A micro-needle tip annular array cathode electron gun and a method for preparing the cathode thereof

Abstract

The invention discloses a micro-needle tip annular array cathode electron gun and a preparation method of its cathode, belonging to the technical field of vacuum electronic devices, wherein the electron gun comprises a cathode, a grid, a dual focusing electrode and an anode; specifically, the cathode is an annular array structure, divided into two by a cone along a symmetry axis, the cut surface is the bottom surface, the tip faces inward, is evenly distributed in a cathode groove, presents a concave shape, and has a pre-focusing effect; the micro-needle tip design of the cathode significantly increases the field enhancement factor, thereby improving the electric field intensity at the tip, increasing the emission current density and reducing the turn-on voltage; the grid is a rhombus grid hole grid, the side length of the rhombus is consistent with the radius of the cathode groove, the electric field distribution is optimized by adjusting the acute angle of the rhombus, and the field emission efficiency is significantly improved; the first focusing electrode is a hyperbolic focusing electrode, the inner wall shape of which is a hyperbola, and the focusing effect is enhanced by guiding the electric field lines to bend toward the anode along the central axis; the electron gun of this design has both high field emission performance and high beam compression ratio.

Description

Technical Field

[0001] The invention relates to the technical field of vacuum electronic devices, and in particular to a micro-needle tip annular array cathode electron gun and a preparation method of a cathode thereof. Background Art

[0002] The electron source is the core of many vacuum electronic devices. At present, the electron source type that has been widely studied and applied in vacuum electronic devices is mainly the hot cathode electron source, which has the advantages of large emission current, high stability and relatively low vacuum requirements. However, the need for heating leads to a more complex structure and thermal radiation is accompanied by energy loss, so the device is difficult to integrate and has high energy consumption; in addition, the preheating process of the device is relatively long, which makes the device startup time longer, making it difficult to meet the application scenarios that require quick startup.

[0003] Compared with hot cathodes, field emission cold cathode electron sources have the advantages of room temperature operation, fast response speed, and low power consumption. Field emission cold cathode electron sources suppress the cathode surface barrier by applying an external electric field, reducing the barrier height and narrowing the width. In this way, a large number of electrons in the emitter penetrate the surface barrier due to the tunneling effect and escape, forming field-induced electron emission, which can be instantaneously started with the application of the electric field, and the response time of the device can reach the nanosecond level. In addition, the fast response capability of the carbon nanotube cold cathode electron source allows it to work in pulse mode.

[0004] Cold cathode electron guns have broad application prospects in many fields, but they still face technical bottlenecks in terms of high starting voltage, electron beam stability and power loss. When optimizing the cathode emission performance, although the field enhancement factor is crucial to improving performance, relying solely on a single field enhancement mechanism is not enough to significantly optimize the emission architecture of the entire electron gun. Therefore, it is necessary to deeply explore the relationship between the cathode geometry and the grid, especially the geometry and related parameters of the grid hole, which have an important influence on the electric field distribution on the cathode surface and the beam current density. In addition, the thickness of the grid, the distance between the grid and the cathode, the shape design of the focusing electrode, and the voltage distribution of each electrode all play a vital role in the focusing effect and transmittance of the electron beam. By accurately adjusting the position of each electrode and its voltage distribution, the divergence of the electron beam can be effectively reduced, the focusing performance of the focusing system can be improved, and the efficiency and stability of field emission can be enhanced. The combined effect of these factors determines the overall performance of the electron gun. Summary of the invention

[0005] Purpose of the invention: In view of the shortcomings of the above-mentioned technology, the purpose of the present invention is to solve the problem that the traditional structure is difficult to take into account low turn-on voltage, large current, high electron transmittance and small focal spot.

[0006] Technical solution: The micro-needle tip annular array cathode electron gun described in the present invention comprises: a cathode, a grid, a dual focusing electrode and an anode arranged in sequence on a coaxial line; the cathode comprises a cathode base and a cathode emission unit; the dual focusing electrode comprises: a first focusing electrode and a second focusing electrode; wherein the electrodes are isolated by ceramic gaskets and combined into an integrated structure, and each electrode can be connected by a wire to be provided with voltage by an external circuit.

[0007] Furthermore, the material of the cathode substrate is silicon, silicon carbide or sapphire, etc.; a cylindrical cathode groove is opened on the cathode substrate, the cathode emission unit is embedded in the groove, and the highest point of the cathode emission unit is located in the same plane as the upper surface of the cathode substrate; the radius of the cathode groove is 0.2~0.5 mm, and the depth is 0.05~0.1 mm.

[0008] Furthermore, the material of the cathode emission unit is silicon, silicon carbide or sapphire, and the material of the surface of the cathode emission unit is carbon nanotubes; the cathode emission unit is a cone divided into two along the symmetry axis, the cut surface is the bottom surface, the tip is facing inward, and is evenly distributed in the cathode groove to form a ring array, and the side facing the gate is approximately the concave cathode structure of the Pierce electron gun; the radius of the bottom surface of the cone is 0.05~0.1mm, and the height is 0.2~0.5mm.

[0009] Furthermore, the gate is a grid, the material of which is a metal such as copper, aluminum or molybdenum, the shape of the gate hole is a rhombus, the number of gate holes and the acute angle of the rhombus can be adjusted according to design requirements, and the side length of the rhombus is the same as the radius of the cathode groove; a high work function metal film is prepared on the surface of the gate; the gate thickness is 0.01~0.1mm.

[0010] Furthermore, the first focusing electrode in the dual focusing electrode is a hyperbolic focusing electrode, which is made of metal such as copper, aluminum or molybdenum, and has a polished surface; its inner wall shape is determined by the minimum inner diameter and the inner wall curvature at the center of the electrode, and the inner wall curvature is determined by the electrode thickness and the difference between the maximum inner diameter and the minimum inner diameter; the minimum inner diameter is 0.15~0.6mm, the thickness is 1~3mm, and the maximum inner diameter is 0.3~0.8mm.

[0011] Furthermore, the material of the anode is tungsten metal, and the surface is gold-plated.

[0012] The method for preparing a cathode of a micro-needle tip annular array cathode electron gun of the present invention comprises the following steps:

[0013] (1) Preparation of cathode emission unit morphology: The cathode emission unit morphology material is silicon carbide (SiC) and is prepared by electron beam lithography (EBL). The specific steps are as follows:

[0014] S1. Cleaning substrate

[0015] First, the SiC substrate is immersed in an ultrasonic cleaning tank containing deionized water to remove surface dirt; then the SiC substrate is placed in a plasma cleaning machine and , oxygen molecules are activated by plasma to react with the surface of the SiC substrate;

[0016] S2. Drying the substrate

[0017] The SiC substrate is used Blow dry;

[0018] S3, silanization treatment

[0019] The SiC substrate is subjected to silanization treatment to form a thin silane molecular layer on the surface of the substrate;

[0020] S4, photoresist spin coating

[0021] Spin-coat the positive thick photoresist AZIPS6090. The thickness of the photoresist is positively correlated with the etching depth. Query the spin-coating curve of AZIPS6090 and set the spin-coating speed to 800~1000RPM.

[0022] S5. Baking

[0023] The photoresist spin-coated on the surface of the SiC substrate is baked to remove the solvent in the photoresist and improve the adhesion of the photoresist;

[0024] S6, electron beam exposure, development

[0025] The processed substrate is placed in an electron beam lithography machine, and the projection part of the cathode emission unit morphology onto the photoresist surface is exposed by electron beam; the exposed substrate is immersed in AZ726MIF developer for development to expose the projection part of the cathode emission unit morphology onto the SiC substrate surface; after the development is completed, the substrate is rinsed with deionized water to completely remove the developer and dissolved photoresist residues, and then Blow dry;

[0026] S7, plasma etching

[0027] Place the developed substrate into the plasma etching equipment, and select the reaction gas and of mixed gas, and The gas flow ratio is , etching out the cathode emission unit morphology;

[0028] S8. Remove photoresist

[0029] Immerse the substrate in AZ100 or N-methylpyrrolidone NMP solution to remove the remaining photoresist, and then Blow dry;

[0030] S9. Repeated processing

[0031] Repeat steps S3 to S8, spin-coat the photoresist, and then perform electron beam exposure and development to expose the projection area of ​​the cathode groove except the cathode morphology to the surface of the SiC substrate, and then etch away the rest of the cathode groove except the cathode morphology, and after de-bonding, obtain the cathode on which carbon nanotubes have not yet grown.

[0032] (2) Preparation of carbon nanotubes (CNTs) on the cathode emission unit surface: First, a silicon oxide film is used as a hard mask, and then the carbon nanotubes (CNTs) are grown by chemical vapor deposition (CVD). The specific steps are as follows:

[0033] a Silicon oxide film hard mask preparation

[0034] A silicon oxide film is used as a hard mask on a SiC substrate with a cathode emission unit morphology, and the substrate is placed in a chemical vapor deposition chamber and silane is introduced. and oxygen , and Gas flow ratio When the film thickness is uniform, Deposited on the upper surface of the SiC substrate, the surface of the cathode emission unit, and the bottom and side walls of the cathode groove except the cathode emission unit, forming a uniform Thin film, thickness about 10~20 nm;

[0035] bSilanization, photoresist coating, baking, electron beam exposure and development

[0036] After silanization treatment, The film surface is spin-coated with photoresist, and then baked after spin coating; then it is placed in an electron beam lithography machine, and the projection pattern of the cathode morphology in the central area onto the photoresist surface is exposed by electron beam, and after exposure, it is immersed in a developer for development, exposing the film covered with The cathode emission unit morphology of the film, after development, the substrate was rinsed with deionized water and then Blow dry;

[0037] c Plasma etching, stripping

[0038] Place it in a plasma etching device to etch away the cathode emission unit surface covering film, and then remove the photoresist to complete The film does the work of the hard mask;

[0039] d Catalyst deposition

[0040] The cathode emission unit is covered with The cathode of the film is placed in a magnetron sputtering chamber, and the catalyst is deposited by magnetron sputtering. Argon gas Ar is used as the sputtering gas to deposit the catalysts Fe, Co, Ni, and Ti on the surface of the cathode emission unit.

[0041] Catalyst annealing

[0042] In hydrogen Annealing the catalyst in an atmosphere to remove oxides on the catalyst surface and optimize the catalyst particle size and distribution;

[0043] f Carbon nanotube growth

[0044] Put it into the chemical vapor deposition chamber, and the vacuum degree in the vacuum chamber is Pa, introduce argon gas Ar to maintain an inert gas environment to prevent sample oxidation; introduce carbon source gas methane, ethylene or acetylene, temperature 500~1000 ℃, carbon source gas flow rate 40sccm, argon gas Ar flow rate 100sccm, working gas pressure 1atm, chemical vapor deposition reaction to grow carbon nanotubes CNT, growth time 10~30 min;

[0045] gRemove mask

[0046] Put it into the plasma etching equipment and etch it away mask, using low power and low gas flow;

[0047] h Annealing treatment

[0048] The finally prepared cathode is placed in an annealing chamber for annealing to remove impurities and improve the crystallinity of the carbon nanotubes CNTs, and then cooled to room temperature to complete the preparation of the carbon nanotube CNTs micro-needle tip ring array cathode.

[0049] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: the cathode of the present invention adopts a conical shape and is divided into two along the symmetry axis, the cut surface is the bottom surface, the tip faces the inside, and is evenly distributed in the cylindrical groove to form a ring array. This design draws on the concept of the arc cathode in the Pierce electron gun, has a good pre-focusing effect, and provides a more ideal incident condition for the subsequent focusing system. The cathode structure adopts a micro-needle tip design, and the curvature radius of the micro-needle tip is controlled by adjusting the radius and height of the cone bottom surface. The smaller the curvature radius, the greater the field enhancement factor, so that the electric field lines in the tip area are more dense, and a stronger local electric field is generated. The high electric field strength can significantly reduce the energy required for electrons to overcome the surface potential barrier, thereby effectively reducing the turn-on voltage. At the same time, in order to avoid the electromagnetic shielding effect caused by the small gap at the cathode tip, which affects the field emission performance, the present invention has fully considered this factor in the design, and the length design of the cathode emission unit leaves enough fault tolerance to ensure that good field emission characteristics can still be maintained under different working conditions.

[0050] The grid in the present invention adopts a diamond grid hole grid design, and the cathode array has N micro-needle tips. In order to ensure the relative area between the cathode array and the grid and make it evenly distributed, and optimize the electric field distribution applied by the grid on the cathode surface, N diamond grid holes are evenly distributed around the center of the grid, and correspondingly there are N grid wires. This design ensures the good cooperation between the N micro-needle tips and the N grid wires in the cathode array, so that the beam spot shape presents a regular circle. In addition, the present invention also studies the situation where the number of cathode emission units and the number of grid wires are not completely one-to-one matched. The results show that the electron pass rate decreases, and the beam spot shape is not a regular circle and the beam spot edge divergence phenomenon is obvious. The length of the grid wire is equal to the side length of the rhombus, and the side length of the rhombus is the same as the radius of the cathode groove. In the design, adjusting the acute angle of the rhombus will not change the side length of the rhombus. The advantage of this design is that the projection of the cathode groove to the grid approximately overlaps with the N triangular areas (half of each rhombus) at the center of the grid, thereby effectively avoiding the additional overlapping part between the grid and the cathode. This design can adjust the relative area between the gate and the cathode by adjusting the acute angle of the diamond-shaped gate holes, optimize the electric field distribution, and thus reduce the interception of electrons by the gate and improve the field emission efficiency.

[0051] The hyperbolic focusing electrode effectively reduces the divergence of the electric field lines and strengthens the electric field concentration by guiding the electric field lines to bend toward the anode along the central axis. This design can effectively focus the electron beam, thereby reducing the scattering of the electron beam and significantly increasing the beam density. However, in order to ensure good focusing of the electron beam on the central axis, the curvature of the inner wall of the hyperbolic focusing electrode needs to be within an appropriate range in order to effectively guide the electron beam to focus on the central axis. An arc that is too large or too small may cause the electrons to be intercepted by the electrode or cause underfocusing. In the application scenario of a microfocus electron gun, the optimized hyperbolic focusing electrode ultimately achieves an electron beam compression ratio of 955 and a focus size of 12μm, proving the effectiveness of the design in focusing performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 It is a structural schematic diagram of the electron gun of the present invention;

[0053] Figure 2 is a schematic structural diagram of a cathode emission unit in Embodiment 1 of the present invention;

[0054] Figure 3 is a schematic structural diagram of the cathode in Example 1 of the present invention;

[0055] Figure 4 is a schematic diagram of the structure of the gate in Example 1 of the present invention;

[0056] Figure 5 This is a schematic diagram of the structure of Embodiment 2 of the present invention;

[0057] Figure 6 is a schematic structural diagram of a cathode emission unit in Embodiment 2 of the present invention;

[0058] Figure 7 is a schematic diagram of the structure of the gate in Example 2 of the present invention;

[0059] Figure 8 The present invention is a flow chart for preparing the carbon nanotube micro-needle tip annular array cathode. DETAILED DESCRIPTION

[0060] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0061] like Figure 1As shown, a micro-needle tip annular array cathode electron gun includes a cathode 1, a grid 2, a dual focusing electrode 3 and an anode 4 arranged in sequence on a coaxial line, and each electrode is isolated by a ceramic insulating ring. The cathode 1 is responsible for emitting electrons and has a pre-focusing effect, the grid 2 is used to adjust the size of the cathode emission current, the dual focusing electrode 3 is used to accurately control the shape and beam spot size of the electron beam, and the anode 4 is used to accelerate the emitted electron beam. Through this structural design, the synergistic effect between the electrodes can significantly optimize the focusing performance and emission efficiency.

[0062] like Figure 3 As shown, the cathode 1 includes a cathode substrate 1-1 and a cathode emission unit 1-2. The cathode emission unit 1-2 is located in a cylindrical cathode groove opened in the cathode substrate 1-1, and its highest point is in the same plane as the upper surface of the cathode substrate 1-1. The cathode substrate 1-1 can be made of silicon, silicon carbide or sapphire, etc. These materials have excellent mechanical strength and thermal conductivity, and have good physical and chemical stability at high temperatures. The morphology of the cathode emission unit 1-2 is as follows Figure 2 As shown, the film was prepared by electron beam lithography (EBL) and then chemical vapor deposition (CVD) was used to deposit silicon dioxide ( ) film is used as a hard mask on the surface of the cathode substrate 1-1 and the bottom and side walls of the cathode groove in the cathode groove except for the morphology of the cathode emission unit 1-2 to ensure that the subsequent carbon nanotubes (CNTs) only grow on the surface of the cathode emission unit 1-2. After the hard mask is completed, CNTs are prepared by chemical vapor deposition (CVD) to finally obtain a CNTs micro-needle tip annular array cathode. The gate 2 is made of metal materials such as copper, aluminum or molybdenum, and the gate hole is in the shape of a rhombus. The side length of the rhombus is the same as the radius of the cathode groove. The number of gate holes and the acute angle of the rhombus can be determined according to design requirements. In order to optimize the electron emission performance, a high work function metal film is deposited on the surface of the gate 2 by chemical vapor deposition (CVD), so that part of the energy of the electrons is directly absorbed by the metal film, effectively reducing the secondary electron emission, thereby avoiding the performance degradation of the electron gun. The material of the dual focusing electrode 3 is copper, aluminum or molybdenum or other metals, wherein the first focusing electrode 3-1 adopts a hyperbolic focusing structure, and its inner wall section is approximately a hyperbola. The opening arc at both ends of the electrode guides the electric field lines to bend toward the anode along the central axis, effectively reducing the divergence of the electric field lines and enhancing the concentration of the electric field, thereby optimizing the focusing of the electron beam, significantly reducing the scattering of the electron beam, and increasing the beam current density. In order to further improve the performance of the electrode, the surface of the dual focusing electrode 3 is polished to reduce the roughness, reduce the scattering or bending of the electron beam, and ensure the stability and directionality of the electron beam. Finally, the anode target surface is gold-plated by chemical vapor deposition (CVD). The high atomic number of gold means that it can effectively generate high-energy X-rays when the electron beam hits it. At the same time, the physical and chemical properties of gold are stable, so that it can remain stable during long-term operation.

[0063] During operation, different voltages are applied to the cathode 1, the grid 2, the first focusing electrode 3-1, the second focusing electrode 3-2 and the anode 4 to form the required electric field distribution inside the electron gun. The electric field applied by the grid 2 on the surface of the cathode 1 causes the electrons in the cathode 1 to overcome the surface potential barrier and escape, thereby generating field emission. The emission current of the cathode 1 is regulated by the grid 2 voltage and the distance between them. The emitted electrons gradually diverge under the action of the space charge repulsion, and the electron beam is focused to a specific position under the action of the dual focusing electrode 3. The anode 4 is responsible for accelerating the electrons emitted from the cathode 1 to move toward the anode 4. The voltage of the anode 4 determines the energy and penetration of the X-rays generated by bremsstrahlung after the electron beam bombards the anode target surface. By adjusting the structural parameters of the cathode 1, the curvature radius of the microneedle tip is reduced, and the field enhancement factor is increased, thereby improving the field emission performance and reducing the exit angle of the electron beam. In addition, by optimizing the structural parameters and voltage distribution of the grid 2 and the dual focusing electrode 3, the electric field distribution inside the electron gun is improved, thereby achieving a high electron pass rate and excellent focusing performance.

[0064] Embodiment 1:

[0065] On the basis of the above, specifically, this embodiment uses CST simulation software to establish a simulation structure of a carbon nanotube field emission cold cathode electron gun, such as Figure 1 As shown, it includes a cathode, a grid, a dual focusing electrode and an anode arranged in sequence on a coaxial line. A cylindrical groove with a radius of 0.2 mm and a height of 0.05 mm is reserved on the cathode substrate, and the cathode emission unit is arranged in the groove. The cathode emission unit has a morphology of a cone with a radius of 0.05 mm and a height of 0.18 mm, which is divided into two along the symmetry axis, with the cut surface being the bottom surface and the tip facing inward, and is evenly distributed in the groove to form a ring array. The surface of the cathode emission unit uses carbon nanotubes as electron emission materials to obtain a carbon nanotube micro-needle tip ring array cathode. The cathode emission unit has a morphology as shown in FIG. Figure 2 shown. Figure 4It is a grid with a thickness of 0.01mm. There are 12 diamond-shaped grid holes evenly distributed around the center of the grid. The side length of the diamond is 0.2mm, the acute angle is 27°, and the distance between the grid and the cathode surface is 0.07mm. The first focusing electrode in the dual focusing electrode is a hyperbolic focusing electrode. The shape of its inner wall is determined by the minimum inner diameter and the curvature of the inner wall at the center of the electrode. The curvature of the inner wall is determined by the electrode thickness and the difference between the maximum inner diameter and the minimum inner diameter. The electrode thickness is 1.2mm, the minimum inner diameter is 0.18mm, the maximum inner diameter is 0.34mm, and the distance from the right surface of the grid is 0.12mm. The second focusing electrode in the dual focusing electrode has an inner diameter of 0.12mm and a thickness of 0.01mm, and is 0.22mm away from the right surface of the first focusing electrode. The anode is 0.12mm away from the right surface of the second focusing electrode. In this structure, the cathode, grid, first focusing electrode, second focusing electrode and anode are applied with voltages of -800V, -200V, 100V, 800V and 120000V respectively. A particle monitor is set on the surface of the anode, and the beam spot size is 12μm, and the scattering degree of the beam spot edge is very low. Finally, the simulation results show that under this voltage configuration, the electron gun can take into account the anode current, electron pass rate and focus. Under the anode voltage of 120kV, the electron gun successfully achieved an electron pass rate of 92.4%, an anode current of 279.1μA and a focal spot size of 12μm, and a beam compression ratio of up to 955. In addition, except for the anode, the working voltage of other electrodes is relatively small, which can effectively reduce energy consumption. This design provides a reference for the research and development of high-energy X-ray sources used in the field of non-destructive testing.

[0066] Embodiment 2:

[0067] In this embodiment, Figure 5 As shown, the purpose is to design a carbon nanotube cold cathode laminar flow electron gun, including a cathode, a grid, a hyperbolic focusing electrode and an anode arranged in sequence on a coaxial line. Since this design does not require a small focus, the pre-focusing effect is weakened by reducing the ratio of the bottom radius to the height of the cathode emission unit morphology (cone). Figure 5 It can be seen that at this time, the thickness of the annular array cathode is greatly reduced. In addition, the curvature radius of the tip is also reduced, and the field enhancement factor is increased; at the same time, a larger cathode-gate spacing is adopted, which can not only reduce the divergence of the electron beam when passing through the gate, but also improve the uniformity of the electron beam and the electron passing rate of the gate. A cylindrical groove with a radius of 0.5mm and a height of 0.05mm is reserved on the cathode substrate, and the cathode emission unit is arranged in the groove. The morphology of the cathode emission unit is a cone with a radius of 0.05mm and a height of 0.48mm. It is divided into two along the symmetry axis, with the cut surface as the bottom surface, the tip facing inward, and evenly distributed in the groove to form a circular array. Carbon nanotubes (CNTs) are used as electron emission materials on the surface of the cathode emission unit to obtain a CNTs micro-needle tip annular array cathode. The morphology of the cathode emission unit is as follows Figure 6 shown. Figure 7 The gate has a thickness of 0.05 mm. There are 20 diamond-shaped holes evenly distributed around the center of the gate. The side length of each diamond-shaped hole is 0.5 mm, the acute angle of the diamond is 16°, and the gate is 1 mm away from the cathode surface. The thickness of the hyperbolic focusing electrode is 3 mm, the minimum inner diameter is 0.6 mm, the maximum inner diameter is 0.8 mm, and the distance from the right surface of the gate is 0.8 mm. The anode is 0.5 mm away from the right surface of the hyperbolic focusing electrode. When working, the cathode potential is set to -11000 V, and the gate, hyperbolic focusing electrode and anode are all 0 V. When electrons are emitted from the cathode and the electron beam passes through the gate area, although the porous structure of the gate may cause local electric field distortion, the motion trajectory of the electron beam does not diverge significantly. The regional potential values ​​between the gate, the hyperbolic focusing electrode and the anode are basically equal, forming an equipotential zone. In this area, electrons drift under the action of space charge force. When approaching the anode, the electron beam diverges slightly, and no obvious electron trajectory crossing phenomenon is observed during the movement to the rear end. The simulation results show that when the cathode emission current is 20.97mA, the gate interception current is 2.56mA, and the corresponding interception rate is only 12.2%. At this time, the anode current is 18.41mA, the cathode emission current density is 2.78, and the electron pass rate is 89.0%. It can be seen that the designed carbon nanotube cold cathode electron source has good laminar electron injection output capability and has a certain reference value in the application of microwave vacuum electronic devices (such as traveling wave tubes, TWT).

[0068] Embodiment 3:

[0069] like Figure 8 As shown, the embodiment of the present invention also provides a method for preparing a cathode of a micro-needle tip annular array cathode electron gun, comprising the following steps:

[0070] (1) Preparation of cathode emission unit morphology: The cathode emission unit morphology material is silicon carbide (SiC) and is prepared by electron beam lithography (EBL). The specific steps are as follows:

[0071] S1. Cleaning substrate

[0072] First, the SiC substrate is immersed in an ultrasonic cleaning tank containing deionized water to remove surface dirt; then the SiC substrate is placed in a plasma cleaning machine and , oxygen molecules are activated by plasma to react with the surface of the SiC substrate;

[0073] S2. Drying the substrate

[0074] The SiC substrate is used Blow dry;

[0075] S3, silanization treatment

[0076] The SiC substrate is subjected to silanization treatment to form a thin silane molecular layer on the surface of the substrate;

[0077] S4, photoresist spin coating

[0078] Spin-coat the positive thick photoresist AZIPS6090. The thickness of the photoresist is positively correlated with the etching depth. Query the spin-coating curve of AZIPS6090 and set the spin-coating speed to 800~1000RPM.

[0079] S5. Baking

[0080] The photoresist spin-coated on the surface of the SiC substrate is baked to remove the solvent in the photoresist and improve the adhesion of the photoresist;

[0081] S6, electron beam exposure, development

[0082] The processed substrate is placed in an electron beam lithography machine, and the projection part of the cathode emission unit morphology onto the photoresist surface is exposed by electron beam; the exposed substrate is immersed in AZ726MIF developer for development to expose the projection part of the cathode emission unit morphology onto the SiC substrate surface; after the development is completed, the substrate is rinsed with deionized water to completely remove the developer and dissolved photoresist residues, and then Blow dry;

[0083] S7, plasma etching

[0084] Place the developed substrate into the plasma etching equipment, and select the reaction gas and of mixed gas, and The gas flow ratio is , etching out the cathode emission unit morphology;

[0085] S8. Remove photoresist

[0086] Immerse the substrate in AZ100 or N-methylpyrrolidone NMP solution to remove the remaining photoresist, and then Blow dry;

[0087] S9. Repeated processing

[0088] Repeat steps S3 to S8, spin-coat the photoresist, and then perform electron beam exposure and development to expose the projection area of ​​the cathode groove except the cathode morphology to the surface of the SiC substrate, and then etch away the rest of the cathode groove except the cathode morphology, and after de-bonding, obtain the cathode on which carbon nanotubes have not yet grown.

[0089] (2) Preparation of carbon nanotubes (CNTs) on the cathode emission unit surface: First, a silicon oxide film is used as a hard mask, and then the carbon nanotubes (CNTs) are grown by chemical vapor deposition (CVD). The specific steps are as follows:

[0090] a Silicon oxide film hard mask preparation

[0091] A silicon oxide film is used as a hard mask on a SiC substrate with a cathode emission unit morphology, and the substrate is placed in a chemical vapor deposition chamber and silane is introduced. and oxygen , and Gas flow ratio When the film thickness is uniform, Deposited on the upper surface of the SiC substrate, the surface of the cathode emission unit, and the bottom and side walls of the cathode groove except the cathode emission unit, forming a uniform Thin film, thickness about 10~20 nm;

[0092] bSilanization, photoresist coating, baking, electron beam exposure and development

[0093] After silanization treatment, The film surface is spin-coated with photoresist, and then baked after spin coating; then it is placed in an electron beam lithography machine, and the projection pattern of the cathode morphology in the central area onto the photoresist surface is exposed by electron beam, and after exposure, it is immersed in a developer for development, exposing the film covered with The cathode emission unit morphology of the film, after development, the substrate was rinsed with deionized water and then Blow dry;

[0094] c Plasma etching, stripping

[0095] Place it in a plasma etching device to etch away the cathode emission unit surface covering film, then remove the photoresist to complete The film does the work of the hard mask;

[0096] d Catalyst deposition

[0097] The cathode emission unit is covered with The cathode of the film is placed in a magnetron sputtering chamber, and the catalyst is deposited by magnetron sputtering. Argon gas Ar is used as the sputtering gas to deposit the catalysts Fe, Co, Ni, and Ti on the surface of the cathode emission unit.

[0098] Catalyst annealing

[0099] In hydrogen Annealing the catalyst in an atmosphere to remove oxides on the catalyst surface and optimize the catalyst particle size and distribution;

[0100] f Carbon nanotube growth

[0101] Put it into the chemical vapor deposition chamber, and the vacuum degree in the vacuum chamber is Pa, introduce argon gas Ar to maintain an inert gas environment to prevent sample oxidation; introduce carbon source gas methane, ethylene or acetylene, temperature 500~1000 ℃, carbon source gas flow rate 40sccm, argon gas Ar flow rate 100sccm, working gas pressure 1atm, chemical vapor deposition reaction to grow carbon nanotubes CNT, growth time 10~30 min;

[0102] gRemove mask

[0103] Put it into the plasma etching equipment and etch it away mask, using low power and low gas flow;

[0104] h Annealing treatment

[0105] The finally prepared cathode is placed in an annealing chamber for annealing to remove impurities and improve the crystallinity of the carbon nanotubes CNTs, and then cooled to room temperature to complete the preparation of the carbon nanotube CNTs micro-needle tip ring array cathode.

Claims

1. A micro-needle tip annular array cathode electron gun, characterized in that: include: A cathode (1), a grid (2), a dual focusing electrode (3) and an anode (4) are arranged in sequence on a coaxial line; the cathode (1) comprises a cathode base (1-1) and a cathode emission unit (1-2); a cylindrical cathode groove is provided on the cathode base (1-1), and the cathode emission unit (1-2) is embedded in the groove; the cathode emission unit (1-2) is in the shape of a cone divided into two along the symmetry axis, with the cut surface being the bottom surface and the tip facing inward, and is evenly distributed in the cathode groove to form a ring array, with one side of the cathode emission unit facing the grid (2) The surface is similar to the concave cathode structure of the Pierce electron gun; the grid (2) is a grid, the grid hole shape is a rhombus, the number of grid holes and the acute angle of the rhombus can be adjusted according to design requirements, and the side length of the rhombus is the same as the radius of the cathode groove; the dual focusing electrode (3) comprises: a first focusing electrode (3-1) and a second focusing electrode (3-2), the first focusing electrode (3-1) is a hyperbolic focusing electrode; wherein the electrodes are isolated by ceramic gaskets and combined into an integrated structure, and each electrode can be connected by a wire to provide voltage from an external circuit.

2. A micro-needle tip annular array cathode electron gun according to claim 1, characterized in that: The material of the cathode substrate (1-1) is silicon, silicon carbide or sapphire; a cylindrical cathode groove is provided on the cathode substrate (1-1), the radius of the cathode groove is 0.2-0.5 mm, and the depth is 0.05-0.1 mm.

3. The micro-needle tip annular array cathode electron gun according to claim 1, characterized in that: The material of the cathode emission unit (1-2) is silicon, silicon carbide or sapphire; the highest point of the cathode emission unit (1-2) is located in the same plane as the upper surface of the cathode base (1-1); the material of the surface of the cathode emission unit (1-2) is carbon nanotubes; the radius of the cone bottom surface is 0.05-0.1 mm, and the height is 0.2-0.5 mm.

4. The micro-needle tip annular array cathode electron gun according to claim 1, characterized in that: The gate (2) is a grid, the material of which is copper, aluminum or molybdenum metal, and a high work function metal film is prepared on the surface of the gate (2); the gate thickness is 0.01-0.1 mm.

5. The micro-needle tip annular array cathode electron gun according to claim 1, characterized in that: The material of the dual focusing electrode (3) is copper, aluminum or molybdenum metal, and the surface is polished; the first focusing electrode (3-1) is a hyperbolic focusing electrode, and the shape of its inner wall is determined by the minimum inner diameter at the center of the electrode and the inner wall curvature, and the inner wall curvature is determined by the electrode thickness and the difference between the maximum inner diameter and the minimum inner diameter; the minimum inner diameter is 0.15~0.6mm, the thickness is 1~3mm, and the maximum inner diameter is 0.3~0.8mm.

6. The micro-needle tip annular array cathode electron gun according to claim 1, characterized in that: The material of the anode (4) is tungsten metal, and the surface is gold-plated.

7. A method for preparing a cathode of a micro-needle tip annular array cathode electron gun according to claim 1, characterized in that: The following steps are involved: (1) Preparation of cathode emission unit morphology: The morphology material of the cathode emission unit is selected from silicon carbide SiC and prepared by electron beam lithography EBL; (2) Preparation of carbon nanotubes (CNTs) on the cathode emission unit surface: First, a silicon oxide film is used as a hard mask, and then chemical vapor deposition (CVD) is used to grow carbon nanotubes (CNTs).

8. The method for preparing a cathode of a micro-needle tip annular array cathode electron gun according to claim 7, characterized in that: Step (1) The specific steps are as follows: S1. Cleaning substrate First, the SiC substrate is immersed in an ultrasonic cleaning tank containing deionized water to remove surface dirt; then the SiC substrate is placed in a plasma cleaning machine and , oxygen molecules are activated by plasma to react with the surface of the SiC substrate; S2. Drying the substrate The SiC substrate is used Blow dry; S3, silanization treatment The SiC substrate is subjected to silanization treatment to form a thin silane molecular layer on the surface of the substrate; S4, photoresist spin coating Spin-coat the positive thick photoresist AZIPS6090. The thickness of the photoresist is positively correlated with the etching depth. Query the spin-coating curve of AZIPS6090 and set the spin-coating speed to 800~1000RPM. S5. Baking The photoresist spin-coated on the surface of the SiC substrate is baked to remove the solvent in the photoresist and improve the adhesion of the photoresist; S6, electron beam exposure, development The processed substrate is placed in an electron beam lithography machine, and the projection part of the cathode emission unit topography onto the photoresist surface is exposed by electron beam; After exposure, the substrate was immersed in AZ726MIF developer for development to expose the projection of the cathode emission unit morphology to the SiC substrate surface. After development, the substrate was rinsed with deionized water to completely remove the developer and dissolved photoresist residues. Blow dry; S7, plasma etching Place the developed substrate into the plasma etching equipment, and select the reaction gas and of mixed gas, and The gas flow ratio is , etching out the cathode emission unit morphology; S8. Remove photoresist Immerse the substrate in AZ100 or N-methylpyrrolidone NMP solution to remove the remaining photoresist, and then Blow dry; S9. Repeated processing Repeat steps S3 to S8, spin-coat the photoresist, and then perform electron beam exposure and development to expose the projection area of ​​the cathode groove except the cathode morphology to the surface of the SiC substrate, and then etch away the rest of the cathode groove except the cathode morphology, and after de-bonding, obtain the cathode on which carbon nanotubes have not yet grown.

9. The method for preparing a cathode of a micro-needle tip annular array cathode electron gun according to claim 7, characterized in that: The specific steps of step (2) are as follows: a Silicon oxide film hard mask preparation A silicon oxide film is used as a hard mask on a SiC substrate with a cathode emission unit morphology, and the substrate is placed in a chemical vapor deposition chamber and silane is introduced. and oxygen ,Will Deposited on the upper surface of the SiC substrate, the surface of the cathode emission unit, and the bottom and side walls of the cathode groove except the cathode emission unit, forming a uniform Thin film, thickness about 10~20 nm; bSilanization, photoresist coating, baking, electron beam exposure and development After silanization treatment, The film surface is spin-coated with photoresist, and then baked after spin coating; then it is placed in an electron beam lithography machine, and the projection pattern of the cathode morphology in the central area onto the photoresist surface is exposed by electron beam, and after exposure, it is immersed in a developer for development, exposing the film covered with The cathode emission unit morphology of the film, after development, the substrate was rinsed with deionized water and then Blow dry; c Plasma etching, stripping Place it in a plasma etching device to etch away the cathode emission unit surface covering film, then remove the photoresist to complete The film does the work of the hard mask; d Catalyst deposition The cathode emission unit is covered with The cathode of the film is placed in a magnetron sputtering chamber, and the catalyst is deposited by magnetron sputtering. Argon gas Ar is used as the sputtering gas to deposit the catalysts Fe, Co, Ni, and Ti on the surface of the cathode emission unit. Catalyst annealing In hydrogen Annealing the catalyst in an atmosphere to remove oxides on the catalyst surface and optimize the catalyst particle size and distribution; f Carbon nanotube growth Put it into the chemical vapor deposition chamber, and the vacuum degree in the vacuum chamber is Pa, introduce argon gas Ar to maintain an inert gas environment to prevent sample oxidation; introduce carbon source gas methane, ethylene or acetylene, temperature 500~1000 ℃, carbon source gas flow rate 40sccm, argon gas Ar flow rate 100sccm, working gas pressure 1atm, chemical vapor deposition reaction to grow carbon nanotubes CNT, growth time 10~30 min; gRemove mask Put it into the plasma etching equipment and etch it away mask, using low power and low gas flow; h Annealing treatment The finally prepared cathode is placed in an annealing chamber for annealing to remove impurities and improve the crystallinity of the carbon nanotubes CNTs, and then cooled to room temperature to complete the preparation of the carbon nanotube CNTs micro-needle tip ring array cathode.

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