Longitudinal-type leky surface acoustic wave on LiNbO<inf>3</inf> 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 em. 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.