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 the voltage. The static response shows a linear increase of 90 nm/V and is maintained for more than 12μm of the tip displacement. The natural frequency shows a linear increase of 16 Hz/V and is maintained throughout a 2.9 kHz shift in the 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 response, 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.
Highlights
Nonlinearity in electrostatic microelectromechanical systems (MEMS) presents a challenging obstacle in the design of many MEMS sensors and actuators
We demonstrate the combined system can create a linear relationship with the side electrode voltage for the static response and first natural frequency
If the bias voltage is set to approximately 2V, the downward bending of the natural frequency curve at low side voltage reaches a point where it matches the slope at higher side voltages
Summary
Nonlinearity in electrostatic microelectromechanical systems (MEMS) presents a challenging obstacle in the design of many MEMS sensors and actuators. The electrostatic force is highly nonlinear and can create instability that leads to pull-in (when the two electrodes collapse together), stiction[2], and even chaos[3]. Much effort has been spent characterizing this system, and it has been shown to eliminate the pullin instability and increase travel ranges by more than an order of magnitude This comes at the expense of requiring a large actuation voltage because the levitation force is relatively weak compared to the attractive force between a pair of parallel plates. The authors have experimentally shown this system can act as a switch by applying a bias voltage to the center electrode[14] This allowed the switch to toggle to and from the pulled-in position for the purpose of creating a more durable switch.
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