Theoretical and experimental mass-sensitivity analysis of polymer-coated SAW and STW resonators for gas sensing applications

Polymer-coated surface transverse waves (STW) resonators have recently been successfully studied for organic gas sensing applications. The first results indicate increased absolute and even relative sensitivity as compared to similar resonators with surface acoustic waves (SAW). However, the gain in sensitivity is accompanied by the adverse effect of an increased attenuation and the advantage frame is difficult to establish quantitatively. In this paper, a new set of experimental samples with Parylene C-coated quartz substrates are studied. The samples are matched in frequency and wavelength. The results are compared and the obtained features explained using available theoretical algorithms for analyzing layered SAW and Love configurations, and a recently developed STW algorithm. The approximate limits of advantageous applicability of the STW resonator gas sensors are discussed.