(Invited) Non-Volatile Resistance Switching Phenomenon in Monolayer h-BN
Authors: Wu Xiaohan , Ge Ruijing , Chen Po-An , Chiang Meng-Hsueh , Akinwande Deji , Lee Jack 
Published: February 2020

Over the last decade, two-dimensional (2D) materials have drawn much attention for the next-generation electron devices, optoelectronics and bioelectronics [1, 2]. Recently, non-volatile resistance switching (NVRS) behavior has been observed in various 2D materials, including graphene oxide, functionalized MoS2 and partially degraded black phosphorus, etc. [3-5], where the resistance can be modulated between a high-resistance state (HRS) and a low-resistance state (LRS) [6]. In addition, there are several reports about NVRS in multi-layer hexagonal boron-nitride (h-BN) [7]. Although 2D materials are widely regarded as promising candidates to overcome vertical scaling obstacle in NVRS based on conventional metal-insulator-metal (MIM) structure [3], few researchers believe that single-layer 2D material can produce NVRS [8] due to excessive leakage current. Sangwan et al. discovered that grain boundaries in single-layer MoS2 can produce NVRS based on planar (horizontal) structure [9]. However, the planar structure without 3D stacking ability has the limitation of low integration density.
Recently, we reported the discovery that NVRS phenomenon is accessible in a variety of single-layer transition metal dichalcogenides (TMDs) in vertical MIM structure [10, 11]. Herein, we report another 2D insulating material, single-layer h-BN, also shows stable and desirable NVRS behavior. Compared with monolayer TMDs with three atomic layers, monolayer h-BN has only one atomic layer and ~0.33 nm in thickness, which is the thinnest active layer in non-volatile resistance memory. These devices can be labelled as “atomristor”, which means the memristor effect in atomically thin nanomaterials.[12]

The h-BN atomristors have been studied using a crossbar structure (Au/h-BN/Au) [See Figure a]. Figure b shows a representative I-V curve of h-BN atomristor, demonstrating forming-free switching with large on/off ratio (up to >106) and low switching voltage (down to <1V). In addition, pulse operation proves its fast switching speed (<15 ns), which is comparable to the state-of-the-art in 2D memory. Ab-initio simulation reveals that the metal ion substitution in sulfur vacancies may be related to the switching from HRS to LRS, and area scaling test result is also consistent with this conductive-bridge-like mechanism. The results of this work indicate a potential universal resistive switching behavior in 2D insulating monolayers, which is applicable to memory technology, neuromorphic computing, RF switch and flexible electronics.
References
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Figure 1