Design and fabrication of SOI technology based MEMS differential capacitive accelerometer structure

Abstract

This paper discusses the design and fabrication of MEMS differential capacitive accelerometer (z-axis sensitive) structure. The accelerometer structure consists of one each movable and reference capacitors in the single accelerometer die fabricated using highly conductive (p-type, resistivity: 0.001 Ω cm) SOI substrate. Resonant frequencies of the designed movable and reference capacitive structures were found to be 9.6 kHz and 150 kHz respectively. Corresponding rest capacitance (at 0 g) of both the capacitors was 2.21 pF. The movable and reference structures showed a deflection of 0.14 µm and 0.6 nm respectively at 50 g applied acceleration. Corresponding changes in capacitances of the movable and reference capacitors were 82.3 fF and < 0.33 fF respectively. The designed accelerometer showed a scale factor sensitivity of the movable capacitor was of ~ 1.65 fF/g. The device demonstrated a dynamic range of in − 17 g to 42 g with a full-scale non-linearity of ~ 3%. Corresponding measured scale factor sensitivity in the centrifuge test was found to be ~ 47 mV/g with an acceleration resolution of ~ 17 mg. The device exhibited cross-axis sensitivity of ~ 2% in the full-scale range. Measured 3 dB bandwidth (380 Hz) of the device matches reasonably with the simulated value (~ 400 Hz).