High-efficiency piezoelectric energy harvesters of c-axis-oriented epitaxial PZT films transferred onto stainless steel cantilevers

We fabricated piezoelectric energy harvesters composed of c-axis-oriented Pb(Zr,Ti)O3 (PZT) films transferred onto stainless steel cantilevers for improved energy conversion efficiency and toughness. PZT films were epitaxially grown on Pt/MgO substrates using rf-magnetron sputtering and transferred to 50-μm-thick stainless steel cantilevers. The transferred PZT films had a low dielectric constant (ɛr = 166) and high transverse piezoelectric coefficient (e31* = d31/s11 = −4.5 C/m2); these values are almost the same as those of the as-grown epitaxial PZT films on MgO substrates. Because of the small thickness of the cantilever, the first resonant frequency could be as low as 126 Hz without a seismic mass at the tip of the cantilever. At an acceleration of 5 m/s2, the energy harvester generated an average output power of 5.3 μW at the optimal load resistance of 50 kΩ. The output power increased monotonically with the acceleration, reaching 244 μW under an acceleration of 50 m/s2 without damage to the cantilever.