A Method to Identify Different Comb Gaps for MEMS Gyroscope at the Wafer Level Based on Negative Electrostatic Stiffness

Abstract

For high-accurate micro-electro-mechanical systems (MEMS) gyroscopes, comb gap errors influence the mechanical coupling errors and limit performance. In this study, an in situ method was proposed to identify the gaps of drive combs, drive-sense combs, and sense combs in MEMS gyroscopes that can be applied at the wafer level. Negative electrostatic stiffness of combs was considered in the model construction of the sense mode and the Y-axis in-phase mode, and the frequency change caused by this was applied to characterize the comb gaps. Eight chips in different positions of a wafer were selected for verification of this method. The results shows that errors of drive comb gaps, drive-sense comb gaps, and sense comb gaps in the chip near the wafer center were 0.67 μm, 0.60 μm, and 0.53 μm, respectively, and those in the chip at the wafer edge were 0.96 μm, 0.95 μm, and 0.71 μm, respectively. The variation of comb gaps was 0.08 μm in a single chip near the wafer center, and 0.03 μm in a single chip at the wafer edge. This work provides a method for the fabless designers to explore the effect of wafer process on the structures and reduce it through careful design.