A Highly Stable MEMS Hydrogen Sensor and Its Fabrication Method

Abstract

This invention discloses a highly stable MEMS hydrogen sensor and its fabrication method. The highly stable MEMS hydrogen sensor is a semiconductor resistive hydrogen sensor based on a metal oxide gas-sensitive coating, comprising, from bottom to top, a silicon nitride support layer, a Pt / Ti heating electrode and sensing electrode, a silicon nitride isolation layer, and a metal oxide gas-sensitive thin film. The metal oxide is high-purity antimony-doped tin dioxide, tetraaminopalladium nitrate, and tetraammineplatinum nitrate. High-purity antimony-doped tin dioxide, tetraaminopalladium nitrate, and tetraammineplatinum nitrate powders are mixed and then used to prepare a gas-sensitive slurry using a mixed solution of terpineol, diethylene glycol butyl ether acetate, ethyl cellulose, dibutyl phthalate, and dioctyl phthalate. The gas-sensitive slurry is dotted onto the central interdigitated electrode region of a MEMS chip, and after vacuum standing and slow heating, the sensor is obtained. This sensor has a low detection limit and stable resolution after high humidity aging.

Description

Technical Field

[0001] This invention belongs to the field of sensing and measurement technology, and relates to a sensor for early warning of thermal runaway in electrochemical energy storage devices, monitoring of hydrogen leakage in the hydrogen energy industry, and monitoring of gas leakage. Specifically, it relates to a highly stable MEMS hydrogen sensor and its preparation method. Background Technology

[0002] Clean energy sources such as lithium-ion batteries, hydrogen fuel cells, and natural gas are playing an increasingly important role in energy transition and industrial applications. However, lithium-ion batteries are prone to heat accumulation and the release of flammable and hazardous gases due to uncontrollable factors. A rapid rise in temperature can easily trigger "thermal runaway" behaviors such as fires and explosions in the battery system. Hydrogen and natural gas, being colorless, odorless, flammable, and explosive, also increase the risk of explosions or fires. 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 natural gas.

[0003] Currently, hydrogen sensors on the market mainly fall into three categories: electrochemical, catalytic combustion, and semiconductor resistive. Electrochemical sensors offer advantages such as fast response speed and linear output, but have a short lifespan and their long-term performance is easily affected by sensor aging. Catalytic combustion sensors have no vulnerable parts and a relatively simple structure, thus exhibiting good stability; however, they are susceptible to poisoning by sulfides and halogen compounds in the environment. Semiconductor resistive sensors, due to their high sensitivity, low power consumption, real-time monitoring, small size, easy integration, and low cost, have great application potential in the field of hydrogen detection.

[0004] Prior art 1 (CN117761130A) proposes a hydrogen gas sensor based on a Pt-modified WO3 composite thin film material. It consists of an Al2O3 insulating ceramic sheet with a sensitive thin film and electrodes on the outer surface, and a resistance wire heating element and thermocouple inside. Its gas-sensing performance decreases by 25% when the humidity increases from 40% to 90%. Prior art 2 (CN117929488B) uses a PDMS solution to hydrophobically treat the sensitive material, constructing a superhydrophobic structure using a Pd-WO3 / WS2 gas-sensing composite material. The detection range for hydrogen is 100~1000 ppm, and the humidity conditions for gas-sensing performance are 40%~80%.

[0005] In summary, existing semiconductor resistive gas sensors typically use metal oxides as the core gas-sensitive material, and their detection performance is easily affected by ambient humidity. In particular, MEMS semiconductor resistive gas sensors integrating microheaters generally suffer from low consistency and poor stability due to the suspended thin-film structure of the microheaters. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention proposes a highly stable MEMS hydrogen sensor and its fabrication method. Based on a MEMS micro-hot plate, a hydrogen sensor with high stability under different environmental humidity conditions is developed, which is suitable for various application scenarios such as thermal runaway safety early warning in electrochemical energy storage devices, hydrogen leakage monitoring in the hydrogen energy industry, and gas leakage monitoring.

[0007] A high-stability MEMS hydrogen sensor is a semiconductor resistive hydrogen sensor based on a metal oxide gas-sensitive coating. From bottom to top, it comprises a silicon nitride support layer, a Pt / Ti heating electrode and sensing electrode, a silicon nitride isolation layer, and a metal oxide gas-sensitive thin film. The metal oxide is high-purity antimony-doped tin dioxide (Sb-SnO2), tetraaminopalladium nitrate, or tetraaminoplatinum nitrate.

[0008] The preparation method of the metal oxide gas-sensitive thin film specifically includes the following steps:

[0009] Step 1: Preparation of metal oxide gas-sensitive functional powder

[0010] High-purity antimony-doped tin dioxide composite oxide (Sb-SnO2) with a diameter of 200 nm to 1 µm was mixed with tetraaminopalladium nitrate and tetraaminoplatinum nitrate powders at a mass ratio of (10 to 20): (0.4 to 0.8): (0.4 to 0.8). The mixture was then ground, dried, and heat-treated to obtain gas-sensitive functional powder.

[0011] Preferably, the antimony doping concentration in the high-purity antimony-doped tin dioxide composite oxide is 0.5% to 5%.

[0012] Preferably, zirconia grinding beads with a diameter of 1-3 mm and anhydrous ethanol are added to the mixed powder, and the mixture is ground using a planetary ball mill. The rotation speed of the planetary ball mill is set to 400-800 rpm, and the grinding time is 4-8 hours.

[0013] Preferably, the dried powder is heat-treated in air at 450~650℃ for 2~4 hours.

[0014] Step 2: Prepare the organic solvent for gas-sensitive slurry.

[0015] A mixture of terpineol, diethylene glycol butyl ether acetate, ethyl cellulose, dibutyl phthalate, and dioctyl phthalate in a mass ratio of (10~40):(5~15):(0.5~4.5):(0.2~0.8):(0.4~1.6) is stirred to obtain an organic solvent for gas-sensitive slurries. The mass ratio of dibutyl phthalate to dioctyl phthalate is 1:2.

[0016] Preferably, a magnetic stirrer is used to stir the mixed solution, with a stirring time of 2 to 10 hours and a speed of 400 to 800 rpm.

[0017] Preferably, ethylene glycol, diethylene glycol butyl ether acetate, ethyl cellulose, dibutyl phthalate, and dioctyl phthalate are mixed and stirred in a mass ratio of (10~40):(5~15):(0.5~4.5):(0.2~0.8):(0.4~1.6).

[0018] Step 3: Preparation of gas-sensitive slurry

[0019] The gas-sensitive functional powder from step 1, the special organic solvent for gas-sensitive slurry from step 2, and triethanolamine are mixed in a mass ratio of (800~2000):(100~300):(5~50), and then ground to obtain the gas-sensitive slurry.

[0020] Preferably, a mixture of gas-sensitive functional powder, a special organic solvent for gas-sensitive slurry, and triethanolamine is placed in a ball mill jar, and zirconia grinding beads with a diameter of 1~3 mm are added. The mixture is then ball-milled at 200~600 rpm for 4~8 hours, and the zirconia grinding beads are sieved out to obtain the gas-sensitive slurry.

[0021] Preferably, the mass ratio of the zirconia grinding beads to the gas-sensitive powder is (10~15):1.

[0022] Step 4: Prepare metal oxide gas-sensitive thin films

[0023] The gas-sensitive slurry obtained in step 3 is dotted and heated to obtain a metal oxide gas-sensitive film.

[0024] A method for fabricating a highly stable MEMS hydrogen sensor specifically includes the following steps:

[0025] Step 1: Integration of gas-sensitive coating

[0026] The aforementioned gas-sensitive slurry is integrated into the central interdigitated electrode region of the MEMS chip using a MEMS chip with an integrated microheater as the sensor electrode chip.

[0027] Preferably, a pneumatic dispensing machine is used for gas-sensitive coating integration, with the dispensing pressure controlled at 0.2~0.3 kPa, the inner diameter of the dispensing needle at 50~160 µm, the outer diameter at 280~320 µm, and the dispensing time at 0.1~0.4 s.

[0028] Step 2: Fabrication of MEMS hydrogen sensor

[0029] The sample was left to stand in a vacuum at room temperature for 12–24 h, and then heated at a heating rate of 2–10 °C / min for 24–72 h under standard atmospheric pressure using a micro-heater integrated with a MEMS chip to obtain a semiconductor resistive MEMS hydrogen sensor.

[0030] The present invention has the following beneficial effects:

[0031] 1. The MEMS hydrogen sensor produced by this invention has a low detection limit, with a theoretical detection limit of up to 20 pp.

[0032] 2. The MEMS hydrogen sensor fabricated by this invention exhibits zero-point resistance and sensitivity drift of less than 5% and resolution of less than 5 ppm in ambient humidity of 20% to 80%. After long-term operation in an environment with 90% relative humidity, its gas-sensing performance decreases by approximately 10%, demonstrating a certain degree of moisture resistance.

[0033] 3. Accelerated life prediction shows that the prepared MEMS hydrogen sensor has a lifespan of at least 10 years and still maintains good stability after long-term operation in high humidity environments. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the highly stable MEMS hydrogen sensor prepared in the example.

[0035] Figure 2 The response / recovery characteristics of the sensor prepared in Example 1 to 500ppm H2 in a 40%RH test environment before high humidity aging;

[0036] Figure 3 The sensor prepared in Example 1 was subjected to 200 h of high humidity aging at 90%RH, and its response / recovery characteristics to 500ppm H2 in a 40%RH test environment.

[0037] Figure 4 The sensor prepared in Example 1 was subjected to 200 h of high humidity aging at 90%RH, and its continuous dynamic response / recovery characteristics to 50~1000 ppm H2 in a 40%RH test environment.

[0038] Figure 5 The response / recovery characteristics of the sensor prepared in Example 2 to 500ppm H2 in a 40%RH test environment before high humidity aging;

[0039] Figure 6 The sensor prepared in Example 2 was subjected to 200 h of high humidity aging at 90%RH, and its response / recovery characteristics to 500ppm H2 in a 40%RH test environment.

[0040] Figure 7The sensor prepared in Example 2 was subjected to 200 h of high humidity aging at 90%RH, and its continuous dynamic response / recovery characteristics to 50~1000 ppm H2 in a 40%RH test environment.

[0041] Figure 8 The sensor prepared in Example 3 was subjected to 200 h of high humidity aging at 90%RH, and its continuous dynamic response / recovery characteristics to 50~1000 ppm H2 in a 40%RH test environment. Detailed Implementation

[0042] The present invention will be further explained and described below with reference to the accompanying drawings.

[0043] Example 1

[0044] This embodiment prepares a highly stable MEMS hydrogen sensor, and the specific steps are as follows:

[0045] Step 1: Preparation of metal oxide gas-sensitive functional powder

[0046] High-purity antimony-doped tin dioxide composite oxide (Sb-SnO2) with a diameter of 200 nm was mixed with tetraaminopalladium nitrate and tetraaminoplatinum nitrate powders at a mass ratio of 20:0.8:0.8. The antimony doping concentration in the high-purity antimony-doped tin dioxide composite oxide was 5%.

[0047] Zirconia grinding beads with a diameter of 1 mm and 5 g of anhydrous ethanol were added to the mixed powder. The mass ratio of the zirconia grinding beads to the mixed powder was 15:1. The mixture was ball-milled for 8 h using a planetary ball mill at a speed of 800 rpm. The solution obtained from the ball milling was filtered, dried, and the zirconia grinding beads were separated. The mixture was then heat-treated in air at 650 °C for 4 h to obtain gas-sensitive functional powder.

[0048] Step 2: Prepare the organic solvent for gas-sensitive slurry.

[0049] Terpineol, diethylene glycol butyl ether acetate, ethyl cellulose, dibutyl phthalate, and dioctyl phthalate were mixed in a mass ratio of 35:15:4:0.6:1.2 and magnetically stirred for 4 hours at a speed of 600 rpm to obtain a special organic solvent for gas-sensitive slurry.

[0050] Step 3: Preparation of gas-sensitive slurry

[0051] The gas-sensitive functional powder from step 1, the special organic solvent for gas-sensitive slurry from step 2, and triethanolamine are mixed at a mass ratio of 1000:150:5, placed in a ball mill jar, and zirconia grinding beads with a diameter of 3 mm are added. The mass ratio of zirconia grinding beads to gas-sensitive functional powder is 15:1. The mixture is ball-milled for 4 hours at a speed of 400 rpm using a planetary ball mill. The zirconia grinding beads are then sieved out to obtain the gas-sensitive slurry.

[0052] Step 4: Integration of gas-sensitive coating

[0053] A MEMS chip with an integrated microheater was used as the sensor electrode chip. The gas-sensitive slurry prepared in step 3 was integrated into the central interdigital electrode area of ​​the MEMS chip using a pneumatic dispensing machine. The dispensing pressure of the pneumatic dispensing machine was controlled at 0.2 kPa, the inner diameter of the dispensing needle was 100 µm, the outer diameter was 280 µm, and the dispensing time was 0.2 s per dispensing.

[0054] Step 5: Fabrication of MEMS hydrogen sensor

[0055] After dispensing, the MEMS chip was left to stand under vacuum at room temperature for 24 h, and then heated for 72 h using a microheater integrated into the MEMS chip at a heating rate of 5 ℃ / min, to obtain the desired result. Figure 1 The high-stability MEMS hydrogen sensor shown is as follows: 1 is a silicon nitride support layer, 2 is a Pt / Ti heating electrode and sensing electrode, 3 is a silicon nitride isolation layer, and 4 is a gas-sensitive coating. The sensor uses interdigitated electrodes of a silicon-based suspended film integrated microheater for outputting electrical signals of the gas-sensitive coating at high temperatures.

[0056] The sensor voltage was set to 5V, and the sensitivity characteristics of the fabricated MEMS sensor were measured using the dynamic gas mixing method. The response / recovery characteristics to 500ppm H2 in a 40%RH test environment are as follows: Figure 2 As shown, before high humidity aging, the sensitivity to 500 ppm H2 in a 40%RH test environment was 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 follows: Figure 3 As shown, after aging at 90%RH for 200 h, 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 follows. Figure 4 As shown, after aging at 90%RH for 200 h, the response / recovery curves for hydrogen at 50ppm-1000ppm in a 40%RH test environment are shown. The detection limit is 50ppm, and it exhibits good resolution for different concentrations of hydrogen.

[0057] Compared to the hydrogen sensors mentioned in existing technologies 1 and 2, the sensor prepared in this embodiment has a lower detection limit, can work in an environment with 90% relative humidity, and its gas-sensing performance decays by about 10% after 200 hours of high-humidity aging. It can maintain high sensitivity and good resolution, and its detection performance and stability are significantly better than those of existing technologies.

[0058] Example 2

[0059] This embodiment prepares a highly stable MEMS hydrogen sensor. The difference from Embodiment 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 high-purity antimony-doped tin dioxide (Sb-SnO2), tetraaminopalladium nitrate, and tetraaminoplatinum nitrate powder are mixed in a mass ratio of 20:0.8:0.64.

[0060] The MEMS sensor prepared in this embodiment exhibits the following response / recovery characteristics to 500ppm H2 in a 40%RH test environment: Figure 5 As shown, before high humidity aging, the sensitivity to 500 ppm H2 in a 40%RH test environment was 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 as follows: Figure 6 As shown, after 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 follows. Figure 7 As shown, after aging at 90%RH for 200 h, the response / recovery curves for hydrogen at 50ppm-1000ppm in a 40%RH test environment are shown. The detection limit is 50ppm, and it exhibits good resolution for different concentrations of hydrogen.

[0061] Compared with the sensor prepared in Example 1, the sensor prepared in this embodiment showed an overall decrease in sensitivity before and after high humidity aging. However, after high humidity aging, it still maintained good stability in sensitivity and still had good resolution.

[0062] Example 3

[0063] This embodiment prepares a highly stable MEMS hydrogen sensor. The difference from Embodiment 1 is that in step 1, high-purity antimony-doped tin dioxide (Sb-SnO2) with a diameter of 1µm and an antimony doping mass ratio of 2% is selected, and high-purity antimony-doped tin dioxide (Sb-SnO2), tetraaminopalladium nitrate, and tetraaminoplatinum nitrate powder are mixed in a mass ratio of 20:0.64:0.8; in step 2, terpineol is replaced with ethylene glycol.

[0064] The MEMS sensor prepared in this embodiment, after being aged at 90%RH for 200 h, exhibits the following continuous dynamic response / recovery characteristics in a 40%RH test environment for 50~1000 ppm H2: Figure 8 As shown, after aging at 90%RH for 200 h, the response / recovery curves for hydrogen in the 50ppm-1000ppm range in a 40%RH test environment are shown. The detection limit is 50ppm, and the resolution is good in the 50ppm-500ppm range.

[0065] Example 4

[0066] This embodiment prepares a highly stable MEMS hydrogen sensor. The difference from Embodiment 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. The high-purity antimony-doped tin dioxide (Sb-SnO2), tetraaminopalladium nitrate, and tetraaminoplatinum nitrate powders are mixed at a mass ratio of 20:0.4:0.4. The planetary ball mill is set to a milling time of 4 hours and a rotation speed of 600 rpm.

[0067] Example 5

[0068] This embodiment prepares a highly stable MEMS hydrogen sensor. 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. High-purity antimony-doped tin dioxide (Sb-SnO2), tetraaminopalladium nitrate, and tetraaminoplatinum nitrate powders are mixed in a mass ratio of 10:0.8:0.64. The planetary ball mill is used for 6 hours at a speed of 400 rpm, followed by heat treatment at 450℃ for 3 hours.

[0069] Example 6

[0070] This embodiment prepares a highly stable MEMS hydrogen sensor. The difference from Embodiment 1 is that in step 5, the MEMS chip is left to stand at room temperature under vacuum for 12 hours, and then heated for 24 hours by a microheater integrated into the MEMS chip at a heating rate of 10 °C / min.

Claims

1. A high-stability MEMS hydrogen sensor, comprising, from bottom to top, 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, characterized in that: The sensor is a semiconductor resistive hydrogen sensor based on a metal oxide gas-sensitive coating, with a theoretical detection limit of 20 ppb. At ambient humidity of 20% to 80%, its zero-point resistance and sensitivity drift are less than 5%, and its resolution is less than 5 ppm. The metal oxide gas-sensitive film is a composite material comprising antimony-doped tin dioxide composite oxide and tetraaminopalladium nitrate and tetraaminoplatinum nitrate. The antimony doping concentration in the antimony-doped tin dioxide composite oxide is 0.5% to 5%.

2. The high-stability MEMS hydrogen sensor as described in claim 1, characterized in that: The mass ratio of the antimony-doped tin dioxide composite oxide to tetraaminopalladium nitrate and tetraaminoplatinum nitrate is (10~20):(0.4~0.8):(0.4~0.8).

3. A method for preparing a metal oxide gas-sensitive thin film, used to prepare a metal oxide gas-sensitive thin film in a high-stability MEMS hydrogen sensor as described in any one of claims 1-2, characterized in that: Antimony-doped tin dioxide composite oxide was mixed with tetraaminopalladium nitrate and tetraaminoplatinum nitrate powders, and then zirconia grinding beads with a diameter of 1-3 mm and anhydrous ethanol were added. The mixture was then ground using a planetary ball mill, dried, and heat-treated to obtain a gas-sensitive functional powder. This powder was dissolved in an organic solvent, and triethanolamine was added and ground to obtain a gas-sensitive slurry. After spot coating and heating, a metal oxide gas-sensitive film was obtained.

4. The method for preparing a metal oxide gas-sensitive thin film as described in claim 3, characterized in that: The organic solvent is a mixed solution of terpineol, diethylene glycol butyl ether acetate, ethyl cellulose, dibutyl phthalate, and dioctyl phthalate.

5. The method for preparing a metal oxide gas-sensitive thin film as described in claim 4, characterized in that: The mass ratio of dibutyl phthalate to dioctyl phthalate is 1:

2.

6. The method for preparing a metal oxide gas-sensitive thin film as described in claim 4, 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).

7. The method for preparing a metal oxide gas-sensitive thin film as described in claim 3, characterized in that: The mass ratio of the gas-sensitive functional powder, organic solvent and triethanolamine is (800~2000):(100~300):(5~50).

8. A method for fabricating a high-stability MEMS hydrogen sensor, characterized in that: Specifically, the following steps are included: Step 1: Using a MEMS chip with an integrated microheater as the sensor electrode chip, the gas-sensitive slurry prepared by any of the methods described in claims 4 to 7 is integrated into the central interdigitated electrode region of the MEMS chip using a pneumatic dispensing machine. Step 2: Allow the mixture to stand in a vacuum at room temperature, then heat it using a micro-heater integrated into the MEMS chip to obtain a semiconductor resistive MEMS hydrogen sensor.

9. The method for fabricating a high-stability MEMS hydrogen sensor as described in claim 8, characterized in that: The dispensing pressure of the pneumatic dispensing machine is controlled at 0.2~0.3 kPa, the inner diameter of the dispensing needle is 50~160 µm, the outer diameter is 280~320 µm, and the dispensing time is 0.1~0.4 s; a micro heater is set to heat at a heating rate of 2~10 ℃ / min for 24~72 h.

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