MEMS power generator with transverse mode thin film PZT

Abstract

A thin film lead zirconate titanate, Pb(Zr,Ti)O-3 (PZT), MEMS power generating device is developed. It is designed to resonate at specific frequencies from an external vibrational energy source, thereby creating electrical energy via the piezoelectric effect. Our cantilever device is designed to have a flat structure with a proof mass added to the end. The Pt/Ti top electrode is patterned into an interdigitated shape on top of the sol-gel-spin coated PZT thin film in order to employ the d(33) mode of the piezoelectric transducer. This d(33) mode design generates 20 times higher voltage than that of the d(31) mode design of the same beam dimension. The base-shaking experiments at the first resonant frequency (13.9 kHz) generate charge proportional to the tip displacement of the cantilever with a linearity coefficient of 4.14 pC/mu m. A 170 mu m x 260 mu m PZT beam generates 1 mu W of continuous electrical power to a 5.2 M Omega resistive load at 2.4 V dc. The corresponding energy density is 0.74 mW h/cm(2), which compares favorably to the values of lithium ion batteries. We expect the next generation design with lower resonant frequencies would harvest sufficient energy from the environmental vibration for wireless miniature sensor networks. (C) 2005 Elsevier B.V. All rights reserved.