Optimum leaky-SAW cut of LiTaO/sub 3/ for minimised insertion loss devices

The paper describes how the propagation loss /spl alpha/ of leaky surface acoustic wave (LSAW) is dependent upon the Al thickness h of grating electrodes and rotation angle /spl theta/ for rotated Y-X LiTaO/sub 3/. Since the energy leak of LSAW originates from the coupling of the slow-shear field component with other components through the surface boundary conditions, zero /spl alpha/ can be realised when the slow-shear component is decoupled. This means that the optimal /spl theta/ giving zero /spl alpha/ should change with h as well as the surface electrical boundary conditions. Since relatively large h of 0.07-0.1 wavelengths is needed for present LSAW devices, the optimal /spl theta/ shifts to 40-42/spl deg/ from the conventional value of 36/spl deg/. Thanks to the minimised propagation loss, experimental results showed that device performances are markedly improved only by increasing /spl theta/ to circa 42/spl deg/ from 36/spl deg/. We also describe the state-of-the-art of the performances obtainable in commercially available LSAW devices based on 42/spl deg/YX-LiTaO/sub 3/.