The realization and performance of vibration energy harvesting MEMS devices based on an epitaxial piezoelectric thin film

This paper focuses on the fabrication and evaluation of vibration energy harvesting devices by utilizing an epitaxial Pb(Zr0.2Ti0.8)O-3 (PZT) thin film. The high quality of the c-axis oriented PZT layer results in a high piezoelectric coefficient and a low dielectric constant, which are key parameters for realizing high performance piezoelectric energy harvesters. Different cantilever structures, with and without a Si proof mass, are realized using micro-patterning techniques optimized for the epitaxial oxide layers, to maintain the piezoelectric properties throughout the process. The characteristics and the energy harvesting performances of the fabricated devices are experimentally investigated and compared against analytical calculations. The optimized device based on a 0.5 mu m thick epitaxial PZT film, a cantilever beam of 1 mm x 2.5 mm x 0.015 mm, with a Si proof mass of 1 mm x 0.5 mm x 0.23 mm, generates an output power, current and voltage of, respectively, 13 mu W g(-2), 48 mu A g(-1) and 0.27 V g(-1) (g = 9.81 m s(-2)) at the resonant frequency of 2.3 kHz for an optimal resistive load of 5.6 k Omega. The epitaxial PZT harvester exhibits higher power and current with usable voltage, while maintaining lower optimal resistive load as compared with other examples present in the literature. These results indicate the potential of epitaxial PZT thin films for the improvement of the performances of energy harvesting devices.