In Operando Characterization of Pt-TaOx-Ta Bipolar Vacancy Change Memories

Abstract

Clear and unambiguous experimental observation of the physical processes leading to resistance change during formation and switching of bipolar valence change memories (VCM) remains one of the main remaining challenges in the characterization and understanding of resistive memory devices[1]. Presented here is a Scanning Transmission Electron Microscopy (STEM) Electron Energy Loss Spectroscopy (EELS) study which reveals a valence change filamentary switching mechanism during low-current bipolar resistive switching operation in Pt-TaOx-Ta resistive memory devices. No change in the film stack is observed in High Angle Annular Dark Field (HAADF) STEM during SET or RESET operation, which is consistent with expectations for a low-current operation VCM. A ~50 nm wide filamentary region is observed in EELS maps analyzed with multivariate statistical analysis disappearing on RESET operation and reappearing during SET operation. In this filamentary region, the Ta O2,3 edge is consistent with oxidized Ta but there is a sharp metallic plasmon feature which is blue shifted in accordance with our previous ab initiopredictions for metallic oxides. [1] Yang Y and Lu W D 2016 Progress in the Characterizations and Understanding of Conducting Filaments in Resistive Switching Devices IEEE Transactions on Nanotechnology 15 465-72