Surface Micromachined Angular Accelerometer With Force Feedback

In response to the growing demand for angular acceleration measurements on computer hard drives, a surface micromachined, force feedback, fully integrated angular accelerometer has been developed. The mechanical sensing structure consists of a 362 μm diameter polysilicon inertial wheel suspended by a quad-symmetric, folded-beam suspension. A differential, parallel plate capacitive pick-off scheme and analog feedback loop are integrated on-chip. The sensor output is the force-balance control voltage which changes linearly with applied angular acceleration. The first generation sensors has a 0.24 μVrms/rad/sec2 sensitivity with a noise floor of 75 rad/sec2/√Hz. In the second generation sensors, the mechanical structure has been optimized within the design constraints to effectively double the sensitivity. Both generations of angular accelerometers are fabricated in the BiMOS2C process of Analog Devices, Inc.