In-situ thermo-reflectance imaging is used to show that the discontinuous, snap-back mode of current-controlled negative differential resistance (CC-NDR) in NbOx-based devices is a direct consequence of current localization and redistribution. Current localisation is shown to result from the creation of a conductive filament either during electroforming or from current bifurcation due to the super-linear temperature dependence of the film conductivity. The snap-back response then arises from current redistribution between regions of low and high current-density due to the rapid increase in conductivity created within the high current density region. This redistribution is further shown to depend on the relative resistance of the low current-density region with the characteristics of NbOx cross-point devices transitioning between continuous and discontinuous snap-back modes at critical values of film conductivity, area, thickness and temperature, as predicted. These results clearly demonstrate that snap-back is a generic response that arises from current localization and redistribution within the oxide film rather than a material-specific phase transition, thus resolving a long-standing controversy.
@article{arxiv.1906.08980,
title = {Current localisation and redistribution as the basis of discontinuous current controlled negative differential resistance in NbOx},
author = {Sanjoy Kumar Nandi and Shimul Kanti Nath and Assaad El Helou and Shuai Li and Xinjun Liu and Peter E. Raad and Robert G. Elliman},
journal= {arXiv preprint arXiv:1906.08980},
year = {2019}
}