Acoustic bulk wave composite resonators

TLDR

The authors introduce a novel acoustic bulk‑wave resonator consisting of a thin ZnO film sputtered onto a thin Si membrane support. The piezoelectric ZnO excites a longitudinal bulk wave that reflects from the free surface of the film and membrane, forming an acoustic cavity that produces parallel and series electrical resonances at the ZnO electrodes for both even and odd modes. Fundamental resonant frequencies near 500 MHz were achieved with parallel Qs exceeding 9000, and the temperature coefficient of resonant frequency was –31 ppm for a Si:ZnO thickness ratio of six.

Abstract

This letter reports on a new and unique form of acoustic bulk wave resonator composed of a thin film of ZnO sputtered onto a thin Si membrane supporting structure. The piezoelectric ZnO is used to excite a longitudinal bulk wave which reflects from the free surface of the film and membrane. The structure thus forms an acoustical cavity which exhibits parallel and series electrical resonance responses at the ZnO film electrodes for both even and odd order modes. Fundamental resonant frequencies near 500 MHz have been achieved with parallel resonant Q’s over 9000. The temperature coefficient of resonant frequency was found to be −31 ppm for a Si to ZnO thickness ratio of six.