Origin of the OFF state variability in ReRAM cells

Salaoru, I., Khiat, A., Berdan, R., Quingjian, L., Papavassiliou, C. and Prodromakis, T. (2014) Origin of the OFF state variability in ReRAM cells. Journal of Physics D: Applied Physics, 47 (14), 1-10. (doi:10.1088/0022-3727/47/14/145102).

Abstract

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.

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Contributors

Author: T. Prodromakis

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