A vacuum packaged differential resonant accelerometer using gap sensitive electrostatic stiffness changing effect

This paper proposes an INS (Inertial Navigation System) grade, surface micro-machined differential resonant accelerometer (DRXL) by using the epitaxially grown thick polysilicon process. This proposed DRXL device produces a differential digital output upon an applied acceleration, and the principle is a gap-dependent electrical stiffness variation of the electrostatic resonator with torsion beam structures. Using this new operating concept, we designed, fabricated and tested the proposed device. The final device was fabricated by using the wafer level vacuum packaging process. The hermetic sealing cap structure was made of Pyrex 7740 glass with Ti layer as gettering material, and this cap wafer was anodically bonded with the polysilicon wafer at vacuum ambience. The measured Q-factor of the vacuum packaged DRXL was about 1/spl times/10/sup 3/ and the estimated inner pressure was about 200[mTorr]. We also achieved 73[Hz] output frequency change per unit G(9.8 m/s/sup c/) input with 12,716[Hz] nominal resonant frequency.