A multi-layer micro gas sensor and its preparation method

Abstract

The present invention provides a multi-level micro gas sensor, comprising a substrate, a bottom insulating layer and at least two gas-sensitive unit layers arranged in sequence from bottom to top, a heating-temperature measuring electrode is arranged between the bottom insulating layer and the substrate, and each gas-sensitive unit layer is tightly fitted; each gas-sensitive unit layer comprises a porous insulating layer and a gas-sensitive film arranged in sequence from bottom to top, and a measuring electrode is arranged between the porous insulating layer and the gas-sensitive film; wherein the cross-sectional area of ​​the porous insulating layer is respectively larger than the coverage area of ​​the measuring electrode and the coverage area of ​​the gas-sensitive film, and the gas-sensitive film completely covers the measuring electrode. The present invention makes full use of the reaction differences of different gas molecules on the gas-sensitive film of the multi-level structure to enhance the selectivity of gas detection; the signal separation capability is enhanced by utilizing the additional information provided by the time difference of the gas diffusion process, and the multi-gas component separation detection capability can be effectively improved after being combined with the time series dynamic signal processing algorithm.

Description

Technical Field

[0001] The invention relates to a gas sensor, in particular to a multi-layer micro gas sensor and a preparation method thereof, belonging to the technical field of sensors. Background Art

[0002] In recent years, the application demand for gas detection has continued to develop, from industrial manufacturing and chemical process control to agriculture and nature conservation, and even to personal health monitoring, smart cities and national defense, and has continued to extend to the direction of accurately identifying gas types and detecting trace analytes.

[0003] Gas sensors are very suitable for applications such as atmospheric environment monitoring, indoor air quality monitoring, and industrial fields due to their fast response, easy operation, safety, portability, and economy. Therefore, research related to gas sensing mainly focuses on optimizing the sensing parameters related to the above indicators. Since gas sensors are susceptible to cross-interference, when used in complex scenarios where multiple gases are mixed, multiple sensors are usually required to form an array. At the same time, modern applications also need to cope with the potential application needs of portability and the Internet of Things, and compress the size of the equipment, which puts higher requirements on the material consumption and processing costs of the manufacturing process. In the prior art, multiple gas sensors usually adopt traditional flat arrays, which have a large device size and are not satisfactory in terms of multi-gas separation and selective identification. Summary of the invention

[0004] Based on the above background, the object of the present invention is to provide a micro gas sensor with a multi-level structure to enhance the selectivity of gas detection and the signal separation capability, and to reduce the device volume of the sensor.

[0005] Another object of the present invention is to provide a method for preparing a multi-layered micro gas sensor, which uses 3D printing for additive manufacturing to make the various gas-sensitive unit layers of the micro gas sensor fit closely together, thereby reducing the device volume of the sensor.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] A multi-level micro gas sensor comprises a substrate, a bottom insulating layer and at least two gas-sensitive unit layers arranged in sequence from bottom to top, a heating-temperature measuring electrode is arranged between the bottom insulating layer and the substrate, and each of the gas-sensitive unit layers is tightly fitted; each of the gas-sensitive unit layers comprises a porous insulating layer and a gas-sensitive film arranged in sequence from bottom to top, a measuring electrode is arranged between the porous insulating layer and the gas-sensitive film; wherein the cross-sectional area of ​​the porous insulating layer is respectively larger than the coverage area of ​​the measuring electrode and the coverage area of ​​the gas-sensitive film, and the gas-sensitive film completely covers the measuring electrode.

[0008] The multi-level micro gas sensor utilizes the differences in diffusion and response of different gas molecules on the gas-sensitive membrane of each gas-sensitive unit layer to enhance the selectivity of gas detection and the signal separation capability. The porous insulating layer in each gas-sensitive unit layer is made of active alumina or pseudo-boehmite material, so that the gas enters the gas-sensitive unit layer below from the upper gas-sensitive unit layer in a natural diffusion manner along different directions between adjacent gas-sensitive unit layers. Since the gas-sensitive unit layers are tightly fitted without leaving any gaps, the outgoing gas of the upper gas-sensitive unit layer is the incoming gas of the lower gas-sensitive unit layer, so that the signal response of different gas-sensitive unit layers still conforms to the response model of a single-layer gas-sensitive membrane, and its response curve can still reflect the time constant representing the gas characteristics.

[0009] Preferably, the projection position of the gas-sensitive film of each gas-sensitive unit layer on the substrate coincides with the projection position of the gas-sensitive film of an adjacent gas-sensitive unit layer on the substrate.

[0010] Preferably, the material of the gas-sensitive film of each gas-sensitive unit layer is metal oxide semiconductor, carbon nanotube, graphene or high molecular conductive polymer.

[0011] Preferably, at least one of the bottom of the bottom insulating layer and the top of the substrate is provided with a protrusion, and the protrusion allows a gap to be formed between the bottom insulating layer and the substrate.

[0012] A method for preparing a multi-layer micro gas sensor, the method comprising the following steps:

[0013] S1. Prepare the finished substrate and the finished bottom insulating layer;

[0014] S2. preparing gas-sensitive material ink, electrode material ink, and insulating material ink for 3D printing, wherein the gas-sensitive material ink is prepared by washing a plurality of gas-sensitive material powders with an organic solvent and then dispersing and mixing them in a binder;

[0015] S3. Using a 3D printing method, a heating-temperature measuring electrode is printed on the bottom surface of the bottom insulating layer using electrode material ink;

[0016] S4. Using a 3D printing method, first use an insulating material ink to print a porous insulating layer on the top surface of the bottom insulating layer product, then use an electrode material ink to print a measuring electrode, and finally use a gas sensitive material ink to print a gas sensitive film to obtain a gas sensitive unit layer;

[0017] S5. Printing a porous insulating layer, a measuring electrode and a gas-sensitive film layer by layer on the surface of the gas-sensitive layer on top of the previous gas-sensitive unit layer to obtain another gas-sensitive unit layer;

[0018] S6. Repeat step S5 according to the set number of gas-sensing unit layers until the number of gas-sensing unit layers obtained meets the set requirements.

[0019] The preparation method of the multi-layer micro gas sensor adopts a 3D printing method to construct a longitudinal array of gas-sensitive unit layers in a layer-by-layer printing manner, so that each gas-sensitive unit layer is closely fitted to each other, thereby reducing the device volume of the sensor.

[0020] Preferably, in step S2, the particle size of the gas-sensitive material powder is less than 100 nm.

[0021] Preferably, in step S2, the organic solvent is ethanol, ethylene glycol, N,N-dimethylformamide, tetrahydrofuran or 2-hexylthiophene.

[0022] Preferably, in step S4 and step S5, after the gas-sensitive unit layer is prepared, it is dried and calcined.

[0023] Preferably, in step S4 and step S5, the thickness of the gas-sensitive film is controlled by the 3D printing speed and the number of printing repetitions, and the thickness of the gas-sensitive film is 1 to 5 μm. In step S3, step S4 and step S5, the thickness of the heating-temperature measuring electrode and the measuring electrode are both 160 to 240 nm.

[0024] Preferably, the 3D printing method is inkjet printing, aerosol jet printing or electrohydrodynamic printing.

[0025] Compared with the prior art, the present invention has the following advantages:

[0026] A multi-layered micro gas sensor of the present invention makes full use of the reaction differences of different gas molecules on the gas-sensitive film of the multi-layered structure to enhance the selectivity of gas detection; the present invention utilizes the additional information provided by the time difference of the gas diffusion process to enhance the signal separation capability, and can effectively improve the multi-gas component separation and detection capability after being combined with the time series dynamic signal processing algorithm. The present invention constructs a tightly fitted longitudinal array of gas-sensitive unit layers, utilizes tiny sensitive areas to provide multi-dimensional data, and reduces the device volume of the sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the provided drawings without paying creative work.

[0028] Figure 1 It is a schematic diagram of the explosion structure of a multi-layer micro gas sensor of the present invention;

[0029] Figure 2The present invention is a schematic flow chart of a method for preparing a multi-layer micro gas sensor.

[0030] In the figure: 1, substrate; 2, heating-temperature measuring electrode; 3, bottom insulating layer; 4, gas-sensitive unit layer; 401, porous insulating layer; 402, measuring electrode; 403, gas-sensitive film. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is further described in detail below through specific embodiments and in conjunction with the accompanying drawings. It should be understood that the implementation of the present invention is not limited to the following embodiments, and any form of modification and / or change made to the present invention will fall within the protection scope of the present invention.

[0032] In the present invention, unless otherwise specified, all parts and percentages are weight units, and the equipment and raw materials used can be purchased from the market or are commonly used in the art. The methods in the following embodiments, unless otherwise specified, are conventional methods in the art. The components or equipment in the following embodiments, unless otherwise specified, are universal standard parts or components known to those skilled in the art, and their structures and principles are known to those skilled in the art through technical manuals or conventional experimental methods.

[0033] The embodiments of the present invention are described in detail below in conjunction with the accompanying drawings. In the following detailed description, for ease of explanation, many specific details are set forth to provide a comprehensive understanding of the embodiments of the present invention. However, one or more embodiments may also be implemented by those skilled in the art without these specific details.

[0034] like Figure 1 As shown, an embodiment of the present invention discloses a multi-level micro gas sensor, comprising a substrate 1, a bottom insulating layer 3 and at least two gas-sensitive unit layers 4 arranged in sequence from bottom to top. A heating-temperature measuring electrode 2 is provided between the bottom insulating layer 3 and the substrate 1, and each gas-sensitive unit layer 4 is tightly fitted. Each gas-sensitive unit layer 4 comprises a porous insulating layer 401 and a gas-sensitive film 403 arranged in sequence from bottom to top, and a measuring electrode 402 is provided between the porous insulating layer 401 and the gas-sensitive film 403. Among them, the cross-sectional area of ​​the porous insulating layer 401 is respectively larger than the coverage area of ​​the measuring electrode 402 and the coverage area of ​​the gas-sensitive film 403, and the gas-sensitive film 403 completely covers the measuring electrode 402. The projection position of the gas-sensitive film 403 of each gas-sensitive unit layer 4 on the substrate 1 coincides with the projection position of the gas-sensitive film 403 of the adjacent gas-sensitive unit layer 4 on the substrate 1.

[0035] Specifically, the thickness of the substrate 1 is 0.01-0.5 mm, and the substrate 1 is made of silicon. Of course, other materials that can replace silicon can also be selected to make the substrate 1 according to the actual application needs. The heating-temperature measuring electrode 2 is attached to the bottom surface of the bottom insulating layer 3. The heating-temperature measuring electrode 2 is made of metals such as platinum, gold, and silver. The two ends of the electrode of the heating-temperature measuring electrode 2 are electrically connected to the edge pins, and the edge pins are used to introduce an external 0-5V voltage power supply to enable the heating-temperature measuring electrode 2 to achieve the heating function. The material of the porous insulating layer 401 of each gas-sensitive unit layer 4 is active alumina or pseudo-boehmite. The material of the gas-sensitive film 403 of each gas-sensitive unit layer 4 is a metal oxide semiconductor, carbon nanotubes, graphene or a high molecular conductive polymer. Among them, the metal oxide semiconductor is In2O3, WO3, ZnO, SnO2, TiO2, NiO, Fe2O3, CuO and their composite materials, and can be doped or loaded with metals such as Au, Pt, Pd, Ce, and Rb to improve the sensing performance. The measuring electrode 402 of each gas-sensing unit layer 4 is in an interdigitated structure, and both ends of the measuring electrode 402 are respectively connected to edge pins, so that the electrical signal of each gas-sensing unit layer 4 can be independently transmitted to an external device.

[0036] The bottom of the bottom insulating layer 3 and the top of the substrate 1 are both provided with protrusions, which provide a gap between the bottom insulating layer 3 and the substrate 1, thereby increasing thermal insulation from the surroundings. Of course, the protrusions can also be provided on either the bottom of the bottom insulating layer 3 or the top of the substrate 1.

[0037] When the micro gas sensor with the multi-level structure is working, the airflow can enter and exit in any direction parallel to the plane of the gas-sensitive film 403, thereby ensuring that the initial concentration of the gas in contact with the top gas-sensitive unit layer 4 remains unchanged. Since the reducing gas in the airflow will react with the gas-sensitive film 403 to a certain extent when it contacts the gas-sensitive film 403, the gas concentration C0 will decrease, that is, the gas concentration exposed on the surface of the gas-sensitive film 403 may actually be C0-C', not C0. The parallel air intake method of the micro gas sensor with the multi-level structure is equivalent to continuously replenishing the gas, so that the gas-sensitive film 403 is continuously exposed to the preset gas concentration C0.

[0038] The multi-level micro gas sensor utilizes the difference in diffusion and response of different gas molecules on the gas-sensitive film 403 of each gas-sensitive unit layer 4 to enhance the selectivity of gas detection and signal separation capability. The porous insulating layer 401 in each gas-sensitive unit layer 4 allows the gas to enter the gas-sensitive unit layer 4 located below from the gas-sensitive unit layer 4 located above in a natural diffusion manner, along different directions, and between adjacent gas-sensitive unit layers 4. Since the gas-sensitive unit layers 4 are tightly fitted without leaving gaps, the outflow of the upper gas-sensitive unit layer 4 is the inflow of the lower gas-sensitive unit layer 4, so that the signal response of different gas-sensitive unit layers 4 still conforms to the response model of the single-layer gas-sensitive film 403, and its response curve can still reflect the time constant representing the characteristics of the gas. Therefore, the response model of the single-layer gas-sensitive film 403 can still be used to distinguish gases by using the characteristics of the response curve of the single-layer gas-sensitive film 403 to gases. The response model of the single-layer gas-sensitive film 403 is described as follows.

[0039] The prepared gas-sensitive film 403 has a porous structure and a large specific surface area and pore size for free diffusion of air molecules and gas molecules. Therefore, the adsorption and desorption of oxygen anions basically occur on the surface of the pores. The sensing function of the internal grains and the sensing function between the grains are mainly determined by the reaction on the pore wall surface during the diffusion process in the pores. Usually, the rate of the surface chemical reaction process is much greater than the diffusion rate of the gas in the pores. Therefore, the dynamic process is described by the diffusion-adsorption equation of the gas in the gas-sensitive film:

[0040]

[0041] where C(x,t) is the gas concentration at point x at time t; D is the diffusion coefficient; γ is the Freundlich adsorption exponent (0<γ<1), and k is a reaction constant that is positively correlated with the surface adsorption coefficient, material density and specific surface area and negatively correlated with the porosity.

[0042] The diffusion-adsorption equation is dimensionlessly analyzed, and based on the fact that the equation's solution conditions are independent of the physicochemical properties, structure, and gas concentration of the test object, the relationship between the response time and recovery time of the Ct curve of the sensing material is established (taking γ = 1 as an example):

[0043]

[0044] Where l is the thickness of the gas-sensitive film, C0 is the initial concentration, and T0 is the dimensionless time under the γ=1 state.

[0045] Since concentration is a variable that is difficult to observe, we further establish the relationship between conductivity and time. p , the density ρ and the electron generation rate δ can represent the concentration of adsorbed gas molecules per unit volume and the number of conductive electrons generated (released) by the reaction per unit volume, describing the observed quantity conductivity:

[0046]

[0047] Where L is the sample length and W is the sample width. Furthermore, the conductivity response process of the inlet and outlet processes can be described by known variables, which are:

[0048]

[0049]

[0050] in:

[0051]

[0052]

[0053]

[0054] It can be seen that the conductivity response time τ we actually measured s and recovery time τ c :

[0055] τ s =τ c ,

[0056]

[0057] The diffusion coefficient D, reaction coefficient k and adsorption index γ of different gas-materials are different, but have certain repeatability. Therefore, the reaction constant obtained by the combined influence of these intrinsic factors also has the essential characteristics of the gas, so that the gas can be distinguished by using the characteristics of the response curve of the single-layer gas-sensitive film 403 to the gas.

[0058] like Figure 2 As shown, an embodiment of the present invention further discloses a method for preparing the multi-layer micro gas sensor, the method comprising the following steps:

[0059] S1. Prepare the finished substrate 1 and the finished bottom insulating layer 3;

[0060] S2. preparing gas-sensitive material ink, electrode material ink, and insulating material ink for 3D printing, wherein the gas-sensitive material ink is prepared by washing a plurality of gas-sensitive material powders with an organic solvent and then dispersing and mixing them in a binder;

[0061] S3. Using a 3D printing method, the electrode material ink is used to print the heating - temperature measuring electrode 2 on the bottom surface of the bottom insulating layer 3 of the finished product;

[0062] S4. Using a 3D printing method, a porous insulating layer 401 is first printed on the top surface of the bottom insulating layer 3 using an insulating material ink, and then a measuring electrode 402 is printed using an electrode material ink, and finally a gas-sensitive film 403 is printed using a gas-sensitive material ink to obtain a gas-sensitive unit layer 4;

[0063] S5. Printing a porous insulating layer 401, a measuring electrode 402 and a gas-sensitive film 403 layer by layer on the surface of the gas-sensitive layer on top of the previous gas-sensitive unit layer 4, to obtain another gas-sensitive unit layer 4;

[0064] S6. Repeat step S5 according to the set number of gas-sensing unit layers 4 until the number of gas-sensing unit layers 4 produced meets the set requirements.

[0065] The preparation method of the multi-layer micro gas sensor adopts a 3D printing method to construct a longitudinal array of gas-sensitive unit layers 4 by printing layer by layer, so that each gas-sensitive unit layer 4 fits tightly together, thereby reducing the device volume of the sensor.

[0066] Wherein, the particle size of the gas-sensitive material powder in step S2 is less than 100nm. The organic solvent in step S2 is ethanol, ethylene glycol, N,N-dimethylformamide, tetrahydrofuran or 2-hexylthiophene. In step S4 and step S5, after the gas-sensitive unit layer 4 is obtained, it is dried and calcined to enhance the structural stability. In step S4 and step S5, the thickness of the gas-sensitive film 403 is controlled by the 3D printing speed and the number of printing repetitions. The thickness of the gas-sensitive film 403 is 1 to 5μm. In step S3, step S4 and step S5, the thickness of the heating-temperature measuring electrode 2 and the measuring electrode 402 are both 160 to 240nm. The 3D printing method is inkjet printing, aerosol jet printing or electrohydrodynamic printing.

[0067] A specific example of the preparation method is as follows.

[0068] Prepare materials and equipment, including dimethylformamide (DMF), indium nitrate (In(NO)3), polystyrene microspheres (PS), zinc cobaltate (ZnCoO4), palladium nitrate (Pd(NO3)2), methanol (CH3OH), pseudoboehmite (Al2O3), phthalic acid (C8H6O4), 2-methylimidazole (C4H6N2), deionized water and surfactant.

[0069] Prepare the finished substrate 1 and the finished bottom insulating layer 3.

[0070] The first gas-sensitive material ink for 3D printing was prepared by dissolving nitric acid crystals in deionized water, stirring continuously at a certain temperature, completely dissolving indium nitrate in a mixture of dimethylformamide and phthalic acid, stirring continuously at 100°C until completely dissolved, centrifuging the mixed solution with a centrifuge, collecting the precipitate, dispersing it with ultrasound, mixing it in an adhesive, and adding it to a dispensing module of a 3D inkjet printer.

[0071] A second gas-sensitive material ink for 3D printing was prepared, PS microspheres were dispersed in methanol, zinc cobaltate was dissolved in the mixture, 2-methylimidazole was added to mix, the mixture was precipitated at room temperature, the precipitate was purified and dried using a centrifuge, palladium nitrate was then impregnated into the mixture using an impregnation method, a binder was added to the dried powder, and the powder was added to a dispensing module of a 3D inkjet printer.

[0072] Electrode material ink for 3D printing was prepared by treating nanosilver with PVP and dissolving it in 2-hexylthiophene, and then adding it to the dispensing module of the 3D inkjet printer.

[0073] Insulating material ink for 3D printing is prepared by dispersing pseudo-boehmite powder in a binder, mixing the mixture to prepare ink, and adding the ink to a dispensing module of a 3D inkjet printer.

[0074] A heating-temperature measuring electrode 2 is printed on the bottom surface of the bottom insulating layer 3 finished product using electrode material ink using a 3D inkjet printer.

[0075] Use a 3D inkjet printer to first print the porous insulating layer 401 on the top surface of the finished bottom insulating layer 3 with insulating material ink, dry it naturally, then use electrode material ink to print the measuring electrode 402, dry and calcine it, and finally use the first gas-sensitive material ink to print the gas-sensitive membrane 403, dry it at 60°C in a forced air drying oven and calcine it to obtain the first gas-sensitive unit layer 4.

[0076] A 3D inkjet printer is used to print a porous insulating layer 401 on the surface of the first gas-sensitive membrane 403 using insulating material ink, which is naturally dried. Then, the measuring electrode 402 is printed using electrode material ink, dried and calcined. Finally, the gas-sensitive membrane 403 is printed using a second gas-sensitive material ink to obtain a second gas-sensitive unit layer 4, thus completing the 3D printing production of the micro gas sensor.

[0077] The micro gas sensor was placed in a muffle furnace and calcined at 450°C for two hours to remove organic matter.

[0078] For ventilation test, place the micro gas sensor into the test system, introduce acetone and ethanol, heat it to a certain temperature, and then record the output data.

[0079] Data output and result analysis: by training, the response pattern of the signal to a specific gas is acquired, and a response pattern recognition database is established, thereby realizing the recognition of the mixed gas.

[0080] The principles and implementation methods of the present invention are described in this article using specific examples. The description of the above embodiments is only used to help understand the method and core ideas of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the scope of protection of the claims of the present invention.

Claims

1. A multi-layer micro gas sensor, characterized in that: The multi-level micro gas sensor comprises a substrate (1), a bottom insulating layer (3) and at least two gas-sensitive unit layers (4) arranged in sequence from bottom to top, a heating-temperature measuring electrode (2) is arranged between the bottom insulating layer (3) and the substrate (1), and each of the gas-sensitive unit layers (4) is tightly fitted to each other; each of the gas-sensitive unit layers (4) comprises a porous insulating layer (401) and a gas-sensitive film (403) arranged in sequence from bottom to top, a measuring electrode (402) is arranged between the porous insulating layer (401) and the gas-sensitive film (403); wherein the cross-sectional area of ​​the porous insulating layer (401) is respectively greater than the coverage area of ​​the measuring electrode (402) and the coverage area of ​​the gas-sensitive film (403). The gas-sensitive film (403) completely covers the measuring electrode (402); the material of the gas-sensitive film (403) of each gas-sensitive unit layer (4) is a metal oxide semiconductor, a carbon nanotube, graphene or a high molecular conductive polymer; the projection position of the gas-sensitive film (403) of each gas-sensitive unit layer (4) on the substrate (1) overlaps with the projection position of the gas-sensitive film (403) of an adjacent gas-sensitive unit layer (4) on the substrate (1); and the porous insulating layer (401) in each gas-sensitive unit layer (4) allows the gas to enter the gas-sensitive unit layer (4) located below from the gas-sensitive unit layer (4) located above in a natural diffusion manner along different directions between adjacent gas-sensitive unit layers (4).

2. A multi-layer micro gas sensor according to claim 1, characterized in that: At least one of the bottom of the bottom insulating layer (3) and the top of the substrate (1) is provided with a protrusion, and the protrusion creates a gap between the bottom insulating layer (3) and the substrate (1).

3. A method for preparing a multi-layer micro gas sensor according to any one of claims 1 to 2, characterized in that: The method comprises the following steps: S1. Prepare the substrate (1) finished product and the bottom insulating layer (3) finished product; S2. preparing gas-sensitive material ink, electrode material ink, and insulating material ink for 3D printing, wherein the gas-sensitive material ink is prepared by washing a plurality of gas-sensitive material powders with an organic solvent and then dispersing and mixing them in a binder; S3. Using a 3D printing method, a heating-temperature measuring electrode (2) is printed on the bottom surface of the bottom insulating layer (3) using an electrode material ink; S4. Using a 3D printing method, first use an insulating material ink to print a porous insulating layer (401) on the top surface of the finished bottom insulating layer (3), then use an electrode material ink to print a measuring electrode (402), and finally use a gas sensitive material ink to print a gas sensitive film (403), to obtain a gas sensitive unit layer (4); S5. Printing a porous insulating layer (401), a measuring electrode (402) and a gas-sensitive film (403) layer by layer on the surface of the gas-sensitive layer on top of the previous gas-sensitive unit layer (4) to obtain another gas-sensitive unit layer (4); S6. Repeat step S5 according to the set number of gas-sensing unit layers (4) until the number of gas-sensing unit layers (4) produced meets the set requirements.

4. The method for preparing a multi-layer micro gas sensor according to claim 3, characterized in that: In the step S2, the particle size of the gas-sensitive material powder is less than 100 nm.

5. The method for preparing a multi-layer micro gas sensor according to claim 3, characterized in that: In the step S2, the organic solvent is ethanol, ethylene glycol, N,N-dimethylformamide, tetrahydrofuran or 2-hexylthiophene.

6. The method for preparing a multi-layer micro gas sensor according to claim 3, characterized in that: In the steps S4 and S5, after the gas sensing unit layer (4) is prepared, it is dried and calcined.

7. The method for preparing a multi-layer micro gas sensor according to claim 3, characterized in that: In the steps S4 and S5, the thickness of the gas-sensitive film (403) is controlled by the 3D printing speed and the number of printing repetitions, and the thickness of the gas-sensitive film (403) is 1 to 5 μm. In the steps S3, S4 and S5, the thickness of the heating-temperature measuring electrode (2) and the measuring electrode (402) are both 160 to 240 nm.

8. The method for preparing a multi-layer micro gas sensor according to claim 3, characterized in that: The 3D printing method is inkjet printing, aerosol jet printing or electrohydrodynamic printing.

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