PARASITIC CHARGING OF DIELECTRIC SURFACES IN CAPACITIVE MICROELECTROMECHANICAL SYSTEMS (MEMS)

Silicon dioxide and silicon nitride coatings are preferably used as di electric layers for short-circuit protection in capacitive silicon mic rosensors and microactuators. However, their tendency to electrostatic charging can diminish the device reliability. Gas discharges in the a ir gap of silicon cantilever actuators have been observed, resulting i n surface charge accumulation on the electrode passivation of the devi ces. Charge decay characteristics were recorded for a silicon oxide pa ssivation and a multilayer passivation by silicon oxide and silicon ni tride. The charges are found to be highly stable in time. Based on the se observations, rules for the application and design of dielectric la yers in microdevices are proposed. (C) 1998 Elsevier Science S.A. All rights reserved.