Abstract
MEMS-based capacitively-transduced micromechanical disk resonators have been demonstrated that dispense with conventional high voltage source direct de-biasing and instead use stored charge on their resonant structures to achieve equivalent performance. In particular, a 103-MHz micromechanical contour-mode disk resonator has been demonstrated with the same Q (∼25,000) and series motional resistance when charge-biased as when biased via a dc voltage source directly connected to its resonant structure. For a stand-alone charge-biased resonator, leaky discharging of the resonant structure in vacuum attenuates the output signal by 3dB after 900s. If a 0.18μF capacitor is charged and attached to the floating resonant structure, the resonator can operate for more than 8.5 days before its signal is attenuated by 3dB, which clearly illustrates the long-term efficacy of this charge-biasing approach. Frequency shifts caused by discharge-induced bias shifts are less than 2.5 ppm per hour with charged 0.18μF capacitor, making plausible a "charge-and-refresh" operating mode with one-hour (or longer) refresh intervals. © 2005 IEEE.