Influence of scalloping on electrostatic forces in comb drive microdevices

Abstract

Deep reactive-ion etching process is one of the most widely used manufacturing processes for micro-electro-mechanical-system (MEMS) devices, but the main problem with this process is that it leads to undesirable fabrication defects such as slanting, scalloping, etc. In this work, we develop analytical model to capture the effect of scalloping on electrostatic forces in a MEMS-based comb structure. In addition, we also modify the formula to include the parameters related to the size as well as number of scallops. To develop the model, we assume the shape of a scallop as elliptical which is characterized by major axis (2a) and semi-minor axis (b). To validate the model, we compare results with finite element results obtained using Coventerware for single as well as multi-scallops. Subsequently, we discuss the combined effect of scalloping and slanting on electrostatic forces in a comb drive structure. The model presented in the paper may be useful at the design stage of various comb drive MEMS devices such as MEMS gyroscopes.