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 /spl mu/m and large overlap area of 12 /spl mu/m/spl times/300 /spl mu/m. Torsional suspension beams 150 /spl mu/m long with a cross-sectional area of 12 /spl mu/m/spl times/3 /spl 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 263-300 mV/g, a nonlinearity less than 0.2% over a range of -4 g to +3 g, a full scale range of -4 g to +6 g and pull-in voltages greater than 8 V. A 3-dB cut-off frequency of 30 Hz was measured in air. The minimum resolution measured by the readout electronics was 0.077 g.