A Novel Design for Enhancing the Sensitivity of a Capacitive MEMS Device

Sensitivity of a capacitive MEMS device mainly depends on gap variation across the inter-digitated electrodes for an applied acceleration. In conventional design, gap variations across the inter-digitated electrodes are typically due to the displacement of the movable electrodes attached to a movable mass, whereas the fixed electrodes remain static. In this paper, a novel design of secondary-mass-spring assembly is proposed to tilt the fixed electrodes along with the displacement of the moving electrode for applied acceleration such that the capacitive sensitivity is enhanced. The proposed structure is fabricated by a SOIMUMP's process. An experimentally measured values of the resonant frequency of the secondary mass and the proof mass are 1.06 and 2.68 kHz, respectively. The static response obtained using COMSOL Multiphysics simulation for applied body load of 1 g along Y-axis gives proof mass displacement sensitivity of 41.8 nm/g, secondary mass tilting of 0.000147°, and capacitive sensitivity improvement of 17.6%. Also, non-linearity of the output response is within ±2.5% for applied acceleration of ±15 g along the Y-axis. The differential arrangement of inter-digitated electrodes nullifies the cross-axis sensitivity. Differential capacitance increment of more than 50% is reported in the frequency range of 800 to 1200 Hz making it suitable for wideband energy harvesting applications.