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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We propose a high-speed charging method of electrets using vacuum ultraviolet irradiation. Due to a large amount of the ionization current at reduced pressure, it takes only a few seconds to charge 15-μm-thick polymer electret film to the surface potential of −900 V. This charging rate is two orders of magnitudes larger than corona/soft-x-ray charging methods. The purity of N2 gas depends on the charging rate since the O2 quenching mechanisms of exited N2 molecule would exist. No charge decay is observed for 3000 h, which indicates charged electrets are as stable as those by other charging methods.

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