U.S. patent application number 09/730855 was filed with the patent office on 2001-06-14 for composite substrate, thin-film electroluminescent device using the substrate, and production process for the device.
This patent application is currently assigned to TDK CORPORATION. Invention is credited to Iwanaga, Daisuke, Nagano, Katsuto, Nakano, Yukie, Nomura, Takeshi, Takayama, Suguru, Takeishi, Taku.
Application Number | 20010003614 09/730855 |
Document ID | / |
Family ID | 26441081 |
Filed Date | 2001-06-14 |
United States Patent
Application |
20010003614 |
Kind Code |
A1 |
Nagano, Katsuto ; et
al. |
June 14, 2001 |
Composite substrate, thin-film electroluminescent device using the
substrate, and production process for the device
Abstract
A composite substrate in which the surface of the insulating
layer is not influenced by the electrode layer and which requires
neither a grinding process nor a sol-gel process, is easy to
produce and can provide a thin-film EL device having a high display
quality when used therein; a thin-film EL device using the
substrate; and a production process for the device. The thin-film
EL device is produced by forming a luminescent layer, other
insulating layer and other electrode layer successively on a
composite substrate comprising a substrate; an electrode layer
embedded in the substrate in such a manner that the electrode layer
and the substrate are in one plane; and an insulating layer formed
on the surface of a composite comprising the substrate and the
electrode layer.
Inventors: |
Nagano, Katsuto; (Tokyo,
JP) ; Takeishi, Taku; (Tokyo, JP) ; Takayama,
Suguru; (Tokyo, JP) ; Nomura, Takeshi; (Tokyo,
JP) ; Nakano, Yukie; (Tokyo, JP) ; Iwanaga,
Daisuke; (Tokyo, JP) |
Correspondence
Address: |
OBLON, SPIVAK, McCLELLAND, MAIER & NEUSTADT, P.C.
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
TDK CORPORATION
Tokyo
JP
|
Family ID: |
26441081 |
Appl. No.: |
09/730855 |
Filed: |
December 7, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09730855 |
Dec 7, 2000 |
|
|
|
PCT/JP00/02232 |
Apr 6, 2000 |
|
|
|
Current U.S.
Class: |
428/210 ;
428/209; 428/697 |
Current CPC
Class: |
Y10T 428/24926 20150115;
Y10T 428/24917 20150115; H05B 33/02 20130101; H05B 33/26 20130101;
H05B 33/10 20130101; H05B 33/22 20130101; H05B 33/12 20130101 |
Class at
Publication: |
428/210 ;
428/209; 428/697 |
International
Class: |
B32B 009/00; B32B
019/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 7, 1999 |
JP |
11-099994 |
Mar 3, 2000 |
JP |
2000-59533 |
Claims
What is claimed is:
1. A composite substrate, comprising a substrate; an electrode
layer embedded in the substrate in such a manner that the electrode
layer and the substrate are in one plane; and an insulating layer
formed on the surface of a composite of the substrate and the
electrode layer.
2. The composite substrate according to claim 1, wherein the
insulating layer comprises a dielectric having a dielectric
constant of 1000 or more.
3. The composite substrate according to claim 1, wherein the
insulating layer contains barium titanate as a main component.
4. The composite substrate according to claim 3, wherein the
insulating layer further contains, as a secondary component, at
least one selected from the group consisting of magnesium oxide,
manganese oxide, tungsten oxide, calcium oxide, zirconium oxide,
niobium oxide, cobalt oxide, yttrium oxide and barium oxide.
5. The composite substrate according to claim 3, wherein the
insulating layer contains, as a secondary component, at least one
selected from the group consisting of SiO.sub.2, MO, Li.sub.2O and
B.sub.2O.sub.3, wherein M is at least one element selected from the
group consisting of Mg, Ca, Sr, and Ba.
6. The composite substrate according to claim 1, wherein the
insulating layer contains barium titanate as a main component and
at least one secondary component selected from the group consisting
of magnesium oxide, manganese oxide, yttrium oxide, barium oxide
and calcium oxide, and silicon oxide as secondary components; and
wherein the content of magnesium oxide in terms of MgO is 0.1 to 3
moles, that of manganese oxide in terms of MnO is 0.05 to 1.0 mole,
that of yttrium oxide in terms of Y.sub.2O.sub.3 is not more than 1
mole, that of barium oxide in terms of BaO and calcium oxide in
terms of CaO is 2 to 12 moles, and that of silicon oxide in terms
of SiO.sub.2 is 2 to 12 moles, based on 100 moles of barium
titanate in terms of BaTiO.sub.3.
7. The composite substrate according to claim 3, wherein the total
content of BaO, CaO and SiO.sub.2 in terms of
(Ba.sub.xCa.sub.1-xO).sub.y.multido- t.SiO.sub.2 is 1 to 10 wt. %
based on the total content of BaTiO.sub.3, MgO, MnO and
Y.sub.2O.sub.3, wherein x satisfies 0.3.ltoreq.x.ltoreq.0.7, and y
satisfies 0.95.ltoreq.y.ltoreq.1.05.
8. The composite substrate according to claim 1, which is a thick
film obtained by sintering the laminate formed by the use of a
sheet-forming process or a print process.
9. The composite substrate according to claim 1, which is obtained
by forming a functional film on the insulating layer, and then
heating the functional film at a temperature of from 600.degree. C.
to a sintering temperature of the substrate or less.
10. The composite substrate according to claim 1, wherein the
substrate and the insulating layer each comprise the same
composition.
11. The composite substrate according to claim 9, wherein said
functional film is from 800.degree. C. to 1,500.degree. C.
12. The composite substrate according to claim 1, wherein said
substrate comprises a glass material in a range of about 20 to 30
wt. % based on the substrate material.
13. The composite substrate according to claim 1, wherein said
substrate has a thickness of from about 1 to 5 mm.
14. The composite substrate according to claim 1, wherein said
electrode layer contains a glass frit as an underlayer thereof,
thereby increasing adhesion of the electrode layer to the
substrate.
15. The composite substrate according to claim 1, wherein the
insulating layer comprises composite titanium oxides,
titanium-based composite oxides, and mixtures thereof.
16. The composite substrate according to claim 1, wherein the
insulating layer has a thickness of 100 .mu.m or less.
17. The composite substrate according to claim 16, wherein the
insulating layer has a thickness of 2 to 20 .mu.m.
18. A thin film EL device, comprising the composite substrate in
claim 1, and a luminescent layer, another insulating layer and
another electrode layer formed successively on the composite
substrate.
19. The thin film EL device according to claim 18, wherein the
electrode layer comprises at least one element selected from the
group consisting of Ag, Au, Pd, Pt, Cu, Ni, W, Mo, Fe and Co, at
least one alloy selected from the group consisting of Ag--Pd,
Ni--Mn, Ni--Cr, Ni--Co and NiAl alloys.
20. A process for producing a thin film EL device, comprising: a)
forming a first insulating layer precursor on a film sheet having a
flat surface by a thick-film production process; b) forming a first
patterned electrode layer precursor thereon; c) forming a substrate
precursor thereon, subjecting the laminate to a binder-removing
treatment and sintering it to obtain a composite substrate having
the first electrode layer and the first insulating layer formed on
the substrate; and d) further laminating a luminescent layer, a
second insulating layer and a second electrode layer on the first
insulating layer successively to obtain the thin-film EL
device.
21. The process for producing the thin film EL device according to
claim 20, wherein a heat treatment is carried out at a temperature
of from 600.degree. C. to a sintering temperature of the substrate
or less, after the formation of the second insulating layer
according to claim 2 or the second electrode layer.
22. The process for producing the thin film EL device according to
claim 20, wherein the substrate precursor is a substrate green
sheet which contains at least one selected from the group
consisting of alumina (Al.sub.2O.sub.3), silica glass (SiO.sub.2),
magnesia (MgO), steatite (MgO.multidot.SiO.sub.2), forsterite
(2MgO.multidot.SiO.sub.2), mullite
(3Al.sub.2O.sub.3.multidot.2SiO.sub.2), beryllia (BeO), zircon, and
Ba-, Sr- and Pb-based perkovskites.
23. The process for producing the thin film EL device according to
claim 20, wherein the composition of the main component of the
substrate precursor is the same as that of the insulating
layer.
24. The process for producing the thin film EL device according to
claim 20, wherein the electrode layer precursor comprises at least
one selected from the group consisting of Ag, Au, Pd, Pt, Cu, Ni,
W, Mo, Fe and Co, or any one of Ag--Pd, Ni--Mn, Ni--Cr, Ni--Co and
Ni--Al alloys.
25. The process for producing the thin film EL device according to
claim 20, wherein the sintering temperature is in a range of 1,100
to 1,400.degree. C.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority to International
Application No. PCT/JP00/02232 filed Apr. 06, 2000, and Japanese
Application Nos. 11-099994 filed Apr. 07, 1999, and 2000-59533
filed Mar. 03, 2000, and the entire content of both applications
are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a composite substrate
containing a dielectric and an electrode, an electroluminescent
(EL) device using the substrate, and a production process for the
device.
[0004] 2. Discussion of the Background
[0005] Electroluminescence is a phenomenon whereby a material emits
light with the application of an electric field. Such a material is
called electroluminescent (EL), and devices wherein this phenomenon
is utilized have been put to practical use in liquid crystal
displays (LCD) and back lights of watches.
[0006] EL devices are classified into two categories of a
dispersion-type device and a thin-film device. The former has a
structure in which a fluorescent material powder is dispersed in an
organic material or an enamel and electrodes are disposed at top
and bottom portions, and the latter contains a thin-film
fluorescent material sandwiched between two electrodes and two
thin-film insulators on an electrical insulating substrate. In
addition, according to the type of driving system, each of the
above two types of device is further classified into a
direct-voltage drive system and an alternating-voltage drive
system. The dispersion-type EL device has been known for a long
time, and it has the advantage of facile preparation. However, the
dispersion-type EL device has a low brightness and a short life, so
that its utilization is limited. On the other hand, the thin-film
EL device has a high brightness and a long life, and has,
consequently, greatly expanded the practical application range of
the EL device.
[0007] Heretofore, in the main type of thin-film EL device, a blue
glass sheet for use in an LCD or a PDP is used as a substrate,
transparent electrodes, such as ITO, are used as electrodes
contacting the substrate, and light emitted from a fluorescent
material is taken out from the side of the substrate. As the
fluorescent material, Mn-containing ZnS capable of emitting
yellowish orange light has been mainly used because it facilitates
the formation of a film and has good light-emission properties. In
order to fabricate a color display, it is essential to use
fluorescent materials capable of emitting the primary colors of
light, i.e., red, green and blue. As such materials, Ce-containing
SrS and Tm-containing ZnS are selected for blue emission,
Sm-containing ZnS and Eu-containing CaS are selected for red
emission, and Tb-containing ZnS and Ce-containing CaS are selected
for green light emission, and research on these materials
continues. Unfortunately, since they are insufficient in
brightness, luminous efficiency and color purity, they have not
been put to practical use.
[0008] In an effort to address these problems, it is considered
that a process of forming a film at high temperature or heat
treatment of a formed film at a high temperature is promising.
However, when such a technique is used, it is impossible to use a
blue glass plate as the substrate from the viewpoint of heat
resistance. Although the use of a quartz substrate having heat
resistance has also been investigated, the quartz substrate is very
expensive, and, therefore, it is not suitable for an application,
such as a display which requires a large area.
[0009] As disclosed in Japanese Patent Application Laid Open No.
50197/1995 and Japanese Patent Publication No. 44072/1995, there
has recently been reported the development of a device in which a
ceramic substrate having electrical insulation properties is used
as a substrate and a thick-film dielectric is substituted for the
thin-film insulator located at the lower portion of a fluorescent
material.
[0010] The basic structure of this device is shown in FIG. 8. The
EL device shown in FIG. 8 has a structure in which a lower
electrode 12, a thick-film dielectric layer 13, a luminescent layer
14, a thin-film insulator layer 15 and an upper electrode 16 are
successively formed on a substrate 11 made of ceramic or the like.
Accordingly, in contrast to the structure of the conventional
thin-film EL device, a transparent electrode is placed at the top
portion in order to take out light of the fluorescent material from
the top portion opposite to the substrate.
[0011] The thick-film dielectric layer of this device has a
thickness of several tens micrometers, which is several hundreds to
several thousands times as much as that of the thin-film insulator
layer. Therefore, the breakage of the insulator caused by pinholes
or the like can be inhibited. Thus, the above device has the
advantage that a high reliability and a high yield at the time of
production can be obtained.
[0012] Voltage drop across the luminescent layer caused by the use
of a thick dielectric can be prevented by forming the dielectric
layer from a material having a high dielectric constant. Further,
the rise of a heat treatment temperature can be allowed by using
the ceramic substrate and the thick-film dielectric. As a result,
the film formation of a highly luminous material, which has
heretofore been impossible owing to the presence of defective
crystals, is made possible.
[0013] However, when the substrate, the electrode and the
dielectric layer are to be laminated by a thick-film forming
process, the surface of the dielectric layer becomes inconveniently
uneven in some cases.
[0014] In the conventional process, a
substrate/electrode/dielectric layer composite substrate is
obtained by first forming the electrode on the substrate of alumina
or the like in a predetermined pattern by a thick-film forming
process such as a print process, forming the dielectric layer on
the electrode by the thick-film forming process, and then sintering
the whole laminate obtained.
[0015] However, as shown in FIG. 9, for example, there has been a
concern that the surface of the dielectric layer 13 may be uneven
owing to the differences in shrinkage ratios and thermal expansion
coefficients between the electrode layer 12 and the dielectric
layer 13 when the electrode layer 12 is formed in a predetermined
pattern. Furthermore, the surface of the dielectric layer 13 is
cracked in some cases owing to the difference in thermal expansion
coefficients between the substrate 11 and the dielectric layer 13.
Thus, when the dielectric layer 13 has an uneven or cracked
surface, the thickness of the dielectric layer 13 becomes
non-uniform, or a peeling phenomenon occurs between the dielectric
layer 13 and the luminescent layer formed thereon, whereby the
performance and the display quality of the device are remarkably
impaired.
[0016] Therefore, in the conventional process, it is necessary to
remove large uneven portions by grinding, for example, and fine
uneven portions by a sol-gel process.
SUMMARY OF THE INVENTION
[0017] Accordingly, it is an object of the present invention is to
provide a composite substrate in which the surface of an insulating
layer does not become uneven by the influence of an electrode layer
and which requires neither a grinding process nor a sol-gel
process, is easy to produce, and can provide a thin-film EL device
having a high display quality when applied thereto.
[0018] It is another object of the present invention is to provide
a thin-film EL device using the above substrate.
[0019] It is yet another object of the present invention is to
provide a production process for the above device.
[0020] The above objects of the present invention are achieved by
the following composite substrates, devices and processes.
[0021] (1) A composite substrate containing a substrate; an
electrode layer embedded in the substrate in such a manner that the
electrode layer and the substrate are in one plane: and an
insulating layer formed on the surface of a composite of the
substrate and the electrode layer.
[0022] (2) A composite substrate according to the above (1),
wherein the insulating layer contains a dielectric having a
dielectric constant of 1000 or more.
[0023] (3) A composite substrate according to the above (1) or (2),
wherein the insulating layer contains barium titanate as a main
component.
[0024] (4) A composite substrate according to the above (3),
wherein the insulating layer contains, as a secondary component, at
least one selected from the group consisting of magnesium oxide,
manganese oxide, tungsten oxide, calcium oxide, zirconium oxide,
niobium oxide, cobalt oxide, yttrium oxide and barium oxide.
[0025] (5) A composite substrate according to the above (3) or (4),
wherein the insulating layer contains, as a secondary component, at
least one selected from the group consisting of SiO.sub.2, MO, and
B.sub.2O.sub.3, wherein M is at least one element of Mg, Ca, Sr
and/or Ba.
[0026] (6) A composite substrate according to any one of the above
(1) to (5), wherein the insulating layer contains barium titanate
as a main component and at least one selected from the group
consisting of magnesium oxide, manganese oxide, yttrium oxide,
barium oxide and calcium oxide, and silicon oxide as secondary
components; and the content of magnesium oxide in terms of MgO is
0.1 to 3 moles, that of manganese oxide in terms of MnO is 0.05 to
1.0 mole, that of yttrium oxide in terms of Y.sub.2O.sub.3 is not
more than 1 mole, that of barium oxide in terms of BaO and calcium
oxide in terms of CaO is 2 to 12 moles, and that of silicon oxide
in terms of SiO.sub.2 is 2 to 12 moles, based on 100 moles of
barium titanate in terms of BaTiO.sub.3.
[0027] (7) A composite substrate according to the above (3),
wherein the total content of BaO, CaO and SiO.sub.2 in terms of
(Ba.sub.xCa.sub.1-xO).sub.y.multidot.SiO.sub.2 (provided that x
satisfies 0.3.ltoreq.x.ltoreq.0.7 and y satisfies
0.95.ltoreq.y.ltoreq.1.05) is 1 to 10 wt. % based on the total
content of BaTiO.sub.3, MgO, MnO and Y.sub.2O.sub.3.
[0028] (8) A composite substrate according to any one of the above
(1) to (7), which is a thick film obtained by sintering the
laminate formed by the use of a sheet-forming process or a print
process.
[0029] (9) A composite substrate according to any one of the above
(1) to (8), which is obtained by forming a functional film on the
insulating layer, and then heating the functional film at a
temperature of from 600.degree. C. to a sintering temperature of
the substrate or less.
[0030] (10) A thin film EL device comprising the composite
substrate in any one of the above (1) to (6), and a luminescent
layer, another insulating layer and another electrode layer formed
successively on the composite substrate.
[0031] (11) A thin film EL device according to the above (10),
wherein the electrode layer contains at least one element of Ag,
Au, Pd, Pt, Cu, Ni, W, Mo, Fe and/or Co; or at least one alloy of
Ag--Pd, Ni--Mn, Ni--Cr, Ni--Co and/or Ni--Al alloys.
[0032] (12) A process for producing a thin film EL device
entailing:
[0033] forming a first insulating layer precursor on a film sheet
having a flat surface by a thick-film production process;
[0034] forming a first patterned electrode layer precursor
thereon;
[0035] forming a substrate precursor thereon, subjecting the
laminate to a binder-removing treatment and sintering it to obtain
a composite substrate having the first electrode layer and the
first insulating layer formed on the substrate; and
[0036] further laminating a luminescent layer, a second insulating
layer and a second electrode layer on the first insulating layer
successively to obtain the thin-film EL device.
[0037] (13) A process for producing the thin film EL device
according to the above (10), wherein a heat treatment is carried
out at a temperature of from 600.degree. C. to a sintering
temperature of the substrate or less, after the formation of the
second insulating layer or the second electrode layer.
[0038] (14) A process for producing the thin film EL device
according to the above (12) or (13), wherein the substrate
precursor is a substrate green sheet which contains at least one
selected from the group consisting of alumina (Al.sub.2O.sub.3),
silica glass (SiO.sub.2), magnesia (MgO), steatite
(MgO.multidot.SiO.sub.2), forsterite (2MgO, SiO.sub.2), mullite
(3Al.sub.2O.sub.3.multidot.2SiO.sub.2), beryllia (BeO), zircon, and
Ba-, Sr- and Pb-based perovskites.
[0039] (15) A process for producing the thin film EL device
according to any one of the above (12) to (14), wherein the
composition of the main component of the substrate precursor is the
same as that of the insulating layer.
[0040] (16) A process for producing the thin film EL device
according to any one of the above (12) to (15), wherein the
electrode layer precursor comprises at least one selected from the
group consisting of Ag, Au, Pd, Pt, Cu, Ni, W, Mo, Fe and Co, or
any one of Ag--Pd, Ni--Mn, Ni--Cr, Ni--Co and Ni--Al alloys.
[0041] (17) A process for producing the thin film EL device
according to any one of the above (12) to (16), wherein the
sintering temperature is in a range of 1,100 to 1,400.degree.
C.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042] A more complete appreciation of the invention and many of
the attendant advantages thereof will be readily obtained as the
same becomes better understood by reference to the following
detailed description when considered in connection with the
accompanying drawings, wherein:
[0043] FIG. 1 is an illustration of a partial section of the
production process of the thin-film EL device of the present
invention;
[0044] FIG. 2 is an illustration of a partial section of the
production process of the thin-film EL device of the present
invention;
[0045] FIG. 3 is an illustration of a partial section of the
production process of the thin-film EL device of the present
invention;
[0046] FIG. 4 is an illustration of a partial section of the
production process of the thin-film EL device of the present
invention;
[0047] FIG. 5 is an illustration of a partial section of the
production process of the thin-film EL device of the present
invention;
[0048] FIG. 6 is an illustration of a partial section of the
production process of the thin-film EL device of the present
invention;
[0049] FIG. 7 is an illustration of a partial section of the
production process of the thin-film EL device of the present
invention;
[0050] FIG. 8 is an illustration of a partial section of the
structure of the conventional thin-film EL device;
[0051] FIG. 9 is an illustration of a partial section of the
structure of the conventional thin-film EL device.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0052] The present invention provides a composite substrate which
contains a substrate; an electrode layer embedded in the substrate
in such a manner that the electrode layer and the substrate are in
one plane; and an insulating layer formed on the surface of a
composite of the substrate and the electrode layer.
[0053] In this way, the electrode layer is formed so as to be
embedded in the substrate and so that the surface of the embedded
electrode layer and that of the substrate may be flat in one plane,
whereby the thickness of the insulating layer (dielectric layer)
can be uniformed. In addition, the thickness of the dielectric
layer is uniformed, whereby the distribution of electric field in
the dielectric layer can be uniformed, with the result that the
distortion of the dielectric layer can be reduced.
[0054] Moreover, the thin-film EL device is constituted by the use
of the above composite substrate, whereby a high-performance
display can be formed by a simple process. In this connection, the
composite substrate having the flat surface can be easily formed by
the production process of the present invention that will be
described later.
[0055] The substrate of the present invention has insulation
properties, does not contaminate an insulating layer (dielectric
layer) and an electrode layer formed thereon, and is not
particularly limited as long as it is capable of maintaining a
predetermined strength. Typical examples of the substrate include
ceramic substrates such as alumina (Al.sub.2O.sub.3), silica glass
(SiO.sub.2), magnesia (MgO), forsterite (2MgO.multidot.SiO.sub.2),
steatite (MgO.multidot.SiO.sub.2), mullite
(3Al.sub.2O.sub.3.multidot.2SiO.sub.2), beryllia (BeO), zirconia
(ZrO.sub.2), aluminum nitride (AlN), silicon nitride (SiN) and
silicon carbonate (SiC+BeO). In addition, Ba-, Sr- and Pb-based
perovskites may also be used, and in this case, the same
composition as used for the insulating layer may be used. Of these
compounds, the alumina substrate is particularly preferable, and
when thermal conductivity is required, beryllia, aluminum nitride,
silicon carbonate and the like are preferable. It is preferable to
form the substrate using the same composition as used for the
insulating layer, because in such case, a phenomenon such as
warping or peeling due to different thermal expansions does not
occur.
[0056] The sintering temperature of the substrate is 800.degree. C.
or higher, preferably 800.degree. C. to 1,500.degree. C., more
preferably 1,200.degree. C. to 1,400.degree. C.
[0057] The substrate may contain a glass material for the purpose
of, for example, lowering the sintering temperature. Typical
examples of the glass material include PbO, B.sub.2O.sub.3,
SiO.sub.2, CaO, MgO, TiO.sub.2 and ZrO.sub.2, and they may be used
alone or in combination of two or more thereof. The content of the
glass material is in a range of about 20 to 30 wt. % based on the
substrate material.
[0058] In preparing a paste for the substrate, an organic binder
may be used. The organic binder is not particularly limited, and it
may be suitably selected from those which are generally used as the
binder for ceramics. Examples of such an organic binder include
ethyl cellulose, acryl resins and butyral resins, and examples of a
solvent include cc-terpineol, butyl carbinol and kerosene. The
contents of the organic binder and the solvent in the paste are not
particularly limited, and they may be the same as generally used.
For example, the content of the binder is in a range of about 1 to
5 wt. %, and that of the solvent is in a range of about 10 to 50
wt. %.
[0059] Furthermore, the paste for the substrate may also contain
additives such as a dispersing agent, a plasticizer and an
insulator as required. The total content of these additives is
preferably 1 wt. % or less.
[0060] The thickness of the substrate is generally in a range of
about 1 to 5 mm, preferably about 1 to 3 mm.
[0061] The electrode material used herein should preferably contain
one or two or more of Ag, Au, Pd, Pt, Cu, Ni, W, Mo, Fe and Co or
any one of Ag--Pd, Ni--Mn, Ni--Cr, Ni--Co and Ni--Al alloys. When
firing is carried out in a reducing atmosphere, base metals may be
selected from these materials. Materials containing one or two or
more of Mn, Fe, Co, Ni, Cu, Si, W, Mo, etc. or any one of Ni--Cu,
Ni--Mn, Ni--Cr, Ni--Co and Ni--Al alloys are more preferable, with
Ni, Cu, and Ni--Cu alloys, etc. being most preferred.
[0062] When the sintering is carried out under an oxidizing
atmosphere, a metal which does not become an oxide under the
oxidizing atmosphere is preferable. Typical examples of the metal
include Ag, Au, Pt, Rh, Ru, Tr, Pb and Pd, and they may be used
alone or in a combination of two or more thereof. Particularly
preferable examples thereof include Ag, Pd and an Ag--Pd alloy.
[0063] The electrode layer may contain a glass frit to enhance its
adhesion to the substrate which is an underlayer of the electrode
layer itself. The glass frit is preferably such as not to lose the
characteristic properties of glass, even when the sintering is
carried out in a neutral or a reducing atmosphere.
[0064] The composition of the glass frit is not particularly
limited, as long as it satisfies the above requirements. Examples
of the glass frit include silicate glass (SiO.sub.2: 20 to 80 wt.
%, Na.sub.2O: 80 to 20 wt. %), borosilicate glass (B.sub.2O.sub.3:
5 to 50 wt. %, SiO.sub.2: 5 to 70 wt. %, PbO: 1 to 10 wt. %,
K.sub.2O: 1 to 15 wt. %) and alumina silicate glass
(Al.sub.2O.sub.3: 1 to 30 wt. %, SiO.sub.2: 10 to 60 wt. %,
Na.sub.2O: 5 to 15 wt. %, CaO: 1 to 20 wt. %, B.sub.2O.sub.3: 5 to
30 wt. %) , and they can be used singly or in a combination of two
or more thereof. If necessary, the glass frit may be mixed with at
least one additive selected from the group consisting of CaO (0.01
to 50 wt. %), SrO (0.01 to 70 wt. %), BaO (0.01 to 50 wt. %), MgO
(0.01 to 5 wt. %), ZnO (0.01 to 70 wt. %), PbO (0.01 to 5 wt. %),
Na.sub.2O (0.01 to 10 wt. %), K.sub.2O (0.01 to 10 wt. %) and
MnO.sub.2 (0.01 to 20 wt. %) in a predetermined ratio. Although the
content of the glass is not particularly limited, it is usually in
a range of about 0.5 to 20 wt. %, preferably about 1 to 10 wt. %
based on the metal component. Furthermore, the total content of the
above additives in the glass is preferably 50 wt. % or less of the
glass component.
[0065] In preparing a paste for the electrode layer, an organic
binder may be used. Examples of the organic binder are the same as
in the case of the above substrate. Further, the paste for the
electrode layer may also contain additives such as dispersant, a
plasticizer and an insulator as required. The total content of
these additives is preferably 1 wt. % or less.
[0066] The thickness of the electrode layer is usually in a range
of about 0.5 to 5 .mu.m, preferably about 1 to 3 .mu.m.
[0067] An insulating material which constitutes the insulating
layer is not particularly limited, and various kinds of insulating
materials can be used. Preferable examples thereof include
composite titanium oxides, titanium-based composite oxides and
mixtures of these oxides.
[0068] An example of the composite titanium oxides is titanium
oxide (TiO.sub.2) containing, as required, any of nickel oxide
(NiO), copper oxide (CuO), manganese oxide (Mn.sub.3O.sub.4),
alumina (Al.sub.2O.sub.3), magnesium oxide (MgO), silicon oxide
(SiO.sub.2) and the like in a total content of 0.001 to 30 wt. %;
and an example of the titanium-based composite oxides is barium
titanate (BaTiO.sub.3). The atomic ratio of Ba/Ti in barium
titanate is preferably in a range of about 0.95 to 1.20.
[0069] The titanium-based composite oxide (BaTiO.sub.3) may contain
at least one selected from the group consisting of magnesium oxide
(MgO), manganese oxide (Mn.sub.3O.sub.4), tungsten oxide
(WO.sub.3), calcium oxide (CaO), zirconium oxide (ZrO.sub.2),
niobium oxide (Nb.sub.2O.sub.5), cobalt oxide (Co.sub.3O.sub.4),
yttrium oxide (Y.sub.2O.sub.3) and barium oxide (BaO) in a total
amount of about 0.001 to 30 wt. %. Furthermore, for the purpose of,
for example, adjusting a sintering temperature and an expansion
coefficient, the insulating layer may contain at least one selected
from the group consisting of SiO.sub.2, MO (provided that M is at
least one element selected from Mg, Ca, Sr and Ba), Li.sub.2O and
B.sub.2O.sub.3 as a secondary component. The thickness of the
insulating layer is not particularly limited, but it is usually in
a range of 5 to 1,000 .mu.m, preferably 5 to 50 .mu.m, more
preferably about 10 to 50 .mu.m.
[0070] The insulating layer may be formed of a dielectric material.
Especially in the case that the composite substrate is applied to
the thin-film EL device, the dielectric material is preferable. The
dielectric material is not particularly limited, and any dielectric
material can be used. Preferable examples of the dielectric
material include composite titanium oxides, titanium-based
composite oxides, and mixtures thereof as mentioned above.
[0071] Examples of the titanium-based composite oxides are the same
as enumerated above. Furthermore, for the purpose of, for example,
adjusting the sintering temperature and the expansion coefficient,
the insulating layer may contain at least one selected from the
group consisting of SiO.sub.2, MO (provided that M is at least one
element selected from Mg, Ca, Sr and Ba), Li.sub.2O and
B.sub.2O.sub.3, as a secondary component.
[0072] The particularly preferable dielectric materials are as
follows. The dielectric layer (insulating layer) contains barium
titanate as a main component and at least one selected from the
group consisting of magnesium oxide, manganese oxide, barium oxide
and calcium oxide, and silicon oxide as secondary components. In
the dielectric layer, the content of the magnesium oxide in terms
of MgO is 0.1 to 3 moles, preferably 0.5 to 1.5 moles, the content
of the manganese oxide in terms of MnO is 0.05 to 1.0 mole,
preferably 0.2 to 0.4 moles, the total content of the barium oxide
in terms of BaO and the calcium oxide in terms of CaO is 2 to 12
moles, and the content of the silicon oxide in terms of SiO.sub.2
is 2 to 12 moles, based on 100 moles of the barium titanate in
terms of BaTiO.sub.3.
[0073] The ratio of (BaO+CaO)/SiO.sub.2 is not particularly limited
but is usually preferably in a range of 0.9 to 1.1. BaO, CaO and
SiO.sub.2 may be contained as
(Ba.sub.xCa.sub.1-xO).sub.y.multidot.SiO.sub.2. In this case, x and
y preferably satisfy 0.3.ltoreq.x.ltoreq.0.7 and
0.95.ltoreq.y.ltoreq.1.05, respectively, to obtain a dense sinter.
The content of (Ba.sub.xCa.sub.1-xO).sub.y.multidot.SiO.sub.2 is
preferably in a range of 1 to 10 wt. %, more preferably 4 to 6 wt.
%, based on the total weight of BaTiO.sub.3, MgO and MnO. The
oxidation state of each of the oxides is not particularly limited,
as long as the content of the metal element constituting each oxide
is within the above range.
[0074] The dielectric layer preferably contains yttrium oxide as a
secondary component in an amount of 1 mole or less in terms of
Y.sub.2O.sub.3 based on 100 moles of barium titanate in terms of
BaTiO.sub.3. The lower limit of the Y.sub.2O.sub.3 content is not
particularly determined but is preferably at least 0.1 mole in
order to achieve a sufficient effect. When yttrium oxide is
contained, the content of
(Ba.sub.xCa.sub.1-xO).sub.y.multidot.SiO.sub.2 is preferably in a
range of 1 to 10 wt. %, more preferably 4 to 6 wt. %, based on the
total content of BaTiO.sub.3, MgO, MnO and Y.sub.2O.sub.3.
[0075] The contents of the above secondary components are limited
because of the following reasons.
[0076] When the content of magnesium oxide is below the above
range, the temperature characteristics of capacitance can not be
within a desired range. When the content of magnesium oxide is
above the above range, the degree of the sintering of the
dielectric layer sharply lowers and the layer is poorly densified.
Consequently, IR accelerated life is reduced and a high dielectric
constant cannot be obtained.
[0077] When the content of manganese oxide is below the above
range, good anti-reduction properties cannot be obtained, IR
accelerated life is not sufficient, and it is difficult to reduce
loss tan .delta.. When the content of manganese oxide is above the
aforesaid range, it is difficult to reduce the change of the
capacitance with time at the time of applying a DC electric
field.
[0078] When the content of BaO+CaO, SiO.sub.2 or
(Ba.sub.xCa.sub.1-xO).sub- .y.multidot.SiO.sub.2 is too low, the
change of the capacitance with time at the application of the DC
electric field increases, and the IR accelerated life is not
sufficient. When this content is too high, the dielectric constant
sharply decreases.
[0079] Yttrium oxide has the effect of improving the IR accelerated
life. When the content of yttrium oxide is above the aforesaid
range, the capacitance decreases, and the degree of the sintering
of the dielectric layer lowers, with the result that the layer is
poorly densified in some cases.
[0080] The dielectric layer may also contain aluminum oxide.
Aluminum oxide has the effect of making the sintering at relatively
low temperatures possible. The content of aluminum oxide in terms
of Al.sub.2O.sub.3 is preferably 1 wt. % or less based on the total
of all the dielectric materials. When the content of aluminum oxide
is too high, the problem of inhibiting the sintering takes
place.
[0081] The thickness of the dielectric layer is preferably 100
.mu.m or less, more preferably 50 .mu.m or less, particularly
preferably 2 to 20 .mu.m.
[0082] An organic binder may be used in preparing an insulating
layer paste. Examples of the organic binder include the same as
those listed for the substrate. Further, the insulating layer paste
may also contain additives such as a dispersing agent, a
plasticizer and an insulator as required. The total content of
these additives is preferably 1 wt. % or less.
[0083] The composite substrate of the present invention is produced
by laminating an insulating layer precursor, an electrode layer
precursor and a substrate precursor by a usual printing process or
a sheet-forming process using the paste, and then sintering the
resultant laminate.
[0084] The surface of the insulating layer (dielectric layer) can
be flattened by first forming a green sheet for an insulating layer
on a film sheet having a flat surface, forming the electrode layer
precursor thereon, followed by the formation of the substrate
precursor and sintering. In this case, since the thickness of the
substrate is much larger than that of the insulating layer, the
other surface of the substrate is not influenced by the electrode
layer.
[0085] The film sheet having the flat surface is not particularly
limited, and a usual resin film sheet can be used. Particularly
preferable is a sheet with chemical resistance that facilitates the
peeling of the green sheet.
[0086] Typical examples of the film sheet include polyethylene
naphthalate (PEN) films, polyethylene terephthalate (PET) films,
polyethylene naphthalate heat-resistant films; fluorine-based films
of homopolymers such as polychlorotrifluoroethylene (PCTFE: Neoflon
CTFE, a product of Daikin Industries, Ltd.), polyvinylidenefluoride
(PVDF: Denka DX film, a product of Denki Kagaku Kogyou Co., Ltd.)
and polyvinylfluoride (PVF: Tedora PVF film, a product of Du Pont
Co., Ltd.) and copolymers such as
tetrafluoroethylene-perfluorovinylether copolymer (PFA: Neoflon:
PFA film, a product of Daikin Industries, Ltd.),
tetrafluoroethylene-hexafluo- ropropylene copolymer (FEP: Toyoflon
film FEP type, a product of Toray Industries, Inc.),
tetrafluoroethylene-ethylene copolymer (ETFE: Tefzel ETFE film, a
product of Du Pont Co., Ltd.; AFLEX film, a product of Asahi Glass
Co., Ltd.); aromatic dicarboxylic acid-bisphenol copolymerized
aromatic polyester polyacrylate films (PAR: Casting, Elmec
manufactured by Kaneka Corporation), polymethylmethacrylate films
(PMMA: Technolloy R526, a product of Sumitomo Chemical Co., Ltd.);
sulfur-containing polymer films such as polysulfone (PSF: Smilite
FS-1200, a product of Sumitomo Bakelite Co., Ltd.) and
polyethersulfone (PES: Smilite FS-1300, a product of Sumitomo
Bakelite Co., Ltd.); polycarbonate films (PC: Panlite, a product of
Teijin Chemicals Ltd.); functional norbomene-based resins (ARTON, a
product of JSR Corporation); polymethacrylate resins (PMMA);
olefinmaleimide copolymers (TI-160, a product of Tosoh
Corporation), paramide (Aramika R: a product of Asahi Chemical
Industry Co., Ltd.), polyimide fluoride, polystyrene, polyvinyl
chloride and cellulose triacetate. PEN films and PET films are
particularly preferable.
[0087] A cellulose-containing sheet such as paper may also be used
and subjected to the sintering together with the sheet.
[0088] The thickness of the film sheet is not particularly limited
but is preferably in a range of 100 to 400 .mu.m from the viewpoint
of handling.
[0089] The conditions for the binder-removing treatment conducted
before the sintering may be those that are usually used. When the
sintering is carried out under a reducing atmosphere, the following
conditions are preferable.
[0090] Heating rate: 5 to 500.degree. C./h, preferably 10 to
400.degree. C./h
[0091] Retention temperature: 200 to 400.degree. C., preferably 250
to 300.degree. C.
[0092] Temperature retention time: 0.5 to 24 hours, preferably 5 to
20 hours
[0093] Atmosphere: in the air
[0094] The atmosphere for the sintering may be suitably selected
according to the types of conductive materials contained in the
electrode layer paste. When the sintering is carried out under a
reducing atmosphere, the sintering atmosphere preferably contains
N.sub.2 as a main component, 1 to 10% of H.sub.2, and H.sub.2O gas
which is obtained by vapor pressure at 10 to 35.degree. C. The
oxygen partial pressure is preferably 10.sup.-8 to 10.sup.-12 Torr.
When the oxygen partial pressure is below the above range, the
conductive materials used in the electrode layer cause the abnormal
sintering, whereby the layer breaks in some cases. When the oxygen
partial pressure is above the above range, the electrode layer is
apt to be oxidized. When the sintering is carried out under an
oxidizing atmosphere, it is carried out in the same manner as it is
carried out in the air.
[0095] The retention temperature at the time of the sintering is
preferably 800 to 1,400.degree. C., more preferably 1,000 to
1,400.degree. C., particularly preferably 1,200 to 1,400.degree. C.
When the retention temperature is below the above range, the
electrode layer is poorly densified. When the retention temperature
is above the above range, the electrode layer is liable to break.
The temperature retention time at the time of the sintering is
preferably 0.5 to 8 hours, particularly preferably 1 to 3
hours.
[0096] The composite substrate is preferably subjected to annealing
after sintered in a reducing atmosphere. The annealing is a
treatment for re-oxidizing the insulating layer, by which IR
accelerated life can be remarkably extended.
[0097] The oxygen partial pressure in an annealing atmosphere is
preferably 10.sup.-6 Torr or higher, particularly preferably
10.sup.-6 to 10.sup.-8 Torr. When the oxygen partial pressure is
below the above range, the insulating layer or the dielectric layer
cannot be re-oxidized easily. When it is above the above range, the
internal electric conductor is liable to be oxidized.
[0098] The retention temperature at the time of the annealing is
preferably 1,100.degree. C. or less, more preferably 1,000 to
1,100.degree. C. When the retention temperature is below the above
range, the insulating layer or the dielectric layer is not
sufficiently oxidized, thereby reducing the longevity of the
composite substrate. When the retention temperature is above the
above range, the electrode layer is oxidized, thereby reducing the
current capacity. Further, the oxidized electrode layer reacts with
the base materials of the insulating layer and the dielectric
layer, thereby reducing the longevity of the composite
substrate.
[0099] The annealing may be carried out only by increasing and
decreasing temperature. In this case, the temperature retention
time is zero and means the same as the maximum temperature. The
temperature retention time is preferably 0 to 20 hours,
particularly preferably 2 to 10 hours. As the atmospheric gas, for
example, a humidified H.sub.2 gas is preferable.
[0100] To humidify an N.sub.2 gas, an H.sub.2 gas or a mixed gas in
the above steps of removing a binder, the sintering and the
annealing, for example, a wetter may be used. In this case, water
temperature is preferably 5 to 75.degree. C.
[0101] The steps of removing a binder, the sintering and the
annealing may be carried out successively or separately.
[0102] When the steps are carried out successively, they are
preferably carried out as follows. After the binder-removing step,
the atmosphere is changed without cooling the composite substrate,
which is then sintered by increasing the temperature to the
retention temperature for the sintering. The resulting composite
substrate is then cooled and subjected to the annealing after the
atmosphere is changed when the temperature reaches the retention
temperature for the annealing.
[0103] When they are carried out separately, after the
binder-removing step, the temperature is increased to a
predetermined retention temperature, maintained at the retention
temperature for a predetermined period of time, and then decreased
to room temperature. In this case, the atmosphere for the
binder-removing step is the same as that in the above sequential
process. As for the annealing step, the temperature is increased to
a predetermined retention temperature, maintained at the retention
temperature for a predetermined period of time, and then decreased
to room temperature. In this case, the atmosphere for the annealing
step is the same as that in the above sequential process. Further,
in the above sequential process, either the annealing step or the
binder-removing step may be carried out separately.
[0104] The composite substrate can be obtained as described
above.
[0105] The composite substrate of the present invention can be
formed into a thin-film EL device by forming functional films such
as a luminescent layer, other insulating layer and other electrode
layer. Particularly, a thin-film EL device having good
characteristic properties can be obtained by using dielectric
materials in the insulating layer of the composite substrate of the
present invention. Since the composite substrate of the present
invention is made of sintering materials, it is suitable for use in
a thin-film EL device obtained by forming a luminescent layer as a
functional film on the substrate and subjecting the resulting
substrate to heat treatment.
[0106] To obtain a thin-film EL device using the composite
substrate of the present invention, a luminescent layer, other
insulating layer and other electrode layer are formed on the
insulating layer of the composite substrate in this order.
[0107] As materials for the luminescent layer, for example, those
disclosed in the article. "The recent trends in developments of
displays", by Shosaku Tanaka, Monthly Display, 1998, April, PP.1 to
10, may be used. Specific examples of the materials include ZnS and
Mn/CdSSe for red emission, ZnS:TbOF and ZnS:Tb for green emission,
and SrS:Ce, (SrS:Ce/ZnS)n, Ca.sub.2Ga.sub.2S.sub.4:Ce and
Sr.sub.2Ga.sub.2S.sub.4:Ce for blue emission.
[0108] For white emission, for example, SrS:Ce/ZnS:Mn is known.
[0109] Above all, the application of the present invention to an EL
device having a blue luminescent layer made of SrS:Ce, which is
studied in the above IDW (International Display Workshop), 1997, X.
Wu, "Multicolor Thin-Film Ceramic Hybrid EL Displays", PP. 593 to
596, gives particularly preferable results.
[0110] The thickness of the luminescent layer is not particularly
limited. However, when it is too large, a driving voltage
decreases, while when it is too small, luminous efficiency lowers.
Specifically, though depending on luminous materials, it is
preferably 100 to 1,000 nm, particularly preferably 150 to 500
nm.
[0111] The luminescent layer may be formed by a vapor deposition
method. Illustrative examples of the vapor deposition method
include a physical vapor deposition method such as sputtering or
deposition and a chemical vapor deposition method such as CVD. Of
these, the chemical vapor deposition method such as CVD is
preferable.
[0112] Further, as is specifically described in the above IDW, when
a luminescent layer made of SrS:Ce is formed by electron-beam
deposition under an H.sub.2S atmosphere, a luminescent layer of
high purity can be obtained.
[0113] The luminescent layer formed is preferably subjected to heat
treatment. The heat treatment may be carried out from the substrate
side after the electrode layer, the insulating layer and the
luminescent layer are laminated or after the electrode layer, the
insulating layer, the luminescent layer, the other insulating
layer, and in some cases, the other electrode layer, are laminated,
by cap annealing. It is preferable to carry out the heat treatment
by the cap annealing. The heat treatment temperature is preferably
600.degree. C. to the sintering temperature of the substrate, more
preferably 600 to 1,300.degree. C., particularly preferably 800 to
1,200.degree. C. The heat treatment time is in a range of 10 to 600
minutes, preferably 30 to 180 minutes. The annealing atmosphere
preferably comprises N.sub.2, Ar, He, or N.sub.2 containing 0.1% or
less of O.sub.2.
[0114] The insulating layer formed on the luminescent layer
preferably has a resistivity of 10.sup.8 .OMEGA..multidot.cm or
more, particularly preferably 10.sup.10 to 10.sup.18
.OMEGA..multidot.cm. Further, it is preferably made of materials
having a relatively high dielectric constant. The dielectric
constant .epsilon. is preferably 3 to 1,000.
[0115] The insulating layer may be formed of materials such as
silicon oxide (SiO.sub.2), silicon nitride (SiN), tantalum oxide
(Ta.sub.2O.sub.5), strontium titanate (SrTiO.sub.3), yttrium oxide
(Y.sub.2O.sub.3), barium titanate (BaTiO.sub.3), lead titanate
(PbTiO.sub.3), zirconia (ZrO.sub.2), silicon hydroxynitride (SiON),
alumina (Al.sub.2O.sub.3) and lead niobate (PbNb.sub.2O.sub.6).
[0116] The insulating layer is formed of these materials in the
same manner as the above luminescent layer is formed.
[0117] In this case, the thickness of the insulating layer is
preferably 50 to 1,000 nm, particularly preferably 100 to 500
nm.
[0118] The production process of the composite substrate and the
thin-film EL device of the present invention will be described with
reference to the accompanying drawings hereinafter.
[0119] First, as shown in FIG. 1, insulating layer (dielectric
layer) green sheets are laminated on a film sheet 11 having a flat
surface to form an insulating layer (dielectric layer) precursor
3.
[0120] Then, as shown in FIG. 2, an electrode layer paste
(electrode layer precursor) 2 is printed thereon in a predetermined
pattern.
[0121] Then, as shown in FIG. 3, a substrate green sheet 1 is
laminated to a required thickness to form a substrate precursor.
Thus, a composite layer precursor is obtained.
[0122] Thereafter, as shown in FIG. 4, the film sheet 11 is peeled
from the obtained composite substrate precursor, which is then
flipped as required and subjected to a binder-removing treatment
and the sintering. The binder-removing treatment and the sintering
are carried out under the conditions described above, and annealing
may also be carried out.
[0123] The obtained composite substrate precursor may be subjected
to the sintering with the film sheet when it is a
cellulose-containing sheet such as paper.
[0124] After the sintering, a composite substrate is obtained.
Further, a thin-film EL device is obtained in the following
manner.
[0125] First, as shown in FIG. 5, a luminescent layer 4 is formed
on the composite substrate. As described above, the luminescent
layer 4 can be formed by electron-beam deposition.
[0126] Then, as shown in FIG. 6, an upper insulating layer is
formed on the luminescent layer 4, and as required, the substrate 1
on which the insulating layer 5 has been formed is subjected to
heat treatment. The heat treatment may be carried out after the
formation of the luminescent layer 4 or after the formation of an
upper electrode layer 6, etc. on the upper insulating layer 5.
[0127] Thereafter, as shown in FIG. 7, an upper electrode layer 6
is formed on the upper insulating layer 5. When the upper electrode
layer 6 is formed after the heat treatment, it is not limited to
heat-resistant materials, and there may be used a transparent
conductive film which is the most favorable in recovering light.
Further, the electrode layer may be a metal film whose thickness is
adjusted as required to improve its light transmittance.
[0128] Although the above example shows the case where only one
luminescent layer is present, the thin-film EL layer is not limited
to the constitution. A plurality of luminescent layers may be
laminated in a film-thickness direction, or a plurality of
luminescent layers (pixels) of different types may be put together
in the form of a matrix and placed in a plane.
[0129] The thin-film EL device of the present invention may also be
used in a high-performance, high-definition display because the use
of the substrate material obtained by the sintering makes it easy
to obtain a luminescent layer capable of high-intensity blue
emission and because the insulating layer on which the luminescent
layer is laminated has a flat surface. Further, it can be produced
by a relatively simple process at a low production cost.
Furthermore, since it is capable of high-efficiency, high-intensity
blue emission, it may be used in combination with a color filter to
form a white emission device.
[0130] As the color filter, a color filter used in an LCD, etc. may
be used. The attributes of the color filter may be adjusted
according to light emitted by the EL device to optimize light
recovery and color purity.
[0131] In addition, when a color filter capable of shielding
short-wave external light which is likely to be absorbed by EL
device materials and a fluorescent conversion layer is used, the
light resistance and display contrast of the EL device can be
improved.
[0132] An optical thin film such as a dielectric multilayer film
may be substituted for the color filter.
[0133] A fluorescent conversion filter film is used to change the
color of emission by absorbing the light from the EL device and
discharging the light from the fluorescent material contained in
the fluorescent conversion filter film. It comprises a binder,
fluorescent materials and light-absorbing materials.
[0134] As the fluorescent materials, those having a high
fluorescent quantum yield are basically used, and those having high
absorptivity in an EL emission wave rage are desirable. From a
practical point of view, a dye laser is suitable, and
rhodamine-based compounds, perylene-based compounds, cyanine-based
compounds, phthalocyanine-based compounds (including
subphthalocyanine), naphthaloimide-based compounds, condensed ring
hydrocarbon-based compounds, condensed heterocyclic compounds,
styryl-based compounds and coumarin-based compounds may be
used.
[0135] The binder is basically formed of materials which do not
cause quenching and is preferably one that makes fine patterning by
photolithography or printing possible.
[0136] The light-absorbing materials are used only when the light
absorption of the fluorescent materials used is not sufficient. The
light-absorbing materials are selected from those which do not
cause quenching.
[0137] The thin-film EL device of the present invention is
generally pulse-driven or alternating-current-driven, and the
impressed voltage is 50 to 300 V.
[0138] Incidentally, although the thin-film EL device has been
described in the above example as one of the applications of the
composite substrate, the composite substrate of the present
invention is not limited to the application and is applicable to a
variety of electric materials. For example, it is applicable to a
thin film/thick-film hybrid high frequency coil device, etc.
[0139] The present invention will now further be described by
reference to certain examples and comparative examples. These
examples are provided solely for purposes of illustration and are
not intended to be limitative.
EXAMPLES
[0140] Examples of the present invention will be described
hereinafter. The EL structures used in the following examples are
such that a luminescent layer, an upper insulating layer and an
upper electrode are laminated successively on the surface of the
insulating layer of the composite substrate using thin-film
processes.
EXAMPLE 1
[0141] A dielectric paste was prepared by mixing barium titanate
powder with a binder (acryl resin) and a solvent (terpineol) to
prepare a dielectric layer precursor. A dielectric layer green
sheet was formed on a PET film having a flat surface by a doctor
blade using the paste. A plurality of the green sheet were
laminated to a predetermined thickness.
[0142] Then, an electrode layer paste prepared by mixing palladium
powder with a binder (ethyl cellulose) and a solvent (terpineol)
was printed on the green sheet laminate in a striped manner. A
substrate precursor was prepared by preparing a paste by mixing
alumina powder with a binder to form substrate green sheets, which
were then laminated. Another substrate precursor was prepared by
using a paste having the same composition as that of the dielectric
paste. A composite substrate green was prepared by laminating the
substrate precursor on the dielectric layer precursor having the
electrode layer printed thereon. The prepared composite substrate
green was subjected to a binder-removing treatment in the air at
260.degree. C. for 8 hours, and then to the sintering in the air at
1,340.degree. C. for 2 hours. The dielectric layer and the
substrate of the prepared composite substrate had thicknesses of
about 30 .mu.m and about 1.5 mm, respectively.
[0143] An EL device was produced by forming a ZnS fluorescence
material-based thin film having a thickness of 0.7 .mu.m on the
composite substrate heated at 250.degree. C. by sputtering using a
Mn-doped ZnS target, heating the resulting composite substrate in a
vacuum at 600.degree. C. for 10 minutes, and forming
Si.sub.3N.sub.4 thin film as a second insulating layer and an ITO
thin film as a second electrode on the composite substrate
successively by sputtering.
[0144] Emission properties were measured by taking out the printed
and sintered electrode and the ITO transparent electrode from the
obtained device structure and applying a 50 .mu.s electric field
with a pulse width of 1 kHz to the electrodes. Further, to measure
the electrical characteristics of the dielectric layer, another
sample was prepared by printing another electrode pattern in the
form of a stripe on the dielectric layer of the above composite
substrate such that one of the electrode patterns was cross the
other electrode pattern at right angles, drying the formed
electrode pattern and sintering the resulting composite
substrate.
[0145] The electrical characteristics of the dielectric layer of
the composite substrate prepared as described above and the
emission properties of the electroluminescent device 0.5 prepared
using the composite substrate are shown in Table 1.
EXAMPLE 2
[0146] A composite substrate and an electroluminescent device
prepared using the composite substrate were prepared in the same
manner as in Example 1 except that in preparing the dielectric
precursor of Example 1, BaTiO.sub.3 was mixed with the
predetermined amounts of MnO, MgO and V.sub.2O.sub.5 in water
before mixed with a binder. The emission properties obtained are
shown in Table 1.
EXAMPLE 3
[0147] A composite substrate and an electroluminescent device
prepared using the composite substrate were prepared in the same
manner as in Example 1 except that the dielectric of Example 2
containing Y.sub.2O.sub.3 was used. The emission properties
obtained are shown in Table 1.
EXAMPLE 4
[0148] A composite substrate and an electroluminescent device
prepared using the composite substrate were prepared in the same
manner as in Example 1 except that the dielectric of Example 3
containing (Ba 0.5, Ca 0.5) SiO.sub.3 was used. The emission
properties obtained are shown in Table 1.
EXAMPLE 5
[0149] A composite substrate and an electroluminescent device
prepared using the composite substrate were prepared in the same
manner as in Example 1 except that the dielectric of Example 3
containing (Ba 0.4, Ca 0.6)SiO3 was used. The emission properties
obtained are shown in Table 1.
EXAMPLE 6
[0150] An electrode layer paste was prepared using the dielectric
and the substrate precursor of Example 4 and Ni powder in place of
Pd powder. Sintering was carried out in the atmosphere comprising
N.sub.2, 5% of H.sub.2, and H.sub.2O gas obtained by vapor pressure
at 35.degree. C. An oxygen partial pressure of 10.sup.-8 Torr was
used. After the sintering, re-oxidization was carried out at
1,050.degree. C. for 3 hours in the atmosphere comprising N.sub.2
and H.sub.2O gas obtained by vapor pressure at 35.degree. C. The
oxygen partial pressure used in the re-oxidization was also
10.sup.-8 Torr. Except for these, a composite substrate and an
electroluminescent device prepared using the composite substrate
were prepared in the same manner as in Example 1. The emission
properties obtained are shown in Table 1.
EXAMPLE 7
[0151] A composite substrate and an electroluminescent device
prepared using the composite substrate were prepared in the same
manner as in Example 1 except that the dielectric precursor and the
electrode layer paste of Example 4 and a paste having the same
composition as that of the dielectric precursor paste were used to
prepare a substrate precursor. The emission properties obtained are
shown in Table 1.
1 TABLE 1 Substrate Lower Dielectric Sintering Dielectric layer
material electrode layer Additives conditions thickness (.mu.m) Ex.
1 Al.sub.2O.sub.3 Pd BaTiO.sub.3 None 1,340.degree. C., in air 30
thick film Ex. 2 Al.sub.2O.sub.3 Pd BaTiO.sub.3 MnO, MgO,
1,340.degree. C., in air 25 thick film V.sub.2O.sub.5 Ex. 3
Al.sub.2O.sub.3 Pd BaTiO.sub.3 Ex. 2 + Y.sub.2O.sub.3 1,340.degree.
C., in air 29 thick film Ex. 4 Al.sub.2O.sub.3 Pd BaTiO.sub.3 Ex. 3
+ (Ba, Ca) 1,340.degree. C., in air 31 thick film SiO.sub.3 Ex. 5
Al.sub.2O.sub.3 Ni BaTiO.sub.3 Same as in Ex. 4 1,340.degree. C.,
in 32 thick film reducing atmosphere Ex. 6 same as dielectric Pd
BaTiO.sub.3 Same as in Ex. 4 1,340.degree. C., in air 28 layer
thick film Comp. Ex. 1 blue plate glass Al Y.sub.2O.sub.3 thin film
-- -- 0.6 Comp. Ex. 2 Blue plate glass Al Si.sub.3N.sub.4 thin film
-- -- 0.6 Relative Dielectric Heat treatment Emission Brightness at
dielectric tan .delta. strength temperature of initiating the time
of constant (%) (V/.mu.m) fluorescent layer (.degree. C.) voltage
(V) application of 210 V Ex. 1 2,420 3.1 15 600 105 1,030 Ex. 2
2,310 1.4 30 600 145 1,050 Ex. 3 2.050 1.5 40 600 140 1,300 Ex. 4
2,260 1.2 45 600 120 1,250 Ex. 5 2,320 1.3 50 600 135 1,350 Ex. 6
2,670 0.8 65 600 130 1,470 Comp. Ex. 1 12 1.1 370 -- 186 150 Comp.
Ex. 2 8 1.0 720 -- 192 60
[0152] As described above, in accordance with the present
invention, there is provided a composite substrate in which the
surface of the insulating layer is not influenced by the electrode
layer and which requires neither a grinding process nor a sol-gel
process, is easy to produce and can provide a thin-film EL device
having a high display quality when used therein; a thin-film EL
device using the substrate; and a production process for the
device.
[0153] Having now described the present invention, it will be
readily apparent to one of ordinary skill in the art that many
changes and modifications may be made to the above-described
embodiments without departing from the spirit and the scope of the
present invention.
* * * * *