Ferroelectric and dielectric study of strontium tantalum based perovskite oxynitride films deposited by reactive rf magnetron sputtering

摘要

Strontium and tantalum based oxynitride perovskite thin films were deposited by reactive magnetron sputtering. Epitaxial films deposited on Nb-SrTiO3 substrates show smooth surfaces with roughness values from 1.5 to 3.6 nm for a thickness of films in the range 20-1600 nm. The samples are yellow with band gap values around 2.35 eV. Piezo-force microscopy characterization pointed out the local piezoelectric and ferroelectric behavior of the oxynitride perovskite films. In the low frequency range, the 1600 nm-thick film exhibits a permittivity of 175 at 10 kHz, with dielectric losses of 0.055. Permittivity is lowered in high frequencies with a value around 65 obtained on a 1520 nm-thick film deposited on MgO substrate, which is textured with a preferential c-axis orientation. No accordability of the permittivity was highlighted at a macroscopic scale. The moderate crystallographic strain evidenced in the 20 nm thin film does not induce a high permittivity. (C) 2016 Elsevier Ltd. All rights reserved.