High Temperature Surface Acoustic Wave Pressure Sensor Based On AlN

High temperature resistant and high pressure resistant pressure sensors are more and more widely used in the aviation,petrole?m and automotive fields,and the demand is also increasing.However,our country's research on high temperature resistant and high pressure resistant pressure sensors is relatively backward.The domestic market's has high-end high temperature resistant,High-pressure pressure sensors are mainly imported.Countries around the world have conducted in-depth research on high-temperature and high-pressure-resistant sensors,but relatively few researches have been conducted on pressure sensors that can withstand high temperature and high pressure at the same time.In addition,the current pressure sensor tends to be miniaturized and miniaturized,preferably integrated.Therefore,research on pressure sensors that can withstand high temperature and high pressure at the same time and realize the miniaturization of sensors is of great significance for solving the vacancy of my country's high-end pressure sensor market.The pressure sensor based on surface acoustic wave can realize passive wireless measurement and adapt to various harsh environments.AlN piezoelectric film can withstand thousands of degrees of high temperature and maintain high stability.In industrial production,AlN thin films are usually prepared by DC or radio frequency magnetron sputtering.The magnetron sputtering process has good compatibility with MEMS technology,which can achieve small size,light weight,and high integration of industrial large-scale Production requirements.Based on the above-mentioned problems and analysis,this paper has carried out research on the AlN-based high temperature and high pressure surface acoustic wave pressure sensor.The specific scientific research work and results are as follows:In order to prepare high-pressure-resistant pressure sensors and study the mechanism of device failure under high pressure,pressure sensitive membranes with different thicknesses and sizes were designed.The COMSOL multiphysics simulation software was used to simulate the resonance mode of the pressure sensor,and the corresponding frequency under different resonance modes of surface acoustic wave was studied.Because the resonance frequency of piezoelectric sensors is greatly affected by temperature,the mechanism of the temperature drift effect of surface acoustic wave sensors is introduced.The negative temperature coefficient of the device comes from the negative temperature coefficient of Young's modulus of the material itself.In order to reduce the temperature drift of the device,SiO₂with a positive first-order Young's modulus temperature coefficient is selected to compensate the temperature drift of the device.Different temperature drift compensation layers are designed,and COMSOL Multiphysics simulation is used to simulate the temperature drift compensation layers of different structures.The results show that the temperature compensation layer at the bottom of the piezoelectric layer can obtain the best temperature drift compensation effect,But due to process limitations,the top temperature compensation layer structure is selected with the second effect.A new type of IDT and reflection grid structure is designed,which can suppress the energy divergence caused by periodic interruption of the bulk acoustic wave at the reflection grid and the interdigital electrode.The strain of the pressure-sensitive membrane is simulated,and the results show that the middle part of the pressure-sensitive membrane is most suitable for fabricating surface acoustic wave resonators.The layout of the pressure sensor is designed according to the guiding idea that the resonator is designed in the strain concentration area to improve the pressure sensitivity,and the device is manufactured using standard MEMS technology.According to the device,a package structure with back cavity pressure and front pressure is designed.The withstand pressure limit of the device was tested,and the withstand pressure limit of different pressure-sensitive membranes was obtained.The analysis found that the pressure resistance of the device would fail prematurely through the back cavity pressure.Combined with the experimental data,it is obtained through simulation that the maxim?m internal stress when the SOI material ruptures is approximately equal to 552MPa.The temperature and pressure characteristics of the pressure sensor are measured,and the resonance frequency under normal temperature and pressure is 468.97MHz.The temperature characteristic test result of the device shows that the sensor can work stably in the environment of-50?500?,and the temperature drift of the device is as low as TCF?-35.5ppm/?;the pressure frequency coefficient of the pressure sensor is PCF?158ppm/MPa,and the pressure measurement range is 0?2 MPa,indicating that the device can withstand high pressure and has high pressure sensitivity.