Characterization of surface acoustic wave propagation in a ZnO layer on a conducting substrate

In recent years many publications about theoretical as well as practical aspects of ZnO layers on dielectric or piezoelectric substrates were published. Up to now, the main research objectives were the compensation of temperature coefficient TCF and the increase of effective coupling k². In this paper we investigate the existence and properties of SAWs on metallic substrates. With the standard FEM code ANSYS, a single crystal LiNbO₃ SAW resonator was analyzed, to determine the accuracy of the FEM model. Calculated data and data taken from literature for the phase velocity were compared. In the next step a ZnO piezoelectric layer on a metallic substrate with Au/Ti seedlayer was simulated. Substrate material data mainly based on a typical metallic alloy were assumed. Different E-moduli were used in order to investigate the change in the SAW propagation behavior. As a preliminary test for this setup a resonator with ZnO/Au/Ti on Silicon was calculated and measured. A harmonic analysis was carried out. The admittance was determined regarding loss mechanisms. Changes in the dispersion curve and coupling factor, due to a variation of the piezoelectric layer height were evaluated. Finally the propagation characteristics of SAW will be presented with respect to the variation of material tensor data and ZnO film thickness.