Type of presentation: Oral

MS-12-O-3240 Switching the Electrical Resistance of Ferroelectrics through Control of Charged Domain Walls

Li L.1, Jokisaari J. R.1, Melville A.2, Adamo C.2, Schlom D. G.2, Pan X. Q.1
1Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI 48109, United States, 2Department of Materials Science and Engineering, Cornell University, Ithaca, NY 14853, United States
linze@umich.edu

Charged domain walls (CDWs) in ferroelectrics, as a result of “head-to-head” or “tail-to-tail” polarization configurations, are of significant scientific and technological importance, as they have been shown to play a critical role in controlling the atomic structure, electric, photoelectric and piezoelectric properties of ferroelectric materials. The accumulation of compensating free charge that screen the bound charge at the CDW can in principle intriguer an insulator-metal transition. In this work, we use in situ transmission electron microscopy (TEM) to study the stability and dynamic behaviors of CDWs in BiFeO3 thin films. We found that the CDW can be manipulated by applying electric field, leading to the switching of electrical resistance of the ferroelectric film due to the distribution of electric charges associated with domain walls.

An epitaxial 20 nm thick BiFeO3 (BFO) film with a 20 nm thick La0.7Sr0.3MnO3 (LSMO) bottom electrode were grown on (110) TbScO3 substrates by reactive molecular-beam epitaxy (MBE). Fig. 1a shows a typical triangular 109° (vertical) /180° (inclined) domain wall junction above the BFO/LSMO interface. Applying a positive voltage results in shrinkage of the triangular domain and thus formation of a CDW with “head-to-head” polarization configuration (Fig. 1b-e). The written CDW is stable after removing the electric field (Fig. 1f). The measured current during the writing process shown in Fig. 1g suggests that, with the increasing of the length of the CDW, the local electrical resistance decreases gradually and suddenly switches to a very low value, suggesting the formation of a metallic conduction channel traversing the full thickness of the film. A subsequent low reading voltage (Fig. 1h) does not change the domain configuration (Fig. 1f), and the reading current suggests a conductive state. Applying a sufficiently large negative voltage results in expansion of the triangular domain and thus annihilation of the CDW (Fig. 2a-c). After the CDW is erased, the reading I-V curve (Fig. 2d) suggests that the ferroelectric film return to its insulating state.

In conclusion, our in-situ TEM studies show the existence of stable CDWs in BiFeO3 thin films and its configuration can be manipulated by applied electric field. It was found that the CDW can be written and erased by applying electric field, and the resulting states with and without CDWs were found to have different electrical resistance, suggesting a route to engineer ferroelectric devices.

the authors gratefully acknowledge the financial support through DOE grant DoE/BES DE-FG02-07ER46416.

Fig. 1: Electrical writing of a CDW. (a)-(f) Dark-field diffraction contrast TEM images extracted from a video showing the writing process by applying a positive bias ramp. (g) Current measured during the writing process. (h) Current measured by applying a low reading voltage after writing.

Fig. 2: Electrical erasing of a CDW. (a)-(c) Dark-field diffraction contrast TEM images extracted from a video showing the erasing process by applying a negative bias ramp. (d) Current measured when applying a low reading voltage after erasing.