A Capacitive Silicon Microaccelerometer With Force Balancing Electrodes

A surface micromachined accelerometer, which senses an inertial motion with an area variation, has been developed. The accelerometer is designed as an interdigital rib structure that has a differential capacitor arrangement. The movable electrodes are mounted on a mass of 7 µm thick polysilicon and a pair of stationary electrodes is formed under the mass with a 1.5 µm gap. Both sides of the movable electrodes are fixed on the mass, and the stationary electrode is formed on the substrate without being suspended. As a result, the mechanical stress and the electrical pulling effects can be reduced in comparison to the comb-type capacitor arrangement. In order to improve the dynamic range and the linearity, a pair of comb-shaped force-balancing electrodes is placed on both sides of the mass. The force-balancing electrodes are fabricated on the same layer as the mass and anchored on a silicon substrate. In particular, differential feedback electrodes enable linear control of mass repositioning.