Titanium Nitride Diffusion Enables Visualization of Filamentary Switching in Ovonic Threshold Switching Selectors

Chalcogenide-based ovonic threshold switching (OTS) selectors are essential for high-density memory and computing applications, yet their switching mechanisms remain controversial due to the lack of direct structural evidence in amorphous materials. In this study, titanium nitride (TiN) diffusion is utilized as a natural tracer to map the spatial location of conductive pathways in As₂Se₃-based OTS devices using four-dimensional scanning transmission electron microscopy combined with angstrom-beam electron diffraction. The results reveal that TiN clusters from the electrode form continuous conductive pathways within the amorphous matrix, thereby providing direct evidence for filamentary switching behavior. Further, by the introduction of a carbon interfacial layer to control diffusion, an ultralow leakage current of 8 pA is achieved in As₂Se₃-based OTS devices. This work not only advances the fundamental understanding of switching mechanisms in OTS devices but also offers practical design guidance for developing highly reliable selectors in the memory community.