Non-Crossing Differential Capacitive MEMS Accelerometer with Electrostatic Spring Tuning

This paper presents the design and simulation of non-crossing differential capacitive MEMS accelerometer with electrostatic spring tuning. The accelerometers were designed with critical damping for 10 g range, mechanical sensitivity of 0.012 μm/g and thickness of 40 μm which is compatible with bulk micromachining process requirements. Simulations were carried out usingIntelliSuite 7.2.Results show that the open loop accelerometer with mechanical spring of 52.3 N/m could be tuned by negative electrostatic spring using 10 V, 7.5 V and 5 V to produce -22 N/m, -12.5 N/m and -5.6 N/m respectively with 12 pairs of electrostatic finger with 1.8 μm gap, and capacitance sensitivity is increased from 20 fF/g to 40 fF/g while the dynamic range decreased to 5.8 g. The designed force-balanced accelerometer has capacitance sensitivity of 10.67 fF/g, mechanical spring of 62.2 N/m and uses 8 pairs of electrostatic finger to produce -17.7 N/m, -9.9 N/m and -4.4 N/m respectively using 10 V, 7.5 V and 5 V. Hence, the dynamic range could be tuned down from 17 g to 14 g and capacitance sensitivity increased to 12 fF/g. The fabricated devices are also shown in this paper. The designed accelerometer with electrostatic spring tuning therefore enable us to tune to the suitable specifications with the needed g measurement.