A wide dynamic range Silicon-on-Insulator MEMS gyroscope with digital force feedback

This paper presents development efforts and initial test data for a Silicon-on-Insulator (SOI) Micro Electro Mechanical System (MEMS), vibratory angular rate sensor intended for hypervelocity and small diameter missiles and munitions. The SOI angular rate sensor (gyroscope), intended for wide dynamic range and harsh environment applications, utilizes advantages offered from the mass and feature sizes achieved by Deep Reactive Ion Etching (DRIE). This particular effort is focused on developing a symmetric device design along with multi-bit sigma-delta force-feedback control to increase dynamic range and reduce susceptibility to environmental parameters, including temperature, vibration, and sustained Z-axis acceleration loading. A prototype, single layer MEMS chip, consisting of a proof mass placed in a three-fold mode-decoupled symmetric suspension, has been fabricated and tested. The mode-decoupled suspension allows only one degree of in-plane motion for each comb drive, thereby attenuating errors due to oscillation axis misalignment. In addition, suspension symmetry maintains matched oscillation mode frequencies through processing and temperature variations, allowing maximized dynamic range in the discrete-time control loop. Attached to the suspension are comb-drives operating in their linear mode. Use of these actuators eliminates deflection-induced nonlinearity in the control loop. The rate sensing performance of these devices in an open-loop configuration has been characterized, and a unit is being flight-tested on a prototype hypervelocity missile. Current efforts will reduce random walk through preamp optimization, add an excitation control loop to improve bias stability, and implement the digital feedback loop to increase dynamic range. This paper presents recent development efforts and initial test data for the SOI-based angular rate sensor, intended for small diameter missiles and munitions applications.