Bulk micromachined energy harvesters employing (K, Na)NbO₃ thin film

In this paper, a micromachined energy harvester employing a lead-free (K, Na)NbO₃ (KNN) thin film was reported. KNN is one of the lead-free piezoelectric materials. It is a promising alternative to Pb(Zr, Ti)O ₃ (PZT). In a micromachined energy harvester, a 2 μm thick KNN film was deposited on a silicon cantilever integrated with a proof mass. The energy harvester achieved an output power of 731 nW and a normalized power density (NPD) of 2.29 μW (g^-2 mm^-3) at the resonant frequency of 1509 Hz with the acceleration of 10 m s^-2. The harvested energy was enhanced considerably by applying bulk micromachining, and was comparable to the PZT-based energy harvesters.