Achieving High Quality Factor Without Vacuum Packaging by High Density Proof Mass Integration in Vibration Energy Harvesters

This paper presents a simple approach to control fluidic damping, and thereby improve the mechanical quality factor at ambient pressure, of AlN-based piezoelectric resonant energy harvesters by using high density proof masses. Using models adapted from the literature, and accounting for the simultaneous transverse and rotational motion of the cantilever beam, scaling laws are extracted for the fluidic quality factor, Qf, as a function of the fluid damping regime, either due to drag or squeeze film forces. Subsequently, we demonstrate the utility of the scaling laws by characterizing silicon-based devices and tungsten tip masses. By accounting for other damping sources and the device operating frequency, we achieve close to an order of magnitude improvement on Qf with this strategy, going from 398 to 4193. Beside potential for footprint reductions and higher power outputs, these results suggest that high density proof mass integration can be an alternative to vacuum packaging for MEMS based vibration energy harvesting.