Threshold current reduction for the metal-insulator transition in NbO_2-x-selector devices: The effect of ReRAM integration

The threshold current for inducing the metal-insulator transition in a NbO_2-x selector element is shown to be affected by the properties of an adjacent memory element when integrated into a hybrid selector-memory device structure. Experimental results are reported for homogeneous NbO_2-x/Nb₂O_5-y and heterogeneous NbO_2-x/HfO₂ device structures, and show that the threshold current is lower in both hybrid structures than in the selector element alone, and is lower in the heterogeneous structure than in the homogeneous structure. Finite element modeling of the selector-memory structure shows that this results primarily from current confinement produced by the filamentary conduction path in the resistive-switching memory layer (i.e. Nb₂O_5-y or HfO₂), an observation that further implies a smaller diameter filament in HfO₂ than in Nb₂O_5-y. The thermal and electrical conductivities of the memory layer are also shown to influence the threshold current, but to a lesser extent.