Microstructural and electrical characteristics of epitaxial BiFeO3 thick films sputtered at different Ar/O2 flow ratios

Abstract

Epitaxial BiFeO₃ films (∼0.5 μm thick) were prepared on (100) LaAlO₃ substrates using radio-frequency (RF) magnetron sputtering. A good heteroepitaxial growth of BiFeO₃ films was confirmed by XRD and TEM analyses. While co-existing rhombohedral and tetragonal-like phases were revealed near the bottom interface of the films in the form of elastic domains to relax the initial misfit stresses, the bulk of the films consists of only the rhombohedral phase. The sputtering atmosphere, i.e. the flow ratio of Ar/O₂ at a fixed sputtering pressure, did not affect the epitaxial growth and phase structure of the BiFeO₃ films. Instead, it showed significant influences on the electrical properties, i.e. dielectric behavior, as well as the ferroelectric and leakage current characteristics. It was shown that, among the four films deposited at different Ar/O₂ flow ratios (2 : 1, 3 : 1, 4 : 1 and 6 : 1), the film with a 4 : 1 flow ratio has the best overall electrical properties, which can be attributed to its stoichiometric physical vapor growth at a balanced Ar/O₂ flow ratio. It showed a remnant polarization (2P_r) of 150 μC cm⁻² and a low leakage current density of about 3.6 × 10⁻⁴ A cm⁻² at 200 kV cm⁻¹.