Current localisation and redistribution as the basis of discontinuous current controlled negative differential resistance in NbOx

TL;DR

This paper demonstrates that the discontinuous negative differential resistance in NbOx devices results from current localization and redistribution, not a material phase transition, clarifying a long-standing controversy.

Contribution

It reveals that snap-back behavior in NbOx devices is due to current localization and redistribution, not phase transitions, providing a new understanding of NDR mechanisms.

Findings

Current localization results from filament formation or bifurcation.

Snap-back arises from current redistribution between regions.

Transition between continuous and discontinuous snap-back modes depends on device parameters.

Abstract

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.