A CMOS-compatible high aspect ratio silicon-on-glass in-plane micro-accelerometer

This paper presents a post-CMOS -compatible micro-machined silicon-on-glass (SOG) in-plane capacitive accelerometer. The accelerometer is a high aspect ratio structure with a 120 mum thick single-crystal silicon proof-mass and 3.4 mum sense gap, bonded to a glass substrate. It is fabricated using a simple 3-mask, 5-step process, and is fully CMOS compatible. A CMOS switched-capacitor readout circuit and an oversampled Sigma-Delta modulator are used to read out capacitance changes from the accelerometer. The CMOS chip is 2.6 x 2.4 mm(2) in size, utilizes chopper stabilization and correlated double sampling techniques, has a 106 dB open-loop dynamic range, a low input offset of 370 muV, and can resolve better than 20 aF. The accelerometer system has a measured sensitivity of 40 mV g(-1) and input referred noise density of 79 mug Hz(-1/2). Using the SOG configuration, a post-CMOS monolithic integration technique is developed. The integration technique utilizes dielectric bridges, silicon islands and the SOG configuration to obtain a simple, robust and post-CMOS-compatible process. Utilizing this technique, an integrated SOG accelerometer has been fabricated using the University of Michigan 3mum CMOS process.