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 12 500 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.

We report two numerical examples of high-velocity surface acoustic waves, a type of surface waves which was recently shown to exist if a thin film is present on a surface. The nonattenuated high-velocity surface waves have been found in diamond orientation with Euler angles (0°,0°,45°) and sapphire orientation with Euler angles (0°,−20.3°,0°), with zinc oxide film. In diamond, the wave has “symmetric” structure with displacement in the symmetry plane while, in sapphire, the example of a “nonsymmetric” solution is presented. The numerical analysis has confirmed that, in both examples, the wave has a true surface nature, with one-partial structure in a substrate.

No abstract

The propagation of surface sagittally polarized waves on the plated surface of a semi-infinite medium with the phase velocity exceeding that of bulk quasitransverse sagittally polarized waves in the substrate is studied analytically and numerically. Such a surface wave is shown to exist in nonpiezoelectric and piezoelectric composites provided both the sagittal plane and the interface are planes of elastic symmetry of the layer and substrate. In the case of a nonpiezoelectric structure, the "fast" surface wave is one-component, involving only the quasi-longitudinal nonuniform mode in the substrate. In piezoelectrics this wave is two-component and incorporates the quasilongitudinal mode and the mode of electrical potential in the substrate. The "fast" wave exists at definite values of the velocity nuF and the layer thickness/wavelength ratio (h/lambda)F. It has been found that one or two surface waves can arise for the same direction of propagation at different nuF and (h/lambda)F, in the case of two surface solutions, both the values of (h/lambda)F being small. The approximate expressions are derived which allow one to elucidate whether the structure under consideration can support the "fast" surface wave and to estimate the corresponding nuF and (h/lambda)F. A comparison is performed of numerical and analytical results.

No abstract

No abstract

No abstract

No abstract