Graphene Nanoribbon Field-effect Transistors Research Articles

All-Armchair Graphene Nanoribbon Field-Effect Uridine Diphosphate Glucose Sensor: First-Principles In-Silico Design and Characterization

Label-free sensors capable of detecting low concentrations of significant biomolecular substances without inducing immune response would simplify experiments, minimize errors, improve real-time observations, and reduce costs in probing living organisms. This paper presents a first-principles, in-silico derived, all-armchair graphene nanoribbon field-effect transistor (g-FET) device for the detection and measurement of low-concentration (pM-nM) uridine diphosphate glucose, UDP-glucose. UDP-glucose is an intermediate reactant in the synthesis of sucrose in a plant cell’s cytoplasm and an extracellular signaling molecule capable of activating downstream defense mechanisms. The unique g-FET configuration for the semiconducting channel and electrodes favors the fabrication of high-density nanoarray sensors. Optimal device electronic transport and switching properties are predicted by screening configurations with different widths, to control bandgap, and lengths, to control thermionic versus tunneling transport across the semiconducting junction. A self-assembled monolayer (SAM) of pyrene derivatives, 1-pyrenebutyric acid, is used to noncovalently functionalize the graphene surface on one end and to covalently ligate the target analyte on the other while providing mechanical, chemical, and electronic signal sensing stability. We find that the device offers a predicted limit of detection (LOD) of 0.997 / $n$ mM/L (where $n$ is the number of sensor units in an array), with high transconductance sensitivity, 0.75– $1.5\mu \text {S}$ for 1–3 UDP-glucose molecules, at low input ( $V_{G}= 0.9$ V) and output voltages $V_{\text {DS}}=0.1$ V. Thus, a $1000\times1000$ nanoarray sensor would yield an LOD = 0.997 nM/L. This low-power, all-armchair g-FET sensor with SAM ligands that may be chosen to bind different biomarkers provides a unique opportunity for high throughput, real-time, low-cost, high-mobility, and minimal-calibration sensing applications.

A computationally efficient hybrid approach based on artificial neural networks and the wavelet transform for quantum simulations of graphene nanoribbon FETs

Numerical modeling of graphene nanoribbon field-effect transistors (GNRFETs) using quantum-mechanical approaches is often associated with a heavy computational burden, indicating the urgent need for new methods to resolve this issue. A computationally efficient hybrid approach for quantum simulations of ballistic GNRFETs is developed herein. The proposed simulation method is based on solving the two-dimensional (2D) Poisson equation using both wavelet-based adaptive meshing and wavelet-based matrix compression techniques, self-consistently, with well-trained neural network models that imitate the mode-space (MS) nonequilibrium Green’s function (NEGF) solver in generating the charge density. The results obtained by applying the hybrid approach show good agreement with NEGF simulations. Numerical experiments reveal that the developed simulation method can offer a speed-up of about one order of magnitude over the conventional MS NEGF approach. The encouraging results obtained in this work indicate that the developed numerical model is particularly appropriate for incorporation into nanoelectronic device simulators to investigate future GNRFET-based circuits.

An ultra-sensitive gas nanosensor based on asymmetric dual-gate graphene nanoribbon field-effect transistor: proposal and investigation

In this paper, a new ultra-sensitive gas nanosensor based on an asymmetric dual-gate graphene nanoribbon field-effect transistor (ADG GNRFET) is proposed. The performance of the proposed gas nanosensor is examined using an atomistic quantum simulation based on the mode space non-equilibrium Green’s function approach, self-consistently coupled to a two-dimensional Poisson’s equation in the ballistic limit. The gas-induced change in work function of sensitive gates is considered as a sensing mechanism, where the threshold voltage shift is taken as a sensing metric. The sensitivity analysis has shown that the gas-induced shift in threshold voltage can be significantly increased by decreasing the ratio of top-oxide capacitance to that of back-oxide, to less than unity. Moreover, the length and width of graphene nanoribbon are found independent of sensor sensitivity. The possibility of reaching ultra-high sensitivities at the nanoscale domain using the proposed ADG GNRFET-based gas sensor makes it an exciting alternative to the conventional FET-based gas sensors.

Inverse Stone Throwers Wales defect and enhancing ION/IOFF ratio and subthreshold swing of GNR transistors

In this paper, the impacts of the inverse Stone Thrower Wales (ISTW) defect as an ad-dimer defect on a double gate graphene nanoribbon field effect transistor (DGT) were studied. A DGT structure with a single ISTW defect is firstly analyzed for different positions of the ISTW defect across the width and along the length of the transistor channel. Then the impact of the random distributed ISTW (RDI) defect is investigated and the results indicate the defect density of 0.5% is more favorable due to its relatively better performance in off and on states. Considering how this ad-dimer defect can lead to enhance the transistor performance, a DGT structure including three ISTW defects in specific locations is also investigated which resulted in increasing the on-off current ratio up to 50 and decreasing the sub-threshold swing. The simulation results also show a decrease in ambipolar conduction and attenuation in kink effect. Our simulations has been done based on self-consistent solution of full 3D Poisson and Schrodinger equations within the non-equilibrium Green's function formalism. In the transistor channel, nanoribbons with non-functionalized edges are used.

Impact of carrier concentration and bandgap on the performance of double gate GNR-FET

Abstract This paper presents the impact of drain carrier density on the drain current saturation of 5 nm channel length double gate graphene nanoribbon field effect transistor (DGGNR-FET) near high drain voltage region. The impact of the substrate and energy band gap on the kink behavior of the device is analyzed by using Nonequilibrium Green's Function with mode space (NEGF_MS) method. We studied the effect of Si, SiC, and the oxide (SiO2) sub'strate on the device performance. The impact of the energy band gap is also examined on the increase in carrier density and current saturation. The necessity of constant carrier density in the drain side for better current saturation is emphasized. The carrier density in the drain side is increased due to the tunnelling from source to drain region (band to band tunnelling) and lateral carrier density modulation. We found that SiC is the better substrate over silicon and SiO2 for better current saturation of DGGNR-FET. Our simulation results provide detailed insight into analog and radio frequency application for the graphene device.

Parameterized Comparison of Nanotransistors Based on CNT and GNR Materials: Effect of Variation in Gate Oxide Thickness and Dielectric Constant

Silicon based technology encounters scaling parameters that prohibit the advancement of transistor technology. Graphene nanoribbons (GNR) and carbon nanotubes (CNT) are often considered the predominating devices to replace silicon technology. Carbon nanotube field effect transistors (CNTFETs) are considered the most promising devices because of their most interesting properties such as high current carrying ability (∼ 1010 A/cm2), excellent carrier mobility, scalability, high reliability for elevated temperature operation, and negligible leakage current. In this paper, a comparative analysis of CNTFET and graphene nanoribbon field effect transistors (GNRFET) is presented. The results of simulations are presented, and comparisons of devices are done based on different parameters listed as ION/IOFF current ratio, trans-conductance, and inverse subthreshold slope using NanoTCAD ViDES. After simulation, it is shown that CNTFET offers better results for ION/IOFF on the order of 106, subthreshold swing (SS) as 74.4 mV/dec, and transconductance as 7.6 μS. Further the effect of oxide thickness and dielectric constant has been studied for both FET devices. At the end, it is concluded that CNTFET offers better simulation result than that of GNRFET.

Design and Simulation of a Frequency Doubler Using Graphene Nanoribbon Field Effect Transistors for Communication Devices

Modeling of a graphene nanoribbon field effect transistor (GNRFET) as a frequency doubler has been extensively explored for developing future communication applications. For its analysis, different types of modifications are applied to the GNRFET model simulated in a Hewlett simulation program with an integrated circuit. The model is demonstrated for its frequency response and conversion gain. It uses an intrinsic GNRFET for frequency doubling which clearly shows a distortionless sinusoidal output at a peak frequency of 20.6 MHz for an applied input of 10.3 MHz. However, after applying doping at different fractions of 0.3%, 3% and 30% in the transistor model, signal decay appears at 30% doping fractions. Results are also shown for increasing the number of dimers (N), increasing the number of channels for conduction and the impact of changing the dielectric constant on the doubler model performance. It is found that as the channel width increases, an increase in the conversion gain from − 26.05 dB to − 20 dB results from an increase in N from 8 to 20 dimer lines. Further, if four graphene nanoribbon (GNR) channels are used in the doubler operation instead of one GNR channel, then a high conversion gain of − 16.47 dB as compared to − 26.05 dB for an individual GNR channel is also calculated. Regarding the impact of different dielectrics, it is revealed that, similar to a conventional transistor, a graphene transistor with a high-K-value dielectric presents the highest gain, but with a high distortion in the output signal. However, using a conventional silicon dioxide (SiO2) dielectric having a low K value gives lower conversion gain, but ideal frequency doubling in the output is attained.

Impact of phonon scattering on digital characteristics and RF performance of graphene nanoribbon FETs

The switching capabilities and RF performance of graphene nanoribbon field-effect transistors (GNRFETs) in the presence of electron-phonon scattering are examined. Self-consistent atomistic simulations based on the nonequilibrium Green's function (NEGF) formalisms are used. We have studied the influence of incoherent transport on the most important digital parameters such as Ion, Ioff, Ion/Ioff, the subthreshold swing, and the drain-induced barrier lowering (DIBL) versus the channel length. Furthermore, the effects of phonon scattering on the gate capacitance and the transconductance are investigated in order to calculate the intrinsic cut-off frequency, switching delay, and the power-delay product of non-ballistic GNRFETs. We have shown that band-to-band tunneling regime is dominated by the phonon-assisted tunneling. Therefore, the off-current and the sub-threshold swing are deteriorated by this phenomenon. Furthermore, the scattering results in a decrease of intrinsic cut-off frequency and increase of the gate delay and energy consumed per switching event.

The effect of channel uniaxial strain on thermal conductivity of graphene nano-ribbon field effect transistor

The effect of channel uniaxial strain on thermal conductivity of graphene nano-ribbon field effect transistor (GNRFET) is analyzed by self-consistent Hückel method. The supposed strains are tensile and its values are 2% to 24% of lattice constant. All of the assumed strains are applied to the channel length direction. Energy band gap, density of states (DOS), phonon transmission, thermal conductivity, and I–V characteristics of the GNRFET have been calculated. The results show that by increasing the strain, the energy band gap of the channel is increased and the drain current is decreased. Also by increasing the band gap, phonon transmission is decreased. Maximum phonon transmission occurs in 8% strain. By considering all of these parameters, the results show that there is a maximum thermal conductivity versus temperature in 8% uniaxial strain that is more than the bare one and its value is decreased intensively in 16% and 24% strain. This is due to maximum phonon transmission that is observed in 8% strain and increasing the DOS around the energy band gap in this value. Also, it is observed that in the energy range of more than 0.75 eV, by increasing the strain, thermal conductivity is increased.

Comparative study of nanoribbon field effect transistors based on silicene and graphene

Silicene nanoribbon is a one-dimensional structure of monolayer silicon atoms that its energy gap depends on the edge shape and the width of the ribbon. In this paper, we design a Silicene nanoribbon field effect transistor (SiNRFET) based on different ribbon widths and then we compare this structure with a graphene nanoribbon field effect transistor (GNRFET). For this purpose, we study the effect of the parameters such as ribbon length and the number of atoms along the ribbon width. Moreover, we investigate effect of the perpendicular electric field on the Ion/Ioff and transfer characteristics of both structures and compare the performance of these transistors. Finally, we derive the output characteristics of SiNRFET and GNRFET as a function of gate voltage and compare them together. The method that we use in this research is the transfer matrix. The electron wave functions are derived in each region of both transistors in order to obtain the current.

Utilizing Graphene Nano-Ribbon Transistor in Data Converters: A Comparative Study

In recent years, efforts to perform more processing operation on a silicon chip have made a strong enthusiasm for making the circuit components smaller in order to reduce the power and increase the speed. Due to silicon constraints, there will be no possibility to follow Moore's law. That's why we should look for an alternative to silicon. Therefore, due to high mobility, high current density, and low noise, the study on Graphene Nano Ribbon (GNR) began. ADCs and DACs have a major share in the electronics industry. An ADC prepares signals for the digital world and microprocessor processing. There are different methods for converting analog to digital signals. Among them, due to unique features such as high speed; Flash ADC has attracted the attention of designers. In this research first, a model for simulating of the GNR field effect transistor (GNRFET), is introduced. Then, this model is used to design a flash ADC. The results of this study indicate that the designed circuit has a desirable performance as an ADC. In addition, compared to a same Si-CMOS sample, errors such as DNL, INL, Offset, and Full scale are reduced. Moreover, GNR-based ADC shows less power consumption. The maximum and minimum power consumption are equal to 27.8% and 17.6% which corresponds to 5-bit and 4-bit GNR-based flash ADCs compared with their CMOS counterpart. Moreover, this research indicates a significant improvement in the delay that is at least 86.3% and maximum 88.6% which corresponds to 5-bit and 3-bit GNR-based flash ADCs.

A Functional Study of a Bilayer Graphene Nanoribbon FET With Four Different Gate Insulators

Bilayer graphene like monolayer graphene has a zero bandgap. To use as a channel material of FETs, its band gap should be open which is crucial for its application in logic circuits. Several methods have been developed to open the band gap in graphene. The simple way is cutting graphene into ribbons. In this paper, a novel structure for a dual-gated bilayer graphene nanoribbon field-effect transistor (BLGNRFET) is suggested, which merges the advantages of high and low dielectric constants. The gate insulator of FET is divided into four parts with different dielectric materials, so the proposed device is called FDI-BLGNRFET. All of the possible state of gate insulators which can happen for these four different parts are surveyed. The simulations are conducted by means of the self-consistent solution of the Poisson and Schrodinger equations within the Non- Equilibrium Green Function (NEGF) and a tight-binding Hamiltonian, in the real space approach. Regarding to the results, for the proposed FDI-BLGNRFET with K1 = K2 = 25 and K3 = K4 = 3.9, the maximum ${I_{ON}}/{I_{OFF}}$ ratio 119% higher than the conventional BLGNRFET is achieved which is still remains inadequate for getting an acceptable $({{I_{ON}}/{I_{OFF}}})$ ratio in CMOS performance.

Graphene-layer and graphene-nanoribbon FETs as THz detectors

We report on detection of sub-THz radiation (129-430 GHz) using graphene based asymmetric field-effect transistor (FET) structures with different channel geometry: monolayer graphene, graphene nanoribbons. In all devices types we observed the similar trends of response on sub-THz radiation. The response fell with increasing frequency at room temperature, but increased with increasing frequency at 77 K. Our calculations show that the change in the trend of the frequency dependence at 77 K is associated with the appearance of plasma waves in the graphene channel. Unusual properties of p-n junctions in graphene are highlighted using devices of special geometry.

Transmission spectrum and IV characteristics of dual-gate Z-shaped graphene nanoribbon FET

In this work, a dual-gate Z-shaped graphene nanoribbon field-effect transistor (DG-ZGNRFET) is presented. The transmission spectrum, current–voltage (IV) and differential conductance (dI/dV) characteristics have been calculated for different biasing configurations of gate voltages. The calculated transmission spectrum predicts the semiconducting nature of the channel as the transmission coefficient is zero around the Fermi level for all biasing configurations of the gate voltages. In this study, when both gates are biased with −1 V, a low threshold voltage, a high I on/I off ratio compared with those of other biasing configurations and a negative differential conductance (NDC) are observed. On the other hand, when either one or both gates are biased with +1 V, a large threshold voltage, a low value of the I on/I off ratio and negligible NDC effects are observed, which are technologically not very favourable conditions in which to operate the DG-ZGNRFET.

Detection of binary amino acid in aqueous solution using double gate graphene nano-ribbon field effect transistor

Detection of binary amino acid in aqueous solution using double gate graphene nano-ribbon field effect transistor

Calculation and Analysis of Graphene Nanoribbons Field Effect Transistor Structure and Characteristics

Because there is no gap between conduction band and valence band of graphene, it is difficult to achieve switching characteristics when transistors are fabricated. In order to open the graphene band gap, researchers have explored many methods, such as tailoring Shi Mocheng quantum dots, nanobelts, nano grids or laying graphene on a special substrate, one of the feasible ways is to regulate the electrical properties of graphene by doping. Through the analysis on the structure and properties of graphene band calculation, with the help of computer aided simulation, the ID and VG characteristics analysis of the Schottky barrier graphene field effect transistor (SBFET) and MOS structure of graphene field effect transistor (MOSFET) are investigated in this study. The results are of high reference value for the study of the structure and properties of graphene nanoribbons.

Variation in characteristics of graphene nanoribbon field-effect transistors caused by edge disorder: Computational simulation of atomistic device

We theoretically investigated the variations in the characteristics of graphene-nanoribbon-based field-effect transistors (GNR FETs) using the nonequilibrium Green’s function method. In this study, the drain current (Id) was calculated as a function of gate voltage (Vg) for GNR FETs with various edge disorder concentrations (P). From the obtained Id–Vg curves, we estimated the device characteristics. We found that the variations of these device characteristics became larger with increasing P, as evidenced by a dramatic change in the shapes of their histograms. Furthermore, we clarified that these variations were caused by Anderson localization originating from the edge disorder.

Boosting the performance of a nanoscale graphene nanoribbon field-effect transistor using graded gate engineering

In this paper, we report the device performance of a new graphene nanoribbon field-effect transistor (GNRFET) with a linearly graded binary metal alloy gate through a quantum simulation study. The proposed device is simulated by solving the Schrodinger equation using the mode space non-equilibrium Green’s function (NEGF) formalism coupled self-consistently with a two-dimensional Poisson equation in the ballistic limit. Comparisons are made for the I–V characteristics, subthreshold swing, voltage gain, and cut-off frequency among conventional GNRFETs and work-function-engineered gate GNRFETs. Moreover, the impact of variation in GNR channel length on device performance is also studied. We have found that the GNRFET endowed with work-function-engineered gate can improve the subthreshold swing and provide higher voltage gain and cut-off frequency than the conventional GNRFET. The obtained results indicate that the proposed device can alleviate the critical problem and further improve immunity against short channel effects of nanoscale GNRFETs for high performance analog sub-10-nm technology.

Role of Biasing and Device Size on Phonon Scattering in Graphene Nanoribbon Transistors

We study the noncoherent transport due to electron–phonon (e-ph) interaction in graphene nanoribbon (GNR) field-effect transistors (GNRFETs) using nonequilibrium Green’s function method in mode space. Phonon dispersion calculations in conjunction with the e-ph interaction computations show that in an armchair GNR, only a small number of phonon modes are coupled to the carriers. Our simulation shows that under a threshold gate voltage, the drain–source current is diminished by the low-energy phonons such as acoustic phonon modes and radial-breathing-like phonon modes, while at great biases of the gate, the current drop is essentially due to high-energy optical phonon modes. The effect of drain voltage on scattering process is discussed, which shows that at higher drain voltages, the ballisticity decreases. We also explore the phonon scattering dependence on the dimensions of GNRFET channel. In larger width ribbon, the impact of phonon scattering decreases. The channel with a length of 30 nm is ballistic up to 90%, and only when its length is increased to approximately 180 nm, transport becomes semiballistic, which infers to an effective mean free path of ~200 nm.

First Principle Study of Doped Graphene for FET Applications

The electronic industry using silicon complementary metal-oxide-semiconductor (CMOS) technology is the leading contender in the market since five decades. Nowadays, silicon CMOS technology is reached to its fundamental limits (physical and geometrical), which is the major roadblock for upcoming technological nodes. As an alternative solution, two-dimensional (2D) materials are in great demand. Graphene is the first 2D material being studied and it is also known as “miracle-material” due to its incredible physical properties. This paper explores the current status of graphene transistor as a potential supplement to the silicon CMOS technology. The absence of an energy bandgap in graphene results in severe shortcomings for logic applications. Various techniques to engineer the bandgap in graphene field-effect transistors (FETs) have been discussed. The use of dopant atoms in graphene and its effect on drain current is studied. The current-voltage characteristics of prototype devices are determined by the first-principles quantum transport calculations. The graphene nanoribbon (GNR) FET and dual-gate (DG) FET structures have been designed and simulated using QuantumWise ATK. A bandgap opening technique in bilayer graphene is proposed and analysed for FET applications as a potential replacement for silicon transistors.