Bipolar resistive switching and synaptic characteristics modulation at sub-μA current level using novel Ni/SiO_x/W cross-point structure

Abstract

Step bias (VSTEP) modulated bipolar resistive switching (BRS) and neuromorphic characteristics are observed at very low current level (sub-μA) in a novel Ni/SiOx/W 2 × 2 μm2 cross-point resistive random access memory (RRAM) structure. Device microstructure and thickness of the switching dielectric layer are exposed by TEM/HRTEM images. Elemental composition of Ni/SiOx/W structure and switching matrix (SiOx) are confirmed by EDS and XPS analysis respectively. Statistical analysis of high resistance state (HRS) and low resistance state (LRS) switching uniformity is performed for 50 randomly selected pristine devices. Repeatable bipolar switching with large memory window of >5 × 102, long program/erase (P/E) endurance of >4 × 106 cycles with small pulse width (200 ns) and good data retention of > 105 s at 100 nA current compliance (CC) level are achieved. Schottky emission and hopping conduction are main mechanisms of the charge carrier transport. Activations energies (EA) are extracted from the Arrhenius plot. At reduced VSTEP of 50 mV, the device emulates ‘learning’ (potentiation) and ‘forgetting’ (depression) function of the biological synapse with very low spiking energy of ∼6.4–14.4 fJ. Oxygen vacancy (VO) based conducting filament regrowth/annihilation is the key mechanism for the conductivity modulation.