Recent advances in fabrication and functions of neuromorphic system based on organic field effect transistor

The development of various artificial electronics and machines would explosively increase the amount of information and data,which need to be processed via in-situ remediation.Bioinspired synapse devices can store and process signals in a parallel way,thus improving fault tolerance and decreasing the power consumption of artificial systems.The organic field effect transistor(OFET)is a promising component for bioinspired neuromorphic systems because it is suitable for large-scale integrated circuits and flexible devices.In this review,the organic semiconductor materials,structures and fabrication,and different artificial sensory perception systems functions based on neuromorphic OFET devices are summarized.Subsequently,a summary and challenges of neuromorphic OFET devices are provided.This review presents a detailed introduction to the recent progress of neuromorphic OFET devices from semiconductor materials to perception systems,which would serve as a reference for the development of neuromorphic systems in future bioinspired electronics.

High-Performance Organic Field-Effect Transistors Based on Two-Dimensional Vat Orange 3 Crystals

The exploration and research of low-cost,environmentally friendly,and sustainable organic semiconductor materials are of immense significance in various fields,including electronics,optoelectronics,and energy conversion.Unfortunately,these semiconductors have almost poor charge transport properties,which range from∼10^(−4) cm^(2)·V^(−1)·s^(−1) to∼10^(−2) cm^(2)·V^(−1)·s^(−1).Vat orange 3,as one of these organic semiconductors,has great potential due to its highly conjugated structure.We obtain high-quality multilayered Vat orange 3 crystals with two-dimensional(2D)growth on h-BN surfaces with thickness of 10–100 nm using physical vapor transport.Raman’s results confirm the stability of the chemical structure of Vat orange 3 during growth.Furthermore,by leveraging the structural advantages of 2D materials,an organic field-effect transistor with a 2D vdW vertical heterostructure is further realized with h-BN encapsulation and multilayered graphene contact electrodes,resulting in an excellent transistor performance with On/Off ratio of 104 and high field-effect mobility of 0.14 cm^(2)·V^(−1)·s^(−1).Our results show the great potential of Vat orange 3 with 2D structures in future nano-electronic applications.Furthermore,we showcase an approach that integrates organic semiconductors with 2D materials,aiming to offer new insights into the study of organic semiconductors.

Dynamic response of a thermal transistor to time-varying signals

Thermal transistor,the thermal analog of an electronic transistor,is one of the most important thermal devices for microscopic-scale heat manipulating.It is a three-terminal device,and the heat current flowing through two terminals can be largely controlled by the temperature of the third one.Dynamic response plays an important role in the application of electric devices and also thermal devices,which represents the devices’ability to treat fast varying inputs.In this paper,we systematically study two typical dynamic responses of a thermal transistor,i.e.,the response to a step-function input(a switching process)and the response to a square-wave input.The role of the length L of the control segment is carefully studied.It is revealed that when L is increased,the performance of the thermal transistor worsens badly.Both the relaxation time for the former process and the cutoff frequency for the latter one follow the power-law dependence on L quite well,which agrees with our analytical expectation.However,the detailed power exponents deviate from the expected values noticeably.This implies the violation of the conventional assumptions that we adopt.

Heterojunction-engineered carrier transport in elevated-metal metal-oxide thin-film transistors

This study investigates the carrier transport of heterojunction channel in oxide semiconductor thin-film transistor(TFT)using the elevated-metal metal-oxide(EMMO)architecture and indium−zinc oxide(InZnO).The heterojunction band diagram of InZnO bilayer was modified by the cation composition to form the two-dimensional electron gas(2DEG)at the interface quantum well,as verified using a metal−insulator−semiconductor(MIS)device.Although the 2DEG indeed contributes to a higher mobility than the monolayer channel,the competition and cooperation between the gate field and the built-in field strongly affect such mobility-boosting effect,originating from the carrier inelastic collision at the heterojunction interface and the gate field-induced suppression of quantum well.Benefited from the proper energy-band engineering,a high mobility of 84.3 cm2·V^(−1)·s^(−1),a decent threshold voltage(V_(th))of−6.5 V,and a steep subthreshold swing(SS)of 0.29 V/dec were obtained in InZnO-based heterojunction TFT.

One memristor–one electrolyte-gated transistor-based high energy-efficient dropout neuronal units

Artificial neural networks(ANN) have been extensively researched due to their significant energy-saving benefits.Hardware implementations of ANN with dropout function would be able to avoid the overfitting problem. This letter reports a dropout neuronal unit(1R1T-DNU) based on one memristor–one electrolyte-gated transistor with an ultralow energy consumption of 25 p J/spike. A dropout neural network is constructed based on such a device and has been verified by MNIST dataset, demonstrating high recognition accuracies(> 90%) within a large range of dropout probabilities up to40%. The running time can be reduced by increasing dropout probability without a significant loss in accuracy. Our results indicate the great potential of introducing such 1R1T-DNUs in full-hardware neural networks to enhance energy efficiency and to solve the overfitting problem.

Performance Limits and Advancements in Single 2D Transition Metal Dichalcogenide Transistor

Two-dimensional(2D)transition metal dichalcogenides(TMDs)allow for atomic-scale manipulation,challenging the conventional limitations of semiconductor materials.This capability may overcome the short-channel effect,sparking significant advancements in electronic devices that utilize 2D TMDs.Exploring the dimension and performance limits of transistors based on 2D TMDs has gained substantial importance.This review provides a comprehensive investigation into these limits of the single 2D-TMD transistor.It delves into the impacts of miniaturization,including the reduction of channel length,gate length,source/drain contact length,and dielectric thickness on transistor operation and performance.In addition,this review provides a detailed analysis of performance parameters such as source/drain contact resistance,subthreshold swing,hysteresis loop,carrier mobility,on/off ratio,and the development of p-type and single logic transistors.This review details the two logical expressions of the single 2D-TMD logic transistor,including current and voltage.It also emphasizes the role of 2D TMD-based transistors as memory devices,focusing on enhancing memory operation speed,endurance,data retention,and extinction ratio,as well as reducing energy consumption in memory devices functioning as artificial synapses.This review demonstrates the two calculating methods for dynamic energy consumption of 2D synaptic devices.This review not only summarizes the current state of the art in this field but also highlights potential future research directions and applications.It underscores the anticipated challenges,opportunities,and potential solutions in navigating the dimension and performance boundaries of 2D transistors.

Effect of external magnetic field on the instability of THz plasma waves in nanoscale graphene field-effect transistors

The instability of plasma waves in the channel of field-effect transistors will cause the electromagnetic waves with THz frequency.Based on a self-consistent quantum hydrodynamic model,the instability of THz plasmas waves in the channel of graphene field-effect transistors has been investigated with external magnetic field and quantum effects.We analyzed the influence of weak magnetic fields,quantum effects,device size,and temperature on the instability of plasma waves under asymmetric boundary conditions numerically.The results show that the magnetic fields,quantum effects,and the thickness of the dielectric layer between the gate and the channel can increase the radiation frequency.Additionally,we observed that increase in temperature leads to a decrease in both oscillation frequency and instability increment.The numerical results and accompanying images obtained from our simulations provide support for the above conclusions.

Device design principles and bioelectronic applications for flexible organic electrochemical transistors

Organic electrochemical transistors(OECTs) exhibit significant potential for applications in healthcare and human-machine interfaces, due to their tunable synthesis, facile deposition, and excellent biocompatibility. Expanding OECTs to the fexible devices will significantly facilitate stable contact with the skin and enable more possible bioelectronic applications. In this work,we summarize the device physics of fexible OECTs, aiming to offer a foundational understanding and guidelines for material selection and device architecture. Particular attention is paid to the advanced manufacturing approaches, including photolithography and printing techniques, which establish a robust foundation for the commercialization and large-scale fabrication. And abundantly demonstrated examples ranging from biosensors, artificial synapses/neurons, to bioinspired nervous systems are summarized to highlight the considerable prospects of smart healthcare. In the end, the challenges and opportunities are proposed for fexible OECTs. The purpose of this review is not only to elaborate on the basic design principles of fexible OECTs, but also to act as a roadmap for further exploration of wearable OECTs in advanced bio-applications.

Implementation of sub-100 nm vertical channel-all-around(CAA) thin-film transistor using thermal atomic layer deposited IGZO channel

In-Ga-Zn-O(IGZO) channel based thin-film transistors(TFT), which exhibit high on-off current ratio and relatively high mobility, has been widely researched due to its back end of line(BEOL)-compatible potential for the next generation dynamic random access memory(DRAM) application. In this work, thermal atomic layer deposition(TALD) indium gallium zinc oxide(IGZO) technology was explored. It was found that the atomic composition and the physical properties of the IGZO films can be modulated by changing the sub-cycles number during atomic layer deposition(ALD) process. In addition, thin-film transistors(TFTs) with vertical channel-all-around(CAA) structure were realized to explore the influence of different IGZO films as channel layers on the performance of transistors. Our research demonstrates that TALD is crucial for high density integration technology, and the proposed vertical IGZO CAA-TFT provides a feasible path to break through the technical problems for the continuous scale of electronic equipment.

Transient Response and Ionic Dynamics in Organic Electrochemical Transistors

The rapid development of organic electrochemical transistors(OECTs)has ushered in a new era in organic electronics,distinguishing itself through its application in a variety of domains,from high-speed logic circuits to sensitive biosensors,and neuromorphic devices like artificial synapses and organic electrochemical random-access memories.Despite recent strides in enhancing OECT performance,driven by the demand for superior transient response capabilities,a comprehensive understanding of the complex interplay between charge and ion transport,alongside electron–ion interactions,as well as the optimization strategies,remains elusive.This review aims to bridge this gap by providing a systematic overview on the fundamental working principles of OECT transient responses,emphasizing advancements in device physics and optimization approaches.We review the critical aspect of transient ion dynamics in both volatile and non-volatile applications,as well as the impact of materials,morphology,device structure strategies on optimizing transient responses.This paper not only offers a detailed overview of the current state of the art,but also identifies promising avenues for future research,aiming to drive future performance advancements in diversified applications.

Layer by Layer Self-assembly Fiber-based Flexible Electrochemical Transistor

Poly(3,4-ethylenedioxyethiophene)-polystyrene sulfonic acid(PEDOT:PSS)/polyallyl dimethyl ammonium chloride modified reduced graphene oxide(PDDA-rGO)was layer by layer self-assembled on the cotton fiber.The surface morphology and electric property was investigated.The results confirmed the dense membrane of PEDOT:PSS and the lamellar structure of PDDA-rGO on the fibers.It has excellent electrical conductivity and mechanical properties.The fiber based electrochemical transistor(FECTs)prepared by the composite conductive fiber has a maximum output current of 8.7 mA,a transconductance peak of 10 mS,an on time of 1.37 s,an off time of 1.6 s and excellent switching stability.Most importantly,the devices by layer by layer self-assembly technology opens a path for the true integration of organic electronics with traditional textile technologies and materials,laying the foundation for their later widespread application.

Photo-driven fin field-effect transistors

The integration between infrared detection and modern microelectronics offers unique opportunities for compact and high-resolution infrared imaging.However,silicon,the cornerstone of modern microelectronics,can only detect light within a limited wavelength range(<1100 nm)due to its bandgap of 1.12 eV,which restricts its utility in the infrared detection realm.Herein,a photo-driven fin field-effect transistor is presented,which breaks the spectral response constraint of conventional silicon detectors while achieving sensitive infrared detection.This device comprises a fin-shaped silicon channel for charge transport and a lead sulfide film for infrared light harvesting.The lead sulfide film wraps the silicon channel to form a“three-dimensional”infrared-sensitive gate,enabling the photovoltage generated at the lead sulfide-silicon junction to effectively modulate the channel conductance.At room temperature,this device realizes a broadband photodetection from visible(635 nm)to short-wave infrared regions(2700 nm),surpassing the working range of the regular indium gallium arsenide and germanium detectors.Furthermore,it exhibits low equivalent noise powers of 3.2×10^(-12) W·Hz^(-1/2) and 2.3×10^(-11) W·Hz^(-1/2) under 1550 nm and 2700 nm illumination,respectively.These results highlight the significant potential of photo-driven fin field-effect transistors in advancing uncooled silicon-based infrared detection.

Atomic layer deposition for nanoscale oxide semiconductor thin film transistors:review and outlook

Since the first report of amorphous In–Ga–Zn–O based thin film transistors,interest in oxide semiconductors has grown.They offer high mobility,low off-current,low process temperature,and wide flexibility for compositions and processes.Unfortunately,depositing oxide semiconductors using conventional processes like physical vapor deposition leads to problematic issues,especially for high-resolution displays and highly integrated memory devices.Conventional approaches have limited process flexibility and poor conformality on structured surfaces.Atomic layer deposition(ALD)is an advanced technique which can provide conformal,thickness-controlled,and high-quality thin film deposition.Accordingly,studies on ALD based oxide semiconductors have dramatically increased recently.Even so,the relationships between the film properties of ALD-oxide semiconductors and the main variables associated with deposition are still poorly understood,as are many issues related to applications.In this review,to introduce ALD-oxide semiconductors,we provide:(a)a brief summary of the history and importance of ALD-based oxide semiconductors in industry,(b)a discussion of the benefits of ALD for oxide semiconductor deposition(in-situ composition control in vertical distribution/vertical structure engineering/chemical reaction and film properties/insulator and interface engineering),and(c)an explanation of the challenging issues of scaling oxide semiconductors and ALD for industrial applications.This review provides valuable perspectives for researchers who have interest in semiconductor materials and electronic device applications,and the reasons ALD is important to applications of oxide semiconductors.

Moiré Synaptic Transistor for Homogeneous-Architecture Reservoir Computing

Reservoir computing has been considered as a promising intelligent computing paradigm for effectively processing complex temporal information.Exploiting tunable and reproducible dynamics in the single electronic device have been desired to implement the “reservoir” and the “readout” layer of reservoir computing system.Two-dimensional moiré materials,with an artificial lattice constant many times larger than the atomic length scale,are one type of most studied artificial quantum materials in community of material science and condensed-matter physics over the past years.These materials are featured with gate-tunable periodic potential and electronic correlation,thus varying the electric field allows the electrons in the moiré potential per unit cell to exhibit distinct and reproducible dynamics,showing great promise in robust reservoir computing.Here,we report that a moiré synaptic transistor can be used to implement the reservoir computing system with a homogeneous reservoir-readout architecture.The synaptic transistor is fabricated based on an h-BN/bilayer graphene/h-BN moiré heterostructure,exhibiting ferroelectricity-like hysteretic gate voltage dependence of resistance.Varying the magnitude of the gate voltage enables the moiré transistor to switch between long-term memory and shortterm memory with nonlinear dynamics.By employing the short-and long-term memories as the reservoir nodes and weights of the readout layer,respectively,we construct a full-moiré physical neural network and demonstrate that the classification accuracy of 90.8% can be achieved for the MNIST(Modified National Institute of Standards and Technology) handwritten digits database.Our work would pave the way towards the development of neuromorphic computing based on moiré materials.

Stretchable organic electrochemical transistors with micro-/nano-structures

Organic electrochemical transistors(OECTs)have attracted attention due to their unique function of converting ionic and biological signals into electronic signals,high transconductance,low energy consumption(below 1 V),stable operation in aqueous media,good biocompatibility[1,2].However,most OECTs are usually built on brittle and stiff substrates,and inappropriate to be adhered to or contacted with delicate human skin,thus impeding their use in wearable electronics.It is desirable to exploit stretchable OECTs to reduce the mechanical mismatch with soft tissues.

P-type cold-source field-effect transistors with TcX_(2) and ReX_(2)(X=S,Se)cold source electrodes:A computational study

Cold-source field-effect transistors(CS-FETs)have been developed to overcome the major challenge of power dissipation in modern integrated circuits.Cold metals suitable for n-type CS-FETs have been proposed as the ideal electrode to filter the high-energy electrons and break the thermal limit on subthreshold swing(SS).In this work,regarding the p-type CS-FETs,we propose TcX_(2) and ReX_(2)(X=S,Se)as the injection source to realize the sub-thermal switching for holes.First-principles calculations unveils the cold-metal characteristics of monolayer TcX_(2) and ReX_(2),possessing a sub-gap below the Fermi level and a decreasing DOS with energy.Quantum device simulations demonstrate that TcX_(2) and ReX_(2) can enable the cold source effects in WSe_(2) p-type FETs,achieving steep SS of 29-38 mV/dec and high on/off ratios of(2.3-5.6)×10^(7).Moreover,multilayer Re S2retains the cold metal characteristic,thus ensuring similar CS-FET performances to that of the monolayer source.This work underlines the significance of cold metals for the design of p-type CS-FETs.

Charge trapping effect at the interface of ferroelectric/interlayer in the ferroelectric field effect transistor gate stack

We study the charge trapping phenomenon that restricts the endurance of n-type ferroelectric field-effect transistors(FeFETs)with metal/ferroelectric/interlayer/Si(MFIS)gate stack structure.In order to explore the physical mechanism of the endurance failure caused by the charge trapping effect,we first establish a model to simulate the electron trapping behavior in n-type Si FeFET.The model is based on the quantum mechanical electron tunneling theory.And then,we use the pulsed I_d-V_g method to measure the threshold voltage shift between the rising edges and falling edges of the FeFET.Our model fits the experimental data well.By fitting the model with the experimental data,we get the following conclusions.(i)During the positive operation pulse,electrons in the Si substrate are mainly trapped at the interface between the ferroelectric(FE)layer and interlayer(IL)of the FeFET gate stack by inelastic trap-assisted tunneling.(ii)Based on our model,we can get the number of electrons trapped into the gate stack during the positive operation pulse.(iii)The model can be used to evaluate trap parameters,which will help us to further understand the fatigue mechanism of FeFET.

Homojunction structure amorphous oxide thin film transistors with ultra-high mobility

Amorphous oxide semiconductors(AOS)have unique advantages in transparent and flexible thin film transistors(TFTs)applications,compared to low-temperature polycrystalline-Si(LTPS).However,intrinsic AOS TFTs are difficult to obtain field-effect mobility(μFE)higher than LTPS(100 cm^(2)/(V·s)).Here,we design ZnAlSnO(ZATO)homojunction structure TFTs to obtainμFE=113.8 cm^(2)/(V·s).The device demonstrates optimized comprehensive electrical properties with an off-current of about1.5×10^(-11)A,a threshold voltage of–1.71 V,and a subthreshold swing of 0.372 V/dec.There are two kinds of gradient coupled in the homojunction active layer,which are micro-crystallization and carrier suppressor concentration gradient distribution so that the device can reduce off-current and shift the threshold voltage positively while maintaining high field-effect mobility.Our research in the homojunction active layer points to a promising direction for obtaining excellent-performance AOS TFTs.

Ultrasensitive detection of methamphetamine by antibody-modified transistor assay

Effective detection of methamphetamine(Met)requires a fast,sensitive,and cheap testing assay.However,commercially available methods require expensive instruments and highly trained operators,which are time-consuming and labor-intensive.Herein,an antibody-modified graphene transistor assay is developed for sensitive and minute-level detection of Met in complex environments.The anti-Met probe captured charged targets within 120 s,leading to a p-doping effect near the graphene channel.The limit of detection reaches 50 aM(5.0×10^(-17)M)Met in solution.The graphene transistor would be a valuable tool for Met detection effective prevention of drug abuse.

High-performance vertical GaN field-effect transistor with an integrated self-adapted channel diode for reverse conduction

A vertical GaN field-effect transistor with an integrated self-adapted channel diode(CD-FET)is proposed to improve the reverse conduction performance.It features a channel diode(CD)formed between a trench source on the insulator and a P-type barrier layer(PBL),together with a P-shield layer under the trench gate.At forward conduction,the CD is pinched off due to depletion effects caused by both the PBL and the metal-insulator-semiconductor structure from the trench source,without influencing the on-state characteristic of the CD-FET.At reverse conduction,the depletion region narrows and thus the CD turns on to achieve a very low turn-on voltage(V_(F)),preventing the inherent body diode from turning on.Meanwhile,the PBL and P-shield layer can modulate the electric field distribution to improve the off-state breakdown voltage(BV).Moreover,the P-shield not only shields the gate from a high electric field but also transforms part of C_(GD)to CGS so as to significantly reduce the gate charge(Q_(GD)),leading to a low switching loss(E_(switch)).Consequently,the proposed CD-FET achieves a low V_(F)of 1.65 V and a high BV of 1446 V,and V_(F),Q_(GD)and E_(switch)of the CD-FET are decreased by 49%,55%and 80%,respectively,compared with those of a conventional metal-oxide-semiconductor field-effect transistor(MOSFET).