Loss reduction of leaky surface acoustic wave by loading with high-velocity thin film

The propagation properties of a leaky surface acoustic wave (LSAW) on rotated Y-cut X-propagating lithium niobate (LN) substrates loaded with an aluminum nitride (AlN) thin film with a higher phase velocity than that of the substrate were investigated theoretically and experimentally. First, from the theoretical calculation, it was found that the minimum attenuation can be obtained at a certain thickness of the AlN thin film for a cut angle ranging from zero to sixty degrees because the cut angle giving the minimum attenuation shifts toward a smaller cut angle as the film thickness is increased. Then, the propagation properties of an LSAW on several rotated Y-cut LN substrates were measured by using an interdigital transducer (IDT) pair with a wavelength of eight micrometers. After the deposition of the AlN thin film, the measured insertion loss of the IDT pair and the propagation loss were markedly decreased.