Nonvolatile resistive switching in Au/BiFeO₃ rectifying junction

Resistive switching in oxides has attracted increasing attention due to the potential application for nonvolatile memory devices [1,2]. Resistive switching has been observed usually in a metal-insulator-metal (MIM) capacitor-like structure, which can be set and reset to low resistance state and high resistance state by applying external voltages with opposite polarities. In an asymmetric MIM structure where a Schottky contact and an Ohmic contact are formed at the two interfaces, respectively, it is generally believed that the Schottky interface dominates the bipolar resistive switching behavior.
BiFeO₃ thin films have been grown on Pt/Ti/SiO₂/Si substrates with pulsed laser deposition. RF sputtered Au has been used for the top electrode. The transport properties of the BiFeO₃ thin films have been previously demonstrated to be sensitive to the interface [3]. In the present work, an interface-related resistive switching behavior with large switching ratio of ~300 has been observed in the Au/BiFeO₃/Pt structure [4]. The different polarities of the external voltage induce an electron trapping or detrapping process, and consequently change the depletion layer width below the Au Schottky contact, which is revealed by capacitance-voltage measurements and by long-term low/high resistance state capacitance transient measurements at zero bias. The resistive switching shows a long term retention and non-destructive read-out character, which is proved by pulsed voltage measurements. A dynamic equilibrium process involving the extension of the depletion region can be used to explain the good retention in the Au/BiFeO₃/Pt structure. The present work can help to further understand the physical origin of bipolar switching in BiFeO₃ and in other thin film oxides with electron trapping centers.

[1] K. Terabe et al., Nature 433, 47 (2005).
[2] R. Waser and M. Aono, Nature Mater. 6, 833 (2007).
[3] Y. Shuai et al., J. Appl. Phys., in press.
[4] Y. Shuai et al., Appl. Phys. Lett. 98, 232901 (2011).