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

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 ξ 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.