Anomalous Platinum and Oxygen Transport during Electroforming of NbOx Memristors

TL;DR

This study uncovers a novel metal-ion transport mechanism involving platinum and oxygen during the electroforming of NbOx memristors, highlighting the influence of electrical dynamics on filament chemistry and device stability.

Contribution

It reveals unexpected platinum and oxygen redistribution during memristor electroforming, emphasizing the role of thermal effects and dynamic electrical operation in filament formation.

Findings

Oxygen enrichment extends from Nb2O5 through NbOx into the Pt electrode.

Formation of a Pt-rich filament along the same path as oxygen enrichment.

Thermal cycling enhances oxygen migration and platinum diffusion.

Abstract

Electroforming of metal-oxide-metal memristors is generally attributed to the creation of oxygen-vacancy filaments within the oxide, with noble metal electrodes such as Pt and Au remaining chemically inert. Here, we demonstrate that electroforming and subsequent operation of Pt/NbOx/Nb2O5/Pt devices can induce an unexpected and highly correlated redistribution of both oxygen and platinum. Time-of-flight secondary ion mass spectrometry reveals a filamentary pathway characterized by micrometer-scale oxygen enrichment extending from the Nb2O5 layer through NbOx and deep into the Pt top electrode. Surprisingly, this is accompanied by the formation of a Pt-rich filament penetrating the oxide stack along the same filamentary path. Finite-element and lumped-element modelling show that current-controlled negative-differential-resistance operation produces localized Joule heating and high-frequency thermal cycling, which strongly enhances oxygen migration and enables thermally assisted Pt diffusion along vacancy-rich pathways. These findings reveal a previously unrecognized metal-ion transport mechanism in NbOx memristors and highlight the critical role of post-forming electrical dynamics in determining filament chemistry, stability, and device reliability.