AlN-based flexible piezoelectric skin for energy harvesting from human motion

In this work we report on the development of a flexible energy harvester based on piezoelectric Aluminum Nitride (AlN) thin film able to scavenge electrical energy from human motion at very low frequencies. Flexible devices integrating thin films with controlled residual stress have been realized on polyimide substrate to obtain a pre-stressed structure (PSS). These devices show an enhancement of the generated output voltage, if compared to a flat-shape structure, when subjected to a deformation: the piezoelectric skin undergoing folding /unfolding states exhibits fast snapping transitions due to the budding effect, which increases the mechanical stress of the piezoelectric structure, improving the generated output voltage. Experimental results demonstrate a maximum peak-to-peak voltage of 0.7 V for a PSS, about six times higher than the corresponding voltage obtained for flat structures. These results have been validated by Finite Element Method (FEM) simulations of the total elastic energy of deformation and the mechanical stress versus the deformation, demonstrating the buckling effect.