Quantum transport properties of tantalum-oxide resistive switching filaments

TL;DR

This study investigates quantum transport in atomic-scale tantalum-oxide resistive switching filaments, revealing their atomic composition, stable diameter during switching, and how oxygen vacancy redistribution modulates conductance.

Contribution

It provides the first detailed quantum transmission analysis of atomic-sized resistive switching filaments using superconducting spectroscopy.

Findings

Filaments are composed of 3-8 Ta atoms at their narrowest point.

Filament diameter remains unchanged during switching.

Switching involves redistribution of oxygen vacancies affecting conductance.

Abstract

Filamentary resistive switching devices are not only considered as promising building blocks for brain-inspired computing architectures, but they also realize an unprecedented operation regime, where the active device volume reaches truly atomic dimensions. Such atomic-sized resistive switching filaments represent the quantum transport regime, where the transmission eigenvalues of the conductance channels are considered as a specific device fingerprint. Here, we gain insight into the quantum transmission properties of close-to-atomic-sized resistive switching filaments formed across an insulating Ta$_2$O$_5$ layer through superconducting subgap spectroscopy. This method reveals the transmission density function of the open conduction channels contributing to the device conductance. Our analysis confirms the formation of truly atomic-sized filaments composed of 3-8 Ta atoms at their narrowest cross-section. We find that this diameter remains unchanged upon resistive switching. Instead, the switching is governed by the redistribution of oxygen vacancies within the filamentary volume. The set/reset process results in the reduction/formation of an extended barrier at the bottleneck of the filament which enhances/reduces the transmission of the highly open conduction channels.