Damping Control for Packaged Micro Mechanical Devices

Abstract

Damping control for packaged micro mechanical devices, such as an accelerometer, is desired to achieve wide frequency range by preventing the overdamping and suppressing the resonance. For capacitive detection type devices, which have narrow gap in a sealed cavity, the control of the cavity pressure is required for the damping control. We developed a novel cavity pressure control method using non-evaporable getters (NEG) and inert gas in anodically bonded glass-silicon structure. From the experiments using deflection of thin silicon diaphragm, the cavity pressure could be controlled at 120 and 5900Pa as designed. In application to the accelerometer, vibration behavior of seismic mass was studied experimentally and simulated by using Molecular Gas film Lubrication (MGL) equation. The result indicates that the critical damping under controlled pressure can be well designed to achieve wide frequency range.