JP2003016906A - Electron emitting element, electron source and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a field emission type electron emitting element capable of performing an efficient electron emission at a low voltage and being manufactured by an easy process, and having a large electron emitting area, an electron source and an image forming device. SOLUTION: An electron emission layer formed of an electron emitting material located within the opening of an insulating layer and arranged on a cathode electrode is formed so that the band gap of an electron injection part to come into contact with the cathode in the electron emission layer smaller than the band gap of the electron emission part on the opening side of the insulating layer in the electron emission layer, and the change rate dE/dW of the band gap of the electron emission material having a thickness directional distance W from the cathode electrode within the electron emission layer is not the maximum in the electron injection part.

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. Mead,
"Operation of Tunnel-Emis
sion Devices ", J. Apply. Phy
s. , 32, 646 (1961) and the like are known.

In a recent example, Toshiaki.
Kusunoki, "Fluctuation-fre
e electron emission from
non-formed metal-insulato
r-metal (MIM) cathodes Fabr
icated by low current Ano
dic oxidation ”, Jpn. J. App
l. Phys. vol. 32 (1993) pp. L16
95, Mutsumi Suzuki et al "An
MIM-Cathode Array for Ca
theode luminescent display
s ", IDW'96, (1996) pp. 529, etc. have been studied.

[0006] As an example of the surface conduction type, as reported by Elinson (MI Elinson Radio Eng. E.
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, 317 (1972)), In ₂ O ₃ / S
nO ₂ thin film (M. Hartwell and
C. G. Fonstad, IEEE Trans. ED
Conf. 519 (1983)) and the like have been reported.

[0007]

In order to apply the electron-emitting device to the image forming apparatus, an emission current for causing the phosphor to emit light with sufficient brightness is required, and the emission current control is low for low power consumption. It is particularly important that it can be driven by voltage. It is also important to be easy to manufacture. From such a viewpoint, a cold cathode electron source has been mainly developed for the image forming apparatus. However, there are still problems in the following points, and an image forming apparatus that can sufficiently satisfy the above requirements has not been created.

The MIM type is a lower electrode (cathode electrode layer)
In this structure, an insulating layer is arranged between the upper electrode and the upper electrode (gate electrode layer), and a voltage is applied between both electrodes to extract electrons. A small electron beam diameter can be realized because the direction of the internal electric field coincides with the direction of the emitted electrons and the potential distribution on the emission surface is not distorted, but electron scattering occurs at the insulating layer and the upper electrode. It is generally inefficient, which is not very preferable for low power consumption.

On the other hand, as an example of the conventional FE type, Spind
A t-type electron-emitting device is shown in FIG. In FIG.
1 is a substrate, 2 is a cathode electrode (low potential electrode), 3 is an insulating layer, 4 is a gate electrode (high potential electrode), 51 is a microchip, and 61 is an equipotential surface. When a bias is applied between the microchip 51 having the curvature r and the gate electrode layer 4, electrons are emitted from the portion of the tip of the microchip 51 where the electric field is concentrated and head toward the anode, so that low voltage driving is possible.
The amount of emitted electrons depends on the gate electrode layer 4 and the microchip 51.
It is determined by the tip distance d, the gate voltage Vg, and the work function of the emitting material. That is, the performance of the device is determined by controlling the distance d between the gate electrode layer 4 and the microchip 51 with good control.

FIG. 17 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 2 made of Nb or the like, an insulating layer 3 made of SiO ₂ or the like, and a gate electrode layer 4 made of Nb or the like are formed on a substrate 1 made of glass or the like. Stack in order.

Then, by the reactive ion etching method,
A circular fine hole penetrating the gate electrode layer 4 and the insulating layer 3 is formed (FIG. 17A).

After that, the sacrificial layer 7 made of aluminum or the like is used.
1 is formed on the gate electrode layer 4 by oblique vapor deposition or the like (FIG. 17B).

A microchip material 81 such as molybdenum is deposited on the structure thus formed by a vacuum vapor deposition method. Here, the deposits on the sacrificial layer block the fine holes as the deposition progresses, and the microchips 51 are formed in a conical shape in the fine holes (FIG. 17C).

Finally, by melting the sacrificial layer 71,
The microchip material 81 is lifted off to complete the device (FIG. 17D).

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 during lift-off short-circuits the microchip 51 and the gate electrode layer 4, and when a voltage is applied between the microchip 51 and the gate electrode layer 4 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 of brightness when applied as an image forming apparatus, for example, and is very annoying.

Further, 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 is 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.

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

There is a method of realizing low voltage driving without forming a microchip such as a Spindt type. For example, JP-A-8-096703 and JP-A-8-096703.
No. 096704 and Japanese Patent Application Laid-Open No. 8-264109 are available.

This is a method of emitting electrons from the thin film arranged in the hole, and has an advantage that the manufacturing method is relatively simple. Furthermore, since the electron emission is performed on the surface,
The concentration of the electric field does not occur, the chip does not break, and the life is long.

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. In particular, recently, as a low work function constituent material, diamond whose electron affinity is said to be close to 0 or negative,
Carbon-based materials such as diamond-like carbon, which has a work function larger than that of diamond but can be produced at a low temperature, have been attracting attention and have been attempted as various electron-emitting devices.

However, even if such a low work function material is used, the energy gap must be overcome in some way in order to inject electrons from the cathode electrode, which is a metal material, and finally draw it out into a vacuum. For example, in the case of diamond, electron injection is said to be extremely difficult. A brief description will be given with reference to FIGS.

FIG. 18 is a schematic diagram of a band gap when diamond is used as an electron emitting material. Ec, Ef, E
v represents a conductor, a Fermi level, and a valence band,
Vac represents a vacuum level. (A) is a band diagram in a state where no voltage is applied, and (b) is a band diagram in a state where a positive voltage is applied to the surface side. As is clear from this figure, since Ec is higher than Vac in the electron emission portion, it does not serve as a barrier for electrons and electron emission is easy, but
At the electron injection part, the electron barrier from the metal electrode to the diamond is very high and the electron cannot be injected, so that the electron cannot be emitted at a low voltage.

FIG. 19 is proposed in Japanese Patent Laid-Open No. 11-154455 to solve this problem. Here, by making the band gap of the electron emission portion wider than that of the electron injection portion, it is possible to perform electron injection to electron emission at a low voltage. However, the electron barrier still remains in the electron injection part, and it is not satisfactory as a device that can sufficiently emit electrons at a low voltage.

The present invention has been made in order to solve the above-mentioned problems of the prior art, and an object of the present invention is to provide a high-efficiency electron emission at a low voltage and a field emission type which is easy to manufacture. An object is to provide an electron-emitting device, an electron source, and an image forming apparatus.

[0025]

In order to achieve the above object, an electron-emitting device according to the present invention has a cathode electrode,
An insulating layer arranged on the cathode electrode and having an opening; a gate electrode arranged on the insulating layer and having an opening communicating with the opening of the insulating layer; and a cathode located in the opening of the insulating layer, the cathode In the electron emission device having an electron emission layer arranged on the electrode, the band gap of the electron injection part in contact with the cathode electrode in the electron emission layer is smaller than the band gap of the electron emission part in the electron emission layer. Characterize.

In the electron emission layer, it is preferable that the rate of change dE / dW of the band gap E at a position where the distance from the cathode electrode in the film thickness direction is W is not the maximum in the electron injection portion.

The rate of change dE / dW may be 0 or negative in the electron injection section.

The rate of change dE / dW may take a maximum value in a substantially central portion of the electron emission layer in the film thickness direction.

The rate of change dE / dW may be minimized in the electron injection section.

The rate of change dE / dW may change continuously.

The rate of change dE / dW may change stepwise.

There may be a portion where the change rate dE / dW changes continuously and a portion where the change rate changes stepwise.

It is preferable that the electron emitting layer contains carbon as a main component.

It is preferable that the electron emission layer contains graphite as a main component.

It is preferable that the electron emission layer contains diamond-like carbon or diamond.

The electron emission layer is a thin film and is arranged substantially parallel to the anode electrode for accelerating and collecting the electrons emitted from the electron emission element.

The electron source of the present invention is characterized in that a plurality of the electron-emitting devices are arranged.

It is preferable that the electron-emitting devices are arranged in a matrix and wired.

The image forming apparatus of the present invention is characterized by including the electron source and an image forming member for forming an image by the electrons emitted from the electron source.

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

Therefore, the electron-emitting device, the electron source, and the image forming apparatus having the features of the present invention can be driven at a low voltage and become a low power consumption device with less deterioration.

[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 band diagram of an electron-emitting device having the most basic structure of the present invention. FIG. 2 is a schematic sectional view and a plan view of the element of the present invention. Further, FIG. 3 is a diagram showing the relationship between the drive voltage and the current when this element is driven (ON-OFF state).

In FIG. 2, 1 is a substrate, 2 is a cathode electrode which is a first electrode, 3 is an insulating layer, 4 is a gate electrode which is a second electrode, and 5 is an electron emission layer.

W1 is the opening width of the gate electrode 4 (including the electron emission layer 5), h1 is the thickness of the insulating layer 3, and H is the distance between the anode electrode 7 and the cathode electrode.

Vg is the cathode electrode 2 and the gate electrode 4
The voltage applied between (including the electron emission layer 5), Va is the voltage applied between the cathode electrode 2 and the anode electrode 7, Ie is the electron emission current, and Eh is the electric field formed by Vg.

When Vg and Va are applied to drive the device, an electric field Eh is formed, and the shape of the equipotential surface inside the hole is determined by Vg, W1, h1, the shape, the dielectric constant of the insulating layer and the like. Outside the hole, the gate electrode 4 and the anode electrode 7 mainly form substantially parallel equipotential surfaces.

Referring to FIG. The symbols shown are the same as those in FIGS. (A) and (b) are shown in FIG.
Similar to 8 and 19, (a) is a no-voltage state, and (b) is a voltage applied state. In this embodiment, an example of diamond-like carbon will be described. In the present embodiment, as shown in FIG. 1, the band gap of the electron emitting portion is larger than the band gap of the electron injecting portion, and the rate of change of the band gap is different. That is, the bandgap does not change so much in the electron injection portion, and the bandgap increases with a gradual change amount. On the other hand, the band gap in the electron emission portion rapidly increases, and the surface finally approaches the vacuum level.

Here, let E be the bandgap of the electron-emitting material whose distance from the cathode electrode in the film thickness direction is W, and pay attention to its rate of change dE / dW.

In FIG. 4, the film thickness (0
Is an electron injection part, 100 is an electron emission part), and the vertical axis represents the bandgap change rate dE / dW in the film thickness direction. This rate of change is small in the electron injection part. By doing so, a tunnel current easily flows in the electron injection portion, and it becomes possible to easily inject electrons into the conductor of the diamond-like carbon film. Furthermore, finally, since the work function of the electron emission portion is small, the electron emission can be performed in a low electric field, and the electron emission can be performed at a low voltage as a whole.

That is, if the rate of change dE / dW in the electron injection portion is not the maximum compared to other regions, the rate of change dE / d
As compared with the case where dW is constant, a tunnel current easily flows in the electron injection portion, and electrons can be easily injected into the conductor of the diamond-like carbon film.

FIG. 3 is a graph of voltage-current characteristics of the diamond-like carbon film formed by the above-mentioned formation.
For comparison with the present invention, an element (X) in which diamond-like carbon is formed so as to have a uniform band gap from the electron injection part to the electron emission part, and dE / dW from the electron injection part to the electron emission part A device (Y) in which the bandgap is gradually widened to a constant value and diamond-like carbon is formed so that the bandgap at the electron emission part is the same as the bandgap at the electron emission part of the device (X). Are also shown. According to the present invention, it was possible to emit electrons at a low voltage.

Here, an example in which the band gap is continuously changed is shown, but the invention is not particularly limited, and it may be continuous or stepwise. Also, both may be mixed. Also, dE / dW
Needless to say, even if is 0 in the electron injection part, it does not violate the essence of the present invention, and further, dE / dW may be negative.

Further, the electron emission area on the device of the present invention is the entire surface of the electron emission layer 5, and since the electron emission area is wide, it has good durability against ion bombardment existing in vacuum.

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 a method of manufacturing the electron-emitting device according to the embodiment of the present invention will be described with reference to FIG. Needless to say, the manufacturing method is not limited to this.

First, the surface of which is thoroughly washed in advance, quartz glass, glass in which the content of impurities such as Na is reduced,
Si on blue plate glass, silicon substrate, etc. by sputtering
Any one of a laminated body in which O ₂ is laminated and an insulating substrate made of ceramics such as alumina is used as the substrate 1, and the cathode electrode 2 is laminated on the substrate 1.

The cathode 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 cathode electrode 2 is, for example, B
e, Mg, Ti, Zr, Hf, V, Nb, Ta, Mo,
Metal or alloy material such as W, Al, Cu, Ni, Cr, Au, Pt, Pd, TiC, ZrC, HfC, TaC, S
Carbides such as iC and WC, HfB ₂ , ZrB ₂ , LaB ₆ ,
Borides such as CeB ₆ , YB ₄ and GdB ₄ , TiN, Zr
It is appropriately selected from nitrides such as N and 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 cathode electrode 2 is several tens nm.
To several mm, and preferably selected from several hundred nm to several μm.

Then, as shown in FIG. 5B, an insulating layer 3 is deposited subsequent to the cathode 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. Preferred materials are SiO ₂ and S
A material having a high breakdown voltage capable of withstanding a high electric field such as iN, Al ₂ O ₃ , CaF, and undoped diamond is desirable.

Further, the gate electrode 4 is deposited subsequent to the insulating layer 3. The gate electrode 4 has conductivity like the cathode electrode 2, and is formed by a general vacuum film forming technique such as a vapor deposition method and a sputtering method, and a photolithography technique.
The material of the gate electrode 4 is, for example, Be, Mg, Ti, Z.
r, Hf, V, Nb, Ta, Mo, W, Al, Cu, N
Metal or alloy material such as i, Cr, Au, Pt, Pd, T
Carbides such as iC, ZrC, HfC, TaC, SiC, and WC, HfB ₂ , ZrB ₂ , LaB ₆ , CeB ₆ , YB ₄ , G
It is appropriately selected from borides such as dB ₄ , nitrides such as TiN, ZrN and HfN, semiconductors such as Si and Ge, organic polymer materials and the like. The thickness of the gate electrode 4 is set in the range of several nm to several μm, preferably several nm to several hundreds n.
It is selected in the range of m.

The cathode electrode 2 and the gate electrode 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. 5C, a mask pattern 41 is formed by the photolithography technique.

Then, as shown in FIG. 5D, a laminated structure is formed in which each insulating layer 3 and part of the gate electrode 4 are 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.

In the etching process, each insulating layer 3,
The etching method may be selected according to the materials of the gate electrode 4 and the cathode electrode 2.

Then, the electron emission layer 5 is formed as shown in FIG. Electron emitting materials are evaporation method, sputtering method, CVD
It is formed by a general film forming technique such as a method. Electron emission layer 5
The material 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 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, the electron emitting material for producing the structure of the present invention is selected. The electron emission material is formed by changing the band gap of the. 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 is changed or the irradiation energy is changed (for example, M. Weier et.al. Physical Re
viewB, Vol.53, Number3 15 / January 1996 P.159
4), the irradiation ion density is changed, and when a gas is used, the gas type and gas flow rate (for example, R. Kleber et.al. Diamond and
It can be controlled by changing Related Materials, 2 (1993) p.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.

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

The width W1 of the opening of the insulating layer in the cathode electrode 2 (including the electron emission layer 5) is determined by the material and resistance of the device, the work function and drive voltage of the material of the cathode electrode 2, and the required electron. It is appropriately set according to the shape of the emission beam. Usually, W1 is selected from the range of several hundred nm to several hundred μm.

Further, as shown in FIG. 14, a plurality of the holes may be arranged to form one pixel. Insulation film height h1
The thickness of the electron emission material is also the material and the resistance value that make up the device,
The work function and drive voltage of the material of the electron-emitting device and the required shape of the electron-emitting beam are set as appropriate. Usually h
1 is selected from the range of several hundreds nm to several tens μm, and is selected from the range of several hundreds nm to several tens μm depending on the thickness of the electron emission material 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. The simple matrix arrangement will be described in detail below.

An electron source obtained by 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, 61 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 X-direction wirings 62 are Dx1 and Dx.
2, ... Dxm, and can be composed 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 body 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 by m wires in the X direction 62, n wires in the Y direction 63, and connections (not shown) made of a conductive metal or the like. It is connected.

The material forming the X-direction wiring 62 and the Y-direction wiring 63, the material forming the wire connection, and the material forming the pair of element electrodes may be the same or may be the same as some or all of the constituent elements. It can 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 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 diagram showing an example of a display panel of the image forming apparatus.

In FIG. 7, 81 is an electron source substrate on which a plurality of electron-emitting devices are arranged, 91 is a rear plate on which the electron source substrate is fixed, and 96 is a fluorescent film as a fluorescent material which is an image forming member on the inner surface of a glass substrate 93. The face plate 94 and the metal back 95 are formed. Reference numeral 92 denotes a support frame, and a rear plate 91 and a face plate 96 are connected to the support frame 92 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 an X-direction wiring and a 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 of the present invention, the phosphor 85 (fluorescent film 94) is aligned and arranged above the electron-emitting device 84 in consideration of the emitted electron trajectory. FIG. 8 shows the fluorescent film 9 used for the panel of the present case.
It is a schematic diagram which shows 4. 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.

The purpose of providing the black stripes and the black matrix is to make the color mixture, for example, inconspicuous by blackening the separately applied portions between the phosphors 85 of the three primary color phosphors required for color display. 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 phosphor 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 acceleration voltage, and to protect the phosphor 85 from damage due to collision of negative ions generated in the envelope. Etc. The metal back 95, after forming the fluorescent film, smoothes the inner surface of the fluorescent film (generally called “filming”).
And then depositing Al using vacuum deposition or the like.

On the face plate 96, a transparent electrode (not shown) may be provided on the outer surface side of the fluorescent film 94 in order to further enhance the conductivity of the fluorescent film 94.

In the present invention, since the electron beam reaches directly above the electron-emitting device 84, the fluorescent film 94 is positioned and arranged directly above the electron-emitting device 84.

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 because the getter placed at a predetermined position (not shown) in the envelope 97 is heated by resistance heating or high-frequency heating immediately before or after the envelope 97 is sealed. Then, it is a process of forming a vapor deposition film. 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 steps, the external terminals Dx1 to Dxm and Dy1 to Dy1 to each electron emitting element are formed.
By applying a voltage via Dyn, electron emission occurs.

Va is a metal back 9 via a high voltage terminal.
5 or a high voltage is applied to the transparent electrode (not shown) 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 an NTSC system television signal 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, 1
301 is an image display panel, 1302 is a scanning circuit, 1
303 is a control circuit, 1304 is a shift register, 130
5 is a line memory, 1306 is a sync signal separation circuit, 13
Reference numeral 07 is a modulation signal generator, and Vx and Va are DC voltage sources.

The display panel 1301 includes terminals Dox1 to Doxm, terminals Doy1 to Doyn, and a high voltage terminal H.
It is connected to an external electric circuit via v. Terminal Dox
1 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.

A modulation signal for controlling the output electron beam of each element of the electron-emitting devices in one row selected by the scanning signal is applied to the terminals Doy1 to Doyn.
The high-voltage terminal Hv receives, for example, 10 k from the DC voltage source Va.
A DC voltage of [V] 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 (schematically shown 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 Dox1 to Doxm of the display panel 1301. Each of the switching elements S1 to Sm has a 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 receives the synchronization signal Tsyn sent from the synchronization signal separation circuit 1306.
Based on c, Tscan, Tsft, and Tmry control signals are generated for each unit.

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 is composed of a vertical sync signal and a horizontal sync signal, but is shown here as a Tsync signal for convenience of explanation. The luminance signal component of the image separated from the television signal is represented as a DATA signal for convenience. The DATA signal is transferred to the shift register 1304.
Entered in.

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. The control signal Tsft can be said to be 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 a control signal Tmry sent from the control circuit 1303.
Accordingly, the contents of Id1 to Idn are stored as appropriate.
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. It is applied to the electron-emitting device in the display panel 1301 through Doyn.

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, electron emission does not occur even if a voltage below the electron emission threshold is applied, but when a voltage above the electron emission threshold is applied, an electron beam is emitted. Is output. At that time, the applied voltage Vf
It is possible to control the intensity of the output electron beam by changing. When a pulse voltage is applied to this element, the electron beam intensity can be controlled by changing the pulse height Ph, and the total amount of charges of the electron beam output can be controlled by changing the pulse width Pw. It is possible.

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 1307 compares, for example, a high-speed oscillator and a counter for counting the number of waves output by the oscillator and the output value of the counter with the output value of the memory. A circuit is used that is a combination of comparators. 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 is mentioned, but the input signal is not limited to this, and the PAL, SECAM, etc.
More than this, TV signals (eg,
High-definition TV) systems such as the MUSE 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.

[0114]

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

Example 1 FIG. 1 is a sectional view of an electron-emitting device prepared according to this example, and FIG. 2 is an example of a plan view.
FIG. 5 shows an example of a method for 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, a substrate 1 made of quartz was sufficiently washed, and then Ta having a thickness of 500 nm was formed as a cathode electrode 2 by a sputtering method.

(Step 2) Next, as shown in FIG. 5B, SiO _{2 having} a thickness of 600 nm was deposited as the insulating layer 3, and Ti having a thickness of 100 nm was deposited as the gate electrode 4 in this order.

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

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

(Step 5) Next, as shown in FIG. 5E, an electron emission layer 5 of diamond-like carbon was deposited on the cathode electrode 2 to a thickness of about 100 nm by the hot filament CVD (HFCVD) method. Reaction gas is CH ₄
A mixed gas of H ₂ and H ₂ was used. At the time of film formation, first, the voltage applied to the cathode was set to −2 KV to form diamond-like carbon having a narrow bandgap, and then the voltage was continuously increased to increase the bandgap for film formation. At this time, the voltage was changed slowly at first and then rapidly, and the band gap was changed rapidly.

(Step 6) Next, as shown in FIG. 5F, the mask pattern 41 was completely removed, and the electron-emitting device of this example was completed.

The electron-emitting device produced as described above was driven with Va arranged as shown in FIG.

FIG. 3 is a graph of voltage-current characteristics of the diamond-like carbon film formed by the above-mentioned formation.
For comparison with the present invention, an element (X) in which diamond-like carbon is formed so as to have a uniform band gap from the electron injection part to the electron emission part, and dE / dW from the electron injection part to the electron emission part A device (Y) in which the bandgap is gradually widened to a constant value and diamond-like carbon is formed so that the bandgap at the electron emission part is the same as the bandgap at the electron emission part of the device (X). Are also shown. According to the present invention, it was possible to emit electrons at a low voltage.

The actual drive voltage is Vg = 20V, Va =
An electron source could be formed with 10 kV and a distance D3 between the electron-emitting device and the anode 12 set to 1 mm.

Here, the electron emitting portion is described as a substantially circular hole as shown in FIG. 2, but it is not particularly limited. For example, it may be formed in a line shape as shown in the plan view of FIG. Absent. The manufacturing 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.

(Second Embodiment) A second embodiment will be described with reference to FIG. FIG. 10 shows a band diagram of the electron emitting material similarly to FIG. In this embodiment, in order to further enhance the injection effect, the band gap at the electron injection portion is made smaller as the distance from the injection portion increases. The manufacturing method is basically the same as that of the first embodiment and is formed by the HFCVD method.
The band change is created by controlling the substrate voltage during film formation. After the film formation is first started at -2KV, the voltage is further reduced once to -3KV, and then the voltage is controlled to -100V. It was changed to form diamond-like carbon having the band structure shown in FIG.

That is, as compared with the rate of change dE / dW at the electron injection portion, after forming an electron emission layer having a smaller rate of change dE / dW, the band is maintained at a constant dE / dW up to the electron emission portion. Diamond-like carbon was formed so that the gap gradually widened.

Since this structure has a bandgap that decreases once, the key is how accurately the potential gradient can be formed in the situation where the film thickness is thin. It's a little difficult to create, but it's very effective.

(Third Embodiment) A third embodiment will be described with reference to FIG. FIG. 11 shows a band diagram of the electron emitting material similarly to FIG. In this embodiment, in order to further improve the electron emission characteristic, the band gap change in the electron emission portion is made small and the electron emission characteristic is designed to have energy in the vicinity of the electron emission portion. The injection part had a band structure similar to that of the first embodiment. The manufacturing method is basically the same as that of the first embodiment, and is formed by the HFCVD method. The band change is created by controlling the substrate voltage during film formation. After starting film formation at -2KV, the voltage is further reduced once to -3KV, and then the voltage is controlled to -100V. Particularly, in the vicinity of the last electron emitting portion, diamond-like carbon having the band structure shown in FIG. 11 was formed by gradually changing the voltage so that the band gap becomes uniform.

That is, the bandgap change rate dE / dW
The diamond-like carbon was formed so that the maximum value was at approximately the center of the electron emission layer in the film thickness direction.

Similar to the second embodiment, this structure is very important to control the film thickness, and has a great effect on improving the efficiency of electron emission characteristics.

(Fourth Embodiment) A fourth embodiment will be described with reference to FIGS. In the present embodiment, unlike the first to third embodiments, an example in which the band structure of the electron emitting material is discontinuous on the way will be described. 12 and 13 are band diagrams of the electron emitting material similarly to FIG. 1, and the same notations have the same meanings. In this embodiment, plasma assisted CVD (PA
A diamond-like carbon film was formed by the CVD method.

In FIG. 12, a C ₂ H ₂ gas is used in the electron injection part to form a diamond-like carbon film of 2 nm with a negative rate of change, and then the gas species is changed to CH ₄ gas,
A mixed gas of H ₂ gas and N ₂ gas, the temperature of which is from room temperature to 600
The electron-emitting material was formed by changing the temperature from 0.degree. C. to n-type diamond-like carbon with wide bandgap and changing to diamond. Further, FIG. 13 shows an example in which the rate of change of the band gap of the wide band gap film is made small to make the injection rate into the wide band gap film easy.

Here, an example in which the band gap of both films is gradually changed is shown, but the invention is not particularly limited, and even if there is a region where the band gap is not changed, it is in accordance with the gist of the present invention. In addition, although an example of a two-layer structure is shown, it is needless to say that this is not particularly limited and three or more layers may be used.

Needless to say, the present invention can be applied not only to this embodiment but also to the Spindt type shown in the conventional example, and similar effects can be obtained.

(Fifth Embodiment) Next, a fifth embodiment of the present invention will be described. FIG. 15A has a structure having a convex structure instead of a hole structure, and the electron emission layer 5 is formed on the uppermost part thereof.

The material and size of the electron-emitting device are
According to Example 1, w1 = 3 μm. However, the film thickness is
The anode electrode 2 is 100 nm, the insulating layer 3 is 500 nm,
The gate electrode 4 was 2 μm. Further, the electron emission layer 5 is
The width w2 is not arranged over the entire surface of the anode electrode, but is 2 μm in this embodiment. The band structure is Example 1
I used the one used in. In this embodiment, the gate electrode 4 is present in the lower part through the insulating layer 3, but if driven in the same manner as in the electron-emitting device driving method applicable to the present invention,
The same effect can be obtained.

(Example 6) An image forming apparatus was prepared using the electron-emitting devices of Examples 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. 7, the X side was connected to the first electrode and the Y side was connected to the second electrode. Element is horizontal 300μ
m, and the length was 300 μm. A phosphor was placed on the top of the device. The gradation is a time gradation and the gate voltage is 2
It was driven at 0V. Since it can be driven at a low voltage, power consumption can be suppressed, matrix driving is possible, and a high-definition image forming apparatus can be formed.

[0140]

As described above, according to the present invention, it is possible to provide an electron-emitting device capable of emitting electrons with high efficiency at a low voltage, having an easy manufacturing process and having a large electron-emitting area.

Further, when such an electron-emitting device is applied to an electron source or an image forming apparatus, it is possible to realize an electron source and an image forming apparatus with low power consumption and excellent performance.

[Brief description of drawings]

FIG. 1 is a band diagram showing a configuration of an electron-emitting device according to the present invention.

2A and 2B are a cross-sectional view and a plan view showing the structure of an electron-emitting device according to the present invention.

FIG. 3 is a diagram showing current-voltage characteristics of the electron-emitting device according to the present invention.

FIG. 4 is a diagram illustrating a band structure of an electron-emitting device according to the present invention.

FIG. 5 is a diagram showing an example of a method for manufacturing 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 block diagram of an image forming apparatus using an electron source having a simple matrix arrangement according to the present invention.

FIG. 10 is a diagram illustrating a band structure of an electron-emitting device according to another embodiment of the present invention.

FIG. 11 is a diagram illustrating a band structure of an electron-emitting device according to another embodiment of the present invention.

FIG. 12 is a diagram illustrating a band structure of an electron-emitting device according to another embodiment of the present invention.

FIG. 13 is a diagram illustrating a band structure of an electron-emitting device according to another embodiment of the present invention.

FIG. 14 is a plan view of an electron-emitting device according to an embodiment of the present invention.

FIG. 15 is a sectional view of an electron-emitting device according to another embodiment of the present invention.

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

FIG. 17 is a diagram showing an example of a method for manufacturing a conventional Spindt-type electron-emitting device.

FIG. 18 is a diagram illustrating a band structure of a conventional electron-emitting device.

FIG. 19 is a diagram illustrating a band structure of a conventional electron-emitting device.

[Explanation of symbols]

1 substrate 2 Cathode electrode (cathode electrode layer) 3 insulating layers 4 Gate electrode (gate electrode layer) 5 Electron emission layer 6 control circuit 7 Anode electrode 8 high voltage power supply

Claims (16)

[Claims] 1. A cathode electrode, an insulating layer disposed on the cathode electrode and having an opening, a gate electrode disposed on the insulating layer and having an opening communicating with the opening of the insulating layer, and the insulating layer. An electron emission layer located in the opening of the electron emission layer disposed on the cathode electrode, and a band gap of an electron injection portion in contact with the cathode electrode in the electron emission layer is An electron-emitting device characterized by having a band gap smaller than that of the emission portion. 2. The rate of change dE / dW of the band gap E at a position where the distance from the cathode electrode in the film thickness direction is W in the electron emission layer is not the maximum in the electron injection portion. The electron-emitting device according to claim 1. 3. The electron-emitting device according to claim 1, wherein the rate of change dE / dW is 0 or negative in the electron injection part. 4. The electron-emitting device according to claim 1, wherein the rate of change dE / dW has a maximum value at a substantially central portion of the electron-emitting layer in a film thickness direction. 5. The rate of change dE / dW is minimized in the electron injecting section.
An electron-emitting device according to item. 6. The electron-emitting device according to claim 1, wherein the rate of change dE / dW changes continuously. 7. The electron-emitting device according to claim 1, wherein the change rate dE / dW changes stepwise. 8. The electron-emitting device according to claim 1, wherein there is a portion where the change rate dE / dW changes continuously and a portion where the change rate changes stepwise. 9. The electron emitting device according to claim 1, wherein the electron emitting layer contains carbon as a main component. 10. The electron emitting device according to claim 1, wherein the electron emitting layer contains graphite as a main component. 11. The electron-emitting device according to claim 1, wherein the electron-emitting layer contains diamond-like carbon or diamond. 12. The electron emission layer is a thin film, and is arranged substantially parallel to an anode electrode for accelerating and collecting electrons emitted from the electron emission device.
12. The electron-emitting device according to any one of items 1 to 11. 13. An electron source comprising a plurality of electron-emitting devices according to claim 1 arranged therein. 14. The electron source according to claim 13, wherein the electron-emitting devices are arranged and wired in a matrix. 15. An electron source according to claim 13 or 14,
And an image forming member that forms an image by electrons emitted from the electron source. 16. The image forming apparatus according to claim 15, wherein the image forming member is a phosphor that emits light by collision of electrons.