Power enhancement of MEMS vibrational electrostatic energy harvester by stray capacitance reduction

We report a design method to enhance the output power of vibrational microelectromechanical system (MEMS) electrostatic energy harvesters by reducing the reactive power that does not contribute to the net output. The mechanism of enhancing the active current while reducing the reactive current is analytically studied using an equivalent circuit model of electret-based velocity-damped resonant-generator. Reduction of the internal parasitic capacitance associated to the contact pads and electrical interconnections significantly improves the power factor and increases the deliverable power. The design strategy is applied to an actual device that produces 1.3 mW from the vibrations of 0.65 G (1 G = 9.8 m s −2 ) at 158 Hz, suggesting a 2.9-fold enhancement of output power by increasing the buried oxide layer thickness from 1 µ m to 3 µ m.