Full-range Dynamic Positioning of Parallel-plate Electrostatic Actuators

⎯ The nonlinear dynamics of a parallel-plate electrostatically driven microstructure has been investigated. Simulations and experimental results on devices fabricated in an epi-poly process confirm that instability is avoided by a timely reversal of the rate of change of the drive voltage. A 5.5V peak sine wave with frequency higher than 300 Hz allows repetitive microstructure motion up to 70% of gap without position feedback. The results of the analysis have been applied to yield a new concept for positioning beyond the static pullin limitation that does include position feedback. The measured momentary actuator displacement is compared with the desired displacement setting and, unlike traditional feedback, the voltage applied to the actuator is changed according to the comparison result between two values. Operation is limited only by the position jitter due to the time delay introduced by the readout circuits and measurements confirm flexible operation up to a mechanical stopper positioned at 2 μm of the 2.25 μm wide gap with a 30 nm ripple.