Theoretical and experimental characterization of SAW propagation for zinc oxide on gallium arsenide including viscosity constants

The viscosity constants for GaAs and ZnO were estimated from available bulk wave loss measurements on single crystal materials to form complex stiffness matrices. The SAW propagation loss was theoretically characterized using a matrix computation and compared with the experimental propagation loss values for the two crystals independently. The matrix method was then used to calculate the SAW propagation properties for a c-axis oriented ZnO film layer on (001)-cut (110)-propagating GaAs. The results were compared to the experimentally measured SAW properties for a 1.7 micron ZnO film on GaAs using thin-film aluminum interdigital patterns formed on the surface of the zinc oxide films. The velocity and loss were measured over a frequency range from 30 MHz to over 1.0 GHz. There was qualitative agreement between theoretical and experimental in the general characteristics of the film thickness dependent velocity dispersion and the frequency dependent propagation loss, but not in the absolute values. The velocity dispersion values agreed to within 3%. The propagation loss in dB/cm averaged three times higher than the theoretical. The major contribution to this loss difference is attributed to the viscosity constant differences between ZnO crystal and film structure