Analysis of leaky surface acoustic waves on LiTaO₃ substrate

We have investigated leaky surface acoustic waves (LSAW) propagating in arbitrary directions of rotated Y-cuts on LiTaO₃ substrates. The inherent physical behavior of LSAW, consisting of coupled modes involving terms decaying into the substrate and a term representing a radiating bulk wave, is fully explained. The high propagation velocity of LSAW, and hence the fundamental mode operation, may lead to a further advance of SAW technology in commercial GHz-systems, especially in low-loss SAW filter applications. But nevertheless, to further reduce the insertion loss, all relevant effects influencing the device performance, e.g. diffraction spreading losses, and spurious bulk waves, have to be considered as well. Thus, we have analyzed the well-known Y-rotated LiTaO₃ substrate with wave propagation in the crystalline X-direction, whereas also deviations from this specific propagation direction are taken into account. Phase velocity and attenuation constant are computed for different rotation angles, as well as for different propagation directions and the measured results are shown to compare with those obtained from the theoretical analysis.