Bulk Mode Disk Resonator With Transverse Piezoelectric Actuation and Electrostatic Tuning

This paper presents a wine-glass bulk mode disk resonator based on a novel transverse piezoelectric actuation technique to achieve bulk mode resonance of the single crystalline silicon disk structure. The device is fabricated in a commercial microelectromechnical systems (MEMS) process, and combines reasonable quality factor and superior motional resistance in a low-cost technology. External capacitive electrodes are used for electrostatic tuning of the resonance frequency, relying on the electrostatic spring softening effect. The resonator was measured to have a resonance frequency of ~15 MHz and a quality factor of ~2000 in atmospheric pressure, increasing to ~5000 in 100-mtorr vacuum. The temperature co-efficient for the frequency of the device was also measured to be about -40 ppm/°C. The resonator requires no dc voltage for operation, but its resonance frequency can be tuned by varying the applied dc voltage on the capacitive electrodes with a factor of 1 ppb/V
²
.