A Flexible Mott Synaptic Transistor for Nociceptor Simulation and Neuromorphic Computing

Designing transparent flexible electronics with multi-biological neuronal functions and superior flexibility is a key step to establish wearable artificial intelligence equipment. Here, a flexible ionic gel-gated VO₂ Mott transistor is developed to simulate the functions of the biological synapse. Short-term and long-term plasticity of the synapse are realized by the volatile electrostatic carrier accumulation and nonvolatile proton-doping modulation, respectively. With the achievement of multi-essential synaptic functions, an important sensory neuron, nociceptor, is perfectly simulated in our synaptic transistors with all key characteristics of threshold, relaxation, and sensitization. More importantly, this synaptic transistor exhibits high tolerance to the bending deformation, and the cycle-to-cycle variations of multi-conductance states in potentiation and depression properties are maintained within 4%. This superior stability further indicates that our flexible device is suitable for neuromorphic computing. Simulation results demonstrate that high recognition accuracy of handwritten digits (>95%) can be achieved in a convolution neural network built from these synaptic transistors. The transparent and flexible Mott transistor based on electrically-controlled VO₂ metal-insulator transition is believed to open up alternative approaches to developing highly stable synapses for future flexible neuromorphic systems.     

Controlled Synthesis of 2D Palladium Diselenide for Sensitive Photodetector Applications

Palladium diselenide (PdSe₂), a thus far scarcely studied group‐10 transition metal dichalcogenide has exhibited promising potential in future optoelectronic and electronic devices due to unique structures and electrical properties. Here, the controllable synthesis of wafer‐scale and homogeneous 2D PdSe₂ film is reported by a simple selenization approach. By choosing different thickness of precursor Pd layer, 2D PdSe₂ with thickness of 1.2–20 nm can be readily synthesized. Interestingly, with the increase in thickness, obvious redshift in wavenumber is revealed by Raman spectroscopy. Moreover, in accordance with density functional theory (DFT) calculation, optical absorption and ultraviolet photoemission spectroscopy (UPS) analyses confirm that the PdSe₂ exhibits an evolution from a semiconductor (monolayer) to semimetal (bulk). Further combination of the PdSe₂ layer with Si leads to a highly sensitive, fast, and broadband photodetector with a high responsivity (300.2 mA W^?1) and specific detectivity (≈10¹³ Jones). By decorating the device with black phosphorus quantum dots, the device performance can be further optimized. These results suggest the as‐selenized PdSe₂ is a promising material for optoelectronic application.     

Fast Photothermoelectric Response in CVD-Grown PdSe2 Photodetectors with In-Plane Anisotropy

PdSe₂, a star photosensitive functional material, has been successfully used in photodetectors based on sensing mechanisms of photogating, photoconductive, and photovoltaic effects. Here, a photothermoelectric (PTE) effect is observed in photodetectors based on PdSe₂ flakes grown by chemical vapor deposition. The unique photoresponse arises from an electron temperature gradient instead of electron–hole separation. Direct evidence of the PTE effect is confirmed by a nonlocal photoresponse under zero bias. Moreover, the PdSe₂ photodetector shows high performance in terms of ultrafast response speed (4 µs), high air-stability, broadband spectrum photodetection, reasonable responsivity, and anisotropic optical response. This study paves a new way for developing high-performance photodetectors based on PdSe₂ layered materials.     

An Artificial Autonomic Nervous System That Implements Heart and Pupil as Controlled by Artificial Sympathetic and Parasympathetic Nerves

The autonomic nervous system maintains homeostasis in organisms through complex neural pathways and responds adaptively to changes in the external and internal environment. The fabrication of an artificial autonomic nervous system is reported that replicates combined effects of sympathetic and parasympathetic nerves on cardiac activity and pupillary control, to mimic the regulation of autonomic nervous system to external changes. The artificial autonomic nerve-controlled pupil contraction and relaxation, modulating the rate of heartbeats for normal cardiac rhythm and arrhythmia as reflected by blink rates of a signal indicator. These functions are switched by using a parallel-channeled synaptic transistor with a special n-i-p heterostructure that has a 2D h-BN insulator in the middle to provide barrier against ion injection into the 2D MoS₂ bottom n-channel and enable short-term plasticity as induced by acetylcholine, and the electrochemical doping reaction occurred at the P3HT nanowire p-channels on top to enable relatively long-term plasticity as induced by noradrenaline. Low-energy consumption down to femtojoule and an ultrahigh paired-pulse facilitation index up to ≈455% are demonstrated. An artificial neural network based on device characteristics achieves a high recognition accuracy for electrocardiogram patterns. This study extends insights into artificial nerves-inspired biological signal processing and recognition.     

Highly In-Plane Anisotropic 2D PdSe2 for Polarized Photodetection with Orientation Selectivity

Polarized photodetection based on anisotropic two-dimensional materials display promising prospects for practical application in optical communication and optoelectronic fields. However, most of the reported polarized photodetection are limited by the lack of valid tunable strategy and low linear dichroism ratio. A peculiar noble metal dichalcogenide—PdSe₂ with a puckered pentagonal structure and abnormal linear dichroism conversion—potentially removes these restrictions and is demonstrated in this study. Herein, azimuth-dependent reflectance difference microscopy combined with anisotropic electrical transport measurements indicate strong in-plane anisotropic optical and electrical properties of two-dimensional PdSe₂. Remarkably, the typical polarization-resolved photodetection exhibits anisotropic photodetection characteristics with a dichroic ratio up to ≈1.8 at 532 nm and ≈2.2 at 369 nm, and their dominant polarization orientation differs by 90° corresponding to the a-axis and b-axis, respectively. The unique orientation selection behavior in polarization-dependent photodetection can be attributed to the intrinsic linear dichroism conversion. The results make 2D PdSe₂ a promising platform for investigating anisotropic structure–property correlations and integrated optical applications for novel polarization-sensitive photodetection.     

Pressure‐Tunable Ambipolar Conduction and Hysteresis in Thin Palladium Diselenide Field Effect Transistors

Few‐layer palladium diselenide (PdSe₂) field effect transistors are studied under external stimuli such as electrical and optical fields, electron irradiation, and gas pressure. The ambipolar conduction and hysteresis are observed in the transfer curves of the as‐exfoliated and unprotected PdSe₂ material. The ambipolar conduction and its hysteretic behavior in the air and pure nitrogen environments are tuned. The prevailing p‐type transport observed at atmospheric pressure is reversibly turned into a dominant n‐type conduction by reducing the pressure, which can simultaneously suppress the hysteresis. The pressure control can be exploited to symmetrize and stabilize the transfer characteristics of the device as required in high‐performance logic circuits. The transistors are affected by trap states with characteristic times in the order of minutes. The channel conductance, dramatically reduced by the electron irradiation during scanning electron microscope imaging, is restored after an annealing of several minutes at room temperature. The work paves the way toward the exploitation of PdSe₂ in electronic devices by providing an experiment‐based and deep understanding of charge transport in PdSe₂ transistors subjected to electrical stress and other external agents.     

Achieving Ultrahigh Electron Mobility in PdSe2 Field-Effect Transistors via Semimetal Antimony as Contacts

Even though atomically thin 2D semiconductors have shown great potential for next-generation electronics, the low carrier mobility caused by poor metal–semiconductor contacts and the inherently high density of impurity scatterings remains a critical issue. Herein, high-mobility field-effect transistors (FETs) by introducing few-layer PdSe₂ flakes as channels is achieved, via directly depositing semimetal antimony (Sb) as drain–source electrodes. The formation of clean and defect-free van der Waals (vdW) stackings at the Sb–PdSe₂ heterointerfaces boosts the room temperature transport characteristics, including low contact resistance down to 0.55 kΩ µm, high on-current density reaching 96 µA µm⁻¹, and high electron mobility of 383 cm² V⁻¹ s⁻¹. Furthermore, metal–insulator transition (MIT) is observed in the PdSe₂ FETs with and without hexagonal boron nitride (h–BN) as buffer layers. However, the layered h–BN/PdSe₂ vdW stacking eliminates the interference of interfacial disorders, and thus the corresponding device exhibits a lower MIT crossing point, larger mobility exponent of γ ∼ 1.73, significantly decreased hopping parameter of T₀, and ultrahigh electron mobility of 2,184 cm² V⁻¹ s⁻¹ at 10 K. These findings are expected to be significant for developing high mobility 2D-based quantum devices.     

Anisotropic Phonon Response of Few‐Layer PdSe2 under Uniaxial Strain

PdSe₂, an emerging 2D material with a novel anisotropic puckered pentagonal structure, has attracted growing interest due to its layer‐dependent electronic bandgap, high carrier mobility, and good air stability. Herein, a detailed Raman spectroscopic study of few‐layer PdSe₂ (two to five layers) under the in‐plane uniaxial tensile strain up to 3.33% is performed. Two of the prominent PdSe₂ Raman peaks are influenced differently depending on the direction of strain application. The $A_g^1$ mode redshifts more than the $A_g^3$ mode when the strain is applied along the a‐axis of the crystal, while the $A_g^3$ mode redshifts more than the $A_g^1$ mode when the strain is applied along the b‐axis. Such an anisotropic phonon response to strain indicates directionally dependent mechanical and thermal properties of PdSe₂ and also allows the identification of the crystal axes. The results are further supported using first‐principles density‐functional theory. Interestingly, the near‐zero Poisson’s ratios for few‐layer PdSe₂ are found, suggesting that the uniaxial tensile strain can easily be applied to few‐layer PdSe₂ without significantly altering their dimensions at the perpendicular directions, which is a major contributing factor to the observed distinct phonon behavior. The findings pave the way for further development of 2D PdSe₂‐based flexible electronics.     

Nonvolatile Ferroelectric Memory Effect in Ultrathin α‐In2Se3

High‐density memory is integral in solid‐state electronics. 2D ferroelectrics offer a new platform for developing ultrathin electronic devices with nonvolatile functionality. Recent experiments on layered α‐In₂Se₃ confirm its room‐temperature out‐of‐plane ferroelectricity under ambient conditions. Here, a nonvolatile memory effect in a hybrid 2D ferroelectric field‐effect transistor (FeFET) made of ultrathin α‐In₂Se₃ and graphene is demonstrated. The resistance of the graphene channel in the FeFET is effectively controllable and retentive due to the electrostatic doping, which stems from the electric polarization of the ferroelectric α‐In₂Se₃. The electronic logic bit can be represented and stored with different orientations of electric dipoles in the top‐gate ferroelectric. The 2D FeFET can be randomly rewritten over more than 10⁵ cycles without losing the nonvolatility. The approach demonstrates a prototype of rewritable nonvolatile memory with ferroelectricity in van der Waals 2D materials.     

Analog Circuit Applications Based on All‐2D Ambipolar ReSe2 Field‐Effect Transistors

Complementary circuits based on 2D materials show great promise for next‐generation electronics. An ambipolar all‐2D ReSe₂ field‐effect transistor (FET) with a hexagonal boron nitride gate dielectric is fabricated and its electronic characteristics are comprehensively studied by temperature dependence and noise measurements. Ambipolar transfer characteristics are achieved owing to the tunable Fermi level of the graphene contact and negligible and 30 meV Schottky barrier heights for the n‐ and p‐channel regimes, respectively. An inverter is also fabricated to demonstrate ambipolar ReSe₂ FET operation in a logic circuit. Furthermore, a p/n switchable unipolar FET is designed and shows potential for building complimentary circuits from a signal device. This work demonstrates the potential of all‐2D ReSe₂ FETs and makes available new approaches for designing next‐generation devices.     

0D/2D Heterostructures Vertical Single Electron Transistor

Mixed-dimensional heterostructures formed by the stacking of 2D materials with nanostructures of distinct dimensionality constitute a new class of nanomaterials that offers multifunctionality that goes beyond those of single dimensional systems. An unexplored architecture of single electron transistor (SET) is developed that employs heterostructures made of nanoclusters (0D) grown on a 2D molybdenum disulfide (MoS₂) channel. Combining the large Coulomb energy of the nanoclusters with the electronic capabilities of the 2D layer, the concept of 0D–2D vertical SET is unveiled. The MoS₂ underneath serves both as a charge tunable channel interconnecting the electrode, and as bottom electrode for each v-SET cell. In addition, its atomic thickness makes it thinner than the Debye screening length, providing electric field transparency functionality that allows for an efficient electric back gate control of the nanoclusters charge state. The Coulomb diamond pattern characteristics of SET are reported, with specific doping dependent nonlinear features arising from the 0D/2D geometry that are elucidated by theoretical modeling. These results hold promise for multifunctional single electron device taking advantage of the versatility of the 2D materials library, with as example envisioned spintronics applications while coupling quantum dots to magnetic 2D material, or to ferroelectric layers for neuromorphic devices.     

超宽禁带半导体金刚石功率电子学研究的新进展

以SiC/GaN为代表的第三代半导体功率电子学已成为当今功率电子学创新发展的主流,超宽禁带半导体金刚石功率电子学将有可能成为下一代固态功率电子学的代表,受到研究人员的广泛关注。介绍了金刚石功率电子学的最新进展,如金刚石单晶、金刚石化学气相沉积同质和异质单晶外延、金刚石多晶外延、金刚石二极管、金刚石MOSFET、金刚石结型场效应晶体管、金刚石双极结型晶体管、金刚石逻辑电路、金刚石射频场效应晶体管和金刚石上GaN HEMT等。还介绍了金刚石材料的大尺寸、低缺陷和p型及n型掺杂等制备技术,金刚石新器件结构设计,金刚石新器件工艺,转移掺杂H端-金刚石沟道和金刚石/GaN界面热阻等研究成果。分析了金刚石功率电子学的发展由来、关键技术突破和发展态势。     

Recent Advances in Transistor‐Based Artificial Synapses

Simulating biological synapses with electronic devices is a re‐emerging field of research. It is widely recognized as the first step in hardware building brain‐like computers and artificial intelligent systems. Thus far, different types of electronic devices have been proposed to mimic synaptic functions. Among them, transistor‐based artificial synapses have the advantages of good stability, relatively controllable testing parameters, clear operation mechanism, and can be constructed from a variety of materials. In addition, they can perform concurrent learning, in which synaptic weight update can be performed without interrupting the signal transmission process. Synergistic control of one device can also be implemented in a transistor‐based artificial synapse, which opens up the possibility of developing robust neuron networks with significantly fewer neural elements. These unique features of transistor‐based artificial synapses make them more suitable for emulating synaptic functions than other types of devices. However, the development of transistor‐based artificial synapses is still in its very early stages. Herein, this article presents a review of recent advances in transistor‐based artificial synapses in order to give a guideline for future implementation of synaptic functions with transistors. The main challenges and research directions of transistor‐based artificial synapses are also presented.     

Small-molecule vacuum processed melamine-C60, organic field-effect transistors

The transfer of benchtop knowledge into large scale industrial production processes represents a challenge in the field of organic electronics. Large scale industrial production of organic electronics is envisioned as roll to roll (R2R) processing which nowadays comprises usually solution-based large area printing steps. The search for a fast and reliable fabrication process able to accommodate the deposition of both insulator and semiconductor layers in a single step is still under way. Here we report on the fabrication of organic field effect transistors comprising only evaporable small molecules. Moreover, both the gate dielectric (melamine) and the semiconductor (C₆₀) are deposited in successive steps without breaking the vacuum in the evaporation chamber. The material characteristics of evaporated melamine thin films as well as their dielectric properties are investigated, suggesting the applicability of vacuum processed melamine for gate dielectric layer in OFETs. The transistor fabrication and its transfer and output characteristics are presented along with observations that lead to the fabrication of stable and virtually hysteresis-free transistors. The extremely low price of precursor materials and the ease of fabrication recommend the evaporation processes as alternative methods for a large scale, R2R production of organic field effect transistors.     

Junction Field-Effect Transistors Based on PdSe2/MoS2 Heterostructures for Photodetectors Showing High Responsivity and Detectivity

2D materials have shown great promise for next-generation high-performance photodetectors. However, the performance of photodetectors based on 2D materials is generally limited by the tradeoff between photoresponsivity and photodetectivity. Here, a novel junction field-effect transistor (JFET) photodetector consisting of a PdSe₂ gate and MoS₂ channel is constructed to realize high responsivity and high detectivity through effective modulation of top junction gate and back gate. The JFET exhibits high carrier mobility of 213 cm² V⁻¹ s⁻¹. What is more, the high responsivity of 6 × 10² A W⁻¹, as well as the high detectivity of 10¹¹ Jones, are achieved simultaneously through the dual-gate modulation. The high performance is attributed to the modulation of the depletion region by the dual-gate, which can effectively suppress the dark current and enhance the photocurrent, thereby realizing high detectivity and responsivity. The JFET photodetector provides a new approach to realize photodetectors with high responsivity and detectivity.     

Strong Interlayer Transition in Few-Layer InSe/PdSe2 van der Waals Heterostructure for Near-Infrared Photodetection

Near infrared (NIR) photodetectors based on 2D materials are widely studied for their potential application in next generation sensing, thermal imaging, and optical communication. Construction of van der Waals (vdWs) heterostructure provides a tremendous degree of freedom to combine and extend the features of 2D materials, opening up new functionalities on photonic and optoelectronic devices. Herein, a type-II InSe/PdSe₂ vdWs heterostructure with strong interlayer transition for NIR photodetection is demonstrated. Strong interlayer transition between InSe and PdSe₂ is predicted via density functional theory calculation and confirmed by photoluminance spectroscopy and Kelvin probe force microscopy. The heterostructure exhibits highly sensitive photodetection in NIR region up to 1650 nm. The photoresponsivity, detectivity, and external quantum efficiency at this wavelength respectively reaches up to 58.8 A W⁻¹, 1 × 10¹⁰ Jones, and 4660%. The results suggest that the construction of vdWs heterostructure with strong interlayer transition is a promising strategy for infrared photodetection, and this work paves the way to developing high-performance optoelectronic devices based on 2D vdWs heterostructures.     

The influence of a doping profile on the characteristics of an ion-implanted GaAs field-effect transistor with a Schottky barrier

A GaAs field-effect ion-implanted transistor with a Schottky barrier is simulated. The doping profile obtained when doping through an insulator mask is determined and the dependences of the static transistor characteristics on the parameters of the doping profile are calculated and analyzed. The physical processes controlling the transistor characteristics in the case of a variation in the parameters of its doping profile and the coefficient of compensation of the substrate are studied. Based on calculations, the optimal doping-profile parameters ensuring the best characteristics for transistors are predicted.     

A Noble Metal Dichalcogenide for High‐Performance Field‐Effect Transistors and Broadband Photodetectors

2D layered materials are an emerging class of low‐dimensional materials with unique physical and structural properties and extensive applications from novel nanoelectronics to multifunctional optoelectronics. However, the widely investigated 2D materials are strongly limited in high‐performance electronics and ultrabroadband photodetectors by their intrinsic weaknesses. Exploring the new and narrow bandgap 2D materials is very imminent and fundamental. A narrow‐bandgap noble metal dichalcogenide (PtS₂) is demonstrated in this study. The few‐layer PtS₂ field‐effect transistor exhibits excellent electronic mobility exceeding 62.5 cm² V^?1 s^?1 and ultrahigh on/off ratio over 10⁶ at room temperature. The temperature‐dependent conductance and mobility of few‐layer PtS₂ transistors show a direct metal‐to‐insulator transition and carrier scattering mechanisms, respectively. Remarkably, 2D PtS₂ photodetectors with broadband photodetection from visible to mid‐infrared and a fast photoresponse time of 175 µs at 830 nm illumination for the first time are obtained at room temperature. Our work opens an avenue for 2D noble‐metal dichalcogenides to be applied in high‐performance electronic and mid‐infrared optoelectronic devices.     

Flexible Vertical Photogating Transistor Network with an Ultrashort Channel for In-Sensor Visual Nociceptor

Humans can clearly perceive surroundings efficiently while consuming little energy because of human intelligence and powerful vision system. Thus, it has been a long-sought dream for human beings to build such an energy-efficient artificial intelligent vision system with emerging devices. Unfortunately, a wearable optoelectronic device for visual nociceptor systems, regarded as a key bionic function to protect the vision, remains to be developed so far. Herein, using the vertical coplanar-multiterminal flexible transient photogating transistor network with a 3 nm ultrashort channel, a wearable artificial vision system with painful-perceptual abilities is successfully demonstrated for flexible electronic-skin (e-skin) applications. The device not only has the ability of ultrafast transient physical disappearance of only 60 s for information security but also establishes a flexible optical in-sensor visual nociceptor (ISVN) e-skin. The optical transition from short-time memory to long-time memory of visual memory is educed by a strong photogating effect, and the higher-level-graded optical painful alarm-sensing system is also demonstrated by this flexible artificial e-skin. Moreover, the proposed devices will achieve painful light sensitization under different spatiotemporal color patterns to avoid external secondary injuries. It provides a good opportunity for future intelligent e-skin taking advantage of its intriguing visual pain-perceptual abilities.     

Tunable Graphene Electronics with Local Ultrahigh Pressure

Fine‐tuning of graphene effective doping is achieved by applying ultrahigh pressures (>10 GPa) using atomic force microscopy (AFM) diamond tips. Specific areas in graphene flakes are irreversibly flattened against a SiO₂ substrate. This work represents the first demonstration of local creation of very stable effective p‐doped graphene regions with nanometer precision, as unambiguously verified by a battery of techniques. Importantly, the doping strength depends monotonically on the applied pressure, allowing a controlled tuning of graphene electronics. Through this doping effect, ultrahigh pressure modifications include the possibility of selectively modifying graphene areas to improve their electrical contact with metal electrodes, as shown by conductive AFM. Density functional theory calculations and experimental data suggest that this pressure level induces the onset of covalent bonding between graphene and the underlying SiO₂ substrate. This work opens a convenient avenue to tuning the electronics of 2D materials and van der Waals heterostructures through pressure with nanometer resolution.