Bipolar resistance switching in multiferroic BiFeO3 polycrystalline films

Bismuth ferrite (BiFeO₃) is an attractive multiferroic material. However, its application as a ferroelectric material in electronic devices is limited by large leakage current. In this letter, a bipolar resistance switching phenomenon was observed in BiFeO₃ polycrystalline films prepared by sol-gel method. The resistance of a fresh film is in an intermediate state and can be transformed into either high-resistive or low-resistive states by applying an external voltage across the film. The I-V curves of the fresh film are nearly centrosymmetric before resistance switching. The resistance ratios between high- and low-resistance states are in the range of 2-3 orders of magnitude. The conductive atomic force microscopy measurements reveal that the grain boundaries are more conductive under a bias voltage of 10 V, and more resistive under 3 V than the grain interior. It was thought that grain boundaries and oxygen vacancies played a key role in the formation of bipolar resistance switching.