High figure of merit (MgHf)_xAl_1-xN thin films for miniaturizing vibrational energy harvesters

In this paper, we report our development of piezoelectric MgHf co-doped AlN films with high power figure of merit (FoM) for vibrational energy harvesters (VEHs). The (MgHf)_xAl_1-xN films were deposited on Pt/Ti/SOI substrates by reactive ion-beam sputtering AlN and MgHf targets simultaneously. These studies revealed that we achieved a high FoM of 22.3 GPa at x = 0.12, increasing three-fold that of the pure AlN. Our micro-machined energy harvester exploiting the developed (MgHf)_0.12Al_0.88N films provided the highest normalized power density (NPD) of 12.04 mW.cm^-3.g^-2 among the state-of-the-art piezoelectric VEHs. The results opened the way for the development of high-performance VEHs using in wireless sensors network.