Boron nitride and molybdenum disulfide as 2D composite element selectors with flexible threshold switching

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Highlights

  • Threshold switching characteristics has been reported in 2D composite nanomaterials.

  • The effectiveness of cross crosstalk suppression was indicated by assembled 1S1R unit.

  • The developmental potentiality to restrain the crosstalk issue was indicated.

Abstract

2D composite nanomaterials of insulating boron nitride (BN) and semiconductor molybdenum disulfide (MoS2)-based flexible threshold switching selectors (Ag/BN+MoS2/Ag based on BM1 and BM2) are fabricated. Both selectors shown excellent bidirectional threshold switching characteristics. The assembled 1S1R unit comprising Ag/BN+MoS2/Ag based on BM1 selector and bipolar rewritable Ag/ZnO/Ag resistive switching memory shows the effectiveness of cross crosstalk suppression. The thermal conductivity of the functional layer based on BM2 decreasing to some extent with the content of BN decreasing, resulting in an increasing trend of Vhold compared with selector based on BM1. And the selectors of Ag/BN+MoS2/Ag based on BM2 were assembled with a unidirectional open WORM Ag/polyvinyl carbazole/Ag memory, it also shows a good effect in restraining the crosstalk. It has large developmental potentiality in flexible 2D composite nanomaterials threshold switching selector to restrain the crosstalk issue for a large RRAM array.

Introduction

In the wake of the traditional silicon-based Flash memory getting closer and closer to its critical point, the burgeoning resistive switching random access memory (RRAM) has been perceived as a great candidate for the next generation nonvolatile memory [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11]. RRAM has fast operation speed, simple two-terminal structure and 3D stacking capability [12], [13], meeting the demand criteria of big data memory. A variety of RRAMs have been developed and studied extensively, it usually adopt metal oxide, or organics films as a functional layer [14], [15], [16], [17], [18], [19], [20]. At the same time, in high density cross array structure of RRAM, crosstalk issue that currents flowing across the neighboring unselected cell results in failure of writing or reading operations, is the biggest obstacle to the practical process of RRAM. For example, if there are three adjacent intersecting cells, and all three cells are in a low resistance state, the reading resistance of the fourth intersecting cell must is in low resistance state regardless of whether the real resistance of the fourth intersecting cell is in the high resistance state or the low resistance state. This phenomenon is called crosstalk phenomenon. Crosstalk issue is the main bottle neck problem suppressing RRAM’s practical application [21], [22], [23]. To settle this trouble, a number of approaches have been presented, for example, the functional units were directly connected to each RRAM cell [24], development of RRAM cells with self-rectifying structure [25], or constituted by two identical bipolar back to back connected RRAM cells [26]. Thereinto, one selector-one resistor (1S1R) solution with two-terminal selector devices linked to memory devices was turning out to be the most prospective scheme to solve the crosstalk issue without compromising the scalability and high density integration of the RRAM array [27], [28], [29].

The selector has aroused great interest among scholars on account of its simple two-terminal construction, non-linear resistance, and wide application. Wang research group made use of metallic doping technology fabricated in sequence Ag-doped MgOx, SiOx, and HfOx-based diffusive threshold switching characteristics and illustrated the feasibility of their selectors in 1S1R integration [30], [31], Zhao research group improved the property of selectors through modulating defects and aggrandized test compliance current [32]. Nonetheless, imperious demands for selectors still motivate us to seek a simple-yet-effective solution for promotion the whole performance, including without limitation to high current compliance and fast switching speed to match the running of RRAMs, nonlinearity capacity, and proper threshold switching voltages.

Recently, the use of 2D materials has achieved remarkable success in research and development of MOSFET, lithium-ion batteries, gas sensors and capacitors bringing many unexpected excellent performance to device [33], [34], [35], [36], for instance, flexibility and clarity. A number of 2D materials such as graphene oxide, MoSe2, as well as black phosphorous have been successfully introduced and combined into RRAM prototypes with the purpose of promoting device’s resistive switching performance and resulting from additional excellent capacities [37]. Taking into consideration of boron nitride (BN) might be a effective scheme to preparation of flexible wearable resistive switching devices and other logic devices on account of its insulating feature and flexibility [38], molybdenum disulfide (MoS2), a famous layered semiconductor among the transition metal dichalcogenide materials system, has exhibited many interesting physical properties, for instance, thickness-dependent band structure, high carrier mobility, photoconductivity, and environmental sensitivity and flexibility and transparency [39], [40]. In this work, a composite 2D materials of BN and MoS2 nanosheets, recorded as BN+MoS2, was introduced as the functional layer for flexible threshold resistive switching selector to suppress the crosstalk issue.

Section snippets

Experimental section

BN was purchased from Hangzhou licheng network Tech. Co., Ltd. (www. lookchem. cn). MoS2 was purchased from Nanjing MKNANO Tech. Co., Ltd. (www. mukenano. com). Put 250 mg of BN and MoS2 to 50 ml of ethanol, respectively, dispersion is carried out by means of ultrasonic concussion for 35 min to form a homogeneous ethanol solution (5 mg/ml), then 3 ml (or 6 ml) of MoS2 solution and 12 ml of BN solution were mixed by magnetic stirring for overnight to form consistent and uniform dispersion of BN

Result and discussion

Schematic diagram of the molecular structure for BN and MoS2 was shown in Fig. 1(a). Fig. 1(b) depicts the schematic view Ag/BN+MoS2/Ag device. And the cross-sectional SEM image of BN+MoS2 thin films before the evaporation of the top Ag electrode was shown in Fig. 1(c), it serves to show the thickness of the BN+MoS2 functional layer was about 130 ± 10 nm. Fig. 1(d,e) shows the AFM topography images of BN+MoS2 thin films based on BM1and BM2, respectively. The root-mean-square roughness of the

Conclusions

In summary, Ag/BN+MoS2/Ag 2D composite nanomaterials of insulating BN and semiconductor MoS2-based threshold switching selectors are fabricated and studied. Under the applied of the electric field, the formation and fusing of conductive channel formed by the defective paths abound in 2D nanomaterials, contributes to the conversion of from HRS to LRS and LRS to HRS occurs simultaneously under the same voltage polarity. Both threshold switching selectors shows bidirectional selectivity, sharp

CRediT authorship contribution statement

Yanmei Sun: Conceptualization, Formal analysis, Investigation, Methodology, Supervision, Validation, Visualization, Writing - original draft, Writing - review & editing. Dianzhong Wen: Investigation, Conceptualization, Supervision. Fengyun Sun: Conceptualization, Investigation.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgements

Funding received from Natural Science Foundation of Heilongjiang Province, China (LH2019F029) and the Basic Research Project of the Basic Research Business of the Provincial University in Heilongjiang Province (RCCX 201702).

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