Electron source, electron beam emission structure, field emission device, and method for manufacturing electron source

Abstract

An electron source (E1) comprises a columnar electrode substrate (S1) that is disposed in an orientation in which an end part thereof on one axial-direction side faces an anode (T). The electrode substrate (S1) has: an annular cutout recess (11) that extends along the circumferential direction at the peripheral edge of the end part of the electrode substrate (S1) on the one axial-direction side; a small-diameter portion (21) that has a shape protruding to the one axial-direction side on the inner-peripheral side of the cutout recess (11) in the electrode substrate (S1); and a large-diameter portion (12) that is the end part of the electrode substrate (S1) on the other axial-direction side and has a greater diameter than the small-diameter portion (21). An electron emission part (3a) is provided to the anode-side facing surface (2a) of the small-diameter portion (21).

Description

Electron source, electron beam emission structure, field emission device, method for manufacturing an electron source

[0001] The present invention relates to an electron source, a method for manufacturing an electron source, an electron beam emission structure, and a field emission device that are applicable to various devices such as an X-ray device, an electron tube, and a lighting device.

[0002] Field emission is a phenomenon in which electrons are emitted in a vacuum atmosphere (for example, in an insulating vacuum container) due to electric field concentration, and it has been studied to configure various field emission devices such as an X-ray device, an electron tube, and a lighting device by utilizing this phenomenon.

[0003] As an example of field emission, it 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) disposed opposite each other at a predetermined distance, and an electron beam can be emitted toward the anode by electrons generated in the electron source due to the application. By irradiating (colliding) such an electron beam onto the anode, a desired function (for example, the resolution of fluoroscopy by external emission of X-rays in the case of an X-ray device) can be exhibited.

[0004] In the electron source, there is one having an electrode substrate such as a Si substrate or a SUS substrate, and a cold cathode provided with an electron emission portion on the end face (hereinafter, simply referred to as the anode-side facing surface as appropriate) on the side of the electrode substrate facing the anode is mentioned.

[0005] In addition, as the electron emission portion, for example, by growing carbon nuclei generated on the anode-side facing surface by the CVD method (directly growing with respect to the anode-side facing surface), a carbon film (graphene, carbon nanotube, etc.) grows three-dimensionally and overlaps to form a carbon nanostructure having an internal hollow shape. Other aspects include growing a carbon film in a flat film shape (long shape) on a substrate (a heat-resistant substrate for transfer, etc.; hereinafter, simply referred to as a transfer substrate as appropriate) in advance, and transferring the carbon film on the transfer substrate to the anode-side facing surface of the electrode substrate (transfer using a brazing material layer, etc.).

[0006] For example, Patent Document 1 discloses a method for forming an electron emission portion made of carbon nanostructures on the anode-facing surface of an electrode substrate using a support jig (a jig indicated by reference numeral 12 in Patent Document 1) having a support hole (a storage hole indicated by reference numeral 12a in Patent Document 1) capable of supporting the electrode substrate.

[0007] The electron beam needs to be focused so that it can be focused along the central axis (hereinafter simply referred to as the central axis) in the direction between the electron source and the anode and irradiated onto the anode. This focusing control can be achieved, for example, by reducing the beam diameter of the electron beam as it approaches the anode from the electron source, or by reducing the focal size (electron spot), which is the region where the electron beam collides with the anode.

[0008] For example, in Patent Documents 2 and 3, it has been investigated how to suppress localized electric field concentration that may occur, for example, in the electron emission section (especially the peripheral part), by providing a guard electrode on the outer circumference of the cold cathode (a guard electrode indicated by reference numeral 5 in Patent Document 2, and a guard electrode indicated by reference numeral 13 in Patent Document 3), thereby making it easier to focus the electron beam.

[0009] In addition, to make it easier to focus and control the electron beam, it is being considered to reduce the electron source diameter (electron emission area) of the electron source by, for example, forming an electron emission section on the anode-facing surface of a small-diameter electrode substrate.

[0010] Japanese Patent Publication No. 2007-186368, Japanese Patent Publication No. 2022-52784, Japanese Patent Publication No. 2010-56062

[0011] As mentioned above, simply using a small-diameter electrode base results in poor handling of the electrode base (for example, ease of work when installing the electron emission section, ease of positioning relative to the central axis, ease of assembly when assembling the electrode base to other components, etc.).

[0012] This could make it difficult to form an electron source with desired physical properties (e.g., film quality of the electron emission section) (e.g., stably formed by CVD). Furthermore, assembly errors between the electrode substrate and other components may become more likely, making desired axial alignment adjustments more difficult. Additionally, variations in the electron beam may occur, leading to increased dispersion and potentially larger beam diameters and focal sizes.

[0013] As a result, simply providing a guard electrode on the outer periphery of the electron source (cold cathode) may not suppress electric field concentration as desired, potentially making it difficult to focus and control the electron beam.

[0014] This invention has been made in view of the above technical problems, and aims to provide a technology that can contribute to preventing the handling of the electrode substrate of an electron source from being impaired, and to making it easier to control the focusing of the electron beam as desired.

[0015] The electron source, electron beam emission structure, field emission device, and method for manufacturing the electron source according to this invention can contribute to solving the aforementioned problems.

[0016] <An Embodiment of an Electron Source> An embodiment of an electron source comprises an electrode substrate positioned such that one end in the axial direction faces the anode. The electrode substrate has an annular notched recess extending along the circumferential direction of the electrode substrate at the peripheral edge of the one end of the electrode substrate, a small-diameter portion protruding to the one side at the central part of the one end of the electrode substrate, and a large-diameter portion at the other end in the axial direction of the electrode substrate that is larger in diameter than the small-diameter portion. The electron emission portion is provided on the tip surface of the small-diameter portion on one side.

[0017] The small-diameter portion may be characterized by having a tapered shape, where at least one side is reduced in diameter to the extent that it is offset from the other side to the one side.

[0018] The tip surface on one side of the small-diameter portion may be characterized by having a curved concave shape.

[0019] The peripheral edge of the tip surface on one side of the small-diameter portion may be characterized by having a curved convex shape.

[0020] <Other Embodiments of an Electron Source> Another embodiment of an electron source comprises an electrode base positioned such that one end in the axial direction faces the anode, and an annular electrode cover provided to engage with the one end of the electrode base. The electrode base has an annular notched recess extending along the circumferential direction of the electrode base at the peripheral edge of the one end of the electrode base, a small-diameter portion protruding to the one end at the central part of the one end of the electrode base, and a large-diameter portion at the other end in the axial direction of the electrode base, which is larger in diameter than the small-diameter portion, and an electron-emitting portion is provided on the tip surface of the one end of the small-diameter portion. The electrode cover is characterized by having an annular cover portion that can be fitted into the notched recess in the engaged state, and a fitting hole that penetrates in the axial direction on the inner circumference side of the annular portion and can be fitted into the small-diameter portion in the engaged state.

[0021] The small-diameter portion may be characterized by having a tapered shape, where at least one side is reduced in diameter to the extent that it is offset from the other side to the one side.

[0022] The tip surface on one side of the small-diameter portion may be characterized by having a curved concave shape.

[0023] The peripheral edge of the tip surface on one side of the small-diameter portion may be characterized by having a curved convex shape.

[0024] The electrode cover may be characterized in that the central portion of one end face has a curved concave shape, and the peripheral edge of the end face has a curved convex shape.

[0025] The fitting hole may be characterized in that at least one side of the inner wall surface of the hole has a tapered shape that is so narrow that it is offset from the other side to the one side.

[0026] The axial dimension of the fitting hole is smaller than the axial dimension of the small diameter portion, and the end face on one side of the electrode cover extends in a direction that intersects the small diameter portion at an inclined angle such that a point on the end face moves from the other side to the one side as the point is offset from the radially outer side to the radially inward side, and in the engaged state, the one side of the small diameter portion protrudes from the fitting hole to the one side.

[0027] The large-diameter portion and the annular cover portion may be characterized by being brazed together with a brazing material interposed between them.

[0028] <An embodiment of an electron beam emission structure> An embodiment of an electron beam emission structure is characterized by comprising an embodiment of the electron source and a cylindrical guard electrode arranged coaxially with the electron source on the outer periphery of the electron source.

[0029] The guard electrode may have a cylindrical portion arranged coaxially with respect to the electron source and surrounding the outer circumference of the electron source, and a reduced-diameter portion protruding in a direction of decreasing diameter from one end of the cylindrical portion, wherein the reduced-diameter portion is close to or in contact with the small-diameter portion of the electrode base.

[0030] The end face on one side of the guard electrode may be characterized by being flush with the electron emission portion, or being offset to the one side of the electron emission portion.

[0031] The peripheral edge of the end face on one side of the guard electrode may be characterized by a shape that protrudes to the one side more than the central part of the end face.

[0032] <Other Embodiments of Electron Beam Emission Structure> Another embodiment of the electron beam emission structure is characterized by comprising another embodiment of the electron source and a cylindrical guard electrode arranged coaxially with the electron source on the outer periphery of the electron source.

[0033] The guard electrode may have a cylindrical portion arranged coaxially with respect to the electron source and surrounding the outer circumference of the electron source, and a reduced-diameter portion protruding in a direction of decreasing diameter from one end of the cylindrical portion, wherein the reduced-diameter portion is close to or in contact with the electrode cover.

[0034] The end face on one side of the guard electrode may be characterized by being flush with the electron emission portion, or being offset to the one side of the electron emission portion.

[0035] The peripheral edge of the end face on one side of the guard electrode may be characterized by a shape that protrudes to the one side more than the central part of the end face.

[0036] <An Embodiment of a Field Radiation Device> An embodiment of a field radiation device is characterized by having an embodiment of the electron beam emission structure. This field radiation device may also be characterized by comprising a voltage control unit capable of changing the voltage applied between the anode and the electron source.

[0037] <Other Embodiments of Field Radiation Devices> Other embodiments of field radiation devices are characterized by having other embodiments of the electron beam emission structure. These field radiation devices may be characterized by comprising a voltage control unit capable of changing the voltage applied between the anode and the electron source.

[0038] <One embodiment of a method for manufacturing an electron source> One embodiment of a method for manufacturing an electron source is that the electron source comprises an electrode substrate in which one end in the axial direction is positioned to face the anode.

[0039] The electrode substrate comprises an annular notched recess extending along the circumferential direction of the electrode substrate at the peripheral edge of one end of the electrode substrate, a small-diameter portion protruding to that side at the central part of the one end of the electrode substrate, and a large-diameter portion at the other end of the electrode substrate in the axial direction, which is larger in diameter than the small-diameter portion, and an electron emission portion is provided on the tip surface of the one end of the small-diameter portion.

[0040] Further, it includes a masking step of covering an annular mask on the one side of the electrode substrate, an electron emission part forming step of providing the electron emission part on the tip surface of the one side in the small-diameter part after the masking step, and a mask removing step of separating the electrode substrate and the mask after the electron emission part forming step.

[0041] And, the mask has a mask annular part that can be fitted into the notch recess in the covering state, and an exposure hole that penetrates in the axial direction on the inner peripheral side of the mask annular part. The electron emission part forming step is characterized by providing the electron emission part through the exposure hole in the covering state.

[0042] In the one aspect, at least the one side in the small-diameter part has a tapered shape that is tapered so as to be biased from the other side to the one side, and at least the one side on the inner wall surface of the exposure hole has a tapered shape that is tapered so as to be biased from the other side to the one side.

[0043] Further, the tip surface of the one side in the small-diameter part may be formed in a curved concave surface shape.

[0044] Further, the peripheral edge of the tip surface of the one side in the small-diameter part may be formed in a curved convex surface shape.

[0045] Further, the electron emission part forming step may be characterized by using a support jig having a support hole capable of accommodating and supporting the electrode substrate covered with the mask.

[0046] Further, it further includes an electrode cover engaging step of engaging and providing an annular electrode cover on the one side of the electrode substrate. The electrode cover has a cover annular part that can be fitted into the notch recess in the engaging state, and a fitting hole that penetrates in the axial direction on the inner peripheral side of the annular part and can be fitted into the small-diameter part in the engaging state.

[0047] Further, it further has an electrode cover engaging step of engaging an annular electrode cover on the one side of the electrode substrate, and the electrode cover has a cover annular portion that can be fitted into the notch recess in the engaged state, and a fitting hole that penetrates in the axial direction on the inner peripheral side of the annular portion and can be fitted into the small-diameter portion in the engaged state, and at least one side of the inner wall surface of the fitting hole is tapered such that the diameter is reduced so as to be biased from the other side to the one side.

[0048] Further, it may be characterized in that the central portion of the end surface on the one side of the electrode cover has a curved concave shape, and the peripheral portion of the end surface has a curved convex shape.

[0049] Further, it further has an electrode cover engaging step of engaging an annular electrode cover on the one side of the electrode substrate, and the electrode cover has a cover annular portion that can be fitted into the notch recess in the engaged state, and a fitting hole that penetrates in the axial direction on the inner peripheral side of the annular portion and can be fitted into the small-diameter portion in the engaged state, the dimension of the fitting hole in the axial direction is smaller than the dimension of the small-diameter portion in the axial direction, the end surface on the one side of the electrode cover extends in a direction intersecting the small-diameter portion at an inclined angle such that a point on the end surface moves from the other side to the one side as the point is biased from the radially outer side to the radially inner side, and in the engaged state, the one side of the small-diameter portion protrudes from the fitting hole to the one side.

[0050] Further, the electrode cover engaging step may be characterized in that both the large-diameter portion and the cover annular portion are brazed with a brazing material interposed therebetween.

[0051] As described above, according to the present invention, it is possible to contribute to easily obtaining desired handleability in the electron source and easily performing focusing control as desired in the electron beam.

[0052] A schematic diagram illustrating the electron source E1 according to Example 1 (cross-sectional view along the central axis). A schematic diagram illustrating the manufacturing method of electron source E1 according to Example 1 (cross-sectional view along the central axis). A schematic diagram illustrating the electron source E2 according to Example 1 (cross-sectional view along the central axis). A schematic diagram illustrating the manufacturing method of electron source E2 according to Example 1 (cross-sectional view along the central axis). A schematic diagram illustrating the electron source E3 according to Example 1 (cross-sectional view along the central axis). A schematic diagram illustrating the electron source E4 according to Example 2 (cross-sectional view along the central axis). A schematic diagram illustrating the electron source E5 according to Example 2 (cross-sectional view along the central axis). A schematic diagram illustrating the electron source E6 according to Example 2 (cross-sectional view along the central axis). A schematic diagram illustrating the electron source E7 according to Example 2 (cross-sectional view along the central axis). A schematic diagram illustrating the electron beam emission structure according to Example 3 (cross-sectional view along the central axis). A schematic diagram illustrating the electron beam emission structure according to Example 3 (cross-sectional view along the central axis). A figure showing an example of electron beam focusing characteristics when field emission is simulated in the electron beam emission structure according to Example 3. A figure showing another example of electron beam focusing characteristics when field emission is simulated in the electron beam emission structure according to Example 3. A figure illustrating the electron beam emission structure according to Example 4 and showing the electron beam focusing characteristics when field emission is simulated.

[0053] The electron source, the method for manufacturing the electron source, the electron beam emission structure, and the field emission device in the embodiments of the present invention are completely different from, for example, a configuration in which an electron emission section is formed on the anode-facing surface of a simple small-diameter electrode substrate.

[0054] In other words, this embodiment includes an electrode substrate in which the electron source is positioned such that one end of the electrode substrate in the axial direction (the axial direction of the electrode substrate; hereinafter referred to as simply the axial direction as appropriate) faces the anode.

[0055] This electrode base comprises an annular notched recess extending along the circumferential direction (hereinafter simply referred to as the circumferential direction) of the electrode base at the peripheral edge of one end in the axial direction of the electrode base, a small-diameter portion protruding toward the axial direction at the central part (inner circumference side of the notched recess) of the end of the end in the axial direction of the electrode base, and a large-diameter portion at the other end in the axial direction (hereinafter simply referred to as the other axial direction) that is larger in diameter than the small-diameter portion.

[0056] In other words, the electrode substrate has a convex cross-section in the axial direction (hereinafter simply referred to as a convex cross-section as appropriate), and an electron emission portion is provided on the anode-facing surface (the tip surface on one side in the axial direction) in the small-diameter portion.

[0057] With the aforementioned electrode substrate having a convex cross-section, the area where the electron emission portion is provided (the anode-facing surface of the small-diameter portion) is reduced in diameter, thus reducing the electron emission area of ​​the electron emission portion (the electron source diameter of the electron source). On the other hand, the side of the electrode substrate opposite the electron emission portion has a relatively large shape (i.e., a shape with a large-diameter portion), which helps to prevent the handling of the electrode substrate (and electron source) from being compromised. Furthermore, it becomes easier to maintain a certain level of mechanical strength, for example.

[0058] For example, in the electrode substrate, the large diameter portion makes it easier to achieve self-supporting stability, and the electrode substrate can be easily supported in a stable state by a support jig. Furthermore, with this stable support state, it becomes easier to form the desired electron emission portion on the anode-facing surface of the small diameter portion. Also, in the electron beam emission structure, the large diameter portion of the electrode substrate makes it easier to support the electrode substrate in a position facing the anode, which helps to suppress assembly errors with other components and makes it easier to perform the desired axial alignment adjustment.

[0059] Therefore, it becomes easier to form an electron source with desired physical properties, and the electron beam of such an electron source can be irradiated onto the anode so as to be focused along the central axis, making it easier to control the focus as desired. Furthermore, a field emission device equipped with such an electron source can more easily perform the desired functions.

[0060] Furthermore, when modifying the design of the electron emission section (for example, modifying the design to give it desired physical properties), the shape of the small-diameter section may be modified as appropriate, but the design modification of the large-diameter section itself can be omitted as appropriate. This allows for the appropriate omission of design modifications in jigs (for example, the support jig W described later) and other components (for example, the support section 13 described later) necessary for creating electron sources and electron beam emission structures.

[0061] In other words, while the electron emission section is redesigned, the support jigs and other components mentioned above can be standardized before and after the design change, potentially contributing to increased manufacturing efficiency (such as lower costs).

[0062] One conventional method involves forming an electron emission region on the anode-facing surface of a relatively large-diameter electrode substrate, then removing the peripheral portion of the electron emission region through cleaning (removal with alcohol, etc.), cutting, polishing, etc., leaving only the central portion of the electron emission region. This method also has the potential to reduce the electron source diameter (electron emission area) of the electron source.

[0063] However, it is difficult to completely remove only the peripheral portion of the electron emission area through cleaning and removal processes. Furthermore, cutting and polishing only the peripheral portion of the electron emission area generates debris (cutting debris, polishing debris, etc. from the electron emission area), which may adhere to and remain on the processed area and surrounding areas (for example, the outer surface of the electrode substrate or the central part of the electron emission area), and may also cause the surface of the processed area and surrounding areas to become rough, which is undesirable.

[0064] In this embodiment, as described above, the electrode substrate of the electron source has a convex cross-section and is configured to have notched recesses, small diameter sections, large diameter sections, electron emission sections, etc., and it is possible to appropriately apply common technical knowledge from various fields (for example, the field of field radiation devices, the field of carbon nanotubes, etc.). For example, it is possible to modify the design as needed by appropriately referring to Patent Documents 1 to 3, etc., and Examples 1 to 4 shown below are one example.

[0065] In the following Examples 1 to 4, detailed explanations have been appropriately omitted, for example, by referring to the same reference numerals and terms for similar content.

[0066] <Example 1> <Schematic Configuration of Electron Source E1> Figure 1 is a schematic diagram illustrating the electron source E1 according to Example 1. The electron source E1 has a columnar (for example, cylindrical) electrode base S1, and is applied in such a manner that one end of the electrode base S1 in the axial direction (the anode-facing surface 2a side described later) is positioned facing the anode (for example, the anode T described later).

[0067] The electrode base S1 has an annular notched recess 11 extending circumferentially at the peripheral edge of one end in the axial direction. Furthermore, a small-diameter portion 21 protruding toward the axial direction is provided at the central part of the end on the axial direction (the inner circumference side of the notched recess 11). Additionally, a large-diameter portion 12, larger in diameter than the small-diameter portion 21, is provided at the other end of the electrode base S1 in the axial direction.

[0068] The electrode substrate S1, with this configuration, has an overall convex cross-sectional shape. In the small-diameter portion 21 of the electrode substrate S1, an electron emission portion 3a is provided on the anode-facing surface 2a, which is the end face on one side in the axial direction.

[0069] <Example of Electrode Substrate S1 Configuration> The electrode substrate S1 has a convex cross-sectional shape as a whole, as described above, and it is sufficient that the electron emission portion 3a provided on the anode-facing surface 2a can perform the desired function (electron emission, etc.) when a voltage of a desired magnitude is applied, and various configurations can be applied.

[0070] One example is a substrate material made from a conductive metal material such as stainless steel (SUS material, etc.) or copper, or an alloy (e.g., Fe-Cr-Ni alloy). When using such a substrate material, for example, the substrate material may be molten and molded into a convex cross-section, or a columnar molded body may be formed beforehand and then cut and polished to form a convex cross-section (forming a notched recess 11). In addition, there are also examples of substrates (silicon substrates, tungsten substrates, etc.) with good bonding properties to carbon (e.g., carbon nanostructures) that are molded into a convex cross-section.

[0071] Furthermore, even if, for example, a relatively small-diameter molded body and a relatively large-diameter molded body are molded separately and connected coaxially, it is possible to achieve a convex cross-section similar to that of the electrode base S1. However, it may be difficult to precisely align the axes of both bodies.

[0072] The shape of the electrode substrate S1 (for example, the dimensions in the axial direction and the radial direction) can be appropriately set according to the target electron source E1, etc.

[0073] For example, as an example of an electrode base S1 to be applied to a field emission device such as a microfocus X-ray tube, the axial dimension of the electrode base S1 may be set to a range of several hundred micrometers to several millimeters, the radial dimension of the small diameter portion 21 may be set to a range of several tens of micrometers to several hundred micrometers, and the radial dimension of the large diameter portion 12 may be set to a range of several hundred micrometers to several tens of millimeters, with each being set as appropriate.

[0074] Furthermore, the peripheral edge of the anode-facing surface 2c may have a curved convex shape, similar to the electron source E3 described later.

[0075] <Example of the configuration of the electron emission unit 3a> The electron emission unit 3a is provided on the anode-facing surface 2a, and by applying a voltage of a desired magnitude, electrons are generated on the surface of the electron emission unit 3a, and these generated electrons are emitted toward the anode T described later to form an electron beam. Various configurations can be applied. A specific example is one in which a thin film is formed on the anode-facing surface 2a (for example, by forming a film using CVD, transfer, etc.).

[0076] When the electron emission section 3a is constructed from carbon nanostructures, it is sufficient if the carbon film (graphene, carbon nanotubes, etc.) grows three-dimensionally and overlaps to form an internally hollow structure, and this can be done by various methods. Alternatively, when the carbon film is constructed by a transfer method, it is sufficient if, for example, a flat (long) carbon film is transferred to the anode-facing surface 2a via a wax layer or the like, and this can be done by various transfer methods.

[0077] When forming such an electron-emitting portion 3a by CVD, for example, it can be formed by sequentially going through the following steps: masking step, electron-emitting portion formation step, and mask removal step.

[0078] <Example of Masking Process> In the masking process, for example, as shown in Figure 2, an annular mask M1 is applied to one side of the electrode substrate S1 in the axial direction.

[0079] The purpose of this mask M1 is to form the electron emission portion 3a only on the anode-facing surface 2a in the subsequent electron emission portion formation process, and it is sufficient if other surfaces (for example, the surface of the notched recess 11) can be appropriately masked.

[0080] In the case of the mask M1 shown in Figure 2, the mask has an annular portion 40 that can be fitted into the notched recess 11 when covered on the electrode substrate S1 (hereinafter simply referred to as the mask covered state), and an exposed hole 4 that penetrates axially on the inner circumference side of the mask annular portion 40. The exposed hole 4 is shaped to be fitted onto the small diameter portion 21 so as to receive the small diameter portion 21 when the mask is covered.

[0081] Specifically, in the case of the exposed hole 4 in Figure 2, the inner wall surface 4a of the hole has a cylindrical shape that extends axially along the outer circumferential surface 1a of the small-diameter portion 21, thereby enabling it to be fitted into the small-diameter portion 21. When the mask is covered, the anode-facing surface 2a of the small-diameter portion 21 is exposed through the exposed hole 4.

[0082] Furthermore, in the mask M1 shown in Figure 2, the outer diameter of the outer surface 4c of the mask M1 and the outer diameter of the outer surface 1c of the large-diameter portion 12 are formed to be the same or substantially equivalent (i.e., flush), but the invention is not limited to this.

[0083] For example, if the outer diameter of the outer peripheral surface 4c is less than or equal to the outer diameter of the outer peripheral surface 1c, then in the subsequent electron emission section formation process, when the electrode base S1 is housed and supported in the support hole W1 of the support jig W described later, the mask M1 can also be housed in the support hole W1 together with the electrode base S1 (i.e., it can be housed in a mask-covered state).

[0084] Furthermore, even if the outer diameter of the outer peripheral surface 4c is larger than the outer diameter of the outer peripheral surface 1c, by appropriately processing the portion of the support hole W1 of the support jig W described later that corresponds to the mask M1 (for example, by enlarging the inner wall surface W2 of the hole), the mask M1 can be accommodated together with the electrode base S1 in the processed support hole W1 (i.e., it can be accommodated with the mask covered).

[0085] Since the mask M1 can be removed in a subsequent mask removal step, it does not need to be fixed to the electrode base S1 by adhesive or the like. Therefore, in the mask-covered state, the annular portion 40 and exposed holes 4 of the mask M1 only need to be able to be detachably fitted into the notched recess 11 and the small-diameter portion 21, respectively.

[0086] Furthermore, while it is preferable that the mask M1 and the electrode base S1 be in close contact with each other without any gaps when the mask is covered, a small clearance may be provided between them in advance, for example, to account for dimensional errors between the two or to allow for detachable fitting.

[0087] Furthermore, in the case of the mask M1 shown in Figure 2, the opening edge surface 41 on one side in the axial direction of the exposed hole 4 and the anode-side opposing surface 2a are flush with each other. However, this is not limited to this, and depending on the shape of the electron emission section 3a formed in the subsequent electron emission section formation process, the two surfaces may be appropriately positioned so that they are offset from each other in the axial direction.

[0088] Furthermore, the mask M1 only needs to have sufficient durability to withstand the formation of the electron emission section 3a in the subsequent electron emission section formation process, and can be made using various materials. One example of such a material is one that can also be used as the substrate material for the electrode substrate S1.

[0089] <Example of electron emission part formation process and mask removal process> First, in the electron emission part formation process, an electron emission part 3a is formed by applying the CVD method using a support jig W in which a support hole W1 is formed, for example as shown in Figure 2.

[0090] In the case of the support hole W1 shown in Figure 2, the shape is such that both the electrode substrate S1 and the mask M1 in the mask-covered state can be accommodated and supported, but it is not limited to this. For example, even if the shape accommodates and supports only the electrode substrate S1 in the mask-covered state (i.e., the mask M1 is supported with the mask protruding from the support hole W1), it is still possible to carry out the electron emission section formation process as appropriate.

[0091] Furthermore, the support jig W may have multiple support holes W1 formed in it, thereby enabling the electron emission part formation process to be carried out simultaneously on multiple electrode substrates S1. In addition, the support jig W only needs to have durability during the electron emission part formation process and can be made using various materials, one example being that it is made of a metallic material such as molybdenum.

[0092] For example, the electrode substrate S1 (and mask M1) in a mask-covered state is housed in the support hole W1 of the support jig W described above (for example, first positioned in the posture shown in Figure 2, then moved in the direction of the dashed arrow to house it) and supported (removably supported), and in this supported state it is placed inside the vacuum chamber of a CVD apparatus (not shown) (under a vacuum atmosphere at a predetermined temperature). Then, inside the vacuum chamber, a carbon film precursor (for example, a precursor produced by plasma decomposition of hydrogen and methane) is deposited on the anode-side opposing surface 2a, and carbon nuclei are generated and grown on the anode-side opposing surface 2a (directly grown on the anode-side opposing surface 2a).

[0093] As a result, a hollow carbon nanostructure is formed on the anode-facing surface 2a, where carbon films (graphene, carbon nanotubes, etc.) grow and overlap three-dimensionally, thereby forming the desired electron emission section 3a. At this time, a carbon nanostructure is also formed on the surface on one side in the axial direction of the mask M1, but this carbon nanostructure will be removed along with the mask M1 in a subsequent mask removal process.

[0094] Alternatively, a carbon film may be grown on a transfer substrate in advance, and the carbon film on the transfer substrate may be transferred to the anode-facing surface 2a of the electrode substrate S1 (and mask M1) in a mask-coated state (see revised table of Publication No. 2000 / 085291). In this case, a carbon film will also be formed (transferred) on one side of the axial direction of the mask M1, but this carbon film will be removed along with the mask M1 in a subsequent mask removal step.

[0095] After this electron emission section formation process, the electrode substrate S1 and the mask M1 are separated in a mask removal process.

[0096] <Example of a carbon nanostructure> When the electron emission section 3a is composed of a carbon nanostructure, it is sufficient that the electron emission section 3a exhibits the desired function, and various embodiments can be applied.

[0097] The surface of a carbon nanostructure is not simply flat, but rather, for example, it may have an island-like structure in which micron-sized granular portions (hereinafter simply referred to as surface granule tops as appropriate) that rise from the surface are formed to be distributed in an island-like manner on the surface (for example, by forming countless surface granular portions densely packed together).

[0098] In the case of carbon nanostructures forming this island-like structure, the surface side of the surface granules has a shape in which tiny fibrous carbon films (for example, streaky graphene) protrude. Furthermore, adjacent surface granules are formed to bond with each other at their root ends.

[0099] The surface granular portion can be formed in a desired shape by appropriately setting the film formation conditions of the applied film formation method (for example, precursor generation conditions, temperature conditions of the anode-side opposing surface 2a, electric field and electric field line density for the anode-side opposing surface 2a, etc.), and a large-grain shape is preferred.

[0100] The large-grained surface granules can be formed as appropriate depending on the shape of the anode-facing surface 2a, etc. Specific examples include a configuration in which the ridged dimension of the surface granules is 10 μm or more, preferably 20 μm or more, more preferably 30 μm or more, and the radial dimension of the largest diameter portion of the surface granules (for example, the base of the upper part of the surface grains) is 10 μm or more, preferably 20 μm or more, more preferably 30 μm or more. Configurations with large grains that can be observed with a stereomicroscope are also possible.

[0101] Furthermore, there is no particular upper limit to the dimensions in the direction of elevation of the granular surface portion or the radial dimensions of the maximum diameter portion; for example, they could be set to about 50 μm each. However, it is preferable to set them appropriately so as to maintain the island-like structure on the surface of the carbon nanostructure.

[0102] Furthermore, the shape of the surface granules can be, but is not limited to, conical, fusiform, or spherical shapes. In addition, the tip of the surface granule in the direction of elevation can be formed to have a curved shape that is obtusely convex in the direction of elevation. This makes it easier to form the tip of the upper surface granule to have a large radial dimension (for example, 5 μm or more, preferably 10 μm or more), which may make it easier to obtain durability against electron beams with high current density.

[0103] Furthermore, the surface granular portions formed on the surface of the carbon nanostructure do not necessarily have to be entirely large-grained; some may be of other grain shapes (e.g., small grain shapes). However, it is preferable to suppress the proportion of these other grain shapes so that they remain within a range that allows the desired function of the target field emission device to be achieved.

[0104] The electron source E1 described above can achieve similar effects even if the shape of the electrode substrate S1 is appropriately changed, for example. One example of such a change is to the electron sources E2 and E3 described later.

[0105] <Modification of electron source E1 (Part 1)> Figure 3 is a schematic diagram illustrating electron source E2. Electron source E2 has an electrode substrate S2 that, like electrode substrate S1, has a convex cross-sectional shape overall.

[0106] The electrode base S2 has a small-diameter portion 22 that protrudes toward the axial direction at the center of one end of the electrode base S2 (on the inner circumference side of the notched recess 11).

[0107] The small-diameter portion 22 has a tapered shape in which one side in the axial direction (the anode-facing surface 2a side) is reduced in diameter as it is offset from the other side in the axial direction to the one side in the axial direction. In the case of the small-diameter portion 22 in Figure 3, one side in the axial direction of the outer circumferential surface 1a of the small-diameter portion 22 has a tapered surface shape (a shape with a tapered surface 1b in Figure 3) as it is reduced in diameter as it is offset from the other side in the axial direction to the one side in the axial direction, resulting in a tapered shape, but it is not limited to this. For example, the entire outer circumferential surface 1a of the small-diameter portion 22 may have the tapered surface shape described above.

[0108] Due to the tapered shape of the small-diameter portion 22 as described above, the anode-facing surface 2b of the small-diameter portion 22 is more easily reduced in diameter compared to, for example, the anode-facing surface 2a of the small-diameter portion 21. Furthermore, the electron-emitting portion 3b formed on the anode-facing surface 2b is also more easily reduced in diameter (i.e., the electron-emitting area is reduced).

[0109] On the other hand, the base side of the small-diameter portion 22 (the side with the large-diameter portion 12) has a relatively large diameter compared to the anode-facing surface 2b of the small-diameter portion 22, so it is possible to obtain mechanical strength similar to that of the small-diameter portion 21, for example.

[0110] In the electron emission section 3b of this electron source E2, as in the case of electron source E1, it is possible to form it by sequentially going through the masking process, electron emission section formation process, and mask removal process described above.

[0111] However, in the case of the electrode substrate S2 of the electron source E2, since the outer surface 1a of the small diameter portion 22 has a tapered shape, it is preferable to apply a mask M2 as shown in Figure 4 rather than simply applying a mask M1 as shown in Figure 2 (a configuration in which a cylindrical inner wall surface 4a is formed in the exposed hole 4).

[0112] The mask M2 shown in Figure 4 is annular, similar to the mask M1, and one side of the inner wall surface 4a of the exposed hole 4 in the axial direction (opening edge surface 41 side) is tapered, similar to the outer circumferential surface 1a of the small diameter portion 22, with the diameter of the small diameter portion 22 tapering as it is offset from the other side in the axial direction to the one side in the axial direction. Specifically, one side of the inner wall surface 4a of the mask M2 in the axial direction has a tapered surface shape (a shape with a tapered surface 4d in Figure 4) that is tapered as it is offset from the other side in the axial direction to the one side in the axial direction, resulting in a tapered shape.

[0113] With a mask M2 as shown in Figure 4, even if the electrode base S2 has a tapered small-diameter portion 22, the mask M2 and the electrode base S2 can easily come into close contact with each other when the mask is applied, and it is possible to prevent any gaps from forming between them.

[0114] In the mask M2 shown in Figure 4, the opening edge surface 41 is positioned offset to the other side in the axial direction compared to the anode-side opposing surface 2b. In this case, depending on the degree of offset, an electron emission portion 3b can also be formed on the anode-side opposing surface 2b side (tapered surface 1b) of the outer circumferential surface 1a of the small diameter portion 22.

[0115] <Modified Electron Source E1 (Part 2)> Figure 5 is a schematic diagram illustrating the electron source E3. The electron source E3 also has an electrode substrate S3 that, like the electrode substrate S1, has a convex cross-sectional shape overall.

[0116] The electrode base S3 has a small-diameter portion 23 that protrudes in the axial direction from the central part (inner circumference side of the notched recess 11) of one end of the electrode base S3. The anode-side opposing surface 2c is formed on the tip surface of the small-diameter portion 23 on one end in the axial direction, and has a curved concave shape (a curved concave surface 2d in Figure 5) that is recessed in the other end in the axial direction.

[0117] In the case of the anode-side opposing surface 2c shown in Figure 5, the entire anode-side opposing surface 2c has a curved concave shape, but it is not limited to this. For example, only the central part of the anode-side opposing surface 2c may have a curved concave shape, while the peripheral part of the anode-side opposing surface 2c may have a curved convex shape.

[0118] With such a curved concave shape on the anode-side opposing surface 2c, the surface of the electron emission portion 3c formed on the anode-side opposing surface 2c also takes on a curved concave shape. As a result, electrons generated on the surface of the electron emission portion 3c are more easily emitted towards the anode T, which will be described later, in a direction biased toward the central axis.

[0119] In the electron emission section 3c of this electron source E3, as with the electron source E1, it is possible to form it by sequentially following the masking process, electron emission section formation process, and mask removal process described above. In the case of the electron source E3, since the shape of the outer peripheral surface 1a of the small diameter section 23 is simply a cylindrical shape extending in the axial direction, it is possible to appropriately apply a mask M1 as shown in Figure 2 (a configuration in which the inner wall surface 4a of the hole is simply cylindrical).

[0120] <Example 2> Each of the electron sources E1 to E3 may contain electrically unstable elements (for example, elements that may cause electric field concentration or abnormal discharge) around the electron emission sections 3a to 3c. For example, in the case of electron sources E1 to E3, since the outer surface 1c is exposed, if a voltage is simply applied in this exposed state, a phenomenon may occur in which unintended electrons are emitted from, for example, the outer surface 1c.

[0121] In such cases, it is preferable to suppress the aforementioned phenomenon by providing an electrode cover C1, such as the electron source E4 shown below, and shielding the outer surface 1c, etc.

[0122] <Schematic Configuration of Electron Source E4> Figure 6 is a schematic diagram illustrating the electron source E4 according to Embodiment 2. Similar to electron source E1, electron source E4 has an electrode base S1 that has a convex cross-sectional shape overall, and an annular electrode cover C1 is engaged with and provided on one side of the electrode base S1 in the axial direction.

[0123] In the case of the electrode cover C1 shown in Figure 6, the cover has an annular portion 50 that can be fitted into the notched recess 11 when engaged with the electrode base S1 (hereinafter referred to as simply the cover engaged state), and a fitting hole 5 that penetrates axially on the inner circumference side of the cover annular portion 50. The fitting hole 5 is shaped to be able to fit into the small diameter portion 21 so as to receive the small diameter portion 21 when the cover is engaged.

[0124] Specifically, in the case of the fitting hole 5 in Figure 6, the inner wall surface 5a of the hole has a cylindrical shape that extends axially along the outer circumferential surface 1a of the small diameter portion 21, thereby enabling fitting into the small diameter portion 21. When the cover is engaged, the anode-facing surface 2a of the small diameter portion 21 is exposed through the fitting hole 5.

[0125] Furthermore, in the electrode cover C1 shown in Figure 6, the outer diameter of the outer circumferential surface 5c of the electrode cover C1 and the outer diameter of the outer circumferential surface 1c of the large diameter portion 12 are formed to be the same or substantially equivalent (i.e., flush), but the invention is not limited to this.

[0126] For example, if the outer diameter of the outer surface 5c is less than or equal to the outer diameter of the outer surface 1c, it may become easier to perform the electrode cover engagement process, for example, when using the support jig W in the electrode cover engagement process described later.

[0127] Furthermore, even if the outer diameter of the outer peripheral surface 5c is larger than the outer diameter of the outer peripheral surface 1c, by appropriately processing the portion of the support hole W1 of the support jig W described later that corresponds to the electrode cover C1 (for example, by enlarging the inner wall surface W2 of the hole), the electrode cover C1 can be accommodated together with the electrode base S1 in the support hole W1 after processing (i.e., it can be accommodated with the cover engaged).

[0128] Furthermore, the electrode cover C1 should be configured in such a way that it can appropriately shield the outer surface 1c, etc., when the cover is engaged. For this reason, when the cover is engaged, the electrode cover C1 and the electrode base S1 may be placed close to each other or in contact so as not to leave any gap, or a clearance may be provided between them as shown in Figure 8, which will be described later.

[0129] In the case of the electrode cover C1 shown in Figure 6, the opening edge surface 51 on one side in the axial direction of the fitting hole 5 and the anode-side opposing surface 2a are flush with each other. However, the design is not limited to this, and depending on the shape of the electron emission portion 3a, for example, they may be appropriately positioned so that they are offset from each other in the axial direction. Preferably, the opening edge surface 51 is positioned offset to one side in the axial direction from the electron emission portion 3a. In this case, for example, the electric field may be more easily relaxed at the periphery of the electron emission portion 3a.

[0130] Furthermore, the electrode cover C1 only needs to have durability when a desired voltage is applied, and can be made using various materials. One example of such a material is one that can also be used as the base material for the electrode substrate S1.

[0131] Furthermore, the electrode cover C1 only needs to be attached to the electrode base S1 so as to maintain the cover engagement state. One example of this is brazing the electrode base S1 with a brazing material (for example, by vacuum brazing).

[0132] The brazing material can be any material that can be placed on the brazing surfaces of both the large-diameter portion 12 of the electrode base S1 and the electrode cover C1 and brazed appropriately. For example, it can be a shape that extends circumferentially along the brazing surface (such as a thin-walled plate or annular shape).

[0133] As a specific example, in the case of the electron source E4 shown in Figure 6, an annular notch groove 53 extending in the circumferential direction is provided on the peripheral edge of the end of the electrode cover C1 on the other side in the axial direction. Furthermore, the electrode cover C1 can be engaged with the notch groove 53 with an annular brazing material 54 extending in the circumferential direction placed in the notch groove 53. Then, the desired brazing can be achieved by melting and solidifying the brazing material 54 under a vacuum atmosphere or the like.

[0134] As described above, the electrode cover C1 having the notched groove 53 allows the electrode cover C1 to be gripped through the notched groove 53, which may make it easier to detach it from the electrode base S1, for example.

[0135] <Example of electrode cover engagement process> In the electron source E4, similar to the case of electron source E1, the electron emission part 3a is formed by sequentially going through the masking process, electron emission part formation process, and mask removal process, and then the electrode cover C1 is engaged by the electrode cover engagement process.

[0136] As described above, this electrode cover engagement step only requires that the electrode cover C1 be appropriately engaged, and various embodiments can be applied. However, it is preferable, for example, to prevent the electrode cover C1 and the electron emission part 3a from colliding with each other, thereby suppressing damage to the electron emission part 3a.

[0137] A specific example is the application of the support jig W used in the electron emission section formation process. In this case, the electrode base S1 is first housed and supported in the support hole W1, and then the electrode cover C1 is engaged with the electrode base S1. At this time, the electrode cover C1 is guided by the inner wall surface W2 of the support hole W1 and engages with the electrode base S1 to become a cover-engaged state, which makes it easier to suppress damage to the electron emission section 3a.

[0138] The electron source E4 described above can achieve similar effects even if the shape of the electrode substrate S1, electrode cover C1, etc., is appropriately changed. One example of such a change is to modify the electron sources E5 to E7, which will be described later.

[0139] <Modified form of electron source E4 (part 1)> Figure 7 is a schematic diagram illustrating electron source E5. Similar to electron source E1, electron source E5 has an electrode base S1 that has a convex cross-sectional shape overall, and an annular electrode cover C2 is engaged with and provided on one side of the electrode base S1 in the axial direction.

[0140] In the case of the electrode cover C2 shown in Figure 7, the central part of the end face 52 on one side in the axial direction of the electrode cover C2 has a curved concave shape (a shape having a curved concave surface 5d in Figure 7). On the other hand, the peripheral part of the end face 52 has a curved convex shape (a shape having a curved convex surface 5e in Figure 7).

[0141] With such an electrode cover C2, the peripheral edge of the end face 52 of the electrode cover C2 is positioned offset to one side in the axial direction compared to the electron emission portion 3a. Therefore, for example, the electric field may be more easily relaxed at the peripheral edge of the electron emission portion 3a.

[0142] <Modified form of electron source E4 (part 2)> Figure 8 is a schematic diagram illustrating electron source E6. Similar to electron source E2, electron source E6 has an electrode base S2 that has a convex cross-sectional shape overall, and an annular electrode cover C3 is engaged with and provided on one side of the electrode base S2 in the axial direction.

[0143] In the case of the electrode cover C3 shown in Figure 8, one side of the inner wall surface 5a of the fitting hole 5 in the axial direction (the side with the opening edge surface 51) is tapered toward one side in the axial direction, similar to the outer circumferential surface 1a of the small diameter portion 22. Specifically, one side of the inner wall surface 5a of the electrode cover C3 in the axial direction has a tapered surface shape (a shape with a tapered surface 5f in Figure 8) that is reduced in diameter as it is offset from the other side in the axial direction toward one side in the axial direction, resulting in a tapered shape.

[0144] With such an electrode cover C3, even if the electrode base S2 has a tapered small-diameter portion 22, both the electrode cover C3 and the electrode base S2 can be engaged, making it possible to shield the outer circumferential surface 1a of the small-diameter portion 22 as desired. The electrode cover C3 and the electrode base S2 may be placed close to each other or in contact with each other without any gap, or a clearance may be provided between them as shown in Figure 8.

[0145] <Modification of electron source E4 (part 3)> Figure 9 is a schematic diagram illustrating electron source E7. Similar to electron source E2, electron source E7 has an electrode base S2 that has a convex cross-sectional shape overall, and an annular electrode cover C4 is engaged with and provided on one side of the electrode base S2 in the axial direction.

[0146] In the case of the electrode cover C4 shown in Figure 9, the axial dimension of the fitting hole 5 is set to be smaller than the axial dimension of the small diameter portion 22. Specifically, the axial dimension of the fitting hole 5 is set to be approximately the same as the axial dimension of the portion of the small diameter portion 22 where the outer surface 1a has a cylindrical shape (i.e., where the tapered surface 1b is not formed).

[0147] As a result, when the electrode cover C4 is engaged, one side of the small-diameter portion 22 in the axial direction (the tapered surface 1b side) protrudes from the fitting hole 5 in the axial direction.

[0148] The end face 52 of the electrode cover C4 extends in a direction that intersects the small diameter portion 22 at an inclined angle, such that as a point on the end face 52 is offset from the radially outer side to the radially inner side (towards the fitting hole 5), the point is offset from the other side in the axial direction to the one side in the axial direction. The peripheral end 55 of the end face 52 may be chamfered as appropriate (e.g., R chamfering, C chamfering, thread chamfering, etc.), as shown in Figure 9.

[0149] With such an electrode cover C4, even if the peripheral edge (tapered surface 1b side) of the electron emission portion 3b in the small diameter portion 22 protrudes from the fitting hole 5 when the cover is engaged, it is possible to sufficiently mitigate the electric field at the peripheral edge of the electron emission portion 3b.

[0150] <<Example 3>> The electron sources E1 to E3 shown in Example 1 can each be applied as a cold cathode to various electron beam emission structures, and one example of this is the configuration shown in Figure 10.

[0151] Figure 10 is a schematic diagram illustrating an electron beam emission structure when the electron source E1 is used as a cold cathode. The electron beam emission structure shown in Figure 10 mainly comprises an electron source E1 and an anode T arranged facing each other, and a guard electrode G1 arranged to cover the outer circumference of the electron source E1. In Figure 10, a power supply E is provided to apply a voltage (tube voltage) between the electron source E1 (and guard electrode G1) and the anode T.

[0152] In the case of the electron source E1 shown in Figure 10, the electron emission portion 3a of the electrode substrate S1 is supported by the support portion 13 in a position facing the anode T. In the case of the support portion 13 shown in Figure 10, the large-diameter portion 12 of the electrode substrate S1 is fitted into the support hole 13a to support the electron source E1, but this is not the only option.

[0153] <Example of Anode T Configuration> The anode T can be any device that can emit X-rays or the like (not shown) when it collides with an electron beam emitted from an electron source E1 (electron emission unit 3a), and various configurations can be applied. In the anode T shown in Figure 10, there is a surface T1 facing the electron emission unit 3a of the anode T to which the electron beam is irradiated (hereinafter simply referred to as the irradiated surface as appropriate), and the electron beam collides with the irradiated surface T1. The irradiated surface T1 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 collides with the irradiated surface T1 will be irradiated in a direction bent from the emission direction of the electron beam (for example, one side of the left and right directions shown).

[0154] <Example of Guard Electrode G1 Configuration> The guard electrode G1 is provided so as to cover the outer periphery of the electron source E1 as described above, and only needs to be able to mitigate the electric field at the periphery of the electron emission section 3a (suppressing localized electric field concentration) and focus the electron beam to the central axis as desired (suppressing the dispersion of electrons emitted from the electron source E1), and various configurations can be applied.

[0155] In the case of the guard electrode G1 shown in Figure 10, it has a cylindrical portion 61 that is arranged coaxially with respect to the electron source E1 (coaxially with respect to the central axis) and surrounds the outer circumference of the electron source E1, and a reduced-diameter portion 62 that protrudes radially inward (reduced diameter) from one end of the cylindrical portion 61 in the axial direction.

[0156] The end of the guard electrode G1 on one side in the axial direction (the reduced diameter portion 62 side in Figure 10) may be in contact with (or close to) the electron source E1, or a predetermined gap may be provided between it and the electron source E1.

[0157] In the case of Figure 10, the inner circumferential surface 63 of the reduced-diameter portion 62 is positioned to engage with the notched recess 11 of the electrode base S1, and the inner circumferential surface 63 and the outer circumferential surface 1a of the small-diameter portion 21 are in contact with (or close to) each other. With such a configuration, it is possible to suppress phenomena such as the unintended emission of electrons from the outer circumferential surface 1c, for example.

[0158] Furthermore, although the end face 64 on one side in the axial direction of the guard electrode G1 and the electron emission portion 3a of the small diameter portion 21 are depicted as being flush with each other, this is not the only way to do so. For example, depending on the strength of the electric field relaxation by the guard electrode G1 and the shape of the electron emission portion 3a, the two may be appropriately positioned so that they are offset from each other in the axial direction. Preferably, the end face 64 is positioned offset to one side in the axial direction from the electron emission portion 3a. In this case, for example, the electric field may be more easily relaxed at the periphery of the electron emission portion 3a.

[0159] Furthermore, the end face 64 is not limited to a shape that simply extends in the radial direction, but can take on various forms. For example, as shown in Figure 11, the peripheral edge of the end face 64 can be made to protrude to one side in the axial direction from the end face 64 (a shape with a curved convex surface 65 in Figure 11). With the guard electrode G1 as shown in Figure 11, the peripheral edge of the end face 52 is positioned offset to one side in the axial direction from the central part of the end face and the electron emission part 3a, so the electric field may be more easily mitigated at the peripheral edge of the electron emission part 3a, for example.

[0160] In addition, the guard electrode G1 may have a configuration that simply includes a cylindrical portion 61 (i.e., a configuration that omits the reduced-diameter portion 62), as long as it can mitigate the electric field at the periphery of the electron emission portion 3a. In this case, for example, the end face 64 (curved convex surface 65 in Figure 11) on one side in the axial direction of the cylindrical portion 61 may be positioned offset to one side in the axial direction from the electron emission portion 3a.

[0161] The guard electrode G1 described above only needs to have durability when a desired voltage is applied, and can be made using various materials. One example of such a material is one that can also be used as the substrate material for the electrode substrate S1.

[0162] <Examples of Field Radiation Device Configurations> According to the electron beam emission structures shown in Figures 10 and 11, it is possible to configure various types of field radiation devices. One example is a vacuum vessel (not shown) in which both ends of a cylindrical insulator are sealed and a vacuum chamber is formed on the inner circumference side of the insulator. Specifically, an anode T is placed on one side in the axial direction of the vacuum chamber in the vacuum vessel, and an electron source E1 and a guard electrode G1 are placed on the other side in the axial direction of the vacuum chamber, with appropriate wiring so that the voltage of the power supply E can be applied as desired.

[0163] <Other> Various configurations can be applied to the voltage application configuration by power supply E. For example, the configuration may include a voltage control unit (not shown) that can appropriately change the voltage.

[0164] Examples of voltage control unit settings include setting the control unit to increase the focusing power of the electron beam when it is necessary to reduce the focal size, such as in microfocus X-rays. Conversely, when it is necessary to irradiate an anode T with a high-power electron beam while minimizing damage to the anode T, the control unit should be set to decrease the focusing power of the electron beam.

[0165] In the electron beam emission structure shown in Figures 10 and 11, when a predetermined voltage is applied by a power supply E, electrons generated at the cold cathode (electron source E1 in the case of Figures 10 and 11) can emit an electron beam toward the anode T. In this case, if, for example, the electric field at the periphery of the electron emission section 3a is relaxed by the guard electrode G1 and the electron beam is focused toward the central axis as desired, then the electron beam focusing characteristics shown in Figure 12 can be obtained.

[0166] Figure 12 shows the focusing characteristics of the electron beam when field emission is simulated. In Figure 12, the horizontal axis extending horizontally in the lower part of the figure represents the central axis of the electron beam emission structure, and the anode T is assumed to be located to the right on this horizontal axis (i.e., one side in the axial direction). The multiple curves and lines drawn extending to the right from the electron emission section 3a in Figure 12 each represent the movement paths of electrons emitted from the electron emission section 3a.

[0167] Figure 12 shows that electrons generated from the central part of the electron emission unit 3a move toward the anode T along the central axis. On the other hand, electrons generated from the peripheral part of the electron emission unit 3a (particularly the position close to the guard electrode G1) move toward the anode T while being biased toward the central axis from the peripheral part, and this indicates that the electron beam is focused toward the central axis.

[0168] Specifically, in the case of the electron beam shown in Figure 12, the region of the electron beam that is radially inward and close to the central axis (indicated by the symbol Y1 in Figure 12) is composed only of electrons generated from the central part of the electron emission unit 3a, while the region of the electron beam that is radially outward (indicated by the symbol Y2 in Figure 12) is composed of electrons generated from both the central and peripheral parts of the electron emission unit 3a.

[0169] <Example 4> In an electron beam emission structure using electron sources E1 to E3 as shown in Example 3, if, for example, the intensity of electric field relaxation by the guard electrode G1 is relatively large, or / or the electron source diameter is relatively small, the electron beam may not be focused as desired, and the focusing characteristics of the electron beam (the electron beam when the electric field emission is simulated in the same way as in Figure 12) may be as shown in Figure 13.

[0170] In the case of the electron beam shown in Figure 13, it can be seen that electrons generated from the central part of the electron emission section 3a move toward the anode T along the central axis. On the other hand, electrons generated from the peripheral part of the electron emission section 3a are biased toward the central axis from the peripheral part, but can be seen to move toward the opposite side of the central axis. Specifically, in the case of the electron beam shown in Figure 13, there are electrons that move while biased toward away from the central axis (for example, electrons in the region indicated by the symbol Y3 in Figure 13), and it can be seen that variations and dispersion of the electron beam are occurring.

[0171] When such variations and dispersion of the electron beam occur, by applying electron sources E4 to E7 as cold cathodes to the electron beam emission structure, it is possible to obtain the focusing characteristics of the electron beam shown in Figure 14 (the electron beam when field emission is simulated, similar to Figure 12).

[0172] In Figure 14, the reduced-diameter portion 62 of the guard electrode G1 is in contact with (or close to) the electrode cover C1 provided on the electrode substrate S1. It can be seen that the electrons generated from the central and peripheral portions of the electron emission portion 3a move toward the anode T along the central axis (for example, as the electrons in the region indicated by the symbol Y4 in Figure 14).

[0173] Therefore, in the electron beam emission structure shown in Figures 10 and 11, by appropriately applying any of the electron sources E1 to E7 as the cold cathode, it is possible to focus the electron beam as desired, even if the intensity of electric field relaxation by the guard electrode G1 is relatively large, and / or the electron source diameter is relatively small, and the variation and dispersion of the electron beam can be appropriately suppressed. In other words, the electron beam can be focused and controlled as desired, and the field emission device can perform the desired function.

[0174] Although the present invention has been described in detail only with respect to the specific examples described above, it will be obvious to those skilled in the art that a wide variety of 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.

[0175] For example, the elements in Examples 1 to 4 may be combined as appropriate, and the contents disclosed in Patent Documents 1 to 3 can also be applied as appropriate to modify the design, making it possible to achieve the same effects as in Examples 1 to 4.

[0176] E1-E7...Electron source, S1-S3...Electrode substrate, G1...Guard electrode, 11...Notched recess, 12...Large diameter section, 21-23...Small diameter section, 2a-2c...Anode-side opposing surface, 3a-3c...Electron emission section, C1-C4...Electrode cover, 5...Matching hole, 50...Cover annular section, M1, M2...Mask, 4...Exposed hole, 40...Mask annular section

Claims

1. An electron source comprising an electrode base positioned such that one end in the axial direction faces the anode, wherein the electrode base has an annular notched recess extending along the circumferential direction of the electrode base at the peripheral edge of the one end of the electrode base, a small-diameter portion protruding to the one side at the central part of the one end of the electrode base, and a large-diameter portion at the other end in the axial direction of the electrode base that is larger in diameter than the small-diameter portion, wherein an electron emission portion is provided on the tip surface of the one side of the small-diameter portion.

2. The electron source according to claim 1, characterized in that at least one side of the small-diameter portion is tapered in shape, with the diameter reduced to the extent that it is offset from the other side to the one side.

3. The electron source according to claim 1, characterized in that the tip surface on one side of the small diameter portion has a curved concave shape.

4. The electron source according to claim 1, characterized in that the peripheral edge of the tip surface on one side of the small diameter portion has a curved convex shape.

5. An electron source comprising: an electrode base positioned such that one end in the axial direction faces the anode; and an annular electrode cover provided to engage with the one end of the electrode base, wherein the electrode base has an annular notched recess extending along the circumferential direction of the electrode base at the peripheral edge of the one end of the electrode base; a small-diameter portion protruding to the one end at the central part of the one end of the electrode base; and a large-diameter portion at the other end in the axial direction of the electrode base, which is larger in diameter than the small-diameter portion, wherein an electron-emitting portion is provided on the tip surface of the one end of the small-diameter portion; and the electrode cover has an annular cover portion that can be fitted into the notched recess in the engaged state; and a fitting hole that penetrates in the axial direction on the inner circumference side of the annular portion and can be fitted into the small-diameter portion in the engaged state.

6. The electron source according to claim 5, characterized in that at least one side of the small-diameter portion is tapered in shape, with the diameter reduced to the extent that it is offset from the other side to the one side.

7. The electron source according to claim 5, characterized in that the tip surface on one side of the small diameter portion has a curved concave shape.

8. The electron source according to claim 5, characterized in that the peripheral edge of the tip surface on one side of the small diameter portion has a curved convex shape.

9. The electron source according to claim 5, characterized in that the central portion of one end face of the electrode cover has a curved concave shape, and the peripheral portion of the end face has a curved convex shape.

10. The electron source according to claim 6, characterized in that at least one side of the inner wall surface of the fitting hole has a tapered shape that is offset from the other side to the one side.

11. The electron source according to claim 6, characterized in that the axial dimension of the fitting hole is smaller than the axial dimension of the small diameter portion, the end face on one side of the electrode cover extends in a direction that intersects the small diameter portion at an inclined angle such that a point on the end face moves from the other side to the one side as the point is deflected from the radially outer side to the radially inward side, and in the engaged state, one side of the small diameter portion protrudes from the fitting hole to the one side.

12. The electron source according to claim 5, characterized in that both the large-diameter portion and the cover annular portion are brazed together with a brazing material interposed between them.

13. An electron beam emission structure comprising: an electron source according to any one of claims 1 to 4; and a cylindrical guard electrode arranged coaxially with the electron source on the outer periphery of the electron source.

14. The electron beam emission structure according to claim 13, wherein the guard electrode has a cylindrical portion arranged coaxially with respect to the electron source and surrounding the outer circumference of the electron source, and a reduced-diameter portion protruding in a direction of decreasing diameter from one end of the cylindrical portion, and the reduced-diameter portion is close to or in contact with the small-diameter portion of the electrode base.

15. The electron beam emission structure according to claim 14, characterized in that the end face on one side of the guard electrode is flush with the electron emission portion, or is positioned offset to the one side of the electron emission portion.

16. The electron beam emission structure according to claim 14, characterized in that the peripheral edge of the one end face of the guard electrode protrudes to the one side more than the central part of the end face.

17. An electron beam emission structure comprising: an electron source according to any one of claims 5 to 12; and a cylindrical guard electrode arranged coaxially with the electron source on the outer periphery of the electron source.

18. The electron beam emission structure according to 17, wherein the guard electrode has a cylindrical portion arranged coaxially with respect to the electron source and surrounding the outer circumference of the electron source, and a diameter-reducing portion protruding in a direction of diameter reduction from one end of the cylindrical portion, and the diameter-reducing portion is close to or in contact with the electrode cover.

19. The electron beam emission structure according to claim 18, characterized in that the end face on one side of the guard electrode is flush with the electron emission portion, or is positioned offset to the one side of the electron emission portion.

20. The electron beam emission structure according to claim 18, characterized in that the peripheral edge of the one end face of the guard electrode protrudes to the one side more than the central part of the end face.

21. A field emission device characterized by having the electron beam emission structure described in claim 13.

22. The field radiation apparatus according to claim 21, further comprising a voltage control unit capable of changing the voltage applied between the anode and the electron source.

23. A field emission device characterized by having the electron beam emission structure described in claim 17.

24. The field emission device according to claim 23, further comprising a voltage control unit capable of changing the voltage applied between the anode and the electron source.

25. A method for manufacturing an electron source, the electron source comprises an electrode base in which one end in the axial direction is positioned facing the anode, the electrode base having an annular notched recess extending along the circumferential direction of the electrode base at the peripheral edge of the one end of the electrode base, a small-diameter portion in the central part of the one end of the electrode base that protrudes to that side, and a large-diameter portion at the other end in the axial direction of the electrode base that is larger in diameter than the small-diameter portion, an electron-emitting portion provided on the tip surface of the one end of the small-diameter portion, the method comprising a masking step of covering the one side of the electrode base with an annular mask, an electron-emitting portion forming step of providing the electron-emitting portion on the tip surface of the one end of the small-diameter portion after the masking step, and a mask removal step of separating the electrode base and the mask after the electron-emitting portion forming step, the mask having a mask annular portion that can be fitted into the notched recess in the covered state, A method for manufacturing an electron source, comprising: an exposed hole having a shape that penetrates in the axial direction on the inner circumference side of the annular portion of the mask; and the electron emission portion forming step characterized in that the electron emission portion is provided through the exposed hole in the covered state.

26. The method for manufacturing an electron source according to claim 25, characterized in that at least one side of the small-diameter portion is tapered in diameter, with the diameter decreasing to the point where it is offset from the other side to the one side, and at least one side of the inner wall surface of the exposed hole is tapered in diameter, with the diameter decreasing to the point where it is offset from the other side to the one side.

27. The method for manufacturing an electron source according to claim 25, characterized in that the tip surface on one side of the small diameter portion has a curved concave shape.

28. The method for manufacturing an electron source according to claim 25, characterized in that the peripheral edge of the tip surface on one side of the small diameter portion has a curved convex shape.

29. The method for manufacturing an electron source according to claim 25, characterized in that the electron emission portion forming step uses a support jig having support holes capable of accommodating and supporting the electrode substrate covered with the mask.

30. The method for manufacturing an electron source according to claim 25, further comprising an electrode cover engagement step of engaging an annular electrode cover with one side of the electrode substrate, wherein the electrode cover has an annular cover portion that can be fitted into the notched recess in the engaged state, and a fitting hole that penetrates in the axial direction on the inner circumference side of the annular portion and can be fitted into the small diameter portion in the engaged state.

31. The method for manufacturing an electron source according to 26, further comprising an electrode cover engagement step of engaging an annular electrode cover with one side of the electrode substrate, wherein the electrode cover has an annular cover portion that can be fitted into the notched recess in the engaged state, and a fitting hole that penetrates in the axial direction on the inner circumference side of the annular portion and can be fitted into the small diameter portion in the engaged state, and at least one side of the inner wall surface of the fitting hole has a tapered shape that is deviated from the other side to the one side.

32. The method for manufacturing an electron source according to claim 30 or 31, characterized in that the central portion of one end face of the electrode cover has a curved concave shape, and the peripheral portion of the end face has a curved convex shape.

33. The method for manufacturing an electron source according to 26, further comprising an electrode cover engagement step of engaging an annular electrode cover with one side of the electrode substrate, wherein the electrode cover has an annular cover portion that can be fitted into the notched recess in the engaged state, and a fitting hole that penetrates the inner circumference of the annular portion in the axial direction and can be fitted into the small diameter portion in the engaged state, wherein the axial dimension of the fitting hole is smaller than the axial dimension of the small diameter portion, the end face of one side of the electrode cover extends in a direction that intersects the small diameter portion at an inclined angle such that a point on the end face moves from the other side to the one side as the point is deflected from the radially outer side to the radially inward side, and in the engaged state, the one side of the small diameter portion protrudes from the fitting hole to the one side.

34. The method for manufacturing an electron source according to any one of claims 30, 31, or 33, characterized in that the electrode cover engagement step involves brazing both the large-diameter portion and the annular portion of the cover with a brazing material interposed between them.

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