The Role of Vacancy Dynamics in Two‐Dimensional Memristive Devices

Abstract

Two‐dimensional layered transition metal dichalcogenides (TMDCs) are promising memristive materials for neuromorphic computing systems. Despite extensive experimental work, the underlying switching mechanisms are still not understood, impeding progress in material and device functionality. This study reveals the dominant role of defect dynamics in the switching process of 2D TMDC materials. The switching process is governed by the formation and annihilation dynamics of a local vacancy depletion zone. It explains the distinct features of the device characteristics observed experimentally, including fundamentally different device behavior previously thought to originate from multiple mechanisms. Key influence factors are identified and discussed with a fully coupled and dynamic charge transport model for electrons, holes, and ionic point defects, including image‐charge‐induced Schottky barrier lowering (SBL). Thermal effects and local Joule heating are considered by coupling the transient heat transfer equation to the electronic properties. The model is validated with hysteresis and pulse measurements for various lateral 2D MoS2‐based devices, strongly corroborating the relevance of vacancy dynamics in TMDC devices and offering a new perspective on the switching mechanisms. The insights gained from this study can be used to extend the functional behavior of 2D TMDC memristive devices in future neuromorphic computing applications.

Spiral WSe2 with Interlayer Twist for Memristive and Neuromorphic Device Applications

“…These parameters critically determine the direction and symmetry of hysteresis in the I−V curve. 35 Bisht et al also reported on how electrical bias in one junction affects neighboring junctions due to graded point defects and their distribution in the inhomogeneous medium of hydrogen-doped nickelate films. 36 Raman, XPS, and KPFM investigations demonstrate the underlying nonhomogeneity and point defects (selenium vacancies) in WSe 2 .…”

Two-Dimensional Tunneling Memtransistor with Thin-Film Heterostructure for Low-Power Logic-in-Memory Complementary Metal-Oxide Semiconductor

“…As the switching processes in the memory devices primarily stem from the number and location of structural defects and compositional impurities, − high-resolution scanning transmission electron microscope (STEM) was employed to identify the defects at the edge and in the interior of the electrochemical exfoliated WSe 2 nanoflakes, as shown in Figure a,b. Four different types of defects, namely monoselenium vacancies (V Se ), diselenium vacancies (V 2Se ), W vacancies (V W ), and W adatoms (W ad ), were observed in the inner region of the exfoliated WSe 2 nanoflakes (Figure c–f).…”

Dynamics of Analog Switching Behavior in Thin Polycrystalline Barium Titanate

“…As the tunnel transparency of the barrier is eliminated, the elastic tunneling is no longer the dominant transport mechanism, and the resistive properties of the ferroelectric film should also be taken into account together with polarization charge screening effects. By analogy with OxRAM [ 8–11 ] and 2D memristive devices [ 12 ] point defects are suggested to be responsible for the resistive switching in a FE‐memristor. It is hard to confirm this assumption since the concentration of the vacancies in a ferroelectric film is extremely low, complicating the direct identification of the defects and the establishment of their role in the resistive switching mechanisms.…”