Experimental evidence for a quantum wire state in HfO2-based VCM-RRAM

We study the reset transition in Pt/HfO₂/Pt RRAM structures showing filamentary resistive switching (RS). Using various electrical reset methodologies we reveal three-state RS phenomena. Between the LRS and the HRS, a rather stable intermediate state is revealed and shown to have the properties of a quantum wire (QW). This QW state is characterized by having conductance of the order of G₀~2e² and represents a natural boundary between two different electron transport regimes. Above the G₀ limit, the conduction is associated to extended quantum transport states which connect the two electrodes, while below it, a spatial gap is opened in the conducting filament (CF) and the conduction is controlled by hopping or tunneling. Analysis of the statistics of conductance during the reset experiments strongly support the existence of these three states and help understanding the evolution of the CF structure during RS.