Fig. 3: Observation of conducting channel by cross-sectional transmission electron microscopy.

a HAADF TEM image of the nanoscale Ta-rich conduction channel. b–d Corresponding EDS elemental mapping of Ta, O, and Hf, respectively. e c8w I–V curves obtained from the ohmic memristive device when Hf metal electrode were negatively biased (Ta electrode positively biased) for SET operation. The inset shows the resistance as a function of applied voltage. f EDS line-scan analysis of the conduction channel region (oval area in b). g I–V characteristics of the ohmic memristive device when operating at high current and voltage ranges. This leads to another SET mode resulting in 8w switching polarity (see also Supplementary Fig. 3f). Both HRS and LRS are highly conductive. The inset shows the corresponding R-V plot. h EDS line-scan analysis (see oval area in j) of the conduction channel region, showing that a larger Ta-rich filament is formed in ohmic memristive devices when operated in 8w polarity (as shown in g). i HAADF image showing Ta-rich cluster observed in 8w switching polarity. j–l EDS elemental mapping of Ta, O, and Hf, respectively. Scale bars, 10 nm. It can be clearly observed that the O migrates from the bottom electrode to the anode (k), generating oxygen-deficient and tantalum-rich filament at the bottom electrode interface.