Influence of residual stress on performance of AlN thin film based piezoelectric MEMS accelerometer structure

摘要

The presence of residual stress is inevitable and major constraint for MEMS devices as they induce deformation, fracture, fatigue and micro structural changes in the structure. This paper presents the influence of residual stresses (up to - 2100 MPa) on the performance of AlN based piezoelectric MEMS accelerometer structure. The MEMS structure consists of an AlN coated silicon proof mass (800 mu m x 800 mu m x 300 mu m) suspended by four beams (400 mu m x 200 mu m x 10 mu m). Under the influence of residual stress (- 2100 MPa), the first three modal frequencies (13.54 kHz, 20.95 kHz and 20.95 kHz) of the accelerometer structure are reduced to 5.19 kHz, 10.17 kHz and 10.17 kHz respectively. The location of proof mass deflection and maximum von-Mises stress also get altered. Hence the structure sensitivity is also modified from 3.64 x 10(-2)/g (at no residual stress) to 2.54 x 10(-4)/g (at - 2100 MPa). The damping factor of the structure also gets modified from 3.96 to 10.38 due to the residual stress. Thus, the accelerometer frequency response (3 dB bandwidth) is found to be diminished from 1.81 to 0.26 kHz due to the presence of residual stress.