Phase-change materials (PCMs) are leading candidates for memory and neuromorphic computing applications. By alternately growing PCM and confinement nanolayers, phase-change heterostructures (PCHs), in particular, TiTe₂/Sb₂Te₃, have been developed to improve the programming consistency of memory devices. However, the crystallization temperature of Sb₂Te₃ is too low for practical use in nonvolatile devices. In this work, we report the fabrication of highly textured TiTe₂/Ge₂Sb₂Te₅ (GST) heterostructure thin films, leveraging the higher crystallization temperature of GST. We deposit the PCH on standard silicon substrates using GST as the seed layer, and determine that the minimum GST thickness required for epitaxial-like growth of PCH thin films is approximately 2 nm. Through atomic-scale structural characterization, we show that the resulting heterostructures consist of atomically flat GST and TiTe₂ nanolayers with sharp interfaces. Although we apply annealing temperatures up to 400 °C, obtaining the ordered hexagonal phase of GST remains challenging. This is because the formation of hexagonal GST requires a continuous vacancy ordering process, but the limited length scale in the vertical direction and the presence of TiTe₂ nanolayers hinder vacancy migration. Finally, we outline the key steps for wafer-scale synthesis of TiTe₂/GST and other PCHs.

Link:Wafer-scale growth of highly textured TiTe2/Ge2Sb2Te5 heterostructure thin films | Applied Physics Letters | AIP Publishing