Merging parallel-plate and levitation actuators to enable linearity and tunability in electrostatic MEMS

Abstract

In this study, a linear electrostatic MEMS actuator is introduced. The system consists of a MEMS cantilever beam with combined parallel-plate and electrostatic levitation forces. By using these two forcing methods simultaneously, the static response and natural frequency can be made to vary linearly with voltage. The static response shows a linear increase of 90nm per volt and is maintained for more than 12µm of tip displacement. The natural frequency shows a linear increase of 16Hz per volt and is maintained throughout a 2.9kHz shift in natural frequency. This wide range of linear displacement and frequency tunability is extremely useful for MEMS sensors and actuators, which suffer from the inherent nonlinearity of electrostatic forces. A theoretical model of the system is derived and validated with experimental data. Static, natural frequency, and frequency response calculations are performed. Merging these two mechanisms enables high oscillation branches for a wide range of frequencies with potential applications in MEMS filters, oscillators and sensors.

A Tunable Electrostatic MEMS Pressure Switch

“…The capacitances were calculated at gaps (between the beam and center electrode) from 0.1µm to 20µm at a step of 0.1µm, which gives numerical profiles of the capacitance as a function of the beam z-direction displacement. A direct solver with a tolerance of 10 −12 is used, which has matched very closely with previous experiments by the authors [11], [16], [17], [19].…”

“…The potential energy of an electrostatic system is given by U = 1 2 CV 2 , where C is the capacitance and V is the applied voltage. Because the system has multiple electrodes, there are multiple capacitances and the potential energy is given by [11],…”

“…The nonlinearity also introduces another complication to the switch. This system shows significant softening nonlinearities in the frequency response from both the side and bias voltage [11]. This makes driving the system at its natural frequency difficult because the natural frequency decreases as the oscillation amplitude increases.…”

“…The actuator proposed by the authors in a previous study [11] can be used as a bifurcation pressure switch because the dynamic pull-in instability is dependent on the ambient pressure. The switch uses an electrostatic levitation electrode configuration [12]- [14] with two input voltages.…”

“…To use the MEMS actuator from [11] as a pressure switch, the beam is excited near its natural frequency through an AC voltage on the side electrodes (herein referred to as the side voltage). If the beam travels too close to the center electrode, dynamic pull-in is triggered and the switch is closed.…”