Design and Characterization of CMOS Micromachined Piezoresistive Accelerometers

-In this article, we present the design and characterization of monolithically integrated CMOS micromachined accelerometers utilizing polysilicon piezoresistors. Despite their lower piezoresistive effect compared to their single crystal counterpart, we achieve enhanced sensitivity by implementing thin support beams to amplify the piezoresistive change upon detection. To facilitate a comprehensive comparison, three designs with proof mass sizes of 100 x 100, 150 x 150, and 200 x 200 mu m2 and a proof-mass thickness of 8.3 mu m were fabricated. These designs were realized using a 0.35 mu m CMOS process followed by post-CMOS wet etching processes. The measured results revealed outof plane resonant frequencies of 8.125, 4.015, and 2.260 kHz for the respective designs. The 200-mu m design exhibited the highest sensitivity, measuring 317.7 mu V/g/V for out-of-plane acceleration, while the 100-mu m design demonstrated a sensitivity of 38.6 mu V/g/V. In addition, the 200-mu m design displayed a sensing resolution of 15 mg, accompanied by a temperature dependence of -2.60 mu V/g/V/degrees C. The results demonstrate the promising potential of CMOS piezoresistive accelerometers for various sensing applications.