Squeeze film air damping ratio analysis of a silicon capacitive micromechanical accelerometer

摘要

The dynamics behavior of most micro-electro-mechanical-system (MEMS) devices is significantly affected by the squeeze-film air damping. Therefore, the correct prediction of the squeeze-film air damping ratio is essential in MEMS devices design. In the paper, a static state test is proposed to measure the squeeze-film air damping ratios of a silicon capacitive micromechanical accelerometer under different pressures. The unsealed chip of capacitive accelerometer is placed in a vacuum extraction chamber and an open loop circuit is developed to apply step signal. By charging the pressure and measuring the overshoot M (p) and the settling time t (s) from the time response of the chip, the damping ratio xi under different pressures can be calculated. Finite element method (FEM) based on the modified Reynolds equation is utilized to simulate the transient response of the micro-structure. Good correlation between experimental and numerical results is obtained. The proposed static state test in this paper provides a new and much easy method to measure the dynamic performances of micro-structures under various pressures.