U.S. patent application number 12/547070 was filed with the patent office on 2010-03-04 for light-emitting device, electronic equipment, and process of producing light-emitting device.
This patent application is currently assigned to SEIKO EPSON CORPORATION. Invention is credited to Hidekazu KOBAYASHI, Koya SHIRATORI, Atsushi YOSHIOKA.
Application Number | 20100051973 12/547070 |
Document ID | / |
Family ID | 41723969 |
Filed Date | 2010-03-04 |
United States Patent
Application |
20100051973 |
Kind Code |
A1 |
KOBAYASHI; Hidekazu ; et
al. |
March 4, 2010 |
LIGHT-EMITTING DEVICE, ELECTRONIC EQUIPMENT, AND PROCESS OF
PRODUCING LIGHT-EMITTING DEVICE
Abstract
A light-emitting device includes a light-reflecting layer, a
first electrode disposed on or above the light-reflecting layer, a
semi-transparent reflective second electrode, a light-emitting
function layer disposed between the first electrode and the second
electrode, and an electron-injection layer disposed between the
light-emitting function layer and the second electrode. The second
electrode is made of an Ag alloy having an Ag content of from 50%
by atoms to 98% by atoms.
Inventors: |
KOBAYASHI; Hidekazu;
(Azumino-shi, JP) ; SHIRATORI; Koya;
(Matsumoto-shi, JP) ; YOSHIOKA; Atsushi;
(Chino-shi, JP) |
Correspondence
Address: |
OLIFF & BERRIDGE, PLC
P.O. BOX 320850
ALEXANDRIA
VA
22320-4850
US
|
Assignee: |
SEIKO EPSON CORPORATION
Tokyo
JP
|
Family ID: |
41723969 |
Appl. No.: |
12/547070 |
Filed: |
August 25, 2009 |
Current U.S.
Class: |
257/88 ; 257/98;
257/E33.068 |
Current CPC
Class: |
H01L 51/5265 20130101;
H01L 51/5234 20130101; H01L 51/5218 20130101; H01L 51/5036
20130101; H01L 2251/558 20130101; H01L 51/5228 20130101; H01L
51/5237 20130101; H01L 51/0021 20130101; H01L 51/5206 20130101;
H01L 51/5246 20130101; H01L 51/5253 20130101; H01L 2251/5315
20130101; H01L 51/5092 20130101; H01L 51/5271 20130101; H01L
27/3206 20130101; H01L 51/5203 20130101; H01L 51/56 20130101 |
Class at
Publication: |
257/88 ; 257/98;
257/E33.068 |
International
Class: |
H01L 33/00 20060101
H01L033/00 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 28, 2008 |
JP |
2008-219266 |
Nov 14, 2008 |
JP |
2008-291997 |
Nov 14, 2008 |
JP |
2008-291998 |
Jul 3, 2009 |
JP |
2009-158522 |
Claims
1. A light-emitting device comprising: a light-reflecting layer; a
first electrode disposed on or above the light-reflecting layer; a
semi-transparent reflective second electrode; a light-emitting
function layer disposed between the first electrode and the second
electrode; and an electron-injection layer disposed between the
light-emitting function layer and the second electrode, wherein the
second electrode is made of an Ag alloy having an Ag content of
from 50% by atoms to 98% by atoms.
2. The light-emitting device according to claim 1, wherein the
second electrode has a resistivity of 31.times.10.sup.-8 .OMEGA.m
or less.
3. The light-emitting device according to claim 1, wherein the
second electrode is made of an alloy of a metal of Mg, Cu, Zn, Pd,
Nd, or Al and Ag.
4. The light-emitting device according to claim 3, wherein the
electron-injection layer is made of LiF, Li.sub.2O, Liq, MgO, or
CaF.sub.2 and has a thickness of 0.5 to 2 nm.
5. A light-emitting device comprising: a light-reflecting layer; a
transparent first electrode disposed on or above the
light-reflecting layer; a semi-transparent reflective second
electrode; a light-emitting function layer disposed between the
first electrode and the second electrode; an electron-injection
layer disposed between the light-emitting function layer and the
second electrode; a first layer disposed on the second electrode
for absorbing stress to the second electrode; and a second layer
made of an inorganic material disposed on the first layer for
absorbing stress, wherein the second electrode is made of an alloy
in which any of Mg, Cu, Zn, Pd, Nd, and Al is mixed with Ag at an
atomic number ratio in the range of 1:3 to 1:50.
6. The light-emitting device according to claim 5, wherein the
second electrode has a thickness in a range of 10 to 30 nm.
7. The light-emitting device according to claim 6, wherein the
first layer is made of a material having a work function of 4.2 eV
or more and being other than Ag.
8. The light-emitting device according to claim 7, wherein the
first layer is made of Zn, Al, Au, SnO.sub.2, ZnO.sub.2, or
SiO,
9. The light-emitting device according to claim 6, wherein the
light-emitting function layer includes an electron-injection layer;
and the first layer is made of the same material as that of the
electron-injection layer.
10. The light-emitting device according to claim 9, wherein the
first layer is made of LiF, Li.sub.2O, Liq, MgO, MgF.sub.2,
CaF.sub.2, SrF.sub.2, NaF, or WF.
11. A light-emitting device comprising: a light-reflecting layer; a
transparent first electrode disposed on or above the
light-reflecting layer; a semi-transparent reflective second
electrode; a light-emitting function layer disposed between the
first electrode and the second electrode; an electron-injection
layer disposed between the light-emitting function layer and the
second electrode; a reduction layer disposed between the
electron-injection layer and the second electrode and made of a
reducible metal material for reducing an electron-injecting
material forming the electron-injection layer; a first layer
disposed on the second electrode and absorbing stress to the second
electrode; and a second layer of an inorganic material disposed on
the first layer, wherein the second electrode is made of Ag.
12. A light-emitting device comprising: a light-reflecting layer; a
transparent first electrode disposed on or above the
light-reflecting layer; a semi-transparent reflective second
electrode; a light-emitting function layer disposed between the
first electrode and the second electrode; a mixture layer disposed
between the light-emitting function layer and the second electrode
and made of a mixture of an electron-injecting material and a
reducible metal material for reducing the electron-injecting
material; a first layer disposed on the second electrode and
absorbing stress to the second electrode; and a second layer of an
inorganic material disposed on the first layer, wherein the second
electrode is made of Ag,
13. The light-emitting device according to claim 11, wherein the
first layer is made of an electron-injecting material.
14. The light-emitting device according to claim 13, wherein the
first layer is made of LiF, Li.sub.2O, Liq, MgO, CaF.sub.2,
SrF.sub.2, NaF, or WF.
15. The light-emitting device according to claim 11, wherein the
first layer is made of LiF; and the reducible metal material is
Al.
16. A light-emitting device comprising: a plurality of
light-emitting elements each including a first electrode, a second
electrode, and a light-emitting layer disposed between the first
electrode and the second electrode; a wall separating the plurality
of light-emitting elements; a first layer partially covering the
second electrodes and easing the concentration of stress to the
second electrodes; and a second layer of an inorganic material
disposed on the first layer, wherein the second electrode covers
the light-emitting layer in each of the plurality of light-emitting
elements and covers the wall separating the plurality of
light-emitting elements.
17. The light-emitting device according to claim 16, wherein the
first layer has openings at positions corresponding to the
light-emitting elements.
18. The light-emitting device according to claim 16, wherein the
first layer is not provided at at least part of a region where the
wall and the second electrode overlap each other, and an auxiliary
electrode is disposed at at least part of the region.
19. Electronic equipment including the light-emitting device
according to claim 1.
Description
BACKGROUND
[0001] 1. Technical Field
[0002] The present invention relates to a light-emitting device,
electronic equipment, and a process of producing the light-emitting
device.
[0003] 2. Related Art
[0004] Recently, various types of light-emitting devices having
light-emitting elements such as organic EL (electroluminescent)
elements or organic light-emitting diodes (hereinafter, referred to
as "OLEDs") called light-emitting polymer elements are proposed.
The light-emitting elements included in such light-emitting devices
usually have a structure in which a light-emitting layer made of an
organic EL material is disposed between two electrodes.
[0005] For example, Japanese Patent No. 2723242 (Patent Document 1)
discloses a light-emitting element composed of an anode, an organic
light-emitting medium disposed on the anode, and a cathode disposed
on the organic light-emitting medium. In Patent Document 1, a
portion of the organic light-emitting medium in contact with the
anode functions as a hole-transporting region, and, at the same
time, a portion of the organic light-emitting medium in contact
with the cathode functions as an electron-transporting region. In
addition, in Patent Document 1, the cathode is made of MgAg
(magnesium-silver alloy) having a composition of Mg:Ag=10:1.
[0006] In a case of a (top emission) configuration in which an
anode is disposed on a substrate, an organic light-emitting medium
is disposed on the anode, a cathode is disposed on the organic
light-emitting medium, and light emitted by the organic
light-emitting medium is extracted from the cathode side on the
opposite side of the substrate, the cathode is required to have
high transparency and therefore is desirable to have a thickness as
thin as possible. However, since resistance value is inversely
proportional to thickness, the resistance value of the cathode in
the configuration disclosed in Patent Document 1 becomes
significantly high by reducing the thickness. Therefore, the
reduction in the thickness causes a problem that the electrical
conductivity of the light-emitting element is decreased.
[0007] The electrical conductivity of the cathode can be enhanced
by increasing the ratio of Ag in the MgAg forming the cathode.
However, in such a case, there is a possibility that asperities are
generated by aggregation of the Ag atoms, and if a layer for
absorbing the effect of such asperities is additionally formed,
there is a possibility of a change in the light-emitting
characteristics.
SUMMARY
[0008] An advantage of some aspects of the invention is to provide
a cathode having both a high electrical conductivity and a high
transparency and a light-emitting device including the cathode,
wherein various problems that the light-emitting device may have by
forming such a cathode are solved.
[0009] The invention can be realized as the following aspects or
application examples.
[0010] In accordance with a first application example of the
invention, a light-emitting device includes a light-reflecting
layer, a first electrode disposed on or above the light-reflecting
layer, a semi-transparent reflective second electrode, a
light-emitting function layer disposed between the first electrode
and the second electrode, and an electron-injection layer disposed
between the light-emitting function layer and the second electrode.
The second electrode is made of an Ag alloy having an Ag content of
from 50% by atoms to 98% by atoms.
[0011] In such a configuration, the electron injection property of
the electron-injection layer can be increased to enhance the light
emission efficiency. Therefore, the display quality of the
light-emitting device can be increased.
[0012] In accordance with a second application example of the
invention, the light-emitting device is preferably designed such
that the second electrode has a resistivity of 31.times.10.sup.-8
.OMEGA.m or less.
[0013] Such a configuration can prevent degradation in electrical
conductivity of a light-emitting element. Therefore, the display
quality of the light-emitting device can be increased.
[0014] In accordance with a third application example of the
invention, the second electrode of the light-emitting device is
preferably made of an alloy of a metal of Mg, Cu, Zn, Pd, Nd, or Al
and Ag and is more preferably made of MgAg.
[0015] In accordance with a fourth application example of the
invention, the electron-injection layer of the light-emitting
device is preferably made of LiF, Li.sub.2O, Liq, MgO, or CaF.sub.2
and is more preferably made of LiF. Here, since the
electron-injection layer is made of an insulating material, the
applied voltage (driving voltage) necessary for allowing the
light-emitting element to emit light is increased with the
thickness of the electron-injection layer. Accordingly, the
thickness of the electron-injection layer is controlled to
preferably 0.5 to 2 nm for inhibiting the increase in the driving
voltage value.
[0016] In accordance with a fifth application example of the
invention, a process of producing the light-emitting device
includes forming a light-reflecting layer on a substrate, forming a
first electrode on the light-reflecting layer, forming a
light-emitting function layer on the first electrode, forming an
electron-injection layer on the light-emitting function layer, and
forming a second electrode on the electron-injection layer. The
step of forming the second electrode on the electron-injection
layer is preferably performed by co-depositing a metal of Mg, Cu,
Zn, Pd, Nd, or Al and Ag on the electron-injection layer at a
deposition rate ratio within a range of 2:1 to 1:50.
[0017] In such a producing process, the resistivity of the second
electrode can be suppressed to 31.times.10.sup.-8 .OMEGA.m or less.
Therefore, in the resulting light-emitting device, degradation in
the electrical conductivity of the light-emitting element can be
inhibited.
[0018] In accordance with a sixth application example of the
invention, a light-emitting device includes a light-reflecting
layer, a transparent first electrode disposed on or above the
light-reflecting layer, a semi-transparent reflective second
electrode, a light-emitting function layer disposed between the
first electrode and the second electrode, an electron-injection
layer disposed between the light-emitting function layer and the
second electrode, a first layer disposed on the second electrode
for absorbing stress to the second electrode, and a second layer
made of an inorganic material disposed on the first layer. The
second electrode is made of an alloy in which any of Mg, Cu, Zn,
Pd, Nd, and Al is mixed with Ag at an atomic number ratio in the
range of 1:3 to 1:50.
[0019] In the light-emitting device having such a configuration,
the second electrode can be prevented from being broken by the
stress or the like during the formation of the second layer, while
a decrease in contrast during black display is inhibited.
Consequently, the decrease in the electrical conductivity of the
light-emitting element can be inhibited.
[0020] In accordance with a seventh application example of the
invention, the second electrode of the light-emitting device
preferably has a thickness in a range of 10 to 30 nm.
[0021] A thickness of the second electrode smaller than 10 nm
causes an increase in the resistance value of the second electrode,
resulting in insufficient electrical conductivity. A thickness
larger than 30 nm results in insufficient transparency of the
second electrode.
[0022] In accordance with an eighth application example of the
invention, the first layer of the light-emitting device is
preferably made of a material having a work function of 4.2 eV or
more and being other than Ag. Specifically, the first layer may be
made of Zn, Al, Au, SnO.sub.2, ZnO.sub.2, or SiO.
[0023] By forming the first layer with such a material, a decrease
in contrast during black display is sufficiently inhibited to
increase the display quality of the light-emitting device. In
addition, examples of the "material other than Ag" are not limited
to metals and include dielectrics.
[0024] In accordance with a ninth application example of the
invention, the light-emitting function layer of the light-emitting
device preferably includes an electron-injection layer that is made
of the same material as that of the first layer. In this
configuration, the first layer may be made of LiF, Li.sub.2O, Liq,
MgO, MgF.sub.2, CaF.sub.2, SrF.sub.2, NaF, or WF.
[0025] In accordance with a tenth application example of the
invention, a light-emitting device includes a light-reflecting
layer, a transparent first electrode disposed on or above the
light-reflecting layer, a semi-transparent reflective second
electrode, a light-emitting function layer disposed between the
first electrode and the second electrode, an electron-injection
layer disposed between the light-emitting function layer and the
second electrode, a reduction layer disposed between the
electron-injection layer and the second electrode and made of a
reducible metal material for reducing the electron-injecting
material forming the electron-injection layer, a first layer
disposed on the second electrode and absorbing stress to the second
electrode, and a second layer of an inorganic material disposed on
the first layer. The second electrode is made of only Ag.
[0026] In such a configuration, the Ag atoms can be prevented from
aggregating into islands by using the reduction layer of a
reducible metal material as a base of the second electrode.
Therefore, the second electrode can be a continuous film. In
addition, since the second electrode is covered by the first layer
having a stress-absorbing ability and the second layer is disposed
on the first layer, the second electrode can be prevented from
being broken by stress.
[0027] In accordance with an eleventh application example of the
invention, a light-emitting device includes a light-reflecting
layer, a transparent first electrode disposed on or above the
light-reflecting layer, a semi-transparent reflective second
electrode, a light-emitting function layer disposed between the
first electrode and the second electrode, a mixture layer disposed
between the light-emitting function layer and the second electrode
and made of a mixture of an electron-injecting material and a
reducible metal material for reducing the electron-injecting
material, a first layer disposed on the second electrode and
absorbing stress to the second electrode, and a second layer of an
inorganic material disposed on the first layer. The second
electrode is made of only Ag.
[0028] In such a configuration, the Ag atoms can be prevented from
aggregating into islands by using the mixture layer made of a
mixture of an electron-injecting material and a reducible metal
material for reducing the electron-injecting material as a base of
the second electrode. Therefore, the second electrode can be a
continuous film. In addition, since the second electrode is covered
by the first layer having a stress-absorbing ability and the second
layer is disposed on the first layer, the second electrode can be
prevented from being broken by stress.
[0029] In accordance with a twelfth application example of the
invention, the first layer of the light-emitting device is
preferably made of an electron-injecting material. In this
configuration, the first layer is preferably made of LiF,
Li.sub.2O, Liq, MgO, CaF.sub.2, SrF.sub.2, NaF, or WF. In more
preferable example, the first layer is made of LiF, and the
reducible metal material is Al.
[0030] In accordance with a thirteenth application example of the
invention, a light-emitting device includes a plurality of
light-emitting elements each including a first electrode, a second
electrode, and a light-emitting layer disposed between the first
electrode and the second electrode; a wall separating the plurality
of light-emitting elements; a first layer partially covering the
second electrodes and easing the concentration of stress to the
second electrodes; and a second layer of an inorganic material
disposed on the first layer. The second electrode covers the
light-emitting layer in each of the plurality of light-emitting
elements and the wall separating the plurality of light-emitting
elements.
[0031] In such a configuration, since the first layer having a
stress-absorbing ability for easing the concentration of stress to
the second electrode partially covers the second electrode, the
second electrode can be prevented from being broken by the
concentration of stress, compared to a configuration in which only
a second layer having a passivation ability, without a first layer,
is disposed on a second electrode. Therefore, a decrease in
electrical conductivity of the light-emitting element can be
inhibited. Furthermore, the second electrode may cover all the
light-emitting elements and the wall on a substrate or may cover a
plurality, but not all, of the light-emitting elements and the wall
separating the plurality of light-emitting elements on a
substrate.
[0032] In accordance with a fourteenth application example of the
invention, the first layer of the light-emitting device preferably
has openings at positions corresponding to the light-emitting
elements.
[0033] In such a configuration, light emitted from the
light-emitting layer can be extracted to the exterior from a region
not being covered by the first layer on the second electrode.
Therefore, the amount of light emitted from the light-emitting
device toward the exterior can be increased, compared to a
configuration in which the entire (whole area of) second electrode
is covered by a first layer.
[0034] In accordance with a fifteenth application example of the
invention, the light-emitting device is preferably configured in
such a manner that the first layer is not provided at at least part
of a region where the wall and the second electrode overlap each
other, and an auxiliary electrode is disposed at at least part of
the region where the first layer is not provided.
[0035] In such a configuration, the light-emitting device can be
produced by a process including (1) depositing a second electrode
on a light-emitting layer in each light-emitting element and a
wall, inside a deposition chamber, (2) subsequently, inside the
deposition chamber, depositing a first layer on the second
electrode at a region where the second electrode overlaps the
light-emitting layer in the zone of each light-emitting element
separated by the wall, and (3) taking out the substrate from the
deposition chamber and then forming an auxiliary electrode on the
second electrode at a region where the second electrode overlaps
the wall. That is, the second electrode and the first layer can be
formed by a continuous deposition process. Consequently,
manufacturing time and cost can be reduced, compared to a
configuration in which the second electrode and the auxiliary
electrode are covered by a first layer.
[0036] In accordance with a sixteenth application example, the
light-emitting device according to the invention can be utilized in
various types of electronic equipment. Typical examples of the
electronic equipment are those utilizing the light-emitting device
as a display, such as personal computers and mobile phones.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] The invention will be described with reference to the
accompanying drawings, wherein like numbers reference like
elements.
[0038] FIG. 1 is a cross-sectional view illustrating a structure of
a light-emitting device according to a first embodiment.
[0039] FIG. 2 is a diagram showing relationships between deposition
rate ratios of Mg and Ag for forming an opposite electrode of an
light-emitting element according to the first embodiment and
resistivities and other factors of the opposite electrode.
[0040] FIG. 3 is a diagram showing a relationship between
deposition rate ratios of Mg and Ag for forming the opposite
electrode of the light-emitting element according to the first
embodiment and surface roughnesses of the opposite electrode.
[0041] FIG. 4 is a graph showing a relationship between voltage
applied between a pixel electrode and an opposite electrode and
current density.
[0042] FIG. 5 is a graph showing a relationship between voltage
applied between a pixel electrode and an opposite electrode and
luminance of a light-emitting element.
[0043] FIG. 6 is a graph showing refractive index characteristics
of MgAg thin films having different Ag contents.
[0044] FIG. 7 is a graph showing optical-loss characteristics of
MgAg thin films having different Ag contents and thicknesses.
[0045] FIG. 8 is a graph showing a relationship between current
density flowing in a light-emitting element and luminance of the
light-emitting element.
[0046] FIG. 9A is a cross-sectional view showing a step of a
process for producing the light-emitting device according to the
first embodiment.
[0047] FIG. 9B is a cross-sectional view showing a step of the
process for producing the light-emitting device according to the
first embodiment.
[0048] FIG. 9C is a cross-sectional view showing a step of the
process for producing the light-emitting device according to the
first embodiment.
[0049] FIG. 9D is a cross-sectional view showing a step of the
process for producing the light-emitting device according to the
first embodiment.
[0050] FIG. 9E is a cross-sectional view showing a step of the
process for producing the light-emitting device according to the
first embodiment.
[0051] FIG. 9F is a cross-sectional view showing a step of the
process for producing the light-emitting device according to the
first embodiment.
[0052] FIG. 10A is a cross-sectional view showing a step of the
process for producing the light-emitting device according to the
first embodiment.
[0053] FIG. 10B is a cross-sectional view showing a step of the
process for producing the light-emitting device according to the
first embodiment.
[0054] FIG. 11 is a diagram showing relationships between the
thickness of an opposite electrode of a light-emitting element
according to a second embodiment and voltage, current efficiency,
and power efficiency.
[0055] FIG. 12 is a cross-sectional view illustrating a structure
of a light-emitting device according to a third embodiment.
[0056] FIG. 13 is a cross-sectional view illustrating a structure
of a light-emitting device according to a fourth embodiment.
[0057] FIG. 14 is a plan view schematically illustrating a judging
device for judging whether a sample is broken or not.
[0058] FIG. 15 is a cross-sectional view schematically illustrating
the judging device for judging whether a sample is broken or
not.
[0059] FIG. 16 is a diagram showing resistance values measured when
a passivation layer is formed directly on a sample and when a
stress-absorbing layer made of LiF is disposed between a
passivation layer and a sample.
[0060] FIG. 17 is a diagrams showing measurement results when the
stress-absorbing layer is made of CaF.sub.2.
[0061] FIG. 18 is a diagrams showing measurement results when the
stress-absorbing layer is made of Li.sub.2O.
[0062] FIG. 19 is a diagrams showing measurement results when the
stress-absorbing layer is made of MgF.sub.2.
[0063] FIG. 20A is a cross-sectional view showing a step of a
process for producing a light-emitting device according to the
fourth embodiment.
[0064] FIG. 20B is a cross-sectional view showing a step of the
process for producing the light-emitting device according to the
fourth embodiment.
[0065] FIG. 20C is a cross-sectional view showing a step of the
process for producing the light-emitting device according to the
fourth embodiment.
[0066] FIG. 20D is a cross-sectional view showing a step of the
process for producing the light-emitting device according to the
fourth embodiment.
[0067] FIG. 20E is a cross-sectional view showing a step of the
process for producing the light-emitting device according to the
fourth embodiment.
[0068] FIG. 21A is a cross-sectional view showing a step of the
process for producing the light-emitting device according to the
fourth embodiment.
[0069] FIG. 21B is a cross-sectional view showing a step of the
process for producing the light-emitting device according to the
fourth embodiment.
[0070] FIG. 21C is a cross-sectional view showing a step of the
process for producing the light-emitting device according to the
fourth embodiment.
[0071] FIG. 22 is a cross-sectional view illustrating a structure
of a light-emitting device according to a fifth embodiment.
[0072] FIG. 23 is a cross-sectional view illustrating a structure
of a light-emitting device according to a sixth embodiment.
[0073] FIG. 24 is a cross-sectional view illustrating a structure
of a light-emitting device according to a seventh embodiment.
[0074] FIG. 25 is a cross-sectional view illustrating a structure
of a light-emitting device according to an eighth embodiment.
[0075] FIG. 26 is a cross-sectional view illustrating a structure
of a light-emitting device according to a ninth embodiment.
[0076] FIG. 27 is a graph showing luminance at low current
operation of the light-emitting device according to the eighth
embodiment.
[0077] FIG. 28 is a cross-sectional view illustrating a structure
of a light-emitting device according to a tenth embodiment.
[0078] FIG. 29 is a plan view illustrating the structure of the
light-emitting device according to the tenth embodiment.
[0079] FIG. 30 is a cross-sectional view of a light-emitting device
as a comparative example in which a stress-absorbing layer covers
the entire second electrode.
[0080] FIG. 31 is a cross-sectional view of a light-emitting device
according to an eleventh embodiment.
[0081] FIG. 32 is a plan view of the light-emitting device
according to the eleventh embodiment.
[0082] FIG. 33 is a cross-sectional view of a light-emitting device
as a comparative example in which a stress-absorbing layer covers
an auxiliary electrode.
[0083] FIG. 34 is a cross-sectional view of a light-emitting device
as a modification in which a light-emitting function layer is
independently formed for each emission color.
[0084] FIG. 35 is a perspective view illustrating a configuration
of a mobile personal computer including the light-emitting device
according to the first embodiment as a display.
[0085] FIG. 36 is a diagram illustrating a configuration of a
mobile phone to which the light-emitting device according to the
first embodiment is applied.
[0086] FIG. 37 is a diagram illustrating a configuration of a
handheld terminal to which the light-emitting device according to
the first embodiment is applied.
DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0087] Various embodiments according to the invention will now be
described with reference to the accompanying drawings. In the
following drawings, the scale of each of the layers and the
portions differs from the actual scale for enabling to visually
recognize the layers and the portions on the drawings.
A: First Embodiment
A-1 Structure of Light-Emitting Device
[0088] FIG. 1 is a cross-sectional view illustrating a structure of
a light-emitting device D1 according to a first embodiment of the
invention. As shown in FIG. 1, the light-emitting device D1 is
configured such that a plurality of light-emitting elements U (Ur,
Ug, and Ub) is arrayed on a surface of a first substrate 10. Each
of the light-emitting elements U is an element generating light
with a wavelength corresponding to any of a plurality of colors
(red, green, and blue). In these elements, a single light-emitting
function layer is common to the plurality of elements, and emission
light with a wavelength corresponding to the respective
light-emitting elements is extracted by controlling the optical
length between the below-described reflecting layer and
semi-reflective opposite electrode in each light-emitting element
for optimizing resonance. In the first embodiment, by the resonance
effect, the light-emitting element Ur emits red light, the
light-emitting element Ug emits green light, and the light-emitting
element Ub emits blue light. The light-emitting device D1 according
to the first embodiment is a top emission type in which light
generated by each light-emitting element U is emitted toward the
opposite side with respect to the first substrate 10. Therefore,
the first substrate 10 may be made of an opaque plate-like material
such as a ceramic or metal sheet, as well as a light-transmissive
plate-like material such as glass.
[0089] The first substrate 10 is provided with wiring (not shown)
for feeding power to the light-emitting elements U to emit light.
Furthermore, the first substrate 10 is provided with circuits (not
shown) for feeding power to the light-emitting elements U.
[0090] As shown in FIG. 1, a wall 12 (separator) is formed on the
first substrate 10. The wall 12 separates the space on a surface of
the first substrate 10 for each light-emitting element U and is
made of a transparent insulative material such as acryl or
polyimide.
[0091] Each of the plurality of light-emitting elements U includes
a light-reflecting layer 14, a pixel electrode 16 as the first
electrode, a light-emitting function layer 18, an
electron-injection layer 49, and an opposite electrode 20 as the
second electrode. As shown in FIG. 1, a plurality of
light-reflecting layers 14 is formed on the first substrate 10. The
light-reflecting layers 14 are arranged so as to correspond to the
respective light-emitting elements U. The light-reflecting layers
14 are made of a light-reflective material. Preferred examples of
such a material include simple metals such as aluminum and silver
and alloys whose main components are aluminum or silver. In the
first embodiment, the light-reflecting layer 14 is made of a silver
alloy available from Furuya Metal Co., Ltd. under the trade name
"APC" and has a thickness of 80 nm.
[0092] The pixel electrodes 16 shown in FIG. 1 are anodes and are
disposed on the respective light-reflecting layers 14 and
surrounded by the wall 12. The pixel electrodes 16 are made of a
transparent, electrically conductive oxide material, such as ITO
(indium tin oxide), IZO (indium zinc oxide, a registered trade name
of Idemitsu Kosan Co., Ltd.), or ZnO.sub.2. In the first
embodiment, the pixel electrodes 16 are made of ITO and have
different thicknesses that correspond to the respective emission
colors of the light-emitting elements U. The details thereof will
be described below. Alternatively, the pixel electrodes 16 made of,
for example, ITO in the light-emitting elements may have the same
thickness. In such a case, the optical lengths corresponding to the
respective light-emitting elements can be obtained by disposing a
transparent layer made of, for example, SiN (silicon nitride) or
SiO (silicon oxide), and having different thicknesses between the
light-reflecting layer 14 and the pixel electrode 16 made of ITO.
Furthermore, a layer that can function as both the light-reflecting
layer 14 and the pixel electrode 16 may be used. For example, Ag
has a high work function and can inject holes to a hole-injection
layer. In this case, the control of the optical length in each
light-emitting element for optimizing the resonance is performed by
the light-emitting function layer 18.
[0093] As shown in FIG. 1, the light-emitting function layer 18 is
formed so as to cover each of the pixel electrodes 16 and the wall
12. That is, the light-emitting function layer 18 continues over
the plurality of light-emitting elements U, and the characteristics
of the light-emitting function layer 18 are equally applied to the
plurality of light-emitting elements U. Though the details are not
shown in the drawing, the light-emitting function layer 18 is
composed of a hole-injection layer disposed on the pixel electrodes
16, a hole-transporting layer disposed on the hole-injection layer,
a light-emitting layer disposed on the hole-transporting layer, and
an electron-transporting layer disposed on the light-emitting
layer.
[0094] In the first embodiment, the hole-injection layer is made of
"HI-406", the trade name of Idemitsu Kosan Co., Ltd., and has a 40
nm thickness; and the hole-transporting layer is made of "HT-320",
the trade name of Idemitsu Kosan Co., Ltd., and has a 15 nm
thickness. The hole-injection layer and the hole-transporting layer
may be formed of a single layer having both functions of the
hole-injection layer and the hole-transporting layer. In addition,
as long as the same functions can be achieved, other material can
be similarly used.
[0095] The light-emitting layer is made of an organic EL material
that emits light by recombining holes and electrons. In the first
embodiment, the organic EL material is a low molecular material and
emits white light. The host material of the light-emitting layer is
"BH-232", the trade name of Idemitsu Kosan Co., Ltd., and red,
green, and blue dopants are mixed with the host material. In the
first embodiment, "RD-001", "GD-206", and "BD-102", the trade names
of Idemitsu Kosan Co., Ltd., are used as the red, green, and blue
dopants, respectively. In the first embodiment, the thickness of
the light-emitting layer is 65 nm. In addition, as long as the same
functions can be achieved, other materials can be similarly
used.
[0096] In the first embodiment, the electron-transporting layer is
made of Alq3 (tris(S8-quinolinolato)aluminum complex) and has a 10
nm thickness, In addition, as long as the same function can be
achieved, other materials can be similarly used.
[0097] The electron-injection layer 49 shown in FIG. 1 enhances the
efficiency of electron injection to the light-emitting function
layer 18 and is formed so as to cover the light-emitting function
layer 18. That is, the electron-injection layer 49 continues over
the plurality of light-emitting elements U. In order to enhance the
efficiency of electron injection to the light-emitting function
layer 18, it is desirable that the potential barrier between the
opposite electrode 20 as the cathode and the light-emitting
function layer 18 is low. Therefore, the material for the
electron-injection layer 49 is preferably a metal compound, such as
a halide (in particular, fluoride) or an oxide, or a quinolinol
complex of an alkali metal or an alkaline-earth metal, such as LiF,
Li.sub.2O, Liq, MgO, or CaF.sub.2. In the first embodiment, the
electron-injection layer 49 is made of LiF (lithium fluoride).
[0098] In addition, since the electron-injection layer 49 is formed
of an insulating material, a larger thickness causes higher driving
voltage of the light-emitting elements U. In order to prevent an
increase in the driving voltage value of the light-emitting
elements U, the thickness of the electron-injection layer 49 is
preferably within the range of 0.5 to 2 nm. In the first
embodiment, the thickness of the electron-injection layer 49 is set
to 1 nm. However, since a quinolinol complex has an
electron-transporting property, the electron-injection layer 49
made of a quinolinol complex can also function as an
electron-transporting layer and therefore have a thickness of up to
about 40 nm.
[0099] The opposite electrode 20 shown in FIG. 1 is a cathode and
is formed so as to cover the electron-injection layer 49. That is,
the opposite electrode 20 continues over the plurality of
light-emitting elements U. The opposite electrode 20 functions as a
semi-transparent reflective layer having a property that part of
light reaching the surface thereof is transmitted and the remaining
light is reflected (i.e., semi-transparent reflectivity) and is
formed of an alloy of a metal of Mg, Cu, Zn, Pd, Nd, or Al and Ag.
In the first embodiment, the opposite electrode 20 is made of MgAg
(magnesium-silver alloy). As described below, in the first
embodiment, the opposite electrode 20 is formed by co-depositing Mg
and Ag on the electron-injection layer 49.
[0100] In order to ensure the transparency of the opposite
electrode 20, the thickness of the opposite electrode 20 is
preferably 30 nm or less. However, if the opposite electrode 20 is
too thin, the resistance thereof becomes high to make panel driving
difficult. Accordingly, the thickness is preferably 10 nm or more.
In the first embodiment, the thickness of the opposite electrode 20
is set to 16 nm.
[0101] The light-emitting function layer 18, the electron-injection
layer 49, and the opposite electrode 20 are common to the plurality
of light-emitting elements U. However, since the individual pixel
electrodes 16 are separated from one another, when current flows
between any of the pixel electrodes 16 and the opposite electrode
20, the light-emitting function layer 18 emits light only at a
position where the light-emitting function layer 18 overlaps that
pixel electrode 16. That is, the wall 12 separates the plurality of
light-emitting elements U.
[0102] In the light-emitting device D1 according to the first
embodiment, a resonator structure that resonates light emitted by
the light-emitting function layer 18 is formed between the
light-reflecting layer 14 and the opposite electrode 20. That is,
light emitted by the light-emitting function layer 18 goes and
returns between the light-reflecting layer 14 and the opposite
electrode 20, and light with a specific wavelength is enhanced by
resonance and passes through the opposite electrode 20 to travel
toward the observer side (upside in FIG. 1) (top emission).
[0103] The thicknesses of the pixel electrodes 16 in the
light-emitting elements U are controlled such that red color in the
white light emitted by the light-emitting function layer 18 is
enhanced in the light-emitting element Ur, green color is enhanced
in the light-emitting element Ug, and blue color is enhanced in the
light-emitting element Ub. More specifically, in the first
embodiment, the pixel electrode 16 of the light-emitting element Ur
has a 110 nm thickness, the pixel electrode 16 of the
light-emitting element Ug has a 70 nm thickness, and the pixel
electrode 16 of the light-emitting element Ub has a 30 nm
thickness.
[0104] As shown in FIG. 1, a passivation layer 24 is disposed on
the opposite electrode 20. The passivation layer 24 is a protection
layer for preventing infiltration of water and the air into the
light-emitting elements U and is formed as a second layer made of
an inorganic material having a low gas transmittance, such as SiN
(silicon nitride) or SiON (silicon oxynitride). In the first
embodiment, the passivation layer 24 is made of SiON and has a 225
nm thickness.
[0105] As shown in FIG. 1, in the first embodiment, a second
substrate 30 is disposed so as to face the plurality of
light-emitting elements U provided on the first substrate 10. The
second substrate 30 is made of a light transmissive material such
as glass and is provided with color filters 32 and a
light-shielding film 34 on the surface thereof facing the first
substrate 10. The light-shielding film 34 is a film having a
light-shielding property and is provided with openings 36 at
positions corresponding to the respective light-emitting elements
U. The color filters 32 are disposed in the openings 36.
[0106] In the first embodiment, a red color filter 32r that
selectively transmits red light is disposed in the opening 36
corresponding to the light-emitting element Ur, a green color
filter 32g that selectively transmits green light is disposed in
the opening 36 corresponding to the light-emitting element Ug, and
a blue color filter 32b that selectively transmits blue light is
disposed in the opening 36 corresponding to the light-emitting
element Ub.
[0107] The second substrate 30 provided with the color filters 32
and the light-shielding film 34 is bonded to the first substrate 10
via a sealing layer 26. The sealing layer 26 is made of a
transparent resin material, for example, a hardening resin such as
an epoxy resin.
[0108] FIG. 2 is a diagram showing the measurement results of
various factors when the deposition rate ratio of Mg and Ag for
forming the opposite electrode 20 of the light-emitting element Ug
according to the first embodiment is 10:1, 2:1, 1:1, 1:3, 1:9,
1:20, 1:50, or 0:100. The resistance values shown in FIG. 2 are
those of the opposite electrode 20. In addition, in FIG. 2, the
values of voltage, current efficiency, and power efficiency are
those when the density of current flowing in the opposite electrode
20 is 17.5 mA/cm.sup.2. The voltage values shown in FIG. 2 are
those applied between the pixel electrode 16 and the opposite
electrode 20. In addition, the current efficiency shown in FIG. 2
is light-emission intensity per ampere of current in the
light-emitting element Ug. The power efficiency shown in FIG. 2 is
light-emission intensity per watt of power in the light emitting
element Ug. The measurement results of various factors shown in
FIG. 2 are only those of the light-emitting element Ug that emits
green light, but other light-emitting elements Ur and Ub show
similar results.
[0109] As shown in FIG. 2 (the thickness of the opposite electrode
20 is 16 nm), it is confirmed that the resistivity when the
deposition rate ratio of Mg and Ag is 10:1 is significantly higher
than those in other cases. The resistivity of the opposite
electrode 20 is preferably 31.times.10.sup.-8 .OMEGA.m or less for
preventing degradation in electrical conductivity of the
light-emitting element. In the first embodiment, the lower limit of
the deposition rate ratio of Mg and Ag (the deposition rate ratio
of Mg and Ag when the ratio of deposition rate of Ag is a minimum)
is 2:1. In addition, it is confirmed by XRF analysis of a
deposition sample that the deposition rate ratio is approximately
equal to the atomic number ratio.
[0110] Next, the upper limit of the deposition rate ratio of Mg and
Ag (the deposition rate ratio of Mg and Ag when the ratio of
deposition rate of Ag is a maximum) will be described. As shown in
FIG. 2, since the resistivity is decreased with an increase in the
ratio of the deposition rate of Ag, the ability of feeding power to
the light-emitting elements is enhanced with an increase in the
ratio of deposition rate of Ag, when the light-emitting elements
are integrated to form a panel.
[0111] Here, it is supposed a case that the opposite electrode 20
is made of only Ag (the case that the deposition rate ratio of Mg
and Ag is 0:100). Since Ag atoms are applied with force to bind to
one another (aggregating force), if the thickness of the opposite
electrode 20 made of only Ag is 30 nm or less, the Ag atoms
aggregate one another into islands to make the electrode film
discontinuous. Since the thickness of the opposite electrode 20 in
the first embodiment is 16 nm, if the opposite electrode is made of
only Ag, the Ag atoms aggregate one another into islands, resulting
in a discontinuous film. Consequently, the resistivity of the
opposite electrode 20 becomes too high to measure,
[0112] FIG. 3 is a diagram showing surface roughness of the
opposite electrode 20 when the deposition rate ratio of Mg and Ag
for forming the opposite electrode 20 of the light-emitting element
Ug is 10:1, 3:1, 1:1, 1:3, 1:10, or 0:10. As shown in FIG. 3, the
value indicating the surface roughness of the opposite electrode 20
in the case that the deposition rate ratio of Mg and Ag is 0:10
(the case that the opposite electrode 20 is made of only Ag) is
larger than those in other cases. That is, it is confirmed that
when the opposite electrode 20 is made of only Ag, the Ag atoms
aggregate one another to generate asperities. In addition, it is
confirmed that when the opposite electrode 20 is made of an alloy
of Mg and Ag, Ag atoms are prevented from aggregating by Mg atoms
intervening between the Ag atoms, resulting in a reduction in
generation of asperities, compared to the case that the opposite
electrode 20 is made of only Ag.
[0113] Thus, though the resistivity is decreased with an increase
in the ratio of the deposition rate of Ag, Ag atoms aggregate one
another into islands when the deposition rate ratio of Mg and Ag
nears 0:100. Consequently, the resistivity of the opposite
electrode 20 becomes significantly high, causing degradation in the
ability of feeding power to the light-emitting elements that are
integrated to form a panel. Therefore, it is necessary to set the
upper limit of the deposition rate ratio of Mg and Ag within a
range that can inhibit degradation of the power-feeding
ability.
[0114] FIG. 4 is a graph showing a relationship between voltage
applied between the pixel electrode 16 and the opposite electrode
20 and current density in the opposite electrode 20 when the
deposition rate ratio of Mg and Ag for forming the opposite
electrode 20 of the light-emitting element Ug is 10:1 1:9, 1:20, or
1:50. In FIG. 4, it is confirmed that the current density under a
constant voltage is increased with the ratio of Ag to Mg, that is,
current can be efficiently injected by increasing the ratio of Ag
to Mg. This is because that in the case of an electron-injection
layer made of LiF, the electron injection property is enhanced by
increasing the ratio of Ag in MgAg forming the opposite electrode
20 (cathode).
[0115] FIG. 5 is a graph showing a relationship between voltage
applied between the pixel electrode 16 and the opposite electrode
20 and luminance of the light-emitting element Ug when the
deposition rate ratio of Mg and Ag for forming the opposite
electrode 20 of the light-emitting element Ug is 10:1, 1:9, 1:20,
or 1:50. In FIG. 5, it is confirmed that the luminance under a
constant voltage is increased with an increase in the Ag ratio. It
is believed that this is caused by the enhancement in the current
injection property as shown in FIG. 4 and an efficient extraction
of light by decreasing the loss in light extraction by increasing
the Ag ratio.
[0116] FIG. 6 shows refractive index characteristics of MgAg thin
films having different Ag contents. FIG. 7 shows optical-loss
characteristics of MgAg thin films having different Ag contents and
different thicknesses. On the vertical axis of FIG. 7, the "R" and
the "T" denote reflectance and transmittance, respectively, of an
MgAg thin film. The "1-(R+T)" denotes light-absorbing ratio of the
MgAg thin film, and a larger value thereof means a larger optical
loss.
[0117] In FIG. 7, a comparison of an MgAg thin film having a 11 nm
thickness and formed at a deposition rate ratio of Mg and Ag of
10:1 and an MgAg thin film having a 10 nm thickness and formed at a
deposition rate ratio of Mg and Ag of 1:10 reveals a difference in
optical loss corresponding to the MgAg ratio when the thicknesses
are similar (10 to 11 nm). In addition, as shown in FIG. 7, it is
confirmed that even if the thickness is increased to 16 nm, a large
optical loss is not caused, when the deposition ratio of Mg and Ag
is 1:10. Therefore, the light-extracting efficiency is enhanced by
increasing the Ag ratio.
[0118] FIG. 8 is a graph showing a relationship between current
density flowing in a light-emitting element Ug and luminance of the
light-emitting element Ug when the deposition rate ratio of Mg and
Ag for forming the opposite electrode 20 of the light-emitting
element Ug is 10:1, 1:9, 1:20, or 1:50. It is confirmed from FIG. 8
that the luminance under a constant current is increased with the
Ag ratio. This is because that when the electron-injection layer is
made of LiF, the electron injection property is enhanced by
increasing the Ag ratio in the cathode (opposite electrode 20)
disposed on the electron-injection layer. In addition, an increase
in the Ag ratio improves the optical constant of the cathode to
decrease the optical loss, resulting in enhancement of the
light-extraction efficiency.
[0119] From the above, it is confirmed that the optimum Mg:Ag ratio
is about 1:20.
[0120] Here, as shown in FIGS. 4, 5, and 8, a higher Ag ratio
accelerates the current to flow in and luminance to flow out.
However, an Mg:Ag of 1:50 makes the current slightly difficult to
flow in and the luminance slightly difficult to flow out. In the
first embodiment, an Mg:Ag of 1:20 looks like an optimum ratio. It
is confirmed by observing light-emitting surfaces that the surface
of a cathode at an Mg:Ag of 1:50 is roughened to cause poor
light-emission and that degradation in characteristics due to a
decrease in the film quality is caused by a too small Mg content.
Accordingly, it is appropriate that the upper limit of the Ag
content is determined to be 98%.
[0121] From the above, in the first embodiment, the deposition rate
ratio of Mg and Ag for forming the opposite electrode 20 is set
within the range of 2:1 to 1:50.
[0122] Furthermore, according to panel calculation, provided that
the light-emitting elements shown in the first embodiment are used;
the display size is 8 inches; the pixel aperture ratio is 60%;
color filters and a circularly polarizing plate are mounted; and
the display luminance is 150 cd/m.sup.2, the sheet resistance
required to the cathode is about 4.5 .OMEGA./.quadrature.. The
sheet resistance of a cathode having a 16 nm thickness estimated
from the resistance values shown in FIG. 2 is about 4.5
.OMEGA./.quadrature. when the Mg:Ag is 1:20. This can satisfy the
requirement above.
[0123] According to the first embodiment, since the resistivity of
the opposite electrode 20 can be thus controlled to a predetermined
standard value (31.times.10.sup.8 .OMEGA.m) or less, there is an
advantage that the light-emitting element can have a good
electrically conductive condition.
[0124] Incidentally, FIG. 2 shows that the values of current
efficiency and power efficiency are high when the deposition rate
ratios of Mg and Ag are 1:3, 1:9, 1:20, 1:50, and 0:100, compared
to those in other cases. This is because that when the Ag content
in the opposite electrode 20 is greater than a predetermined
standard value (50% by atoms), LiF forming the electron-injection
layer 49 sufficiently exhibits the electron injection property to
further enhance the electrical conductivity of the light-emitting
element. Therefore, it is also possible to set the deposition rate
ratio of Mg and Ag in the range of 1:1 to 1:50 (more preferably 1:3
to 1:50) such that the electron-injection layer 49 sufficiently
exhibits the electron injection property to impart a better
electrically conductive condition to the light-emitting
element.
A-2: Process of Producing Light-Emitting Device
[0125] Next, a process of producing the light-emitting device D1 of
the first embodiment will be described with reference to FIGS. 9A
to 9F, 10A, and 10B.
[0126] First, a plurality of light-reflecting layers 14 is formed
in a matrix form on a first substrate 10 by a known method (Step
P1: FIG. 9A), and pixel electrodes 16 are formed on the
light-reflecting layers 14 (Step P2: FIG. 9B). Subsequently, a wall
12 is formed in a grid pattern (Step P3: FIG. 9C). For example,
acryl or polyimide as a material for the wall 12 is mixed with a
photosensitive material, and the wall 12 can be patterned by
photolithographic exposure.
[0127] Then, a light-emitting function layer 18 is formed by a
known method, such as deposition, so as to cover the wall 12 and
the pixel electrodes 16 (Step P4: FIG. 9D). Then, an
electron-injection layer 49 is formed on the light-emitting
function layer 18 (Step P5: FIG. 9E). Furthermore, an opposite
electrode 20 is formed on the electron-injection layer 49 (Step P6:
FIG. 9F).
[0128] In Step P6, the opposite electrode 20 is formed by
co-depositing Mg and Ag on the electron-injection layer 49. As
described above, the deposition rate ratio of Mg and Ag is
preferably set within the range of 2:1 to 1:50.
[0129] Then, a passivation layer 24 is formed on the opposite
electrode 20 (Step P7: FIG. 10A). Furthermore, a sealing layer 26
is applied onto the passivation layer 24, and then a second
substrate 30 provided with color filters 32 and a light-shielding
film 34 is bonded (Step P8: FIG. 10B). The light-emitting device D1
according to the first embodiment is thus produced.
B: Second Embodiment
[0130] In a second embodiment, the deposition rate ratio of Mg and
Ag for forming the opposite electrode 20 is set to 1:9. Since the
other configuration is the same as that of the first embodiment,
the description thereof is omitted,
[0131] FIG. 11 is a diagram showing measurement results of various
factors in each case that the thickness of the opposite electrode
20 of the light-emitting element Ug according to the second
embodiment is 10 nm, 13 nm, or 16 nm, The sheet resistance values
shown in FIG. 11 are those of the opposite electrode 20, and the
values of voltage, current efficiency, and power efficiency are
those when the density of current flowing in the opposite electrode
20 is set to 17.5 mA/cm.sup.2. In addition, though it is not shown
in the drawing, the values of the various factors when the
thickness of the opposite electrode 20 is 20 nm are equivalent to
those when the thickness is 16 nm.
[0132] As shown in FIG. 11, it is confirmed that the sheet
resistance of the opposite electrode 20 is decreased with an
increase in the thickness thereof and the characteristics such as
voltage, current efficiency, and power efficiency are almost
constant regardless of the thickness. That is, a larger thickness
of the opposite electrode 20 is preferred within the range of 30 nm
or less, in which the transparency of the opposite electrode 20 can
be ensured. In addition, a larger thickness of the opposite
electrode 20 has an advantage that the purity of color that is
enhanced by resonance is raised.
C: Third Embodiment
[0133] FIG. 12 is a cross-sectional view illustrating a structure
of a light-emitting device D2 according to a third embodiment of
the invention. In the above-described embodiments, the
light-emitting function layer 18 is common to all the
light-emitting elements U, but in the third embodiment, the
light-emitting function layer 18 is independently formed for each
emission color of the light-emitting elements U.
[0134] As shown in FIG. 12, the light-emitting function layers 18
(18r, 18g, and 18b) each include a hole-injection layer 41 disposed
on the pixel electrode 16, a hole-transporting layer 43 disposed on
the hole-injection layer 41, a light-emitting layer 45 (45r, 45g,
or 45b) disposed on the hole-transporting layer 43, and an
electron-transporting layer 47 disposed on the light-emitting layer
45. The light-emitting function layer 18r of the light-emitting
element Ur contains the light-emitting layer 45r made of an organic
EL material that generates light of an R (red) wavelength range.
The light-emitting function layer 18g of the light-emitting element
Ug contains the light-emitting layer 45g made of an organic EL
material that generates light of a G (green) wavelength range. The
light-emitting function layer 18b of the light-emitting element Ub
contains the light-emitting layer 45b made of an organic EL
material that generates light of a B (blue) wavelength range. As
shown in FIG. 12, the light-emitting function layers 18 are formed
in the respective zones of the light-emitting elements U separated
by a wall 12, and the adjacent light-emitting function layers 18
are not connected to each other.
[0135] In FIG. 12, the thicknesses of the hole-transporting layers
43 in the light-emitting elements U are controlled such that red
color is enhanced in the light-emitting element Ur, green color is
enhanced in the light-emitting element Ug, and blue color is
enhanced in the light-emitting element Ub. Furthermore, in the
third embodiment, the emission color of each light-emitting element
U is enhanced by controlling the thickness of the hole-transporting
layer 43 in each light-emitting element U, but the configuration is
not limited thereto. The emission color of each light-emitting
element U can be also enhanced by controlling the thickness of the
pixel electrode 16, the hole-injection layer 41, the light-emitting
layer 45, or the electron-transporting layer 47.
[0136] Also in the third embodiment, as in the above-described
embodiments, since the resistivity of the opposite electrode 20 can
be set to a predetermined standard value (31.times.10.sup.8
.OMEGA.m) or less by setting the deposition rate ratio of Mg and Ag
for forming the opposite electrode 20 within the range of 2:1 to
1:50, the light-emitting element can have a good electrically
conductive condition.
D: Fourth Embodiment
D-1: Structure of Light-Emitting Device
[0137] FIG. 13 is a cross-sectional view illustrating a structure
of a light-emitting device D3 according to a fourth embodiment of
the invention. As shown in FIG. 13, the light-emitting device D3
has a configuration in which a plurality of light-emitting elements
U (Ur, Ug, and Ub) is arrayed on a surface of a first substrate 10.
Each light-emitting element U is an element generating light of a
wavelength that corresponds to any of a plurality of colors (red,
green, and blue). In the fourth embodiment, the light-emitting
element Ur emits red light, the light-emitting element Ug emits
green light, and the light-emitting element Ub emits blue light.
The light-emitting device D3 according to the fourth embodiment is
a top emission type in which light generated by each light-emitting
element U is emitted toward the opposite side with respect to the
first substrate 10. Therefore, the first substrate 10 may be made
of an opaque plate-like material such as a ceramic or metal sheet,
as well as a light-transmissive plate-like material such as
glass.
[0138] The first substrate 10 is provided with wiring (not shown)
for feeding power to the light-emitting elements U to emit light.
Furthermore, the first substrate 10 is provided with circuits (not
shown) for feeding power to the light-emitting elements U.
[0139] As shown in FIG. 13, a wall 12 (separator) is formed on the
first substrate 10. The wall 12 separates the space on a surface of
the first substrate 10 for each light-emitting element U and is
made of a transparent insulative material such as acryl or
polyimide.
[0140] Each of the plurality of light-emitting elements U includes
a light-reflecting layer 14, a pixel electrode 16, a light-emitting
function layer 18, and an opposite electrode 20. As shown in FIG.
13, a plurality of light-reflecting layers 14 is formed on the
first substrate 10. The light-reflecting layers 14 are arranged so
as to correspond to the respective light-emitting elements U. The
light-reflecting layers 14 are made of a light-reflective material.
Preferred examples of such a material include simple metals such as
aluminum and silver and alloys whose main components are aluminum
or silver. In the fourth embodiment, the light-reflecting layers 14
are made of a silver alloy available from Furuya Metal Co., Ltd.
under the trade name "APC" and have a thickness of 80 nm.
[0141] The pixel electrodes 16 shown in FIG. 13 are anodes and are
disposed on the respective light-reflecting layers 14 and
surrounded by the wall 12. The pixel electrodes 16 are made of a
transparent, electrically conductive oxide material, such as ITO,
IZO, or ZnO.sub.2. In the fourth embodiment, the pixel electrodes
16 are made of ITO and have different thicknesses that correspond
to the respective emission colors of the light-emitting elements U.
The details thereof will be described below. Alternatively, a
transparent layer may be disposed between a reflective layer made
of, for example, Ag and the pixel electrode 16. The optical length
to obtain optimal resonance for the light emission wavelength
required by the corresponding pixel can be optimized by optimizing
the thickness of the first electrode (pixel electrode) or the
transparent layer. Alternatively, the light-emitting function
layers may have different thicknesses that correspond to the
respective pixels described below.
[0142] The light-emitting function layer 18 is formed so as to
cover each of the pixel electrodes 16 and the wall 12. That is, the
light-emitting function layer 18 continues over the plurality of
light-emitting elements U, and the characteristics of the
light-emitting function layer 18 are equally applied to the
plurality of light-emitting elements U. Though the details are not
shown in the drawing, the light-emitting function layer 18 is
composed of a hole-injection layer disposed on the pixel electrodes
16, a hole-transporting layer disposed on the hole-injection layer,
a light-emitting layer disposed on the hole-transporting layer, an
electron-transporting layer disposed on the light-emitting layer,
and an electron-injection layer disposed on the
electron-transporting layer.
[0143] In the fourth embodiment, the hole-injection layer is made
of "Hi-406", the trade name of Idemitsu Kosan Co., Ltd., and has a
40 nm thickness. The hole-transporting layer is made of "HT-320",
the trade name of Idemitsu Kosan Co., Ltd., and has a 15 nm
thickness. The hole-injection layer and the hole-transporting layer
may be formed of a single layer having both functions of the
hole-injection layer and the hole-transporting layer.
[0144] The light-emitting layer is made of an organic EL material
that emits light by recombining holes and electrons. In the fourth
embodiment, the organic EL material is a low molecular material and
emits white light. The host material of the light-emitting layer is
"BH-232", the trade name of Idemitsu Kosan Co., Ltd., and red,
green, and blue dopants are mixed with the host material. In the
fourth embodiment, "RD-001", "GD-206", and "BD-102", the trade
names of Idemitsu Kosan Co., Ltd., are used as the red, green, and
blue dopants, respectively. In the fourth embodiment, the thickness
of the light-emitting layer is 65 nm.
[0145] In the fourth embodiment, the electron-transporting layer is
made of Alq3 (tris(8-quinolinolato)aluminum complex) and has a 10
nm thickness. The electron-injection layer is made of LiF (lithium
fluoride) and has a 1 nm thickness. Furthermore, the
electron-transporting layer and the electron-injection layer may be
formed of a single layer having both functions of the
electron-transporting layer and the electron-injection layer.
[0146] The below-described light-emitting function layers 18 of a
light-emitting device D5 according to a sixth embodiment, a
light-emitting device D6 according to a seventh embodiment, and a
light-emitting device D7 according to an eighth embodiment each
have the same configuration as that of the light-emitting function
layer 18 of the light-emitting device D3 according to the fourth
embodiment.
[0147] The opposite electrode 20 shown in FIG. 13 is a cathode and
is formed so as to cover the light-emitting function layer 18. That
is, the opposite electrode 20 continues over the plurality of
light-emitting elements U. The opposite electrode 20 functions as a
semi-transparent reflective layer having a property that part of
light reaching the surface thereof is transmitted and the remaining
light is reflected (i.e., semi-transparent reflectivity) and is
formed of a simple metal such as magnesium or silver or an alloy
whose main component is magnesium or silver. In the fourth
embodiment, the opposite electrode 20 is made of MgAg
(magnesium-silver alloy). As described below, in the fourth
embodiment, the opposite electrode 20 is formed by co-depositing Mg
and Ag on the light-emitting function layer 18.
[0148] The thickness of the opposite electrode 20 is preferably
within the range of 10 to 30 nm. This is because that when the
thickness of the opposite electrode 20 is less than 10 nm, the
resistance value of the opposite electrode 20 is high, resulting in
insufficient electrical conductivity and that when the thickness is
greater than 30 nm, the transparency of the opposite electrode 20
cannot be sufficiently ensured. In the fourth embodiment, the
thickness of the opposite electrode 20 is 10 nm.
[0149] The light-emitting function layer 18 and the opposite
electrode 20 are common to the plurality of light-emitting elements
U. However, since the individual pixel electrodes 16 are separated
from one another, when current flows between any of the pixel
electrodes 16 and the opposite electrode 20, the light-emitting
function layer 18 emits light only at a position where the
light-emitting function layer 18 overlaps that pixel electrode 16.
That is, the wall 12 separates the plurality of light-emitting
elements U.
[0150] In the light-emitting device D3 according to the fourth
embodiment, a resonator structure that resonates light emitted by
the light-emitting function layer 18 is formed between the
light-reflecting layer 14 and the opposite electrode 20. That is,
the light emitted by the light-emitting function layer 18 goes and
returns between the light-reflecting layer 14 and the opposite
electrode 20, and light with a specific wavelength is enhanced by
resonance and passes through the opposite electrode 20 to travel
toward the observer side (upside in FIG. 13) (top emission).
[0151] The thicknesses of the pixel electrodes 16 in light-emitting
elements U are controlled such that red color in the white light
emitted by the light-emitting function layer 18 is enhanced in the
light-emitting element Ur, green color is enhanced in the
light-emitting element Ug, and blue color is enhanced in the
light-emitting element Ub. More specifically, in the fourth
embodiment, the pixel electrode 16 of the light-emitting element Ur
has a 110 nm thickness, the pixel electrode 16 of the
light-emitting element Ug has a 70 nm thickness, and the pixel
electrode 16 of the light-emitting element Ub has a 27 nm
thickness.
[0152] The stress-absorbing layer 22 shown in FIG. 13 is a first
layer for absorbing stress to the opposite electrode 20 and is
formed so as to cover the opposite electrode 20. The
stress-absorbing layer 22 has light transmittance and moisture
resistance and is made of a material that is softer than those of
the opposite electrode 20 and the below-described passivation layer
24. The stress-absorbing layer 22 is made of the same material as
that of the electron-injection layer of the light-emitting function
layer 18, for example, LiF, LiO.sub.2, Liq, MgO, MgF.sub.2,
CaF.sub.2, SrF.sub.2, NaF, or WF. In the fourth embodiment, the
stress-absorbing layer 22 is made of LiF and has a 10 nm
thickness.
[0153] As shown in FIG. 13, the passivation layer 24 is disposed on
the stress-absorbing layer 22. The passivation layer 24 is a
protection layer for preventing infiltration of water and the air
into the light-emitting elements U and is formed as a second layer
made of an inorganic material having a low gas transmittance, such
as SiN (silicon nitride) or SiON (silicon oxynitride). In the
fourth embodiment, the passivation layer 24 is made of SiON
(silicon oxynitride) and has a 400 nm thickness.
[0154] As shown in FIG. 13, in the fourth embodiment, a second
substrate 30 is disposed so as to face the plurality of
light-emitting elements U disposed on the first substrate 10. The
second substrate 30 is made of a light transmissive material such
as glass and is provided with color filters 32 and a
light-shielding film 34 on the surface facing the first substrate
10. The light-shielding film 34 is a film having a light-shielding
property and is provided with openings 36 at positions
corresponding to the respective light-emitting elements U. The
color filters 32 are disposed in the openings 36.
[0155] In the fourth embodiment, a red color filter 32r that
selectively transmits red light is disposed in the opening 36
corresponding to the light-emitting element Ur, a green color
filter 32g that selectively transmits green light is disposed in
the opening 36 corresponding to the light-emitting element Ug, and
a blue color filter 32b that selectively transmits blue light is
disposed in the opening 36 corresponding to the light-emitting
element Ub.
[0156] The second substrate 30 provided with the color filters 32
and the light-shielding film 34 is bonded to the first substrate 10
via a sealing layer 26. The sealing layer 26 is made of a
transparent resin material, for example, a hardening resin such as
an epoxy resin. The structure of the light-emitting device D3 of
the fourth embodiment is as above.
[0157] Incidentally, when the opposite electrode 20 is made of MgAg
as in fourth embodiment, it is preferred to increase the ratio of
Ag, which is superior to Mg in electrical conductivity, for
enhancing the conductive property of the light-emitting elements U.
However, since Ag atoms are applied with force to bind to one
another (aggregating force), if the Ag content of the opposite
electrode 20 is greater than a predetermined standard value, the Ag
atoms aggregate with one another to generate asperities. In such a
case, when the passivation layer 24 is formed directly on the
opposite electrode 20, the load of the passivation layer 24 is
applied to the opposite electrode 20. Therefore, if the asperities
of the opposite electrode 20 are excessive, the opposite electrode
20 is broken, resulting in a problem that the electrical
conductivity of the light-emitting elements U is decreased.
[0158] In the fourth embodiment, it has been found that when the
ratio of the deposition rate of Ag (equivalent to the atomic number
ratio in XRF analyzer) is less than Mg:Ag=1:3, the opposite
electrode 20 is not broken even if the passivation layer 24 is
formed directly on the opposite electrode 20, whereas when the
atomic number ratio of Ag is greater than Mg:Ag=1:3, the Ag atoms
aggregate with one another to generate asperities to cause breakage
of the opposite electrode 20 due to the passivation layer 24 formed
directly on the opposite electrode 20. From the finding above, in
the fourth embodiment, the deposition rate ratio (equivalent to the
atomic number ratio in XRF analyzer) of Mg and Ag for forming the
opposite electrode 20 is set in the range of 1:3 to 1:50, and also
a configuration in which the passivation layer 24 is disposed on
the stress-absorbing layer 22 covering the opposite electrode 20 is
employed.
[0159] In the fourth embodiment, since the atomic number ratio of
Ag is set to Mg:Ag=1:3 or more, asperities are generated in the
opposite electrode 20. However, since the passivation layer 24 is
formed on the stress-absorbing layer 22 covering the opposite
electrode 20, the load of the passivation layer 24 is dispersed to
the stress-absorbing layer 22. This prevents the opposite electrode
20 from being broken due to stress, resulting in an advantage that
the light-emitting elements U have a good electrically conductive
condition.
[0160] FIG. 14 is a plan view schematically illustrating a judging
device 50 for judging whether a sample of the opposite electrode 20
produced at an atomic number ratio of Mg and Ag of 1:9 is broken or
not. FIG. 15 is a cross-sectional view taken along the line XV-XV
in FIG. 14.
[0161] The judging device 50 is composed of a testing substrate 42,
four testing electrodes 44 (from 44a to 44d) disposed on the
testing substrate 42, a wall 46 in a grid pattern for separating
the four testing electrodes 44, and a testing thin metal film 48
disposed on the testing electrodes 44 at regions separated by the
wall 46 (regions surrounded by the openings B shown in FIG. 14) and
on the wall 46. The testing thin metal film 48 is a sample of the
opposite electrode 20 produced at an atomic number ratio of Mg and
Ag of 1:9.
[0162] In the fourth embodiment, the method for judging whether a
sample is broken or not will be described with reference to FIG.
15. The resistance value of a current path from the testing
electrode 44a to the adjacent testing electrode 44b via a sample
(testing thin metal film 48) (or a current path from the testing
electrode 44b to the testing electrode 44a via the sample) is
measured by bringing terminals of a tester into contact with the
testing electrodes 44a and 44b. If the sample is broken, the
resistance value measured by the tester is significantly high.
Therefore, whether the sample is broken or not can be judged based
on the resistance value.
[0163] FIG. 16 is a diagram showing resistance values measured by
the tester when a passivation layer 24 is formed directly on a
sample (testing thin metal film 48) and when a stress-absorbing
layer 22 having a thickness of 10 nm, 25 nm, or 50 nm is disposed
between a passivation layer 24 and a sample. In all cases shown in
FIG. 16, the samples have a 13 nm thickness, and the
stress-absorbing layers 22 are made of LiF.
[0164] As shown in FIG. 16, it is confirmed that the resistance
value when the passivation layer 24 is formed directly on a sample
is significantly large (about 10 M.OMEGA.), resulting in breakage
of the sample. On the other hand, when a stress-absorbing layer 22
made of LiF is disposed between the passivation layer 24 and the
sample, the resistance values are approximately the same, about 5
.OMEGA., in all cases that the thickness of the stress-absorbing
layer 22 is 10 nm, 25 nm, or 50 nm, and therefore no breakage is
observed in the samples.
[0165] FIG. 17 is a diagram showing resistance values when the
stress-absorbing layer 22 is made of CaF.sub.2, instead of LiF, and
has a thickness of 10 nm, 25 nm, or 50 nm. In all cases shown in
FIG. 17, the resistance is measured for a configuration in which a
stress-absorbing layer 22 is disposed between the passivation layer
24 and the sample. As shown in FIG. 17, the resistance values are
approximately the same, about 5 .OMEGA., in all cases that the
thickness of the stress-absorbing layer 22 is 10 nm, 25 nm, or 50
nm.
[0166] FIG. 18 is a diagrams showing resistance values when the
stress-absorbing layer 22 is made of Li.sub.2O and has a thickness
of 10 nm, 25 nm, or 50 nm. In all cases shown in FIG. 18, the
resistance is measured for a configuration in which a
stress-absorbing layer 22 is disposed between the passivation layer
24 and the sample. Also in the cases shown in FIG. 18, the
resistance values are approximately the same, about 5 .OMEGA., in
all cases that the thickness of the stress-absorbing layer 22 made
of Li.sub.2O is 10 nm, 25 nm, or 50 nm.
[0167] FIG. 19 is a diagrams showing resistance values when the
stress-absorbing layer is made of MgF.sub.2 and has a thickness of
10 nm, 25 nm, or 50 nm. In all cases shown in FIG. 19, the
resistance is measured for a configuration in which a
stress-absorbing layer 22 is disposed between the passivation layer
24 and the sample. Also in the cases shown in FIG. 19, the
resistance values are approximately the same, about 5 .OMEGA., in
all cases that the thickness of the stress-absorbing layer 22 made
of MgF.sub.2 is 10 nm, 25 nm, or 50 nm.
[0168] From the above, it is confirmed that a sample is prevented
from being broken due to stress by employing a configuration in
which a stress-absorbing layer 22 is disposed between the
passivation layer 24 and the sample.
D-2: Process of Producing Light-Emitting Device
[0169] Next, a process of producing any of the light-emitting
device D3 of the fourth embodiment, the below-described
light-emitting device D7 of an eighth embodiment, and the
below-described light-emitting device D8 of a ninth embodiment will
be described with reference to FIGS. 20A to 20E and FIGS. 21A to
21C.
[0170] First, a plurality of light-reflecting layers 14 is formed
in a matrix form on a first substrate 10 by a known method (Step
P1: FIG. 20A), and pixel electrodes 16 are formed on the
light-reflecting layers 14 (Step P2: FIG. 20B). Subsequently, a
wall 12 is formed in a grid pattern (Step P3: FIG. 20C). For
example, acryl or polyimide as a material for the wall 12 is mixed
with a photosensitive material, and the wall 12 can be patterned by
photolithographic exposure.
[0171] Then, a light-emitting function layer 18 is formed by a
known method, such as deposition, so as to cover the wall 12 and
the pixel electrodes 16 (Step P4: FIG. 20D). Furthermore, an
opposite electrode 20 is formed on the light-emitting function
layer 18 (Step P5: FIG. 20E),
[0172] In Step P5, the opposite electrode 20 is formed by
co-depositing Mg and Ag on the light-emitting function layer 18. As
described above, in the fourth embodiment, the deposition rate
ratio (equivalent to the atomic number ratio in XRF analyzer) of Mg
and Ag is preferably set within the range of 1:3 to 1:50.
[0173] Then, a stress-absorbing layer 22 is formed on the opposite
electrode 20 (Step P6: FIG. 21A), and a passivation layer 24 is
formed on the stress-absorbing layer 22 (Step P7: FIG. 21B). Here,
the stress-absorbing layer 22 is preferably formed by deposition
(heat deposition). In such a method, the light-emitting function
layer 18 and the opposite electrode 20 as bases are inhibited from
being damaged. In addition, the passivation layer 24 is preferably
formed with a device including a plasma generator. In such a
method, a dense film layer can be formed, resulting in an increase
in reliability of the light-emitting elements U and the
light-emitting device D3 (D7, D8).
[0174] Furthermore, a sealing layer 26 is applied onto the
passivation layer 24, and then a second substrate 30 provided with
color filters 32 and a light-shielding film 34 is bonded (Step P8:
FIG. 21C). The light-emitting device D3 according to the fourth
embodiment is thus produced.
E: Fifth Embodiment
[0175] FIG. 22 is a cross-sectional view illustrating a structure
of a light-emitting device D4 according to a fifth embodiment of
the invention. In the above-described fourth embodiment, the
light-emitting function layer 18 is common to all the
light-emitting elements U. In the fifth embodiment, the
light-emitting function layer 18 is independently formed for each
emission color of the light-emitting elements U.
[0176] As shown in FIG. 22, the light-emitting function layers 18
(18r, 18g, and 18b) are each composed of a hole-injection layer 41
disposed on the pixel electrode 16, a hole-transporting layer 43
disposed on the hole-injection layer 41, a light-emitting layer 45
(45r, 45g, or 45b) disposed on the hole-transporting layer 43, an
electron-transporting layer 47 disposed on the light-emitting layer
45, and an electron-injection layer 49 disposed on the
electron-transporting layer 47. The light-emitting function layer
18r of the light-emitting element Ur contains the light-emitting
layer 45r made of an organic EL material that generates light of an
R (red) wavelength range. The light-emitting function layer 18g of
the light-emitting element Ug contains the light-emitting layer 45g
made of an organic EL material that generates light of a G (green)
wavelength range. The light-emitting function layer 18b of the
light-emitting element Ub contains the light-emitting layer 45b
made of an organic EL material that generates light of a B (blue)
wavelength range. As shown in FIG. 22, the light-emitting function
layers 18 are formed in the respective zones of the light-emitting
elements U separated by a wall 12, and the adjacent light-emitting
function layers 18 are not connected to each other.
[0177] In FIG. 22, the thicknesses of the hole-transporting layers
43 in the light-emitting elements U are controlled such that red
color is enhanced in the light-emitting element Ur, green color is
enhanced in the light-emitting element Ug, and blue color is
enhanced in the light-emitting element Ub. In the fifth embodiment,
the emission color of each light-emitting element U is enhanced by
controlling the thickness of the hole-transporting layer 43 in each
light-emitting element U, but the configuration is not limited
thereto. The emission color of each light-emitting element U can be
also enhanced by controlling the thickness of the pixel electrode
16, the hole-injection layer 41, the light-emitting layer 45, the
electron-transporting layer 47, or the electron-injection layer
49.
[0178] In also the fifth embodiment, as in the above-described
embodiments, the deposition rate ratio (atomic number ratio) of Mg
and Ag for forming the opposite electrode 20 is set within the
range of 1:3 to 1:50. Then, the opposite electrode 20 is covered by
a stress-absorbing layer 22, and a passivation layer 24 is disposed
on the stress-absorbing layer 22. Therefore, the load of the
passivation layer 24 is dispersed to the stress-absorbing layer 22.
This prevents the opposite electrode 20 from being broken due to
stress.
F: Sixth Embodiment
[0179] FIG. 23 is a cross-sectional view illustrating a structure
of a light-emitting device D5 according to a sixth embodiment of
the invention. Though the details are not shown in the drawing, the
light-emitting function layer 18 is composed of a hole-injection
layer disposed on the pixel electrodes 16, a hole-transporting
layer disposed on the hole-injection layer, a light-emitting layer
disposed on the hole-transporting layer, and an
electron-transporting layer disposed on the light-emitting
layer.
[0180] As shown in FIG. 23, an electron-injection layer 49 is
disposed on the light-emitting function layer 18 for enhancing the
efficiency of electron injection to the light-emitting function
layer 18. In the sixth embodiment, the electron-injection layer 49
is made of LiF and has a 1 nm thickness.
[0181] As shown in FIG. 23, a reduction layer 51 is disposed on the
electron-injection layer 49. The reduction layer 51 is made of a
reducible metal material for reducing the electron-injecting
material forming the electron-injection layer 49. In the sixth
embodiment, the reduction layer 51 is made of Al and has a 2 nm
thickness.
[0182] As shown in FIG. 23, an opposite electrode 20 is disposed on
the reduction layer 51. In the sixth embodiment, the opposite
electrode 20 is made of only Ag. The thickness of the opposite
electrode 20 is desirably in the range of 10 to 20 nm as in the
above-described fourth embodiment. In the sixth embodiment, the
thickness of the opposite electrode 20 is set to 13 nm. In the
above-mentioned points, the configuration of the sixth embodiment
is different from that of the fourth embodiment. Since the other
configuration is the same as that of the fourth embodiment, the
description thereof is omitted.
[0183] In the sixth embodiment, the Ag atoms forming the opposite
electrode 20 can be prevented from aggregating with one another
into islands (breakage of the film) by using the reducible metal
material (Al in the sixth embodiment) forming the reduction layer
51 as a base of the opposite electrode 20. Consequently, the
opposite electrode 20 can be a continuous film. However, the
aggregation of the Ag atoms cannot be completely inhibited, and the
opposite electrode 20 according to the sixth embodiment has
asperities. In addition, since the material of the opposite
electrode 20 is different from that of the passivation layer 24
disposed thereon, their physical constants, such as a thermal
expansion coefficient, are different. Therefore, stress is
generated between these layers. In particular, the stress increases
with the ratio of Ag and causes peeling of the opposite electrode
20, resulting in a decrease in electrical conductivity of the
light-emitting elements U.
[0184] In the sixth embodiment, as in the fourth embodiment, the
opposite electrode 20 is covered by a stress-absorbing layer 22,
and a passivation layer 24 is formed on the stress-absorbing layer
22. Therefore, the load of the passivation layer 24 is dispersed to
the stress-absorbing layer 22. This prevents the opposite electrode
20 from being broken due to stress.
[0185] The sixth embodiment exemplarily shows a configuration in
which the light-emitting function layer 18 is common to all the
light-emitting elements U. However, as in the fifth embodiment, the
light-emitting function layer 18 may be independently formed for
each emission color of the light-emitting elements U.
G: Seventh Embodiment
[0186] FIG. 24 is a cross-sectional view illustrating a structure
of a light-emitting device D6 according to a seventh embodiment of
the invention. In the seventh embodiment, a mixture layer 53 made
of a mixture of an electron-injecting material and a reducible
metal material for reducing the electron-injecting material is
disposed on the light-emitting function layer 18, and the opposite
electrode 20 is disposed on the mixture layer 53. The configuration
in the seventh embodiment is different from that of the sixth
embodiment in the above points, but since the other configuration
is the same as that of the sixth embodiment, the description
thereof is omitted. In the seventh embodiment, the
electron-injecting material is LiF, and the reducible metal
material is Al.
[0187] The Ag atoms forming the opposite electrode 20 can be also
prevented from aggregating with one another into islands (breakage
of the film) by using the mixture layer 53 made of a mixture of an
electron-injecting material and a reducible metal material as a
base of the opposite electrode 20, as in the seventh embodiment.
Since the material of the opposite electrode 20 is different from
that of the passivation layer 24 disposed thereon, their physical
constants, such as a thermal expansion coefficient, are different.
Therefore, stress is generated between these layers. In particular,
the stress increases with the ratio of Ag and causes peeling of the
opposite electrode 20.
[0188] In also the seventh embodiment, as in the sixth embodiment,
the opposite electrode 20 is covered by a stress-absorbing layer
22, and a passivation layer 24 is formed on the stress-absorbing
layer 22. Therefore, the load of the passivation layer 24 is
dispersed to the stress-absorbing layer 22. This can prevent the
opposite electrode 20 from being broken due to stress.
[0189] The seventh embodiment exemplarily shows a configuration in
which the light-emitting function layer 18 is common to all the
light-emitting elements U. However, as in the fifth embodiment, the
light-emitting function layer 18 may be independently formed for
each emission color of the light-emitting elements U.
H: Eighth Embodiment
[0190] FIG. 25 is a cross-sectional view illustrating a structure
of a light-emitting device D7 according to an eighth embodiment of
the invention. The light-emitting device D7 according to the eighth
embodiment has a configuration similar to that of the
light-emitting device D3 according to the fourth embodiment. That
is, the light-emitting device D7 is a top emission type
light-emitting device having three kinds of light-emitting elements
U (Ur, Ug, and Ub) arrayed on a surface of a first substrate 10.
The light-emitting element Ur emits red light, the light-emitting
element Ug emits green light, and the light-emitting element Ub
emits blue light. The light-emitting elements U each have a
structure in which a light-reflecting layer 14, a pixel electrode
16, a light-emitting function layer 18, and an opposite electrode
20 are laminated on the first substrate 10.
[0191] The three kinds of the light-emitting elements U (Ur, Ug,
and Ub) are provided with a common light-emitting function layer
18. The color of emitted light is determined by an effect of
enhancing light of a specific wavelength range by resonance between
the light-reflecting layer 14 and the opposite electrode 20 and an
effect of coloring by color filters 32 (32r, 32g, or 32b). Since
the other configuration is the same as that of the light-emitting
device D3 according to the fourth embodiment, the description
thereof is omitted.
[0192] The light-emitting device D7 according to the eighth
embodiment is slightly different from the light-emitting devices D
(D3, D4, D5, and D6) according to the above-described embodiments
in the sealing layer thereof. The sealing layer in the eighth
embodiments is configured of an organic buffer layer 64, a gas
barrier layer 66, and a transparent adhesion layer 68. However,
such a configuration can be also applied to the light-emitting
devices D (D3, D4, D5, and D6) according to the above-described
embodiments.
[0193] The gas barrier layer 66 is a layer for preventing
infiltration of water and the like from the exterior, as the
passivation layer 24, and is made of SiO (silicon oxide) and has a
thickness of 200 to 400 nm. The organic buffer layer 64 is made of
an epoxy resin (or an acrylic resin or the like) and flattens
unevenness due to the wall 12 and other components. The transparent
adhesion layer 68 is made of an epoxy resin and bonds the first
substrate 10 and the second substrate 30.
[0194] Furthermore, the second substrate 30 of the light-emitting
device D7 according to the eighth embodiment is provided with an
over coat layer 35 on the side of the color filters 32 for
protecting the color filters 32 and is provided with a circularly
polarizing plate 70 on the other side. The circularly polarizing
plate 70 inhibits a decrease in display quality due to reflection
by the light-reflecting layer 14 or the like by using a property
that the direction of rotation of polarization is reversed. Both of
the two components can be also applied to the light-emitting
devices D (D3, D4, D5, and D6) according to the above-described
embodiments.
[0195] Furthermore, in the light-emitting device D7 according to
the eighth embodiment, the electron-injection layer, the uppermost
layer of the light-emitting function layer 18, is made of LiF and
has a 1 nm thickness. The electron-injection layer may be made of,
for example, Li.sub.2O, MgO, or CaF.sub.2, as well as LiF, as a
film having a thickness of 0.5 to 2 nm, preferably 1 nm. In
addition, a layer made of Liq (lithium quinolate) and having a
thickness of 1 to 20 nm can have both functions of the
electron-injection layer and the electron-transporting layer.
[0196] Furthermore, the opposite electrode 20 of the light-emitting
device D7 according to the eighth embodiment is made of MgAg
(magnesium-silver alloy) as in the light-emitting device D3
according to the fourth embodiment. The mixture ratio is
Mg:Ag=1:20, and the thickness is 10 nm. Ag has high reflectivity
and electrical conductivity and is therefore suitable as a material
of the second electrode. However, in the case that a thin film with
a 30 nm thickness or less is formed by deposition, the film is not
even and has rough film quality, resulting in a decrease in the
reflectivity and electrical conductivity. A film made of a mixture
of Ag and another metal can be even and can be simultaneously
enhanced in the electrical conductivity.
[0197] The opposite electrode 20 may be made of an alloy of Ag with
a metal other than Mg or a laminate of such alloys. Specifically,
an alloy of Ag with Cu, Zn, Pd, Nd, or Al can be used. In addition,
a laminate of such alloys, for example, a laminate of AgCu and AgPd
can be used.
[0198] The light-emitting device D7 according to the eighth
embodiment is largely different from the light-emitting devices D3,
D4, D5, and D6 in the material forming the stress-absorbing layer
22. That is, the stress-absorbing layer 22 of the light-emitting
device D7 according to the eighth embodiment is made of a metal,
other than Ag, having a work function of 4.2 eV or more, or a
dielectric, such as Zn, Al, Au, SnO.sub.2, ZnO.sub.2, or SiO. The
reasons thereof will be described below.
[0199] The stress-absorbing layer 22 is formed for absorbing stress
to the opposite electrode 20 during the formation of the
passivation layer 24. In addition, degradation of Ag (blackening by
oxidation and opacification) contained in the opposite electrode 20
is inhibited by O.sub.2 plasma applied before the formation of the
passivation layer 24. Therefore, the material of the
stress-absorbing layer 22 in each of the light-emitting devices
(D3, D4, D5, and D6) according to the fourth to seventh embodiments
is determined such that the material is softer than those of the
opposite electrode 20 and the passivation layer 24. In addition,
the stress-absorbing layer 22 is required to have light
transmittance and moisture resistance.
[0200] However, subsequent experiments have revealed that in the
case of the stress-absorbing layer 22 is made of a material having
a work function of less than 4.2 eV (electron volt), the
light-emitting element U slightly emits light during black display
as a light-emitting device D, resulting in a reduction in contrast.
Furthermore, additional experiments have revealed that the light
emission (during black display) can be inhibited by forming the
stress-absorbing layer 22 with a material having a work function of
4.2 eV (electron volt) or more. In the light-emitting device D7
according to the eighth embodiment, on the basis of such
experimental results, the stress-absorbing layer 22 is made of Zn
(zinc). Specifically, the stress-absorbing layer 22 is formed by
depositing Zn so as to have a thickness of 3 nm. By using such a
material, the light-emitting device D7 according to the eighth
embodiment can have an opposite electrode 20 having favorable
electrical conductivity and transparency as in the light-emitting
devices (D3, D4, D5, and D6) according to the fourth to seventh
embodiments and can reduce the light emission during black display,
resulting in enhancement of contrast.
[0201] FIG. 27 is a graph showing light emission during black
display, that is, luminance at low current operation of the
light-emitting device D7 according to the eighth embodiment.
Specifically, luminance (cd/m.sup.2) when a current of 0.00033
mA/cm.sup.2 is applied is shown on the vertical axis. Hereinafter,
the luminance in such a low current operation is simply referred to
as "luminance". Lower luminance can achieve higher contrast of the
light-emitting device. Furthermore, as a comparison, the luminance
of a light-emitting device having the same components as those of
the light-emitting device D7 except that the stress-absorbing layer
22 is made of a material other than Zn is shown. On the horizontal
axis, the material and the thickness of each stress-absorbing layer
22 are shown. As shown in the drawing, the measurement result of
the light-emitting device D7 according to the eighth embodiment,
that is, the measurement result of the stress-absorbing layer 22
made of Zn and having a 3 nm thickness is shown at the right of the
graph.
[0202] In the light-emitting devices used for the measurement of
luminance, except the "standard" light-emitting device shown at the
left of the graph as a reference, the electron-injection layer is
made of LiF and has a 1 nm thickness, and the opposite electrode 20
is made of MgAg (1:20). In the "standard" light-emitting device,
the electron-injection layer is made of LiF and has a 1 nm
thickness, and the opposite electrode 20 is made of MgAg (10:1). In
such a combination of the electron-injection layer and the opposite
electrode 20 (of the "standard" light-emitting device), since the
light-extracting efficiency is low, despite the low luminance, it
is inadequate to a top-emission-type light-emitting device.
Accordingly, in the light-emitting devices D (D3, D4, D5, D6, and
D7) according to the embodiments of the invention, the opposite
electrode 20 is made of only Ag or a material whose main component
is Ag.
[0203] The luminance of the light-emitting device D7 according to
the eighth embodiment is 0.00033 cd/m.sup.2. The luminance of a
light-emitting device including a stress-absorbing layer 22 made of
SnO.sub.2 (tin oxide) and having a 5 nm thickness is 0.00032
cd/m.sup.2, and therefore such a light-emitting device is further
excellent. On the other hand, the luminance of a light-emitting
device including a stress-absorbing layer 22 made of Al and having
a 3 nm thickness is 0.00312 cd/m.sup.2, which is about ten times
that of the stress-absorbing layer 22 made of Zn or SnO.sub.2.
Here, regarding the work function of each of the above-mentioned
materials, Zn has of 4.9 eV, SnO.sub.2 has of 5.0 eV, and Al has of
4.2 eV. Therefore, it is confirmed that it is preferable to form
the stress-absorbing layer 22 with a material having a work
function of 4.2 eV or more.
[0204] Luminance in the case of a LiF layer having a 5 nm thickness
is 0.00053 cd/m.sup.2. It is believed that since the work function
of LiF is large, 5.0 eV, whereas that of Li (lithium) itself is
low, the luminance is thus low. In addition, it is believed that
favorable results can be obtained in cases of using another
material, for example, Au (with a work function of 4.8 eV) or SiO
(with a work function of 5.0 eV). On the other hand, luminance in
the case of using only Mg is further higher than that in the case
of using Al. This reveals that Mg is unfavorable as the material of
the stress-absorbing layer 22. However, in the case of using Mg as
a compound with another material such as MgO or MgF.sub.2, not as
only Mg, the above is not applied.
[0205] Thus, in the light-emitting device D7 according to the
eighth embodiment, as in the light-emitting devices D3, D4, D5, and
D6 according to the fourth to seventh embodiments, the opposite
electrode 20 exhibiting enhanced light-extracting efficiency during
light emission is obtained by providing the stress-absorbing layer
22 between the opposite electrode 20 and the passivation layer 24.
Furthermore, light emission during black display is reduced by
forming the stress-absorbing layer 22 with Zn, which has a work
function of 4.9 eV, resulting in enhancement of contrast.
Therefore, the display quality is further increased.
I: Ninth Embodiment
[0206] FIG. 26 is a cross-sectional view illustrating a structure
of a light-emitting device D8 according to a ninth embodiment of
the invention. In the eighth embodiment, the light-emitting
function layer 18 is common to all the light-emitting elements U,
but in the light-emitting device D8 according to the ninth
embodiment, as in the light-emitting device D4 according to the
fifth embodiment, the light-emitting function layer 18 is
independently formed for each emission color of the light-emitting
elements U.
[0207] That is, as shown in FIG. 26, the light-emitting function
layers 18 (18r, 18g, and 18b) are each composed of a hole-injection
layer 41 disposed on the pixel electrode 16, a hole-transporting
layer 43 disposed on the hole-injection layer 41, a light-emitting
layer 45 (45r, 45g, or 45b) disposed on the hole-transporting layer
43, an electron-transporting layer 47 disposed on the
light-emitting layer 45, and an electron-injection layer 49
disposed on the electron-transporting layer 47.
[0208] The light-emitting function layer 18r of the light-emitting
element Ur contains the light-emitting layer 45r made of an organic
EL material that generates light of an R (red) wavelength range.
The light-emitting function layer 18g of the light-emitting element
Ug contains the light-emitting layer 45g made of an organic EL
material that generates light of a G (green) wavelength range. The
light-emitting function layer 18b of the light-emitting element Ub
contains the light-emitting layer 45b made of an organic EL
material that generates light of a B (blue) wavelength range.
[0209] In addition, as in the light-emitting device D4, in the
light-emitting device D8 according to the ninth embodiment, the
thicknesses of the hole-transporting layers 43 are controlled such
that the color of light emitted by each of the light-emitting
elements U (Ur, Ug, and Ub) is enhanced. The configurations of
other components are the same as those of the light-emitting device
D7 according to the eighth embodiment. That is, the
stress-absorbing layer 22 is made of Zn and has a 3 nm thickness.
Therefore, a description of each component is omitted.
[0210] In the light-emitting device D8 according to the ninth
embodiment, as in the light-emitting device D7 according to the
eighth embodiment, an opposite electrode 20 exhibiting enhanced
light-extracting efficiency during light emission is obtained by
providing a stress-absorbing layer 22 between the opposite
electrode 20 and the passivation layer 24. Furthermore, light
emission during black display is reduced by forming the
stress-absorbing layer 22 with Zn, which has a work function of 4.9
eV, resulting in enhancement of contrast. Therefore, the display
quality is further increased.
J: Tenth Embodiment
[0211] FIG. 28 is a cross-sectional view illustrating a structure
of a light-emitting device D9 according to a tenth embodiment of
the invention, and FIG. 29 is a plan view of the light-emitting
device D9.
[0212] As shown in FIG. 28, the light-emitting device D9 has a
configuration in which a plurality of light-emitting elements U
(Ur, Ug, and Ub) is arrayed on a surface of a first substrate 10.
Each light-emitting element U is an element generating light with a
wavelength corresponding to any of a plurality of colors (red,
green, and blue). In the tenth embodiment, the light-emitting
element Ur emits red light, the light-emitting element Ug emits
green light, and the light-emitting element Ub emits blue light.
The light-emitting device D9 according to the tenth embodiment is a
top emission type in which light generated by each light-emitting
element U is emitted toward the opposite side with respect to the
first substrate 10. Therefore, the first substrate 10 may be made
of an opaque plate-like material such as a ceramic or metal sheet,
as well as a light-transmissive plate-like material such as glass.
The first substrate 10 is provided with wiring (not shown) for
feeding power to the light-emitting elements U to emit light.
Furthermore, the first substrate 10 is provided with circuits (not
shown) for feeding power to the light-emitting elements U.
[0213] On the first substrate 10, a wall 12 (separator) is
provided. As shown in FIG. 29, the wall 12 is provided with
openings A at positions corresponding to the light-emitting
elements U and is thereby formed in a grid pattern. The wall 12 is
made of a transparent insulative material such as acryl or
polyimide. As described below, the plurality of light-emitting
elements U is separated by the grid patterned wall 12 and is
thereby arrayed in a matrix form.
[0214] As shown in FIG. 28, each of the plurality of light-emitting
elements U includes a pixel electrode 16, a light-emitting function
layer 18, and an opposite electrode 20. Furthermore, the
light-emitting device D9 according to the tenth embodiment and the
below-described light-emitting device D10 according to an eleventh
embodiment have a configuration in which the pixel electrode 16
includes a light-reflecting layer 14. That is, the pixel electrode
16 is configured of the light-reflecting layer 14 disposed on a
first substrate 10 and a transparent electrode 15 covering the
light-reflecting layer 14. The pixel electrodes 16 are disposed on
the first substrate 10 and are surrounded by the wall 12 in a plan
view.
[0215] The light-reflecting layers 14 are made of a metal material
having high reflectance, for example, a simple metal, such as
aluminum or silver, or an alloy whose main component is aluminum or
silver. In the tenth embodiment, the light-reflecting layers 14 are
made of a silver alloy available from Furuya Metal Co., Ltd. under
the trade name "APC" and have an 80 nm thickness. The transparent
electrodes 15 are made of a transparent, electrically conductive
oxide material, such as ITO, IZO, or ZnO.sub.2. In the tenth
embodiment, the transparent electrodes 15 are made of ITO and have
different thicknesses that correspond to the respective emission
colors of the light-emitting elements U. The details thereof will
be described below.
[0216] The light-emitting function layer 18 is formed so as to
cover each of the transparent electrodes 15 and the wall 12. That
is, the light-emitting function layer 18 continues over the
plurality of light-emitting elements U, and the characteristics of
the light-emitting function layer 18 are equally applied to the
plurality of light-emitting elements U. Though the details are not
shown in the drawing, the light-emitting function layer 18 is
composed of a hole-injection layer disposed on the transparent
electrodes 15, a hole-transporting layer disposed on the
hole-injection layer, a light-emitting layer disposed on the
hole-transporting layer, an electron-transporting layer disposed on
the light-emitting layer, and an electron-injection layer disposed
on the electron-transporting layer.
[0217] In the tenth embodiment, the hole-injection layer is made of
"HI-406", the trade name of Idemitsu Kosan Co., Ltd., and has a 40
nm thickness. The hole-transporting layer is made of "HT-320", the
trade name of Idemitsu Kosan Co., Ltd., and has a 15 nm thickness.
The hole-injection layer and the hole-transporting layer may be
formed of a single layer having both functions of the
hole-injection layer and the hole-transporting layer.
[0218] The light-emitting layer is made of an organic EL material
that emits light by recombining holes and electrons. In the tenth
embodiment, the organic EL material is a low molecular material and
emits white light. The host material of the light-emitting layer is
"BH-232", the trade name of Idemitsu Kosan Co., Ltd., and red,
green, and blue dopants are mixed with the host material. In the
tenth embodiment, "RD-001", "GD-206", and "BD-102", the trade names
of Idemitsu Kosan Co., Ltd., are used as the red, green, and blue
dopants, respectively. In the tenth embodiment, the thickness of
the light-emitting layer is 65 nm.
[0219] In the tenth embodiment, the electron-transporting layer is
made of Alq3 (tris(8-quinolinolato)aluminum complex) and has a 10
nm thickness. The electron-injection layer is made of LiF (lithium
fluoride) and has a 1 nm thickness. The electron-transporting layer
and the electron-injection layer may be formed of a single layer
having both functions of the electron-injection layer and the
electron-transporting layer.
[0220] The opposite electrode 20 is a cathode and is formed so as
to cover the light-emitting function layer 18. That is, the
opposite electrode 20 continues over the plurality of
light-emitting elements U. The opposite electrode 20 functions as a
semi-transparent reflective layer having a property that part of
light reaching the surface thereof is transmitted and the remaining
light is reflected (i,e., semi-transparent reflectivity) and is
formed of, for example, a single metal, such as magnesium or
silver, or an alloy whose main component is magnesium or silver. In
the tenth embodiment, the opposite electrode 20 is made of a
magnesium-silver alloy (MgAg) and has a 10 nm thickness.
[0221] The light-emitting function layer 138 and the opposite
electrode 20 are common to the plurality of light-emitting elements
U. However, since the individual pixel electrodes 16 are separated
from one another, when current flows between any of the pixel
electrodes 16 and the opposite electrode 20, the light-emitting
function layer 18 emits light only at a position where the
light-emitting function layer 18 overlaps that pixel electrode 16.
That is, the wall 12 separates the plurality of light-emitting
elements U, and a region surrounded by the wall 12, namely, the
region of the pixel electrode 16 can be called a zone of the
light-emitting element U.
[0222] In each light-emitting element U, a resonator structure that
resonates light emitted by the light-emitting function layer 18 is
formed between the light-reflecting layer 14 and the opposite
electrode 20. That is, the light emitted by the light-emitting
function layer 18 goes and returns between the light-reflecting
layer 14 and the opposite electrode 20, and light with a specific
wavelength is enhanced by resonance and passes through the opposite
electrode 20 to be emitted toward the observer side (upside in FIG.
28) (top emission).
[0223] The thicknesses of the transparent electrodes 15 in the
light-emitting elements U are controlled such that red color in the
white light emitted by the light-emitting function layer 18 is
enhanced in the light-emitting element Ur, green color is enhanced
in the light-emitting element Ug, and blue color is enhanced in the
light-emitting element Ub. More specifically, in the tenth
embodiment, the transparent electrode 15 of the light-emitting
element Ur has a 110 nm thickness, the transparent electrode 15 of
the light-emitting element Ug has a 70 nm thickness, and the
transparent electrode 15 of the light-emitting element Ub has a 27
nm thickness.
[0224] As shown in FIG. 28, a stress-absorbing layer 22 is
partially disposed on the opposite electrode 20 for easing the
concentration of stress to the opposite electrode 20. The
stress-absorbing layer 22 has light transmittance and moisture
resistance and is made of a material that is softer than those of
the opposite electrode 20 and the below-described passivation layer
24. Preferred examples of the material of the stress-absorbing
layer 22 include lithium fluoride (LiF), lithium oxide (LiO.sub.2),
sodium fluoride (NaF), calcium fluoride (CaF.sub.2), calcium oxide
(CaO), magnesium fluoride (MgF.sub.2), magnesium oxide (MgO), and
polytetrafluoroethylene. In the tenth embodiment, the
stress-absorbing layer 22 is made of lithium fluoride (LiF), which
is the same material as that of the electron-injection layer, and
has a 45 nm thickness.
[0225] In the tenth embodiment, the stress-absorbing layer 22
covers the opposite electrode 20 at at least part of a region where
the opposite electrode 20 overlaps the wall 12, but does not cover
the opposite electrode 20 at at least part a region where the
opposite electrode 20 overlaps the light-emitting function layer 18
in the zone of a light-emitting element U separated by the wall 12.
More specifically, the configuration is as follows. In FIG. 29, the
shaded portion is the stress-absorbing layer 22. As shown in FIG.
29, the stress-absorbing layer 22 is provided with a plurality of
openings B that correspond to the respective zones (regions
surrounded by the openings A) of the light-emitting elements U
separated by the wall 12.
[0226] As shown in FIG. 29, each opening B is located at a central
area of the zone of each light-emitting element U separated by the
wall 12 [(the opening space of the opening B)<(the opening space
of the opening A)]. That is, the stress-absorbing layer 22 covers
the opposite electrode 20 at a region where the opposite electrode
20 overlaps the wall 12 and at a region in the zone (including the
peripheral region) of each light-emitting element U separated by
the wall 12 other than the central area of the zone, but does not
cover the opposite electrode 20 at the central area in the zone of
each light-emitting element U separated by the wall 12. The regions
of the opposite electrode 20 not being covered by the
stress-absorbing layer 22 are the openings B in FIG. 29.
[0227] As shown in FIG. 28, a passivation layer 24 is disposed on
the stress-absorbing layer 22. The passivation layer 24 is a
protection layer for preventing infiltration of water and the air
into the light-emitting elements U and is made of an inorganic
material having a low gas transmittance, such as SiN (silicon
nitride), SiON (silicon oxynitride), or SiO(silicon oxide). In the
tenth embodiment, the passivation layer 24 is made of SiON and has
a 225 nm thickness.
[0228] As shown in FIG. 28, in the tenth embodiment, a second
substrate 30 is disposed so as to face the plurality of
light-emitting elements U disposed on the first substrate 10. The
second substrate 30 is made of a light transmissive material such
as glass and is provided with color filters 32 and a
light-shielding film 34 on the surface facing the first substrate
10. The light-shielding film 34 is a film having a light-shielding
property and is provided with openings 36 at positions
corresponding to the respective light-emitting elements U. The
color filters 32 are disposed in the openings 36.
[0229] In the tenth embodiment, a red color filter 32r that
selectively transmits red light is disposed in the opening 36
corresponding to the light-emitting element Ur, a green color
filter 32g that selectively transmits green light is disposed in
the opening 36 corresponding to the light-emitting element Ug, and
a blue color filter 32b that selectively transmits blue light is
disposed in the opening 36 corresponding to the light-emitting
element Ub.
[0230] The second substrate 30 provided with the color filters 32
and the light-shielding film 34 is bonded to the first substrate 10
via a sealing layer 26. The sealing layer 26 is made of a
transparent resin material, for example, a hardening resin such as
an epoxy resin.
[0231] As described above, in the tenth embodiment, the
stress-absorbing layer 22 partially covers the opposite electrode
20 for easing the concentration of stress to the opposite electrode
20. The stress-absorbing layer 22 is made of a material that is
softer than those of the opposite electrode 20 and the passivation
layer 24, and the load of the passivation layer 24 is dispersed to
the stress-absorbing layer 22. Consequently, the opposite electrode
20 can be prevented from being broken due to the concentration of
stress, compared to a configuration in which only the passivation
layer 24 is disposed on the opposite electrode 20 without providing
the stress-absorbing layer 22. Therefore, this has an advantage
that a decrease in electrical conductivity of the light-emitting
elements U can be inhibited.
[0232] FIG. 30 is a cross-sectional view of a light-emitting device
(hereinafter, referred to as comparative example 1) having a
configuration in which the entire opposite electrode 20 is covered
by a stress-absorbing layer 22. In the comparative example 1, since
the stress-absorbing layer 22 covers the opposite electrode 20 at a
region where the opposite electrode 20 overlaps the light-emitting
function layer 18 in the zone of each light-emitting element U
separated by a wall 12, the amount of light passing through the
opposite electrode 20 and the stress-absorbing layer 22 and
traveling toward the observer side from the light-emitting function
layer 18 is smaller than that in a configuration in which the
stress-absorbing layer 22 does not cover the opposite electrode 20.
Therefore, the amount of light emitted from the light-emitting
device toward the observer side may be insufficiently ensured.
[0233] On the other hand, in the tenth embodiment, the
stress-absorbing layer 22 on the opposite electrode 20 is provided
with the plurality of openings B at positions that correspond to
the central areas of the zones of the light-emitting elements U
separated by the wall 12. Therefore, the loss of light emitted by
the light-emitting function layer 18 and passing through the
openings B is smaller than that of light passing through the
stress-absorbing layer 22, and a greater amount of emission light
can be extracted to the observer side, compared to the case in
which the stress-absorbing layer 22 is formed over the entire
opposite electrode 20. Therefore, according to the tenth
embodiment, there is an advantage that the amount of light emitted
from the light-emitting device D9 toward the observer side can be
ensured compared to that in comparative example 1.
[0234] Incidentally, when unevenness is formed between a region
where the opposite electrode 20 overlaps the wall 12 and a region
of the opposite electrode 20 in the zone of each light-emitting
element U separated by the wall 12, asperities arising from the
unevenness occur on the opposite electrode 20. In such a case,
there is a high possibility that stress is excessively concentrated
on the opposite electrode 20 at a region where the opposite
electrode 20 overlaps the peripheral region of the zone of each
light-emitting element U separated by the wall 12.
[0235] In the tenth embodiment, the stress-absorbing layer 22
covers the opposite electrode 20 at the peripheral region of the
zone of each light-emitting element U separated by the wall 12.
Therefore, according to the tenth embodiment, even if unevenness is
formed between a region where the opposite electrode 20 overlaps
the wall 12 and the peripheral region of the zone of each
light-emitting element U separated by the wall 12, excessive
concentration of stress to the opposite electrode 20 at the
peripheral region of the zone of each light-emitting element U
separated by the wall 12 can be inhibited. Consequently, the
opposite electrode 20 can be prevented from being broken. In
addition, in the tenth embodiment, the opposite electrode 20 is not
covered by the stress-absorbing layer 22 at the central area of the
zone of each light-emitting element U separated by the wall 12.
Therefore, according to the tenth embodiment, there is an advantage
that the amount of light emitted from the light-emitting device D9
toward the observer side can be ensured, while preventing the
opposite electrode 20 from being broken by excessive concentration
of stress to the opposite electrode 20.
K: Eleventh Embodiment
[0236] FIG. 31 is a cross-sectional view of a light-emitting device
D10 according to an eleventh embodiment of the invention. FIG. 32
is a plan view of the light-emitting device D10 according to the
eleventh embodiment. In the light-emitting device D10 according to
the eleventh embodiment, an auxiliary electrode 40 is disposed on
the opposite electrode 20 for reducing the resistance of the
opposite electrode 20. As shown in FIGS. 31 and 32, the auxiliary
electrode 40 is formed in a grid pattern on the opposite electrode
20 at a region where the opposite electrode 20 overlaps the wall
12. The auxiliary electrode 40 is made of a metal material that is
excellent in electrical conductivity, such as aluminum, gold, or
silver.
[0237] In the light-emitting device D10 according to the eleventh
embodiment, the stress-absorbing layer 22 completely covers the
opposite electrode 20 at a region where the opposite electrode 20
overlaps the light-emitting function layer 18 in the zone of each
light-emitting element U separated by the wall 12, but does not
cover the auxiliary electrode 40. In these points, the
light-emitting device D10 is different from the light-emitting
device D9 according to the tenth embodiment. Since the other
configuration is the same as that of the light-emitting device D9
of the tenth embodiment, the description thereof is omitted.
[0238] FIG. 33 is a cross-sectional view of a light-emitting device
(hereinafter, referred to as comparative example 2) having a
configuration in which a stress-absorbing layer 22 covers an
opposite electrode 20 in a region where the opposite electrode 20
overlaps a light-emitting function layer 18 in the zone of each
light-emitting element U separated by a wall 12 and also covers an
auxiliary electrode 40. The light-emitting device of the
comparative example 2 is produced by a process including (1)
depositing an opposite electrode 20 on the light-emitting function
layer 18 in the zone of each light-emitting element U separated by
the wall 12 and on the wall 12, inside a deposition chamber, (2)
taking out the first substrate 10 deposited with the opposite
electrode 20 from the deposition chamber and then forming an
auxiliary electrode 40 on the opposite electrode 20 at a region
where the opposite electrode 20 overlaps the wall 12, and (3)
putting the first substrate 10 in the deposition chamber again and
depositing a stress-absorbing layer 22 on the opposite electrode 20
at a region where the opposite electrode 20 overlaps the
light-emitting function layer 18 in the zone of each light-emitting
element U separated by the wall 12 and on the auxiliary electrode
40.
[0239] On the other hand, in the eleventh embodiment, the
light-emitting device D10 is produced by a process including (1)
depositing an opposite electrode 20 on a light-emitting function
layer 18 in each zone separated by a wall 12 and on the wall 12,
inside a deposition chamber, (2) subsequently, inside the
deposition chamber, depositing a stress-absorbing layer 22 on the
opposite electrode 20 at a region where the opposite electrode 20
overlaps the light-emitting function layer 18 in the zone of each
light-emitting element U separated by the wall 12, and (3) taking
out the first substrate 10 deposited with the opposite electrode 20
and the stress-absorbing layer 22 from the deposition chamber and
then forming an auxiliary electrode 40 on the opposite electrode 20
at a region where the opposite electrode 20 overlaps the wall 12.
That is, in the eleventh embodiment, since the opposite electrode
20 and the stress-absorbing layer 22 are formed by a continuous
deposition process, there is an advantage that the manufacturing
time is reduced, compared to the comparative example 2.
L: Modification
[0240] Embodiments of the invention are not limited to the
above-described embodiments, and, for example, the following
modifications are possible. In addition, a combination of two or
more of the following modifications is possible.
(1) Modification 1
[0241] In the above-described embodiments, a low molecular material
is used as the organic EL material forming the light-emitting layer
of the light-emitting function layer 18. However, the organic EL
material forming the light-emitting layer may be a high molecular
material. In such a case, the light-emitting layer is formed by ink
jetting or spin coating in the space separated by the wall 12,
i.e., in the recess defined by the pixel electrode 16 as a bottom
and the wall 12 as a side wall.
(2) Modification 2
[0242] In the light-emitting devices (D1 to D10) according to the
above-described embodiments, color filters 32 are provided on the
light-emitting side for raising the purity (color purity) of light
to be emitted. However, the configuration is not limited to such a
configuration, and, for example, the color filters 32 may not be
provided.
[0243] Light with high purity can be emitted from each of the three
kinds of light-emitting elements (Ur, Ug, and Ub), without using
the color filters 32, by independently providing a light-emitting
function layer 18 for each emission color of the light-emitting
elements U, as in the light-emitting device D2 of the third
embodiment shown in FIG. 12 or the light-emitting device D4 of the
fifth embodiment shown in FIG. 22.
[0244] FIG. 34 shows a light-emitting device of a modification. The
light-emitting device has a configuration similar to that of the
light-emitting device D9 according to the tenth embodiment, and the
light-emitting function layer 18 is independently provided to each
emission color of the light-emitting elements U. That is, the pixel
electrodes 16 are each composed of a light-reflecting layer 14
disposed on a first substrate 10 and a transparent electrode 15
covering the light-reflecting layer 14. Furthermore, a
light-emitting function layer 18r is formed in the light-emitting
element Ur, a light-emitting function layer 18g is formed in the
light-emitting element Ug, and a light-emitting function layer 18b
is formed in the light-emitting element Ub. Each zone of the
light-emitting elements U is also provided with an opening B.
Therefore, light with high purity can be generated by each of the
three kinds of light-emitting elements (Ur, Ug, and Ub), without
using the color filters 32, and the light with high purity can be
sufficiently emitted toward the observer side through the opening
B.
(3) Modification 3
[0245] In each embodiment above, the opposite electrode 20 is a
cathode of the light-emitting elements U, but may be an anode.
(4) Modification 4
[0246] In the light-emitting device D9 according to the tenth
embodiment, the opposite electrode 20 is not covered by the
stress-absorbing layer 22 at a region that corresponds to the
central area of the zone of each light-emitting element U separated
by the wall 12, but the configuration is not limited thereto. The
opposite electrode 20 may not be covered by the stress-absorbing
layer 22 at the entire area corresponding to the zone of each
light-emitting element U.
[0247] In the light-emitting device D9 according to the tenth
embodiment, the opposite electrode 20 is completely covered by the
stress-absorbing layer 22 at a region where the opposite electrode
20 overlaps the wall 12, but the configuration is not limited
thereto. For example, the opposite electrode 20 may be covered by
the stress-absorbing layer 22 only at part of a region where the
opposite electrode 20 overlaps the wall 12. In other words, any
configuration can be employed, as long as the opposite electrode 20
is covered by the stress-absorbing layer 22 at at least part of the
region where the opposite electrode 20 overlaps the wall 12.
(5) Modification 5
[0248] In the light-emitting device D10 according to the eleventh
embodiment, the opposite electrode 20 is completely covered by the
stress-absorbing layer 22 at a region that corresponds to the zone
of each light-emitting element U, but the configuration is not
limited thereto. For example, the opposite electrode 20 may not be
covered by the stress-absorbing layer 22 at a region that
corresponds to the central area of the zone of each light-emitting
element U. In other words, any configuration can be employed, as
long as the opposite electrode 20 is covered by the
stress-absorbing layer 22 at at least part of the region that
corresponds to the zone of each light-emitting element U, but the
auxiliary electrode 40 is not covered by the stress-absorbing layer
22.
[0249] In the configuration in which the opposite electrode 20 is
not covered by the stress-absorbing layer 22 at part of the region
corresponding to the zone of each light-emitting element U, as in
the light-emitting device D9 according to the tenth embodiment,
there is an advantage that the amount of light emitted from the
light-emitting device toward the observer side can be ensured
compared to that in comparative example 1. That is, if a region
where stress is concentrated can be determined in advance, it is
preferred to selectively form a stress-absorbing layer 22 at the
stress-concentrating region. The stress-concentrating region
corresponds to the region where unevenness due to the wall 12 is
formed. In particular, when the shape of each light-emitting
element U is a rectangle, stress is concentrated at each corner of
the light-emitting element.
M: Applications
[0250] Electronic equipment utilizing the light-emitting device
according to the invention will now be described. FIG. 35 is a
perspective view illustrating a configuration of a mobile personal
computer whose display is the light-emitting device D1 according to
the first embodiment. The personal computer 2000 includes a display
of the light-emitting device D1 and a body 2010. The body 2010 is
provided with a power switch 2001 and a keyboard 2002. Since the
light-emitting device D1 employs OLED elements having both high
electrical conductivity and high transparency, a high quality image
can be displayed. Furthermore, the display in the configuration
shown in FIG. 35 may be any of the light-emitting devices (D2 to
D10) according to the other embodiments.
[0251] FIG. 36 shows a configuration of a mobile phone to which the
light-emitting device D1 according to the first embodiment is
applied. The mobile phone 3000 includes a plurality of operation
buttons 3001, a scroll button 3002, and a display of the
light-emitting device D1. The image displayed on the light-emitting
device D1 is scrolled by operating the scroll button 3002.
Furthermore, the display in the configuration shown in FIG. 36 may
be any of the light-emitting devices (D2 to D10) according to the
other embodiments.
[0252] FIG. 37 shows a configuration of a handheld terminal (PDA:
personal digital assistant) to which the light-emitting device D1
according to the first embodiment is applied. The handheld terminal
4000 includes a plurality of operation buttons 4001, a power switch
4002, and a display of the light-emitting device D1. Various types
of information, such as addresses and schedules, are displayed on
the light-emitting device D1 by operating the power switch 4002.
Furthermore, the display in the configuration shown in FIG. 37 may
be any of the light-emitting devices (D2 to D10) according to the
other embodiments.
[0253] Examples of the electronic equipment to which the
light-emitting device according to the invention is applied
include, in addition to those shown in FIGS. 35 to 37, a digital
still camera, a TV set, a video camera, a car navigation system, a
pager, an electronic notebook, electronic paper, a calculator, a
word processor, a workstation, a videophone, a POS terminal, a
printer, a scanner, a photocopier, a video player, and equipment
having a touch panel.
[0254] The entire disclosure of Japanese Patent Application No.
2008-219266, filed Aug. 28, 2008, No. 2008-291997, filed Nov. 14,
2008, No. 2009-158522, filed Jul. 3, 2009, and No. 2008-291998
filed Nov. 14, 2008 are expressly incorporated by reference
herein.
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