Stable charge-biased capacitive resonators with encapsulated switches

A large dc bias voltage (tens of volts) is often useful for the operation of capacitive MEMS devices. Charge-biasing techniques have been demonstrated to be able to replace a bias voltage source by trapping an equivalent charge on an electrically floating electrode. This work presents a charge-biased resonator that uses an electrostatically actuated mechanical switch with a pull-in voltage of 36 V to introduce a voltage-equivalent charge of 10-15V onto a resonant body. The switch and resonator are hermetically sealed in a clean vacuum cavity, within an epitaxial polysilicon encapsulation process (epi-seal). No charge leakage has been observed, even at an elevated temperature of 125°C for weeks.