BACKGROUND OF THE INVENTION
Field of the Invention
[0001] The present invention relates to an image display apparatus using an electron-emitting
device as an electron source, and particularly, to the diffusion prevention of metal
used for a wiring of the image display apparatus.
Description of the Related Art
[0002] In recent years, two types of the electron-emitting device are known, that is, a
thermal electron source and a cold cathode electron source, and the cold cathode electron
source includes an electron emission type-device, metal/insulating layer/metal type-device,
a surface conduction electron-emitting device, or the like. There is a known display
apparatus in which the surface conduction electron-emitting device is used among the
cold cathode electron sources.
[0003] Such an apparatus, even with a large screen, can be relatively easily constructed
by combining a rear plate having a large number of the surface conduction electron-emitting
devices arranged as the electron source with a face plate including phosphor emitting
visible light. Electrons emitted from the electron-emitting device are accelerated
and caused to enter an image forming member made of the phosphor to obtain the brightness.
In the image display apparatus, it is necessary to electrically isolate the electron-emitting
devices from each other since they respond to an input signal, and therefore an insulating
substrate is generally used. However, when a surface of the insulating substrate is
exposed near an electron-emitting site, electric potential of the surface becomes
unstable, and the electron emission becomes unstable.
[0004] When high voltage is applied to the phosphor of an image forming member, electric
potential is induced on an insulation surface around the opposing electron-emitting
device due to capacitive division, which is determined by dielectric constants of
a vacuum and an insulator. The better the insulation is, the longer the time constant
this electric potential would have, and the surface would remain charged. When the
electrons are emitted from the electron-emitting device in such a condition, the electrons
also collide with the charged insulation surface. In this case, the accelerated electrons
cause charged particle such as electrons and ions to be injected into the insulation
surface to induce secondary electrons. Particularly under high electric field, the
resultant abnormal discharge significantly degrades electron emission characteristics
of the device, resulting in damage to the device in the worst case. As a countermeasure
for such abnormal discharge thus induced, Japanese Patent Application Laid-Open No.
2006-127794 (
U.S. Patent Publication No. 2006/0087219) discloses such a technique that a part of the electron-emitting device excluding
an electron-emitting site is covered by an insulating layer so that discharge current
is not flown in the electron-emitting device.
[0005] As another countermeasure, Japanese Patent Application Laid-Open No.
2002-358874 discloses a method for providing an anti static film around the electron-emitting
device by splaying solution obtained by dispersing an electroconductive fine particle
in organic solvent.
[0006] It is necessary that the above anti static film is connected to a power source to
cause the charge to escape. Such a configuration is generally adopted that ensures
electrical connection between the anti static film and the power source by bringing
electroconductive material, such as the wiring, connected to the power source into
contact with the anti static film. However, it is considered that, when a fine particle
dispersed film containing SnO
x is used as the anti static film, the metal used in the wiring is, because of a thermal
process, diffused to the fine particle of the anti static film, and a metal crystal
substance separates out and grows on a fine particle surface. When this metal is heated
in the vacuum, and voltage is applied thereto, such a problem may arise that electrons
are emitted from the metal crystal substance, and desired image characteristics can
not be obtained.
SUMMARY OF THE INVENTION
[0007] An object of the present invention is to prevent wiring metal from being diffused
to a fine particle when a fine particle dispersed film is disposed on a wiring, and
to prevent image characteristics from being degraded because of the diffusion, in
an image display apparatus using an electron-emitting device.
[0008] The image display apparatus of the present invention includes a first substrate including,
at least, a first wiring, a second wiring intersecting with the first wiring through
an insulating layer, and an electron-emitting device provided with a pair of device
electrodes connected to the first wiring and the second wiring respectively, and a
second substrate, which is disposed facing the first substrate, including, at least,
an electrode whose electronic potential is defined higher than that of the second
wiring, and an image forming member which emits light while irradiated by the electron
emitted from the above electron-emitting device, and the image display apparatus of
the present invention further includes a fine particle dispersed film, which is electrically
connected to the second wiring, on the first substrate, and includes an electroconductive
shielding layer for shielding the second wiring from the fine particle dispersed film
between the second wiring and the fine particle dispersed film.
[0009] According to the present invention, the wiring metal is prevented from being diffused
to the fine particle of the anti static film even when subjected to the thermal process.
Thus, it is possible to prevent the image characteristics from being degraded because
of the diffusion, and to provide the highly-reliable image display apparatus.
[0010] Further features of the present invention will become apparent from the following
description of exemplary embodiments with reference to the attached drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1A is a schematic view illustrating in order the steps for producing a first
substrate according to an exemplary embodiment of an image display apparatus of the
present invention.
[0012] FIG. 1B is a schematic view illustrating in order the steps for producing the first
substrate according to the exemplary embodiment of the image display apparatus of
the present invention.
[0013] FIG. 1C is a schematic view illustrating in order the steps for producing the first
substrate according to the exemplary embodiment of the image display apparatus of
the present invention.
[0014] FIG. 1D is a schematic view illustrating in order the steps for producing the first
substrate according to the exemplary embodiment of the image display apparatus of
the present invention.
[0015] FIG. 1E is a schematic view illustrating in order the steps for producing the first
substrate according to the exemplary embodiment of the image display apparatus of
the present invention.
[0016] FIG. 1F is a schematic view illustrating in order the steps for producing the first
substrate according to the exemplary embodiment of the image display apparatus of
the present invention.
[0017] FIG. 1G is a schematic plain view of the first substrate according to the exemplary
embodiment of the image display apparatus of the present invention.
[0018] FIG. 1H is a partially enlarger sectional view along a line 1H-1H in FIG. 1G.
[0019] FIG. 2A is a schematic view illustrating a configuration of an electron-emitting
device used for the first substrate in FIGS. 1A, 1B, 1C, 1D, 1E, 1F, 1G and 1H.
[0020] FIG. 2B is a cross-section 2B-2B in FIG. 2A.
[0021] FIG. 3 is a schematic view illustrating an example of a display panel of the image
display apparatus constructed by using the first substrate in FIGS. 1A, 1B, 1C, 1D,
1E, 1F, 1G and 1H.
DESCRIPTION OF THE EMBODIMENTS
[0022] FIG. 2A illustrates an exemplary configuration of a surface conduction electron-emitting
device preferably used for the present invention, and FIG. 1G illustrates an exemplary
configuration of a first substrate, in which the electron-emitting device in FIG.
2A is used, of the image display apparatus of the present invention. FIGS. 1A, 1B,
1C, 1D, 1E and 1F are views illustrating producing steps for the first substrate in
FIG. 1G. In the figures, Reference numeral 1 denotes a substrate, Reference numerals
2 and 3 denote device electrodes, Reference numeral 4 denotes a first wiring, Reference
numeral 5 denotes an insulating layer, Reference numeral 6 denotes a second wiring,
Reference numeral 7 denotes a shielding layer, Reference numeral 8 denotes an electroconductive
film, Reference numeral 9 denotes an electron-emitting site formed in the electroconductive
film 8, and Reference numeral 10 denotes an anti static film. Meanwhile, FIG. 2B is
a cross-section 2B-2B in FIG. 2A, and for the convenience of the description, the
anti static film 10 is omitted in FIG. 2A. Even in FIG. 1G, for the convenience of
the description, the anti static film 10 is illustrated with a part omitted.
[0023] A configuration of the first substrate according to the present invention will be
described below by using, as an example, the steps for producing the first substrate
in FIGS. 1A, 1B, 1C, 1D, 1E, 1F, 1G and 1H.
[0024] A pair of the device electrodes 2 and 3 are formed with metal material at each intersecting
point of the after-mentioned first wiring 4 and the second wiring 6 on the cleaned
substrate 1 (FIG. 1A).
[0025] The following substrates can be used as the substrate 1: a glass substrate obtain
by stacking SiO
2 formed, by the spattering method, on silica glass, glass in which a contained amount
of impurity such as Na is reduced, and soda lime glass; and a ceramics substrate such
as alumina and a Si substrate.
[0026] The device electrodes 2 and 3 are formed by a method for forming a metal thin film
by using a vacuum-based film-forming method such as a vacuum-evaporating method, a
spattering method and a plasma CVD method, and patterning by the photolithography
method to etch the metal thin film. In addition, a method is also used, in which the
metal organic paste containing organic metal is offset-printed by using the glass
intaglio printing, and the method can be arbitrarily selected.
[0027] In the device electrodes 2 and 3, for example, electrode distance L (refer to FIG.
2A) is caused to be several dozen to several hundreds µm, and film thickness d is
caused to be several dozen to several hundreds nm. It is enough that material of the
device electrodes is electroconductive material. For example, the material includes
a print conductor including metal such as Ni, Cr, Au, Mo, W, Pt, Ti, Al, Cu and Pd
or alloy of such metal, metal such as Pd, Ag, Au, RuO
2 and Pd-Ag or oxide of such metal, and glass. The material also includes semiconductor
material such as polysilicon, and a transparent conductor such as In
2O
3-SnO
2.
[0028] Next, the first wiring 4 in the form of a matrix wiring is formed by using electroconductive
paste (FIG. 1B). As the forming method, the first wiring 4 can be formed by a screen
printing method or the photolithography method. In this case, the first wiring 4 is
formed so as to be connected to the device electrode 3. It is preferable in this first
wiring 4 that film thickness is formed thicker to reduce electric resistance, and
metal such as Ag, Au, Cu, Ni, Pt and Pd, or alloy of such metals is used as the electroconductive
paste.
[0029] Next, in the matrix wiring, the insulating layer 5 is formed by using glass paste,
which isolates the first wiring 4 from the later-formed second wiring 6 (FIG. 1C).
Meanwhile, as illustrated in FIG. 1C, it is better that the insulating layer 5 is
formed not only on the first wiring 4, but also in a part in which the second wiring
6 is formed, and thereby, it is preferable that the second wiring 6 can be also securely
isolated from the device electrode 3. As a method for forming the insulating layer
5, the screen printing method or the photolithography method can be selected. The
glass paste used for the insulating layer 5 includes frit glass, whose main component
is lead oxide or bismuth oxide, mixed with appropriate polymer such as cellulose,
organic solvent and a vehicle.
[0030] Next, the second wiring 6, which is in the form of the matrix wiring as intersecting
with the first wiring 4, is formed on the insulating layer 5 by using the electroconductive
paste (FIG. 1D). As the method for forming the second wiring 6, the screen printing
method or the photolithography method can be selected. As the electroconductive paste,
it is preferable that metal such as Ag, Au, Cu, Ni, Pt and Pd, or alloy of such metals
is, for example, used to reduce the electric resistance in a similar way to the first
wiring 4.
[0031] Next, the shielding layer 7 is formed on the second wiring 6 (FIG. 1E). As the method
for forming the shielding layer 7, the screen printing method, the photolithography
method or an ink-jet method can be selected.
[0032] In this case, it is necessary to form the shielding layer 7 so that the second wiring
6 is not exposed, so that it is preferable to cover at least 80% or more of a surface
of the second wiring 6, which faces an after-mentioned second substrate.
[0033] To secure electrical connection between the second wiring 6 and the later-formed
anti static film made of the fine particle dispersed film, the shielding layer 7 needs
to satisfy an electric potential rule for a spacer, so that the shielding layer 7
is electroconductive. The following material can be, for example, selected as material
of the shielding layer 7: metal such as Pt, Ru, Ag, Au, Ti, In, Cu, Ni, Cr, Fe, Zn,
Sn, Ta, W and Pd; and glass paste or a fine particle film including oxide such as
PdO, SnO
2, In
2O
3, PbO and Sb
2O
3. Particularly, to satisfy the adherence with the insulating layer 5 and the electric
potential rule, it is preferable to select metal fine particle paste whose main component
is Ni, and which include a small amount of glass powder.
[0034] It is enough that the shielding layer 7 is thick to the extent that metal can be
prevented from being diffused from the second wiring 6 in a baking step, and the thickness
is not particularly restricted, however, from a viewpoint of the thickness when a
panel is formed, the thickness is generally 0.2 µm to 10 µm, preferably 1 µm or more,
and 1 µm to 5 µm.
[0035] Next, the electroconductive film 8 is formed through a pair of the device electrodes
2 and 3 (FIG. 1F). A specific example of a material includes metal such as Pt, Ru,
Ag, Au, Ti, In, Cu, Cr, Fe, Zn, Sn, Ta, W and Pd, and oxide such as PdO, SnO
2, In
2O
3, PbO and Sb
2O
3. In addition, the specific example includes boride such as HfB
2, ZrB
2, LaB
6, CeB
6, YB
4 and CdB
4, carbide such as TiC, ZrC, HfC, TaC, SiC and WC, and nitride such as TiN, ZrN and
HfN. Further, the specific example includes semiconductor of Si and Ge, carbon, Ag,
Mg, NiCu, Pb and Sn. Such electroconductive film 8 is made of a fine particle film.
Meanwhile, the fine particle film described here means a film obtained by assembling
a plurality of fine particles, and a microstructure of the fine particle film includes
not only such a condition that the fine particles are arranged as being individually
dispersed, but also such a condition that the fine particles are adjacent to each
other, or are overlapped by each other (including island-like condition). The inkjet
method is preferably used for forming the electroconductive film 8. A principle and
a configuration of the inkjet method are very simple, and this is because the inkjet
method includes many advantages such as it is easy to speed-up and to reduce a size
of a droplet. Actually, after solution of organic metal compound including the above
electroconductive material is provided as the droplet only at a predetermined position
to be dried, since the organic metal compound is thermally decomposed by the thermal
process, the electroconductive film 8 is formed, which is made of metal or metal oxide.
[0036] Next, the anti static film 10 for preventing the charge on a surface of the substrate
1 is formed on the substrate 1 (on the first substrate). It is preferable that the
anti static film 10 includes a sheet resistance value of approximately 10
10 Ohms per square to 10
12 Ohms per square to prevent the charge from being discharged. When the electron source
is constructed, it is requested from a permissible value for leak current between
the first wiring 4 and the second wiring 6 that the sheet resistance value is 10
8 Ohms per square or more. The anti static film 10 is the fine particle dispersed film
obtained by spray-applying the organic solution, in which the electroconductive fine
particle is dispersed, and dry-eliminating the spray-applied organic solution. As
the electroconductive fine particle, the fine particle, whose main component is carbon
material, SnO
x or chrome oxide, is preferably used, and SnO
x, in which antimony is doped, is the more preferable main component. As the organic
solution, alcohol-type solution is preferably used, and for example, mixed solution
of isopropyl alcohol (IPA) and ethyl alcohol is preferably used.
[0037] Next, the electroconductive film 8 is electro-energized, and the electron-emitting
site 9 is formed (FIG. 1G). Meanwhile, FIG. 1G illustrates the anti static film 10
with a part omitted to describe the electron-emitting site 9. And, FIG. 1H shows a
partially enlarged sectional view along a line 1H-1H in FIG. 1G. The electron-emitting
site 9 is a high-resistance gap formed in a part of the electroconductive film 8 (FIG.
2A), and depends on film thickness, film quality, material and an electro energization
condition of the electroconductive film 8. The electroconductive fine particle may
be included in the gap of the electron-emitting site 9, whose particle size is in
a range of several hundreds pm to several dozen nm. This electroconductive fine particle
includes a part or all of elements of material included in the electroconductive film
8. Carbon and carbon compound may be included in the electron-emitting site 9 including
the gap and the electroconductive film 8 near the electron-emitting site 9.
[0038] The image display apparatus of the present invention will be described by using FIG.
3, which is constructed with the electron source in which a plurality of such electron-emitting
devices are matrix-arranged. FIG. 3 is a schematic view illustrating en example of
a display panel of a preferable exemplary embodiment of the image display apparatus
of the present invention. In FIG. 3, Reference numeral 11 denotes an electron-emitting
device, Reference numeral 12 denotes a supporting frame, Reference numeral 13 denotes
a face plate (second substrate), Reference numeral 13a denotes a substrate, Reference
numeral 13b denotes a fluorescent film (image forming member), Reference numeral 13c
denotes an anode electrode (metal back), Reference numeral 14 denotes a rear plate
(first substrate).
[0039] The rear plate 14 is an electron source substrate in which a plurality of the electron-emitting
devices 11 are matrix-arranged. The face plate 13 is made up of the fluorescent film
13b including a light-emitting substance such as the phosphor and the metal back 13c
as the anode electrode, which are formed inside the substrate 13a. The metal back
13c is defined to be at the higher electronic potential than the second wiring 6,
and since the electron emitted from the electron-emitting device 11 is irradiated
to the fluorescent film 13b, the fluorescent film 13b emits light. Reference numeral
12 is the supporting frame, and the rear plate 14 and the face plate 13 are seal-bonded
by using the frit glass. In this seal-bonding, for example, to vacuumize the inside
of the image display apparatus, the inside of the image display apparatus is baked
in the vacuum to be seal-bonded. On the other hand, a support (not-illustrated) referred
to as a spacer can alternatively be provided between the face plate 13 and the rear
plate 14, so that the image display apparatus can be adapted to have sufficient strength
for the atmospheric pressure.
[0040] In the image display apparatus of the present invention, even when the fine particle
dispersed film including SnO
x is provided as the anti static film 10 on a surface of the rear plate 14, the shielding
layer 7 on the second wiring 6 prevents the metal of the second wiring 6 from being
diffused to the above fine particle. Thus, a metal granularity substance and a metal
single crystal do not separate out and grow in the anti static film 10 even through
a vacuum baking process for the seal-bonding, and the abnormal discharge can be prevented
when the voltage is applied in the electron emission.
[0042] (Exemplary embodiment 1)
[0043] By using a high-softening point glass substrate used for a plasma display, Pt with
film thickness of approximately 20 nm is patterned by a photolithoetching method,
and a plurality of pairs of the device electrodes are formed as illustrated in FIG.
1A.
[0044] Next, whole surface film forming is executed by the screen printing by using Ag-based
photo paste, and the formed film is dried at approximately 100°C for approximately
15 minutes. The dried film is patterned by using the photolithography method, and
a useless part is eliminated. Further, the film is baked at 500°C for approximately
15 minutes, and the first wiring with film thickness of approximately 8 µm is formed
as illustrated in FIG. 1B.
[0045] Next, the whole surface film forming is executed by the screen printing by using
Bi-based photosensitive glass paste, the formed film is dried at approximately 150°C
for approximately 10 minutes, the dried film is patterned by using the photolithography
method, and a useless part is eliminated. Further, the film is baked at 500°C, and
the insulating layer is formed as illustrated in FIG. 1C. In the present example,
to improve the reliability of the insulation, a plurality of the same insulating layers
are stacked, and the insulating layer with layer thickness of approximately 30 µm
is formed.
[0046] Next, the Ag-based paste is film-formed by the screen printing, is dried at approximately
100°C for approximately 15 minutes, and is baked at approximately 400°C for approximately
15 minutes, thereby, the second wiring is formed as illustrated in FIG. 1D. In the
present example, to satisfy the resistance value, a plurality of the same wiring layers
are stacked, and the second wiring layer with layer thickness of approximately 30
µm is formed.
[0047] On the above second wiring, the glass paste, whose main component is indium oxide
as the electroconductive material, and which includes a small amount of stannum oxide,
is film-formed by the screen printing, is dried at approximately 100°C for approximately
15 minutes, and is baked at approximately 400°C for approximately 15 minutes, thereby,
the shielding layer with layer thickness of approximately 3 µm is formed as illustrated
in FIG. 1E. The ratio of the indium oxide and glass powder used in this case is indium
oxide/glass paste = 0.67 mass%. The ratio of a part covered by the shielding layer
of the second wiring is approximately 80%.
[0048] Next, since the Pd-based organic solution is output by the inkjet method, a pattern
with film thickness of approximately 5 nm is formed, so that each pair of the device
electrodes communicates with each other, thereby, the electroconductive film made
of Pd is formed as illustrated FIG. 1F.
[0049] Next, the solution, in which the fine particle made of antimony oxide is dispersed
in the mixed solution of the IPA and the ethyl alcohol, is splay-applied on the substrate,
thereby, the anti static film is formed.
[0050] The electroconductive film is electro-energized, and the electron-emitting site is
formed as illustrated in FIG. 1G to be the electron-emitting device.
[0051] The rear plate formed as described above is opposed to the face plate provided with
the fluorescent film and the metal back, and then vacuum-sealed along with the supporting
frame to form a panel, in which the existence of the abnormal discharge is checked.
As a result of the check, the abnormal discharge due to the diffusion and the separation
of Ag used for the second wiring has not been observed. EPMA analysis performed on
the interface of Ag and the glass paste, which are samples, has not shown Ag diffused
in the part of the glass paste layer at and above 1 µm from an Ag surface. Meanwhile,
even when the first wiring and the second wiring are formed with Cu, the diffusion
of Cu has not been observed.
[0052] (Exemplary embodiment 2)
[0053] The rear plate is produced in a similar way to the exemplary embodiment 1 excluding
that the shielding layer is formed by using the glass paste including an antimony
oxide particle and the stannum oxide as covering approximately 100% of the second
wiring.
[0054] The rear plate thus formed is used and vacuum-sealed with the face plate, in a similar
way to the exemplary embodiment 1, and when the existence of the abnormal discharge
is checked, the abnormal discharge due to the diffusion and the separation of Ag used
for the second wiring has not been observed. EPMA analysis performed on the interface
of Ag and the glass paste, which are samples, has not shown Ag diffused in the part
of the glass paste layer at and above 1 µm from an Ag surface. Meanwhile, even when
the first wiring and the second wiring are formed with Cu, the diffusion of Cu has
not been observed.
[0055] (Exemplary embodiment 3)
[0056] The rear plate is produced in a similar way to the exemplary embodiment 1 excluding
that the shielding layer is formed by using the metal fine particle paste, whose main
component is nickel, and which includes a small amount of glass powder, as covering
approximately 80% of the second wiring.
[0057] The rear plate thus formed is used and vacuum-sealed with the face plate, in a similar
way to the exemplary embodiment 1, and when the existence of the abnormal discharge
is checked, the abnormal discharge due to the diffusion and the separation of Ag used
for the second wiring has not been observed. The abnormal discharge is not checked,
which is induced because of the diffusion and the separation of Ag used for the second
wiring. Cross-section TEM observation and EDX analysis performed on the interface
of Ag and the glass paste, which are samples, have not shown Ag diffused in the part
of the metal nickel layer at and above 1 µm from an Ag surface. Meanwhile, even when
the first wiring and the second wiring are formed with Cu, the diffusion of Cu has
not been observed.
[0058] While the present invention has been described with reference to exemplary embodiments,
it is to be understood that the invention is not limited to the disclosed exemplary
embodiments. The scope of the following claims is to be accorded the broadest interpretation
so as to encompass all such modifications and equivalent structures and functions.
In the image display apparatus using the electron-emitting device, wiring metal is
prevented from being diffused to a fine particle when a fine particle dispersed film
is disposed on the wiring, and the image characteristic is prevented from being degraded
because of the diffusion. A first wiring 4 and a second wiring 6 intersecting with
the first wiring 4 through an insulating layer are formed on an insulation substrate
1, and after an electroconductive shielding layer 7 is formed on the second wiring
6, a anti static film made of a fine particle dispersed film is formed.