Field-effect Transistor Configuration Research Articles

Study of graphene p-n junctions formed by the electrostatic modification of the SiO2 substrate.

We study the transport properties of mm-scale CVD graphene p-n junctions, which are formed in a single gated graphene field effect transistor configuration. Here, an electrical-stressing-voltage technique served to modify the electrostatic potential in the SiO2/Si substrate and create the p-n junction. We examine the transport characteristics about the Dirac points that are localized in the perturbed and unperturbed regions in the graphene channel and note the quantitative differences in the Hall effect between the perturbed and unperturbed regions. The results also show that the longitudinal resistance is highly sensitive to the external magnetic field when the Hall bar device operates as a p-n junction.

High-responsivity, high-detectivity, broadband infrared photodetector based on MoS2/BP/MoS2 junction field-effect transistor

Sensitivity stands as a critical figure of merit in assessing the performance of a photodetector and can be characterized by two distinct parameters: responsivity or detectivity. Simultaneous optimization of these two parameters is essential to ensure the applicability of a single detector across various scenarios, yet it remains a persistent challenge for mid-infrared photodetector. Here, we demonstrate that the construction of a photoconductive detector based on a MoS2/BP/MoS2 npn junction field-effect transistor configuration can effectively balance the tradeoffs between photoresponsivity and detectivity. In this device, the black phosphorus layer serves as the channel, while the top and bottom MoS2 layers act as photogates to boost the photocurrent. Consequently, a high-performance room-temperature-operating mid-infrared photodetector with a responsivity and detectivity reaching 9.04 A W−1 and 5.36 × 109 cm Hz1/2 W−1 (1550 nm), and 7.25 A W−1 and 4.29 × 109 cm Hz1/2 W−1 (3600 nm) is achieved. Our study provides an alternative structural design, enabling the applications of mid-infrared photodetectors across multiple scenarios.

Non-covalent planarizing interactions yield highly ordered and thermotropic liquid crystalline conjugated polymers.

Controlling the multi-level assembly and morphological properties of conjugated polymers through structural manipulation has contributed significantly to the advancement of organic electronics. In this work, a redox active conjugated polymer, TPT-TT, composed of alternating 1,4-(2-thienyl)-2,5-dialkoxyphenylene (TPT) and thienothiophene (TT) units is reported with non-covalent intramolecular S⋯O and S⋯H-C interactions that induce controlled main-chain planarity and solid-state order. As confirmed by density functional theory (DFT) calculations, these intramolecular interactions influence the main chain conformation, promoting backbone planarization, while still allowing dihedral rotations at higher kinetic energies (higher temperature), and give rise to temperature-dependent aggregation properties. Thermotropic liquid crystalline (LC) behavior is confirmed by cross-polarized optical microscopy (CPOM) and closely correlated with multiple thermal transitions observed by differential scanning calorimetry (DSC). This LC behavior allows us to develop and utilize a thermal annealing treatment that results in thin films with notable long-range order, as shown by grazing-incidence X-ray diffraction (GIXD). Specifically, we identified a first LC phase, ranging from 218 °C to 107 °C, as a nematic phase featuring preferential face-on π-π stacking and edge-on lamellar stacking exhibiting a large extent of disorder and broad orientation distribution. A second LC phase is observed from 107 °C to 48 °C, as a smectic A phase featuring sharp, highly ordered out-of-plane lamellar stacking features and sharp tilted backbone stacking peaks, while the structure of a third LC phase with a transition at 48 °C remains unclear, but resembles that of the solid state at ambient temperature. Furthermore, the significance of thermal annealing is evident in the ∼3-fold enhancement of the electrical conductivity of ferric tosylate-doped annealed films reaching 55 S cm-1. More importantly, thermally annealed TPT-TT films exhibit both a narrow distribution of charge-carrier mobilities (1.4 ± 0.1) × 10-2 cm2 V-1 s-1 along with a remarkable device yield of 100% in an organic field-effect transistor (OFET) configuration. This molecular design approach to obtain highly ordered conjugated polymers in the solid state affords a deeper understanding of how intramolecular interactions and repeat-unit symmetry impact liquid crystallinity, solution aggregation, solution to solid-state transformation, solid-state morphology, and ultimately device applications.

Advances in graphene-based electrochemical biosensors for on-site pesticide detection

The infiltration of pesticides into agricultural soils has emerged as a critical concern, posing substantial threats to the agriculture industry due to soil and water contamination. The detection of these contaminants is critical towards implementing effective environmental remediation strategies and achieving ecosystem sustainability. Electrochemical sensor technology has been demonstrated to be highly promising for this application. Graphene and its derivatives and composites are widely used as modifying materials in these sensors to enhance their analytical performance. This short review discusses recent progress in the application of graphene-based electrochemical sensors in three-electrode and field-effect transistor configurations for the detection of pesticides posing significant risks to the agricultural sector. It highlights the growing significance of graphene-based sensors in mitigating pesticide-related environmental challenges and underscores their role in ensuring the health and diversity of agricultural ecosystems.

Molecularly Imprinted Polymer Interface on Screen-Printed ZnO Nanorod Field Effect Transistors for Serotonin Detection in Clinical Samples.

Ultrasensitive detection of serotonin is crucial for the early diagnosis of several diseases like Parkinson's and Alzheimer's. Most of the existing detection strategies are still not suitable for sensitive point-of-care applications. This study presents direct molecular imprinting of serotonin on the surface of three-dimensional zinc oxide (ZnO) nanorod devices connected in a field effect transistor (FET) configuration to achieve ultrasensitive, real-time, and rapid detection with a convenient and affordable approach, which has significant potential for translation to clinical settings. This strategy has enabled pushing the detection limit to 0.1 fM in a physiological analyte in real time with screen-printed electrodes, thereby resulting in the convenient batch fabrication of sensors for clinical validation. The response of the sensor with the clinical sample has been correlated with that of the gold standard and has been observed to be statistically similar.

Two-Dimensional Silver-Chalcogenolate-Based Cluster-Assembled Material: A p-type Semiconductor.

We have synthesized and characterized a new two-dimensional honeycomb architecture resembling a single-layer of atomically precise silver cluster-assembled material (CAM), [Ag12(StBu)6(CF3COO)6(4,4'-azopyridine)3] (Ag12-azo-bpy). The interlayer noncovalent van der Waals interactions within the single-crystals were successfully disrupted, leading to the creation of this unique structure. The optimized Ag12-azo-bpy CAM demonstrates a valence band that is localized on the Ag12 cluster node situated near the Fermi energy level. This localization induces electron injection from the linker to the cluster node, facilitating efficient charge transportation along the plane. Exploiting this single-layer structure as a distinctive platform for p-type channel material, it was employed in a field-effect transistor configuration. Remarkably, the transistor exhibits a high hole mobility of 1.215 cm2 V-1 s-1 and an impressive ON/OFF current ratio of ∼4500 at room-temperature.

Unlocking the Potential of Field Effect Transistor (FET) Biosensors: A Perspective on Methodological Advances in Computational and Molecular Biology

AbstractField‐effect transistor (FET)‐based sensors are increasingly gaining relevance in diagnostic, healthcare, and environmental monitoring applications. A FET operates by transducing chemical interactions between a surface‐immobilized bioreceptor and the target analyte into a detectable electrical signal. FET biosensors can detect and monitor molecules (i.e., biomarkers, small molecules, viruses, bacterias) present in liquid samples, making a “liquid gate” configuration of FETs the most suitable approach. However, this FET architecture presents dimensional constraints that affect bioreceptors’ stability and immobilization in the liquid phase. To overcome these limitations, herein, a combination of computational and molecular biology techniques for improving bioreceptors' applicability in biosensing is proposed. This results in the optimized and problem‐tailored protein receptors for specific FET biosensors applications, thus enhancing their overall performance. The interplay between the computational and experimental approaches will represent a ground‐breaking solution for the development of next‐generation biosensors.

Field-effect bulk mobilities in polymer semiconductor films measured by sourcemeters.

Semiconducting polymers inherently exhibit polydispersity in terms of molecular structure and microscopic morphology, which often results in a broad distribution of energy levels for localized electronic states. Therefore, the bulk charge mobility strongly depends on the free charge density. In this study, we propose a method to measure the charge-density-dependent bulk mobility of conjugated polymer films with widely spread localized states using a conventional field-effect transistor configuration. The gate-induced variation of bulk charge density typically ranges within ±1018cm-3; however, this range depends significantly on the energetic dispersion width of localized states. The field-effect bulk mobility and field-effect mobility near the semiconductor-dielectric interface along with their dependence on charge density can be simultaneously extracted from the transistor characteristics using various gate voltage ranges.

Metal Halide Perovskite Photo-Field-Effect Transistors with Chiral Selectivity.

Organic-inorganic (hybrid) metal halide perovskites (MHPs) incorporating chiral organic ligand molecules are naturally sensitive to left- and right-handed circular polarized light, potentially enabling selective circular polarized photodetection. Here, the photoresponses in chiral MHP polycrystalline thin films made of ((S)-(-)-α-methyl benzylamine)2PbI4 and ((R)-(+)-α-methyl benzylamine)2PbI4, denoted as (S-MBA)2 PbI4 and (R-MBA)2PbI4, respectively, are investigated by employing a thin-film field-effect transistor (FET) configuration. The left-hand-sensitive films made of (S-MBA)2PbI4 perovskite show higher photocurrent under left-handed circularly polarized (LCP) light than under right-handed circularly polarized (RCP) illumination under otherwise identical conditions. Conversely, the right-hand-sensitive films made of (R-MBA)2PbI4 are more sensitive to RCP than LCP illumination over a wide temperature range of 77-300 K. Furthermore, based on FET measurements, we found evidence of two different carrier transport mechanisms with two distinct activation energies in the 77-260 and 280-300 K temperature ranges, respectively. In the former temperature range, shallow traps are dominant in the perovskite film, which are filled by thermally activated carriers with increasing temperature; in the latter temperature range, deep traps with one order of magnitude larger activation energy dominate. Both types of chiral MHPs show intrinsic p-type carrier transport behavior regardless of the handedness (S or R) of these materials. The optimal carrier mobility for both handedness of material is around (2.7 ± 0.2) × 10-7 cm2 V-1 s-1 at 270-280 K, which is two magnitudes larger than those reported in nonchiral perovskite MAPbI3 polycrystalline thin films. These findings suggest that chiral MHPs can be an excellent candidate for selective circular polarized photodetection applications, without additional polarizing optical components, enabling simplified construction of detection systems.

Sensitivity of Al-Doped Zinc-Oxide Extended Gate Field Effect Transistors to Low-Dose X-ray Radiation

Herein, we investigated the applicability of thick film and bulk disk forms of aluminum-doped zinc oxide (AZO) for low-dose X-ray radiation dosimetry using the extended gate field effect transistor (EGFET) configuration. The samples were fabricated using the chemical bath deposition (CBD) technique. A thick film of AZO was deposited on a glass substrate, while the bulk disk form was prepared by pressing the collected powders. The prepared samples were characterized via X-ray diffraction (XRD) and field emission scanning electron microscope (FESEM) to determine the crystallinity and surface morphology. The analyses show that the samples are crystalline and comprise nanosheets of varying sizes. The EGFET devices were exposed to different X-ray radiation doses, then characterized by measuring the I-V characteristics pre- and post-irradiation. The measurements revealed an increase in the values of drain-source currents with radiation doses. To study the detection efficiency of the device, various bias voltages were also tested for the linear and saturation regimes. Performance parameters of the devices, such as sensitivity to X-radiation exposure and different gate bias voltage, were found to depend highly on the device geometry. The bulk disk type appears to be more radiation-sensitive than the AZO thick film. Furthermore, boosting the bias voltage increased the sensitivity of both devices.

A highly stable room temperature titania nanostructure-based thin film transistor (TFT) alcohol sensor

The present study is concerned with the room temperature field-induced alcohol sensitivity of nanostructured TiO2 thin films in field-effect transistor (TFT) configurations.

Self-powered high-sensitivity all-in-one vertical tribo-transistor device for multi-sensing-memory-computing

Devices with sensing-memory-computing capability for the detection, recognition and memorization of real time sensory information could simplify data conversion, transmission, storage, and operations between different blocks in conventional chips, which are invaluable and sought-after to offer critical benefits of accomplishing diverse functions, simple design, and efficient computing simultaneously in the internet of things (IOT) era. Here, we develop a self-powered vertical tribo-transistor (VTT) based on MXenes for multi-sensing-memory-computing function and multi-task emotion recognition, which integrates triboelectric nanogenerator (TENG) and transistor in a single device with the simple configuration of vertical organic field effect transistor (VOFET). The tribo-potential is found to be able to tune ionic migration in insulating layer and Schottky barrier height at the MXene/semiconductor interface, and thus modulate the conductive channel between MXene and drain electrode. Meanwhile, the sensing sensitivity can be significantly improved by 711 times over the single TENG device, and the VTT exhibits excellent multi-sensing-memory-computing function. Importantly, based on this function, the multi-sensing integration and multi-model emotion recognition are constructed, which improves the emotion recognition accuracy up to 94.05% with reliability. This simple structure and self-powered VTT device exhibits high sensitivity, high efficiency and high accuracy, which provides application prospects in future human-mechanical interaction, IOT and high-level intelligence.

Conductivity inversion of methyl viologen-modified random networks of single-walled carbon nanotubes

One of the challenges of using carbon nanotubes electronics is achieving precise control of the conductivity type. It is particularly difficult to obtain the n-type conductive nanotubes. One of the most common methods of CNTs modification allowing to change their conductivity type is chemical functionalization. This paper describes the results of studies on non-covalent modification of randomly oriented single-walled carbon nanotubes (SWCNT) layers with methyl viologen (MV), which allows for the change of the conductivity of SWCNT from p- to n-type. The properties of pristine and MV-modified SWCNT have been compared using Scanning Electron Microscopy, Raman spectroscopy, and X-ray Photoelectron Spectroscopy. The SWCNT conductivity type change was confirmed by photo-conductance under ultraviolet illumination and measurements in the field effect transistor configuration.

Field effect transistor‐based tactile sensors: From sensor configurations to advanced applications

AbstractThe past several decades have witnessed great progress in high‐performance field effect transistors (FET) as one of the most important electronic components. At the same time, due to their intrinsic advantages, such as multiparameter accessibility, excellent electric signal amplification function, and ease of large‐scale manufacturing, FET as tactile sensors for flexible wearable devices, artificial intelligence, Internet of Things, and other fields to perceive external stimuli has also attracted great attention and become a significant field of general concern. More importantly, FET has a unique three‐terminal structure, which enables its different components to detect external mechanics through different sensing mechanisms. On one hand, it provides an important platform to shed deep insights into the underlying mechanisms of the tactile sensors. On the other hand, these properties could in turn endow excellent components for the construction of tactile matrix sensor arrays with high quality. With special emphasis on the configuration of FETs, this review classified and summarized structure‐optimized FET tactile sensors with gate, dielectric layer, semiconductor layer, and source/drain electrodes as sensing active components, respectively. The working principles and the state‐of‐the‐art protocols in terms of high‐performance tactile sensors are detail discussed and highlighted, the innovative pixel distribution and integration analysis of the transistor sensor matrix array concerning flexible electronics are also introduced. We hope that the introduction of this review can provide some inspiration for future researchers to design and fabricate high‐performance FET‐based tactile sensor chips for flexible electronics and other fields.image

Bimetallic Alloys b-AsxP1-x at High Concentration Differences: Ideal for Photonic Devices.

Black arsenic phosphorus (b-AsxP1-x) is expected to be one of the primary materials for future photonic devices. However, the x-factor is randomly estimated and applied in photonic devices in current studies, rather than systematically analyzing it for a comprehensive understanding. Herein, AsxP1-x switches from a direct band gap semiconductor to an indirect band gap one at x = 0.75. AsxP1-x at x ≤ 0.25 is capable of broadband absorption, while b-AsxP1-x at x ≥ 0.75 can only absorb at specific wavelengths in the perspective of the electron energy transition. Additionally, the optoelectronic response of the integral field-effect transistor configurations constructed with b-AsxP1-x is investigated systematically as a photodetector device. The photonic response characteristics show high polarization sensitivity at x ≥ 0.75, but a typical circuit system signal at x ≤ 0.25. These results suggest that b-AsxP1-x with high concentration differences is a perfect candidate for photonic material.

TETHYS: A simulation tool for graphene hydrodynamic models

We present a simulation tool, TETHYS (i.e., Two-dimensional Emitter of THz, Hydrodynamic Simulation), developed with the aim of studying hydrodynamic models for electronic transport in graphene, being particularly tailored for the simulation of the configuration of top-gated graphene field-effect transistors (GFET) near room temperature. We present the model governing the system and briefly discuss its validity and physical parameters; then we proceed to discuss the algorithms and numerical methods used in its implementation, namely, two-step Richtmyer and weighted forward-time centred-space schemes, which address the hyperbolic and parabolic parts of the model, respectively. An abridged usage guide and description of the output are also provided, as well as two illustrative simulation cases: the Dyakonov–Shur instability and the boundary layer of pulsatile electric flow. The simulation program here brought forward is uncomplicated and lightweight, yet robust and accurate, having a wide variety of applicable scenarios and configurations to explore. Program summaryProgram Title: TETHYSCPC Library link to program files:https://doi.org/10.17632/s28zwgpnpw.1Developer's repository link:github.com/pcosme/TETHYS-Graphene-Hydrodynamic-SimulationLicensing provisions: MITProgramming language: C++Nature of problem: The main objective of this code is to simulate and analyse the electronic conduction on gated (mono-layer) graphene resorting to a hydrodynamic model [1]. Note that, given the Dirac-like dispersion relation of such material, the mass of the carriers is ill-defined; and, in fact, the mass of the fluid element varies with the number density, which sets this system apart from other 2D electron fluids [2]. The model assumes enough doping, so that only one kind of carriers, electrons or holes, participates in the dynamics of the system. Moreover, the simulation is limited to the fully degenerate limit.Thus, these assumptions correspond to the situation of a regular GFET and this application can be used to explore atypical phenomena arising from the effects of uniform and static magnetic field and Hall viscosity, and even spatially non-uniform gate capacitance.Furthermore, this software was designed with the intent of examining unstable nonlinear modes that may lead to the emission of radiation in the THz range [3].Solution method: The fluid equations (continuity, momentum and energy transport) are solved with a split-operator technique, with a second-order finite-volume Lax–Wendroff method [4] for the hyperbolic part and a forward-time centred-space of second-order stencil to tackle the dissipation and heat diffusion. That is, the fields of number density, velocity/momentum density and temperature are calculated over a rectangular grid and stored at a HDF5 file for further processing.Then, the obtained field profiles are used to compute the relevant macroscopic electronic quantities, such as drain-to-source current or dissipated power, and, particularly, the electric dipole moment of the charge distribution, which can subsequently be used to characterize the emitted far-field radiation. This is mostly done by numerically integrating the data in space, with the necessary time derivatives obtained by Gaussian convolution.

Surface-potential-modulated piezoresistive effect of core–shell 3C-SiC nanowires

The effect of surface potential on the carrier mobility and piezoresistance of core–shell silicon carbide nanowires (SiC NWs) was investigated to realize small and sensitive SiC-microelectromechanical systems sensors. The p-type cubic crystalline SiC (3C-SiC) NWs were synthesized via the vapor–liquid–solid method and coated with silicon dioxide (SiO2) or aluminum oxide (Al2O3) dielectric shells to form core–shell structured NWs with different surface potentials. Four-point bending devices (FBDs) with a field-effect transistor (FET) configuration integrating a single core–shell 3C-SiC NW as the FET channel were fabricated to apply an additional electric field and strain to the core–shell 3C-SiC NWs. The fixed oxide charge densities of the SiO2 and Al2O3 shells showed positive and negative values, respectively, which were equivalent to electric fields of the order of several hundred thousand volt per centimeter in absolute values. In the core–shell 3C-SiC NWs with originally low impurity concentrations, the electric field induced by the fixed oxide charge of the shells can determine not only the electrical conduction but also the charge carriers in the NWs. Bending tests using the FBDs showed that the piezoresistive effect of the SiO2-coated NW was almost the same as that of the as-grown 3C-SiC NW reported previously, regardless of the gate voltage, whereas that of the Al2O3-coated NW was considerably enhanced at negative gate voltages. The enhancement of the piezoresistive effect was attributed to the piezo-pinch effect, which was more pronounced in the NW, where the carrier density at the core–shell interface is enhanced by the electric field of the dielectric.

Comparison of electrical and optical transduction modes of DNA-wrapped SWCNT nanosensors for the reversible detection of neurotransmitters.

In this study, we compare the electrical and optical signal transduction of nanoscale biosensors based on single-walled carbon nanotubes (SWCNTs). Solution processable single-stranded (ss) DNA-wrapped SWCNTs were used for the fabrication of the distinct sensors. For electrical measurements, SWCNTs were assembled from solution onto pre-patterned electrodes by electric-field-assisted assembly in field-effect transistor (FET) configuration. A combination of micro- and nano-fabrication and microfluidics enabled the integration into a sensing platform that allowed real-time and reversible detection. For optical measurements, the near-infrared (NIR) fluorescence of the SWCNTs was acquired directly from solution. The detection of important biomolecules was investigated in high-ionic strength solution (0.5xPBS). Increase in fluorescence intensities correlated with a decrease in the SWCNTs electrical current and enabled detection of the important biomolecules dopamine, epinephrine, and ascorbic acid. For riboflavin, however, a decrease in the fluorescence intensity could not be associated with changes in the SWCNTs electrical current, which indicates a different sensing mechanism. The combination of SWCNT-based electrical and optical transduction holds great potential for selective detection of biomarkers in next generation portable diagnostic assays.

Radio-Frequency C - V Measurements with Subattofarad Sensitivity

We demonstrate the use of radio-frequency (rf) resonators to measure the capacitance of nano-scale semiconducting devices in field-effect transistor configurations. The rf resonator is attached to the gate or the lead of the device. Consequently, tuning the carrier density in the conducting channel of the device affects the resonance frequency, quantitatively reflecting its capacitance. We test the measurement method on InSb and InAs nanowires at dilution-refrigerator temperatures. The measured capacitances are consistent with those inferred from the periodicity of the Coulomb blockade of quantum dots realized in the same devices. In an implementation of the resonator using an off-chip superconducting spiral inductor we find sensitivity values reaching down to 75~zF/$\sqHz$ at 1~kHz measurement bandwidth, and noise down to 0.45~aF at 1~Hz bandwidth. We estimate the sensitivity of the method for a number of other implementations. In particular we predict typical sensitivity of about 40~zF/$\sqHz$ at room temperature with a resonator comprised of off-the-shelf components. Of several proposed applications, we demonstrate two: the capacitance measurement of several identical 80~nm-wide gates with a single resonator, and the field-effect mobility measurement of an individual nanowire with the gate capacitance measured in-situ.

Remote Floating-Gate Field-Effect Transistor with 2-Dimensional Reduced Graphene Oxide Sensing Layer for Reliable Detection of SARS-CoV-2 Spike Proteins.

Despite intensive research of nanomaterials-based field-effect transistors (FETs) as a rapid diagnostic tool, it remains to be seen for FET sensors to be used for clinical applications due to a lack of stability, reliability, reproducibility, and scalability for mass production. Herein, we propose a remote floating-gate (RFG) FET configuration to eliminate device-to-device variations of two-dimensional reduced graphene oxide (rGO) sensing surfaces and most of the instability at the solution interface. Also, critical mechanistic factors behind the electrochemical instability of rGO such as severe drift and hysteresis were identified through extensive studies on rGO-solution interfaces varied by rGO thickness, coverage, and reduction temperature. rGO surfaces in our RFGFET structure displayed a Nernstian response of 54 mV/pH (from pH 2 to 11) with a 90% yield (9 samples out of total 10), coefficient of variation (CV) < 3%, and a low drift rate of 2%, all of which were calculated from the absolute measurement values. As proof-of-concept, we demonstrated highly reliable, reproducible, and label-free detection of spike proteins of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in a saliva-relevant media with concentrations ranging from 500 fg/mL to 5 μg/mL, with an R2 value of 0.984 and CV < 3%, and a guaranteed limit of detection at a few pg/mL. Taken together, this new platform may have an immense effect on positioning FET bioelectronics in a clinical setting for detecting SARS-CoV-2.