Flexures for large stroke electrostatic actuation in MEMS

Abstract

The stroke of a microelectromechanical systems (MEMS) stage suspended by a flexure mechanism and actuated by electrostatic comb-drives is limited by pull-in. A method to analyze the electrostatic stability of a flexure mechanism and to optimize the stroke with respect to the footprint of flexure mechanisms is presented. Four flexure mechanisms for large stroke are investigated; the standard folded flexure, the slaved folded flexure, the tilted folded flexure and the Watt flexure. Given a certain stroke and load force, the flexures are optimized to have a minimum wafer footprint. From these optimizations it is concluded that the standard folded flexure mechanism is the best flexure mechanism for relatively small strokes (up to 40 m) and for larger strokes it is better to use the tilted folded flexure. Several optimized flexure mechanisms have been fabricated and experimentally tested to reach a stroke of 100 m. The displacement of the fabricated stages as a function of the actuation voltage could be predicted with 82% accuracy, limited by the fairly large tolerances of our fabrication process.