Resonant Microaccelerometer With Tunable and On/Off Switchable Sensitivity

We report on an experimental feasibility study of a resonant accelerometer with a purely electrostatic (ES) transmission of an inertial force between the proof mass (PM) and the vibrating sensing beam (resonator), enabling tuning and ON/OFF switching of the device scale factor (SF) by voltage. The sensing beams are anchored at one end, and at the other end are attached, through a linkage-type force amplification compliant mechanism, to the force-transmitting frames interacting with the PM solely through ES forces. At zero acceleration, the ES forces induce identical axial tension in the two resonators. In the presence of acceleration, the displacement of the PM disturbing the ES field results in changes in the axial tension in the beams and, therefore, in the resonators’ frequencies. Consequently, the sensitivity to inertial input is tunable via voltage, and the input signal transmission can be switched ON or OFF. The device was fabricated from the 25 μm thick silicon-on-insulator (SOI) wafer, with 2000 μm × 2010 μm PM and 100 μm × 2010 μm frames. The response of 300 μm long, 3.5 μm wide resonators was sensed capacitively, in both open-loop and closed-loop excitation scenarios, in a baseline state without an inertial load in the sensing directions, and in a ±g turn-table test. Consistent with the model predictions, the differential SF tunability from zero up to ≈ 87 Hz/g was observed in the experiments.