ZnO:Li Thin Film Piezoelectric Pressure Sensor Research

For the dynamic pressure measurement(0?100 kPa)of electronic sphygmomanometer and oxygen generator,combined with the piezoelectric working modes of ZnO:Li thin film d₃₁ and d₃₃,this paper presented two piezoelectric pressure sensor structures based on MEMS technology,namely parallel plate electrode piezoelectric pressure sensor(PESPE)and interdigital electrode piezoelectric pressure sensor(PESIE).The sensor is composed of elastic element and piezoelectric element.The elastic element is square silicon diaphragm,and the piezoelectric elements are Ti/Pt/ZnO:Li/Si O₂/Al and ZnO:Li/Al respectively.When the sensor senses the applied pressure(P),the elastic element produces elastic deformation,and ZnO:Li thin film converts the elastic deformation into output voltage based on piezoelectric effect,which can realize the pressure measurement in a certain range.The electronic structure and elastic properties before and after Li doped ZnO were analyzed by program package VASP.The preparation of ZnO:Li piezoelectric thin films was studied by RF magnetron sputtering.The microstructure and piezoelectric properties of the thin films were analyzed by XRD,EDS,AFM and quasi-static piezoelectric coefficient tester.When the sputtering power and deposition temperature were 125 W and 300?respectively,the piezoelectric coefficients d₃₁ and d₃₃ of ZnO:Li thin films were 1.5 p C/N and 2.2 p C/N,respectively.The structural simulation model of the pressure sensor was established by the multi-physical field coupling simulation software COMSOL multiphysics 5.6,and the effects of structural parameters on the mechanical and pressure-sensitive characteristics of the pressure sensor were studied.The simulation results showed that the resonant frequency of the pressure sensor is 6.3 MHz,and the sensitivity of pespe and pesie are 0.12 m V/kPa and 3.25 m V/kPa respectively in the range of 0?100 kPa.On this basis,this paper used MEMS technology to study the wafer level fabrication and chip packaging process of ZnO:Li thin film piezoelectric pressure sensor chip on 4-inch silicon wafer.At room temperature,the self built dynamic pressure testing device was used to study the pressure-sensitive characteristics of the sensor.For the parallel plate electrode type pressure sensor,when P=10 kPa,the peak to peak value of output voltage was 17.10m V,and when P>20 kPa,the peak to peak value of output voltage remained about 20.36m V.For interdigital electrode type pressure sensor,when P=150 kPa,the peak to peak value of output voltage was 28.27 m V,the rise time was 0.2 s and the fall time was 6.4 s;In the range of 0?150 kPa,the sensitivity was 0.13 m/kPa,indicating that the structure can realize the measurement of dynamic pressure.