Morphology analysis of the reconstruction of nano-filaments during aborted reset operation in Cu-based ReRAM devices

This paper presents a detailed physical analysis of the counterintuitive strengthening effect observed in Cu/TaOₓ/Pt-based resistive random-access memory (ReRAM) devices during an aborted reset operation. While our prior work [26] announced this phenomenon in a short letter, here, we develop a comprehensive electro-thermal model that links the observed resistance reduction directly to an atomic reconstruction of the conductive filament (CF). We demonstrate that the transformation from a truncated conical filament to a lower-resistance, hourglass-shaped structure is driven by the synergistic action of intense electric fields and localized Joule heating, which are both highly confined to the filament's tip. This reconstruction of CF is governed by the fundamental physics of Cu atom diffusivity and ion electromigration within the TaOₓ matrix. Our model, constrained by volume conservation and supported by electrostatic and thermal simulations, successfully optimizes the filament geometry to predict a maximum resistance reduction factor of ~ 11, which aligns precisely with experimental data for high-resistance filaments. Furthermore, we identify a critical two-phase reset process: a reinforcement phase dominated by electromigration and a final rupture phase. The experimental dependence on voltage ramp rate is quantitatively explained by calculating the timescales required for Cu ion mobility, conclusively showing that slower ramps allow sufficient time for atomic rearrangement. This detailed analysis resolves the controversy surrounding filament morphology and provides profound insights into CF dynamics that are critical for advancing the reliability and design of ReRAM devices, particularly for neuromorphic computing applications.