A novel large displacement electrostatic actuator: pre-stress comb-drive actuator

Abstract

This investigation proposes a novel large vertical displacement electrostatic actuator, called the pre-stress comb-drive actuator (PCA), which exhibits no pull-in and no hysteresis characteristics. The proposed PCA consists of a set of comb fingers fabricated along the composite beam and substrate. One end of the composite beam is clamped to the anchor, whereas the other end is elevated vertically by the residual stress. The actuation occurs when the electrostatic force, induced by the fringe effect, pulls the composite beam downward to the substrate. A post-heat treatment process was employed to increase the initial lift height of the PCA to obtain a large actuation stroke. A mathematical model, based on a newly developed modeling approach, is introduced to estimate the static characteristic of the PCA. A PCA was fabricated using the PolyMUMPs process based on the proposed design concept. Following packaging and applying a post-heat treatment process, a 110 µm initial tip height and a 90 µm vertical motion range were achieved. Neither pull-in nor hysteresis was observed. The simulation results were closely matched with the observations. This work also studies the frequency response and measurement of the maximum vibration of the PCA.

Micro actuated grating for multi-beam optical pickups

“…To overcome the limited actuation distance, Rosa et al proposed an external electrode bi-morph actuator to operate over the entire range of motion by preventing electrostatic pull-in instability [8]. However, the fringe effect between the moving and the fixed external electrodes is relatively insufficient to obtain enough actuating force.Accordingly, the bimorph actuator used in this paper is based on the design demonstrated by Chiou et al [9], which used comb-shape external electrodes and post heat treatment to achieve higher actuation distance under lower voltages.…”

A Novel Capacitive Sensing Principle for Microdevices

“…Many experimental and theoretical studies have been done on the pull-in instability problem involved in actuation. And various approaches such as the pre-stress combdrive method [7], voltage control method [8], additional suppression comb electrodes [9], and offset-drive method [10] etc. have been presented to control the pull-in or extend the actuator travel range beyond the limitation of pull-in.…”

Computation of capacitance and electrostatic forces for the electrostatically driving actuators considering fringe effects

“…This in turn requires profound investigations on the capacitance of the mechanical structures and the charge density distribution on the surfaces of the MEMS devices. From the very beginning of the MEMS field research, capacitance has always been an important factor to be studied for MEMS structures because the displacement, sensitivity, instability and dynamics of the electrostatically driving structures depend crucially upon interplay of electrical and mechanical forces generated within the devices (Chiou and Lin 2005;Chen and Lee 2004;Chena et al 2008;Huang and Ganyu 2004;Zhou and Dowd 2003;Jeong and Ha 2005;Borovic et al 2006). The electrostatic forces changes the dynamic behaviors of the MEMS structures and the electrostatic charges redistribute when the Abstract Many micro-electro-mechanical systems sensors and actuators adopted electrostatically driving structures, whose electrostatic forces or driving voltages should be considered and evaluated based on calculating the capacitance and electrostatic forces of the structures, such as parallel plate capacitors, plate combs and sector combs.…”