Design, simulation, and fabrication of silicon-on-insulator MEMS vibratory decoupled gyroscope

This paper reports the design and fabrication of a 2-degree-of-freedom (DOF) decoupled vibratory gyroscope based on a silicon-on-insulator (SOI) MEMS process. The 2-DOF capacitive comb structure is deliberately designed to have a decoupled drive and sense mode oscillation to prevent the unstable operation due to mechanical coupling, resulting in a low zero rate out-put drift. It is well known that the closer are the drive and sense resonances, the higher is the angular rate resolution of the gyroscope. Generally, this is achieved by using symmetric suspensions, but it results in a reduced bandwidth. The proposed design has been configured to achieve a bandwidth of about 150 Hz, while ensuring the decoupled operation of the drive and sense modes. An analytical method has been employed to study the steady state response of the 2-DOF structure. FEM analysis has been carried out in CoventorWare$^{\circledR}$ MEMS Design software and the simulation results show that the drive resonance occurs at 21.48 kHz and sense resonance at 21.63 kHz, which are in close agreement with the theoretical results. The structure is designed with a 15 $\mu$m thick device layer. Fabrication of the design is proposed using a two mask process based on Deep reactive-ion etching (DRIE) and sacrificial wet release etching on a SOI wafer. DRIE etching with an aspect ratio of 1:5 has been successfully carried out as desired and the results have been presented.