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

Abstract

Devices exploiting negative differential resistance (NDR) are of particular interest for analogue computing applications, including oscillator-based neural networks1. These devices typically exploit the continuous S-shaped current-voltage characteristic produced by materials with a strong temperature dependent electrical conductivity2 but recent studies have also highlighted the existence of a second, discontinuous (snap-back) characteristic that has the potential to provide additional functionality. The development of devices based on this characteristic is currently limited by uncertainty over the underlying physical mechanism, which remains the subject of active debate3-4. Here, we use in-situ thermo-reflectance imaging and a simple model to finally resolve this issue. Specifically, we show that the snap-back response is a direct consequence of current localization and redistribution within the oxide film, and confirm the veracity of the model by experimentally verifying predicted material and device dependencies. These results conclusively demonstrate that the snap-back characteristic is a generic response of materials with a strong temperature dependent conductivity and therefore has the same physical origin as the S-type characteristic. This is a significant outcome that resolves a longstanding controversy and provides a solid foundation for engineering functional devices with specific NDR characteristics. Show more