High-Performance Photoinduced Memory with Ultrafast Charge Transfer Based on MoS2 /SWCNTs Network Van Der Waals Heterostructure

High-Speed Optoelectronic Nonvolatile Memory Based on van der Waals Heterostructures

High-performance optoelectronic nonvolatile memory is promising candidate for next-generation information memory devices. Here, a floating-gate memory is constructed based on van der Waals heterostructure, which exhibits a large storage window ratio (≈75.5%) and an extremely high on/off ratio (107 ), as well as an ultrafast electrical writing/erasing speed (40 ns). The enhanced performance enables as-fabricated devices to present excellent multilevel data storage, robust retention, and endurance performance. Moreover, stable optical erasing operations can be achieved by illuminating the device with a laser pulse, showcasing outstanding optoelectronic storage performance (optical erasing speed ≈ 2.3 ms). The nonvolatile and high-speed characteristics of these devices hold significant potential for the integration of high-performance nonvolatile memory.

High-Sensitivity 2D MoS2/1D MWCNT Hybrid Dimensional Heterostructure Photodetector

A photodetector based on a hybrid dimensional heterostructure of laterally aligned multiwall carbon nanotubes (MWCNTs) and multilayered MoS₂ was prepared using the micro-nano fixed-point transfer technique. Thanks to the high mobility of carbon nanotubes and the efficient interband absorption of MoS₂, broadband detection from visible to near-infrared (520-1060 nm) was achieved. The test results demonstrate that the MWCNT-MoS2 heterostructure-based photodetector device exhibits an exceptional responsivity, detectivity, and external quantum efficiency. Specifically, the device demonstrated a responsivity of 3.67 × 10³ A/W (λ = 520 nm, V_ds = 1 V) and 718 A/W (λ = 1060 nm, V_ds = 1 V). Moreover, the detectivity (D*) of the device was found to be 1.2 × 10¹⁰ Jones (λ = 520 nm) and 1.5 × 10⁹ Jones (λ = 1060 nm), respectively. The device also demonstrated external quantum efficiency (EQE) values of approximately 8.77 × 10⁵% (λ = 520 nm) and 8.41 × 10⁴% (λ = 1060 nm). This work achieves visible and infrared detection based on mixed-dimensional heterostructures and provides a new option for optoelectronic devices based on low-dimensional materials.

Impact of Planar and Vertical Organic Field-Effect Transistors on Flexible Electronics

The development of flexible and conformable devices, whose performance can be maintained while being continuously deformed, provides a significant step toward the realization of next-generation wearable and e-textile applications. Organic field-effect transistors (OFETs) are particularly interesting for flexible and lightweight products, because of their low-temperature solution processability, and the mechanical flexibility of organic materials that endows OFETs the natural compatibility with plastic and biodegradable substrates. Here, an in-depth review of two competing flexible OFET technologies, planar and vertical OFETs (POFETs and VOFETs, respectively) is provided. The electrical, mechanical, and physical properties of POFETs and VOFETs are critically discussed, with a focus on four pivotal applications (integrated logic circuits, light-emitting devices, memories, and sensors). It is pointed out that the flexible function of the relatively newer VOFET technology, along with its perspective on advancing the applicability of flexible POFETs, has not been reviewed so far, and the direct comparison regarding the performance of POFET- and VOFET-based flexible applications is most likely absent. With discussions spanning printed and wearable electronics, materials science, biotechnology, and environmental monitoring, this contribution is a clear stimulus to researchers working in these fields to engage toward the plentiful possibilities that POFETs and VOFETs offer to flexible electronics.

Fast, Multi-Bit, and Vis-Infrared Broadband Nonvolatile Optoelectronic Memory with MoS2 /2D-Perovskite Van der Waals Heterojunction

Nonvolatile optoelectronic memory (NVOM) integrating the functions of optical sensing and long-term memory can efficiently process and store a large amount of visual scene information, which has become the core requirement of multiple intelligence scenarios. However, realizing NVOM with vis-infrared broadband response is still challenging. Herein, the room temperature vis-infrared broadband NVOM based on few-layer MoS₂ /2D Ruddlesden-Popper perovskite (2D-RPP) van der Waals heterojunction is realized. It is found that the 2D-RPP converts the initial n-type MoS₂ into p-type and facilitates hole transfer between them. Furthermore, the 2D-RPP rich in interband states serves as an effective electron trapping layer as well as broadband photoresponsive layer. As a result, the dielectric-free MoS₂ /2D-RPP heterojunction enables the charge to transfer quickly under external field, which enables a large memory window (104 V), fast write speed of 20 µs, and optical programmable characteristics from visible light (405 nm) to telecommunication wavelengths (i.e., 1550 nm) at room temperature. Trapezoidal optical programming can produce up to 100 recognizable states (>6 bits), with operating energy as low as 5.1 pJ per optical program. These results provide a route to realize fast, low power, multi-bit optoelectronic memory from visible to the infrared wavelength.

Highly Sensitive MoS2 Photodetectors Enabled with a Dry-Transferred Transparent Carbon Nanotube Electrode

Fabricating electronic and optoelectronic devices by transferring pre-deposited metal electrodes has attracted considerable attention, owing to the improved device performance. However, the pre-deposited metal electrode typically involves complex fabrication procedures. Here, we introduce our facile electrode fabrication process which is free of lithography, lift-off, and reactive ion etching by directly press-transferring a single-walled carbon nanotube (SWCNT) film. We fabricated Schottky diodes for photodetector applications using dry-transferred SWCNT films as the transparent electrode to increase light absorption in photoactive MoS₂ channels. The MoS₂ flake vertically stacked with an SWCNT electrode can exhibit excellent photodetection performance with a responsivity of ∼2.01 × 10³ A/W and a detectivity of ∼3.2 × 10¹² Jones. Additionally, we carried out temperature-dependent current-voltage measurement and Fowler-Nordheim (FN) plot analysis to explore the dominant charge transport mechanism. The enhanced photodetection in the vertical configuration is found to be attributed to the FN tunneling and internal photoemission of charge carriers excited from indium tin oxide across the MoS₂ layer. Our study provides a novel concept of using a photoactive MoS₂ layer as a tunneling layer itself with a dry-transferred transparent SWCNT electrode for high-performance and energy-efficient optoelectronic devices.

Ga2O3 based multilevel solar-blind photomemory array with logic, arithmetic, and image storage functions

Photomemories offer great opportunities for multifunctional integration of optical sensing, data storage, and processing into one single device. However, little attention has been paid to photomemories working in the solar-blind region so far, which may have unique advantages of insusceptibility to ambient light and higher capacity. Herein, we propose and demonstrate a Ga₂O₃ based solar-blind photomemory array with logic, arithmetic, and optoelectronic memory functions. The device shows n-type field effect-transistor performance with an on/off ratio as high as 10⁶, a responsivity of 8 × 10³ A W^-1, and a detectivity of 1.42 × 10¹⁴ Jones, all of which are amongst the best values ever reported for Ga₂O₃ based photodetectors. Based on the trapping and de-trapping process of holes in Ga₂O₃, multilevel data storage can be realized from the device. Simultaneously, the optical and electrical mixed basic logic of reconfigurable "AND" and "OR" operations have been realized in a single cell through the co-regulation of solar-blind light and the grid voltage. In addition, the photomemory can perform counting and addition operations, and the photomemory array can be utilized to realize solar-blind image storage. The results suggest that Ga₂O₃ may have potential applications in high-performance information storage, computing, and communications.

Emerging 2D Memory Devices for In-Memory Computing

It is predicted that the conventional von Neumann computing architecture cannot meet the demands of future data-intensive computing applications due to the bottleneck between the processing and memory units. To try to solve this problem, in-memory computing technology, where calculations are carried out in situ within each nonvolatile memory unit, has been intensively studied. Among various candidate materials, 2D layered materials have recently demonstrated many new features that have been uniquely exploited to build next-generation electronics. Here, the recent progress of 2D memory devices is reviewed for in-memory computing. For each memory configuration, their operation mechanisms and memory characteristics are described, and their pros and cons are weighed. Subsequently, their versatile applications for in-memory computing technology, including logic operations, electronic synapses, and random number generation are presented. Finally, the current challenges and potential strategies for future 2D in-memory computing systems are also discussed at the material, device, circuit, and architecture levels. It is hoped that this manuscript could give a comprehensive review of 2D memory devices and their applications in in-memory computing, and be helpful for this exciting research area.

Optically stimulated synaptic transistor based on MoS2/quantum dots mixed-dimensional heterostructure with gate-tunable plasticity

In this Letter, we report an optically stimulated synaptic transistor based on MoS₂/quantum dots mixed-dimensional (MD) heterostructure, where the channel conductance shows a non-linear response to the optical stimuli. Paired-pulse facilitation is realized with the index above 200%, and the optical synaptic plasticity can be modulated by adjusting the amplitude, duration time, frequency, and power of light spikes. In addition, the long-term plasticity shows a gate-tunability, which can be attributed to the unique photoelectric coupling in MoS₂/quantum dots MD heterostructure. This work opens up a new way to explore optically stimulated synaptic devices based on designed device structure and provides a feasible method to achieve plasticity modulation by gate voltage, which plays an important role in developing neuromorphic devices with complicated functions.

Emerging Opportunities for Electrostatic Control in Atomically Thin Devices

Electrostatic control of charge carrier concentration underlies the field-effect transistor (FET), which is among the most ubiquitous devices in the modern world. As transistors and related electronic devices have been miniaturized to the nanometer scale, electrostatics have become increasingly important, leading to progressively sophisticated device geometries such as the finFET. With the advent of atomically thin materials in which dielectric screening lengths are greater than device physical dimensions, qualitatively different opportunities emerge for electrostatic control. In this Review, recent demonstrations of unconventional electrostatic modulation in atomically thin materials and devices are discussed. By combining low dielectric screening with the other characteristics of atomically thin materials such as relaxed requirements for lattice matching, quantum confinement of charge carriers, and mechanical flexibility, high degrees of electrostatic spatial inhomogeneity can be achieved, which enables a diverse range of gate-tunable properties that are useful in logic, memory, neuromorphic, and optoelectronic technologies.

Ultralow Power Wearable Heterosynapse with Photoelectric Synergistic Modulation

Although the energy consumption of reported neuromorphic computing devices inspired by biological systems has become lower than traditional memory, it still remains greater than bio-synapses (≈10 fJ per spike). Herein, a flexible MoS2-based heterosynapse is designed with two modulation modes, an electronic mode and a photoexcited mode. A one-step mechanical exfoliation method on flexible substrate and low-temperature atomic layer deposition process compatible with flexible electronics are developed for fabricating wearable heterosynapses. With a pre-spike of 100 ns, the synaptic device exhibits ultralow energy consumption of 18.3 aJ per spike in long-term potentiation and 28.9 aJ per spike in long-term depression. The ultrafast speed and ultralow power consumption provide a path for a neuromorphic computing system owning more excellent processing ability than the human brain. By adding optical modulation, a modulatory synapse is constructed to dynamically control correlations between pre- and post-synapses and realize complex global neuromodulations. The novel wearable heterosynapse expands the accessible range of synaptic weights (ratio of facilitation ≈228%), providing an insight into the application of wearable 2D highly efficient neuromorphic computing architectures.

Gate stimulated high-performance MoS2-In(OH) x Se phototransistor

Two-dimensional (2D) materials such as graphene and MoS₂ have shown great potential in photodetection platforms. Photoresponsivity and photoresponse speed are two important parameters illustrating photodetector performances. Although various hybrid structures have been designed, the trade-off between photoresponsivity and photoresponse speed has not been well balanced. In this work, MoS₂ film and In(OH) _x Se nanoparticles are combined together to form the hybrid phototransistor. Utilizing both the photoconducting and photogating effects, the photoresponsivity increases about one order of magnitude with a value of 10² A W^-1. The ratio of photocurrent and dark current increases to a value of 10⁴. Considering the slow photo recovery speed, a 2 ms gate voltage pulse is applied after turning off the light, which results in a complete recovery of current. The photoconducting effect, photogating effect and gate voltage stimulation simultaneously promote the superior comprehensive photoresponse performances. This method can be further explored and utilized for realizing high performance photodetectors.

Robust trap effect in transition metal dichalcogenides for advanced multifunctional devices

Defects play a crucial role in determining electric transport properties of two-dimensional transition metal dichalcogenides. In particular, defect-induced deep traps have been demonstrated to possess the ability to capture carriers. However, due to their poor stability and controllability, most studies focus on eliminating this trap effect, and little consideration was devoted to the applications of their inherent capabilities on electronics. Here, we report the realization of robust trap effect, which can capture carriers and store them steadily, in two-dimensional MoS2xSe2(1-x) via synergistic effect of sulphur vacancies and isoelectronic selenium atoms. As a result, infrared detection with very high photoresponsivity (2.4 × 105 A W-1) and photoswitching ratio (~108), as well as nonvolatile infrared memory with high program/erase ratio (~108) and fast switching time, are achieved just based on an individual flake. This demonstration of defect engineering opens up an avenue for achieving high-performance infrared detector and memory.