Conventional out-of-plane micro electrostatic actuators use attractive force and suffer from the “pull-in” effect, which leads to small stroke and low reliability.

In this thesis, two novel micro electrostatic actuators are developed:​ a three-layer repulsive force actuator and a two-layer repulsive force actuator. Both actuators are able to overcome the “pull-in” effect associated with conventional electrostatic actuators by generating a repulsive force instead of an attractive force to achieve large stroke and high reliability. Both novel actuators are compatible with surface micromachining technology.

Theoretical models of the novel actuators are developed to be used as design and optimization tools. Prototypes are developed to experimentally verify and assess the performance of the novel actuators.

A translation micromirror driven by the three-layer repulsive force actuator was designed for application in adaptive optics. The predicted stroke for a mirror size of 400 μm x 400 μm is 6 μm.

A rotation micromirrror based on the two-layer repulsive force actuator was developed and fabricated. The rotation micromirror has a mirror size of 312 μm x 312 μm and achieves a mechanical rotation of 2.2°. A conventional design of the same size can only rotate 0.2° because of the “pull-in” effect.

A translation micromirror driven by the two-layer repulsive force actuator was also designed and fabricated. The translation micromirror has a mirror size of 250 μm x 250 μm and provides a translation of 1.8 μm, which is three times that of conventional designs.

Two RF MEMS tunable capacitors driven by the two-layer repulsive force actuator were designed, i.e., a stand-alone tunable capacitor and an above-IC tunable capacitor. Model predictions indicate that the stand-alone tunable capacitor can achieve a tuning ratio from 5:​1 to 30:​1 with a stiffness varying from 5 N/m to 80 N/m, and that the aboveiIC tunable capacitor can achieve a tuning ratio of 5.8:​1 with a stiffness of 2 N/m and a tuning ratio of 4.8:​1 with a stiffness of 5 N/m. Conventional MEMS tunable capacitors can only achieve a tuning ratio of 1.5:​1 due to the “pull-in” effect.