Electroforming in VO ₂ Switch: Phase Transformation and Electromigration Phenomena

Transition metal oxides provide a versatile platform for memristive devices, with vanadium oxide compounds attracting particular attention due to their sharp and ultrafast insulator-to-metal transition. However, their practical implementation is often constrained by structural and electrical modifications induced by high electric fields, commonly referred to as electroforming. In this work, we investigate the electroforming process in VO₂ thin films deposited by atomic layer deposition and pulsed laser deposition, analyzing their microstructure and functional characteristics before and after electrical actuation. Detailed examination of the VO₂ channel morphology and cross sections reveals pronounced phase transformations and electromigration phenomena associated with the switching process. Scanning transmission electron microscopy analysis reveals substantial structural reconfiguration, formation of new phases, and oxygen redistribution under electrical stress. These transformations result in noticeable modifications of key device parameters, including a median decrease of up to 72% in threshold voltage and 95% in channel resistance, ultimately reducing the ON/OFF ratio up to a factor of 160 in our experiments. At the same time, controlled electrical conditioning provides a pathway to exploit electroforming for reducing the stochasticity of switching events and enhancing fatigue resistance over >10³ voltage cycles. Overall, this study elucidates the interplay between structural evolution and electrical functionality in VO₂-memristors, providing insights for enhancing their stability, reproducibility, and long-term reliability of VO₂ switches.