Z-axis differential silicon-on-insulator resonant accelerometer with high sensitivity

The design, fabrication and testing of a z-axis micro-machined resonant accelerometer with differential detection fabricated by silicon-on-insulator (SOI) microelectromechanical system technology are reported. The sensor chip was developed by a silicon-direct-bonding SOI wafer (10 + 2 + 290 mu m). Z-axis acceleration is differentially detected by using two H-style vibrating beams through a frequency shift caused by the inertial force acting as bending stress loading. To improve the sensitivity of the accelerometer, an amplifying mechanism formed by vibrating beams, supporting beams and seismic-mass, which are respectively designed with their thickness as 10, 30 and 300 mu m, is adopted, from which the transformation efficiency between the external acceleration and the bending stress of the vibrating beams would be improved obviously. The electromagnetically excitation and detection is adopted to make the closed-loop control of the sensor easier. Testing results show that the Q-factors of the two vibrating beams are about 400 in the air and the differential sensitivity measured by two H-style resonators can reach to 584 Hz/g.