High-stability MEMS hydrogen sensor and preparation method thereof

Abstract

The invention discloses a high-stability MEMS hydrogen sensor and a preparation method thereof. The high-stability MEMS hydrogen sensor is a semiconductor resistance type hydrogen sensor based on a metal oxide gas sensitive coating and sequentially comprises a silicon nitride supporting layer, a Pt / Ti heating electrode, a sensing electrode, a silicon nitride isolating layer and a metal oxide gas sensitive film from bottom to top. The metal oxides are high-purity antimony doped tin dioxide, tetraamino palladium nitrate and tetraammineplatinum nitrate. The preparation method comprises the following steps: mixing high-purity antimony-doped tin dioxide powder, tetraamino palladium nitrate powder and tetraammineplatinum nitrate powder, preparing gas-sensitive slurry from a mixed solution of terpilenol, diethylene glycol butyl ether acetate, ethyl cellulose, dibutyl phthalate and dioctyl phthalate, dispensing the gas-sensitive slurry on a central interdigital electrode area of an MEMS chip, and performing vacuum drying to obtain the gas-sensitive MEMS chip. And performing vacuum standing and slow heating to obtain the sensor. The sensor is low in detection lower limit and stable in resolution ratio after high-humidity aging.

Description

Technical Field

[0001] The present invention belongs to the technical field of sensing measurement, and relates to a sensor applied to thermal runaway safety warning of electrochemical energy storage devices, hydrogen leakage monitoring in the hydrogen energy industry, and gas leakage monitoring, specifically to a highly stable MEMS hydrogen sensor and a preparation method thereof. Background Art

[0002] Clean energy sources such as lithium-ion batteries, hydrogen fuel cells, and natural gas play an increasingly important role in energy transformation and industrial applications. However, lithium-ion batteries are prone to heat accumulation and release of flammable and dangerous gases due to uncontrollable factors, and are extremely likely to induce "thermal runaway" behaviors such as fire and explosion in the battery system accompanied by a rapid rise in temperature. Hydrogen, natural gas, etc. are colorless, odorless, flammable, and explosive, increasing the risk of explosion or fire accidents. Therefore, efficient risk warning is a prerequisite for the healthy and sustainable development of clean energy sources such as lithium-ion batteries, hydrogen fuel cells, and gas.

[0003] Currently, there are mainly three types of hydrogen sensors on the market: electrochemistry type, catalytic combustion type, and semiconductor resistance type. Among them, the electrochemistry type sensor has the advantages of fast reaction speed and linear output, but has a short lifespan and its long-term performance is easily affected by sensor aging. The catalytic combustion type sensor has no vulnerable parts and a relatively simple structure, so it has good stability, but is easily poisoned under the influence of sulfides and halogen compounds in the environment. The semiconductor resistance type sensor has great application potential in the field of hydrogen detection due to its high sensitivity, low power consumption, real-time monitoring, small size, easy integration, and low cost.

[0004] Prior art 1 (CN117761130A) proposes a hydrogen gas sensor based on a Pt-modified WO3 composite thin film material, which consists of an Al2O3 insulating ceramic sheet with a sensitive thin film and electrodes on the outer surface and a resistance wire heater and a thermocouple inside. When the humidity rises from 40% humidity to 90%, its gas sensing performance decays by 25%. Prior art 2 (CN117929488B) uses a PDMS solution to perform hydrophobic treatment on the sensitive material, and constructs a superhydrophobic structure by hydrophobic treatment of the Pd-WO3 / WS2 gas-sensitive composite material. The detection range of hydrogen is 100 - 1000 ppm, and the humidity conditions for gas sensing performance detection are 40% - 80%.

[0005] In summary, in the prior art, semiconductor resistance type gas sensors usually use metal oxides as the core gas-sensitive materials, and their detection performance is easily affected by environmental humidity. Especially for MEMS semiconductor resistance type gas sensors integrated with micro heaters, due to the suspended thin film structure of the micro heaters, there are generally problems such as low consistency and poor stability. Summary of the Invention

[0006] In view of the deficiencies of the prior art, the present invention proposes a high-stability MEMS hydrogen sensor and its preparation method. Based on the MEMS microhotplate, a hydrogen sensor with high stability under different environmental humidities is developed, which is applicable to various application scenarios such as thermal runaway safety warning of electrochemical energy storage devices, hydrogen leakage monitoring in the hydrogen energy industry, and gas leakage monitoring.

[0007] A high-stability MEMS hydrogen sensor, which is a semiconductor resistance type hydrogen sensor based on a metal oxide gas-sensitive coating, includes a silicon nitride support layer, a Pt / Ti heating electrode and a sensing electrode, a silicon nitride isolation layer, and a metal oxide gas-sensitive thin film from bottom to top. The metal oxides are high-purity antimony-doped tin dioxide (Sb-SnO2), palladium nitrate tetraamine, and platinum nitrate tetraamine.

[0008] The preparation method of the metal oxide gas-sensitive thin film specifically includes the following steps: Step 1, prepare the metal oxide gas-sensitive functional powder Mix high-purity antimony-doped tin dioxide composite oxide (Sb-SnO2) with a diameter of 200 nm to 1 µm, palladium nitrate tetraamine, and platinum nitrate tetraamine powders in a mass ratio of (10 to 20):(0.4 to 0.8):(0.4 to 0.8), grind, dry, and perform heat treatment to obtain the gas-sensitive functional powder.

[0009] Preferably, the doping concentration of antimony in the high-purity antimony-doped tin dioxide composite oxide is 0.5% to 5%.

[0010] Preferably, zirconia ball milling beads with a diameter of 1 to 3 mm and anhydrous ethanol are added to the mixed powder, and grinding is performed by a planetary ball mill. Set the rotation speed of the planetary ball mill to 400 to 800 rpm and the grinding time to 4 to 8 h.

[0011] Preferably, the dried powder is heat-treated in air at 450 to 650 °C for 2 to 4 h.

[0012] Step 2, prepare a special organic solvent for the gas-sensitive slurry Mix terpineol, diethylene glycol butyl ether acetate, ethyl cellulose, dibutyl phthalate, and dioctyl phthalate in a mass ratio of (10 to 40):(5 to 15):(0.5 to 4.5):(0.2 to 0.8):(0.4 to 1.6), and stir to obtain a special organic solvent for the gas-sensitive slurry. Among them, the mass ratio of dibutyl phthalate to dioctyl phthalate is 1:2.

[0013] Preferably, a magnetic stirrer is used to stir the mixed solution, set the stirring time to 2 to 10 h, and the rotation speed to 400 to 800 rpm.

[0014] Preferably, ethylene glycol, diethylene glycol butyl ether acetate, ethyl cellulose, dibutyl phthalate, and dioctyl phthalate with a mass ratio of (10~40):(5~15):(0.5~4.5):(0.2~0.8):(0.4~1.6) are mixed and stirred.

[0015] Step 3: Prepare the gas-sensitive slurry The gas-sensitive functional powder in Step 1, the special organic solvent for the gas-sensitive slurry in Step 2, and triethanolamine are mixed in a mass ratio of (800~2000):(100~300):(5~50), and ground to obtain the gas-sensitive slurry.

[0016] Preferably, the mixture of the gas-sensitive functional powder, the special organic solvent for the gas-sensitive slurry, and triethanolamine is placed in a ball mill tank, and zirconia ball mill beads with a diameter of 1~3 mm are added. Ball mill for 4~8 h at 200~600 rpm, and then screen out the zirconia ball mill beads to obtain the gas-sensitive slurry.

[0017] Preferably, the mass ratio of the zirconia ball mill beads to the gas-sensitive powder is (10~15):1.

[0018] Step 4: Prepare the metal oxide gas-sensitive film The gas-sensitive slurry obtained in Step 3 is dot-coated and heated to obtain the metal oxide gas-sensitive film.

[0019] A preparation method of a high-stability MEMS hydrogen sensor specifically includes the following steps: Step 1: Gas-sensitive coating integration An MEMS chip integrated with a micro-heater is used as the sensor electrode chip, and the above gas-sensitive slurry is integrated into the central interdigital electrode area of the MEMS chip.

[0020] Preferably, a pneumatic dispenser is used for gas-sensitive coating integration, controlling the dispensing pressure to be 0.2~0.3 kPa, the inner diameter of the dispensing needle to be 50~160 µm, the outer diameter to be 280~320 µm, and the dispensing time to be 0.1~0.4 s.

[0021] Step 2: Fabrication of the MEMS hydrogen sensor Vacuum stand still at room temperature for 12~24 h, and then heat at a heating rate of 2~10 °C / min for 24~72 h through the micro-heater integrated in the MEMS chip under standard atmospheric pressure to obtain a semiconductor resistive MEMS hydrogen sensor.

[0022] The present invention has the following beneficial effects: 1. The MEMS hydrogen sensor fabricated by the present invention has a low detection limit, and the theoretical detection limit can reach 20 pp.

[0023] 2. The zero-point resistance and sensitivity drift of the MEMS hydrogen sensor fabricated by the present invention are less than 5% under the environmental humidity of 20% - 80%, and the resolution is less than 5 ppm. After long-term operation in an environment with 90% relative humidity, the gas-sensing performance decays by about 10%, indicating certain moisture resistance.

[0024] 3. Through accelerated life prediction, the service life of the fabricated MEMS hydrogen sensor is at least 10 years, and it still has good stability after long-term operation in a high-humidity environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the highly stable MEMS hydrogen sensor prepared in the embodiment; Figure 2 Response / recovery characteristics of the sensor prepared in Example 1 to 500 ppm H2 in a 40% RH test environment before high-humidity aging; Figure 3 Response / recovery characteristics of the sensor prepared in Example 1 to 500 ppm H2 in a 40% RH test environment after 200 h of high-humidity aging at 90% RH; Figure 4 Continuous dynamic response / recovery characteristics of the sensor prepared in Example 1 to 50 - 1000 ppm H2 in a 40% RH test environment after 200 h of high-humidity aging at 90% RH; Figure 5 Response / recovery characteristics of the sensor prepared in Example 2 to 500 ppm H2 in a 40% RH test environment before high-humidity aging; Figure 6 Response / recovery characteristics of the sensor prepared in Example 2 to 500 ppm H2 in a 40% RH test environment after 200 h of high-humidity aging at 90% RH; Figure 7 Continuous dynamic response / recovery characteristics of the sensor prepared in Example 2 to 50 - 1000 ppm H2 in a 40% RH test environment after 200 h of high-humidity aging at 90% RH; Figure 8 Continuous dynamic response / recovery characteristics of the sensor prepared in Example 3 to 50 - 1000 ppm H2 in a 40% RH test environment after 200 h of high-humidity aging at 90% RH. DETAILED DESCRIPTION OF THE INVENTION

[0026] The present invention will be further explained and illustrated below with reference to the accompanying drawings.

[0027] Example 1

[0028] In this embodiment, a highly stable MEMS hydrogen sensor is prepared, and the specific steps are as follows: Step 1: Prepare metal oxide gas-sensitive functional powder Mix high-purity antimony-doped tin dioxide composite oxide (Sb-SnO2) with a diameter of 200 nm, palladium nitrate tetramine, and platinum nitrate tetramine powders in a mass ratio of 20:0.8:0.8. The doping concentration of antimony in the high-purity antimony-doped tin dioxide composite oxide is 5%.

[0029] Add zirconia milling beads with a diameter of 1 mm and 5 g of absolute ethanol to the mixed powder. The mass ratio of the zirconia milling beads to the mixed powder is 15:1. Use a planetary ball mill to mill for 8 h, set the rotation speed to 800 rpm, perform suction filtration on the milled solution, separate the zirconia milling beads after drying, and heat-treat in air at 650 °C for 4 h to obtain the gas-sensitive functional powder; Step 2: Prepare a special organic solvent for gas-sensitive paste Mix terpineol, diethylene glycol butyl ether acetate, ethyl cellulose, dibutyl phthalate, and dioctyl phthalate in a mass ratio of 35:15:4:0.6:1.2, and magnetically stir with a magnetic stirrer for 4 h, set the rotation speed to 600 rpm, to obtain a special organic solvent for gas-sensitive paste.

[0030] Step 3: Prepare gas-sensitive paste Mix the gas-sensitive functional powder in Step 1, the special organic solvent for gas-sensitive paste in Step 2, and triethanolamine in a mass ratio of 1000:150:5, put them into a ball mill tank, and add zirconia milling beads with a diameter of 3 mm. The mass ratio of the zirconia milling beads to the gas-sensitive functional powder is 15:1. Use a planetary ball mill to mill for 4 h, with a rotation speed of 400 rpm, and sieve out the zirconia milling beads to obtain the gas-sensitive paste.

[0031] Step 4: Gas-sensitive coating integration Use an MEMS chip integrated with a micro-heater as the sensor electrode chip, and integrate the gas-sensitive paste prepared in Step 3 into the central interdigital electrode area of the MEMS chip through a pneumatic dispenser. The dispensing pressure of the pneumatic dispenser is controlled at 0.2 kPa, the inner diameter of the dispensing needle is 100 µm, the outer diameter is 280 µm, and the dispensing time each time is 0.2 s.

[0032] Step 5: Fabrication of MEMS hydrogen sensor After dispensing, let the MEMS chip stand at room temperature in vacuum for 24 h, and then heat it through the micro-heater integrated in the MEMS chip at a heating rate of 5 °C / min for 72 h to obtain as Figure 1The high-stability MEMS hydrogen sensor shown, where 1 is a silicon nitride support layer, 2 is a Pt / Ti heating electrode and a sensing electrode, 3 is a silicon nitride isolation layer, 4 is a gas-sensitive coating, and the sensor uses interdigital electrodes of a silicon-based suspended membrane integrated micro-heater for the output of electrical signals of the gas-sensitive coating at high temperatures.

[0033] Set the sensor voltage to 5V, and use the dynamic gas distribution method to measure the sensitive characteristics of the prepared MEMS sensor. The response / recovery characteristics to 500 ppm H2 in a 40% RH test environment are as Figure 2 shown. Before high-humidity aging, the sensitivity to 500 ppm H2 in a 40% RH test environment is 11.5. After 200 h of high-humidity aging at 90% RH, the response / recovery characteristics to 500 ppm H2 in a 40% RH test environment are as Figure 3 shown. After 200 h of high-humidity aging at 90% RH, the sensitivity to 500 ppm H2 in a 40% RH test environment is 10.2; the continuous dynamic response / recovery characteristics to 50 - 1000 ppm H2 are as Figure 4 shown. After 200 h of high-humidity aging at 90% RH, the response / recovery curve to 50 ppm - 1000 ppm hydrogen in a 40% RH test environment, the detection limit is 50 ppm, and it shows good resolution for different concentrations of hydrogen.

[0034] Compared with the hydrogen sensors mentioned in the prior arts 1 and 2, the sensor prepared in this embodiment has a lower detection limit, can work in an environment with 90% relative humidity, and after 200 h of high-humidity aging, the gas-sensitive performance decays by about 10%, can maintain high-sensitivity characteristics and good resolution, and its detection performance and stability are significantly better than the prior arts.

[0035] Example 2

[0036] In this embodiment, a high-stability MEMS hydrogen sensor is prepared. The difference from Example 1 is that in step 1, high-purity antimony-doped tin dioxide (Sb-SnO2) with a diameter of 300 nm and an antimony doping mass ratio of 2% is selected, and the high-purity antimony-doped tin dioxide (Sb-SnO2), palladium nitrate tetramine, and platinum nitrate tetraamine powders are mixed according to a mass ratio of 20:0.8:0.64.

[0037] The response / recovery characteristics of the MEMS sensor prepared in this embodiment to 500 ppm H2 in a 40% RH test environment are as Figure 5 shown. Before high-humidity aging, the sensitivity to 500 ppm H2 in a 40% RH test environment is 4.1. After 200 h of high-humidity aging at 90% RH, the response / recovery characteristics to 500 ppm H2 in a 40% RH test environment are asFigure 6 As shown, after high humidity aging at 90% RH for 200 h, the sensitivity to 500 ppm H2 in a 40% RH test environment is 5.7; the continuous dynamic response / recovery characteristics to 50 - 1000 ppm H2 are as Figure 7 shown. After high humidity aging at 90% RH for 200 h, the response / recovery curve to 50 ppm - 1000 ppm hydrogen in a 40% RH test environment has a detection limit of 50 ppm and shows good resolution for different concentrations of hydrogen.

[0038] Compared with the sensor prepared in Example 1, the sensitivity of the sensor prepared in this example decreases overall before and after high humidity aging. However, after high humidity aging, it still maintains good stability in terms of sensitivity and still has good resolution.

[0039] Example 3

[0040] In this example, a highly stable MEMS hydrogen sensor is prepared. The difference from Example 1 is that in step 1, high - purity antimony - doped tin dioxide (Sb - SnO2) with a diameter of 1 µm and an antimony doping mass ratio of 2% is selected, and the high - purity antimony - doped tin dioxide (Sb - SnO2), palladium nitrate tetraamine, and platinum nitrate tetraamine powders are mixed according to a mass ratio of 20:0.64:0.8; in step 2, terpineol is replaced by ethylene glycol.

[0041] After the MEMS sensor prepared in this example undergoes high humidity aging at 90% RH for 200 h, the continuous dynamic response / recovery characteristics to 50 - 1000 ppm H2 in a 40% RH test environment are as Figure 8 shown. After high humidity aging at 90% RH for 200 h, the response / recovery curve to 50 ppm - 1000 ppm hydrogen in a 40% RH test environment has a detection limit of 50 ppm and has good resolution in the range of 50 ppm - 500 ppm.

[0042] Example 4

[0043] In this example, a highly stable MEMS hydrogen sensor is prepared. The difference from Example 1 is that in step 1, high - purity antimony - doped tin dioxide (Sb - SnO2) with a diameter of 500 nm and an antimony doping mass ratio of 1% is selected, and the high - purity antimony - doped tin dioxide (Sb - SnO2), palladium nitrate tetraamine, and platinum nitrate tetraamine powders are mixed according to a mass ratio of 20:0.4:0.4. And the ball - milling time of the planetary ball mill is set to 4 h and the rotation speed is 600 rpm.

[0044] Example 5

[0045] In this embodiment, a highly stable MEMS hydrogen sensor is prepared. The difference from Embodiment 1 is that in Step 1, high-purity antimony-doped tin dioxide (Sb-SnO2) with a diameter of 800 nm and an antimony doping mass ratio of 0.5% is selected, and the high-purity antimony-doped tin dioxide (Sb-SnO2), palladium nitrate tetramine, and platinum nitrate tetraamine powders are mixed according to a mass ratio of 10:0.8:0.64. The ball milling time of the planetary ball mill is set to 6 h, the rotation speed is 400 rpm, and then heat treatment is carried out at 450 °C for 3 h.

[0046] Embodiment 6

[0047] In this embodiment, a highly stable MEMS hydrogen sensor is prepared. The difference from Embodiment 1 is that in Step 5, the MEMS chip is left standing at room temperature in a vacuum for 12 h, and then heated by the micro-heater integrated in the MEMS chip at a heating rate of 10 °C / min for 24 h.

Claims

1. A highly stable MEMS hydrogen sensor, which sequentially includes a silicon nitride support layer, a Pt / Ti heating electrode and a sensing electrode, a silicon nitride isolation layer, and a metal oxide gas-sensitive thin film from bottom to top, and is characterized in that: The sensor is a semiconductor resistive hydrogen sensor based on a metal oxide gas-sensitive coating, and the metal oxide gas-sensitive thin film is a composite of antimony-doped tin dioxide composite oxide and palladium tetraamine nitrate and platinum tetraamine nitrate.

2. The high-stability MEMS hydrogen sensor according to claim 1, wherein: The mass ratio of the antimony-doped tin dioxide composite oxide to palladium tetraamine nitrate and platinum tetraamine nitrate is (10~20):(0.4~0.8):(0.4~0.8).

3. The high-stability MEMS hydrogen sensor according to claim 1, wherein: The doping concentration of antimony in the antimony-doped tin dioxide composite oxide is 0.5%~5%.

4. A method for preparing a metal oxide gas-sensitive thin film, which is used to prepare the metal oxide gas-sensitive thin film in the high-stability MEMS hydrogen sensor as described in any one of claims 1 to 3, and is characterized in that: Mix the antimony-doped tin dioxide composite oxide with palladium tetraamine nitrate and platinum tetraamine nitrate powders to form a gas-sensitive functional powder, dissolve it in an organic solvent, add triethanolamine and grind to obtain a gas-sensitive slurry, and obtain a metal oxide gas-sensitive thin film after dot coating and heating.

5. The preparation method of a metal oxide gas-sensitive thin film according to claim 4, characterized in that: The organic solvent is a mixed solution of terpineol, diethylene glycol butyl ether acetate, ethyl cellulose, dibutyl phthalate, and dioctyl phthalate.

6. The preparation method of a metal oxide gas-sensitive thin film according to claim 5, characterized in that: The mass ratio of dibutyl phthalate to dioctyl phthalate is 1:

2.

7. The preparation method of a metal oxide gas-sensitive thin film according to claim 5, characterized in that: The mass ratio of ethylene glycol, diethylene glycol butyl ether acetate, ethyl cellulose, dibutyl phthalate, and dioctyl phthalate is (10~40):(5~15):(0.5~4.5):(0.2~0.8):(0.4~1.6).

8. The preparation method of a metal oxide gas-sensitive thin film according to claim 4, characterized in that: The mass ratio of the gas-sensitive functional powder, organic solvent, and triethanolamine is (800~2000):(100~300):(5~50).

9. A preparation method of a high-stability MEMS hydrogen sensor, characterized in that: Specifically, it includes the following steps: Step 1: Use a MEMS chip integrated with a micro-heater as the sensor electrode chip, and use a pneumatic dispenser to integrate the gas-sensitive slurry prepared by the method according to any one of claims 4 to 8 into the central interdigital electrode area of the MEMS chip; Step 2: Let it stand still in vacuum at room temperature, and then heat it through the micro-heater integrated in the MEMS chip to obtain a semiconductor resistive MEMS hydrogen sensor.

10. The preparation method of a highly stable MEMS hydrogen sensor according to claim 9, characterized in that: Control the dispensing pressure of the pneumatic dispenser to be 0.2~0.3 kPa, the inner diameter of the dispensing needle to be 50~160 µm, the outer diameter to be 280~320 µm, and the dispensing time to be 0.1~0.4 s; set the micro-heater to heat at a heating rate of 2~10 °C / min for 24~72 h.

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