Interdigitated-electrode-based mems-scale piezoelectric energy harvester modeling and optimization using finite element method

This paper presents a novel optimization method for interdigitated electrode (IDE)-based, cantilever-type piezoelectric energy harvesters at microelectromechanical system (MEMS) scale. A new two-stage approach based on the finite element method is proposed to examine the performance of such devices. First, detailed electrostatic poling simulations are presented. The results of these poling orientation simulations are used while calculating electrical energy and conversion efficiency in response to a constant external force. The proposed approach is used to find the optimum piezoelectric material thickness and IDE geometry for a cantilever beam which is constructed on top of a 4-μm Si structural layer and a 1-μm SiO₂ isolation layer. Cantilever and IDE lengths are fixed at 320 μm and 240 μm, respectively, whereas the lead zirconate titanate (PZT) thickness, IDE finger widths, and number of finger pairs are varied. Maximum output energy of 0.37 pJ for a 15-μN force is obtained at a PZT thickness of 0.6 μm and an IDE consisting of 12 finger pairs. This energy is reduced to 1.5 fJ for 5 μm PZT thickness with 2 electrode finger pairs, which shows that device geometry has a significant impact on device performance. The proposed method presents an accurate framework for the rapid design and performance prediction of novel piezoelectric energy harvester structures.