Relation between charge on free electrodes and the response of electrostatic MEMS actuators and sensors

Abstract

ABSTRACT Stability is an important factor in the study of electrostatic MEMS switches and sensors. Their response issigni cantly improved by either applying a large dc bias or by depositing a prescribed value of charge on theoating electrodes. This charge is related to the pull-in voltages. Measurement of charge without causingloading is recommended; so instead of incorporating any eld operated transistor circuitry for this purpose,methods are developed to relate the charge magnitude to the dynamical response of the actuators. Elata et al.developed ecient and reliable ways of charge monitoring without causing loading to the device. These methodsrely on energy of the system instead of performing integration in the time domain. Based on their work, thispaper examines the alterations in the dynamic response of actuators. The positive and negative pull-in voltagesin the voltage displacement plane are symmetrically located with respect to charge on the oating electrode.This fact is exploited to carry out indirect charge measurement from the average of the two pull-in values. Aregression scheme is proposed that predicts the charge from the voltage shift based on limited measurements ofcapacitance of the actuator.Keywords: MEMS, Electrostatic actuators, Pull-in voltage, Floating electrode charge