U.S. patent application number 11/262986 was filed with the patent office on 2006-09-21 for electron-emitting devices, electron sources, and image-forming apparatus.
This patent application is currently assigned to CANON KABUSHIKI KAISHA. Invention is credited to Shinichi Kawate, Takeo Tsukamoto.
Application Number | 20060208654 11/262986 |
Document ID | / |
Family ID | 26599100 |
Filed Date | 2006-09-21 |
United States Patent
Application |
20060208654 |
Kind Code |
A1 |
Kawate; Shinichi ; et
al. |
September 21, 2006 |
Electron-emitting devices, electron sources, and image-forming
apparatus
Abstract
Provided are electron-emitting devices, electron sources, and
image-forming apparatus improved in electron emission efficiency
and in convergence of trajectories of emitted electrons. An
electron-emitting device has a first electrode and a second
electrode placed in opposition to each other with a gap between
first and second electrodes on a surface of a substrate, and a
plurality of fibers electrically connected to the first electrode
and containing carbon as a main component, and the fibers are
placed on a surface of the first electrode facing the second
electrode.
Inventors: |
Kawate; Shinichi; (Kanagawa,
JP) ; Tsukamoto; Takeo; (Kanagawa, JP) |
Correspondence
Address: |
FITZPATRICK CELLA HARPER & SCINTO
30 ROCKEFELLER PLAZA
NEW YORK
NY
10112
US
|
Assignee: |
CANON KABUSHIKI KAISHA
Tokyo
JP
|
Family ID: |
26599100 |
Appl. No.: |
11/262986 |
Filed: |
November 1, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09940642 |
Aug 29, 2001 |
7012362 |
|
|
11262986 |
Nov 1, 2005 |
|
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Current U.S.
Class: |
315/169.2 ;
313/311; 313/495; 313/497 |
Current CPC
Class: |
Y10S 977/939 20130101;
Y10S 977/842 20130101; H01J 2201/30469 20130101; Y10S 977/843
20130101; H01J 31/127 20130101; H01J 9/025 20130101; B82Y 10/00
20130101; H01J 1/304 20130101 |
Class at
Publication: |
315/169.2 ;
313/495; 313/497; 313/311 |
International
Class: |
H01J 63/04 20060101
H01J063/04; G09G 3/10 20060101 G09G003/10 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 1, 2000 |
JP |
265821/2000 |
Aug 24, 2001 |
JP |
254638/2001 |
Claims
1.-30. (canceled)
31. An electron-emitting device comprising: (A) first and second
electrodes disposed on an electrically-insulating substrate,
wherein a gap is formed between said first and second electrodes,
the first electrode contains Ti, Zr or Nb, and a surface containing
an oxide of Ti, Zr or Nb of the first electrode is disposed on only
a position facing the second electrode, and the first electrode is
exposed at a surface thereof except for the position facing the
second electrode; and a fibrous carbon grown through a catalyst
particle disposed on said surface facing said second electrode
wherein there is a gap between the fibrous carbon and said second
electrode.
32. (canceled)
33. The electron-emitting device according to claim 31, wherein an
electron emission position from said fibrous carbon is more distant
from a surface of said substrate than a position, being the most
distant from said surface of said substrate, of a surface of said
second electrode.
34. The electron-emitting device according to claim 31, wherein
said second electrode and said first electrode are formed into a
substantially planar shape on a surface of said substrate, a
thickness of said first electrode is larger than a thickness of
said second electrode, and a voltage is applied between said first
and second electrodes so that a potential of said second electrode
is higher than that of said first electrode, thereby emitting an
electron from said fibrous carbon.
35. The electron-emitting device according to claim 31, wherein
said substrate is thicker in a region where said first electrode is
formed than in a region where said second electrode is formed, and
a voltage is applied between said first and second electrodes so
that a potential of said second electrode is higher than that of
said first electrode, thereby emitting an electron from said
fibrous carbon.
36. (canceled)
37. An image-forming apparatus comprising: a plurality of
electron-emitting devices, each being an electron-emitting device
according to claim 31; and a fluorescent member.
38. An image-forming apparatus comprising: a plurality of
electron-emitting devices, each being an electron-emitting device
according to claim 33; and a fluorescent member.
39.-43. (canceled)
44. An image-forming apparatus comprising: a plurality of
electron-emitting devices, each being an electron-emitting device
according to claim 39; and a fluorescent member.
45. An image-forming apparatus comprising: a plurality of
electron-emitting devices, each being an electron-emitting device
according to claim 40; and a fluorescent member.
46. (canceled)
47. (canceled)
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to electron-emitting devices
for emission of electrons, electron sources using them, and
image-forming apparatus using the electron sources. The
image-forming apparatus according to the present invention can be
used in display devices for television broadcasting and the like,
display devices of video conference systems, computers, etc.,
optical printers constructed with use of a photosensitive drum or
the like, and so on.
[0003] 2. Related Background Art
[0004] Conventionally, field emission type (FE type)
electron-emitting devices configured to apply a strong electric
field of not less than 10.sup.6 V/cm to metal and thereby emit
electrons from the metal surface are drawing attention as one of
cold electron sources.
[0005] If such FE type cold electron sources become practically
available, it will become feasible to construct low-profile
emissive type image display devices and they will also contribute
to reduction in power consumption and reduction in weight.
[0006] Known as an example of a vertical FE type is a device in
which, as shown in FIG. 13, an emitter 135 is of the shape of a
circular cone or a quadrangular pyramid formed from a substrate 131
approximately in the vertical direction; for example, one disclosed
in C. A. Spindt, "Physical Properties of thin-film field emission
cathodes with molybdenum cones," J. Appl. Phys., 47, 5248 (1976) or
the like (hereinafter referred to as a Spindt type).
[0007] On the other hand, a lateral FE structure is shown in FIG.
14. In the figure, numeral 141 designates a substrate, 142 an
emitter electrode, 143 an insulating layer, 145 an emitter, 146 an
anode, and 147 a profile of an electron beam irradiating the anode.
The emitter 145 sharp-pointed at the tip is arranged in parallel
with a gate electrode 144 for extracting electrons from the emitter
tip, on the substrate and the collector (anode electrode) is
disposed above the substrate on which the gate electrode and the
emitter electrode are placed (see U.S. Pat. No. 4,728,851, U.S.
Pat. No. 4,904,895, and so on).
[0008] As an example of the electron-emitting devices using fibrous
carbon, Japanese Patent Application Laid-Open No. 8-115652
discloses a configuration in which thermal decomposition is
implemented in the presence of organic compound gas on fine
particles of catalyst metal whereby fibrous carbon is deposited in
a fine gap.
[0009] As electroconductive layers for carbon nanotubes, Japanese
Patent Application Laid-Open No. 11-194134 and European Patent
EP0913508A2 describe metal layers of titanium (Ti), zirconium (Zr),
niobium (Nb), tantalum (Ta), and molybdenum (Mo). Japanese Patent
Application Laid-Open No. 11-139815 describes Si as an
electroconductive substrate.
[0010] The beam profiles of the electron-emitting devices according
to the prior arts will be described referring to FIGS. 13 and
14.
[0011] In FIG. 13, which shows the Spindt type electron-emitting
device according to the foregoing prior art, numeral 131 denotes
the substrate, 132 the emitter electrode, 133 the insulating layer,
134 the gate, and 135 the emitter connected to the emitter
electrode 132. When Vf is placed between the emitter 135 and the
gate 134, the electric field becomes stronger at the tip of the
projection of the emitter 135 and then electrons are emitted from
the vicinity of the tip of the cone into the vacuum.
[0012] Since the electric field at the tip of the emitter is formed
in such a certain finite area as to follow the shape of the emitter
tip, the extracted electrons are drawn in the vertical direction
relative to the potential from the finite area at the emitter
tip.
[0013] At this time, electrons are also emitted at various angles.
As a result, electrons with large angle components are drawn in
directions toward the internal peripheral surface in the hole
formed in the gate 134.
[0014] As a consequence, where the hole is circular, an electron
distribution obtained on the anode 136 in the figure becomes a
substantially circular beam profile 137. This indicates that the
resultant beam profile is in close relation with the shape of the
gate and the distance to the emitter.
[0015] The lateral FE configuration as shown in FIG. 14 is the
prior art in which electrons are emitted in the aligned extraction
direction.
[0016] In FIG. 14, numeral 141 designates the substrate, 142 the
emitter electrode, 143 the insulating layer, 144 the gate, and 145
the emitter, and the anode 146 is provided on a substrate opposed
to the substrate on which the emitter and gate are disposed.
[0017] In the case of the lateral FE configuration constructed in
this way, some of electrons emitted from the emitter 145 are
extracted (or emitted) into the vacuum, but the rest are taken into
the gate 144.
[0018] In the configuration shown in FIG. 14, the direction of the
electric field vector for emission of electrons (the electric field
from the emitter 145 toward the gate 144) is different from the
direction of the electric field vector toward the anode 146. As a
result, the electron distribution (electron beam spot) becomes
large.
SUMMARY OF THE INVENTION
[0019] The prior arts as described above had the following
problems.
[0020] Since in the foregoing Spindt type the gate and the
substrate were constructed in the layered structure, a large gate
capacitance and a lot of parasitic capacitances to the emitter were
made. Further, the driving voltage was as high as several ten
volts, and there was the drawback of large capacitive power
consumption because of the configuration. The Spindt type
configuration also had the problem that the beam profile became
expanded at the positive electrode (anode).
[0021] The foregoing lateral FE configuration had the advantage of
capability of reducing the capacitance of the device but had the
disadvantage of increasing the driving voltage, because the large
distance between the emitter and the gate required several hundred
volts for driving. This configuration also had the problem that the
beam profile was expanded at the positive electrode (anode).
[0022] It is also conceivable to provide the above Spindt type and
lateral FE type electron-emitting devices with a beam focusing
means, but this raises problems of complexity in a fabrication
method, increase in the device area, decrease in electron emission
efficiency, and so on.
[0023] The present invention has been accomplished in order to
solve the above problems and an object of the invention is to
provide electron-emitting devices that are reduced in the device
capacitance and the driving voltage and improved in the electron
emission efficiency and that can provide a high-definition beam
stably over a long period, and electron sources and image-forming
apparatus using them.
[0024] In order to achieve the above object, an electron-emitting
device according to the present invention comprises a first
electrode and a second electrode arranged in opposition to each
other with a gap between first and second electrodes on a surface
of a substrate, and a plurality of fibers electrically connected to
the first electrode and comprising carbon as a main component, and
the fibers are placed on a surface of the first electrode facing
the second electrode.
[0025] In order to achieve the above object, another
electron-emitting device according to the present invention
comprises an extraction electrode and a cathode electrode formed in
opposition to each other with a gap between the extraction
electrode and the negative electrode on an electrically insulating
substrate, a first layer formed on the negative electrode and
having an oxide of Ti, an oxide of Zr, or an oxide of Nb on a
surface thereof, and a fibrous carbon grown through a catalyst
particle disposed on a side wall surface of the first layer on the
extraction electrode side.
[0026] An electron source according to the present invention is
characterized by a plurality of above-stated electron-emitting
devices arrayed.
[0027] An image-forming apparatus according to the present
invention is characterized by use of the above electron source.
[0028] According to the present invention, it is feasible to
provide the electron-emitting devices presenting a small electron
beam spot on the anode, achieving excellent electron emission
efficiency, and having excellent durability, a small capacitance
component, and excellent stability. The electron sources using the
electron-emitting devices can realize quick responsivity and low
power consumption. The image-forming apparatus using the electron
sources can provide high-definition images with high luminance over
a long period, in addition to the quick responsivity and low power
consumption.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] FIGS. 1A and 1B are schematic views showing an
electron-emitting device according to an embodiment and Example 1
of the present invention;
[0030] FIGS. 2A and 2B are schematic views showing another
electron-emitting device according to Example 2 of the present
invention;
[0031] FIGS. 3A and 3B are schematic views showing still another
electron-emitting device according to Example 3 of the present
invention;
[0032] FIGS. 4A and 4B are schematic views showing still another
electron-emitting device according to Example 4 of the present
invention;
[0033] FIGS. 5A, 5B, 5C, 5D and 5E are step diagrams for production
of the electron-emitting device according to Example 1 of the
present invention;
[0034] FIG. 6 is a diagram for explaining the operation of the
electron-emitting device;
[0035] FIG. 7 is a characteristic diagram of the fundamental
operation of the electron-emitting device;
[0036] FIG. 8 is a schematic plan view of an electron source
according to an embodiment of the present invention;
[0037] FIG. 9 is a perspective view of an image-forming apparatus,
partly broken, according to an embodiment of the present
invention;
[0038] FIG. 10 is a block diagram of an image-forming apparatus
according to an embodiment of the present invention;
[0039] FIG. 11 is a schematic structure diagram of fibrous carbons
(carbon nanotubes);
[0040] FIG. 12 is a schematic structure diagram of fibrous carbons
(graphite nanofibers);
[0041] FIG. 13 is a schematic structure diagram of the vertical FE
configuration according to the prior art; and
[0042] FIG. 14 is a schematic structure diagram of the lateral FE
configuration according to the prior art.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0043] The embodiments of the present invention will be
illustratively described hereinafter in detail with reference to
the drawings. It is, however, noted that, as to the dimensions,
materials, shapes, relative locations, etc. of the components
described in the embodiments, the scope of the invention is by no
means intended to be limited only to those unless otherwise stated
specifically.
[0044] The inventors conducted research on materials that permitted
fine (several nm order) nuclei (catalyst particles) to be formed
thereon from a catalyst and that formed stable electrical coupling
with fibrous carbons grown from the nuclei by thermal
decomposition.
[0045] From the research, the inventor found that preferable
materials permitting the growth of the fibrous carbons through the
catalyst and achieving electrical coupling therewith were materials
selected from Ti, Zr, and Nb and oxidized in part (at the interface
in contact with the fibrous carbons or the catalyst), or oxide
semiconductors of materials selected from Ti, Zr, and Nb.
[0046] From detailed investigation, the inventor further found that
the fibrous carbons were able to be produced at the position of the
catalyst particles with good repeatability, by use of a member in
which the catalyst particles (particularly preferably, Pd
particles) were placed on an oxide of a material selected from Ti,
Zr, and Nb.
[0047] In tandem with it, the inventor also found that materials on
which no fibrous carbon grew or on which a growth rate of fibrous
carbon was low, were Ta, Cr, Au, Ag, Pt, and materials of the same
kinds as the catalyst materials.
[0048] The growth of the fibrous carbons over these materials is
also valid in the layered structure. For example, Cr was deposited
over the entire surface of a substrate, a fine region of titanium
oxide was further formed on the Cr layer, and the entire surface of
the substrate was coated with palladium oxide. With use of this
substrate, the fibrous carbons were selectively grown only above
titanium oxide.
[0049] Then the electron-emitting devices, electron sources, and
image-forming apparatus using the fibrous carbons according to the
present invention, using the technology of forming the fibrous
carbons at a desired position with good repeatability as described
above, will be described below in comparison with the prior art
examples.
[0050] First, the inventors also conducted research about a method
of forming a high-definition electron beam. The high-definition
beam forming method will be described below.
[0051] In general, the operating voltage Vf of the FE device is
determined by the electric field at the tip portion of the emitter,
which is derived by the Poisson's equation, and the current density
of electron emission current obtained according to a relation
called the Fowler-Nordheim equation, using the electric field and a
work function at the emitter portion as parameters.
[0052] As for the electric field necessary for the electron
emission, the smaller the distance d between the emitter tip and
the gate electrode, or the smaller the radius r of the emitter tip,
the stronger the electric field is established.
[0053] On the other hand, the maximum X-directional size Xd of the
electron beam on the anode (for example, the maximum range from the
center of the circular beam profile 137 in FIG. 13) is expressed in
the form proportional to {square root over ((Vf/Va))} in simple
computation.
[0054] As apparent from this relation, increase in Vf results in
increase in the beam size.
[0055] From this consideration, the distance d and radius r need to
be set as small as possible in order to decrease Vf.
[0056] The beam profiles of the conventional configurations will be
described below using FIGS. 13 and 14. In the figures, numerals
common thereto denote as follows: 131, 141 the substrate; 132, 142
the emitter electrode; 133, 143 the insulating layer; 135, 145 the
emitter; 136, 146 the anode; 137, 147 the shape of the electron
beam irradiating the anode.
[0057] In the case of the foregoing Spindt type, as shown in FIG.
13, when Vf is applied between the emitter 135 and the gate 134,
the electric field becomes stronger at the tip of the projection of
the emitter 135, and electrons are taken out from near the tip of
the conical emitter into the vacuum.
[0058] Since the electric field at the tip of the emitter 135 is
formed in such a certain finite area as to follow the shape of the
tip of the emitter 135, electrons extracted are drawn in the
vertical direction relative to the potential from the finite area
of the tip of the emitter 135.
[0059] At this time, electrons are emitted at various angles and
electrons with large angle components are drawn in directions
toward the gate. When the gate 134 is circular, the electron
distribution on the anode 136 becomes the substantially circular
beam profile 137 as shown in the figure.
[0060] Namely, the resultant beam profile is in close relation with
the shape of the extraction gate and the distance to the
emitter.
[0061] In the case of the lateral FE configuration (FIG. 14)
wherein electrons are extracted in the aligned extraction
direction, the very strong electric field (lateral electric field)
is created substantially in parallel to the surface of the
substrate 141 between the emitter 145 and the gate 144, so that
among electrons emitted from the emitter 145, some electrons 149
are drawn into the vacuum and the remaining electrons are taken
into the gate electrode 144.
[0062] In the case of the configuration shown in this FIG. 14, the
direction of the electric field vector for the emission of
electrons (the electric field directed from the emitter 145 toward
the gate 144) is different from the direction of the electric field
vector directed toward the anode (anode electrode) 146. For this
reason, the emitted electrons form a large electron distribution
(beam spot) on the anode 146.
[0063] Here let us further consider the electric field for
extracting electrons from the emitter electrode 145 (which will be
called a "lateral electric field" herein for convenience' sake and
the enhancement effect of the electric field by the emitter shape
will be ignored herein) and the electric field directed toward the
anode (which will be called a "vertical electric field"
herein).
[0064] In the configurations of FIG. 13 and FIG. 14, the foregoing
"lateral electric field" can also be referred to as an "electric
field in the substantially parallel direction to the surface of the
substrate 131 (141)". Particularly, in the configuration of FIG.
14, it can also be referred to as an "electric field in the facing
direction of the gate 144 and the emitter 145".
[0065] In the configurations of FIG. 13 and FIG. 14, the foregoing
"vertical electric field" can also be referred to as an "electric
field in the substantially normal direction to the surface of the
substrate 131 (141)" or as an "electric field in the facing
direction of the substrate 131 (141) and the anode 136 (146)".
[0066] As described previously, electrons emitted from the emitter
145 are first drawn by the lateral electric field to fly toward the
gate 144 and thereafter they are moved up by the vertical electric
field to reach the anode 146.
[0067] Important points at this time are a ratio of strengths of
the lateral electric field and the vertical electric field and the
relative position of electron emission point.
[0068] When the lateral electric field is stronger in order of
magnitude than the vertical electric field, most of the electrons
emitted from the emitter fly in trajectories gradually bent by
radial potentials formed by the lateral electric field and directed
toward the gate. Part of the electrons colliding with the gate are
again emitted because of scattering, and thereafter are repeatedly
scattered as spreading on the gate while drawing trajectories
similar to ellipses many times and as reducing the number of
emitted electrons, before they are captured by the vertical
electric field. When the scattered electrons then cross an
equipotential line made by the gate potential (which is also called
a stagnation point"), they are moved up by the vertical electric
field for the first time.
[0069] When the lateral electric field and the vertical electric
field are approximately equal in strength to each other, the
extracted electrons also fly in trajectories bent by the radial
potentials, but the binding by the electric field becomes weaker,
so that there appear trajectories of electrons captured by the
vertical electric field without colliding with the gate 144.
[0070] It was verified that with the lateral electric field and
vertical electric field approximately equal in strength to each
other, as the position of the electron emission point from the
emitter 145 was gradually lifted up from the plane to which the
gate 144 belonged, toward the plane to which the anode 146 belonged
(see FIG. 6), the emitted electrons could fly in trajectories
captured by the vertical electric field without colliding with the
gate 144 at all.
[0071] Research was conducted about the electric field ratios and
it was found from the research that, where d represented the
spacing between the gate electrode 144 and the tip of the emitter
electrode 145, V1 the potential difference (the potential
difference between the gate electrode and the emitter electrode)
during driving of the device, H the distance between the positive
electrode (anode) and the substrate (device), and V2 (Va) the
potential difference between the positive electrode (anode) and the
negative electrode (emitter electrode), the extracted electrons
drew the trajectories colliding with the gate when the lateral
electric field was 50 or more times stronger than the vertical
electric field.
[0072] The inventor also discovered that there existed a height s
causing no substantial scattering on the gate electrode 2 (which is
defined by a distance between a plane including part of the surface
of the gate electrode 2 and being substantially parallel to the
surface of the substrate 1 and a plane including the surface of the
electron-emitting member 4 and being substantially parallel to the
surface of the substrate 1 (see FIG. 6)). This height s is
dependent upon the ratio of the vertical electric field and the
lateral electric field (strength of the vertical electric
field/strength of the lateral electric field) and the height
becomes lower with decrease in the vertical-lateral electric field
ratio and becomes higher with increase in the lateral electric
field.
[0073] A practical fabrication range of the height s is not less
than 10 nm nor more than 10 .mu.m.
[0074] In the conventional configuration shown in FIG. 14, since
the gate 144 and the emitter (142, 145) were formed at the same
height on the same plane and since the lateral electric field was
stronger by one or more figures than the vertical electric field,
there was the strong tendency that the number of extracted
electrons into the vacuum decreased because of the collision with
the gate.
[0075] Further, in the conventional configuration, since the
thickness and width of the gate electrode and the relative
positions of the gate, emitter, and anode were determined for the
purpose of enhancing the intensity of the lateral electric field,
the electron distribution on the anode became expanded.
[0076] As described previously, in order to make small the
distribution of electrons reaching the anode 146, it is necessary
to consider 1) decreasing the driving voltage (Vf), 2) aligning the
extraction directions of electrons, 3) trajectories of electrons,
and, further, in the case involving the scattering on the gate, 4)
the scattering mechanisms of electrons (particularly, elastic
scattering).
[0077] The electron-emitting devices using the fibrous carbons
according to the present invention realize both the size reduction
of the electron distribution on the anode electrode and improvement
in the electron emission efficiency (decrease of emitted electrons
absorbed by the gate electrode).
[0078] Configurations of the electron-emitting devices according to
the present invention will be described below in further detail
with reference to the drawings. FIGS. 1A and 1B are schematic views
showing an example of the electron-emitting device according to the
present invention, wherein FIG. 1A is a plan view thereof and FIG.
1B a cross-sectional view along 1B-1B in FIG. 1A. FIG. 6 is a
schematic cross-sectional view showing a state of driving of the
electron-emitting apparatus according to the present invention in
which the anode electrode is placed above the electron-emitting
device of the present invention.
[0079] In FIGS. 1A and 1B and FIG. 6, numeral 1 designates an
electrically insulating substrate, 2 an extraction electrode (also
called "gate electrode" or "second electrode"), 3 a negative
electrode (also called "first electrode" or "cathode electrode"), 4
fibrous carbons being an emitter material (also called
"electron-emitting material" or "electron-emitting member"), and 5
a first layer for selective growth of the fibrous carbons, which is
an oxide of a material selected from Ti, Zr, and Nb, described
previously. The fibrous carbons constituting the electron-emitting
material 4 are electrically connected to the electrode 3. Numeral 6
denotes a second layer.
[0080] In the present invention, the important structure is that
the negative electrode 3 and the extraction electrode 2 are placed
with a gap in between on the surface of the substrate and a
plurality of fibrous carbons 4 are placed on a surface of the
negative electrode 3 facing the extraction electrode 2. In other
words, the plurality of fibrous carbons extending in the facing
direction of the negative electrode 3 and the extraction electrode
2 are located on the negative electrode 3 in the gap between the
negative electrode 3 and the extraction electrode 2. This
configuration permits electrons to be emitted by a lower electric
field.
[0081] Further, in the present invention, the important structure
is that, in order to prevent unnecessary electrons from being
emitted, the fibrous carbons are not placed on the surfaces except
for the surface facing the extraction electrode 2. This structure
can restrain the expansion of the electron beam irradiating the
anode electrode.
[0082] In the example of FIGS. 1A, 1B, the first layer 5 and the
second layer 6 are provided for controlling the region where the
fibrous carbons are formed. Namely, the first layer 5 is made of a
material permitting the fibrous carbons 4 to grow thereon, while
the second layer 6 is made of a material not permitting the fibrous
carbons 4 to grow thereon, as compared with the first layer 5. The
first layer and second layer described above are preferably
electrically conductive. Particularly, the second layer is
especially preferably electrically conductive, because it is
exposed in vacuum. In the configuration as shown in FIGS. 1A, 1B,
unless the first layer 5 is electrically conductive, electrical
connection cannot be established between the negative electrode 3
and the fibrous carbons; therefore, the first layer 5 is preferably
selected from electroconductive materials.
[0083] The example with provision of the second layer 6 was
described herein, but this layer does not always have to be
provided. For example, it is also possible to construct an
electron-emitting device of the present invention by making the
negative electrode 3 of a material selected from Ti, Zr, and Nb and
oxidizing only a surface thereof facing the extraction electrode 2
among its surfaces (i.e., by placing the first layer).
[0084] In the form shown in FIGS. 1A, 1B, all the first layer 5
does not have to be made of an oxide, but it is also possible to
make at least only the surface facing to the extraction electrode 2
among the surfaces of the first layer 5, of an oxide. This
structure makes the second layer not always necessary. Even if the
first layer is thick, such structure can enhance the electrical
connection between the negative electrode 3 and the fibrous
carbons.
[0085] The electron-emitting device according to the present
invention can also be constructed in such a way that the negative
electrode 3 is made of a material. selected from Ti, Zr, and Nb,
the surface thereof (including the surface facing the extraction
electrode. 2) is oxidized, and the surfaces other than the surface
facing the extraction electrode 2 (i.e., the surface on which the
fibrous carbons are laid) are coated with a layer (the second
layer) made of a material permitting no growth of fibrous carbons
as compared with the oxide of the material selected from Ti, Zr,
and Nb.
[0086] In the electron-emitting apparatus of the present invention,
as shown in FIGS. 1A, 1B and FIG. 6, the plane including the
surface of the electron-emitting member 4 and being substantially
parallel to the surface of the substrate 1 is preferably more
distant from the surface of the substrate than the plane including
part of the surface of the gate electrode 2 and being substantially
parallel to the surface of the substrate 1. In other words, in the
electron-emitting apparatus of the present invention, the plane
including part of the surface of the electron-emitting member 4 and
being substantially parallel to the surface of the substrate 1 is
located between the anode electrode 61 and the plane including part
of the surface of the extraction electrode 2 and being
substantially parallel to the surface of the substrate. This
structure can realize the reduction of electrons absorbed into the
gate electrode and the reduction of the spot size of the electron
beam impinging on the anode electrode.
[0087] Further, in the electron-emitting device of the present
invention, the electron-emitting member 4 is located at the height
s (defined as the distance between the plane including part of the
surface of the gate electrode 2 and being substantially parallel to
the surface of the substrate 1 and the plane including the surface
of the electron-emitting member 4 and being substantially parallel
to the surface of the substrate 1) at which no substantial
scattering of electrons occurs on the gate electrode 2.
[0088] The above height s is dependent upon the ratio of the
vertical electric field and the lateral electric field (intensity
of the vertical electric field/intensity of the lateral electric
field), and the height needs to be decreased with decrease in the
ratio of the vertical electric field and the lateral electric field
and to be increased with increase in the intensity of the lateral
electric field; the practical range of the height s is not less
than 10 nm nor more than 10 .mu.m.
[0089] This structure can be readily realized, for example, by
making the thickness of the negative electrode 3 larger than the
thickness of the extraction electrode 2. Alternatively, it can also
be realized by forming the negative electrode 3 and the extraction
electrode 2 in equivalent thickness and placing the first layer 5
on the negative electrode 3.
[0090] In the electron-emitting apparatus of the present invention,
where, in the structure shown in FIG. 6, d represents the distance
of the gap between the negative electrode 3 and the gate electrode
2, Vf the potential difference during driving of the
electron-emitting device (the voltage between the negative
electrode 3 and the gate electrode 2), H the distance between the
anode electrode 61 and the surface of the substrate 1 on which the
device is placed, and Va the potential difference between the anode
electrode 61 and the negative electrode 3, the electric field
(lateral electric field) during the driving: E1=Vf/d is set to be
not less than 1 times nor more than 50 times stronger than the
electric field (vertical electric field) between the anode 61 and
the cathode 3: E2=Va/H.
[0091] This setting can almost nullify the ratio of electrons
colliding with the gate electrode 2 to electrons emitted from the
negative electrode 3. As a result, there are provided the
electron-emitting device and the electron-emitting apparatus with
the extremely small spread of the emitted electron beam and with
high electron emission efficiency.
[0092] The "lateral electric field" stated in the present invention
can be referred to as the "electric field in the direction
substantially parallel to the surface of the substrate 1". In
another sense, it can also be referred to as the "electric field in
the facing direction of the gate 2 and the cathode electrode 3".
The "vertical electric field"stated in the present invention can be
referred to as the "electric field in the direction substantially
normal to the surface of the substrate 1" or the "electric field in
the facing direction of the substrate 1 and the anode electrode
61".
[0093] The electrically insulating substrate 1 can be either of
laminations in which SiO.sub.2 is laid by sputtering or the like on
a well-cleaned surface of either of silica glass, glasses partly
replaced with K or the like while reducing the impurity content of
Na and others, soda lime glass, silicon substrates, etc. insulating
substrates of ceramics such as alumina or the like, and so on.
[0094] The extraction electrode 2 and the negative electrode 3 are
electrically conductive and are made by either of the ordinary
vacuum film-forming technologies such as vacuum evaporation,
sputtering, and the like, or the photolithography technology.
[0095] The materials of the extraction electrode 2 and the negative
electrode 3 are adequately selected, for example, from carbon,
metals, nitrides of metals, carbides of metals, borides of metals,
semiconductors, and metal semiconductors coumpounds.
[0096] The thicknesses of the extraction electrode 2 and the
negative electrode 3 are set in the range of several ten nm to
several ten .mu.m. Preferably, they are desirably made of either of
heat resistant materials such as carbon, metals, nitrides of
metals, and carbides of metals.
[0097] When there is a worry that a potential drop or the like can
occur because of the small thickness of the electrodes or when such
devices are used in a matrix array, a low-resistant metal material
for wiring is sometimes used in portions not associated with the
emission of electrons as occasion may demand.
[0098] In comparison of electric field intensities between the
electron emission field of the cathode material used (the lateral
electric field) and the vertical electric field necessary for the
formation of image, the gap between the extraction electrode 2 and
the negative electrode 3 (the width of the gap) and the driving
voltage are preferably designed so that the electron emission field
becomes approximately 1 times to 50 times stronger than the
vertical electric field.
[0099] In the present invention, the emitter (electron-emitting
member) 4 is comprised of fibrous carbons.
[0100] The fibrous carbons are preferably those obtained by forming
nuclei with use of a catalyst and growing the fibrous carbons from
the nuclei by thermal decomposition.
[0101] According to the present invention, the "fibrous carbons"
can also be said as "columnar substances comprising carbon as a
main component" or "linear substances comprising carbon as a main
component". The "fibrous carbons" can also be mentioned as "fibers
comprising carbon as a main component". More specifically, the
"fibrous carbons" in the present invention embrace carbon
nanotubes, graphite nanofibers, and amorphous carbon fibers. Among
these, the graphite nanofibers are most preferable for the
electron-emitting member 4.
[0102] The gap between the extraction electrode 2 and the negative
electrode 3 and the driving voltage are preferably designed so
that, in comparison of electric field intensities between the
electron emission field of the electron-emitting member (the
lateral electric field) and the vertical electric field necessary
for the formation of image, the electron emission field becomes
approximately 1 times to 50 times stronger than the vertical
electric field, as described previously.
[0103] When a light emitting member such as a phosphor or the like
is placed on the positive electrode (anode electrode), the
necessary vertical field is preferably in the range of not less
than 10.sup.1 V/.mu.m nor more than 10 V/.mu.m. For example, where
the gap between the positive electrode (anode electrode) and the
negative electrode is 2 mm and 10 kV is placed in the gap, the
vertical electric field at this time is 5 V/.mu.m. In this case,
the emitter material (electron-emitting member) 4 to be used is one
having the electron emission field larger than 5 V/.mu.m, and the
spacing and driving voltage can be determined so as to realize the
selected electron emission field.
[0104] The aforementioned fibrous carbons are preferably applicable
as materials having the threshold electric field of several V/.mu.m
as described above.
[0105] FIG. 11 and FIG. 12 show examples of forms of the fibrous
carbons suitably applicable to the present invention. In each
figure the left view schematically shows a form observed at the
optical microscope level (approximately 1000.times.), the center
view a form observed at the scanning electron microscope (SEM)
level (approximately 30,000.times.), and the right view a form of
carbon observed at the transmission electron microscope (TEM) level
(approximately 1 million.times.).
[0106] As shown in FIG. 11, the form of cylindrical shape of
graphen is called a carbon nanotube (a multiple structure of
cylinders is called a multiwall nanotube), and the threshold
thereof becomes the lowest, particularly, in the structure in which
the tube is open at the tip.
[0107] As another example, fibrous carbons may be produced at
relatively low temperatures are shown in FIG. 12. A fibrous carbon
of this form is comprised of a lamination of graphens (which is
thus sometimes called "graphite nanofiber" and the rate of
amorphous structure of which increases depending upon the
temperature). More specifically, the graphite nanofiber indicates a
fibrous substance in which graphens are layered (laminated) in the
longitudinal direction thereof (in the axis direction of the
fiber). In other words, as shown in FIG. 12, it is a fibrous
substance in which a plurality of graphens are arranged and layered
(laminated) so as not to be parallel to the axis of fiber.
[0108] On the other hand, a carbon nanotube is a fibrous substance
in which graphens are arranged (in cylindrical shape) around the
longitudinal direction (the axis direction of fiber). In other
words, it is a fibrous substance in which graphens are arranged
substantially in parallel to the axis of the fiber.
[0109] A single surface of graphite will be called a "graphen" or
"graphen sheet". More specifically, graphite is a lamination in
which carbon planes, each of which is a spread of regular hexagons
consisting of covalent bonds of carbon atoms in sp.sup.2 hybrid,
are layered at intervals of distance of 3.354 .ANG.. Each of the
carbon planes is called a "graphen" or "graphen sheet".
[0110] All the fibrous carbons have the threshold for the emission
of electron in the range of approximately 1 to 10 V/.mu.m and are
very suitable for the emitter (electron-emitting member) 4 of the
present invention.
[0111] Particularly, the electron-emitting devices using the
graphite nanofibers can be those capable of emitting electrons at a
low electric field and yielding a large emission current, capable
of being produced readily, and exhibiting stable electron emission
characteristics, without having to be limited to the device
structure of the present invention shown in FIGS. 1A, 1B and
others. For example, an electron-emitting device can be constructed
by making the emitter of graphite nanofibers and preparing the
electrode for control of electron emission from this emitter, and a
light emitting apparatus such as a lamp or the like can also be
formed by using a light emitting member which emits light under
irradiation of electrons emitted from the graphite nanofibers.
Further, it is also possible to construct an image display
apparatus such as a display or the like by arraying a plurality of
such electron-emitting devices using the graphite nanofibers and
preparing an anode electrode having a light emitting member such as
a phosphor or the like. In the electron-emitting apparatus, the
light emitting apparatus, and the image display apparatus using the
graphite nanofibers, stable electron emission can be implemented
without need for maintaining the interior in such an ultrahigh
vacuum as required in the conventional electron-emitting devices,
and a high electron emission amount can be ensured at a low
electric field; therefore, the apparatus can be fabricated
extremely simply with high reliability.
[0112] The aforementioned fibrous carbons can be made by
decomposing a hydrocarbon gas under use of a catalyst (a material
for promoting deposition of carbon). The carbon nanotubes and
graphite nanofibers differ depending upon the type of the catalyst
and the temperature of decomposition.
[0113] The catalyst materials, such as Fe, Co, Pd, Ni and alloy of
material selected from those materials can be used as the nuclei
for formation of the fibrous carbons.
[0114] Particularly, in the case of Pd, the graphite nanofibers can
be produced at low temperatures (temperatures of not less than
400.degree. C.). On the other hand, when the catalyst is Fe or Co,
the temperature for production of carbon nanotubes needs to be not
less than 800.degree. C. Since the production of the graphite
nanofiber material using Pd can be implemented at low temperatures,
it is also preferable in terms of influence on the other members
and the production cost.
[0115] Further, in the case of the Pd catalyst, using the property
that the oxide thereof is readily reduced by hydrogen at low
temperatures (room temperature), it is feasible to use palladium
oxide as a nucleation material.
[0116] By employing the hydrogen reduction treatment of palladium
oxide, it became feasible to form the initial aggregated nuclei at
relatively low temperatures (200.degree. C. or less) without use of
thermal aggregation of metal thin film or production and
evaporation of ultrafine particles accompanied by a danger of
explosion which are conventionally used as ordinary nucleation
techniques.
[0117] The foregoing hydrocarbon gas can be, for example, either of
hydrocarbon gases such as ethylene, methane, propane, propylene,
and so on, or vapors of organic solvents such as ethanol, acetone,
and so on.
[0118] The raw materials for the fibrous carbons can also be such
raw materials as CO, CO.sub.2, and the like, in addition to the
foregoing hydrocarbon gases.
[0119] The material of the layer 5 allowing the growth of fibrous
carbons 4 is a mixture of Ti and an oxide thereof resulting from
partial oxidation of Ti, or an oxide semiconductor of Ti; or a
mixture of Zr and an oxide thereof resulting from partial oxidation
of Zr, or an oxide semiconductor of Zr; or a mixture of Nb and an
oxide thereof resulting from partial oxidation of Nb, or an oxide
semiconductor of Nb, as described previously. The foregoing oxide
of Ti, oxide of Zr, or oxide of Nb is placed at least on the
surface for the fibrous carbons 4 to be placed, among the surfaces
of the layer 5.
[0120] These oxides of Ti, Zr, and Nb are stoichiometrically
insulators, but weakly oxidized substances thereof or suboxides
thereof possess a number of defects inside and thus form
semiconductors of the oxygen deficient type or the like.
[0121] The layer 5 and the catalyst particles placed on the layer 5
can be produced, for example, by a method of baking Pd on the layer
of Ti, Zr, or Nb at the temperature of about 300.degree. C. for
about several ten minutes to form palladium oxide and
simultaneously oxidizing the layer of Ti, Zr, or Nb as well. The
baking temperature and time of this level, however, do not oxidize
the entire layer, though depending upon the thickness of the layer
of Ti, Zr, or Nb, but oxidize only the surface. Since such oxide
has the semiconductorlike nature as described above, the layer 5
thus formed results in possessing electrical conductivity.
[0122] The second layer 6 is comprised of a material on which no
substantial growth of fibrous carbon occurs, as compared with the
first layer 5, even if the catalyst particles are placed thereon.
Such materials can be aforementioned Ta, Cr, Au, Ag, Pt, or
materials of the same kinds as the catalyst materials. Then the
region except for the side face of the first layer 5 on the
extraction electrode 2 side is covered by the second layer 6.
[0123] As a result, only the side wall of the layer 5 on the
extraction electrode 2 side is exposed, and thus the fibrous
carbons 4 grow only on the side wall on the extraction electrode 2
side in the subsequent step of growth of fibrous carbons.
[0124] If the device should not have the conductive layer 6 on
which the fibrous carbons do not grow through the fine catalyst
particles, the fibrous carbons would grow over the entire surface
of the conductive layer 5 on which the fibrous carbons can grow
through the fine catalyst particles. In this case, the fibrous
carbons apart from the gate electrode 2 would be involved in
emission of electrons, though it is a little, and such electrons
could disturb the beam profile and uniformity.
[0125] In contrast with it, the electron-emitting device according
to the present embodiment can be constructed in the configuration
wherein there exists no fibrous carbons on the side walls except
for the side wall on the extraction electrode 2 side, and it is
thus feasible to prevent the disturbance of the beam profile and
uniformity.
[0126] The position of the electron emission point in the emitter
region and the operation thereof will be described below referring
to FIG. 6 and FIG. 7.
[0127] The instant device having the gap length d of several .mu.m
was placed in a vacuum chamber 60, as shown in FIG. 6, and then the
interior thereof was evacuated well down to about 10.sup.-4 Pa by
an vacuum pump 65. While the positive electrode (hereinafter
referred to as an anode) 61 was set at the position of the height H
of several millimeters from the substrate 1, a high voltage Va of
several kV was applied from a voltage source.
[0128] A fluorescent member 62 with an electroconductive film
coating thereon was placed on the anode 61.
[0129] A pulse voltage of about several ten V was applied as the
driving voltage Vf between the electrode 2 and the electrode 3 to
measure the device current If and electron emission current Ie.
Naturally, the driving voltage Vf was applied so that the potential
at the gate electrode 2 was higher than that at the negative
electrode 3.
[0130] At this time, equipotential lines 63 are formed as shown,
and the electric field is most concentrated at the part indicated
by point 64 closest to the anode 61 among the fibrous carbons 4 of
the electron-emitting material and inside the gap.
[0131] It is speculated that electrons are emitted from the site
where the electric field is most concentrated in the
electron-emitting material located in the vicinity of this field
concentrating point 64.
[0132] The Ie characteristic of the device was that shown in FIG.
7. Namely, Ie demonstrated a sudden rise from about half of the
applied voltage, and If, not shown, was similar to the
characteristic of Ie but considerably smaller than Ie.
[0133] Based on this principle, an electron source and an
image-forming apparatus comprised of a plurality of
electron-emitting devices according to the embodiment of the
present invention will be described hereinafter with reference to
FIG. 8 to FIG. 10. FIG. 8 is a schematic plan view of electron
source according to an embodiment of the present invention, FIG. 9
a perspective view of an image-forming apparatus, partly broken,
according to an embodiment of the present invention, and FIG. 10 a
block diagram of an image-forming apparatus according to an
embodiment of the present invention.
[0134] In FIG. 8, numeral 81 denotes an electron source substrate,
82 X-directional wires, and 83 Y-directional wires. Numeral 84
denotes electron-emitting devices according to the embodiment of
the present invention, and 85 interconnections.
[0135] In this configuration the placement of plural
electron-emitting devices 84 is accompanied by increase in the
capacitance of the devices, and there arises a problem that in the
matrix wiring shown in FIG. 8, waves become dull because of the
capacitance component, so as to fail to attain expected gradation
even with application of short pulses according to pulse width
modulation.
[0136] In order to avoid it, it is preferable to employ a structure
for reducing the increase of the capacitance component except for
that in the electron emission section, for example, by placing an
interlayer electric film (rear plate 91) right next to the electron
emission section, as shown in FIG. 9.
[0137] In FIG. 8, the m X-directional wires 82 consist of DX.sub.1,
DX.sub.2, . . . , DX.sub.m and are made of an aluminum based wiring
material in the thickness of about 1 .mu.m and in the width of 300
.mu.m by evaporation. However, the material, thickness, and width
of the wires are properly designed according to respective
cases.
[0138] On the other hand, the Y-directional wires 83 consist of n
wires of DY.sub.1, DY.sub.2, . . . , DY.sub.n 0.5 .mu.m thick and
100 .mu.m wide and are made in similar fashion to the X-directional
wires 82.
[0139] An interlayer dielectric film not shown is disposed between
these m X-directional wires 82 and n Y-directional wires 83, so as
to electrically isolate them from each other (where m and n are
positive integers).
[0140] The unrepresented interlayer dielectric film is made of
SiO.sub.2 in the thickness of about 0.8 .mu.m by sputtering or the
like.
[0141] The interlayer dielectric film is formed in the desired
shape over the entire surface or in part of the substrate 81 after
formation of the X-directional wires 82, and the thickness of the
interlayer dielectric film is determined so that the device
capacitance per device is not more than 1 pF and the device
withstand voltage 30 V in the present embodiment, particularly, in
order to resist the potential difference at intersections between
the X-directional wires 82 and the Y-directional wires 83. The
X-directional wires 82 and Y-directional wires 83 are drawn out as
respective external terminals.
[0142] Pairs of electrodes (not shown) making up the
electron-emitting devices 84 according to the embodiment of the
present invention are electrically connected by the m X-directional
wires 82, n Y-directional wires 83, and interconnections 85 of an
electroconductive metal or the like.
[0143] Connected to the X-directional wires 82 is an unrepresented
scanning signal applying means for applying a scanning signal for
selection of a row of electron-emitting devices 84 according to the
embodiment of the present invention, arrayed in the
X-direction.
[0144] Connected to the Y-directional wires 83 on the other hand is
an unrepresented modulation signal generating means for modulating
each column of electron-emitting devices 84 according to the
embodiment of the present invention, arrayed in the Y-direction,
according to an input signal.
[0145] The driving voltage applied to each electron-emitting device
is supplied as a difference signal between a scanning signal and a
modulation signal applied to the device. In the embodiment of the
present invention, electrical connection is established so that the
Y-directional wires are at a higher potential while the
X-directional wires at a lower potential. This connection yields
the beam converging effect, which is a feature of the embodiment of
the present invention.
[0146] In the above configuration, the individual devices can be
selected to be driven independently by use of the simple matrix
wiring.
[0147] An image-forming apparatus constructed by use of the
electron source of this simple matrix configuration will be
described referring to FIG. 9. FIG. 9 shows a display panel of the
image-forming apparatus wherein soda lime glass is used as a
material of a glass substrate.
[0148] In FIG. 9, numeral 81 designates an electron source
substrate loaded with a plurality of electron-emitting devices, 91
a rear plate to which the electron source substrate 81 is fixed,
and 96 a face plate wherein a florescent film 94, a metal back 95,
etc. are formed on an internal surface of glass substrate 93.
Numeral 92 denotes a support frame, and the rear plate 91 and face
plate 96 are coupled to this support frame 92 with frit glass or
the like. Numeral 97 represents an envelope which is sealed by
baking it in the temperature range of 450.degree. C. in vacuum for
ten minutes.
[0149] Numeral 84 indicates the electron emission regions and
numerals 82 and 83 denote the X-directional wires and Y-directional
wires, respectively, which are connected to the pairs of device
electrodes of the electron-emitting devices according to the
embodiment of the present invention.
[0150] The envelope 97 is composed of the face plate 96, the
support frame 92, and the rear plate 91, as described above. When
an unrepresented support called a spacer is interposed between the
face plate 96 and the rear plate 91, the envelope 97 can be
constructed with sufficient strength against the atmospheric
pressure.
[0151] The metal back 95 can be made in such a way that after
production of the fluorescent film, the internal surface of the
fluorescent film is subjected to a smoothing process (normally
called "filming") and thereafter Al is deposited thereon by vacuum
evaporation or the like.
[0152] The face plate 96 is further provided with a transparent
electrode (not shown) on the outer surface side of the fluorescent
film 94, in order to further enhance the electrical conductivity of
the fluorescent film 94.
[0153] During the aforementioned sealing operation, in the color
display case, correspondence has to be made between respective
color phosphors and electron-emitting devices and thus sufficient
alignment is essential.
[0154] Next, a scanning circuit 102 shown in FIG. 10 will be
described below. This circuit is provided with M switching devices
inside (schematically indicated by S1 to Sm in the figure). Each
switching device selects either an output voltage of a dc voltage
source Vx or 0 V (the ground level) to be electrically connected to
a terminal Dx1 to Dxm of display panel 101.
[0155] Each switching device of S1 to Sm operates based on a
control signal Tscan from a control circuit 103 and can be
constructed, for example, of a combination of switching devices
such as FETs.
[0156] The dc voltage source Vx is set to output such a constant
voltage that the driving voltage applied to non-scanned devices is
not more than the electron emission threshold voltage, based on the
characteristics of the electron-emitting devices (electron emission
threshold voltage) according to the embodiment of the invention, in
the case of the present example.
[0157] The control circuit 103 has the function of matching
operations of respective portions so as to implement appropriate
display based on image signals supplied from the outside. The
control circuit 103 generates control signals of Tscan, Tsft, and
Tmry to the respective portions, based on a synchronizing signal
Tsync supplied from a synchronizing signal separating circuit
106.
[0158] The synchronizing circuit 106 is a circuit for separating
the synchronizing signal component and luminance signal component
from a TV signal of the NTSC system supplied from the outside, and
can be composed of an ordinary frequency separating (filter)
circuit or the like.
[0159] Although the synchronizing signal separated by the
synchronizing signal separating circuit 106 consists of a vertical
synchronizing signal and a horizontal synchronizing signal, it is
illustrated as a Tsync signal herein for convenience' sake of
description. The luminance signal component of an image separated
from the aforementioned TV signal is indicated as a DATA signal for
convenience' sake. This DATA signal is entered into a shift
register 104.
[0160] The shift register 104 performs serial-parallel conversion
for each line of an image with reception of DATA signals serially
supplied in time sequence and operates based on the control signal
Tsft sent from the control circuit 103. Namely, the control signal
Tsft can also be called as a shift clock for the shift register
104.
[0161] Data of one line of an image after the serial-parallel
conversion (corresponding to driving data for N devices out of the
electron-emitting devices) is outputted as N parallel signals of
Id1 to Idn from the shift register 104.
[0162] A line memory 105 is a storage device for storing the data
of one line of an image for a required time and is configured to
store the contents of Id1 to Idn properly according to the control
signal Tmry sent from the control circuit 103. The stored contents
are outputted as I'd1 to I'dn to enter a modulation signal
generator 107.
[0163] The modulation signal generator 107 is a signal source for
appropriately modulating each of the electron-emitting devices of
the present embodiment according to each of the image data I'd1 to
I'dn, and output signals therefrom are applied through terminals
Doy1 to Doyn to the electron-emitting devices of the present
embodiment in the display panel 101.
[0164] As described previously, the electron-emitting devices
according to the embodiment of the present invention have the
following basic characteristics concerning the emission current
Ie.
[0165] Namely, there is the definite threshold voltage Vth for the
emission of electrons and electrons are emitted only when a voltage
not less than Vth is applied.
[0166] At voltages not less than the electron emission threshold,
the emission current also varies according to variation in the
applied voltage to the devices. For this reason, when the pulse
voltage is applied to the instant devices, for example, electrons
are not emitted with application of a voltage not more than the
electron emission threshold but an electron beam is outputted with
application of a voltage not less than the electron emission
threshold.
[0167] On that occasion, the intensity of the output electron beam
can be controlled by varying the peak height Vm of pulses. It is
also possible to control the total charge amount of the output
electron beam by changing the width Pw of pulses.
[0168] Accordingly, either of the voltage modulation method, the
pulse width modulation method, etc. can be employed as a method of
modulating the electron-emitting devices according to input
signals. For carrying out the voltage modulation method, the
modulation signal generator 107 can be a circuit of the voltage
modulation method configured to generate voltage pulses of a fixed
length and modulate peak heights of pulses adequately according to
input data.
[0169] For carrying out the pulse width modulation method, the
modulation signal generator 107 can be a circuit of the pulse width
modulation method configured to generate voltage pulses of a fixed
peak height and modulate widths of the voltage pulses adequately
according to input data.
[0170] The shift register 104 and the line memory 105 are of the
digital signal type.
[0171] The modulation signal generator 107 is, for example, a D/A
converting circuit and an amplifying circuit or the like is added
thereto as occasion demands. In the case of the pulse width
modulation method, the modulation signal generator 107 is, for
example, a circuit consisting of a combination of a fast oscillator
and a counting device (counter) for counting the number of waves
from the oscillator with a comparing device (comparator) for
comparing an output value of the counter with an output value of
the memory.
[0172] The configuration of the image-forming apparatus stated
herein is just an example of the image-forming apparatus to which
the present invention is applicable, and a variety of modifications
can be made based on the technical concept of the present
invention. The input signals were of the NTSC system, but the input
signals are not limited to this system; for example, it is also
possible to employ the PAL system, SECAM system, etc., and systems
of TV signals consisting of a larger number of scanning lines than
them (for example, high-definition TV systems including the MUSE
system).
EXAMPLES
[0173] More specific examples based on the above embodiments will
be described below in detail.
Example 1
[0174] In the present example, the basic configuration is comprised
of the configuration shown in FIGS. 1A and 1B as described in the
above-stated embodiment.
[0175] The steps for fabrication of the electron-emitting device
according to the present example will be described below in detail
with reference to FIGS. 5A to 5E.
(Step 1)
[0176] After a silica substrate used as the substrate 1 was cleaned
well, a Ti layer 5 nm thick and a Pt layer 500 nm thick, not shown,
were first consecutively evaporated over the entire surface of the
substrate by sputtering, in order to form the extraction electrode
2 and the negative electrode 3.
[0177] Then a resist pattern was formed with an unrepresented
positive photoresist (AZ1500 available from Clariant) by the
photolithography process.
[0178] Using the patterned photoresist as a mask, the Pt layer and
Ti layer were then subjected to dry etching with Ar gas to pattern
the extraction electrode 2 and the negative electrode 3 with the
electrode gap (the width of gap) of 5 .mu.m (a state shown in FIG.
5A).
[0179] The patterning of a thin film or a resist by the
photolithography process, film formation, lift-off, etching, etc.
will be referred to hereinafter simply as patterning.
(Step 2)
[0180] Then an unrepresented Cr layer was deposited in the
thickness of about 100 nm over the entire surface of the substrate
by electron beam evaporation and the positive photoresist (AZ1500
available from Clariant) was patterned thereon.
[0181] Using the patterned photoresist as a mask, a region (100
.mu.m.times.80 .mu.m) to cover the conductive layer for growth of
fibrous carbons through the catalyst particles was then formed on
the negative electrode 3 and the Cr layer in the opening portion
was removed with a cerium nitrate based etchant.
[0182] Then a Ti layer for growth of fibrous carbons through the
catalyst particles was evaporated in the thickness of 50 nm by
sputtering.
[0183] Then the unnecessary Ti layer and resist were removed
simultaneously (lift-off method), thereby forming the Ti conductive
layer 5 (a state shown in FIG. 5B).
(Step 3)
[0184] By the patterning similar to step 2, the Ti conductive layer
5 was covered by the Ta conductive layer 6 (140 .mu.m.times.100
.mu.m) not permitting the growth of fibrous carbons through the
catalyst particles, so as to expose only the side wall of the Ti
conductive layer 5 on the extraction electrode side (a state shown
in FIG. 5C).
(Step 4)
[0185] In the subsequent step, an unrepresented Cr layer of about
100 nm was patterned so as to expose only side walls of the Pt/Ti
layers (equivalent of the negative electrode 3), the Ti conductive
layer 5, and the Ta conductive layer 6 on the extraction electrode
side.
[0186] Then a complex solution obtained by adding isopropyl alcohol
or the like to a Pd complex was applied onto the entire surface of
the substrate by spin coating.
[0187] After the application, a heat treatment was carried out at
300.degree. C. in the atmosphere to form a palladium oxide layer in
the thickness of about 10 nm over the entire surface. Thereafter,
Cr was removed with the cerium nitrate based etchant to lift off
the unnecessary palladium oxide thereby, thus forming the patterned
palladium oxide layer.
[0188] After evacuation of atmosphere, the substrate was heated to
200.degree. C. to carry out a heat treatment in a 2% hydrogen
stream diluted with nitrogen. At this stage the catalyst particles
52 were formed in particle diameters of about 3 to 10 nm on the
wall surfaces in the surface of device. The density of the
particles at this time was estimated as about 10.sup.11 to
10.sup.12 particles/cm.sup.2 (a state shown in FIG. 5D).
(Step 5)
[0189] In the subsequent step, a heat treatment was conducted at
500.degree. C. in a 0.1% ethylene stream diluted with nitrogen for
ten minutes. The resultant was observed with the scanning electron
microscope and it was verified therefrom that a number of fibrous
carbons 4 extending in fibrous shape as bent were formed in the
diameters of about 10 nm to 25 nm only on the wall surface of the
Ti conductive layer 5 permitting the growth of fibrous carbons
through the catalyst particles among the catalyst particles on the
wall surfaces.
[0190] The thickness of the fibrous carbons 4 at this time was
about 500 nm. No fibrous carbon 4 was recognized on the wall
surfaces of the Pt layer (negative electrode 3) and the Ta
conductive layer 6 not permitting the growth of fibrous carbons
through the catalyst particles (a state shown in FIG. 5E).
[0191] The electron-emitting device fabricated as described above
was set in the vacuum chamber 60 as shown in FIG. 6 and the
interior thereof was evacuated well down to the vacuum of
2.times.10.sup.-5 Pa by the evacuator 65.
[0192] Then the anode voltage of Va=10 kV was applied to the
positive electrode (anode) 61 H=2 mm apart from the device, as
shown in FIG. 6. At this time, while the pulse voltage consisting
of the driving voltage (the voltage placed between the electrodes
2, 3) Vf=20 V was applied to the device, the flowing device current
If and electron emission current Ie were measured.
[0193] The If and Ie characteristics of the device were those shown
in FIG. 7. Namely, Ie demonstrated a sudden increase from about
half of the applied voltage and the electron emission current Ie of
about 1 .mu.A was measured at Vf of 15 V. On the other hand, If was
similar to the characteristic of Ie but values thereof were a
figure or more smaller than those of Ie.
[0194] The resultant beam was approximately of a rectangular shape
slender in the Y-direction and short in the X-direction.
[0195] Beam widths were measured under such conditions that the
voltage (Vf) placed between the negative electrode 3 and the gate
electrode 2 was fixed at 15 V, the anode distance was fixed at H of
2 mm, the anode voltage was either of 5 kV and 10 kV, and the gap
(width of gap) was either of 1 .mu.m and 5 .mu.m, and the results
are presented in Table 1 below. TABLE-US-00001 TABLE 1 Va = 5 kV Va
= 10 kV Gap: 1 .mu.m X-direction 60 .mu.m X-direction 30 .mu.m
Y-direction 170 .mu.m Y-direction 150 .mu.m Gap: 5 .mu.m
X-direction 93 .mu.m X-direction 72 .mu.m Y-direction 170 .mu.m
Y-direction 150 .mu.m
[0196] It was feasible to change the electric field necessary for
the driving, by varying the growth conditions. Particularly, an
average particle size of Pd particles obtained by the reduction
treatment of palladium oxide is associated with the diameters of
fibers formed by the growth thereafter.
[0197] The mean particle size of Pd particles was able to be
controlled by the Pd concentration of the coated Pd complex and the
rotational speed of the spin coating.
[0198] The carbon fibers of this device were observed with the
transmission electron microscope and they were of the layered
structure of graphens as shown on the right side of FIG. 12. The
layer intervals of the graphens (in the direction of C-axis) were
unclear at the temperature as low as about 500.degree. C, and were
0.4 nm. As the temperature increased, the grating intervals became
clearer, and at 700.degree. C. the intervals were 0.34 nm, which
was close to 0.335 nm of graphite.
[0199] By employing the configuration of the electron-emitting
device according to the present example, as described above, the
electron-emitting device was realized with the properties of the
reduced capacitance and driving voltage, the high efficiency, and
the small beam size.
Example 2
[0200] The electron-emitting device according to Example 2 will be
described below with reference to FIGS. 2A and 2B. FIGS. 2A and 2B
are schematic views of the electron-emitting device according to
Example 2 of the present invention, wherein FIG. 2A is a plan view
thereof and FIG. 2B a cross-sectional view along 2B-2B in FIG.
2A.
[0201] The electron-emitting device in the present example was
fabricated in the same manner as in Example 1 in the structure and
others except that the thickness of the extraction electrode 2 in
Example 1 was changed to 200 nm, and If and Ie were measured
therewith.
[0202] In the structure of the instant device, the thickness of the
negative electrode 3 was larger than the thickness of the
extraction electrode 2 whereby the electron emission position was
able to be set surely at a higher position (on the anode side) from
the extraction electrode 2.
[0203] This configuration decreased the number of electrons flying
in the trajectories colliding with the gate, so as to be able to
prevent the phenomena of decrease of efficiency and increase of the
beam size.
[0204] As a consequence, in the structure of the present device,
the electron emission current Ie of about 1 pA was also measured at
Vf of 20 V. On the other hand, If was similar to the characteristic
of Ie but values thereof were two figures smaller than those of Ie.
The beam sizes at this time were also approximately the same as in
Table 1.
[0205] By employing the configuration of the electron-emitting
device according to the present example, as described above, the
electron-emitting device was realized with the properties of the
reduced capacitance and driving voltage, the high efficiency, and
the small beam size.
Example 3
[0206] The electron-emitting device according to Example 3 will be
described with reference to FIGS. 3A and 3B. FIGS. 3A and 3B are
schematic views of the electron-emitting device according to
Example 3 of the present invention, wherein FIG. 3A is a plan view
thereof and FIG. 3B a cross-sectional view along 3B-3B in FIG.
3A.
[0207] In the present example, the conductive layer 5 was formed up
to an almost middle point of the gap across the gap from on the
surface of the negative electrode 3 to on the surface of the
substrate in step 2 in Example 1, whereby the gap distance was made
to about half.
[0208] Since in the present device the gap distance was smaller
than in Example 1, the electric field was about two times stronger
than in Example 1. This permitted the voltage for the driving to be
reduced to about 8 V. Since the conductive layer 5 was used as an
electrical connection layer for the fibrous carbons 4, it became
feasible to emit electrons stably from the fibrous carbons 4 in the
gap.
[0209] By employing the configuration of the electron-emitting
device according to the present example, as described above, the
electron-emitting device was realized with the properties of the
reduced capacitance and driving voltage, the high efficiency, and
the small beam size.
Example 4
[0210] The electron-emitting device according to Example 4 will be
described with reference to FIGS. 4A and 4B. FIGS. 4A and 4B are
schematic views of the electron-emitting device according to
Example 4 of the present invention, wherein FIG. 4A is a plan view
thereof and FIG. 4B a cross-sectional view along 4B-4B in FIG.
4A.
[0211] The present example is different as follows in step 1 and
step 2 described in foregoing Example 1, and the other steps of the
present example are the same as in Example 1.
(Step 1)
[0212] After the silica substrate used as the substrate 1 was
cleaned well, consecutive evaporation by sputtering was conducted
to form a Ti layer 5 nm thick and a Pt layer 500 nm thick as the
cathode (emitter) electrode 3 and a Ti layer 100 nm thick as the
conductive layer 5 permitting the growth of fibrous carbons.
[0213] Then a resist pattern was formed with the positive
photoresist (AZ1500 available from Clariant) by the
photolithography process.
[0214] Using the patterned photoresist as a mask, the Ti conductive
layer 5 was then etched by dry etching with CF.sub.4 and thereafter
the Pt and Ti layers were etched by dry etching with Ar, thereby
forming the negative electrode 3.
[0215] Using the negative electrode 3 as a mask, the silica
substrate was etched to the depth of about 500 nm with mixed acids
consisting of hydrofluoric acid and ammonium fluoride.
[0216] Subsequently, a Ti layer 5 nm thick and a Pt layer 30 nm
thick were again consecutively evaporated as the extraction
electrode 2 by sputtering. The photoresist on the negative
electrode 3 was removed and thereafter a resist pattern was again
formed for formation of the gate electrode shape with the positive
photoresist (AZ1500 available from Clariant).
[0217] Using the patterned photoresist as a mask, the Pt layer and
the Ti layer were then etched by dry etching with Ar to form the
extraction electrode 2 in such structure that a step difference
between steps acted as a gap.
[0218] Then a resist pattern was formed on the cathode and fine
particles of Ni were formed in the thickness of about 5 nm by
resistance heating evaporation with good straight-ahead nature.
After that, an oxidation treatment was carried out at 350.degree.
C. for 30 minutes. The steps after this step were the same as those
in Example 1.
[0219] The configuration of this device permitted formation of a
finer gap and made it feasible to emit electrons from about 6
V.
[0220] Since the height of the electron-emitting material (film
thickness) was large, electrons were not emitted only from the
upper part of the film but were also emitted from the middle point,
so as to be able to prevent the decrease of efficiency and the
increase of the beam size due to the collision of electrons with
the gate electrode.
Example 5
[0221] An image-forming apparatus comprised of a plurality of
electron-emitting devices according to the above examples will be
described.
[0222] The electron-emitting devices of Example 1 were arrayed in a
matrix pattern as shown in FIG. 8, thus completing the electron
source substrate 81.
[0223] Using this electron source substrate 81, the positive
electrode (anode) substrate 96 having the fluorescent member 94 was
placed at the distance of 2 mm above the electron-emitting devices
84, thus fabricating the image-forming apparatus shown in FIG.
9.
[0224] When the apparatus was driven by the pulse voltage of Vf=20
V and Va (voltage applied to the anode)=10 kV, the properties
similar to those in Example 1 were also yielded in the
image-forming apparatus.
[0225] According to the present invention, as described above, the
fibrous carbons are grown only on the side wall surface of the
conductive layer on the extraction electrode side, whereby it is
feasible to decrease electrons emitted from the other surfaces than
the conductive layer, to enhance the electron emission efficiency,
and to improve convergence of trajectories of emitted
electrons.
[0226] When the electron-emitting devices superior in the electron
emission efficiency and in the convergence of electron trajectories
as described are applied to the electron source, the electron
source can be realized with high quality. When this electron source
is applied to the image-forming apparatus, the image-forming
apparatus can implement formation of higher definition images.
* * * * *