Research On ZnO Piezoelectric Film Force Sensor Based On MEMS Technology

Zinc oxide?ZnO?is a hexagonal wurtzite type II-VI compound semiconductor material with wide band gap?³.37eV?,high exciton binding energy?⁶0meV?and good mechanical,electrical,optical and piezoelectric characteristics.Based on the piezoelectric properties of ZnO thin films,ZnO piezoelectric thin film force transducer was studied,designed and fabricated by MEMS technology on monocrystalline silicon substrate.The piezoelectric structure consists of ZnO piezoelectric thin film,bottom and top electrodes was fabricated on the silicon cantilever beam.When the external force is applied on the cantilever beam,the cantilever would present elastic deformation,the bottom and top electrodes of the ZnO piezoelectric thin film generate output charges,which could realize the measurement of the external force.In this paper,ZnO piezoelectric films were prepared by RF magnetron sputtering method.X-ray diffraction?XRD?,scanning electron microscopy?SEM?,UV-Visible spectrophotometer,step profiler and X-ray photoelectron spectroscopy?XPS?were adopted to analyze the microstructure,surface morphology,band gap and other characteristics of the ZnO thin films.The influences of sputtering power,oxygen-argon ratio,deposition times,annealing temperature and Li doping on the properties of ZnO thin films were studied.The ZnO thin films grown on silicon substrate show a good?002?preferred orientation.When the other preparation conditions were fixed,the diffraction peak intensity was increased with the augment of sputtering power.Through the optical characteristic analysis of the ZnO thin films which were deposited on the glass substrates,the bandgap of the ZnO thin films could reach 3.30eV.To study the piezoelectric coefficient(d₃₃)of the ZnO piezoelectric thin films,the Al/Zn O/Pt/Ti/SiO₂/Si multilayer structure was fabricated with the optimized preparation conditions.The results measured by piezoelectric reaction microscopy?PFM?showed that the d₃₃ of Li doped ZnO thin film is 13.75pm/V,and the d₃₃ of the pure ZnO thin film under the same conditions is 10.7pm/V.On the basis,this paper take the structure and characteristic simulation results of the ZnO piezoelectric thin film force sensor into account,and the ZnO piezoelectric thin film force sensor chip was fabricated by MEMS technology and mask method,and was packaged by inner bonding method.The characteristic test of the ZnO piezoelectric thin film force sensor was performed by the test system which comprised of the scanning signal generator,the vibration table and the oscilloscope.When the measuring range is from 0?N to 30?N,the inherent frequency of the sensor is 928.8Hz,and the sensitivity could reach 5.553mV/?N.