Electron beam emission structure and field emission device

Abstract

The outer peripheral side of a columnar electrode base (11) of a cold cathode (1) oriented 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: a 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 the 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).

Description

Electron beam emission structures and field emission devices

[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.

[0002] Field emission is a phenomenon in which electrons are emitted into a vacuum atmosphere (e.g., in an insulating vacuum vessel) due to the concentration of an electric field. Utilizing this phenomenon has been studied 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 the application of the voltage can be used to emit an electron beam toward the anode. By irradiating (colliding) this electron beam on the anode, a desired function (for example, radioscopic resolution due to the external emission of X-rays in the case of an X-ray device) 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 emitting portion provided on an end face of the electrode substrate facing an anode (hereinafter simply referred to as an anode-side facing surface). The electron emitting portion may be, for example, a carbon film structure formed by stacking multiple graphene sheets to form a hollow interior.

[0005] 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.

[0006] For example, Patent Documents 1 and 2 discuss methods for 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.

[0007] Patent No. 4390847 Patent No. 5424098

[0008] Even if a guard electrode is simply provided or the anode-side 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, and other components require axial alignment to be positioned coaxially with the central axis. However, if there are assembly errors due to tolerances of the components such as the electron source and guard electrode, it becomes difficult to achieve the desired axial alignment. This can lead to variations in the electron beam, which can easily cause dispersion and increase 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 reduced too much, it may become difficult to stably form an electron-emitting portion with desired physical properties (e.g., film quality) for the electron source (e.g., by CVD or the like). Furthermore, the above-mentioned assembly errors may be more likely to occur, making it more difficult to perform the desired axis alignment 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 view of the above technical problems, and aims to provide a technique that can contribute to making it easier to control the focusing of electron beams and to making it easier for a field emission device to exhibit the desired functions.

[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 emitting portion provided on the 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 substrate is characterized by having a cylindrical portion arranged coaxially with respect to the axis and surrounding the outer periphery of the columnar electrode substrate, an annular substrate tapering portion that protrudes from the anode side end of the cylindrical portion toward the axis and overlaps with the peripheral portion of the electron emission portion in the extension direction of the axis, and an electron beam passage hole that penetrates the inner periphery of the substrate tapering portion in the extension direction.

[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 cylindrical electrode base, and the anode-side end of the electrode cover protrudes toward the axis and has an annular cover tapered 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-emitting portion may be formed in a concave shape.

[0017] The cylindrical electrode substrate may be characterized in that the cylindrical portion and the substrate 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 passage 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 by having one aspect of the electron beam emission structure described above, and may further be characterized by including a voltage control unit that can change the voltage applied between the anode and the focusing electrode.

[0021] As described above, the present invention can contribute to facilitating the control of the focusing of electron beams and making it easier for the field emission device to perform the desired functions.

[0022] 1 is a schematic diagram (cross-sectional view along the central axis) illustrating an electron beam emission structure according to Example 1; FIG. 2 is a diagram illustrating the focusing characteristics of an electron beam when simulating field emission in the electron beam emission structure shown in FIG. 1; FIG. 3 is a schematic diagram (cross-sectional view along the central axis) illustrating an electron beam emission structure according to Example 2; FIG. 4 is a schematic diagram (cross-sectional view along the central axis) illustrating an electron beam emission structure according to Example 3; and FIG. 5 is a schematic diagram (cross-sectional view along the central axis) illustrating an electron beam emission structure according to Example 4.

[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 anode-side opposing surface is formed in a concave shape.

[0024] That is, in this embodiment, the outer periphery of a columnar electrode substrate of a cold cathode arranged facing an anode is surrounded by a focusing electrode having a cylindrical electrode substrate (cylindrical portion) arranged coaxially with the axis of the columnar electrode substrate. The anode-side end of the cylindrical electrode substrate has an annular substrate tapered portion that overlaps with the peripheral edge of the anode-side columnar electrode substrate (electron-emitting portion) in the extension direction of the axis of the columnar electrode substrate, and electron beam passage holes that penetrate the inner periphery of the substrate tapered portion in the extension direction of the axis.

[0025] In this electron beam emission structure in which the outer periphery of the cold cathode is surrounded by a focusing electrode, for example, when electrons generated at the periphery of the electron emission section are emitted toward the anode, their movement toward the anode is blocked by the reduced diameter portion of the base and they are likely to be trapped, whereas when electrons generated at the center of the electron emission section are emitted toward the anode, they are likely to move through the electron beam passage holes.

[0026] That is, the focusing electrode can not only electrically control the focusing of the electron beam by simply applying a voltage between the focusing electrode and the anode, but also physically control the focusing of the electron beam (by a function similar to that of an aperture). This allows, for example, the beam diameter and focal spot size of the electron beam to be reduced as desired. A field emission device employing such an electron beam emission structure can easily perform the desired functions of the field emission device.

[0027] This embodiment may be configured to have the above-described cold cathode and focusing electrode, and may appropriately apply common technical knowledge from various fields (for example, the field of field emission devices, the field of carbon nanotubes, etc.) For example, design modifications may be made as necessary by appropriately referring to Patent Documents 1 and 2, and examples thereof include Examples 1 to 4 shown below.

[0028] In the following first to fourth embodiments, detailed explanations will be omitted as appropriate, for example, by using the same reference numerals for overlapping contents.

[0029] As an example of a conventional field emission device, in the case of an X-ray tube with a focal spot size of the order of μm, an impregnated hot cathode formed by combining an oxide cathode that emits electrons is used, rather than a thermionic electron source formed simply by using a tungsten filament. Such an impregnated hot cathode can be made relatively small and has been considered to be capable of generating a large electron current.

[0030] A typical electron source is a hot cathode with an electron source diameter of several μm to several tens of μm (e.g., 50 μm) that generates an electron current on the order of amperes. It is also known that an aperture (an aperture corresponding to the electron source diameter) is interposed between the hot cathode and the anode, restricting the electron current while irradiating 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 produce a larger output than 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, making it difficult to extend their lifespan. Furthermore, impregnated hot cathodes tend to be expensive and difficult to manufacture.

[0032] Therefore, in recent years, a field emission type cold cathode using a carbon film, typically carbon nanotubes, has been attracting attention. One example of such a cold cathode is an electron emission section having a carbon film structure formed by depositing a carbon film on the surface of the cold cathode (electrode substrate) facing the anode.

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

[0034] Therefore, in a configuration in which the diameter of the cold cathode electron source is simply reduced (hereinafter referred to simply as the conventional configuration), the portion of the electron-emitting portion that is easily affected by film formation (i.e., the center portion of the electron-emitting portion) also becomes smaller, making it difficult to obtain the desired physical properties and resulting in unstable electron generation. Furthermore, the above-mentioned assembly errors are more 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 below, the electron beam can be not only electrically focused by simply applying a voltage between the focusing electrode and the anode, but also physically focused, which reduces the need to use a cold cathode with a small electron source diameter that makes axial centering difficult as in the conventional configuration, and makes it easier to use components 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, the influence of the assembly error can be sufficiently suppressed to fall within an acceptable range. Furthermore, since it is easy to secure a portion of the electron-emitting portion that is easily free from influences during film formation (i.e., the central portion of the electron-emitting portion), it is easy to obtain the desired physical properties. Furthermore, electrons can be stably generated and passed through the electron beam passage hole.

[0037] As a result, it becomes easier to control the focusing of the electron beam as desired, and variations and dispersion can be suppressed, making it possible to reduce, for example, the beam diameter and focal spot size as desired. Also, it becomes easier to achieve the desired functions in the field emission device.

[0038] <<Example 1>> <Schematic Configuration of Example 1> Fig. 1 is a schematic configuration diagram for explaining an electron beam emission structure according to Example 1. The electron beam emission structure shown in Fig. 1 includes, as main elements, 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 supply E1 for applying a voltage (tube voltage) between the cold cathode 1 and the anode 2, and a power supply E2 for applying a voltage between the anode 2 and the focusing electrode 3 are also 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 section 4 is provided on the anode-side 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 insulation from the cold cathode 1, but this is not limitative. For example, a desired insulation 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 the axis. An annular base reduced diameter portion 33 is provided at an end 32 of the cylindrical portion 30 on the anode 2 side, the end 32 being formed to protrude from the end 32 toward the cold cathode axis and have a reduced diameter. An electron beam passage hole 34 is provided on the inner periphery of the base reduced diameter portion 33, penetrating in the direction of extension 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 is configured to overlap with the peripheral edge portion 41 of the electron emitter 4 in the direction of extension of the cold cathode axis. As a result, the opening shape of the electron beam passage hole 34 on the electron emitter 4 side is configured to be smaller than the surface shape of the electron emitter 4.

[0043] <Configuration example of cold cathode 1> The columnar electrode base 11 of the cold cathode 1 is capable of being provided with an electron emission section 4, and electrons can be generated in the electron emission 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 configurations can be applied.

[0044] One example of such a structure is one in which a conductive metal material such as stainless steel (SUS material, etc.) or copper is formed into a columnar shape (for example, a cylindrical shape).Other examples include a structure in which a substrate such as a Si substrate is formed into a columnar shape, as long as it can generate electrons in the electron-emitting portion 4.

[0045] <Configuration example of anode 2> The anode 2 may be any anode that can be struck by an electron beam emitted from the electron emitter 4 and emit X-rays or the like (not shown) due to the impact of the impacting electron beam, and various configurations are applicable. The anode 2 in FIG. 1 has a surface 21 (hereinafter simply referred to as the "irradiated surface") that faces the electron emitter 4 of the anode 2 and is irradiated with the electron beam, and the electron beam is configured to impact the irradiated surface 21. The irradiated surface 21 may be configured to be inclined at a predetermined angle with respect to the emission direction of the electron beam. In this case, the X-rays or the like generated by the electron beam that impacts the irradiated surface 21 are irradiated in a direction bent from the emission direction of the electron beam (for example, to 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 diameter reducing portion 33 and an electron beam passage hole 34, and it is only necessary that it is configured to surround the outer periphery of the columnar electrode base 11, and various configurations are applicable.

[0047] One example of such a cylindrical electrode substrate 31 is one made of a conductive metal material similar to the columnar electrode substrate 11 and formed into a cylindrical shape (e.g., a shape having a cylindrical cylindrical 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 the power source E2. In the case of the cylindrical electrode substrate 31 shown in FIG. 1 , the tip surface 32 a of the end portion 32 on the anode 2 side has a curved shape that is convex toward the anode 2 side.

[0048] The substrate reduced diameter portion 33 has a shape that protrudes from the end portion 32 toward the cold cathode axis, and is configured to overlap with the peripheral portion 41 of the electron emission portion 4 in the extension direction of the cold cathode axis, and various forms 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 electrons emitted from the peripheral edge 41 of the electron emitter 4 from moving 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 formed, but this is not limiting and they may be separate components. For example, if 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 formed, 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.

[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 emission portion 4, and various configurations can be applied.

[0052] For example, the diameter and shape of the electron beam passage holes 34 may be appropriately set in consideration of the electron beams that correspond to the intended use of the field emission device.

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

[0054] Such a funnel-shaped electron beam passage hole 34 can prevent, for example, electron beams passing through the electron beam passage hole 34 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 emitting section 4 as long as it is a radiator that can generate electrons on the surface of the electron emitting section 4 by applying a voltage of a desired magnitude from the power supply E1 and can emit the generated electrons toward the anode 2. A specific example is a carbon film structure made of a material such as carbon (carbon nanotubes, etc.), which is formed as a thin film (for example, by forming a film by a CVD method, etc.) on the anode-side facing surface 12 of the columnar electrode substrate 11 as shown in the figure.

[0056] 1, various types of field emission devices can be configured, such as 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, the anode 2 is arranged on one side of the vacuum chamber in the vacuum vessel, and the cold cathode 1 and focusing electrode 3 are arranged on the other side of the vacuum chamber, with appropriate wiring to apply the desired voltages to the power sources E1 and E2.

[0057] <Others> The voltage application configuration by the power sources E1 and E2 can be configured in various ways, for example, by providing a voltage control unit (not shown) that can change the voltage as appropriate.

[0058] 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 2 with an electron beam of high output (power) while suppressing damage to the anode 2, it can be set to decrease the focusing power of the electron beam.

[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 to be 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 vacuum degree 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 left and right at the bottom of the drawing indicates the central axis of the electron beam emission structure, with the electron emitter 4 located at the left vertical axis of the horizontal axis and the anode 2 located at the right vertical axis of the horizontal axis. The distances from the horizontal axis to the top of the left and right vertical axes indicate the distances from the central axis of the electron beam emission structure (i.e., the distances equivalent to half the beam diameter). The multiple curved lines indicate the paths of electrons emitted from the electron emitter 4. Arrow A indicates the position of the emission side surface 33 a, and arrow B indicates the position of the tip surface 32 a. In other words, the electron beam passage hole 34 is located between the positions indicated by arrows A and B.

[0062] According to FIG. 2, the movement of electrons generated in the peripheral portion 41 (region indicated by the 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 symbol D in FIG. 2 ) of the electron emitter 4 are emitted from the central portion 42, pass through the electron beam passage hole 34, and then reach 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 passage hole 34 tend to be biased in the direction of expanding the beam diameter along the hole inner wall surface 34 a, trapping by the hole inner wall surface 34 a is suppressed, and after passing through the electron beam passage hole 34, they are biased in a direction approaching the central axis.

[0064] Therefore, according to the first embodiment described above, electrons emitted from the peripheral portion 41 of the electron-emitting portion 4 (i.e., the peripheral portion 41 that is relatively susceptible to the effects of film formation) are easily trapped by being blocked from moving 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 that is relatively easy to avoid the effects of film formation and where desired physical properties can be obtained) are easily allowed to reach the anode 2 through the electron beam passing holes 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. Furthermore, if a voltage control unit is provided, it becomes possible to appropriately set the focusing power of the electron beam depending on the intended use and usage of the field emission device.

[0066] <<Example 2>> <Schematic Configuration of Example 2> Fig. 3 is a schematic configuration diagram for explaining an 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 substrate 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 positioned coaxially with respect to 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 the 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 direction of extension 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 the end 51, and may be cylindrical in shape so as to 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 does not cause dielectric breakdown, such as a high-melting-point material such as molybdenum, tungsten, or stainless steel, and is formed into a cylindrical shape (for example, a cylindrical shape).

[0070] 3, a gap is provided between the electrode cover 5 and the focusing electrode 3, thereby providing insulation from the focusing electrode 3, but this is not limiting. For example, a desired insulation state may be achieved by interposing an insulator (not shown) between the electrode cover 5 and the focusing electrode 3. Furthermore, the electrode cover 5 may be in contact with the columnar electrode base 11 or at the same potential, but it is preferable to set the gap between the electron emitter 4 and the cover reduced diameter portion 52 appropriately 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] Furthermore, it is preferable that the cover reduced diameter portion 52 has a shape that can suppress 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 Figure 3, one end surface 52a facing the anode 2 has a flat surface shape that extends in the radial direction of the electrode cover 5.

[0072] According to the second embodiment described above, in addition to the same effects as those of the first embodiment, the following can be said. That is, the outer periphery of the columnar electrode base 11 (for example, the peripheral edge 41 side of the electron emitter 4) may contain electrically unstable elements (for example, elements that may cause electric field concentration or abnormal discharge), but by surrounding the outer periphery with the electrode cover 5, it is possible to suppress such unstable elements. Specifically, the electric field may be more easily relaxed at the peripheral edge 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> <Schematic Configuration of Example 3> Fig. 4 is a schematic configuration 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-facing surface 12 of the columnar electrode substrate 11, and the electron emission portion 4 is formed so as to cover the recess 12a. As a result, the surface of the center portion 42 of the electron emission portion 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 are possible. 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 Figure 4, both the surface of the central portion 42 of the electron emitter 4 and the inner surface of the cover reduced diameter portion 52 extend continuously between them.

[0076] According to the above-described third embodiment, in addition to the same effects as those of the first and second embodiments, the following can be said: 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 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>> <Schematic Configuration of Example 4> Fig. 5 is a schematic configuration 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-bonded contact with the emission side surface 33a of the base reduced diameter portion 33. A through hole 61 that penetrates the inner peripheral side of the annular flange portion 6 in the extension direction of the cold cathode axis (penetrating so as to be coaxial with the cold cathode axis) is provided.

[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 they are prevented from moving toward the anode 2. Furthermore, an electron beam formed by electrons emitted from the central portion 42 of the electron emitting portion 4 passes through the electron beam passage hole 34 via the through hole 61.

[0080] <Configuration Examples of Annular Flange Portion 6> The annular flange portion 6 may have any configuration as long as it can pass an electron beam generated by electrons emitted from the central portion 42 of the electron emitting portion 4, and various configurations are applicable.

[0081] For example, the diameter and shape of the through-hole 61 may be appropriately set in consideration of the electron beam corresponding 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 passage hole 34 side is smaller than the opening shape (hole diameter) of the electron beam passage 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 separate components, but this is not limiting and the two may be integrally configured in advance. The annular flange portion 6 and the base reduced diameter portion 33 may be joined by press-fitting, brazing, or the like, but may also be joined in a detachable manner. This allows the annular flange portion 6 to be replaced as needed, for example, if the annular flange portion 6 is damaged or deteriorated.

[0083] According to the fourth embodiment described above, in addition to the same effects as those of the first embodiment, the following can be said: Forming the small opening-shaped through-holes 61 in the annular flange portion 6 is sufficiently easy and easy to process compared to, for example, forming the small opening-shaped electron beam passage holes 34 on the inner circumferential 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 passage hole 34 small enough to correspond 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 having such an annular flange portion 6 can be constructed with relatively easy and favorable processability, and the target beam diameter can be easily achieved.

[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, Examples 1 to 4 may be combined as appropriate. Specific examples include applying the recess 12a to the electron beam emission structure shown in Figures 1, 3, and 5, applying the annular flange portion 6 to the electron beam emission structure shown in Figures 3 and 4, and applying the electrode cover 5 to the electron beam emission structure in Figure 5. In addition, the contents disclosed in Patent Documents 1 and 2 can be applied as appropriate to modify the design, and the same effects as those of Examples 1 to 4 can be achieved.

[0087] DESCRIPTION OF SYMBOLS 1 cold cathode, 11 columnar electrode base, 12a recess 2 anode 3 focusing electrode, 30 cylindrical portion, 31 cylindrical electrode base, 33 base reduced diameter portion, 34 electron beam passage hole 4 electron emission portion 5 electrode cover 6 annular flange portion, 61 through hole

Claims

1. An electron beam emission structure comprising: 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 face of the columnar electrode base facing the anode; and a focusing electrode having a cylindrical electrode base and provided insulated from the cold cathode, wherein the cylindrical electrode base has: a cylindrical portion arranged coaxially with the axis and surrounding an 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 a peripheral portion of the electron emission portion in the extension direction of the axis; and an electron beam passage hole penetrating the inner periphery of the base reduced diameter portion in the extension direction.

2. The electron beam emission structure described in claim 1, characterized in that the cold cathode is surrounded on the outer periphery of the columnar electrode base by a cylindrical electrode cover that is arranged coaxially with respect to the axis between the columnar electrode base and the cylindrical 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.

3. An electron beam emission structure according to claim 1 or 2, wherein the surface of said electron emission portion is formed in a concave shape.

4. An electron beam emission structure according to claim 1 or 2, wherein said cylindrical electrode substrate is constructed such that said cylindrical portion and said substrate reduced diameter portion are separate bodies.

5. An electron beam emission structure according to claim 1 or 2, characterized in that an annular flange portion coaxial with said axis is provided on said electron emission portion side of said reduced diameter portion of said base.

6. An electron beam emission structure according to claim 1 or 2, characterized in that 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. A field emission device comprising the electron beam emission structure according to claim 1 or 2.

8. A 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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