Breaking the quantum PIN code of atomic synapses

TL;DR

This paper investigates atomic synapses used in neuromorphic hardware by analyzing quantum conductance channels, revealing atomic-scale filament formation in Nb₂O₅ memristors through superconducting measurements.

Contribution

It provides the first quantum characterization of filamentary conductance in atomic synapses using Andreev reflection processes.

Findings

Atomic-sized metallic filaments form at the ON state.

Quantum transmission probabilities reveal filament conductance.

Superconducting electrodes enable detailed conductance analysis.

Abstract

Atomic synapses represent a special class of memristors whose operation relies on the formation of metallic nanofilaments bridging two electrodes across an insulator. Due to the magnifying effect of this narrowest cross-section on the device conductance, a nanometer scale displacement of a few atoms grants access to various resistive states at ultimately low energy costs, satisfying the fundamental requirements of neuromorphic computing hardware. Yet, device engineering lacks the complete quantum characterization of such filamentary conductance. Here we analyze multiple Andreev reflection processes emerging at the filament terminals when superconducting electrodes are utilized. Thereby the quantum PIN code, i.e. the transmission probabilities of each individual conduction channel contributing to the conductance of the nanojunctions is revealed. Our measurements on Nb$_2$O$_5$ resistive switching junctions provide a profound experimental evidence that the onset of the high conductance ON state is manifested via the formation of truly atomic-sized metallic filaments.