Organic Synaptic Transistor Research Articles

A Retina-Inspired Optoelectronic Synapse Using Quantum Dots for Neuromorphic Photostimulation of Neurons.

Neuromorphic electronics, inspired by the functions of neurons, have the potential to enable biomimetic communication with cells. Such systems require operation in aqueous environments, generation of sufficient levels of ionic currents for neurostimulation, and plasticity. However, their implementation requires a combination of separate devices, such as sensors, organic synaptic transistors, and stimulation electrodes. Here, a compact neuromorphic synapse that combines photodetection, memory, and neurostimulation functionalities all-in-one is presented. The artificial photoreception is facilitated by a photovoltaic device based on cell-interfacing InP/ZnS quantum dots, which induces photo-faradaic charge-transfer mediated plasticity. The device sends excitatory post-synaptic currents exhibiting paired-pulse facilitation and post-tetanic potentiation to the hippocampal neurons via the biohybrid synapse. The electrophysiological recordings indicate modulation of the probability of action potential firing due to biomimetic temporal summation of excitatory post-synaptic currents. The results pave the way for the development of novel bioinspired neuroprosthetics and soft robotics and highlight the potential of quantum dots for achieving versatile neuromorphic functionality in aqueous environments.

TIPS-pentacene organic field-effect transistor for optoelectronic neuromorphic simulation

Biological learning and memory of visual information are carried out through the regulation of synaptic weight by visual neuron synapses. Replicating the cognitive processes and light-induced adaptability of the human brain holds immense significance for the advancement of artificial intelligence. Here, we propose an organic photoelectric synaptic transistor based on 6,13-bis(triisopropylsilylethynyl) pentacene. The device showcases a memory window greater than 20 V and current on/off ratio of 106. Synaptic behavior transition is exhibited from short-term plasticity to long-term plasticity under photoelectric pulse modulation, including paired-pulse facilitation, spike time dependent plasticity, spike number dependent plasticity and optical enhancement/electrical inhibition. In addition, we simulate the learning and adaptation process of the synaptic device after long-term light stimulation, and recognize visual information by perceiving light pulses in different time domains.

An n-type organic synaptic transistor with dopant-sensitive plasticity enables sensory-adaptive robotics

Sensory intelligence of biological depends on the activity of synapses, which promotes enormous research on artificial synapses and bio-inspired sensory systems. Here, we propose a strategy of increasing channel permeability with doping concentration to demonstrate for the first time the application of n-type organic synaptic transistors (OSTs) in neuromorphic sensory robotic system. The threshold voltage and operating current of the OST are dominated by the concentration of N-DMBI molecular to implement tunable and reliable plasticity. As a result, the N-DMBI-doped OST exhibits essential synaptic functions and persistent memory as the dopant increases within a certain range (≤7 wt%). We construct a neuromorphic sensory robotic system with sensorimotor functionality by combining the n-type OST with a flexible tactile sensor and a dexterous manipulator. The robotic system demonstrates sensory memory and adaption in response to tactile stimuli. We believe this work provides a novel resource for the development of advanced sensory-intelligence systems that have neuronal properties.

Ultrasoft and High-Adhesion Block Copolymers for Neuromorphic Computing.

The "von Neumann bottleneck" is a formidable challenge in conventional computing, driving exploration into artificial synapses. Organic semiconductor materials show promise but are hindered by issues such as poor adhesion and a high elastic modulus. Here, we combine polyisoindigo-bithiophene (PIID-2T) with grafted poly(dimethylsiloxane) (PDMS) to synthesize the triblock-conjugated polymer (PIID-2T-PDMS). The polymer exhibited substantial enhancements in adhesion (4.8-68.8 nN) and reductions in elastic modulus (1.6-0.58 GPa) while maintaining the electrical characteristics of PIID-2T. The three-terminal organic synaptic transistor (three-terminal p-type organic artificial synapse (TPOAS)), constructed using PIID-2T-PDMS, exhibits an unprecedented analog switching range of 276×, surpassing previous records, and a remarkable memory on-off ratio of 106. Moreover, the device displays outstanding operational stability, retaining 99.6% of its original current after 1600 write-read events in the air. Notably, TPOAS replicates key biological synaptic behaviors, including paired-pulse facilitation (PPF), short-term plasticity (STP), and long-term plasticity (LTP). Simulations using handwritten digital data sets reveal an impressive recognition accuracy of 91.7%. This study presents a polyisoindigo-bithiophene-based block copolymer that offers enhanced adhesion, reduced elastic modulus, and high-performance artificial synapses, paving the way for the next generation of neuromorphic computing systems.

Unraveling the Mechanism of the Light‐Triggered Synaptic Plasticity in Organic Photoelectric Synaptic Transistors

AbstractLight‐triggered synaptic plasticity (LTSP) induced by electron trapping in organic photoelectric synaptic transistors (OPSTs) offers potential prospects in neuromorphic wearable artificial intelligence. However, a consistent and universal comprehend for LTSP behaviors especially on oxygen effect in OPSTs is still a critical challenge hindering their practical applications. A mechanism on strong dependency between the oxygen‐induced and polar‐group electron trapping in OPSTs, is successfully unveiled in this study for the first time. And the interaction between the oxygen and polar dielectric interface can be enhanced by properly modulating the specific surface area of thin‐film semiconductors. This effectively binds the oxygen near conducting channel and further improves the trapping efficiency for photogenerated electrons, undergoing the time‐dependent photocurrent generation and subsequent prolonged decay, forming the typical LTSP behaviors. These experimental demonstrations differ from previous reports and therefore may contribute an innovative perspective in the design of functional layers for high‐performance OPST devices.

Near‐Infrared‐Sensing Flexible Organic Synaptic Transistors with Water‐Processable Charge‐Trapping Polymers for Potential Neuromorphic Computing/Skin Applications

Neuromorphic devices, which can mimic the human body's neural system, are rising as an essential technology for artificial intelligence. Here, two types of organic synaptic transistors (OSTRs), OSTR‐A and OSTR‐B, are fabricated on either glass or polymer film using water‐processable charge‐trapping gate‐insulating layers that are prepared by reacting ethylenediamine (EDA) and poly(2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid) (PAMPSA). OSTR‐A is designed to function as a basic artificial synapse by gate pulse stimulation only, while OSTR‐B has additional near‐infrared (NIR)‐absorbing conjugated polymer layers for further sensing of NIR light upon gate voltage stimulations. The PAMPSA:EDA films are found to contain permanent charge bridges (ion pairs of –SO3− +NH3‐) that play a charge‐trapping role in OSTRs. Both devices with the PAMPSA:EDA layers exhibit clear postsynaptic current (PSC) signals upon gate voltage pulses, leading to long‐term potentiation/depression characteristics. The flexible OSTR‐B devices can sense the NIR light (905 nm) upon gate pulse stimulation and their PSC signals are well maintained even after bending (>5000 times). Artificial neural network simulations disclose that the flexible OSTR‐B devices can stably perform synaptic operations under the NIR light with high accuracy (>90%) even after repeated bending (5000 times), indicative of potential use in artificial neuromorphic skin applications.

Recent progress of organic photonic synaptic transistors for artificial visual systems: structure configuration and innovative applications

This article provides a comprehensive review of organic photonic synaptic transistors (OPSTs) used for artificial visual systems (AVSs). The typical structures and some innovative applications of OPSTs in AVSs were discussed.

A covalent organic polymer-based transistor with multifunctional memory and synaptic functions

An organic synaptic transistor was fabricated with a covalent organic polymer MT-TP to mimic the behavior of biological synapses.

Fully Printed Dual-Gate Organic Electrochemical Synaptic Transistor With Neurotransmitter-Mediated Plasticity

Fully Printed Dual-Gate Organic Electrochemical Synaptic Transistor With Neurotransmitter-Mediated Plasticity

Overcoming the Trade‐off Between Efficient Electrochemical Doping and High State Retention in Electrolyte‐Gated Organic Synaptic Transistors

AbstractTo achieve superior device performance such as low threshold voltage Vth, high maximum on‐current Ion,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 Vth, highest Ion,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.

Humidity/Oxygen-Insensitive Organic Synaptic Transistors Based on Optical Radical Effect.

For most organic synaptic transistors based on the charge trapping effect, different atmosphere conditions lead to significantly different device performance. Some devices even lose the synaptic responses under vacuum or inert atmosphere. The stable device performance of these organic synaptic transistors under varied working environments with different humidity and oxygen levels can be a challenge. Herein, a moisture- and oxygen-insensitive organic synaptic device based on the organic semiconductor and photoinitiator molecules is reported. Unlike the widely reported charge trapping effect, the photoinduced free radical is utilized to realize the photosynaptic performance. The resulting synaptic transistor displays typical excitatory postsynaptic current, paired-pulse facilitation, learning, and forgetting behaviors. Furthermore, the device exhibits decent and stable photosynaptic performances under high humidity and vacuum conditions. This type of organic synaptic device also demonstrates high potential in ultraviolet B perception based on its environmental stability and broad ultraviolet detection capability. Finally, the contrast-enhanced capability of the device is successfully validated by the single-layer-perceptron/double-layer network based Modified National Institute of Standards and Technology pattern recognition. This work could have important implications for the development of next-generation environment-stable organic synaptic devices and systems.

Recent advancements in implantable neural links based on organic synaptic transistors

AbstractThe progress of brain synaptic devices has witnessed an era of rapid and explosive growth. Because of their integrated storage, excellent plasticity and parallel computing, and system information processing abilities, various field effect transistors have been used to replicate the synapses of a human brain. Organic semiconductors are characterized by simplicity of processing, mechanical flexibility, low cost, biocompatibility, and flexibility, making them the most promising materials for implanted brain synaptic bioelectronics. Despite being used in numerous intelligent integrated circuits and implantable neural linkages with multiple terminals, organic synaptic transistors still face many obstacles that must be overcome to advance their development. A comprehensive review would be an excellent tool in this respect. Therefore, the latest advancements in implantable neural links based on organic synaptic transistors are outlined. First, the distinction between conventional and synaptic transistors are highlighted. Next, the existing implanted organic synaptic transistors and their applicability to the brain as a neural link are summarized. Finally, the potential research directions are discussed.

Low-energy-consumption organic synaptic transistors with high recognition accuracy enabled by Schottky barrier regulation

Low-energy-consumption organic synaptic transistors with high recognition accuracy enabled by Schottky barrier regulation

Enhanced Multiwavelength Response of Flexible Synaptic Transistors for Human Sunburned Skin Simulation and Neuromorphic Computation.

In biological species, optogenetics and bioimaging work together to regulate the function of neurons. Similarly, the light-controlled artificial synaptic system not only enhances computational speed but also simulates complex synaptic functions. However, reported synaptic properties are mainly limited to mimicking simple biological functions and single-wavelength responses. Therefore, the development of flexible synaptic devices with multiwavelength optical signal response and multifunctional simulation remains a challenge. Here, flexible organic light-stimulated synaptic transistors (LSSTs) enabled by alumina oxide (AlOX ), with a simple fabrication process, are reported. By embedding AlOX nanoparticles, the excitons separation efficiency is improved, allowing for multiple wavelength responses. Optimized LSSTs can respond to multiple optical and electrical signals in a highly synaptic manner. Multiwavelength optical synaptic plasticity, electrical synaptic plasticity, sunburned skin simulation, learning efficiency model controlled by photoelectric cooperative stimulation, neural network computing, "deer" picture learning and memory functions are successfully proposed, which promote the development for future artificial intelligent systems. Furthermore, as prepared flexible transistors exhibit mechanical flexibility with bending radius down to 2.5mm and improved photosynaptic plasticity, which facilitating development of neuromorphic computing and multifunction integration systems at the device-level.

Top-Gated Organic Synaptic Transistor With PS/PVA Hybrid as Trapping Layer for Excitatory Behavior Modulation

Top-Gated Organic Synaptic Transistor With PS/PVA Hybrid as Trapping Layer for Excitatory Behavior Modulation

Molecular Tailoring to Achieve Long‐Term Plasticity in Organic Synaptic Transistors for Neuromorphic Computing

Organic synaptic transistors (OSTs) using intrinsic polymer semiconductors are demonstrated to be suitable for neuromorphic bioelectronics. However, diketopyrrolopyrrole (DPP)‐based copolymers are not applicable to neuromorphic computing systems because the DPP polymer film has demonstrated only short‐term plasticity with short retention (<50 ms) in synaptic devices because of their intrinsic difficulty of electrochemical doping. To expand their applications toward neuromorphic computing that requires long‐term plasticity, artificial synapses with extended retention time should be developed. Herein, molecular tailoring approach to extend the retention time in the ion‐gel‐gated OSTs that use DPP is suggested. The molecular structure is controlled by changing alkyl spacer lengths of side chains. As a result, the doping process is more favorable in DPP with long alkyl spacer, which is confirmed by high doping concentration and slow dedoping rate. Therefore, dedoping of ions is more suppressed in DPP with long alkyl side chain that exhibits extended retention time (≈800 s) of the OSTs. These optimized DPP‐based OSTs obtain high pattern recognition accuracy of ≈96.0% in simulations of an artificial neural network. Molecular tailoring strategies provide a guideline to overcome the intrinsic problem of short synaptic retention time of the OSTs for use in neuromorphic computing.

Optically Readable Organic Electrochemical Synaptic Transistors for Neuromorphic Photonic Image Processing.

Optically readable organic synaptic devices have great potential in both artificial intelligence and photonic neuromorphic computing. Herein, a novel optically readable organic electrochemical synaptic transistor (OR-OEST) strategy is first proposed. The electrochemical doping mechanism of the device was systematically investigated, and the basic biological synaptic behaviors that can be read by optical means are successfully achieved. Furthermore, the flexible OR-OESTs are capable of electrically switching the transparency of semiconductor channel materials in a nonvolatile manner, and thus the multilevel memory can be achieved through optical readout. Finally, the OR-OESTs are developed for the preprocessing of photonic images, such as contrast enhancement and denoising, and feeding the processed images into an artificial neural network, achieving a recognition rate of over 90%. Overall, this work provides a new strategy for the implementation of photonic neuromorphic systems.

Humidity-dependent synaptic characteristics in gelatin-based organic transistors

Organic synaptic transistors based on gelatin gate dielectric exhibit humidity-dependent synaptic characteristics. The device showed excellent field-effect transistor behavior without hysteresis when measured in a vacuum and dry air, but clear pinched hysteresis loops appeared in a humid environment. A large difference in the hysteresis window was observed under a small scanning range of gate voltage in different humid conditions, while the difference vanished under a large scanning range of gate voltage. The excitatory postsynaptic current strongly relies on stimulus pulse width, which is more pronounced in high humidity conditions, suggesting that slow proton transportation through a sequence of hopping may be responsible for the less pronounced dependence of stimulus amplitude with a short stimulus pulse width. The simulation of an artificial neural network for handwritten digit recognition revealed that the ultimate recognition accuracy at high relative humidity is higher than that at low relative humidity due to the large nonlinearity factor resulting from inadequate and low transportation of protons in the gelatin film under ambient conditions with low relative humidity. This work provides valuable insights into the effects of humidity on the performance of gelatin-based organic synaptic transistors, which could be useful for the development of environment-dependent synaptic devices.

Retina‐Inspired Artificial Synapses with Ultraviolet to Near‐Infrared Broadband Responses for Energy‐Efficient Neuromorphic Visual Systems

AbstractNeuromorphic visual system with image perception, memory, and preprocessing functions is expected to simulate basic features of the human retina. Organic optoelectronic synaptic transistors emulating biological synapses may be promising candidates for constructing neural morphological visual system. However, the sensing wavelength range of organic optoelectronic synaptic transistors usually limits their potential in artificial multispectral visual perception. Here, retina‐inspired optoelectronic synaptic transistors that present broadband responses covering ultraviolet, visible, and near‐infrared regions are demonstrated, which leverage the wide‐range photoresponsive charge trapping layer and the heterostructure formed between PbS quantum dots and organic semiconductor. Simplified neuromorphic visual arrays are developed to simulate comprehensive image perception, memory, and preprocessing functions. Benefitting from the flexibility of the charge trapping and organic semiconductor layers, a flexible neuromorphic visual array can be fabricated, having an ultralow power consumption of 0.55 fJ per event under a low operating voltage of −0.01 V. More significantly, an accelerating image preprocessing effect can be observed in a wide wavelength range even beyond the perception range of the human visual system, due to the gate‐adjustable synaptic plasticity. These devices are highly promising for implementing neuromorphic visual systems with broadband perception, increasing image processing efficiency, and promoting the development of artificial vision.

Super-Flexible, Transparent Synaptic Transistors Based on Pullulan for Neuromorphic Electronics

With the development of artificial intelligence, super-flexibility and transparent neuromorphic electronics are gradually showing high application value in the fields of wearable see-through electronics and biomedical applications. However, it is still a huge problem to realize synaptic devices with super-flexibility and transparent characteristics. Here, an organic synaptic transistor (OST) based on natural pullulan is fabricated with super-flexibility and high transmittance (~83.3%), which enables it to achieve conformal and non-destructive attachment to arbitrary-shaped objects without affecting viewing. Various synaptic behaviors are successfully simulated even under extreme bending, showing outstanding mechanical stability. Moreover, our OSTs can achieve ultrarapid degradation in ambient water, which will reduce the generation of electronic waste. This work provides a guide for the development of super-flexible and transparent neuromorphic electrons, demonstrating a great step toward next-generation artificial intelligence.