Improved anchor design for flat MEMS structure by suppressing deformation due to buried-oxide stress on silicon-on-insulator wafer

Abstract Silicon-on-insulator (SOI) wafers are used in many micro-electromechanical system (MEMS) devices because of their stable mechanical properties. However, one of the disadvantages of using the SOI configuration is residual stress deformation; strong residual stresses in the buried-oxide layer deform the device and deteriorate its performance. This could prevent the development of high-precision sensors and actuators. In recent years, a new deformation mode caused by this residual stress has been reported, involving tilting of the suspended MEMS structure owing to local deformation of the anchor. However, methods to solve this problem have not yet been proposed. In this study, we propose a simple T-shaped support as a solution to the tilt deformation. We verified its effects by finite element analysis and experiments; the proposed structure was observed to successfully reduce the tip displacement of a SOI-based cantilever by one-fourth. In addition, we applied the proposed method to a parallel-plate accelerometer as a demonstration to confirm that the sensitivity variations of the device reduced from 10.8% to 6.8% using the proposed support structure. Thus, we believe that the proposed design can contribute to the development of extremely accurate MEMS sensors and optical devices.