SAW velocity reduction and spurious modes suppression on the layer structure

Abstract

This paper discusses use of the layered structure for the SAW velocity reduction. First, it is shown that insertion of SiO2 is crucial between the piezoelectric layer and the base substrate to keep large electromechanical coupling factor even when the SAW velocity is reduced. It is also shown that use of high velocity substrate such as Si is also crucial for bringing spurious resonances much higher than the main resonance. Impact of Si orientation is also discussed. Next, suppression of transverse mode resonances and lateral leakage is studied. It is shown that the double busbar structure offers Q enhancement through good lateral energy confinement, and its combination with the piston design also gives good transverse mode suppression. Furthermore, discussions are extended to a strong spurious resonance appears near the anti-resonance.