Reduced Variability in Threshold Switches Using Heterostructures of SiO${_x}$ and Vertically Aligned MoS${_2}$

TL;DR

This study demonstrates that heterostructures of SiO${_x}$ and vertically aligned MoS${_2}$ significantly reduce variability and improve the speed and reliability of threshold switching in memristor devices, advancing memory and neuromorphic applications.

Contribution

The paper introduces a novel SiO${_x}$/VAMoS${_2}$ heterostructure that enhances threshold switching performance and reduces variability compared to SiO${_x}$ alone, with a physics-based model explaining ion migration mechanisms.

Findings

Higher on-threshold and hold voltages (~0.4 V) in heterostructures.

Faster switching times down to 356 ns under 4 V pulse.

Lower cycle-to-cycle on-current variability (3.0%).

Abstract

Layered two-dimensional (2D) materials provide unique structural features, such as physical gaps between their layers that are only connected through van der Waals (vdW) forces. These vdW gaps can guide the migration of intercalated ions and thus regulate filament growth in resistive switching (RS) devices. Vertically aligned 2D materials and their heterostructures provide vdW gap-mediated ion transport in memristor crossbars, providing great potential for high-density integration and reliable RS performance. Nevertheless, the fundamental switching mechanisms and their contributions to the RS remain inadequately understood. In this work, we investigate silver (Ag) filament-based threshold switching (TS) in heterostructures comprising vertically aligned 2D molybdenum disulfide (VAMoS${_2}$) grown via sulfurization and silicon oxide (SiO${_x}$). Compared to SiO${_x}$-only devices, the SiO${_x}$/VAMoS${_2}$ devices exhibit TS with higher on-threshold and hold voltages, each approximately 0.4 V, faster switching times down to 356 ns under a 4 V pulse, and a lower cycle-to-cycle on-current variability of 3.0%. A physics-based, variability-aware model reveals that confined Ag ion migration within the vdW gaps in VAMoS${_2}$ forms ultrathin seed filaments, which guide filament growth in the SiO${_x}$ layer. These findings establish SiO${_x}$/VAMoS${_2}$ heterostructures as a promising concept for reliable TS in vertical device architectures for emerging memories and neuromorphic computing.