A bulk micromachined z-axis single crystal silicon gyroscope for commercial applications

In this paper, a bulk micromachined z-axis single crystal silicon gyroscope is presented. The symmetrical and double decoupled structures can greatly suppress the mechanical coupling and easily realize the match of resonant frequencies between the driving mode and sensing mode. Finite element method (FEM) simulation shows that the mechanical intercoupling is less than 0.6% in orthogonal direction and 0.1% in parallel direction. Silicon on glass (SOG) process is utilized to fabricate the gyroscope, therefore large proof mass and capacitance can be achieved with an aspect ratio about 20. The resonant frequencies of driving mode and sensing mode are 4,027 Hz and 4,111 Hz, respectively, which are in good agreement with calculated values. The deviation of bandwidth from design caused by fabrication imperfection is less than 1%. Large quality factors of the working modes are obtained which are 216 and 85 at atmosphere environment, respectively, because large gap between proof mass and substrate is fabricated, and slide film air damping is designed to dominate the operation. Test results show that the scale factor of the gyroscope is 0.9 mv/deg/s in the range of plusmn250deg/s. The signal-to-noise ratio (SNR) is more than 100 at a 10 Hz angular vibration input with a 0.4deg amplitude. The noise equivalent angular rate is 0.008deg/s/Hz^1/2.