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The charge neutrality point (CNP) is one of the essential parameters in the development of graphene field-effect transistors (GFETs). For GFET with an intrinsic graphene channel layer, the CNP is typically near-zero-volt gate voltage, implying that a well-balanced density of electrons and holes exists in the graphene channel layer. Fabricated GFET, however, typically exhibits CNP that is either positively or negatively shifted from the near-zero-volt gate voltage, implying that the graphene channel layer is unintentionally doped, leading to a unipolar GFET transfer characteristic. Furthermore, the CNP is also modulated in time, indicating that charges are dynamically induced in the graphene channel layer. In this work, understanding and mitigating the CNP shift were attempted by introducing passivation layers made of polyvinyl alcohol and polydimethylsiloxane onto the graphene channel layer. The CNP was found to be negatively shifted, recovered back to near-zero-volt gate voltage, and then positively shifted in time. By analyzing the charge density, carrier mobility, and correlation between the CNP and the charge density, it can be concluded that positive CNP shifts can be attributed to the charge trapping at the graphene/SiO2 interface. The negative CNP shift, on the other hand, is caused by dipole coupling between dipoles in the polymer layer and carriers on the surface of the graphene layer. By gaining a deeper understanding of the intricate mechanisms governing the CNP shifts, an ambiently stable GFET suitable for next-generation electronics could be realized. [ABSTRACT FROM AUTHOR]

In this paper, we analyze the modulation characteristics and the ultimate modulation frequency of the terahertz (THz) hot-electron FET bolometers with the graphene channels (GCs), metal gate (MG), and gate barrier layers (BLs) in a wide temperature range. Our results predict that the responsivity of GC-FET bolometers decreases with decreasing operating temperature. This is attributed to a dramatic drop in the thermionic GC-MG current (characterized by the relatively large activation energy) and its modulated component when the temperature lowers. A further decrease in the temperature results in a fairly strong responsivity roll-off. In contrast, the responsivity of the GC-FET detectors with the temperature-adjusted load resistance rises with decreasing temperature because the temperature lowering leads to an increase in the electron energy relaxation time and promotes more effective heating by the impinging THz radiation. In this case, the weakening of the thermionic current is compensated by the commensurate increase in the load resistance. [ABSTRACT FROM AUTHOR]

In this paper, we propose and analyze the terahertz (THz) bolometric vector detectors based on the graphene-channel field-effect transistors (GC-FET) with the black-P gate barrier layer or with the composite b-BN/black-P/b-BN gate layer. The phase difference between the signal received by the FET source and drain substantially affects the plasmonic resonances. This results in a resonant variation of the detector response on the incoming THz signal phase shift and the THz radiation angle of incidence. [ABSTRACT FROM AUTHOR]

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Two-dimensional (2D) transition metal dichalcogenides (TMDs) are excellent candidates for electronic applications because of their high carrier mobility, tunable bandgap energy depending on the number of layers, monolayer thickness, and the absence of dangling bonds on their surfaces. Despite these advantages, the crystalline structures of TMDs contain intrinsic defects such as vacancies, adatoms, grain boundaries, and substitutional impurities, which can cause large contact resistance at the source/drain interface. Customized engineering of interfaces and defects, which provides a method to modulate the properties of TMDs, is crucial as it can significantly enhance device performance. Herein, we explored a novel electrode to enhance the interface between electrode and semiconductor materials. we report the synthesis of high-quality atomically thin MoO2 using atmospheric pressure chemical vapor deposition (APCVD) and its application to field-effect transistors. To improve crystallinity of MoO2, we investigated the influence of hydrogen concentration, a key parameter in the reduction process, on the synthesis of high-crystallinity MoO₂. By adding NaCl to MoO₃ powder, we optimized the synthesis of high-crystallinity MoO₂. Utilizing the optimized MoO₂, we fabricated transistors that exhibited a mobility of 29.1 cm²/V∙s and an on/off ratio of 1.78 × 10⁴, demonstrating excellent performance. Our findings confirm that single-crystal MoO2 can be effectively applied as a contact electrode in high-performance two-dimensional semiconductor devices. [ABSTRACT FROM AUTHOR]

Liquid metal (LM) electronic ink (e‐ink) is a promising new‐generation material for printed electronics. Extended from this ideal platform, such ink can be post‐processed or loaded with semiconductor nanoparticles to further make semiconductors in the forms of dots, wires, and films on its surface. In this way, targeted semiconductors can be quickly fabricated and patterned as desired with low cost at around room temperature. This leads to the unconventional bottom‐up strategy for direct manufacture of functional devices. Along this direction, a series of p–n junction diodes, field‐effect transistors, and light‐emitting devices have been developed. LM‐printed semiconductor would significantly innovate the classical processes of preparing integrated circuits and electronic devices. To push forward further progress of this cutting‐edge frontier, this article is dedicated to present an overview of LM‐printed semiconductor. The material category of LM semiconductor e‐inks and their synthesis approaches is introduced. Then the core strategies toward printing semiconductors are systematically outlined. Following that, the typical printed semiconductor materials and electronic devices thus constructed as well as their potential applications are summarized. Finally, scientific and technical challenges thus raised are interpreted. Perspective in the area is given. [ABSTRACT FROM AUTHOR]

Recently, field‐effect transistors (FETs) have emerged as a novel type of multiparameter, high‐performance, highly integrated platform for biochemical detection, leveraging their classical three‐terminal structure, working principles, and fabrication methods. Notably, graphene materials, known for their exceptional electrical and optical properties as well as biocompatibility, serve as a fundamental component of these devices, further enhancing their advantages in biological detection. This review places special emphasis on recent advancements in graphene field‐effect transistor (GFET)‐based biosensors and focuses on four main areas: i) the basic concepts of FETs and the specific electrical properties of GFETs; ii) various state‐of‐the‐art approaches to enhance the performance of GFET‐based biosensors in terms of operating principles and the "3S"—stability, sensitivity, and specificity; iii) multiplexed detection strategies for GFET‐based biosensors; and iv) the current challenges and future perspectives in the field of GFET‐based biosensors. It is hoped that this article can profoundly elucidate the development of GFET biosensors and inspire a broader audience. [ABSTRACT FROM AUTHOR]

In food safety analysis, the detection and control of foodborne pathogens and their toxins are of great importance. Monitoring of virus transmission is equally important, especially in light of recent findings that coronaviruses have been detected in frozen foods and packages during the current global epidemic of coronavirus disease 2019. In recent years, field-effect transistor (FET) biosensors have attracted considerable scholarly attention for pathogenic microorganisms and toxins detection and sensing due to their rapid response time, high sensitivity, wide dynamic range, high specificity, label-free detection, portability, and cost-effectiveness. FET-based biosensors can be modified with specific recognition elements, thus providing real-time qualitative and semiquantitative analysis. Furthermore, with advances in nanotechnology and device design, various high-performance nanomaterials are gradually applied in the detection of FET-based biosensors. In this article, we review specific detection in different biological recognition elements are immobilized on FET biosensors for the detection of pathogenic microorganisms and toxins, and we also discuss nonspecific detection by FET biosensors. In addition, there are still unresolved challenges in the development and application of FET biosensors for achieving efficient, multiplexed, in situ detection of pathogenic microorganisms and toxins. Therefore, directions for future FET biosensor research and applications are discussed. [ABSTRACT FROM AUTHOR]

Highlights: The review provides a brief overview of the basic structure, operating mechanism, and key performance indicators of flexible graphene field-effect transistors. The review details the preparation strategy of flexible graphene field-effect transistors focusing on material selection and patterning techniques. The review analyzes the latest strategies for developing wearable and implantable flexible biomedical sensors based on flexible graphene field-effect transistors. Flexible electronics are transforming our lives by making daily activities more convenient. Central to this innovation are field-effect transistors (FETs), valued for their efficient signal processing, nanoscale fabrication, low-power consumption, fast response times, and versatility. Graphene, known for its exceptional mechanical properties, high electron mobility, and biocompatibility, is an ideal material for FET channels and sensors. The combination of graphene and FETs has given rise to flexible graphene field-effect transistors (FGFETs), driving significant advances in flexible electronics and sparked a strong interest in flexible biomedical sensors. Here, we first provide a brief overview of the basic structure, operating mechanism, and evaluation parameters of FGFETs, and delve into their material selection and patterning techniques. The ability of FGFETs to sense strains and biomolecular charges opens up diverse application possibilities. We specifically analyze the latest strategies for integrating FGFETs into wearable and implantable flexible biomedical sensors, focusing on the key aspects of constructing high-quality flexible biomedical sensors. Finally, we discuss the current challenges and prospects of FGFETs and their applications in biomedical sensors. This review will provide valuable insights and inspiration for ongoing research to improve the quality of FGFETs and broaden their application prospects in flexible biomedical sensing. [ABSTRACT FROM AUTHOR]

Precise control over polarity in field‐effect transistors (FETs) plays a pivotal role in the design and construction of complementary metal–oxide–semiconductor (CMOS) logic circuits. In particular, achieving such precise polarity control in 2D semiconductors is crucial for the further development of advanced electronic applications beyond unit devices. This paper presents a systematic investigation on the reversible transition of carrier types in a 2D MoTe2 semiconductor under different annealing atmospheres. Photoemission spectroscopy and density functional theory (DFT) calculations demonstrate that annealing processes in vacuum and in ambient air induce a modification in the density of states, resulting in alterations in p‐type or n‐type characteristics. These reversible changes are attributed to the physisorption and elimination of oxygen on the surface of MoTe2. Furthermore, it is found that the device geometry affects the polarity of the transistor. By strategically manipulating both the annealing conditions and the geometric configuration, the n‐ and p‐type unipolar characteristics of MoTe2 FETs are successfully modulated and ultimately demonstrating that the functionality of not only a complementary inverter with a high voltage gain of ≈20, but also more complex logic circuits of NAND and NOR gates. [ABSTRACT FROM AUTHOR]

The ionizing radiation low-cost and portable sensors based on nanostructured materials are in demand in many fields such as safety, medicine, space, and scientific research. Graphene field-effect transistors (FETs) have high potential for radiation detection. In this study, the graphene FETs were created by depositing a film-forming suspension of reduced graphene oxide (rGO) nanoparticles on the sili- con substrate with a SiO2 or thermally oxidized porous silicon (por-Si) layer and air-drying at room temperature. The electrical characteristics of the rGO-based FETs were studied in DC and AC modes. The dependencies of the drain current on the gate voltage have linear sections, the position of which depends on the sign of the drain-source voltage. It was found that the position of the Dirac point in the FETs based on the rGO-SiO2-Si and rGO-por-Si-Si structures was near the 0.8 V gate voltage. The possibility of using the obtained FETs as ionizing radiation detectors was investigated. A linear increase in the internal resistance of the rGO film in AC mode was established with increasing duration of irradiation with ẞ-particles and y-quanta formed as a result of the decay of the 226 Ra radium isotope. The radiation detector based on the rGO-por-Si-Si structure is characterized by a higher sensitivity to ionizing radiation, which is probably due to the greater thickness of the por-Si compared to the SiO2 layer. The radiation-induced change in electrical resistance of the studied FETs was greater in the low- frequency range. We explored possible mechanisms of the ionizing radiation influence on the rGO-based FETs conductivity. [ABSTRACT FROM AUTHOR]

The recent emergence of Janus 2D materials like SnSSe, derived from SnS2, reveals unique electrical and optical features, such as asymmetrical electronic structure, enhanced carrier mobility, and tunable bandgap. Previous theoretical studies have discuss the electronic properties of Janus SnSSe, but experimental evidence is limited. This study presents a two‐step method for synthesizing Janus SnSSe, involving hydrogen plasma treatment and in situ selenization. Optimized conditions (38 W, 1.5 min, 250 °C) are determined using Raman spectroscopy and AFM analysis. XPS confirmed SnSSe's elemental composition, while KPFM reveals a significant reduction in the work function (from 5.26 down to 5.14 eV) for the first time, indicating asymmetrically induced n‐type doping. Finally, field‐effect transistors (FETs) derived from SnSSe exhibited significantly enhanced mobility and on‐current, as well as n‐type doping, compared to SnS2‐based FETs. These findings lay a crucial foundation for developing high‐performance 2D electronic and optoelectronic devices. [ABSTRACT FROM AUTHOR]

Highlights The review provides a brief overview of the basic structure, operating mechanism, and key performance indicators of flexible graphene field-effect transistors. The review details the preparation strategy of flexible graphene field-effect transistors focusing on material selection and patterning techniques. The review analyzes the latest strategies for developing wearable and implantable flexible biomedical sensors based on flexible graphene field-effect transistors.

Over the last few decades, field-effect transistor (FET)-based biosensors have demonstrated great potential across various industries, including medical, food, agriculture, environmental, and military sectors. These biosensors leverage the electrical properties of transistors to detect a wide range of biomolecules, such as proteins, DNA, and antibodies. This article presents a comprehensive review of advancements in the architectures of FET-based biosensors aiming to enhance device performance in terms of sensitivity, detection time, and selectivity. The review encompasses an overview of emerging FET-based biosensors and useful guidelines to reach the best device dimensions, favorable design, and realization of FET-based biosensors. Consequently, it furnishes researchers with a detailed perspective on design considerations and applications for future generations of FET-based biosensors. Finally, this article proposes intriguing avenues for further research on the topology of FET-based biosensors.

Incorporating atomically thin 2D semiconductors (2DSCs) into the vertical complementary field‐effect transistors (CFETs) is of great significance in enabling devices to break through the sub‐nanometer scaling limit. However, due to the lack of effective doping technology and the difficult‐to‐control electrode interface, simultaneously realizing high‐performance p‐type and n‐type devices using a single metal electrode presents great challenges for 2D‐CFETs design. In this study, an innovative electrical contact strategy is proposed by constructing van der Waals heterojunction (vdWH) using 2DSCs to regulate the electrical contact properties between the metal electrode and 2DSC channel. First‐principles calculations reveal that degenerate or quasi‐degenerate complementary doping is achieved in a series of transition metal dichalcogenides (TMDs) by designing (quasi‐)broken‐gap vdWHs and utilizing their interlayer charge transfer. Metal‐2DSC contact barriers can be effectively regulated by introducing 2DSC intercalation and constructing vdWH. P‐type (quasi‐)Ohmic contacts are realized between Au electrode and various TMD channels, as well as between WTe2 channel and different metal electrodes. Moreover, quantum transport simulations present the remarkable on‐current over 102 µA µm−1 in both p‐type and n‐type 2D‐FETs by employing the vdWH and metal‐vdWH electrodes. The proposed vdWH strategy is applicable to various metal‐2DSC contacts and will shed light on future high‐performance 2D‐CFET integrations. [ABSTRACT FROM AUTHOR]

Excellent stability, low cost, high response, and sensitivity of indium oxide (In2O3), a metal oxide semiconductor, have been verified in the field of gas sensing. Conventional In2O3 gas sensors employ simple and easy–to–manufacture resistive components as transducers. However, the swift advancement of the Internet of Things has raised higher requirements for gas sensors based on metal oxides, primarily including lowering operating temperatures, improving selectivity, and realizing integrability. In response to these three main concerns, field–effect transistor (FET) gas sensors have garnered growing interest over the past decade. When compared with other metal oxide semiconductors, In2O3 exhibits greater carrier concentration and mobility. The property is advantageous for manufacturing FETs with exceptional electrical performance, provided that the off–state current is controlled at a sufficiently low level. This review presents the significant progress made in In2O3 FET gas sensors during the last ten years, covering typical device designs, gas sensing performance indicators, optimization techniques, and strategies for the future development based on In2O3 FET gas sensors. [ABSTRACT FROM AUTHOR]

Electrolyte‐gated field effect transistors and electrochemical transistors have emerged as powerful components for bioelectronic sensors and biopotential recording devices. A set of parameters must be considered when developing devices to amplify weak electrophysiological signals. These include maximum transconductance values, cut‐off frequencies, and large on/off current ratios. Organic polymer‐based devices have recently dominated the field, especially when considering flexibility as a key factor. Oxide semiconductors may also offer these features, as well as advantages like higher mobility. Herein, flexible, ultrathin, indium tin oxide (ITO) electrolyte‐gated transistors are reported. These accumulation‐mode devices combine n‐type operation with µe = 9.5 cm2 Vs−1, high transconductance (gm = 44 mS), and on/off ratios (105) as well as optically transparent layouts. While oxides are normally considered brittle, mechanically flexible ITO layers are obtained by room temperature deposition of amorphous layers onto parylene C. This process results in low strain, producing devices that survive bending. ITO electrochemically degrades, however, with cycling. To overcome this, the surface is passivated with high dielectric constant inert capping layers of Ta2O5 or Ta2O5/AlN. This greatly improves stability while preserving low gate voltages. Based on their overall performance, ITO‐based EGFETs are promising for bioelectronics. [ABSTRACT FROM AUTHOR]

In this work, the Landauer approach-based short channel model of a graphene field effect transistor has been presented. The quasi-ballistic and ballistic transport mechanism is explained by this approach for nanoscale transistors. The concept of the virtual source is considered to obtain the carrier density in active regions. Here, we apply the Landauer approach for short-channel graphene field effect transistors relating to the parameter in the virtual source model. The mobility of the model has been improved including various scattering effects like impurity scattering, acoustic phonon scattering, and optical phonon scattering. The dynamic resistance model is considered due to asymmetry transport in the electron branch and hole branch. The proposed model has been verified with several experimental works for model validation. The comparisons of the model simulation with several experimental results that have been reported in the literature match well for different short channel lengths of graphene. [ABSTRACT FROM AUTHOR]

The field-effect transistors (FETs) based on reduced graphene oxide (rGO) with SiO2, porous silicon (PS), and oxidized porous silicon (PSox) supporting layers were obtained. The influence of charged impurities in the silicon substrate and electrically active defects in the support layers on the electrical properties of the FETs was studied based on the capacitance-voltage characteristic analysis. Localized electron states in the SiO2, PS, and PSox supporting layers that affect the charge transfer in the rGO-based FETs were determined using thermally stimulated depolarization spectroscopy. The influence mechanisms of various supporting layers on the electrical characteristics of the obtained FETs are discussed. [ABSTRACT FROM AUTHOR]

Quantum point contacts with a short (100-nm) channel in a high-mobility two-dimensional electron gas of GaAs/Al(Ga)As heterostructures and a short-channel p-type field-effect transistor in a silicon-on-insulator structure were fabricated and studied experimentally and by modeling at the Rzhanov Institute of Semiconductor Physics, Siberian Branch, Russian Academy of Sciences, Novosibirsk, Russia, in order to study the response of the samples to weak irradiation by an electromagnetic field with a frequency of ~2 GHz. This response in the tunneling mode at a temperature of 4.2 K turned out to be giant and was observed against the background of features caused by impurity disorder. [ABSTRACT FROM AUTHOR]

Quasi‐2D perovskites have attracted significant attention because of their environmental robustness and superior long‐term stability compared with their 3D counterparts. However, they typically consist of a mixture of multiple quantum wells with different optoelectrical properties, which degrades the electronic properties and hinders further electronic applications. Here, to challenge this issue, a surface p‐doping strategy involving the introduction of a thiophene‐containing polymer onto the surface of quasi‐2D tin perovskites is reported. The tin ions in the perovskites effectively interact with the sulfur atoms in the thiophene moieties, thereby generating hole carriers and inducing p‐doping. The resulting doped quasi‐2D perovskites exhibit excellent surface crystallinity, lower trap density, and enhanced charge carrier transport capability along the perovskite semiconductor channels. Consequently, the doped quasi‐2D tin perovskite‐based transistors exhibit a high field‐effect mobility of 53 cm2V−1s−1 (7 cm2V−1s−1 for the control device) and an outstanding on/off ratio (>107), together with superior operational stability. [ABSTRACT FROM AUTHOR]

Since two‐dimensionalal (2D) materials have distinct chemical and physical properties, they are widely used in various sectors of modern technologies. In the domain of diagnostic biodevices, particularly for point‐of‐care (PoC) biomedical diagnostics, 2D‐based field‐effect transistor biosensors (bio‐FETs) demonstrate substantial potential. Here, in this review article, the operational mechanisms and detection capabilities of biosensing devices utilizing graphene, transition metal dichalcogenides (TMDCs), black phosphorus, and other 2D materials are addressed in detail. The incorporation of these materials into FET‐based biosensors offers significant advantages, including low detection limits (LOD), real‐time monitoring, label‐free diagnosis, and exceptional selectivity. The review also highlights the diverse applications of these biosensors, ranging from conventional to wearable devices, underscoring the versatility of 2D material‐based FET devices. Additionally, the review provides a comprehensive assessment of the limitations and challenges faced by these devices, along with insights into future prospects and advancements. Notably, a detailed comparison of FET‐based biosensors is tabulated along with various other biosensing platforms and their working mechanisms. Ultimately, this review aims to stimulate further research and innovation in this field while educating the scientific community about the latest advancements in 2D materials‐based biosensors. [ABSTRACT FROM AUTHOR]

The impact of radiation on MoS2-based devices is an important factor in the utilization of two-dimensional semiconductor-based technology in radiation-sensitive environments. In this study, the effects of gamma irradiation on the electrical variations in MoS2 field-effect transistors with buried local back-gate structures were investigated, and their related effects on Al2O3 gate dielectrics and MoS2/Al2O3 interfaces were also analyzed. The transfer and output characteristics were analyzed before and after irradiation. The current levels decreased by 15.7% under an exposure of 3 kGy. Additionally, positive shifts in the threshold voltages of 0.50, 0.99, and 1.15 V were observed under irradiations of 1, 2, and 3 kGy, respectively, compared to the non-irradiated devices. This behavior is attributable to the comprehensive effects of hole accumulation in the Al2O3 dielectric interface near the MoS2 side and the formation of electron trapping sites at the interface, which increased the electron tunneling at the MoS2 channel/dielectric interface. [ABSTRACT FROM AUTHOR]

Effective Ohmic contact between metals and their conductive channels is a crucial step in developing high-performance Ga2O3-based transistors. Distinct from bulk materials, excess thermal energy of the annealing process can destroy the low-dimensional material itself. Given the thermal budget concern, a feasible and moderate solution (i.e., Ar-containing plasma treatment) is proposed to achieve effective Ohmic junctions with (100) β-Ga2O3 nanosheets. The impact of four kinds of plasma treatments (i.e., gas mixtures SF6/Ar, SF6/O2/Ar, SF6/O2, and Ar) on (100) β-Ga2O3 crystals is comparatively studied by X-ray photoemission spectroscopy for the first time. With the optimal plasma pre-treatment (i.e., Ar plasma, 100 W, 60 s), the resulting β-Ga2O3 nanosheet field-effect transistors (FETs) show effective Ohmic contact (i.e., contact resistance RC of 104 Ω·mm) without any post-annealing, which leads to competitive device performance such as a high current on/off ratio (>107), a low subthreshold swing (SS, 249 mV/dec), and acceptable field-effect mobility ( μ e f f , ~21.73 cm2 V−1 s−1). By using heavily doped β-Ga2O3 crystals (Ne, ~1020 cm−3) for Ar plasma treatments, the contact resistance RC can be further decreased to 5.2 Ω·mm. This work opens up new opportunities to enhance the Ohmic contact performance of low-dimensional Ga2O3-based transistors and can further benefit other oxide-based nanodevices. [ABSTRACT FROM AUTHOR]

Amorphous IGZO (a‐IGZO) thin‐film transistors (TFTs) are standard backplane electronics to power active‐matrix organic light‐emitting diode (AMOLED) televisions due to their high carrier mobility and negligible low leakage characteristics. Despite their advantages, limitations in color depth arise from a steep subthreshold swing (SS) (≤ 0.1 V/decade), necessitating costly external compensation for IGZO transistors. For mid‐size mobile applications such as OLED tablets and notebooks, it is important to ensure controllable SS value (≥ 0.3 V/decade). In this study, a conversion mechanism during plasma‐enhanced atomic layer deposition (PEALD) is proposed as a feasible route to control the SS. When a pulse of a diethylzinc (DEZn) precursor is exposed to the M2O3 (M = In or Ga) surface layer, partial conversion of the underlying M2O3 to ZnO is predicted on the basis of density function theory calculations. Notably, significant distinctions between In‐Ga‐Zn (Case I) and In‐Zn‐Ga (Case II) films are observed: Case II exhibits a lower growth rate and larger Ga/In ratio. Case II TFTs with a‐IGZO (subcycle ratio of In:Ga:Zn = 3:1:1) show reasonable SS values (313 mV decade−1) and high mobility (µFE) of 29.3 cm2 Vs−1 (Case I: 84 mV decade−1 and 33.4 cm2 Vs−1). The rationale for Case II's reasonable SS values is discussed, attributing it to the plausible formation of In‐Zn defects, supported by technology computer‐aided design (TCAD) simulations. [ABSTRACT FROM AUTHOR]

Semi‐floating gate field‐effect transistors (SFG‐FETs) based on 2D materials have received much attention due to their unique optoelectronic characteristics, potential applications in near‐memory computing and constructing sensing‐memory‐processing units. Here, the non‐volatile and gate‐controlled multistate photovoltaic response of a WSe2/h‐BN/graphene SFG‐FET is investigated both in experimental and theoretical aspects. Due to the ambipolar carrier transport of WSe2 channel, both electrons and holes can be stored in the graphene floating gate layer, which results in two evident memory windows on the round sweep transfer characteristic curve. Different charge‐stored states of the SFG layer enable the channel to form a lateral junction that can be adjusted by the gate voltage, which leads to the gate‐controlled multistate photovoltaic response. A theoretical model is implemented to explain the memory and the multistate photovoltaic response behaviors in a quasi‐quantitative level. The relationship between the charge‐stored states in the SFG and the photo‐response, as well as its dependence on the gate voltage are systematically analyzed. These research results provide a reliable way for realizing high‐performance multi‐functional photodetectors based on SFG‐FETs and for thorough understanding the complicated optoelectronic behaviors of SFG‐FETs. [ABSTRACT FROM AUTHOR]

An affinity nanobiosensor is presented that uses an aptamer-functionalized Ni3(HITP)2 metal-organic framework (MOF). The device is a field-effect transistor (FET) with the MOF as the conducting channel and is functionalized with an aptamer for specific biomarker recognition. Binding between the aptamer and the target biomarker induces a change in the carrier density in the MOF, resulting in measurable changes in FET characteristics for determination of the biomarker concentration. In situ synthesis of the MOF enhances the adhesion between the MOF film and electrodes to reduce noise during sensor operations while also allowing devices to be potentially mass-producible at a reduced cost. Thanks to the porous structure of the MOF, the aptamer surface density on the MOF is optimized to enhance sensitivity for biomarker measurements. Experimental results show that the MOF nanobiosensor is capable of reliable and sensitive measurements of tumor necrosis factor α (TNF-α) with a responsivity of 0.38 mV/pM and a limit of detection of 8.7 pM, which are 2.7 times the responsivity and 34% of the limit of detection of a comparison aptameric sensor that used manually transferred graphene as a transduction material. [ABSTRACT FROM AUTHOR]

Carbon monoxide (CO) poses significant health risks to humans, impacts the lifespan and efficiency of hydrogen fuel cells as a primary impurity, and is also used for early insulation fault diagnosis in equipment. However, portable CO detectors with low detection limits are still lacking. In this work, we demonstrate a floating-gate field-effect transistor (FG-FET) for a CO gas sensor, in which the carbon nanotubes (CNTs) and tin oxide (SnO2) film are separated by Y2O3 layer and act as channel and sensing layer, respectively. Thanks to the wettability of Y2O3 and the secondary annealing process in the preparation of SnO2 by sol-gel method, the structure not only ensures the stability of the channel but also possesses an optimized interface state with sensing material, protecting the stability of the device and facilitating excellent transmission of the sensing signal. The SnO2/CNT FG-FET sensor achieved effective monitoring of 1 ppb of CO at 150°C, breaking the current CO detection limit. Furthermore, the sensor demonstrates good regular response in the range of 1-30 ppb CO gas concentration. The prepared CO sensor features an extremely low detection limit, ultrahigh sensitivity, and excellent selectivity, providing an idea for high-performance FET gas sensor development. [ABSTRACT FROM AUTHOR]

Numerous efforts have been undertaken to mitigate the Debye screening effect of FET biosensors for achieving higher sensitivity. There are few reports that show sub-femtomolar detection of biomolecules by FET mechanisms but they either suffer from significant background noise or lack robust control. In this aspect, deformed/crumpled graphene has been recently deployed by other researchers for various biomolecule detection like DNA, COVID-19 spike proteins and immunity markers like IL-6 at sub-femtomolar levels. However, the chemical vapor deposition (CVD) approach for graphene fabrication suffers from various surface contamination while the transfer process induces structural defects. In this paper, an alternative fabrication methodology has been proposed where glass substrate has been initially texturized by wet chemical etching through the sacrificial layer of synthesized silver nanoparticles, obtained by annealing of thin silver films leading to solid state dewetting. Graphene has been subsequently deposited by thermal reduction technique from graphene oxide solution. The resulting deformed graphene structure exhibits higher sensor response towards glial fibrillary acidic protein (GFAP) detection with respect to flat graphene owing to the combined effect of reduced Debye screening and higher surface area for receptor immobilization. Additionally, another interesting aspect of the reported work lies in the biomolecule capture by dielectrophoretic (DEP) transport on the crests of the convex surfaces of graphene in a coplanar gated topology structure which has resulted in 10 aM and 28 aM detection limits of GFAP in buffer and undiluted plasma respectively, within 15 min of application of analyte. The detection limit in buffer is almost four decades lower than that documented for GFAP using biosensors which is is expected to pave way for advancing graphene FET based sensors towards ultrasensitive point-of-care diagnosis of GFAP, a biomarker for traumatic brain injury. [ABSTRACT FROM AUTHOR]

A novel highly π-extended heteroarene Benzo[1,2-b:4,5-b']di(naphtho[1,2-d]thiophene) (DBTBT) was used for organic field-effect transistors (OFETs). The mobilities of OFET were greatly improved from 0.34–0.58 cm2V−1s−1 to 1.02–1.75 cm2V−1s−1 by morphology tuning through 2 steps' controlling substrate temperature. More importantly, the OFETs showed a good ambient stability in 30 days measurements. The flexible OFET arrays were prepared on polyethylene terephthalate substrate with octadecyl trichlorosilane modified polymethylsilsesquioxane/polyacrylonitrile gate dielectrics and demonstrated a 100% yield. Further, this flexible cell was used for ultraviolet light detection, which showed good ability of detecting low power light (such as λ = 254 nm, 7 μW/cm2). [ABSTRACT FROM AUTHOR]

The challenge in developing molecule-based electronic materials lies in the uncontrollable or unpredictable nature of their crystal structures, which are crucial for determining both electrical properties and thin-film formability. This review summarizes the findings of a research project focused on the systematic development of crystalline organic semiconductors (OSCs) and organic ferroelectrics by integrating experimental, computational, and data sciences. The key outcomes are as follows: 1) Data Science: We developed a method to identify promising materials from crystal structure databases, leading to the discovery of unique molecule-based ferroelectrics. 2) Computational Science: The origin of high layered crystallinity in π-core – alkyl-chain-linked molecules was clarified based on intermolecular interaction calculations. We proposed a stepwise structure optimization method tailored for layered OSCs. 3) Material Development: We developed various alkylated layered OSCs, which exhibit high mobility, heat resistance, and solubility. We discovered several unique phenomena, including frozen liquid crystal phases, significant polar/antipolar control, and phase control through mixing, leveraging the variability of alkyl chain length. We also developed molecule-based ferroelectrics showing peculiar ferroelectricity, including multiple polarization reversal, competing ferroelectric/antiferroelectric order, and spinner-type configurations with π-skeletons. 4) Advanced Structural Analysis: By combining cryo-electron microscopy and X-ray-free electron laser (XFEL), we enabled crystal structure analysis for ultrathin crystals that are usually difficult to analyse. 5) Device Development: Utilizing the self-organized growth of layered OSCs through solution processes, we developed a method to produce exceptionally clean semiconductor – insulator interfaces, achieving field-effect transistors that show sharp (near theoretical limit) and stable switching at low voltages.

The electronic properties of electrode materials play a crucial role in defining their electrochemical behavior in energy conversion and storage devices. The assembly of van der Waals heterostructures and fabrication into mesoscopic devices enable the dependence of an electrochemical response on electronic properties to be systematically interrogated. Here, we evaluate the effect of charge carrier concentration on heterogeneous electron transfer at few-layer MoS2 electrodes by combining spatially resolved electrochemical measurements with field-effect electrostatic manipulation of band alignment. Steady-state cyclic voltammograms and finite-element simulations reveal a strong modulation of the measured electrochemical response for outer-sphere charge transfer at the electrostatic gate voltage. In addition, spatially resolved voltammetric responses, obtained at a series of locations at the surface of few-layer MoS2, reveal the governing role of in-plane charge transport on the electrochemical behavior of 2D electrodes, especially under conditions of low carrier densities.

Abstract In recent years, graphene field-effect-transistors (GFETs) have demonstrated an outstanding potential for terahertz (THz) photodetection due to their fast response and high-sensitivity. Such features are essential to enable emerging THz applications, including 6G wireless communications, quantum information, bioimaging and security. However, the overall performance of these photodetectors may be utterly compromised by the impact of internal resistances presented in the device, so-called access or parasitic resistances. In this work, we provide a detailed study of the influence of internal device resistances in the photoresponse of high-mobility dual-gate GFET detectors. Such dual-gate architectures allow us to fine tune (decrease) the internal resistance of the device by an order of magnitude and consequently demonstrate an improved responsivity and noise-equivalent-power values of the photodetector, respectively. Our results can be well understood by a series resistance model, as shown by the excellent agreement found between the experimental data and theoretical calculations. These findings are therefore relevant to understand and improve the overall performance of existing high-mobility graphene photodetectors. Graphical Abstract

Abstract Widespread distribution of porcine epidemic diarrhea virus (PEDV) has led to catastrophic losses to the global pig farming industry. As a result, there is an urgent need for rapid, sensitive and accurate tests for PEDV to enable timely and effective interventions. In the present study, we develop and validate a floating gate carbon nanotubes field-effect transistor (FG CNT-FET)-based portable immunosensor for rapid identification of PEDV in a sensitive and accurate manner. To improve the affinity, a unique PEDV spike protein-specific monoclonal antibody is prepared by purification, and subsequently modified on FG CNT-FET sensor to recognize PEDV. The developed FET biosensor enables highly sensitive detection (LoD: 8.1 fg/mL and 100.14 TCID50/mL for recombinant spike proteins and PEDV, respectively), as well as satisfactory specificity. Notably, an integrated portable platform consisting of a pluggable FG CNT-FET chip and a portable device can discriminate PEDV positive from negative samples and even identify PEDV and porcine deltacoronavirus within 1 min with 100% accuracy. The portable sensing platform offers the capability to quickly, sensitively and accurately identify PEDV, which further points to a possibility of point of care (POC) applications of large-scale surveillance in pig breeding facilities.

Bottom-up assembled nanomaterials and nanostructures allow for the studies of rich and unprecedented quantum-related and mesoscopic transport phenomena. However, it can be difficult to quantify the correlations between the geometrical or structural parameters obtained from advanced microscopy and measured electrical characteristics when they are made into macroscopic devices. Here, we propose a strategy to connect the nanomaterial morphologies and the device performance through a Monte Carlo device model and apply it to understand the scaling trends of bottom-up synthesized armchair graphene nanoribbon (GNR) transistors. A new nanofabrication process is developed for GNR transistors with channel length down to 7 nm. The impacts of the GNR spatial distributions and the device geometries on the device performance are investigated systematically through comparison of experimental data with the model. Through this study, challenges and opportunities of transistor technologies based on bottom-up synthesized GNRs are pinpointed, paving the way to the further improvement of the GNR device performance for future transistor technology nodes.

Field-effect transistor (FET)-based biosensors exhibit excellent performance characteristics such as small size, ease of mass production, high versatility, and comparably low cost. In recent years, numerous FET biosensors based on various nanomaterials including silicon nanowires, carbon nanotubes, graphene, and transition metal dichalcogenides have been developed to detect a wide range of biomarkers that play a crucial role in early disease diagnosis, therapeutic monitoring and prognostic assessment. This review provides an overview of the structure, working principle, functionalization strategies and detection factors associated with FET biosensors based on diverse nanomaterials. Additionally, this paper discusses the applications of these diagnostic devices for detecting clinically relevant biomarkers such as nucleic acids, metabolites, proteins, cancer biomarkers, and hormones among others. The concluding section provides a comprehensive overview of the numerous challenges encountered in the widespread implementation of nanomaterial-based FET biosensors for clinical detection, while also presenting the future prospects for these biosensors based on current research advancements. Field-effect transistor (FET)-based biosensors exhibit excellent performance characteristics such as small size, ease of mass production, high versatility, and comparably low cost. In recent years, numerous FET biosensors based on various nanomaterials have been developed to detect a wide range of biomarkers that play a crucial role in early disease diagnosis, therapeutic monitoring and prognostic assessment. This review provides an overview of the structure, working principle, functionalization strategies and detection factors associated with field-effect transistor biosensors based on diverse nanomaterials. Additionally, this article discusses the applications of these diagnostic devices for detecting clinically relevant biomarkers such as nucleic acids, metabolites, proteins, cancer biomarkers, hormones among others. [ABSTRACT FROM AUTHOR]

The remarkable successes of graphene have sparked increasing interest in elemental two‐dimensional (2D) materials, also referred to as Xenes. Due to their chemical simplicity and appealing physiochemical properties, Xenes have shown particular potential for numerous (opto) electronic, iontronic, and energy applications. Among them, layered α‐phase tellurene has demonstrated the most promise, thanks to the recent successes in the chemical synthesis of highly crystalline 2D tellurene. However, the general electronic and electrochemical properties of tellurene in electrolyte systems remain ambiguous, hindering their further development. In this work, we studied the electrostatic gating, electrocatalysis, and electrochemical stability of tellurene in electrolyte systems. Our results show that tellurene obtained from both hydrothermal and chemical vapor deposition methods, two mainstream synthetic approaches for Xenes, demonstrates thickness‐dependent ambipolar transport with high hole mobility and stability in both aqueous electrolytes and ionic liquids. More importantly, the electrochemical properties of tellurene are investigated via the emerging on‐chip electrochemistry. Pristine tellurene demonstrates hydrogen evolution reaction with low Tafel slopes and remarkable electrochemical stability in acidic electrolytes over a large potential window. Our study provides a comprehensive understanding of the iontronic and electrochemical properties of tellurene, paving the way for the broad adoption of Xenes in sensors, synaptic devices, and electrocatalysis. [ABSTRACT FROM AUTHOR]

The rapid development in information technologies necessitates rapid advancements of their supporting hardware. In particular, new computing paradigms are needed to overcome the bottleneck of traditional von Neumann architecture. Bottom‐up innovation, especially at the materials and devices level, has the potential to disrupt existing technologies through their emergent phenomena. As a new type of conceptual device, 2D ferroelectric field‐effect transistor (FeFET) is highly sought after due to its potential integration with modern semiconductor processes. Its low power consumption, area efficiency, and ultra‐fast operation provide an extra edge over traditional technologies. This review highlights recent developments in 2D FeFET, covering their device construction, working mechanisms, 2D ferroelectric polarization mechanism, multi‐functional applications and prospects. In particular, the combination of 2D semiconductor and ferroelectric dielectric materials for multi‐functionality applications is discussed. This includes non‐volatile memories (NVM), neural network computing, non‐volatile logic operation, and photodetectors. As a novel device platform, 2D semiconductor and ferroelectric interfaces are bestowed with a plethora of emergent physical mechanisms and applications. [ABSTRACT FROM AUTHOR]

Graphene with an atomically thin structure is considered to be a highly sensitive transducer capable of converting diverse external stimuli into measurable electrical signals. The generated signals, such as current and resistance, can be extracted through electrical contact to graphene. Conventional methods for contact formation are usually based on physical deposition of conductive materials on the target graphene. Here, we propose a method for in situ chemical synthesis of electrical contacts to graphene as an alternative approach that complements conventional physical methods. CO2 laser irradiation on a polyimide film with monolayer graphene on top can convert the polyimide surface to conductive electrodes of laser-induced graphene (LIG) that electrically connect to the existing graphene channel. Laser-scribing conditions, such as the power and scan rate, can modulate the contact resistance of the LIG–graphene junction. Various arbitrary shapes of in situ LIG contacts can be scribed to the direct writing ability of the laser. The proposed in situ LIG contact method can be extended to other carbon nanomaterials, such as carbon nanotubes and PEDOT:PSS. As a proof of concept of the in situ LIG contacts to graphene for electronic device applications, graphene field-effect transistors were demonstrated on a graphene-supported polyimide substrate with LIG–graphene junctions as source/drain electrodes. Our approach will pave the way for the simple and low-cost fabrication of versatile graphene electronic devices by utilizing the existing LIG technology specialized for energy devices and sensors. [ABSTRACT FROM AUTHOR]

FET-based charge carrier mobility measurements in low-conductivity materials, as well as semiconductor materials with a high density of trapping states, such as nanocrystals and polycrystalline films, are highly distorted due to charge accumulation in the transistor structure. In this work, a comparative study of the measurement of the mobility of charge carrier in conductive polymers, nanocrystals and polycrystalline films, using the analysis of output and transfer characteristics, was carried out. It is shown that using output characteristics instead of transfer characteristics for calculating the charge carrier mobility helps to avoid a systematic error in the measurement. [ABSTRACT FROM AUTHOR]

Graphene-based materials are actively being investigated as sensing elements for the detection of different analytes. Both graphene grown by chemical vapor deposition (CVD) and graphene oxide (GO) produced by the modified Hummers' method are actively used in the development of biosensors. The production costs of CVD graphene- and GO-based sensors are similar; however, the question remains regarding the most efficient graphene-based material for the construction of point-of-care diagnostic devices. To this end, in this work, we compare CVD graphene aptasensors with the aptasensors based on reduced GO (rGO) for their capabilities in the detection of NT-proBNP, which serves as the gold standard biomarker for heart failure. Both types of aptasensors were developed using commercial gold interdigitated electrodes (IDEs) with either CVD graphene or GO formed on top as a channel of liquid-gated field-effect transistor (FET), yielding GFET and rGO-FET sensors, respectively. The functional properties of the two types of aptasensors were compared. Both demonstrate good dynamic range from 10 fg/mL to 100 pg/mL. The limit of detection for NT-proBNP in artificial saliva was 100 fg/mL and 1 pg/mL for rGO-FET- and GFET-based aptasensors, respectively. While CVD GFET demonstrates less variations in parameters, higher sensitivity was demonstrated by the rGO-FET due to its higher roughness and larger bandgap. The demonstrated low cost and scalability of technology for both types of graphene-based aptasensors may be applicable for the development of different graphene-based biosensors for rapid, stable, on-site, and highly sensitive detection of diverse biochemical markers. [ABSTRACT FROM AUTHOR]

In this study, the development and characterization of 2D ferroelectric field‐effect transistor (2D FeFET) devices are presented, utilizing nanoscale ferroelectric HfZrO2 (HZO) and 2D semiconductors. The fabricated device demonstrated multi‐level data storage capabilities. It successfully emulated essential biological characteristics, including excitatory/inhibitory postsynaptic currents (EPSC/IPSC), Pair‐Pulse Facilitation (PPF), and Spike‐Timing Dependent Plasticity (STDP). Extensive endurance tests ensured robust stability (107 switching cycles, 105 s (extrapolated to 10 years)), excellent linearity, and high Gmax/Gmin ratio (>105), all of which are essential for realizing multi‐level data states (>7‐bit operation). Beyond mimicking synaptic functionalities, the device achieved a pattern recognition accuracy of ≈94% on the Modified National Institute of Standards and Technology (MNIST) handwritten dataset when incorporated into a neural network, demonstrating its potential as an effective component in neuromorphic systems. The successful implementation of the 2D FeFET device paves the way for the development of high‐efficiency, ultralow‐power neuromorphic hardware which is in sub‐femtojoule (48 aJ/spike) and fast response (1 µs), which is 104 folds faster than human synapse (≈10 ms). The results of the research underline the potential of nanoscale ferroelectric and 2D materials in building the next generation of artificial intelligence technologies. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials hold great promise for future applications, notably their use as biosensing channels in the field-effect transistor (FET) configuration. On the road to implementing one of the most widely used 2D materials, graphene, in FETs for biosensing, key issues such as operation conditions, sensitivity, selectivity, reportability, and economic viability have to be considered and addressed correctly. As the detection of bioreceptor-analyte binding events using a graphene-based FET (gFET) biosensor transducer is due to either graphene doping and/or electrostatic gating effects with resulting modulation of the electrical transistor characteristics, the gFET configuration as well as the surface ligands to be used have an important influence on the sensor performance. While the use of back-gating still grabs attention among the sensor community, top-gated and liquid-gated versions have started to dominate this area. The latest efforts on gFET designs for the sensing of nucleic acids, proteins and virus particles in different biofluids are presented herewith, highlighting the strategies presently engaged around gFET design and choosing the right bioreceptor for relevant biomarkers. [ABSTRACT FROM AUTHOR]

In this study, we demonstrate the generation and storage of random voltage values using a ring oscillator consisting of feedback field-effect transistors (FBFETs). This innovative approach utilizes the logic-in-memory function of FBFETs to extract continuous output voltages from oscillatory cycles. The ring oscillator exhibited uniform probability distributions of 51.6% for logic 0 and 48.4% for logic 1. The generation of analog voltages provides binary random variables that are stored for over 5000 s. This demonstrates the potential of the ring oscillator in advanced physical functions and true random number generator technologies. [ABSTRACT FROM AUTHOR]

Achieving a low resistance contact is essential for developing two-dimensional (2D) material-based field-effect transistors (FETs). While n-type contacts to 2D semiconductors have been studied, understanding and designs for p-type contacts to 2D semiconductors remain very limited. In this study, we propose and computationally explore three strategies to improve the contact resistance in p-type 2D FETs, which remains a critical bottleneck of 2D logic technology, through the engineering of van der Waals (vdW) material heterostructures: (i) intercalating a graphene layer between a high-work-function metal and 2D semiconductor, which can result in low contact resistance of ~ 60 Ω μm for the graphene-intercalated contact between a high-work-function metal and WSe2 semiconductor; (ii) engineering the atomic stacking order between a vdW metal and 2D semiconductor, which can result in contact resistance of ~ 50 Ω μm; (iii) sandwiching the 2D layered semiconductor between vdW metals from both sides, which can further reduce the contact resistance to ~ 47 Ω μm and ~ 36 Ω μm for cases (i) and (ii), respectively. Experimental fabrication and characterization illustrate the feasibility of structural engineering of contacts. The above structural designs can lead to significantly reduced metal-induced gap states (MIGS) and low barrier height for holes, resulting in low contact resistance. They are also naturally compatible with the gate-all-around (GAA) transistor structure. In addition to contact materials selection, vdW structural design offers an alternative approach for achieving low contact resistance to p-type 2D FETs. [ABSTRACT FROM AUTHOR]

Abstract Since two‐dimensionalal (2D) materials have distinct chemical and physical properties, they are widely used in various sectors of modern technologies. In the domain of diagnostic biodevices, particularly for point‐of‐care (PoC) biomedical diagnostics, 2D‐based field‐effect transistor biosensors (bio‐FETs) demonstrate substantial potential. Here, in this review article, the operational mechanisms and detection capabilities of biosensing devices utilizing graphene, transition metal dichalcogenides (TMDCs), black phosphorus, and other 2D materials are addressed in detail. The incorporation of these materials into FET‐based biosensors offers significant advantages, including low detection limits (LOD), real‐time monitoring, label‐free diagnosis, and exceptional selectivity. The review also highlights the diverse applications of these biosensors, ranging from conventional to wearable devices, underscoring the versatility of 2D material‐based FET devices. Additionally, the review provides a comprehensive assessment of the limitations and challenges faced by these devices, along with insights into future prospects and advancements. Notably, a detailed comparison of FET‐based biosensors is tabulated along with various other biosensing platforms and their working mechanisms. Ultimately, this review aims to stimulate further research and innovation in this field while educating the scientific community about the latest advancements in 2D materials‐based biosensors.

Epitaxially-fused superlattices of colloidal quantum dots (QD epi-SLs) may exhibit electronic minibands and high-mobility charge transport, but electrical measurements of epi-SLs have been limited to large-area, polycrystalline samples in which superlattice grain boundaries and intragrain defects suppress/obscure miniband effects. Systematic measurements of charge transport in individual, highly-ordered epi-SL grains would facilitate the study of minibands in QD films. Here, we demonstrate the air-free fabrication of microscale field-effect transistors (μ-FETs) with channels consisting of single PbSe QD epi-SL grains (2-7 μm channel dimensions) and analyze charge transport in these single-grain devices. The eight devices studied show p-channel or ambipolar transport with a hole mobility as high as 3.5 cm2 V-1 s-1 at 290 K and 6.5 cm2 V-1 s-1 at 170-220 K, one order of magnitude larger than that of previous QD solids. The mobility peaks at 150-220 K, but device hysteresis at higher temperatures makes the true mobility-temperature curve uncertain and evidence for miniband transport inconclusive.