Spatially-Resolved Study of the Electronic Transport and Resistive Switching in Polycrystalline Bismuth Ferrite

Abstract

Ferroelectric materials attract much attention for applications in resistive memory devices due to the large current difference between insulating and conductive states and the ability of carefully controlling electronic transport via the polarization set-up. Bismuth ferrite films are of special interest due to the combination of high spontaneous polarization and antiferromagnetism, implying the possibility to provide multiple physical mechanisms for data storage and operations. Macroscopic conductivity measurements are often hampered to unambiguously characterize the electric transport, because of the strong influence of the diverse material microstructure. Here, we studied the electronic transport and resistive switching phenomena in polycrystalline bismuth ferrite using advanced conductive atomic force microscopy (CAFM) at different temperatures and electric fields. The new approach to the CAFM spectroscopy and corresponding data analysis are proposed, which allow deep insight into the material band structure at high lateral resolution. Contrary to many studies via macroscopic methods, postulating electromigration of the oxygen vacancies, we demonstrate resistive switching in bismuth ferrite to be caused by the pure electronic processes of trapping/releasing electrons and injection of the electrons by the scanning probe microscopy tip. The electronic transport was shown to be comprehensively described by the combination of the space charge limited current model, while a Schottky barrier at the interface is less important due to the presence of the built-in subsurface charge.

Defining ferroelectric characteristics with reversible piezoresponse: PUND switching spectroscopy PFM characterization

“…When we directly compare the shapes of the current and piezoresponse at lower DC voltages, there doesn't appear to be a clear similarity, unlike the case of the electromechanical response stimulated by Joule heating [19,37]. The current increase can be associated with the resistive switching induced by the polarization reversal, similar to what has been observed in polycrystalline BiFeO 3 [38]. These measurements provide conclusive evidence that the instability of the hysteresis loop shape is not a result of parasitic effects but is a consequence of spontaneous backswitching.…”

“…When using SPM probe for switching, external screening is essentially suppressed because of the presence of the surface dielectric layer, which represents chemically disrupted material termination and contamination layer [9]. The main mechanism of the polarization screening in this case is the charge injection from SPM probe with further redistribution of the charge carriers by means of the bulk conductivity mechanism [38]. The rapid drop-off of the electric field at the probe does not allow trapped injected charge to spread out and screen polarization, while it tends to pull up injected charge back inside the probe under the action of the depolarization field of the newly created domain.…”