U.S. patent application number 12/289568 was filed with the patent office on 2009-03-12 for electroluminescent device.
This patent application is currently assigned to MITSUBISHI CHEMICAL CORPORATION. Invention is credited to Shinji ARAMAKI, Tetsuya AYA, Keishin HANDA.
Application Number | 20090066219 12/289568 |
Document ID | / |
Family ID | 33136114 |
Filed Date | 2009-03-12 |
United States Patent
Application |
20090066219 |
Kind Code |
A1 |
HANDA; Keishin ; et
al. |
March 12, 2009 |
Electroluminescent device
Abstract
The electroluminescent device successively comprises a cathode,
an electroluminescent layer, a transparent electrode layer, an
evanescent light-scattering layer comprising a matrix composed of a
low-refractive material containing light-scattering particles, and
a transparent sheet/plate. Such an electroluminescent device is
decreased in total reflection not only at a boundary surface
between a transparent substrate and an outside air layer but also
at a boundary surface of the transparent electrode layer on its
light extraction side, and therefore, is considerably improved in
light extraction efficiency. In addition, in the electroluminescent
device provided with a barrier layer, the transparent electrode
layer and the electroluminescent layer can be well protected so
that deterioration of electroluminescent pigments and occurrence of
dark spots can be effectively prevented, resulting in enhanced life
of the device.
Inventors: |
HANDA; Keishin;
(Yokkaichi-shi, JP) ; ARAMAKI; Shinji;
(Yokkaichi-shi, JP) ; AYA; Tetsuya;
(Yokkaichi-shi, JP) |
Correspondence
Address: |
NIXON & VANDERHYE, PC
901 NORTH GLEBE ROAD, 11TH FLOOR
ARLINGTON
VA
22203
US
|
Assignee: |
MITSUBISHI CHEMICAL
CORPORATION
Tokyo
JP
|
Family ID: |
33136114 |
Appl. No.: |
12/289568 |
Filed: |
October 30, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11220912 |
Sep 8, 2005 |
7462984 |
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12289568 |
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PCT/JP2004/003159 |
Mar 11, 2004 |
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11220912 |
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Current U.S.
Class: |
313/503 ;
313/506 |
Current CPC
Class: |
H01L 51/5268 20130101;
H01L 51/5253 20130101; H01L 51/524 20130101 |
Class at
Publication: |
313/503 ;
313/506 |
International
Class: |
H05B 33/00 20060101
H05B033/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 12, 2003 |
JP |
2003-066845 |
Mar 12, 2003 |
JP |
2003-066846 |
Mar 18, 2003 |
JP |
2003-073943 |
Apr 17, 2003 |
JP |
2003-113055 |
Claims
1.-2. (canceled)
3. An electroluminescent device successively comprising a cathode,
an electroluminescent layer, a transparent electrode layer and a
transparent sheet/plate, wherein an evanescent light-scattering
layer (A) comprising a matrix composed of a low-refractive material
containing light-scattering particles is provided between the
transparent electrode layer and the transparent sheet/plate, and a
barrier layer is provided between the evanescent light-scattering
layer (A) and the transparent electrode layer to prevent a material
within the evanescent light-scattering layer (A) from being
transferred into the transparent electrode layer.
4. An electroluminescent device successively comprising a cathode,
an electroluminescent layer, a transparent electrode layer and a
transparent sheet/plate, wherein an evanescent light-scattering
layer (A) comprising a matrix composed of a low-refractive material
containing light-scattering particles is provided between the
transparent electrode layer and the transparent sheet/plate, a
barrier layer is provided between the evanescent light-scattering
layer (A) and the transparent electrode layer to prevent a material
within the evanescent light-scattering layer (A) from being
transferred into the transparent electrode layer, and the matrix
constituting the evanescent light-scattering layer (A) has a
refractive index which is substantially identical to that of the
transparent sheet/plate and lower than that of the transparent
electrode layer.
5. An electroluminescent device according to claims 3 or 4, wherein
the evanescent light-scattering layer (A) contains the
light-scattering particles in an amount of 1 to 40% by volume, and
not less than 60% by weight of the light-scattering particles have
a particle size of 20 to 400 nm.
6. An electroluminescent device according to claims 3 or 4, wherein
a thickness of the evanescent light-scattering layer (A) is not
less than 2 times an average particle size of the light-scattering
particles.
7. An electroluminescent device according to claims 3 or 4, wherein
not less one-third by weight of the light-scattering particles are
present within a region extending at a distance of 600 nm or less
from a boundary surface between the transparent electrode layer and
the barrier layer.
8. An electroluminescent device according to claims 3 or 4, wherein
the light-scattering particles are composed of silica, colloidal
silica, titania, zirconia, ITO (indium tin oxide), ATO (antimony
tin oxide) or alumina.
9. An electroluminescent device according to claim 3 or 4, wherein
the barrier layer has a refractive index which is substantially
identical to or higher than that of the transparent electrode
layer.
10. An electroluminescent device according to claim 3 or 4, wherein
the barrier layer has a thickness of 50 to 400 nm.
11. An electroluminescent device according to claim 3 or 4, wherein
the barrier layer has a thickness of 100 to 200 nm.
12.-21. (canceled)
22. An electroluminescent device according to claim 1, wherein the
transparent sheet/plate is a transparent substrate.
23. An electroluminescent device according to claim 1, wherein the
cathode is formed on a transparent substrate, and the transparent
sheet/plate is a protective cover.
Description
TECHNICAL FIELD
[0001] The present invention relates to electroluminescent (EL)
devices, and more particularly to electroluminescent devices
capable of extracting light from an electroluminescent layer
thereof at a high efficiency.
BACKGROUND ART
[0002] Conventional electroluminescent devices used in EL displays
or EL illumination apparatuses have a layer structure including a
cathode, an electroluminescent layer, a transparent electrode
(anode) and a transparent substrate. These electroluminescent
devices are operated by utilizing such a light emission principle
that holes injected from the anode and electrons injected from the
cathode are recombined with each other in the electroluminescent
layer, so that an emission center therein is excited by the
recombination energy to emit a light therefrom.
[0003] In the EL displays, although it is required to efficiently
extract the emitted light on a side of the transparent substrate,
the light extraction efficiency (which means a percentage of light
extracted outside from the device to that generated in the
electroluminescent layer) on the side of the transparent substrate
is as low as about 20% owing to reflection of the emitted light at
a boundary surface between the transparent substrate and an outside
air layer.
[0004] In order to decrease reflection of light at the boundary
between the transparent substrate and the air layer, there has been
proposed a method of disposing a low-refractive layer between the
transparent substrate and the transparent electrode layer to
refract light having a large incident angle to substrate from
transparent electrode, thereby enhancing the light extraction
efficiency (Japanese Patent Application Laid-Open (KOKAI) No.
2002-278477).
[0005] In the above conventional method, the reflection of light at
the boundary surface between the transparent substrate and the air
layer is prevented by providing the low-refractive layer. However,
this method has failed to take account of reflection of light at a
boundary surface between the transparent electrode layer and the
low-refractive layer. Rather, in the method, there tends to be
caused such a problem that the provision of the low-refractive
layer promotes total reflection of light at the boundary between
the transparent electrode layer and the low-refractive layer. The
total reflection light thus produced is attenuated upon light guide
due to reflection caused inside of the transparent electrode layer
and the light-emitting layer as well as at the cathode, and,
therefore, cannot be extracted outside from the device.
[0006] The present invention has been conducted to overcome the
above conventional problems. An object of the present invention is
to provide an electroluminescent device in which the total
reflection not only at a boundary surface between a transparent
substrate and an outside air layer but also at a boundary surface
of a transparent electrode layer on its light extraction side is
decreased, and which is fully improved light extraction
efficiency.
DISCLOSURE OF THE INVENTION
[0007] The above object of the present invention can be
accomplished by the following embodiments (1) to (8).
[0008] (1) In a first aspect of the first invention, there is
provided an electroluminescent device successively comprising a
cathode, an electroluminescent layer, a transparent electrode layer
and a transparent sheet/plate, wherein an evanescent
light-scattering layer (A) comprising a matrix composed of a
low-refractive material containing light-scattering particles is
provided between the transparent electrode layer and the
transparent sheet/plate.
[0009] (2) In a second aspect of the first invention, there is
provided an electroluminescent device successively comprising a
cathode, an electroluminescent layer, a transparent electrode
layer, a low refractive layer and a transparent sheet/plate,
wherein an evanescent light-scattering layer (A) comprising a
matrix composed of a low-refractive material containing
light-scattering particles is provided between the transparent
electrode layer and the low-refractive layer, and the matrix
constituting the evanescent light-scattering layer (A) has a
refractive index which is substantially identical to that of the
low-refractive layer and is lower than that of the transparent
electrode layer.
[0010] (3) In a first aspect of the second invention, there is
provided an electroluminescent device successively comprising a
cathode, an electroluminescent layer, a transparent electrode layer
and a transparent sheet/plate, wherein an evanescent
light-scattering layer (A) comprising a matrix composed of a
low-refractive material containing light-scattering particles is
provided between the transparent electrode layer and the
transparent sheet/plate, and a barrier layer is provided between
the evanescent light-scattering layer (A) and the transparent
electrode layer to prevent a material within the evanescent
light-scattering layer (A) from being transferred into the
transparent electrode layer.
[0011] The barrier layer having a refractive index substantially
identical to or higher than that of the transparent electrode layer
as well as a light absorption in a visible range lower than that of
the transparent electrode layer, causes a part of guided light in
the transparent electrode layer to be transferred thereinto, and
prevents attenuation of light upon light guide. Therefore, it is
also expected to attain such an effect of further improving the
light extraction efficiency.
[0012] (4) In a second aspect of the second invention, there is
provided an electroluminescent device successively comprising a
cathode, an electroluminescent layer, a transparent electrode
layer, a low-refractive layer and a transparent sheet/plate,
wherein an evanescent light-scattering layer (A) comprising a
matrix composed of a low-refractive material containing
light-scattering particles is provided between the transparent
electrode layer and the low-refractive layer; a barrier layer is
provided between the evanescent light-scattering layer (A) and the
transparent electrode layer to prevent a material within the
low-refractive layer from being transferred into the transparent
electrode layer; and the matrix constituting the evanescent
light-scattering layer (A) has a refractive index which is
substantially identical to that of the low-refractive layer and is
lower than that of the transparent electrode layer.
[0013] (5) In a first aspect of the third invention, there is
provided an electroluminescent device successively comprising a
cathode, an electroluminescent layer, a transparent electrode
layer, a low-refractive layer and a transparent sheet/plate,
wherein the transparent electrode layer contains light-scattering
particles.
[0014] (6) In a second aspect of the third invention, there is
provided an electroluminescent device successively comprising a
cathode, an electroluminescent layer, a transparent electrode
layer, a low-refractive layer and a transparent sheet/plate,
wherein an evanescent light-scattering layer (B) which contains
light-scattering particles, is provided between the transparent
electrode layer and the transparent sheet/plate, and a matrix
constituting the evanescent light-scattering layer (B) has a
refractive index which is substantially identical to that of the
transparent electrode layer.
[0015] (7) In a first aspect of the fourth invention, there is
provided an electroluminescent device successively comprising a
cathode, an electroluminescent layer, a transparent electrode
layer, a low-refractive layer and a transparent sheet/plate,
wherein a boundary surface between the transparent electrode layer
and the transparent sheet/plate is provided with light-scattering
roughness.
[0016] (8) In a second aspect of the fourth invention, there is
provided an electroluminescent device successively comprising a
cathode, an electroluminescent layer, a transparent electrode
layer, a low-refractive layer and a transparent sheet/plate,
wherein a high-refractive layer having a refractive index
substantially identical to that of the transparent electrode layer
is provided between the transparent electrode layer and the
transparent sheet/plate, and a boundary surface between the
high-refractive layer and the transparent sheet/plate is provided
with light-scattering roughness.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1(a) is an explanatory view showing a layer structure
of an electroluminescent device according to the first invention,
and FIG. 1(b) is an explanatory view of total reflection of light
having a large incident angle to substrate from transparent
electrode.
[0018] FIG. 2 is an explanatory view showing another layer
structure of an electroluminescent device according to the first
invention.
[0019] FIG. 3 is an explanatory view showing the other layer
structure of an electroluminescent device according to the first
invention.
[0020] FIG. 4 is an explanatory view showing a layer structure of
an electroluminescent device according to the second invention.
[0021] FIG. 5 is an explanatory view showing another layer
structure of an electroluminescent device according to the second
invention.
[0022] FIG. 6 is an explanatory view showing the other layer
structure of an electroluminescent device according to the second
invention.
[0023] FIG. 7 is an explanatory view showing a layer structure of
an electroluminescent device according to the third invention.
[0024] FIG. 8 is an explanatory view showing another layer
structure of an electroluminescent device according to the third
invention.
[0025] FIG. 9 is an explanatory view showing the other layer
structure of an electroluminescent device according to the third
invention.
[0026] FIG. 10 is an explanatory view showing a layer structure of
an electroluminescent device according to the fourth invention.
[0027] FIG. 11 is an explanatory view showing another layer
structure of an electroluminescent device according to the fourth
invention.
[0028] FIG. 12 is an explanatory view showing the other layer
structure of an electroluminescent device according to the fourth
invention.
[0029] FIG. 13(a) is an explanatory view showing a layer structure
of a conventional electroluminescent device, and FIG. 13(b) is an
explanatory view of total reflection of light having a large
incident angle to substrate from transparent electrode.
[0030] FIG. 14 is an explanatory view showing another layer
structure of the conventional electroluminescent device.
PREFERRED EMBODIMENT FOR CARRYING OUT THE INVENTION
[0031] The present invention is described in detail below.
[0032] In advance of explaining the present invention, the
conventional electroluminescent device is described by referring to
FIG. 13(a), FIG. 13(b) and FIG. 14. FIG. 13(a) is an explanatory
view showing a layer structure of the conventional
electroluminescent device, and FIG. 13(b) is an explanatory view of
total reflection of light having a large incident angle to
substrate from transparent electrode. FIG. 14 is an explanatory
view showing another layer structure of the conventional
electroluminescent device.
[0033] As shown in FIG. 13(a), the conventional electroluminescent
device has a layer structure including at least a substrate 5, a
transparent electrode layer (anode) 3, an electroluminescent layer
2 and a cathode 1. In electroluminescent devices, it is required to
efficiently extract light emitted in the electroluminescent layer 2
on the side of the transparent substrate 5. However, as shown in
FIG. 13(b), the light 11 emitted in the electroluminescent layer 2
which has a large incident angle to substrate from transparent
electrode undergoes total reflection at a boundary surface between
the substrate 5 and air 7, and is mainly converted into a guided
light 12 which proceeds inside of the substrate 5 while undergoing
total reflection in the plane direction. Due to generation of the
guided light 12, the light extraction efficiency from the substrate
5 tends to be decreased to about 20%.
[0034] To solve the above problem, the electroluminescent device as
shown in FIG. 14 is provided on the surface of the substrate 5
facing the side of the electroluminescent layer 2, with a
low-refractive layer 4. Therefore, the light 11 having a large
incident angle to substrate from transparent electrode is refracted
at the low-refractive layer 4, so that generation of guided light
is prevented, resulting in enhanced light extraction efficiency. In
such an electroluminescent device, although the total reflection at
the boundary surface between the substrate 5 and the air layer 7 is
decreased, light reflection at a boundary surface between the
transparent electrode layer 3 and the low-refractive layer 4 is
increased.
[0035] Further, the total reflection light is attenuated upon being
guided by reflection inside of the transparent electrode layer or
light emitting layer as well as reflection on the cathode, and
cannot be extracted outside from the device (reference literatures:
Chu Chinan, et al., the preliminary report of "Spring Meeting of
Institute of Allied Physics", 2003, 27P-A-16, and Fujita, et al.,
the preliminary report of "Spring Meeting of Institute of Allied
Physics", 2003, 29-YN-13).
[0036] To solve the above conventional problems, in the
electroluminescent device of the present invention, light
reflection at a boundary surface of the transparent electrode layer
3 opposite to the electroluminescent layer 2 (namely, on a side of
the transparent electrode layer 3 opposite to its surface
contacting with the electroluminescent layer 2) can be
decreased.
[0037] First, basic layers constituting the electroluminescent
device of the present invention include a substrate, a cathode, an
electroluminescent layer, a transparent electrode layer, a
low-refractive layer (which may not be provided), a substrate or
protective cover as a transparent sheet/plate, etc.
[0038] First, the cathode, electroluminescent layer, transparent
electrode layer, low-refractive layer, substrate and protective
cover, etc., which are used in the present invention, are
explained.
(A) Cathode:
[0039] The cathode is disposed in an opposed relation to the
transparent electrode layer such that the electroluminescent layer
is sandwiched between the cathode and the transparent electrode
layer. The cathode is composed of aluminum, tin, magnesium, indium,
calcium, gold, silver, copper, nickel, chromium, palladium,
platinum, magnesium-silver alloys, magnesium-indium alloys,
aluminum-lithium alloys, etc. In particular, among these cathodes,
preferred is a cathode composed of aluminum. The thickness of the
cathode is usually 10 to 1000 nm, preferably 30 to 500 nm, more
preferably 50 to 300 nm. The cathode may be produced by a vacuum
film-forming process such as vapor deposition and sputtering.
(B) Electroluminescent Layer:
[0040] The electroluminescent layer is composed of a material
exhibiting a light emission phenomenon upon applying an electric
field thereto. As the material of the electroluminescent layer,
there may be used conventionally used inorganic EL materials such
as activated zinc oxide represented by the formula: ZnS:X (wherein
X is an activating element such as Mn, Tb, Cu and Sm), CaS:Eu,
SrS:Ce, SrGa.sub.2S.sub.4:Ce, CaGa.sub.2S.sub.4:Ce, CaS:Pb and
BaAl.sub.2S.sub.4:Eu; and conventionally used organic EL materials
such as low-molecular pigment-based organic EL materials such as
aluminum complexes of 8-hydroxyquinoline, aromatic amines and
anthracene single crystals; and conjugated polymer-based organic EL
materials such as poly(p-phenylenevinylene),
poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene],
poly(3-alkylthiophene) and polyvinyl carbazole. The thickness of
the electroluminescent layer is usually 10 to 1000 nm, preferably
30 to 500 nm, more preferably 50 to 200 nm. The electroluminescent
layer may be produced by a vacuum film-forming process such as
vapor deposition and sputtering, or a coating process using
chloroform, etc., as a solvent.
(C) Transparent Electrode Layer 3:
[0041] The transparent electrode layer has a function as an anode
for the electroluminescent device. As the material of the
transparent electrode layer, there may be used thin films composed
of composite oxides such as tin-added indium oxide (generally
called "ITO"), aluminum-added zinc oxide (generally called "AZO")
and indium-added zinc oxide (generally called "IZO"). Among these
materials, preferred is ITO.
[0042] The transparent electrode layer may be produced by a vacuum
film-forming process such as vapor deposition and sputtering. The
thus formed transparent electrode preferably has a light
transmittance in visible light range as large as possible, for
example, usually 50 to 99%. The lower limit of the light
transmittance of the transparent electrode layer is preferably 60%,
more preferably 70%. The electric resistance of the transparent
electrode is preferably as small as possible calculated as a sheet
resistivity value thereof, preferably 1 to 100.OMEGA./.quadrature.
(=1 cm.sup.2). The upper limit of the sheet resistivity value of
the transparent electrode is usually 70.OMEGA./.quadrature., more
preferably 50.OMEGA./.quadrature.. Also, the thickness of the
transparent electrode is not particularly limited as long as the
light transmittance and sheet resistivity value thereof satisfy the
above specified ranges, and usually 0.01 to 10 .mu.m. From the
standpoint of a good conductivity, the lower limit of the thickness
of the transparent electrode is preferably 0.03 .mu.m, more
preferably 0.05 .mu.m. On the other hand, from the standpoint of a
good light transmittance, the upper limit of the thickness of the
transparent electrode is preferably 1 .mu.m, more preferably 0.5
.mu.m.
[0043] The transparent electrode layer is formed into patterns
required as an electrode of the electroluminescent device by a
photo-lithographic method, etc. In addition, the transparent
electrode layer may also be produced by a coating method.
(D) Low-Refractive Layer:
[0044] It is important that the refractive index of the
low-refractive layer is lower than that of the transparent
electrode layer, and is preferably lower than that of the
transparent sheet/plate. The refractive index of the low-refractive
layer is usually 1.1 to 1.9, preferably 1.1 to 1.6, more preferably
1.2 to 1.5, still more preferably 1.2 to 1.35. When the refractive
index of the low-refractive layer is too low, the resultant film
layer tends to be insufficient in mechanical strength. Further, in
the case where the low-refractive layer is composed of a silicate
material, the content of silanol therein tends to be increased,
resulting in higher hydrophilicity thereof which is disadvantageous
to the EL device. When the refractive index of the low-refractive
layer is too high, an amount of total reflection light on a side of
the low-refractive layer facing the transparent sheet/plate or on a
side of the transparent sheet/plate facing air tends to be
increased, resulting in poor light extraction efficiency.
[0045] The refractive index of the low-refractive layer may be
measured using an "ellipsometer" (manufactured by "Sopra") on the
basis of Standard D542. However, in the case where a matrix portion
of the low-refractive layer is composed of a meso(nano)-porous
material or a particle-dispersing material, it may be difficult to
accurately measure the refractive index using the "ellipsometer"
because of an inclined structure thereof, etc. In such a case where
the measurement using the "ellipsometer" is difficult, the
refractive index may be measured by "PRISM COUPLER MODEL 2010"
manufactured by Metricon Inc., U.S.A. (in which the refractive
index is measured according to a mode of guided light generated in
the film) using a laser having a wavelength of 405 nm or 633
nm.
[0046] Examples of the material of the low-refractive layer may
include silica, transparent fluoride resins such as cyclic Teflon,
magnesium fluoride, etc. In particular, among these materials,
preferred is porous silica. The silica may contain, if required,
organic components for the purposes of hydrophobicity-imparting
treatment, flexibilizing treatment or prevention of cracks.
[0047] The porous silica film may be produced, for example, through
the following steps: (1) a step of preparing a raw solution for
forming the porous silica film; (2) a step of applying the thus
prepared raw solution onto a substrate to form a primary coating
film; (3) a step of polymerizing the thus formed primary coating
film to form an intermediate film; (4) a step of contacting the
intermediate film with a water-soluble organic solvent to form a
porous silica film; and (5) a step of drying the porous silica
film.
[0048] However, in view of the aimed object of forming the
low-refractive film, the production method is not particularly
limited to the method including the above steps as long as the
requirements therefor are satisfied. For example, porous films
(meso-porous films) obtained by the production processes described
in the following literatures may also be used as long as the
requirement for the low-refractive film are satisfied: Japanese
Patent Application Laid-Open (KOKAI) No. 2002-278477, U.S. Pat. No.
6,592,764, "Technical Report of Ulvac Inc.", No. 57, September,
2002, pp. 34-36, and IDW2002 Preliminary Report, pp. 1163-1166.
[0049] Next, the above respective steps are explained.
(1) Step of Preparing a Raw Solution for Forming the Porous Silica
Film:
[0050] The raw solution for forming the porous silica film contains
alkoxysilanes as main components, and is a water-containing organic
solution containing a raw compound capable of being polymerized by
hydrolysis reaction and dehydration condensation reaction.
[0051] The water-containing organic solution as the raw solution
may contain alkoxysilanes, a hydrophilic organic solvents and water
as well as a catalyst, if required.
[0052] Examples of the alkoxysilanes may include tetraalkoxysilanes
such as tetramethoxysilane, tetraethoxysilane,
tetra(n-propoxy)silane, tetraisopropoxysilane and
tetra(n-butoxy)silane; trialkoxysilanes such as trimethoxysilane,
triethoxysilane, methyl trimethoxysilane, methyl triethoxysilane,
phenyl trimethoxysilane and phenyl triethoxysilane; dialkoxysilanes
such as dimethyl dimethoxysilane, dimethyl diethoxysilane, diphenyl
dimethoxysilane and diphenyl diethoxysilane; compounds obtained by
bonding two or more trialkoxysilyl groups through an organic
residue, such as bis(trimethoxysilyl)methane,
bis(triethoxysilyl)methane, 1,2-bis(trimethoxysilyl)ethane,
1,2-bis(triethoxysilyl)ethane, 1,4-bis(trimethoxysilyl)benzene,
1,4-bis(triethoxysilyl)benzene and
1,3,5-tris(trimethoxysilyl)benzene; and compounds in which an alkyl
substituent group bonded to a silicon atom has a reactive
functional group, such as 3-aminopropyl trimethoxysilane,
3-aminopropyl triethoxysilane, 3-glycidyloxypropyl
trimethoxysilane, 3-glycidyloxypropyl triethoxysilane,
3-mercaptopropyl trimethoxysilane, 3-acryloyloxypropyl
trimethoxysilane and 3-carboxypropyl trimethoxysilane; as well as
partially hydrolyzed products or oligomers thereof.
[0053] Among these alkoxysilanes, preferred are tetramethoxysilane,
tetraethoxysilane, trimethoxysilane, triethoxysilane, and oligomers
of tetramethoxysilane or tetraethoxysilane. In particular, the
oligomers of tetramethoxysilane are still more preferred in the
consideration of well-controlled reactivity and gelation
thereof.
[0054] Further, the above alkoxysilanes may be blended with
monoalkoxysilanes having two or three hydrogen atoms, alkyl groups
or aryl groups bonded to the silicon atom. In the case where the
monoalkoxysilanes are blended with the alkoxysilanes, the resultant
porous silica film is well hydrophobilized and enhanced in water
resistance. Examples of the monoalkoxysilanes may include
triethylmethoxysilane, triethylethoxysilane,
tripropylmethoxysilane, triphenylmethoxysilane,
triphenylethoxysilane, diphenylmethyl methoxysilane and
diphenylmethyl ethoxysilane. The amount of the monoalkoxysilanes
blended is not more than 70 mol % based on the whole alkoxysilanes.
When the amount of the monoalkoxysilanes blended is more than 70
mol %, the obtained raw solution may fail to be gelled.
[0055] In addition, when the above alkoxysilanes is used in
combination with alkoxysilanes having a fluorinated alkyl group or
a fluorinated acryl group such as
(3,3,3-trifluoropropyl)trimethoxysilane,
(3,3,3-trifluoropropyl)triethoxysilane, pentafluorophenyl
trimethoxysilane and pentafluorophenyl triethoxysilane, the
obtained porous silica film is excellent in water resistance,
moisture resistance, anti-staining property, etc.
[0056] The oligomers contained in the raw solution may be in the
form of a crosslinked, cage-type molecule (such as
silsesqui-oxane).
[0057] The degree of condensation of a condensate contained in the
water-containing organic solution is adjusted such that the
solution exhibits such a transparency that the light transmittance,
for example, as measured at a wavelength of 400 nm, a temperature
of 23.degree. C. and an optical path length of 10 mm is usually 90
to 100%. The lower limit of the light transmittance of the solution
is preferably not less than 92%, more preferably not less than
95%.
[0058] Meanwhile, upon applying the raw solution, it is required
that the components contained in the solution are polymerized to
some extent (i.e., in such a condition that the condensation
reaction thereof proceeds to some extent). The degree of the
polymerization is preferably adjusted to such an extent that no
insoluble solids are recognized by visual observation. This is
because if any insoluble solids which can be visually observed are
present in the raw solution before application thereof, large
roughness tend to be formed on the surface of the obtained coating
film, resulting in deteriorated quality of the film.
[0059] As the organic solvent, there are preferably used those
solvents capable of allowing the alkoxysilanes, water and the
below-mentioned hydrophilic organic compound having a boiling point
of not less than 80.degree. C. as components of the raw solution,
to be miscible with each other. Examples of the organic solvent
usable in the present invention may include alcohols such as
monohydric alcohols having 1 to 4 carbon atoms, dihydric alcohols
having 1 to 4 carbon atoms and polyhydric alcohols such as glycerol
and pentaerythritol; ethers or esters of the above alcohols such as
diethyleneglycol, ethyleneglycol monomethyl ether, ethyleneglycol
dimethyl ether, 2-ethoxyethanol, propyleneglycol monomethyl ether
and propyleneglycol methyl ether acetate; ketones such as acetone
and methyl ethyl ketone; amides such as formamide, N-methyl
formamide, N-ethyl formamide, N,N-dimethyl formamide, N,N-diethyl
formamide, N-methyl acetamide, N-ethyl acetamide, N,N-dimethyl
acetamide, N,N-diethyl acetamide, N-methyl pyrrolidone, N-formyl
morpholine, N-acetyl morpholine, N-formyl piperidine, N-acetyl
piperidine, N-formyl pyrrolidine, N-acetyl pyrrolidine,
N,N'-diformyl piperadine and N,N'-diacetyl piperadine; lactones
such as .gamma.-butyrolactone; ureas such as tetramethyl-urea and
N,N'-dimethyl imidazoline; and dimethyl sulfoxides. These
water-soluble organic solvents may be used singly or in the form of
a mixture of any two or more thereof. Among these organic solvents,
from the standpoint of a good film-forming property on the
substrate (especially volatility), preferred are acetone, methyl
ethyl ketone and monohydric alcohols having 1 to 4 carbon atoms;
more preferred are methanol, ethanol, n-propanol, isopropyl alcohol
and acetone; and still more preferred are methanol and ethanol.
[0060] As the hydrophilic organic compound having a boiling point
of not less than 80.degree. C., there may be used such organic
compounds containing a hydrophilic functional group such as a
hydroxyl group, a carbonyl group, an ether bond, an ester bond, a
carbonate bond, a carboxyl group, an amide bond, an urethane bond
and a urea bond in a molecular structure thereof. The hydrophilic
organic compound may contain plural kinds of hydrophilic functional
groups selected from the above functional groups in a molecular
structure thereof. The "boiling point" used herein means a boiling
point as measured under a pressure of 760 mmHg. In the case where
the hydrophilic organic compound used has a boiling point less than
80.degree. C., the resultant porous silica film tends to be
extremely decreased in porosity thereof. Examples of the
hydrophilic organic compound having a boiling point of not less
than 80.degree. C. may include alcohols having 3 to 8 carbon atoms,
polyhydric alcohols having 2 to 6 carbon atoms, and phenols. Among
these hydrophilic organic compounds, preferred are alcohols having
3 to 8 carbon atoms, diols having 2 to 8 carbon atoms, triols
having 3 to 8 carbon atoms and tetraols having 4 to 8 carbon atoms.
Specific examples of the more preferred hydrophilic organic
compounds may include alcohols having 4 to 7 carbon atoms such as
n-butanol, isobutyl alcohol, t-butyl alcohol, n-pentanol,
cyclopentanol, n-hexanol, cyclohexanol and benzyl alcohol; diols
having 2 to 4 carbon atoms such as ethyleneglycol, propyleneglycol
and 1,4-butanediol; triols having 3 to 6 carbon atoms such as
glycerol and trishydroxymethyl ethane; and tetraols having 4 to 5
carbon atoms such as erythritol and pentaerythritol. The
hydrophilic organic compounds having a too large number of carbon
atoms tend to be deteriorated in hydrophilicity.
[0061] The catalyst may be optionally blended in the porous silica
film, if required. As the catalyst, there may be used those
substances capable of promoting the hydrolysis reaction and
dehydration condensation reaction of the above alkoxysilanes.
Specific examples of the catalyst may include acids such as
hydrochloric acid, nitric acid, sulfuric acid, formic acid, acetic
acid, oxalic acid and maleic acid; amines such as ammonia,
butylamine, dibutylamine and triethylamine; bases such as pyridine;
Lewis acids such as aluminum acetylacetone complexes; and metal
chelate compounds.
[0062] Examples of metals contained in the metal chelate compounds
as the catalyst may include titanium, aluminum, zirconium, tin and
antimony. Specific examples of the metal chelate compounds are as
follows.
[0063] Specific examples of the aluminum complexes may include
aluminum chelate compounds such as
di-ethoxy-mono(acetylacetonate)aluminum, [0064]
di-n-propoxy-mono(acetylacetonate)aluminum, [0065]
di-isopropoxy-mono(acetylacetonate)aluminum, [0066]
di-n-butoxy-mono(acetylacetonate)aluminum, [0067]
di-sec-butoxy-mono(acetylacetonate)aluminum, [0068]
di-tert-butoxy-mono(acetylacetonate)aluminum, [0069]
monoethoxy-bis(acetylacetonate)aluminum, [0070]
mono-n-propoxy-bis(acetylacetonate)aluminum, [0071]
monoisopropoxy-bis(acetylacetonate)aluminum, [0072]
mono-n-butoxy-bis(acetylacetonate)aluminum, [0073]
mono-sec-butoxy-bis(acetylacetonate)aluminum, [0074]
mono-tert-butoxy-bis(acetylacetonate)aluminum, [0075]
tris(acetylacetonate)aluminum, [0076]
diethoxy-mono(ethylacetonate)aluminum, [0077]
di-n-propoxy-mono(ethylacetonate)aluminum, [0078]
diisopropoxy-mono(ethylacetonate)aluminum, [0079]
di-n-butoxy-mono(ethylacetonate)aluminum, [0080]
di-sec-butoxy-mono(ethylacetonate)aluminum, [0081]
di-tert-butoxy-mono(ethylacetonate)aluminum, [0082]
monoethoxy-bis(ethylacetonate)aluminum, [0083]
mono-n-propoxy-bis(ethylacetonate)aluminum, [0084]
monoisopropoxy-bis(ethylacetonate)aluminum, [0085]
mono-n-butoxy-bis(ethylacetonate)aluminum, [0086]
mono-sec-butoxy-bis(ethylacetonate)aluminum, [0087]
mono-tert-butoxy-bis(ethylacetonate)aluminum and [0088]
tris(ethylacetonate)aluminum.
[0089] Specific examples of the titanium complexes may include
[0090] triethoxy-mono(acetylacetonate)titanium, [0091]
tri-n-propoxy-mono(acetylacetonate)titanium, [0092]
triisopropoxy-mono(acetylacetonate)titanium, [0093]
tri-n-butoxy-mono(acetylacetonate)titanium, [0094]
tri-sec-butoxy-mono(acetylacetonate)titanium, [0095]
tri-tert-butoxy-mono(acetylacetonate)titanium, [0096]
diethoxy-bis(acetylacetonate)titanium, [0097]
di-n-propoxy-bis(acetylacetonate)titanium, [0098]
diisopropoxy-bis(acetylacetonate)titanium, [0099]
di-n-butoxy-bis(acetylacetonate)titanium, [0100]
di-sec-butoxy-bis(acetylacetonate)titanium, [0101]
di-tert-butoxy-bis(acetylacetonate)titanium, [0102]
monoethoxy-tris(acetylacetonate)titanium, [0103]
mono-n-propoxy-tris(ethylacetonate)titanium, [0104]
monoisopropoxy-tris(ethylacetonate)titanium, [0105]
mono-n-butoxy-tris(ethylacetonate)titanium, [0106]
mono-sec-butoxy-tris(ethylacetonate)titanium, [0107]
mono-tert-butoxy-tris(ethylacetonate)titanium, [0108]
tetrakis(acetylacetonate)titanium, [0109]
triethoxy-mono(ethylacetonate)titanium, [0110]
tri-n-propoxy-mono(ethylacetonate)titanium, [0111]
triisopropoxy-mono(ethylacetonate)titanium, [0112]
tri-n-butoxy-mono(ethylacetonate)titanium, [0113]
tri-sec-butoxy-mono(ethylacetonate)titanium, [0114]
tri-tert-butoxy-mono(ethylacetonate)titanium, [0115]
diethoxy-bis(ethylacetonate)titanium, [0116]
di-n-propoxy-bis(ethylacetonate)titanium, [0117]
diisopropoxy-bis(ethylacetonate)titanium, [0118]
di-n-butoxy-bis(ethylacetonate)titanium, [0119]
di-sec-butoxy-bis(ethylacetonate) titanium, [0120]
di-tert-butoxy-bis(ethylacetonate)titanium, [0121]
monoethoxy-tris(ethylacetonate)titanium, [0122]
mono-n-propoxy-tris(ethylacetonate)titanium, [0123]
monoisopropoxy-tris(ethylacetonate)titanium, [0124]
di-n-butoxy-bis(ethylacetonate)titanium, [0125]
mono-sec-butoxy-tris(ethylacetonate)titanium, [0126]
mono-tert-butoxy-tris(ethylacetonate)titanium, [0127]
tetrakis(ethylacetonate)titanium, [0128]
mono(acetylacetonate)tris(ethylacetonate)titanium, [0129]
bis(acetylacetonate)bis(ethylacetonate)titanium and [0130]
tris(acetylacetonate)mono(ethylacetonate)titanium.
[0131] Further, in addition to the above catalyst, there may also
be used a basic catalyst such as a weak-alkaline compound, for
example, ammonia. In this case, the concentration of silica, the
kind of organic solvent, etc., are suitably controlled. Also, upon
preparation of the water-containing organic solution, the
concentration of the catalyst in the solution is preferably
prevented from being rapidly increased. More specifically, there
may be used a method of mixing the alkoxysilanes with a part of the
organic solvent and then with water, and finally mixing the
resultant mixture with a remaining part of the organic solvent and
the base.
[0132] In particular, as the catalyst, there are more preferably
used Lewis acids such as hydrochloride acid which is highly
volatile and, therefore, readily removable, and aluminum
acetylacetone complexes. The amount of the catalyst added is
usually 0.001 to 1 mol, preferably 0.01 to 0.1 mol based on 1 mol
of the alkoxysilanes. When the amount of the catalyst used is more
than 1 mol, precipitates of coarse gelled particles tend to be
produced, thereby failing to form a uniform porous silica film.
[0133] The raw solution for forming the porous silica film of the
present invention is produced by blending the above raw components
with each other. The amount of the alkoxysilanes blended is
preferably 10 to 60% by weight, more preferably 20 to 40% by weight
based on the total weight of the raw solution. When the amount of
the alkoxysilanes blended is more than 60% by weight, the porous
silica film tends to be broken upon the film-forming process. On
the other hand, when the amount of the alkoxysilanes blended is
less than 10% by weight, the hydrolysis reaction and dehydration
condensation reaction tend to be extremely slow, resulting in
deteriorated film-forming property of the solution (unevenness of
film thickness).
[0134] The amount of water blended is usually 0.01 to 10 times,
preferably 0.05 to 7 times, more preferably 0.07 to 5 times the
weight of the alkoxysilanes used. When the amount of water blended
is less than 0.01 time the weight of the alkoxysilanes, the
hydrolysis reaction and condensation reaction may fail to proceed
sufficiently, resulting in production of white turbid film. On the
other hand, when the amount of water blended is more than 10 times
the weight of the alkoxysilanes, a surface tension of the raw
solution tends to be extremely large, resulting in poor
film-forming property of the solution (cissing of the solution
applied).
[0135] Water is required for hydrolysis of the alkoxysilanes and
further is important from the standpoint of enhancing a
film-forming property of the raw solution for producing the aimed
porous silica film. The amount of water which is defined by a molar
ratio of water to the alkoxide group, is usually 0.1 to 1.6 mol,
preferably 0.3 to 1.2 mol, more preferably 0.5 to 0.7 mol based on
1 mol of the alkoxide group contained in the alkoxysilane.
[0136] Water may be added at any time after dissolving the
alkoxysilanes in the organic solvent, and is preferably added after
fully dispersing the alkoxysilanes, the catalyst and other
additives in the solvent.
[0137] Water used in the present invention may be subjected to any
one or both of ion exchange treatment and distillation treatment.
When the porous silica film of the present invention is used in
application fields which tend to be especially adversely affected
by the presence of fine particles, such as semiconductor materials
and optical materials, the porous silica film is required to have a
high purity. Therefore, in these applications, there is preferably
used an ultrapure water obtained by further subjecting distilled
water to ion-exchange treatment. In this case, for example, there
may be used water obtained by passing through a filter having a
mesh size of 0.01 to 0.5 .mu.m.
[0138] When the water-containing organic solution contains the
hydrophilic organic compound having a boiling point of not less
than 80.degree. C., the content of the hydrophilic organic compound
having a boiling point of not less than 80.degree. C. is usually
not more than 90% by weight, preferably not more than 85% by weight
based on the total weight of the organic solvent and the
hydrophilic organic compound having a boiling point of not less
than 80.degree. C. When the content of the hydrophilic organic
compound having a boiling point of not less than 80.degree. C. is
more than 90% by weight, the resultant porous silica film tends to
suffer from white turbidity during the film-forming process, or
tends to be broken.
[0139] When the content of the hydrophilic organic compound having
a boiling point of not less than 80.degree. C. is too small, the
porous silica film tends to exhibit an extremely low porosity, so
that it may be difficult to obtain the porous silica film having a
low refractive index. In general, the content of the hydrophilic
organic compound having a boiling point of not less than 80.degree.
C. is usually not less than 30% by weight, preferably not less than
50% by weight, more preferably not less than 60% by weight based on
the total weight of the organic solvent and the content of the
hydrophilic organic compound having a boiling point of not less
than 80.degree. C. Accordingly, the content of the hydrophilic
organic compound having a boiling point of not less than 80.degree.
C. in the water-containing organic solution is usually 30 to 90% by
weight, preferably 50 to 85% by weight, more preferably 60 to 85%
by weight based on the total weight of the organic solvent and the
content of the hydrophilic organic compound having a boiling point
of not less than 80.degree. C.
[0140] The temperature of the atmosphere used upon preparation of
the coating solution as well as the mixing order of the respective
components are optional. In order to obtain a uniform coating
solution, water is preferably added finally. Further, in order to
suppress excessive hydrolysis reaction and condensation reaction of
the silicon alkoxide in the coating solution, the coating solution
is prepared at a temperature of usually 0 to 60.degree. C.,
preferably 15 to 40.degree. C., more preferably 15 to 30.degree.
C.
[0141] Upon preparation of the coating solution, the stirring
operation of the coating solution is also optional. The coating
solution is preferably stirred using a stirrer in every mixing
operation.
[0142] In addition, after completion of preparation of the coating
solution, it is preferred that the coating solution is aged to
promote the hydrolysis reaction and dehydration condensation
reaction of the silicon alkoxides. During the aging period, since
it is preferable that the resultant hydrolyzed and condensed
product of the silicon alkoxides is uniformly dispersed in the
coating solution, the coating solution is preferably continuously
stirred.
[0143] The temperature used during the aging period is optional. In
general, the aging temperature may be a room temperature, or the
coating solution may be either continuously or intermittently
heated during the aging period. Among them, in order to form a
coating film having a three-dimensional nano-porous structure owing
to the hydrolyzed and condensed product of the silicon alkoxides,
it is preferred that the coating solution is rapidly heat-aged.
Further, the heat-aging is preferably initiated immediately after
preparing the coating solution, i.e., usually within 15 days,
preferably within 12 days, more preferably within 3 days, still
more preferably within one day after completion of preparing the
coating solution.
[0144] More specifically, the coating solution is usually heat-aged
at a temperature of 40 to 70.degree. C. for 1 to 5 hours. Upon the
heat-aging, the coating solution is preferably stirred to obtain a
coating film having a uniform porous structure. In particular, from
the standpoint of formation of the porous structure, the coating
solution is suitably heat-aged at a temperature near 60.degree. C.
for 2 to 3 hours.
[0145] The raw solution has a viscosity of usually 0.1 to 1000 cP,
preferably 0.5 to 500 cP, more preferably 1 to 100 cP from the
standpoint of facilitated production of the coating solution.
(2) Step of Forming a Primary Coating Film from the Thus Prepared
Raw Solution:
[0146] The primary coating film is formed by applying the
water-containing organic solution as the raw solution onto the
substrate. Examples of the substrate may include substrates
composed of semiconductors such as silicon and germanium, compound
semiconductors such as gallium-arsenic and indium-antimony, ceramic
substrates and metals, glass substrates, transparent substrate such
as synthetic resin substrates, etc.
[0147] When forming the porous silica film of the present invention
onto the substrate, properties of the resultant porous silica film
tend to be influenced by properties of surface of the substrate. In
this case, the substrate may be subjected to not only
surface-washing but also surface treatments. Examples of the
surface-washing of the substrate may include dipping treatments in
acids such as sulfuric acid, hydrochloric acid, nitric acid and
phosphoric acid, alkalis such as aqueous sodium hydroxide solution,
or an oxidative mixed solution containing hydrogen peroxide
together with sulfuric acid, hydrochloric acid, ammonia, etc. In
particular, in the consideration of a good adhesion to the porous
silica film, it is preferred that the surface of the silicon
substrate or transparent glass substrate is treated with acids such
as sulfuric acid and nitric acid.
[0148] As the method of applying the raw solution onto the
substrate, there may be used known methods such as a cast-coating
method of spreading the raw solution over the substrate using a bar
coater, an applicator, a doctor blade, etc.; a dipping method of
dipping the substrate in the raw solution and then raising the
substrate from the solution; and a spin-coating method. Among these
methods, the cast-coating method and spin-coating method are
preferred in view of uniform application of the raw solution.
[0149] When applying the raw solution by the cast-coating method,
the casting speed is usually 0.1 to 1000 m/min, preferably 0.5 to
700 m/min, more preferably 1 to 500 m/min.
[0150] When applying the raw solution by the spin-coating method,
the spinning speed is usually 10 to 100000 rpm, preferably 50 to
50000 rpm, more preferably 100 to 10000 rpm.
[0151] In the dip-coating method, the dipping and raising
operations of the substrate may be conducted at an optional speed.
The raising speed is usually 0.01 to 50 mm/sec, preferably 0.05 to
30 mm/sec, more preferably 0.1 to 20 mm/sec. The speed for dipping
the substrate in the coating solution is not particularly limited,
and is preferably substantially identical to the raising speed. The
dipping procedure from dipping the substrate in the coating
solution until raising the substrate therefrom may be continued for
appropriate period of time. The dipping procedure may be continued
for a period of usually from 1 sec to 48 hours, preferably from 3
sec to 24 hours, more preferably from 5 sec to 12 hours. The
application of the coating solution may be conducted either in air
or in an inert gas atmosphere such as nitrogen and argon. The
temperature used upon applying the coating solution is usually 0 to
60.degree. C., preferably 10 to 50.degree. C., more preferably 20
to 40.degree. C. The relative humidity in the atmosphere is usually
5 to 90%, preferably 10 to 80%, more preferably 15 to 70%.
Meanwhile, since the drying speed used in the dip-coating method is
slow as compared to that in the spin-coating method, the
dip-coating method tends to form a stable film with a less
distortion by sol-gel reaction after applying the coating solution.
Accordingly, in some cases, the dip-coating method is more
preferred since a film having a well-controlled structure can be
produced by the surface treatment of the substrate.
[0152] The film-forming temperature is usually 0 to 100.degree. C.,
preferably 10 to 80.degree. C., more preferably 20 to 70.degree.
C.
(3) Step of Polymerizing the Thus Formed Primary Coating Film to
Form an Intermediate Film:
[0153] The coating film is polymerized, i.e., converted into a
higher-molecular compound to form an intermediate film. The
polymerization reaction is referred to a so-called sol-gel method,
and includes two elementary reactions, i.e., a hydrolysis reaction
of the alkoxysilanes and a dehydration condensation reaction
between silanol groups produced by the hydrolysis reaction.
[0154] The hydrolysis reaction may be caused by addition of water.
Water may be added directly in a liquid state, or in the form of an
aqueous alcohol solution or water vapor, though not particularly
limited thereto. When water is rapidly added, the hydrolysis
reaction and dehydration condensation reaction of the alkoxysilanes
tend to proceed too rapidly according to kinds of the
alkoxysilanes, resulting in precipitation of solids. For this
reason, in order to prevent precipitation of solids, a method of
adding water for a sufficient period of time, a method of uniformly
adding water under the coexistence of an alcohol solvent, a method
of adding water at a low temperature to suppress occurrence of
undesirable reactions thereupon, etc., may be used singly or in
combination thereof.
[0155] When the hydrolysis and condensation reactions of the
alkoxysilanes proceed by the sol-gel method, the condensed product
of the alkoxysilanes is gradually polymerized and converted into a
high-molecular compound thereof. In the hydrolysis and condensation
reactions, there tend to be caused the phase separation which is
considered to occur due to the change in phase equilibrium.
However, in the present invention, owing to a good balance between
composition of the raw solution and a degree of hydrophilicity of
each of the alkoxysilanes and the hydrophilic organic compound
having a boiling point of not less than 80.degree. C., the phase
separation can be controlled to a nanometer scale. As a result, a
separate phase of the hydrophilic organic compound is still held
within a network structure of gels composed of the condensed
product of the alkoxysilanes upon forming the coating film onto the
substrate, thereby forming the intermediate film thereon.
[0156] For the above reason, it is important to control the
hydrophilicity of the hydrophilic organic compound having a boiling
point of not less than 80.degree. C. When the hydrophilicity is
expressed by a dielectric constant, the dielectric constant of the
hydrophilic organic compound is preferably 10 to 20, more
preferably 13 to 19.
[0157] In the consideration of a well-balanced degree of the
hydrophilicity, the water-containing organic solution as the raw
solution preferably contains an organic solvent having a dielectric
constant of not less than 23 (more specifically, such as methanol
and ethanol). In particular, when the weight ratio of the organic
solvent having a dielectric constant of not less than 23 to the
hydrophilic organic compound having a boiling point of not less
than 80.degree. C. is controlled to preferably from 5:5 to 2:8,
more preferably 4:6 to 2:8, it is possible to achieve a more
desirable phase separation behavior.
(4) Step of Contacting the Intermediate Film with a Water-Soluble
Organic Solvent to Form a Porous Silica Film (Extraction Step):
[0158] When the intermediate film is contacted with a water-soluble
organic solvent, the hydrophilic organic compound contained in the
intermediate film is extracted and removed therefrom, and further
water contained therein is also removed therefrom. Since water
contained in the intermediate film is not only dissolved in the
organic solvent but also adsorbed inside of film-constituting
substances, in order to effectively remove water from the
intermediate film, it is required to control the content of water
in the organic solvent. The water content in the organic solvent is
usually 0 to 10% by weight, preferably 0 to 5% by weight, more
preferably 0 to 3% by weight. When the removal of water from the
intermediate film is insufficient, pores of the porous film tend to
be eliminated due to breakage thereof or decreased in size upon
subjecting the film to subsequent heating or drying step.
[0159] Examples of the method of extracting and removing the
hydrophilic organic compound contained in the intermediate film may
include a method of dipping the intermediate film in a
water-soluble organic solvent, a method of washing the surface of
the intermediate film with the water-soluble organic solvent, a
method of spraying the water-soluble organic solvent onto the
surface of the intermediate film, a method of blowing a vapor of
the water-soluble organic solvent onto the surface of the
intermediate film, etc. Among these methods, preferred are the
dipping method and the washing method. The time of contact between
the intermediate film and the water-soluble organic solvent is
usually from 1 sec to 24 hours. From the standpoint of a good
productivity, the upper limit of the contact time is preferably 12
hours, more preferably 6 hours. On the other hand, the lower limit
of the contact time is preferably 10 sec, more preferably 30 sec,
because it is required to fully remove the hydrophilic organic
compound having a boiling point of not less than 80.degree. C. and
water from the intermediate film.
(5) Step of Drying the Porous Silica Film:
[0160] The drying step is conducted for the purposes of removing
residual volatile components form the porous silica film and/or
promoting the hydrolysis and condensation reactions of the
alkoxysilanes. The drying temperature is usually 20 to 500.degree.
C., preferably 30 to 400.degree. C., more preferably 50 to
350.degree. C. The drying time is usually from 1 min to 50 hours,
preferably from 3 min to 30 hours, more preferably from 5 min to 15
hours. The porous silica film may be dried by known methods such as
an air-blowing method, a drying method under reduced pressure and
combination thereof. Meanwhile, when volatile components are
rapidly removed due to too strong drying, the porous silica film
tends to suffer from cracks. Therefore, the moderate drying method
such as air-blowing is preferably used. The air-blowing method may
be followed by drying under reduced pressure in order to fully
remove the volatile components from the porous silica film.
[0161] Meanwhile, the previous extraction step may be replaced with
the present drying step. More specifically, the removal of the
hydrophilic organic compound having a boiling point of not less
than 80.degree. C. from the intermediate film produced in the above
step (3) may be conducted not by the extraction step described in
the above step (4) but by the drying step explained in this
step.
[0162] The laminated substrate which is capable of removing the
hydrophilic organic compound by the above drying method, may be
produced by such a specific method comprising at least a step of
applying a water-containing organic solution containing raw
compounds composed mainly of alkoxysilanes to be subjected to
hydrolysis and dehydration condensation reactions, and the
hydrophilic organic compound having a boiling point of not less
than 80.degree. C., onto a substrate to form a primary coating film
thereon; a step of subjecting the water-containing organic solution
constituting the primary coating film to hydrolysis and dehydration
condensation reactions to form an intermediate film; a step of
contacting the intermediate film with a catalyst for promoting the
hydrolysis and dehydration condensation reactions to form a dense
layer in a surface region of the intermediate film; and a step of
drying the intermediate film to remove the hydrophilic organic
compound having a boiling point of not less than 80.degree. C.
therefrom and form the porous silica film.
(E) Substrate:
[0163] As the substrate, there may be used those having a
refractive index of usually 1.4 to 1.9, preferably 1.45 to 1.70,
more preferably 1.47 to 1.65, still more preferably 1.48 to 1.60.
When the refractive index of the substrate is more than 1.9, the
difference in refractive index between the substrate and air tends
to be too large, resulting in increased amount of total reflection
light at a boundary surface therebetween. Since the thickness of
the substrate is generally more than 100 .mu.m, especially in the
application fields of EL displays, large total reflection in the
substrate causes the total reflection light to be returned to the
light-scattering layer and scattered again therein, resulting in
increase in amount of light scattered and emitted therefrom. For
this reason, there tends to be caused mixing of emitted light
between pixels having a size of not more than 100 .mu.m square,
resulting in undesirable phenomenon which tends to cause
deterioration of resolution or definition, such as pixel blurring
and color blurring.
[0164] Meanwhile, for the above reason, the light extraction layer
in which light is diffused or scattered is disposed as close to the
transparent electrode layer as possible, in particular when used in
applications of EL displays. The distance from the transparent
electrode layer to the light extraction layer is more preferably
not more than 2 times a size of one side of pixel, most preferably
not more than the size of one side of pixel.
[0165] When the refractive index of the substrate is more than 1.9,
a large amount of external light tends to be reflected on the
surface of the substrate, resulting in deteriorated resolution or
definition of the displays. As to the substrate having a refractive
index less than 1.4, there are not available any suitable
self-supporting materials for transparent substrates.
[0166] The refractive index used herein means an average refractive
index in a whole depth direction of the substrate, which is
determined by the measurement using an ellipsometer according to
ASTM D-542, and is expressed by the value based on a sodium D ray
(589.3 nm) at 23.degree. C. Examples of the transparent substrate
having the above-specified refractive index may include those
transparent substrate composed of materials generally used for this
purpose. Specific examples of the material for the transparent
substrates may include various shot glasses such as BK7, SF11,
LaSFN9, BaK1 and F2; glasses such as synthesized fused silica
glass, optical crown glass, heat-resistance borosilicate glass,
sapphire, soda glass and no-alkali glass; and synthetic resins,
e.g., acrylic resins such as polymethacrylates and crosslinked
acrylates, aromatic polycarbonate resins such as bisphenol A
polycarbonate, styrene resins such as polystyrene, amorphous
polyolefin resins such as polycycloolefins, epoxy resins, polyester
resins such as polyethylene terephthalate, polysulfone resins such
as polyether sulfone, and polyether imide resins. Among these
materials, preferred are shot glasses such as BK7 and BaK1,
synthesized fused silica glass, optical crown glass,
heat-resistance borosilicate glass, soda glass, no-alkali glass,
acrylic resins, aromatic polycarbonate resins and amorphous
polyolefin resins, and more preferred are shot glasses such as BK7,
synthesized fused silica glass, optical crown glass,
heat-resistance borosilicate glass, soda glass, no-alkali glass,
acrylic resins, aromatic polycarbonate resins and polyether sulfone
resins.
[0167] The thickness of the substrate is usually 0.1 to 10 mm. From
the standpoints of good mechanical strength and gas-barrier
property, the lower limit of the thickness of the substrate is
preferably 0.2 mm, more preferably 0.3 mm. Also, from the
standpoints of light weight, compactness and light transmittance,
the upper limit of the thickness of the substrate is preferably 5
mm, more preferably 3 mm.
[0168] The light transmittance of the laminated substrate is
preferably not less than 80%, more preferably not less than 85%,
still more preferably not less than 90% as measured at a wavelength
of sodium D ray (589.3 nm).
(F) Protective Cover:
[0169] The material for the protective cover is not particularly
limited as long as it can be formed into a transparent flat sheet.
Examples of the material for the protective cover may include, in
addition to the above-mentioned various glass materials and resin
materials used for the substrate, transparent coating materials
having no self-supporting property, e.g., UV-curable or
thermosetting acrylic resins, sol-gel reactive materials (silicate
materials), etc. The thickness of the protective cover is usually
10 to 1000 .mu.m, preferably 100 to 200 .mu.m.
(G) Other Layers:
[0170] The electroluminescent device may also be provided with
known hole injection layer and hole transporting layer between the
electroluminescent layer and the transparent electrode layer, and
further with known electron injection layer and electron
transporting layer between the electroluminescent layer and the
cathode. In addition, if required, the electroluminescent device
may be provided on a light extraction side of the substrate, with
films or membranes such as an anti-reflection film, a polarizing
film and a phase difference film.
[0171] Next, the electroluminescent device of the present invention
is explained by referring to the accompanying drawings. FIG. 1(a)
is an explanatory view showing a layer structure of an
electroluminescent device according to the first invention, and
FIG. 1(b) is an explanatory view of total reflection of light
having a large incident angle to substrate from transparent
electrode. FIGS. 2 and 3 are explanatory views showing other layer
structures of an electroluminescent device according to the first
invention. FIG. 4 is an explanatory view showing a layer structure
of an electroluminescent device according to the second invention.
FIGS. 5 and 6 are explanatory views showing other layer structures
of an electroluminescent device according to the second invention.
FIG. 7 is an explanatory view showing a layer structure of an
electroluminescent device according to the third invention. FIGS. 8
and 9 are explanatory views showing other layer structures of an
electroluminescent device according to the third invention. FIG. 10
is an explanatory view showing a layer structure of an
electroluminescent device according to the fourth invention. FIGS.
11 and 12 are explanatory views showing other layer structures of
an electroluminescent device according to the fourth invention.
<First Invention>
[0172] The electroluminescent device shown in FIG. 1(a) (embodiment
(1)) has such a layer structure in which a cathode 1, an
electroluminescent layer 2, a transparent electrode layer 3, an
evanescent light-scattering layer A 4a and a transparent substrate
5 are successively laminated on each other in this order.
[0173] The evanescent light-scattering layer A 4a is a layer
composed of a matrix composed of a low-refractive material and
light-scattering particles. As the material of the matrix, there
may be used the materials exemplified as those for
above-exemplified low-refractive layer. Examples of the
light-scattering particles contained in the evanescent
light-scattering layer A 4a may include silica (refractive index:
1.46), colloidal silica (refractive index: 1.3 to 1.4, which varies
depending upon production method and structure of the device),
titania (refractive index: 2.4 to 2.7, which varies depending upon
amorphous or crystalline state of the layer), zirconia (refractive
index: 2.0), ITO (indium tin oxide; refractive index: 1.8 to 1.9,
which varies depending upon composition or crystalline state of the
layer), ATO (antimony tin oxide; refractive index: 1.9), alumina
(refractive index: 1.8), etc. In particular, there may be suitably
used those particles which exhibit as low a light absorption in
visible range as possible, i.e., a high transparency, and has as
large a difference in refractive index from that of the matrix as
possible.
[0174] In the present invention, the difference between refractive
indices of the matrix and the light-scattering particles dispersed
in the matrix is important, and it is not important that one of the
matrix and the light-scattering particles has a larger refractive
index than that of the other. Although the particles having a
smaller refractive index than that of the matrix, e.g., fine air
bubbles, are usable in the present invention, there are usually
used such particles having a larger refractive index than that of
the matrix. The difference between refractive indices of the matrix
and the light-scattering particles is usually not less than 0.1,
preferably not less than 0.3, more preferably not less than 0.5,
still more preferably not less than 0.9. The upper limit of the
difference between refractive indices of the matrix and the
light-scattering particles is not present in principle, but usually
about 1.5 in the consideration of availability of materials
therefor.
[0175] Meanwhile, in order to incorporate the light-scattering
particles into the matrix, the particles may be simply added to the
raw solution upon the step (1) of preparing the raw solution for
forming the porous silica film as the low-refractive layer.
[0176] The size and shape of the light-scattering particles are not
particularly limited as long as the particles have a function of
diffusing or scattering an evanescent light (in some cases,
referred to as "evanescent wave" or "near-field light"). That is,
it is important that the light-scattering particles exhibit a
function of preventing the evanescent light from being returned to
the transparent electrode layer and allowing the light to enter
into a light extraction side (on the side of the transparent
sheet/plate). The amount of the evanescent light (evanescent light
penetration distance) is usually from about 100 to about 600 nm,
calculated as the distance measured from a boundary surface between
the transparent electrode and the evanescent light-scattering layer
A toward the side of the evanescent light-scattering layer A.
Therefore, it is important that the light-scattering particles are
present within such a region, and have a diameter capable of
exhibiting the light scattering function. In particular, the
light-scattering particles preferably have the size and shape
capable of causing mie scattering.
[0177] For example, the particle size of the light-scattering
particles as an optical size thereof is usually larger than
1/20.lamda., preferably larger than 1/10.lamda. (wherein .lamda. is
a wavelength of light to be scattered (usually a visible light
having a wavelength of 400 to 700 nm)). When the particle size is
too large, the light scattering film layer tends to be deteriorated
in flatness. If the light scattering film layer shows such a poor
flatness, the electric field within the EL light-emitting layer
tends to become non-uniform, resulting in problems such as
deteriorated luminance and short life of the device.
[0178] When the particle size is too small, the particles may fail
to show a good light-scattering effect, resulting in increase in
refractive index of the matrix in the low-refractive layer. For the
above reasons, the physical particle size calculated as a particle
size of the particles corresponding to weight ratio of not less
than 60% (hereinafter occasionally referred to as "60%-weight ratio
particle size") is usually 20 to 400 nm, preferably 40 to 200 nm,
more preferably 60 to 120 nm.
[0179] The 60%-weight ratio particle size is measured as
follows.
[0180] (1) The section of the scattering layer was observed by
FIB-SEM.
[0181] FIB is an abbreviation of a focus ion beam
processing/observing apparatus. As the FIB apparatus, there was
used "FB-2000A" manufactured by Hitachi Limited. Upon processing
the section, Pt (platinum)-sputter film was formed before the FIB
processing.
[0182] Before producing the section by FIB, a W (tungsten) film was
locally formed at its corresponding position, and an observation
hole (about 20 .mu.m.times.30 .mu.m square) was formed by FIB.
Thus, the surface to be observed was finished by lowering the ion
beam current. Ion species used were Ga.sup.+, and acceleration
voltage for ion beam was controlled to 30 kV.
[0183] The SEM observation was conducted using "S4100" manufactured
by Hitachi Limited. The observation condition was controlled such
that the acceleration voltage was 5.0 kV, and the sample film was
inclined at an angle of about 80.degree. from the vertical
direction (which corresponds to such a condition that the section
of the film was observed substantially from a front side thereof)
to photograph an image of the observation surface of the hole
formed by FIB at a magnification of 10000 times (.times.10000).
[0184] The obtained photo image of the section observed were
examined by the following procedure.
[0185] The images having a width of 20 .mu.m in the plane direction
of the scattering film were randomly collected from 20 positions on
the sample film, and the particle sizes of the particles observed
in the images were measured. When a sectional shape of the particle
is distorted, the particle size of such a particle having a
circular sectional shape with substantially the same area as that
of the particle to be observed is regarded as the particle size of
the distorted particle.
[0186] As to the respective particles thus observed, the weight of
the particles was calculated assuming that the third power of the
particle size is proportional to the weight of the particle, and
the particle size of particles corresponding to not less than 60%
by weight of the whole particles was determined.
[0187] Meanwhile, the agglomerated massive particles were
respectively regarded as a single particle.
[0188] If the above procedure was not applicable because of
brittleness of the scattering film or unclear particle shape upon
SEM or TEM observation, the particle size was measured by the
following method.
[0189] Meanwhile, this evaluation method is also applicable to the
case where the particles are fine voids.
[0190] (2) Upon preparing the coating solution before forming the
scattering film, a suspension of the particles was subjected to
measurement of a particle size distribution thereof using a
particle size distribution analyzer.
[0191] As the particle size distribution analyzer, there was used a
"MICROTEC particle size distribution analyzer Model 9230"
manufactured by Nikkiso Co., Ltd. The solvent used for suspending
the particles is not particularly limited as long as the particles
are well suspended therein. In the case where the film formation is
conducted by the sol-gel method in which titania particles are
dispersed in a silicate solution, alcohol-based solvents may be
suitably used.
[0192] From the thus measured particle size distribution, data
concerning the particle size, frequency and cumulative ratios are
obtained. Assuming that the particle size is regarded as that of
substantially spherical particles, the 60%-weight ratio particle
size was determined from the data by the same method as above.
[0193] The thickness of the evanescent light-scattering layer is
preferably not less than 2 times an average particle size of the
light-scattering particles. Thus, by suitably controlling the
particle size and the thickness of the evanescent light-scattering
layer, the particles can effectively exhibit the light-scattering
effect.
[0194] The average particle size of the particles is expressed by
the value corresponding to 50 vol % thereof, which is determined
from the particle size distribution measured by the above method
(FIB-SEM method, or the method of measuring the particle size
distribution of the dispersion containing the particles in the case
where the FIB-SEM method is not applicable).
[0195] The content of the light-scattering particles in the
evanescent light-scattering layer is usually 1 to 40% by volume,
preferably 5 to 20% by volume. When the content of the particles is
too small, the evanescent light-scattering layer may fail to
exhibit a sufficient light-scattering effect. When the content of
the particles is too large, the evanescent light-scattering layer
tends to show a too high hiding effect, resulting in a less amount
of light extracted.
[0196] The thickness of the evanescent light-scattering layer A is
usually not less than 2 times the average particle size of the
light-scattering particles. When the particle size and the
thickness of the evanescent light-scattering layer are thus
controlled, the particles can efficiently exhibit a
light-scattering effect. More specifically, the thickness of the
evanescent light-scattering layer A is usually from 100 to 1000 nm,
preferably 300 to 700 nm. As a matter of course, the thickness of
the evanescent light-scattering layer A is controlled such that the
light-scattering particles are present within the range where the
evanescent light is penetrated. More specifically, although it
varies depending upon the thickness of the evanescent
light-scattering layer A containing the light-scattering particles
and the wavelength used, it is important that the light-scattering
particles are present within usually 1 .mu.m (1000 nm), preferably
within 600 nm from the boundary surface between the layer A and the
transparent electrode layer. In particular, it is more preferred
that not less than one-third (weight ratio) of the light-scattering
particles are present within 600 nm from the boundary surface
between the layer A and the transparent electrode layer.
[0197] When the thickness of the evanescent light-scattering layer
A is too small, the thickness of the light scattering layer
(abundance of the particles contained within the evanescent light
penetration region) tends to be smaller as compared to the
below-mentioned evanescent light penetration distance, resulting in
insufficient light-scattering effect. When the thickness of the
evanescent light-scattering layer A is too large, although the
light scattering is conducted without problems, the too large
thickness tends to be disadvantageous from the standpoints of
flatness of the layer and prevention of cracks therein. Meanwhile,
the boundary surface between the evanescent light-scattering layer
A and the transparent electrode is preferably a flat surface. This
is because the transparent electrode film formed by a vacuum method
(which means a vacuum vapor deposition method, etc.) is directly
adversely affected by roughness present on the underlying coat.
[0198] More specifically, in order to produce uniform and stable
light, it is required to maintain a uniform electric field within
the electroluminescent layer. If roughness are present on the
transparent electrode, the electric field within the
electroluminescent layer tends to become non-uniform, resulting in
deterioration in EL pigments and, therefore, causing defects such
as dark spots.
[0199] Next, the total reflection at the boundary surface between
the transparent electrode layer and the evanescent light-scattering
layer A in the electroluminescent device is explained by referring
to FIGS. 1(a) and 1(b).
[0200] The light produced in the electroluminescent layer 2 is
emitted to a side of the transparent electrode layer 3 directly or
after being reflected on the cathode 1 and then passed through the
electroluminescent layer 2. Next, the light entering into the
evanescent light-scattering layer A 4a is incident onto a boundary
surface between the transparent substrate 5 and the evanescent
light-scattering layer A 4a at an incident angle substantially
perpendicular to the surface of the transparent substrate 5.
Therefore, the total reflection at a boundary surface between the
transparent substrate 5 and an outside air layer is decreased.
Further, the light-scattering particles contained in the evanescent
light-scattering layer A 4a serves for reducing total reflection of
the evanescent light passing through the boundary surface between
the transparent electrode layer 3 and the evanescent
light-scattering layer A 4a, resulting in enhancement of the light
extraction efficiency.
[0201] More specifically, among the light which is emitted from the
electroluminescent layer 2 and passed through the transparent
electrode layer 3 and then is incident onto the boundary surface
between the transparent electrode layer 3 and the evanescent
light-scattering layer A 4a, the light having an incident angle
smaller than the critical angle directly enters into the evanescent
light-scattering layer A 4a from the transparent electrode layer 3.
On the other hand, the light 11a having an incident angle larger
than the critical angle is penetrated through the boundary surface
and then undergoes total reflection, and is returned as a total
reflection light 12a to the transparent electrode layer 3. Upon the
total reflection, the light is penetrated on the side of the
evanescent light-scattering layer A 4a relative to the boundary
surface, so that the electric field and magnetic field of the
incident light also extend from the boundary surface and are
present on the side of the evanescent light-scattering layer A 4a.
The maximum penetration distance of the evanescent light 13 is
substantially 500 to 600 nm in the direction perpendicular to the
transparent electrode when the thickness of the transparent
electrode layer is 100 nm and the refractive index of the
evanescent light-scattering layer A 4a is 1.3. The evanescent light
13 penetrated on the side of the evanescent light-scattering layer
A 4a is scattered by the light-scattering particles which are
present in the vicinity of the boundary surface of the evanescent
light-scattering layer A 4a. As a result, the evanescent light 13
is captured into the side of the evanescent light-scattering layer
A 4a containing the light-scattering particles without being
returned as a total reflection light to the transparent electrode
layer 3. The light captured into the side of the evanescent
light-scattering layer A 4a containing the light-scattering
particles is scattered by the light-scattering particles and
diffused, and then scattered into the evanescent light-scattering
layer A 4a containing the light-scattering particles directly or
after being reflected, for example, by an aluminum reflection film
of the cathode. As a result, the reflectance of the total
reflection light at the boundary surface is decreased, so that a
larger amount of light enters into the evanescent light-scattering
layer A 4a from the transparent electrode layer 3, resulting in
enhancement in light extraction efficiency of the
electroluminescent device.
[0202] The electroluminescent device shown in FIG. 2 (embodiment
(2)) has such a layer structure in which a cathode 1, an
electroluminescent layer 2, a transparent electrode layer 3, an
evanescent light-scattering layer A 4b, a low-refractive layer 4
and a transparent substrate 5 are laminated on each other in this
order.
[0203] The refractive index of a matrix component of the evanescent
light-scattering layer A 4b is substantially identical to that of
the low-refractive layer 4.
[0204] Meanwhile, the "substantially identical refractive index"
used herein means that the difference between refractive indices of
the layers to be compared, for example, the difference between the
refractive index of the matrix component of the evanescent
light-scattering layer A 4b and the refractive index of the
low-refractive layer 4 is usually not more than 0.3, preferably not
more than 0.2, more preferably not more than 0.1.
[0205] As the materials of the low-refractive layer 4 and the
matrix component of the low-refractive layer 4b (evanescent
light-scattering layer A 4b), there may be used the same material
as used for the matrix component (other than the particles) of the
evanescent light-scattering layer A 4a shown in FIG. 1(a). In
particular, the matrix component of the evanescent light-scattering
layer A 4b preferably has the same composition as that of the
low-refractive layer 4, though both may be different from each
other.
[0206] The thickness of the low-refractive layer 4 is usually 100
to 1000 nm, preferably 300 to 700 nm from the standpoints of
evanescent light penetration distance upon total reflection at the
boundary surface, flatness of the film or prevention of cracks. The
thickness of the evanescent light-scattering layer A 4b is usually
100 to 1000 nm, preferably 300 to 700 nm.
[0207] The content of the light-scattering particles in the
evanescent light-scattering layer A 4b is the same as the content
of the light-scattering particles in the evanescent
light-scattering layer A 4a as described above.
[0208] In the electroluminescent device of the embodiment (2), the
total reflection at the boundary surface between the transparent
electrode layer 3 and the low-refractive layer 4b is decreased
similarly to the electroluminescent device of the embodiment (1).
More specifically, in the case where the light passing from the
electroluminescent layer 2 through the transparent electrode layer
3 is incident onto the boundary surface between the transparent
electrode layer 3 and the evanescent light-scattering layer A 4b at
an incident angle larger than the critical reflection angle, the
light is penetrated through the boundary surface to the side of the
evanescent light-scattering layer A 4b, and undergoes total
reflection. Upon the total reflection, similarly to the case shown
in FIG. 1(b), the light is penetrated to the side of the evanescent
light-scattering layer A 4b relative to the boundary surface, so
that the electric field or magnetic field of the incident light is
also present on the side of the evanescent light-scattering layer A
4b relative to the boundary surface.
[0209] Since the particles capable of scattering the evanescent
light are present in a portion of the evanescent light-scattering
layer A 4b near the boundary surface, the light penetrated to the
side of the evanescent light-scattering layer A 4b is scattered by
the particles. As a result, the light is directly or indirectly
scattered in the evanescent light-scattering layer A 4b without
being returned as a total reflection light to the side of the
transparent electrode layer 3. Thus, by incorporating the
light-scattering particles in the evanescent light-scattering layer
A 4b, the reflectance of total reflection light is lowered, so that
a larger amount of light enters from the transparent electrode
layer 3 to the evanescent light-scattering layer A 4b.
[0210] Since the matrix component of the evanescent
light-scattering layer A 4b and the low-refractive layer 4 are
substantially identical in refractive index to each other, no total
reflection is caused at the boundary surface between the evanescent
light-scattering layer A 4b and the low-refractive layer 4. As a
result, the light entering from the transparent electrode layer to
the evanescent light-scattering layer A 4b and then reaching the
boundary surface between the evanescent light-scattering layer A 4b
and the low-refractive layer 4, substantially directly enters into
the low-refractive layer 4, resulting in enhancement in light
extraction efficiency of the electroluminescent device.
[0211] In the electroluminescent device shown in FIG. 3, a cathode
1 is formed on a substrate 5, and on the cathode 1 are successively
provided an electroluminescent layer 2, a transparent electrode
layer 3 and an evanescent light-scattering layer A 4a. On the
evanescent light-scattering layer A 4a is further provided a
protective cover 6 as a transparent sheet/plate. Meanwhile, in this
embodiment, the substrate 5 may not be transparent, and the
protective cover exhibits an optical function as the transparent
substrate used in the embodiment (1). The device of the embodiment
(1) is referred to as "bottom emission-type EL" whereas the device
of the embodiment shown in FIG. 3 is referred to as "top
emission-type EL".
[0212] Also, in the electroluminescent device (top emission type)
shown in FIG. 3, a low-refractive layer 4 containing no particles
may be an air layer (voids) without problems concerning a structure
of the device. In this case, since the refractive index of the air
layer is 1.0, the thickness thereof is not particularly limited
because the air layer is free from problems concerning flatness of
the film and prevention of cracks.
[0213] The embodiment shown in FIG. 3 is different from the
embodiment shown in FIG. 1 in that the substrate 5 is disposed on
the side of the cathode 1. Also, in the embodiment shown in FIG. 2,
the substrate 5 may be disposed on the side of the cathode 1.
[0214] In the present invention, the guided light in the
transparent electrode layer is extracted by using light scattering
phenomenon. Therefore, by positively utilizing a wavelength
dependence of the light scattering efficiency, the light extraction
efficiency of a specific color can be increased, and a life of
light emitting pigment for the specific color can be prolonged.
[0215] For example, when rayleigh scattering or combination of mie
scattering and rayleigh scattering is used while varying the
particle size or refractive index of the particles, a sufficient
scattering efficiency is ensured, so that a blue color light can be
extracted with a high efficiency.
[0216] Further, when the material whose refractive index is rapidly
raised near blue color light in visible range, for example,
titania, is selectively used in the composition of the particles,
it becomes possible to extract a blue color light at a higher
efficiency as compared to the other color lights.
[0217] Meanwhile, on the contrary, for example in the case where
air bubbles having a size corresponding to that of the particles
are dispersed, since the refractive index of air undergoes
substantially no change due to wavelength, it may be more effective
to suppress the wavelength dependence of the light extraction
efficiency.
[0218] In the electroluminescent device for emission of white color
light or full color light, in general, pigments on the short
wavelength side have a lower luminance, or exhibit a shorter half
life of luminance when light having the same luminance is emitted.
For this reason, for example, if the extraction efficiency for blue
color light can be enhanced, it is not required to design such a
configuration in which only an area occupied by blue pigments is
increased. As a result, it is possible to enhance a luminance per
unit area, and decrease a current flowing through the blue
pigments, thereby improving the life of pigments. Also, in the
applications using a white light source, by improving the
extraction efficiency of blue color light and life of pigments
therefor, it is possible to minimize an amount of offset from white
color upon measurement.
[0219] Meanwhile, in the top emission type according to the
embodiment shown in FIG. 3, it is required to form the transparent
electrode layer and the light extraction layer after forming the
electroluminescent layer. In this case, since the
electroluminescent layer tends to be decreased in emission
luminance due to crystallization or deterioration thereof upon
exposure to a temperature as high as not less than 100.degree. C.,
the treating temperature used upon formation of the light
extraction layer is usually not more than 150.degree. C.,
preferably not more than 120.degree. C., more preferably not more
than 100.degree. C., and the pressure of the treating atmosphere is
generally an ordinary pressure.
[0220] In the above method, in the case where the low-refractive
layer is formed from a porous silica material, there is preferably
used such a film-forming process in which formation of a porous
structure is conducted, for example, using a mold composed of the
above high-boiling hydrophilic organic compound at a relatively low
temperature.
[0221] As an alternative method, there may be used such a method in
which after previously successively forming the low-refractive
layer, if required, and the evanescent light-scattering layer A on
a separate transparent substrate such as a plastic film, the
resultant optical film is attached onto the transparent electrode
to form a light extraction film. When the optical film is attached
onto the transparent electrode, the evanescent light-scattering
layer A also acts as a bonding layer or an adhesive layer. In such
a method, the processes requiring the heating or use of organic
solvents has been already completed upon production of the film, so
that the light extraction layer can be formed without damaging the
electroluminescent layer.
[0222] As the transparent substrate such as plastic films, there
may be suitably used any substrates as long as the substrates are
composed of a transparent flexible material. Examples of the
suitable substrate may include PET (polyethylene terephthalate)
film, PEN (polyethylene naphthalate) film, PES (polyether sulfone)
film, PC (polycarbonate) film, APO (amorphous polyolefin, cyclic
polyolefin) film, etc., though not particularly limited
thereto.
[0223] The transparent substrate may be used as the protective
cover shown in FIG. 3. In addition, the transparent substrate film
may be provided mainly on the light emission side thereof with a
functional layer such as a gas-barrier layer, an anti-reflection
layer and a circular polarizer layer, if required.
[0224] The transparent substrate film is first formed thereon with
the low-refractive layer, if required. When the transparent
substrate is composed of a plastic film, since formation of the
porous silica film on the transparent substrate cannot be conducted
at a temperature higher than 200.degree. C., the above attaching
method can be suitably used therefor.
<Second Invention>
[0225] In the electroluminescent device shown in FIG. 4 (embodiment
(3)), a barrier layer 10 is disposed between the transparent
electrode layer 3 and the evanescent light-scattering layer A 4a of
the electroluminescent device according to the embodiment (1). More
specifically, the electroluminescent device of the embodiment (3)
has such a layer structure in which a cathode 1, an
electroluminescent layer 2, a transparent electrode layer 3, the
barrier layer 10, an evanescent light-scattering layer A 4a and a
transparent substrate 5 are successively laminated on each other in
this order.
[0226] Further, as the electroluminescent device of the embodiment
(3), there may be exemplified the embodiment A using a
high-refractive barrier layer having a refractive index identical
to or higher than that of the transparent electrode layer, and the
embodiment B using a low-refractive barrier layer having a
refractive index lower than that of the transparent electrode
layer.
[0227] In the embodiment A, since the barrier layer 10 has a
refractive index identical to or higher than that of the
transparent electrode layer 3, the light entering from the
transparent electrode layer 3 into the barrier layer 10 undergoes
no total reflection. Examples of the material constituting the
barrier layer 10 may include ZrO.sub.2, TiO.sub.2, Al.sub.2O.sub.3,
CeO.sub.2, TiN, Ta.sub.2O.sub.3, Ta.sub.2O.sub.5, SiO.sub.xN.sub.y,
SiN, SiO.sub.x, SnO.sub.2, Sb.sub.2O.sub.5, Y.sub.2O.sub.3,
La.sub.2O.sub.3, In.sub.2O.sub.3, and mixtures thereof. These
materials are usable as long as they exhibit no or less visible
light absorption and have a dense film structure. In particular,
those materials mainly composed of inorganic compounds can be
suitably used. In this embodiment, since the barrier layer 10 has a
refractive index identical to or higher than that of the
transparent electrode layer 3, a part of the guided light is
transferred from the transparent electrode layer to the barrier
layer. In this case, the material of the barrier layer preferably
exhibits a less light absorption in a visible light wavelength
range than the material of the transparent electrode layer. The
maximum absorption of the barrier layer in a visible light range is
more preferably not more than 5%, still more preferably not more
than 3%, most preferably not more than 1% per a thickness of 100
nm. Under the consideration in which the above thickness is
replaced with a guided light penetration distance, even though a
light absorption per guided light penetration distance of 100 nm is
several %, if the guided light penetration distance in a plane of
the transparent electrode layer or the barrier layer reaches
several microns or more (in general, the size of one pixel used in
EL displays reaches several ten microns square or more), the light
absorption is very large and, therefore, cannot be ignored for the
purpose of enhancing the light extraction efficiency. Accordingly,
by using the barrier layer having a refractive index identical to
or higher than that of the transparent electrode layer 3 and
exhibiting a less light absorption in a visible light wavelength
range, it can be expected to attain, in addition to the barrier
effect, such an effect of enhancing the light extraction
efficiency.
[0228] The thickness of the barrier layer 10 is not particularly
limited, and is usually not less than 20 nm, preferably not less
than 50 nm, more preferably 100 nm in order to fully exhibit a
barrier property thereof. Also, in order to suppress a light
absorption, the upper limit of the thickness of the barrier layer
is usually 1000 nm, preferably 400 nm.
[0229] In the embodiment B, the barrier layer 10 has a refractive
index lower than that of the transparent electrode layer 3.
Examples of the material constituting the low-refractive barrier
layer having a ver small thickness may include fluoride materials
such as MgF.sub.2 and NaF, various porous materials such as
SiO.sub.2 and nano-porous silica, and mixtures thereof. The
thickness of the barrier layer is very small, more specifically, is
usually not more than 500 nm, preferably not more than 300 nm, more
preferably not more than 200 nm. Meanwhile, in the consideration of
prevention of scattering, the lower limit of the thickness of the
barrier layer is usually 20 nm, preferably 50 nm, more preferably
100 nm. In the embodiment B, the light coming from the side of the
transparent electrode layer 3 tends to undergo total reflection at
the boundary surface between the low-refractive barrier layer 10
and the transparent electrode layer 3. Further, since the thickness
of the barrier layer is small, upon the total reflection, the
evanescent light penetration region from the boundary surface
reaches not only the barrier layer 10 but also the evanescent
light-scattering layer A 4a. As a result, the evanescent light is
scattered by the particles contained in the evanescent
light-scattering layer A 4a, and extracted therein. When the
thickness of the barrier layer is larger than the above upper
limit, the evanescent light fails to reach the evanescent
light-scattering layer A 4a, so that the light extraction
efficiency is not sufficiently increased.
[0230] In the case where the barrier layer has refractive index
identical to or higher than that of the transparent electrode layer
and exhibits a less light absorption than in visible light range
than that of the transparent electrode layer, a part of the guided
light in the transparent electrode layer is transferred into the
barrier layer, and attenuation of the guided light is decreased.
Therefore, it is expected to attain such an effect of enhancing the
light extraction efficiency. In this case, the upper limit of the
thickness of the barrier layer is determined without particularly
considering the evanescent light penetration distance. However, in
the case where the film is formed by a vacuum process, when the
film thickness is more than 1000 .mu.m, the resultant film tends to
become brittle or tends to be peeled off by itself. For these
viewpoints, the thickness of the barrier layer is preferably not
more than 500 nm.
[0231] Also, in the case of a wet-coating film, when the film
thickness is more than 10 .mu.m, it may be difficult to ensure
flatness required for EL devices. From this viewpoint, the
thickness of the wet-coating film as the barrier layer is
preferably not more than 5 .mu.m, more preferably not more than 3
.mu.m, most preferably not more than 1 .mu.m.
[0232] The barrier layer may be produced, for example, by vapor
deposition method.
[0233] The barrier layer serves for preventing diffusible
substances contained in the low-refractive layer, e.g.,
low-molecular components such as residual monomers and water from
being transferred into the side of the transparent electrode layer.
For example, since the evanescent light-scattering layer A 4a is
preferably produced by hydrolysis of alkoxysilanes, the resultant
evanescent light-scattering layer A 4a tends to contain residual
low-molecular components such as monomers or oligomers of the
alkoxysilanes, solvents, water and catalysts. Further, in some
cases, upon assembling processes of EL devices, low-molecular
substances or migratable substances tend to be mixed therein from
outside and remain therein. These low-molecular substances exhibit
a diffusing property, so that there tend to be caused such a risk
that these substances are penetrated through the transparent
electrode layer 3 and adversely affect the electroluminescent
layer. The barrier layer serves for preventing the diffusion of
such substances and protecting the transparent electrode layer or
the electroluminescent layer.
[0234] In the electroluminescent device of the embodiment (3), the
total reflection at the boundary surface between the barrier layer
10 and the evanescent light-scattering layer A 4a is decreased
similarly to the above embodiment (1). In the case where the light
passing from the electroluminescent layer 2 through the transparent
electrode layer 3 and the barrier layer 10 is incident onto the
boundary surface between the barrier layer 10 and the evanescent
light-scattering layer A 4a at an incident angle larger than the
critical angle, the light undergoes total reflection at the
boundary surface. Upon the total reflection, similarly to the first
invention, there is caused such a phenomenon that the light is
penetrated to the side of the evanescent light-scattering layer A
4a relative to the boundary surface. As a result, the electric
field or magnetic field of the incident light is also present on
the side of the evanescent light-scattering layer A 4a relative to
the boundary surface.
[0235] Since the particles capable of scattering the evanescent
light are present in a portion of the evanescent light-scattering
layer A 4a near the boundary surface, the light penetrated to the
side of the evanescent light-scattering layer A 4a is scattered by
the particles. As a result, the light is directly or indirectly
scattered in the evanescent light-scattering layer A 4a without
being returned as total reflection light to the side of the barrier
layer 10. Thus, by incorporating the light-scattering particles in
the evanescent light-scattering layer A 4a, a reflectance of the
total reflection is decreased, so that a larger amount of light
enters from the barrier layer 10 to the evanescent light-scattering
layer A 4a. As a result, the electroluminescent device is enhanced
in light extraction efficiency.
[0236] In the electroluminescent device shown in FIG. 5 (embodiment
(4)), a barrier layer 10 is disposed between the transparent
electrode layer 3 and the evanescent light-scattering layer A 4b of
the electroluminescent device according to the embodiment (2). More
specifically, the electroluminescent device of the embodiment (4)
has such a layer structure in which a cathode 1, an
electroluminescent layer 2, a transparent electrode layer 3, the
barrier layer 10, an evanescent light-scattering layer A 4b, a
low-refractive layer 4 and a transparent substrate 5 are
successively laminated on each other in this order.
[0237] The barrier layer 10 may have both structures shown in the
embodiments A and B of the embodiment (3).
[0238] In the electroluminescent device of the embodiment (4), in
the case of the embodiment A in which the barrier layer 10 has a
refractive-index identical to or higher than that of the
transparent electrode layer 3, the total reflection of light at the
boundary surface between the barrier layer 10 and the evanescent
light-scattering layer A 4b is decreased similarly to the
embodiment A of the embodiment (3).
[0239] Since the refractive index of the matrix of the evanescent
light-scattering layer A 4b is substantially identical to that of
the low-refractive layer 4, no total reflection is caused at the
boundary surface between the evanescent light-scattering layer A 4b
and the low-refractive layer 4. As a result, the light entering
from the side of the transparent electrode layer to the evanescent
light-scattering layer A 4b reaches the boundary surface between
the evanescent light-scattering layer A 4b and the low-refractive
layer 4, and then enters into the low-refractive layer 4
substantially without change. Consequently, the electroluminescent
device is enhanced in light extraction efficiency.
[0240] Also, in the embodiment (4), the barrier layer 10 may
exhibit a low refractive index and have a very small thickness
similarly to the embodiment B of the embodiment (3). In this case,
similarly to the embodiment A, the light extraction efficiency can
be enhanced.
[0241] FIG. 6 shows an electroluminescent device of a top emission
type as shown in the embodiment (3). In this embodiment, a cathode
1 is formed on a substrate 5, and on the cathode 1 are successively
provided an electroluminescent layer 2, a transparent electrode
layer 3, a barrier layer 10 and an evanescent light-scattering
layer A 4a. On the evanescent light-scattering layer A 4a is
further provided a protective cover 6. Optically, the protective
cover has a function as the substrate of the embodiment (3).
[0242] Meanwhile, only in the electroluminescent device of a top
emission type as shown in FIG. 6 in which the substrate 5 is
disposed on the side of the cathode 1, the low-refractive layer 4
containing no particles may be replaced with an air layer (voids)
without problems concerning a structure of the device. In this
case, the refractive index of the air layer is 1.0. Also, the upper
limit of the thickness of the air layer is not particularly limited
because the air layer is free from problems concerning flatness of
the film and prevention of cracks.
[0243] The electroluminescent device shown in FIG. 6 is of a top
emission type in which the substrate 5 of the embodiment (3) is
disposed on the side of cathode 1. In the embodiment (4), the
device may also be of a top emission type in which the substrate 5
is similarly disposed on the side of the cathode.
[0244] Meanwhile, in the second invention, the thickness of the
transparent electrode may be determined so as to satisfy the above
light transmittance and sheet resistivity value. Specifically, the
thickness of the transparent electrode is preferably 10 to 500 nm,
and the lower limit thereof is more preferably 50 nm, still more
preferably 100 nm in the consideration of a good conductivity. On
the other hand, in the consideration of light transmittance as well
as prevention of peeling-off of film layers and cracks in the film,
the upper limit of the thickness of the transparent electrode is
more preferably 300 nm, still more preferably 200 nm.
<Third Invention>
[0245] The electroluminescent device shown in FIG. 7 (embodiment
(5)) has such a layer structure in which a cathode 1, an
electroluminescent layer 2, a transparent electrode layer 3a
containing light-scattering particles, a low-refractive layer 4 and
a transparent substrate 5 are successively laminated on each other
in this order.
[0246] The transparent electrode layer 3a containing
light-scattering particles is a layer in which the light-scattering
particles are dispersed in a matrix of the transparent electrode.
As the matrix, there may be used the materials for the transparent
electrode layer as described previously.
[0247] The transparent electrode layer 3a containing
light-scattering particles may be produced by such a coating method
of applying a raw solution containing the light-scattering
particles. Examples of the coating solution for forming the
transparent electrode layer 3a containing light-scattering
particles may include a coating solution prepared by dispersing
fine particles of conductive materials such as ITO or semiconductor
materials together with conductive polymers or other resin binders
in an organic solvent, the conductive polymers by themselves, etc.,
though not particularly limited thereto. In order to incorporate
the light-scattering particles in the above matrix, the particles
may be merely added to the coating solution. Using the coating
solution, patterns required as an electrode for the
electroluminescent device are formed by a printing method such as a
photo-lithographic method and an ink-jet printing method.
Meanwhile, after patterning, the resultant patterns have a line
width of usually about 1 to 10 .mu.m, though not particularly
limited thereto. The thickness of the transparent electrode layer
containing light-scattering particles is not particularly limited
as long as it is substantially identical to the thickness of the
transparent electrode layer described previously, and is preferably
2 times or more the average particle size of the light-scattering
particles.
[0248] As the particles contained in the transparent electrode
layer 3a containing light-scattering particles, there may be used
the same light-scattering particles as contained in the above
evanescent light-scattering layer A.
[0249] The content of the light-scattering particles in the
transparent electrode layer is usually 0.1 to 40% by volume,
preferably 1 to 10% by volume. When the content of the
light-scattering particles is too small, it is not possible to
attain a sufficient light scattering effect. When the content of
the light-scattering particles is too large, the light extraction
efficiency tends to be deteriorated because of the high hiding
effect.
[0250] In the electroluminescent device of the embodiment (5), the
transparent electrode layer 3a containing light-scattering
particles serves for increasing an amount of light entering from
the transparent electrode layer 3a containing light-scattering
particles into the low-refractive layer 4 and thereby enhancing the
light extraction efficiency in the following manner. That is, among
the light which is incident to the boundary surface between the
transparent electrode layer 3a containing light-scattering
particles and the low-refractive layer 4, the light having an
incident angle smaller than the critical angle directly enters from
the transparent electrode layer 3a containing light-scattering
particles into the low-refractive layer 4. On the other hand, the
light having an incident angle larger than the critical angle
undergoes total reflection at the boundary surface facing the
low-refractive layer 4, and then returned to the transparent
electrode layer 3a containing light-scattering particles. A part of
the light thus returned to the transparent electrode layer 3a
containing light-scattering particles is scattered by the particles
contained in the transparent electrode layer 3a containing
light-scattering particles. Further, a part of the scattered light
is incident again onto the boundary surface facing the
low-refractive layer 4. Among the scattered light being incident
again onto the boundary surface facing the low-refractive layer 4,
the light having an incident angle smaller than the critical angle
enters from the transparent electrode layer 3a containing
light-scattering particles into the low-refractive layer 4 without
undergoing total reflection. Among the scattered light being
incident again onto the boundary surface, the light having an
incident angle larger than the critical angle is returned again to
the side of the transparent electrode layer 3a containing
light-scattering particles, and a part of the light thus returned
is scattered again by the particles. When this operation is
repeated, a remaining part of the light also gradually enters into
the side of the low-refractive layer 4.
[0251] Among the light subjected to total reflection at the
boundary surface between the low-refractive layer 4 and the
transparent electrode layer 3a containing light-scattering
particles, the light reaching the boundary surface between the
electroluminescent layer 2 and the transparent electrode layer 3a
containing light-scattering particles undergoes total reflection
when the incident angle thereof to this boundary surface is larger
than the critical angle, and proceed again toward the boundary
surface between the low-refractive layer 4 and the transparent
electrode layer 3a containing light-scattering particles.
Thereafter, the behavior of the light is the same as described
above, i.e., the light gradually enters into the low-refractive
layer 4.
[0252] On the other hand, the light which is incident onto the
boundary surface between the transparent electrode layer 3a
containing light-scattering particles and the electroluminescent
layer 2 from the side of the transparent electrode layer 3a
containing light-scattering particles at an incident angle smaller
than the critical angle directly enters into the electroluminescent
layer 2, and then is reflected on the boundary surface between the
electroluminescent layer 2 and the cathode 1. The reflected light
is penetrated again through the electroluminescent layer 2 and the
transparent electrode layer 3a containing light-scattering
particles, and returned to the boundary surface between the
transparent electrode layer 3a containing light-scattering
particles and the low-refractive layer 4. Thereafter, the behavior
of the light is the same as described above.
[0253] Thus, in this embodiment, the total reflection on the side
of the transparent electrode layer-relative to the low-refractive
layer 4 is decreased, resulting in enhancement of light extraction
efficiency.
[0254] The electroluminescent device shown in FIG. 8 (embodiment
(6)) has such a layer structure in which a cathode 1, an
electroluminescent layer 2, a transparent electrode layer 3, an
evanescent light-scattering layer B 3b, a low-refractive layer 4
and a transparent substrate 5 are successively laminated on each
other in this order.
[0255] The refractive index of a matrix component of the evanescent
light-scattering layer B 3b is substantially identical to that of
the transparent electrode layer 3. For example, in the embodiment
(6), the difference between refractive indices of the matrix
component of the evanescent light-scattering layer B 3b and the
transparent electrode layer 3 is usually not more than 0.3,
preferably not more than 0.2, more preferably not more than
0.1.
[0256] As the matrix material of the evanescent light-scattering
layer B 3b in the embodiment (6), there may be used the same
material as that of the transparent electrode layer 3. Also,
although the matrix component of the evanescent light-scattering
layer B 3b preferably has the same composition as that of the
transparent electrode layer 3, both may be different in composition
from each other.
[0257] The evanescent light-scattering layer B 3b used in the
embodiment (6) may be formed by the same method as the method for
producing the transparent electrode layer 3 used in the embodiment
(5). The transparent electrode layer 3 containing no particles may
be formed by using a coating solution containing no particles, or
may also be formed by a film-forming process such as vapor
deposition and sputtering.
[0258] The thickness of the transparent electrode layer 3 used in
the embodiment (6) is generally 2 times or more the average
particle size of the light-scattering particles, and is usually 100
to 5000 nm, preferably 200 to 1000 nm. The thickness of the
evanescent light-scattering layer B 3b is usually 100 to 5000 nm,
preferably 200 to 1000 nm.
[0259] As the particles contained in the evanescent
light-scattering layer B 3b, there may be used the same
light-scattering particles as used in the above evanescent
light-scattering layer A.
[0260] The content of the light-scattering particles in the
evanescent light-scattering layer B 3b is usually 0.1 to 40% by
volume, preferably 1 to 10% by volume. When the content of the
particles is too small, the evanescent light-scattering layer B 3b
may fail to exhibit a sufficient light-scattering effect. When the
content of the particles is too large, the evanescent
light-scattering layer B 3b tends to show a too high hiding effect,
resulting in a poor light extraction efficiency thereof.
[0261] In the electroluminescent device of the embodiment (6), the
evanescent light-scattering layer B 3b which is disposed between
the transparent electrode layer 3 and the low-refractive layer 4
serves for increasing an amount of light entering from the
transparent electrode layer 3 into the low-refractive layer 4 and
enhancing the light extraction efficiency as follows. That is,
since the refractive index of the matrix of the evanescent
light-scattering layer B 3b is substantially identical to that of
the transparent electrode layer 3, no total reflection is caused at
the boundary surface between the transparent electrode layer 3 and
the evanescent light-scattering layer B 3b.
[0262] Among the light which enters from the transparent electrode
layer 3 into the evanescent light-scattering layer B 3b, passes
through the evanescent light-scattering layer B 3b and then is
incident onto the boundary surface between the evanescent
light-scattering layer B 3b and the low-refractive layer 4, the
light having an incident angle smaller than the critical angle
directly enters from the evanescent light-scattering layer B 3b
into the low-refractive layer 4, whereas the light having an
incident angle larger than the critical angle undergoes total
reflection at the boundary surface facing to the low-refractive
layer 4, and then returned to the evanescent light-scattering layer
B 3b. A part of the light thus returned to the evanescent
light-scattering layer B 3b is scattered by the particles contained
in the evanescent light-scattering layer B 3b. Further, a part of
the scattered light is incident again onto the boundary surface
facing to the low-refractive layer 4. Among the scattered light
being incident again onto the boundary surface facing to the
low-refractive layer 4, the light having an incident angle smaller
than the critical angle enters from the evanescent light-scattering
layer B 3b into the low-refractive layer 4 without undergoing total
reflection. Among the scattered light being incident again onto the
boundary surface, the light having an incident angle larger than
the critical angle is returned again to the side of the evanescent
light-scattering layer B 3b, and a part of the light thus returned
is scattered again by the particles. When this operation is
repeated, a remaining part of the light also gradually enters into
the side of the low-refractive layer 4.
[0263] Among the light undergoing total reflection at the boundary
surface between the low-refractive layer 4 and the evanescent
light-scattering layer B 3b, the light reaching the boundary
surface between the evanescent light-scattering layer B 3b and the
transparent electrode layer 3 directly enters into the transparent
electrode layer 3 owing to no difference in refractive index
therebetween, and is returned to the boundary surface between the
transparent electrode layer 3 and the electroluminescent layer 2.
The light which is incident onto the boundary surface at an
incident angle larger than the critical angle, undergoes total
reflection at the boundary surface, and proceeds again toward the
boundary surface between the low-refractive layer 4 and the
evanescent light-scattering layer B 3b. Thereafter, the behavior of
the light is the same as described above, so that the light
gradually enters into the low-refractive layer 4.
[0264] On the other hand, the light being incident onto the
boundary surface between the transparent electrode layer 3 and the
electroluminescent layer 2 from the side of the transparent
electrode layer 3 at an incident angle smaller than the critical
angle directly enters into the electroluminescent layer 2, and then
is reflected on the boundary surface between the electroluminescent
layer 2 and the cathode 1. The reflected light is penetrated again
through the electroluminescent layer 2 and the transparent
electrode layer 3, and returned to the boundary surface between the
transparent electrode layer 3 and the evanescent light-scattering
layer B 3b. Thereafter, the behavior of the light is the same as
described above.
[0265] Thus, also, in the electroluminescent device of the
embodiment (6), the total reflection on the side of the transparent
electrode layer 3 relative to the low-refractive layer 4 is
decreased, resulting in enhanced light extraction efficiency
thereof.
[0266] Meanwhile, the evanescent light-scattering layer B 3b
provided in the embodiment (6) may be replaced with a
particle-containing layer whose matrix is composed of a material
having substantially the same refractive index as that of the
transparent electrode layer 3 containing no particles. Examples of
the matrix material may include aromatic resins such as polyether
sulfones, and those resins having a good transparency which are
obtained by dispersing fine particles of a high-refractive material
such as titania and zirconia in the aromatic resins. Examples of
the material of the light-scattering particles may include titania,
zirconia, silica, air, etc. These particles may be dispersed in a
size capable of scattering the light.
[0267] In the embodiments (5) and (6), the substrate 5 is disposed
as an outermost surface layer as viewed from the side of the
electroluminescent layer 2 (bottom emission type). Alternatively,
the substrate may be disposed on an outside of the cathode, and a
protective cover may be disposed as an outermost surface layer as
viewed from the side of the electroluminescent layer 2 (top
emission type).
[0268] FIG. 9 shows a top emission type of the embodiment (5) in
which a cathode 1 is formed on a substrate 5, and on the cathode 1
are successively formed an electroluminescent layer 2, a
transparent electrode layer 3, an evanescent light-scattering layer
B 3b, and a low-refractive layer 4 on which a protective cover 6 is
further provided. The embodiment shown in FIG. 9 has such a
structure in which the substrate 5 in the embodiment (5) is
disposed on the side of the cathode 1. Also, in the embodiment (6),
the substrate 5 may be disposed on the side of the cathode 1.
<Fourth Invention>
[0269] The electroluminescent device shown in FIG. 10 (embodiment
(7)) has such a layer structure in which a cathode 1, an
electroluminescent layer 2, a transparent electrode layer 3, a
low-refractive layer 4 and a transparent substrate 5 are
successively laminated on each other in this order, and a
light-scattering rough surface is provided at a boundary surface
between the low-refractive layer 4 and the transparent electrode
layer 3.
[0270] In order to form the boundary surface between the
low-refractive layer 4 and the transparent electrode layer 3 into
such a light-scattering rough surface, after forming the
low-refractive layer 4, the surface thereof is subjected to
treatment for forming roughness thereon, and then the transparent
electrode layer 3 is formed on the thus formed rough surface of the
low-refractive layer 4.
[0271] Examples of the method of forming the roughness on the
low-refractive layer 4 may include a method of subjecting the
surface of the low-refractive-layer thus formed to corona
treatment, plasma treatment, blast treatment, etc., to form a
coarsely etched surface, a method of physically transferring an
rough surface pattern on the surface of the low-refractive layer, a
method of rubbing the surface of the low-refractive layer with the
rough surface, a method of forming the low-refractive layer while
contacting with the rough surface, or a method of applying or
embedding fine particles having a size capable of scattering light
into the surface of the low-refractive layer by any suitable
method.
[0272] After subjecting the low-refractive layer 4 to the treatment
for forming roughness on the surface thereof, the transparent
electrode layer 3 is uniformly formed on the rough surface.
Therefore, the transparent electrode layer 3 is preferably formed
by a coating method of applying a raw coating solution on the rough
surface of the low-refractive layer 4.
[0273] As the composition of the coating solution for forming the
transparent electrode layer 3, there may be used, for example,
those compositions prepared by dispersing ITO fine particles
together with conductive polymers or other resin binders in an
organic solvent, or conductive polymer materials, though not
particularly limited thereto.
[0274] Using the coating solution, patterns required as an
electrode of the electroluminescent device are formed by a
photo-lithographic method, an ink-jet printing method, etc. The
line width of the respective patterns is normally about 1 to 10
.mu.m, though not particularly limited thereto.
[0275] In the embodiment (7), since the boundary surface between
the transparent electrode layer 3 and the low-refractive layer
(which may be omitted in some cases) is formed into a
light-scattering rough surface, total reflection on the boundary
surface is decreased, so that an amount of light entering from the
transparent electrode layer 3 into the low-refractive layer 4 is
increased, resulting in enhanced light extraction efficiency. In
order to fully decrease the total reflection, the surface roughness
Ra of the boundary surface is usually 5 to 200 nm, preferably 10 to
100 nm, more preferably 20 to 50 nm.
[0276] The surface roughness Ra of the boundary surface is usually
about 5 to 200 nm, preferably about 10 to 100 nm, more preferably
about 20 to 50 nm; and Rmax thereof is usually about 30 to 600 nm,
preferably about 50 to 500 nm, more preferably about 100 to 300
nm.
[0277] The surface roughness parameters Ra and Rmax may be
evaluated using a probe-type surface roughness meter "KLA-Tencor
P-15 Model" manufactured by KLA-Tencor Inc., according to the
method prescribed in JIS B 0601. In the measurement, one scanning
distance is usually 0.5 .mu.m, and an average value obtained from
three scanning operations is regarded as the measured value.
[0278] The shape and size of roughness formed on the coarse surface
are not particularly limited as long as the surface has a function
of scattering light. The size of roughness formed on the coarse
surface is more than 1/10 of a wavelength of light to be scattered
thereon (usually 400 to 700 nm because of visible light). In
general, when the size of roughness is up to several times the
wavelength, the light scattering efficiency is increased with
increase in size of the roughness. However, when the size of the
roughness is too large, a coating layer formed thereon tends to be
deteriorated in flatness.
[0279] In the electroluminescent device of the embodiment (7),
since the boundary surface between the transparent electrode layer
3 and the low-refractive layer is formed into a light-scattering
rough surface, total reflection at the boundary surface is
decreased, so that an amount of light entering from the transparent
electrode layer 3 to the low-refractive layer 4 directly or
indirectly after reflection on the cathode, is increased, resulting
in enhanced light extraction efficiency. More specifically, the
guided light on the side of light-emitting layer relative to the
transparent electrode layer is extracted from the light-scattering
coarse surface (rough surface), refracted in the direction near
perpendicular to the transparent substrate through the
low-refractive layer, and then enters into the transparent
substrate, thereby preventing total reflection at a boundary
surface between the transparent substrate and the air layer.
[0280] The electroluminescent device shown in FIG. 11 (embodiment
(8)) has such a layer structure in which a cathode 1, an
electroluminescent layer 2, a transparent electrode layer 3c, a
high-refractive layer 8, a low-refractive layer 4 and a transparent
substrate 5 are successively laminated on each other in this order,
and a light-scattering rough surface is provided at a boundary
surface between the low-refractive layer 4 and the high-refractive
layer 8.
[0281] The refractive index of the high-refractive layer 8 is
substantially identical to that of the transparent electrode layer
3c. More specifically, the difference between refractive indices of
the high-refractive layer 8 and the transparent electrode layer 3c
is usually not more than 0.3, preferably not more than 0.2, more
preferably not more than 0.1.
[0282] The composition of the high-refractive layer 8 may be the
same as or difference from that of the transparent electrode layer
3c. As the composition of the high-refractive layer 8 which is
different from that of the transparent electrode layer 3c, there
may be exemplified compositions having a good transparency which
are prepared by dispersing fine particles (nanoparticles) of
high-refractive materials such as ATO (antimony tin oxide), ITO,
zirconia and titania in a high-refractive resin such as polyether
sulfone resins and polyether imide resins, or resin materials
containing these resins. These compositions is preferably dissolved
or dispersed in an organic solvent to form a coating solution
thereof.
[0283] The high-refractive layer 8 is preferably formed by the
coating method similarly to the transparent electrode layer 3 in
the embodiment (7). The reason why the coating method is preferred
is that the boundary surface of the transparent electrode facing to
the side of the electroluminescent layer is required to have a good
flatness. The coating method enables formation of the flat surface
by filling roughness of the underlying layer. In a vacuum process
such as vapor deposition and sputtering, the roughness of the
underlying layer tends to be readily reflected onto the surface of
the upper layer, so that it may be difficult to form a surface
having a good flatness. Meanwhile, the reason why the boundary
surface of the transparent electrode facing to the side of the
electroluminescent layer is required to have a good flatness, is
that a uniform electric field is to be produced within the
electroluminescent layer. If the electric field is non-uniform, EL
pigments tends to be deteriorated, resulting in defects such as
dark spots. The transparent electrode layer 3c may be formed by the
same coating method as used for formation of the above transparent
electrode layer 3, or by a film-forming process such as vapor
deposition and sputtering.
[0284] The thickness of the transparent electrode layer 3c is
substantially identical to that of the above transparent electrode
layer 3. For example, the thickness of the high-refractive layer 8
is usually 100 to 3000 nm, preferably 500 to 1000 nm in the
consideration of facilitated film formation and flattening of
roughness on the underlying layer.
[0285] In the electroluminescent device of this embodiment, since
the boundary surface between the high-refractive layer 8 and the
low-refractive layer 4 is formed into a light-scattering rough
surface, the total reflection on the boundary surface is decreased,
so that an amount of light entering from the side of the
transparent electrode layer 3c into the low-refractive layer 4 is
increased, resulting in enhanced light extraction efficiency. The
range of surface roughness of the rough boundary surface is
substantially identical to that shown in FIG. 7.
[0286] In the embodiments (7) and (8), the substrate 5 is disposed
as an outermost surface layer as viewed from the side of the
electroluminescent layer 2 (bottom emission type). However, as
shown in FIG. 12, the substrate may be disposed outside of the
cathode, and a protective cover may be disposed as an outermost
surface layer as viewed from the side of the electroluminescent
layer 2 (top emission type). In the top emission type embodiment
shown in FIG. 12, a cathode 1 is formed on a substrate 5, and on
the cathode 1 are successively formed an electroluminescent layer
2, a transparent electrode layer 3, and a low-refractive layer 4 on
which a protective cover 6 is further provided. Meanwhile, in this
embodiment, the substrate 5 is not necessarily transparent.
Optically, the protective cover used in this embodiment exhibits a
function of the transparent substrate in the embodiment (7). Also,
only in this embodiment, the low-refractive layer may be replaced
with air itself (voids) without problems concerning a structure of
the device.
[0287] The embodiment shown in FIG. 12 has such a structure in
which the substrate 5 in the embodiment (7) is disposed on the side
of the cathode 1. Also, in the embodiment (8), the substrate 5 may
be disposed on the side of the cathode 1.
EXAMPLES
[0288] The present invention is described in more detail by
Reference Examples corresponding to Examples, but the Reference
Examples are only illustrative and not intended to limit the scope
of the present invention. Meanwhile, in the following Reference
Examples and Comparative Examples, neither cathode nor
electroluminescent layer were formed, and a fluorescent pigment
layer was formed on a transparent electrode layer. The fluorescent
pigment layer was irradiated with excitation light to extract a
fluorescence from the side of a substrate and measure an amount of
light extracted using a fluorescence spectrometer/luminance meter
manufactured by Hitachi Ltd., in the following procedure. That is,
excitation light having a wavelength of not more than 400 nm was
irradiated on a rear surface (the side on which fluorescent pigment
was vapor-deposited) of the obtained laminate, from the side of the
fluorescent pigment layer, and an intensity of the extracted light
having a wavelength of 420 to 750 nm was measured by a detector
disposed in the direction of 45.degree. as an incident angle to
substrate from transparent electrode on the surface facing a glass
substrate to obtain a light emission energy integrated as to a
whole wavelength. The measurement was conducted using a
fluorescence spectrometer/luminance meter "F-4500 Model"
manufactured by Hitachi Ltd. Meanwhile, the light emission energy
as measured was expressed by the relative value on the basis of the
result obtained in Comparative Example 1.
[0289] The average particle size was measured by FIB-SEM
method.
[0290] The refractive index was measured using an "ellipsometer"
(manufactured by "Sopra") on the basis of Standard D542. However,
in the case where it was difficult to measure a refractive index of
the matrix portion composed of a meso(nano)-porous material or a
particle-dispersed material using the "ellipsometer", the
refractive index was measured at 25.degree. C. by a laser having a
wavelength of 633 nm using "PRISM COUPLER MODEL 2010" manufactured
by Metricon Inc., USA.
Reference Examples 1 to 5
[0291] These Reference Examples were conducted for explaining the
first invention.
Reference Example 1
Corresponding to Embodiment (1)
[0292] A glass plate having a thickness of 0.7 mm and a size of 75
mm square which was composed of a non-alkali glass "AN100" produced
by Asahi Glass Co., Ltd., was immersed in 0.1N nitric acid for
about one hour to subject the surface thereof to degreasing
treatment, washed with pure water and then dried in an oven at
60.degree. C., thereby obtaining a glass substrate 1.
[0293] Separately, a small amount of an acid catalyst (aluminum
acetylacetonate) was added to a mixed solution containing 30% by
weight of an oligomer of tetramethoxysilane ("MS51" produced by
Mitsubishi Chemical Corporation), 50% by weight of BtOH, 8% by
weight of desalted water and 12% by weight of MeOH, and then silica
fine particles having an average particle size of 120 nm and
containing particles having a particle size of from 70 to 150 nm in
an amount of not less than 60% by weight, were added to the
resultant solution such that the weight ratio of the silica fine
particles to MS51 was 10%. The resultant mixture was stirred at
60.degree. C. for 3 hours, and allowed to stand for one week for
aging.
[0294] The thus obtained coating solution was applied onto the
glass substrate 1 using a dip coater. The coated glass substrate
was dried for 15 min, immersed in methanol for 5 min, taken out and
dried for 5 min, and then heated in an oven at 150.degree. C. for
15 min, thereby forming an evanescent light-scattering layer A 4a
thereon. Meanwhile, upon the dip-coating, a protective film was
attached onto a rear surface of the substrate, and peeled off after
coating, thereby forming the coating film on only one surface
thereof.
[0295] It was confirmed that the thickness of the thus obtained
evanescent light-scattering layer A 4a was 600 nm and had a
structure in which light-scattering particles were overlapped on
each other in about five layers. As a result of measuring a
refractive index of a matrix portion of the evanescent
light-scattering layer A 4a using an ellipsometer manufactured by
"Sopra", it was confirmed that the refractive index was 1.27 at a
wavelength of 550 nm. Further, as a result of measuring the
refractive index using "PRISM COUPLER MODEL 2010" manufactured by
Metricon Inc., USA., in which a laser having a wavelength of 633 nm
was used, it was confirmed that the refractive index was 1.29.
[0296] The thickness of a vapor-deposited film or a sputtered film
was measured by time management from a calibration curve or a
quartz oscillation-type film thickness meter. The thickness of the
coating film was measured by a light interference-type thickness
meter or by measuring the step formed by scratching the film. The
thickness of a thick plate such as a glass substrate was measured
using micro-calipers, etc.
[0297] Cold sputtering process was conducted to form a 1000
.ANG.-thick ITO transparent electrode 3 on the evanescent
light-scattering layer A 4a, and then a 1000 .ANG.-thick film
composed of ALQ3 (aluminum quinoline complex: pigment emitting a
green fluorescence) was vapor-deposited on the ITO transparent
electrode layer. As a result, it was confirmed that the refractive
index of the ITO layer was 1.9.
[0298] Further, it was confirmed that the amount of light extracted
from the above device was 170% when expressed by a relative value
on the basis of the amount of light extracted in the
below-mentioned Comparative Example 1.
Comparative Example 1
Corresponding to the Prior Art Shown in FIG. 14
[0299] The same procedure as defined in Reference Example 1 was
conducted except that no silica fine particles were added to the
coating solution for forming the evanescent light-scattering layer,
thereby producing a fluorescent device having a layer structure
corresponding to that shown in FIG. 14, and measuring the amount of
light extracted therefrom by the same method.
Comparative Example 2
Corresponding to the Prior Art Shown in FIG. 13a)
[0300] The same procedure as defined in Reference Example 1 was
conducted except that the evanescent light-scattering layer was
omitted, thereby producing a fluorescent device having a layer
structure corresponding to that shown in FIG. 13a, and measuring
the amount of light extracted therefrom by the same method.
[0301] As a result, it was confirmed that the amount of light
extracted from the above device was 91% on the basis of that in
Comparative Example 1.
Reference Example 2
Corresponding to Embodiment (2) Shown in FIG. 2
[0302] The coating solution containing no silica fine particles
used in Comparative Example 1 was coated to form a low-refractive
layer 4 having a thickness of 500 nm, and further the coating
solution containing silica fine particles used in Reference Example
1 was applied onto the low-refractive layer to form an evanescent
light-scattering layer 4b having a thickness of 600 nm thereon.
[0303] On the evanescent light-scattering layer 4b, cold sputtering
process was conducted by the same method as defined in Reference
Example 1, thereby forming a 1000 .ANG.-thick ITO transparent
electrode layer, and further a 1000 .ANG.-thick ALQ3 layer was
vapor-deposited on the ITO transparent electrode layer.
[0304] As a result, it was confirmed that the amount of light
extracted from the above device was 190% on the basis of that in
Comparative Example 1.
Reference Example 3
[0305] A glass substrate was prepared by the same method as defined
in Reference Example 1. A coating solution was prepared as follows.
That is, a small amount of an acid catalyst (aluminum
acetylacetonate) was added to a mixed solution containing 30% by
weight of "MS51" (oligomer of tetramethoxysilane) produced by
Mitsubishi Chemical Corporation, 50% by weight of butyl alcohol, 8%
by weight of desalted water and 12% by weight of methanol. In this
case, titania particles having an average particle size of 200 nm
were previously dispersed in butyl alcohol such that the weight
percentage of the titania particles in the resultant
particle-containing layer was 8% by weight. Meanwhile, the weight
percentage of the particles in the particle-containing layer was
measured by the same method as used above for measurement of the
particle size distribution in the film. The conversion of volume
into weight was conducted by measuring a density of the particles
and a matrix of the layer. In the case where the matrix was porous,
the density was calculated from X-ray reflectance or refractive
index measured. The resultant mixed solution was stirred at
60.degree. C. for 3 hours, and allowed to stand for one week for
aging.
[0306] The thus aged coating mixed solution was applied onto the
glass substrate by the same method as defined in Reference Example
1. As a result, it was confirmed that the thickness of the
particle-containing low-refractive layer (evanescent
light-scattering layer) was 500 nm, and the refractive index of the
matrix portion thereof was 1.40.
[0307] Under this condition, the light transmittance in the
direction perpendicular to the substrate was measured and compared
with the light transmittance in the direction perpendicular to the
substrate as described in Reference Example 1 to measure an amount
of light scattered. The measurement of the light transmittance was
conducted using an ultraviolet/visible light absorptiometer "HP8453
Model" manufactured by Hewlett Packard Inc.
[0308] Also, in order to ascertain a good flatness of the surface
itself (free from scattering on the surface), the surface roughness
was measured using a probe-type surface roughness tester "P-15
Model" manufactured by KLA-Tencor Inc. As a result of the
measurement using a scanning distance of 0.5 .mu.m, it was
confirmed that the surface roughness Ra was 4 nm.
[0309] The thus obtained laminate was subjected to cold sputtering
process by the same method as defined in Reference Example 1 to
form a 1000 .ANG.-thick ITO transparent electrode thereon. Further,
a 1000 .ANG.-thick layer composed of a green fluorescent pigment
ALQ3 (8-hydroxyquinoline aluminum) and a 1000 .ANG.-thick layer
composed of a red fluorescent pigment PPD (phenanthryl phenylene
diamine) were respectively formed on the ITO transparent electrode
by vapor-deposition, thereby preparing one test specimen for each
pigment layer.
[0310] Using the thus prepared laminates, the fluorescence
intensity thereof was measured by the same method as defined in
Reference Example 1. More specifically, the peak fluorescence
intensity was measured in the direction of 30.degree. (as an
incident angle to substrate from transparent electrode) when
measured from the vertical direction of a light emission side of
the glass substrate. The peak fluorescence intensity of the test
specimen vapor-deposited with ALQ3 was measured using a wavelength
of 550 nm, whereas the peak fluorescence intensity of the test
specimen vapor-deposited with PPD was measured using a wavelength
of 450 nm.
[0311] The scattering loss of light was measured according to the
above procedure. As a result, it was confirmed that the scattering
loss of light based on the amount of light penetrated through the
resultant laminate was 39% at a wavelength of 450 nm and 28% at a
wavelength of 550 nm.
[0312] The light extraction efficiency of the respective
fluorescent pigment-deposited laminates based on that in the
below-mentioned Comparative Example 3 was as follows.
[0313] That is, it was confirmed that the light extraction
efficiency was 240% for PPD at wavelength of 450 nm, and 190% for
ALQ3 at a wavelength of 550 nm.
[0314] As a result, it was recognized that the light extraction
efficiency was enhanced over a whole visible light range, and in
particular, the light extraction efficiency of blue color light was
remarkably enhanced as compared to that of green color light.
Comparative Example 3
[0315] The same procedure as defined in Reference Example 3 was
conducted except that no titania particles were added to the
coating solution, thereby producing a fluorescent device, and
measuring the amount of light extracted therefrom by the same
method.
[0316] As a result of measuring the surface roughness by the same
method as defined in Reference Example 3, it was confirmed that the
surface roughness Ra was 2 nm.
Reference Example 4
[0317] A polycarbonate resin "7020AD2" produced by Mitsubishi
Engineering-Plastics Corporation, was dissolved in methylene
chloride, and then titania particles (titanium dioxide) having a
particle size of 200 nm were dispersed in the obtained solution
such that the weight percentage of the titania particles in the
resultant particle-containing layer was 10% by weight. The obtained
dispersion was applied together with a solvent onto a glass
substrate produced by the same method as defined in Reference
Example 1 using a dip coater, and then dried at room temperature,
thereby forming an evanescent light-scattering layer
(particle-containing layer).
[0318] It was confirmed that the thickness of the evanescent
light-scattering layer was 600 nm, and the refractive index of the
matrix portion thereof as measured was 1.59. Further, as a result
of measuring the surface roughness by the same method as defined in
Reference Example 3, it was confirmed that the surface roughness Ra
was 4 nm.
[0319] An ITO film and a pigment layer were successively formed on
the resultant coated substrate by the same method as defined in
Reference Example 3, and the resultant laminate was subjected to
the measurement of fluorescence intensity. The measurement of the
fluorescence intensity was conducted in the direction of 30.degree.
from the direction perpendicular to the light emission side of the
glass substrate.
[0320] As a result, it was confirmed that the amount of light
extracted from the above device was 170% (at a wavelength of 550
nm) as a relative value as measured in the same direction in the
below-mentioned Comparative Example 4.
Comparative Example 4
[0321] The same procedure as defined in Reference Example 4 was
conducted except that no alumina particles were added to the
coating solution, thereby producing a fluorescent device, and
measuring the amount of light extracted therefrom by the same
method. As a result of measuring the surface roughness by the same
method as defined in Reference Example 4, it was confirmed that the
surface roughness Ra was 2 nm.
Reference Example 5
[0322] After forming a 200 .ANG.-thick silica deposited film having
a combined function as anchor coat and a barrier coat on a 120
.mu.m-thick PET film produced by Mitsubishi Polyester Film
Corporation, an evanescent light-scattering layer
(particle-containing layer) was formed on the silica deposited film
by the same method as defined in Reference Example 4. Meanwhile,
before the evanescent light-scattering layer was completely dried
up, the thus formed laminated film was closely contacted with an
ITO-coated glass substrate. As a result, it was possible to adhere
the film onto the ITO surface.
[0323] On the evanescent light-scattering layer of the film were
successively formed an ITO layer and an ALO3 layer by the same
method as defined in Reference Example 3, and further the resultant
laminate was evaluated.
[0324] As a result, it was confirmed that the thickness of the
evanescent light-scattering layer was 600 nm, and the refractive
index of a matrix portion thereof was 1.59. Further, as a result of
the measurement using a probe-type surface roughness tester "P-15"
manufactured by KLA-Tencor Inc., it was confirmed that the surface
roughness Ra was 4 nm.
[0325] The thus obtained substrate was subjected to measurement of
fluorescence intensity thereof by the same method as defined in
Reference Example 3. Further, the peak fluorescence intensity was
measured in the direction of 30.degree. (as an incident angle to
substrate from transparent electrode) from the vertical direction
of a light emission side of the glass substrate.
[0326] It was confirmed that the amount of light extracted from the
above device was 160% on the basis of the amount of light extracted
(at a wavelength of 550 nm) as similarly measured in the
below-mentioned Comparative Example 5. From the results, it is
expected that even when the laminate is used as an optical film for
light extraction in a top emission type device, the light
extraction efficiency is increased.
Comparative Example 5
[0327] The same procedure as defined in Reference Example 5 was
conducted except that the thickness of the film was changed to 2700
nm, thereby producing a fluorescent device, and measuring the
amount of light extracted therefrom by the same method. As a result
of measuring the surface roughness of a surface before forming the
transparent conductive film thereon using a probe-type surface
roughness tester "P-15" manufactured by KLA-Tencor Inc., it was
confirmed that the surface roughness Ra was 3 nm.
Reference Example 6
[0328] The same procedure as defined in Reference Example 4 was
conducted except that the thickness of the evanescent
light-scattering layer was changed to 1000 nm, thereby producing a
device and measuring the amount of light extracted therefrom. As a
result, it was confirmed that the amount of light extracted from
the above device was 150% (at a wavelength of 550 nm) on the basis
of the amount of light extracted in Comparative Example 4.
Comparative Example 6
[0329] The same procedure as defined in Reference Example 4 was
conducted except that the thickness of the evanescent
light-scattering layer was changed to 2700 nm, thereby producing a
device and measuring the amount of light extracted therefrom.
Although not limited to this Example, the required thickness was
achieved by repeating the coating operation plural times, if
required. As a result, it was confirmed that the amount of light
extracted from the above device was 80% (at a wavelength of 550 nm)
on the basis of the amount of light extracted in Comparative
Example 4. It was considered that the device became opaque because
of too large thickness of the evanescent light-scattering
layer.
Reference Examples 7 and 8 and Comparative Examples 7 and 8
[0330] These Reference Examples and Comparative Examples were
conducted for explaining the second invention.
Reference Example 7
Corresponding to Embodiment (3) Shown in FIG. 4
[0331] A glass plate having a thickness of 0.7 mm and a size of 75
mm square which was composed of a non-alkali glass "AN100" produced
by Asahi Glass Co., Ltd., was immersed in 0.1N nitric acid for
about one hour to subject the surface thereof to degreasing
treatment, washed with pure water and then dried in an oven at
60.degree. C., thereby obtaining a glass substrate 1.
[0332] Separately, a small amount of an acid catalyst (aluminum
acetylacetonate) was added to a mixed solution containing 30% by
weight of an oligomer of tetramethoxysilane ("MS51" produced by
Mitsubishi Chemical Corporation), 50% by weight of BtOH, 8% by
weight of desalted water and 12% by weight of MeOH, and then
titania fine particles having an average particle size of 120 nm
and containing particles having a particle size of from 70 to 150
nm in an amount of not less than 60% by weight, were added together
with a surfactant to the resultant solution such that the weight
ratio of the titania fine particles to MS51 was 10%. The resultant
mixture was stirred at 60.degree. C. for 3 hours, and allowed to
stand for one week for aging.
[0333] The thus aged coating solution was applied onto the glass
substrate 1 using a dip coater. The coated glass substrate was
dried for 15 min, immersed in methanol for 5 min, taken out and
dried for 5 min, and then heated in an oven at 150.degree. C. for
15 min, thereby forming an evanescent light-scattering layer 4a
thereon. Meanwhile, upon the dip-coating, a protective film was
adhered onto a rear surface of the substrate, and peeled off after
coating, thereby forming the coating film on only one surface
thereof.
[0334] It was confirmed that the thickness of the evanescent
light-scattering layer 4a was 600 nm and had a structure in which
light-scattering particles were overlapped on each other in about
five layers. As a result of measuring a refractive index of a
low-refractive film composed of only a matrix material (material
other than the fine particles) using an ellipsometer manufactured
by "Sopra", it was confirmed that the refractive index was 1.27 at
a wavelength of 550 nm.
[0335] Further, as a result of measuring the refractive index by
"PRISM COUPLER MODEL 2010" manufactured by Metricon Inc., USA, in
which a laser having a wavelength of 633 nm was used, it was
confirmed that the refractive index was 1.29.
[0336] Zirconium oxide was vapor-deposited on the evanescent
light-scattering layer 4a to form a 300 nm-thick barrier layer 10.
Further, ITO was cold-sputtered to form a 1000 .ANG.-thick
transparent electrode layer 3 on the barrier layer, and then a 1000
.ANG.-thick film composed of ALQ3 (fluorescent pigment:
(8-hydroxyquinolinolate)aluminum) was vapor-deposited on the ITO
transparent electrode layer. As a result of the measurement, it was
confirmed that the refractive index of the ITO layer was 1.9.
[0337] Further, it was confirmed that the amount of light extracted
from the above device was 170% on the basis of the amount of light
extracted in the below-mentioned Comparative Example 7.
Comparative Example 7
[0338] The same procedure as defined in the below-mentioned
Reference Example 8 was conducted except that no titania fine
particles were added to the coating solution for forming an
evanescent light-scattering layer, thereby producing a fluorescent
light-emitting device having a layer structure corresponding to
that shown in FIG. 14 and measuring an amount of light extracted
from the device by the same method.
Comparative Example 8
[0339] The same procedure as defined in Comparative Example 7 was
conducted except that the low-refractive layer 4 was omitted to
form a layer structure shown in FIG. 13a, thereby producing a
electroluminescent device and measuring an amount of light
extracted from the device by the same method.
[0340] As a result, it was confirmed that the amount of light
extracted was 91% on the basis of that of Comparative Example
7.
Reference Example 8
Corresponding to Embodiment (4) Shown in FIG. 5
[0341] The coating solution containing no titania fine particles as
used in Comparative Example 7 was coated to form a low-refractive
layer 4 having a thickness of 500 nm, and further the coating
solution containing titania fine particles as used in Reference
Example 7 was applied onto the low-refractive layer to form an
evanescent light-scattering layer 4b having a thickness of 600 nm
thereon.
[0342] Zirconium oxide was vapor-deposited on the evanescent
light-scattering layer 4b to form a barrier layer 10 having a
thickness of 300 nm. Then, ITO was cold-sputtered onto the barrier
layer to form a transparent electrode layer 3 having a thickness of
1000 .ANG., and further a 1000 .ANG.-thick ALQ3 layer was formed on
the ITO layer by vapor deposition, by the same method as defined in
Reference Example 7.
[0343] As a result of measuring an amount of light extracted from
the thus obtained device by the same method as defined in Reference
Example 7, it was confirmed that the amount of light extracted from
the device of Reference Example 8 was 190% on the basis of that of
Comparative Example 7.
Reference Examples 9 to 13 and Comparative Examples 9 to 11
[0344] These Reference Examples and Comparative Examples were
conducted for explaining the third invention.
Reference Example 9
Corresponding to Embodiment (5) Shown in FIG. 7
[0345] A glass plate having a thickness of 0.7 mm and a size of 75
mm square which was composed of a non-alkali glass "AN100" produced
by Asahi Glass Co., Ltd., was immersed in 0.1N nitric acid for
about one hour to subject the surface thereof to degreasing
treatment, washed with pure water and then dried in an oven at
60.degree. C., thereby obtaining a glass substrate 1.
[0346] Separately, a small amount of an acid catalyst (aluminum
acetylacetonate) was added to a mixed solution containing 30% by
weight of an oligomer of tetramethoxysilane ("MS51" produced by
Mitsubishi Chemical Corporation), 50% by weight of BtOH, 8% by
weight of desalted water and 12% by weight of MeOH, and the
resultant mixture was stirred at 60.degree. C. for 3 hours, and
allowed to stand for one week for aging.
[0347] The thus obtained coating solution was applied onto the
glass substrate 1 using a dip coater. The coated glass substrate
was dried for 15 min, immersed in methanol for 5 min, taken out and
dried for 5 min, and then heated in an oven at 150.degree. C. for
15 min, thereby forming a low-refractive layer 4 thereon.
Meanwhile, upon the dip-coating, a protective film was adhered onto
a rear surface of the substrate, and peeled off after coating,
thereby forming the coating film on only one surface thereof.
[0348] It was confirmed that the thickness of the low-refractive
layer 4 was 600 nm. As a result of measuring a refractive index of
the low-refractive layer using an ellipsometer manufactured by
"Sopra", it was confirmed that the refractive index was 1.27 at a
wavelength of 550 nm. Further, as a result of measuring the
refractive index using "PRISM COUPLER MODEL 2010" manufactured by
Metricon Inc., USA, it was confirmed that the refractive index was
1.31 at a wavelength of 633 nm.
[0349] Next, an evanescent light-scattering layer B 3a was formed
on the low-refractive layer 4 by the following procedure. That is,
small amounts of a polythiophene-based conductive polymer and
poly(3-alkylthiophene) were added to ITO fine particles having an
average particle size of 50 nm, and then titania particles having
an average particle size of 120 nm were dispersed in the mixture
such that the content of the titania particles was 5% by weight on
the basis of the total weight of the resultant mixture. The thus
obtained mixture was dissolved and dispersed in chloroform, and the
obtained coating solution was applied onto the low-refractive layer
using a spin coater and then dried. As a result, it was confirmed
that the obtained coating film had a thickness of 1000 nm, and the
refractive index of a matrix portion of the obtained film was
1.8.
[0350] Further, a 1000 .ANG.-thick film composed of ALQ3
(fluorescent pigment) was formed on the thus formed evanescent
light-scattering layer B 3a by vapor-deposition.
[0351] As a result, it was confirmed that the amount of light
extracted from the above device was 170% on the basis of that of
the below-mentioned Comparative Example 9.
Comparative Example 9
[0352] The same procedure as defined in Reference Example 9 was
conducted except that no titania fine particles were added to the
coating solution for forming a transparent electrode layer, thereby
producing a fluorescent device having a layer structure
corresponding to that shown in FIG. 14 and measuring an amount of
light extracted from the device by the same method.
Comparative Example 10
[0353] The same procedure as defined in Comparative Example 9 was
conducted except that the low-refractive layer 4 was omitted to
form a layer structure corresponding to that shown in FIG. 13a,
thereby producing a fluorescent device and measuring an amount of
light extracted from the device by the same method.
[0354] As a result, it was confirmed that the amount of light
extracted was 91% on the basis of that of Comparative Example
9.
Reference Example 10
Corresponding to Embodiment (6) Shown in FIG. 8
[0355] The same procedure as defined in Reference Example 9 was
conducted except that after forming an evanescent light-scattering
layer B 3b having a thickness of 500 nm using the coating solution,
the same coating solution as used above except for containing no
titania fine particles was applied thereonto to form a transparent
electrode layer 3 having a thickness of 500 nm, and further a 1000
.ANG.-thick ALQ3 layer was formed thereon by vapor deposition.
[0356] As a result, it was confirmed that the amount of light
extracted from the above device was 160% on the basis of that of
Comparative Example 9.
Reference Example 11
[0357] The same procedure as defined in Reference Example 9 was
conducted except that no low-refractive layer was formed, thereby
producing a fluorescent light-emitting device and measuring an
amount of light extracted from the device by the same method. As a
result, it was confirmed that the amount of light extracted from
the above device was 150% on the basis of that of Comparative
Example 9.
Reference Example 12
[0358] A glass substrate was prepared by the same method as defined
in Reference Example 9. A coating solution for forming a
high-refractive light-scattering film was prepared by the following
procedure. That is, tetraisopropyloxytitanium
(Ti(O-i-C.sub.3H.sub.7) 4) and anhydrous ethanol (C.sub.2H.sub.5OH)
were mixed with each other under stirring at room temperature at a
mixing molar ratio of 1:4. In this case, silica particles having an
average particle size of 200 nm were previously dispersed in
anhydrous ethanol such that the weight percentage of the silica
particles in the resultant particle-containing layer was 10% by
weight. Meanwhile, the weight percentage of the particles in the
particle-containing layer was measured by the same method as used
for the above measurement of the particle size distribution
therein. The conversion of volume into weight was conducted by
measuring a density of the particles and a matrix of the layer. In
the case where the matrix was porous, the density was calculated
from X-ray reflectance or refractive index measured.
[0359] A mixed solution containing ethanol, water and hydrochloric
acid at a molar ratio of 4:1:0.08 was added to the above prepared
solution at 0.degree. C. using a burette to accelerate a hydrolysis
reaction of the solution, thereby obtaining a titania sol. The
resultant silica sol was applied on the substrate, and the obtained
coating layer was heated at 300.degree. C. for 10 min, thereby
forming an evanescent light-scattering layer. As a result, it was
confirmed that the thickness of the obtained evanescent
light-scattering layer was 500 nm, and the refractive index of a
matrix portion of the layer was 2.1.
[0360] Onto the evanescent light-scattering layer, ITO was
cold-sputtered to form a 500 .ANG.-thick transparent conductive
film. As a result of the measurement, it was confirmed that the
refractive index of the transparent conductive film was 1.9.
Further, a light-emitting layer was formed on the ITO layer by the
same method as defined in Reference Example 9, thereby producing a
fluorescent device. As a result, it was confirmed that the amount
of light extracted from the above device was 170% on the basis of
that of the below-mentioned Comparative Example 11.
Comparative Example 11
[0361] The same procedure as defined in Reference Example 12 was
conducted except that no silica particles were added to the coating
solution, thereby producing a fluorescent light-emitting device and
measuring an amount of light extracted from the device by the same
method.
Reference Example 13
[0362] The same procedure as defined in Reference Example 11 was
conducted except that the ITO transparent conductive film was
formed by the same procedure as defined in Reference Example 12,
before forming the light-emitting layer, thereby producing a
fluorescent light-emitting device and measuring an amount of light
extracted from the device by the same method. As a result, it was
confirmed that the amount of light extracted from the above device
was 140% on the basis of that of Comparative Example 9.
Reference Examples 14 to 17 and Comparative Examples 12 to 15
[0363] These Reference Examples and Comparative Examples were
conducted for explaining the fourth invention.
Reference Example 14
Corresponding to Embodiment (7) Shown in FIG. 10
[0364] A glass plate having a thickness of 0.7 mm and a size of 75
mm square which was composed of a non-alkali glass "AN100" produced
by Asahi Glass Co., Ltd., was immersed in 0.1N nitric acid for
about one hour to subject the surface thereof to degreasing
treatment, washed with pure water and then dried in an oven at
60.degree. C., thereby obtaining a glass substrate 1.
[0365] Separately, a small amount of an acid catalyst (aluminum
acetylacetonate) was added to a mixed solution containing 30% by
weight of an oligomer of tetramethoxysilane ("MS51" produced by
Mitsubishi Chemical Corporation), 50% by weight of BtOH, 8% by
weight of desalted water and 12% by weight of MeOH, and the
resultant mixture was stirred at 60.degree. C. for 3 hours, and
allowed to stand for one week for aging.
[0366] The thus obtained coating solution was applied onto the
glass substrate 1 using a dip coater. The coated glass substrate
was dried for 15 min, immersed in methanol for 5 min, taken out and
dried for 5 min, and then heated in an oven at 150.degree. C. for
15 min, thereby forming a low-refractive layer 4 thereon.
Meanwhile, upon the dip-coating, a protective film was adhered onto
a rear surface of the substrate, and peeled off after coating,
thereby forming the coating film on only one surface thereof.
[0367] It was confirmed that the thickness of the low-refractive
layer 4 was 600 nm. As a result of measuring a refractive index of
the low-refractive layer using an ellipsometer manufactured by
"Sopra", it was confirmed that the refractive index was 1.27 at a
wavelength of 550 nm. Further, as a result of measuring the
refractive index using "PRISM COUPLER MODEL 2010" manufactured by
Metricon Inc., USA in which a laser having a wavelength of 633 nm
was used, it was confirmed that the refractive index was 1.30.
[0368] The thus formed low-refractive layer 4 was subjected to the
following treatment for forming roughness thereon. That is, the
whole surface the low-refractive layer was lightly rubbed with a
sandpaper having 1000-mesh fine roughness to roughen the surface.
Then, the roughened surface was fully air-blown to remove rub-off
matters therefrom. As a result, it was confirmed that the thus
treated low-refractive layer 4 exhibited a surface roughness Ra of
100 nm and Rmax of 500 nm.
[0369] Next, a transparent electrode layer 3 was formed on the
low-refractive layer 4 by the following procedure. That is, a
polythiophene-based conductive polymer together with the same
amount of poly(3-alkylthiophene) were added to ITO fine particles
having an average particle size of 50 nm. The obtained mixture was
dissolved and dispersed in chloroform, and the resultant coating
solution was applied onto the low-refractive layer using a spin
coater and then dried. As a result, it was confirmed that the
obtained coating film had a thickness of 800 nm, and the refractive
index of a matrix portion of the obtained film was 1.8.
[0370] Further, a 1000 .ANG.-thick film composed of ALQ3
(fluorescent pigment) was formed on the transparent electrode layer
3 by vapor deposition.
[0371] As a result, it was confirmed that the amount of light
extracted from the above device was 190% on the basis of that of
the below-mentioned Comparative Example 12.
Comparative Example 12
[0372] The same procedure as defined in Reference Example 14 was
conducted except that the low-refractive layer 4 was subjected to
no treatment for forming roughness thereon, thereby producing a
fluorescent device having a layer structure corresponding to that
shown in FIG. 14 and measuring an amount of light extracted from
the device by the same method. As a result, it was confirmed that
the thus treated low-refractive layer 4 exhibited a surface
roughness Ra of 2 nm and Rmax of 20 nm.
Comparative Example 13
[0373] The same procedure as defined in Comparative Example 12 was
conducted except that the low-refractive layer 4 was omitted to
form a layer structure corresponding to that shown in FIG. 13a,
thereby producing a fluorescent light-emitting device and measuring
an amount of light extracted from the device by the same method. As
a result, it was confirmed that the glass substrate exhibited a
surface roughness Ra of 1 nm and Rmax of 5 nm.
[0374] Also, it was confirmed that the amount of light extracted
from the above device was 91% on the basis of that of Comparative
Example 12.
Reference Example 15
Corresponding to Embodiment (8) Shown in FIG. 11
[0375] The same procedure as defined in Reference Example 14 was
conducted except that after a high-refractive layer 8 having a
thickness of 1000 nm (1 .mu.m) was formed using the coating
solution, ITO was cold-sputtered to form a 100 nm-thick transparent
electrode layer 3A on the high-refractive layer, and further a 1000
.ANG.-thick ALQ3 layer was formed on the ITO layer by vapor
deposition. As a result of the measurement, it was confirmed that
the refractive index of the ITO layer was 1.85.
[0376] Also, it was confirmed that the amount of light extracted
from the above device was 170% on the basis of that of Comparative
Example 12.
Reference Example 16
[0377] A glass substrate was prepared by the same method as defined
in Reference Example 14. One surface of the glass substrate was
subjected to blast treatment using an apparatus "NEWMA BLASTER SGK
Model" manufactured by Fuji Seisakusho Co., Ltd. After the blast
treatment, the glass substrate was immersed in 0.1N nitric acid for
about one hour to subject the treated surface thereof to degreasing
treatment. Then, the thus treated substrate was subjected to
ultrasonic washing with pure water, and then dried in an oven at
60.degree. C. As a result of the measurement, it was confirmed that
the treated surface exhibited a surface roughness Ra of 100 nm and
Rmax of 600 nm.
[0378] Next, a coating solution prepared under the following
conditions was applied on the substrate by dip-coating method to
form a coating film thereon. Meanwhile, upon the dip-coating, a
protective film was adhered onto a rear surface of the substrate,
and peeled off after coating, thereby forming the coating film on
only one surface thereof.
[0379] Tetraisopropyloxytitanium (Ti(O-i-C.sub.3H.sub.7) 4) and
anhydrous ethanol (C.sub.2H.sub.5OH) were mixed with each other
under stirring at room temperature at a mixing molar ratio of 1:4.
Then, a mixed solution containing ethanol, water and hydrochloric
acid at a molar ratio of 4:1:0.08 was added to the resultant
mixture at 0.degree. C. using a burette to accelerate a hydrolysis
reaction thereof, thereby obtaining a titania sol. The resultant
titania sol was applied onto the substrate, and the obtained
coating layer was heated at 300.degree. C. for 10 min, thereby
forming a coating film having a thickness of 600 nm. As a result of
the measurement, it was confirmed that the refractive index of a
matrix portion of the coating film was 2.1.
[0380] Onto the coating film, ITO was cold-sputtered by the same
method as defined in Reference Example 15 to form a transparent
conductive film. Further, a light-emitting layer was similarly
formed on the ITO layer, thereby producing a fluorescent device and
measuring an amount of light extracted from the device. As a
result, it was confirmed that the amount of light extracted from
the above device was 220% on the basis of that of the
below-mentioned Comparative Example 14.
Comparative Example 14
[0381] The same procedure as defined in Reference Example 16 was
conducted except that no blast treatment was conducted, thereby
producing a fluorescent light-emitting device and evaluating the
device by the same method.
Reference Example 17
[0382] A glass substrate was subjected to blast treatment by the
same method as defined in Reference Example 16. Next, a coating
solution prepared by dissolving a polycarbonate resin "7020AD2"
produced by Mitsubishi Engineering-Plastics Corporation, was
applied onto the treated surface of the substrate using a spin
coater, and then dried to form a coating film thereon. As a result,
it was confirmed that the coating film had a thickness of 800 nm,
and the refractive index of a matrix portion of the coating film
was 1.59.
[0383] Onto the coating film, ITO was cold-sputtered by the same
method as defined in Reference Example 15 to form a transparent
conductive film. Further, a light-emitting layer was similarly
formed on the ITO layer, thereby producing a fluorescent device and
measuring an amount of light extracted from the device. As a
result, it was confirmed that the amount of light extracted from
the above device was 160% on the basis of that of the
below-mentioned Comparative Example 15.
Comparative Example 15
[0384] The same procedure as defined in Reference Example 17 was
conducted except that the glass substrate was subjected to no blast
treatment, thereby producing a fluorescent light-emitting device
and evaluating the device by the same method.
INDUSTRIAL APPLICABILITY
[0385] As described above, in accordance with the present
invention, the light extraction efficiency of the
electroluminescent device can be remarkably enhanced. According to
the present invention, irrespective of inorganic or organic
materials, applications of displays and applications of surface
light-emitting sources, the light extraction efficiency of the
electroluminescent device can be extensively enhanced.
[0386] In particular, when a barrier layer is provided in the
device, a transparent electrode layer or an electroluminescent
layer can be suitably protected, so that deterioration of
electroluminescent pigments and formation of dark spots can be
prevented, and the life of the device can be prolonged.
* * * * *