Surface Acoustic Wave Propagation Properties with ZnO Thin Film for Thermo-Electric Sensor Applications

Abstract

The frequency of surface acoustic wave (SAW) devices is decided by the width of the interdigital transducer fingers and the acoustic velocity of the piezoelectric substrate. Any change in the device can be easily detected as a frequency shift or amplitude difference by employing the delay line. In this study, we present a finite element modeling of SAW propagation properties with ZnO thin film for thermo-electric sensor applications. An SAW device is fabricated on an ST-X quartz piezoelectric substrate, where the propagating direction is towards the x-axis. The SAW sensor is designed aiming at a target frequency of 79 MHz. Afterwards, we carry out a comparative analysis of frequency characteristics based on a ZnO thin film for thermo-electric sensor applications. The applied temperature on the top of the ZnO thin film generates a voltage because of the thermo-electric properties of ZnO. Accordingly, the shape of the film also transforms by virtue of the piezoelectric properties of ZnO. Owing to a direct coupling between the thermo-electric and piezoelectric effects of ZnO thin film, the frequency peak splits from 79 MHz and a variation in amplitude is also observed.