Spatially Correlated Oxygen Vacancies, Electrons and Conducting Paths in TiO₂ Thin Films

Resistive switching, characterized by reversible changes in material resistance under external electric fields, underpins resistive random-access memory (ReRAM) technology, which holds promise for next-generation memory and neuromorphic devices owing to its fast switching speed, nonvolatility, and structural simplicity. Among materials exhibiting resistive switching, transition metal oxides emerge as leading candidates for ReRAM components due to their high CMOS compatibility. However, complex thermal, electrical, chemical, and mechanical interactions during switching introduce variability, leaving the underlying mechanisms insufficiently understood. Therefore, this study investigates the ionic-electronic dynamics involved in resistive switching, focusing on the electroforming and reset processes in TiO₂ thin films─a representative transition metal oxide─through a colocalized, multimodal scanning probe microscopy (SPM) approach. Conductive atomic force microscopy (C-AFM) induces resistive switching and visualizes modulated spatial current pathways, while electrochemical strain microscopy (ESM) and Kelvin probe force microscopy (KPFM) capture corresponding ionic and electronic interplays at the same switching event and site. This integrated strategy provides direct nanoscale correlations that are difficult to resolve with single-mode or separate modality measurements, revealing how defect ion modulation and electron injection in concert govern the switching behavior. Furthermore, topography degradation observed during reset processes suggests that facilitated diffusion of injected oxygen ions along defect-enriched sites enhances retention properties of high resistance states. Based on these findings, the study proposes a potential switching mechanism, emphasizing the role of ionic-electronic dynamics.