A laterally driven symmetric micro-resonator for gyroscopic applications

Abstract

Conventional microgyroscopes of the vibrating type require resonant frequency tuning of the driving and sensing modes to achieve high sensitivity These tuning conditions depend on each microgyroscope fabricated, even though the microgyroscopes are identically designed. A new micromachined resonator, which is applicable to microgyroscopes with self-tuning characteristics, is presented. Since the laterally driven two-degrees-of-freedom resonator was designed as a symmetric structure with identical stiffness in two orthogonal axes, the resonator is applicable to vibrating microgyroscopes, which do not need mode tuning. A dynamic model of the resonator was derived considering gyroscopic applications. The dynamic model was evaluated by experimental comparison with fabricated resonators. The resonators were fabricated using a simple process of a single polysilicon layer deposited on an insulator layer. The feasibility of the resonator as a vibrating microgyroscope with self-tuning capability is discussed. The fabricated resonators of a particular design have process-induced non-uniformities that cause different resonant frequencies. For several resonators, the standard deviations of the driving and sensing resonant frequencies were as high as 1232 and 1214 Hz, whereas the experimental average detuning frequency was 91.75 Nz. The minimum detuned frequency was 68 Hz with 0.034 mV s(-1) sensitivity. The sensitivity of the microgyroscope was low due to process-induced non-uniformity; however, the angular rate bandwidth was wide. This resonator could be successfully applicable to a vibrating microgyroscope with high sensitivity, if improvements in uniformity of the fabrication process are achieved. Further developments in improved integrated circuits are expected to lower the noise level even more.