Fabrication and Evaluation of Highly (110)-Oriented Potassium Niobate Thin Films Prepared by RF-Magnetron Sputtering

Abstract

Epitaxial (110)-oriented KNbO3 thin films were deposited on a (100) MgO substrate by RF-magnetron sputtering. To clarify the sputtering conditions necessary for obtaining a highly oriented KNbO3 thin film, the relationships among the degree of orientation, the composition ratio of K/Nb, and the lattice plane spacing were evaluated for KNbO3 thin films deposited using several types of target. In the deposition method using dual targets of KNbO3 and K2CO3, a higher orientation and a larger K/Nb ratio were incompatible. In single-target sputtering with a mixture target of KNbO3:K2CO3, as the substrate temperature decreased, although the K/Nb ratio increased and the (220)-plane spacing approached that of orthorhombic bulk KNbO3, the orientation deteriorated. Using a single K-rich target, K5NbOx, containing no CO2, a highly (110)-oriented KNbO3 thin film with a K/Nb ratio of 0.40 and a (220)-plane spacing near that of orthorhombic bulk KNbO3 was obtained by increasing the RF power applied to the O2-radical source. Moreover, the displacement current in the oriented KNbO3 thin film with a K/Nb ratio of 0.40 was observed when an electric field was applied to the interdigital transducer formed on the thin film. This indicates the existence of spontaneous polarization in the oriented KNbO3 thin film.