Improved dielectric constant of SrMnO3 thin films via oxygen annealing

Abstract

Multi-state device based on dielectric materials have an interesting topic that can be used to step-adjust charge storage using external voltages. Of these materials, SrMnO3 has been shown to exhibit dielectric constant changes due to phase transitions in various epitaxial strain regions. Previously, the change of dielectric constant was observed using a PMN-PT with the largest piezoelectric constant of about 1420 pC/N as a substrate. However, previous studies have failed to confirm the ferroelectricity due to the stoichiometry problem caused by oxygen vacancies, and the dielectric constant has a very small value. Here, we report an experimental investigation of SrMnO3 for the quantity of oxygen vacancies and dielectric constant through oxygen annealing. Our experimental X-ray photoelectron spectroscopy (XPS) data reveals peak-intensity changes of oxygen 1s orbital and Mn 2p orbital as annealing temperature and time. The relative quantity of oxygen vacancies decreases from 3.85 to 0.63 by calculating the peak-intensity ratio. In addition, we find that out-of-plane ferroelectricity in the 2% tensile strain region and increase the remnant polarization to 51.2 μC/cm2. This enhancement of remnant polarization also results in an increase in the dielectric constant. The SrMnO3 films were deposited onto La0.7Sr0.3MnO3 (LSMO) / (001)-oriented PMN-PT substrate using pulsed laser deposition (PLD). The films grow epitaxially along the [001] direction when measured by high resolution transmission electron microscopy (HRTEM) and X-ray diffraction (XRD) analyses. A SrMnO3 thin film reduces the oxygen vacancies and increases the dielectric constant from 4.76 to 20.4 through oxygen annealing, respectively. Our study suggests that annealing process at oxygen atmosphere is a promising technique to enhance the dielectric constant of SrMnO3 for multi-state device.