Nanoristors: highly uniform, sub-500-millivolt, large-scale, and robust molybdenum disulfide nanograined memristors

Memristors are garnering attention as promising electronic synapse and nonvolatile memory devices owing to their high density and analog switching with low energy consumption. However, most conventional memristors suffer not only from device-to-device and cycle-to-cycle variations but also from a destructive conductive filament (CF)-forming process, which are issues that must be addressed to use memristors in practical applications. Here, we demonstrate a highly robust and reliable memristor array using molybdenum disulfide (MoS₂) nanograins, named nanoristors. MoS₂ films with 7-10 nm nanograins were synthesized using plasma-enhanced chemical vapor deposition. We confirmed that tens of thousands of grain boundaries exist in a 1 μm × 1 μm area, resulting in memory operation with exceptionally high uniformity and excellent endurance (>2300 cycles). Moreover, vertically formed grain boundaries and defects work as a guiding route for Ag⁺ ion diffusion, resulting in forming-free operation with a low switching voltage of less than 500 mV. Furthermore, the MoS₂ nanoristor successfully emulated potentiation and depression characteristics which are essential for online learning in neuromorphic systems. The face recognition functionality of the MoS₂ nanoristor-based synapse device is evaluated using the device-to-system simulation. As the proposed approach of fabricating nanograined MoS₂ leads to highly uniform and robust operation of memristors, it is expected that nanoristors fabricated using layered nanomaterials will open up new opportunities for achieving electronic synapse and memory devices for application in neuromorphic electronic systems.