JP2000100317A - Field electron emission device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To orient carbon nano-tubes at a high density, by producing the carbon nano-tubes on one surface of a substrate by heating a substrate made of a covalent carbide under vacuum, so that they extend from the flat surface of the substrate in one direction toward a positive electrode. SOLUTION: Nano-tubes 40, made of carbon atoms only, are produced and oriented in one direction from within a substrate toward its upper surface by heating, under vacuum, the substrate made of a covalent carbite, a compound of carbon and a non-metallic element. A graphite layer 42 with a non-cylindrical flat network structure of carbon atoms is formed on the side surfaces and an under surface of a substrate part 36 with an upper surface 38 thereof excluded. Accordingly, all the surfaces of the substrate part 36 are covered by the conductive nano-tubes 40 or the graphite layers 42. an field emission-type display device(FED) can be thereby obtained, which is equipped with an emitter 28 having a high current density and uniform characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a field emission display (FED), a cathode ray tube (CaD).
The present invention relates to a field electron emission device used for an electron beam source such as a cathode ray tube (CRT), a flat lamp, and an electron gun.

[0002]

2. Description of the Related Art For example, a field electron emission device that emits electrons from an electron source (emitter) toward an anode in a vacuum by field emission is a display device or a light emitting device that excites a phosphor with the electrons, or an electric field microscope. Are suitably used for electron guns and the like. Here, "field emission (field electron emission)"
This means that electrons are drawn from the surface of a solid to a vacuum level using a quantum mechanical tunneling phenomenon by the action of a strong electric field. The energy difference between the vacuum level and the surface of a metal or semiconductor is represented by a work function φ. For example, in a normal metal material, the work function φ is as large as several (eV). Never jump into the vacuum. However, if the potential level is reduced by lowering the vacuum level by applying a strong electric field from the outside, electrons stochastically jump into the vacuum due to the tunnel effect. This is field emission, and the smaller the work function φ, the more electrons can be emitted with a smaller electric field.

Conventionally, as the above-mentioned field electron emission device, for example, a molybdenum film formed on a silicon substrate is used.
An emitter composed of a cone (eg, Spindt et a
l. "Physical properties of thin-film field emission
cathodes with molybdenum cones ", J. Appl. Phys., Vol.
47, No. 12, 1976, pp. 5248-5263, etc.) and those composed of an emitter made of diamond formed on a molybdenum substrate by CVD (for example, Xu et al. "FIELD-DEPEND").
ENCE OF THE AREA-DENSITY OF `COLD 'ELECTRONEMISSIO
N SITES ON BROAD-AREA CVD DIAMOND FILMS ", Electroni
cs Letters, 2nd September 1993 Vol.29 No.18, pages 1596 to 1597, etc.) and an emitter composed of a silicon single crystal cone (whisker) coated on its surface with a polycrystalline diamond film by plasma CVD or the like (Eg Liu et al. "Electron emission from diamond
coated silicon field emitters ", Appl.Phys.Lett.65 (2
2), 28 November 1994, pages 2842 to 2844).

[0004] However, the above-mentioned conventional field emission device has a problem that a high emission current value and efficiency cannot be obtained because the number density of the emitters is as low as tens of thousands (pieces / cm ² ) at most. . In addition, the emitter emits field electrons in a vacuum hermetic space, but is oxidized by various gases remaining in the hermetic space.
Because it is damaged by ions and changes over time,
There were also problems such as noise and variations in characteristics and a decrease in emission current due to deterioration. Further, when a conical emitter such as a molybdenum cone or a silicon cone is used,
The film forming process for forming them into a cone with a uniform height and sharpness is complicated, and when the emitter is made of diamond, electrons are generated uniformly because the surface of the emitter is flat. It was difficult to make it. In addition,
In order to obtain high electron emission efficiency, it is desired to make the radius of curvature at the tip of the emitter as small as possible.

[0005]

Therefore, for example, as described in Japanese Patent Application Laid-Open No. H10-149760,
It has been proposed that the emitter be composed of a number of carbon nanotubes (hereinafter simply referred to as nanotubes). This technology is described, for example, in Heer et al. "A CarbonNanotu
be Field-Emission Electron Source ", SCIENCE VOL.270
17 NOVEMBER 1995, pp. 1179-1180, Saito et al. "Co
nical beams from open nanotubes ", NATURE VOL389 9 O
CTOBER 1997, pages 554-555, or Gulyaev et a
l. "Work function estimate for emitted from nanotub
e carbon cluster films ", J.Vac.Sci.Technol.B 15 (2),
As reported in Mar / Apr 1997, pp. 422-424, electron emission occurs efficiently from the tip of the nanotube.
Alternatively, it is based on research results that the emission characteristics are excellent. Here, a nanotube is a combination of carbon atoms in a cylindrical shape, and a plurality of graphite sheets (graphene sheets or graphite layers) having different diameters are nested, and the overall diameter is 2 to 50 ( It is a fine structure having dimensions of about nm) and a length of about 1 to 100 (μm). The peripheral wall of the nanotube is mainly made of carbon (C)
A five-membered ring or a seven-membered ring
By introducing the member ring, it is closed in a dome shape, and its radius of curvature is as small as about 10 (nm). Therefore, when used as an emitter, it is not necessary to sharpen it by a complicated process because the radius of curvature at the tip is originally small, and since it is composed only of carbon atoms, it has high oxidation resistance in a vacuum and has high chemical resistance. Since it has excellent stability and high ion impact resistance, there is an advantage that deterioration hardly occurs even when driven for a long time.

[0006] However, the nanotubes used in the above publications and literatures are characterized in that, for example, amorphous carbon is arc-discharged under an inert gas atmosphere such as argon (Ar) or helium (He) or laser irradiation is performed on the amorphous carbon. It has been manufactured by evaporating carbon by a method such as a method of condensing (condensing (recombining)) on the surface of a carbon rod or the like. For this reason, amorphous carbon, graphite, fullerene, and the like are generated at the same time as the nanotubes, and it has been difficult to separate only the nanotubes from these mixtures. In addition, since it is desired that electrons are uniformly generated at a constant voltage in the emitter of the field electron emission device, the directions, heights, arrangement densities, etc., of the tips of the plurality of nanotubes are made substantially uniform. Although necessary, it is extremely difficult to align nanotubes produced in a discrete manner. Therefore, since the electric field intensity is not uniform and electrons are not uniformly emitted (that is, the emission current is not uniform), the efficiency can be kept low even if it can be used as a fine electron source. It has been substantially impossible to construct a display device such as an FED, a lighting device, or the like that requires uniform luminance over a wide area.

Japanese Patent Application Laid-Open No. 10-012124 discloses that an aluminum film formed on a glass substrate is oxidized and pores extending from the surface in the thickness direction are provided at regular intervals. A method of manufacturing an electron-emitting device in which a catalyst metal is embedded in the inside and a nanotube is grown in the pores by a CVD method is described. According to this method, the growth direction of the nanotube is limited to the direction from the bottom of the pore to the opening, so that a plurality of nanotubes can be oriented in a certain direction toward the anode. However, in this structure, aluminum oxide for forming pores between the nanotubes is inevitably present, so that the arrangement density of the nanotubes, that is, the number density of the emitters cannot be increased so much. There was a problem that it became extremely complicated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a field electron emission device provided with a highly oriented nanotube as an emitter.

[0009]

In order to achieve the above object, the gist of the present invention is to apply a voltage between an emitter and an anode which are arranged opposite to each other in an airtight space. A field electron emission device of the type in which electrons are emitted from an emitter, wherein (a) the emitter is configured to heat a substrate made of a covalently bonded carbide from a flat surface of the substrate to the anode by heating the substrate under vacuum. The object is to have a plurality of carbon nanotubes formed on one side thereof so as to extend along the direction.

[0010]

As described above, the emitter of the field electron emission device is heated in a vacuum from a substrate made of a carbon compound having a covalent bond, so that the emitter moves in one direction from the flat surface of the substrate to the anode. It is configured to have a plurality of nanotubes generated on one side thereof so as to extend along. Here, the term “covalently bonded carbide” refers to carbon and nonmetallic elements (elements that are weaker in positivity than those that form ionic carbides between carbon and have a smaller atomic radius than those that form interstitial carbides). And also referred to as a covalent carbide. When such a substrate is heated in a vacuum, the non-metallic elements constituting the covalent carbide are selectively removed from the surface gradually since the carbon is stable up to a relatively high temperature under the vacuum. Nanotubes consisting only of carbon atoms are oriented and produced in the direction of movement of the nonmetallic element, that is, in one direction from the inside of the substrate to the surface. Moreover, the formation of nanotubes due to the removal of the nonmetallic element occurs on the entire surface of the substrate, and the nonmetallic element cannot remain on the surface side, so that the nanotubes are densely formed on the substrate surface. . As described above, a field emission device including an emitter having nanotubes oriented at a high density is obtained.

[0011]

Another aspect of the present invention, preferably, (b) the plurality of nanotubes have open ends at the anode side. In this way, the tip of the nanotube whose tip is opened is constituted by the end face of the cylindrical graphite layer, and the radius of curvature at the tip is substantially the same as that of the carbon atom located there. Approximately matches the radius. In addition, since the nanotubes are formed by nesting a plurality of cylindrical graphite layers, the end face of the graphite layer provided on the inner peripheral side is opened by opening the tip closed in a dome shape. Is exposed. Therefore, the tip of the nanotube is composed of the end faces of a plurality of graphite layers each having a radius of curvature substantially equal to the atomic radius of the carbon atom, and electrons are emitted from the individual carbon atoms located at the open tip. . Therefore, the radius of curvature at the tip is extremely small,
In addition, since the number of substantial electron emission positions (emission sites) increases, the electron emission efficiency is dramatically improved.

The open-ended nanotube as described above can be obtained, for example, by performing a heat treatment at a temperature of about 450 to 750 (° C.) for a predetermined time in the presence of oxygen. Since the five-membered or seven-membered ring introduced so that the tip of the nanotube closes has a smaller bonding force than the six-membered ring which is a basic component of graphite,
The domes are preferentially decomposed by the application of heat, so that the dome-shaped tip (commonly referred to as the "cap") is separated from the location of the five- or seven-membered ring. The above processing time is preferably about 10 seconds to 3 minutes, and is appropriately set according to the processing temperature. Note that 450
If the temperature is lower than (° C.) or shorter than 10 seconds, the 5-membered ring and the 7-membered ring are not decomposed, so that the tip cannot be opened. On the other hand, at temperatures higher than 750 (° C) or longer than 3 minutes, 6
The member rings are also decomposed and the nanotubes are lost.

The opening of the tip of the nanotube can also be performed by plasma etching from the tip side. With this configuration, it is possible to preferably suppress the nanotubes from being degraded by oxygen during the opening treatment of the tip or the emission characteristics being degraded by the adsorption of oxygen. The gas used for etching is
Hydrogen, argon, helium, nitrogen, or a mixed gas thereof is suitably used.

Preferably, (c) a cathode is provided at a position facing the anode in the hermetic space, and the emitter is electrically connected to the cathode by fixing the substrate to the cathode. Is what it is. With this configuration, the emitter made of the nanotube is electrically connected to the cathode by fixing the substrate on the cathode provided at the position facing the anode in the airtight space. When nanotubes are formed on the surface by heating the covalent carbide, non-metallic elements are also removed from portions other than the surface of the substrate, that is, the side and back surfaces, and a graphite layer (in the nanotube structure) is formed on the surface layer. Are formed. Therefore, even though the conductivity of the covalent carbide forming the substrate is low, the nanotubes can be easily fixed only on the cathode since the entire substrate is covered with a conductor after the heat treatment in which the nanotubes are generated. The continuity between the emitter made of and the cathode is ensured. Moreover, since the densely formed nanotubes are in electrical contact with each other as described above,
Electric current is also supplied to the inner peripheral side through the nanotube itself. Therefore, the driving voltage can be easily applied to the emitter formed on the substrate via the separately provided cathode, so that the structure of the field electron emission device is simplified. The cathode can be provided, for example, by printing a thick film conductor paste.

[0015] Preferably, the covalent carbide is made of silicon carbide (SiC). In this way, it is possible to obtain an emitter composed of nanotubes that are more densely and uniformly oriented. This is silicon (S
It is presumed that i) functions particularly suitably as a catalyst for graphitizing carbon atoms. Note that silicon carbide is generally classified into α-type (α-SiC) and β-type (β-SiC), and a nanotube can be suitably formed regardless of which one is used as a substrate. The α-form and the β-form are classified into a large number of polymorphs of silicon carbide which are present in a large number. The cubic 3C is called β-form, and other non-equiaxed crystals (hexagonal 2
H, 4H, 6H and rhombohedral 15R) are referred to as α-form. Here, 2H and the like follow Ramsdell's notation.

Preferably, the surface of the substrate on which the nanotubes are formed is a plane parallel to the crystal plane of a covalent carbide single crystal. In this case, since the nanotubes tend to be oriented in a direction perpendicular to the crystal plane of the covalent carbide single crystal, the orientation on the surface is further enhanced. More preferably, the surface is a lamination surface in a direction in which the first layer in which only carbon is present and the second layer in which only non-metallic elements are present are alternately stacked. By doing so, the orientation of the nanotubes can be further enhanced. It is considered that this is because the nonmetallic element easily moves to the surface side between carbon atoms. The lamination plane is, for example, a (0001) plane in a hexagonal compound such as a 2H α-SiC single crystal and a (111) plane in a cubic compound such as a β-SiC single crystal. Plane.

Preferably, the heat treatment under vacuum is performed in a vacuum atmosphere having a degree of vacuum of 10 ^-10 to 10 ^-3 (Torr). In this case, the nanotubes can be more uniformly formed on the surface of the substrate. Note that 10 ^-3 (T
If the degree of vacuum is lower than orr), oxidation proceeds from the substrate surface, and the uniformity of the nanotube tends to be impaired. While 10
^{If the} degree of vacuum is higher than ^-10 (Torr), the graphite layer does not become cylindrical, and nanotubes are hardly formed. Therefore, the above range of the degree of vacuum is desirable. More preferably, the degree of vacuum is in the range of ^10-7 to ^10-4 (Torr).

Preferably, the heat treatment under vacuum is performed in a temperature range of 1200 to 2000 (° C.). 1
If the temperature is lower than 200 (° C.), the covalent carbide is not decomposed, so that nanotubes are hardly formed. On the other hand, if the temperature exceeds 2000 (° C.), a phenomenon occurs in which the formed nanotubes are further bonded and grow large, so that it is difficult to control the diameter of the nanotubes. That is, since the surface of the substrate made of covalent carbide tends to be disturbed in the process of forming nanotubes as the processing temperature increases, the temperature of the non-metallic element forming the covalent carbide from the substrate surface at high temperatures Ease of detachment (removability) becomes less uniform. Therefore, the bonding form of the carbon atoms is changed according to the path through which the non-metallic element escapes, and the uniformity of the diameter of the nanotube is reduced, so that the control becomes difficult.

[0019]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a sectional view schematically showing a main part of the configuration of an FED 10 according to one embodiment of the present invention. In the figure,
The FED 10 includes a substantially flat front plate 12 having a light-transmitting property,
A back plate 14 disposed in parallel with the back plate 14 is joined via a frame-shaped spacer 16, so that the inside is 10 ⁻⁶ (Torr).
Hereafter, preferably, it is configured in an airtight container having a vacuum degree of 10 ⁻⁷ (Torr) or less. The front plate 12 and the rear plate 14 are each made of a soda-lime-glass flat plate having a thickness of about 1 to 2 (mm). However, the back plate 14 may be made of another material having electrical insulation such as ceramics or enamel. The spacer 16 is made of, for example, a material having the same coefficient of thermal expansion as the constituent material of the front plate 12 and the back plate 14, such as soda-lime glass or a 426 alloy having an insulating layer on the surface. And has a uniform thickness of, for example, about 0.3 (mm).

On the inner surface 18 of the front plate 12, a plurality of anodes (anodes) 20 made of transparent ITO (Indium Tin Oxide) or the like are arranged in stripes along one direction. ing. This anode 20
1 (μm) by thin film process such as sputtering or evaporation
It is provided with a film thickness of about
(Ω / □). On the lower surface of each of the plurality of anodes 20, a phosphor layer 22 for emitting, for example, red, green, and blue light is provided so that the three colors are repeatedly arranged. The phosphor layer 22 generates, for example, visible light by being excited by a slow electron beam (Zn, Cd) S: Ag, Cl (red), ZnGa ₂ O ₄ : Mn (green), or ZnS: Cl.
(Blue), for example, 10 to
It is formed by a thick film screen printing method or the like with a thickness determined for each color of about 20 (μm).

On the other hand, on the inner surface 24 of the back plate 14, for example, a plurality of striped cathodes 26 are arranged and formed along the other direction orthogonal to the anode 20 described above. Cathode 26
Is, for example, Ni, Cr, Au, Ag, Mo, W, Pt, Ti, Al, C
It is a thick-film printed conductor composed of a metal such as u or Pd, an alloy, or a metal oxide and glass. On each of the plurality of cathodes 26, an emitter 28 serving as a source of electrons, as described later, is fixed in a state of being electrically connected to the cathode 26 by, for example, a conductive adhesive. The distance between the emitter 28 and the anode 20 is, for example, several tens (μm) to several tens.
(mm). Above the emitter 28, a plurality of stripe-shaped gate electrodes 30 arranged in a direction orthogonal to the cathode 26, that is, along one direction similar to the anode 20, are electrically connected to the emitter 28 by the insulating film 32. It is provided in an insulated state. Gate electrode 30
Is made of, for example, chromium (Cr), and has a plurality of electron passage holes 34 each having a diameter of about 1 to 2 (μm) at each intersection with the cathode 26. The insulating film 32 is made of an insulating material such as silicon dioxide (SiO ₂ ). Each of the gate electrode 30 and the insulating film 32 is formed by a vacuum deposition method, a printing method, a sputtering method, or the like.

Therefore, the cathode 26 and the gate electrode 30
When a signal voltage and a scan voltage are respectively applied to the cathode 26, electrons are emitted from an emitter 28 fixed on the cathode 26 by a field emission generated based on a large voltage gradient therebetween. The electrons fly toward the anode 20 through an electron passage hole 34 provided in the gate electrode 30 by applying a predetermined positive voltage to the anode 20 provided on the front plate 12. As a result, electrons collide with the phosphor layer 22 provided on the anode 20, and the phosphor layer 22 emits light by electron beam excitation. Therefore, by applying a positive voltage to a desired anode 20 in synchronization with the scanning timing of the gate electrode 30, the phosphor layer 22 at a desired position is caused to emit light. By being emitted, a desired image is displayed. Note that the details of the driving method are not necessary for understanding the present invention, and a description thereof will be omitted.

FIG. 2 is a diagram showing the structure of the emitter 28 in detail. In the figure, an emitter 28 has a substrate portion 36 made of, for example, silicon carbide and a surface 38 of the substrate portion 36 having a size of, for example, about 10 ¹¹ (pieces / cm ² ) or more [for example, 10,000
440000 (books / μm ² )] and a large number of nanotubes 40 densely erected and brought into contact with each other. These many nanotubes 40
Each of them has a size of, for example, a diameter of about 5 to 10 (nm) and a length of about 0.2 (μm), and is oriented in a direction substantially perpendicular to the surface 38 and faces toward the anode 20. The tip is located at a substantially uniform height. As apparent from the manufacturing method described later and FIG.
And is continuous at the molecular level from the surface 38, and is integrally provided on the substrate portion 36 without performing any bonding processing or the like. The emission of electrons from the emitter 28 in the above-described driving process is performed from the tips of the nanotubes 40. Therefore, in this embodiment, a large number of nanotubes 40 provided on the surface 38 of the emitter 28 are used. Each function substantially as an emitter.

As shown in the molecular structure model whose tip is enlarged in FIG. 3, the nanotube 40 has a plurality of (for example, two to ten) nanotubes whose peripheral wall is formed by connecting six-membered rings of carbon atoms 44 in a network. Cylindrical graphite layers 46a, 46b,... 46k (hereinafter, simply referred to as graphite layers 46 unless otherwise specified) are nested to form a cylindrical structure having a multilayer structure of about 2 to 10 layers. It is composed of a graphite layer 46. At the tip of each nanotube 40, the end face of the graphite layer 46 having a multiplex structure is exposed. That is, the nanotube 40 has a shape whose tip toward the anode 20 is open, and a plurality of carbon atoms 4 constituting an end face of the graphite layer 46 are formed.
4 will emit electrons. Therefore, the radius of curvature of the nanotube 40 substantially corresponds to the radius of the carbon atom 44. The diameter of the graphite layer 46a located at the outermost periphery, that is, the diameter od of the nanotube 40 is, for example, about 5 to 10 (nm), and the diameter id of the graphite layer 46k located at the innermost periphery is, for example, about 3 (nm).
Therefore, in this embodiment, the diameter od =
An extremely large number of emission sites (electron emission positions) exist in an extremely fine region of about 10 (nm) or less. The distance g between the graphite layers 46 is about 3.34 (Å), which is substantially equal to the distance between the layers of flat graphite, and the graphite layers 46 are independent of each other at least near the tip.

Returning to FIG. 2, a graphite layer 42 having a flat and non-cylindrical network structure of carbon atoms is formed on the side surface and the back surface of the substrate portion 36 except for the front surface 38. Therefore, the substrate portion 36 is configured such that the entire surface is covered with the conductive nanotubes 40 (that is, the cylindrical graphite layer) and the graphite layer 42. The silicon carbide forming the substrate portion 36 has extremely low conductivity, but the surface is provided with high conductivity by being covered with graphite in this way.
Therefore, the nanotubes 40 provided on the surface 38 and the cathode 26 are electrically connected via the graphite layer 42 and the conductive adhesive, and thus the cathode 26 is provided as described above.
By applying a voltage between the gate electrode 30 and the gate electrode 30, the nanotube 40 is energized and electrons are emitted from the tip. At this time, a plurality of nanotubes 4
0 are in contact with each other, so that those located on the inner peripheral side through those located on the peripheral
And electrons are emitted substantially uniformly from substantially the entire surface of the emitter 28 provided on each of the plurality of cathodes 26, so that a substantially uniform electric field is formed. Therefore, since the emitter is composed of a plurality of nanotubes 40 densely arranged in one direction, the FED 10 having the emitter 28 with high current density and uniform characteristics can be obtained.

By the way, the emitter 28 as described above is
For example, it is manufactured as follows. Hereinafter, the manufacturing method will be described with reference to FIGS. 4 (a) to 4 (d) showing each step of the process. First, for example, when the (0001) plane appears on the surface 48,
A substrate 50 made of a silicon carbide single crystal of β-type having a mold or a (111) plane appearing on a surface 48 is prepared, and placed in a vacuum furnace 52 so that the surface 48 faces upward. Fig. 4 (a)
Indicates this state. Next, the substrate 50 is heated in the vacuum furnace 52 at a temperature of about 1700 (° C.) for about 0.5 hour. During this heat treatment, the inside of the vacuum furnace 52 is maintained at a degree of vacuum of, for example, about 10 ⁻⁷ to 10 ⁻⁴ (Torr).
As a result, silicon constituting silicon carbide is gasified from surface 48 of substrate 50 and is gradually removed, and silicon removal layer 54 consisting of only carbon atoms 44 near surface 48 has a thickness of, for example, 0.1.
It is formed to a depth of about 1 (μm). FIG. 4B shows this state. At this time, the silicon removal layer 54 is
As shown in (c), the nanotubes 40 that are highly oriented in the [0001] direction in the α type and in the [111] direction in the β type are densely formed.

That is, silicon carbide is formed by stacking layers in which tetrahedrons made of silicon and carbon are arranged in a plane, and as shown in FIG. 5A, and a stack of ABC formed by parallel movement.
As shown in the above, a stack of AC ′ (or BA ′, CB ′) formed by a combination of translation and rotation by 60 ° is a basic structure, and these combinations may have an extremely large number of polymorphs. Are known. The cubic structure (ie, β-type silicon carbide), which is one of the polymorphs, is composed of, for example, a unit cell as shown in FIG. 5 (c). Atom 44
This is a plane parallel to a plane connecting a, 44b, and 44c. On this (111) plane, a layer made of only carbon 44 and a layer made of only silicon 56 are alternately stacked. Since the silicon atoms 56 can easily move in the direction perpendicular to the alternately stacked surfaces as described above, the carbon atoms 44 escape from the surface 48 while changing the carbon atoms 44 into a six-membered ring structure by the catalytic action accompanying the movement. It is considered something.

FIG. 6 is a model diagram showing the process of forming the nanotube 40. As silicon atoms 56 escape from silicon carbide, a molecular structure of only carbon 44 is formed on substrate 50 in order from surface 48 (shown by phantom lines). The molecules thus formed are connected in a network as described above.
Although the graphite has a six-membered ring structure, the six-membered ring structure grows epitaxially along the moving direction of the silicon atoms 56, and the growth direction of the graphite is determined according to the crystal plane of the surface 48 of the substrate 50. It is considered something. Therefore, when the silicon removal layer 54 becomes deeper with the progress of the heat treatment, a cylindrical graphite
The sheet is formed so as to extend in the thickness direction of the substrate 50, that is, in the traveling direction of the silicon removal layer 54, and inherits the crystal structure of silicon carbide to some extent and is continuous with the substrate portion 36 at the molecular level as shown in the drawing. It is presumed that nanotubes 40 densely arranged and oriented in a direction substantially perpendicular to the surface 38 are obtained. Although the end surface of the cylindrical graphite layer 46 is exposed at the tip of the nanotube 40 in the figure, in practice, the tip is a five-membered ring or It is closed in a dome shape by introducing a seven-membered ring.

Referring back to FIG. 4, the substrate 50 is
After the nanotubes 40 are formed on the surface 48 of the substrate 50, the substrate 50 is heat-treated in a heating furnace 58. The heat treatment conditions include, for example, a temperature of 500 (° C.) in an air atmosphere (oxidizing atmosphere),
Processing time is about 1 minute. FIG. 4C shows this state. Thereby, of the tip of the nanotube 40,
A portion composed of a five-membered ring or the like having a smaller bonding force than that of the six-membered ring is broken, and the tip is separated from the portion. When opened, the emitter 28 as shown in FIG. 2 is obtained.

FIG. 7 is a view for explaining a test method for evaluating the characteristics of the emitter 28 formed as described above. In the figure, an anode 20 and an emitter 28 are arranged to face each other with an interval of, for example, d = 0.42 (mm). These are provided on a glass plate or the like similarly to the electrode structure in the FED 10, and are connected to electrode leads formed by a thick-film printed conductor or the like, but they are all omitted in the figure. With the arrangement as described above, the potential of the anode 20 is applied between the anode 20 and the emitter 28.
When a voltage was applied in the range of 0 to 3 (V) and the emission current was measured by the ammeter 60, an emission current of 100 (μA) or more was obtained at an anode potential of 1.5 (kV). This experimental condition means that a sufficient emission current for light emission can be obtained with a voltage gradient of about 3 (V / μm), and it has been confirmed that the emitter 28 has a suitable ability as the emitter of the FED 10.

Further, in the same manner as in the above test, FIG.
The characteristics of the emitter 28 formed by treating the substrate 50 in hydrogen plasma for about 30 seconds instead of the heat treatment shown in FIG. This emitter 28 is also open at the tip of the nanotube 40 as in the case of the heat treatment, and the anode potential 1.
An emission current of more than 100 (μA) was obtained at 5 (kV).
That is, if the end of the nanotube 40 is opened to expose the end face of the graphite layer 46, the emitter 28 that can obtain a large emission current can be manufactured regardless of the method.

Also, using the emitter 28 described above, FIG.
A similar test was conducted with the distance d between the electrodes at 0.7 (mm) of about 0.7 (mm), and a voltage gradient of 2.2 (kV) or more and 100 (μA)
It was confirmed that the above emission current was obtained. That is, according to the field emission device including the emitter 28 of the present embodiment, a large emission current can be obtained at a relatively low voltage even when the distance d between the electrodes is relatively large.

In short, according to the present embodiment, the FED 10
Of the flat surface 4 of the substrate 50 by heating the substrate 50 made of silicon carbide single crystal under vacuum.
A plurality of nanotubes 40 are formed on the surface 48 (the surface 38 after the formation of the nanotubes 40) so as to extend in one direction from 8 to the anode 20. Therefore, when substrate 50 is heated under vacuum, silicon 56 is selectively removed from surface 48 gradually,
Along with that, a nanotube 4 consisting of only carbon atoms 44
Zeros are generated oriented in the direction of movement of the silicon 56, that is, in one direction from the inside of the substrate 50 toward the surface 48. In addition, nanotube formation due to the escape of the silicon 56 occurs over substantially the entire surface 48 of the substrate, and since the silicon 56 cannot remain on the surface 48 side, the nanotubes 40 are formed densely there. This results in the FED 10 having the emitter 28 with the densely oriented nanotubes 40.

In this embodiment, since the end of the nanotube 40 is open, the end is formed by the end face of the cylindrical graphite layer 46. Therefore, the radius of curvature at the end is small. Substantially corresponds to the radius of the carbon atom 44 located there. Moreover, since the nanotube 40 is formed by nesting a plurality of cylindrical graphite layers 46, the graphite layer provided on the inner peripheral side by opening the dome-shaped closed end is opened. The end face of 46 is exposed. Therefore, the tip of the nanotube 40 is constituted by the end faces of a plurality of graphite layers 46 each having a radius of curvature substantially equal to the atomic radius of the carbon atom 44, and electrons from the individual carbon atoms 44 located at the open tip. Is released. Therefore, since the radius of curvature at the tip is extremely small and the number of electron emission positions (emission sites) is substantially increased, the electron emission efficiency is drastically increased as described above.

In this embodiment, a cathode 26 is provided at a position facing the anode 20 in the airtight space.
The emitter 28 and the nanotube 40 provided on the surface thereof are connected to the cathode 26 via the graphite layers 42 formed on the side and back surfaces of the substrate 36 by fixing the substrate 36 to the cathode 26. It is made conductive. Therefore, the plurality of nanotubes 40 of the emitter 28 and the cathode 26 are simply fixed on the cathode 26.
There is an advantage that continuity is easily ensured.

In this embodiment, the surface 48 of the substrate 50 on which the nanotubes 40 are formed has a cubic β-type.
Like the (111) plane in SiC, it is a plane parallel to the lamination plane of the tetrahedron constituting the silicon carbide single crystal. for that reason,
An extremely highly oriented nanotube 40 can be obtained.

FIG. 8 is a diagram schematically showing the configuration of a field electron emission device 62 used as a flat lamp or the like according to another embodiment of the present invention. The element 62 of this embodiment has an electrode configuration substantially similar to that of the FED 10 except that the gate electrode 30 is not provided and the anode 20 and the cathode 26 are provided in common on the entire surface. . Even in such a diode structure, since the number of emission sites is dramatically increased as described above, the field electron emission device 62 having high efficiency can be obtained by appropriately setting the interval between the anode 20 and the emitter 28. Obtainable.

While the embodiment of the present invention has been described in detail with reference to the drawings, the present invention can be embodied in still another mode.

For example, in the embodiment, the present invention
The case where the present invention is applied to the D10, the field electron emission device 62 for a flat lamp, and the like has been described. The present invention can be similarly applied to various field electron emission devices such as a gun.

Further, in the embodiment, the emitter 28 having the nanotubes 40 densely arranged with high orientation was manufactured by heat-treating the substrate 50 made of silicon carbide in a vacuum. 40
As a starting material for obtaining, another material such as boron carbide is preferably used as long as it is a covalently bonded carbide from which a nonmetallic element is removed by heating in vacuum.

In the embodiment, the nanotube 4
Although the emitter 28 is formed by opening the tip by further performing a heat treatment in the presence of oxygen after forming 0, the opening treatment of the tip is not necessarily performed. However, by opening the tip as described above, the substantial radius of curvature of the emitter 28 is significantly reduced, and the emission site is also significantly increased, so that the efficiency of the emitter 28 is further enhanced. It is more desirable to open.

In the embodiment, the nanotube 4
0 was formed to a size of about 5 to 10 (nm) in diameter and about 0.2 (μm) in length, but its size depends on the degree of vacuum and temperature during heat treatment, depending on the application of the field electron emission device. Is changed as appropriate.

In the embodiment, the emitter 28 is fixed to the cathode 26 with a conductive adhesive. However, in the case where the cathode 26 is formed of the above-described thick-film printed conductor, the emitter 28 is fixed. The emitter 28 may be fixed simultaneously during the sintering process.

Although not specifically exemplified, the present invention
Various changes can be made without departing from the spirit of the invention.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a configuration of an FED according to an embodiment of the present invention.

FIG. 2 is a diagram showing in detail a configuration of an emitter provided in the FED of FIG. 1;

FIG. 3 is a diagram illustrating the structure of the emitter of FIG. 2 at a molecular level.

FIGS. 4 (a) to 4 (d) are diagrams illustrating each stage in a process of manufacturing the emitter of FIG. 2;

5 (a) to 5 (c) are diagrams illustrating a crystal structure of silicon carbide used in the manufacturing process of FIG.

FIG. 6 is a model diagram illustrating a nanotube generation process in the manufacturing process of FIG.

FIG. 7 is a diagram for explaining an implementation state of a characteristic evaluation test of the emitter of FIG. 2;

FIG. 8 is a view for explaining another embodiment of the field electron emission device of the present invention.

[Explanation of symbols]

 10: FED (Field Electron Emission Device) 20: Anode 26: Cathode 28: Emitter 40: Nanotube

Claims (3)

[Claims] 1. A field electron emission device of a type in which electrons are emitted from an emitter by applying a voltage between an emitter and an anode arranged opposite to each other in an airtight space, wherein the emitter is a shared device. A plurality of carbon nanotubes are formed on one surface of the substrate made of the associative carbide so as to extend in one direction from the flat surface of the substrate to the anode by heating the substrate under vacuum. Field electron emission device. 2. The field electron emission device according to claim 1, wherein the plurality of carbon nanotubes have open ends at the anode side. 3. A cathode is provided at a position facing the anode in the hermetic space, and the emitter is electrically connected to the cathode by fixing the substrate to the cathode. One or two field electron emission devices.