Analytical study on the capacitive accelerometer´s fingers in microelectromechanical systems (MEMS)

This paper presents new analytical study on the capacitive accelerometer´s fingers which utilizes branched comb finger electrode instead of the conventional straight finger electrode. It employs capacitive sensing using overlap-area variation between comb electrode and the suspension beam to provide higher sensitivity without compromising pull-in voltage, full-scale range, or bandwidth besides the ease of fabrication. Mathematical formulations of each structure are derived and analyzed using numerical analysis. Three shapes of finger electrodes, which consist of branched fingers, triangle shaped fingers and semi-circle shaped fingers are compared to obtain the optimal shape with the highest capacitance and sensitivity. The result shows that the semi-circle shaped electrodes have the highest capacitance of 915 fF and sensitivity of -449.4 pF/μm for a single 240 μm×4.6 μm suspension beam with 3 μm structure thickness followed by the triangle shaped fingers with capacitance of 29 fF and -124.7 pF/μm and the branched comb fingers with 42.5 fF and -106.3 pF/μm.