A high sensitivity Z-axis torsional silicon accelerometer

This paper presents a high sensitivity silicon micromachined capacitive accelerometer fabricated using a three mask, dissolved wafer process. High electrical sensitivity is obtained by using high aspect-ratio comb fingers with narrow air gaps of 2 mu m and large overlap area of 12 mu mx300 mu m. Torsional suspension beams 150 mu m long with a cross-sectional area of 12 mu mx3 mu m are used to improve the mechanical gain (form factor). By using a varying overlap area method, the dynamic range, the pull-in voltage and the bandwidth are improved. The fabricated accelerometers yielded sensitivities of 263-300mV/g, a nonlinearity less than 0.2% over a range of -4g to +3g, a full scale range of -4g to +6g and pull-in voltages greater than 8V. A 3dB cut-off frequency of 30Hz was measured in air. The minimum resolution measured by the readout electronics was 0.077g.