Optimized STW devices with buried electrodes based on a mixed FEM/BEM numerical model

STW resonators on quartz are preferred over SAW due to their superior acceleration sensitivity, power handling, improved aging behavior, and 60% higher velocity. The achieved resonator Q at high frequencies using a metallic grating is lower than expected, mainly due to bulk mode scattering losses. The purpose of this study is to find the grating geometry which can reduce the propagation attenuation of the STW. STW propagation on Y+α°, X+90° propagation quartz cut (Euler angles 0,90-α,90) has been examined using a mixed FEM/BEM numerical model developed for buried electrodes for SAW propagation. It was found that by adjusting the a/p of the metal strips and by partially burying the electrodes one obtains SAW-like propagation properties with low propagation attenuation. For practical device design it is also necessary to be able to predict the turn-over temperature. To this end, simplified assumptions have been made to model the electrode and the piezoelectric substrate dilatations with temperature, and incorporated in the mixed FEM/BEM numerical model PerIDT presented at last year's Ultrasonics Symposium. The optimized partially buried strip structure is used to obtain STW resonators with increased Q with predicted turnover temperature. Comparison with experiments will be shown. Partially buried electrode STW resonators with improved Q have been developed with the aid of the mixed FEM/BEM numerical model PerIDT.