Field emission cathode

Abstract

The invention relates to a field emission cathode, and the cathode comprises a grid mesh structure which comprises grid mesh wires and a plurality of holes; for the cross section, perpendicular to the electron emission direction, in any hole, the size of the cross section changes in the forward direction along with the first distance between the hole and the center point of the grid mesh structure; aiming at a second distance between any two adjacent holes, the second distance reversely changes along with a third distance between the two adjacent holes and the central point of the grid mesh structure; the emitter comprises a plurality of carbon nanotubes arranged in an array; for any carbon nanotube, the height of the carbon nanotube is reversely changed along with a fourth distance between the carbon nanotube and the central point of the emitter; the fifth distance between every two adjacent emitters is the same; and the edge contour of the emitter is arc-shaped or step-shaped. According to the field emission cathode provided by the embodiment of the invention, the problem of non-uniform field intensity among the carbon nanotubes at different positions can be solved.

Description

Technical Field

[0001] The present application relates to the field of field emission technology, and in particular to a field emission cathode. Background Art

[0002] Field emission technology, which uses a strong electric field to induce electrons to tunnel from a material's surface, offers advantages such as fast response, low power consumption, and radiation resistance. It plays a key role in materials characterization, photolithography, high-frequency radiation, and space exploration. Carbon nanotubes (CNTs) offer advantages such as low work function, high aspect ratio, and excellent electrical and thermal conductivity. Furthermore, the relatively uniform field strength across the CNT surface can increase the current density and overall stability of the field emission cathode, thereby enhancing field emission performance. Therefore, CNTs are an ideal material for field emission cathodes. Grids are often considered key components of field emission cathodes because they improve the field strength distribution on the emitter's surface, thereby enhancing cathode field emission performance.

[0003] In existing technology, CNT arrays are often used as emitters in field emission cathodes. To ensure structural consistency between the grid and emitter, all holes in the grid are of uniform size, and the distances between adjacent holes are consistent. However, this uniform grid and CNT array combination of field emission cathodes does not address the problem of uneven field strength between CNTs at different locations within the array. Summary of the Invention

[0004] Based on this, it is necessary to provide a field emission cathode to address the problem of uneven field intensity.

[0005] The present invention provides a field emission cathode, which includes:

[0006] A grid structure comprising grid wires and a plurality of holes; wherein, for a cross section of any hole perpendicular to the electron emission direction, the size of the cross section varies in a positive direction with a first distance between the hole and a center point of the grid structure; and wherein, for a second distance between any two adjacent holes, the second distance varies in a negative direction with a third distance between the two adjacent holes and the center point of the grid structure;

[0007] An emitter comprises a plurality of CNTs arranged in an array; for any CNT, the height of the CNT varies inversely with a fourth distance between the CNT and the center point of the emitter; the fifth distance between two adjacent emitters is the same; and the edge profile of the emitter is arc-shaped or stepped.

[0008] In one embodiment, the field emission cathode further comprises:

[0009] A glass insulating layer is located between the grid structure and the emitter, and a target substrate for fixing the emitter.

[0010] In one embodiment, the emitter is grown on an initial substrate based on a chemical vapor deposition method and then transferred to the target substrate based on a thermal compression bonding process.

[0011] In one embodiment, a buffer layer and a catalyst layer are deposited on the surface of the initial substrate, a metal alloy layer and a solder alloy layer are deposited on the surface of the target substrate, and a dielectric layer and a metal conductive layer are deposited on the surface of the grid wire.

[0012] In one embodiment, the mesh wire, the initial substrate, and the target substrate are all made of silicon.

[0013] In one embodiment, the grid structure is obtained after deep silicon etching is performed on the silicon substrate based on a photoresist mask on the surface of the silicon substrate, and the photoresist mask is generated after photolithography is performed on a photoresist layer on the surface of the silicon substrate.

[0014] In one embodiment, the dielectric layer and the buffer layer are formed based on the chemical vapor deposition method, and the metal conductive layer and the catalyst layer are formed based on the physical vapor deposition method.

[0015] In one embodiment, the field emission cathode is obtained by integrally packaging the grid structure, the emitter, and the glass insulating layer based on a metal bonding process.

[0016] In one embodiment, the metal bonding process is a gold-gold bonding process or a gold-tin alloy bonding process.

[0017] In one embodiment, the first central axis of the grid structure coincides with the second central axis of the emitter, and both the first central axis and the second central axis are parallel to the electron emission direction.

[0018] The above-mentioned field emission cathode, the grid structure, includes grid wires and multiple holes. For the cross section perpendicular to the electron emission direction in any hole, the size of the cross section changes positively with the first distance between the hole and the center point of the grid structure. For the second distance between any two adjacent holes, the second distance changes negatively with the third distance between the two adjacent holes and the center point of the grid structure. In this way, when an external voltage is applied to the field emission cathode, since the size of the hole close to the center point of the grid structure is smaller and the distance between adjacent holes is larger, the electric field strength of the field emission cathode can be enhanced to compensate for the field strength attenuation in the central area of ​​the emitter. At the same time, since the size of the hole far from the center point of the grid structure is larger and the distance between adjacent holes is smaller, the electric field lines of the field emission cathode can be extended outward, thereby reducing the local field strength peak and suppressing the edge effect. The emitter includes multiple CNTs arranged in an array. For any CNTs, the height of the CNTs changes with the third distance between the two adjacent holes. The fourth distance between the CNTs and the center point of the emitter changes in the opposite direction, and the fifth distance between two adjacent emitters is the same. In this way, since the height of the CNTs close to the center point of the emitter is higher and the height of the CNTs far from the center point of the emitter is lower, this can further balance the field strength difference between the center area and the edge area of ​​the emitter, suppress local overshoot, thereby achieving high cathode emission efficiency and improving current density; the edge profile of the emitter is arc-shaped or stepped, which can reduce the geometric curvature of the edge of the emitter, and transform the sharp edge into a smooth transition morphology, which can effectively suppress the edge field strength concentration phenomenon, improve the uniformity of the field strength distribution, and thereby increase the effective emission area; the embodiment of the present application can dynamically compensate for the field strength gradient change through the design of the non-uniform grid structure and the design of the emitter structure, break through the optimization limitations of a single structure, and achieve the field emission cathode to maintain high emission efficiency stability under a wide current density range, while improving the ability to resist thermal damage. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 A comparison diagram of the field emission cathode in the background art and the field emission cathode in the embodiment of the present application;

[0020] Figure 2 Schematic diagram of the electric field distribution and electron distribution of the field emission cathode in an embodiment of the present application;

[0021] Figure 3 is a schematic diagram of a field emission cathode in an embodiment of the present application;

[0022] Figure 4 and Figure 5 Schematic diagram of the method for preparing a field emission cathode in an embodiment of the present application.

[0023] Reference numerals:

[0024] Uniform grid 101 in the background technology; non-uniform grid structure 102 in the embodiment of the present application; cathode electron 103; emitter 104 in the embodiment of the present application; emitter 105 in the background technology; glass insulating layer 106; target substrate 107; silicon substrate 301; photoresist 302; non-uniform aperture grid 303; deposited dielectric layer 304; metal conductive layer 305; initial substrate 306; catalyst layer 307; CNTs array 308; target substrate 309; structured CNTs array 310. DETAILED DESCRIPTION

[0025] To make the above-mentioned objects, features, and advantages of the present application more clearly understood, the specific embodiments of the present application are described in detail below with reference to the accompanying drawings. The following description sets forth many specific details to facilitate a full understanding of the present application. However, the present application can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the scope of the present application. Therefore, the present application is not limited to the specific embodiments disclosed below.

[0026] In the description of the present application, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present application.

[0027] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of such features. Throughout the description of this application, "plurality" means at least two, for example, two, three, etc., unless otherwise specifically defined.

[0028] In this application, unless otherwise specified or limited, terms such as "mounted," "connected," "connect," and "fixed" should be interpreted broadly. For example, they can refer to fixed connections, removable connections, or integration; mechanical connections or electrical connections; direct connections or indirect connections through an intermediary; and internal communication between two components or interaction between two components, unless otherwise specified. Those skilled in the art will understand the specific meanings of these terms in this application based on the specific circumstances.

[0029] In this application, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Furthermore, when a first feature is "above," "above," or "above" a second feature, it may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is "below," "below," or "below" a second feature, it may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0030] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it may be directly on the other element or there may be an intermediate element. When an element is considered to be "connected to" another element, it may be directly connected to the other element or there may be an intermediate element. The terms "vertical", "horizontal", "upper", "lower", "left", "right" and similar expressions used in this application are for illustrative purposes only and do not represent the only implementation method.

[0031] The problem of uneven field strength in the background technology is specifically manifested in two aspects: field emission heterogeneity and cumulative thermal damage. Among them, the field emission heterogeneity phenomenon refers to the fact that under the long-term action of the electric field, the CNTs emitter will produce significant edge effects and shielding effects due to its one-dimensional nanostructure characteristics, resulting in preferential electron emission in the edge area and CNTs with protruding surface morphology, while the field strength of CNTs in the center area of ​​the array is suppressed to below the emission threshold, forming an electron emission blind zone, resulting in a decrease in overall emission efficiency; the cumulative thermal damage effect refers to the fact that under high current density, the current density of the active emission point can reach 5 to 8 times that of the ordinary area. These CNTs are subjected to the thermal effects and electrical breakdown risks caused by the local field strength unevenness during operation, which will lead to local damage and release of particles or impurities. These damage products will be deposited on the grid surface, further deteriorating the local field strength distribution and reducing the overall emission performance and cathode stability.

[0032] The field emission cathode in the background art and the field emission cathode in the embodiment of the present application are respectively as follows Figure 1 As shown in the left and right figures in the figure. 101 in the figure is the uniform grid in the background art, 102 is the non-uniform grid structure in the embodiment of the present application, 103 is the cathode electron, 104 is the emitter in the embodiment of the present application, 105 is the emitter in the background art, 106 is the glass insulating layer, and 107 is the base for fixing the emitter.

[0033] In the embodiment of the present application, the grid structure includes grid wires and multiple holes. For the cross section perpendicular to the electron emission direction in any hole, the size of the cross section changes positively with the first distance between the hole and the center point of the grid structure. For the second distance between any two adjacent holes, the second distance changes negatively with the third distance between the two adjacent holes and the center point of the grid structure. In this way, when an external voltage is applied to the field emission cathode, since the size of the hole close to the center point of the grid structure is smaller and the distance between adjacent holes is larger, the electric field strength of the field emission cathode can be enhanced to compensate for the field strength attenuation in the central area of ​​the emitter. At the same time, since the size of the hole far from the center point of the grid structure is larger and the distance between adjacent holes is smaller, the electric field lines of the field emission cathode can be extended outward, thereby reducing the local field strength peak and suppressing the edge effect. The emitter includes multiple CNTs arranged in an array. For any CNTs, the height of the CNTs changes with the third distance between the two adjacent holes. The fourth distance between the CNTs and the center point of the emitter changes in the opposite direction, and the fifth distance between two adjacent emitters is the same. In this way, since the height of the CNTs close to the center point of the emitter is higher and the height of the CNTs far from the center point of the emitter is lower, this can further balance the field strength difference between the center area and the edge area of ​​the emitter, suppress local overshoot, thereby achieving high cathode emission efficiency and improving current density; the edge profile of the emitter is arc-shaped or stepped, which can reduce the geometric curvature of the edge of the emitter, and transform the sharp edge into a smooth transition morphology, which can effectively suppress the edge field strength concentration phenomenon, improve the uniformity of the field strength distribution, and thereby increase the effective emission area; the embodiment of the present application can dynamically compensate for the field strength gradient change through the design of the non-uniform grid structure and the design of the emitter structure, break through the optimization limitations of a single structure, and achieve the field emission cathode to maintain high emission efficiency stability under a wide current density range, while improving the ability to resist thermal damage.

[0034] The electric field distribution diagram of the field emission cathode in the embodiment of the present application is as follows Figure 2 (a) shows the schematic diagram of the spatial distribution cross section of the field emission cathode electron after emission. Figure 2 (b) where 201 is the electric field line. Figure 2 (a) It can be seen that after the coordinated regulation of the non-uniform grid structure and the emitter structure in the embodiment of the present application, the electric field line 201 is basically horizontal, the field intensity is evenly distributed, and the difference in the global emission density is significantly reduced. Figure 2 (b) It can be seen that the regulated electron beam is evenly distributed and the electron emission trajectory is focused.

[0035] See also Figure 3The field emission cathode in the embodiment of the present application includes: a grid structure 102, including grid wires and multiple holes; for a cross section perpendicular to the electron emission direction in any hole, the size of the cross section changes positively with a first distance between the hole and the center point of the grid structure 102; for a second distance between any two adjacent holes, the second distance changes negatively with a third distance between the two adjacent holes and the center point of the grid structure 102; an emitter 104, including multiple CNTs arranged in an array; for any CNTs, the height of the CNTs changes negatively with a fourth distance between the CNTs and the center point of the emitter; the fifth distance between two adjacent emitters is the same; the edge profile of the emitter 104 is arc-shaped or stepped.

[0036] Among them, the first distance is the distance between the center point of the hole and the center point of the grid structure 102, the second distance is the distance between the center points of two adjacent holes, the third distance is the distance between the center point of the two adjacent holes that is less distant from the center point of the grid structure 102 and the center point of the grid structure 102, the fourth distance is the distance between the center point of the CNTs and the center point of the emitter, and the fifth distance is the distance between the center points of two adjacent emitters; the blank areas in the grid structure 102 represent holes, and the black rectangles represent grid filaments.

[0037] Optionally, the size of the cross section changes positively with the first distance between the hole and the center point of the grid structure 102, specifically meaning: the larger the first distance, the larger the size of the cross section, and the smaller the first distance, the smaller the size of the cross section; the second distance changes negatively with the third distance between two adjacent holes and the center point of the grid structure 102, specifically meaning: the larger the third distance, the smaller the second distance, and the smaller the third distance, the larger the second distance; the height of the CNTs changes negatively with the fourth distance between the CNTs and the center point of the emitter, specifically meaning: the larger the fourth distance, the smaller the height of the corresponding CNTs, and the smaller the fourth distance, the larger the height of the corresponding CNTs.

[0038] Optionally, when the field emission cathode includes at least two emitters 104 , the distances between two adjacent emitters 104 are the same.

[0039] Optionally, the thickness of the mesh structure 102 may be, but not limited to, within the range of 100 μm to 1000 μm, the width of the mesh wire may be, but not limited to, within the range of 10 μm to 50 μm, and the length of the mesh wire may be, but not limited to, within the range of 100 μm to 300 μm.

[0040] Optionally, the shape of the cross section in the hole perpendicular to the electron emission direction may be, but is not limited to, a circle, an ellipse or a polygon, and the size of the cross section may be, but is not limited to, within the range of 10 μm to 100 μm, and the greater the distance between the cross section and the center point of the grid structure 102, the larger the size of the cross section. For example, the size of the cross section may vary with a gradient along the first distance, and the gradient change rate may be within the range of 0.5 to 1.0 μm / mm. The second distance between two adjacent holes may be, but is not limited to, within the range of 10 μm to 500 μm, and the greater the third distance between the two adjacent holes and the center point of the grid structure 102, the smaller the corresponding second distance. For example, the second distance may vary with a gradient along the third distance, and the gradient change rate may be within the range of -2.0 to -4.0 μm / mm.

[0041] Optionally, the fifth distance between two adjacent emitters may be, but is not limited to, within the range of 100 μm to 1000 μm, the height of a single CNT may be, but is not limited to, within the range of 50 μm to 1000 μm, and the side length of the emitter 104 may be, but is not limited to, within the range of 100 μm to 1000 μm.

[0042] Optionally, the edge profile of the emitter is obtained by a laser processing process; specifically, laser etching is performed along the edge profile of the CNTs array, so that the height of the CNTs in the edge area is lower, which can suppress overheating of the edge. At this time, the height of the CNTs in the central area is higher than that of the CNTs in the edge area, which can compensate for the emission efficiency of the central area; for example, the height of the CNTs can change gradiently with the fourth distance, and the gradient change rate can be but is not limited to -1.5μm / mm.

[0043] Optionally, the field emission cathode further includes: a glass insulating layer 106 located between the grid structure and the emitter, and a target substrate 107 for fixing the emitter.

[0044] Optionally, the thickness of the glass insulating layer 106 may be, but is not limited to, within the range of 10 μm to 100 μm, the thickness of the target substrate 107 may be, but is not limited to, within the range of 200 μm to 1000 μm, and the distance between the grid structure 102 and the emitter 104 may be, but is not limited to, within the range of 10 μm to 100 μm.

[0045] Optionally, the material of the glass insulating layer 106 may be, but is not limited to, borosilicate glass, and a laser cutting process may be used to precisely control the thickness of the glass insulating layer 106 to precisely control the distance between the grid structure 102 and the emitter 104, wherein the thickness error of the glass insulating layer 106 is within the range of -0.5 μm to 0.5 μm.

[0046] Optionally, the emitter 104 is grown on an initial substrate based on a chemical vapor deposition method and then transferred to the target substrate 107 based on a thermal compression bonding process.

[0047] Optionally, in order to make the CNTs array uniform and consistent, the dimensions of the cross sections of different CNTs arrays perpendicular to the electron emission direction are the same, and the distances between two adjacent CNTs arrays are the same.

[0048] Optionally, in the process of generating a CNTs array, a photolithography technique is first used to generate an arrangement pattern corresponding to the CNTs array on the initial substrate, and then a chemical vapor deposition method is used to generate a vertical CNTs array on the initial substrate based on the generated arrangement pattern, and finally the generated CNTs array is transferred to the target substrate 107 based on a hot pressing bonding process.

[0049] Optionally, in the process of forming the CNTs array, the chemical vapor deposition method used is acetylene ( ) as carbon source, hydrogen ( ) is the carrier gas, and the flow ratio is controlled as , the growth pressure of the CNTs array was maintained at 30 kPa.

[0050] Optionally, when the CNTs array is transferred to the target substrate 107 by using a thermocompression bonding process, the reaction temperature is generally in the range of 300-400°C.

[0051] Optionally, a buffer layer and a catalyst layer are deposited on the surface of the initial substrate, a metal alloy layer and a solder alloy layer are deposited on the surface of the target substrate, and a dielectric layer and a metal conductive layer are deposited on the surface of the grid wire.

[0052] Optionally, before generating the CNTs array on the initial substrate, a buffer layer and a catalyst layer are sequentially deposited on the initial substrate; wherein the buffer layer is generated based on chemical vapor deposition, the type of chemical vapor deposition method may be but is not limited to plasma enhanced chemical vapor deposition or atomic layer deposition, the thickness of the buffer layer may be but is not limited to being in the range of 1nm to 500nm, and the material of the buffer layer may be but is not limited to Al2O3; the catalyst layer is generated based on physical vapor deposition, the type of physical vapor deposition method may be but is not limited to electron beam evaporation or magnetron sputtering, the thickness of the catalyst layer may be but is not limited to being in the range of 1nm to 100nm, and the material of the catalyst layer may be but is not limited to Fe, Co, Ni or their alloys.

[0053] Optionally, before transferring the CNTs array onto the target substrate 107 , a metal alloy layer and a solder alloy layer are sequentially deposited on the target substrate 107 ; wherein the solder alloy layer is generally made of Au, Sn, or Au-Sn alloy.

[0054] Optionally, a dielectric layer and a metal conductive layer are sequentially deposited on the surface of the mesh wire of the generated mesh structure 102; wherein, the dielectric layer is generated based on chemical vapor deposition, and the material of the dielectric layer may be but is not limited to TiN, and the thickness of the dielectric layer may be but is not limited to being in the range of 1μm to 10μm; the metal conductive layer is generated based on physical vapor deposition, and the metal conductive layer includes an adhesion layer and a conductive layer, and the material of the adhesion layer may be but is not limited to Ti, Cr or Ni, and the thickness of the adhesion layer may be but is not limited to being in the range of 50nm to 100nm. The conductive layer generally adopts a metal with good conductivity, strong high-temperature stability and excellent bombardment resistance, such as Au, Mo or W, and the thickness of the conductive layer may be but is not limited to being in the range of 10nm to 1000nm.

[0055] Optionally, the materials of the grid wire, the initial substrate and the target substrate 107 are all silicon.

[0056] Optionally, the grid structure is obtained after deep silicon etching is performed on the silicon substrate based on a photoresist mask on the surface of the silicon substrate, and the photoresist mask is generated after photolithography is performed on a photoresist layer on the surface of the silicon substrate.

[0057] Optionally, the photoresist layer is formed after spin coating the photoresist on the silicon substrate; before spin coating the photoresist, the surface of the silicon substrate is cleaned with acetone, isopropyl alcohol and ethanol in sequence, then blown clean with N2, and finally oxygen cleaning or other cleaning methods are used to remove water molecules and other gas molecules adsorbed on the surface of the silicon substrate.

[0058] Optionally, the field emission cathode is obtained by integrally packaging the grid structure, the emitter, and the glass insulating layer based on a metal bonding process.

[0059] Optionally, the metal bonding process is a gold-gold bonding process or a gold-tin alloy bonding process; the bonding temperature can be but is not limited to the range of 300°C to 400°C, the bonding pressure can be but is not limited to the range of 10MPa to 15MPa, and the bonding time can be but is not limited to the range of 5min to 10min.

[0060] Optionally, the first central axis of the grid structure coincides with the second central axis of the emitter, and both the first central axis and the second central axis are parallel to the electron emission direction.

[0061] Optionally, a high-precision mechanical alignment system built into a bonding machine may be used to fix and align the grid structure 102 and the emitter 104 through a bonding machine alignment fixture to ensure that the first central axis and the second central axis are strictly aligned.

[0062] Optionally, the bonding machine is equipped with a mechanical alignment fixture and a micron-level displacement platform to ensure that the grid-emitter alignment accuracy is less than 1μm.

[0063] Optionally, the preparation process of the field emission cathode in the embodiment of the present application is as follows: Figure 4 and Figure 5 As shown, it includes the grid structure preparation process 4 (a), the emitter preparation process 4 (b) and the field emission cathode bonding process 4 (c).

[0064] Optionally, the grid structure preparation process 4(a) includes the following steps:

[0065] (1) On a polished silicon substrate 301, the surface of the silicon substrate 301 is cleaned with acetone, isopropyl alcohol and ethanol in sequence, then blown clean with N2, and finally oxygen cleaning or other cleaning methods are used to remove water molecules and other gas molecules adsorbed on the surface of the silicon substrate 301, and a photoresist 302 is coated on the silicon substrate 301.

[0066] (2) The grid aperture is gradually changed from the edge to the middle, and the grid spacing is gradually changed from the edge to the middle. According to the pre-designed aperture and spacing, a non-uniform aperture grid 303 is obtained using a photolithography process.

[0067] (3) A dielectric layer 304 and a metal conductive layer 305 are deposited on the surface of the grid as grid electrodes. The metal conductive layer includes an adhesion layer and a conductive layer. The adhesion layer is generally made of materials such as Ti, Cr, and Ni, and has a thickness of 50 nm to 100 nm. The conductive layer is generally made of metals with good conductivity, high temperature stability, and excellent bombardment resistance, such as Au, Mo, and W, and has a thickness of 10 nm to 1000 nm.

[0068] Optionally, the emitter preparation process 4(b) includes the following steps:

[0069] (1) Depositing a buffer layer and a catalyst layer 307 on the surface of a clean initial substrate 306.

[0070] (2) Using photolithography technology, a CNT array pattern with a specific array spacing and single-point diameter is defined on the initial substrate 306, so that the CNT array has uniformity and consistency. A vertically oriented CNT array 308 is grown on the initial substrate 306 using chemical vapor deposition.

[0071] (3) A metal alloy and a solder alloy are sequentially deposited on the surface of the target substrate to transfer the CNTs array 308 to the target substrate 309.

[0072] (4) Laser processing is used to mechanically round the corners of the CNTs array 308 to obtain a structured CNTs array 310 with rounded edges.

[0073] Optionally, the field emission cathode bonding process 4(c) includes the following steps:

[0074] (1) Using the high-precision mechanical alignment system built into the bonding machine, the non-uniform grid structure 102 and the emitter 104 are fixed and aligned through the bonding machine alignment fixture to ensure that the center through hole of the grid is strictly aligned with the center axis of the emitter array.

[0075] (2) A glass insulating layer 106 with a thickness error of ±0.5 μm is set between the grid and the emitter. The edge of the glass layer is trimmed by a laser cutting machine to ensure thickness uniformity and form a precise cathode-gate spacing.

[0076] (3) Using gold-gold bonding or gold-tin alloy bonding process, the bonding temperature can be 300℃~400℃, the pressure can be 10MPa~15MPa, and the duration is 5min~10min. The gold-tin alloy bonding layer is melted under high temperature and pressure in the bonding machine, and the grid, glass insulation layer and emitter array are packaged into an integrated module to obtain a complete field emission cathode structure.

[0077] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0078] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and these modifications and improvements fall within the scope of protection of the present application. Therefore, the scope of protection of the present patent application shall be determined by the appended claims.

Claims

1. A field emission cathode, characterized in that: The field emission cathode comprises: A grid structure comprising grid wires and a plurality of holes; wherein, for a cross section of any hole perpendicular to the electron emission direction, the size of the cross section varies in a positive direction with a first distance between the hole and a center point of the grid structure; and wherein, for a second distance between any two adjacent holes, the second distance varies in a negative direction with a third distance between the two adjacent holes and the center point of the grid structure; An emitter comprises a plurality of carbon nanotubes arranged in an array; for any carbon nanotube, the height of the carbon nanotube varies inversely with the fourth distance between the carbon nanotube and the center point of the emitter; the fifth distance between two adjacent emitters is the same; and the edge profile of the emitter is arc-shaped or stepped.

2. The field emission cathode according to claim 1, characterized in that The field emission cathode further comprises: A glass insulating layer is located between the grid structure and the emitter, and a target substrate for fixing the emitter.

3. The field emission cathode according to claim 2, characterized in that The emitter is grown on an initial substrate based on a chemical vapor deposition method and then transferred to the target substrate based on a thermal compression bonding process.

4. The field emission cathode according to claim 3, characterized in that: A buffer layer and a catalyst layer are deposited on the surface of the initial substrate, a metal alloy layer and a solder alloy layer are deposited on the surface of the target substrate, and a dielectric layer and a metal conductive layer are deposited on the surface of the grid wire.

5. The field emission cathode according to claim 4, characterized in that: The materials of the grid wire, the initial substrate and the target substrate are all silicon.

6. The field emission cathode according to claim 5, characterized in that: The grid structure is obtained after deep silicon etching is performed on the silicon substrate based on a photoresist mask on the surface of the silicon substrate, and the photoresist mask is generated after photolithography is performed on a photoresist layer on the surface of the silicon substrate.

7. The field emission cathode according to claim 4, characterized in that: The dielectric layer and the buffer layer are generated based on the chemical vapor deposition method, and the metal conductive layer and the catalyst layer are generated based on the physical vapor deposition method.

8. The field emission cathode according to claim 2, characterized in that: The field emission cathode is obtained by integrally packaging the grid structure, the emitter, and the glass insulating layer based on a metal bonding process.

9. The field emission cathode according to claim 8, characterized in that The metal bonding process is a gold-gold bonding process or a gold-tin alloy bonding process.

10. The field emission cathode according to claim 1, characterized in that: The first central axis of the grid structure coincides with the second central axis of the emitter, and both the first central axis and the second central axis are parallel to the electron emission direction.

Images