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 mum/g and thickness of 40 mum which is compatible with bulk micromachining process requirements. Simulations were carried out using IntelliSuite 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 mum 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.