Flexible, stretchable, and bendable materials, including inorganic semiconductors, organic polymers, graphene, and transition metal dichalcogenides (TMDs), are attracting great attention in such areas as wearable electronics, biomedical technologies, foldable displays, and wearable point-of-care biosensors for healthcare. Among a broad range of layered TMDs, atomically thin layered molybdenum disulfide (MoS2) has been of particular interest, due to its exceptional electronic properties, including tunable bandgap and charge carrier mobility. MoS2 atomic layers can be used as a channel or a gate dielectric for fabricating atomically thin field-effect transistors (FETs) for electronic and optoelectronic devices. This review briefly introduces the processing and spectroscopic characterization of large-area MoS2 atomically thin layers. The review summarizes the different strategies in enhancing the charge carrier mobility and switching speed of MoS2 FETs by integrating high-κ dielectrics, encapsulating layers, and other 2D van der Waals layered materials into flexible MoS2 device structures. The photoluminescence (PL) of MoS2 atomic layers has, after chemical treatment, been dramatically improved to near-unity quantum yield. Ultraflexible and wearable active-matrix organic light-emitting diode (AM-OLED) displays and wafer-scale flexible resistive random-access memory (RRAM) arrays have been assembled using flexible MoS2 transistors. The review discusses the overall recent progress made in developing MoS2 based flexible FETs, OLED displays, nonvolatile memory (NVM) devices, piezoelectric nanogenerators (PNGs), and sensors for wearable electronic and optoelectronic devices. Finally, it outlines the perspectives and tremendous opportunities offered by a large family of atomically thin-layered TMDs.

Flexible Molybdenum Disulfide (MoS2) Atomic Layers for Wearable Electronics and Optoelectronics

The Future of Memristors: Materials Engineering and Neural Networks

Resistive random access memory (RRAM) devices are receiving increasing extensive attention due to their enhanced properties such as fast operation speed, simple device structure, low power consumption, good scalability potential and so on, and are currently considered to be one of the next-generation alternatives to traditional memory. In this review, an overview of RRAM devices is demonstrated in terms of thin film materials investigation on electrode and function layer, switching mechanisms and artificial intelligence applications. Compared with the well-developed application of inorganic thin film materials (oxides, solid electrolyte and two-dimensional (2D) materials) in RRAM devices, organic thin film materials (biological and polymer materials) application is considered to be the candidate with significant potential. The performance of RRAM devices is closely related to the investigation of switching mechanisms in this review, including thermal-chemical mechanism (TCM), valance change mechanism (VCM) and electrochemical metallization (ECM). Finally, the bionic synaptic application of RRAM devices is under intensive consideration, its main characteristics such as potentiation/depression response, short-/long-term plasticity (STP/LTP), transition from short-term memory to long-term memory (STM to LTM) and spike-time-dependent plasticity (STDP) reveal the great potential of RRAM devices in the field of neuromorphic application.

https://www.mdpi.com/2079-4991/10/8/1437/pdf

Advances of RRAM Devices: Resistive Switching Mechanisms, Materials and Bionic Synaptic Application.

A Review of Resistive Switching Devices: Performance Improvement, Characterization, and Applications

https://www.tandfonline.com/doi/pdf/10.1080/14686996.2020.1730236

Decade of 2D-materials-based RRAM devices: a review.

All-inorganic halide perovskites are considered as favorable materials for various electronic applications because of their superior functionality and stability. In this study, the inorganic rubidi...

Compliance Current-Dependent Dual-Functional Bipolar and Threshold Resistive Switching in All-Inorganic Rubidium Lead-Bromide Perovskite-Based Flexible Device

Recently, several types of lead halide perovskites have been actively researched for resistive switching (RS) memory or artificial synaptic devices due to their current–voltage hysteresis along with the feasibility of fabrication, low-temperature processability and superior charge mobility. However, the toxicity and environmental pollution potential of lead halide perovskites severely restrict their large-scale commercial prospects. In the present work, the environmentally friendly and uniform CsSnCl3 perovskite films are introduced to act as an active layer in the flexible memristors. Ag/CsSnCl3/ITO devices demonstrate bipolar RS with excellent electrical properties such as forming free characteristics, good uniformity, low operating voltages, a high ON/OFF ratio (102) and a long retention time (>104 s). The RS mechanism has been well explained in the outline of electric field-induced formation and rupture of Ag filaments in the CsSnCl3 layer. The metallic nature of the conducting filament has been further confirmed by temperature-dependent variation of low and high resistance states. Additionally, various pulse measurements have been carried out to mimic some of the basic synaptic functions including postsynaptic current, paired-pulse facilitation, long-term potentiation and long-term depression under normal as well as bending conditions. Our work provides the opportunity for exploring artificial synapses based on lead-free halide perovskites for the development of next-generation flexible electronics.

Nonvolatile resistive switching and synaptic characteristics of lead-free all-inorganic perovskite-based flexible memristive devices for neuromorphic systems

Halide perovskite (HP) materials are actively researched for resistive switching (RS) memory devices due to their current-voltage hysteresis along with low-temperature processability, superior charge mobility, and simple fabrication. In this study, all-inorganic RbPbI3 perovskite has been doped with Cl in the halide site and incorporated as a switching media in the Ag/RbPbI3-xClx/ITO structure, since pure RbPbI3 is nonswitchable. Five compositions of the RbPbI3-xClx (x = 0, 0.3, 0.6, 0.9, and 1.2) films are fabricated, and the conductivity was found to be increasing upon increase in Cl concentration, as revealed by dielectric and I-V measurements. The device with a 20% chloride-substituted film exhibits a higher on/off ratio, extended endurance, long retention, and high-density storage ability. Finally, a plausible explanation of the switching mechanism from iodine vacancy-mediated growth of conducting filaments (CFs) is provided using conductive atomic force microscopy (c-AFM). The c-AFM measurements reveal that pure RbPbI3 is insulating in nature, whereas Cl-doped films demonstrate resistive switching behavior.

Induced Vacancy-Assisted Filamentary Resistive Switching Device Based on RbPbI3-xClx Perovskite for RRAM Application.

Uniform, large-scale growth of WS2 nanodomains via CVD technique for stable non-volatile RRAM application

https://iopscience.iop.org/article/10.1088/2053-1591/ab154d/pdf

Ujjal Das

Papers

Compliance Current-Dependent Dual-Functional Bipolar and Threshold Resistive Switching in All-Inorganic Rubidium Lead-Bromide Perovskite-Based Flexible Device

Nonvolatile resistive switching and synaptic characteristics of lead-free all-inorganic perovskite-based flexible memristive devices for neuromorphic systems

Induced Vacancy-Assisted Filamentary Resistive Switching Device Based on RbPbI3-xClx Perovskite for RRAM Application.

Uniform, large-scale growth of WS2 nanodomains via CVD technique for stable non-volatile RRAM application

A multi-level bipolar memristive device based on visible light sensing MoS2 thin film