Schottky barrier induced asymmetry in the negative differential resistance response of Nb/NbOx/Pt cross-point devices

TL;DR

This paper investigates how Schottky barriers influence the polarity-dependent negative differential resistance in Nb/NbOx/Pt devices, revealing how contact resistance and device parameters affect NDR behavior relevant for neuromorphic and memory applications.

Contribution

It introduces an extended thermal model that accounts for contact resistance effects, explaining the polarity-dependent NDR responses in metal/oxide/metal devices.

Findings

Polarity dependence of NDR is linked to Schottky barrier effects.

Device area and oxide stoichiometry influence NDR response.

Thermal localization correlates with observed NDR behaviors.

Abstract

The negative differential resistance (NDR) response of Nb/NbOx/Pt cross-point devices is shown to have a polarity dependence due to the effect of the metal/oxide Schottky barriers on the contact resistance. Three distinct responses are observed under opposite polarity testing: bipolar S-type NDR, bipolar snap-back NDR, and combined S-type and snap-back NDR, depending on the stoichiometry of the oxide film and device area. In-situ thermoreflectance imaging is used to show that these NDR responses are associated with strong current localisation, thereby justifying the use of a previously developed two-zone, core shell thermal model of the device. The observed polarity dependent NDR responses, and their dependence on stoichiometry and area are then explained by extending this model to include the effect of the polarity dependent contact resistance. This study provides an improved understanding of the NDR response of metal/oxide/metal structures and informs the engineering of devices for neuromorphic computing and non-volatile memory applications.