about 70 nm thick emitting layer 16
and an about 20 nm thick electron-transporting layer 17 are
sequentially deposited by a vacuum evaporation process. Then, a
plurality of about 150 nm thick striped upper electrodes 18 made of
Mg--Ag alloy are formed by a vacuum co-evaporation process. In this
case, the upper electrodes 18 are normal to the lower electrodes
formed by the ITO layer 14. Then, the upper electrodes 18 are
sealed by resin, to complete the organic electroluminescent
element.
[0026] According to the inventors' experiment, the organic
electroluminescent device of FIG. 1E was driven to show an
excellent diode characteristic having a rectification ratio of more
than 10.sup.4.
[0027] Thus, in the first embodiment, since the lower electrodes
12a and the amorphous carbon fillers 14a filled between the lower
electrodes 12a are formed by the same RIE chamber, the
manufacturing cost can be decreased.
[0028] A second embodiment of the method for manufacturing an
organic electroluminescent device according to the present
invention will be explained next with reference to FIGS. 2A, 2B,
2C, 2D, 2E and 2F.
[0029] First, referring to FIG. 2A, an about 80 nm thick ITO layer
22 is deposited on a transparent insulating substrate 21 made of
glass by a sputtering process.
[0030] Next, referring to FIG. 2B, a photoresist layer is coated on
the ITO layer 22 by a spin-coating process. Then,the photoresist
layer is patterned by a photolithography and developing process to
form a photoresist pattern layer 23 having striped elements along a
predetermined direction.
[0031] Next, referring to FIG. 2C, the transparent insulating
substrate 21 is put in an RIE chamber, and the ITO layer 12 is
etched by an RIE process using HI/Ar mixture gas, to form lower
electrodes 22a.
[0032] Next, referring to FIG. 2D, an about 80 nm thick amorphous
carbon layer 24 is deposited by a reactive ion process using
CH.sub.4/H.sub.4 mixture gas in the same RIE chamber as in the step
as illustrated in FIG. 2C.
[0033] Next, referring to FIG. 2E, a so-called lift-off operation
is performed upon the photoresist pattern layer 23, so that the
photoresist pattern layer 23 and a part of the amorphous carbon
layer 24 thereon are simultaneously removed. As a result, amorphous
carbon fillers 24a are filled between the lower electrodes 22a. In
this case, as occasion demands, a flattening process such as a CMP
process is performed upon the amorphous carbon fillers 24a. Note
that the amorphous carbon fillers 24a are 5 nm to 1 .mu.m thick,
preferably, 20 to 300 nm thick.
[0034] Finally, referring to FIG. 2F, an about 50 nm thick
hole-transporting layer 25, an about 70 nm thick emitting layer 26
and an about 20 nm thick electron-transporting layer 27 are
sequentially deposited by a vacuum evaporation process. Then, a
plurality of about 150 nm thick striped upper electrodes 28 made of
Mg--Ag alloy are formed by a vacuum evaporation process. In this
case, the upper electrodes 28 are normal to the lower electrodes
formed by the ITO layer 24. Then, the upper electrodes 28 are
sealed by resin, to complete the organic electroluminescent
element.
[0035] According to the inventors' experiment, the organic
electroluminescent device of FIG. 2F was driven to show an
excellent diode characteristic having a rectification ratio of more
than 10.sup.4.
[0036] Even in the second embodiment, since the lower electrodes
22a and the amorphous carbon fillers 24a filled between the lower
electrodes 22a are formed by the same RIE chamber, the
manufacturing cost can be decreased.
[0037] In the above-described second embodiment, although the
fillers 24a is made of amorphous carbon, the fillers 24a can be
made of other material such as silicon oxide or silicon
nitride.
[0038] In the above-described embodiments, the hole-transporting
layer 15(25), the emitting layer 16(26) and the
electron-transporting layer 17(27) are sandwiched by the lower
electrodes 12(22) and the upper electrodes 18(28). However, the
hole-transporting layer 15(25) and/or the electron-transporting
layer 17(27) can be omitted.
[0039] Also, the lower electrodes are made of ITO. However, the
lower electrodes can be made of other materials having a work
function of larger than 4.5 eV depending upon the material of the
emitting layer 16(26) to inject holes into the emitting layer
16(26) or the hole-transporting layer 15(25). For example, metal
oxide such as IZO(IDIXO) or tin oxide (NESA), Au, Ag, Pt or Cu can
be used.
[0040] There is no particular limitation on a material for the
hole-transporting layer 15(25). Any ordinary hole-transporting
material may be used. For example, the hole-transporting layer
15(25) is made of a tripheny/diamine such as bis(di(p-tolyl)
aminophenyl)-1, 1-cyclohexane (see FIG. 3A), N, N'-diphenyl-N,
N'-bis(3-methylphenyl)-1, 1'-biphenyl-4, 4'-diamine (see FIG. 3B)
or N, N'-diphenyl-N, N'-bis(1-naphtyl)-1, 1'-biphenyl)-4,
4'-diamine (see FIG. 3C), star burst molecules (see FIGS. 3D, 3E
and 3F), a poly(p-phenylenevynylene) derivative, a polyaniline
derivative or a polythiophene derivative. Also, the
hole-transporting layer 15(25) is made of other conductive
polymers. Further, the hole-transporting layer 15(25) is made of a
mixture of a conductive polymer and Lewis acid such as
FeCl.sub.3.
[0041] There is no particular limitation on a material for the
emitting layer 16(26). Any ordinary light-emitting material may be
used. For example, the emitting layer 16(26) is made of a
distyrylarylene derivative (see JP-A-2-247278 & JP-A-5-17765),
a coumarin derivative, a dicyanomethylenephrane derivative, a
perylene derivative (see JP-A-63-264692), an aromatic derivative
(see JP-A-8-298186 & JP-A-9-268284), an anthracene compound
(see JP-A-9-157643, JP-A-9-268283 & JP-A-10-72581), or a
quinacridone derivative (see JP-A--5-70773).
[0042] There is no particular limitation on a material for the
electron transporting layer 17(27). Any ordinary
electron-transporting material may be used. For example, the
electron-transporting layer 17(27) is made of an oxadiazole
derivative such as 2-(4-biphenyl)-5-(4-t-butyrphenyl)-1, 3,
4-oxadiazole derivative (see FIG. 4A) or bis
{2-(4-t-butryphenyl)-1, 3, 4-oxadiazole}-m-phenylene (see FIG. 4B),
a triazole derivative (see FIGS. 4C and 4D), a quinolinol metal
complex (see FIGS. 4E, 4F, 4G and 4H), bathophenanthroline (see
FIG. 4I), or bathocuprolene (see FIG. 4J).
[0043] The upper electrodes 18(28) is preferably made of conductive
material having a small work function to inject electrons into the
emitting layer 16(26) (or the electron-transporting layer 17(27)).
For example, the upper electrodes 18(28) are made of In, Al, Mg,
Mg--In alloy, Mg--Al alloy, Al--Li alloy, Al--Sc--Li alloy or
Mg--Ag alloy. Note that, since the lower electrodes which, in this
case, serve as anodes are transparent, the upper electrodes 18(28)
serving as cathodes are preferably made of conductive material
having a high reflectivity to reflect light emitted from the
emitting layer 16(26).
[0044] In the above-described embodiments, the ITO layer 12(22) is
formed by a sputtering process; however, the ITO layer 12(22) can
be formed by a vacuum evaporation process, an ion-plating process,
a chemical vapor deposition (CVD) process, a sol-gel coating
process, a spray process or a spin-coating process.
[0045] Also, the organic layers such as the hole-transporting layer
15(25), the emitting layer 16(26) and the electron-transporting
layer 17(27) are formed by a vacuum evaporation process; however,
the organic layers can be formed by a molecular beam epitaxial
(MBE) process, a dipping process, a coating process such as a
spin-coating process, a casting process, a bar-coating process, or
a roll-coating process using solutions of materials. In this case,
the thickness of the organic layers can be optimized That is, the
thinner each of the organic layers, the larger the number of
defects such as pinholes. On the other hand, the thicker each of
the organic layers, the higher the voltage applied thereto for
injecting carriers. In view of this, the thickness of each of the
organic layers is preferably several nm to lam.
[0046] Additionally, the upper electrodes 18(28) are formed by a
vacuum evaporation process; however, the upper electrodes 18(28)
can be formed by a magnetron sputtering process, an ion-plating
process, a; CVD process, a sol-gel coating process, a spray process
or a spin-coating process.
[0047] In the above-described embodiments, other dry etching
processes such as a plasma etching process can be used instead of
the RIE process. Also, in the RIE process, various kind of gases
can be used. For example, halogen gas such as CF.sub.4 gas
hydrocarbon gas such as CH.sub.4 gas, inert gas such as Ar gas, or
hydrogen gas can be used. Also, when depositing amorphous carbon,
other carbon gas such as CH.sub.4 gas can be used.
[0048] As explained hereinabove, according to the present
invention, since the formation of lower electrodes and the
formation of fillers between the lower electrodes are carried out
in the same chamber, the manufacturing cost can be decreased.
* * * * *