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ACS Appl Mater Interfaces. 2017 Mar 29;9(12):10820-10824. doi: 10.1021/acsami.6b16268. Epub 2017 Mar 16.

Direct Probing of the Dielectric Scavenging-Layer Interface in Oxide Filamentary-Based Valence Change Memory.

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IMEC , Kapeldreef 75, B-3001 Heverlee (Leuven), Belgium.
Department of Applied Physics, Eindhoven University of Technology , Eindhoven 5612AZ, The Netherlands.
Peter Grünberg Institute and Jülich Aachen Research Alliance , Jülich 52425, Germany.
KU Leuven , Department of Physics and Astronomy, Celestijnenlaan 200D, B-3001 Leuven, Belgium.


A great improvement in valence change memory performance has been recently achieved by adding another metallic layer to the simple metal-insulator-metal (MIM) structure. This metal layer is often referred to as oxygen exchange layer (OEL) and is introduced between one of the electrodes and the oxide. The OEL is believed to induce a distributed reservoir of defects at the metal-insulator interface thus providing an unlimited availability of building blocks for the conductive filament (CF). However, its role remains elusive and controversial owing to the difficulties to probe the interface between the OEL and the CF. Here, using Scalpel SPM we probe multiple functions of the OEL which have not yet been directly measured, for two popular VCMs material systems: Hf/HfO2 and Ta/Ta2O5. We locate and characterize in three-dimensions the volume containing the oxygen exchange layer and the CF with nanometer lateral resolution. We demonstrate that the OEL induces a thermodynamic barrier for the CF and estimate the minimum thickness of the OEL/oxide interface to guarantee the proper switching operations is ca. 3 nm. Our experimental observations are combined to first-principles thermodynamics and defect kinetics to elucidate the role of the OEL for device optimization.


RRAM; filament; oxygen-exchange-layer; scalpel SPM; scavenging layer


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