Wide-beam high-brightness field emission electron source and preparation method thereof

Abstract

The invention belongs to the technical field of electronic components, and particularly relates to a wide-beam high-brightness field emission electron source and a preparation method thereof.A GaN epitaxial layer grows on a substrate, a SiO2 layer grows on the GaN epitaxial layer, a first SiN medium protection layer, single crystal gold and a second SiN medium protection layer are sequentially deposited on the SiO2 layer, an electrode is arranged between the single crystal gold and GaN, and the first SiN medium protection layer, the single crystal gold and the second SiN medium protection layer are sequentially deposited on the second SiN medium protection layer. The epitaxial layer at the bottom is an emission cathode, the single crystal gold layer at the top is a receiving electrode, the air channel in the middle is obtained through BOE solution etching, and the length of the air channel is equal to the thickness of the SiO2 layer. According to the invention, stable emission current can be taken into account while the voltage required by emission electrons is greatly reduced. More importantly, the structure of the device is simple and efficient in implementation process and low in cost, the air channel is formed through wet etching of the BOE solution, and the device has the good capability of being suitable for large-scale device integration.

Description

Technical Field

[0001] The invention belongs to the technical field of electronic components, and in particular relates to a wide-beam high-brightness field emission electron source and a preparation method thereof. Background Art

[0002] An electron source is an electronic component that can provide a vacuum free electron beam and is a hot topic in the field of vacuum electronics. At present, as a key component of many vacuum electronic devices and electronic equipment such as X-ray tubes, microwave tubes, and cathode ray tubes, electron sources are widely used in aerospace, medical, and scientific research equipment. In long-term research, people have found that the quality of the generated electron beam can be effectively improved by regulating the performance of the emission cathode material and the emission mode of the electrons. Common electron source emission modes include thermal emission, optical emission, field emission, and a combination of different emission modes.

[0003] Among them, thermal emission refers to heating the emission material to a very high temperature, when the electrons obtain very high energy, and at the same time, with the assistance of an external accelerating electric field, they detach from the surface of the cathode material to form an electron beam. The earliest electron tubes operated by thermal emission. Because the emission material must be heated to a very high temperature, there are high requirements for the stability and emission performance of the material. The earliest emission material was tungsten filament (heating temperature was about 2500°C, but the life of such materials was short, and the stability requirements for other components were high, which increased the cost. Subsequently, some artificial crystals, such as lanthanum hexaboride and cerium hexaboride, were put into use. Although the emission temperature of these materials has been reduced to 1400°C ~ 1800°C, the life and lateral emittance have been significantly improved, but their vacuum requirements are higher than W, and the cost is higher. The preparation process of thermal emission electron devices is simple and the machine is mature, but in the thermal emission electron devices prepared by traditional processes, the bunch generated by the thermal emission cathode is very long, so the longitudinal instability of the beam is reduced, and it is not The increase in stability strength causes the optimal performance of the device to be unable to meet certain practical application requirements. For example, in electron microscopes, thermal emission electrons have low brightness and a wide beam diffusion range, which reduces the resolution of the image. Although dry etching processes such as electron beam lithography (EBL), focused ion beam etching (FBI) and reactive ion etching (RIE) have advantages such as high resolution, these methods have slow speeds, high equipment costs, and limited processing materials, which causes serious cost problems in actual production. Therefore, thermal emission electronic devices have poor device performance, high preparation costs, and complex preparation processes.

[0004] Compared with traditional thermal emission, field emission has the advantages of small energy dispersion, long life and good focusing. Field emission is a special electron emission phenomenon, that is, under the action of a strong electric field, electrons directly tunnel through the potential barrier from the solid surface into the vacuum. The essence of field emission is the quantum tunneling effect. When a sufficiently strong electric field is applied, the potential barrier on the solid surface becomes narrower, and electrons may directly tunnel through the potential barrier into the vacuum, thereby forming electron emission. Field emission is divided into cold field emission and hot field emission. Thermal field emission combines heat and electric field to reduce the work function and increase the emission current. Cold field emission is achieved by applying a high electric field at low temperature. However, in the preparation process of field emission electronic devices, it is necessary to comprehensively consider the electric field distribution, electron emission efficiency and heat dissipation factors, which makes the preparation process more complicated. In order to ensure that the emitted electrons have low dispersion, the electron source has high requirements for vacuum during emission. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a wide beam high brightness field emission electron source and a preparation method thereof, which uses a simple and efficient high current wide beam electron source prepared by wet etching. The structure of the device is simple and efficient, and the cost is low. The air channel can be quickly formed by wet etching with a BOE solution, and it is suitable for large-scale device integration. The length of the air channel is 40nm to 60nm, and the generation of electrons can be achieved in an air environment. The prepared electron source can significantly reduce the voltage required to emit electrons while taking into account the stable emission current.

[0006] The present invention is achieved through the following technical solutions.

[0007] A method for preparing a wide-beam high-brightness field emission electron source comprises the following steps:

[0008] A GaN epitaxial layer is grown on the substrate using an epitaxial method.

[0009] A SiO2 layer is grown on the GaN epitaxial layer by plasma enhanced chemical vapor deposition.

[0010] With the assistance of a mask, a first SiN dielectric protection layer is grown on the SiO2 layer by plasma enhanced chemical vapor deposition, a single crystal gold layer is grown on the first SiN dielectric protection layer by magnetron sputtering, and a second SiN dielectric protection layer is grown on the first SiN dielectric protection layer and on one side of the single crystal gold layer by plasma enhanced chemical vapor deposition to form a single crystal gold layer with a SiN-protected pore structure.

[0011] The SiO2 layer at the bottom of the hole structure is etched with BOE solution to expose the GaN epitaxial layer. An air channel is formed in the SiO2 layer after etching. The exposed GaN epitaxial layer is the source and the single crystal gold layer is the drain. The longitudinal length of the air channel is 40nm to 60nm.

[0012] In a preferred embodiment of the present invention, the longitudinal length of the air channel is equal to the thickness of the SiO2 layer.

[0013] In a preferred embodiment of the present invention, the specific operation of etching is: under normal temperature and ultrasonic conditions, the entire device is placed in a BOE solution, at room temperature, the etching rate is 90nm / min, the time is 1min~2min, and the BOE solution is a mixed solution prepared by HF:NH4F at a volume ratio of 1:6.

[0014] In a preferred embodiment of the present invention, the pore structure is a single-pore structure or a multi-pore structure, the cross-sectional shape of a single pore is circular, and the diameter of a single pore is 50 nm to 150 nm.

[0015] In a preferred embodiment of the present invention, the thickness of the GaN epitaxial layer is 3μm to 5μm, and the process parameters for growing the GaN epitaxial layer are: first, NH3 and trimethylaluminum (TMAl) with hydrogen as the carrier are introduced at 900℃ to 1000℃ to grow an AlN buffer layer; then NH3 and trimethylgallium (TMGa) with hydrogen as the carrier are introduced at 950℃ to 1060℃ with a gas flow rate of 425cm / s and grown for 30min to obtain a GaN epitaxial layer.

[0016] In a preferred embodiment of the present invention, when growing a SiO2 layer, the growth temperature is 200°C to 400°C, the precursors are SiH4 and N2O, the gas flow rates of SiH4 and N2O are 20sccm to 100sccm and 100sccm to 500sccm respectively, and the pressure is 1000mTorr to 1500mTorr.

[0017] In a preferred embodiment of the present invention, the first SiN dielectric protective layer has a thickness of 5-10 nm and is grown by PECVD, using SiH4 and NH3 gases, with a flow ratio of about 1:3, a temperature of 200-400° C., a pressure of 1-10 Torr, and an RF power of 300-500 W. The second SiN dielectric protective layer is formed by the same process as the first SiN dielectric protective layer, but needs to be deposited after the single crystal gold deposition is completed.

[0018] In a preferred embodiment of the present invention, the thickness of the single crystal gold layer is 40nm~100nm. When magnetron sputtering the single crystal gold layer, the target material used is Au target, the temperature is 300℃~700℃, the working gas pressure is 0.1Torr~10Torr, the sputtering power is 150W~300W, and the Ar flow rate is 10sccm~50sccm.

[0019] The thickness of the second SiN dielectric protective layer is the same as that of the single crystal gold layer. It is grown using PECVD, with the gases SiH4 and NH3 used at a flow ratio of 1:3, a temperature of 200-400°C, a pressure of 1-10Torr, and an RF power of 300-500W.

[0020] In a preferred embodiment of the present invention, Ti, Al, Ni and Au are sequentially deposited on the source electrode using CVD technology, and then annealed to form a first ohmic contact layer.

[0021] Ti, Al, Ni and Au are deposited in sequence on the drain electrode using CVD technology to form a second ohmic contact layer.

[0022] The present invention also provides a wide-beam high-brightness field emission electron source prepared by the preparation method.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention prepares a field emission electron source with wide beam and high brightness by a simple thin film deposition method combined with wet etching. The prepared electron source has a low dependence on the vacuum degree when in use, and can obtain a wide beam and high brightness emission current even in an air environment, which is specifically embodied in:

[0025] The present invention grows a GaN epitaxial layer on a substrate by using an epitaxial method; grows a SiO2 layer on the GaN epitaxial layer by using plasma enhanced chemical vapor deposition; grows a first SiN dielectric protection layer on the SiO2 layer by using plasma enhanced chemical vapor deposition with the assistance of a mask, grows a single crystal gold layer on the first SiN dielectric protection layer by using a magnetron sputtering process, grows a second SiN dielectric protection layer on the first SiN dielectric protection layer and on one side of the single crystal gold layer by using plasma enhanced chemical vapor deposition, and forms a single crystal gold layer with a pore structure protected by SiN; etches the SiO2 layer at the bottom of the pore structure by using a BOE solution, and exposes the GaN epitaxial layer, and forms an air channel in the SiO2 layer after etching, wherein the exposed GaN epitaxial layer is a source electrode, and the single crystal gold layer is a drain electrode; the longitudinal length of the air channel is 40nm to 60nm. The simple thin film stacking structure in the above preparation process makes the device easy to prepare. The thin film deposition technology with mask assistance or direct growth is compatible with the current mainstream semiconductor device manufacturing process, which can achieve low-cost and large-scale manufacturing. The air channel of 40nm to 60nm is formed by wet etching of BOE solution, which is efficient and suitable for large-scale device integration. The prepared electron source is characterized by a vertical structure and GaN as the emission cathode. GaN, Au and air channel ensure the stability and service life of the device. By utilizing the field enhancement effect of the 40nm to 60nm air channel, electron emission can be achieved at a relatively low voltage (the turn-on voltage is only 5-7V), and a single hole can achieve mA-level emission current. Further through device integration, the emission current can be gradually accumulated to increase the emission current, thereby making a wide beam high-brightness electron source device. In addition, the length of the air channel is 40nm to 60nm, which is less than the average free path of electrons in the air of 68nm. Even in the air, the emitted electrons will not be dispersed, reducing the dependence of the electron source on the vacuum degree when used.

[0026] The field emission electron source of the present invention uses low materials and processing costs, and the prepared electron source can achieve electron emission at a relatively low voltage (the turn-on voltage is only 5-7V, while the turn-on voltage of a traditional field emission electron source is several thousand volts). Through device integration, a wide-beam electron source device can be made. The present invention uses a simple thin film deposition method in combination with BOE etching to simply and efficiently prepare a wide-beam high-brightness field emission electron source, which has the characteristics of simplicity and high efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 It is a schematic structural diagram of the wide-beam high-brightness field emission electron source of the present invention.

[0028] Figure 2 The present invention is a flow chart for the structural preparation of a wide-beam, high-brightness field emission electron source.

[0029] Figure 3A schematic diagram of the structure of the array arrangement of the prepared devices is shown.

[0030] Figure 4 In the figure, (a) is the current-voltage characteristic curve of the single-hole device of Example 1, and (b) is the current-voltage characteristic curve of the double-hole device of Example 2.

[0031] Figure 5 In the figure, (a) is the fitting curve of FN of the single-hole device of Example 1, and (b) is the fitting curve of FN of the double-hole device of Example 2. DETAILED DESCRIPTION

[0032] In order to enable those skilled in the art to better understand the technical solution of the present invention and implement it, the present invention is further described below in conjunction with specific embodiments and drawings, but the embodiments are not intended to limit the present invention. The experimental methods and detection methods described in the following embodiments are conventional methods unless otherwise specified; the reagents and materials described are all commercially available unless otherwise specified.

[0033] The present invention provides a method for preparing a wide-beam high-brightness field emission electron source, comprising the following steps:

[0034] like Figure 2 In step 1, a GaN epitaxial layer 2 is grown on a substrate 1 using an epitaxial method.

[0035] like Figure 2 In step 2, a SiO2 layer 3 is grown on the GaN epitaxial layer 2 by plasma enhanced chemical vapor deposition.

[0036] like Figure 2 In step 3, with the assistance of the mask 9, a first SiN dielectric protection layer 4 is sequentially grown on the SiO2 layer 3 by plasma enhanced chemical vapor deposition, and a single crystal gold layer 5 is grown on the first SiN dielectric protection layer 4 by magnetron sputtering process, as shown in FIG. Figure 2 In step 4, a second SiN dielectric protection layer 8 is grown on the first SiN dielectric protection layer 4 and on one side of the single crystal gold layer 5 by plasma enhanced chemical vapor deposition, and the mask plate 9 is removed to form a hole structure 6, that is, a single crystal gold layer with a hole structure protected by SiN is formed.

[0037] like Figure 2 In step 5, the SiO2 layer 3 at the bottom of the hole structure 6 is etched with a BOE solution to expose the GaN epitaxial layer 2. An air channel 7 is formed in the SiO2 layer 3 after etching. The exposed GaN epitaxial layer 2 is the source electrode, and the single crystal gold layer 5 is the drain electrode. According to the FN tunneling characteristics, the channel formed by the air channel 7 formed by the GaN layer and the single crystal gold layer can achieve a field enhancement effect, and the emitted electrons can be emitted from the hole.

[0038] The structure of the field emission electron source prepared by the above method is as follows: Figure 1 As shown, the transistor is composed of a single crystal gold layer 5, a second SiN dielectric protection layer 8 (and the single crystal gold layer 5 are located on the first SiN dielectric protection layer 4, and the second SiN dielectric protection layer 8 is in contact with one side of the single crystal gold layer 5), the first SiN dielectric protection layer 4, the SiO2 layer, the n-type (10 19 cm -3 ) of GaN epitaxial layer 2 and sapphire substrate 1. When the device structure of the present invention is in operation, electrodes are set on the source and drain to form an ohmic contact layer. When an electric field is applied between the two thin films of the source and drain, since the nanochannel has an enhancing and amplifying effect on the electric field, only a very small voltage is required to form a large value of electric field between the receiving electrode and the collecting electrode, which can make GaN with a low electron affinity (2.7eV~3.3eV) easily emit electrons from the hole, and can achieve mA-level emission current. The simple thin film stacking structure makes the device easy to prepare. The thin film deposition technology with mask assistance or direct growth is compatible with the current mainstream semiconductor device manufacturing process, and can achieve low-cost, large-scale manufacturing. Wet etching by BOE solution can quickly form an air channel, which is suitable for large-scale device integration. The longitudinal length of the formed air channel is 40nm~60nm, which is less than the average free path of electrons in the air of 68nm. Even in the air, the emitted electrons will not be dispersed, reducing the dependence of the electron source on the vacuum degree when used.

[0039] The invention is specifically described below through the following examples.

[0040] Example 1

[0041] A method for preparing a wide-beam high-brightness field emission electron source comprises the following steps:

[0042] (1) A GaN epitaxial layer was grown on a sapphire substrate using an epitaxial method. The process parameters were as follows: first, a layer of AlN buffer layer was grown by introducing NH3 and TMAl with hydrogen as carrier at 950°C; then, NH3 and TMGa with hydrogen as carrier were introduced at 1000°C with a gas flow rate of 425 cm / s for 30 min to obtain a film with a thickness of about 4.5 μm.

[0043] (2) After the GaN epitaxial layer is grown, a SiO2 layer with a thickness of 50 nm is uniformly grown using plasma enhanced chemical vapor deposition (PECVD). The temperature is 260°C, the gas flow rates of SiH4 and N2O are 100 sccm and 500 sccm respectively, and the pressure is 1500 mtorr.

[0044] (3) After the SiO2 layer is grown, a first SiN dielectric protective layer with a thickness of 5 nm is grown on the SiO2 layer with the assistance of a mask plate by plasma enhanced chemical vapor deposition, a single crystal gold layer with a thickness of 50 nm is grown on the first SiN dielectric protective layer by magnetron sputtering, and a second SiN dielectric protective layer with a thickness of 50 nm is grown on the first SiN dielectric protective layer and on one side of the single crystal gold layer by plasma enhanced chemical vapor deposition to form a single crystal gold layer with a pore structure protected by SiN; when growing the first SiN dielectric protective layer, the gases used are SiH4 and NH3, the flow ratio is 1:3, the temperature is 300°C, the pressure is 1 Torr, and the RF power is 300W. When magnetron sputtering the single crystal gold layer, the target material used is a gold target, the temperature is 300°C, the working gas pressure is 0.1 Torr, the sputtering power is 200W, and the Ar flow rate is 10sccm. The second SiN dielectric protective layer is deposited in the same process as the first SiN dielectric protective layer, but needs to be deposited after the single crystal gold deposition is completed. When growing the second SiN dielectric protective layer, the gases used are SiH4 and NH3, the flow ratio is 1:3, the temperature is 300°C, the pressure is 1Torr, and the RF power is 300 W. The prepared single crystal gold layer has a single hole structure, and the diameter of the hole formed in the single crystal gold is 100nm.

[0045] (4) After the single crystal gold layer is deposited, the device is further etched with BOE (Buffered Oxide Etchant, HF: NH4F = 1: 6) solution under ultrasonic conditions for 1 min. The etching rate at room temperature is about 90 nm / min. At this time, the GaN layer covered by the SiO2 layer is exposed and becomes the emission cathode. The exposed part in the horizontal direction becomes the air channel with a vertical length of 50 nm.

[0046] In the device structure prepared as above, the top single crystal gold layer is the drain (receiving electrode), and the bottom epitaxial GaN layer is the source (emitter). A nanometer-scale (thickness is equivalent to the thickness of the SiO2 layer) air channel is formed between the emitter and the receiving electrode. Ti, Al, Ni and Au are deposited on the source electrode in sequence using CVD technology, and then annealed at 850℃ for 40s to form the first ohmic contact layer; Ti, Al, Ni and Au are deposited on the drain electrode in sequence using CVD technology to form the second ohmic contact layer.

[0047] Example 2

[0048] A method for preparing a wide-beam high-brightness field emission electron source comprises the following steps:

[0049] (1) A GaN epitaxial layer was grown on a sapphire substrate using an epitaxial method. The process parameters were as follows: first, a layer of AlN buffer layer was grown by introducing NH3 and TMAl with hydrogen as carrier at 950°C; then, NH3 and TMGa with hydrogen as carrier were introduced at 1000°C with a gas flow rate of 425 cm / s for 30 min to obtain a film with a thickness of about 4.5 μm.

[0050] (2) After the GaN epitaxial layer is grown, a SiO2 layer with a thickness of 50 nm is uniformly grown using plasma enhanced chemical vapor deposition (PECVD). The temperature is 260°C, the gas flow rates of SiH4 and N2O are 100 sccm and 500 sccm respectively, and the pressure is 1500 mtorr.

[0051] (3) After the SiO2 layer is grown, a first SiN dielectric protective layer with a thickness of 5 nm is grown on the SiO2 layer with the assistance of a mask plate by plasma enhanced chemical vapor deposition, a single crystal gold layer with a thickness of 50 nm is grown on the first SiN dielectric protective layer by magnetron sputtering, and a second SiN dielectric protective layer with a thickness of 50 nm is grown on the first SiN dielectric protective layer and on one side of the single crystal gold layer by plasma enhanced chemical vapor deposition to form a single crystal gold layer with a pore structure protected by SiN; when growing the first SiN dielectric protective layer, the gases used are SiH4 and NH3, the flow ratio is 1:3, the temperature is 300°C, the pressure is 1 Torr, and the RF power is 300W. When magnetron sputtering the single crystal gold layer, the target material used is a gold target, the temperature is 300°C, the working gas pressure is 0.1 Torr, the sputtering power is 200W, and the Ar flow rate is 10sccm. The second SiN dielectric protective layer is deposited in the same process as the first SiN dielectric protective layer, but needs to be deposited after the single crystal gold deposition is completed. When growing the second SiN dielectric protective layer, the gases used are SiH4 and NH3, the flow ratio is 1:3, the temperature is 300°C, the pressure is 1Torr, and the RF power is 300 W. The prepared single crystal gold layer has a double-pore structure, and the pore diameter of the formed single crystal gold is 100nm.

[0052] (4) After the single crystal gold layer is deposited, the device is further etched with BOE (Buffered Oxide Etchant, HF: NH4F = 1: 6) solution under ultrasonic conditions for 1 min. The etching rate at room temperature is about 90 nm / min. At this time, the GaN layer covered by the SiO2 layer is exposed and becomes the emission cathode. The exposed part in the horizontal direction becomes the air channel with a vertical length of 50 nm.

[0053] In the device structure prepared as above, the top single crystal gold layer is the drain (receiving electrode), and the bottom epitaxial GaN layer is the source (emitter). A nanometer-scale (thickness is equivalent to the thickness of the SiO2 layer) air channel is formed between the emitter and the receiving electrode. Ti, Al, Ni and Au are deposited on the source electrode in sequence using CVD technology, and then annealed at 850℃ for 40s to form the first ohmic contact layer; Ti, Al, Ni and Au are deposited on the drain electrode in sequence using CVD technology to form the second ohmic contact layer.

[0054] Example 3

[0055] A method for preparing a wide beam high brightness field emission electron source comprises the following steps:

[0056] (1) A GaN epitaxial layer was grown on a sapphire substrate using an epitaxial method. The process parameters were as follows: first, a layer of AlN buffer layer was grown by introducing NH3 and TMAl with hydrogen as carrier at 950°C; then, NH3 and TMGa with hydrogen as carrier were introduced at 1000°C with a gas flow rate of 425 cm / s for 30 min to obtain a film with a thickness of about 4.5 μm.

[0057] (2) After the GaN epitaxial layer is grown, a SiO2 layer with a thickness of 40 nm is uniformly grown using plasma enhanced chemical vapor deposition (PECVD). The temperature is 260°C, the gas flow rates of SiH4 and N2O are 100 sccm and 500 sccm respectively, and the pressure is 1500 mtorr.

[0058] (3) After the SiO2 layer is grown, a first SiN dielectric protective layer with a thickness of 5 nm is grown on the SiO2 layer with the assistance of a mask plate by plasma enhanced chemical vapor deposition, a single crystal gold layer with a thickness of 50 nm is grown on the first SiN dielectric protective layer by magnetron sputtering, and a second SiN dielectric protective layer with a thickness of 50 nm is grown on the first SiN dielectric protective layer and on one side of the single crystal gold layer by plasma enhanced chemical vapor deposition to form a single crystal gold layer with a pore structure protected by SiN; when growing the first SiN dielectric protective layer, the gases used are SiH4 and NH3, the flow ratio is 1:3, the temperature is 200°C, the pressure is 10 Torr, and the RF power is 400 W. When magnetron sputtering the single crystal gold layer, the target material used is a gold target, the temperature is 300°C, the working gas pressure is 0.1 Torr, the sputtering power is 200 W, and the Ar flow rate is 10 sccm. The second SiN dielectric protective layer is deposited in the same process as the first SiN dielectric protective layer, but needs to be deposited after the single crystal gold deposition is completed. When growing the second SiN dielectric protective layer, the gases used are SiH4 and NH3, the flow ratio is 1:3, the temperature is 200℃, the pressure is 10Torr, and the RF power is 400W. The prepared single crystal gold layer is a porous array structure, such as Figure 3 As shown, the diameter of the pores in the formed single crystal gold is 100nm. The appropriate pore spacing effectively avoids interference between different pores during etching. The circular structure is conducive to achieving a more uniform electric field distribution and avoiding excessive concentration of the electric field.

[0059] (4) After the single crystal gold layer is deposited, the device is further etched with BOE (Buffered Oxide Etchant, HF: NH4F = 1: 6) solution under ultrasonic conditions for 70 seconds. The etching rate at room temperature is about 90nm / min. At this time, the GaN layer covered by the SiO2 layer is exposed and becomes the emission cathode. The exposed part in the horizontal direction becomes the air channel with a vertical length of 40nm.

[0060] In the device structure prepared as above, the top single crystal gold layer is the drain (receiving electrode), and the bottom epitaxial GaN layer is the source (emitter). A nanometer-scale (thickness is equivalent to the thickness of the SiO2 layer) air channel is formed between the emitter and the receiving electrode. Ti, Al, Ni and Au are deposited on the source electrode in sequence using CVD technology, and then annealed at 850℃ for 40s to form the first ohmic contact layer; Ti, Al, Ni and Au are deposited on the drain electrode in sequence using CVD technology to form the second ohmic contact layer.

[0061] Example 4

[0062] A method for preparing a wide beam high brightness field emission electron source comprises the following steps:

[0063] (1) A GaN epitaxial layer was grown on a sapphire substrate using an epitaxial method. The process parameters were as follows: first, a layer of AlN buffer layer was grown by introducing NH3 and TMAl with hydrogen as carrier at 950°C; then, NH3 and TMGa with hydrogen as carrier were introduced at 1000°C with a gas flow rate of 425 cm / s for 30 min to obtain a film with a thickness of about 4.5 μm.

[0064] (2) After the GaN epitaxial layer is grown, a SiO2 layer with a thickness of 60 nm is uniformly grown using plasma enhanced chemical vapor deposition (PECVD). The temperature is 260°C, the gas flow rates of SiH4 and N2O are 100 sccm and 500 sccm respectively, and the pressure is 1500 mtorr.

[0065] (3) After the SiO2 layer is grown, a first SiN dielectric protective layer with a thickness of 5 nm is grown on the SiO2 layer with the assistance of a mask plate by plasma enhanced chemical vapor deposition, a single crystal gold layer with a thickness of 50 nm is grown on the first SiN dielectric protective layer by magnetron sputtering, and a second SiN dielectric protective layer with a thickness of 50 nm is grown on the first SiN dielectric protective layer and on one side of the single crystal gold layer by plasma enhanced chemical vapor deposition to form a single crystal gold layer with a pore structure protected by SiN; when growing the first SiN dielectric protective layer, the gases used are SiH4 and NH3, the flow ratio is 1:3, the temperature is 300°C, the pressure is 1 Torr, and the RF power is 300W. When magnetron sputtering the single crystal gold layer, the target material used is a gold target, the temperature is 300°C, the working gas pressure is 0.1 Torr, the sputtering power is 200W, and the Ar flow rate is 10sccm. The second SiN dielectric protective layer is deposited in the same process as the first SiN dielectric protective layer, but needs to be deposited after the single crystal gold deposition is completed. When growing the second SiN dielectric protective layer, the gases used are SiH4 and NH3, the flow ratio is 1:3, the temperature is 300°C, the pressure is 1Torr, and the RF power is 300 W. The prepared single crystal gold layer is a porous array structure, and the pore diameter of the formed single crystal gold is 100nm.

[0066] (4) After the single crystal gold layer is deposited, the device is further etched with BOE (Buffered Oxide Etchant, HF: NH4F = 1: 6) solution under ultrasonic conditions for 2 minutes. The etching rate at room temperature is about 90nm / min. At this time, the GaN layer covered by the SiO2 layer is exposed and becomes the emission cathode. The exposed part in the horizontal direction becomes the air channel with a vertical length of 60nm.

[0067] In the device structure prepared as above, the top single crystal gold layer is the drain (receiving electrode), and the bottom epitaxial GaN layer is the source (emitter). A nanometer-scale (thickness is equivalent to the thickness of the SiO2 layer) air channel is formed between the emitter and the receiving electrode. Ti, Al, Ni and Au are deposited on the source electrode in sequence using CVD technology, and then annealed at 850℃ for 40s to form the first ohmic contact layer; Ti, Al, Ni and Au are deposited on the drain electrode in sequence using CVD technology to form the second ohmic contact layer.

[0068] Example 5

[0069] A method for preparing a wide-beam high-brightness field emission electron source comprises the following steps:

[0070] (1) A GaN epitaxial layer was grown on a sapphire substrate using an epitaxial method. The process parameters were as follows: first, a layer of AlN buffer layer was grown by introducing NH3 and TMAl with hydrogen as carrier at 900°C; then, NH3 and TMGa with hydrogen as carrier were introduced at 1060°C with a gas flow rate of 425 cm / s for 30 min to obtain a film with a thickness of about 3 μm.

[0071] (2) After the GaN epitaxial layer is grown, a SiO2 layer with a thickness of 50 nm is uniformly grown using plasma enhanced chemical vapor deposition (PECVD). The temperature is 260°C, the gas flow rates of SiH4 and N2O are 100 sccm and 500 sccm respectively, and the pressure is 1500 mtorr.

[0072] (3) After the SiO2 layer is grown, a first SiN dielectric protective layer with a thickness of 5 nm is grown on the SiO2 layer with the assistance of a mask plate by plasma enhanced chemical vapor deposition, a single crystal gold layer with a thickness of 50 nm is grown on the first SiN dielectric protective layer by magnetron sputtering, and a second SiN dielectric protective layer with a thickness of 50 nm is grown on the first SiN dielectric protective layer and on one side of the single crystal gold layer by plasma enhanced chemical vapor deposition to form a single crystal gold layer with a pore structure protected by SiN; when growing the first SiN dielectric protective layer, the gases used are SiH4 and NH3, the flow ratio is 1:3, the temperature is 300°C, the pressure is 1 Torr, and the RF power is 300W. When magnetron sputtering the single crystal gold layer, the target material used is a gold target, the temperature is 300°C, the working gas pressure is 0.1 Torr, the sputtering power is 200W, and the Ar flow rate is 10sccm. The second SiN dielectric protective layer is deposited in the same process as the first SiN dielectric protective layer, but needs to be deposited after the single crystal gold deposition is completed. When growing the second SiN dielectric protective layer, the gases used are SiH4 and NH3, the flow ratio is 1:3, the temperature is 300°C, the pressure is 1Torr, and the RF power is 300 W. The prepared single crystal gold layer is a porous array structure, and the pore diameter of the formed single crystal gold is 150nm.

[0073] (4) After the single crystal gold layer is deposited, the device is further etched with BOE (Buffered Oxide Etchant, HF: NH4F = 1: 6) solution under ultrasonic conditions for 1 min. The etching rate at room temperature is about 90 nm / min. At this time, the GaN layer covered by the SiO2 layer is exposed and becomes the emission cathode. The exposed part in the horizontal direction becomes the air channel with a vertical length of 50 nm.

[0074] In the device structure prepared as above, the top single crystal gold layer is the drain (receiving electrode), and the bottom epitaxial GaN layer is the source (emitter). A nanometer-scale (thickness is equivalent to the thickness of the SiO2 layer) air channel is formed between the emitter and the receiving electrode. Ti, Al, Ni and Au are deposited on the source electrode in sequence using CVD technology, and then annealed at 850℃ for 40s to form the first ohmic contact layer; Ti, Al, Ni and Au are deposited on the drain electrode in sequence using CVD technology to form the second ohmic contact layer.

[0075] Example 6

[0076] A method for preparing a wide-beam high-brightness field emission electron source comprises the following steps:

[0077] (1) A GaN epitaxial layer was grown on a sapphire substrate using an epitaxial method. The process parameters were as follows: first, a layer of AlN buffer layer was grown by introducing NH3 and TMAl with hydrogen as carrier at 1000°C; then, NH3 and TMGa with hydrogen as carrier were introduced at 1060°C with a gas flow rate of 425 cm / s for 30 min to obtain a film with a thickness of about 5 μm.

[0078] (2) After the GaN epitaxial layer is grown, a SiO2 layer with a thickness of 50 nm is uniformly grown using plasma enhanced chemical vapor deposition (PECVD). The temperature is 260°C, the gas flow rates of SiH4 and N2O are 100 sccm and 500 sccm respectively, and the pressure is 1500 mtorr.

[0079] (3) After the SiO2 layer is grown, a first SiN dielectric protective layer with a thickness of 5 nm is grown on the SiO2 layer with the assistance of a mask plate by plasma enhanced chemical vapor deposition, a single crystal gold layer with a thickness of 50 nm is grown on the first SiN dielectric protective layer by magnetron sputtering, and a second SiN dielectric protective layer with a thickness of 50 nm is grown on the first SiN dielectric protective layer and on one side of the single crystal gold layer by plasma enhanced chemical vapor deposition to form a single crystal gold layer with a pore structure protected by SiN; when growing the first SiN dielectric protective layer, the gases used are SiH4 and NH3, the flow ratio is 1:3, the temperature is 300°C, the pressure is 1 Torr, and the RF power is 300W. When magnetron sputtering the single crystal gold layer, the target material used is a gold target, the temperature is 300°C, the working gas pressure is 0.1 Torr, the sputtering power is 200W, and the Ar flow rate is 10sccm. The second SiN dielectric protective layer is deposited in the same process as the first SiN dielectric protective layer, but needs to be deposited after the single crystal gold deposition is completed. When growing the second SiN dielectric protective layer, the gases used are SiH4 and NH3, the flow ratio is 1:3, the temperature is 300°C, the pressure is 1Torr, and the RF power is 300 W. The prepared single crystal gold layer is a porous array structure, and the pore diameter of the formed single crystal gold is 50nm.

[0080] (4) After the single crystal gold layer is deposited, the device is further etched with BOE (Buffered Oxide Etchant, HF: NH4F = 1: 6) solution under ultrasonic conditions for 1 min. The etching rate at room temperature is about 90 nm / min. At this time, the GaN layer covered by the SiO2 layer is exposed and becomes the emission cathode. The exposed part in the horizontal direction becomes the air channel with a vertical length of 50 nm.

[0081] In the device structure prepared as above, the top single crystal gold layer is the drain (receiving electrode), and the bottom epitaxial GaN layer is the source (emitter). A nanometer-scale (thickness is equivalent to the thickness of the SiO2 layer) air channel is formed between the emitter and the receiving electrode. Ti, Al, Ni and Au are deposited on the source electrode in sequence using CVD technology, and then annealed at 850℃ for 40s to form the first ohmic contact layer; Ti, Al, Ni and Au are deposited on the drain electrode in sequence using CVD technology to form the second ohmic contact layer.

[0082] Figure 4In the figure, (a) is the current-voltage characteristic curve of the single-hole device of Example 1, and (b) is the current-voltage characteristic curve of the double-hole device of Example 2. The numbers in the figure represent the measurement order. It can be seen from the figure that as the number of measurements increases, the current gradually increases and tends to be stable, which is mainly due to the influence of the surface morphology of the material in the device. After the voltage reaches the turn-on voltage, the device enters the FN emission state and the current increases rapidly. When the voltage reaches 10V, the emission current of the single-hole device can reach about 10mA, while the current of the porous device, before entering the FN emission, is Schottky emission, and the emission current at this time is relatively small. Draw a tangent to the emission curve, and the voltage at the intersection with the horizontal axis is the turn-on voltage, Von. It can be seen from the figure that the turn-on voltage Von of the device is generally between 5V and 7V. The turn-on voltage of a traditional field emission electron source is several thousand volts.

[0083] Figure 5 What is shown is the fitting curve of the device emission current expression. By analyzing the fitting curve, the characteristics of the device field emission and various characteristic parameters, such as the field enhancement factor β and the effective field emission area α, can be obtained. (a) is the fitting curve of FN of the single-hole device in Example 1, and (b) is the fitting curve of FN of the double-hole device in Example 2. The numbers in the figure represent the measurement order. The typical fitting curve of FN emission is a concave curve, which shows the transition from Schottky emission to FN emission. In the stage with higher voltage, the field enhancement factor β and the field emission area α in the FN formula can be further calculated by the slope and intercept of the linear fitting line.

[0084] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, they are also intended to be included.

Claims

1. A method for preparing a wide beam high brightness field emission electron source, characterized in that: The following steps are involved: Growing a GaN epitaxial layer on a substrate using an epitaxial method; Growing a SiO2 layer on the GaN epitaxial layer by plasma enhanced chemical vapor deposition; With the assistance of a mask, a first SiN dielectric protection layer is grown on the SiO2 layer by plasma enhanced chemical vapor deposition, a single crystal gold layer is grown on the first SiN dielectric protection layer by a magnetron sputtering process, and a second SiN dielectric protection layer is grown on the first SiN dielectric protection layer and on one side of the single crystal gold layer by plasma enhanced chemical vapor deposition to form a single crystal gold layer with a pore structure protected by SiN; The SiO2 layer at the bottom of the hole structure is etched with BOE solution to expose the GaN epitaxial layer. An air channel is formed in the SiO2 layer after etching. The exposed GaN epitaxial layer is the source and the single crystal gold layer is the drain. The longitudinal length of the air channel is 40nm to 60nm.

2. The method for preparing a wide beam high brightness field emission electron source according to claim 1, characterized in that: The longitudinal length of the air channel is equal to the thickness of the SiO2 layer.

3. The method for preparing a wide beam high brightness field emission electron source according to claim 1, characterized in that: The specific operation of etching is: at room temperature and under ultrasonic conditions, the entire device is placed in a BOE solution with an etching rate of 90 nm / min and a time of 1 min to 2 min. The BOE solution is a mixed solution of HF:NH4F prepared at a volume ratio of 1:

6.

4. The method for preparing a wide beam high brightness field emission electron source according to claim 1, characterized in that: The pore structure is a single-pore structure or a multi-pore structure, the cross-sectional shape of a single pore is circular, and the diameter of a single pore is 50nm to 150nm.

5. The method for preparing a wide beam high brightness field emission electron source according to claim 1, characterized in that: The thickness of the GaN epitaxial layer is 3μm to 5μm, and the process parameters for growing the GaN epitaxial layer are: first, NH3 and trimethylaluminum with hydrogen as a carrier are introduced at 900°C to 1000°C to grow an AlN buffer layer; then NH3 and trimethylgallium with hydrogen as a carrier are introduced at 950°C to 1060°C with a gas flow rate of 425cm / s and grown for 30 minutes to obtain a GaN epitaxial layer.

6. The method for preparing a wide beam high brightness field emission electron source according to claim 1, characterized in that: When growing the SiO2 layer, the growth temperature is 200°C to 400°C, the precursors are SiH4 and N2O, the gas flow rates of SiH4 and N2O are 20sccm to 100sccm and 100sccm to 500sccm respectively, and the pressure is 1000mTorr to 1500mTorr.

7. The method for preparing a wide beam high brightness field emission electron source according to claim 1, characterized in that: The thickness of the first SiN dielectric protective layer is 5nm~10nm. During the growth, the gases used are SiH4 and NH3, the flow ratio is 1:3, the temperature is 200℃~400℃, the pressure is 1Torr~10Torr, and the RF power is 300W~500W.

8. The method for preparing a wide beam high brightness field emission electron source according to claim 1, characterized in that: The thickness of the single crystal gold layer is 40nm to 100nm. When magnetron sputtering the single crystal gold layer, the target material used is a gold target, the temperature is 300℃ to 700℃, the working gas pressure is 0.1Torr to 10Torr, the sputtering power is 150W to 300W, and the Ar flow rate is 10sccm to 50sccm; The thickness of the second SiN dielectric protective layer is the same as that of the single crystal gold layer. During growth, the gases used are SiH4 and NH3, the flow ratio is 1:3, the temperature is 200°C to 400°C, the pressure is 1Torr to 10Torr, and the RF power is 300W to 500W.

9. The method for preparing a wide beam high brightness field emission electron source according to claim 1, characterized in that: Ti, Al, Ni and Au are deposited in sequence on the source electrode by chemical vapor deposition technology, and then annealed to form a first ohmic contact layer; Ti, Al, Ni and Au are sequentially deposited on the drain electrode using chemical vapor deposition technology to form a second ohmic contact layer.

10. A wide-beam, high-brightness field emission electron source prepared according to the preparation method according to any one of claims 1 to 9.

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