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

Epitaxial (110)-oriented KNbO 3 thin films were deposited on a (100) MgO substrate by RF-magnetron sputtering. To clarify the sputtering conditions necessary for obtaining a highly oriented KNbO 3 thin film, the relationships among the degree of orientation, the composition ratio of K/Nb, and the lattice plane spacing were evaluated for KNbO 3 thin films deposited using several types of target. In the deposition method using dual targets of KNbO 3 and K 2 CO 3 , a higher orientation and a larger K/Nb ratio were incompatible. In single-target sputtering with a mixture target of KNbO 3 :K 2 CO 3 , as the substrate temperature decreased, although the K/Nb ratio increased and the (220)-plane spacing approached that of orthorhombic bulk KNbO 3 , the orientation deteriorated. Using a single K-rich target, K 5 NbO x , containing no CO 2 , a highly (110)-oriented KNbO 3 thin film with a K/Nb ratio of 0.40 and a (220)-plane spacing near that of orthorhombic bulk KNbO 3 was obtained by increasing the RF power applied to the O 2 -radical source. Moreover, the displacement current in the oriented KNbO 3 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 KNbO 3 thin film.