JP2003016908A - Electron emitting element, electron source and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electron emitting element allowing an efficient electron emission at a low voltage with a small electron beam diameter and manufacturable by an easy process, an electron source and an image forming device. SOLUTION: In this electron emitting element, an opening extending through a second electrode 4 and an insulating layer 3 is formed, and electrons are emitted from electron emitting materials 5A and 5B on the first electrode 2 through the opening by applying a voltage between the first electrode 2 and the second electrode 4. The electron emitting quantity is larger in the electron emitting material central part 5A than the electron emitting material peripheral part 5B within the opening. In such a structure, the scattering of electrons from the peripheral part is suppressed, and electrons having a high convergent property from the central part can be used. Namely, since the spread of electron beams emitted to vacuum is minimized, and substantially all of the emitted electrons become electron emitting currents, an efficient electron emission can be performed at a low voltage.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron-emitting device, an electron source and an image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, two types of electron emitters, a thermoelectron source and a cold cathode electron source, are known. The cold cathode electron source is a field emission type (hereinafter referred to as FE type), metal / insulating layer /
There are a metal type (hereinafter referred to as MIM type), a surface conduction electron-emitting device, and the like.

As an example of the FE type, W. P. Dyke &
W. W. Dolan, "Field Emissio
n ", Advance in Electron Ph
ysics, 8, 89 (1956) or C.I.
A. Spindt, "PHYSICAL Proper
ties of thin-film field em
ision cathodes with molly
bdenium cones ", J. Appl. Phy
s. , 47, 5248 (1976) and the like are known.

An example of the MIM type is C.I. A. Mea
d, "Operation of Tunnel-Em
"Ission Devices", J. Apply. P
hys. , 32,646 (1961) and the like are known.

As an example of the surface conduction type, a report by Elinson (MI Elinson Radio Eng.
electron Phys. , 10 (1965)) and the like. In this surface conduction electron-emitting device, electrons are emitted by passing a current through a thin film of a small area formed on a substrate in parallel to the film surface. It utilizes the phenomenon. As the surface conduction type element, one using the SnO ₂ thin film described in the above-mentioned report of Erinson, one using an Au thin film, (G. Dittmer. Thin Solid
Films, 9, 35 (1972)), In ₂ O ₃ / Sn
O ₂ thin film (M. Hartwell and
C. G. Fonstad, IEEE Trans. ED
Conf. , 519 (1983)) and the like have been reported.

[0006]

In order to apply the electron-emitting device to the image forming apparatus, it is necessary to have an emission current that causes the phosphor to emit light with sufficient brightness. Further, in order to improve the definition of the display, it is required that the diameter of the electron beam with which the phosphor is irradiated is small. And it is important to be easy to manufacture.

FIG. 14 shows a Spindt type electron-emitting device as an example of a conventional FE type. In FIG. 16, 1 is a substrate, 4 is a cathode electrode layer (low potential electrode), 3 is an insulating layer,
Reference numeral 2 is a gate electrode layer (high potential electrode), 5 is a microchip, and 6 is an equipotential surface. When a bias is applied between the microchip 5 having the curvature r and the gate electrode layer 2, electrons are emitted from the tip of the microchip 5 toward the anode. The amount of emitted electrons is determined by the distance d between the gate electrode layer 2 and the tip of the microchip 5, the gate voltage Vg, and the work function of the emitting material. That is, it is a factor that determines the performance of the device that the distance d between the gate electrode layer 2 and the microchip 5 is well controlled.

FIG. 15 shows a general manufacturing process of a Spindt type electron-emitting device. The manufacturing process will be described with reference to this figure. First, a cathode electrode layer 4 made of Nb or the like, an insulating layer 3 made of SiO ₂ or the like and a gate electrode layer 2 made of Nb or the like are formed on a substrate 1 made of glass or the like. Stack in order. After that, a circular fine hole penetrating the gate electrode layer 2 and the insulating layer 3 is formed by the reactive ion etching method (FIG. 15A).

After that, the sacrificial layer 7 made of aluminum or the like is used.
Is formed on the gate electrode layer 2 by oblique vapor deposition or the like (see FIG. 1).
5 (b)).

A microchip material 81 such as molybdenum is deposited on the structure thus formed by a vacuum vapor deposition method. Here, the deposit on the sacrificial layer fills the fine holes as the deposition progresses, and the microchip 51 is formed in a conical shape in the fine holes (FIG. 15C).

Finally, the sacrificial layer 71 is melted to lift off the microchip material 81 to complete the device (FIG. 15D).

However, in such a manufacturing method, it is difficult to control the distance d with good reproducibility, and the amount of emission current varies from device to device. Further, a metal piece or the like generated at the time of lift-off short-circuits the microchip 51 and the gate electrode layer 2, and when a voltage is applied between the microchip 51 and the gate electrode layer 2 during driving, heat is generated at the short-circuited portion, and the short-circuited portion is generated. And destruction of the surrounding area occurs. This reduces the effective emission area. The variation due to each element as described above causes unevenness in brightness when applied as an image forming apparatus, for example, and is very annoying.

Furthermore, in this example, since electrons are emitted from one emission point, if the emission current density is increased in order to cause the phosphor to emit light, thermal destruction of the electron emission portion is induced, and the FE element It will limit the lifespan. In addition, the ions existing in a vacuum may sputter the tip of the microchip intensively to shorten the life of the device.

It should be noted that the electrons emitted into the vacuum travel perpendicularly to the equipotential surface, but in the structure shown in FIG. 14, the equipotential surface 61 is formed in the hole along the microchip 51. become. Therefore, the electrons emitted from the tip of the microchip 51 tend to spread. A part of the emitted electrons is absorbed by the gate electrode layer 2 and the amount of electrons reaching the anode is reduced. The amount of electrons absorbed in the gate electrode layer 2 is
It tends to increase as the distance d decreases.

In order to overcome such drawbacks of the FE element, various examples have been proposed as individual solutions.

As an example of preventing the spread of the electron beam, there is an example in which a focusing electrode is arranged above the electron emitting portion. In this example, the emitted electron beam is focused by the negative potential of the focusing electrode, but in this example, a more complicated process than the above-described manufacturing process is required, which causes an increase in manufacturing cost.

As an example of reducing the electron beam diameter without disposing the focusing electrode, another example of reducing the electron beam diameter is a method of not forming a microchip such as a Spindt type. For example, JP-A-8-096703
JP-A-8-096704 and JP-A-8-096704.

This has the advantage that a flat equipotential surface is formed on the electron emission surface and the spread of the electron beam is reduced because electrons are emitted from the thin film arranged in the hole. Further, by using a low work function constituent material as the electron emitting substance, electrons can be emitted without forming a microchip, and a low driving voltage can be achieved. There is also an advantage that the manufacturing method is relatively simple. Further, since the electrons are emitted on the surface, the electric field is not concentrated, the chip is not broken, and the life is long. However, in these examples, a potential distribution that is correlated with the hole depth and the distance between the gate electrode layers is formed around the hole. Therefore, although not as in the Spindt type, the emitted electrons also tend to spread and the emitted electrons are emitted. The problem that some of the electrons are absorbed or scattered by the gate electrode layer 2 has not been solved. JP-A-8-11
In Japanese Patent No. 5654, the beam is converged by allowing the particle emission surface to exist at a position deeper than the surface on the insulating layer side. In this example,
There is a problem that process precision such as depth and height of the particle emission material is required.

An example of improving the electron emission efficiency is described in JP-A-10-289650. Figure 1
6 shows the configuration. The amount of electrons emitted from the cathode electrode layer 4 by applying a positive potential to the gate electrode layer 2 and the second gate electrode layer 11 (where 0 <| Vg1 | ≦ | Vg2 |) with respect to the cathode electrode layer 4. Is increasing
After all, the emitted electrons tend to spread.

On the other hand, in the MIM type, an insulating layer is arranged between the lower electrode (cathode electrode layer) and the upper electrode (gate electrode layer),
This is a structure in which a voltage is applied between both electrodes to extract electrons.
Since the direction of the internal electric field coincides with the direction of emitted electrons and the potential distribution on the emission surface is not distorted, a small electron beam diameter can be realized, but electron scattering occurs at the insulating layer 3 and the upper electrode 2. Therefore, it is generally inefficient.

When the application to the image forming apparatus such as the display as described above is considered by the field emission type electron emission device, (1) the electron beam diameter is small, and (2) the electron emission is highly efficient at a low voltage. It is necessary that (3) the manufacturing process be easy, but it has been difficult for the conventional electron-emitting device to satisfy these at the same time.

The present invention was made in order to solve the above-mentioned problems of the prior art. The object of the present invention is to make the electron beam diameter small, to enable high-efficiency electron emission at low voltage, and to improve the manufacturing process. Easy field emission type electron emission device,
An object is to provide an electron source and an image forming apparatus.

[0023]

In order to achieve the above object, the present invention employs the following configurations.

That is, a first conductive layer formed on an insulating substrate, an insulating layer laminated on the cathode electrode layer, and a second conductive layer laminated on the insulating layer. ,
A through hole penetratingly formed on the first conductive layer from the insulating layer to the second conductive layer; and an electron emission layer laminated on the first conductive layer in the through hole, An electron-emitting device that emits electrons from the electron-emitting layer by applying a voltage between the first conductive layer and the second conductive layer. The amount of emitted electrons is larger in the central portion than in the peripheral portion of the surface that faces the inside of the through hole and emits electrons.

According to this structure, the electrons easily diverging from the peripheral portion can be suppressed, and the electrons with high convergence from the central portion can be mainly used, so that the spread of the electron beam emitted in the vacuum is small, For example, the diameter of the electron beam emitted by the phosphor on the anode side can be reduced.

Further, it is preferable that an electron emission threshold value of a central portion of a surface which faces the inside of the through hole and emits electrons is lower than an electron emission threshold value of the peripheral portion.

Further, it is preferable that the band structure is different between the central part and the peripheral part of the surface which emits electrons facing the inside of the through hole.

Further, the band structure may be continuously changed from the central portion of the surface which emits electrons facing the inside of the through hole to the peripheral portion.

Further, the band structure may be changed stepwise from the central portion to the peripheral portion of the surface which emits electrons facing the inside of the through hole.

Further, it is preferable that the work function of the central part of the surface which emits electrons facing the inside of the through hole is smaller than the work function of the peripheral part.

Further, it is preferable that the band gap at the center of the surface which emits electrons facing the inside of the through hole is wider than the band gap at the peripheral portion of the electron emitting layer.

Further, the electron barrier at the portion of the electron emission layer which is in contact with the first conductive layer is lower in the central portion than in the peripheral portion of the surface which faces the inside of the through hole and emits electrons. Good.

The band structure may change in the layer thickness direction of the electron emission layer.

The electron emitting material preferably contains carbon as a main component.

The layer containing the electron emitting material preferably contains at least one of diamond and diamond-like carbon.

According to each of the above-mentioned configurations, since there is no obstacle that obstructs the trajectory of the emitted electrons and no potential that obstructs them, almost all of the emitted electrons become an electron emission current, so that a low voltage is applied. Thus, highly efficient electron emission is possible.

The structure is very simple and the manufacturing process is easy.

Another aspect of the invention is an electron source for emitting electrons, which is characterized in that it is formed by arranging a plurality of electron-emitting devices having the above structure.

Further, such an electron source is preferably formed by matrix-wiring the electron-emitting devices.

Another aspect of the present invention is an image forming apparatus having a function of forming an image, comprising an electron source having the above structure and an image forming member for forming an image by the electrons emitted from the electron source. Is characterized by.

Further, it is preferable that the image forming member is a phosphor that emits light by collision of electrons.

[0042]

BEST MODE FOR CARRYING OUT THE INVENTION Preferred embodiments of the present invention will be illustratively described in detail below with reference to the drawings. However, the dimensions of the components described in this embodiment,
Unless otherwise specified, the material, the shape, the relative arrangement, and the like are not intended to limit the scope of the present invention thereto.

FIG. 1 is a schematic sectional view showing an electron-emitting device having the most basic constitution of the present invention, in which (a) is a sectional view,
(B) is a plan view. Further, FIG. 2 is a diagram showing current-voltage characteristics when this element is driven.

In FIG. 1, 1 is a substrate, 2 is a first electrode, 3 is an insulating layer, and 4 is a second electrode. Reference numeral 5 denotes an electron emission layer, which is divided into 5A and 5B. 5A is an opening (hole)
5B is a material and structure located in the central portion of which has a low threshold voltage for electron emission, while 5B is a material and structure having a high threshold voltage of electron emission opposite to the central portion. Here, the second electrode 4 is a layer from which electrons are not emitted, and the first electrode 2 and the electron emission layer 5 are
Indicate different conductive materials, but the same material does not matter.

W1 is the width of the first electrode (including the electron emission layer 5), h1 is the thickness of the insulating layer 3, and H is the distance between the anode 12 and the low potential electrode.

Vg is a voltage applied between the second electrode 4 and the first electrode 2 (including the electron emission layer 5), and Va is a voltage applied between the first electrode and the anode 12. , Ie
Is the electron emission current. Eh is an electric field formed by Vg. When Vg and Va are applied to drive the element, an electric field Eh is formed, and Vg, W1, h1, shape,
The shape of the equipotential surface inside the hole is determined by the dielectric constant of the insulating layer. The current-voltage characteristics of the electron-emitting materials 5A and 5B are shown in FIG. 2, which is an equipotential surface which is substantially parallel to the gate 4 and Va outside the hole. 5A causes electron emission at a low threshold voltage (A), while 5B causes electron emission at a high threshold voltage (B). Therefore, if an intermediate voltage is set, it is possible to cause electron emission only from the center even with the same voltage setting.

FIG. 3 shows the result of simulation of the orbits of electrons emitted from the device of the present invention in the holes. The equipotential surface is convex upward, the electrons emitted into the vacuum take an orbit to the outside, and the electrons emitted from around the electron-emitting device collide and scatter with the second insulating film or the second electrode. However, the orbit of the electron should spread greatly, but the part where the electron is actually emitted is the central part of the hole, and the electron is drawn out of the hole without being scattered to the periphery. After leaving the hole, the Y direction is accelerated by Va and collides with the fluorescent plate. The X direction that affects the beam spread can be approximated by a uniform velocity motion of the initial velocity Vx in the X direction when the beam exits the hole. In order to reduce the beam diameter, it is important to eliminate scattered components and to reduce Vx. In the embodiment of the present invention, non-scattering and low Vx can be realized. The beam size tends to expand as the electric field Eh increases and Va decreases, and these parameters are design items for selecting values suitable for the intended use of the electron-emitting device. In the present embodiment, the electron emission from the edge of the electron emitting material, which has been conventionally pointed out, is further suppressed. While the electric field is likely to be concentrated at the edge and electrons are easily emitted, the electric field tends to be turbulent because of the shape effect and is disturbed, and the electrons tend to diverge.Furthermore, process stability cannot be guaranteed and the electron beam diameter is small. To be an obstacle.

In the device of the present invention, as described above, electrons can be taken out without scattering, so that almost all the emitted electrons become Ie, which is very efficient even at low voltage.

Further, the electron emission surface on the device of the present invention is the surface of the electron emission layer 5A, and the electron emission area is a wide area instead of an acute angle portion, so that it has good durability against ion bombardment.

Furthermore, the device of the present invention has a very simple structure in which lamination is repeated, the manufacturing process is easy, and the device can be manufactured with high yield. (The manufacturing method will be described later).

The electron-emitting device according to the embodiment of the present invention described above will be described in more detail. An example of the method of manufacturing the electron-emitting device according to the embodiment of the present invention will be described with reference to FIG. 4, but it goes without saying that the manufacturing method is not limited to this. First, the surface thereof is thoroughly washed in advance, quartz glass, glass with a reduced content of impurities such as Na, soda lime glass, a laminated body in which SiO ₂ is laminated on a silicon substrate by a sputtering method, insulation of ceramics such as alumina, etc. One of the conductive substrates is used as the substrate 1, and the first electrode 2 is laminated on the substrate 1.

The first electrode 2 is generally conductive and is formed by a general vacuum film forming technique such as a vapor deposition method and a sputtering method. The material of the first electrode 4 is, for example, Be, M
g, Ti, Zr, Hf, V, Nb, Ta, Mo, W, A
Metal or alloy material such as 1, Cu, Ni, Cr, Au, Pt, Pd, TiC, ZrC, HfC, TaC, Si
Carbides such as C and WC, HfB ₂ , ZrB ₂ , LaB ₆ and C
borides such as eB ₆ , YB ₄ , GdB ₄ , TiN, ZrN,
It is appropriately selected from nitrides such as HfN, semiconductors such as Si and Ge, organic polymer materials, amorphous carbon, graphite, diamond-like carbon, carbon in which diamond is dispersed, and carbon compounds. The thickness of the first electrode 2 is set in the range of several tens nm to several mm, and is preferably selected in the range of several hundred nm to several μm.

Then, as shown in FIG. 4B, an insulating layer 3 is deposited subsequent to the first electrode 2. The insulating layer 3 is formed by a general vacuum film forming method such as a sputtering method, a CVD method, or a vacuum vapor deposition method, and the thickness thereof is set in the range of several nm to several μm, preferably several tens nm. It is selected from the range of several hundred nm. SiO ₂ and Si are preferable materials.
A material having a high breakdown voltage that can withstand a high electric field, such as O, SiN, Al ₂ O ₃ , CaF, and undoped diamond, is desirable.

Further, a second electrode 4 is deposited following the insulating layer 3.
To do. The second electrode 4 has the same conductivity as the first electrode 2.
We have a general vacuum film forming technique such as vapor deposition method and sputtering method.
It is formed by a technique and a photolithography technique. Second
The material of the electrode 4 is, for example, Be, Mg, Ti, Zr,
Hf, V, Nb, Ta, Mo, W, Al, Cu, Ni,
Metal or alloy material such as Cr, Au, Pt, Pd, Ti
Carbonization of C, ZrC, HfC, TaC, SiC, WC, etc.
Thing, HfB₂, ZrB₂, LaB₆, CeB₆, YB _Four, G
dB_FourSuch as borides, nitriding of TiN, ZrN, HfN, etc.
Materials, semiconductors such as Si and Ge, organic polymer materials, etc.
To be selected. The thickness of the second electrode 4 is from several nm
It is set in the range of several μm, preferably several nm to several hundreds n
It is selected in the range of m.

The electrodes 2 and 4 may be made of the same material or different materials, and may be formed by the same method or different methods.

Next, as shown in FIG. 4C, a mask pattern 41 is formed by the photolithography technique.

Then, as shown in FIG. 4D, a laminated structure is formed in which a part of each layer is removed from the cathode electrode 2. However, this etching process may be stopped on the cathode electrode 2, or a part of the cathode electrode 2 may be etched.

The etching process is performed for each layer 3, 4,
The etching method may be selected according to the materials of 2 and 3. Then, the electron emission layer 5 is formed as shown in FIG. The electron emitting material is formed by a general film forming technique such as a vapor deposition method, a sputtering method or a CVD method. The material of the electron emission layer 5 is appropriately selected from, for example, amorphous carbon, graphite, diamond-like carbon, carbon and carbon compounds in which diamond is dispersed, AlN, AlGaN, and the like. A diamond thin film having a low work function, diamond-like carbon, etc. are preferable. The film thickness of the electron emission layer 5 is set in the range of several nm to several hundred nm, and preferably selected in the range of several nm to several tens nm. Here, in order to form the structure of the present invention, the electron emission threshold of the electron emission material is formed so as to be different in the plane. Various methods have been used to change the threshold voltage for electron emission. One is to change the band gap and
In addition to the method of controlling the electron emission portion, an example of controlling the electron emission threshold by controlling the film thickness has also been reported.
(RD Forrest et. Al., Appl.
ied Physics Letters, Volu
me 73, Number 25, p. 3784 1
988) There are various methods for changing the band gap of the electron-emitting material. For example, in the case of diamond-like carbon, depending on the film forming method, the temperature may be changed or the irradiation energy may be changed (for example, M. Weier).
et. al. Physical Review B,
Vol. 53, Number3 15 / Januar
y 1996 P.I. 1594), the irradiation ion density is changed, and when a gas is used, the gas species and the gas flow rate (for example, R. Kleberet. Al. Diamond an
d Related Materials, 2 (19
93) p. It is possible to control by changing 246) and is not particularly limited. Both can be achieved by setting and controlling each parameter during film formation. If more precise, it is possible to apply feedback while measuring the band gap. Alternatively, a method of partially modifying the film by ion implantation or electron irradiation after depositing the electron emitting material may be used. It is important and preferable that the production method can be performed in a self-aligned manner in order to simplify the production method.

Further, here, without depositing the electron emission layer 5,
In some cases, the electron emission layer 5 is deposited on the first electrode before forming the holes.

Width W of the first electrode (including the electron emission layer 5)
1 is appropriately set depending on the material and resistance of the element, the work function and drive voltage of the material of the first electrode, and the required shape of the electron emission beam. Usually, W1 is selected from the range of several hundred nm to several hundred μm. Further, as shown in FIG. 5, one pixel may be formed by arranging a plurality of the holes. The height h1 of the insulating film and the thickness of the electron emission material are also appropriately set depending on the material and resistance of the element, the work function and drive voltage of the material of the electron emission element, and the required shape of the electron emission beam. Usually, h1 is selected from the range of several hundred nm to several tens of μm, and the thickness of the electron emitting material is also selected from the range of several hundred nm to several tens of μm, depending on h1.

Application examples of the electron-emitting device to which the present invention is applied will be described below. By arranging a plurality of electron-emitting devices of the present invention on a substrate, for example, an electron source or an image forming apparatus can be constructed.

Various arrangements of electron-emitting devices are adopted. As an example, a plurality of electron-emitting devices are arranged in a matrix in the X and Y directions, one of the electrodes of the plurality of electron-emitting devices arranged in the same row is commonly connected to a wiring in the X direction, and the same column is used. There is a simple matrix arrangement in which the other of the electrodes of the plurality of electron-emitting devices arranged in the above is commonly connected to the wiring in the Y direction.

An electron source obtained by adopting a simple matrix arrangement and arranging a plurality of electron-emitting devices to which the present invention can be applied will be described below with reference to FIG. In FIG. 6, 6
Reference numeral 1 is an electron source substrate, 62 is an X-direction wiring, and 63 is a Y-direction wiring. Reference numeral 64 is an electron-emitting device of the present invention, and 65 is a wire connection.

The m number of X-direction wirings 62 are Dx1 and Dx.
2, ... Dxm, and can be made of a conductive metal or the like formed by a vacuum deposition method, a printing method, a sputtering method, or the like. The wiring material, film thickness, and width are appropriately designed. Y
The directional wiring 63 is composed of n wirings Dy1, Dy2, ... Dyn, and is formed similarly to the X-directional wiring 62. An interlayer insulating layer (not shown) is provided between the m X-direction wirings 62 and the n Y-direction wirings 63 to electrically isolate the two (m and n are both Positive integer).

The interlayer insulating layer (not shown) is made of SiO ₂ or the like formed by a vacuum deposition method, a printing method, a sputtering method or the like. For example, it is formed in a desired shape on the entire surface or a part of the base 61 on which the X-direction wiring 62 is formed, and in particular, the film thickness and material are set so as to withstand the potential difference at the intersection of the X-direction wiring 62 and the Y-direction wiring 63. The manufacturing method is set appropriately. The X-direction wiring 62 and the Y-direction wiring 63 are drawn out as external terminals.

A pair of electrodes (not shown) forming the electron-emitting device 64 are electrically connected to each other by m X-direction wirings 62, n Y-direction wirings 63 and a connection 65 made of a conductive metal or the like. There is.

The material forming the X-direction wiring 62 and the Y-direction wiring 63, the material forming the connection 65, and the material forming the pair of element electrodes may be the same or may be the same as some of the constituent elements. Each may be different. These materials are appropriately selected, for example, from the materials of the device electrodes (electrodes 2 and 4) described above. When the material forming the element electrode and the wiring material are the same, the wiring connected to the element electrode can also be referred to as an element electrode.

A scanning signal applying means (not shown) for applying a scanning signal for selecting a row of the electron-emitting devices 64 arranged in the X direction is connected to the X-direction wiring 62. On the other hand, Y
The directional wiring 63 includes the electron-emitting devices 64 arranged in the Y direction.
A modulation signal generating means (not shown) is connected to modulate each column according to the input signal. The driving voltage applied to each electron-emitting device is supplied as a difference voltage between the scanning signal and the modulation signal applied to the device.

In the above structure, individual elements can be selected and driven independently by using simple matrix wiring. An image forming apparatus configured by using an electron source having such a simple matrix arrangement will be described with reference to FIG.

FIG. 7 is a schematic view showing an example of the display panel of the image forming apparatus. In FIG. 7, 81 is an electron source substrate having a plurality of electron-emitting devices, 91 is a rear plate to which the electron source substrate 91 is fixed, 96 is a glass substrate 93, and a fluorescent film 94 as a phosphor serving as an image forming member is provided on the inner surface of the glass substrate 93. It is a face plate on which a metal back 95 and the like are formed. 92
Is a support frame, and the support frame 92 includes a rear plate 91,
The face plate 96 is connected using frit glass or the like. Reference numeral 97 denotes an envelope, which is sealed and formed by baking in an atmosphere or nitrogen in a temperature range of 400 to 500 ° C. for 10 minutes or more.

Reference numeral 84 corresponds to the electron-emitting device in FIG. Reference numerals 62 and 63 are X-direction wiring and Y-direction wiring connected to the pair of device electrodes 2 and 4 of the electron-emitting device.

The envelope 97 is composed of the face plate 96, the support frame 92 and the rear plate 91 as described above. Since the rear plate 91 is provided mainly for the purpose of reinforcing the strength of the base body 81, if the base body 81 itself has sufficient strength, the separate rear plate 91 can be omitted. That is, the support frame 92 is directly sealed to the base body 81, and the face plate 96, the support frame 92 and the base body 81 are used to seal the enclosure 9
7 may be configured. On the other hand, by installing a support member (not shown) called a spacer between the face plate 96 and the rear plate 91, it is possible to configure the envelope 97 having sufficient strength against atmospheric pressure.

In the image forming apparatus using the electron-emitting device according to the present embodiment, the phosphor (fluorescent film 94) is aligned and arranged above the electron-emitting device 84 in consideration of the emitted electron orbit.

FIG. 8 is a schematic view showing a mode of use when the fluorescent film 94 is used as a panel. In the case of a color fluorescent film, it is composed of a black conductive material 86 called a black stripe shown in FIG. 8A or a black matrix shown in FIG.

In the case of color display, the purpose of providing the black stripes and the black matrix is to make the mixed portions between the phosphors 85 of the three primary color phosphors black so as to make the mixed colors inconspicuous, and to make the phosphor film. This is to suppress the decrease in contrast due to external light reflection at 94. As the material of the black stripe, in addition to a commonly used material containing graphite as a main component, a material having conductivity and having little light transmission and reflection can be used.

As a method for applying the fluorescent substance to the glass substrate 93, a precipitation method, a printing method or the like can be adopted regardless of monochrome or color. A metal back 95 is usually provided on the inner surface side of the fluorescent film 94. The purpose of providing a metal back is
Of the light emitted from the phosphor, the light to the inner surface side
To improve the brightness by mirror-reflecting to the 6 side, to act as an electrode for applying an electron beam accelerating voltage, and to protect the phosphor 94 from damage due to collision of negative ions generated in the envelope. Etc. The metal back 95 is subjected to a smoothing process (generally called “filming”) on the inner surface of the fluorescent film after the fluorescent film is produced.
And then depositing Al using vacuum deposition or the like.

The face plate 96 further includes a fluorescent film 9
In order to improve the conductivity of No. 4, a transparent electrode (not shown) may be provided on the outer surface side of the fluorescent film 94. In the present invention, since the electron beam reaches directly above the electron emitting element 84, the fluorescent film 94 is arranged directly above the electron emitting element 84.
Aligned and configured.

Next, the envelope (panel) which has been subjected to the sealing step.
The vacuum sealing step of sealing the will be described.

In the vacuum sealing step, the envelope (panel) 97 is heated and kept at 80 to 250 ° C., and exhausted through an exhaust pipe (not shown) by an exhaust device such as an ion pump or a sorption pump. Then, after the atmosphere is made sufficiently low in organic substances, the exhaust pipe is heated by a burner to melt and seal. A getter process can be performed to maintain the pressure after the envelope 97 is sealed. This is the envelope 97
Immediately before or after the sealing of (1) and (2) after heating, the getter placed at a predetermined position (not shown) in the envelope 97 is heated by heating using resistance heating or high frequency heating to form a vapor deposition film. Processing. The getter usually has Ba as a main component and maintains the atmosphere in the envelope 97 by the adsorption action of the vapor deposition film.

In the image forming apparatus constructed by using the electron source of the simple matrix arrangement manufactured by the above process, the external terminals Dx1 to Dxm, Dy1 to Dy1 to each electron emitting element are formed.
By applying a voltage via Dyn, electron emission occurs. Va applies a high voltage to the metal back 95 or a transparent electrode (not shown) via a high voltage terminal to accelerate the electron beam. The accelerated electrons collide with the fluorescent film 94,
Light emission occurs and an image is formed.

Next, a configuration example of a drive circuit for performing television display based on a television signal of the NTSC system on a display panel constructed by using an electron source having a simple matrix arrangement will be described with reference to FIG. . In FIG. 9, 13
01 is an image display panel, 1302 is a scanning circuit, 13
Reference numeral 03 is a control circuit, and 1304 is a shift register. 1
305 is a line memory, 1306 is a sync signal separation circuit,
1307 is a modulation signal generator, and Vx and Va are DC voltage sources. The display panel 1301 has terminals Dox1 to Dox1.
oxm, terminals Doy1 to Doyn, and high-voltage terminal Hv
It is connected to an external electric circuit via. Terminal Dox1
To Doxm, a scanning signal for sequentially driving an electron source provided in the display panel, that is, an electron emitting device group matrix-wired in a matrix of M rows and N columns row by row (N elements) is applied. To be done.

A modulation signal is applied to the terminals Dy1 to Dyn for controlling the output electron beam of each element of the electron-emitting devices in one row selected by the scanning signal. The high-voltage terminal Hv receives, for example, 10 K [V] from the DC voltage source Va.
Is supplied, which is an accelerating voltage for giving enough energy to excite the phosphor to the electron beam emitted from the electron-emitting device.

The scanning circuit 1302 will be described. The circuit is provided with M switching elements inside (indicated by S1 to Sm in the figure).
Each switching element selects either the output voltage of the DC voltage source Vx or 0 [V] (ground level), and is electrically connected to the terminals Dx1 to Dxm of the display panel 1301. Each of the switching elements S1 to Sm operates based on the control signal Tscan output from the control circuit 1303, and can be configured by combining switching elements such as FETs.

In the case of the present example, the DC voltage source Vx causes the drive voltage applied to the element which is not scanned based on the characteristics (electron emission threshold voltage) of the electron emission element to be equal to or lower than the electron emission threshold voltage. It is set to output such a constant voltage.

The control circuit 1303 has a function of matching the operation of each unit so that an appropriate display is performed based on an image signal input from the outside. The control circuit 1303
Sync signal Tsy sent from sync signal separation circuit 1306
Tscan and Tsf for each part based on nc
Generate t and Tmry control signals.

The sync signal separation circuit 1306 is a circuit for separating the sync signal component and the luminance signal component from the NTSC system television signal input from the outside, and uses a general frequency separation (filter) circuit or the like. Can be configured. The sync signal separated by the sync signal separation circuit 1306 includes a vertical sync signal and a horizontal sync signal, but it is shown here as a Tsync signal for convenience of description. The luminance signal component of the image separated from the television signal is represented as a DATA signal for convenience. The DATA signal is input to the shift register 1304.

The shift register 1304 is for serial / parallel conversion of the DATA signal serially input in time series for each line of the image, and is based on the control signal Tsft sent from the control circuit 1303. It can be said that the control signal Tsft is the shift clock of the shift register 1304. The serial / parallel converted image data for one line (corresponding to drive data for N electron emission elements) is output from the shift register 1304 as N parallel signals Id1 to Idn.

The line memory 1305 is a storage device for storing data for one line of an image for a required time, and stores the contents of Id1 to Idn as appropriate in accordance with the control signal Tmry sent from the control circuit 1303. The stored contents are output as I′d1 to I′dn and input to the modulation signal generator 1307.

The modulation signal generator 1307 is a signal source for appropriately driving and modulating each of the electron-emitting devices according to each of the image data I′d1 to I′dn, and the output signal thereof is from the terminals Doy1 to Doy1. Display panel 1 through Doyn
It is applied to the electron-emitting device in 301.

As described above, the electron-emitting device to which the present invention can be applied has the following basic characteristics with respect to the emission current Ie. That is, a clear threshold voltage Vth is required for electron emission.
Therefore, electron emission occurs only when a voltage higher than Vth is applied. For a voltage equal to or higher than the electron emission threshold value, the emission current also changes according to the change in the voltage applied to the device. From this, when a voltage is applied to this element, for example, no electron emission occurs even if a voltage below the electron emission threshold is applied, but an electron beam is output when a voltage above the electron emission threshold is applied. . At that time, the intensity of the output electron beam can be controlled by changing the applied voltage Vf. Further, when a pulse voltage is applied to this element, the electron beam intensity is changed by changing the pulse height Ph.
By changing the pulse width Pw, it is possible to control the total amount of charges of the output electron beam.

Therefore, as a method of modulating the electron-emitting device according to the input signal, a voltage modulation method, a pulse width modulation method or the like can be adopted. When implementing the voltage modulation method, a circuit of the voltage modulation method is used as the modulation signal generator 1307, which generates a voltage pulse of a fixed length and appropriately modulates the peak value of the pulse according to the input data. be able to.

When implementing the pulse width modulation method,
As the modulation signal generator 1307, it is possible to use a circuit of a pulse width modulation system that generates a voltage pulse having a constant peak value and appropriately modulates the width of the voltage pulse according to input data.

The shift register 1304 and the line memory 1
The digital signal type 305 and the analog signal type 305 can be adopted. This is because the serial / parallel conversion and storage of the image signal may be performed at a predetermined speed.

When the digital signal type is used, it is necessary to convert the output signal DATA of the sync signal separation circuit 1306 into a digital signal.
A D converter may be provided. In connection with this, the circuit used for the modulation signal generator 1307 is slightly different depending on whether the output signal of the line memory 1305 is a digital signal or an analog signal. That is, in the case of the voltage modulation method using a digital signal, for example, a D / A conversion circuit is used for the modulation signal generator 1307, and an amplification circuit or the like is added if necessary. In the case of the pulse width modulation method, the modulation signal generator 13
As the circuit 07, for example, a circuit in which a high-speed oscillator, a counter that counts the number of waves output from the oscillator, and a comparator that compares the output value of the counter with the output value of the memory is used. If necessary, an amplifier for voltage-amplifying the pulse-width-modulated modulation signal output from the comparator up to the driving voltage of the electron-emitting device can be added.

In the case of the voltage modulation method using an analog signal, the modulation signal generator 1307 can employ, for example, an amplifier circuit using an operational amplifier or the like, and a level shift circuit or the like can be added if necessary. In the case of the pulse width modulation method, for example, a voltage control type oscillation circuit (VCO)
Can be adopted, and an amplifier for amplifying the voltage up to the driving voltage of the electron-emitting device can be added if necessary.

In the image display device (FIG. 21) to which the present invention having such a structure can be applied, a voltage is applied to each electron-emitting device through the terminals Dox1 to Doxm and Doy1 to Doyn outside the container. Causes electron emission. A high voltage is applied to the metal back 95 or a transparent electrode (not shown) via the high voltage terminal Hv to accelerate the electron beam. The accelerated electrons collide with the fluorescent film 94,
Light emission occurs and an image is formed.

The configuration of the image forming apparatus described here is an example of the image forming apparatus to which the present invention can be applied, and various modifications can be made based on the technical idea of the present invention. As for the input signal, the NTSC system has been mentioned, but the input signal is not limited to this, and the PAL, SECAM system, etc., and a TV signal composed of a larger number of scanning lines (for example, the MUSE system, etc.). High-definition TV) system can also be adopted.

The image forming apparatus of the present invention can be used not only as a display apparatus for television broadcasting, a display apparatus such as a TV conference system and a computer, but also as an image forming apparatus as an optical printer constituted by using a photosensitive drum or the like. Can be used.

[0099]

EXAMPLES Examples of the present invention will be described in detail below.

[Embodiment 1] FIG. 1 is a sectional view of an electron-emitting device manufactured according to this embodiment, and FIG. 2 is an example of a plan view.
FIG. 4 shows an example of a method of manufacturing the electron-emitting device of this embodiment. The manufacturing process of the electron-emitting device of this embodiment will be described in detail below.

(Step 1) First, as shown in FIG. 5A, after using quartz for the substrate 1 and performing sufficient cleaning, a Ti film having a thickness of 500 nm was formed as the first electrode 2 by the sputtering method. did.

(Step 2) Next, as shown in FIG. 5B, 600 nm thick SiO ₂ was deposited as the insulating layer 3 and 100 nm thick Ti was deposited as the gate electrode 4 in this order.

(Step 3) Next, as shown in FIG. 5C, the spin coating of a positive photoresist (AZ1500 / Clariant) and the photomask pattern are exposed and developed by photolithography. The pattern 41 was formed.

(Step 4) As shown in FIG. 5D, using the mask pattern 41 as a mask, the Ta gate electrode 4 and the insulating layer 3 are dry-etched using CF 4 gas, respectively, and stopped at the cathode electrode 2. , A circular hole having a width w1 of 3 μm was formed.

(Step 5) Subsequently, as shown in FIG. 5E, an electron emission layer 5 of diamond-like carbon was deposited on the first electrode 4 by the rf sputtering method. As a film forming method, a high frequency power supply of 13.56 MHz was used, and the gas was a mixed gas of Ar and H2 at 5 mTorr. The power was 500 W, the substrate susceptor was tilted 30 degrees with respect to the filament, and the substrate was rotated once with the center of the substrate as the axis of rotation for 10 seconds to form a film for 10 minutes. The voltage applied to the substrate during film formation is approximately -200V, and 65n at the center of the hole.
m, the film thickness was reduced toward the periphery of the hole. In FIG. 10, the horizontal axis indicates the film thickness, and the vertical axis indicates the electron emission threshold value. The threshold value becomes the lowest at 65 nm, and the threshold value for electron emission increases as the film thickness decreases from that. Therefore, the electron emission material α-C: H could be formed so that the electron emission occurs only in the central portion when viewed at a certain reference voltage A point.

(Step 6) As shown in FIG. 4F, the mask pattern 41 was completely removed, and the electron-emitting device of this example was completed.

The electron-emitting device manufactured as described above was driven with Va arranged as shown in FIG. The actual drive voltage was Vg = 20 V, Va = 10 kV, and the distance D3 between the electron-emitting device and the anode 12 was 1 mm, so that the electron source could be formed. Here, using an electrode coated with a phosphor as the anode 12, the size of the electron beam was observed. The electron beam size referred to here is the size up to a region of 10% of the peak luminance of the phosphor that has emitted light.
As a result, the beam diameter was 200 μm, and the emission due to the scattering component, which was observed when the entire surface of the hole was formed of the same emitting material, was not observed.

Here, as shown in FIG. 1, the electron emission portion is described as a substantially circular hole, but it is not particularly limited and may be formed in a line shape, for example. Similar effects were obtained at this time, and the beam diameter could be reduced. The creation method is exactly the same except that the patterning shape is changed. It is possible to arrange a plurality of line patterns, and a large emission area can be obtained. Although the electron-emitting material is diamond-like carbon in this example, it goes without saying that other materials including diamond may be used.

[Embodiment 2] As Embodiment 2, an example in which the band gap of the electron-emitting material is changed within the plane will be described. The manufacturing method is the same as that of the first embodiment except the electron-emitting material film forming step of FIG. In this embodiment, FCVA
(Filtered cathodic vacuum
An electron emission layer 5 of diamond-like carbon was deposited on the first electrode 4 by the arc method. As a film forming method, first, a film was formed under the condition that diamond-like carbon having a small band gap of about 10 nm was uniformly formed in the holes. The voltage applied to the substrate during film formation is -300.
V. Then, the voltage applied to the substrate during film formation was set to -10.
The band gap is widened by setting it to 0 V, the substrate susceptor is tilted 30 degrees with respect to the filament, and the substrate center is rotated once for one rotation in 10 seconds. The film was formed so as to be larger than the peripheral portion. Since the ion-like irradiation density of the diamond-like carbon film at the peripheral portion is small, the band gap becomes narrower than that at the central portion. FIG. 11 shows a comparison between a vertical band diagram of the central portion and a vertical band diagram of the film peripheral portion. (A) is a band structure in the central portion and is in an electric field-free state. Ec, Ef, and Ev represent a conductor, a Fermi level, and a valence pair, respectively, and Vac represents a vacuum level. (B)
[Fig. 4] is a band diagram of a peripheral book in a non-electric field state. (C),
Each of (d) shows a state in which a voltage is applied. In the central portion, there are few electron barriers from injection to electron emission, and electrons are emitted at a low threshold value. On the other hand, in the peripheral portion of the film, the band gap is small in the electron emitting portion and the energy difference from the vacuum level is large, so a large electric field is required for electron emission, and the electron emission threshold value is higher than in the central portion of the film. Therefore, when a constant voltage is applied to the gate electrode, electrons are emitted only from the central portion of the electron emission film. Furthermore, there is no clear boundary between the central part and the peripheral part, and the electric field will not be strengthened at the boundary part. Therefore, there are no electrons that collide with the insulating film on the side wall of the hole and the gate electrode and are scattered, the electrons are extracted outside the hole, and the electrons are then extracted to the anode, so that a small beam diameter can be achieved.

The electron-emitting device manufactured as described above was driven with Va arranged as shown in FIG. The actual drive voltage was Vg = 20 V, Va = 10 kV, and the distance D3 between the electron-emitting device and the anode 12 was 1 mm, so that the electron source could be formed. Here, using an electrode coated with a phosphor as the anode 12, the size of the electron beam was observed. The electron beam size referred to here is the size up to a region of 10% of the peak luminance of the phosphor that has emitted light.
As a result, the beam diameter was 200 μm, and the emission due to the scattering component, which was observed when the entire surface of the hole was formed of the same emitting material, was not observed.

Here, the electron-emitting portion has been described as an example in which the band structure is different between the central portion and the peripheral portion of the electron-emitting material, but the invention is not limited to this method and, for example, the band structure of the electron-injecting portion is changed. That is, it is possible to prepare an electron emitting material having a wide band gap so that the electron barrier is large at the peripheral portion of the emitting material and the electron barrier with the metal cathode is large. At this time, the surface of the electron-emitting material may be common, and by controlling the electron injection, the electron-emission occurs only from the central portion of the electron-emitting material in the hole, so that the same effect as in the above-mentioned embodiment is obtained. Is obtained. In addition, it is possible to create a film that has a band structure that suppresses electron conduction in the conduction part between them, in which electrons fall to a low level with a narrow band gap, and it is somewhat complicated in terms of process. However, it is needless to say that a plurality of portions of the electron emitting portion, the electron conducting portion, the electron injecting portion or all of the band structures may be changed, and similar effects can be obtained. Further, the difference in the in-plane band structure is also shown as an example which is continuous, but it is not particularly limited, and the same effect can be obtained even if it is stepwise.

[Embodiment 3] As Embodiment 3, an example in which the band structure is changed in the vertical direction will be described. The electron emission layer 5 of diamond-like carbon was deposited on the first electrode 4 by about 50 nm by the FCVA method as in the second embodiment. When forming the film, first, the voltage applied to the cathode was set to -300 V to form diamond-like carbon having a narrow band gap, and then the voltage was continuously lowered to increase the band gap to form the film. At this time, the substrate susceptor was tilted at 30 degrees with respect to the filament, and the substrate center was set to the rotation axis, and the
The film was formed by rotating and using the gate electrode as a mask so that the ion density in the central portion was higher than that in the peripheral portion. FIG. 12 shows the band structure of the central portion and the peripheral portion of the film at this time. In the central part, electrons can be transported without any very smooth barrier from injection to electron emission and reach electron emission, while in the peripheral part, the electron barrier is high at the last electron emission, and the electron emission threshold is higher than in the central part. Get higher Therefore, when a constant voltage is applied to the gate electrode, electrons are emitted only from the central portion of the electron emission film. Furthermore, there is no clear boundary between the central part and the peripheral part, and the electric field will not be strengthened at the boundary part. Therefore, there are no electrons that collide with the insulating film on the side wall of the hole and the gate electrode and are scattered, the electrons are extracted outside the hole, and the electrons are then extracted to the anode, so that a small beam diameter can be achieved. The electron-emitting device manufactured as described above was arranged and driven as shown in FIG. Drive voltage is Vg = 18V, Va
= 5 kV, the distance H between the electron-emitting device and the anode 12 is 1
mm. Here, using an electrode coated with a phosphor as the anode 12, the size of the electron beam was observed. The electron beam size referred to here is the size up to a region of 10% of the peak luminance of the phosphor that has emitted light. As a result, the beam diameter was 180 μm, and the beam diameter could be further reduced.

[Embodiment 4] Next, a fourth embodiment of the present invention will be described. FIG. 13A shows a structure having a convex structure instead of a hole structure, and the electron emission film 5 is formed on the uppermost part thereof. According to Example 1, the material and size of the electron-emitting device were set to w1 = 3 μm. However, the film thickness of the anode electrode 2 was 100 nm, the insulating layer 3 was 500 nm, and the gate electrode 4 was 2 μm. Further, the electron emission layer is not arranged on the entire surface of the upper part of the anode electrode but has a width of w2, which is 2 μm in this embodiment. The band structure used was that used in Example 2. In this embodiment, the gate electrode 4 is
Although it exists under the insulating layer 3, the same effect can be obtained by driving in the same manner as the electron-emitting device driving method applicable to the present invention.

[Embodiment 5] An image forming apparatus was manufactured using the electron-emitting devices of Embodiments 1 to 4. As an example, a case where the device of Example 1 is used is shown.

The device of Example 1 was replaced with 320 × 240 MTX.
Arranged in a shape. As for the wiring, as shown in FIG. 6, the X side was connected to the second electrode and the Y side was connected to the first electrode. Element is horizontal 200μ
m, and the pitch was 200 μm in the vertical direction. A phosphor was placed on the top of the device. As a result, it is possible to form a high-definition image forming apparatus that is capable of matrix driving.

[0116]

As described above, according to the present invention,
It is possible to provide an electron-emitting device having a small electron beam diameter, high-efficiency electron emission at a low voltage, and an easy manufacturing process.

By applying such an electron-emitting device to an electron source or an image forming apparatus, it is possible to improve the performance of the electron source or the image forming apparatus.

[Brief description of drawings]

FIG. 1 is a cross-sectional view and a plan view showing the structure of an electron-emitting device according to the present invention.

FIG. 2 is a diagram showing current-voltage characteristics of the electron-emitting device according to the present invention.

FIG. 3 is a diagram showing electron trajectories of an electron-emitting device according to the present invention.

FIG. 4 is a diagram showing an example of a method for manufacturing an electron-emitting device according to the present invention.

FIG. 5 is a plan view showing an electron-emitting device according to the present invention.

FIG. 6 is a schematic configuration diagram showing an electron source having a simple matrix arrangement according to the present invention.

FIG. 7 is a schematic configuration diagram showing an image forming apparatus using an electron source having a simple matrix arrangement according to the present invention.

FIG. 8 is a diagram showing a fluorescent film in the image forming apparatus according to the present invention.

FIG. 9 is a diagram showing a block diagram in the image forming apparatus according to the present invention.

FIG. 10 is a diagram showing an electron emission threshold of the electron emitting device according to the present invention.

FIG. 11 is a band diagram of an electron emitting material of an electron emitting device according to the present invention.

FIG. 12 is a band diagram of an electron emitting material of an electron emitting device according to the present invention.

FIG. 13 is a cross-sectional view showing the structure of an electron-emitting device according to the present invention.

FIG. 14 is a cross-sectional view schematically showing an example of a conventional Spindt type electron-emitting device.

FIG. 15 is a diagram showing an example of a method for manufacturing a conventional Spindt-type electron-emitting device.

FIG. 16 is a sectional view schematically showing an example of a conventional Spindt-type electron-emitting device with a focusing electrode.

[Explanation of symbols]

1 substrate 2 High potential electrode 3 insulating layers 4 Low potential electrode 5 Electron-emitting device 6 control circuit 7 Anode 8 high voltage power supply 51 microchips 61 equipotential surface 71 Sacrificial layer 81 Microchip material 61,81 electron source substrate 62 X-direction wiring 63 Y direction wiring 64,84 Electron emitting device 65,95 connection 91 Rear plate 92 Support frame 93 glass substrate 94 Fluorescent film 95 metal back 96 face plate 97 Package 86 Black conductive material 85 high voltage terminal 1301 image display panel 1302 scanning circuit 1303 control circuit 1304 shift register 1305 line memory 1306 Sync signal separation circuit 1307 Modulation signal generator

Claims (15)

[Claims] 1. A first conductive layer formed on an insulating substrate, an insulating layer laminated on the first conductive layer, and a second conductive layer laminated on the insulating layer. Layer, a through hole formed on the first conductive layer so as to penetrate from the insulating layer to the second conductive layer, and an electron emission layered on the first conductive layer in the through hole. An electron-emitting device that emits electrons from the electron-emitting layer when a voltage is applied between the first conductive layer and the second conductive layer. The electron emission element is characterized in that the amount of electrons emitted from the layer is larger in the central portion of the surface of the through hole than in the peripheral portion of the surface that emits electrons. 2. The electron-emitting device according to claim 1, wherein an electron-emission threshold value in a central portion of a surface which emits electrons facing the inside of the through hole is lower than an electron-emission threshold value in the peripheral portion. 3. The electron-emitting device according to claim 1, wherein a band structure is different between a central portion and a peripheral portion of a surface which emits electrons facing the inside of the through hole. 4. The electron-emitting device according to claim 3, wherein a band structure continuously changes from a central portion of a surface of the through hole which emits electrons to a peripheral portion thereof. 5. The electron-emitting device according to claim 3, wherein the band structure is changed stepwise from the central portion of the surface which emits electrons facing the inside of the through hole to the peripheral portion. 6. The work function of a central portion of a surface, which faces the inside of the through hole and emits electrons, is smaller than a work function of the peripheral portion. The electron-emitting device described. 7. A band gap in a central portion of a surface which emits electrons facing the inside of the through hole is wider than a band gap in a peripheral portion of the electron emitting layer.
6. The electron-emitting device according to any one of 6. 8. The electron barrier in a portion of the electron emission layer that is in contact with the first conductive layer is lower in the central portion than in the peripheral portion of the surface that faces the inside of the through hole and emits electrons. The electron-emitting device according to any one of claims 1 to 7, which is characterized in that. 9. The electron-emitting device according to claim 1, wherein a band structure is changed in a thickness direction of the electron-emitting layer. 10. The electron-emitting device according to claim 1, wherein the electron-emitting material contains carbon as a main component. 11. The electron-emitting device according to claim 10, wherein the electron-emitting material contains at least one of diamond and diamond-like carbon. 12. An electron source formed by arranging a plurality of electron-emitting devices according to any one of claims 1 to 11. 13. The electron source according to claim 12, wherein the electron emitters are formed by matrix wiring. 14. An image forming apparatus comprising: the electron source according to claim 12 or 13; and an image forming member that forms an image by electrons emitted from the electron source. 15. The image forming apparatus according to claim 14, wherein the image forming member is a phosphor that emits light by collision of electrons.