A wide-beam high-brightness field emission electron source and a method for manufacturing the same
By using a wet etching method to form air channels on GaN epitaxial layers, the problems of beam instability and high fabrication cost of thermionic electronic devices have been solved. This method enables high-brightness emission current and low-cost large-scale device integration in an air environment, and is suitable for aerospace, medical and scientific research equipment.
Patent Information
- Application Number
- CN202411502777.8
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- Filing Date
- 2024-10-25
- Publication Date
- 2026-02-03
- Estimated Expiration
- 2044-10-25
AI Technical Summary
Existing thermionic emission electronic devices suffer from problems such as beam longitudinal instability, high manufacturing costs, complex processes, and high vacuum requirements, making it difficult to meet the needs of certain practical applications, such as reduced image resolution in electron microscopes and high costs of dry etching.
A wide-beam, high-brightness field emission electron source was prepared by wet etching. An air channel was formed on the GaN epitaxial layer, and the SiO2 layer was etched with BOE solution to expose the GaN epitaxial layer as the source and the single-crystal gold layer as the drain. Combined with a simple thin film deposition process, a SiN-protected hole structure was formed to achieve the field enhancement effect.
Achieving high-brightness emission current in an air environment reduces dependence on vacuum, simplifies fabrication processes, lowers costs, and is suitable for large-scale device integration. The emission current can reach the mA level, and the turn-on voltage is only 5-7V, making it suitable for aerospace, medical, and scientific research equipment.
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Figure CN119361396B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of electronic components technology, specifically relating to a wide-beam, high-brightness field emission electron source and its preparation method. Background Technology
[0002] An electron source is an electronic component that provides a free electron beam in a vacuum and is a hot research topic in the field of vacuum electronics. Currently, as a key component in many vacuum electronic devices and equipment such as X-ray tubes, microwave tubes, and cathode ray tubes, electron sources are widely used in aerospace, medical, and scientific research equipment. Through long-term research, it has been found that the quality of the generated electron beam can be effectively improved by controlling the performance of the emitting cathode material and the electron emission mode. Common electron source emission modes include thermal emission, optical emission, field emission, and combinations of different emission modes.
[0003] Thermoe emission refers to heating the emitting material to a very high temperature, at which point electrons gain high energy and, with the assistance of an external accelerating electric field, detach from the cathode material surface, forming an electron beam. The earliest electron tubes operated using thermoe emission. Because the emitting material needs to be heated to such a high temperature, high requirements are placed on the material's stability and emission performance. The earliest emitting material was tungsten filament (heated to approximately 2500℃), but this material has a short lifespan and requires high stability from other components, increasing costs. Subsequently, some artificial crystals, such as lanthanum hexaboride and cerium hexaboride, were used. Although the emission temperature of these materials was reduced to 1400℃~1800℃, and their lifespan and transverse emissivity were significantly improved, their vacuum requirements were higher than tungsten, resulting in higher costs. Thermoe emission electronic devices have simple fabrication processes and mature machinery; however, in traditionally fabricated thermoe emission electronic devices, the cathode produces a very long beam, thus reducing the longitudinal instability of the beam. Increased stability intensity means that the optimal performance of the device cannot meet the requirements of certain practical applications. For example, in electron microscopy, thermionic electrons have lower brightness and a wider beam diffusion range, leading to reduced image resolution. 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, their slow speed, high equipment cost, and limited processing materials cause serious cost problems in actual production. Therefore, thermionic electron devices suffer from poor device performance, high fabrication costs, and complex fabrication processes.
[0004] Compared to traditional thermionic emission, field emission offers advantages such as low energy dispersion, long lifetime, and good focusing. Field emission is a special electron emission phenomenon where electrons tunnel directly through a potential barrier from a solid surface into a vacuum under the influence of a strong electric field. The essence of field emission is the quantum tunneling effect. When a sufficiently strong electric field is applied, the potential barrier at the solid surface narrows, allowing electrons to tunnel directly through the barrier into the vacuum, thus achieving electron emission. Field emission is divided into cold field emission and hot field emission. Hot field emission combines heat and an electric field, reducing the work function and increasing the emission current. Cold field emission achieves field emission by applying a high electric field at low temperatures. However, the fabrication of field emission electronic devices requires comprehensive consideration of electric field distribution, electron emission efficiency, and heat dissipation, making the fabrication process more complex. Furthermore, to ensure low electron dispersion, a high vacuum level is required during electron emission. Summary of the Invention
[0005] To address the aforementioned technical problems, this invention provides a wide-beam, high-brightness field emission electron source and its fabrication method. The simple and efficient high-current wide-beam electron source is fabricated using wet etching. The device's structure is relatively simple and efficient to implement, with low cost. Wet etching with BOE solution can quickly form air channels, making it suitable for large-scale device integration. The air channel length is 40nm–60nm, allowing electron generation in an air environment. The fabricated electron source can significantly reduce the voltage required for electron emission while maintaining a stable emission current.
[0006] The present invention is achieved through the following technical solution.
[0007] A method for preparing a wide-beam, high-brightness field emission electron source includes the following steps:
[0008] GaN epitaxial layers are grown on a substrate using an epitaxial method.
[0009] A SiO2 layer was grown on the GaN epitaxial layer using plasma-enhanced chemical vapor deposition.
[0010] With the aid of a photomask, a first SiN dielectric protective layer is grown on the SiO2 layer using plasma-enhanced chemical vapor deposition. A single-crystal gold layer is grown on the first SiN dielectric protective layer using magnetron sputtering. A second SiN dielectric protective layer is grown on the first SiN dielectric protective layer and on one side of the single-crystal gold layer using plasma-enhanced chemical vapor deposition, forming a single-crystal gold layer with a pore structure protected by SiN.
[0011] The SiO2 layer at the bottom of the hole structure was etched using BOE solution to expose the GaN epitaxial layer. An air channel was 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 40 nm to 60 nm.
[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 etching operation is as follows: under room temperature and ultrasonic conditions, the entire device is placed in a BOE solution, and the etching rate is 90 nm / min for 1 min to 2 min at room temperature. The BOE solution is a mixed solution of HF:NH4F prepared in 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 50nm to 150nm.
[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 as follows: first, NH3 and trimethylaluminum (TMAl) with hydrogen as a carrier are introduced at 900℃ to 1000℃ to grow an AlN buffer layer; then, NH3 and trimethylgallium (TMGa) with hydrogen as a carrier are introduced at 950℃ to 1060℃ with a gas flow rate of 425cm / s for 30min to obtain the GaN epitaxial layer.
[0016] In a preferred embodiment of the present invention, when growing the SiO2 layer, the growth temperature is 200℃~400℃, the precursors are SiH4 and N2O, the gas flow rates of SiH4 and N2O are 20sccm~100sccm and 100sccm~500sccm respectively, and the pressure is 1000mTorr~1500mTorr.
[0017] In a preferred embodiment of the present invention, the thickness of the first SiN dielectric protective layer is 5-10 nm, and it is grown using PECVD with SiH4 and NH3 gases in a flow ratio of approximately 1:3, at a temperature of 200-400°C, a pressure of 1-10 Torr, and a radio frequency power of 300-500 W. The second SiN dielectric protective layer uses the same process as the first SiN dielectric protective layer, but it 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 to 100nm. When magnetron sputtering the single crystal gold layer, the target material used is an Au 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.
[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 SiH4 and NH3 gases in a flow ratio of 1:3, at a temperature of 200-400℃, a pressure of 1-10 Torr, and an RF power of 300-500W.
[0020] In a preferred embodiment of the present invention, Ti, Al, Ni and Au are deposited sequentially on the source electrode using CVD technology, followed by annealing to form a first ohmic contact layer.
[0021] Ti, Al, Ni and Au are sequentially deposited 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 above-described preparation method.
[0023] Compared with the prior art, the present invention has the following beneficial effects:
[0024] This invention fabricates a field emission electron source with a wide beam and high brightness using a simple thin-film deposition method combined with wet etching. The fabricated electron source has low dependence on vacuum level during use, and can obtain a wide beam and high brightness emission current even in an air environment. Specifically, it is reflected in the following aspects:
[0025] This invention grows a GaN epitaxial layer on a substrate using an epitaxial method; a SiO2 layer is grown on the GaN epitaxial layer using plasma-enhanced chemical vapor deposition (PECVD); with the aid of a mask, a first SiN dielectric protective layer is grown on the SiO2 layer using PECVD; a single-crystal gold layer is grown on the first SiN dielectric protective layer using magnetron sputtering; a second SiN dielectric protective layer is grown on the first SiN dielectric protective layer and located on one side of the single-crystal gold layer using PECVD, forming a single-crystal gold layer with a hole structure protected by SiN; the SiO2 layer at the bottom of the hole structure is etched using a BOE solution to expose the GaN epitaxial layer, and an air channel is formed in the SiO2 layer after etching. The exposed GaN epitaxial layer serves as the source, and the single-crystal gold layer serves as the drain; the longitudinal length of the air channel is 40 nm to 60 nm. The simple thin-film stacking structure described above facilitates device fabrication. Mask-assisted or direct-growth thin-film deposition techniques are compatible with current mainstream semiconductor device manufacturing processes, enabling low-cost, large-scale manufacturing. Wet etching with BOE solution forms 40nm–60nm air channels, offering high efficiency and suitability for large-scale device integration. The fabricated electron source features a vertical structure and uses GaN as the emission cathode. GaN, Au, and the air channel ensure device stability and lifespan. Utilizing the field enhancement effect of the 40nm–60nm air channel, electron emission can be achieved at a relatively low voltage (turn-on voltage only 5-7V), and a single aperture can achieve mA-level emission current. Further device integration allows for incremental accumulation of the emission current, enabling the fabrication of wide-beam, high-brightness electron source devices. Furthermore, the 40nm–60nm length of the air channel is less than the mean free path of electrons in air (68nm), ensuring that emitted electrons do not disperse even in air, reducing the dependence of the electron source on vacuum levels.
[0026] The field emission electron source of this invention uses low-cost materials and has low processing costs. The fabricated electron source can achieve electron emission at a relatively low voltage (only 5-7V, while traditional field emission electron sources require several kilovolts). Through device integration, a wide-beam electron source device can be fabricated. This invention utilizes a simple thin-film deposition method combined with BOE etching to easily and efficiently fabricate a wide-beam, high-brightness field emission electron source, exhibiting the characteristics of simplicity and high efficiency. Attached Figure Description
[0027] Figure 1 This is a schematic diagram of the structure of the wide-beam, high-brightness field emission electron source of the present invention.
[0028] Figure 2 This is a flowchart illustrating the fabrication process of the wide-beam, high-brightness field emission electron source of the present invention.
[0029] Figure 3A schematic diagram of the array-arranged fabrication device is shown.
[0030] Figure 4 In the figure, (a) is the current-voltage characteristic curve of the single-hole device in Example 1, and (b) is the current-voltage characteristic curve of the double-hole device in Example 2.
[0031] Figure 5 In the figure, (a) is the fitting curve of FN for the single-hole device in Example 1, and (b) is the fitting curve of FN for the double-hole device in Example 2. Detailed Implementation
[0032] To enable those skilled in the art to better understand and implement the technical solutions of the present invention, the present invention will be further described below with reference to specific embodiments and accompanying drawings. However, the embodiments described are not intended to limit the present invention. Unless otherwise specified, the experimental methods and detection methods described in the following embodiments are conventional methods; unless otherwise specified, the reagents and materials described are commercially available.
[0033] This 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 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 using plasma-enhanced chemical vapor deposition.
[0036] like Figure 2 In step 3, with the assistance of mask 9, a first SiN dielectric protective layer 4 is sequentially grown on the SiO2 layer 3 using plasma-enhanced chemical vapor deposition. A single-crystal gold layer 5 is then grown on the first SiN dielectric protective layer 4 using magnetron sputtering. Figure 2 In step 4, a second SiN dielectric protective layer 8 is grown on the first SiN dielectric protective layer 4 and on one side of the single crystal gold layer 5 using plasma-enhanced chemical vapor deposition. The mask 9 is then removed to form a pore structure 6, thus forming a single crystal gold layer with a pore structure protected by SiN.
[0037] like Figure 2 In step 5, the SiO2 layer 3 at the bottom of the hole structure 6 is etched using BOE solution, exposing the GaN epitaxial layer 2. An air channel 7 is formed in the SiO2 layer 3 after etching. The exposed GaN epitaxial layer 2 serves as the source, and the single-crystal gold layer 5 serves as the drain. Based on the FN tunneling characteristics, the channel formed by the GaN layer and the single-crystal gold layer 7 can achieve a field enhancement effect, and emitted electrons can be emitted from the hole.
[0038] The field emission electron source structure prepared by the above method is as follows: Figure 1 As shown, the transistor, from top to bottom, consists of a single-crystal gold layer 5, a second SiN dielectric protective layer 8 (which, along with the single-crystal gold layer 5, is located on the first SiN dielectric protective layer 4, and the second SiN dielectric protective layer 8 and the single-crystal gold layer 5 are in contact on one side), the first SiN dielectric protective layer 4, a SiO2 layer, and an n-type (10) transistor. 19 cm -3 The device structure comprises a GaN epitaxial layer 2 and a sapphire substrate 1. During operation, electrodes are placed on the source and drain to form an ohmic contact layer. When an electric field is applied between the source and drain thin films, the nanochannel amplifies the electric field, requiring only a small voltage to create a large electric field between the receiver and collector. This allows GaN, with its low electron affinity (2.7 eV–3.3 eV), to easily emit electrons from the holes, achieving emission currents in the mA range. The simple thin film stacking structure facilitates device fabrication. Mask-assisted or direct growth thin film deposition techniques are compatible with current mainstream semiconductor device manufacturing processes, enabling low-cost, large-scale manufacturing. Wet etching with BOE solution allows for rapid formation of air channels, suitable for large-scale device integration. The formed air channel has a longitudinal length of 40 nm–60 nm, less than the mean free path of electrons in air (68 nm). Even in air, emitted electrons do not disperse, reducing the dependence of the electron source on vacuum levels.
[0039] The following examples will provide a detailed explanation.
[0040] Example 1
[0041] A method for preparing a wide-beam, high-brightness field emission electron source includes the following steps:
[0042] (1) An epitaxial layer of GaN was grown on a sapphire substrate using an epitaxial method. The process parameters were as follows: first, an AlN buffer layer was grown by introducing NH3 and TMAl with hydrogen as the carrier at 950°C; then, NH3 and TMGa with hydrogen as the carrier were introduced at 1000°C with a gas flow rate of 425 cm / s for 30 min to obtain a thin film with a thickness of about 4.5 μm.
[0043] (2) After the GaN epitaxial layer was grown, a SiO2 layer with a thickness of 50 nm was uniformly grown using plasma-enhanced chemical vapor deposition (PECVD). The temperature was 260 °C, the gas flow rates of SiH4 and N2O were 100 sccm and 500 sccm, respectively, and the pressure was 1500 mtorr.
[0044] (3) After the SiO2 layer is grown, with the aid of a mask, a first SiN dielectric protective layer with a thickness of 5 nm is grown sequentially on the SiO2 layer using 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 using magnetron sputtering. On the first SiN dielectric protective layer and located on one side of the single-crystal gold layer, a second SiN dielectric protective layer with a thickness of 50 nm is grown using plasma-enhanced chemical vapor deposition, forming a single-crystal gold layer with a porous structure protected by SiN. When growing the first SiN dielectric protective layer, the gases used are SiH4 and NH3 with a flow ratio of 1:3, a temperature of 300℃, a pressure of 1 Torr, and an RF power of 300 W. When magnetron sputtering the single-crystal gold layer, a gold target is used, the temperature is 300℃, 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 uses the same process as the first SiN dielectric protective layer, but it 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, with a flow ratio of 1:3, a temperature of 300℃, a pressure of 1 Torr, and a radio frequency power of 300W. The prepared single-crystal gold layer has a single-pore structure, and the pore diameter of the formed single-crystal gold is 100 nm.
[0045] (4) After the single-crystal gold layer is deposited, the device is further etched under ultrasonic conditions using a BOE (Buffered Oxide Etchant, HF:NH4F = 1:6) solution for 1 minute. The etching rate at room temperature is approximately 90 nm / min. At this point, the GaN layer covered by the SiO2 layer is exposed, becoming the emission cathode. The laterally exposed portion becomes an air channel with a longitudinal length of 50 nm.
[0046] In the device structure fabricated as described above, the top single-crystal gold layer serves as the drain (receiver), and the bottom epitaxial GaN layer serves as the source (emitter). A nanometer-scale air channel (with a thickness comparable to that of the SiO2 layer) is formed between the emitter and receiver. Ti, Al, Ni, and Au are sequentially deposited on the source using CVD technology, followed by annealing at 850°C for 40 seconds to form the first ohmic contact layer. Similarly, Ti, Al, Ni, and Au are sequentially deposited on the drain 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 includes the following steps:
[0049] (1) An epitaxial layer of GaN was grown on a sapphire substrate using an epitaxial method. The process parameters were as follows: first, an AlN buffer layer was grown by introducing NH3 and TMAl with hydrogen as the carrier at 950°C; then, NH3 and TMGa with hydrogen as the carrier were introduced at 1000°C with a gas flow rate of 425 cm / s for 30 min to obtain a thin film with a thickness of about 4.5 μm.
[0050] (2) After the GaN epitaxial layer was grown, a SiO2 layer with a thickness of 50 nm was uniformly grown using plasma-enhanced chemical vapor deposition (PECVD). The temperature was 260 °C, the gas flow rates of SiH4 and N2O were 100 sccm and 500 sccm, respectively, and the pressure was 1500 mtorr.
[0051] (3) After the SiO2 layer is grown, with the aid of a mask, a first SiN dielectric protective layer with a thickness of 5 nm is grown sequentially on the SiO2 layer using 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 using magnetron sputtering. On the first SiN dielectric protective layer and located on one side of the single-crystal gold layer, a second SiN dielectric protective layer with a thickness of 50 nm is grown using plasma-enhanced chemical vapor deposition, forming a single-crystal gold layer with a porous structure protected by SiN. When growing the first SiN dielectric protective layer, the gases used are SiH4 and NH3 with a flow ratio of 1:3, a temperature of 300℃, a pressure of 1 Torr, and an RF power of 300 W. When magnetron sputtering the single-crystal gold layer, a gold target is used, the temperature is 300℃, 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 uses the same process as the first SiN dielectric protective layer, but it 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 in a flow ratio of 1:3, the temperature is 300℃, the pressure is 1 Torr, and the RF power is 300W. The prepared single-crystal gold layer has a dual-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 under ultrasonic conditions using a BOE (Buffered Oxide Etchant, HF:NH4F = 1:6) solution for 1 minute. The etching rate at room temperature is approximately 90 nm / min. At this point, the GaN layer covered by the SiO2 layer is exposed, becoming the emission cathode. The laterally exposed portion becomes an air channel with a longitudinal length of 50 nm.
[0053] In the device structure fabricated as described above, the top single-crystal gold layer serves as the drain (receiver), and the bottom epitaxial GaN layer serves as the source (emitter). A nanometer-scale air channel (with a thickness comparable to that of the SiO2 layer) is formed between the emitter and receiver. Ti, Al, Ni, and Au are sequentially deposited on the source using CVD technology, followed by annealing at 850°C for 40 seconds to form the first ohmic contact layer. Similarly, Ti, Al, Ni, and Au are sequentially deposited on the drain 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 includes the following steps:
[0056] (1) An epitaxial layer of GaN was grown on a sapphire substrate using an epitaxial method. The process parameters were as follows: first, an AlN buffer layer was grown by introducing NH3 and TMAl with hydrogen as the carrier at 950°C; then, NH3 and TMGa with hydrogen as the carrier were introduced at 1000°C with a gas flow rate of 425 cm / s for 30 min to obtain a thin film with a thickness of about 4.5 μm.
[0057] (2) After the GaN epitaxial layer was grown, a SiO2 layer with a thickness of 40 nm was uniformly grown using plasma-enhanced chemical vapor deposition (PECVD). The temperature was 260 °C, the gas flow rates of SiH4 and N2O were 100 sccm and 500 sccm, respectively, and the pressure was 1500 mtorr.
[0058] (3) After the SiO2 layer is grown, with the aid of a mask, a first SiN dielectric protective layer with a thickness of 5 nm is grown sequentially on the SiO2 layer using 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 using magnetron sputtering. On the first SiN dielectric protective layer and located on one side of the single-crystal gold layer, a second SiN dielectric protective layer with a thickness of 50 nm is grown using plasma-enhanced chemical vapor deposition, forming a single-crystal gold layer with a porous structure protected by SiN. When growing the first SiN dielectric protective layer, the gases used are SiH4 and NH3 with a flow ratio of 1:3, a temperature of 200℃, a pressure of 10 Torr, and an RF power of 400 W. When magnetron sputtering the single-crystal gold layer, a gold target is used, the temperature is 300℃, 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 uses the same process as the first SiN dielectric protective layer, but it 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, with a flow ratio of 1:3, a temperature of 200℃, a pressure of 10 Torr, and an RF power of 400W. The fabricated single-crystal gold layer has a porous array structure, such as... Figure 3 As shown, the formed single-crystal gold has a hole diameter of 100 nm. The appropriate hole spacing effectively avoids interference between different holes during etching. The circular structure facilitates a more uniform electric field distribution, preventing excessive electric field concentration.
[0059] (4) After the single-crystal gold layer is deposited, the device is further etched using BOE (Buffered Oxide Etchant, HF:NH4F = 1:6) solution under ultrasonic conditions for 70 seconds. The etching rate at room temperature is approximately 90 nm / min. At this point, the GaN layer covered by the SiO2 layer is exposed, becoming the emission cathode. The laterally exposed portion becomes the air channel, with a longitudinal length of 40 nm.
[0060] In the device structure fabricated as described above, the top single-crystal gold layer serves as the drain (receiver), and the bottom epitaxial GaN layer serves as the source (emitter). A nanometer-scale air channel (with a thickness comparable to that of the SiO2 layer) is formed between the emitter and receiver. Ti, Al, Ni, and Au are sequentially deposited on the source using CVD technology, followed by annealing at 850°C for 40 seconds to form the first ohmic contact layer. Similarly, Ti, Al, Ni, and Au are sequentially deposited on the drain 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 includes the following steps:
[0063] (1) An epitaxial layer of GaN was grown on a sapphire substrate using an epitaxial method. The process parameters were as follows: first, an AlN buffer layer was grown by introducing NH3 and TMAl with hydrogen as the carrier at 950°C; then, NH3 and TMGa with hydrogen as the carrier were introduced at 1000°C with a gas flow rate of 425 cm / s for 30 min to obtain a thin film with a thickness of about 4.5 μm.
[0064] (2) After the GaN epitaxial layer was grown, a SiO2 layer with a thickness of 60 nm was uniformly grown using plasma-enhanced chemical vapor deposition (PECVD). The temperature was 260 °C, the gas flow rates of SiH4 and N2O were 100 sccm and 500 sccm, respectively, and the pressure was 1500 mtorr.
[0065] (3) After the SiO2 layer is grown, with the aid of a mask, a first SiN dielectric protective layer with a thickness of 5 nm is grown sequentially on the SiO2 layer using 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 using magnetron sputtering. On the first SiN dielectric protective layer and located on one side of the single-crystal gold layer, a second SiN dielectric protective layer with a thickness of 50 nm is grown using plasma-enhanced chemical vapor deposition, forming a single-crystal gold layer with a porous structure protected by SiN. When growing the first SiN dielectric protective layer, the gases used are SiH4 and NH3 with a flow ratio of 1:3, a temperature of 300℃, a pressure of 1 Torr, and an RF power of 300 W. When magnetron sputtering the single-crystal gold layer, a gold target is used, the temperature is 300℃, 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 uses the same process as the first SiN dielectric protective layer, but it 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 in a flow ratio of 1:3, the temperature is 300℃, the pressure is 1 Torr, and the RF power is 300W. The fabricated single-crystal gold layer has 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 under ultrasonic conditions using a BOE (Buffered Oxide Etchant, HF:NH4F = 1:6) solution for 2 minutes. The etching rate at room temperature is approximately 90 nm / min. At this point, the GaN layer covered by the SiO2 layer is exposed, becoming the emission cathode. The laterally exposed portion becomes an air channel with a longitudinal length of 60 nm.
[0067] In the device structure fabricated as described above, the top single-crystal gold layer serves as the drain (receiver), and the bottom epitaxial GaN layer serves as the source (emitter). A nanometer-scale air channel (with a thickness comparable to that of the SiO2 layer) is formed between the emitter and receiver. Ti, Al, Ni, and Au are sequentially deposited on the source using CVD technology, followed by annealing at 850°C for 40 seconds to form the first ohmic contact layer. Similarly, Ti, Al, Ni, and Au are sequentially deposited on the drain 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 includes the following steps:
[0070] (1) An epitaxial layer of GaN was grown on a sapphire substrate using an epitaxial method. The process parameters were as follows: first, an AlN buffer layer was grown by introducing NH3 and TMAl with hydrogen as the carrier at 900℃; then, NH3 and TMGa with hydrogen as the carrier were introduced at 1060℃ with a gas flow rate of 425cm / s for 30min to obtain a thin film with a thickness of about 3μm.
[0071] (2) After the GaN epitaxial layer was grown, a SiO2 layer with a thickness of 50 nm was uniformly grown using plasma-enhanced chemical vapor deposition (PECVD). The temperature was 260 °C, the gas flow rates of SiH4 and N2O were 100 sccm and 500 sccm, respectively, and the pressure was 1500 mtorr.
[0072] (3) After the SiO2 layer is grown, with the aid of a mask, a first SiN dielectric protective layer with a thickness of 5 nm is grown sequentially on the SiO2 layer using 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 using magnetron sputtering. On the first SiN dielectric protective layer and located on one side of the single-crystal gold layer, a second SiN dielectric protective layer with a thickness of 50 nm is grown using plasma-enhanced chemical vapor deposition, forming a single-crystal gold layer with a porous structure protected by SiN. When growing the first SiN dielectric protective layer, the gases used are SiH4 and NH3 with a flow ratio of 1:3, a temperature of 300℃, a pressure of 1 Torr, and an RF power of 300 W. When magnetron sputtering the single-crystal gold layer, a gold target is used, the temperature is 300℃, 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 uses the same process as the first SiN dielectric protective layer, but it 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 in a flow ratio of 1:3, the temperature is 300℃, the pressure is 1 Torr, and the RF power is 300W. The fabricated single-crystal gold layer has 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 under ultrasonic conditions using a BOE (Buffered Oxide Etchant, HF:NH4F = 1:6) solution for 1 minute. The etching rate at room temperature is approximately 90 nm / min. At this point, the GaN layer covered by the SiO2 layer is exposed, becoming the emission cathode. The laterally exposed portion becomes an air channel with a longitudinal length of 50 nm.
[0074] In the device structure fabricated as described above, the top single-crystal gold layer serves as the drain (receiver), and the bottom epitaxial GaN layer serves as the source (emitter). A nanometer-scale air channel (with a thickness comparable to that of the SiO2 layer) is formed between the emitter and receiver. Ti, Al, Ni, and Au are sequentially deposited on the source using CVD technology, followed by annealing at 850°C for 40 seconds to form the first ohmic contact layer. Similarly, Ti, Al, Ni, and Au are sequentially deposited on the drain 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 includes the following steps:
[0077] (1) An epitaxial layer of GaN was grown on a sapphire substrate using an epitaxial method. The process parameters were as follows: first, an AlN buffer layer was grown by introducing NH3 and TMAl with hydrogen as the carrier at 1000℃; then, NH3 and TMGa with hydrogen as the carrier were introduced at 1060℃ with a gas flow rate of 425cm / s for 30min to obtain a thin film with a thickness of about 5μm.
[0078] (2) After the GaN epitaxial layer was grown, a SiO2 layer with a thickness of 50 nm was uniformly grown using plasma-enhanced chemical vapor deposition (PECVD). The temperature was 260 °C, the gas flow rates of SiH4 and N2O were 100 sccm and 500 sccm, respectively, and the pressure was 1500 mtorr.
[0079] (3) After the SiO2 layer is grown, with the aid of a mask, a first SiN dielectric protective layer with a thickness of 5 nm is grown sequentially on the SiO2 layer using 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 using magnetron sputtering. On the first SiN dielectric protective layer and located on one side of the single-crystal gold layer, a second SiN dielectric protective layer with a thickness of 50 nm is grown using plasma-enhanced chemical vapor deposition, forming a single-crystal gold layer with a porous structure protected by SiN. When growing the first SiN dielectric protective layer, the gases used are SiH4 and NH3 with a flow ratio of 1:3, a temperature of 300℃, a pressure of 1 Torr, and an RF power of 300 W. When magnetron sputtering the single-crystal gold layer, a gold target is used, the temperature is 300℃, 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 uses the same process as the first SiN dielectric protective layer, but it 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 with a flow ratio of 1:3, a temperature of 300℃, a pressure of 1 Torr, and an RF power of 300W. The fabricated single-crystal gold layer has a porous array structure, with a pore diameter of 50nm.
[0080] (4) After the single-crystal gold layer is deposited, the device is further etched under ultrasonic conditions using a BOE (Buffered Oxide Etchant, HF:NH4F = 1:6) solution for 1 minute. The etching rate at room temperature is approximately 90 nm / min. At this point, the GaN layer covered by the SiO2 layer is exposed, becoming the emission cathode. The laterally exposed portion becomes an air channel with a longitudinal length of 50 nm.
[0081] In the device structure fabricated as described above, the top single-crystal gold layer serves as the drain (receiver), and the bottom epitaxial GaN layer serves as the source (emitter). A nanometer-scale air channel (with a thickness comparable to that of the SiO2 layer) is formed between the emitter and receiver. Ti, Al, Ni, and Au are sequentially deposited on the source using CVD technology, followed by annealing at 850°C for 40 seconds to form the first ohmic contact layer. Similarly, Ti, Al, Ni, and Au are sequentially deposited on the drain 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 in Example 1, and (b) is the current-voltage characteristic curve of the double-hole device in Example 2. The numbers in the figure represent the measurement sequence. As can be seen from the figure, the current gradually increases and tends to stabilize as the number of measurements increases. This 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 multi-hole device is Schottky emission before entering FN emission, and the emission current is smaller at this time. The voltage at the intersection of the tangent line of the emission curve and the horizontal axis is the turn-on voltage, Von. As can be seen from the figure, the turn-on voltage Von of this device is generally between 5V and 7V. The turn-on voltage of the traditional field emission electron source is several kilovolts.
[0083] Figure 5 The figures show fitted curves of the device's emission current expression. Analysis of these curves reveals the device's field emission characteristics and various feature parameters, such as the field enhancement factor β and the effective field emission area α. (a) shows the fitted curve of the FN emission of the single-hole device in Example 1, and (b) shows the fitted curve of the FN emission of the double-hole device in Example 2. The numbers in the figures indicate the measurement order. A typical FN emission fitted curve is concave downwards, indicating the transition from Schottky emission to FN emission. At higher voltage levels, the field enhancement factor β and the field emission area α in the FN formula can be further calculated from the slope and intercept of the linearly fitted line.
[0084] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, it is intended to include any modifications and variations that fall within the scope of the claims and their equivalents.
Claims
1. A method for preparing a wide-beam, high-brightness field emission electron source, characterized in that, Includes the following steps: GaN epitaxial layers are grown on substrates using epitaxial methods. A SiO2 layer was grown on the GaN epitaxial layer using plasma-enhanced chemical vapor deposition. With the aid of a photomask, a first SiN dielectric protective layer is grown on the SiO2 layer using plasma-enhanced chemical vapor deposition (PECVD). A single-crystal gold layer is then grown on the first SiN dielectric protective layer using magnetron sputtering. A second SiN dielectric protective layer is grown on the first SiN dielectric protective layer and located on one side of the single-crystal gold layer using PECVD. The photomask is then removed, forming a single-crystal gold layer with a hole structure protected by SiN. The second SiN dielectric protective layer and the single-crystal gold layer are located in the same layer, with the second SiN dielectric protective layer situated between the single-crystal gold layer and the hole structure. The hole structure penetrates both the first and second SiN dielectric protective layers. The SiO2 layer at the bottom of the hole structure is etched using 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 emitter cathode, and the single crystal gold layer is the receiver. The longitudinal length of the air channel is equal to the thickness of the SiO2 layer, and the longitudinal length of the air channel is 40nm~60nm. The pore structure is a porous structure, with a circular cross-sectional shape for each pore and a diameter of 50nm~150nm.
2. The method for preparing a wide-beam, high-brightness field emission electron source according to claim 1, characterized in that, The specific etching operation is as follows: Under room temperature and ultrasonic conditions, the entire device is placed in 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 in a volume ratio of 1:
6.
3. 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~5μm. The process parameters for growing the GaN epitaxial layer are as follows: first, NH3 and trimethylaluminum with hydrogen as the carrier are introduced at 900℃~1000℃ to grow an AlN buffer layer; then, NH3 and trimethylgallium with hydrogen as the carrier are introduced at 950℃~1060℃ with a gas flow rate of 425 cm / s for 30 min to obtain the GaN epitaxial layer.
4. 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℃~400℃, the precursors are SiH4 and N2O, the gas flow rates of SiH4 and N2O are 20sccm~100sccm and 100sccm~500sccm respectively, and the pressure is 1000mTorr~1500mTorr.
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 first SiN dielectric protective layer is 5nm~10nm. During growth, the gases used are SiH4 and NH3 with a flow ratio of 1:3, the temperature is 200℃~400℃, the pressure is 1Torr~10Torr, and the RF power is 300W~500W.
6. 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~100nm. When sputtering the single crystal gold layer with magnetron sputtering, the target material used is a gold 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. The thickness of the second SiN dielectric protective layer is the same as the thickness of the single crystal gold layer. During growth, the gases used are SiH4 and NH3 with a flow ratio of 1:3, the temperature is 200℃~400℃, the pressure is 1Torr~10Torr, and the radio frequency power is 300W~500W.
7. 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 sequentially on the emission cathode using chemical vapor deposition, followed by annealing to form the first ohmic contact layer; Ti, Al, Ni and Au are deposited sequentially on the receiving electrode using chemical vapor deposition to form a second ohmic contact layer.
8. A wide-beam, high-brightness field emission electron source prepared by the preparation method according to any one of claims 1 to 7.