Graphene Field-effect Transistors Research Articles

Nano Thermal Simulation of Graphene Field Effect Transistor Based on Ballistic Diffusive Model

This paper investigates temperature evolution in graphene field-effect transistors. We present a refined Ballistic-diffusive equation model (BDE) tailored for scrutinizing the phonon transport within GNRFET transistors. Furthermore, we examine the influence of the channel length on thermal characteristics. COMSOL Multiphysics is employed to compute the phonon transport and temperature distribution in nano-GNRFET. Our results reveal that the phonon transport anticipated by the suggested BDE model closely corresponds to that derived from the Boltzmann transport equation. The proposed model proficiently gauges the thermal performance of GNRFET, with the outcomes suggesting that the characteristic length of the GNR has a negligible impact on the temperature increase.

Modular Fabrication of Microfluidic Graphene FET for Nucleic Acids Biosensing.

Graphene field-effect transistors (GFETs) are widely used in biosensing due to their excellent properties in biomolecular signal amplification, exhibiting great potential for high-sensitivity and point-of-care testing in clinical diagnosis. However, difficulties in complicated fabrication steps are the main limitations for the further studies and applications of GFETs. In this study, a modular fabrication technique is introduced to construct microfluidic GFET biosensors within 3 independent steps. The low-melting metal electrodes and intricate flow channels are incorporated to maintain the structural integrity of graphene and facilitate subsequent sensing operations. The as-fabricated GFET biosensor demonstrates excellent long-term stability, and performs effectively in various ion environments. It also exhibits high sensitivity and selectivity for detecting single-stranded nucleic acids at a 10fm concentration. Furthermore, when combined with the CRISPR/Cas12a system, it facilitates amplification-free and rapid detection of nucleic acids at a concentration of 1fm. Thus, it is believed that this modular-fabricated microfluidic GFET may shed light on further development of FET-based biosensors in various applications.

Analysis of Local Properties and Performance of Bilayer Epitaxial Graphene Field Effect Transistors on SiC.

Epitaxial bilayer graphene, grown by chemical vapor deposition on SiC substrates without silicon sublimation, is crucial material for graphene field effect transistors (GFETs). Rigorous characterization methods, such as atomic force microscopy and Raman spectroscopy, confirm the exceptional quality of this graphene. Post-nanofabrication, extensive evaluation of DC and high-frequency properties enable the extraction of critical parameters such as the current gain (fmax) and cut-off frequency (ft) of hundred transistors. The Raman spectra analysis provides insights into material property, which correlate with Hall mobilities, carrier densities, contact resistance and sheet resistance and highlights graphene's intrinsic properties. The GFETs' performance displays dispersion, as confirmed through the characterization of multiple transistors. Since the Raman analysis shows relatively homogeneous surface, the variation in Hall mobility, carrier densities and contact resistance cross the wafer suggest that the dispersion of GFET transistor's performance could be related to the process of fabrication. Such insights are especially critical in integrated circuits, where consistent transistor performance is vital due to the presence of circuit elements like inductance, capacitance and coplanar waveguides often distributed across the same wafer.

Emergent Inhomogeneity and Nonlocality in a Graphene Field-Effect Transistor on a Near-Parallel Moiré Superlattice of Transition Metal Dichalcogenides.

At near-parallel orientation, twisted bilayers of transition metal dichalcogenides exhibit interlayer charge transfer-driven out-of-plane ferroelectricity. Here, we report detailed electrical transport in a dual-gated graphene field-effect transistor placed on a 2.1° twisted bilayer WSe2. We observe hysteretic transfer characteristics and an emergent charge inhomogeneity with multiple local Dirac points evolving with an increasing electric displacement field (D). Concomitantly, we also observe a strong nonlocal voltage signal at D ∼ 0 V/nm that decreases rapidly with increasing D. A linear scaling of the nonlocal signal with longitudinal resistance suggests edge mode transport, which we attribute to the breaking of valley symmetry of graphene due to the spatially fluctuating electric field from the underlying polarized moiré domains. A quantitative analysis suggests the emergence of finite-size domains in graphene that modulate the charge and the valley currents simultaneously. This work underlines the impact of interfacial ferroelectricity that can trigger a new generation of devices.

Gain-type photodetector with GFET-coupled MoS2/WSe2 heterojunction

Due to its exceptional photovoltaic properties and freedom from crystal lattice matching constraints, transition-metal dichalcogenides (TMDCs) have gained increased attention as a prospective two-dimensional (2D) layered material. Van der Waals heterojunctions (vdWHs) constituted of these materials afford chances for the advancement of high-performance photodetectors and solar cells. However, low light absorption efficiency and electron/hole traps at heterointerfaces make it difficult to improve the response speed and sensitivity of TMDCs vdWH based photodetectors. Here, we designed and realized a GFET-coupled MoS2/WSe2 heterojunction gain photodetector. An interfacial amplification effect is induced when a graphene field-effect transistor (GFET) is coupled to a MoS2/WSe2 heterojunction because of the lengthy carrier lifetime of MoS2 and the ultrahigh mobility of graphene. This effect leads to a high gain for our device, enhancing the photovoltaic response. Compared to the pristine MoS2/WSe2 heterojunction, the device exhibits two to three orders of magnitude improvement in responsivity, up to 50 A/W. Rising and decaying times of 67 μs and 2 μs are also achieved, respectively. By utilizing the strong correlation between the incident light spot position and the photocurrent, the device also enables sensitive detection of the spot position. This research offers an attainable method for developing gain-type, high-speed photodetectors.

Ge‐based graphene FET for low‐temperature electronics

AbstractA graphene field‐effect transistor (GFET) based on chemical vapour deposited (CVD) Ge‐based graphene was reported and the low‐temperature electrical characteristics primarily investigated. The self‐alignment technique was used to fabricate a GFET to reduce parasitic effects and improve transconductance and cut‐off frequency. To further explore the electrical properties, the direct current and radio frequency characteristics of the GFET were studied over a temperature range from 4.2 to 300 K, considering the temperature‐dependent resistivity of intrinsic Ge. The direct current characteristic of the GFET for 110‐nm gate length, particularly the transconductance performance, exhibits a tiny variation of only 5% across this temperature range. However, the cut‐off frequency experiences a considerable increase, improving several tens of times when the temperature decreases to 4.2 K, with a maximum value of 3.49 GHz. This work illustrates a meaningful advancement in applying GFETs in the low‐temperature, high‐frequency domain.

Ge‐based graphene FET for low‐temperature electronics

AbstractA graphene field‐effect transistor (GFET) based on chemical vapour deposited (CVD) Ge‐based graphene was reported and the low‐temperature electrical characteristics primarily investigated. The self‐alignment technique was used to fabricate a GFET to reduce parasitic effects and improve transconductance and cut‐off frequency. To further explore the electrical properties, the direct current and radio frequency characteristics of the GFET were studied over a temperature range from 4.2 to 300 K, considering the temperature‐dependent resistivity of intrinsic Ge. The direct current characteristic of the GFET for 110‐nm gate length, particularly the transconductance performance, exhibits a tiny variation of only 5% across this temperature range. However, the cut‐off frequency experiences a considerable increase, improving several tens of times when the temperature decreases to 4.2 K, with a maximum value of 3.49 GHz. This work illustrates a meaningful advancement in applying GFETs in the low‐temperature, high‐frequency domain.

Performance analysis of graphene field effect transistor at nanoscale regime

In this paper, we examine the response of charge carriers in a dual-gate graphene field-effect transistor (GFET). We have conducted an investigation into the input-output properties of both monolayer and bilayer graphene channels. Additionally, we demonstrated the relationship between surface potential and quantum capacitance using equivalent circuit modelling. We offer precise mathematical equations that define the border points separating distinct regions. These equations guarantee the continuity of the Jacobian matrix, which is crucial for the successful implementation of a circuit simulator. We can classify the current-voltage (I-V) characteristics of bilayer graphene into three distinct regions: triode, unipolar, and ambipolar. The equivalent circuit modelling findings indicated that GFETs had superior output characteristics and transconductance behavior compared to FETs. We observed a direct correlation between transconductance and gate voltage across various drain-to-source voltages.Nevertheless, with a higher gate voltage, there was a corresponding drop in the transconductance value. The threshold voltage for this dual-gate GFET is dependent on the back gate voltage. The GFET's threshold value decreased as the back gate voltage increased.

Mitigation of electronic crosstalk interference in graphene transistor biosensors

The need for higher sensitivity and parallel detection of multiple biological targets drives the research on electronic biosensing platforms based on two-dimensional (2D) materials. However, signal fidelity from individual sensors may be compromised due to the existing nonidealities of 2D electronic devices. Here, we use graphene field effect transistors (gFETs) as a model system to investigate a multisensor device architecture. We identify two potential sources of crosstalk interference between sensors in such a platform: resistive interference through shared gFET channels and capacitive coupling through the shared device substrate. Having illustrated these sources of interference, we offer solutions to mitigate them for ensuring the fidelity of the biosensor signal. This study provides important practical insights for researchers working on 2D biosensor platforms.

Ultrasensitive graphene field-effect transistor biosensor for rapidly detecting miRNA-208a

MicroRNA-208a (miR208a) is a cardiac-specific miRNA and can provide an earlier prediction for AMI onset than currently used cardiac biomarkers. Graphene field-effect transistor (GFET) biosensor, as the promising candidate for next-generation biosensor, has been demonstrated for real-time detection of a variety of bioactive molecules with ultrasensitivity from nM to fM level. Currently, research on GFET sensors mostly focuses on the properties of the devices themselves, rather than aiming for ultra-sensitive detection based on biochemical substances. In this study, we developed a liquid-gated graphene field-effect transistor-based biosensor for detection of miR208a and designed a portable device to adapt with it for a fast readout of the electronic response, achieving a detection range of 0.01-1 pM, detection limit of 5.3 fM and detection time of 40minutes. Our work provides a reliable strategy to rapidly and ultrasensitively quantifying miRNA-208a, which also holds great potential to be extended in a wide range of applications of other disease markers and lead to powerful tools for healthcare.

Sub-femtomolar vertical graphene field effect immunosensor for detection of lung tumor markers

Lung cancer is the main cancer that endangers human life worldwide, with the highest mortality rate. The detection of lung tumor markers is of great significance for the early diagnosis and subsequent treatment of lung cancer. In this study, a vertical graphene field effect transistor (VGFET) immunosensor based on graphene/C60 heterojunction was created to offer quantitative detections for the lung tumor markers carcinoembryonic antigen (CEA), cytokeratin 19 fragment (Cyfra21-1), and neuron-specific enolase (NSE). The experimental results showed that the sensitive range for standard antigen is between 1 pg/ml to 100 ng/ml, with a limit of detection (LOD) of 5.6 amol/ml for CEA, 33.3 amol/ml for Cyfra 21–1 and 12.8 amol/ml for NSE (1 pg/ml for all). The detection accuracy for these tumor markers was compared with the clinically used method for clinical patients on serum samples. Results are highly consistent with clinically used immunoassay in its efficient diagnosis concentration range. Subsequently, the mesoporous silica nanospheres (MSNs) with an average size of 90 nm were surface modified with glutaraldehyde, and a second antibody was assembled on MSNs, which fixes nanospheres on the antigen and amplified the field effect. The LODs for three markers are 100 fg/ml (0.56 amol/ml for CEA) under optimal circumstances of detection. This result indicates that specific binding to MSNs enhances local field effects and can achieve higher sensing efficiency for tumor marker detection at extremely low concentrations, providing effective assistance for the early diagnosis of lung cancer.

Quantitative assessment of thermal resistance in graphene field-effect transistors based on a phonon hydrodynamics and van der Waals coupling approach

In the progressive miniaturization of graphene field-effect transistors (GrFETs), pronounced thermal boundary resistance (TBR) and increasing ballistic-diffusive thermal resistance pose formidable challenges to thermal management. Quantitative analysis of thermal resistance is crucial for advancing efficient thermal designs in GrFETs using state-of-the-art technology. The inherently low-dimensional structure nature of graphene means that thermal conduction in GrFETs, governed by phonon hydrodynamic transport and van der Waals (vdW) interactions, cannot be accurately described by traditional Fourier's law-based models or the single-mode relaxation time approximation. This study introduces an innovative thermal simulation framework that addresses these challenges by incorporating phonon hydrodynamics equations and considering weak vdW coupling. Our findings indicate that thermal conduction in GrFETs is predominantly facilitated by flexural (ZA) phonons, and their thermal transport efficiency is significantly influenced by substrate perturbations. Specifically, the TBR in GrFETs is closely associated with the weak vdW coupling between ZA phonons and substrate atoms. Furthermore, this study employs dimensionless thermal resistance ratios and Knudsen numbers to explore the impact of silicon's geometric dimensions, heat source size, and ballistic phenomena on the substrate's thermal resistance. These insights provide substantial theoretical support for the development of efficient thermal management strategies in GrFETs.

Ultrafast Opto-Electronic and Thermal Tuning of Third-Harmonic Generation in a Graphene Field Effect Transistor.

Graphene is a unique platform for tunable opto-electronic applications thanks to its linear band dispersion, which allows electrical control of resonant light-matter interactions. Tuning the nonlinear optical response of graphene is possible both electrically and in an all-optical fashion, but each approach involves a trade-off between speed and modulation depth. Here, lattice temperature, electron doping, and all-optical tuning of third-harmonic generation are combined in a hexagonal boron nitride-encapsulated graphene opto-electronic device and demonstrate up to 85% modulation depth along with gate-tunable ultrafast dynamics. These results arise from the dynamic changes in the transient electronic temperature combined with Pauli blocking induced by the out-of-equilibrium chemical potential. The work provides a detailed description of the transient nonlinear optical and electronic response of graphene, which is crucial for the design of nanoscale and ultrafast optical modulators, detectors, and frequency converters.

Sensitive detection of infectious disease utilizing carbon Sphere@Fe3O4 micromotor combined with graphene field-effect transistor

BackgroundRapid on-site detection of infectious diseases is considerably essential for preventing and controlling major epidemics and maintaining social and public safety. However, the complexity of the natural environment in which infectious disease pathogens exist severely disrupts the performance of on-site detection, and rapid detection can become meaningless because of the cumbersome sample pretreatment process. ResultHerein, a new detection platform based on a carbon sphere@Fe3O4 micromotor (CS@Fe3O4) in combination with a graphene field-effect transistor (GFET) was designed and used for the on-site detection of SARS-CoV-2 coronavirus pathogens. The CS@Fe3O4 micromotor, surface-modified with anti-SARS-CoV-2 coronavirus antibody, could move at a velocity of 79.4 μm/s in a solution containing hydrogen peroxide (H2O2) and exhibited capture rates of 67.9% and 36.2% for the SARS-CoV-2 pathogen in phosphate buffered saline (PBS) and soil solutions, respectively. After magnetic field separation, the captured micromotor was used for GFET detection, with detection limits of 4.6 and 15.6 ag/mL in PBS and soil solutions, respectively. Significance and noveltyThis detection platform can be employed to avoid complex sample pretreatment procedures and achieve rapid on-site detection of SARS-CoV-2 coronavirus pathogens in complex environments. This study introduces a novel approach for the on-site detection of infectious diseases.

Enhancing Radio Frequency Performance of Graphene Field-Effect Transistors through Machine-Learning-Based Physical Prediction and Optimization

Enhancing Radio Frequency Performance of Graphene Field-Effect Transistors through Machine-Learning-Based Physical Prediction and Optimization

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.

A Quasi-Ballistic Model for Short Channel Monolayer Graphene Field Effect Transistor Including Scattering Effects

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.

High mobility graphene field effect transistors on flexible EVA/PET foils

Monolayer graphene is a promising material for a wide range of applications, including sensors, optoelectronics, antennas, EMR shielding, flexible electronics, and conducting electrodes. Chemical vapor deposition (CVD) of carbon atoms on a metal catalyst is the most scalable and cost-efficient method for synthesizing high-quality, large-area monolayer graphene. The usual method of transferring the CVD graphene from the catalyst to a target substrate involves a polymer carrier which is dissolved after the transfer process is completed. Due to often unavoidable damage to graphene, as well as contamination and residues, carrier mobilities are typically 1000–3000 cm2(Vs)−1 , unless complex and elaborate measures are taken. Here, we report on a simple scalable fabrication method for flexible graphene field-effect transistors that eliminates the polymer interim carrier, by laminating the graphene directly onto office lamination foils, removing the catalyst, and depositing Parylene N as a gate dielectric and encapsulation layer. The fabricated transistors show field- and Hall-effect mobilities of 7000–10 000 cm2(Vs)−1 with a residual charge-carrier density of 2×1011 1 cm−2 at room temperature. We further validate the material quality by terahertz time-domain spectroscopy and observation of the quantum Hall effect at low temperatures in a moderate magnetic field of ∼5 T. The Parylene encapsulation provides long-term stability and protection against additional lithography steps, enabling vertical device integration in multilayer electronics on a flexible platform.

Ultrasensitive Graphene Field-Effect Biosensors Based on Ferroelectric Polarization of Lithium Niobate for Breast Cancer Marker Detection.

Herein, we present a novel ultrasensitive graphene field-effect transistor (GFET) biosensor based on lithium niobate (LiNbO3) ferroelectric substrate for the application of breast cancer marker detection. The electrical properties of graphene are varied under the electrostatic field, which is generated through the spontaneous polarization of the ferroelectric substrate. It is demonstrated that the properties of interface between graphene and solution are also altered due to the interaction between the electrostatic field and ions. Compared with the graphene field-effect biosensor based on the conventional Si/SiO2 gate structure, our biosensor achieves a higher sensitivity to 64.7 mV/decade and shows a limit of detection down to 1.7 fM (equivalent to 12 fg·mL-1) on the detection of microRNA21 (a breast cancer marker). This innovative design combining GFETs with ferroelectric substrates holds great promise for developing an ultrahigh-sensitivity biosensing platform based on graphene that enables rapid and early disease diagnosis.

Heat Flow Overshooting in Suspended Graphene

ABSTRACT In this work we found that when the hydrodynamic heat conduction in suspended graphene is in the under-damped free oscillation regime the disturbance of heat flux at the boundaries of graphene and the joint action of the initial heat flux and its time change rate can cause the heat flow overshooting which refers to the excess heat flux established in the heat conduction medium when two heat flow wave-fronts meet. The overshooting can make the maximum amplitude of the heat flux more than twice that of the initial heat flux, which poses a great danger to the next high-frequency and high-efficiency electronic devices based on graphene, such as the graphene field-effect transistors. Interestingly, results show that when the scale ratio of graphene with rectangular shape in the heat flow direction to its vertical direction is greater than a certain value, the overshooting caused by the disturbance of the heat flux at the boundaries no longer occurs. For the overshooting induced by the uneven distribution of the initial heat flux and its time change rate, it is shown that if the length in the region with the higher heat flux and time change rate in the direction of heat flow is less than a critical value the overshooting phenomenon can be avoided. These findings provide a new way for thermal management of electronic devices based on graphene.