COMPARATIVE STUDIES ON POLYMER COATED SAW AND STW RESONATORS FOR CHEMICAL GAS SENSOR APPLICATIONS

摘要

This paper presents and compares experimental data from pcrformance tests on polymer coated 433 MHz surface acoustic wave (SAW) and I GHz surface transverse wave (STW) based two-port resonators for chcmical gas sensor applications. The acoustic devices were coated with gas sensitivc polymer films of diffcrent thickness' and viscoelastic properties as parylene C, poly-(2-hydroxyethylmethacrylale) (PHEMA) and poly-(n-butyl-methacrylate) (PBMA). Then they were gas probed using perchloroethylene and water. The SAW versus STW sensor scnsitivitics, insertion loss, loaded Q and distortion of thc frequency and phase responses during gas probing were evaluated and compared. It was found that STW devices, when coated with thin sensitive polymer layers, retain Iow loss, high Q and low noisc and feature substantially higher relative gas sensitivities compared to their SAW counterparts. Coated SAW sensors can stand substantially thicker soft polymer films than STW ones but at thc expense of highly degraded electrical and noisc perlbnnance and moderate increase in rclative sensitivity.