Shear-horizontal-type surface acoustic wave on langasite with Au or Ta2O5 thin film

The propagation characteristics of a pure shear-horizontal-type surface acoustic wave on rotated Y-cut 90°X propagation langasite, having Euler angles of (0°, θ, 90°), with a high-density thin film, such as a gold (Au) film or a tantalum pentoxide (Ta₂O₅) dielectric film, are investigated. The theoretical analysis showed that, by loading the substrate with these films, the coupling factor increases to approximately 1.0% under a certain condition. In fact, the measured values of the coupling factor were 0.80% and 0.61% for a sample with a Au film thickness of 0.015 wavelength (λ) and a sample with a Ta₂O₅ film thickness of 0.047 λ, respectively. For both films, the measured frequency shifts with temperature change showed that a temperature characteristic with a zero temperature coefficient of delay, the same as ST-90°X quartz with a free surface, can be obtained by choosing the appropriate film thickness.