Acoustic characterization of TiO2 film for humidity sensors applications

The change in the SAW phase velocity due to the presence of a TiO2 thin film on the propagation surface of a piezoelectric substrate has been used for the determination of the elastic constants of the layer. The relative change Delta v/v in the SAW phase velocity v(0) is expressed, using the perturbation theory, in function of the material density and of the elastic constants of the film. A comparison between the values of Delta v/v obtained with exact calculations, the approximate theory and the experimental values allowed us to evaluate the physical constants of TiO2 films to be used as sensitive membranes in relative humidity sensors applications.