An analysis of self-supported circular structures for reduced stress sensitivity in SAW devices

The mechanical stress sensitivity of surface acoustic wave (SAW) devices built on a self-supported circular quartz structure (of BVA type) was investigated. An attempt was made to reduce this sensitivity by using the symmetry properties of circular structures commonly used in the design of bulk acoustic wave devices. These structures are coupled with planar stress-compensated SAW quartz cuts that are the equivalent for SAW of the well-known SC-cut of bulk waves. Since the BVA-like structure chosen for this study does not permit analytical solutions of quasi-static mechanical stress problems, a finite element model has been used and a number of computing tools have been implemented to couple the finite element results with a perturbation method based on variational equations. It is noted that the theoretical prediction of the sensitivity of these SAW-BVA devices to symmetrical radial compression and to normal bending effects could yield new kinds of optimized resonator structures insensitive to both acceleration effects and thermoelastic effects