Optimization of sensitivity induced by surface conductivity and sorbed mass in surface acoustic wave gas sensors

Acoustic transmissions in surface acoustic wave (SAW) gas sensors based on multilayered structures consisting of sensitive layer/piezoelectric film/non-piezoelectric substrate are studied with the transfer matrix method, in which the shifts of the central frequencies of SAW sensors induced by the variations of surface conductivities and sorbed masses are evaluated. According to the results, the sensitivities of SAW gas sensors using different piezoelectric films are optimized by simultaneously considering the variations of surface conductivities and masses caused by sorbates on the surfaces of the sensors. It is found that the frequency shift induced by the variation of surface conductivity is closely related with the initial conductivity and relative dielectric constant of the sensitive layer, while the frequency shift induced by the sorbed mass is almost independent on them. Furthermore, the operating frequencies, SAW modes and characteristics of sensitive layers are optimized in order to achieve high sensitivities according to the responses of the SAW gas sensors to different types of the detected gases.