MEMS gas sensor and preparation method therefor

Abstract

A MEMS gas sensor and a preparation method therefor, comprising an insulating substrate (1), a heating electrode (403), an insulating layer (105) and a testing unit, which are overlappingly disposed. The testing unit comprises a testing electrode, a sensing unit (2), and a selective separation membrane (3); the sensing unit (2) has a nanowire array structure formed by multiple nanowires disposed at intervals, and the selective separation membrane (3) covers the surface of the sensing unit and a recessed portion; the nanowires comprise a first metal and a second metal, the first metal being Pd, and the second metal being at least one selected from Ni, Cu, Ag, Au and Ir; the selective separation membrane (3) comprises an inner separation membrane (301) and an outer separation membrane (302) which are stacked in sequence; the inner separation membrane (301) comprises polytetrafluoroethylene, and the outer separation membrane (302) is a mixed matrix membrane having a covalent organic framework material as a filler and a polymer of intrinsic microporosity as a matrix. The MEMS gas sensor possesses excellent sensitivity for low-concentration gas monitoring, and tolerance stability for high-concentration gas, as well as excellent anti-interference performance and response speed.

Description

MEMS gas sensor and preparation method thereof

[0001] The present application claims priority from the Chinese patent application No. 202410852964.2 filed on June 27, 2024, and entitled "MEMS gas sensor and preparation method thereof", the whole content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application belongs to the field of micro-electro-mechanical technology, and particularly relates to a MEMS gas sensor, a preparation method and application thereof. BACKGROUND

[0003] Hydrogen sensors are classified into optical sensors, acoustic sensors, thermal conductivity sensors, catalytic sensors, work function sensors, resistance sensors and electrochemical sensors according to the differences in action principles and testing methods. These sensors mainly rely on the changes in refractive index, spectral absorption, temperature, mass structure and electrical properties caused by the interaction between sensitive material elements and hydrogen to produce optical, electrical and other signals through digital-to-analog conversion. Among them, optical sensors have strong specificity and fast signal transmission, but are limited by equipment volume and investment cost, and have great one-sidedness in terms of control density and monitoring spatio-temporal refinement; acoustic, thermal conductivity and work function types are small in size and low in power consumption, but have poor long-term stability, target selectivity and hysteresis; catalytic, electrochemical and resistance hydrogen sensors generally have relatively high sensitivity and sampling frequency, simple element structure, and convenient and fast signal processing, but are limited by power supply pipeline burying specifications and cannot realize flexible expansion of monitoring points and inspection routes; and in complex environments or when dealing with multi-component mixed target gas, the performance of detection range, response rate, anti-interference and environmental adaptability is often unsatisfactory.

[0004] At present, MEMS semiconductor gas sensors can effectively make up for the defects of traditional detection methods such as monopoly, high consumption and low efficiency due to low power consumption, strong selectivity, easy expansion, high integration and large dynamic measurement range. However, there is no mature hydrogen sensor on the market at present, the main reason is that the MEMS gas sensor at this stage cannot balance the contradiction between detection sensitivity and detection concentration range, that is, it realizes the detection sensitivity of low concentration hydrogen, but cannot realize the tolerance stability of high concentration hydrogen, or it realizes the tolerance stability of high concentration hydrogen, but cannot realize the detection sensitivity of low concentration hydrogen, in addition, it also cannot balance the contradiction between anti-interference and response speed, that is, it realizes the anti-interference in complex environment or multi-component mixed gas atmosphere, but cannot realize the faster response speed, or it realizes the faster response speed, but cannot realize the anti-interference in complex environment or multi-component mixed gas atmosphere. Therefore, how to provide a MEMS gas sensor with excellent low concentration gas monitoring sensitivity, high concentration gas tolerance stability, anti-interference and response speed is a technical problem to be solved in the art. SUMMARY

[0005] The application provides a MEMS gas sensor to solve the defects in the prior art that it is difficult to balance the detection sensitivity of low concentration gas and the tolerance stability of high concentration gas, and it is difficult to balance the anti-interference and the response speed, so that the MEMS gas sensor has excellent low concentration gas monitoring sensitivity, high concentration gas tolerance stability and excellent anti-interference and response speed.

[0006] The application also provides a preparation method of the MEMS gas sensor, which can prepare the MEMS gas sensor with excellent performance, and the preparation process is simple and easy to operate.

[0007] In a first aspect, the application provides a MEMS gas sensor, comprising an insulating substrate, a heating electrode, an insulating layer and a test unit which are stacked;

[0008] The test unit comprises a test electrode, a sensitive unit and a selective separation film;

[0009] The test electrode and the sensitive unit are respectively arranged on the surface of the insulating layer away from the heating electrode;

[0010] The sensitive unit has a nanowire array structure formed by a plurality of spaced nanowires, and any two adjacent nanowires form a recess with the insulating layer;

[0011] The selective separation film covers the surface of the sensitive unit and the recess;

[0012] The nanowire comprises a first metal and a second metal, the first metal is Pd, and the second metal is selected from at least one of Ni, Cu, Ag, Au, and Ir.

[0013] The selective separation membrane comprises an inner layer separation membrane and an outer layer separation membrane arranged in sequence, and the outer layer separation membrane is located on the side of the inner layer separation membrane away from the insulating substrate.

[0014] The inner layer separation membrane comprises polytetrafluoroethylene, and the outer layer separation membrane is a mixed matrix membrane with a covalent organic framework material as a filler and a self-microporous polymer as a matrix.

[0015] The MEMS gas sensor as described above, wherein the molar ratio of the first metal to the second metal is 1:(0.1-0.5); and / or,

[0016] The mass ratio of the covalent organic framework material to the self-microporous polymer is (10-80 mg):1 g.

[0017] The MEMS gas sensor as described above, wherein the hydrogen permeability of the covalent organic framework material is >4000 GPU, and the pore size is 0.5-0.8 nm; and / or,

[0018] The covalent organic framework material is selected from at least one of three-dimensional COF-300 and two-dimensional N-COF.

[0019] The three-dimensional COF-300 is prepared by condensation reaction of tetrakis(4-aminophenyl)methane and p-xylylene formaldehyde, and the two-dimensional N-COF is prepared by condensation reaction of tris(4-aminophenyl)amine and 1,3,5-triformylbenzene.

[0020] The self-microporous polymer is prepared by condensation reaction of 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobifluorene monomers and tetrafluoro-p-xylylene dinitrile monomers.

[0021] The MEMS gas sensor as described above, wherein the outer layer separation membrane is prepared by a method comprising the following processes:

[0022] The covalent organic framework material is subjected to amidation treatment to obtain an amidated covalent organic framework material.

[0023] The amidated covalent organic framework material, the self-microporous polymer, and chloroform are mixed to obtain an outer layer slurry; the outer layer slurry is coated on a pre-set substrate, and after baking, the outer layer separation membrane is obtained by peeling off.

[0024] The MEMS gas sensor as described above, wherein the test electrode is arranged on a first partial region of the surface of the insulating layer away from the heating electrode, and the sensing unit is arranged on a second partial region of the surface of the insulating layer away from the heating electrode.

[0025] The insulating layer comprises Al2O3.

[0026] The MEMS gas sensor as described above, wherein the test electrode comprises a first test electrode and a second test electrode arranged in a spaced manner, the nanowire array structure in the sensing unit is arranged between the first test electrode and the second test electrode, and the extending direction of the nanowire is from the first test electrode to the second test electrode.

[0027] The MEMS gas sensor as described above, wherein the heating electrode comprises a titanium metal layer and a platinum metal layer arranged in a stacked manner, and the platinum metal layer is located on the surface of the titanium metal layer away from the insulating substrate.

[0028] The MEMS gas sensor as described above, further comprising a cantilever beam unit.

[0029] The test electrode and the heating electrode are connected to different electrode plates through different cantilever beam units.

[0030] The second aspect of the present application provides a preparation method of the MEMS gas sensor of the first aspect, comprising the following steps:

[0031] arranging a heating electrode on the surface of the insulating substrate, depositing an insulating layer on the surface of the heating electrode away from the insulating substrate, and depositing a test electrode and a sensing unit on the surface of the insulating layer away from the heating electrode, respectively;

[0032] The sensing unit comprises a plurality of nanowires arranged in a spaced manner to form a nanowire array structure, and two adjacent nanowires form a recess with the insulating layer.

[0033] covering the surface of the sensing unit and the recess with a selective separation film to obtain the MEMS gas sensor.

[0034] The preparation method as described above, wherein the block copolymer and the solvent are mixed to obtain a first slurry, the first slurry is coated on the surface of the insulating layer, and after drying, laser annealing treatment is performed, then a first metal and a second metal are deposited through dry etching or wet deposition to form a metal nanowire array to obtain the sensing unit.

[0035] The block copolymer is selected from at least one of polystyrene-r-poly(methyl methacrylate) and polystyrene-b-poly(2-vinylpyridine).

[0036] The implementation of the present application has at least the following beneficial effects:

[0037] The MEMS gas sensor provided by the present application can maximize the advantages of each component by the mutual coordination of the special structure design and the material of each structural unit, so that the MEMS gas sensor has excellent low-concentration gas monitoring sensitivity, high-concentration gas tolerance stability, excellent anti-interference and response speed. BRIEF DESCRIPTION OF DRAWINGS

[0038] Fig. 1 is a schematic diagram of the cross-sectional structure of the MEMS gas sensor in an embodiment of the present application;

[0039] Fig. 2 is a schematic diagram of the partial cross-sectional structure of the MEMS gas sensor in an embodiment of the present application;

[0040] Fig. 3 is a schematic diagram of the top view structure of the MEMS gas sensor in an embodiment of the present application;

[0041] Fig. 4 is an SEM image of the sensitive unit on the MEMS gas sensor in an embodiment of the present application;

[0042] Fig. 5 is an SEM image of the partial cross-section of the MEMS gas sensor in Fig. 2;

[0043] Fig. 6 is a time-response sensitivity curve of the MEMS gas sensor in Example 1 and Comparative Examples 1-3 under different hydrogen concentrations (0.1-8 vol %), wherein the response sensitivity S is: S = R H2 / R air -1(R air is the sensor resistance in air; R H2 is the sensor resistance in hydrogen);

[0044] Fig. 7 is a hydrogen concentration-response sensitivity curve of the MEMS gas sensor in Example 1 and Comparative Examples 1-3 under different hydrogen concentrations (0.1-8 vol %);

[0045] Fig. 8 is a sensitivity test diagram of the MEMS gas sensor in Example 1 and Comparative Examples 1-3 to hydrogen in the presence of H2, CO, methane (CH4), ethanol (C2H5OH), NO2 interference gas;

[0046] Fig. 9 is a cycle stability test diagram of the MEMS gas sensor in Example 1 and Comparative Examples 1-3 in 4 vol % hydrogen concentration.

[0047] Explanation of reference signs:

[0048] 1-insulating substrate; 101-silicon wafer; 102-first SiO2 layer; 103-silicon nitride layer; 104-second SiO2 layer; 105-insulating layer; 2-sensitive unit; 3-selective separation film; 301-inner layer separation film; 302-outer layer separation film; 401-first test electrode; 402-second test electrode; 403-heating electrode; 5-recess. DETAILED DESCRIPTION

[0049] In order to make the objects, technical solutions and advantages of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below in conjunction with the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative work fall within the protection scope of the present application.

[0050] As shown in FIGS. 1-4, in a first aspect of the present application, a MEMS gas sensor is provided, comprising an insulating substrate 1, a heating electrode 403, an insulating layer 105 and a test unit which are stacked; the test unit comprises a test electrode, a sensitive unit 2 and a selective separation film 3; the test electrode and the sensitive unit 2 are respectively arranged on the surface of the insulating layer 105 away from the heating electrode 403; the sensitive unit 2 has a nanowire array structure formed by a plurality of spaced nanowires, and any two adjacent nanowires form a recess 5 with the insulating layer 105; the selective separation film 3 covers the surface of the sensitive unit 2 and the recess 5; wherein the nanowires contain a first metal and a second metal, the first metal is Pd, and the second metal is selected from at least one of Ni, Cu, Ag, Au and Ir; the selective separation film 3 comprises an inner layer separation film 301 and an outer layer separation film 302 which are stacked in sequence, wherein the outer layer separation film 302 is located on the side of the inner layer separation film 301 away from the insulating substrate 1; the inner layer separation film 301 contains polytetrafluoroethylene; and the outer layer separation film 302 is a mixed matrix membrane with covalent organic framework material as filler and self-porous polymer as matrix.

[0051] In the present application, the material of the nanowire is a binary palladium alloy, which has excellent mechanical properties, thermal stability and resistance to poisoning, such as PdNi, PdCu, PdAg, PdAu, PdIr alloy, etc. At low hydrogen partial pressure, Ag, Au and Ir can increase the Pd lattice parameter, reduce the energy required for hydrogen to occupy the vacancy, and promote the dissolution of hydrogen; while at high hydrogen partial pressure, Ag, Au and Ir fill part of the 4d electron state of Pd, leaving vacancies in the outer electron orbit of Pd, and the excess electrons in the outer orbit of Ag, Au and Ir will transfer to the outer orbit of Pd, so that the contribution of the adsorbed H atom to the number of electrons in the outer orbit of Pd will be reduced, and the mutual attraction between Pd and H atom caused by electron interaction will be weakened, resulting in the weakening of the adsorption force and solubility of hydrogen, thereby reducing the solubility of hydrogen. This buffering effect of low concentration expansion and high concentration contraction not only ensures the excellent minimum detection limit of Pd, but also significantly inhibits the phase transition of Pd from α to β, thereby enhancing the stability of the sensitive unit 2. The addition of Ni and Cu reduces the hydrogen atoms that can enter the crystal lattice by reducing the Pd lattice, thereby improving the critical hydrogen concentration of the phase transition from α to β, but also sacrificing the intrinsic sensitivity of Pd to hydrogen. Therefore, the present application preferably uses PdAg, PdAu and PdIr alloy.

[0052] In the nanowire array structure, a plurality of nanowires are arranged at intervals on the surface of the insulating substrate 1, and the nanowires protrude from the insulating substrate 1, i.e. the nanowires form a convex part with a certain height on the surface of the insulating substrate 1, and each two adjacent nanowires form a concave part 5 with the insulating substrate 1. The distance between any two adjacent nanowires is 30-200 nm.

[0053] In the present application, the cross section of each nanowire along the height direction can be isosceles trapezoidal, etc., i.e. the diameter of the nanowire changes in gradient along the height direction, and the maximum diameter is 9-12 μm.

[0054] By designing the special structure and material of the nanowire array structure, the first aspect can improve the adsorption specific surface area, the utilization rate of the sensitive unit 2 and the desorption and diffusion rate of hydrogen in the Pd bulk phase, and enhance the surface reaction kinetics; the second aspect can minimize the low coordination defect sites of the nanowire, promote the path guiding effect, improve the electron transmission efficiency to reduce the blocking phenomenon; the third aspect, in view of the fact that the external induced stress required for phase transition inhibition is mainly concentrated in the area where the nanowire structure contacts the insulating substrate 1, therefore the ultra-thin characteristics of the ultra-fine nanowire can put most of the nanowire bulk phase under the protection of the inhibition stress, because the substrate has a certain stress protection effect on the nanowires arranged on the surface. The stress protection effect generally ranges around 10 nm, therefore, the thinner and thinner the nanowire, the greater the proportion of the stress effect range in the nanowire bulk phase. In addition, the regularity of the nanowire array structure is conducive to the construction of stable and consistent carrier channels, and reduces the difference in transport characteristics of the sensitive layer between different devices.

[0055] Figure 2 is a schematic diagram of a partial cross-sectional structure of a MEMS gas sensor in an embodiment of the present application.

[0056] In some embodiments, the mass ratio or molar ratio of the first metal and the second metal is 1:(0.1-0.5)(2-10); and / or, the mass ratio of the covalent organic framework material to the self-microporous polymer is (10-80 mg):1 g.

[0057] In the present application, the selective separation membrane 3 includes an inner layer separation membrane 301 and an outer layer separation membrane 302, the inner layer separation membrane 301 is directly in contact with the sensitive unit 2 and the recess 5, and the outer layer separation membrane 302 is located on the side of the inner layer separation membrane 301 away from the insulating substrate 1, that is, directly in contact with the gas, so as to maximize the performance advantages of the inner layer separation membrane 301 and the outer layer separation membrane 302. Among them, the inner layer separation membrane 301 is in direct contact with the sensitive unit 2, and the material of polytetrafluoroethylene (PTFE) is selected, so that the inner layer separation membrane 301 has excellent chemical stability and hydrophobicity, corrosion resistance and aging resistance, and can work for a long time at-180-250℃, and the PTFE film has good permeability to hydrogen, can significantly reduce the surface activation energy barrier of the Pd alloy nanostructure, isolate humidity interference, and improve the gas-electric response rate. In addition, PTFE has excellent wetting and spreading properties after surface plasma treatment, and enhances the bonding force between the selective separation membrane 3 and the sensitive unit 2; and the outer layer separation membrane 302 is in direct contact with the gas, and a mixed matrix membrane system with covalent organic framework (COFs) material as filler and self-microporous polymer (PIMs) as matrix is adopted. COFs is a new type of crystalline adjustable topological network structure porous polymer, which has excellent thermal stability (>300℃) and high compatibility with polymer matrix, and hydrogen selective permeability exceeding 3000 GPU, which is the key core of hydrogen selective separation in the membrane. PIMs has good film-forming property, especially the unique rigid backbone hinders the free internal rotation and effective packing of the molecular structure, which can promote the formation of continuous micropores in the membrane, so that PIMs shows permeability far exceeding traditional high polymer and moderate gas selectivity. Moreover, the partial polar groups (such as cyano group) in PIMs have similar chemical properties to halogen, so they can be converted into various functional groups such as tetrazolyl, carboxyl and amidoxime group through specific reactions, achieving performance controllable improvement and function expansion.

[0058] In the present application, the nanowire array is formed by template guiding and directional self-assembly of block polymers, and then palladium alloy is deposited on the nanowire array to form a nanowire array. The block copolymer is selected from at least one of polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) and polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP).

[0059] For example, a short-chain neutral polystyrene-r-poly(methyl methacrylate) (PS-r-PMMA) random copolymer (Mn= 17 kg / mol) is used as the base wetting layer, and a polystyrene-b-poly(methyl methacrylate) (PS-b-PMMA) with lamellar microphase separation structure is used as an example, in which the number average molecular weight (Mn) of the PS block and the PMMA block is 25 kg / mol and 26 kg / mol, respectively. To achieve precise thickness control, the PS-b-PMMA is mixed with a toluene solution to obtain a slurry with a mass concentration of 2-8% of PS-b-PMMA, which is spin-coated onto the base wetting layer or coated onto the base wetting layer by dip coating. Subsequently, the slurry is vacuum dried at 60 °C for 4 hours to remove residual solvent, and a PS-b-PMMA polymer layer is formed on the surface of the base wetting layer to obtain a primary film. The primary film is subjected to laser annealing treatment, specifically, a high-power solid-state green light (λ = 532 nm) laser is used to irradiate the base wetting layer, and the light beam is focused into an elliptical shape (width 100 μm, length 600 μm) after passing through a lens, and the power density is modulated between 0-10 -4 W / μm 2 Alternatively, a low-duty-cycle pulsed near-infrared focused laser (pulse frequency = 300 kHz, pulse duration = 200 ns) with a wavelength of 1064 nm is used for irradiation annealing. The entire annealing process is carried out at room temperature, and the scanning rate is controlled at 1-5000 μm / s.

[0060] The primary film after laser annealing treatment is subjected to patterned metallization treatment, which can be carried out by dry etching or wet deposition. For example, in the dry etching process, the PS-b-PMMA polymer layer is treated by Ar / O2 reactive ion etching (CO plasma etching can also be used), in which the etching selectivity ratio of PS to PMMA is about 1:2, so that the PMMA is removed first and the remaining PS serves as a nanograting base. Then, a first Cu-based sacrificial shadow pattern (SSP) is formed on the top of the protruding part of the nanograting base by inclined physical vapor deposition (PVD), and a second SSP is formed on the side of the protruding part of the nanograting base by inclined PVD in the opposite direction, with a deposition angle of 60° and -60°. In this way, the sacrificial layer can only be deposited on the convex part and cannot penetrate into the concave part 5. After the formation of the SSPs, palladium alloy is deposited vertically through the gaps between the SSPs and deposited on the bottom of the concave valley of the nanograting pattern. Finally, the SSPs and the metal layer deposited thereon are selectively removed using a dilute Cu etchant (10 vol% ammonium persulfate aqueous solution), and the remaining PS grating is removed by Ar plasma etching, thereby forming a perfectly aligned nanowire array structure.

[0061] The block copolymer can be selectively removed in reactive ion etching (RIE) due to the difference in chemical properties between different homopolymer segments, one phase is reserved and the other phase is removed, and the high-contrast and high-fine structure formed is used as a mask for the next step of metal deposition. In addition to RIE dry etching combined with alternating magnetron sputtering or atomic vapor deposition, wet deposition based on metal salt solution immersion method can also be used for high-resolution Pd nano-alloy pattern transfer. For example, in the wet deposition process, a cylindrical phase polystyrene-b-poly(2-vinylpyridine) (PS-b-P2VP) with a total molecular weight of 116 kg / mol is used, and the volume fraction f P2VP =0.31) of P2VP. After laser local annealing of the primary film formed by PS-b-P2VP, immersion in an acidic solution containing metal salt (such as Na2PdCl4 acid solution), the remaining 1 pair of lone pair electrons on the outermost nitrogen atom in the homopolymer P2VP is easily combined with the free cation through a covalent bond, the pyridine residue in P2VP is protonated, and then forms a complex with the negatively charged metal complex ion, that is, the P2VP block is combined with the ionized Na + The replacement reaction occurs, the PS block is complexed with PdCl4 2- To form an organometallic salt, after a period of immersion, deionized water is used for washing and drying in a N2 gas stream, and the immersion time of the metal precursor is related to the diameter of the nanowire. Too short immersion time will result in discontinuous structure and quality defects. In order to maximize the complexation, the immersion time is usually not less than 60 minutes; then Ar / O2 plasma etching is used to remove the PS block, and metal nanowire arrays with P2VP morphology are obtained; finally, rapid thermal processing (RTP) sintering at 400-600°C for 5 minutes in a 5vol% H2 / Ar reducing atmosphere is performed, and a nanowire array structure is formed. If the immersion metal salt solution is replaced by HAuCl4, CuCl2, NiCl2, Na2PtCl4 or a mixed solution, then metal nanowire arrays of Au, Cu, Ni, Pt and their alloys can be obtained.

[0062] In the present application, COFs can be two-dimensional or three-dimensional materials. The inherent pore size of general COFs is 0.6-3 nm, but under the induction of dislocation shrinkage effect such as mutual entanglement and insertion during film formation, the actual effective pore size will generally be smaller than the inherent value. The stacking layer spacing / gap range of some materials is only 0.3-0.4 nm, which can be used to separate H2 CO2 CO CH4 Gas molecules with similar kinetic diameters. In some embodiments, the hydrogen permeability of the covalent organic framework material is > 4000 GPU and the pore size is 0.5-0.8 nm. By selecting a covalent organic framework material with high hydrogen permeability and a specific intrinsic pore size, the performance of the MEMS gas sensor is improved

[0063] In some embodiments, the covalent organic framework material is selected from at least one of three-dimensional COF-300 and two-dimensional N-COF. The intrinsic pore size of the three-dimensional COF-300 is 0.7-0.8 nm, and the intrinsic pore size of the two-dimensional N-COF is 0.5-0.6 nm.

[0064] wherein the three-dimensional COF-300 is prepared by condensation reaction of tetrakis(4- aminophenyl) methane and terephthalaldehyde; and the two-dimensional N-COF is prepared by condensation reaction of tris(4-aminophenyl)amine and 1,3,5-triformylbenzene.

[0065] Specifically, the COF-300 can be prepared by dehydration condensation reaction between the amino group of tetrakis(4-aminophenyl) methane (TAPM) and the aldehyde group of terephthalaldehyde (TPA). For example, TAPM, TPA and 1,4-dioxane are placed in a glass tube, and acetic acid aqueous solution is added for ultrasonic treatment. The glass tube containing the mixed solution is then subjected to liquid nitrogen freezing treatment, vacuum degassing treatment, and thawing treatment in sequence and repeated three times. The glass tube is then placed in liquid nitrogen for freezing, vacuum degassing, and sealed with a flame gun under static vacuum. After sealing, the glass tube is placed in warm water for thawing. The liquid nitrogen freezing treatment, vacuum degassing treatment, and thawing treatment are repeated three times. The glass tube is then incubated at 120°C for 72 hours. After the temperature drops to room temperature, the glass tube is unsealed, and the solid is removed and subjected to Soxhlet extraction with tetrahydrofuran for 50 hours. After vacuum drying at room temperature, COF-300 is obtained. The preparation process of N-COF includes the following steps: tris(4-aminophenyl)amine, 1,3,5-triformylbenzene, tetrahydrofuran, and toluene are uniformly mixed by ultrasonic treatment, and acetic acid solution is added. Subsequently, the glass tube containing the mixed solution is quickly frozen in a liquid nitrogen bath, vacuumized and sealed. After warming to room temperature in a constant temperature oven, heating is performed to 120°C. The reaction is carried out in a convection oven for 72 hours. The obtained N-COF precipitate is separated by vacuum filtration, and then subjected to solvent replacement treatment with diethyl ether for three days. Finally, the N-COF product is obtained by vacuum activation at 120°C for 8 hours.

[0066] The PIM material can be PIM-1 material which is relatively mature at present, has a pore size distribution of 0.4-0.8 nm, a free volume fraction of about 20%, and high gas permeability (CO2 flux can reach 10,000 Barrer), and excellent solution processing performance. In some embodiments, the self-microporous polymer is prepared by condensation reaction of 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spiro-bisindane monomer and tetrafluoro-p-phenylenedinitrile monomer. At present, the synthesis method of PIM-1 is low-temperature synthesis method, and equal amounts of 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spiro-bisindane (TTSBI) monomer and tetrafluoro-p-phenylenedinitrile (TFTPN) monomer are uniformly dissolved in anhydrous N,N-dimethylformamide, and the reaction is carried out at 50-60°C for 1-3 days. Since the low-temperature synthesis method has the disadvantages of long time consumption and low efficiency, in an embodiment of the present application, a high-temperature synthesis method is used to prepare PIM-1 material. Specifically, anhydrous K2CO3 is used as a reaction catalyst, and TTSBI and TFTPN are subjected to condensation reaction in dimethylacetamide solvent to prepare the required PIM-1 sample. Specifically, a certain amount of TTSBI, TFTPN and K2CO3 are sequentially added to a three-necked flask filled with nitrogen, dimethylacetamide and toluene are further added, and after stirring uniformly, the mixture is moved to an oil bath at 160°C for condensation reflux for 40 minutes. After the reaction is completed, the fluorescent yellow viscous solution is slowly poured into methanol to obtain a fluorescent yellow solid, and the initial product is obtained by suction filtration and drying in a vacuum oven at 100°C. The initial product is dissolved in chloroform, and the polymer particles are precipitated in methanol. After repeated suction filtration-purification for three times, the PIM-1 sample is finally obtained.

[0067] To further enhance the compatibility between the COF and the PIM material and effectively eliminate the interfacial defects generated in the film preparation process, a chemical cross-linking method can be used to prepare a mixed matrix film. In some embodiments, the outer separation film 302 is prepared by a method comprising the following processes: subjecting the covalent organic framework material to amidation treatment to obtain an amidated covalent organic framework material; mixing the amidated covalent organic framework material, the self-microporous polymer and chloroform to obtain an outer layer slurry; coating the outer layer slurry on a predetermined substrate, and peeling off after baking to obtain the outer separation film 302.

[0068] Specifically, taking COF-300 as an example, 2-methyl-2-butene, water-soluble sodium hypochlorite solution and glacial acetic acid are sequentially added to a 1, 4-dioxane suspension containing a COF-300 sample; the two-phase suspension is left to stand at room temperature in the dark for 24 hours, after which the sodium hypochlorite solution is supplemented; the amidated solid is collected by centrifugation or filtration, washed with water, 10% sodium thiosulfate, water and acetone in sequence, and then sequentially Soxhlet extracted with dioxane, methanol and acetone for 24 hours each, and after supercritical carbon dioxide activation treatment, vacuum dried at room temperature for 16 hours, and then vacuum dried at 120 DEG C for 2 hours, to finally obtain an amidated COF-300 sample; a certain amount of the amidated COF-300 is ultrasonically dispersed in chloroform, and then a chloroform solution of PIM-1 is slowly added in portions with stirring for 24 hours; the above mixture dispersion is spin-coated on a pre-set substrate at a rotation speed of 2000 rpm, and after soft baking in a nitrogen-filled tube furnace, the outer layer separation film 302 is peeled off.

[0069] The inner layer separation film 301 and the outer layer separation film 302 can be compounded in a room temperature ultra-high vacuum direct current radio frequency magnetron sputtering system, the chamber base pressure is kept at 10 -7 mbar, and the deposition pressure is 5x10 -3 mbar.

[0070] In the present application, the insulating substrate 1 comprises a P-type silicon wafer 101, an ONO structure layer and an insulating layer 105 which are sequentially stacked.

[0071] In the specific implementation process of the present application, a 4-inch P-type (100) silicon wafer 101 (P-type silicon wafer) with a thickness of 500 μm can be selected as the processing substrate; before processing, the P-type silicon wafer 101 is sequentially ultrasonically cleaned with acetone, isopropyl alcohol and deionized water, then dried with nitrogen, and dried in an oven at 150 DEG C for 30 minutes. Subsequently, a thermal oxidation reaction is simultaneously performed on the front and back surfaces of the P-type silicon wafer 101, a first SiO2 layer 102 is deposited on the front surface, and a silicon nitride layer 103 is further deposited on the surface of the first SiO2 layer 102 using low pressure chemical vapor deposition (LPCVD), and a second SiO2 layer 104 is further prepared on the silicon nitride layer 103 using atmospheric pressure chemical vapor deposition (APCVD), to finally form an ONO structure layer (SiO2-Si3N4-SiO2) on the P-type silicon wafer 101.

[0072] In the present application, the heating electrode 403 is arranged on the surface of the insulating substrate, the insulating layer 105 is arranged on the surface of the heating electrode 403 away from the insulating substrate, the test electrode is arranged on a first partial region of the surface of the insulating layer 105 away from the heating electrode, and the sensitive unit is arranged on a second partial region of the surface of the insulating layer 105 away from the heating electrode, wherein the insulating layer comprises Al2O3.

[0073] The heating electrode 403 comprises a titanium metal layer and a platinum metal layer which are sequentially stacked, and the platinum metal layer is located away from the surface of the insulating substrate 1. Specifically, the Ti layer can increase the adhesion of the Pt layer on the surface by using the double-layer metal electrode of the titanium metal (Ti) layer and the platinum metal (Pt) layer. The test electrode can be an electrode formed by a single platinum metal layer. The heating electrode 403 and the test electrode are alternately sputtered to achieve the stacked arrangement.

[0074] The heating electrode 403 can be a Pt electrode which is conventional in the art.

[0075] The patterning of the heating electrode 403 can adopt an inverted photolithography process, so that the photoresist is tightly bonded to the ONO substrate after spin coating, pre-baking, and then mask exposure. The non-exposed area will be dissolved in the developer, and the pattern on the photo mask is transferred to the substrate.

[0076] The sensitive unit 2 is in direct contact with the insulating layer 105, which can further inhibit the phase change of the Pd nano-alloy in the sensitive unit 2 from α to β. In the present application, the insulating layer 105 can be deposited by atomic vapor deposition or magnetron sputtering.

[0077] The test electrode and the sensitive unit 2 are both arranged on the surface of the insulating layer away from the heating electrode 403, and are arranged on the first partial area and the second partial area of the insulating layer, respectively.

[0078] In some embodiments, as shown in FIGS. 1 and 3, the test electrode comprises a first test electrode 401 and a second test electrode 402 which are arranged at intervals, the nanowire array structure in the sensitive unit 2 is arranged between the first test electrode 401 and the second test electrode 402, and the extension direction of the nanowire is from the first test electrode 401 to the second test electrode 402.

[0079] In some embodiments, a cantilever beam unit is further included; the test electrode and the heating electrode 403 are connected to different electrode plates through different cantilever beam units.

[0080] The present application can adopt a four-suspension beam, a single-suspension beam, etc. In some preferred embodiments, considering that the heat of the cantilever micro-hotplate can only be guided to the substrate through the suspended support beam, according to the heat diffusion theory equation, the number of support beams determines the number of heat conduction paths, and a single-suspension beam is preferred. The power consumption at the same working temperature can be significantly reduced, the effective thermal mass is reduced, and the thermal response speed is improved. At the same time, the single-suspension beam is more convenient for high-density integration, such as parallel comb teeth, symmetric combination, polygonal array, etc.

[0081] It should be noted that, in order to realize accurate overlay of the exposure pattern of the latter mask, the mask direction alignment bar needs to be aligned with the silicon wafer (100) direction in the first lithography, and the overlay marks used between different process layers are arranged on both sides of the center area of the wafer, and the left and right cameras of the lithography machine are used for observation and alignment during overlay. After the measurement electrode is prepared, the insulating layer 105 of the non-contact area of the device electrode needs to be etched using a CF4inductively coupled plasma (ICP) dry etching process, and the etching depth is until the bulk silicon. After the ICP windowing of the device is completed, it is loaded into a cleaning basket, and further application of tetramethylammonium hydroxide anisotropic wet etching is used to etch the bulk silicon under the thin film cantilever to realize the film-beam suspension. It should be noted that when the etching window is a square and parallel to the cutting edge of the silicon wafer, the etching structure of the (100) plane is a 4 inverted pyramid trapezoidal pyramid formed by four (111) planes at an angle of 54.74° with the surface.

[0082] In a second aspect of the present application, a preparation method of the MEMS gas sensor provided in the first aspect is provided, including the following steps: depositing a plurality of spaced nanowires on the surface of the insulating substrate 1 to form a nanowire array structure of the sensitive unit 2, and forming a recess 5 with the insulating substrate 1 between two adjacent nanowires; covering the surface of the sensitive unit 2 and the recess 5 with a selective separation film 3 to obtain the MEMS gas sensor.

[0083] In some embodiments, the block copolymer and the solvent are mixed to obtain a first slurry; the first slurry is coated on the surface of the insulating substrate 1, and after drying, laser annealing treatment is performed, and then dry etching or wet deposition is performed to form a metal nanowire array to obtain the sensitive unit 2; the block copolymer is selected from at least one of polystyrene-r-poly(methyl methacrylate) and polystyrene-b-poly(2-vinylpyridine); and / or, 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobiphenyl indane monomers, tetrafluoro-p-phenyldicarbonitrile, and K2CO3 are sequentially added to a three-necked flask filled with nitrogen, then dimethylacetamide and toluene are added, and after stirring uniformly, the mixture is transferred to an oil bath at 150-170℃ for condensation reflux for 40 minutes to obtain a fluorescent yellow viscous solution; the fluorescent yellow viscous solution is slowly poured into methanol to obtain a fluorescent yellow solid, which is filtered and dried in a vacuum oven at 90-110℃ to obtain a primary product; the primary product is dissolved in chloroform, and the polymer particles are precipitated in methanol, and after repeated filtration-purification for three times, a self-microporous polymer is obtained.

[0084] The MEMS gas sensor is used after micro-hotplate performance test, which includes resistance of the heating electrode 403, insulation between the heating electrode 403 and the measuring electrode, and resistance temperature coefficient test. Finally, different driving voltages are applied to the MEMS gas sensor, the resistance-power consumption relationship corresponding to the design scheme is obtained, the temperature is calculated by using the determined resistance temperature coefficient, the power consumption-temperature relationship is established, and the qualitative conclusion about the peak temperature in the finite element analysis simulation is verified based on the relationship.

[0085] The application is further described below by specific examples and comparative examples. Unless otherwise specified, the reagents, materials and instruments used in the following description are conventional reagents, conventional materials and conventional instruments, which are commercially available. The reagents and materials involved can also be synthesized by conventional synthesis methods.

[0086] In the following examples, the preparation process of the self-porous polymer (PIM-1) is as follows: 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spiro-bisindane monomer, tetrafluoro-p-phenylenedinitrile, K2CO3 are sequentially added to a three-necked flask filled with nitrogen, then dimethylacetamide and toluene are added, and after stirring uniformly, the mixture is transferred to a 160℃ oil bath for condensation reflux for 40 minutes to obtain a fluorescent yellow viscous solution; the fluorescent yellow viscous solution is slowly poured into methanol to obtain a fluorescent yellow solid, which is filtered and dried in a 100℃ vacuum oven to obtain a primary product; the primary product is dissolved in chloroform and precipitated in methanol to obtain polymer particles, which are repeatedly filtered and purified three times to obtain the self-porous polymer (PIM-1).

[0087] The preparation process of COF-300 is as follows: tetra(4-aminophenyl)methane (TAPM), p-phenylenediformaldehyde (TPA) and 1,4-dioxane are placed in a glass tube, acetic acid aqueous solution is added for ultrasonic treatment, liquid nitrogen freezing treatment, vacuum degassing treatment and thawing treatment are sequentially performed and repeated three times to obtain a mixed solution; wherein the glass tube containing the mixed solution is frozen in liquid nitrogen, vacuum degassed, and the glass tube is sealed by a flame gun under static vacuum, and then thawed in warm water after sealing, and the liquid nitrogen freezing treatment, vacuum degassing treatment and thawing treatment are repeated three times, and then the glass tube is incubated at 120℃ for 72 hours, and then the temperature is reduced to room temperature, the solid is taken out and extracted with tetrahydrofuran for 50 hours, and then vacuum dried at room temperature to obtain COF-300.

[0088] 2-methyl-2-butene, aqueous sodium hypochlorite solution and glacial acetic acid were added to a 1,4-dioxane suspension containing COF-300 sample successively; the two-phase suspension was left standing at room temperature in dark for 24 hours, after which the sodium hypochlorite solution was supplemented; the amidated solid was collected by centrifugation or filtration, washed with water, 10% sodium thiosulfate, water and acetone successively, then extracted with dioxane, methanol and acetone respectively for 24 hours successively, after supercritical carbon dioxide activation treatment, vacuum dried at room temperature for 16 hours, and then vacuum dried at 120℃ for 2 hours, to obtain the amidated COF-300 sample; the amidated COF-300 was ultrasonically dispersed in chloroform, then the chloroform solution of PIM-1 was added slowly in portions, and stirred for 24 hours; the above mixture dispersion was spin-coated on a preset substrate at a rotation speed of 2000 rpm, and finally peeled off after soft baking in a nitrogen-filled tube furnace, to obtain the outer separation membrane 302; wherein the mass ratio of COF-300 to PIM-1 is (10-80 mg):1 g.

[0089] The inner separation membrane 301 and the outer separation membrane 302 were compounded in a room-temperature ultra-high vacuum direct-current radio frequency magnetron sputtering system to obtain the selective separation membrane 3, the chamber base pressure was kept at 10 -7 mbar, and the deposition pressure was 5×10 -3 mbar.

[0090] Example 1

[0091] The preparation of the MEMS gas sensor of the present example includes the following steps:

[0092] (1) A 4-inch P-type (100) double-polished silicon wafer with a thickness of 500 μm was provided, which was ultrasonically cleaned with acetone, isopropyl alcohol and deionized water successively, then dried with nitrogen, and dried in an oven at 150℃ for 30 minutes, then a thermal oxidation reaction was simultaneously performed on the front and back surfaces of the silicon wafer, a first SiO2 layer 102 was formed on the front surface, a silicon nitride layer 103 was formed on the surface of the first SiO2 layer 102 by high-temperature low-pressure chemical vapor deposition (LPCVD), and a second SiO2 layer 104 was deposited on the surface of the silicon nitride layer 103, to finally form an ONO structure layer (SiO2-Si3N4-SiO2);

[0093] (2) A heating electrode 403 was deposited on the surface of the second SiO2 layer 104, an aluminum oxide insulating layer was deposited on the surface of the heating electrode 403, a nanowire array structure formed by a plurality of spaced-apart palladium-gold alloy (Au3Pd7) nanowires was deposited on the surface of the aluminum oxide insulating layer to obtain a sensitive unit 2 and a test electrode, and any two adjacent palladium-gold alloy nanowires and the insulating layer 105 formed a recess 5;

[0094] (3) depositing a selective separation film 3 on the surface of the sensitive unit 2 and the recess 5; the selective separation film 3 comprises an inner layer separation film 301 and an outer layer separation film 302 which are sequentially stacked, wherein the outer layer separation film 302 is located on the side of the inner layer separation film 301 away from the insulating substrate 1; the inner layer separation film 301 comprises polytetrafluoroethylene; and the outer layer separation film 302 is a mixed matrix membrane with covalent organic framework material as filler and self-porous polymer as matrix.

[0095] Comparative Example 1

[0096] The preparation process is basically the same as that of Example 1, except that step (3) is omitted, i.e. no selective separation film 3 is provided, and other conditions remain unchanged, to obtain the MEMS semiconductor sensor of the present example.

[0097] Comparative Example 2

[0098] The preparation process is basically the same as that of Example 1, except that in step (2): the palladium-gold alloy nanowire is replaced by a palladium nanowire, and other conditions remain unchanged, to obtain the MEMS semiconductor sensor of the present example.

[0099] Comparative Example 3

[0100] The preparation process is basically the same as that of Example 1, except that in step (2): the palladium-gold alloy nanowire is replaced by a palladium nanowire, and step (3) is omitted, i.e. no selective separation film 3 is provided, to obtain the MEMS semiconductor sensor of the present example.

[0101] Test Example

[0102] The response sensitivity, anti-interference (selectivity), and stability tests are based on an environmental probe test system, which adopts a static method, i.e., under constant temperature conditions, the resistance change of the sensitive unit on the MEMS gas sensor to a certain concentration of target gas is tested to obtain the steady-state response to the measured atmosphere. The system hardware mainly consists of six parts: an in-situ cell, a material substrate, a humidity atmosphere control module, a temperature control module, a signal processing module, and a computer terminal. The in-situ cell is the place where the gas-sensitive reaction occurs and is also the core of the entire platform. It includes an adjustable wavelength flat light source, an air flow channel, a cooling water channel, a signal switching circuit, a heating table, and is connected to a humidity-controllable gas-liquid gas mixing system (concentration control range 1 ppb-50000 ppm), which can simultaneously realize the rapid replacement / balancing of the concentration and humidity of the atmosphere in the chamber and the online detection of gas-sensitive, humidity-sensitive, and other performances. The platform is also connected to a vacuum pump group for performance testing under different air pressures. The signal switching circuit is composed of a probe, a circuit board, and a serial port connector. The signal on the material substrate is introduced to the circuit board through the probe, and then transmitted to the signal processing module through the serial port. The silver metal heating table is located below the material substrate, and the cooling water channel surrounds the test chamber to avoid damage from thermal stress during testing. The array (6x6, 12x12) material substrate is composed of a high-temperature ceramic substrate (or silicon substrate) and a micro-machined Pt interdigital electrode, which can simultaneously characterize the gas-sensitive performance of up to 144 materials. The atmosphere environment in the in-situ cell is mainly adjusted by a dynamic gas mixing method: the background gas (air or N2, Ar, and other inert gases) and the measured gas are introduced from the carrier gas path and the atmosphere path respectively, mixed, and then introduced into the in-situ cell. The type and concentration of the atmosphere are adjusted by a mass flow meter, and the total flow control range can vary in the range of 0.1-1000 sccm. The working temperature of the sensitive material is controlled by a mK2000 high-precision temperature control module, and the temperature control range is room temperature-500°C, with an accuracy of better than ±0.001°C. During the experiment, considering that the resistance change of some material films can span multiple orders of magnitude, the real-time resistance value of the material is obtained by using a matching resistance series voltage division method. After testing, the error of the system in measuring 1Ω-50GΩ resistance values is not more than 0.5%, the current range is 100pA-200mA, the voltage range is ±200mV-±20V, and the test mode can meet the volt-ampere curve Id-Vd, Id-Vg, gas-sensitive response curve I-t, R-t, etc.

[0103] The test results are shown in FIGS. 6-9, in which Au3Pd7@ separation film represents Example 1, Au3Pd7 represents Comparative Example 1, Pd@ separation film represents Comparative Example 2, and Pd represents Comparative Example 3.

[0104] According to FIGS. 5 to 8, compared with Comparative Examples 1-3, the MEMS gas sensor provided by the present application has excellent low-concentration gas monitoring sensitivity, high-concentration gas tolerance stability, and excellent anti-interference and response speed. In particular, according to FIG. 8, in the cycle test of 4 vol% hydrogen in the MEMS gas sensors in Comparative Example 2 and Comparative Example 3, 2.4% and 1.6% performance attenuation occurred, respectively, while the attenuation rates of the MEMS sensors in Example 1 and Comparative Example 1 were less than 0.6%.

[0105] FIG. 7 is a hydrogen concentration-response sensitivity curve of the MEMS gas sensors in Example 1 and Comparative Examples 1-3 under different hydrogen concentrations (0.1-8 vol%).

[0106] The above describes preferred embodiments of the present application and experimental verification in detail. It should be understood that those skilled in the art can make many modifications and changes according to the concept of the present application without creative labor. Therefore, any technical solution obtained by logical analysis, reasoning or limited experiment on the basis of the prior art according to the concept of the present application should be within the protection scope of the present application.

Claims

1. A MEMS gas sensor, characterized by, The test unit comprises a test electrode, a sensitive unit and a selective separation membrane. The test electrode and the sensitive unit are respectively arranged on the surface of the insulating layer away from the heating electrode. The sensitive unit has a nanowire array structure formed by a plurality of spaced nanowires, and any two adjacent nanowires form a recess with the insulating layer. The selective separation membrane covers the surface of the sensitive unit and the recess. The nanowire comprises a first metal and a second metal, the first metal is Pd, and the second metal is selected from at least one of Ni, Cu, Ag, Au and Ir. The selective separation membrane comprises an inner separation membrane and an outer separation membrane which are sequentially stacked, and the outer separation membrane is located away from the inner separation membrane. The inner separation membrane comprises polytetrafluoroethylene; and the outer separation membrane is a mixed matrix membrane with covalent organic framework material as filler and self-microporous polymer as matrix. The molar ratio of the first metal to the second metal is 1:(0.1-0.5); and / or 2. The MEMS gas sensor of claim 1, wherein, The mass ratio of the covalent organic framework material to the self-microporous polymer is (10-80 mg):1 g. The hydrogen permeability of the covalent organic framework material is >4000 GPU, and the pore size is 0.5-0.8 nm; and / or 3. The MEMS gas sensor of claim 2, wherein, The covalent organic framework material is selected from at least one of three-dimensional COF-300 and two-dimensional N-COF. The three-dimensional COF-300 is prepared by condensation reaction of tetrakis(4-aminophenyl)methane and terephthaldehyde; and the two-dimensional N-COF is prepared by condensation reaction of tris(4-aminophenyl)amine and 1,3,5-triformylbenzene. The self-microporous polymer is prepared by condensation reaction of 5,5',6,6'-tetrahydroxy-3,3,3',3'-tetramethyl-1,1'-spirobifluorene monomer and tetrafluoro-p-xylylene dinitrile monomer. The outer separation membrane is prepared by a method comprising the following steps:

4. The MEMS gas sensor of claim 1, wherein, The covalent organic framework material is subjected to amidation treatment to obtain an amidated covalent organic framework material; The amidated covalent organic framework material, the self-microporous polymer and chloroform are mixed to obtain an outer layer slurry; the outer layer slurry is coated on a pre-set substrate, and after baking, the outer layer separation membrane is obtained by peeling off. The test electrode is arranged on a first partial region of the surface of the insulating layer away from the heating electrode, and the sensitive unit is arranged on a second partial region of the surface of the insulating layer away from the heating electrode.

5. The MEMS gas sensor of claim 1, wherein, The insulating layer comprises Al2O3. The test electrode comprises a first test electrode and a second test electrode which are spaced apart, 6. The MEMS gas sensor of claim 5, wherein, The nanowire array structure in the sensitive unit is arranged between the first test electrode and the second test electrode, and the extension direction of the nanowire is from the first test electrode to the second test electrode. The heating electrode comprises a titanium metal layer and a platinum metal layer which are sequentially stacked, and the platinum metal layer is located away from the surface of the titanium metal layer.

7. The MEMS gas sensor of claim 6, wherein, It also comprises a cantilever beam unit.

8. The MEMS gas sensor of claim 6, wherein, The test electrode and the heating electrode are connected to different electrode plates through different cantilever beam units. The method comprises the following steps:

9. A method of manufacturing a MEMS gas sensor according to any one of claims 1 to 8, characterized in that, ​ A heating electrode is arranged on a surface of an insulating substrate; an insulating layer is deposited on a surface of the heating electrode away from the surface of the insulating substrate, and a test electrode and a sensitive unit are respectively deposited on a surface of the insulating layer away from the heating electrode; The sensitive unit is formed by a plurality of spaced nanowires to form a nanowire array structure, and two adjacent nanowires form a recess with the insulating layer. A selective separation film is coated on surfaces of the sensitive unit and the recess to obtain a MEMS gas sensor.

10. The method of claim 9, wherein, The block copolymer and a solvent are mixed to obtain a first slurry; the first slurry is coated on a surface of the insulating layer, dried, and then subjected to laser annealing treatment, and then a first metal and a second metal are deposited by dry etching or wet deposition to form a metal nanowire array to obtain the sensitive unit. The block copolymer is at least one selected from polystyrene-r-poly(methyl methacrylate) and polystyrene-b-poly(2-vinylpyridine).

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