MUO16- Deposition methods of BiFeO₃ thin films

Bismuth iron oxide (BiFeO₃ or BFO) is a particularly interesting multiferroic perovskite with ferroelectric and antiferromagnetic transition temperatures significantly above room temperature. In this work, BiFeO ₃ films are synthesized by a chemical solution deposition (CSD) sol-gel process on platinized silicon substrates and by physical vapor deposition (PVD) through RF-sputtering on iridium-sapphire substrates. The crystallization behavior and phase assemblage of these films was examined by X-ray diffraction (XRD). Analysis of CSD-prepared films revealed that a 0.25 M solution with 5% excess bismuth annealed at 550 °C in air produced polycrystalline films with the lowest occurrence of non-perovskite Bismuth iron oxide phases. For films made by PVD, the absence of oxygen during sputtering was found to enhance phase purity, and using a target with 7% excess bismuth allowed phase-pure films to be prepared at 600 °C. Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) were used to investigate the microstructure of the BiFeO₃ films. Porosity was found to be a significant problem in CSD-prepared films that were dried on a hotplate at 300 °C before annealing. Lowering the temperature of this drying step or omitting it was found to decrease root-mean-square (rms) surface roughness. The microstructure of the sputtered films was found to be dense, uniform, and crack-free a surface roughness of to 16 nm for BiFeO₃ sputtered at 600 °C.