Laterally-driven electrostatic attractive- and repulsive-force microactuators for frequency tuning and quality-factor control

Abstract

This thesis investigates laterally-driven electrostatic attractive- and repulsive-force microactuators whose frequency and quality-factor can be adjusted electrically. In the attractive-force microactuators, a set of a triangular tuning-comb arrays with linearly varied finger length is used for frequency tuning. Quality-factors are adjusted by the electrostatic force, reducing the damping gap between two planar microstructures. The electrostatic repulsive-force microactuators are designed to use the lateral repulsive-force induced by asymmetry of in-plane electric field. The resonanat frequency and quality-factor of the repulsive-force microactuator have been adjusted by the change of DC bias voltage. The attractive-force and repulsive-force microactuators are fabricated by a 4-mask surface-micromachining process. Actuation and tuning forces of each microactuator are characterized by analytical and numerical simulations. The resonant frequency and quality-factor of each of microactuators are measured and compared with the theoretical values. A 3.3% reduction of the resonant frequency of the attractive-force microactuator was achieved from the initial resonant frequency of 2.42kHz for the tuning voltage increase of 20V, resulting in the equivalent stiffness modification rate of -$4.9\times 10^{-5}N/m/V^2$. The resonant frequency of the repulsive-force microactuator were increased from 11.7kHz to 12.7kHz for the DC bias voltage increase of 80V from 60V, resulting in the frequency tuning sensitivity of 0.11%/V. The quality-factor of the attractive-force microactuator can be reduced at the rate of 62/V in the control voltage range of 1.75~2.25V; thereby demonstrating the maximum 50% reduction of quality factor for the electrostatic control voltage in the range of 1.75~2.25V. The measured quality-factor of the repulsive-force microactuator varies from 12 to 13 for the DC bias voltage range of 60~140V. It is concluded that the resonant frequency and quality-factor of...