High Performance Mems Micro-Gyroscope

This,paper reports on JPL's on-going research into MEMS gyroscopes. [1-4] This paper will describe the gyroscope's fabrication-methods, a new 8-electrode layout developed to improve performance and performance statistics of a batch of six gyroscopes (of the 8-electrode design) recently rate tested. Previously in our group, T. Tang and R. Gutierrez presented the results of their extensive use of ethylene diamine pyrocatechol (EDP) to deep-etch the inertial-sensitive resonators and post-supporting structures in a 4-electrode gyroscope design. Today, JPL is utilizing an in-house STS DRIE, replacing the old wet-etching steps. This has demonstrated superior precision in machining symmetry of the resonators, thus significantly reducing native rocking mode frequency-splits. A performance test of six gyros has shown an average, un-tuned, frequency split of 0.4% (11Hz split for rocking modes at 2.7KHz). The new JPL MEMS gyroscope has a unique 8-electrode layout, whose large electrodes can provide significant electrostatic softening of the resonator's springs. This allows matching of the Coriolis sensitive rocking modal frequencies to be improved from the native 0.4% to an average tuned frequency split of 0.02%. In separate tests, electrostatic tuning in the 8-electrode design has demonstrated the ability to match frequency-splits to within 10mHz, thus ensuring full degeneracy in even a very high Q device. In addition, a newly selected ceramic package-substrate has improved the device's dampening loses such that a mean Q of 28,000 was achieved in the six gyroscope tested. These Q's were measured via the ring-down time method. The improved fabrication development and other modifications described have led to the JPL's MEMS gyroscope achieving an average bias instability (Allan variance 1/f floor estimate) of 11degree/hr with best in the group being 2degree/hr. In an independent test, Honeywell Inc., reported one of our MEMS gyroscopes as achieving 1degree/hr bias instability flicker floor estimate measured at constant temperature.