Memory Switching and Threshold Switching in a 3D Nanoscaled NbOX System

The 3D crossbar arrays provide a cost-effective approach for high-density integration of resistive switching random-access memory (RRAM). A selector device or self-selective cells can be used to inhibit the sneaking current from the unselected cells. The coexistence of memory switching (MS) with inherent nonlinearity and threshold switching (TS) with high current density in an individual material system will lead to technological benefits for memory integration and neuromorphic computing. However, the reported conductive filament (CF)-type MS and TS combining devices cannot meet the requirements for practical applications, as these devices lack built-in nonlinearity in memory mode and display low current density and large relaxing time in the selector mode. In this letter, we report a 3D TiN/TiO ₂ /NbO _X /Pt device with MS and TS before and after the forming processes. In the MS mode, this device shows >50 nonlinearity, a 100 ON/OFF ratio, non-volatility, and stable homogeneous switching due to vacancy redistribution. In the TS mode, owing to the metal–insulator transition, a high ON-state current (1.6 MA/cm ² ), high switching speed (<40 ns), and low relaxation time (<50 ns) are observed.