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

Abstract

The utility model 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 sheet, the thickness of the grid electrode substrate is 0.1 mm-3mm, and the thermal conductivity of the material of the grid electrode substrate is greater than 200W / (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] This utility model relates to the field of vacuum electronic devices, and in particular to a gate for a vacuum electronic device, an electron gun equipped with the gate, and an X-ray tube equipped with the electron gun. Background Technology

[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 industrial, medical, and scientific instruments. Typically, the grid is positioned between the emitting electrode (cathode) and the anode of the vacuum electronic device. By applying a potential to the grid relative to the cathode, the electron beam current from the cathode, passing through the grid, and reaching the anode is controlled. This allows for adjustments to the electron beam intensity, beam size, beam direction, and even the switching on and off of the electron beam.

[0003] Depending on the electron emission mechanism of the cathode material (such as field emission, thermionic emission, and thermo-field emission), the gate potential for thermionic and thermo-field emission is typically below several hundred volts, while the gate potential for field emission is typically below several thousand volts. Because the gate is subjected to long-term bombardment by electron beams, the gate material needs to have high voltage resistance, high temperature resistance, resistance to electron bombardment, excellent mechanical stability, resistance to deformation, low coefficient of thermal expansion, and low saturated vapor pressure.

[0004] Currently, the most common gate structures are molybdenum, tungsten, and nickel grids or meshes with single or multiple apertures. The gate is positioned directly above the cathode electron emitting material and parallel to its plane. The distance between the gate and the cathode is very small, typically less than 1 mm, mostly below 0.5 mm, or even 0.1 or 0.2 mm. To achieve high electron throughput, the gate thickness is usually thin, ranging from 0.05 to 0.3 mm. During use, these thin metal grids with grid or mesh structures are bombarded by electron beams for extended periods. Except for less than 1% of the electron energy being converted into X-rays on the gate, almost all of the electron kinetic energy is converted into heat. Therefore, the long-term bombardment force of the electron beam, and the large amount of heat accumulated on the gate that cannot be dissipated in time, cause deformation of the thin metal grid or mesh structure. This affects the electric field between the gate and the cathode, as well as the position of the apertures on the grid relative to the cathode, leading to the failure of electron beam modulation. In some cases, the small distance between the gate and the cathode and the deformation of the gate can even cause a short circuit between them. In addition, when an electron beam bombards the grid, it generates X-rays. The X-ray yield is related to the thickness and atomic number of the grid material. The higher the atomic number of the grid material, the higher the X-ray yield. When the thickness does not exceed the electron's path of freedom in the material, the thicker the grid material, the higher the X-ray yield. Molybdenum, tungsten, and nickel grids or meshes all have large atomic numbers and high X-ray yields. However, the X-rays generated by this non-anode target surface are undesirable, so additional shielding measures are required to shield the X-rays generated on the grid.

[0005] Prior art: Chinese invention patent application No. 202011302224.X discloses a graphene sponge gate structure with high electron transmittance. This structure uses a graphene sponge grid structure to replace existing metal micro-grids, improving the gate's electron transmittance and electron collimation while maintaining conductivity and a certain mechanical strength, thus enhancing the gate's bombardment resistance. However, due to manufacturing process limitations, it is difficult to control the direction of the electron beam through-holes on this graphene sponge gate to align with the electron beam emission direction. Furthermore, the metal film layer on the surface of the sponge graphene lacks pores, hindering electron passage. Therefore, its electron transmittance is very low at gate voltages below 5kV, making it suitable only for applications with higher gate voltages (5-30kV). Furthermore, because it is difficult to control the direction of the electron beam through-hole to be consistent with the direction of electron beam emission, and because of the metal film covering the surface, this gate is more suitable for field emission cathodes in applications requiring a quasi-parallel electric field to improve the collimation of electron emission, but not suitable for applications requiring pre-focusing of the gate, such as thermal emission and thermal field emission cathodes; moreover, this porous sponge gate is not suitable for applications requiring a single-hole gate. Utility Model Content

[0006] In view of the shortcomings of the prior art described above, the purpose of this utility model is to provide a gate for vacuum electronic devices that still has a high electron throughput at a gate voltage of less than 5kV, and is also well applicable to various cathode emission materials such as field emission, thermal emission, and thermal field emission.

[0007] To achieve the above objectives, this utility model provides a gate for a vacuum electronic device, the gate comprising a gate substrate, the gate substrate being a flat sheet with a thickness of 0.1 mm to 3 mm, and the thermal conductivity of the material of the gate substrate being greater than 200 W / (mK);

[0008] The gate substrate has at least one electron beam via extending along its thickness direction. The axial direction of the electron beam via is perpendicular to two surfaces of the gate substrate in the thickness direction. The electron beam via gives the gate substrate a via portion and a solid portion other than the via portion.

[0009] The gate substrate has an outer coating layer fixed on the surface of the solid portion. The outer coating layer is made of a metallic material and has a thickness of 10nm-50μm.

[0010] The above-mentioned gate can be selected as follows: the material of the gate substrate is any one of diamond, cubic boron nitride, single crystal SiC, beryllium oxide and graphene.

[0011] The above-mentioned gate options are as follows: the diameter of the electron beam via is 0.1mm to 1mm; when there are multiple electron beam vias, the duty cycle between the via portion and the solid portion is determined by the electron throughput of the electron beam and the heat dissipation capacity of the gate. Typically, the duty cycle between the via portion and the solid portion on the gate substrate can be selected as 2.

[0012] The aforementioned gate can be made of any one of gold, copper, chromium, nickel, molybdenum, and tungsten.

[0013] An alternative to the gate described above is that the outer coating layer is fixedly attached to the surface of the solid portion by magnetron sputtering, chemical vapor deposition, or evaporation.

[0014] An alternative to the gate described above is that the surface roughness of the two surfaces in the thickness direction of the gate substrate does not exceed Ra0.8.

[0015] An alternative to the gate described above is that the gate substrate has a transition layer between the solid portion and the outer wrapping layer, and the thickness of the transition layer does not exceed 150 nm.

[0016] The gate described above can be made of titanium, chromium, or nickel.

[0017] The aforementioned gate can be configured such that the transition layer is fixedly attached to the surface of the solid portion 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.

[0018] This application also provides an electron gun, including a cathode and a gate as described above, wherein the cathode has an electron emitter and the gate is fixed 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 an internal vacuum cavity, an anode sealed to one end of the tube shell, and an electron gun as described above. The anode has an anode target, and the electron gun is sealed to the other end of the tube shell. The cathode, the grid, and the anode target are arranged sequentially along the electron beam emission direction.

[0020] As described above, the grid, electron gun, and X-ray tube for vacuum electronic devices involved in this utility model have the following beneficial effects.

[0021] 1. The high thermal conductivity of the gate substrate enables the heat generated by the electron beam bombarding the gate substrate to be quickly dissipated, preventing the gate substrate from deforming due to heat accumulation and ensuring the electron beam control function of the gate.

[0022] 2. The electron beam through-hole is machined on a directly purchased flat sheet, reliably ensuring that the axis of the electron beam through-hole is aligned with the electron beam emission direction. The grid substrate has a flat sheet structure. The outer sheath does not cover the two ends of the electron beam through-hole along its axis, thus not obstructing the passage of electrons. Ultimately, this greatly improves the electron throughput, enabling the grid to maintain a high electron throughput even at low kV levels (below 5kV), and making it suitable for various cathode emission materials such as field emission, thermal emission, and thermal field emission. Simultaneously, the increased electron throughput reduces the heat and X-rays generated on the grid substrate, thereby lowering the shielding requirements for X-rays generated by the grid when using it.

[0023] 3. The outer coating layer can not only conduct electrons that bombard the gate substrate away, but also prevent the gate substrate from being damaged by electron bombardment, giving the gate substrate excellent mechanical stability and structural strength, and resistance to electron bombardment. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the gate structure used in vacuum electronic devices in this application.

[0025] Figure 2 for Figure 1 Enlarged view of circle A.

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

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

[0028] Component designation explanation

[0029] 10 Gate substrate

[0030] 11 Through-hole section

[0031] 12. Solid Part

[0032] 20 Electron Beam Through-Aperture

[0033] 30 Outer wrapping layer

[0034] 40 Transition Layer

[0035] 50 electron guns

[0036] 51 Cathode

[0037] 52 gate

[0038] 53 Focused electrode

[0039] 531 Neck

[0040] 532 Main Body

[0041] 60 tube shell

[0042] 70 Anode

[0043] 71 Anode Target Detailed Implementation

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

[0045] It should be understood that the structures, proportions, sizes, etc., depicted in the accompanying drawings are merely for illustrative purposes to aid those skilled in the art and are not intended to limit the scope of this invention. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to size, without affecting the effectiveness and purpose of this invention, should still fall within the scope of the disclosed technical content. Furthermore, the terms "upper," "lower," "left," "right," "middle," and "one" used in this specification are merely for clarity and not intended to limit the scope of this invention. Changes or adjustments to their relative relationships, without substantially altering the technical content, should also be considered within the scope of this invention.

[0046] It should also be noted that when a component is referred to as being "fixed to" or "set on" another component, it can be directly on the other component or may be connected to an intermediary component. When a component is referred to as being "connected to" another component, it can be directly connected to the other component or indirectly connected to the other component through an intermediary component.

[0047] Furthermore, the use of terms such as "first" and "second" in this application is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. Additionally, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed in this application.

[0048] This application relates to the field of X-ray tube technology, and in particular to a gate 52 for a vacuum electronic device, an electron gun 50 including the gate 52, and an X-ray tube including the electron gun 50.

[0049] like Figure 4 As shown, the X-ray tube involved in this application includes a tube shell 60 with an internal vacuum cavity, an anode 70 sealed to one end of the tube shell 60, and an electron gun 50 sealed to the other end of the tube shell 60; wherein, the anode 70 has an anode target 71; as Figure 3As 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 fixed to 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 sequentially along the electron beam emission direction. When the X-ray tube is working, the electron emitter of the cathode 51 emits electrons, which are accelerated by the electric field and pass through the electron beam through-hole 20 of the grid 52, bombarding the anode target 71 to generate X-rays. The X-rays are then emitted from the window assembly on the tube shell 60.

[0050] Furthermore, the gate 52 involved in this utility model is completely different from existing molybdenum, tungsten and nickel gate sheets or grids.

[0051] Specifically: such as Figure 1 and Figure 2 As shown, the gate 52 involved in this application includes a gate substrate 10, which is a flat sheet with a thickness of 0.1 mm to 3 mm. The thermal conductivity of the material of the gate substrate 10 is greater than 200 W / (mK). At least one electron beam through-hole 20 is provided on the gate substrate 10, which is used for the passage of electron beam current. When there is one electron beam through-hole 20, the gate 52 is a single-hole structure. The single-hole structure of the gate 52 is usually used when the cathode 51 has a single electron emitter. When there are multiple electron beam through-holes 20, the gate 52 is a multi-hole structure. The multi-hole structure of the gate 52 is usually used when the cathode 51 has multiple electron emitters, such as when it is used for an array of electron emitters. The multiple electron beam through-holes 20 correspond one-to-one with the multiple electron emitters of the cathode 51. In particular, the gate substrate 10 is a commercially available flat wafer product, and then the electron beam via 20 is fabricated on the existing flat wafer. In this way, it can be reliably ensured that the axis of the electron beam via 20 is perpendicular to the two surfaces of the gate substrate 10 in the thickness direction (i.e., Figure 1 (The upper and lower surfaces in the view) ensure that the axis of the electron beam via 20 is strictly aligned with the electron beam emission direction. The through-structure of the electron beam via 20 on the gate substrate 10 gives the gate substrate 10 a via portion 11 and a solid portion 12 other than the via portion 11. The solid portion 12 is also the non-via portion of the gate substrate 10. Further, in the gate 52 involved in this application, the required electron beam via 20 is first processed on the directly purchased gate substrate 10. Then, an outer cladding layer 30 is fixed on the surface of the solid portion 12 of the gate substrate 10. The surface of the solid portion 12 includes two surfaces in the thickness direction of the gate substrate 10, the outer peripheral surface, and the hole wall of the electron beam via 20. In this case, the outer cladding layer 30 of the gate substrate 10 will not cover the electron beam via 20, or in other words, the electron beam via 20 also axially penetrates the outer cladding layer 30. Furthermore, the material of the outer cladding layer 30 is a metallic material, and the thickness is 10nm-50μm.

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

[0053] First, the thermal conductivity of the gate substrate 10 is significantly higher than that of traditional molybdenum and tungsten grids or meshes. Thus, during the operation of the X-ray tube, the heat generated by the electron beam bombarding the gate substrate 10 is quickly conducted away, avoiding the accumulation of heat on the gate substrate 10. This also prevents the flat sheet gate substrate 10 from deforming, thereby keeping the electric field between the gate 52 and the cathode 51, as well as the position of the electron beam through-hole 20 on the gate 52 relative to the cathode 51, unchanged, ensuring the electron beam control function of the gate 52.

[0054] Secondly, the electron beam through-hole 20 is machined on a directly purchased flat sheet, which reliably ensures that the axis of the electron beam through-hole 20 is consistent with the electron beam emission direction, thereby reducing the interception of electrons by the hole wall of the electron beam through-hole 20 and improving the electron throughput.

[0055] Third, the gate substrate 10 is a flat sheet with a thickness of 0.1 mm to 3 mm, which gives the gate substrate 10 high mechanical stability and structural strength, as well as high electron throughput. The higher the electron throughput, the fewer electrons are intercepted, and the easier it is for electrons to pass through the electron beam through-hole 20. This results in less heat and X-rays generated on the gate substrate 10, better preventing deformation of the flat sheet gate substrate 10. It also reduces the shielding requirements for X-rays generated by the gate 52 when using the gate, simplifying the structure of vacuum electronic devices.

[0056] Fourth, the surface of the solid portion 12 of the gate substrate 10 is covered by an outer cladding layer 30. Electrons directly bombard the outer cladding layer 30 of the gate substrate 10. The outer cladding layer 30 has at least the following functions in this application: 1. The outer cladding layer 30 has conductive properties. Through the conductivity of the outer cladding layer 30, electrons bombarding the gate substrate 10 can be conducted away, preventing the gate substrate 10 from deforming due to heat accumulation; 2. The material of the outer cladding layer 30 is a metallic 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 giving the gate substrate 10 high mechanical stability and structural strength; 3. The thickness of the outer cladding layer 30 The thickness is 10nm-50μm, which is very thin. This can increase the bonding force between the outer coating layer 30 and the gate substrate 10, prevent the outer coating layer 30 from falling off due to long-term electron bombardment, and reduce the X-ray yield when electrons bombard the gate 52. This reduces the shielding requirement for X-rays generated by the gate 52 when using the gate 52, and simplifies the structure of vacuum electronic devices. 4. The outer coating layer 30 does not cover both ends of the electron beam through-hole 20 in the axial direction, so it will not hinder the passage of electrons. This allows the gate 52 of this application to still have a high electron throughput at a gate voltage of less than 5kV. At the same time, it can be well applied to various cathode emission materials such as field emission, thermal emission and thermal field emission.

[0057] Furthermore, the gate substrate 10 is preferably made of a high thermal conductivity material that is resistant to high temperature, has high mechanical stability at high temperature, is resistant to deformation, has a low coefficient of expansion and a low saturated vapor pressure. The thermal conductivity of the material of the gate substrate 10 is preferably greater than 1000 W / (mK), more preferably greater than 1300 W / (mK).

[0058] Preferably, the gate substrate 10 is made of a high thermal conductivity insulating material, such as diamond, cubic boron nitride, single-crystal SiC, beryllium oxide, etc. Among these, the thermal conductivity of the gate substrate 10 made of cubic boron nitride and diamond is as high as 1300 W / (mK) or even 2400 W / (mK). Furthermore, 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. Even though the gate substrate 10 is made of a high thermal conductivity insulating material, the surface of the gate substrate 10 is covered by a conductive outer coating layer 30, which is used to set the potential of the gate 52 and control the electron beam current during use.

[0059] Preferably, the gate substrate 10 is made of a conductive material with high thermal conductivity, such as graphene. Furthermore, the gate 52 is an electrode in the X-ray tube, and a corresponding potential needs to be set on it during use. The conductivity of the gate substrate 10 itself allows it to be used to set the potential of the gate 52 and control the electron beam current. However, the gate substrate 10 is a graphene sheet, which is not resistant to electron bombardment. But because the surface of the graphene sheet is covered by an outer layer 30 of metallic material, it effectively prevents damage from electron bombardment, thus maintaining high structural strength.

[0060] Furthermore, the outer coating layer 30 is made of a metal material that is resistant to high pressure, electron bombardment, and low saturated vapor pressure, preferably gold, copper, chromium, nickel, molybdenum, and tungsten. Additionally, the thickness of the outer coating layer 30 is preferably 20 nm to 5 μm, and particularly preferably 20 nm to 1 μm, which better increases the bonding force between the outer coating layer 30 and the gate substrate 10, and better prevents the outer coating layer 30 from detaching due to long-term electron bombardment.

[0061] Furthermore, when the material of the gate substrate 10 is a low atomic number material such as diamond, cubic boron nitride, and graphene, the atomic number of diamond, cubic boron nitride, and graphene does not exceed 7, which is significantly lower than the atomic number of existing molybdenum, tungsten, and nickel gate sheets or grids, thus greatly reducing the X-ray yield on the gate substrate 10. With this configuration, when the electron beam bombards the gate substrate 10, less X-ray is generated on the gate 52, which helps to reduce the shielding requirements for the X-rays generated by the gate 52 when using the gate 52.

[0062] Furthermore, the gate substrate 10 is a commercially available flat sheet, which can be a circular sheet, a rectangular sheet, or a sheet of other shapes. The cross-sectional shape of the electron beam via 20 can be circular, square, or other special shapes designed to meet electron throughput requirements. The diameter of the electron beam via 20 is 0.1 mm to 1 mm, preferably 0.1 mm to 0.4 mm. When there are multiple electron beam vias 20, adjacent electron beam vias 20 are isolated by the solid portion 12 of the gate substrate 10 (i.e., the material of the gate substrate 10), and the duty cycle between the via portion 11 and the solid portion 12 on the gate substrate 10 is 2. The duty cycle is the ratio of the diameter of the electron beam via 20 to the size of its adjacent solid portion 12, representing the spacing between two adjacent electron beam vias 20. The duty cycle is designed and confirmed using the electron beam current throughput index and the heat dissipation capability of the gate. For example, in one embodiment, the diameter of the electron beam aperture 20 is 0.2 mm, and the dimension of the solid portion 12 in the radial direction of the electron beam aperture 20 (i.e., the wall thickness between two adjacent electron beam apertures 20) is 0.1 mm.

[0063] Furthermore, the electron beam vias 20 can be fabricated on the purchased gate substrate 10 using various methods such as femtosecond laser processing, electron beam processing, and plasma etching. Alternatively, they can be fabricated on the purchased gate substrate 10 using a patterned mask wet etching method, reliably fabricating electron beam vias 20 on two surfaces that are strictly perpendicular to the thickness direction of the gate substrate 10. Alternatively, the gate substrate sheet can be grown using methods such as CVD. During the growth of the gate substrate sheet, fine needles nearly perpendicular to the substrate surface are placed on the substrate, and the gate substrate sheet is grown using methods such as CVD. Finally, the fine needles are removed using methods such as chemical etching, thereby obtaining a gate substrate sheet with electron beam vias 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 not exceeding Ra0.2, and more preferably not exceeding 5nm, 10nm, 15nm, 30nm, or 50nm. This setting increases the bonding strength between the gate substrate 10 and the outer cladding layer 30 while reducing the surface roughness of the outer cladding layer 30, thereby preventing high-voltage arcing between the gate 52 and the cathode 51. Preferably, a smooth surface can be obtained by polishing the surface of the gate substrate 10 using methods such as mechanical polishing, mechanical-chemical polishing, thermochemical polishing, or ion beam polishing, thereby reducing the surface roughness of the gate substrate 10.

[0065] Furthermore, the surface of the gate substrate 10 may be covered only by the outer coating layer 30; in this case, the outer coating layer 30 is fixedly attached to the surface of the solid portion 12 by magnetron sputtering, chemical vapor deposition, or evaporation. Alternatively, as Figure 2 As shown, the gate substrate 10 has a transition layer 40 between the solid portion 12 and the outer coating layer 30. The transition layer 40 is made of materials such as titanium, chromium, and nickel, and its thickness does not exceed 150 nm, preferably not exceeding 5 nm, 10 nm, 15 nm, 30 nm, or 50 nm. The transition layer 40 is fixedly attached to the surface of the solid portion 12 by magnetron sputtering, chemical vapor deposition, or evaporation, and the outer coating layer 30 is fixedly attached to the surface of the transition layer 40 by magnetron sputtering, chemical vapor deposition, or evaporation. The provision of the transition layer 40 better increases the bonding strength between the outer coating layer 30 and the gate substrate 10, preventing the outer coating layer 30 from detaching due to long-term electron bombardment.

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

[0067] The gate substrate 10 is a diamond plate-type thin film with a thickness of 0.1 mm and a surface roughness of no more than 50 nm. The diamond plate-type thin film has an electron beam through-hole 20 with a diameter of 0.2 mm. The surface of the diamond plate-type thin film 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 method for fabricating the gate 52 includes the following steps in sequence.

[0069] S1. Purchase a 0.1mm thick diamond sheet and polish its surface to ensure a surface roughness of no more than 50nm. Alternatively, directly purchase a 0.1mm thick diamond sheet with a surface roughness of no more than 50nm.

[0070] S2. The surface of the diamond sheet is sequentially subjected to ultrasonic cleaning with acetone, rinsing with deionized water, and dehydration with alcohol, and then dried.

[0071] S3. Electron beam through-hole 20 is machined on the diamond sheet: The diamond sheet is fixed on the precision displacement stage of the femtosecond laser processing device. The spot size and power of the femtosecond laser are adjusted, and a through-hole with a size of 0.2 mm is machined in a direction perpendicular to the bottom plane of the diamond sheet using multiple laser impacts. This through-hole is the electron beam through-hole 20. When the gate 52 has a multi-hole structure, multiple through-holes need to be machined. In this case, the drilling position is adjusted using the precision displacement stage to machine multiple through-holes on the diamond sheet.

[0072] S4. The diamond sheet with through holes is subjected to ultrasonic cleaning with acetone, rinsing with deionized water and dehydration with alcohol in sequence, and then dried.

[0073] S5. Place the diamond sheet with through holes into the vacuum chamber of the vacuum coating machine. The vacuum level in the vacuum chamber should not be less than 1×10⁻⁶. -3 Pa, temperature 200-300℃; adjust the power and time of magnetron sputtering to sputter a chromium film of no more than 50 nm on the surface of the diamond sheet and the inner surface (i.e., the hole wall) of the through hole, the chromium film forming a transition layer 40.

[0074] S6. Switch the target material of the vacuum coating machine, adjust the power and time of magnetron sputtering, and sputter a molybdenum film of no more than 50 nm on the surface of the diamond sheet and the inner surface (i.e., the hole wall) of the through hole. The molybdenum film constitutes the outer coating layer 30.

[0075] S7. The diamond sheet with through holes coated with chromium and molybdenum films is subjected to ultrasonic cleaning with acetone, rinsing with deionized water and dehydration with alcohol in sequence, and then dried.

[0076] S8. Place the dried diamond sheet into a vacuum heating furnace, ensuring the vacuum level inside the furnace is not less than 1×10⁻⁶. -3 Pa, the temperature is set not lower than 400℃, and this temperature is adjusted according to the type of metal material of the transition layer 40 and the outer wrapping layer 30. After holding at this temperature for 3 hours, it is cooled with the furnace.

[0077] S9. At this point, the gate 52 based on the diamond gate substrate 10 is fabricated.

[0078] In summary, the gate 52 involved in this application has the following beneficial effects: The gate substrate 10 is made of materials such as diamond, which have high thermal stability, low coefficient of expansion, high mechanical stability, and especially high thermal conductivity. A transition layer 40 made of materials such as titanium, chromium, and nickel is sequentially deposited, as well as an outer coating layer 30 made of materials such as gold, copper, chromium, nickel, molybdenum, and tungsten. This gives the gate 52 excellent properties such as high voltage resistance, high temperature resistance, resistance to electron bombardment, excellent mechanical stability, deformation resistance, low coefficient of thermal expansion, and low saturated vapor pressure. At the same time, it also has high thermal conductivity, so that the heat generated by the electron beam bombarding the gate 52 is quickly conducted away by the high thermal conductivity gate substrate 10, as well as the conductive transition layer 40 and outer coating layer 30, preventing the gate 52 from accumulating heat and causing high temperature deformation. This improves the reliability of the gate 52 in controlling the electron beam, extends the life of the gate 52, and ultimately improves the stability and life of the electron gun 50 and the X-ray tube. Furthermore, the thinner thickness of the gate substrate 10 and the alignment of the electron beam aperture 20 with the electron beam axis improve electron throughput, especially when the gate voltage 52 is low (below 5kV), maintaining a high electron throughput. This makes it suitable for various cathode emission materials such as field emission, thermal emission, and thermal field emission. In addition, the gate substrate 10 is made of a low atomic number material, resulting in a very low X-ray yield, which helps reduce X-rays generated by electron beam bombardment of the gate 52 and lowers the shielding requirements for X-rays generated by the gate 52 when using it.

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

[0080] Furthermore, the gate 52 and the focusing electrode 53 can be insulated from each other using an insulating material such as ceramic, allowing different potentials to be applied to them; alternatively, the gate 52 and the focusing electrode 53 can be integrated and subjected to the same potential. Figure 3 As shown, the focusing electrode 53 includes a neck 531 and a main body 532 arranged sequentially along the direction away from the gate 52. The neck 531 has a through hole that allows the electron beam to pass through, and the main body 532 has an electrode cavity with its opening facing the anode 70. The electron beam through hole 20 of the gate 52, the through hole of the neck 531 in the focusing electrode 53, and the electrode cavity of the main body 532 are sequentially connected along the electron beam emission direction. The size of the electrode cavity of the main body 532 is much larger than the size of the through hole of the neck 531, so the main body 532 and the neck 531 are connected by a conical surface transition.

[0081] Furthermore, such as Figure 4 As shown, the X-ray tube involved in this application has a single-gate structure. In other embodiments, multiple gates 52 can be used as needed for control. The X-ray tube can be a reflective target structure or a transmission target structure. X-ray tubes are mainly used in the industrial field, but can also be used in various fields such as medical and scientific instruments.

[0082] In summary, this utility model effectively overcomes the various shortcomings of the prior art and has high industrial application value.

[0083] The above embodiments are merely illustrative of the principles and effects of this utility model and are not intended to limit the scope of this utility model. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of this utility model. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in this utility model should still be covered by the claims of this utility model.

Claims

1. A gate 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 / (mK). The gate substrate has at least one electron beam via extending along its thickness direction. The axial direction of the electron beam via is perpendicular to two surfaces of the gate substrate in the thickness direction. The electron beam via gives the gate substrate a via portion and a solid portion other than the via portion. The gate substrate has an outer coating layer fixed on the surface of the solid portion. The outer coating layer is made of a metallic material and has a thickness of 10nm-50μm.

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

3. The gate for a vacuum electronic device according to claim 1, characterized in that: The diameter of the electron beam via is 0.1 mm to 1 mm; when there are multiple electron beam vias, the duty cycle between the via portion and the solid portion on the gate substrate is 2.

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

5. The gate 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 means of magnetron sputtering, chemical vapor deposition, or evaporation.

6. The gate 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 gate for a vacuum electronic device according to claim 1, characterized in that: The gate substrate has a transition layer between the solid portion and the outer wrapping layer, and the thickness of the transition layer does not exceed 150 nm.

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

9. The gate 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, comprising a cathode having an electron emitter, characterized in that: It also includes the gate according to any one of claims 1-9, the gate being fixed on one side of the cathode along the electron beam emission direction.

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

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