Optimal cut of langasite for high performance SAW devices

The results of a theoretical and experimental investigation of the SAW propagation characteristics in an optimal region of langasite defined by the Euler angles (-15°-+10°,120°-165°,20°-45°) are presented. Based on temperature coefficients of the elastic constants derived from experimental data, some optimal orientations of langasite characterized by high electromechanical coupling factor (K²), zero power flow angle (PFA) and low or zero temperature coefficient of frequency (TCF) are found. It is shown that the SAW velocity in the region of interest is highly anisotropic, and this results in a significant amount of diffraction which must be taken into account in the search for orientations useful for SAW devices. An orientation having simultaneously zero PFA, zero TCF, negligible diffraction, and relatively high piezoelectric coupling has been found and verified experimentally. The experimental results are in excellent agreement with the calculated SAW characteristics. The frequency response of a SAW device fabricated on the optimal cut of langasite is presented and demonstrates that high performance SAW filters can be realized on this optimal cut of langasite.