A high-temperature high-selectivity flexible GaN-based HEMT hydrogen sensor and a preparation method thereof

Abstract

A high-temperature and high-selectivity flexible GaN-based HEMT hydrogen sensor and a preparation method thereof, the sensor comprises, from top to bottom, a flexible porous carbon fiber packaging layer, an AlGaN / GaN epitaxial structure and a flexible porous carbon fiber substrate layer; the epitaxial structure comprises, from bottom to top, an AlN nucleation layer, an AlGaN transition buffer layer, a GaN channel layer, an AlGaN barrier layer and a double-layer cap layer; a source electrode, a drain electrode and a Pt gate electrode are arranged on the barrier layer and are isolated by the cap layer; an iron-containing zeolite molecular sieve is embedded in the inner side of the packaging layer as a filter medium and is in contact with the Pt gate electrode, the pore diameter of the zeolite molecular sieve is 3.3 Å~ 3.4 Å, and the zeolite molecular sieve is used for selectively transmitting hydrogen and filtering out interfering gases; the device parameters are optimized by a TCAD simulator, and a temporary bonding and debonding process is used to realize the lossless transfer of the epitaxial layer to the high-temperature-resistant flexible carbon fiber substrate; the sensor can withstand a high temperature of 1000 DEG C, has excellent flexibility and air flow disturbance resistance, and can effectively solve the problems of in-situ accurate sensing and selective detection of hydrogen in the high-temperature exhaust gas of an aero-engine.

Description

Technical Field

[0001] This invention relates to the field of gas sensing technology, specifically proposing a high-temperature, high-selectivity flexible GaN-based HEMT hydrogen sensor and its fabrication method. Background Technology

[0002] High-temperature gas sensing technology shows great promise in the prediction and diagnosis of aero-engine faults. By measuring the composition and concentration of aero-engine exhaust gases in real time, key parameters for power system health monitoring and diagnosis can be obtained. The exhaust temperatures of current aero-engines reach 600-800℃, and some models even reach 1000℃. Traditional gas analysis methods, such as insertion sampling analysis and spectral remote sensing, suffer from poor real-time performance, complex structures, and low detection accuracy. Furthermore, due to the extremely high flow velocity and temperature of aero-engine exhaust gases, rigid sensors are easily affected by gas disturbances, while flexible sensors typically cannot withstand high temperatures. Therefore, there is an urgent need to explore novel high-temperature resistant flexible gas sensing technologies to solve the problem of accurate in-situ sensing of high-temperature exhaust gases in the near field of aero-engines.

[0003] Gallium nitride (GaN), a typical representative of third-generation semiconductor materials, is an excellent material for developing microelectronic and optoelectronic devices. Compared with first- and second-generation semiconductor materials, GaN semiconductor materials have unique and superior properties, such as wide bandgap, high carrier mobility (2000 cm² / (V·s)), high thermal conductivity, high critical breakdown electric field strength, high temperature resistance, high pressure resistance, corrosion resistance, and radiation resistance. GaN-based gas sensors can exhibit high stability in corrosive and high-temperature environments, and GaN-based HEMT devices have the potential to be made flexible and exhibit good bending and tensile resistance. GaN-based HEMTs (High Electron Mobility Transistors) form a high electron concentration channel near the heterojunction: a two-dimensional electron gas (2DEG), which has high sensitivity to the adsorption of gases such as hydrogen and good stability under high temperature and large temperature changes. Third-generation semiconductor gas sensors based on this structure have advantages such as miniaturization, low loss, low noise, and high temperature resistance. For the flexible fabrication of GaN-based HEMT devices, due to the high temperature of GaN epitaxial growth, it is currently not possible to directly grow GaN semiconductor materials on flexible substrates and fabricate HEMT devices. The mainstream fabrication approach involves thinning rigid substrates to give compound semiconductor transistors preliminary flexible properties such as bending and stretching, and then further combining them with flexible substrates. However, this process is extremely prone to damage, leading to severe performance degradation. Therefore, new solutions are urgently needed for the flexible fabrication of GaN-based HEMT gas sensors.

[0004] Existing technologies include research on rigid GaN-based HEMT hydrogen sensors, but the highest temperature they can currently withstand is 800℃, which is insufficient to withstand the 1000℃ high temperatures required by aero-engines. Furthermore, there is the issue of interference from other gases in hydrogen sensing. Currently, there is no technology for the flexible fabrication of GaN-based HEMT gas sensors. For other GaN-based HEMT devices, it is difficult to fabricate wafer-level continuous thin-film flexible GaN-based HEMT devices in a single step. Moreover, flexible transfer substrates are not heat-resistant, and after flexibility, they are prone to varying degrees of performance degradation or even complete failure due to unstable interfacial contact.

[0005] Song et al. from Ohio State University [Song J, Flynn JS, Brandes GR, et al. Hightemperature hydrogen sensors based on AlGaN / GaN heterostructures[C] / / SENSORS,2004 IEEE. IEEE, 2004: 158-161.] used Pt / IrPt / PdAg as the sensing gate, enabling hydrogen sensing at temperatures ranging from 200 to 800°C, with the highest sensing temperature reaching 800°C. The sensor structure was developed using metal-organic chemical vapor deposition (MOCVD) to grow an epitaxial layer on a sapphire substrate. The epitaxial layer consisted of a 40 nm AlN nucleation layer, a 3 μm undoped GaN channel layer, and a 20 nm undoped Al0.3Ga0.7N barrier layer. This represents the highest known temperature tolerance for a GaN-based HEMT hydrogen sensor, but it still falls short of the 1000°C temperatures achievable in aero-engines, and it cannot address the interference from other gases in hydrogen sensing. There is currently no effective method for the flexible fabrication of GaN-based HEMT hydrogen sensors. Summary of the Invention

[0006] To overcome the shortcomings of the existing technology, the present invention aims to provide a high-temperature, high-selectivity flexible GaN-based HEMT hydrogen sensor and its fabrication method. By optimizing the device structural parameters through simulation, and utilizing temporary bonding and debonding processes, a non-destructive transfer of the GaN epitaxial layer from a rigid substrate to a high-temperature resistant flexible carbon fiber substrate is achieved. This sensor can withstand temperatures up to 1000℃ and possesses excellent flexibility and resistance to airflow disturbances, effectively solving the problem of in-situ accurate sensing and selective detection of hydrogen in high-temperature exhaust gases from aero-engines.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A high-temperature, high-selectivity flexible GaN-based HEMT hydrogen sensor includes a flexible porous carbon fiber encapsulation layer 10, an AlGaN / GaN epitaxial structure, and a flexible porous carbon fiber substrate layer 11 arranged sequentially. The AlGaN / GaN epitaxial structure includes, from bottom to top: an AlN nucleation layer 8, an AlxGa1-xN transition buffer layer 7, a GaN channel layer 6, an AlyGa1-yN barrier layer 5, and a capping layer 2 on the AlyGa1-yN barrier layer 5. A source 1, a gate 3, and a drain 4 are disposed on the AlyGa1-yN barrier layer 5, and the source 1, gate 3, and drain 4 are isolated from each other by the capping layer 2. The flexible porous carbon fiber encapsulation layer 10 covers the AlGaN / GaN epitaxial structure and is in direct contact with the source 1, drain 4 and capping layer 2; The surface of the gate 3 is provided with a high-temperature resistant filter medium 12, which is a zeolite molecular sieve containing iron wire, embedded inside the flexible porous carbon fiber encapsulation layer 10 and in direct contact with the Pt gate 3, and its sieve hole diameter is 3.3Å~3.4Å.

[0008] The capping layer 2 is a double capping layer composed of an Al2O3 layer and a SiN layer, wherein the Al2O3 layer is in direct contact with the AlyGa1-yN barrier layer 5, and the SiN layer is in direct contact with the flexible porous carbon fiber encapsulation layer 10.

[0009] In the AlGaN / GaN epitaxial structure: the thickness of the AlN nucleation layer is 10nm to 30nm, the thickness of the AlxGa1-xN transition buffer layer is 300nm to 1000nm, where the value of x ranges from 0.05 to 0.25, the thickness of the GaN channel layer is 0.9μm to 1.3μm, the thickness of the AlyGa1-yN barrier layer is 10nm to 40nm, where the value of y ranges from 0.1 to 0.4, the thickness of the Al2O3 layer is 10nm to 200nm, and the thickness of the SiN layer is 10nm to 30nm.

[0010] The source and drain electrodes are both composed of Ti / Al / Ni / Au composite metal layers, with thicknesses of 10nm~20nm / 50nm~120nm / 30nm~50nm / 30nm~50nm respectively; the distance between the source and the gate is 0.5μm~2.5μm, the gate length is 1μm~4μm, the gate width is 100μm~300μm, and the gate thickness is 2nm~220nm.

[0011] Both the flexible porous carbon fiber substrate layer 11 and the flexible porous carbon fiber encapsulation layer 10 are prepared using the following process: Using polyacrylonitrile as raw material, the following electrochemical treatments are performed sequentially: pre-oxidation at 200℃~300℃ for 30min~120min, low-temperature graphitization at 300℃~1000℃ for 2h~8h, high-temperature graphitization at 1000℃~1800℃ for 1h~4h, anodizing with 0.1mol / L~4mol / L ammonium bicarbonate solution at 10℃~40℃ and a current density of 0.1A / m²~10A / m² for 10s~300s, followed by deionized water washing and sizing with epoxy resin at a working concentration of 0.1wt%~10wt% to obtain pure carbon fiber; the pure carbon fiber yarn is then subjected to low-tension warping, rapier weaving at 80r / min~200r / min, and heat treatment at 200℃~300℃ for 60min~110min. The carbon fiber is then impregnated and shaped in a flexible resin with a solid content of 1wt% to 10wt% to form a dense, high-temperature resistant flexible carbon fiber cloth; the low tension refers to controlling the tension of a single carbon fiber yarn to 1cN to 10cN, and ensuring that the tension difference between the yarns on the same warp beam does not exceed ±2cN.

[0012] The flexible porous carbon fiber encapsulation layer 10 has a dense grid-like pore structure, with pores that allow gas molecules to pass through, and a multi-level pore structure with pore sizes ranging from 0.5 nm to 50 μm.

[0013] A method for fabricating a high-temperature, high-selectivity flexible GaN-based HEMT hydrogen sensor includes the following steps: S1. The electrical characteristics of GaN-based HEMT devices under operating conditions of 25℃~1000℃ were simulated using TCAD simulation software to determine the size range of key layers of the epitaxial structure; the y-value of the AlyGa1-yN barrier layer was 0.1~0.4, and the thickness was 10nm~40nm; the thickness of the GaN channel layer was 0.9μm~1.3μm; the gate length was 1μm~4μm, and the width was 100μm~300μm; the source-gate spacing was 0.5μm~2.5μm.

[0014] S2. An AlGaN / GaN epitaxial structure was grown on a rigid sapphire substrate using metal-organic chemical vapor deposition. The source, drain, and Pt gate were fabricated using MEMS technology to obtain a rigid hydrogen sensor. S3. Iron-containing zeolite molecular sieves were prepared by acid co-hydrolysis hydrothermal method and transferred to the Pt gate surface by contact printing process. S4. The rigid sapphire substrate is removed using a temporary bonding-debonding process to obtain a substrate-free AlGaN / GaN epitaxial layer; S5. The substrate-free epitaxial layer is bonded to the flexible porous carbon fiber substrate 11, and then covered with a flexible porous carbon fiber encapsulation layer 10 of the same material to obtain a flexible hydrogen sensor.

[0015] Step S2 specifically includes: S21. An AlN nucleation layer, an AlxGa1-xN transition buffer layer, a GaN channel layer, and an AlyGa1-yN barrier layer are sequentially epitaxially grown on a sapphire substrate. S22. After cleaning the grown GaN epitaxial wafer, positive photoresist masking photolithography is used to form an active region pattern, and then dry etching is used to form an active region isolation structure with a depth of 50nm to 100nm on the active region pattern. S23. Using negative photoresist masking photolithography, source, gate, and drain patterns are formed at the edge of the active region on the epitaxial wafer after S22. Au, Ni, Al, and Ti metals are deposited sequentially in the source, gate, and drain patterns using vacuum evaporation. Then, metal lift-off is performed using acetone ultrasonication. Finally, a rapid thermal annealing process is used to prepare a Ti / Al / Ni / Au composite metal layer as the source and drain. S24. Same as S23, Pt gate is prepared using photolithography, vacuum evaporation and metal stripping processes; S25. The epitaxial wafer processed in S24 is used to form a cap layer pattern using a negative photoresist masking photolithography process. The patterns are rectangles between the source and the gate and rectangles between the gate and the drain. Al2O3 and Si3N4 are deposited in the pattern in sequence, and then the cap layer is prepared by ultrasonic peeling with acetone (2).

[0016] Step S3 specifically includes: A silicon source and an iron source are stirred in an alcohol-water system at pH 2–5 and a temperature of 40–80°C for 1–6 hours to complete co-hydrolysis and condensation, yielding an iron-containing silica sol. The iron-containing silica sol is then dropped into an aqueous solution containing an alkali source and an aluminum source and allowed to stand for 6–24 hours to obtain an aluminosilicate precursor gel. The precursor gel is then subjected to hydrothermal crystallization at 150–200°C for 24–168 hours, followed by washing and drying to obtain an iron-containing mordenite molecular sieve. The molecular sieve is dispersed in a volatile solvent to prepare an ink. An elastic stamp is dipped into the ink and then bonded to a Pt grid at a pressure of 0.5 N–50 N for 10–300 seconds. After peeling off the stamp, the molecular sieve is heat-treated at 300–500°C for 1–4 hours to complete the transfer of the molecular sieve.

[0017] Step S4 specifically includes: Using a SiC wafer as a temporary carrier and high-temperature wax as a bonding medium, the epitaxial layer was temporarily bonded to the SiC carrier under a pressure of 0.1 MPa to 1.0 MPa and a temperature of 150°C to 200°C. The sapphire substrate was thinned to 50 μm to 150 μm by mechanical grinding, and the remaining sapphire substrate was removed by a combination of wet and dry etching, with the AlN nucleation layer as the etching stop layer. The bonded structure was placed in an acetone solution at 30°C to 60°C and sonicated for 5 min to 20 min to dissolve the high-temperature wax and complete the debonding, resulting in a substrate-free epitaxial layer.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: (A) This invention can operate normally in high-temperature environments, with a maximum withstand temperature of 1000℃, exceeding the 800℃ high temperature that currently known GaN-based hydrogen sensors can withstand. This is mainly due to the use of high-temperature resistant flexible carbon fiber cloth for the high-temperature resistant flexible substrate and packaging material, forming a structure of "upper packaging layer - epitaxial layer - lower substrate layer"; and the structural parameters of the GaN-based epitaxial layer were designed and optimized by Silvaco under 1000℃ conditions, and the epitaxial layer also exhibits good performance under the simulated 1000℃ conditions.

[0019] (B) In this invention, iron-containing zeolite molecular sieves are used as a filter medium and bonded to a Pt gate by contact printing. The diameter of the sieve is about 3.3 Å-3.4 Å. Interfering gases with molecular dynamic diameters larger than this size are screened out. Gases such as carbon monoxide, which are highly interfering with hydrogen, can be screened out, thus improving the selectivity for hydrogen.

[0020] (C) This invention uses polyacrylonitrile as raw material, and after pre-oxidation, low-temperature and high-temperature graphitization and surface treatment, it can withstand high temperature. Then, it uses a fiber loom to stretch and weave to make a high-temperature resistant flexible carbon fiber cloth substrate and encapsulation layer, which provides a flexible substrate and encapsulation material for GaN-based HEMT hydrogen sensors.

[0021] (D) This invention proposes a non-destructive flexible thin film fabrication method for GaN-based devices and an ultra-thin epitaxial layer holding technique. The method utilizes high-temperature wax for temporary bonding and debonding of epitaxial wafers. During temporary bonding, the rigid substrate is removed by mechanical grinding and dry / wet etching, and then transferred to a flexible substrate by the holding technique. The GaN-based HEMT hydrogen sensor achieves non-destructive flexibility and can reduce the interference of gas flow on the sensor.

[0022] (E) This invention proposes a test platform with a high-temperature probe station as the main test chamber and a method for high-temperature gas-sensing testing and verification of a high-temperature, highly selective flexible GaN-based HEMT hydrogen sensor on the curved surface of a tailpipe in a laboratory environment, which can be used to explore and verify the device performance. Attached Figure Description

[0023] Figure 1 This is a two-dimensional cross-sectional view of the rigid GaN-based HEMT epitaxial layer portion of the present invention and verification of Pt gates of different shapes.

[0024] Figure 2 Different shapes of Pt gates verified by this invention Figure 3a These are the output characteristic curves of different Al compositions in the rigid GaN-based HEMT epitaxial layer of this invention; Figure 3b These are transconductance curves for different Al compositions in the rigid GaN-based HEMT epitaxial layer of this invention. Figure 3c This is an output characteristic curve of the rigid GaN-based HEMT epitaxial layer with different barrier layer thicknesses according to the present invention; Figure 3d This refers to the transconductance curves of the rigid GaN-based HEMT epitaxial layer with different barrier layer thicknesses in this invention. Figure 3e This is an output characteristic curve showing different channel layer thicknesses in the rigid GaN-based HEMT epitaxial layer of this invention; Figure 3f This refers to the transconductance curves of different channel layer thicknesses in the rigid GaN-based HEMT epitaxial layer of this invention. Figure 3g This refers to the output characteristic curves of the rigid GaN-based HEMT epitaxial layer with different gate lengths in this invention. Figure 3h This refers to the transconductance curves of different gate lengths in the rigid GaN-based HEMT epitaxial layer of this invention. Figure 3i This refers to the output characteristic curves of different gate widths in the rigid GaN-based HEMT epitaxial layer of this invention. Figure 3j This refers to the transconductance curves of different gate widths in the rigid GaN-based HEMT epitaxial layer of this invention. Figure 3k This refers to the output characteristic curves of different gate-source pitches in the rigid GaN-based HEMT epitaxial layer of this invention. Figure 3l This refers to the transconductance curves of different gate-source distances in the rigid GaN-based HEMT epitaxial layer of this invention. Figure 4 This is a two-dimensional cross-sectional view of the flexible GaN-based HEMT hydrogen sensor of the present invention.

[0025] Figure 5 This is a flowchart of the epitaxial flexible integration technology based on temporary bonding and debonding processes of the present invention.

[0026] Figure 6 This is a flowchart of the flexible carbon fiber cloth manufacturing process.

[0027] In the figure, 1-source, 2-capping layer, 3-gate, 4-drain, 5-AlyGa1-yN barrier layer, 6-GaN channel layer, 7-AlGaN transition buffer layer, 8-AlN nucleation layer, 9-sapphire substrate, 10-upper flexible carbon fiber cloth encapsulation layer, 11-lower flexible carbon fiber cloth substrate layer, 12-high temperature resistant filter medium. Detailed Implementation

[0028] The following are specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent modifications made based on the technical solutions of this application fall within the protection scope of the present invention.

[0029] Following the above technical solutions, such as Figure 1 , Figure 2 As shown in Figure 3, a high-temperature, high-selectivity flexible GaN-based HEMT hydrogen sensor can specifically detect hydrogen at the ppm concentration level in a high-temperature flowing gas environment.

[0030] A high-temperature, high-selectivity flexible GaN-based HEMT hydrogen sensor includes a flexible porous carbon fiber encapsulation layer 10, an AlGaN / GaN epitaxial structure, and a flexible porous carbon fiber substrate layer 11 arranged sequentially. The AlGaN / GaN epitaxial structure includes, from bottom to top: an AlN nucleation layer 8, an AlxGa1-xN transition buffer layer 7, a GaN channel layer 6, an AlyGa1-yN barrier layer 5, and a capping layer 2 on the AlyGa1-yN barrier layer 5. A source 1, a gate 3, and a drain 4 are disposed on the AlyGa1-yN barrier layer 5, and the source 1, gate 3, and drain 4 are isolated from each other by the capping layer 2. The flexible porous carbon fiber encapsulation layer 10 covers the AlGaN / GaN epitaxial structure and is in direct contact with the source 1, drain 4 and capping layer 2; The surface of the gate 3 is provided with a high-temperature resistant filter medium 12, which is a zeolite molecular sieve containing iron wire, embedded inside the flexible porous carbon fiber encapsulation layer 10 and in direct contact with the Pt gate 3, and its sieve hole diameter is 3.3Å~3.4Å.

[0031] The process steps will now be explained in sequence: Figure 1This is an epitaxial structure for a high-temperature resistant, rigid AlGaN / GaN-based HEMT rigid hydrogen sensor. Figures 3a-3lTo investigate the optimal parameters of the high-temperature rigid AlGaN / GaN-based HEMT rigid hydrogen sensor epitaxial structure, simulations were conducted using Silvaco software at 1000℃ with different epitaxial layer structural dimensions and process parameters within an empirical range. The simulation principle is as follows: Simulations were performed at 1000℃ for different structural parameter ranges to obtain the device's output and transfer characteristic curves. The transconductance curve was then derived from the transfer characteristic curve. The output characteristic curve reflects the magnitude of the device's output signal; a larger signal is desired for better observation results. The transconductance curve reflects the device's sensing sensitivity; a larger and smoother transconductance is desired for stable and good sensitivity. The optimal structural parameters were obtained by combining these two factors. Key structural parameters include the Al composition and thickness of the AlGa1-yN barrier layer 5, the thickness of the GaN channel layer 6, the length and width of the gate 3, and the distance between the gate 3 and the source 1. The simulation results are as follows: For the AlyGa1-yN barrier layer 5, the simulated Al composition ranges from 0.1 to 0.4 μm, and the thickness ranges from 10 nm to 40 nm. A larger thickness results in a larger output current. The transconductance is highest and smoothest at a thickness of 20 nm. Therefore, the final parameters are an Al composition of 0.25 μm and a barrier layer thickness of 20 nm. For the GaN channel layer 6, the simulated thickness ranges from 0.9 to 1.3 μm. A larger channel layer thickness results in a larger output current. The larger the current, the smaller the transconductance. Considering all factors, the final parameter is 1.1µm. The simulated length range of gate 2 is 1-4µm. The smaller the gate length, the larger the output current, the larger the transconductance, and the smoother the current. The width range is 100µm-300µm. The larger the gate width, the larger the output current, the larger the transconductance, and the smoother the current. Therefore, the final parameter is 1µm in length and 300µm in width. The simulated distance between gate 2 and source 1 is 0.5µm-2.5µm. The smaller the gate-source distance, the larger the output current, the larger the transconductance, and the smoother the current. The final parameter is 0.5µm. Furthermore, simulations revealed that the remaining structural parameters had almost no impact on the device's output characteristics. Based on process requirements, the following structural parameters were determined: the sapphire substrate 9 had a thickness of 50µm-350µm; the AlN nucleation layer 8 had a thickness of 10nm-30nm; the Al composition of the AlGaN transition layer 7 was 0.05-0.25, with a thickness of 300nm-900nm; the source 1 and drain 4 had thicknesses and compositions of Ti / Al / Ni / Au (20 / 100 / 50 / 50 nm); the cap layer thickness was SiN / Al2O3 (20nm / 200nm); and the step between the GaN channel layer 6 and the AlGaN transition layer 7 was 1µm on each side to prevent crosstalk between devices. With a gate length of 1µm, the effects of long rod-shaped gates, sawtooth gates, meandering gates, and staggered toothed gates on device performance were investigated. The results showed that the long rod-shaped gate device exhibited superior performance.The above parameters are determined by combining simulation results with the process parameters to identify the optimal parameters.

[0032] Figure 4 This is a high-temperature, high-selectivity flexible GaN-based HEMT hydrogen sensor. For Figure 1 To make rigid devices more flexible, the first step is to fabricate a non-destructive flexible thin film GaN epitaxial layer, employing an epitaxial flexible integration technology based on temporary bonding and debonding processes. Figure 5 Using SiC wafers as temporary carriers and high-temperature wax as temporary bonding material, the epitaxial layer is temporarily bonded at 0.1MPa-1.0MPa pressure and 150-200℃ temperature using an ultrathin epitaxial layer holding technique. The substrate is then thinned to 50um-150um through mechanical grinding and polishing. The substrate is further removed by dry and wet etching, with an AlN nucleation layer as the etching stop layer. Finally, the high-temperature wax is removed by ultrasonication in a solvent such as acetone at 30-60℃ for 5-20 minutes, separating the epitaxial layer from the SiC temporary carrier and completing the debonding process.

[0033] Figure 4 The preparation process of the medium-high temperature resistant filter media 12 is as follows: An iron-containing mordenite zeolite molecular sieve is prepared using a conventional acid co-hydrolysis hydrothermal method. A silicon source and an iron source are co-hydrolyzed and condensed in an alcohol-water system at pH 2-5 and 40℃-80℃ for 1-6 hours. The resulting iron-containing silica gel sol is then added dropwise to an aqueous solution containing an alkali source and an aluminum source for 6-24 hours to obtain an aluminosilicate precursor gel. The precursor gel is then crystallized under conventional hydrothermal crystallization conditions at 150-200℃ for 24-168 hours, followed by washing and drying to obtain the iron-containing mordenite zeolite molecular sieve. Using conventional contact printing technology, iron-containing zeolite molecular sieves are dispersed in a volatile solvent to make ink. After being dipped into an elastic stamp, the ink is bonded to a Pt gate under a pressure of 0.5N-50N for 10-300s. After peeling off the stamp, the ink is heat-treated at 300-500℃ for 1-4h, thus serving as a high-temperature resistant filter medium. This ink is then transferred to the Pt gate through contact printing. Since the molecular dynamics diameter of hydrogen is 2.89Å, while the molecular dynamics diameter of interfering gases such as CO is above 3.4Å, and the sieve pore diameter of the filter medium is around 3.3Å-3.4Å, hydrogen can be separated from its interfering gases (such as carbon monoxide).

[0034] The preparation process of flexible carbon fiber cloth substrate 11 is as follows ( Figure 6Using high-tensile-strength polypropylene fiber as raw material, the process involves pre-oxidation in a pre-oxidation furnace at 200-300℃, low-temperature graphitization at 300-1000℃, high-temperature graphitization at 1000-1800℃, electrochemical treatment at 10℃-40℃ with 0.1-4mol ammonium bicarbonate solution for 10-300s, washing with deionized water, and sizing with 0.1%-10% working concentration epoxy resin to obtain pure carbon fiber. The pure carbon fiber yarn is then subjected to low-tension warping, rapier weaving at 80-200r / min, heat treatment at 200℃-300℃, and impregnation and shaping with flexible resin containing 1%-10% solids to form a dense, high-temperature resistant flexible carbon fiber fabric.

[0035] Figure 4 The flexible carbon fiber cloth encapsulation layer 10 has a dense grid-like structure. The dense porous structure can effectively reduce the impact of airflow scouring, smoke and other factors on the gas sensitivity detection of the sensor, and does not affect the grid contact with the gas to be measured.

[0036] Both the flexible porous carbon fiber substrate and the flexible porous carbon fiber encapsulation layer are prepared using the following process: polyacrylonitrile is used as the raw material, and the following processes are performed sequentially: pre-oxidation at 200℃~300℃ for 30~120 min, low-temperature graphitization at 300℃~1000℃ for 2~8 h, high-temperature graphitization at 1000℃~1800℃ for 1~4 h, and 0.1 mol / L~4 mol / L ammonium bicarbonate solution is used at 10~40°C for 0.1~10... Electrochemical treatment involving anodizing at a current density of A / m² for 10s~300s, followed by deionized water washing and sizing with epoxy resin at a working concentration of 0.1wt%~10wt%, yields pure carbon fiber. The pure carbon fiber yarn is then warped under low tension, rapier woven at 80r / min~200r / min, heat-treated at 200℃~300℃ for 60~110min, and then impregnated and shaped in a flexible resin with a solid content of 1wt%~10wt%, forming a dense, high-temperature resistant flexible carbon fiber fabric. The low tension refers to controlling the tension of a single carbon fiber yarn at 1~10 cN, and ensuring that the tension difference between yarns on the same warp beam does not exceed ±2 cN.

[0037] The flexible porous carbon fiber encapsulation layer has a dense grid-like pore structure, with pores that allow gas molecules to pass through, and a multi-level pore structure with pore sizes ranging from 0.5 nm to 50 μm.

[0038] A method for fabricating a high-temperature, high-selectivity flexible GaN-based HEMT hydrogen sensor includes the following steps: S1. The electrical characteristics of GaN-based HEMT devices under operating conditions of 25℃~1000℃ were simulated using TCAD simulation software to determine the size range of key layers of the epitaxial structure; the y-value of the AlyGa1-yN barrier layer was 0.1~0.4, and the thickness was 10nm~40nm; the thickness of the GaN channel layer was 0.9μm~1.3μm; the gate length was 1~4μm, and the width was 100~300μm; the source-gate spacing was 0.5~2.5μm.

[0039] S2. The AlGaN / GaN epitaxial structure of claim 1 is grown on a rigid sapphire substrate by metal-organic chemical vapor deposition, and the source, drain and Pt gate are fabricated by MEMS process to obtain a rigid hydrogen sensor. S21. An AlN nucleation layer, an AlGaN transition buffer layer, a GaN channel layer, and an AlyGa1-yN barrier layer are epitaxially grown sequentially on a sapphire substrate. S22. The grown GaN epitaxial wafers were ultrasonicated with acetone for 5 min, soaked in ethanol solution, and cleaned with deionized water. Active region patterns were formed using EPG535 positive photoresist masking photolithography. The pattern size was a rectangle with a length of 9 μm and a width of 300 μm. The cleaned substrates were spin-coated with EPG535 positive photoresist in two steps on a spin coater at 500 r, 10 s, 150 rpm / s and 3000 r, 40 s, 10000 rpm / s. The substrates were pre-baked at 95°C for 10 min on a hot baking plate, and then exposed to extreme ultraviolet light for 7 s using ultraviolet lithography. After exposure, the substrates were developed in 2.38% TMAH solution for 10 s-30 s to form active region patterns. Then, a dry etching process using a Cl2 / BCl3 gas etching source was performed to form an active region isolation structure with a depth of 50 nm to 100 nm on the aforementioned pattern. S23. The epitaxial wafer processed above is used to form source and gate patterns using RNDF-06-2523 negative resist masking photolithography. The pattern consists of two rectangles with a length of 1µm and a width of 300µm at the edge of the active region. RNDF-06-2523 negative resist is applied to the substrate using a spin coater in two steps: 500 rpm, 10 s, 150 rpm / s; and 2000 rpm, 30 s, 10000 rpm / s. The substrate is then preheated at 110°C for 120 s on a hot-baking plate, followed by extreme ultraviolet (EUV) exposure for 10 s using UV lithography. After exposure, the substrate is placed... Develop in 2.38% TMAH solution for 13-15 seconds, then bake on a hot baking plate for 120 seconds to form source and drain patterns. Vacuum evaporation is used to deposit Au (20nm), Ni (100nm), Al (50nm), and Ti (50nm) metals sequentially in the patterns on the substrate. Then, metal stripping is performed using acetone and ultrasonication, and a Ti / Al / Ni / Au composite metal layer is prepared as the source and drain by rapid thermal annealing at 850°C for 2 minutes under nitrogen gas. S24. The epitaxial wafer treated above is used to form a gate pattern using RNDF-06-2523 negative resist masking photolithography. The pattern is a rectangle with a length of 1µm and a width of 300µm. The RNDF-06-2523 negative resist is applied to the substrate using a spin coater in two steps: 500 rpm, 10 s, 150 rpm / s; 2000 rpm, 30 s, 10000 rpm / s. The substrate is then preheated at 110°C for 120 s on a hot-baking plate, followed by extreme ultraviolet (EUV) exposure for 10 s using UV lithography. After the photolithography is completed, the substrate is placed in a 2.38% TMAH solution for development for 13-15 seconds, and then baked on a hot baking plate for 120 seconds to form a gate pattern. The substrate is then subjected to vacuum evaporation to deposit Au (20nm), Ni (100nm), Al (50nm), and Ti (50nm) metals in sequence in the pattern. The metals are then removed by ultrasonic stripping with acetone to prepare a 220nm thick Pt gate with a source-gate spacing of 0.5μm.

[0040] S25. The epitaxial wafer treated as described above is used to form a cap layer pattern using RNDF-06-2523 negative resist masking photolithography. The patterns are a rectangle with a length of 0.5 μm and a width of 300 μm between the source and gate, and a rectangle with a length of 5.5 μm and a width of 300 μm between the gate and drain. The RNDF-06-2523 negative resist is applied to the substrate using a spin coater at 500 rpm, 10 s, 150 rpm / s; 2000 rpm, 30 s, 10000 rpm / s. The substrate is spin-coated in two steps, pre-baked at 110°C for 120 seconds on a hot baking plate, and then exposed to extreme ultraviolet light for 10 seconds using ultraviolet lithography. After exposure, the substrate is developed in 2.38% TMAH solution for 13-15 seconds, and then post-baked on a hot baking plate for 120 seconds to form a cap layer pattern. The substrate is then subjected to magnetron sputtering to deposit 200 nm Al2O3 and 20 nm Si3N4 in sequence in the pattern, and then exfoliated with acetone and ultrasound to prepare a 220 nm thick cap layer. S3. Iron-containing zeolite molecular sieves were prepared by acid co-hydrolysis hydrothermal method and transferred to the Pt gate surface by contact printing process; the specific method includes: The silicon source and iron source were stirred in an alcohol-water system at pH 2-5 and temperature 40℃-80℃ for 1-6 hours to complete co-hydrolysis and condensation, yielding an iron-containing silica sol. The iron-containing silica sol was then dropped into an aqueous solution containing an alkali source and an aluminum source and allowed to stand for 6-24 hours to obtain an aluminosilicate precursor gel. The precursor gel was subjected to hydrothermal crystallization at 150℃-200℃ for 24-168 hours, and after washing and drying, an iron-containing mordenite zeolite molecular sieve was obtained. The molecular sieve was dispersed in a volatile solvent to prepare an ink. An elastic stamp was dipped into the ink and then bonded to a Pt grid with a pressure of 0.5N-50N for 10-300 seconds. After peeling off the stamp, the molecular sieve was heat-treated at 300℃-500℃ for 1-4 hours to complete the transfer. S4. A temporary bonding-debonding process is used to remove the rigid sapphire substrate to obtain a substrate-free AlGaN / GaN epitaxial layer; specific methods include: Using a SiC wafer as a temporary carrier and high-temperature wax as a bonding medium, the epitaxial layer is temporarily bonded to the SiC carrier under a pressure of 0.1 MPa to 1.0 MPa and a temperature of 150°C to 200°C. The sapphire substrate is thinned to 50 μm to 150 μm by mechanical grinding, and the remaining sapphire substrate is removed by a combination of wet and dry etching, with the AlN nucleation layer as the etching stop layer. The bonded structure is placed in an acetone solution at 30°C to 60°C and sonicated for 5 min to 20 min to dissolve the high-temperature wax and complete the debonding, resulting in a substrate-free epitaxial layer.

[0041] S5. The substrate-free epitaxial layer is bonded to the high-temperature resistant flexible carbon fiber cloth substrate of claim 3, and then covered with a flexible porous carbon fiber encapsulation layer of the same material to obtain a flexible hydrogen sensor.

[0042] The working process of this invention is as follows: High-temperature, highly selective flexible GaN sensors can be mounted on any surface in a high-temperature gas environment by attaching a flexible substrate to the surface. The target gas comes into contact with the sensor, and the sensor comes into contact with a high-temperature filter medium through the porous structure of the encapsulation layer made of high-temperature resistant flexible carbon fiber cloth. Hydrogen can pass through the filter medium by molecules of different molecular dynamic diameters, while interfering gases such as carbon monoxide cannot pass through and are filtered out. The gas passing through the molecular sieve is adsorbed on the Pt gate surface. The hydrogen molecular bonds break and reach the adsorption sites of Pt, thus changing the metal work of the Pt gate. This alters the height of the Schottky barrier formed between the Pt gate and the underlying barrier layer, causing a change in the two-dimensional electron gas (2DEG) between the AlyGa1-yN barrier layer and the GaN channel layer. Ultimately, this changes the source-drain current of the device, and the output characteristics of the sensor at different hydrogen concentrations can be reflected by the changes in the source-drain current.

[0043] Example 1. A method for fabricating a high-temperature, high-selectivity flexible GaN-based HEMT hydrogen sensor: S1. Simulation optimization of device parameters: The electrical characteristics of GaN-based HEMT devices under 1000℃ conditions were simulated using TCAD simulation software to determine the size range of key layers in the epitaxial structure; the y-value of the AlyGa1-yN barrier layer was set to 0.25 and the thickness to 20nm; the GaN channel layer thickness was set to 1.1μm; the gate length was set to 1μm and the width to 300μm; and the source-gate spacing was set to 0.5μm.

[0044] S2. Fabrication of a rigid GaN-based HEMT device: The AlGaN / GaN epitaxial structure described in claim 1 is grown on a rigid sapphire substrate using metal-organic chemical vapor deposition (MOCVD), and the source, drain, and Pt gate are fabricated using MEMS technology to obtain a rigid hydrogen sensor; specifically including: S21. An AlN nucleation layer, an AlGaN transition buffer layer, a GaN channel layer, and an AlyGa1-yN barrier layer are epitaxially grown sequentially on a sapphire substrate. S22. The grown GaN epitaxial wafer was ultrasonicated with acetone for 5 min, soaked in ethanol solution, and cleaned with deionized water. The active region pattern was formed by photolithography using EPG535 positive photoresist with a pattern size of 9 μm long and 300 μm wide. The cleaned substrate was spin-coated with EPG535 positive photoresist in two steps at 500 r, 10 s, 150 rpm / s and 3000 r, 40 s, 10000 rpm / s. The substrate was pre-baked at 95°C for 10 min on a hot baking plate, and then exposed to extreme ultraviolet light for 7 s using ultraviolet lithography. After exposure, the substrate was developed in 2.38% TMAH solution for 10 s to form the active region pattern. Then, a dry etching process using Cl2 / BCl3 gas etching source was performed to form a 50 nm deep active region isolation structure on the aforementioned pattern. S23. The epitaxial wafer processed above is used to form source and gate patterns using RNDF-06-2523 negative resist masking photolithography. The patterns are two rectangles with a length of 1µm and a width of 300µm at the edge of the active region. RNDF-06-2523 negative resist is used on the substrate for two-step spin coating at 500 rpm for 10 seconds and 150 rpm / s; then at 2000 rpm for 30 seconds and 10000 rpm / s. The substrate is then preheated at 110°C for 120 seconds, followed by extreme ultraviolet (EUV) exposure for 10 seconds. After exposure, the substrate is... The substrate was developed in 2.38% TMAH solution for 15 seconds, and then baked on a hot baking plate for 120 seconds to form source and drain patterns. Au (20nm), Ni (100nm), Al (50nm), and Ti (50nm) metals were deposited sequentially in the patterns using a vacuum evaporation process on the substrate. The metal was then removed by ultrasonic stripping with acetone and rapidly annealed at 850°C for 2 minutes under nitrogen gas to prepare a Ti / Al / Ni / Au composite metal layer as the source and drain. S24. The epitaxial wafer treated above is used to form a gate pattern using RNDF-06-2523 negative resist masking photolithography. The pattern is a rectangle with a length of 1µm and a width of 300µm. The RNDF-06-2523 negative resist is applied to the substrate using a spin coater in two steps: 500 rpm, 10 s, 150 rpm / s; and 2000 rpm, 30 s, 10000 rpm / s. The substrate is then preheated at 110°C for 120 s on a hot-baking plate, followed by extreme ultraviolet (EUV) exposure for 10 s using UV lithography. After exposure, the substrate is placed in a 2.38% TMAH solution for development for 15 seconds, and then baked on a hot baking plate for 120 seconds to form a gate pattern. The substrate is then subjected to vacuum evaporation to deposit Au (20nm), Ni (100nm), Al (50nm), and Ti (50nm) metals in sequence in the pattern. The metals are then removed by ultrasonic stripping with acetone to prepare a 220nm thick Pt gate with a source-gate spacing of 0.5μm.

[0045] S25. The epitaxial wafer processed as described above is used to form a cap layer pattern using RNDF-06-2523 negative resist masking photolithography. The patterns are a rectangle with a length of 0.5 μm and a width of 300 μm between the source and gate, and a rectangle with a length of 5.5 μm and a width of 300 μm between the gate and drain. The RNDF-06-2523 negative resist is applied to the substrate using a spin coater at 500 rpm for 10 s and 150 rpm; 2000 rpm for 30 s and 10000 rpm. The substrate is spin-coated in two steps, pre-baked at 110°C for 120 seconds on a hot baking plate, and then exposed to extreme ultraviolet light for 10 seconds using UV lithography. After exposure, the substrate is developed in a 2.38% TMAH solution for 15 seconds, and then post-baked on a hot baking plate for 120 seconds to form a cap layer pattern. The substrate is then subjected to magnetron sputtering to deposit 200 nm Al2O3 and 20 nm Si3N4 in sequence in the pattern, and then ultrasonically exfoliated with acetone to prepare a 220 nm thick cap layer.

[0046] S3. Preparation of filterable media and transfer to the gate: Iron-containing mordenite zeolite molecular sieves were prepared by acid co-hydrolysis hydrothermal method and transferred to the Pt gate surface by contact printing process; specifically: silicon source and iron source were stirred in an alcohol-water system at pH=2 and temperature of 80℃ for 1h to complete co-hydrolysis condensation and obtain iron-containing silica sol; the iron-containing silica sol was dropped into an aqueous solution containing alkali source and aluminum source and allowed to stand for 24h to obtain aluminosilicate precursor gel; the precursor gel was placed in a hydrothermal crystallization environment at 180℃ for 168h, and after washing and drying, iron-containing mordenite zeolite molecular sieves were obtained; the molecular sieves were dispersed in a volatile solvent to prepare ink, and after being dipped in the ink with an elastic stamp, it was adhered to the Pt gate with a pressure of 25N for 180s, and after peeling off the stamp, it was heat-treated at 400℃ for 1h to complete the transfer of molecular sieves.

[0047] S4. Flexible transfer of epitaxial layer: A temporary bonding-debonding process is used to remove the rigid sapphire substrate, resulting in a substrate-free AlGaN / GaN epitaxial layer; specifically including: Using a SiC wafer as a temporary carrier and high-temperature wax as a bonding medium, the epitaxial layer was temporarily bonded to the SiC carrier at a pressure of 0.5 MPa and a temperature of 150 °C. The sapphire substrate was thinned to 50 μm by mechanical grinding, and the remaining sapphire substrate was removed by a combination of wet and dry etching, with the AlN nucleation layer as the etching stop layer. The bonded structure was placed in a 30 °C acetone solution and sonicated for 20 min to dissolve the high-temperature wax and complete the debonding, resulting in a substrate-free epitaxial layer.

[0048] S5. Flexible integrated packaging: A substrate-free epitaxial layer is bonded to the high-temperature resistant flexible carbon fiber cloth substrate described in claim 3, and then covered with a flexible porous carbon fiber packaging layer of the same material to obtain a flexible hydrogen sensor.

[0049] A high-temperature gas-sensitive testing platform was constructed, using a high-temperature probe station capable of being heated to 1000℃ as the test chamber. The source and leakage current response of the sensor was tested at 1000℃ to verify its sensing performance on curved surfaces and in a high-temperature hydrogen environment. All structural parameters were optimized and verified by Silvaco at 1000℃. The overall dimensions of the active region of the device are 9µm × 300µm × 1.96µm.

[0050] Example 2 S1. Simulation optimization of device parameters: The electrical characteristics of GaN-based HEMT devices under 1000℃ conditions were simulated using TCAD simulation software to determine the size range of key layers in the epitaxial structure; the y-value of the AlyGa1-yN barrier layer was set to 0.25 and the thickness to 20nm; the thickness of the GaN channel layer was set to 1.1μm; the gate length was set to 2μm and the width to 200μm; and the source-gate spacing was set to 1μm.

[0051] S2. Fabrication of a rigid GaN-based HEMT device: The AlGaN / GaN epitaxial structure described in claim 1 is grown on a rigid sapphire substrate using metal-organic chemical vapor deposition (MOCVD), and the source, drain, and Pt gate are fabricated using MEMS technology to obtain a rigid hydrogen sensor; specifically including: S21. An AlN nucleation layer, an AlGaN transition buffer layer, a GaN channel layer, and an AlyGa1-yN barrier layer are epitaxially grown sequentially on a sapphire substrate. S22. The grown GaN epitaxial wafer was ultrasonicated with acetone for 5 min, soaked in ethanol solution, and cleaned with deionized water. The active region pattern was formed by photolithography using EPG535 positive photoresist masking. The pattern size was a rectangle with a length of 9 μm and a width of 200 μm. The cleaned substrate was spin-coated with EPG535 positive photoresist in two steps on a spin coater at 500 r, 10 s, 150 rpm / s and 3000 r, 40 s, 10000 rpm / s. The substrate was pre-baked at 95°C for 10 min on a hot baking plate, and then exposed to extreme ultraviolet light for 7 s using ultraviolet lithography. After exposure, the substrate was developed in 2.38% TMAH solution for 10 s to form the active region pattern. Then, a dry etching process using a Cl2 / BCl3 gas etching source was performed to form a 50 nm deep active region isolation structure on the aforementioned pattern. S23. The epitaxial wafer processed above is used to form source and gate patterns using RNDF-06-2523 negative resist masking photolithography. The patterns are two rectangles with a length of 1µm and a width of 200µm at the edge of the active region. RNDF-06-2523 negative resist is used on the substrate for two-step spin coating at 500 rpm for 10 seconds and 150 rpm / s; then at 2000 rpm for 30 seconds and 10000 rpm / s. The substrate is then preheated at 110°C for 120 seconds, followed by extreme ultraviolet (EUV) exposure for 10 seconds. After exposure, the substrate is... The substrate was developed in 2.38% TMAH solution for 15 seconds, and then baked on a hot baking plate for 120 seconds to form source and drain patterns. Au (20nm), Ni (100nm), Al (50nm), and Ti (50nm) metals were deposited sequentially in the patterns using a vacuum evaporation process on the substrate. The metal was then removed by ultrasonic stripping with acetone and rapidly annealed at 850°C for 2 minutes under nitrogen gas to prepare a Ti / Al / Ni / Au composite metal layer as the source and drain. S24. The epitaxial wafer treated above is used to form a gate pattern using RNDF-06-2523 negative resist masking photolithography. The pattern is a rectangle with a length of 2µm and a width of 200µm. The RNDF-06-2523 negative resist is applied to the substrate using a spin coater in two steps: 500 rpm, 10 s, 150 rpm / s; 2000 rpm, 30 s, 10000 rpm / s. The substrate is then preheated at 110°C for 120 s on a hot-baking plate, followed by extreme ultraviolet (EUV) exposure using UV lithography for 10 seconds. After exposure, the substrate is placed in a 2.38% TMAH solution for development for 15 seconds, and then baked on a hot baking plate for 120 seconds to form a gate pattern. The substrate is then subjected to vacuum evaporation to deposit Au (20nm), Ni (100nm), Al (50nm), and Ti (50nm) metals in sequence in the pattern. The metals are then removed by ultrasonic stripping with acetone to prepare a 220nm thick Pt gate with a source-gate spacing of 1μm.

[0052] S25. The epitaxial wafer treated as described above is used to form a cap layer pattern using RNDF-06-2523 negative resist masking photolithography. The patterns are a rectangle with a length of 1µm and a width of 200µm between the source and gate, and a rectangle with a length of 5µm and a width of 200µm between the gate and drain. The RNDF-06-2523 negative resist is applied to the substrate using a spin coater at 500 rpm for 10 s and 150 rpm / s; and at 2000 rpm for 30 s and 10000 rpm / s. The substrate was spin-coated in two steps, pre-baked at 110°C for 120 seconds on a hot baking plate, and then exposed to extreme ultraviolet light for 10 seconds using ultraviolet lithography. After exposure, the substrate was developed in a 2.38% TMAH solution for 15 seconds and then post-baked on a hot baking plate for 120 seconds to form a cap layer pattern. The substrate was then subjected to magnetron sputtering to deposit 200 nm Al2O3 and 20 nm Si3N4 in sequence in the pattern. Finally, the substrate was ultrasonically peeled off with acetone to prepare a 220 nm thick cap layer.

[0053] S3. The obtained device is then processed to fabricate a filter medium and transfer it to the gate, followed by flexible transfer of the epitaxial layer and flexible integration packaging. The fabrication process is the same as in Example 1. Example 3 S1. Simulation optimization of device parameters: The electrical characteristics of GaN-based HEMT devices under 1000℃ conditions were simulated using TCAD simulation software to determine the size range of key layers in the epitaxial structure; the y-value of the AlyGa1-yN barrier layer was set to 0.25 and the thickness to 20nm; the GaN channel layer thickness was set to 1.1μm; the gate length was set to 3μm and the width to 100μm; and the source-gate spacing was set to 2μm.

[0054] S2. Fabrication of a rigid GaN-based HEMT device: The AlGaN / GaN epitaxial structure described in claim 1 is grown on a rigid sapphire substrate using metal-organic chemical vapor deposition (MOCVD), and the source, drain, and Pt gate are fabricated using MEMS technology to obtain a rigid hydrogen sensor; specifically including: S21. An AlN nucleation layer, an AlGaN transition buffer layer, a GaN channel layer, and an AlyGa1-yN barrier layer are epitaxially grown sequentially on a sapphire substrate. S22. The grown GaN epitaxial wafer was ultrasonicated with acetone for 5 min, soaked in ethanol solution, and cleaned with deionized water. The active region pattern was formed by photolithography using EPG535 positive photoresist masking. The pattern size was a rectangle with a length of 9 μm and a width of 100 μm. The cleaned substrate was spin-coated with EPG535 positive photoresist in two steps on a spin coater at 500 r, 10 s, 150 rpm / s and 3000 r, 40 s, 10000 rpm / s. The substrate was pre-baked at 95°C for 10 min on a hot baking plate, and then exposed to extreme ultraviolet light for 7 s using ultraviolet lithography. After exposure, the substrate was developed in 2.38% TMAH solution for 10 s to form the active region pattern. Then, a dry etching process using a Cl2 / BCl3 gas etching source was performed to form a 50 nm deep active region isolation structure on the aforementioned pattern. S23. The epitaxial wafer processed above is used to form source and gate patterns using RNDF-06-2523 negative resist masking photolithography. The patterns are two rectangles with a length of 1µm and a width of 100µm at the edge of the active region. RNDF-06-2523 negative resist is spin-coated onto the substrate in two steps on a spin coater: 500 rpm, 10 s, 150 rpm / s; 2000 rpm, 30 s, 10000 rpm / s. The substrate is then preheated at 110°C for 120 s on a hot-baking plate, followed by extreme ultraviolet (EUV) exposure for 10 s using UV lithography. After exposure, the substrate is... The substrate was developed in 2.38% TMAH solution for 15 seconds, and then baked on a hot baking plate for 120 seconds to form source and drain patterns. Au (20nm), Ni (100nm), Al (50nm), and Ti (50nm) metals were deposited sequentially in the patterns using a vacuum evaporation process on the substrate. The metal was then removed by ultrasonic stripping with acetone and rapidly annealed at 850°C for 2 minutes under nitrogen gas to prepare a Ti / Al / Ni / Au composite metal layer as the source and drain. S24. The epitaxial wafer treated above is used to form a gate pattern using RNDF-06-2523 negative resist masking photolithography. The pattern is a rectangle with a length of 3µm and a width of 100µm. The RNDF-06-2523 negative resist is applied to the substrate using a spin coater in two steps: 500 rpm, 10 s, 150 rpm / s; 2000 rpm, 30 s, 10000 rpm / s. The substrate is then preheated at 110°C for 120 s on a hot-baking plate, followed by extreme ultraviolet (EUV) exposure using UV lithography for 10 seconds. After exposure, the substrate is placed in a 2.38% TMAH solution for development for 15 seconds, and then baked on a hot baking plate for 120 seconds to form a gate pattern. The substrate is then subjected to vacuum evaporation to deposit Au (20nm), Ni (100nm), Al (50nm), and Ti (50nm) metals in sequence in the pattern. The metals are then removed by ultrasonic stripping with acetone to prepare a 220nm thick Pt gate with a source-gate spacing of 2μm.

[0055] S25. The epitaxial wafer treated as described above is used to form a cap layer pattern using RNDF-06-2523 negative resist masking photolithography. The patterns are a rectangle with a length of 2µm and a width of 100µm between the source and gate, and a rectangle with a length of 2µm and a width of 100µm between the gate and drain. The RNDF-06-2523 negative resist is applied to the substrate using a spin coater at 500 rpm for 10 s and 150 rpm / s; and at 2000 rpm for 30 s and 10000 rpm / s. The substrate was spin-coated in two steps, pre-baked at 110°C for 120 seconds on a hot baking plate, and then exposed to extreme ultraviolet light for 10 seconds using ultraviolet lithography. After exposure, the substrate was developed in a 2.38% TMAH solution for 15 seconds and then post-baked on a hot baking plate for 120 seconds to form a cap layer pattern. The substrate was then subjected to magnetron sputtering to deposit 200 nm Al2O3 and 20 nm Si3N4 in sequence in the pattern. Finally, the substrate was ultrasonically peeled off with acetone to prepare a 220 nm thick cap layer.

[0056] S3. The obtained device is then processed to fabricate a filter medium and transfer it to the gate, followed by flexible transfer of the epitaxial layer and flexible integration packaging. The fabrication process is the same as in Example 1. Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high-temperature, high-selectivity flexible GaN-based HEMT hydrogen sensor, characterized in that, It includes a flexible porous carbon fiber encapsulation layer (10), an AlGaN / GaN epitaxial structure, and a flexible porous carbon fiber substrate layer (11) arranged sequentially from top to bottom; the AlGaN / GaN epitaxial structure includes, from bottom to top: an AlN nucleation layer (8), an AlxGa1-xN transition buffer layer (7), a GaN channel layer (6), an AlyGa1-yN barrier layer (5), and a capping layer (2) located on the AlyGa1-yN barrier layer (5); The AlyGa1-yN barrier layer (5) is provided with a source (1), a gate (3) and a drain (4), and the source (1), the gate (3) and the drain (4) are isolated from each other by a capping layer (2); The flexible porous carbon fiber encapsulation layer (10) covers the AlGaN / GaN epitaxial structure and is in direct contact with the source (1), drain (4) and capping layer (2); The surface of the gate (3) is provided with a high-temperature resistant filter medium (12), which is a ferrite zeolite molecular sieve containing iron wire, embedded in the inner side of the flexible porous carbon fiber encapsulation layer (10) and in direct contact with the gate (3).

2. The hydrogen sensor according to claim 1, characterized in that, The capping layer (2) is a double-layer capping layer composed of an Al2O3 layer and a SiN layer, wherein the Al2O3 layer and the AlyGa1 layer are... The yN barrier layer (5) is in direct contact with the SiN layer and the flexible porous carbon fiber encapsulation layer (10).

3. The sensor according to claim 1, characterized in that, In the AlGaN / GaN epitaxial structure: the thickness of the AlN nucleation layer (8) is 10nm to 30nm, the thickness of the AlxGa1-xN transition buffer layer (7) is 300nm to 1000nm, where the value of x is 0.05 to 0.25, the thickness of the GaN channel layer (6) is 0.9μm to 1.3μm, the thickness of the AlyGa1-yN barrier layer (5) is 10nm to 40nm, where the value of y is 0.1 to 0.4, the thickness of the Al2O3 layer is 10nm to 200nm, and the thickness of the SiN layer is 10nm to 30nm.

4. The sensor according to claim 1, characterized in that the source (1) and drain (2) of the electrode are both composed of Ti / Al / Ni / Au composite metal layers, and the thickness of each layer is 10nm~20nm / 50nm~120nm / 30nm~50nm / 30nm~50nm respectively; the distance between the source (1) and the gate (3) is 0.5μm~2.5μm, the length of the gate (3) is 1μm~4μm, the width of the gate (3) is 100μm~300μm, the thickness of the gate (3) is 2nm~220nm, and the gate (3) is a Pt gate.

5. The sensor according to claim 1, characterized in that, The flexible porous carbon fiber encapsulation layer (10) has a dense grid-like pore structure, with pores that allow gas molecules to pass through, and a multi-level pore structure with pores ranging from 0.5 nm to 50 μm.

6. A method for preparing a high-temperature, high-selectivity flexible GaN-based HEMT hydrogen sensor according to any one of claims 1 to 5, characterized in that, Includes the following steps: S1. The electrical characteristics of GaN-based HEMT devices under operating conditions of 25℃~1000℃ were simulated using TCAD simulation software to determine the size range of key layers of the epitaxial structure; the y value of the AlyGa1-yN barrier layer (5) was 0.1~0.4 and the thickness was 10nm~40nm; the thickness of the GaN channel layer (6) was 0.9μm~1.3μm; the length of the gate (3) was 1μm~4μm and the width was 100μm~300μm; the distance between the source (1) and the gate (3) was 0.5μm~2.5μm. S2. The AlGaN / GaN epitaxial structure of claim 1 is grown on a rigid sapphire substrate by metal-organic chemical vapor deposition, and the source (1), drain (2) and Pt gate are fabricated by MEMS process to obtain a rigid hydrogen sensor; S3. Iron-containing zeolite molecular sieves were prepared by acid co-hydrolysis hydrothermal method and transferred to the Pt gate surface by contact printing process. S4. The rigid sapphire substrate is removed using a temporary bonding-debonding process to obtain a substrate-free AlGaN / GaN epitaxial layer; S5. The substrate-free epitaxial layer is bonded to the flexible porous carbon fiber substrate (11), and then covered with a flexible porous carbon fiber encapsulation layer (10) of the same material to obtain a flexible hydrogen sensor.

7. The preparation method according to claim 6, characterized in that, Step S2 specifically includes: S21. An AlN nucleation layer (8), an AlxGa1-xN transition buffer layer (7), a GaN channel layer (6), and an AlyGa1-yN barrier layer (5) are epitaxially grown sequentially on a sapphire substrate. S22. After cleaning the grown GaN epitaxial wafer, positive photoresist masking photolithography is used to form an active region pattern, and then dry etching is used to form an active region isolation structure with a depth of 50nm to 100nm on the active region pattern. S23. Using negative photoresist masking lithography, source and drain patterns are formed at the edge of the active region on the epitaxial wafer after S22. Au, Ni, Al and Ti metals are deposited sequentially in the source and drain patterns using vacuum evaporation. Then, metal lift-off is performed using acetone ultrasonication. Finally, a rapid thermal annealing process is used to prepare a Ti / Al / Ni / Au composite metal layer as the source and drain. S24. Same as S23, Pt gate is prepared using photolithography, vacuum evaporation and metal stripping processes; S25. The epitaxial wafer processed in S24 is used to form a cap layer pattern using a negative photoresist masking photolithography process. The patterns are rectangles between the source and the gate and rectangles between the gate and the drain. Al2O3 and Si3N4 are deposited in the pattern in sequence, and then the cap layer is prepared by ultrasonic peeling with acetone (2).

8. The preparation method according to claim 6, characterized in that, The specific method of step S3 includes: A silicon source and an iron source are stirred in an alcohol-water system at pH 2–5 and a temperature of 40–80°C for 1–6 hours to complete co-hydrolysis and condensation, yielding an iron-containing silica sol. The iron-containing silica sol is then dropped into an aqueous solution containing an alkali source and an aluminum source and allowed to stand for 6–24 hours to obtain an aluminosilicate precursor gel. The precursor gel is then subjected to hydrothermal crystallization at 150–200°C for 24–168 hours, followed by washing and drying to obtain an iron-containing mordenite molecular sieve. The molecular sieve is dispersed in a volatile solvent to prepare an ink. An elastic stamp is dipped into the ink and then bonded to a Pt grid at a pressure of 0.5 N–50 N for 10–300 seconds. After peeling off the stamp, the molecular sieve is heat-treated at 300–500°C for 1–4 hours to complete the transfer of the molecular sieve.

9. The preparation method according to claim 6, characterized in that, Step S4 specifically includes: Using a SiC wafer as a temporary carrier and high-temperature wax as a bonding medium, the epitaxial layer was temporarily bonded to the SiC carrier under a pressure of 0.1MPa to 1.0MPa and a temperature of 150℃ to 200℃. The sapphire substrate was thinned to 50μm to 150μm by mechanical grinding, and the remaining sapphire substrate was removed by a combination of wet etching and dry etching. The AlN nucleation layer (8) was used as the etching stop layer. The bonded structure was placed in an acetone solution at 30℃ to 60℃ and sonicated for 5min to 20min to dissolve the high-temperature wax and complete the debonding, resulting in a substrate-free epitaxial layer.

10. The preparation method according to claim 6, characterized in that, The flexible porous carbon fiber substrate (11) and the flexible porous carbon fiber encapsulation layer (10) are both prepared using the following process: using polyacrylonitrile as raw material, pre-oxidation is performed at 200℃~300℃ for 30min~120min, low-temperature graphitization is performed at 300℃~1000℃ for 2h~8h, high-temperature graphitization is performed at 1000℃~1800℃ for 1h~4h, electrochemical treatment of anodic oxidation is performed using 0.1mol / L~4mol / L ammonium bicarbonate solution at 10℃~40℃ and 0.1A / m²~10A / m² current density for 10s~300s, followed by cleaning with deionized water and sizing with epoxy resin at 0.1wt%~10wt% working concentration to obtain pure carbon fiber; the pure carbon fiber yarn is then warped under low tension at 80r / min~200r / min. Rapier weaving, heat treatment at 200℃~300℃ for 60min~110min, and then impregnation and shaping in a flexible resin with a solid content of 1wt%~10wt% to form a dense, high-temperature resistant flexible carbon fiber cloth; the low tension refers to controlling the tension of a single carbon fiber yarn at 1cN~10cN, and ensuring that the tension difference between yarns on the same warp beam does not exceed ±2cN.

Images