Tunnel electroresistance in BiFeO3 junctions: size does matter

Inferroelectrictunnel junctions, the tunnelresistance depends on thepolarization orientation of theferroelectric tunnel barrier, giving rise to tunnel electroresistance. These devices are promising to be used as memristors in neuromorphic architectures and as non-volatile memory elements. For both applications, device scalability is essential, which requires a clear understanding of the relationship betweenpolarization reversal andresistance change as the junction size shrinks. Here we show a robust tunnel electroresistance in BiFeO3-based junctions with diameters ranging from 1200 to 180  nm. We demonstrate that the tunnel electroresistance and the corresponding fraction of reversedferroelectric domains change drastically with the junction diameter: while the micron-size junctions display a reversal in less than 10% of the area, the smallest junctions show an almost completepolarization reversal. Modeling the electric-field distribution, we highlight the critical role of the bottomelectroderesistance which significantly diminishes the actualelectric field applied to theferroelectric barrier in the mixedpolarization state. A polarization-dependent criticalelectric field below which further reversal is prohibited is found to explain the large differences between theferroelectric switchability of nano- and micron-size junctions. Our results indicate thatferroelectric junctions are downscalable and suggest that specific junction shapes facilitate completepolarization reversal.
Source: Applied Physics Letters - Category: Physics Authors: Source Type: research