Comparative Electrode Design for Piezoelectric MEMS Kinetic Energy Harvester

Abstract

Microsystem based piezoelectric kinetic energy harvesters have been extensively investigated over the past decade. The most popular structure of these devices includes a cantilever consisting of a substrate, and a parallel capacitor (electrode/piezoelectric/electrode) layout. This type of structure has the ability to harvest energy by working in the d₃₁ mode where the electrical potential is taken in the 3 (out of plane direction) while the strain/stress occurs in the 1 (in plane direction) direction. However, the d₃₁ piezoelectric properties are approximately half the value compared to the d₃₃ mode. Therefore, operating in the d₃₃ mode should result in increased power output. A ferroelectric material that is able to alter its polarity is needed to investigate this potential design enhancement. This paper investigates the performance of both parallel plate capacitor and interdigitated electrode MEMS energy harvesters using lead zirconate titanate thin films using finite element modelling and experimental results to demonstrate the increase in power density, and the effects of varying the electrode configurations and dimensions.