Flexible neuromorphic electronics that emulate biological neuronal systems constitute a promising candidate for next‐generation wearable computing, soft robotics, and neuroprosthetics. For ...realization, with the achievement of simple synaptic behaviors in a single device, the construction of artificial synapses with various functions of sensing and responding and integrated systems to mimic complicated computing, sensing, and responding in biological systems is a prerequisite. Artificial synapses that have learning ability can perceive and react to events in the real world; these abilities expand the neuromorphic applications toward health monitoring and cybernetic devices in the future Internet of Things. To demonstrate the flexible neuromorphic systems successfully, it is essential to develop artificial synapses and nerves replicating the functionalities of the biological counterparts and satisfying the requirements for constructing the elements and the integrated systems such as flexibility, low power consumption, high‐density integration, and biocompatibility. Here, the progress of flexible neuromorphic electronics is addressed, from basic backgrounds including synaptic characteristics, device structures, and mechanisms of artificial synapses and nerves, to applications for computing, soft robotics, and neuroprosthetics. Finally, future research directions toward wearable artificial neuromorphic systems are suggested for this emerging area.
Flexible neuromorphic electronics are studied for their application in next‐generation wearable computing, soft robotics, and neuroprosthetics. These applications require synaptic devices and integrated systems that are flexible, consume little power, are biocompatible, and are amenable to high‐density integration. Recent progress in flexible neuromorphic electronics, from basic background to applications is surveyed, and future research is suggested.
Requirements and recent advances in research on organic neuroelectronics are outlined herein. Neuroelectronics such as neural interfaces and neuroprosthetics provide a promising approach to diagnose ...and treat neurological diseases. However, the current neural interfaces are rigid and not biocompatible, so they induce an immune response and deterioration of neural signal transmission. Organic materials are promising candidates for neural interfaces, due to their mechanical softness, excellent electrochemical properties, and biocompatibility. Also, organic nervetronics, which mimics functional properties of the biological nerve system, is being developed to overcome the limitations of the complex and energy‐consuming conventional neuroprosthetics that limit long‐term implantation and daily‐life usage. Examples of organic materials for neural interfaces and neural signal recordings are reviewed, recent advances of organic nervetronics that use organic artificial synapses are highlighted, and then further requirements for neuroprosthetics are discussed. Finally, the future challenges that must be overcome to achieve ideal organic neuroelectronics for next‐generation neuroprosthetics are discussed.
Organic neuroelectronics have been researched to treat and diagnose neurological diseases. The organic materials provide large advantages for neural interfaces. Also, organic nervetronics provides efficient data processing by emulating functional behavior of neural systems. Recent progress in organic neural interfaces and neuroprosthetics, with aspects of materials, devices, and systems, and finally suggests future directions, is presented.
Abstract To achieve superior device performance such as low threshold voltage V th , high maximum on‐current I on,max , and long retention time in electrolyte‐gated organic synaptic transistors, ...efficient electrochemical doping and high state retention are essential. However, these characteristics generally show a trade‐off relationship. This work introduces an effective strategy to increase retention time while promoting efficient electrochemical doping. The approach involves blending two polymer semiconductors (PSCs) that have the same backbone but different types of side chains. Polymer synaptic transistors (PSTs) with the blend film showed the lowest V th , highest I on,max , longest retention time, and superior cyclic stability compared to PSTs that used films containing only one of the PSCs. The improvement in electrical and synaptic properties achieved through the blend strategy is consistently reproducible and comprehensive. It is attributed this improvement to the increased redox activity and constrained morphological changes observed in the blended PSCs during electrochemical doping, as confirmed by several electrochemical characterizations. This work is the first to increase retention time in PSTs without increasing the crystallinity of polymer film or sacrificing the electrochemical doping efficiency, which has been regarded as an unavoidable compromise in this field. This method provides an effective way to tune synaptic properties for various neuromorphic applications.
Organic neuromorphic electronics are inspired by a biological nervous system. Bio-inspired computing mimics learning and memory in a brain (i.e., the central nervous system), and bio-inspired soft ...robotics and nervous prosthetics mimics the neural signal transmission of afferent/efferent nerves (i.e., the peripheral nervous system). Synaptic decay time of nerves differ among biological organs, so the decay time of artificial synapses should be tuned for their specific uses in neuro-inspired electronics. However, controlling a synaptic decay constant in a fixed synaptic device geometry for broad applications was not been achieved in previous research of neuromorphic electronic devices despite the importance to achieve broad applications from neuromorphic computing to neuro-prosthetics. Here, we tailored the synaptic decay constant of organic synaptic transistors with fixed materials and devices structure rather than changing the form of presynaptic spikes, which enabled broad applications from neuromorphic computing to neuro-prosthetics. To achieve this, the relation between crystallinity of the polymer semiconductor film and the synaptic decay constant was revealed. The crystallinity of the polymer controlled electrochemical-doping kinetics and resultant synaptic behaviors of artificial synaptic transistors. In this way, we demonstrated not only long-term retention for learning and memory that is useful for neuromorphic computing in ion-gel gated organic synaptic transistor (IGOST) but also the short-term retention for fast synaptic transmission that is useful for emulating peripheral nerves such as sensory and motor nerve. To prove the feasibility of our approach in a two different ways, we first simulated pattern recognition on the MNIST dataset of handwritten digits using an IGOST with long-term retention due to increased crystallinity and then, developed artificial auditory sensory nerves that combines an IGOST with short term retention due to disordered chain morphology in a polymer semiconductor, with a triboelectric acoustic sensor. We expect that our approach will provide a universal strategy to realize wide neuromorphic electronic applications.
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•Synaptic decay of ion-gel gated organic synaptic transistors (IGOSTs) was easily modulated.•The relation between the crystallinity and electrochemical doping kinetics in the IGOSTs were discovered.•Artificial auditory nerve with short-term decay and artificial neural networks with long-term memory were demonstrated.•Versatile neuromorphic application from neuromorphic computing to neuro-prosthetics was achieved.
This article reviews artificial nerve electronics (nervetronics), an emerging field in which the goal is to develop bioinspired electronics that implement biological sensory functions. An artificial ...synapse is a fundamental core technology of artificial sensory nerves that can emulate functional properties of a biological synapse. Use of artificial synapses reduces the energy consumption and increases the sensitivity of low-level perception in artificial sensory nerves. Wearable and implantable devices require artificial sensory nerves that are flexible and stretchable. Therefore, development of organic artificial synapses that have these qualities is a central focus in nervetronics. Here, we review the concept and mechanism of organic artificial synapses for use as basic elements of flexible and stretchable artificial nerves. Next, we outline the research direction of the flexible and stretchable artificial sensory nerves so far, and finally, identify challenges of artificial sensory nerves that must be solved to enable actual application of this developing technology.
In November 2021, 14 international travel-related severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) B.1.1.529 (omicron) variant of concern (VOC) patients were detected in South Korea. ...Epidemiologic investigation revealed community transmission of the omicron VOC. A total of 80 SARS-CoV-2 omicron VOC-positive patients were identified until December 10, 2021 and 66 of them reported no relation to the international travel. There may be more transmissions with this VOC in Korea than reported.
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