Design and sensitivity analysis of MEMS 3D capacitive comb type accelerometer

This paper presents design and sensitivity analysis of a 3D inter-digitated combs and folded beam structure based MEMS accelerometer. Initially a mathematical model of the accelerometer is developed and its effects on the displacement sensitivity and capacitance sensitivity are analyzed. It is observed that the sensitivity of accelerometer can be improved through optimal selection of design parameters viz. beam length, beam width, overlap area, mass width, number of fingers. Finally the structure is designed in COMSOL multiphysics simulation tool to extract the device sensitivities. The structure of comb type 3D accelerometer comprises of a proof mass, 24 sensing fingers, 8 driving fingers, folded beams (springs) and two anchors. The beam length is 350 μm, beam width is 2 μm, spring constant is 0.4564 N/m, anchor area is 40×40 μm2, mass width is 70 μm and mass length is 350 μm. The obtained value of displacement between combs is 0.154 nm when 1 g acceleration is applied on the movable mass and displacement sensitivity is 0.154 nm/g. The corresponding capacitance sensitivity is 7.85×10-18 F. The stress analysis at different values of acceleration is also carried out.