Growth and piezoelectric properties of amorphous and crystalline (K_1−xNa_x)NbO₃₋based thin films

(K_1−xNa_x)NbO₃ (KNN)-based piezoelectric thin films have been extensively studied for application in micro-electromechanical systems. However, growing homogenous crystalline (K_1−xNa_x)NbO₃ (CKNN) films with good piezoelectric properties is difficult because Na₂O and K₂O evaporate during the growth process at high temperatures. Recently, amorphous (K_1−xNa_x)NbO₃ (AKNN) films containing KNN nanocrystals with good piezoelectric properties have been fabricated at low temperatures. Furthermore, [001]-oriented crystalline (K_1−xNa_x)NbO₃ (OCKNN) films with excellent piezoelectric properties have been grown at low temperatures (≤ 350 °C) using a metal-oxide nanosheet seed layer. This novel method is excellent for the growth of homogeneous KNN thin films. These films were deposited on a polymer substrate; thus, they can be utilized in future flexible electronic devices. In this study, the structural and piezoelectric properties of AKNN- and CKNN-based films fabricated at high temperatures, along with the growth process and application of OCKNN-based thin films at low temperatures, are reviewed.