U.S. patent application number 11/133410 was filed with the patent office on 2005-09-22 for organic el element and method of manufacturing the same, organic el display device using the element, organic el material, and surface emission device and liquid crystal display device using the material.
This patent application is currently assigned to FUJITSU LIMITED. Invention is credited to Yoshikawa, Kota.
Application Number | 20050208206 11/133410 |
Document ID | / |
Family ID | 26598910 |
Filed Date | 2005-09-22 |
United States Patent
Application |
20050208206 |
Kind Code |
A1 |
Yoshikawa, Kota |
September 22, 2005 |
Organic EL element and method of manufacturing the same, organic EL
display device using the element, organic EL material, and surface
emission device and liquid crystal display device using the
material
Abstract
In an organic EL element, an organic EL layer is interposed
between anodes and cathodes formed on a substrate. Each of the
cathodes is made of a first conductive film that comes into contact
with the organic EL layer and a second conductive film that
constitutes a laminated structure together with the first
conductive film. The first conductive film contains any one of an
alkaline metal and an alkaline earth metal. The second conductive
film contains any one of at least one type metal selected from a
group consisting of Ru (ruthenium), Rh (rhodium), Ir (iridium), Os
(osmium) and Re (rhenium) and its oxide.
Inventors: |
Yoshikawa, Kota; (Kawasaki,
JP) |
Correspondence
Address: |
ARMSTRONG, KRATZ, QUINTOS, HANSON & BROOKS, LLP
1725 K STREET, NW
SUITE 1000
WASHINGTON
DC
20006
US
|
Assignee: |
FUJITSU LIMITED
Kawasaki
JP
|
Family ID: |
26598910 |
Appl. No.: |
11/133410 |
Filed: |
May 20, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11133410 |
May 20, 2005 |
|
|
|
09916314 |
Jul 30, 2001 |
|
|
|
Current U.S.
Class: |
427/66 ; 313/503;
313/506; 428/690; 428/917 |
Current CPC
Class: |
H01L 27/3244 20130101;
H01L 27/3281 20130101; C08G 61/126 20130101; C09K 11/06 20130101;
H05B 33/14 20130101; H01L 51/5088 20130101; H01L 27/3211 20130101;
H01L 51/5231 20130101; C09K 2211/1425 20130101; Y10S 428/917
20130101; H01L 51/5253 20130101; C07D 271/107 20130101; H01L 51/007
20130101; H01L 2251/558 20130101; H01L 27/32 20130101; H01L 51/0038
20130101; C07D 271/10 20130101 |
Class at
Publication: |
427/066 ;
428/917; 428/690; 313/503; 313/506 |
International
Class: |
H05B 033/10; H05B
033/26 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 31, 2000 |
JP |
2000-262567 |
Jan 17, 2001 |
JP |
2001-8785 |
Claims
1-3. (canceled)
4. An organic EL element manufacturing method comprising the steps
of: forming an anode on a substrate; forming an organic EL layer on
said anodes; forming a first conductive film, that contains any one
of an alkaline metal and an alkaline earth metal, on said organic
EL layer; and forming a second conductive film laminated on said
first conductive film and containing a metal that is able to
prevent entering of an oxygen and a moisture into said first
conductive film when said metal is oxidized.
5. An organic EL element manufacturing method according to claim 4,
wherein said second conductive film contains any one of at least
one type metal selected from a group consisting of Ru (ruthenium),
Rh (rhodium), Ir (iridium), Os (osmium) and Re (rhenium) and its
oxide.
6. An organic EL element manufacturing method according to claim 4,
wherein said second conductive film is formed of any one of a TiN
film and a laminated film made of TiN and Ti.
7-8. (canceled)
9. An organic EL element manufacturing method comprising the steps
of: forming an anode on a substrate; forming a buffer layer, which
contains at least one type metal selected from a group consisting
of Ru, Mo, and V, on said anode; oxidizing a surface of said buffer
layer; forming an organic EL layer on said buffer layer; and
forming a cathode.
10. An organic EL element manufacturing method according to claim
9, wherein said cathode contains any one of an alkaline metal and
an alkaline earth metal.
11. (canceled)
12. An organic EL display device manufacturing method comprising
the steps of: forming a first electrode on a substrate; forming an
organic EL layer formed of organic EL material, in which a
conjugate length of polymer is changed in response to light
irradiation, on said first electrode; irradiating partially a light
onto said organic EL layer to change said conjugate length; and
forming a second electrode on said organic EL layer.
13-19. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to an organic EL
(Electroluminescence) element having a structure in which an
organic EL layer is put between a pair of electrodes, an organic EL
display device employing the element, organic EL material, and a
plane emission device and a display device employing the
material.
[0003] 2. Description of the Prior Art
[0004] In recent years, the organic EL element (the organic LED) is
well appreciated as the spontaneous emission element. The organic
EL element has the advantage that such element can be driven by the
low voltage rather than the inorganic EL element and also the
advantage that such element can be manufactured without complicated
manufacturing processes in contrast to the inorganic LED in the
prior art.
[0005] Also, in comparison with the liquid crystal display device
that is widely used at present as the display of the mobile device,
the organic EL element has a quick response speed, has a simple
device structure, and needs no back-light. Therefore, the organic
EL element has the advantage that such element can be reduced in
weight. In addition, since the organic EL element is the solid
state element, such element has the merit that it is resistant to
the impact.
[0006] The organic EL element has the structure that the EL
emission layer (the organic EL layer) is put between the cathode
and the anode. The metal having the large work function is employed
as the anode and the metal having the small work function is
employed as the cathode, so that supplies of the hole and the
electron can be made smooth. Normally, ITO (Indium-Tin Oxide) as
the transparent conductor is employed as the anode.
[0007] Also, the metal containing the alkaline metal or the
alkaline earth metal such as Na (sodium), Na--K (sodium-potassium)
alloy, Mg (magnesium), Li (lithium), Mg/Cu (magnesium/copper)
mixture, In (indium), etc. is employed as the cathode.
[0008] Alq.sub.3, BeBq.sub.3, DCM, DPVBi, quinacridone derivative,
coumalin, etc., for example, is employed as the EL emission layer.
Normally, the monomer EL emission layer is formed by the vacuum
evaporation method, and the polymer EL emission layer is formed by
the spin coating method. Accordingly, the polymer EL emission layer
has the advantage that the film formation is easy and also the
mechanical strength is high.
[0009] In addition, in order to lower the operating threshold
voltage of the organic EL element, the trial for forming the buffer
layer on the cathode side or the anode side is made. For example,
sometimes the layer made of ruthenium oxide (referred to as "RuO"
hereinafter), molybdenum oxide (referred to as "MoO" hereinafter),
or vanadium oxide (referred to as "VO" hereinafter) is formed as
the buffer layer between the anode and the organic EL layer in the
prior art. The layer made of RuO, MoO, or VO is formed by the
sputter method.
[0010] By the way, if the organic EL element is used for a long
time, the luminous efficiency is lowered due to the influence of
the oxygen and the moisture and also the defect called the dark
spot is caused. This is due to the fact that the alkaline metal or
the alkaline earth metal employed as the cathode is easily
oxidized.
[0011] In Patent Application Publication (KOKAI) Hei 7-169567 as
the preceding literature, in order to avoid the degradation of the
luminous efficiency of the organic EL element due to the oxygen and
the moisture, it is proposed that the laminated body consisting of
the anode, the organic EL layer, and the cathode should be covered
with the layer formed of material that can adsorb, occlude, or
consume the oxygen (referred to as a "sealing layer"
hereinafter).
[0012] Then, the material such as magnesium oxide, magnesium
carbonate, iron oxide, titanium oxide, bentonite, or the like, that
is impregnated with platinum, palladium, rhodium, ruthenium, or
silver at a concentration of less than 5 wt %, etc. are set forth
as the material of the sealing layer.
[0013] However, the problems discussed in the following are pointed
out in the organic EL element disclosed in the above literature.
That is, since the laminated body consisting of the anode, the
organic EL layer, and the cathode is covered with the insulating
sealing layer, the leading electrode that is extended to the
outside of the sealing layer must be provided to the anode and the
cathode respectively. As a result, the manufacturing steps become
complicated and also the rise of the product cost is brought
about.
[0014] Also, as described above, sometimes the buffer layer made of
RuO, MoO, or VO is formed by the sputter method in order to lower
the operating threshold voltage.
[0015] However, this method has the drawback that the large
unevenness is formed. If it is tried to form the RuO.sub.2 layer of
30 nm thickness by the sputter method, for example, the hillock
having a height of 50 to 100 nm is locally generated. As a result,
there is the possibility that, if the thickness of the organic EL
layer is reduced, conversely the short-circuit defect is
caused.
[0016] In addition, in case the full-color image display device
using the organic EL elements is fabricated, the organic EL
elements for the red color emission, the organic EL elements for
the green color emission, and the organic EL elements for the blue
color emission must be aligned in both the horizontal direction and
the vertical direction in the predetermined order.
[0017] Therefore, the technology for patterning finely the organic
EL layers is requested. As the fine pattern technology used in
manufacturing the semiconductor device, the lift-off method and the
etching method are well known.
[0018] However, in the case of the monochromatic image display
device, it may be considered that, for example, the upper
electrodes (the cathodes) of respective pixels are formed by the
lift-off method. But it is difficult to apply the lift-off method
to the manufacture of the full-color image display device.
[0019] Further, since the organic EL layer is formed of the monomer
or polymer organic, such organic EL layer has the drawback that it
cannot be worked by the fine pattern technology such as the dry
etching, etc.
[0020] Moreover, the above organic EL element is noted with
interest as the back-light device in place of the cold-cathode lamp
that is employed in the liquid crystal display device. The
cold-cathode lamp, that is employed as the back-light device in the
prior art, has the low luminous efficiency and also occupies about
30% of the overall cost of the liquid crystal display device, which
is a factor of the cost up.
[0021] The monomer and polymer materials are known as the organic
EL material. Normally the film of the monomer EL material can be
formed by the vacuum evaporation method, whereas the film of the
polymer EL material can be formed by the coating method. Therefore,
the polymer EL material is advantageous in manufacturing cost.
[0022] Since the back-light device using the polymer organic EL
material can be driven by the low voltage, the reduction in the
consumption power of the liquid crystal display device can be
expected and also the cost down and the reduction in size of the
device can be expected rather than the cold-cathode lamp in the
prior art.
[0023] However, the actual circumstances are that the organic EL
material that is available in practical use has not been developed
yet.
SUMMARY OF THE INVENTION
[0024] Therefore, in view of the above circumstances, it is an
object of the present invention to provide an organic EL element
and a method of manufacturing the same, that is capable of
simplifying its manufacturing steps, lowering the product cost, and
avoiding the degradation in the luminescence characteristic and the
short-circuit defect of an organic EL layer due to the oxygen and
the moisture not to cover a laminated body consisting of an anode,
the organic EL layer, and a cathode with an insulating sealing
layer, and an organic EL display device employing the organic EL
element.
[0025] Also, it is another object of the present invention to
provide organic EL material available in practical use, that can be
driven by a low voltage, is capable of achieving the reduction in
the power consumption, and achieving the cost down and the
reduction in size, and a plane emission device and a display device
employing the material.
[0026] In order to achieve the above objects, an organic EL element
of the present invention comprises:
[0027] an organic EL layer formed between an anode and a cathode;
and
[0028] the cathode consisting of a first conductive film that
contacts to the organic EL layer and a second conductive film that
constitutes a laminated structure together with the first
conductive film, the first conductive film containing any one of an
alkaline metal and an alkaline earth metal, and the second
conductive film containing a metal that is able to prevent entering
of an oxygen and a moisture into the first conductive film when the
metal is oxidized.
[0029] Also, an organic EL element manufacturing method of the
present invention comprises the steps of:
[0030] forming an anode on a substrate;
[0031] forming an organic EL layer on the anodes;
[0032] forming a first conductive film, that contains any one of an
alkaline metal and an alkaline earth metal, on the organic EL
layer; and
[0033] forming a second conductive film laminated on the first
conductive film and containing a metal that is able to prevent
entering of an oxygen and a moisture into the first conductive film
when the metal is oxidized.
[0034] Also, an organic EL element of the present invention
comprises:
[0035] an anode;
[0036] a buffer layer which is formed of at least one type metal
selected from a group consisting of Ru, Mo, and V on the anode and
a surface of which is oxidized;
[0037] an organic EL layer formed to be contacted to an oxidized
surface of the buffer layer; and
[0038] a cathode formed on said organic EL layer.
[0039] Also, an organic EL element manufacturing method of the
present invention comprises the steps of:
[0040] forming an anode on a substrate;
[0041] forming a buffer layer, which contains at least one type
metal selected from a group consisting of Ru, Mo, and V, on the
anode;
[0042] oxidizing a surface of the buffer layer;
[0043] forming an organic EL layer on the buffer layer; and
[0044] forming a cathode.
[0045] Also, an organic EL display device of the present invention
comprises:
[0046] a substrate;
[0047] a lower electrode formed on the substrate;
[0048] an organic EL layer formed on the lower electrode to have
areas in which a conjugate length of polymer is different each
other so that these areas have two different luminous colors or
more; and
[0049] an upper electrode formed on the organic EL layer.
[0050] Also, an organic EL display device manufacturing method of
the present invention comprises the steps of:
[0051] forming a first electrode on a substrate;
[0052] forming an organic EL layer formed of organic EL material,
in which a conjugate length of polymer is changed in response to
light irradiation, on the first electrode;
[0053] irradiating partially a light onto the organic EL layer to
change the conjugate length; and
[0054] forming a second electrode on the organic EL layer.
[0055] Further, in order to achieve the above objects, organic EL
material of the present invention consists of:
[0056] material made of organic material expressed by a general
formula (1) 1
[0057] (Where A is a residue obtained by removing at least four
hydrogen atoms from an aromatic compound or a heterocyclic
compound,
[0058] X is an atomic group to which at least two groups that are
selected from a group consisting of a residue obtained by removing
at least two hydrogen atoms from benzene and a residue obtained by
removing at least two hydrogen atoms from cyclohexane are
bonded,
[0059] Y is an atomic group to which a residue obtained by removing
at least two hydrogen atoms from benzene is bonded or at least two
residues each obtained by removing at least two hydrogen atoms from
benzene are bonded, and
[0060] k, m and n are an integer respectively.)
[0061] Also, a plane emission device employing organic material of
the present invention, comprises:
[0062] a transparent substrate;
[0063] a transparent conductive film for covering one surface of
the transparent substrate;
[0064] an alignment film formed on a surface of the transparent
conductive film;
[0065] a luminous layer made of organic material expressed by a
general formula (2) 2
[0066] (Where A is a residue obtained by removing at least four
hydrogen atoms from an aromatic compound or a heterocyclic
compound,
[0067] X is an atomic group to which at least two groups that are
selected from a group consisting of a residue obtained by removing
at least two hydrogen atoms from benzene and a residue obtained by
removing at least two hydrogen atoms from cyclohexane are
bonded,
[0068] Y is an atomic group to which a residue obtained by removing
at least two hydrogen atoms from benzene is bonded or at least two
residues each obtained by removing at least two hydrogen atoms from
benzene are bonded, and
[0069] k, m and n are an integer respectively.); and
[0070] an electrode layer formed on a surface of the luminous
layer.
[0071] Also, a display device employing organic material of the
present invention, comprises:
[0072] a transparent substrate;
[0073] a transparent conductive film for covering one surface of
the transparent substrate;
[0074] an alignment film formed on a surface of the transparent
conductive film;
[0075] a luminous layer made of organic material expressed by a
general formula (3) 3
[0076] (Where A is a residue obtained by removing at least four
hydrogen atoms from an aromatic compound or a heterocyclic
compound,
[0077] X is an atomic group to which at least two groups that are
selected from a group consisting of a residue obtained by removing
at least two hydrogen atoms from benzene and a residue obtained by
removing at least two hydrogen atoms from cyclohexane are
bonded,
[0078] Y is an atomic group to which a residue obtained by removing
at least two hydrogen atoms from benzene is bonded or at least two
residues each obtained by removing at least two hydrogen atoms from
benzene are bonded, and
[0079] k, m and n are an integer respectively.);
[0080] an electrode layer formed on a surface of the luminous
layer;
[0081] a liquid crystal layer arranged on a second surface on an
opposite side to the first surface of the transparent substrate;
and
[0082] a polarizing plate arranged on the liquid crystal layer.
[0083] According to the organic EL element and the method of
manufacturing the same of the present invention, the cathode is
composed of the first conductive film that contacts to the organic
EL layer and the second conductive film formed on the first
conductive film, and entering of the oxygen and the moisture into
the first conductive film can be prevented by oxidizing the second
conductive film.
[0084] Therefore, the degradation of the luminous characteristic of
the organic EL layer and the generation of the short-circuit defect
can be prevented not to cover the laminated body consisting of the
anode, the organic EL layer, and the cathode with the insulating
sealing layer, and thus the generation of the dark spot can be
suppressed for a long time.
[0085] Also, according to the organic EL display device
manufacturing method of the present invention, the manufacturing
steps can be simplified and thus the product cost can be
lowered.
[0086] Also, according to another organic EL element of the present
invention, the buffer layer that contains at least one type metal
selected from the group consisting of Ru, Mo, and V is provided
between the anode and the organic EL layer, and only the side
surface of the buffer layer that contacts to the organic EL layer
is oxidized by the short-time annealing, the laser annealing, the
plasma oxidation, the anodic oxidation, or the like. Therefore, the
unevenness of the surface of the buffer layer is small, and the
generation of disadvantages such as the short circuit, etc. can be
avoided if the organic EL layer is thinned.
[0087] Also, according to the organic EL display device of the
present invention, since the areas for emitting the lights in
different color by changing the conjugate length of polymer
constituting the organic EL layer respectively are formed, the
multi-color emission organic EL display device can be easily
manufactured.
[0088] Also, according to the organic EL material of the present
invention, since such organic EL material contains the benzene ring
in the principal chain and contains the oxadiazole in the side
chain, for example, it can emits the polarized light.
[0089] As a result, if the organic EL material of the present
invention is employed in the back-light panel, the plane emission
device that can be driven by the low voltage and can reduce the
power consumption can be obtained. Also, since the display device
that is constructed by the back-light panel using the organic EL
material, the liquid crystal panel, and the polarizing plate can
obtain the polarized light from the luminous layer made of the
organic EL material, there is no necessity that the polarizing
plate is provided between the back-light panel and the liquid
crystal panel and thus the utilization factor of the light can be
increased.
BRIEF DESCRIPTION OF THE DRAWINGS
[0090] FIG. 1 is a sectional view showing an organic EL element
according to a first embodiment of the present invention;
[0091] FIG. 2 is a plan view showing an arrangement of anodes and
cathodes that constitute a display device in which organic EL
elements shown in FIG. 1 are arranged in a matrix fashion;
[0092] FIG. 3 is a plan view showing an example in which the
organic EL elements shown in FIG. 1 are applied to an active-matrix
organic EL display device;
[0093] FIGS. 4A to 4D are views showing respective steps of
manufacturing an organic EL element according to a second
embodiment of the present invention in section;
[0094] FIGS. 5A to 5D are views showing respective steps of
manufacturing an organic EL display element according to a third
embodiment of the present invention in plan; and
[0095] FIG. 6 is a sectional view showing the pertinent portion of
a liquid crystal display device that is constructed by using
organic EL elements according to a fourth embodiment of the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0096] Embodiments of the present invention will be explained with
reference to the accompanying drawings hereinafter.
First Embodiment
[0097] FIG. 1 is a sectional view showing an organic EL element
according to a first embodiment of the present invention.
[0098] An ITO film of about 200 nm thickness is formed as an anode
12 on a glass substrate 11. Also, a
poly[3-(4-alkylphenyl)thiophene] film of about 150 nm thickness is
formed as an organic EL layer (a luminous layer) 13 in the
predetermined area on the anode 12.
[0099] In addition, a laminated film having the double-layered
structure consisting of a first conductive film 14a made of the
conductor containing Mg and a second conductive film 14b made of
the conductor containing Ru is formed as a cathode 14 on the
organic EL layer 13. In this example, a thickness of the first
conductive film 14a is about 100 nm, and a thickness of the second
conductive film 14b is about 50 nm.
[0100] The anode 12 is not limited to ITO, and any conductor having
the large work function may be employed. In this case, if the light
is irradiated to the substrate 11 side, the anode 12 must be formed
of the conductor that can transmit the light.
[0101] The first conductive film 14a may be formed of the conductor
containing the alkaline metal or the alkaline earth metal that has
the small work function. For example, MgAg, AlLi, LiF, etc. may be
employed as the material of the first conductive film 14a. Assume
that the first conductive film 14a is formed of MgAg.
[0102] Also, the second conductive film 14b is not limited to the
conductor containing Ru, and also may be formed of the conductor
that has the high barrier characteristic to the oxygen, more
particularly, the metal or its oxide selected from the group
consisting of Ru, Rh, Ir, Os and Re.
[0103] The oxides of Ru, Rh, Ir, Os and Re have also the
conductivity. Accordingly, the conductivity of the cathode 14 is
never damaged by the oxidation.
[0104] In addition, a TiN film or a laminated film consisting of
TiN and Ti (referred to as a "TiN/Ti film" hereinafter) may be
employed as the second conductive film 14b. These films have also
the good barrier characteristic to the oxygen, and can prevent the
oxidation of the first conductive film 14a. Also, the conductivity
of both the TiN film and the TiN/Ti film is in no way degraded even
if they are exposed to the oxygen-containing atmosphere for a long
time.
[0105] Further, a laminated film consisting of the conductive film,
the conductive film containing the metal selected from the group
consisting of Ru, Rh, Ir, Os and Re or its oxide, and the TiN film
or the TiN/Ti film may be employed as the second conductive film
14b.
[0106] In the organic EL element constructed in this manner
according to the first embodiment, if the positive voltage is
applied to the anode 12 and the negative voltage is applied to the
cathode 14, the organic EL layer can emit the light.
[0107] In the first embodiment, since the second conductive film
14b containing Ru is formed on the first conductive film 14a that
contains Mg as the alkaline metal, Ru in the second conductive film
14b is oxidized to prevent the entering of the oxygen into the
first conductive film 14a even if the organic EL element is exposed
to the atmosphere containing the oxygen or the moisture for a long
time. Accordingly, the oxidation in the first conductive film 14a
can be avoided.
[0108] As a result, in the organic EL element according to the
first embodiment, the degradation of the luminescence
characteristic due to the oxygen or the moisture can be avoided and
also the generation of the dark spot can be suppressed. Also, since
the oxidation of the first conductive film 14a can be avoided, the
peeling-off between the organic EL layer 13 and the first
conductive film 14a can be prevented. In addition, there is no
necessity that the laminated body consisting of the anode 12, the
organic EL layer 13, and the cathode 14 should be covered with the
insulating material, and thus the manufacture of the element can be
facilitated.
[0109] A method of manufacturing the organic EL element according
to the first embodiment will be explained hereunder.
[0110] First, the ITO film of about 200 nm thickness is formed on
the overall upper surface of the glass substrate 11 by the sputter
method. Then, the poly[3-(4-alkylphenyl)thiophene] film of 150 nm
thickness is formed on the overall upper surface of the glass
substrate 11 by the spin coating method, and is used as the organic
EL layer 13.
[0111] In the first embodiment, the material of the organic EL
layer 13 is not limited to the above
poly[3-(4-alkylphenyl)thiophene. Various organic EL emission
materials of the monomer series or the polymer series may be
employed as the organic EL layer 13.
[0112] Then, the first conductive film 14a is formed by forming the
MgAg film of about 100 nm thickness on the organic EL layer 13 by
virtue of the sputter method. Then, the second conductive film 14b
is formed by forming the Ru film of about 50 nm thickness
thereon.
[0113] Then, a pair of terminals that are connected to the anode 12
and the cathode 14 respectively are formed by sputtering the metal
such as Au, Al, or the like while using a metal mask. Accordingly,
the organic EL element according to the first embodiment can be
completed.
[0114] As shown in FIG. 2, if the anodes 12 are formed like the
stripe shape and the cathodes 14 are formed like the stripe shape
in the direction that orthogonally intersects with the anodes 12,
the display device in which a plurality of organic EL elements
(intersecting portions of the anodes 12 and the cathodes 14) 15 are
arranged on the glass substrate 11 in a matrix fashion can be
constructed.
[0115] In this display device, like the simple-matrix liquid
crystal display device, if the positive signal is supplied in
sequence to a plurality of anodes 12 aligned in the vertical
direction at a timing in synchronism with the horizontal
synchronizing signal and also the negative signal is supplied in
sequence to a plurality of cathodes 14 aligned in the horizontal
direction within one horizontal synchronization period, desired
images can be displayed on the organic EL display device.
[0116] Also, the present invention can be applied to the
active-matrix organic EL display device shown in FIG. 3. More
particularly, if the cathode 14 is formed every pixel and also the
voltage applied to the cathodes 14 via switching elements 19, each
being connected to a data line 16, a power supplying line 17, and a
scanning line 18, is controlled every pixel, the desired images can
be displayed on the organic EL display device. In this case, since
the anode 12 is used as the common electrode for respective pixels,
there is no necessity of the patterning.
[0117] In addition, in the above first embodiment, the case is
explained where the organic EL layer 13 is directly formed on the
anode 12 and the cathode 14 is directly formed on the organic EL
layer 13. The buffer layer may be provided between the anode 12 and
the organic EL layer 13 or between the organic EL layer 13 and the
cathode 14.
Second Embodiment
[0118] FIGS. 4A to 4D are sectional views showing a method of
manufacturing an organic EL element according to a second
embodiment of the present invention.
[0119] The second embodiment shows an example of the organic EL
element in which the buffer layer is provided between the anode and
the organic EL layer.
[0120] First, as shown in FIG. 4A, the ITO film of 200 nm thickness
is formed on an upper side of a glass substrate 21 by the sputter
method to construct an anode (lower electrode) 22.
[0121] Then, as shown in FIG. 4B, the Ru (ruthenium) film of 30 nm
thickness is formed on the anode 22 by the sputter method to
construct a buffer layer 23. Then, as shown in FIG. 4C, the
short-time annealing (RTA) is carried out at the temperature of
700.degree. C. for 3 to 5 seconds by using the RTA (Rapid Thermal
Annealing) equipment that heats by the lamp.
[0122] The Ru on the surface of the buffer layer 23 is oxidized by
this short-time annealing. In this case, since RuO can be generated
in a very short time, the particle size of the RuO is small and
thus the situation that the large unevenness is formed on the
surface of the buffer layer 23 can be avoided.
[0123] In this case, it is preferable that a thickness of the
buffer layer 23 (the thickness before RTA) should be set smaller
than 50 nm. This is because, if the thickness of the buffer layer
23 exceeds 50 nm, the light generated from an organic EL layer 24
is absorbed by the buffer layer 23 and thus the apparent
luminescence intensity is lowered. Also, Mo or V as well as above
Ru may be employed as the material of the buffer layer 23.
[0124] Then, as shown in FIG. 4D, the poly[3-(4-alkylphenyl)
thiophene film of about 150 nm thickness is formed on the buffer
layer 23 by the spin coating method to construct the organic EL
layer 24. The material of the organic EL layer 24 is not limited to
the above poly[3-(4-alkylphenyl)thiophene, and various organic EL
materials of the monomer series or the polymer series may be
employed.
[0125] Then, the AlLi film of about 20 nm thickness is formed on
the organic EL layer 24 by the sputter method to construct a
cathode (upper electrode) 25. Accordingly, the organic EL element
according to the second embodiment can be completed. In this case,
the material of the cathode 25 is not limited to the above AlLi,
and the conductor containing the alkaline metal or the alkaline
earth metal may be employed. Also, as described in the first
embodiment, the cathode 25 may be formed to have the double-layered
structure.
[0126] Actually measured results of the operating threshold voltage
and the surface unevenness of the buffer layer after the above
organic EL element is actually manufactured will be explained
hereunder.
[0127] TDP/Alq.sub.3 is employed as the material of the EL emission
layer 24 and then the organic EL element is formed by the above
methods, and then the operating threshold voltage is measured. As a
result, an emission starting voltage is 7 V if no buffer layer 23
is provided whereas the emission starting voltage is 3.5 V if the
buffer layer 23 is provided by the above method, whereby the
reduction in the threshold voltage can be confirmed.
[0128] Also, when the unevenness of the surface of the buffer layer
23 is measured, such unevenness is 5 nm to 10 nm in the second
embodiment. In contrast, in case RuO.sub.2 is formed as the buffer
layer by the sputtering, the unevenness of the surface of the
buffer layer is 50 nm to 100 nm. As a result, the validity of the
second embodiment can be checked.
[0129] According to the second embodiment, RuO, MoO, or VO that is
effective to lower the operating threshold voltage is formed by
forming the metal film of Ru, Mo, or V as the buffer layer 23 and
then oxidizing the surface of the buffer layer 23 by the RTA. In
this case, since the surface of the buffer layer 23 is oxidized in
a short time, the situation that the large unevenness is formed on
the surface of the buffer layer 23 can be avoided.
[0130] As a consequence, the short-circuit between the anode 22 and
the cathode 25 can be avoided even if the thickness of the organic
EL layer 24 is reduced, and thus the organic EL element having the
low operating threshold voltage can be fabricated.
[0131] The second embodiment can be applied to the simple-matrix
organic EL display device and the active-matrix organic EL display
device, like the first embodiment.
[0132] In the second embodiment, the surface of the buffer layer 23
is oxidized by the RTA equipment that uses the lamp to heat. The
surface of the buffer layer 23 may be oxidized by the laser beam
irradiation, the plasma oxidation method, or the anodic oxidation
method.
[0133] In case the surface of the buffer layer 23 is oxidized by
the laser beam irradiation, the XeCl excimer laser is employed, for
example. The surface of the buffer layer 23 is oxidized in a short
time by scanning the laser beam, that is shaped into the
rectangular shape having a narrow width, in the width direction.
The energy of the laser beam is set to 390 mJ/cm.sub.2, for
example.
[0134] In case the surface of the buffer layer 23 is oxidized by
the plasma oxidation method, such surface of the buffer layer 23 is
exposed to the plasma containing the oxygen to oxidize the surface
of the buffer layer 23. For example, the plasma oxidation process
is performed by the RF O.sub.2 plasma method under the conditions
that the processing time is 10 minutes, the pressure is 40 Pa, and
the power is 200 W.
[0135] In case the surface of the buffer layer 23 is oxidized by
the anodic oxidation method, the mixed solution consisting of
tartaric acid, ethylene glycol, and ammonia solution is employed as
the electrolysis solution and the Pt (platinum) electrode is
employed as the anode, for example. Then, the surface of the buffer
layer 23 is anodic-oxidized by supplying a constant current of 5 mA
to deposit a RuO.sub.2 film.
[0136] The similar advantages such as the reduction in the
operating threshold voltage, the avoidance of the formation of the
uneven surface of the buffer layer, etc. can be achieved even when
the surface of the buffer layer 23 is oxidized by any one of above
methods.
Third Embodiment
[0137] FIGS. 5A to 5D are plan views showing manufacturing steps of
an organic EL display device according to a third embodiment of the
present invention.
[0138] This third embodiment shows an example of a method of
manufacturing the full-color organic EL display device.
[0139] First, as shown in FIG. 5A, an ITO film of about 200 nm
thickness is formed by sputtering ITO on the overall upper surface
of a glass substrate 31. Then, anodes (lower electrodes) 32 are
formed by patterning the ITO film into a stripe shape by virtue of
the photolithography. In this case, a width of the anode 32 is set
to 20 .mu.m, for example.
[0140] Then, an EL emission layer 33 is formed by forming
poly[3-(4-alkylphenyl)thiophene] on the overall display area of the
glass substrate 31 by virtue of the spin coating method to have a
thickness of 1500 .ANG..
[0141] In the present invention, the material of the EL emission
layer 33 is not limited to poly[3-(4-alkylphenyl) thiophene]. But
such EL emission layer 33 must be formed of the polymer whose
conjugate length can be changed by the light irradiation.
[0142] Then, as shown in FIG. 5B, the ArF laser beam is irradiated
onto areas other than the red-color pixel area (R) (i.e., the
green-color pixel area (G) and the blue-color pixel area (B)) under
the condition of 1000 mJ/cm.sup.2. As a result, the EL emission
layer that is not subjected to the laser beam irradiation emits the
red-color light (the wavelength of about 650 nm) whereas the EL
emission layer that is subjected to the laser beam irradiation
emits the green-color light (the wavelength of about 510 nm)
because the conjugate length is shortened.
[0143] In FIG. 5B, the red-color light emitting portion of the
organic EL layer is denoted by 33R and the green-color light
emitting portion is denoted by 33G.
[0144] In this case, since the relationship between the irradiation
intensity of the laser beam and the emitted color of the EL
emission layer is different depending on the material of the EL
emission layer, the laser beam irradiation conditions must be
changed appropriately to meet the material.
[0145] Then, as shown in FIG. 5C, the ArF laser beam is irradiated
onto the blue-color pixel area of the EL emission layer under the
condition of 4000 mJ/cm.sup.2. As a result, the EL emission layer
that is subjected to the laser beam irradiation emits the
blue-color light (the wavelength of about 460 nm) because the
conjugate length is further shortened. In FIG. 5C, the blue-color
light emitting portion of the organic EL layer is denoted by
33B.
[0146] Then, as shown in FIG. 5D, cathodes (upper electrodes) 34
are formed on the EL emission layer 33 by the lift-off method. That
is, photoresist is coated on the overall upper surface of the glass
substrate, and then windows used to form the upper electrodes are
opened in the resist film via exposing and developing steps. Then,
AlLi is sputtered on the overall upper surface of the glass
substrate to have a thickness of 200 nm, and then the AlLi film on
the resist film is removed together with the resist. Thus, the
cathodes 34 are formed.
[0147] The material of the cathodes 34 is not limited to above
AlLi. Any conductor that contains the alkaline metal or the
alkaline earth metal having the small work function may be
employed.
[0148] In the third embodiment, as described above, the RGB-color
emitting pixels are formed by using the polymer whose conjugate
length can be changed by the laser beam irradiation to change the
emitted color. In other words, since the multi-color emitting
organic EL element can be formed not to employ the fine pattern
technology such as the dry etching, etc., that requires the area
separation of the organic EL layer 33 pixel by pixel, the number of
manufacturing steps can be reduced and thus the production cost of
the device can be reduced. Thus, the full-color EL display device
having three RGB-color pixels can be implemented.
[0149] In the third embodiment, the organic EL layer 33 is formed
directly on the anodes (lower electrodes) 32, and then the cathodes
(upper electrodes) 34 are formed directly on the organic EL layer
33. In this case, the buffer layer may be formed at least between
in the anodes 32 and the organic EL layer 33 and between the
organic EL layer 33 and the cathodes 34.
[0150] In the third embodiment, the manufacturing method of the
simple-matrix organic EL display device is explained. Also, the
present invention can be applied to the manufacture of the
active-matrix organic EL display device.
Fourth Embodiment
[0151] Next, organic EL material and a plane emission device and a
display device using the same according to a fourth embodiment of
the present invention will be explained with reference to FIG. 6
hereunder.
[0152] The organic EL material of the present invention can be
expressed by a following general formula (4). 4
[0153] As apparent from the above general formula (4), a principal
chain is constructed by the repetition unit consisting of the
residue of the benzene, from which four hydrogen atoms are removed,
and the vinylene group. Two side chains are bonded to the benzene
ring constituting the principal chain.
[0154] One of the side chains is the univalent ether group having
the carbon number m. Here m is an integer to satisfy the condition
of 5.ltoreq.m.ltoreq.15, and 1 is an integer to give the number of
molecules of one hundred thousand to five millions.
[0155] Next, the chemical structure of the other of the side chains
will be explained hereunder.
[0156] The alkylenedioxy group having the carbon number n, the
biphenylene group, the residue of oxadiazole from which two
hydrogen atoms are removed, the phenylene group, and the univalent
other group having the carbon number k+1 are bonded in series to
the benzene ring constituting the principal chain in this
order.
[0157] This side chain portion has properties like the liquid
crystal. Here n is an integer to satisfy the condition of
5.ltoreq.n.ltoreq.15, and k is an integer to satisfy the condition
of 5.ltoreq.k.ltoreq.15. If k, m, n are set too small, the compound
expressed by the general formula (4) is difficult to dissolve into
the organic solvent. In contrast, if k, m, n are set too large, the
synthesis of the compound becomes difficult.
[0158] Next, the method of synthesizing the organic EL material
will be explained hereunder.
[0159] First, the benzene derivative expressed by a following
general formula (5) is prepared. 5
[0160] Also, the oxadiazole derivative expressed by a following
general formula (6) is prepared. 6
[0161] The compound expressed by a following general formula (7) is
obtained by mixing the benzene derivative expressed by the above
general formula (5) and the oxadiazole derivative expressed by the
above general formula (6) and then adding the potassium hydroxide
to the resultant solution. 7
[0162] Further, the polymerization reaction is caused by adding
KOC(CH.sub.3).sub.3 to this compound. Thus, the organic EL material
expressed by the above general formula (4) can be synthesized.
[0163] Next, a liquid crystal display device serving as the organic
EL display device of the present invention employing the above
organic EL material will be explained hereunder.
[0164] The liquid crystal display device shown in FIG. 6 in section
is constructed to include a back-light panel 1, a liquid crystal
panel 70, and a polarizing plate 80.
[0165] The back-light panel 1 has a laminated structure by stacking
a transparent substrate 2, a transparent electrode 3, an alignment
film 4, a luminous layer 5 and an electrode 6 in this order. The
transparent electrode 3 is formed of the indium tin oxide (ITO),
and its thickness is about 200 nm. The ITO film is formed by the
sputtering.
[0166] The alignment film 4 is formed of the mixture consisting of
poly 3,4-ethylenedioxythiophene (PEDOT) and polystyrenesulfonate
(PSS). The alignment film 4 is formed by the spin coating method,
and its thickness is about 200 nm. The rubbing process is applied
to a surface of the alignment film 4. Polyaniline, etc. may be used
as the material of the alignment film.
[0167] Next, a method of forming the luminous layer 5 will be
explained hereunder.
[0168] The solution, in which the organic EL material expressed by
the above general formula (4) is dissolved in the organic solvent
such as toluene, chloroform, etc., is spin-coated on the surface of
the alignment film 4. After the coating, the substrate is heated to
exceed the mesomorphic temperature of the organic EL material and
then is cooled down to the room temperature. When the temperature
is in excess of the mesomorphic temperature, the side chain
portions containing oxadiazole as the organic EL material expressed
by the above general formula (4) are aligned in parallel with the
rubbing direction of the alignment film 4.
[0169] When the substrate is cooled down to the room temperature
into the solid state, this alignment state can be maintained
without the influence of the external electric field, etc. The
electrode 6 is a conductive film made of AlLi alloy having a
thickness of about 300 nm. The AlLi alloy film is formed by the
vacuum evaporation, etc., for example. The liquid crystal panel 70
is the active-matrix panel employing thin film transistors (TFTs),
for example. Since the TFT liquid crystal panel has the well known
structure, the outline thereof will be explained hereunder.
[0170] Transparent pixel electrodes 74 arranged in a matrix fashion
are formed on an opposing surface of a TFT side transparent
substrate 71. A transparent opposing substrate 72 is arranged in
parallel with the TFT side transparent substrate 71 so as to oppose
to the pixel electrodes 74.
[0171] A transparent common electrode 75 is formed on an opposing
surface of the opposing substrate 72. A liquid crystal layer
containing liquid crystal material is put between the TFT side
transparent substrate 71 and the opposing substrate 72.
[0172] Although not shown in FIG. 6, an alignment film, TFTs, a
black matrix, and others are formed. A rotating angle of a linearly
polarized light, that propagate through a liquid crystal layer 73
in the thickness direction, can be controlled by applying the
voltage between the pixel electrodes 74 and the common electrode
75.
[0173] The TFT side transparent substrate 71 is adhered to the
transparent substrate 2 of the back-light panel 1. The polarizing
plate 80 is adhered to an outer surface of the opposing substrate
72. If viewed along the direction perpendicular to the substrate
surface, the polarization axis of the polarizing plate 80
intersects orthogonally with the rubbing direction of the alignment
film 4.
[0174] Next, the operational principle of the liquid crystal
display device shown in FIG. 6 will be explained hereunder.
[0175] When the carriers are injected into the luminous layer 5 by
applying the DC voltage to both electrodes such that the electrode
6 act as the negative electrode and the transparent electrode 3
acts as the positive electrode, the polarized light is irradiated
from the luminous layer 5 to the liquid crystal panel 70 side. The
polarization direction of the irradiated light is in parallel with
the alignment direction of the side chains containing oxadiazole in
the above general formula (4), i.e., the rubbing direction of the
alignment film 4.
[0176] If the polarized direction is not rotated when the polarized
light passes through the liquid crystal panel 70, such polarized
light does not pass through the polarizing plate 80 and thus the
black display state is obtained. If the polarized direction is
rotated by 90 degree, the polarized light passes through the
polarizing plate 80 and thus the white display state is obtained.
If the rotating angle is between 0 degree and 90 degree, the
intermediate tone display state is obtained.
[0177] In the liquid crystal display device shown in FIG. 6, the
polarized light is irradiated from the back-light panel 1. For this
reason, no polarizing plate is arranged between the back-light
panel 1 and the liquid crystal panel 70.
[0178] Therefore, the utilization factor of the irradiated light
can be increased. Also, both the reduction in the consumption power
and the reduction in size can be achieved rather than the case
where the cold-cathode lamp is employed.
[0179] In the above fourth embodiment, the biphenylene group is
bonded to the carbon atom on the principal chain side of oxadiazole
in the above general formula (4). This biphenylene group may be
replaced with the atomic group to which two or more phenylene
groups and two or more cyclohexylene groups are bonded in
total.
[0180] A general formula (8) shown in the following shows the case
where the biphenylene group is replaced with the atomic group to
which one phenylene group and one cyclohexylene group are bonded.
8
[0181] A general formula (9) shown in the following shows the case
where the biphenylene group is replaced with the atomic group to
which two phenylene groups and one cyclohexylene group are bonded
like a chain. 9
[0182] Also, in the above fourth embodiment, the case is shown
where one phenylene group is bonded to the carbon atom at the top
end side of the side chain of the oxadiazole in the above general
formula (4). This one phenylene group may be replaced with the
atomic group to which two phenylene groups or more are bonded like
a chain. Also, the case is explained where the benzene ring is
contained in the principal chain of the organic EL material. The
structure that the residue which is obtained by removing a part of
hydrogen atoms from condensed polycyclic hydrocarbon, heterocyclic
compound, or condensed heterocyclic compound is contained in
addition to the benzene ring may be employed.
[0183] As an example of the condensed polycyclic hydrocarbon, there
may be listed naphthalene, anthracene, or the like. As an example
of the heterocyclic compound, there may be listed pyrrole,
thiophene, furan, or the like. Also, as an example of the condensed
heterocyclic compound, there may be listed carbazole, fluorine, or
the like.
[0184] The present invention is not limited to the above
embodiments, and various variations, modifications, and
combinations may be applied.
* * * * *