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Filamentary-based oxide resistive memory is considered as a disruptive technology for nonvolatile data storage and reconfigurable logic. Currently accepted models explain the resistive switching in these devices through the presence/absence of a conductive filament (CF) that is described as a reversible nanosized valence-change in an oxide material. During device operation, the CF cycles billion of times at subnanosecond speed, using few tens of microamperes as operating current and thus determines the whole device's performance. Despite its importance, the CF observation is hampered by the small filament size and its minimal compositional difference with the surrounding material. Here we show an experimental solution to this problem and provide the three-dimensional (3D) characterization of the CF in a scaled device. For this purpose we have recently developed a tomography technique which combines the high spatial resolution of scanning probe microscopy with subnanometer precision in material removal, leading to a true 3D-probing metrology concept. We locate and characterize in three-dimensions the nanometric volume of the conductive filament in state-of-the-art bipolar oxide-based devices. Our measurements demonstrate that the switching occurs through the formation of a single conductive filament. The filaments exhibit sizes below 10 nm and present a constriction near the oxygen-inert electrode. Finally, different atomic-size contacts are observed as a function of the programming current, providing evidence for the filament's nature as a defects modulated quantum contact. [ABSTRACT FROM AUTHOR]

In this work, we observe the switching mechanisms in non-filamentary resistive switching (RS) devices, investigated through a nanosized conductive tip used as a movable (virtual) top-electrode. The correlation between different conductive states of vacancy-modulated conductive oxide (VMCO) cells and the conductive domains in thin TiO 2 is provided. We observe the appearance of uniformly distributed conductive spots whose conductance can be reversibly modulated using a scanning biased conductive tip. Although TiO 2 has been often used as a material system for filamentary RS, these results clearly demonstrate the non-filamentary switching nature of valence change memory (VCM) cells. This supports their strong potentials in the area of applications where aggressive scaling and low-current operation is required. [ABSTRACT FROM AUTHOR]

The basic unit of information infilamentary-based resistive switchingmemories is physically stored in a conductive filament. Therefore,the overall performance of the device is indissolubly related to theproperties of such filament. In this Letter, we report for the firsttime on the three-dimensional (3D) observation of the shape of theconductive filament. The observation of the filament is done in ananoscale conductive-bridging device, which is programmed under realoperative conditions. To obtain the 3D-information we developed adedicated tomography technique based on conductive atomic force microscopy.The shape and size of the conductive filament are obtained in three-dimensionswith nanometric resolution. The observed filament presents a conicalshape with the narrow part close to the inert-electrode. On the basisof this shape, we conclude that the dynamic filament-growth is limitedby the cation transport. In addition, we demonstrate the role of theprogramming current, which clearly influences the physical-volumeof the induced conductive filaments. [ABSTRACT FROM AUTHOR]