Double-Deck MEMS Electrostatic Vibrational Energy Harvester with Airborne Interconnection

Abstract

Lowering internal impedance, i.e., stray capacitance and resistance, is essential to enhance the output power of microelectromechanical system (MEMS) vibrational energy harvesters particularly when the structure is made of a silicon-on-insulator (SOI) wafer which has a distributed stray capacitance across the buried oxide (BOX) layer. Instead of using silicon as a material for electrical interconnection, we used an out-of-plane aluminum bonding wire to complete the on-chip electrical interconnection between the contact pads on the chip frame and the suspended movable electrodes. Compared with the conventional design using silicon-based interconnections, the maximum deliverable power has been enhanced almost six-fold because of the reduced stray capacitance between the SOI layer and the substrate, as well as reduced internal electrical resistance. The mechanical stability of the bonded wire during the excitation vibration has also been experimentally confirmed. A typical power density of 763 µW/cm³ is obtained when excited by 0.5 G (1 G = 9.8 m/s²) sinusoidal vibrations at 157 Hz.