P2G-2 Capacitively Coupled VHF Silicon Bulk Acoustic Wave Filters

This work reports on the implementation of VHF MEMS bandpass filters by capacitive coupling of Silicon Bulk Acoustic wave Resonators (SiBAR) fabricated using the HARPSS-on-SOI fabrication process. Such resonators operate in their horizontal width extensional modes with quality factors (Q) in the range of 10,000-100,000. With the comparatively large electrode area and deep submicron capacitive transduction gaps these resonators have also exhibited relatively low impedances. Compared with existing technologies such as quartz crystals, SAW filters, capacitively-coupled SiBARs have demonstrated the smallest form factor high-Q filters in the VHF range that can be integrated with silicon electronics on a common substrate. Filters with center frequencies up to 150MHz are demonstrated by coupling of two SiBAR resonators in their fundamental width- extensional modes. Tuning of the filter bandwidth by varying the DC polarization voltages on the resonators is investigated.