Lead-Free Piezoelectric MEMS Energy Harvesters of (K,Na)NbO₃Thin Films on Stainless Steel Cantilevers

Abstract

We fabricated piezoelectric MEMS energy harvesters (EHs) of lead-free (K,Na)NbO 3 (KNN) thin films on microfabricated stainless steel cantilevers. The use of metal substrates makes it possible to fabricate thin cantilevers owing to a large fracture toughness compared with Si substrates. KNN films were directly deposited onto Pt-coated stainless steel cantilevers by rf-magnetron sputtering, thereby simplifying the fabrication process of the EHs. From XRD measurement, we confirmed that the KNN films on Pt-coated stainless steel cantilevers had a perovskite structure with a preferential (001) orientation. The transverse piezoelectric coefficient e 31f and relative dielectric constant ε r were measured to be -3.8 C/m 2 and 409, respectively. From the evaluation of the power generation performance of a KNN thin-film EH (length: 7.5 mm, width: 5.0 mm, weight of tip mass: 25 mg), we obtained a large average output power of 1.6 µW under vibration at 393 Hz and 10 m/s 2 .