Optimized Stoneley wave device by proper choice of glass overcoat

The characteristics of a Stoneley wave propagated along an interface between a piezoelectric material and an isotropic material were investigated both theoretically and experimentally. First, the condition for the existence of Stoneley waves was shown for various piezoelectric materials. A rule of thumb for selecting the combination of the two materials was obtained. Then, LiTaO₃ was selected as the piezoelectric material and SiO₂ was selected the isotropic material. After the calculation of the Stoneley wave characteristics, actual devices were fabricated and measured. The experimental results were found to be in good agreement with the theory; zero slope temperature and high electromechanical coupling coefficient ( K²=1.5%) were obtained for Stoneley wave propagation between SiO₂/X-148° LiTaO₃. As a result, future surface-acoustic-wave (SAW) devices can be made without any package