Covalent Organic Frameworks for Neuromorphic Devices

Advancements in Nanowire-Based Devices for Neuromorphic Computing: A Review

Neuromorphic computing, inspired by the highly interconnected and energy-efficient way the human brain processes information, has emerged as a promising technology for post-Moore's law era. This emerging technology can emulate the structures and the functions of the human brain and is expected to overcome the fundamental limitation of the current von Neumann computing architecture. Neuromorphic devices stand out as the key components of future electronic systems, exhibiting potential in shaping the landscape of neuromorphic computing. Especially, nanowire (NW)-based neuromorphic devices, with their advantages of high integration, high-speed computing, and low power consumption, have recently emerged as candidates for neuromorphic computing technology. Here, a critical overview of the current development and relevant research in the field of NW-based neuromorphic devices are provided. Neuromorphic devices based on different NW materials are comprehensively discussed, including Ag NW-based, organic NW-based, metal oxide NW-based, and semiconductor NW-based devices. Finally, as a foresight perspective, the potentials and the challenges of these NW-based neuromorphic devices for use as future brain-like electronics are discussed.

2D Conjugated Polymer Thin Films for Organic Electronics: Opportunities and Challenges

2D conjugated polymers (2DCPs) possess extended in-plane π-conjugated lattice and out-of-plane π-π stacking, which results in enhanced electronic performance and potentially unique band structures. These properties, along with predesignability, well-defined channels, easy postmodification, and order structure attract extensive attention from material science to organic electronics. In this review, the recent advance in the interfacial synthesis and conductivity tuning strategies of 2DCP thin films, as well as their application in organic electronics is summarized. Furthermore, it is shown that, by combining topology structure design and targeted conductivity adjustment, researchers have fabricated 2DCP thin films with predesigned active groups, highly ordered structures, and enhanced conductivity. These films exhibit great potential for various thin-film organic electronics, such as organic transistors, memristors, electrochromism, chemiresistors, and photodetectors. Finally, the future research directions and perspectives of 2DCPs are discussed in terms of the interfacial synthetic design and structure engineering for the fabrication of fully conjugated 2DCP thin films, as well as the functional manipulation of conductivity to advance their applications in future organic electronics.

Multilevel Conductance States of Vapor-Transport-Deposited Sb2S3 Memristors Achieved via Electrical and Optical Modulation

The pursuit of advanced brain-inspired electronic devices and memory technologies has led to explore novel materials by processing multimodal and multilevel tailored conductive properties as the next generation of semiconductor platforms, due to von Neumann architecture limits. Among such materials, antimony sulfide (Sb2S3) thin films exhibit outstanding optical and electronic properties, and therefore, they are ideal for applications such as thin-film solar cells and nonvolatile memory systems. This study investigates the conduction modulation and memory functionalities of Sb2S3 thin films deposited via the vapor transport deposition technique. Experimental results indicate that the Ag/Sb2S3/Pt device possesses properties suitable for memory applications, including low operational voltages, robust endurance, and reliable switching behavior. Further, the reproducibility and stability of these properties across different device batches validate the reliability of these devices for practical implementation. Moreover, Sb2S3-based memristors exhibit artificial neuroplasticity with prolonged stability, promising considerable advancements in neuromorphic computing. Leveraging the photosensitivity of Sb2S3 enables the Ag/Sb2S3/Pt device to exhibit significant low operating potential and conductivity modulation under optical stimulation for memory applications. This research highlights the potential applications of Sb2S3 in future memory devices and optoelectronics and in shaping electronics with versatility.

Programming Tetrathiafulvalene-Based Covalent Organic Frameworks for Promoted Photoinduced Molecular Oxygen Activation

Despite the pivotal role of molecular oxygen (O2) activation in artificial photosynthesis, the activation efficiency is often restricted by sluggish exciton dissociation and charge transfer kinetics within polymer photocatalysts. Herein, we propose two tetrathiafulvalene (TTF)-based imine-linked covalent organic frameworks (COFs) with tailored donor-acceptor (D-A) structures, TTF-PDI-COF and TTF-TFPP-COF, to promote O2 activation. Because of enhanced electron push-pull interactions that facilitated charge separation and transfer behavior, TTF-PDI-COF exhibited superior photocatalytic activity in electron-induced O2 activation reactions over TTF-TFPP-COF under visible light irradiation, including the photosynthesis of (E)-3-amino-2-thiocyano-α,β-unsaturated compounds and H2O2. These findings highlight the significant potential of the rational design of COFs with D-A configurations as suitable candidates for advanced photocatalytic applications.

Coexistance of the Negative Photoconductance Effect and Analogue Switching Memory in the CuPc Organic Memristor for Neuromorphic Vision Computing

A bioinspired in-sensing computing paradigm using emerging photoelectronic memristors pursues multifunctionality with low power consumption and high efficiency for processing large amounts of sensing information. An organic semiconductor memristor strategy based on the CuPc functional layer integrates a negative photoconductance (NPC) effect and an analogue switching memory (ASM) effect in the same pixel. The NPC effect, present in the pure capacitance state at low bias voltage, provides high-performance short/long-term synaptic plasticity modulable by light pulse parameters. The interface charge effect along with defeat site trapping and detrapping is responsible for the pure capacitance effect and the NPC effect, with electron tunneling and electric-field-driven band dynamics responsible for ASM. This work reveals an organic memristor approach for hardware implementation of a neuromorphic vision computing system, emulating retinal bipolar cells via light-dominated NPC and electrically induced ASM with stable, tunable conductance states.

One-Dimensional Covalent Organic Framework-Based Multilevel Memristors for Neuromorphic Computing

Memristors are essential components of neuromorphic systems that mimic the synaptic plasticity observed in biological neurons. In this study, a novel approach employing one-dimensional covalent organic framework (1D COF) films was explored to enhance the performance of memristors. The unique structural and electronic properties of two 1D COF films (COF-4,4'-methylenedianiline (MDA) and COF-4,4'-oxydianiline (ODA)) offer advantages for multilevel resistive switching, which is a key feature in neuromorphic computing applications. By further introducing a TiO2 layer on the COF-ODA film, a built-in electric field between the COF-TiO2 interfaces could be generated, demonstrating the feasibility of utilizing COFs as a platform for constructing memristors with tunable resistive states. The 1D nanochannels of these COF structures contributed to the efficient modulation of electrical conductance, enabling precise control over synaptic weights in neuromorphic circuits. This study also investigated the potential of these COF-based memristors to achieve energy-efficient and high-density memory devices.

COF-Based Photocatalysts for Enhanced Synthesis of Hydrogen Peroxide

Covalent Organic Frameworks (COFs), with their intrinsic structural regularity and modifiable chemical functionality, have burgeoned as a pivotal material in the realm of photocatalytic hydrogen peroxide (H2O2) synthesis. This article reviews the recent advancements and multifaceted approaches employed in using the unique properties of COFs for high-efficient photocatalytic H2O2 production. We first introduced COFs and their advantages in the photocatalytic synthesis of H2O2. Subsequently, we spotlight the principles and evaluation of photocatalytic H2O2 generation, followed by various strategies for the incorporation of active sites aiming to optimize the separation and transfer of photoinduced charge carriers. Finally, we explore the challenges and future prospects, emphasizing the necessity for a deeper mechanistic understanding and the development of scalable and economically viable COF-based photocatalysts for sustainable H2O2 production.

Definition of a Localized Conducting Path via Suppressed Charge Injection in Oxide Memristors for Stable Practical Hardware Neural Networks

Oxide-based memristors have been demonstrated as suitable options for memory components in neuromorphic systems. In such devices, the resistive switching characteristics are caused by the formation of conductive filaments (CFs) comprising oxygen vacancies. Thus, the electrical performance is primarily governed by the CF structure. Despite various approaches for regulating the oxygen vacancy distributions in oxide memristors, controlling the CF structure without modifying the device configuration related to material compatibility is still a challenge. This study demonstrates an effective strategy for localizing CF distributions in memristors by suppressing charge injection during the formation of conducting paths. As the injected charge quantity is reduced in the electroforming process of the oxide memristor, the CF distributions become narrower, leading to more reproducible and stable resistive switching characteristics in the device. Based on these findings, a reliable hardware neural network comprising oxide memristors is constructed to recognize complex images. The developed memristor has been employed as a synaptic memory component in systems without degradation for a long time. This promising concept of oxide memristors acting as stable synaptic components holds great potential for developing practical neuromorphic systems and their expansion into artificial intelligent systems.