Threshold Switching in Vertically Aligned MoS${_2}$/SiO${_x}$ Heterostructures based on Silver Ion Migration

Abstract

Threshold switching (TS) is a phenomenon where non-permanent changes in electrical resistance of a two-terminal device can be controlled by modulating the voltage bias. TS based on silver (Ag) conductive filaments has been observed in many materials, including layered two-dimensional (2D) transition metal dichalcogenides (TMDs). 2D TMDs are particularly promising for metal ion movement due to their van der Waals (vdW) gaps between their sheets, facilitating ion migration and filament formation without disturbing covalent chemical bonds. In this work, we demonstrate the heterostructure growth of vertically aligned molybdenum disulfide (VAMoS${_2}$) with an amorphous silicon oxide (SiO${_x}$) layer on top after sulfurization. We show that Ag ions migrate through this material stack, enabling TS. Our Ag/SiO${_x}$/VAMoS${_2}$/gold (Au) devices exhibit TS at low voltages of ~0.63 V, with high on-state currents over 200 ${\mu}$A and stable switching exceeding 10${^4}$ cycles. Moreover, we identify two rate-limiting steps for filament formation through a physics-based dynamical model and simulate the switching kinetics. Our devices show a fast on-switching time of 311 ns and spontaneous relaxation in 233 ns. These findings deepen the understanding of SiOx/MoS${_2}$-based RS devices and demonstrate the promise for applications in emerging memories and neuromorphic computing systems.