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)NbO 3 films prepared on single-crystal SrTiO 3 substrates by the hydrothermal deposition technique. First, we measured the vibration energy harvesting properties by a unimorph Pt/(K,Na)NbO 3 //SrRuO 3 //SrTiO 3 cantilever. Based on the fact that the elastic stiffness of (K,Na)NbO 3 is lower than that of SrTiO 3 substrate, it can be understood that increasing film thickness leads to decreasing Q m , 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)NbO 3 //SrRuO 3 //SrTiO 3 cantilever. The output power of this type of harvester was more than 400% greater when the film thickness was increased from 3.5 to 22.3 μ m due to the almost constant Q m value.