Z-axis Capacitive Accelerometer with novel beams using SOG Structure

A differential capacitive silicon z-axis micro-accelerometer with special tethers, based on anisotropy etching, anodic bonding and DRIE (Deep Reactive Ion Etching) technology is proposed and a novel inertia structure is designed. The device with a three-layer structure can provide a variable sensitivity as changing the thickness of the beam fabricated by one set of masks. The simulation of the static and modal performances and the optimized design of the accelerometer are accomplished with the FEM (finite element method). The key techniques in the fabrication are investigated and the process flow is designed, furthermore, corner compensation structure is used in the masks to avoid convex corner undercutting, which is simulated and optimized by process simulation as IntelliSuite. The damping coefficient formula is used to optimize the system dynamic characteristics by adjusting system-damping ratio to 0.678 through changing the parameters of the proof mass. The mechanical sensitivity of the accelerometer varies from 0.12pF/g to 8.7×10^-3pF/g as the thickness of the beam from 20μm to 50μm. This is a very important result in terms of making variable accelerometers adopted for variable sensitivity and measure range using one set of masks.