Optimizing phase and microstructure of chemical solution-deposited bismuth ferrite (BiFeO3) thin films to reduce DC leakage

Polycrystalline bismuth ferrite (BiFeO3 or BFO) thin films were prepared by chemical solution deposition to explore the impact of processing conditions including annealing temperature, percent excess bismuth, and gel drying temperature on film microstructure and properties. Incorporating 0–5 % excess Bi and annealing at 550 °C in air produced stoichiometric single-phase BiFeO3 films. Deviation from this temperature yielded the bismuth-rich Bi36Fe2O57 phase at temperatures below 550 °C or the bismuth-deficient Bi2Fe4O9 phase at temperatures above 550 °C, both of which contributed to higher DC leakage. However, even single-phase BiFeO3 films produced at 550 °C show high DC leakage (~1.2 × 10−1 A/cm2 at 140 kV/cm) due to a porous microstructure. We have thus investigated unconventional thermal treatments that significantly increase film densification while maintaining phase purity. Under these revised thermal treatment conditions, room temperature leakage current values are reduced by three orders of magnitude to ~1.0 × 10−4 A/cm2 at 140 kV/cm.