In this paper, we propose a passive gap-spacing control method in order to avoid stiction between top and bottom structures in in-plane sensor/actuator/generator applications. A patterned electret using a high-performance perfluoro polymer material is employed to induce a repulsive electrostatic force. An out-of-plane repulsive force is successfully demonstrated with our early prototype, in both air and liquid. By using the present electret-based levitation method to keep the air gap, a MEMS electret generator has been developed for energy-harvesting applications. A dual-phase electrode arrangement is adopted in order to reduce the horizontal electrostatic damping force. With the present prototype, about 0.5 μW is obtained for both phases of the generator, resulting in a total power output of 1.0 μW at an acceleration of 2 g with 63 Hz. With our electromechanical model of the generator, we have confirmed that the model can mimic the response of the generator prototype.

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A complete electromechanical model of vibrationdriven micro electret power generators has been developed, and its characteristics are directly compared with experimental data to verify the model. Nonlinear power management circuit for rectification and impedance conversion is also assumed. It is found that the electrostatic damping force acting on the seismic mass is dependent on the external circuit. From coupling simulation with a mechanical vibration model, it is also found that the circuit parameters should be optimized dependent on the oscillation condition.

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