Electron beam emission structure and field emission device

Abstract

To provide a technique that allows an electron beam to be easily focused and controlled, thereby capable of contributing to making it easier to exhibit desired functions of a field emission device.SOLUTION: The outer peripheral side of a columnar electrode base 11 of a cold cathode 1 arranged to face an anode 2 is surrounded by a focusing electrode 3 having a cylindrical electrode base 31 (cylindrical part 30) arranged coaxially with the axis of the columnar electrode base 11. The cylindrical electrode base 31 has: the cylindrical part 30 that is arranged coaxially with the cold cathode axis and surrounds the outer peripheral side of the columnar electrode base 11; an annular base diameter reduction part 33 that protrudes from an end 32 of the cylindrical part 30 on the anode 2 side to the cold cathode axis side and overlaps a peripheral edge part 41 of an electron emission part 4 in an extension direction of the cold cathode axis; and an electron beam passing hole 34 that penetrates in the extension direction on the inner peripheral side of the base diameter reduction part 33.SELECTED DRAWING: Figure 1

Description

[Technical field]

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

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

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

[0004] The electron source may be a cold cathode having an electrode substrate such as a Si substrate or a SUS substrate, and an electron emission portion provided on the end face of the electrode substrate facing the anode (hereinafter simply referred to as the anode-side facing surface). The electron emission portion may be, for example, a carbon film structure formed by stacking graphene sheets in multiple layers to form a hollow interior.

[0005] The electron beam is required 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 performed, 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 spot size (electron spot), which is the area where the electron beam collides with the anode.

[0006] For example, Patent Documents 1 and 2 discuss ways of making it easier to focus the electron beam by providing a guard electrode on the outer periphery of the cold cathode or by forming the surface facing the anode into a concave shape. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Patent No. 4390847 [Patent Document 2] Patent No. 5424098 Summary of the Invention [Problem to be solved by the invention]

[0008] Even if a guard electrode is simply provided or the anode-facing surface is formed into a concave shape as in Patent Documents 1 and 2, the electron beam may not be focused as desired for the reasons described below, and the field emission device may not be able to perform the desired function.

[0009] For example, the electron source, guard electrode, etc. require axial centering adjustment (alignment) so that they are positioned coaxially with the central axis. However, if there is an assembly error due to the tolerance of the components such as the electron source and guard electrode, it is difficult to adjust the axial centering as desired. This may cause the electron beam to vary and become dispersed, and may result in an increase in the beam diameter and focal spot size.

[0010] Therefore, it is conceivable to reduce the diameter of the electron beam immediately after it is formed by the electron source by reducing the diameter of the electron source. However, if the diameter of the electron source is made too small, it may be difficult to stably form (for example, stably form by a CVD method or the like) an electron emission section having desired physical properties (for example, film quality, etc.) for the electron source. In addition, the above-mentioned assembly errors may be easily generated, making it more difficult to perform the desired axis centering adjustment.

[0011] It is also possible to control the focusing of the electron beam using an electromagnetic coil or the like, but providing such an electromagnetic coil would result in the field emission device becoming larger and more expensive, and the focusing control would also become complex and difficult.

[0012] The present invention has been made in consideration of the above technical problems, and has an object to provide a technique that can contribute to facilitating control of the focusing of an electron beam and making it easier for a field emission device to exhibit the desired functions. [Means for solving the problem]

[0013] The electron beam emission structure and field emission device according to the present invention can contribute to solving the above-mentioned problems. One aspect of the electron beam emission structure includes a cold cathode having a columnar electrode base arranged with one end of its axis facing an anode, and an electron emission portion provided on an end surface of the columnar electrode base facing the anode, and a focusing electrode having a cylindrical electrode base and provided insulated from the cold cathode.

[0014] The cylindrical electrode base is characterized in having a cylindrical portion arranged coaxially with respect to the axis and surrounding the outer periphery of the columnar electrode base, a ring-shaped base reduced diameter portion protruding toward the axis from the anode side end of the cylindrical portion and overlapping with the peripheral portion of the electron emission portion in the extension direction of the axis, and an electron beam passing hole penetrating in the extension direction on the inner periphery side of the base reduced diameter portion.

[0015] The cold cathode may also be characterized in that the outer periphery of the columnar electrode base is surrounded by a cylindrical electrode cover that is arranged coaxially with respect to the axis between the columnar electrode base and the tubular electrode base, and the anode side end of the electrode cover protrudes toward the axis and has an annular cover reduced diameter portion that overlaps with the peripheral portion of the electron emission portion in the extension direction of the axis.

[0016] The surface of the electron emission portion may be formed in a concave shape.

[0017] The cylindrical electrode base may be characterized in that the cylindrical portion and the base reduced diameter portion are separate bodies.

[0018] The electron emitting device may further be characterized in that an annular flange portion coaxial with the axis is provided on the electron emitting portion side of the reduced diameter portion of the base.

[0019] The electron beam passing aperture may have a shape in which the aperture diameter increases from the electron emission portion side toward the anode side.

[0020] One aspect of the field emission device is characterized in that it has one aspect of the electron beam emission structure described above, and may further include a voltage control unit capable of changing a voltage applied between the anode and the focusing electrode. Effect of the Invention

[0021] As described above, the present invention can contribute to facilitating control of the focusing of an electron beam and facilitating the performance of a desired function of a field emission device. [Brief description of the drawings]

[0022] [Figure 1] FIG. 1 is a schematic configuration diagram (cross-sectional view taken along the central axis) for explaining an electron beam emission structure according to a first embodiment. [Diagram 2] FIG. 2 is a graph showing the focusing characteristics of an electron beam when simulating field emission in the electron beam emission structure shown in FIG. 1. [Diagram 3] FIG. 11 is a schematic configuration diagram (cross-sectional view taken along the central axis) for explaining an electron beam emission structure according to a second embodiment. [Figure 4] FIG. 11 is a schematic configuration diagram (cross-sectional view taken along the central axis) for explaining an electron beam emission structure according to a third embodiment. [Diagram 5] FIG. 11 is a schematic configuration diagram (cross-sectional view taken along the central axis) for explaining an electron beam emission structure according to a fourth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0023] The electron beam emission structure and field emission device in the embodiments of the present invention are completely different from the structures shown in, for example, Patent Documents 1 and 2 in which a guard electrode is simply provided or the shape of the anode-side facing surface is concave.

[0024] That is, in this embodiment, the outer periphery of a columnar electrode base of a cold cathode arranged facing an anode is surrounded by a focusing electrode having a cylindrical electrode base (cylindrical portion) arranged coaxially with the axis of the columnar electrode base. The anode-side end of the cylindrical electrode base has an annular base reduced diameter portion that overlaps with the peripheral portion of the anode side (electron emission portion) of the columnar electrode base in the extension direction of the axis of the columnar electrode base, and an electron beam passing hole that penetrates the inner periphery of the base reduced diameter portion in the extension direction of the axis.

[0025] In this way, with the electron beam emission structure in which the outer periphery of the cold cathode is surrounded by the focusing electrode, for example, electrons generated at the peripheral portion of the electron emission section, when emitted toward the anode, tend to be trapped by the reduced diameter portion of the base, while electrons generated at the center of the electron emission section, when emitted toward the anode, tend to move through the electron beam passing hole.

[0026] That is, in the focusing electrode, the electron beam can be not only electrically focused by applying a voltage between the focusing electrode and the anode, but also physically focused (focused by a function like an aperture). This makes it possible to reduce, for example, the beam diameter and focal size of the electron beam as desired. A field emission device to which such an electron beam emission structure is applied can easily achieve the desired functions of the field emission device.

[0027] This embodiment only needs to have a cold cathode and a focusing electrode as described above, and common technical knowledge in various fields (for example, the field of field emission devices, the field of carbon nanotubes, etc.) can be appropriately applied. For example, the design can be modified by appropriately referring to Patent Documents 1 and 2 as necessary, and the following Examples 1 to 4 are given as examples.

[0028] In the following Examples 1 to 4, detailed explanations will be omitted as appropriate by, for example, applying the same reference numerals to overlapping contents.

[0029] ≪Reference example≫ As an example of a conventional field emission device, in the case of an X-ray tube with a focal spot size in the order of μm, a mode is known in which an impregnated hot cathode composed of an oxide cathode that emits electrons is used, rather than a thermionic source composed of a tungsten filament. Such an impregnated hot cathode can be made relatively small and is said to be capable of generating a large electron flow.

[0030] As a general electron source, there is a hot cathode with an electron source diameter of several μm to several tens of μm (for example, 50 μm) that generates an electron flow on the order of amperes. It is also known that by interposing an aperture (an aperture according to the electron source diameter) between the hot cathode and the anode, the electron flow is restricted while being irradiated to the anode, thereby functioning as a reflection type X-ray tube. This reflection type X-ray tube is considered to have the advantage of being able to increase the output compared to a transmission type X-ray tube.

[0031] However, the hot cathodes described above are installed in a vacuum atmosphere (for example, in a vacuum vessel), and depending on the degree of vacuum in the vacuum atmosphere, the tungsten filament is easily consumed, so it has been considered difficult to extend their life. In addition, impregnated hot cathodes tend to be expensive and difficult to manufacture.

[0032] In recent years, therefore, a configuration that uses a field emission type cold cathode using a carbon film, typically a carbon nanotube, has been attracting attention. One example of such a configuration is one in which a carbon film or the like is formed on the surface of a cold cathode (electrode substrate) facing an anode to form an electron emission section with a carbon film structure.

[0033] However, when the electron emission section having a carbon film structure formed on the cold cathode is affected by electric field concentration, plasma flow, and the like that may occur during the film formation (hereinafter, simply referred to as film formation effects), the desired physical properties (film quality, etc.) may not be obtained. For example, while the central part of the electron emission section is easily affected by the film formation effects and the desired physical properties can be obtained, the peripheral part of the electron emission section is easily affected by the film formation effects, and therefore the desired physical properties cannot be obtained, and the generation of electrons tends to become unstable.

[0034] Therefore, in the case of a configuration in which the diameter of the cold cathode electron source is simply reduced (hereinafter, simply referred to as the conventional configuration), the portion of the electron emission section where the influence during film formation can be easily avoided (i.e., the center of the electron emission section) also becomes small, making it difficult to obtain the desired physical properties and unstable electron generation. In addition, the above-mentioned assembly errors are likely to occur, making it more difficult to adjust the desired axis centering. As a result, the electron beam cannot be focused as desired, and the electron beam may become uneven and dispersed, resulting in a large beam diameter and focal spot size.

[0035] On the other hand, according to the electron beam emission structure such as those in Examples 1 to 4 described later, the electron beam can be not only electrically focused by applying a voltage between the focusing electrode and the anode, but also physically focused, which reduces the need to apply a cold cathode with a small electron source diameter that may make it difficult to adjust the axis centering as in the conventional configuration, and makes it easier to apply a component of a certain size (for example, a cold cathode with a certain electron source diameter).

[0036] In this case, even if an assembly error exists, it is possible to sufficiently suppress the influence of the assembly error and keep it within an allowable range. Also, in the electron emission section, it is easy to secure a portion (i.e., the center portion of the electron emission section) that is easily affected during film formation, so that it is easy to obtain the desired physical properties. Also, electrons can be stably generated and passed through the electron beam passing hole.

[0037] As a result, it becomes easier to control the focusing of the electron beam as desired, and the variation and dispersion can be suppressed, so that, for example, the beam diameter and the focal spot size can be made small as desired. Also, the field emission device can easily exhibit the desired functions.

[0038] Example 1 <Outline of the configuration of the first embodiment> Fig. 1 is a schematic diagram for explaining an electron beam emission structure according to Example 1. The electron beam emission structure shown in Fig. 1 mainly comprises a cold cathode 1 and an anode 2 arranged opposite to each other, and a focusing electrode 3 arranged so as to cover the outer periphery of the cold cathode 1. In the case of Fig. 1, a power source E1 for applying a voltage (tube voltage) between the cold cathode 1 and the anode 2, and a power source E2 for applying a voltage between the anode 2 and the focusing electrode 3 are provided.

[0039] The cold cathode 1 has a columnar electrode substrate 11 arranged with one end of its axis facing the anode 2 (i.e., arranged coaxially with respect to the central axis), and an electron emission portion 4 is provided on the anode-facing surface 12, which is the end face of the columnar electrode substrate 11 on the anode 2 side.

[0040] The focusing electrode 3 has a cylindrical electrode base 31 that is disposed coaxially with the axis of the columnar electrode base 11 (hereinafter simply referred to as the cold cathode axis), surrounds the outer periphery of the columnar electrode base 11, and is configured to be insulated from the cold cathode 1. In the case of the focusing electrode 3 shown in FIG. 1, a gap is provided between the focusing electrode 3 and the cold cathode 1, thereby providing an insulated state from the cold cathode 1, but this is not limiting. For example, a desired insulating state can be achieved by interposing an insulator (not shown) between the cold cathode 1 and the focusing electrode 3.

[0041] The cylindrical electrode base 31 has a cylindrical portion 30 shaped to surround the outer periphery of the columnar electrode base 11, and the cylindrical portion 30 is positioned coaxially with respect to the axis. An annular base reduced diameter portion 33 is provided at an end portion 32 on the anode 2 side of the cylindrical portion 30 and has a reduced diameter that protrudes from the end portion 32 toward the cold cathode axis. An electron beam passage hole 34 is provided at the inner periphery of the base reduced diameter portion 33, penetrating in the extension direction of the cold cathode axis (penetrating coaxially with the cold cathode axis).

[0042] As described above, the base reduced diameter portion 33 is configured to protrude from the end portion 32 toward the cold cathode axis and overlap with the peripheral portion 41 of the electron emitter 4 in the extending direction of the cold cathode axis. As a result, the opening shape of the electron beam passing hole 34 on the electron emitter 4 side is configured to be smaller than the surface shape of the electron emitter 4.

[0043] <Example of cold cathode 1 configuration> The columnar electrode base 11 of the cold cathode 1 is capable of being provided with an electron emitting section 4, and it is sufficient that electrons can be generated in the electron emitting section 4 by applying a voltage of a desired magnitude from a power source E1, and the electrons can be emitted toward the anode 2 to form an electron beam (not shown), and various embodiments can be applied.

[0044] One example of such a material is a conductive metal material such as stainless steel (SUS material, etc.) or copper, which is formed into a columnar shape (for example, a cylindrical shape).Other materials may be formed by forming a substrate such as a Si substrate into a columnar shape, as long as the electron emission portion 4 can generate electrons.

[0045] <Example of anode 2 configuration> The anode 2 may be any type that can be struck by the electron beam emitted from the electron emitter 4 and can emit X-rays or the like (not shown) by the struck electron beam, and various configurations are possible. The anode 2 in FIG. 1 has a surface 21 (hereinafter simply referred to as the irradiated surface) that faces the electron emitter 4 of the anode 2 and is irradiated with the electron beam, and the electron beam collides with the irradiated surface 21. The irradiated surface 21 may be configured to be inclined at a predetermined angle with respect to the emission direction of the electron beam. In this case, the X-rays or the like generated by the electron beam that collides with the irradiated surface 21 are irradiated in a direction bent from the emission direction of the electron beam (for example, one of the left and right directions in the figure).

[0046] <Configuration example of focusing electrode 3> The cylindrical electrode base 31 of the focusing electrode 3 has a base reduced diameter portion 33 and an electron beam passage hole 34, and it is sufficient that it is configured to surround the outer periphery of the columnar electrode base 11, and various configurations can be applied.

[0047] One example of such a case is one made of a conductive metal material similar to the columnar electrode substrate 11, and formed into a cylindrical shape (for example, a shape having a cylindrical tubular portion 30) from the metal material. Alternatively, a substrate such as a Si substrate may be formed into a cylindrical shape, as long as it can focus an electron beam by applying a voltage of a desired magnitude from a power source E2. In the case of the cylindrical electrode substrate 31 shown in FIG. 1, the tip surface 32a of the end portion 32 on the anode 2 side has a curved shape that is convex toward the anode 2 side.

[0048] The base reduced diameter portion 33 may be configured in any manner so long as it protrudes from the end portion 32 toward the cold cathode axis and overlaps with the peripheral portion 41 of the electron emission portion 4 in the extension direction of the cold cathode axis, and various configurations can be applied.

[0049] 1, the surface 33a facing the electron emitter 4 (hereinafter simply referred to as the emission side surface) has a flat surface shape extending in the radial direction of the focusing electrode 3. This emission side surface 33a blocks the movement of electrons emitted from the peripheral portion 41 of the electron emitter 4 toward the anode 2, making them more likely to be trapped.

[0050] 1, the base reduced diameter portion 33 and the cylindrical portion 30 are depicted as being integrally configured, but this is not limiting and they may be separate. For example, when it is difficult to process the cylindrical electrode base 31 in which the base reduced diameter portion 33 and the cylindrical portion 30 are both integrally configured, the two may be produced as separate components. Alternatively, the two may be joined appropriately by press fitting, brazing, or the like, and then arranged as shown in FIG. 1.

[0051] The electron beam passage hole 34 needs only to penetrate the inner periphery of the base reduced diameter portion 33 in the direction of extension of the cold cathode axis and be configured to allow the passage of an electron beam generated by electrons emitted from the central portion 42 of the electron emitting portion 4, and various configurations can be applied.

[0052] For example, the diameter, shape, etc. of the electron beam passing holes 34 may be appropriately set in consideration of the electron beam corresponding to the intended use of the field emission device.

[0053] In the case of the electron beam passing hole 34 shown in FIG. 1, it has a funnel shape in which the hole diameter increases from the emission side surface 33a toward the tip surface 32a (anode 2 side), and the hole inner wall surface 34a has a convex curved shape toward the cold cathode axis side (or the anode 2 side).

[0054] According to such a funnel-shaped electron beam passing hole 34, for example, the electron beam passing through the electron beam passing hole 34 can be prevented from colliding with or being trapped by the hole inner wall surface 34a.

[0055] <Configuration Example of Electron Emitting Section 4> Various configurations can be applied to the electron emitter 4, so long as it generates electrons on the surface of the electron emitter 4 by applying a voltage of a desired magnitude from the power source E1 and emits the generated electrons toward the anode 2 (radiator). A specific example is a carbon film structure made of a material such as carbon (carbon nanotubes, etc.), which is formed in a thin film form (for example, formed by depositing a film by a CVD method, etc.) on the anode-facing surface 12 of the columnar electrode substrate 11 as shown in the figure.

[0056] <Example of the configuration of a field emission device> According to the electron beam emission structure shown in Fig. 1, it is possible to configure various types of field emission devices, and one example of such a device is a vacuum container (not shown) in which both ends of a cylindrical insulator are sealed and a vacuum chamber is formed on the inner circumference of the insulator. Specifically, the anode 2 is arranged on one side of the vacuum chamber in the vacuum container, and a cold cathode 1 and a focusing electrode 3 are arranged on the other side of the vacuum chamber, and wiring is appropriately performed so that the voltages of the power sources E1 and E2 can be applied as desired.

[0057] <Other> The voltage application configuration by the power sources E1 and E2 can be implemented in various ways, for example, by providing a voltage control unit (not shown) capable of appropriately changing the voltage.

[0058] As an example of the setting of the voltage control section, when it is necessary to reduce the focal spot size as in microfocus X-rays, etc., the focusing force of the electron beam can be set to be large. Also, when it is desired to irradiate the anode 2 with an electron beam of high output (power) while suppressing damage to the anode 2, the focusing force of the electron beam can be set to be small.

[0059] The voltage applied by the power supply E2 only needs to be large enough to focus the electron beam by the focusing electrode 3, and can be set sufficiently small compared to the voltage (tube voltage) applied by the power supply E1, making it possible to suppress the amount of electrons. Therefore, in the vacuum atmosphere in which the electron beam emission structure is installed, the degree of vacuum in the vacuum atmosphere (hereinafter simply referred to as the degree of vacuum in the installation atmosphere) is suppressed so as not to deteriorate.

[0060] <Verification example> In the electron beam emission structure shown in FIG. 1, the focusing characteristics of the electron beam were investigated by simulating field emission, and the results shown in FIG. 2 were obtained.

[0061] In FIG. 2, the horizontal axis extending in the left-right direction at the bottom of the figure indicates the central axis of the electron beam emission structure, and the electron emission section 4 is located at the position of the left vertical axis of the horizontal axis, and the anode 2 is located at the position of the right vertical axis of the horizontal axis. In addition, in the left vertical axis and the right vertical axis, the distance from the horizontal axis to the upper side of the figure indicates the distance from the central axis of the electron beam emission structure (i.e., the distance equivalent to half the beam diameter). The multiple curved lines indicate the movement paths of electrons emitted from the electron emission section 4. In addition, the arrow A indicates the position of the emission side surface 33a, and the arrow B indicates the position of the tip surface 32a. In other words, the electron beam passage hole 34 is located between the positions indicated by the arrows A and B.

[0062] According to FIG. 2, the movement of electrons generated in the peripheral portion 41 (region indicated by reference symbol C in FIG. 2) of the electron emitting portion 4 is blocked immediately after being emitted from the peripheral portion 41.

[0063] On the other hand, electrons generated in the central portion 42 (region indicated by the symbol D in FIG. 2) of the electron emitter 4 end up being emitted from the central portion 42, passing through the electron beam passing hole 34, and then reaching the anode 2. Focusing on the movement path of the electrons that reach the anode 2, it can be seen that although the electrons moving within the electron beam passing hole 34 tend to be biased in the direction of expanding the beam diameter along the hole inner wall surface 34a, trapping by the hole inner wall surface 34a is suppressed, and after passing through the electron beam passing hole 34, they are biased in a direction approaching the central axis.

[0064] Therefore, according to the above-described Example 1, electrons emitted from the peripheral portion 41 of the electron emitting portion 4 (i.e., the peripheral portion 41 which is relatively susceptible to the influence during film formation) are easily trapped by blocking their movement toward the anode 2. On the other hand, electrons emitted from the central portion 42 of the electron emitting portion 4 (i.e., the central portion 42 which is relatively easy to avoid the influence during film formation and where desired physical properties can be obtained) are easily allowed to reach the anode 2 through the electron beam passing hole 34.

[0065] This makes it possible to suppress the variation and dispersion of the electron beam, reduce the beam diameter and focal spot size as desired, and achieve the desired function of the field emission device. In addition, if a voltage control unit is provided, it becomes possible to appropriately set the focusing force of the electron beam according to the intended use and usage of the field emission device.

[0066] Example 2 <Outline of the configuration of the second embodiment> Fig. 3 is a schematic diagram for explaining the electron beam emission structure according to Example 2. In the electron beam emission structure shown in Fig. 3, the outer periphery of a columnar electrode base 11 is surrounded by a cylindrical electrode cover 5.

[0067] The electrode cover 5 is interposed between the columnar electrode base 11 and the cylindrical electrode base 31, and is provided so as to be positioned coaxially with the cold cathode axis. An annular reduced diameter cover portion 52 that protrudes from the end 51 toward the cold cathode axis and has a reduced diameter is provided at an end 51 of the electrode cover 5 on the anode 2 side. A through hole 53 is provided on the inner periphery of the reduced diameter cover portion 52, penetrating in the extension direction of the cold cathode axis (penetrating coaxially with the cold cathode axis), thereby exposing the central portion 42 of the electron emitter 4.

[0068] <Configuration example of electrode cover 5> The electrode cover 5 has a cover reduced diameter portion 52 at an end portion 51 and may be tubular in shape so long as it can surround the outer periphery of the columnar electrode substrate 11, and various configurations are possible.

[0069] One example of such a material is one that is made of a material that does not cause dielectric breakdown, such as a high melting point material such as molybdenum, tungsten, or stainless steel, and that is molded into a tubular shape (for example, a cylindrical shape).

[0070] 3, a gap is provided between the electrode cover 5 and the focusing electrode 3, thereby providing an insulated state with respect to the focusing electrode 3, but the present invention is not limited to this. For example, a desired insulating state may be achieved by interposing an insulator (not shown) between the electrode cover 5 and the focusing electrode 3. Also, the electrode cover 5 may be in contact with the columnar electrode base 11 or at the same potential, but it is preferable to appropriately set the distance between the electron emitter 4 and the cover reduced diameter portion 52 so that they do not interfere with each other too much (for example, set so that the electron emitter 4 is not damaged by being pressed by the cover reduced diameter portion 52).

[0071] Moreover, it is preferable that the cover reduced diameter portion 52 has a shape capable of suppressing electric field concentration that may occur around the cover reduced diameter portion 52. In the case of the cover reduced diameter portion 52 shown in FIG. 3, one end face 52a facing the anode 2 has a flat surface shape extending in the radial direction of the electrode cover 5.

[0072] According to the above-described second embodiment, in addition to the same effects as those of the first embodiment, the following can be said. That is, the outer periphery side of the columnar electrode base 11 (e.g., the peripheral portion 41 side of the electron emitter 4) may contain electrically unstable elements (e.g., elements that may cause electric field concentration or abnormal discharge), but the configuration in which the outer periphery side is surrounded by the electrode cover 5 makes it possible to suppress the unstable elements. Specifically, the electric field may be easily relaxed in the peripheral portion 41 of the electron emitter 4.

[0073] Furthermore, it is possible to prevent electrons emitted from the electron emitting portion 4, particularly from the peripheral portion 41, from colliding with the focusing electrode 3. This prevents the degree of vacuum in the installation atmosphere from deteriorating.

[0074] Example 3 <Outline of the Third Embodiment> Fig. 4 is a schematic diagram for explaining an electron beam emission structure according to Example 3. In the electron beam emission structure shown in Fig. 4, a recess 12a is provided in the center of the anode-side facing surface 12 of the columnar electrode substrate 11, and the electron emission section 4 is formed so as to cover the recess 12a. As a result, the surface of the center section 42 of the electron emission section 4 is formed in a concave shape.

[0075] The recess 12a can be formed by appropriately shaping the anode-side facing surface 12, and various configurations can be applied. For example, as shown in Patent Documents 1 and 2, it is preferable to form the recess 12a in a shape having a certain radius of curvature to suppress electric field concentration that may occur around the recess 12a. In the case of Fig. 4, both the surface of the central portion 42 of the electron emission portion 4 and the surface on the inner circumferential side of the cover reduced diameter portion 52 extend so as to be continuous between them.

[0076] According to the above-described embodiment 3, in addition to the same effects as those of the embodiments 1 and 2, the following can be said: That is, electrons generated on the surface of the electron emitting portion 4 that is particularly formed in a concave shape are emitted toward the anode 2 in a direction biased toward the central axis, and are more likely to pass through the electron beam passing hole 34.

[0077] This makes it possible to further suppress the electrons colliding with the focusing electrode 3, making it easier to maintain a desired degree of vacuum in the installation atmosphere. Also, it becomes easier to obtain a high current density in the electron beam, which can contribute to an increase in the tube current.

[0078] Example 4 <Outline of the Fourth Embodiment> Fig. 5 is a schematic diagram for explaining an electron beam emission structure according to Example 4. In the electron beam emission structure shown in Fig. 5, an annular flange portion 6 that is coaxial with the cold cathode axis is provided on the electron emission portion 4 side of the base reduced diameter portion 33. In the case of the annular flange portion 6 shown in Fig. 5, one end face 6a of the annular flange portion 6 is provided in surface-bonding with the emission side face 33a of the base reduced diameter portion 33. A through hole 61 that penetrates in the extension direction of the cold cathode axis (penetrating so as to be coaxial with the cold cathode axis) is provided on the inner peripheral side of the annular flange portion 6.

[0079] When such an annular flange portion 6 is provided, electrons emitted from the peripheral portion 41 of the electron emitting portion 4 are easily trapped by the other end surface 6b of the annular flange portion 6, as the electrons are prevented from moving toward the anode 2. In addition, an electron beam formed by electrons emitted from the central portion 42 of the electron emitting portion 4 passes through the electron beam passing hole 34 via the through hole 61.

[0080] <Configuration example of annular flange portion 6> The annular flange portion 6 may have any configuration as long as it can pass the electron beam generated by the electrons emitted from the central portion 42 of the electron emitting portion 4, and various configurations can be applied.

[0081] For example, the diameter and shape of the through hole 61 may be appropriately set assuming an electron beam according to the intended use of the field emission device. In the case of the annular flange portion 6 shown in Fig. 5, the opening shape (hole diameter) of the through hole 61 on the electron beam passing hole 34 side is smaller than the opening shape (hole diameter) of the electron beam passing hole 34 on the through hole 61 side.

[0082] 5, the annular flange portion 6 and the base reduced diameter portion 33 are depicted as being configured separately, but this is not limiting, and the two may be configured as an integral body in advance. The annular flange portion 6 and the base reduced diameter portion 33 may be joined appropriately by press-fitting, brazing, or the like, but may also be joined in a detachable manner. This allows, for example, the annular flange portion 6 to be replaced as appropriate when it is damaged or deteriorated.

[0083] According to the above-described embodiment 4, in addition to the same effects as those of embodiment 1, the following can be said: Forming the small opening-shaped through-hole 61 in the annular flange portion 6 is sufficiently easy and has good workability compared to, for example, forming the small opening-shaped electron beam passage hole 34 on the inner periphery side of the base reduced diameter portion 33 of the cylindrical electrode base 31.

[0084] Therefore, for example, when the target beam diameter of the electron beam is relatively small and it is difficult to process the opening shape of the electron beam passing hole 34 small corresponding to the target beam diameter, an annular flange portion 6 having a through hole 61 corresponding to the target beam diameter may be applied. The cylindrical electrode base 31 provided with such an annular flange portion 6 can be constructed with relatively easy and good processability, and can easily achieve the target beam diameter.

[0085] 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.

[0086] For example, the embodiments 1 to 4 may be appropriately combined. Specific examples include applying the recess 12a to the electron beam emission structure shown in Fig. 1, Fig. 3, and Fig. 5, applying the annular flange portion 6 to the electron beam emission structure shown in Fig. 3 and Fig. 4, and applying the electrode cover 5 to the electron beam emission structure in Fig. 5. In addition, the contents disclosed in Patent Documents 1 and 2 may be appropriately applied to modify the design, and the same effects as those of the embodiments 1 to 4 can be achieved. [Explanation of symbols]

[0087] 1...cold cathode, 11...column electrode base, 12a...recessed part 2...Anode 3... Focusing electrode, 30... Cylindrical part, 31... Cylindrical electrode base, 33... Base diameter reduced part, 34... Electron beam passage hole 4...Electron emission part 5…Electrode cover 6... annular flange portion, 61... through hole

Claims

1. a cold cathode having a columnar electrode base disposed with one end of its axis facing an anode, the columnar electrode base having an electron emission portion provided on an end surface of the columnar electrode base facing the anode; a focusing electrode having a cylindrical electrode base and being insulated from the cold cathode; Equipped with The cylindrical electrode base is a cylindrical portion disposed coaxially with the axis and surrounding an outer periphery of the columnar electrode base; a ring-shaped base reduced diameter portion that protrudes from an end of the cylindrical portion on the anode side toward the axis and overlaps a peripheral portion of the electron emission portion in an extension direction of the axis; an electron beam passage hole penetrating in the extending direction on an inner circumferential side of the base reduced diameter portion; 1. An electron beam emission structure comprising:

2. the cold cathode is configured such that an outer periphery of the columnar electrode base is surrounded by a cylindrical electrode cover that is disposed coaxially with the axis between the columnar electrode base and the cylindrical electrode base, 2. The electron beam emission structure according to claim 1, wherein the anode side end of the electrode cover protrudes toward the axis and has an annular cover reduced diameter portion that overlaps with the peripheral portion of the electron emission portion in the extension direction of the axis.

3. 3. The electron beam emission structure according to claim 1, wherein the surface of said electron emission portion is formed in a concave shape.

4. 3. The electron beam emission structure according to claim 1, wherein the cylindrical electrode base is configured such that the cylindrical portion and the base reduced diameter portion are separate bodies.

5. 3. The electron beam emission structure according to claim 1, wherein an annular flange portion is provided coaxially with the axis of said base reduced diameter portion on the electron emission portion side.

6. 3. The electron beam emission structure according to claim 1, wherein the electron beam passage holes have a shape in which the diameter of the holes increases from the electron emission portion side toward the anode side.

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

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

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