UHF Composite Bulk Wave Resonators

Abstract

At VHF and UHF the fabrication of bulk wave resonators and monolithic filters by conventional techniques is difficult or impossible due to the thin fragile nature of the r equired structure. This paper reports on a class of miniature bulk wave resonators that have been fabricated using thin film and microelectronic materials processing techniques. The resonators are composed of a thin sputtered ZnO film on a thin single crystal membrane that in turn is supported by the bulk of the Si substrate or wafer. The resonators have fundamental mode resonant frequencies near 500 MHz and have exhibited Q's as high as 9000. The resonator area is less than 150 microns square and with supporting substrate is less than 1 mm square. The supporting theory for the resonators shows that they have the unique property of operation on both even and odd overtones in contrast to conventional thickness mode resonators which offer only odd overtone operation.