MEMS Cantilevered Energy Harvester with Tapered Thickness for Stress Control

This paper reports on the improvement of the output power of piezoelectric energy harvesters (PEHs). A tapered thickness structure of a cantilever beam for uniform stress, tungsten proof mass, thick piezoelectric film, and series connection of the piezoelectric films are utilized for PEHs to increase the output power. The three-dimensional (3D) etching process of Si enables the formation of tapered thickness beam structure, which increases not only the output power, but the beam strength. The 3D shape allows to increase the weight of the proof mass, contributing to increase the output voltage and power. Furthermore, output voltage is enhanced by using series-connection of PZT cells to improve the circuit efficiency. The open-circuit output voltage and optimum power with resistance load of the fabricated harvesting device revealed 14.4 V
0-P
and 92 μW at an acceleration of 9.8 m/s
²
. The output power was improved by 8.9 times higher than that of the conventional model.