Study And Fabrication Of High Temperature Resistance Surface Acoustic Wave Sensor Based On AlN Piezoelectric Film

MEMS pressure sensors is the most widely used device in MEMS sensors,which has the advantages of small size,wireless passive,low cost,etc.At present,the mainstream MEMS pressure sensors are all traditional piezoresistive Si-based pressure sensors.With the rapid development of aerospace,automotive electronics,petroleum exploration and other industries,the demand of measuring high-temperature environmental pressures exceeding 100? in automotive engine fuel chambers,petroleum pipelines,has increased dramatically.The demand for high temperature resistant pressure sensors in aerospace,automotive,medical and other high-end markets is increasing.However,traditional piezoresistive Si-based MEMS pressure sensors use the semiconductor characteristics,resulting in poor temperature stability and inability to work stably in high-temperature environments exceeding 100?,making it difficult to meet the increasing pressure measurement in high-temperature scenarios.Piezoelectric sensors based on AlN piezoelectric films have the potential to break through the temperature limitations of piezoresistive Si-based sensors.In this sensor,the silicon substrate only plays a supporting role and does not have any effect on the performance of the device;the AlN piezoelectric film can work stably under high temperature environment and has good temperature stability.However,this piezoelectric sensor has a problem that the resonance frequency drifts with temperature changes.In order to solve the above problems,this paper carried out research on the design and fabrication of piezoelectric pressure sensors based on AlN thin films,the main research contents are as follows:1.In this thesis,the finite element simulation researches of the pressure sensors are carried out:(a)The different acoustic resonance modes excited in the piezoelectric sensors are discussed;(b)The strain distribution of the diaphragms with different shapes of pressure sensors under pressure are studied;(c)The temperature drift of piezoelectric pressure sensors at high temperature and the method for temperature drift compensation are studied,separately.Through the above simulations,the following results are obtained:(a)the piezoelectric pressure sensor of the acoustic wave excited by the interdigital transducer can excite both surface acoustic wave and bulk acoustic wave modes;(b)The pressure sensor which carries on a rectangular diaphragm demonstrate higher sensitivity than the one which carries a circuit diaphragm;(c)Silicon dioxide gets positive temperature coefficient of Youngs modulus,it can be used as a temperature compensation material to suppress the temperature drift effect of the pressure sensor.At the same time,by deposition an Al film layer which owns a high thermal expansion coefficient,the piezoelectric film can generate thermal stress to suppresses temperature drifting of pressure sensor.2.Through the above simulation results,a pressure sensor with a double SiO2 film temperature compensation layer and a rectangular vacuum cavity is designed.This kind of design can better suppress the temperature drift effect,improve the sensitivity and resolution of the pressure sensor and has the ability to measure absolute pressure.Then,the pressure sensor is manufactured using the MEMS process flow.3.Building temperature and pressure test systems separately to test the temperature and pressure characteristics of pressure sensor.The temperature test range of the pressure is 20? to 220?;the pressure test range of the sensor is 0 MPa to 0.4 MPa.The deviation between the test result and the simulation result is small.The test result shows that the piezoelectric surface acoustic wave pressure sensor has good working performance at high temperature,and also provides guidance for further research in the future.