Electron beam emission structure and field emission device

Abstract

To provide a technique that can contribute to making it easier to achieve a desired function of a field emission device by facilitating the reduction of a beam diameter and a focal size of an electron beam.SOLUTION: In a cold cathode 1 having a columnar electrode substrate 11 arranged in a posture where one end of the axial center is opposite to an anode 2, a radial dimension of an anode side opposing surface 12 is set to 0.1 mm to 1 mm, and an electron emission part 4 made of a carbon nano-structure is formed on the anode side opposing surface 12. The surface of the carbon nano-structure is formed so that granular portions 40 that protrude from the surface are distributed in an island-like pattern on the surface to form an island structure. The granular portions 40 are formed so that a dimension in a direction of the protrusion is 10 μm or more and a radial dimension at the largest diameter part of the granular portion is 10 μm or more.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an electron beam emission structure and a field emission device that can be applied to various devices such as X-ray devices, electron tubes, and lighting devices. [Background technology]

[0002] Field emission is a phenomenon in which electrons are emitted into a vacuum atmosphere (for example, into an insulating vacuum container) due to the concentration of an electric field, and there have been studies on utilizing this phenomenon to construct various field emission devices such as X-ray devices, electron tubes, and lighting devices.

[0003] An example of field emission is a configuration in which a predetermined voltage can be applied to both an electron source (such as a cold cathode) and an anode (target) that are arranged facing each other at a predetermined distance, and an electron beam can be emitted toward the anode by electrons generated in the electron source by the application of the voltage. By irradiating (colliding) such an electron beam on the anode, a desired function (for example, the radioscopic resolution by external emission of X-rays in the case of an X-ray device) can be achieved (for example, Patent Documents 1 to 5).

[0004] The electron source may be a cold cathode having an electrode substrate such as a Si substrate or a SUS substrate, and an electron emission portion provided on the end face of the electrode substrate facing the anode (hereinafter simply referred to as the anode-side facing surface).The electron emission portion may be a carbon nanostructure formed by growing carbon nuclei generated on the anode-side facing surface by a CVD method, and then three-dimensionally growing and overlapping carbon films (graphene, carbon nanotubes, etc.) to form a hollow structure.

[0005] It is required to control the focusing of the electron beam so that the electron beam can be focused on a central axis between the electron source and the anode (hereinafter simply referred to as the central axis) and irradiated onto the anode. Examples of the focusing control include reducing the beam diameter of the electron beam as it approaches the anode from the electron source by using a focusing electrode or reducing the focal spot size (electron spot), which is the area where the electron beam collides with the anode. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Patent No. 4565089 [Patent Document 2] Patent No. 5264055 [Patent Document 3] Patent No. 4408891 [Patent Document 4] Patent No. 4390847 [Patent Document 5] Patent Publication No. 2022-073816 Summary of the Invention [Problem to be solved by the invention]

[0007] In recent years, as the demand for smaller beam diameters and focal spot sizes increases, for example in the case of electron beams in microfocus X-ray tubes, studies have begun to be conducted on reducing the diameter of the electrode substrate. However, simply reducing the diameter of the electrode substrate reduces the amount of electrons generated, lowering the tube current, which may prevent the field emission device from fulfilling its desired functions.

[0008] Furthermore, even if a high current density can be obtained in an electron beam from a small diameter electrode substrate, the electron emission portion formed on the electrode substrate is likely to have low durability against the electron beam of high current density, and as a result, there is a risk that the field emission device will not be able to perform the desired function.

[0009] It is possible to reduce the beam diameter and focal spot size by controlling the focusing of the electron beam using an electromagnetic coil or the like. However, providing such an electromagnetic coil would result in an increase in the size and cost of the field emission device, and the focusing control would also be complex and difficult.

[0010] The present invention has been made in consideration of the above technical problems, and has an object to provide a technology that can contribute to facilitating the reduction of the beam diameter and focal spot size of an electron beam and making it easier for a field emission device to perform the desired functions. [Means for solving the problem]

[0011] The electron beam emission structure and the field emission device according to the present invention can contribute to solving the above-mentioned problems. One aspect of the electron beam emission structure includes a columnar electrode substrate arranged with one end of the axis facing an anode, a cold cathode having an electron emission part on the end surface of the columnar electrode substrate on the anode side, and a cylindrical focusing electrode arranged coaxially with the axis while being insulated from the cold cathode and surrounding the outer periphery of the columnar electrode substrate. The end surface has a radial dimension of 0.1 mm to 1 mm, the electron emission part is made of a carbon nanostructure obtained by growing carbon nuclei generated on the end surface, and the surface of the carbon nanostructure is formed such that granular parts protruding from the surface are distributed in an island shape on the surface to form an island structure, and the granular parts have a dimension in the protruding direction of 10 μm or more and a radial dimension at a maximum diameter part of the granular parts of 10 μm or more.

[0012] The granular portion may have a tip end in the protruding direction that is curved and protrudes at an obtuse angle toward the protruding direction.

[0013] The tip portion may have a radial dimension of 5 μm or more.

[0014] The cold cathode may be characterized in that an outer periphery of the columnar electrode base is surrounded by a cylindrical electrode cover that is arranged coaxially with respect to the axis between the columnar electrode base and the focusing electrode.

[0015] The electrode cover may also be characterized in that an opening edge surface on the anode side has an inclined shape such that a point on the opening edge surface moves toward the anode side as it approaches the radial outside from the inside of the electrode cover.

[0016] One aspect of a field emission device is characterized in that it has any one of the electron beam emission structures described above. Also, it may be characterized in that it includes a voltage control unit capable of changing a voltage applied between the anode and the focusing electrode. Effect of the Invention

[0017] As described above, the present invention can contribute to making it easier to reduce the beam diameter and focal spot size of an electron beam, and to making it easier for a field emission device to exhibit the desired functions. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a schematic configuration diagram (cross-sectional view taken along the central axis) for explaining an electron beam emission structure according to a first embodiment. [Diagram 2] FIG. 2 is a schematic configuration diagram (cross-sectional view taken along the central axis) for explaining an example of a columnar electrode substrate 11. [Diagram 3] Electron image of the surface of a carbon nanostructure observed with an electron microscope (electron image of the peripheral area of ​​the surface). [Figure 4] Electron image (oblique view) of a granular portion 40 of a carbon nanostructure observed with an electron microscope. [Diagram 5] Observation results of current density characteristics versus applied voltage in a verification example (observation results showing IV characteristics). [Figure 6] FIG. 11 is a schematic configuration diagram (cross-sectional view taken along the central axis) for explaining an electron beam emission structure according to a second embodiment. [Figure 7]FIG. 11 is a schematic configuration diagram (cross-sectional view taken along the central axis) for explaining an electron beam emission structure according to a third embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The electron beam emission structure and field emission device in the embodiments of the present invention are completely different from, for example, a structure in which the diameter of an electrode substrate is simply reduced.

[0020] That is, in this embodiment, a cold cathode has a columnar electrode substrate arranged with one end of its axis facing an anode, and an electron emission part is provided on the anode-side facing surface of the columnar electrode substrate. The radial dimension of the anode-side facing surface of the columnar electrode substrate is 0.1 mm to 1 mm, and the electron emission part is made of a carbon nanostructure obtained by growing carbon nuclei generated on the anode-side facing surface.

[0021] The surface of the carbon nanostructure is formed such that granular portions protruding from the surface are distributed in an island shape on the surface, forming an island structure. The granular portions are characterized in that the dimension in the protruding direction (hereinafter simply referred to as the protruding direction) is 10 μm or more, and the radial dimension at the maximum diameter part of the granular portions (for example, base part 41 in FIG. 4 described later) is 10 μm or more (hereinafter simply referred to as the large grain shape).

[0022] In this way, in an electron emission section made of a carbon nanostructure formed on the anode-side facing surface with a radial dimension of 0.1 mm to 1 mm, by forming large grain-shaped granular parts distributed in an island shape on the surface of the carbon nanostructure to form an island structure, it becomes easy to emit an electron beam with a high current density and also easy to obtain durability against the electron beam with a high current density. As a result, it becomes possible to fully exert the desired functions of the field emission device.

[0023] This embodiment may have a configuration having the above-mentioned cold cathode, etc., and may appropriately apply common technical knowledge in various fields (for example, the field of field emission devices, the field of carbon nanostructures, etc.). For example, the design may be modified as necessary by appropriately referring to Patent Documents 1 to 5, etc., and the following Examples 1 to 3 are given as examples.

[0024] In the following Examples 1 to 3, detailed explanations will be omitted as appropriate by, for example, applying the same reference numerals to overlapping contents.

[0025] ≪Reference example≫ As an example of a conventional field emission device, in the case of an X-ray tube with a focal spot size in the order of μm, a mode is known in which an impregnated hot cathode composed of an oxide cathode that emits electrons is used, rather than a thermionic source composed of a tungsten filament. Such an impregnated hot cathode can be made relatively small and is said to be capable of generating a large electron flow.

[0026] As a general electron source, there is a hot cathode with an electron source diameter of several μm to several tens of μm (for example, 50 μm) that generates an electron flow on the order of amperes. It is also known that by interposing an aperture (an aperture according to the electron source diameter) between the hot cathode and the anode, the electron flow is restricted while being irradiated to the anode, thereby functioning as a reflection type X-ray tube. This reflection type X-ray tube is considered to have the advantage of being able to increase the output compared to a transmission type X-ray tube.

[0027] However, the hot cathodes described above are installed in a vacuum atmosphere (for example, in a vacuum vessel), and depending on the degree of vacuum in the vacuum atmosphere, the tungsten filament is easily consumed, so it has been considered difficult to extend their life. In addition, impregnated hot cathodes tend to be expensive and difficult to manufacture.

[0028] In recent years, therefore, a configuration that uses a field emission type cold cathode using a carbon film, typically a carbon nanotube, has been attracting attention. One example of a typical X-ray tube that uses a cold cathode is one in which a carbon film is formed on the anode-facing surface of an electrode base having a radial dimension of about several mm (e.g., 5 mm) to form an electron emission part of a carbon nanostructure, and the tube current is about several mA.

[0029] In the case of the electron emission portions of Patent Documents 1 to 5, granular portions are formed on the surface so as to be distributed in an island-like manner to form an island structure, but the granular portions have a smaller size and shape (for example, a tapered shape with a radial dimension of about several nm to several μm; hereinafter, simply referred to as a small grain shape) compared to Examples 1 to 3 described below.

[0030] If the electrode base of such an X-ray tube is simply made smaller (for example, to about 0.5 mm), it may be possible to reduce the beam diameter and focal spot size of the electron beam, but the area of ​​the anode-facing surface of the electrode base (the surface area of ​​the electron-emitting portion) will be reduced, resulting in a decrease in the amount of electrons generated and a low tube current. Furthermore, even if a high current density can be obtained in the electron beam from the small area of ​​the anode-facing surface (electron-emitting portion), the electron-emitting portion may not be able to withstand the high current density of the electron beam, and its lifespan may be shortened.

[0031] As a specific example, when the radial dimension of the electrode substrate is reduced from 5 mm to 0.5 mm, the surface area of ​​the electron-emitting portion is reduced to about 1 / 100, and the tube current is also reduced to about 1 / 100. In order to achieve the tube current (e.g., 1 mA) before the reduction in diameter in such a reduced diameter configuration, it is conceivable to increase the current density of the electron beam by about 100 times, but the electron-emitting portion would not be able to withstand the electron beam with such a high current density.

[0032] In contrast, for example, in the case of the electron beam emission structure of Examples 1 to 3 described later, the radial dimension of the anode-facing surface of the cathode is set relatively small (set within the range of 0.1 mm to 1 mm), while each granular portion forming an island structure on the surface of the electron emission portion (carbon nanostructure) formed on the anode-facing surface is made large. This not only makes it possible to reduce the beam diameter and focal size of the electron beam, but also makes it easier to emit an electron beam with a high current density and makes it easier to obtain durability against the electron beam with the high current density. As a result, even a field emission device such as a microfocus X-ray tube can easily exhibit the desired function.

[0033] Example 1 <Outline of the configuration of the first embodiment> Fig. 1 is a schematic diagram for explaining an electron beam emission structure according to Example 1. The electron beam emission structure shown in Fig. 1 mainly comprises a cold cathode 1 and an anode 2 arranged opposite to each other, and a focusing electrode 3 arranged so as to cover the outer periphery of the cold cathode 1. In the case of Fig. 1, a power source E1 for applying a voltage (tube voltage) between the cold cathode 1 and the anode 2, and a power source E2 for applying a voltage between the anode 2 and the focusing electrode 3 are provided.

[0034] The cold cathode 1 has a columnar electrode substrate 11 arranged with one end of its axis facing the anode 2 (i.e., arranged coaxially with respect to the central axis), and an electron emission section 4 made of a carbon nanostructure is provided on the anode-facing surface 12, which is the end face of the columnar electrode substrate 11 on the anode 2 side.

[0035] The focusing electrode 3 has a cylindrical electrode base 31 that is disposed coaxially with the axis of the columnar electrode base 11 (hereinafter simply referred to as the cold cathode axis), surrounds the outer periphery of the columnar electrode base 11, and is configured to be insulated from the cold cathode 1. In the case of the focusing electrode 3 shown in FIG. 1, a gap is provided between the focusing electrode 3 and the cold cathode 1, thereby providing an insulated state from the cold cathode 1, but this is not limiting. For example, a desired insulating state can be achieved by interposing an insulator (not shown) between the cold cathode 1 and the focusing electrode 3.

[0036] <Example of cold cathode 1 configuration> The columnar electrode base 11 of the cold cathode 1 is capable of providing an electron emitting section 4 on an anode-facing surface 12 having a radial dimension of 0.1 mm to 1 mm, and various configurations can be applied as long as electrons are generated in the electron emitting section 4 by applying a voltage of a desired magnitude from a power source E1, and the electrons are emitted toward the anode 2 to form an electron beam (not shown).

[0037] One example of such a material is a conductive metal material (e.g., an Fe-Cr-Ni alloy) formed into a columnar shape (e.g., a cylindrical shape).Another example is a substrate (e.g., a silicon substrate or a tungsten substrate) that has good bonding properties with carbon (carbon nanostructures) formed into a columnar shape.

[0038] Furthermore, the shape is not limited to a simple columnar shape, and may be tapered toward the anode-side facing surface 12, as in the columnar electrode substrate 11 shown in Fig. 2. This allows the radial dimension of the anode-side facing surface 12 to be set small, while the radial dimension on the opposite side to the anode-side facing surface 12 can be set large, making it easier to maintain a certain level of mechanical strength, for example.

[0039] <Example of anode 2 configuration> The anode 2 may be any anode that can be struck by the electron beam emitted from the electron emitter 4 and emit X-rays or the like (not shown) by the impacting electron beam, and various configurations are possible. The anode 2 in FIG. 1 has a surface 21 (hereinafter simply referred to as the irradiated surface) that faces the electron emitter 4 of the anode 2 and is irradiated with the electron beam, and the electron beam is configured to impact the irradiated surface 21. The irradiated surface 21 may be configured to be inclined at a predetermined angle with respect to the emission direction of the electron beam. In this case, the X-rays or the like generated by the electron beam that impacts the irradiated surface 21 are irradiated in a direction bent from the emission direction of the electron beam (for example, one of the left and right directions in the figure).

[0040] <Configuration example of focusing electrode 3> The cylindrical electrode base 31 of the focusing electrode 3 may be configured to surround the outer periphery of the columnar electrode base 11 so as not to impede the field emission from the cold cathode 1, and various configurations are possible.

[0041] One example of such a cylindrical electrode substrate 31 is made of a conductive metal material similar to the columnar electrode substrate 11, and is formed into a cylindrical shape (for example, a shape having a cylindrical tubular portion 30) from the metal material. Alternatively, a substrate such as a Si substrate may be formed into a cylindrical shape, as long as the electron beam can be focused by applying a voltage of a desired magnitude from the power source E2. In the case of the cylindrical electrode substrate 31 shown in FIG. 1, an annular substrate reduced diameter portion 33 is provided at an end portion 32 on the anode 2 side of the cylindrical electrode substrate 31, the end portion 32 being provided with a reduced diameter protruding from the end portion 32 toward the cold cathode axis center.

[0042] <Configuration Example of Electron Emitting Section 4> The electron emitter 4 is composed of a carbon nanostructure formed on the anode-facing surface 12, and various configurations can be applied as long as it is capable of generating electrons on the surface of the electron emitter 4 by applying a voltage of the desired magnitude from a power source E1 and emitting the generated electrons toward the anode 2 (radiator).

[0043] A specific example is one in which the electrode is formed as a thin film (eg, formed by deposition using a CVD method or the like) on the anode-facing surface 12 of the columnar electrode substrate 11 as shown in the figure.

[0044] 1, the surface of the electron emitter 4 is recessed toward the anode-side facing surface 12 and is concave. With such an electron emitter 4 having a concave surface, electrons generated on the surface are more likely to be emitted toward the anode 2 in a direction biased toward the central axis. This contributes to reducing the beam diameter and focal spot size of the electron beam.

[0045] The method for making the surface of the electron-emitting portion 4 concave is not particularly limited, but one example is a method in which the electron-emitting portion 4 is formed on the anode-side facing surface 12 that has been previously formed into a concave shape.

[0046] <Examples of carbon nanostructure configurations> The carbon nanostructure of the electron emission portion 4 needs only to have an island-shaped structure on its surface and be capable of emitting electrons generated by application of a voltage of a desired magnitude from the power source E1 to the anode 2 side (radiator), and various configurations can be applied.

[0047] The carbon nanostructures themselves that form the island-like structure can be formed by, for example, appropriately applying a well-known film formation method, and although there is no particular limitation, one example is that they can be formed by applying a CVD method.

[0048] As a specific example of the CVD method, first, the columnar electrode substrate 11 is placed in an atmosphere at a prescribed temperature (e.g., in a chamber), and a precursor of a carbon film (e.g., a precursor generated by plasma decomposition of hydrogen and methane) is deposited on the anode-facing surface 12, and carbon nuclei are generated and grown on the anode-facing surface 12.

[0049] This results in the formation of a hollow carbon nanostructure in which carbon films (graphene, carbon nanotubes, etc.) grow three-dimensionally and overlap each other.

[0050] The surface of this carbon nanostructure is not simply flat, but is formed so that granular portions 40 protruding from the surface are distributed in an island-like manner, as shown in Figures 3 and 4 (for example, as shown in Figure 3, countless granular portions 40 are densely packed together), forming an island-like structure.

[0051] 3 and 4, the surface side of the granular portion 40 has a shape in which a minute fibrous carbon film (for example, graphene that appears striated in FIG. 4) protrudes. Adjacent granular portions 40 are formed so as to be bonded to each other at their respective base portions 41.

[0052] The granular portion 40 can be formed into a desired shape by appropriately setting the film formation conditions of the applied film formation method (e.g., precursor generation conditions, temperature conditions of the anode-side facing surface 12, electric field and electric field line density with respect to the anode-side facing surface 12, etc.), and preferably into a large grain shape.

[0053] Examples of granular portion 40 having a large grain shape include an embodiment in which the dimension of granular portion 40 in the protruding direction is 10 μm or more, preferably 20 μm or more, and more preferably 30 μm or more, and the radial dimension of the maximum diameter part of granular portion 40 (for example, base portion 41 in Figure 4) is 10 μm or more, preferably 20 μm or more, and more preferably 30 μm or more, and examples include an embodiment in which the large grain shape can be confirmed with a stereo microscope.

[0054] There is no particular upper limit to the dimension of the granular portion 40 in the protruding direction or the radial dimension of the maximum diameter portion, and each can be set to, for example, approximately 50 μm, but it is preferable to set them appropriately so as to maintain the island structure on the surface of the carbon nanostructure.

[0055] The shape of the granular portion 40 may be, for example, a cone shape, a frustum shape, a spindle shape, a sphere shape, etc. as shown in Figs. 3 and 4, but is not limited thereto.

[0056] In addition, the tip 42 in the protruding direction of the granular portion 40 may be formed to have a curved shape that is convex at an obtuse angle toward the protruding direction. This makes it easier to form the tip 42 so that the radial dimension is large (for example, 5 μm or more, preferably 10 μm or more), and there is a possibility that durability against an electron beam with a high current density may be easily obtained.

[0057] Furthermore, the granular portions 40 formed on the surface of the carbon nanostructure do not all need to be large grain shapes, and some may be other grain shapes (e.g., small grain shapes), but it is preferable to suppress the proportion of the other grain shapes (e.g., suppress it to 30% or less, preferably 20% or less, and more preferably 10% or less) so that it is within a range in which the desired function of the intended field emission device can be achieved.

[0058] <Example of the configuration of a field emission device> According to the electron beam emission structure shown in FIG. 1, it is possible to configure various types of field emission devices. One example is a vacuum container (not shown) in which both ends of a cylindrical insulator are sealed and a vacuum chamber is formed on the inner periphery of the insulator.

[0059] Specifically, an anode 2 is arranged on one side of the vacuum chamber in the vacuum vessel, and a cold cathode 1 and a focusing electrode 3 are arranged on the other side of the vacuum chamber, and the power sources E1 and E2 are appropriately wired so that the voltages can be applied as desired. Also, a Wehnelt extraction electrode (not shown) or the like can be configured so that the tube current can be appropriately controlled.

[0060] <Other> The voltage application configuration by the power sources E1 and E2 can be implemented in various ways, for example, by providing a voltage control unit (not shown) capable of appropriately changing the voltage.

[0061] As an example of the setting of the voltage control section, when it is necessary to reduce the focal spot size as in microfocus X-rays, etc., the focusing force of the electron beam can be set to be large. Also, when it is desired to irradiate the anode 2 with an electron beam of high output (power) while suppressing damage to the anode 2, the focusing force of the electron beam can be set to be small.

[0062] The voltage applied by the power supply E2 may be large enough to focus the electron beam by the focusing electrode 3, and compared to the voltage (tube voltage) applied by the power supply E1, it can be set sufficiently small (for example, within a range of 90% to 100% of the tube voltage), making it possible to suppress the amount of electrons. Therefore, in the vacuum atmosphere in which the electron beam emission structure is installed, the degree of vacuum in the vacuum atmosphere is suppressed so as not to deteriorate.

[0063] <Verification example> Based on Example 1, an X-ray tube device (hereinafter simply referred to as the example device) having the electron beam emission structure of Fig. 1 was created, and the current density characteristics relative to the applied voltage of the power supply E1 were observed, resulting in the results shown in Fig. 5 (results indicated by the symbol "◯" in Fig. 5). Also, in an X-ray tube device (hereinafter simply referred to as the comparative example device) created based on Patent Documents 1 to 5, the current density characteristics relative to the applied voltage of the power supply E1 were observed in the same manner as in the example device, resulting in the results shown in Fig. 5 (results indicated by the symbol "●" in Fig. 5).

[0064] In the example device, a columnar electrode base 11 having a shape as shown in Fig. 2 and a radial dimension of the anode-side facing surface 12 of 0.5 mm was used, and an electron emission portion 4 made of carbon nanostructures having an island structure as shown in Fig. 3 and Fig. 4 was formed on the anode-side facing surface 12. In the comparative example device, a columnar electrode base 11 having a radial dimension of the anode-side facing surface 12 of 5 mm was used, and an electron emission portion 4 made of carbon nanostructures having an island structure made of small granular portions was formed on the anode-side facing surface 12.

[0065] The results shown in FIG. 5 show that in the example device, although the anode-side facing surface has a small diameter (smaller than that of the comparative example device), a high current density is obtained at a low applied voltage.

[0066] In the example device, when the applied voltage of the power source E1 was set to 180 kV, the current density was 5 mA / mm 2 It was confirmed that the above electron beams could be emitted. In addition, it was confirmed that the cold cathode 1 of the embodiment device can perform the desired function even when applied in a wide range of voltages, has sufficient durability even in a high voltage range (for example, several kV to 300 kV), and can obtain an actual current of 5 mA. When applied in a general voltage range, changes over time can be sufficiently suppressed, making it possible to achieve a long life.

[0067] Therefore, according to the above-described first embodiment, not only can the beam diameter and focal spot size of the electron beam be reduced, but it also becomes easier to emit an electron beam with a high current density and to obtain durability against the electron beam with the high current density.

[0068] Example 2 <Outline of the configuration of the second embodiment> Fig. 6 is a schematic diagram for explaining an electron beam emission structure according to Example 2. In the electron beam emission structure shown in Fig. 6, the outer periphery of a columnar electrode base 11 is surrounded by a cylindrical electrode cover 5. The electrode cover 5 is interposed between the columnar electrode base 11 and a cylindrical electrode base 31, and is provided so as to be positioned coaxially with respect to the cold cathode axis.

[0069] <Configuration example of electrode cover 5> The electrode cover 5 may be in any shape as long as it is cylindrical and capable of surrounding the outer periphery of the columnar electrode base 11, and various configurations are possible.

[0070] One example of such a material is one that is made of a material that does not cause dielectric breakdown, such as a high melting point material such as molybdenum, tungsten, or stainless steel, and that is molded into a tubular shape (for example, a cylindrical shape).

[0071] 6, a gap is provided between the electrode cover 5 and the focusing electrode 3, thereby providing an insulated state with respect to the focusing electrode 3, but this is not limiting. For example, a desired insulating state may be achieved by providing an insulator (not shown) between the electrode cover 5 and the focusing electrode 3.

[0072] In addition, the end 51 of the electrode cover 5 on the anode 2 side may be configured to have a reduced diameter protruding from the end 51 toward the cold cathode axis, so as to overlap with the peripheral portion of the electron emission portion 4 in the extension direction of the cold cathode axis.

[0073] The electrode cover 5 may be in contact with the columnar electrode base 11 or at the same potential as the columnar electrode base 11, but it is preferable to appropriately set the distance between the electron emitter 4 and the electrode cover 5 so that they do not interfere with each other too much. For example, in the case of the end 51 having a reduced diameter as described above, it is possible to set the electron emitter 4 so that it is not damaged by being pressed by the end 51.

[0074] According to the above-described second embodiment, in addition to the same effects as those of the first embodiment, the following can be said. That is, the outer periphery of the columnar electrode base 11 (e.g., the peripheral portion of the electron-emitting portion 4) may contain electrically unstable elements (e.g., elements that may cause electric field concentration or abnormal discharge), but the configuration in which the outer periphery is surrounded by the electrode cover 5 makes it possible to suppress the unstable elements. Specifically, the electric field may be easily relaxed at the peripheral portion of the electron-emitting portion 4.

[0075] Example 3 <Outline of the Third Embodiment> Fig. 7 is a schematic diagram for explaining an electron beam emission structure according to Example 3. In the electron beam emission structure shown in Fig. 7, an opening edge surface 52 on the anode 2 side of the electrode cover 5 does not simply have a shape extending in the radial direction of the electrode cover 5 (for example, a flat shape as shown in Fig. 6), but has a shape extending in a direction intersecting the cold cathode axis at an inclined angle (hereinafter, simply referred to as an inclined shape).

[0076] Specifically, the opening edge surface 52 has an inclined shape that moves toward the anode 2 as the point on the opening edge surface 52 approaches the outside from the inside in the radial direction of the electrode cover 5 .

[0077] This inclined shape may be in any shape as long as it can suppress electric field concentration that may occur around the electron emitting portion 4. In the case of Fig. 7, both the concave surface of the electron emitting portion 4 and the opening edge surface 52 extend so as to be continuous between them.

[0078] According to the above-described embodiment 3, in addition to the same effects as those of the embodiments 1 and 2, the following can be said: That is, the electrically unstable elements described in the embodiment 2 can be more easily suppressed, and specifically, the electric field can be more easily relaxed in the peripheral portion of the electron emission portion 4.

[0079] Although the present invention has been described in detail above only with respect to the specific examples, it will be apparent to those skilled in the art that various modifications are possible within the scope of the technical concept of the present invention, and it is natural that such modifications fall within the scope of the claims.

[0080] For example, the embodiments 1 to 3 may be appropriately combined. As a specific example, the columnar electrode substrate 11 shown in Fig. 2 may be applied to the electron beam emission structure shown in Fig. 6. In addition, the contents disclosed in Patent Documents 1 to 5 may be appropriately applied to modify the design, and the same effects as those of the embodiments 1 to 3 may be achieved. [Explanation of symbols]

[0081] 1...cold cathode, 11...column electrode base, 12...anode side opposing surface 2...Anode 3…Focusing electrode 4...electron emitting portion, 40...granular portion, 41...base portion, 42...tip portion 5...electrode cover, 52...opening edge surface

Claims

1. a cold cathode having a columnar electrode base disposed with one end of its axis facing an anode, the columnar electrode base having an electron emission portion on an end surface facing the anode; a cylindrical focusing electrode that is insulated from the cold cathode and is arranged coaxially with respect to the axis and surrounds an outer periphery of the columnar electrode base; Equipped with The radial dimension of the end face is 0.1 mm to 1 mm, the electron emission portion is made of a carbon nanostructure obtained by growing carbon nuclei generated on the end surface, a surface of the carbon nanostructure is formed such that granular portions protruding from the surface are distributed in an island-like shape on the surface, forming an island-like structure; 2. An electron beam emission structure, wherein the granular portion has a dimension in the protruding direction of 10 μm or more, and a radial dimension at a maximum diameter portion of the granular portion of 10 μm or more.

2. 2. The electron beam emission structure according to claim 1, wherein the tip of the granular portion in the protruding direction has a curved shape that protrudes at an obtuse angle toward the protruding direction.

3. 3. The electron beam emission structure according to claim 1, wherein the diameter of said tip portion is 5 [mu]m or more.

4. 3. The electron beam emission structure according to claim 1, wherein the cold cathode is surrounded on the outer periphery of the columnar electrode base by a cylindrical electrode cover arranged coaxially with respect to the axis between the columnar electrode base and the focusing electrode.

5. 5. The electron beam emission structure according to claim 4, wherein the opening edge surface on the anode side of the electrode cover has an inclined shape such that a point on the opening edge surface moves toward the anode side as it approaches from the inside to the outside in the radial direction of the electrode cover.

6. 3. A field emission device comprising the electron beam emission structure according to claim 1.

7. 7. The field emission device according to claim 6, further comprising a voltage control section capable of changing the voltage applied between said anode and said focusing electrode.

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