Electron source manufacturing method

Abstract

To provide a technology that can contribute to making it easier to obtain desired handling properties in an electron source and to making it easier to control the focusing of an electron beam as desired. [Solution] An electron source E1 includes a columnar electrode base S1 with one axial end facing an anode T. The electrode base S1 has an annular cutout recess 11 extending circumferentially at the peripheral edge of the one axial end of the electrode base S1, a small diameter portion 21 that protrudes to one axial end on the inner periphery of the cutout recess 11 in the electrode base S1, and a large diameter portion 12 that is at the other axial end of the electrode base S1 and has a diameter larger than that of the small diameter portion 21. An electron emission portion 3a is provided on an anode-facing surface 2a of the small diameter portion 21.

Description

[Technical Field]

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

[0002] Field emission is a phenomenon in which electrons are emitted into a vacuum atmosphere (for example, in an insulating vacuum container) due to the concentration of an electric field. Studies have been conducted to utilize 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 the electrons generated in the electron source by this application can emit an electron beam toward the anode. By irradiating (colliding) this electron beam on the anode, a desired function (for example, in the case of an X-ray device, radioscopic resolution due to the external emission of X-rays) can be achieved.

[0004] Examples of electron sources include cold cathodes that have an electrode substrate such as a Si substrate or a SUS substrate, and that have an electron emission section provided on the end face of the electrode substrate that faces the anode (hereinafter simply referred to as the anode-side facing surface).

[0005] The electron emission portion may be, for example, a carbon nanostructure in which carbon films (graphene, carbon nanotubes, etc.) are three-dimensionally grown and overlapped to form a hollow interior by growing carbon nuclei (growth directly on the anode-facing surface) generated on the anode-facing surface by a CVD method. Other examples include a carbon nanostructure in which a flat (elongated) carbon film is first grown on a substrate (such as a heat-resistant substrate for transfer; hereinafter simply referred to as a transfer substrate), and the carbon film on the transfer substrate is then transferred (using a brazing layer, etc.) to the anode-facing surface of the electrode base.

[0006] For example, Patent Document 1 discloses a mode in which an electron emission section made of carbon nanostructures is formed on the anode-facing surface of an electrode substrate using a support jig (denoted by reference numeral 12 in Patent Document 1) having a support hole (denoted by reference numeral 12a in Patent Document 1) capable of supporting the electrode substrate.

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

[0008] For example, Patent Documents 2 and 3 consider providing a guard electrode (guard electrode indicated by reference numeral 5 in Patent Document 2, guard electrode indicated by reference numeral 13 in Patent Document 3) on the outer periphery of the cold cathode, thereby suppressing localized electric field concentration that can occur, for example, in the electron-emitting portion (especially the peripheral portion), and making it easier to focus the electron beam.

[0009] In addition, in order to make it easier to control the focusing of the electron beam, it is also being considered to reduce the electron source diameter (electron emission area) of the electron source, for example by forming an electron emission portion on the anode-facing surface of a small-diameter electrode substrate. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-186368 [Patent Document 2] Japanese Patent Publication No. 2022-52784 [Patent Document 3] Japanese Patent Application Laid-Open No. 2010-56062 Summary of the Invention [Problem to be solved by the invention]

[0011] If a simple small-diameter electrode substrate is used as described above, the handleability of the electrode substrate (for example, the ease of providing the electron-emitting section, the ease of positioning relative to the central axis, the ease of assembly when assembling the electrode substrate to other components, etc.) will be reduced.

[0012] This may make it difficult to form (for example, stably form by CVD or the like) an electron source having desired physical properties (for example, the film quality of the electron-emitting portion). Also, assembly errors between the electrode substrate and other components may be more likely to occur, making it more difficult to achieve the desired axial centering adjustment. Furthermore, the electron beam may be more likely to be dispersed, resulting in larger beam diameters and focal spot sizes.

[0013] As a result, even if a guard electrode is simply provided on the outer periphery of the electron source (cold cathode), it is not possible to suppress the electric field concentration as desired, and it may become difficult to control the focusing of the electron beam.

[0014] The present invention has been made in consideration of the above technical problems, and aims to provide a technology that can contribute to preventing the electrode substrate of the electron source from being impaired in handleability and facilitating desired focusing control of the electron beam. [Means for solving the problem]

[0015] The method for manufacturing an electron source according to the present invention can contribute to solving the above-mentioned problems. In one aspect of the method for manufacturing an electron source, the electron source includes an electrode substrate disposed with one end portion on one side in an axial direction facing an anode.

[0016] The electrode substrate has a ring-shaped cutout recess extending circumferentially around the peripheral edge of the one end of the electrode substrate, a small diameter portion protruding to one side in the center 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, the large diameter portion being larger than the small diameter portion, and an electron emission portion is provided on the tip surface on the one side of the small diameter portion.

[0017] The method also includes a masking step of covering one side of the electrode substrate with a ring-shaped mask, an electron emission portion forming step of providing the electron emission portion on the tip surface of one side of the small diameter portion after the masking step, and a mask removal step of separating the electrode substrate and the mask after the electron emission portion forming step.

[0018] The mask has a mask annular portion that can be fitted into the cutout recess in the covered state, and an exposure hole that penetrates the inner periphery of the mask annular portion in the axial direction, and the electron emission portion forming process is characterized in that the electron emission portion is provided through the exposure hole in the covered state.

[0019] In one aspect, at least one side of the small diameter portion may have a tapered shape that is reduced in diameter as it biases from the other side toward the one side, and at least one side of the inner wall surface of the exposure hole may have a tapered shape that is reduced in diameter as it biases from the other side toward the one side.

[0020] The tip end surface on the one side of the small diameter portion may be curved and concave.

[0021] The small diameter portion may have a peripheral edge portion of the tip end surface on the one side thereof that has a curved convex shape.

[0022] The electron-emitting portion forming step may be characterized by using a support jig having a support hole capable of receiving and supporting the electrode substrate covered with the mask.

[0023] The method may further include an electrode cover engagement step of engaging an annular electrode cover with the one side of the electrode base, wherein the electrode cover has a cover annular portion that can be fitted into the cutout recess in the engaged state, and a fitting hole that penetrates the inner peripheral side of the annular portion in the axial direction and can be fitted into the small diameter portion in the engaged state.

[0024] The method may further include an electrode cover engagement step of engaging an annular electrode cover with the one side of the electrode base, wherein the electrode cover has a cover annular portion that can fit into the cutout recess in the engaged state, and a fitting hole that penetrates the inner peripheral side of the annular portion in the axial direction and can fit into the small diameter portion in the engaged state, and at least the one side of the inner wall surface of the fitting hole has a tapered shape that is reduced in diameter so as to be biased from the other side toward the one side.

[0025] The electrode cover may have a central portion on one end surface thereof that is curved concave, and a peripheral portion on the end surface thereof that is curved convex.

[0026] The method may further include an electrode cover engagement step of engaging an annular electrode cover with the one side of the electrode base, wherein the electrode cover has a cover annular portion that can be fitted into the cutout recess in the engaged state, and a fitting hole that penetrates the inner peripheral side 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, and the one end face of the electrode cover extends in a direction that intersects with the small diameter portion at an oblique angle so that a point on the end face moves from the other side to the one side as the point is biased from the radial outside to the radial inside, and the one side of the small diameter portion protrudes from the fitting hole to the one side in the engaged state.

[0027] The electrode cover engaging step may be characterized by brazing both the large diameter portion and the annular cover portion with a brazing material interposed therebetween. [Effects of the Invention]

[0028] As described above, the present invention can contribute to making it easier to obtain desired handling properties in an electron source and easier to control the focusing of an electron beam as desired. [Brief explanation of the drawings]

[0029] [Figure 1] 1 is a schematic configuration diagram (cross-sectional view along the central axis) for explaining an electron source E1 according to a first embodiment. [Figure 2] 1 is a schematic configuration diagram (cross-sectional view along the central axis) for explaining a manufacturing method of an electron source E1 according to a first embodiment. [Figure 3] 1 is a schematic configuration diagram (cross-sectional view along the central axis) for explaining an electron source E2 according to a first embodiment. [Figure 4] 1 is a schematic configuration diagram (cross-sectional view along the central axis) for explaining a manufacturing method of an electron source E2 according to a first embodiment. [Figure 5] 1 is a schematic configuration diagram (cross-sectional view along the central axis) for explaining an electron source E3 according to a first embodiment. [Figure 6] FIG. 10 is a schematic configuration diagram (cross-sectional view along the central axis) for explaining an electron source E4 according to a second embodiment. [Figure 7] FIG. 10 is a schematic configuration diagram (cross-sectional view along the central axis) for explaining an electron source E5 according to a second embodiment. [Figure 8] FIG. 10 is a schematic configuration diagram (cross-sectional view along the central axis) for explaining an electron source E6 according to a second embodiment. [Figure 9] FIG. 10 is a schematic configuration diagram (cross-sectional view along the central axis) for explaining an electron source E7 according to a second embodiment. [Figure 10] FIG. 10 is a schematic configuration diagram (cross-sectional view along the central axis) for explaining an electron beam emission structure according to a third embodiment. [Figure 11] FIG. 10 is a schematic configuration diagram (cross-sectional view along the central axis) for explaining an electron beam emission structure according to a third embodiment. [Figure 12] FIG. 10 is a diagram showing an example of the focusing characteristics of an electron beam when simulating field emission in the electron beam emission structure according to the third embodiment. [Figure 13] 10 is a diagram showing another example of the focusing characteristics of the electron beam when simulating field emission in the electron beam emission structure according to the third embodiment. FIG. [Figure 14] 10A and 10B are diagrams for explaining the electron beam emission structure according to the fourth embodiment and showing the focusing characteristics of the electron beam when field emission is simulated. DETAILED DESCRIPTION OF THE INVENTION

[0030] 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 a configuration in which an electron emission section is formed on the surface of a small-diameter electrode substrate facing the anode, for example.

[0031] That is, in this embodiment, the electron source is provided with an electrode substrate whose end on one side (hereinafter simply referred to as one side in the axial direction) in the axial direction (axial direction of the electrode substrate; hereinafter simply referred to as the axial direction) is positioned facing the anode.

[0032] This electrode substrate has an annular cutout recess extending along the circumferential direction of the electrode substrate (hereinafter simply referred to as the circumferential direction) at the peripheral edge of the end portion on one axial side of the electrode substrate, a small diameter portion protruding to one side in the axial direction at the center (inner circumferential side of the cutout recess) of the end portion on one axial side of the electrode substrate, and a large diameter portion at the end portion on the other axial side of the electrode substrate (hereinafter simply referred to as the other axial side) and having a diameter larger than that of the small diameter portion.

[0033] That is, the electrode substrate has a convex cross section in the axial direction (hereinafter referred to simply as a convex cross section), and an electron emission section is provided on the anode-facing surface of the small diameter portion (the tip surface on one side in the axial direction).

[0034] In the electrode substrate having the above-described convex cross section, the electron emission area of ​​the electron emission section (the diameter of the electron source of the electron source) can be reduced because the diameter of the portion where the electron emission section is provided (the surface of the small diameter section facing the anode) is reduced. On the other hand, the opposite side of the electron emission section of the electrode substrate has a relatively large shape (i.e., a shape having a large diameter section), which prevents the electrode substrate (and the electron source) from being impaired in handleability. In addition, it is easier to maintain a certain level of mechanical strength, for example.

[0035] For example, in an electrode substrate, the large diameter portion facilitates self-supporting, making it easier to stably support the electrode substrate using a support jig. Furthermore, this stable support also facilitates the formation of a desired electron-emitting portion on the anode-facing surface of the small diameter portion. In an electron beam emission structure, the large diameter portion of the electrode substrate also facilitates supporting the electrode substrate in a position facing the anode, making it easier to suppress assembly errors with other components and facilitates the desired axial centering adjustment.

[0036] Therefore, it becomes easy to form an electron source having desired physical properties, and the electron beam of the electron source can be irradiated onto the anode so as to be focused on the central axis, making it easy to control the focusing as desired, and the field emission device equipped with the electron source can easily exhibit the desired functions.

[0037] Furthermore, when changing the design of the electron emission section (for example, changing the design to give it desired physical properties), for example, the shape of the small diameter section can be changed as appropriate, but the design change of the large diameter section itself can be omitted as appropriate. This makes it possible to appropriately omit design changes in jigs (for example, the support jig W described below) and other components (for example, the support section 13 described below) required to create the electron source, electron beam emission structure, etc.

[0038] In other words, while the design of the electron emission section is changed, the support jigs and other components as described above can be made common before and after the design change of the electron emission section, which may contribute to manufacturing efficiency (lower costs, etc.).

[0039] One conventional method is to form an electron-emitting portion on the anode-facing surface of a relatively large-diameter electrode substrate, and then remove the peripheral portion of the electron-emitting portion by cleaning and removing (removing with alcohol, etc.), cutting and polishing, etc., so that only the center portion of the electron-emitting portion remains. This method also has the potential to reduce the electron source diameter (electron-emitting area) of the electron source.

[0040] However, it is difficult to completely remove only the peripheral edge of the electron-emitting portion by cleaning and removing processing. Furthermore, cutting and polishing only the peripheral edge of the electron-emitting portion generates debris (cutting debris, polishing debris, etc. of the electron-emitting portion) that may adhere to or remain on the processed portion or its surroundings (for example, the outer periphery of the electrode substrate or the center of the electron-emitting portion), and may also roughen the surface of the processed portion or its surroundings, which is undesirable.

[0041] In this embodiment, as described above, it is sufficient that the electrode substrate of the electron source has a convex cross section and is configured to have a notched recess, a small diameter portion, a large diameter portion, an electron emission portion, etc., and common technical knowledge in various fields (for example, the field of field emission devices, the field of carbon nanotubes, etc.) can be applied as appropriate. For example, design modifications can be made as necessary by appropriately referring to Patent Documents 1 to 3, etc., and examples thereof include Examples 1 to 4 shown below.

[0042] In the following Examples 1 to 4, for example, the same contents will be omitted in detail as appropriate by citing the same symbols and terms.

[0043] Example 1 <Schematic configuration of electron source E1> 1 is a schematic diagram illustrating an electron source E1 according to Example 1. The electron source E1 has a columnar (e.g., cylindrical) electrode base S1, and is applied so that an end portion on one side in the axial direction of the electrode base S1 (the side of an anode-side facing surface 2a described later) faces an anode (e.g., an anode T described later).

[0044] The electrode substrate S1 has an annular cutout recess 11 extending circumferentially on the periphery of one end portion in the axial direction. A small diameter portion 21 protruding toward one side in the axial direction is provided in the center of the end portion on one side in the axial direction (inner peripheral side of the cutout recess 11). A large diameter portion 12 having a diameter larger than that of the small diameter portion 21 is provided at the end portion on the other side in the axial direction of the electrode substrate S1.

[0045] The electrode substrate S1 having such a configuration has a convex cross section as a whole. An electron-emitting portion 3a is provided on the anode-facing surface 2a, which is the end face on one side in the axial direction, of the small-diameter portion 21 of the electrode substrate S1.

[0046] <Configuration example of electrode substrate S1> As described above, the electrode substrate S1 has a shape with a convex cross section as a whole, and various configurations can be applied as long as the electron emission portion 3a provided on the anode-side facing surface 2a can perform the desired function (electron emission, etc.) when a voltage of the desired magnitude is applied.

[0047] Examples of such a substrate include those made using a substrate material such as a conductive metal material, such as stainless steel (e.g., SUS material) or copper, or an alloy (e.g., an Fe-Cr-Ni alloy). When using such a substrate material, the substrate material may be molten and molded into a molded body with a convex cross section, or a columnar molded body may be formed in advance and then cut and polished to form a convex cross section (to form a notched recess 11). Other examples include those made by molding a substrate (e.g., a silicon substrate or a tungsten substrate) that has good bonding properties with carbon (e.g., a carbon nanostructure) into a convex cross section.

[0048] Furthermore, for example, even if a relatively small diameter molded body and a relatively large diameter molded body are molded separately and then connected coaxially, it is possible to form a cross-sectional convex shape similar to the electrode base S1, but it may be difficult to accurately adjust the axial centering of the two bodies.

[0049] The shape of the electrode substrate S1 (for example, the axial dimension and the radial dimension) can be set appropriately depending on the intended electron source E1 and the like.

[0050] For example, as an example of the electrode substrate S1 when applied to a field emission device such as a microfocus X-ray tube, the axial dimension of the electrode substrate S1 may be set within a range of several hundred μm to several mm, the radial dimension of the small diameter portion 21 may be set within a range of several tens of μm to several hundred μm, and the radial dimension of the large diameter portion 12 may be set within a range of several hundred μm to several tens of mm, each of which may be appropriately set.

[0051] The peripheral edge of the anode-side facing surface 2c may have a curved convex shape, similar to the electron source E3 described later.

[0052] <Configuration Example of Electron Emission Section 3a> The electron-emitting portion 3a is provided on the anode-side facing surface 2a, and various modes can be applied as long as electrons are generated on the surface of the electron-emitting portion 3a by applying a voltage of a desired magnitude and the generated electrons are emitted toward the anode T described below to form an electron beam. A specific example is one formed as a thin film on the anode-side facing surface 2a (for example, formed by deposition using a CVD method, a transfer method, or the like).

[0053] When the electron emission portion 3a is made of a carbon nanostructure, it may be formed by various methods as long as carbon films (graphene, carbon nanotubes, etc.) are three-dimensionally grown and overlapped to form a hollow interior. When it is made of a carbon film by a transfer method, it may be formed by transferring a carbon film, for example, to the anode-side facing surface 2a via a brazing material layer or the like, and it may be formed by various transfer methods.

[0054] When such an electron-emitting portion 3a is formed by the CVD method, it can be formed, for example, by sequentially going through the following masking step, electron-emitting portion forming step, and mask removing step.

[0055] <An example of the masking process> In the masking step, for example, as shown in FIG. 2, one axial side of the electrode substrate S1 is covered with a ring-shaped mask M1.

[0056] This mask M1 is intended to form the electron emission section 3a only on the anode-side facing surface 2a in the subsequent electron emission section formation process, and it is sufficient if it can appropriately mask surfaces other than the anode-side facing surface 2a (for example, the surface of the cutout recess 11).

[0057] 2, the mask M1 has a mask annular portion 40 that can be fitted into the cutout recess 11 when the mask is fitted onto the electrode substrate S1 (hereinafter simply referred to as the mask-covered state), and an exposure hole 4 that penetrates the inner periphery of the mask annular portion 40 in the axial direction. The exposure hole 4 has a shape that can be fitted into the small diameter portion 21 so as to receive the small diameter portion 21 when the mask is covered.

[0058] 2, the inner wall surface 4a of the exposure hole 4 has a cylindrical shape extending in the axial direction along the outer peripheral surface 1a of the small diameter portion 21, thereby enabling it to be fitted into the small diameter portion 21. In the mask-covered state, the anode-facing surface 2a of the small diameter portion 21 is exposed through the exposure hole 4.

[0059] Furthermore, in the mask M1 of FIG. 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 approximately equivalent (i.e., flush), but this is not limited to this.

[0060] For example, if the outer diameter of the outer surface 4c is equal to or smaller than the outer diameter of the outer surface 1c, when the electrode substrate S1 is accommodated and supported in the support hole W1 of the support jig W described below in the subsequent electron emission portion formation process, the mask M1 can also be accommodated in the support hole W1 together with the electrode substrate S1 (i.e., can be accommodated in a mask-covered state).

[0061] 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 corresponding to the mask M1 in the support hole W1 of the support jig W described below (for example, by enlarging the diameter of the hole inner wall surface W2), the mask M1 can be accommodated in the processed support hole W1 together with the electrode substrate S1 (i.e., it can be accommodated in a mask-covered state).

[0062] The mask M1 does not need to be fixed to the electrode substrate S1 by adhesive or the like so that it can be removed in a subsequent mask removal step. Therefore, in the mask-covered state, the mask annular portion 40 and the exposure hole 4 of the mask M1 simply need to be detachably fitted into the notched recess 11 and the small diameter portion 21, respectively.

[0063] Furthermore, in the mask-covered state, it is preferable that the mask M1 and the electrode substrate S1 are in close contact with each other so that no gaps are left, but it is also possible to provide a small clearance between the two in advance, for example, taking into consideration dimensional errors between the two and the need for a detachable fit.

[0064] In addition, in the case of the mask M1 shown in Figure 2, the opening edge surface 41 on one side of the axial direction of the exposure hole 4 and the anode-side facing surface 2a are both flush, but this is not limited to this, and the two may be appropriately set to be positioned offset from each other in the axial direction, for example, depending on the shape of the electron emission section 3a to be formed in the subsequent electron emission section formation process, etc.

[0065] The mask M1 may be made of various materials as long as it is durable enough to form the electron-emitting portions 3a in the subsequent electron-emitting portion forming step, including materials that can also be used for the substrate of the electrode substrate S1.

[0066] <Example of electron emission section formation process and mask removal process> First, in the electron-emitting portion forming step, a support jig W having a support hole W1 as shown in FIG. 2 is used, and the electron-emitting portion 3a is formed by applying the CVD method.

[0067] 2, the support hole W1 has a shape that can accommodate and support both the mask-covered electrode substrate S1 and the mask M1, but is not limited to this. For example, even if the support hole W1 has a shape that accommodates and supports only the mask-covered electrode substrate S1 (i.e., supports the mask M1 in a state where it protrudes from the support hole W1), it is still possible to appropriately perform the electron-emitting portion forming step.

[0068] The support jig W may have a plurality of support holes W1 formed therein, which allows the electron-emitting portion forming step to be carried out simultaneously on a plurality of electrode substrates S1. The support jig W may be made of any material as long as it is durable enough for the electron-emitting portion forming step, and may be made of any of a variety of materials, one example of which is a metal material such as molybdenum.

[0069] For example, the mask-covered electrode substrate S1 (and mask M1) is accommodated (for example, first placed in the orientation shown in FIG. 2 and then moved in the direction of the dashed arrow to accommodate) and supported (detachably supported) in the support hole W1 of the support jig W as described above, and the electrode substrate S1 is placed in this supported state in a vacuum chamber (under a vacuum atmosphere at a predetermined temperature) of a CVD apparatus (not shown). Then, in the vacuum chamber, a precursor of a carbon film (for example, a precursor generated by plasma decomposition of hydrogen and methane) is deposited on the anode-side facing surface 2a, and carbon nuclei are generated and grown on the anode-side facing surface 2a (growth directly on the anode-side facing surface 2a).

[0070] As a result, hollow carbon nanostructures are formed on the anode-side facing surface 2a, in which carbon films (graphene, carbon nanotubes, etc.) grow three-dimensionally and overlap, thereby forming the desired electron emission portions 3a. At this time, carbon nanostructures are also formed on the surface on one side of the mask M1 in the axial direction, but these carbon nanostructures will be removed together with the mask M1 in the subsequent mask removal step.

[0071] 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-side facing surface 2a of the mask-covered electrode substrate S1 (and mask M1) (see Publication No. 2000 / 085291). In this case, a carbon film is also formed (transferred) on one surface of the mask M1 in the axial direction, but this carbon film will be removed together with the mask M1 in a subsequent mask removal step.

[0072] After the electron-emitting portion forming step, the mask-covered electrode substrate S1 and the mask M1 are removed in a mask removing step.

[0073] <Example of carbon nanostructure> When the electron emitting portion 3a is made of a carbon nanostructure, it is sufficient that the electron emitting portion 3a exhibits a desired function, and various embodiments can be applied.

[0074] The surface of a carbon nanostructure is not simply flat, but may have an island-like structure in which, for example, micron-sized granular portions (hereinafter simply referred to as "surface granular portions") protrude from the surface and are distributed in an island-like manner on the surface (for example, countless surface granular portions are densely packed).

[0075] In the case of carbon nanostructures with this island structure, the surface side of the surface granular portions has a shape like a protruding fine fibrous carbon film (e.g., striated graphene), and adjacent surface granular portions are formed so as to be bonded to each other at their bases.

[0076] The surface granular portion 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 2a, electric field and electric field line density on the anode-side facing surface 2a, etc.), and preferably into a large-grain shape.

[0077] The large-grain surface granular portions may be formed as appropriate depending on the shape of the anode-side opposing surface 2a, etc. Specific examples include an embodiment in which the dimension of the surface granular portions in the protruding direction is 10 μm or more, preferably 20 μm or more, and more preferably 30 μm or more, and the dimension of the maximum diameter portion of the surface granular portions (for example, the base portion of the upper part of the surface grain) in the radial direction is 10 μm or more, preferably 20 μm or more, and more preferably 30 μm or more, and an embodiment in which the large-grain shape can be confirmed with a stereomicroscope is also included.

[0078] There is no particular upper limit to the dimension in the protruding direction of the surface granular portion or the radial dimension of the maximum diameter portion, and each can be set to, for example, about 50 μm, but it is preferable to set them appropriately to an extent that maintains the island structure on the surface of the carbon nanostructure.

[0079] The shape of the surface granular portion may be, for example, a cone shape, a frustum shape, a spindle shape, a sphere shape, or the like, but is not limited thereto. The tip of the surface granular portion in the protruding direction 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 of the upper surface grain so that the radial dimension is large (for example, 5 μm or more, preferably 10 μm or more), which may make it easier to obtain durability against, for example, a high-current-density electron beam.

[0080] Furthermore, the surface granular portions 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 such other grain shapes so that they are within a range that allows the desired function of the intended field emission device to be exerted.

[0081] The electron source E1 described above can achieve the same effects even if the shape of the electrode substrate S1 is appropriately changed, for example. One example of this is changing it to electron sources E2 and E3, which will be described later.

[0082] <Modification of electron source E1 (part 1)> 3 is a schematic diagram illustrating the configuration of the electron source E2. The electron source E2 has an electrode substrate S2 that has a convex cross section as a whole, similar to the electrode substrate S1.

[0083] The electrode substrate S2 is provided with a small diameter portion 22 projecting toward one side in the axial direction at the center of the end portion on one side in the axial direction of the electrode substrate S2 (inner peripheral side of the cutout recess 11).

[0084] This small diameter portion 22 has a tapered shape in which one axial side of the small diameter portion 22 (the anode-side facing surface 2a side) is reduced in diameter as it is biased from the other axial side to one axial side. In the case of the small diameter portion 22 in FIG. 3, one axial side of the outer circumferential surface 1a of the small diameter portion 22 forms a tapered surface shape (a shape having a tapered surface 1b in FIG. 3) in which the diameter is reduced as it is biased from the other axial side to one axial side, thereby forming a tapered shape, but the present invention 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.

[0085] Due to the tapered small diameter portion 22 as described above, the anode-side facing surface 2b of the small diameter portion 22 can be easily reduced in diameter compared to, for example, the anode-side facing surface 2a of the small diameter portion 21. Moreover, the electron emitting portion 3b formed on the anode-side facing surface 2b can also be easily reduced in diameter (i.e., the electron emitting area can be reduced).

[0086] On the other hand, the base side of the small diameter portion 22 (the side of the large diameter portion 12) has a larger diameter than the anode-side facing surface 2b side of the small diameter portion 22, and therefore it is possible to obtain mechanical strength similar to that of the small diameter portion 21, for example.

[0087] The electron-emitting portion 3b of this electron source E2 can also be formed by sequentially going through the masking step, the electron-emitting portion forming step, and the mask removing step, as in the case of the electron source E1.

[0088] However, in the case of the electrode substrate S2 of the electron source E2, since the outer peripheral surface 1a of the small diameter portion 22 has a tapered surface shape, it is preferable to use a mask M2 as shown in FIG. 4 rather than simply using a mask M1 as shown in FIG. 2 (in which a cylindrical hole inner wall surface 4a is formed in the exposure hole 4).

[0089] The mask M2 shown in Fig. 4 is annular like the mask M1, and one axial side (opening edge surface 41 side) of the hole inner wall surface 4a of the exposure hole 4 has a tapered shape in which the diameter of the one axial side of the small diameter portion 22 is reduced as it is biased from the other axial side to the one axial side, similar to the outer circumferential surface 1a of the small diameter portion 22. Specifically, the one axial side of the hole inner wall surface 4a of the mask M2 has a tapered surface shape (a shape having a tapered surface 4d in Fig. 4) in which the diameter is reduced as it is biased from the other axial side to the one axial side, resulting in a tapered shape.

[0090] With the mask M2 as shown in FIG. 4, even if the electrode substrate S2 has a tapered small diameter portion 22, the mask M2 and the electrode substrate S2 tend to come into close contact with each other when the mask is covered, making it possible to prevent a gap from being formed between them.

[0091] 4, the opening edge surface 41 is positioned offset toward the other axial direction from the anode-side facing surface 2b. In this case, depending on the degree of the offset, the electron-emitting portion 3b can also be formed on the outer circumferential surface 1a of the small diameter portion 22 on the anode-side facing surface 2b side (tapered surface 1b).

[0092] <Modification of electron source E1 (part 2)> 5 is a schematic diagram for explaining the configuration of the electron source E3. The electron source E3 also has an electrode substrate S3 having a cross-sectional shape that is convex as a whole, similar to the electrode substrate S1.

[0093] The electrode substrate S3 has a small diameter portion 23 that protrudes toward one side in the axial direction at the center of the end portion on one side in the axial direction of the electrode substrate S3 (inner peripheral side of the cutout recess 11). An anode-side facing surface 2c that has a curved concave shape recessed toward the other side in the axial direction (a shape having a curved concave surface 2d in FIG. 5) is formed on the tip surface on one side in the axial direction of the small diameter portion 23.

[0094] 5, the entire anode-side facing surface 2c has a curved concave shape, but this is not limited thereto. For example, only the central portion of the anode-side facing surface 2c may have a curved concave shape, and the peripheral portion of the anode-side facing surface 2c may have a curved convex shape.

[0095] With the anode-side facing surface 2c having such a curved concave shape, the surface of the electron-emitting portion 3c formed on the anode-side facing surface 2c also has a curved concave shape, which makes it easier for electrons generated on the surface of the electron-emitting portion 3c to be emitted toward the anode T (described later) in a direction biased toward the central axis.

[0096] The electron-emitting portion 3c of this electron source E3 can be formed through the above-mentioned masking step, electron-emitting-portion forming step, and mask removing step in this order, as in the electron source E1. In the case of the electron source E3, the shape of the outer circumferential surface 1a of the small-diameter portion 23 is simply a cylindrical shape extending in the axial direction, so that the mask M1 (in which the hole inner wall surface 4a is simply a cylindrical shape) as shown in FIG. 2 can be applied as appropriate.

[0097] Example 2 The electron sources E1 to E3 may contain electrically unstable elements (elements that may cause electric field concentration or abnormal discharge, for example) around the electron-emitting portions 3 a to 3 c, respectively. For example, in the case of the electron sources E1 to E3, the outer peripheral surface 1 c is exposed, and simply applying a voltage in this exposed state may result in a phenomenon in which unintended electrons are emitted from the outer peripheral surface 1 c, for example.

[0098] In such a case, it is preferable to suppress the above-mentioned phenomenon by providing an electrode cover C1 as in the case of an electron source E4 shown below and shielding the outer peripheral surface 1c and the like.

[0099] <Schematic configuration of electron source E4> 6 is a schematic diagram illustrating an electron source E4 according to Example 2. Similar to the electron source E1, the electron source E4 has an electrode base S1 having a convex cross-sectional shape as a whole, and an annular electrode cover C1 is engaged with and provided on one side of the electrode base S1 in the axial direction.

[0100] 6, the electrode cover C1 has a configuration including a cover annular portion 50 that can be fitted into the cutout recess 11 when engaged with the electrode base S1 (hereinafter simply referred to as the cover engaged state), and a fitting hole 5 that has a shape that penetrates the inner periphery of the cover annular portion 50 in the axial direction. The fitting hole 5 has a shape that can be fitted into the small diameter portion 21 so as to receive the small diameter portion 21 in the cover engaged state.

[0101] 6, the hole inner wall surface 5a has a cylindrical shape extending in the axial direction along the outer peripheral surface 1a of the small diameter portion 21, thereby enabling the fitting hole 5 to be fitted into the small diameter portion 21. In the cover engaged state, the anode-side facing surface 2a of the small diameter portion 21 is exposed through the fitting hole 5.

[0102] In addition, in the electrode cover C1 of Figure 6, the outer diameter of the outer surface 5c of the electrode cover C1 and the outer diameter of the outer surface 1c of the large diameter portion 12 are formed to be the same or approximately equivalent (i.e., flush), but this is not limited to this.

[0103] For example, if the outer diameter of the outer peripheral surface 5c is equal to or smaller than the outer diameter of the outer peripheral surface 1c, when using a support jig W in the electrode cover engaging step described below, the electrode cover engaging step may be easier to carry out.

[0104] 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 corresponding to the electrode cover C1 in the support hole W1 of the support jig W described below (for example, by enlarging the hole inner wall surface W2), the electrode cover C1 can be accommodated together with the electrode base S1 in the processed support hole W1 (i.e., it can be accommodated in a cover-engaged state).

[0105] The electrode cover C1 may be configured in any manner as long as it can appropriately shield the outer peripheral surface 1c etc. in the cover engaged state. Therefore, in the cover engaged state, the electrode cover C1 and the electrode base S1 may be close to or abutting each other so as not to leave a gap, or a clearance may be provided between them as shown in Fig. 8 described later.

[0106] 6, the opening edge surface 51 on one axial side of the fitting hole 5 and the anode-side facing surface 2a are flush with each other, but this is not limiting, and they may be appropriately set to be positioned offset from each other in the axial direction, for example, depending on the shape of the electron emitting portion 3a, etc. Preferably, the opening edge surface 51 is positioned offset to one axial side from the electron emitting portion 3a, and in this case, for example, the electric field may be more easily relaxed around the periphery of the electron emitting portion 3a.

[0107] The electrode cover C1 may be made of various materials as long as it is durable enough to withstand the application of a desired voltage, including materials that can also be used for the substrate of the electrode substrate S1.

[0108] The electrode cover C1 may be provided on the electrode base S1 so as to maintain a cover engagement state, and one example of this is brazing (for example, vacuum brazing) the electrode base S1 using a brazing material.

[0109] The brazing material may 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, and examples thereof include materials having a shape (thin-walled extended plate, ring-shaped, etc.) extending circumferentially along the brazing surfaces.

[0110] 6, an annular cutout groove 53 extending in the circumferential direction is provided on the peripheral edge of the other end of the electrode cover C1 in the axial direction. The electrode cover C1 can be brought into a cover engagement state with an annular brazing material 54 extending in the circumferential direction disposed in the cutout groove 53. The brazing material 54 is melted in a vacuum atmosphere or the like and then solidified, thereby achieving the desired brazing.

[0111] According to the electrode cover C1 having the cutout groove 53 as described above, the electrode cover C1 can be grasped through the cutout groove 53, which may make it easier to detach the electrode cover C1 from the electrode base S1, for example.

[0112] <Example of electrode cover engagement step> In the electron source E4, as in the case of the electron source E1, the electron emission section 3a is formed by sequentially going through the aforementioned masking process, electron emission section forming process, and mask removal process, and then the electrode cover C1 is brought into an engaged state by the electrode cover engagement process.

[0113] As described above, this electrode cover engagement process can be carried out in various ways as long as the electrode cover C1 can be appropriately engaged, but it is preferable to prevent the electrode cover C1 and the electron-emitting portion 3a from colliding with each other, thereby preventing damage to the electron-emitting portion 3a.

[0114] A specific example is to apply the support jig W used in the electron-emitting portion forming step. In this case, first, the electrode base S1 is accommodated in the support hole W1 and supported, 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 enter a cover engagement state, which makes it easier to suppress damage to the electron-emitting portion 3a.

[0115] The electron source E4 shown above can achieve the same effects even if the shapes of the electrode base S1 and the electrode cover C1 are appropriately changed, and one example of this is changing it to electron sources E5 to E7 described below.

[0116] <Modification of electron source E4 (part 1)> 7 is a schematic diagram illustrating the configuration of electron source E5. Similar to electron source E1, electron source E5 has an electrode base S1 having a convex cross-sectional shape as a whole, and an annular electrode cover C2 is engaged with and provided on one axial side of the electrode base S1.

[0117] 7, the central portion of the end face 52 on one axial side of the electrode cover C2 has a curved concave shape (a shape having a curved concave surface 5d in FIG. 7), while the peripheral portion of the end face 52 has a curved convex shape (a shape having a curved convex surface 5e in FIG. 7).

[0118] With such an electrode cover C2, the peripheral portion of the end face 52 of the electrode cover C2 is positioned more biased toward one side of the axial direction than the electron emitting portion 3a, so that, for example, the electric field may be more easily relaxed at the peripheral portion of the electron emitting portion 3a.

[0119] <Modification of electron source E4 (part 2)> 8 is a schematic diagram illustrating the configuration of the electron source E6. Similar to the electron source E2, the electron source E6 has an electrode base S2 having a convex cross section as a whole, and an annular electrode cover C3 is engaged with and provided on one axial side of the electrode base S2.

[0120] 8, one axial side (opening edge surface 51 side) of the hole inner wall surface 5a of the fitting hole 5 is tapered toward the one axial side, similar to the outer circumferential surface 1a of the small diameter portion 22. Specifically, the one axial side of the hole inner wall surface 5a of the electrode cover C3 forms a tapered surface shape (a shape having a tapered surface 5f in FIG. 8) whose diameter decreases as it deviates from the other axial side toward the one axial side, resulting in a tapered shape.

[0121] With this 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 to cover 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 or in contact with each other so as to leave no gap between them, or a clearance may be provided between them as shown in FIG.

[0122] <Modification of electron source E4 (part 3)> 9 is a schematic diagram illustrating the configuration of electron source E7. Similar to electron source E2, electron source E7 has an electrode base S2 having a convex cross section as a whole, and an annular electrode cover C4 is engaged with and provided on one axial side of the electrode base S2.

[0123] 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 equal to the axial dimension of the small diameter portion 22 at a portion where the outer circumferential surface 1a has a cylindrical shape (i.e., a portion where the tapered surface 1b is not formed).

[0124] As a result, when the electrode cover C4 is in the cover engagement state, one axial side (the tapered surface 1b side) of the small diameter portion 22 protrudes from the fitting hole 5 to one axial side.

[0125] The end surface 52 of the electrode cover C4 extends in a direction intersecting with the small diameter portion 22 at an inclined angle so that the more a point on the end surface 52 is biased from the radially outer side to the radially inner side (toward the fitting hole 5), the more the point is biased from the other axial side to one axial side. A peripheral edge 55 of the end surface 52 may be appropriately chamfered (for example, R chamfering, C chamfering, or slight chamfering), as shown in Fig. 9, for example.

[0126] With such an electrode cover C4, even if the peripheral portion (tapered surface 1b side) of the electron emitting portion 3b in the small diameter portion 22 protrudes from the fitting hole 5 when the cover is engaged, it is possible to sufficiently alleviate the electric field at the peripheral portion of the electron emitting portion 3b.

[0127] Example 3 The electron sources E1 to E3 shown in the first embodiment can be applied to various electron beam emission structures as cold cathodes, one example of which is shown in FIG.

[0128] Fig. 10 is a schematic diagram illustrating an electron beam emission structure in which an electron source E1 is used as a cold cathode. The electron beam emission structure shown in Fig. 10 mainly comprises an electron source E1 and an anode T arranged opposite each other, and a guard electrode G1 arranged to cover the outer periphery of the electron source E1. In Fig. 10, a power supply E is provided to apply a voltage (tube voltage) between the electron source E1 (and the guard electrode G1) and the anode T.

[0129] 10, the electron source E1 is supported by a support portion 13 in a position where the electron-emitting portion 3a of the electrode substrate S1 faces the anode T. In the case of the support portion 13 shown in FIG. 10, the large-diameter portion 12 of the electrode substrate S1 is fitted into a support hole 13a to support the electron source E1, but the present invention is not limited to this.

[0130] <Example of anode T configuration> The anode T may be any anode that can be struck by an electron beam emitted from the electron source E1 (electron emitter 3a) and emit X-rays or the like (not shown) due to the impact of the electron beam, and various configurations are possible. The anode T in FIG. 10 has a surface T1 (hereinafter simply referred to as the "irradiated surface") that faces the electron emitter 3a of the anode T and is irradiated with the electron beam, and the electron beam is configured to impact 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 impacts the irradiated surface T1 are irradiated in a direction bent from the emission direction of the electron beam (for example, to one of the left and right directions in the figure).

[0131] <Configuration example of guard electrode G1> As described above, the guard electrode G1 is provided to cover the outer periphery of the electron source E1, and may be any electrode capable of, for example, mitigating the electric field at the periphery of the electron-emitting portion 3a (suppressing localized electric field concentration) and focusing the electron beam onto the central axis as desired (suppressing the dispersion of electrons emitted from the electron source E1), and various embodiments can be applied.

[0132] In the case of the guard electrode G1 shown in Figure 10, it has a cylindrical portion 61 that is arranged coaxially (coaxially with respect to the central axis) with respect to the electron source E1 and surrounds the outer periphery of the electron source E1, and a reduced diameter portion 62 that protrudes (reduced in diameter) radially inward from one end of the cylindrical portion 61 in the axial direction.

[0133] The end of the guard electrode G1 on one side in the axial direction (the reduced diameter portion 62 side in the case of FIG. 10) may be in contact with (or close to) the electron source E1, or a predetermined gap may be provided between the electron source E1.

[0134] 10, the inner circumferential surface 63 of the reduced diameter portion 62 is positioned to engage with the notched recess 11 of the electrode substrate 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 this configuration, if a phenomenon occurs in which electrons are unintentionally emitted from the outer circumferential surface 1c, for example, this phenomenon can be suppressed.

[0135] Furthermore, although the end face 64 on one axial side of the guard electrode G1 and the electron emitter 3a of the small diameter portion 21 are depicted as being flush with each other, this is not limitative. For example, depending on the strength of the electric field relaxation provided by the guard electrode G1 and the shape of the electron emitter 3a, the two may be appropriately positioned so as to be offset from each other in the axial direction. Preferably, the end face 64 is positioned so as to be offset from the electron emitter 3a to one axial side. In this case, the electric field may be more easily relaxed, for example, at the periphery of the electron emitter 3a.

[0136] Furthermore, the end face 64 is not limited to a shape extending simply in the radial direction, and various other shapes are possible. For example, as shown in Fig. 11, the peripheral portion of the end face 64 may be shaped to protrude further toward one side in the axial direction than the end face 64 (a shape having a curved convex surface 65 in Fig. 11). With the guard electrode G1 as shown in Fig. 11, the peripheral portion of the end face 52 is positioned more biased toward one side in the axial direction than the center portion of the end face and the electron-emitting portion 3a, which may make it easier to alleviate the electric field, for example, at the peripheral portion of the electron-emitting portion 3a.

[0137] Note that the guard electrode G1 may be configured to have only the cylindrical portion 61 (i.e., omitting the tapered portion 62) as long as it can reduce the electric field around the electron-emitting portion 3a. In this case, for example, the end face 64 (the curved convex surface 65 in FIG. 11 ) on one axial side of the cylindrical portion 61 may be configured to be biased toward one axial side relative to the electron-emitting portion 3a.

[0138] The guard electrode G1 described above may be made of various materials as long as they are durable enough to withstand the application of a desired voltage, including, for example, materials that can also be used for the substrate of the electrode substrate S1.

[0139] <Configuration example of a field emission device> 10 and 11, it is possible to configure various types of field emission devices, one example of which is a vacuum vessel (not shown) in which both ends of a cylindrical insulator are sealed and a vacuum chamber is formed inside the insulator. Specifically, an anode T is arranged on one axial side of the vacuum chamber in the vacuum vessel, and an electron source E1 and a guard electrode G1 are arranged on the other axial side of the vacuum chamber, with appropriate wiring to apply the voltage of a power source E as desired.

[0140] <Other> The voltage application configuration by the power supply E can be configured in various ways, for example, by providing a voltage control unit (not shown) that can change the voltage as appropriate.

[0141] As an example of setting the voltage control unit, when it is necessary to reduce the focal spot size as in microfocus X-rays, etc., it can be set to increase the focusing power of the electron beam. Also, when it is desired to irradiate the anode T with an electron beam of high output (power) while minimizing damage to the anode T, it can be set to decrease the focusing power of the electron beam.

[0142] In the electron beam emission structure shown in Figures 10 and 11, when a predetermined voltage is applied from a power supply E, electrons generated in a cold cathode (electron source E1 in the case of Figures 10 and 11) can emit an electron beam toward an anode T. In this case, if the electric field around the periphery of the electron emitter 3a is alleviated by the guard electrode G1, for example, and the electron beam can be focused onto the central axis as desired, the electron beam focusing characteristics shown in Figure 12 can be obtained.

[0143] Fig. 12 shows the focusing characteristics of an electron beam when simulating field emission. In Fig. 12, the horizontal axis extending left and right at the bottom of the figure indicates the central axis of the electron beam emission structure, and the anode T is disposed to the right of the horizontal axis (i.e., on one side of the axial direction). The multiple curves and lines drawn extending from the electron emission portion 3a in Fig. 12 to the right indicate the travel paths of electrons emitted from the electron emission portion 3a.

[0144] 12, it can be seen that electrons generated from the center of the electron-emitting portion 3a move along the central axis toward the anode T. On the other hand, electrons generated from the peripheral portion of the electron-emitting portion 3a (particularly at a position close to the guard electrode G1) move toward the anode T while being biased in a direction approaching the central axis from the peripheral portion, which means that the electron beam is focused on the central axis.

[0145] Specifically, in the case of the electron beam shown in Figure 12, the region of the electron beam that is close to the central axis in the radially inner direction (the region indicated by symbol Y1 in Figure 12) is composed only of electrons generated from the center of the electron-emitting section 3a, and the region of the electron beam that is outside in the radial direction (the region indicated by symbol Y2 in Figure 12) is composed of electrons generated from the center and peripheral portions of the electron-emitting section 3a.

[0146] Example 4 In the electron beam emission structure using the electron sources E1 to E3 as shown in Example 3, for example, if the strength of the electric field relaxation by the guard electrode G1 is relatively large and / or if the diameter of the electron source is relatively small, the electron beam may not be focused as desired, and the focusing characteristics of the electron beam may be as shown in FIG. 13 (electron beam when field emission is simulated as in FIG. 12).

[0147] In the case of the electron beam shown in Fig. 13, it can be seen that electrons generated from the center of the electron-emitting portion 3a move along the central axis toward the anode T. On the other hand, it can be seen that electrons generated from the peripheral portion of the electron-emitting portion 3a are biased in a direction approaching the central axis from the peripheral portion, but move to the opposite side of the central axis. Specifically, in the case of the electron beam shown in Fig. 13, there are electrons that move while biased away from the central axis (for example, electrons in the region indicated by symbol Y3 in Fig. 13), and it can be seen that variation and dispersion of the electron beam occurs.

[0148] When such variations or dispersion of the electron beam occurs, 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 (electron beam when simulating field emission as in Figure 12).

[0149] In the case of FIG. 14, the electrode cover C1 provided on the electrode base S1 is provided with a guard electrode G1. The reduced diameter portion 62 is in contact with (or close to) the anode T. It can be seen that the electrons generated from the central portion and peripheral portion of the electron-emitting portion 3a move along the central axis toward the anode T (for example, moving like the electrons in the region indicated by symbol Y4 in FIG. 14).

[0150] 10 and 11, by appropriately using any of the electron sources E1 to E7 as a cold cathode, it is possible to focus the electron beam as desired and appropriately suppress the variation and dispersion of the electron beam, even if the strength of the electric field relaxation by the guard electrode G1 is relatively large and / or the diameter of the electron source is relatively small. In other words, the electron beam can be focused as desired, and the field emission device can perform the desired function.

[0151] 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.

[0152] For example, Examples 1 to 4 may be combined as appropriate, and the contents disclosed in Patent Documents 1 to 3 may also be applied as appropriate to modify the design, thereby achieving the same effects as Examples 1 to 4. Furthermore, technical ideas other than those claimed that can be understood from the above-described embodiments are described below.

[0153] [1-1] An electrode substrate is provided with an end portion on one side in an axial direction facing an anode, The electrode substrate is an annular cutout recess extending along the circumferential direction of the electrode substrate at a peripheral edge portion at the one end portion of the electrode substrate; a small diameter portion at a center of the one end of the electrode substrate, the small diameter portion having a shape that protrudes to the one side; a large diameter portion at the other end of the electrode substrate in the axial direction, the large diameter portion being larger than the small diameter portion; and an electron source having an electron emitting portion provided on the tip surface on one side of the small diameter portion;

[0154] [1-2] The electron source according to [1-1], wherein at least the one side of the small diameter portion has a tapered shape whose diameter is reduced so as to be biased from the other side to the one side.

[0155] [1-3] The electron source according to [1-1], wherein the tip surface on one side of the small diameter portion has a curved concave shape.

[0156] [1-4] The electron source according to [1-1], wherein the peripheral edge of the tip surface on the one side of the small diameter portion has a curved convex shape.

[0157] [1-5] An electron source according to any one of [1-1] to [1-4]; a cylindrical guard electrode disposed coaxially with the electron source on an outer periphery of the electron source; 1. An electron beam emission structure comprising:

[0158] [1-6] The guard electrode is a cylindrical portion disposed coaxially with the electron source and surrounding an outer periphery of the electron source; a reduced diameter portion protruding in a direction of reducing diameter from the one end of the cylindrical portion; and The electron beam emission structure according to [1-5], wherein the reduced diameter portion is adjacent to or abuts on the small diameter portion of the electrode substrate.

[0159] [1-7] An electron beam emission structure according to [1-6], characterized in that the end face on one side of the guard electrode is flush with the electron emission section or is positioned offset toward the one side from the electron emission section.

[0160] [1-8] An electron beam emission structure according to [1-6], characterized in that the peripheral portion of the end face on one side of the guard electrode is shaped to protrude toward the one side more than the center portion of the end face.

[0161] [1-9] A field emission device having the electron beam emission structure according to [1-5].

[0162] [1-10] The field emission device according to [1-9], further comprising a voltage control section capable of changing the voltage applied between the anode and the electron source.

[0163] [2-1] an electrode substrate disposed with one end portion in an axial direction facing an anode; an annular electrode cover provided to engage with the one side of the electrode base; Equipped with The electrode substrate is an annular cutout recess extending along the circumferential direction of the electrode substrate at a peripheral edge portion at the one end portion of the electrode substrate; a small diameter portion at a center of the one end of the electrode substrate, the small diameter portion having a shape that protrudes to the one side; a large diameter portion at the other end of the electrode substrate in the axial direction, the large diameter portion being larger than the small diameter portion; and an electron emission portion is provided on the tip end surface on the one side of the small diameter portion, The electrode cover is a cover annular portion that can be fitted into the notched recess in the engaged state; a fitting hole that penetrates an inner circumferential side of the annular portion in the axial direction and is fittable with the small diameter portion in the engaged state; An electron source comprising:

[0164] [2-2] The electron source according to [2-1], wherein at least the one side of the small diameter portion has a tapered shape whose diameter is reduced so as to be biased from the other side to the one side.

[0165] [2-3] The electron source according to [2-1], wherein the tip surface on the one side of the small diameter portion has a curved concave shape.

[0166] [2-4] The electron source according to [2-1], wherein the peripheral edge of the tip surface on the one side of the small diameter portion has a curved convex shape.

[0167] [2-5] The electron source according to [2-1], wherein the central portion of the end face on one side of the electrode cover has a curved concave shape, and the peripheral portion of the end face has a curved convex shape.

[0168] [2-6] The electron source according to [2-2], characterized in that at least the one side of the inner wall surface of the fitting hole has a tapered shape whose diameter is reduced so as to be biased from the other side to the one side.

[0169] [2-7] 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 one end surface of the electrode cover extends in a direction intersecting with the small diameter portion at an oblique 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, The electron source according to [2-2], wherein in the engaged state, the one side of the small diameter portion protrudes from the fitting hole to the one side.

[0170] [2-8] The electron source according to any one of [2-1] to [2-7], characterized in that the large diameter portion and the cover annular portion are brazed together with a brazing material interposed therebetween.

[0171] [2-9] An electron source according to any one of [2-1] to [2-8]; a cylindrical guard electrode disposed coaxially with the electron source on an outer periphery of the electron source; 1. An electron beam emission structure comprising:

[0172] [2-10] The guard electrode is a cylindrical portion disposed coaxially with the electron source and surrounding an outer periphery of the electron source; a reduced diameter portion protruding in a direction of reducing diameter from the one end of the cylindrical portion; and The electron beam emission structure according to [2-9], wherein the reduced diameter portion is in close proximity to or in contact with the electrode cover.

[0173] [2-11] An electron beam emission structure according to [2-10], characterized in that the end face on one side of the guard electrode is flush with the electron emission section or is positioned offset toward the one side from the electron emission section.

[0174] [2-12] An electron beam emission structure according to [2-10], characterized in that the peripheral portion of the end face on one side of the guard electrode is shaped to protrude toward the one side more than the center portion of the end face.

[0175] [2-13] A field emission device having the electron beam emission structure according to [2-9].

[0176] [2-14] A field emission device according to [2-13], further comprising a voltage control section capable of changing the voltage applied between the anode and the electron source. [Explanation of symbols]

[0177] E1~E7...electron source, S1~S3...electrode base, G1...guard electrode 11... notched recess, 12... large diameter portion, 21 to 23... small diameter portion, 2a to 2c... anode side facing surface, 3a to 3c... electron emitting portion C1 to C4...electrode covers, 5...fitting hole, 50...cover annular portion M1, M2... mask, 4... exposure hole, 40... mask annular portion

Claims

1. A method for manufacturing an electron source, comprising: the electron source includes an electrode substrate disposed with one end portion on one side in an axial direction facing an anode, The electrode substrate is an annular cutout recess extending along the circumferential direction of the electrode substrate at a peripheral edge portion at the one end portion of the electrode substrate; a small diameter portion at a center of the one end of the electrode substrate, the small diameter portion having a shape that protrudes to the one side; a large diameter portion at the other end of the electrode substrate in the axial direction, the large diameter portion being larger than the small diameter portion; and an electron emission portion is provided on the tip end surface on the one side of the small diameter portion, a masking step of covering the one side of the electrode substrate with an annular mask; an electron emission portion forming step of providing the electron emission portion on the tip end surface on the one side of the small diameter portion after the masking step; a mask removing step of separating the electrode substrate from the mask after the electron emission portion forming step; and The mask is a mask annular portion that can be fitted into the notched recess in the covered state; an exposure hole having a shape penetrating in the axial direction on the inner circumferential side of the mask annular portion; and The method for manufacturing an electron source, wherein the electron-emitting portion forming step provides the electron-emitting portion through the exposure hole in the covered state.

2. At least the one side of the small diameter portion has a tapered shape whose diameter is reduced so as to be biased from the other side to the one side, 2. The method for manufacturing an electron source according to claim 1, wherein at least one side of the inner wall surface of the exposure hole has a tapered shape whose diameter is reduced so as to be biased from the other side to the one side.

3. 2. The method for manufacturing an electron source according to claim 1, wherein the tip surface on one side of the small diameter portion has a curved concave shape.

4. 2. The method for manufacturing an electron source according to claim 1, wherein the peripheral edge of the tip surface on one side of the small diameter portion is curved convexly.

5. 2. The method for manufacturing an electron source according to claim 1, wherein the electron-emitting portion forming step uses a support jig having a support hole capable of receiving and supporting the electrode substrate covered with the mask.

6. an electrode cover engaging step of engaging and providing an annular electrode cover on the one side of the electrode base, The electrode cover is a cover annular portion that can be fitted into the notched recess in the engaged state; a fitting hole that penetrates an inner circumferential side of the annular portion in the axial direction and is fittable with the small diameter portion in the engaged state; 2. The method for manufacturing an electron source according to claim 1, further comprising:

7. an electrode cover engaging step of engaging and providing an annular electrode cover on the one side of the electrode base, The electrode cover is a cover annular portion that can be fitted into the notched recess in the engaged state; a fitting hole that penetrates an inner circumferential side of the annular portion in the axial direction and is fittable with the small diameter portion in the engaged state; and 3. The method for manufacturing an electron source according to claim 2, wherein at least the one side of the inner wall surface of the fitting hole has a tapered shape whose diameter is reduced so as to deviate from the other side to the one side.

8. 8. The method for manufacturing an electron source according to claim 6, wherein a central portion of the end face on one side of the electrode cover is curved concave, and a peripheral portion of the end face is curved convex.

9. an electrode cover engaging step of engaging and providing an annular electrode cover on the one side of the electrode base, The electrode cover is a cover annular portion that can be fitted into the notched recess in the engaged state; a fitting hole that penetrates an inner circumferential side of the annular portion in the axial direction and is fittable with the small diameter portion in the engaged state; and 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 one end surface of the electrode cover extends in a direction intersecting with the small diameter portion at an oblique 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, 3. The method for manufacturing an electron source according to claim 2, wherein, in the engaged state, the one side of the small diameter portion protrudes from the fitting hole to the one side.

10. 10. The method for manufacturing an electron source according to claim 6, wherein the electrode cover engaging step comprises brazing both the large diameter portion and the annular cover portion with a brazing material interposed therebetween.

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