Quantum Transport Properties of Nanosized Ta₂O₅ Resistive Switches: Variable Transmission Atomic Synapses for Neuromorphic Electronics

Abstract

Filamentary resistive switching (RS) devices are not only considered as promising building blocks for brain-inspired computing architectures but also realize an unprecedented operation regime where the active device volume reaches truly atomic dimensions. Such atomically sized RS filaments represent the quantum transport regime, where the transmission eigenvalues of the conductance channels are considered a specific device fingerprint. Here, we gain insight into the quantum transmission properties of close-to-atomic-sized RS filaments formed across an insulating Ta2O5 layer through superconducting subgap spectroscopy. This method reveals the transmission density function of the open conduction channels contributing to the device’s 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 RS. Instead, the switching is governed by the redistribution of oxygen vacancies or tantalum cations 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. This transmission variability facilitates neuromorphic electronic applications in nanosized artificial synapses reaching the ultimate atomic scale.