Effect of film thickness on output power of a piezoelectric vibration energy harvester using hydrothermally synthesized (K,Na)NbO₃ film

Abstract

The dependence of the output power of piezoelectric vibration energy harvesters on film thickness was systematically investigated using {100}c-oriented epitaxial (K,Na)NbO3 films prepared on single-crystal SrTiO3 substrates by the hydrothermal deposition technique. First, we measured the vibration energy harvesting properties by a unimorph Pt/(K,Na)NbO3//SrRuO3//SrTiO3 cantilever. Based on the fact that the elastic stiffness of (K,Na)NbO3 is lower than that of SrTiO3 substrate, it can be understood that increasing film thickness leads to decreasing Qm, resulting in the decrease in output power as film thickness increased under the same input acceleration condition. In the next step, these cantilevers were attached to an Al plate having a much larger volume than the Pt/(K,Na)NbO3//SrRuO3//SrTiO3 cantilever. The output power of this type of harvester was more than 400% greater when the film thickness was increased from 3.5 μm to 22.3 μm due to the almost constant Q m value.