Longitudinal-type leky surface acoustic wave on LiNbO3 with high-velocity thin film

The loss reduction of a longitudinal-type leaky surface acoustic wave (LLSAW) by loading with a dielectric thin film with a higher velocity than the substrate is proposed. An aluminum nitride (AlN) thin film was adopted as a high-velocity thin film, and the propagation properties of an LLSAW on an X36°Y-LiNbO₃ (LN) substrate were investigated theoretically and experimentally. First, the elastic constants c₁₁ and c₄₄ of an AlN thin film deposited by RF magnetron sputtering were determined from the measured phase velocity of a Rayleigh-type SAW, and they were 61 and 68% of those of a single-crystal AlN thin film. Next, from the theoretical calculation for the LLSAW on the X36°Y-LN substrate, it was found that the LLSAW attenuation can be reduced to zero by loading with an AlN thin film. Then, the propagation properties of the LLSAW on the X36°Y-LN substrate were measured by using an interdigital transducer pair with a wavelength (λ) of 8 εm. When the film thickness was 0.25 λ, the measured propagation loss decreased from 0.28 dB/λ for the sample without a film to 0.03 dB/λ.