Piezoelectric Micro Power Generator for Energy Harvesting

A thin film lead zirconate titanate Pb(Zr,Ti)O3 (PZT), power generating device is developed. It is designed to resonate at specific vibrational frequencies from an ambient, vibrational energy source, thereby creating electrical energy via the piezoelectric effect. The energy harvesting device uses the piezoelectric d33 mode and is fabricated with three mask steps. Our cantilever device was designed to have a flat structure with a proof mass added to the end. A method for controlling the bowing curvature of the cantilever was applied by modulating the residual stress and elastic properties of the composite beam. The top electrode of Ti and Pt was patterned into an interdigitated shape on top of the sol-gel-spin coated PZT thin film in order to employ the d33 mode of the piezoelectric. This d33 mode design can generate at least a 20 times higher voltage than that of the d31 mode design. The device was mechanically excited by base shaking experiments, which revealed that our device has three resonance modes. The base-shaking experiments at the first resonant frequency (13.9 kHz) demonstrated that the generated charge is proportional to the tip displacement of the cantilever with an approximate linearity coefficient of 4.14 pC/μm. The total system can deliver 1μW of continuous electrical power to a 5.2MΩ resistive load at 2.4V DC. The corresponding energy density is 0.74 mW-h/cm, which compares favorably to current chemical batteries (i.e. lithium ion). We expect the optimized design to generate a much higher power level than we have now by targeting and harvesting from lower frequency vibrations.