Grid electrode for vacuum electronic device, electron gun and X-ray tube

Abstract

The invention provides a grid electrode used for a vacuum electronic device, an electron gun and an X-ray tube, the grid electrode comprises a grid electrode substrate, the grid electrode substrate is a flat plate type sheet, the thickness of the grid electrode substrate is 0.1 mm-3 mm, and the thermal conductivity of the material of the grid electrode substrate is larger than 200 W / (m.K); an electron beam through hole is formed in the gate substrate, the axial direction of the electron beam through hole is perpendicular to the two surfaces of the gate substrate in the thickness direction, and the electron beam through hole enables the gate substrate to be provided with a through hole part and an entity part except the through hole part; after the electron beam through hole is machined in the gate substrate, an outer wrapping layer is fixedly arranged on the surface of the entity part, the outer wrapping layer is made of a metal material, and the thickness of the outer wrapping layer is 10 nm to 50 [mu] m. According to the grid electrode, a large amount of heat generated when electron beams bombard the grid electrode can be conducted away, the high electron passing rate is still achieved under the low kV smaller than 5 kV, and the grid electrode is well suitable for field emission, heat emission, thermal field emission and other various cathode emission materials.

Description

Technical Field

[0001] The present invention relates to the field of vacuum electronic devices, and particularly to a grid for a vacuum electronic device, an electron gun equipped with the grid, and an X-ray tube equipped with the electron gun. Background Art

[0002] A grid is an electrode used in various vacuum electronic devices such as X-ray tubes, magnetrons, traveling wave tubes, and electron microscopes, and is widely used in fields such as industry, medicine, and scientific instruments. Generally, the grid is disposed between the emission electrode (i.e., the cathode) and the anode of the vacuum electronic device. By applying a potential relative to the cathode to the grid, it is used to regulate the electron beam current that comes from the cathode and reaches the anode after passing through the grid, and plays roles such as adjusting the electron beam current intensity, electron beam spot size, electron beam spot direction, and even turning on and off the electron beam current.

[0003] According to the different electron emission mechanisms of the cathode material (such as field emission, thermionic emission, and thermionic field emission), the grid potential for thermionic emission and thermionic field emission is usually below several hundred volts, while the grid potential for field emission is usually below several thousand volts. Due to the grid being bombarded by the electron beam current for a long time, the grid material is required to have high voltage resistance, high temperature resistance, resistance to electron bombardment, excellent mechanical stability, resistance to deformation, low thermal expansion coefficient, and low saturated vapor pressure.

[0004] Currently, the most common grids are molybdenum, tungsten, and nickel grid plates or grids with single-hole or multi-hole structures. The grid is set directly above the cathode electron emission material and parallel to the plane where the cathode electron emission material is located. At the same time, the distance between the grid and the cathode is very small, usually less than 1 mm, mostly less than 0.5 mm, and even 0.1 or 0.2 mm. In order to have a high electron passing rate, the thickness of the grid is usually thin, ranging from 0.05 to 0.3 mm. During the use of this kind of thin metal grid of grid plate or grid structure, it is bombarded by the electron beam current for a long time. Except for less than 1% of the electron energy generating X-rays on the grid, almost all of the electron kinetic energy will be converted into heat energy. Therefore, the long-term bombardment force of the electron beam current and the large amount of heat accumulated on the grid due to the bombardment of the electron beam current and unable to be conducted away in time cause the thin metal grid of grid plate or grid structure to deform, thus affecting the electric field between the grid and the cathode and the position of the mesh holes on the grid relative to the cathode, resulting in the failure of the electron beam current regulation function, and even short circuit between the grid and the cathode due to the small distance between the grid and the cathode and the deformation of the grid. In addition, when the electron beam current bombards the grid, X-rays will be generated on the grid. The yield of X-rays is related to the thickness and atomic number of the grid material. The larger the atomic number of the grid material, the greater the X-ray yield. When the thickness does not exceed the free path of electrons in the material, the thicker the grid material, the greater the X-ray yield. The grid plates or grids made of molybdenum, tungsten, and nickel all have relatively large atomic numbers and high X-ray yields. However, this kind of X-ray generated by non-anode target surface is not desired, so additional shielding measures need to be taken to shield the X-rays generated on the grid.

[0005] Prior art: The Chinese invention patent application with the application number 202011302224.X discloses a graphene sponge grid structure with high electron transmittance, which uses a graphene sponge grid structure to replace the existing metal micro-grid, improves the electron passing rate of the grid and the collimation of electron movement, and still maintains conductivity and certain mechanical strength, enhancing the bombardment resistance of the grid. However, due to manufacturing process problems, it is very difficult to control the direction of the electron beam through holes on it to be consistent with the electron beam emission direction, and the metal film layer on the surface of the sponge graphene has no mesh holes, which will hinder the passage of electrons. Therefore, its electron passing rate is very low under a grid voltage of less than 5 kV, and it is only suitable for occasions with a relatively high grid voltage (5 - 30 kV). In addition, because it is very difficult to control the direction of the electron beam through holes on it to be consistent with the electron beam emission direction and the metal film layer covering the surface, this grid is more suitable for occasions where the field emission cathode needs a quasi-parallel electric field to improve the collimation of electron emission, rather than for occasions such as thermionic emission and thermally assisted field emission cathodes that require pre-focusing of the grid. Moreover, this kind of porous sponge grid is not suitable for occasions that require a single-hole grid. Summary of the Invention

[0006] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a gate for a vacuum electronic device, which still has a high electron passing rate under a gate voltage of less than 5 kV, and can be well applied to various cathode emission materials such as field emission, thermionic emission, and thermionic field emission.

[0007] To achieve the above purpose, the present invention provides a gate for a vacuum electronic device. The gate includes a gate substrate, the gate substrate is a flat sheet with a thickness of 0.1 mm to 3 mm, and the thermal conductivity of the material of the gate substrate is greater than 200 W / (m·K);

[0008] At least one electron beam through hole penetrating along the thickness direction is provided on the gate substrate. The axial direction of the electron beam through hole is perpendicular to the two surfaces in the thickness direction of the gate substrate. The electron beam through hole makes the gate substrate have a through hole part and a solid part other than the through hole part;

[0009] After the electron beam through hole is processed on the gate substrate, an outer wrapping layer is fixedly arranged on the surface of the solid part of the gate substrate. The material of the outer wrapping layer is a metal material and the thickness is 10 nm - 50 μm.

[0010] An optional solution of the above-mentioned gate is: the material of the gate substrate is any one of diamond, cubic boron nitride, single crystal SiC, beryllium oxide, and graphene.

[0011] An optional solution of the above-mentioned gate is: the diameter of the electron beam through hole is 0.1 mm to 1 mm; when there are multiple electron beam through holes, the duty ratio of the through hole part to the solid part is determined by the electron passing rate of the electron beam and the heat dissipation ability of the gate. Usually, the duty ratio between the through hole part and the solid part on the gate substrate can be selected to be 2.

[0012] An optional solution of the above-mentioned gate is: the material of the outer wrapping layer is any one of gold, copper, chromium, nickel, molybdenum, and tungsten.

[0013] An optional solution of the above-mentioned gate is: the outer wrapping layer is fixedly attached to the surface of the solid part by magnetron sputtering, chemical vapor deposition, or evaporation.

[0014] An optional solution of the above-mentioned gate is: the surface roughness of the two surfaces in the thickness direction of the gate substrate does not exceed Ra0.8.

[0015] An optional solution of the above-mentioned gate is: a transition layer is provided between the solid part and the outer wrapping layer of the gate substrate, and the thickness of the transition layer does not exceed 150 nm.

[0016] An optional solution of the above-mentioned gate is: the material of the transition layer is titanium, chromium, or nickel.

[0017] Optional solutions for the above-mentioned gate are as follows: the transition layer is fixedly attached to the surface of the solid part by means of magnetron sputtering, chemical vapor deposition, or evaporation, and the outer wrapping layer is fixedly attached to the surface of the transition layer by means of magnetron sputtering, chemical vapor deposition, or evaporation.

[0018] This application also provides an electron gun, including a cathode and the gate as described above. The cathode has an electron emitter, and the gate is fixedly arranged on one side of the cathode along the electron beam emission direction.

[0019] This application also provides an X-ray tube, including a tube shell with a vacuum tube cavity inside, an anode sealed and connected to one end of the tube shell, and the electron gun as described above. The anode has an anode target, the electron gun is sealed and connected to the other end of the tube shell, and the cathode, the gate, and the anode target are arranged in sequence along the electron beam emission direction.

[0020] As described above, the gate, electron gun, and X-ray tube for vacuum electronic devices involved in the present invention have the following beneficial effects.

[0021] 1. The high thermal conductivity characteristic of the gate substrate enables the heat generated when the electron beam current bombards the gate substrate to be quickly conducted away, avoiding deformation of the gate substrate due to heat accumulation, and ensuring the electron beam current regulation function of the gate.

[0022] 2. The electron beam through-hole is processed on a directly purchased flat thin sheet, reliably ensuring that the axis of the electron beam through-hole is consistent with the electron beam emission direction; the gate substrate is a flat thin sheet structure; the outer wrapping layer does not cover both ends of the axis of the electron beam through-hole and will not hinder the passage of electrons; ultimately, the electron passing rate is greatly improved, enabling the gate to still have a high electron passing rate at a low kV of less than 5 kV and being well applicable to various cathode emission materials such as field emission, thermal emission, and thermionic field emission. At the same time, the increase in the electron passing rate reduces the heat and X-rays generated on the gate substrate, thereby reducing the shielding requirement for the X-rays generated by the gate when in use.

[0023] 3. The setting of the outer wrapping layer can not only conduct away the electrons bombarding the gate substrate but also prevent the gate substrate from being damaged by electron bombardment, enabling the gate substrate to have excellent mechanical stability and structural strength and being resistant to electron bombardment. Description of the Drawings

[0024] Figure 1 It is a schematic structural diagram of the gate for vacuum electronic devices in this application.

[0025] Figure 2 It is Figure 1 The enlarged view of circle A of

[0026] Figure 3 This is a schematic structural diagram of an electron gun in this application.

[0027] Figure 4 This is a schematic structural diagram of an X-ray tube in this application.

[0028] Description of Component Labels

[0029] 10 Grid Substrate

[0030] 11 Through-Hole Portion

[0031] 12 Solid Portion

[0032] 20 Electron Beam Through-Hole

[0033] 30 Outer Wrapping Layer

[0034] 40 Transition Layer

[0035] 50 Electron Gun

[0036] 51 Cathode

[0037] 52 Grid

[0038] 53 Focusing Electrode

[0039] 531 Neck

[0040] 532 Main Body

[0041] 60 Tube Housing

[0042] 70 Anode

[0043] 71 Anode Target Detailed Implementation Manner

[0044] The following specific embodiments illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification.

[0045] It should be noted that the structures, ratios, sizes, etc. shown in the drawings of this specification are only used to cooperate with the content disclosed in the specification for those skilled in the art to understand and read, and are not used to limit the limiting conditions under which the present invention can be implemented. Therefore, they do not have technical essential significance. Any modification of the structure, change in the proportional relationship, or adjustment of the size, without affecting the effects that the present invention can produce and the purposes that can be achieved, should still fall within the scope covered by the technical content disclosed in the present invention. At the same time, the terms such as "upper", "lower", "left", "right", "middle", and "one" cited in this specification are only for the convenience of narration and are not used to limit the scope under which the present invention can be implemented. The change or adjustment of their relative relationships, without substantial change in the technical content, should also be regarded as the scope within which the present invention can be implemented.

[0046] It should also be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or there may be an intermediate element present at the same time. When an element is referred to as being "connected to" another element, it can be directly connected to the other element or it can also be indirectly connected to the other element through an intermediate element.

[0047] In addition, the descriptions involving "first", "second", etc. in this application are only for descriptive purposes and should not be construed as indicating or implying their relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" can explicitly or implicitly include at least one of such features. In addition, the technical solutions between various embodiments can be combined with each other, but it must be based on the fact that those of ordinary skill in the art can implement them. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0048] This application relates to the technical field of X-ray tubes, and particularly relates to a grid 52 for a vacuum electronic device, an electron gun 50 including the grid 52, and an X-ray tube including the electron gun 50.

[0049] As Figure 4 shown, the X-ray tube involved in this application includes a tube shell 60 with a vacuum tube cavity inside, an anode 70 hermetically connected to one end of the tube shell 60, and an electron gun 50 hermetically connected to the other end of the tube shell 60; wherein, the anode 70 has an anode target 71; as Figure 3 shown, the electron gun 50 includes a cathode 51 and a grid 52. The cathode 51 has an electron emitter, and the grid 52 is fixedly arranged on one side of the cathode 51 along the electron beam emission direction; in the X-ray tube, the cathode 51, the grid 52, and the anode target 71 are arranged in sequence along the electron beam emission direction. When the X-ray tube works, the electron emitter of the cathode 51 emits electrons, the electrons are accelerated by an electric field and pass through the electron beam through-hole 20 of the grid 52, bombard the anode target 71, generate X-rays, and the X-rays then emit from the window assembly on the tube shell 60.

[0050] Furthermore, the grid 52 involved in the present invention is completely different from the existing molybdenum, tungsten, and nickel grid sheets or grids.

[0051] Specifically: As Figure 1 and Figure 2As shown in the figure, the gate 52 involved in the present application includes a gate substrate 10. The gate substrate 10 is a flat sheet with a thickness of 0.1 mm to 3 mm, and the thermal conductivity of the material of the gate substrate 10 is greater than 200 W / (m·K). At least one electron beam through-hole 20 penetrating along the thickness direction of the gate substrate 10 is provided on the gate substrate 10, and the electron beam through-hole 20 is used for the passage of the electron beam current. When there is one electron beam through-hole 20, the gate 52 is a single-hole structure, and the gate 52 with a single-hole structure is usually used in the case of a single electron emitter of the cathode 51. When there are multiple electron beam through-holes 20, the gate 52 is a multi-hole structure, and the gate 52 with a multi-hole structure is usually used in the case of multiple electron emitters of the cathode 51, such as in the case of an array electron emitter. The multiple electron beam through-holes 20 correspond one-to-one to the multiple electron emitters of the cathode 51. In particular, the gate substrate 10 is a flat sheet product that can be directly purchased on the market, and then the electron beam through-holes 20 are processed on the ready-made flat sheet. In this way, it can be reliably ensured that the axis of the electron beam through-hole 20 is perpendicular to the two surfaces in the thickness direction of the gate substrate 10 (i.e., Figure 1 the upper surface and the lower surface in the view), ensuring that the axis of the electron beam through-hole 20 is strictly the electron beam emission direction. The through-hole structure of the electron beam through-holes 20 on the gate substrate 10 makes the gate substrate 10 have a through-hole part 11 and a solid part 12 other than the through-hole part 11. The solid part 12 is also the non-through-hole part of the gate substrate 10. Further, in the gate 52 involved in the present application, the required electron beam through-holes 20 are first processed on the directly purchased gate substrate 10, and then an outer wrapping layer 30 is fixedly provided on the surface of the solid part 12 of the gate substrate 10. The surface of the solid part 12 includes the two surfaces in the thickness direction of the gate substrate 10, the outer peripheral surface, and the hole wall of the electron beam through-hole 20. Then, the outer wrapping layer 30 of the gate substrate 10 does not cover the electron beam through-holes 20, or in other words, the electron beam through-holes 20 also axially penetrate the outer wrapping layer 30. And the material of the outer wrapping layer 30 is a metal material with a thickness of 10 nm - 50 μm.

[0052] The gate 52 involved in the present application has the following advantages.

[0053] First, the thermal conductivity of the gate substrate 10 is significantly higher than that of the gate sheets or gate meshes made of traditional molybdenum and tungsten materials. Thus, during the operation of the X-ray tube, the heat generated when the electron beam current bombards the gate substrate 10 is quickly conducted away, avoiding the accumulation of heat on the gate substrate 10, and thus avoiding the deformation of the flat sheet-shaped gate substrate 10. Thereby, the electric field between the gate 52 and the cathode 51 and the position of the electron beam through-holes 20 on the gate 52 relative to the cathode 51 are kept unchanged, ensuring the electron beam current regulation function of the gate 52.

[0054] Second, the electron beam vias 20 are processed on a directly purchased flat sheet, which reliably ensures that the axial direction of the electron beam vias 20 is consistent with the electron beam emission direction, thereby reducing the interception of electrons by the hole walls of the electron beam vias 20 and increasing the electron passing rate.

[0055] Third, the gate substrate 10 is a flat sheet with a thickness of 0.1 mm to 3 mm. While enabling the gate substrate 10 to have high mechanical stability and structural strength, it also has a high electron passing rate. The higher the electron passing rate, the fewer electrons are intercepted, and the easier it is for electrons to pass through the electron beam vias 20. Then, less heat and X-rays are generated on the gate substrate 10, better avoiding deformation of the flat sheet gate substrate 10 and reducing the shielding requirement for the X-rays generated on the gate 52 when using the gate 52, thus simplifying the structure of the vacuum electronic device.

[0056] Fourth, the surface of the solid part 12 of the gate substrate 10 is covered by an outer wrapping layer 30. Electrons directly bombard the outer wrapping layer 30 of the gate substrate 10. The outer wrapping layer 30 has at least the following functions in this application: 1. The outer wrapping layer 30 has conductive properties. Through the conductive effect of the outer wrapping layer 30, the electrons bombarding the gate substrate 10 can be conducted away, avoiding deformation of the gate substrate 10 due to heat accumulation. 2. The material of the outer wrapping layer 30 is a metal material, which is resistant to high voltage and electron bombardment. It also serves as a protective material to prevent the gate substrate 10 from being damaged by electron bombardment, thereby enabling the gate substrate 10 to have high mechanical stability and structural strength. 3. The thickness of the outer wrapping layer 30 is 10 nm - 50 μm, which is very thin. It can increase the bonding force between the outer wrapping layer 30 and the gate substrate 10, prevent the outer wrapping layer 30 from falling off due to long-term electron bombardment, and can also reduce the yield of X-rays when electrons bombard the gate 52, thus reducing the shielding requirement for the X-rays generated on the gate 52 when using the gate 52 and simplifying the structure of the vacuum electronic device. 4. The two ends of the axial direction of the electron beam vias 20 are not covered by the outer wrapping layer 30, which does not hinder the passage of electrons, enabling the gate 52 of this application to still have a high electron passing rate under a gate 52 voltage of less than 5 kV, and being well applicable to various cathode 51 emission materials such as field emission, thermionic emission, and thermo-field emission.

[0057] Furthermore, the gate substrate 10 is preferably made of a high thermal conductivity material with high temperature resistance, high mechanical stability at high temperatures, anti-deformation, low expansion coefficient, and low saturation vapor pressure. The thermal conductivity of the material of the gate substrate 10 is preferably greater than 1000 W / (m·K), and more preferably greater than 1300 W / (m·K).

[0058] Preferably, the gate substrate 10 is made of an insulating material with high thermal conductivity. For example, the material of the gate substrate 10 is diamond, cubic boron nitride, single crystal SiC, beryllium oxide, etc. Among them, the gate substrate 10 made of cubic boron nitride and diamond has a thermal conductivity as high as 1300 W / (m·K), or even 2400 W / (m·K). In addition, the gate 52 is an electrode in the X-ray tube, and a corresponding potential needs to be set on the gate 52 during use. At this time, even if the gate substrate 10 is made of an insulating material with high thermal conductivity, since the surface of the gate substrate 10 is covered by the conductive outer coating layer 30, the outer coating layer 30 is used to set the potential of the gate 52 and regulate the electron beam current during use.

[0059] Preferably, the gate substrate 10 is made of a conductive material with high thermal conductivity. For example, the material of the gate substrate 10 is graphene. In addition, the gate 52 is an electrode in the X-ray tube, and a corresponding potential needs to be set on the gate 52 during use. The conductive property of the gate substrate 10 itself enables it to be used to set the potential of the gate 52 and regulate the electron beam current during use. However, the gate substrate 10 is a graphene flat sheet, which is not resistant to electron bombardment itself. But since the surface of the graphene flat sheet is covered by the outer coating layer 30 made of a metal material, it effectively prevents the graphene flat sheet from being damaged by electron bombardment, so that the gate substrate 10 still has high structural strength.

[0060] Furthermore, the outer coating layer 30 is made of a metal material with high voltage resistance, electron bombardment resistance and low saturated vapor pressure, preferably gold, copper, chromium, nickel, molybdenum and tungsten, etc. And the thickness of the outer coating layer 30 is preferably 20 nm - 5 μm, particularly preferably 20 nm - 1 μm, which can better increase the bonding force between the outer coating layer 30 and the gate substrate 10 and better prevent the outer coating layer 30 from falling off due to long-term electron bombardment.

[0061] Furthermore, when the material of the gate substrate 10 is a material with a low atomic number such as diamond, cubic boron nitride and graphene, since the atomic numbers of diamond, cubic boron nitride and graphene do not exceed 7, which is significantly lower than the atomic numbers of the materials of the existing molybdenum, tungsten and nickel gate plates or gate meshes, the yield of X-rays on the gate substrate 10 is greatly reduced. After such setting, when the electron beam current bombards the gate substrate 10, less X-rays are generated on the gate 52, which helps to reduce the shielding requirement for the X-rays generated by the gate 52 during the use of the gate 52.

[0062] Furthermore, the gate substrate 10 is a flat sheet that can be purchased on the market. The gate substrate 10 can be a circular sheet, a rectangular sheet, or a sheet of other shapes. The cross-sectional shape of the electron beam through-hole 20 can be circular, square, or other special shapes designed to meet the electron passing rate. The diameter of the electron beam through-hole 20 is 0.1 mm to 1 mm, preferably 0.1 mm to 0.4 mm. When there are multiple electron beam through-holes 20, the adjacent electron beam through-holes 20 are isolated by the solid part 12 of the gate substrate 10 (i.e., the material of the gate substrate 10), and the duty ratio between the through-hole part 11 and the solid part 12 on the gate substrate 10 is 2. The duty ratio is also the ratio of the diameter of the electron beam through-hole 20 to the size of the solid part 12 adjacent to it, characterizing the spacing between two adjacent electron beam through-holes 20. The duty ratio is designed and confirmed based on the electron beam current passing rate index and the heat dissipation ability of the gate. For example, in one embodiment, the diameter of the electron beam through-hole 20 is 0.2 mm, and the size of the solid part 12 in the radial direction of the electron beam through-hole 20 (i.e., the wall thickness between two adjacent electron beam through-holes 20) is 0.1 mm.

[0063] Furthermore, the electron beam through-hole 20 can be processed on the purchased gate substrate 10 by various methods such as femtosecond laser processing, electron beam processing, and plasma etching, or can also be processed on the purchased gate substrate 10 by the method of wet etching with a patterned mask plate, reliably processing the electron beam through-hole 20 that is strictly perpendicular to the two surfaces in the thickness direction of the gate substrate 10. Alternatively, the gate substrate sheet is grown by methods such as CVD, etc.; when growing the gate substrate sheet, fine needles that are nearly perpendicular to the surface of the growing substrate are set on the growing substrate, then the gate substrate sheet is grown by methods such as CVD, etc., and finally the fine needles are removed by chemical etching and other methods to obtain the gate substrate sheet with the electron beam through-hole 20.

[0064] Furthermore, the surface roughness of the two surfaces in the thickness direction of the gate substrate 10 does not exceed Ra0.8, preferably does not exceed Ra0.2, and more preferably does not exceed 5 nm, 10 nm, 15 nm, 30 nm, or 50 nm. After such setting, it can not only increase the bonding strength between the gate substrate 10 and the outer wrapping layer 30, but also reduce the surface roughness of the outer wrapping layer 30, thereby preventing high-voltage arcing between the gate 52 and the cathode 51. Preferably, the surface of the gate substrate 10 can be polished by polishing methods such as mechanical polishing, mechanical chemical polishing, thermal chemical polishing, and ion beam polishing to obtain a smooth surface, so as to reduce the surface roughness of the gate substrate 10.

[0065] Furthermore, the surface of the gate substrate 10 can be only covered by the outer wrapping layer 30; at this time, the outer wrapping layer 30 is fixedly attached to the surface of the solid part 12 by magnetron sputtering, chemical vapor deposition, or evaporation. Or, as Figure 2As shown, a transition layer 40 is provided between the solid part 12 and the outer wrapping layer 30 of the gate substrate 10. The material of the transition layer 40 is titanium, chromium, nickel, etc. The thickness of the transition layer 40 does not exceed 150 nm, preferably not exceeding 5 nm, 10 nm, 15 nm, 30 nm, or 50 nm. At this time, the transition layer 40 is fixedly attached to the surface of the solid part 12 by magnetron sputtering, chemical vapor deposition, or evaporation, and the outer wrapping layer 30 is fixedly attached to the surface of the transition layer 40 by magnetron sputtering, chemical vapor deposition, or evaporation. The setting of the transition layer 40 better increases the bonding strength between the outer wrapping layer 30 and the gate substrate 10, preventing the outer wrapping layer 30 from falling off due to long-term electron bombardment.

[0066] The following provides a preferred embodiment of the gate 52 involved in the present application.

[0067] The gate substrate 10 is a diamond flat sheet with a thickness of 0.1 mm and a surface roughness not exceeding 50 nm; there is an electron beam through hole 20 on the diamond flat sheet, and the diameter of the electron beam through hole 20 is 0.2 mm; the surface of the diamond flat sheet and the hole wall of the electron beam through hole 20 are covered with an inner chromium film and an outer molybdenum film.

[0068] The manufacturing method of the gate 52 successively includes the following steps.

[0069] S1. Purchase a diamond sheet with a thickness of 0.1 mm, polish its surface to make its surface roughness not exceed 50 nm. Or, directly purchase a diamond sheet with a surface roughness not exceeding 50 nm and a thickness of 0.1 mm.

[0070] S2. Ultrasonically clean the surface of the diamond sheet with acetone, rinse it with deionized water, and dehydrate it with alcohol, and then dry it.

[0071] S3. Process the electron beam through hole 20 on the diamond sheet: Fix the diamond sheet on the precision displacement stage of the femtosecond laser processing device, adjust the spot size and power of the femtosecond laser, and use the form of multiple laser impacts to process a through hole in the direction perpendicular to the bottom plane of the diamond sheet. The size of the hole is 0.2 mm, and this through hole is the electron beam through hole 20. When the gate 52 is a porous structure, multiple through holes need to be processed. At this time, through the precision displacement stage, adjust the punching position to process multiple through holes on the diamond sheet.

[0072] S4. Ultrasonically clean the diamond sheet with through holes with acetone, rinse it with deionized water, and dehydrate it with alcohol, and then dry it.

[0073] S5. Place the diamond sheet with through holes in the vacuum chamber of the vacuum coating machine. The vacuum degree in the vacuum chamber is not lower than 1×10 -3Pa, the temperature is 200 - 300 °C; adjust the power and time of magnetron sputtering, and sputter a chromium film not exceeding 50 nm on the surface of the diamond thin sheet and the inner surface (i.e., the hole wall) of the through-hole, and this chromium film constitutes the transition layer 40.

[0074] S6. Switch the target of the vacuum coating machine, adjust the power and time of magnetron sputtering, and sputter a molybdenum film not exceeding 50 nm on the surface of the diamond thin sheet and the inner surface (i.e., the hole wall) of the through-hole, and this molybdenum film constitutes the outer wrapping layer 30.

[0075] S7. Ultrasonically clean the diamond thin sheet with through-holes coated with chromium film and molybdenum film in acetone, rinse it with deionized water, and dehydrate it with alcohol, and then dry it.

[0076] S8. Put the dried diamond thin sheet into a vacuum heating furnace, the vacuum degree in the vacuum heating furnace is not lower than 1×10 -3 Pa, the temperature is set not lower than 400 °C, and this temperature is adjusted according to the types of metal materials of the transition layer 40 and the outer wrapping layer 30, keep it warm for 3 h and then cool it with the furnace;

[0077] S9. Thus, the fabrication of the gate 52 based on the diamond gate substrate 10 is completed.

[0078] In summary, the gate 52 involved in the present application has the following beneficial effects: The gate substrate 10 is made of materials such as diamond with high thermal stability, low expansion coefficient, high mechanical stability, especially high thermal conductivity. The transition layer 40 prepared from materials such as titanium, chromium, nickel, etc. and the outer wrapping layer 30 prepared from materials such as gold, copper, chromium, nickel, molybdenum, and tungsten are successively deposited, so that the gate 52 has excellent characteristics such as high voltage resistance, high temperature resistance, anti-electron bombardment, excellent mechanical stability, anti-deformation, low thermal expansion coefficient, and low saturation vapor pressure, and at the same time has a very high thermal conductivity, realizing that the heat generated by the electron beam current bombarding the gate 52 is quickly conducted away by the gate substrate 10 with high thermal conductivity, and the conductive transition layer 40 and outer wrapping layer 30, preventing the gate 52 from accumulating heat and generating high-temperature deformation, improving the reliability of the gate 52 to regulate the electron beam current, extending the service life of the gate 52, and ultimately improving the stability and service life of the electron gun 50 and the X-ray tube. Further, the thickness of the gate substrate 10 is relatively thin, and the electron beam through-hole 20 coincides with the axis direction of the electron beam, improving the electron passing rate. Especially when the voltage of the gate 52 is relatively low (lower than 5 kV), it still maintains a high electron passing rate, and is suitable for various cathode 51 emission materials such as field emission, thermal emission, and thermionic field emission. In addition, the gate substrate 10 is made of materials with a low atomic number, has a very low X-ray yield, is beneficial to reducing the X-rays generated by the electron beam bombarding the gate 52, and reducing the shielding requirement for the X-rays generated by the gate 52 when using the gate 52.

[0079] Further, as Figure 3As shown, the electron gun 50 involved in the present application further includes other electrodes such as the focusing electrode 53. The grid electrode 52 is located between the electron emitter of the cathode 51 and the focusing electrode 53. The distance between the grid electrode 52 and the cathode 51 is set to be 0.1 - 1 mm, preferably 0.1 - 0.4 mm. The distance between the grid electrode 52 and the focusing electrode 53 is set to be 0.1 - 3 mm, preferably 0.1 - 0.5 mm. By applying a potential different from that of the cathode 51 to the grid electrode 52, the electrons emitted by the cathode 51 are regulated. The material of the electron emitter of the cathode 51 can be various cathode emission materials such as a thermionic cathode 51, a field emission cathode 51, or a thermo-field emission cathode 51. In addition, Figure 3 An embodiment showing the use of the grid electrode 52 in the electron gun 50 is presented. In other embodiments, the grid electrode 52 can also be used in various vacuum electron devices such as electron microscopes, electron beam tubes, magnetrons, traveling wave tubes, etc. that require a grid electrode 52.

[0080] Furthermore, the grid electrode 52 and the focusing electrode 53 can be insulated by an insulating material such as ceramics, and different potentials can be applied to them; or, the grid electrode 52 and the focusing electrode 53 are integrated and the same potential is applied to them. As Figure 3 shown, the focusing electrode 53 includes a neck portion 531 and a main body portion 532 that are sequentially distributed along the direction away from the grid electrode 52. A through-hole allowing the electron beam to pass through is provided in the neck portion 531. An electrode inner cavity is provided in the main body portion 532, and the opening faces the anode 70. The electron beam through-hole 20 of the grid electrode 52, the through-hole of the neck portion 531 in the focusing electrode 53, and the electrode inner cavity of the main body portion 532 are sequentially connected along the electron beam emission direction. The size of the electrode inner cavity of the main body portion 532 is much larger than the size of the through-hole of the neck portion 531. Therefore, the main body portion 532 and the neck portion 531 are connected by a conical surface transition.

[0081] Furthermore, as Figure 4 shown, the X-ray tube involved in the present application has a single-grid structure. In other embodiments, multiple grid electrodes 52 can be used according to the regulation needs. The X-ray tube can be a reflection target structure or a transmission target structure. The X-ray tube is mainly applied in the industrial field and can also be applied in various fields such as medical treatment and scientific instruments.

[0082] In summary, the present invention effectively overcomes various drawbacks in the prior art and has high industrial utilization value.

[0083] The above embodiments are only illustrative of the principles and effects of the present invention and are not used to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A grid for a vacuum electronic device, characterized in that: The gate includes a gate substrate which is a flat sheet with a thickness of 0.1 mm to 3 mm, and the thermal conductivity of the material of the gate substrate is greater than 200 W / (m·K); At least one electron beam through-hole penetrating along the thickness direction is provided on the gate substrate, the axial direction of the electron beam through-hole is perpendicular to the two surfaces in the thickness direction of the gate substrate, and the electron beam through-hole makes the gate substrate have a through-hole part and a solid part other than the through-hole part; After the electron beam through-hole is machined on the gate substrate, an outer coating layer is fixedly arranged on the surface of the solid part of the gate substrate, and the material of the outer coating layer is a metal material with a thickness of 10 nm - 50 μm.

2. The grid for a vacuum electronic device according to claim 1, characterized in that: The material of the gate substrate is any one of diamond, cubic boron nitride, single crystal SiC, beryllium oxide and graphene.

3. The grid for a vacuum electronic device according to claim 1, characterized in that: The diameter of the electron beam through-hole is 0.1 mm to 1 mm; when there are multiple electron beam through-holes, the duty ratio between the through-hole part and the solid part on the gate substrate is 2.

4. The grid for a vacuum electronic device according to claim 1, characterized in that: The material of the outer coating layer is any one of gold, copper, chromium, nickel, molybdenum and tungsten.

5. The grid for a vacuum electronic device according to claim 1, characterized in that: The outer coating layer is fixedly attached to the surface of the solid part by magnetron sputtering, chemical vapor deposition, or evaporation.

6. The grid for a vacuum electronic device according to claim 1, characterized in that: The surface roughness of the two surfaces in the thickness direction of the gate substrate does not exceed Ra0.

8.

7. The grid for a vacuum electronic device according to claim 1, characterized in that: A transition layer is provided between the solid part and the outer coating layer of the gate substrate, and the thickness of the transition layer does not exceed 150 nm.

8. The grid for a vacuum electronic device according to claim 7, characterized in that: The material of the transition layer is titanium, chromium, or nickel.

9. The grid for a vacuum electronic device according to claim 7, characterized in that: The transition layer is fixedly attached to the surface of the solid part by magnetron sputtering, chemical vapor deposition, or evaporation, and the outer coating layer is fixedly attached to the surface of the transition layer by magnetron sputtering, chemical vapor deposition, or evaporation.

10. An electron gun includes a cathode having an electron emitter, characterized in that: It also includes the gate according to any one of claims 1 - 9, and the gate is fixedly arranged on one side of the cathode along the electron beam emission direction.

11. An X-ray tube, comprising a tube housing with a vacuum tube cavity inside, and an anode hermetically connected to one end of the tube housing, the anode having an anode target, characterized in that: It also includes the electron gun according to claim 10, the electron gun is hermetically connected to the other end of the tube shell, and the cathode, the gate and the anode target are arranged in sequence along the electron beam emission direction.

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