Crystalline Structure of Highly Piezoelectric (K,Na)NbO3 Films Deposited by RF Magnetron Sputtering

Abstract

We have previously reported (K,Na)NbO3 (KNN) films, whose piezoelectric properties are the highest reported thus far. In this study, we investigate the detailed crystalline structures of these KNN films after deposition on Pt/MgO and Pt/Ti/SiO2/Si substrates by RF magnetron sputtering. The KNN film on Pt/MgO was epitaxially grown on the Pt lower electrode with a perfect <001> orientation in the perovskite structure. The KNN film on Pt/Ti/SiO2/Si was polycrystalline with a preferential <001> orientation in the perovskite structure having dense columnar grains. X-ray diffraction measurements revealed that the KNN films grown on Pt/MgO and Pt/Ti/SiO2/Si were tetragonal; the lattice parameters c and a were related as c/a > 1. The KNN film on Pt/MgO had a higher c/a value than the KNN film on Pt/Ti/SiO2/Si, indicating that the former had more compressed strain. We conclude that this difference in compressed strain may contribute to the difference in piezoelectric properties of the KNN films on Pt/MgO and Pt/Ti/SiO2/Si.