Analysis of the interaction of surface acoustic waves with charge carriers in layered structures

We have computed the propagation behavior of surface acoustic waves (SAW´s) under a non-piezoelectric, conducting layer on a semi-infinite piezoelectric substrate. Due to the finite conductivity of the film which is deposited on the substrate surface the interaction of the SAW with the charge carriers in this layer involves changes in both attenuation and dispersion. In our analysis, mass loading and stress loading are taken exactly into account. We also include the space charge density distribution in the film by using and comparing four different space charge models. As an example, we present the phase velocity and the attenuation coefficient of the fundamental SAW mode propagating on a 128rotYX LiNbO₃ substrate coated with a thin layer of amorphous silicon (a:Si) as a function of the silicon conductivity and the film thickness. It is found that an appropriately dimensioned semiconducting film may be used as an efficient absorbing material in SAW devices for consumer and commercial applications