Pull-in dynamics: analysis and modeling of the transitional regime

A meta-stable deflection just beyond pull-in displacement of a parallel-plate electrostatic actuator has been identified and it is demonstrated that this effect ultimately governs the pull-in time in critically damped systems. The modeling of this meta-stable regime, therefore, largely determines the reliability of the overall calculation of the pull-in dynamic transition. An analytical model is derived and compared with measurements. The model accuracy, despite its simplicity, is sufficient to make it a valuable tool for the design of MEMS switches outside vacuum and for sensors based on measuring pull-in time. A first test on a pull-in time-operated accelerometer provides a sensitivity of 0.92 μs/μg and a noise level at 72 μg/√Hz.