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Dr Themis Prodromakis

University of Southampton
Nano Group, Southampton Nanofabrication Centre
Southampton, SO17 1BJ, UK
+44 (0)23 8059 8803

Origin of the OFF state variability in ReRAM cells

Authors: Salaoru, I., Khiat, A., Berdan, R., Quingjian, L., Papavassiliou, C. and Prodromakis, T.

Published by: Journal of Physics D: Applied Physics

This work exploits the switching dynamics of nanoscale Resistive Random Access Memory (ReRAM) cells with particular emphasis on the origin of the observed variability when consecutively cycled/programmed at distinct memory states. It is demonstrated that this variance is a common feature of all ReRAM elements and is ascribed to the formation and rupture of conductive filaments that expand across the active core, independently of the material employed as the active switching core, the causal physical switching mechanism, the switching mode (bipolar/unipolar) or even the unit cells' dimensions. Our hypothesis is supported through both experimental and theoretical studies on TiO2 and In2O3:SnO2 (ITO) based ReRAM cells while programmed at three distinct resistive states. Our prototypes employed TiO2 or ITO active cores over 5×5 μm2 and 100x100 μm2 cells' areas, with all tested devices demonstrating both unipolar and bipolar switching modalities. In the case of TiO2-based cells, the underlying switching mechanism is based on the non-uniform displacement of ionic species that foster the formation of conductive filaments. On the other hand, the resistive switching observed in the ITO-based devices is considered to be due to a phase change mechanism. The selected experimental parameters allowed us to demonstrate that the observed programming variance is a common feature of all ReRAM devices, proving that its origin is dependent upon randomly oriented local disorders within the active core that have a substantial impact in the overall state variance particularly for high-resistive states.

Funding Research Councils:
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