Theoretical Analysis of Acoustoelectrical Sensitivity in SAW Gas Sensors

The theoretical studies on acoustoelectrical (AE) sensitivity in SAW gas sensors are presented. The analysis was based on normalized parameter ξ=σs/v0Cs (where: σs – is the film's electrical surface conductivity, v0 – SAW velocity, Cs – sum of the substrate's and environment's electrical permittivities) which determines the value of AE sensitivity. The electrical surface conductivities in the bi-layer structure are correlated by the σs1= x σs2 dependence. The investigations revealed that for single and bi-layer sensor structures the maximum value of AE sensitivity is obtained for ξmax= ∼0.6. For bi-layer structures this sensitivity is lower. However we also found the positions of the maximum values in a function of x parameter dependent on different values of normalized conductivity of the second film.