High coupling and highly stable shear-horizontal-type surface acoustic wave on langasite with Au or Ta2O5 thin film

In this study, the propagation characteristics of a pure shear-horizontal-type surface acoustic wave on rotated Y-cut 90° X propagation langasite (at 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 with these films, coupling factor increases to about 1.0% for a certain condition. In fact, the measured coupling factors for θ = 20° were 0.80% and 0.61%, for the samples with a Au film thickness of 0.015 wavelength (λ) and a Ta2O5 film thickness of 0.047 λ, respectively. For both films, the measured frequency shifts in the temperature change for θ = 20° showed that a temperature characteristic with a zero temperature coefficient of delay in the same as the ST-90°X quartz with a free surface can be obtained by appropriately choosing the film thickness.