One mechanically decoupled Z-axis gyroscope

Mechanical coupling between the two working modes usually makes the micromachined Coriolis vibratory gyroscope's operation unstable. In this paper, one Z-axis gyroscope which is sensitive to angular rotation about one axis normal to the plane of the silicon chip was mechanically decoupled through sixteen independent suspension beams. The sixteen beams were classified into four groups, ie. inner drive beams, inner sense beams, outer drive beams and outer sense beams. The coupling on drive mode from sense mode was almost canceled due to the approximate zero deformation in axial direction of the inner drive beams during operation. To evaluate the effect of decoupling, the system level model was built up using Multi Port Element Network method. The simulation results showed that the coupling was decreased approximately 2930 times with the presented geometry size. Finally, the Z-axis gyroscope was fabricated through bulk micromachining process. The biased comb fingers, whose motor fingers were not at the mid-point between the two adjacent stator fingers, were taken to increase the bonding area between the glass and silicon wafer. The fabrication results showed that the larger bonding area was really helpful for preventing the movable structure breaking off from the substrate, because there is nearly zero breaking-off happening in one 4 inch wafer during the process experiment.