The experimental and theoretical characterization of the SAW propagation properties for zinc oxide films on silicon carbide

The surface acoustic wave (SAW) propagation properties of zinc oxide (ZnO) films on silicon carbide (SIC) have been theoretically and experimentally characterized in the film thickness-to-acoustic wavelength ratio range up to 0.12. The experimental characterization of the SAW propagation properties was performed with a linear array of interdigital transducer (IDT) structures. The measurements characterized the velocity and propagation loss of two surface modes, a generalized SAW (GSAW) mode with velocities between 6000 and 7000 m/s, and a high velocity Pseudo-SAW (HVPSAW) mode with velocities between 8500 and 12500 m/s. The experimentally determined characteristics of the two waves have been compared with the results of calculations based on published data for SiC and ZnO. Simulation of wave characteristics was performed with various values of the elastic constant C-13, which is absent in the published set of material constants for SiC, within the interval permitted by the requirement of positive elastic energy in a hexagonal crystal. The best agreement between the measured and calculated propagation losses of the HVPSAW has been obtained for C-13 near zero. Although for the GSAW mode the calculated velocity dispersion has been found nearly insensitive to the value of C-13 and consistent with the experimental data, for the HVPSAW, some disagreement between measured and calculated velocities, which increased with ZnO film thickness, has been observed for any C-13 value. Theoretical analysis of HVPSAW has revealed the existence of a previously unknown high velocity SAW (HVSAW). The displacement components of this wave have been analyzed as functions of depth and confirmed its pure surface, one-partial character.