Self-limiting excitation of MEMS devices with surface electrodes

Abstract

An excitation method for MEMS devices with planar electrodes is described. The stationary part of the device (the stator) consists of three electrode arrays arranged in the 'ABCABC' order. 'A', 'B', and 'C' carry time-independent potentials and together form a spatially-periodic electrostatic profile. The moving part of the device (the translator) has two electrode arrays 'ababab', with 'a' and 'b' carrying time-dependent out-of-phase voltages. When the frequency of the time-dependent voltage is close to the natural frequency of the spring-mass system, the translator is driven into resonance. By adjusting the spatial phase of the stationary profile, the driving force on the translator can be maximized for any equilibrium position. Physical misalignment between the stator and translator resulting from imperfect fabrication can be corrected electrically. A dynamical equation describing translator motion is derived and analyzed for resonant and parametric driving. In both cases, the driving force depends on the translator displacement in a periodic fashion. Such nonlinearity of the driving force results in self-stabilization of forced oscillations. This property has implications for the stability of vibratory gyroscopes.