Design and simulation of Vertical Bi-Directional fringe field tuning of new improved MEMS accelerometer using SOI Technology for stress compensation

Abstract

A new conceptual utilization of Silicon on Insulator (SOI) wafer is reported for bi-directional vertical electrostatic fringe field tuning of the Micro Electro Mechnical Systems (MEMS) micro accelerometer for compensating stress induced curling (up and down), sensitivity and mechanical dynamic response. The buried oxide (BOX) layer-based SOI wafer provides bi-directional electrodes for applying bias voltages independently. Residual stress induced curved deflection due to stress gradient is targeted for tuning and reducing its effects using fringe field electrode configuration in SOI wafer technology. Movable silicon structure is electrostatically (utilizing fringe field) brought back near to original mean position with softened stiffness (increase in sensitivity) and reducing drastically the effects of stress gradients. The simulations are carried out using COVENTORWARE and COMSOL Multiphysics software. The deflection results obtained by both software agree within 7.69% for maximum deviation. There is a deviation in change in capacitance (del C) of 5.89% when stress gradient of 0.1 MPa/μm and 17.62% when stress gradient of 4 MPa/μm is applied on the structure at 30 g. This deviation can be tuned by above mentioned Bi directional tuning. Additionally, non-linearity induced by stress gradient in sensitivity can also be tuned by electrostatic fringe field effectively upto 18.64% when higher stress gradient (4 MPa/μm) was affecting the structure. Maximum disagreement of 4.72% between analytical and simulated results promises the design of proposed tuning concept. The proposed tuning concept can be utilized for other MEMS devices suffering from stress gradient issues.