Double Gate Graphene Nanoribbon Research Articles

Design of Dual-Band Rectifier Circuit for RF Energy Harvesting Using Double-Gate Graphene Nanoribbon (GNR) Vertical Tunnel FET

Design of Dual-Band Rectifier Circuit for RF Energy Harvesting Using Double-Gate Graphene Nanoribbon (GNR) Vertical Tunnel FET

Effectiveness of Graphene Nano-Ribbon Tunnel Field Effect Transistor for Bio-Molecular Identification

This paper examines the Double gate Graphene Nano-ribbon Tunnel Field-Effect Transistor (DG GNR TFET) for bio-sensing applications. The biomolecules are Streptavidin, APTES, Biotin, DNA and protein. Differentiation between biomolecules is possible based on dielectric permittivity and charge concentration. The protein switching ratio ([Formula: see text]/[Formula: see text] is 25.7 times that of Streptavidin and around 300 times that without any biomolecule in the cavity. The maximum current sensitivity among the biomolecules is achieved by protein biomolecule for VGS = 0.7[Formula: see text]V. The sub-threshold swing obtained for a biomolecule in DG GNR TFET is 40 mV/dec compared to that of 80[Formula: see text]mV/dec for an empty cavity. The device characteristics reveal that the drain current is maximum with a biomolecule in a cavity compared to an empty cavity. Results obtained emphasize that double gate Graphene Nano-Ribbon TFET is suitable as a biosensor. The simulations are executed using Silvaco Technology Computer Aided Design (TCAD).

Sensitivity and Stability Analysis of Double-Gate Graphene Nanoribbon Vertical Tunnel FET for Different Gas Sensing

Sensing and detecting gases are crucial from the application point of view. The essential condition for present-time gas sensors is light, compact, less power dissipation, highly sensitive, thermally stable, and a good selection regards several gases. Due to the significant potential and modulation of the energy bandgap, two-dimensional material has recently attracted researchers attention. Graphene nanoribbon (GNR) is one of the candidates from the two-D material; it is extracted from the strip of one-dimensional graphene material, which can be a suitable contender for gas sensing devices. Therefore, in this work, the detailed investigation of the gas sensor of various gas has been reported by employing two-dimensional material-based DG-GNR VTFET as a sensor. Different gases, including Oxygen, Ammonia as well as Hydrogen gas, have been scrutinized for sensitivity and stability in several temperature ranges. In the present work, several catalytic metals are utilized in the gate electrode of the proposed device architecture for the different gas sensing applications. The intrinsic physics of the proposed gas sensor has been carried out in detail in the factor of different gas molecules and gas pressure. Finally, the temperature parameter varies to analyze the stability of the proposed device sensor within 200 K–400 K.

Performance enhancement of an ultra-scaled double-gate graphene nanoribbon tunnel field-effect transistor using channel doping engineering: Quantum simulation study

In this paper, new graphene nanoribbon tunnel field-effect transistors (GNRTFETs) endowed with specific doping profiles are proposed, assessed, and compared with the conventional design through a computational investigation. The used quantum simulation is based on solving self-consistently the Poisson and Schrödinger equations using the non-equilibrium Green's function formalism in the ballistic limit. The numerical study deals with GNRTFET designs with 5 nm gate length while comparing their I-V transfer proprieties, subthreshold swing, charge density, current ratio, intrinsic delay, and power-delay product. The proposed designs, which are endowed with new doping profiles, have been found efficient in mitigating the direct source-to-drain tunneling issue of ultrascaled GNR-based TFET and in improving the ambipolar behavior while boosting the performance of the GNRTFETs. As interesting results, highly improved minimum leakage current, subthreshold swing, and switching parameters have been recorded by means of the proposed channel doping engineering-based approach. The obtained substantial improvements in the performance of ultrascaled GNRTFETs make the proposed approach as a promising way for the continual shrinking of tunnel field-effect transistors (sub-5-nm) while maintaining the required high-performance.

Inverse Stone-Thrower-Wales defect and transport properties of 9AGNR double-gate graphene nanoribbon FETs

Defect-based engineering of carbon nanostructures is becoming an important and powerful method to modify the electron transport properties in graphene nanoribbon FETs. In this paper, the impact of the position and symmetry of the ISTW defect on the performance of low dimensional 9AGNR double-gate graphene nanoribbon FET (DG-GNRFET) is investigated. Analyzing the transmission spectra, density of states and current-voltage characteristics shows that the defect effect on the electron transport is considerably varied depending on the positions and the orientations (the symmetric and asymmetric configuration) of the ISTW defect in the channel length. Based on the results, the asymmetric ISTW defect leads to a more controllability of the gate voltages over drain current, and drain current increases more than 5 times. The results have also confirmed the ISTW defect engineering potential on controlling the channel electrical current of DG-AGNR FET.

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.

A computational study of a novel graphene nanoribbon field effect transistor

In this paper, using gate structure engineering and modification of channel dopant profile, we propose a new double gate graphene nanoribbon field effect transistor (DG-GNRFET) mainly to suppress the band-to-band tunneling (BTBT) of carriers. In the new device, the intrinsic part of the channel is replaced by an intrinsic-lightly doped-intrinsic [Formula: see text] configuration in a way that only the intrinsic parts are covered by the gate contact. Transport characteristics of the device are investigated theoretically using the nonequilibrium Green’s function (NEGF) formalism. Numerical simulations show that off-current, ambipolar behavior, on/off-current ratio and the switching characteristics such as intrinsic delay and power-delay product are improved. In addition, the new device demonstrates better sub-threshold swing and less drain-induced barrier lowering (DIBL).

Analyses of Short Channel Effects of Single-Gate and Double-Gate Graphene Nanoribbon Field Effect Transistors

Short channel effects of single-gate and double-gate graphene nanoribbon field effect transistors (GNRFETs) are studied based on the atomistic pz orbital model for the Hamiltonian of graphene nanoribbon using the nonequilibrium Green’s function formalism. A tight-binding Hamiltonian with an atomistic pz orbital basis set is used to describe the atomistic details in the channel of the GNRFETs. We have investigated the vital short channel effect parameters such as Ion and Ioff, the threshold voltage, the subthreshold swing, and the drain induced barrier lowering versus the channel length and oxide thickness of the GNRFETs in detail. The gate capacitance and the transconductance of both devices are also computed in order to calculate the intrinsic cut-off frequency and switching delay of GNRFETs. Furthermore, the effects of doping of the channel on the threshold voltage and the frequency response of the double-gate GNRFET are discussed. We have shown that the single-gate GNRFET suffers more from short channel effects if compared with those of the double-gate structure; however, both devices have nearly the same cut-off frequency in the range of terahertz. This work provides a collection of data comparing different features of short channel effects of the single gate with those of the double gate GNRFETs. The results give a very good insight into the devices and are very useful for their digital applications.

Double-Gate Graphene Nanoribbon Field-Effect Transistor for DNA and Gas Sensing Applications: Simulation Study and Sensitivity Analysis

In this paper, new sensors based on a double-gate (DG) graphene nanoribbon field-effect transistor (GNRFET), for high-performance DNA and gas detection, are proposed through a simulation-based study. The proposed sensors are simulated by solving the Schrodinger equation using the mode space non-equilibrium Green’s function formalism coupled self-consistently with a 2D Poisson equation under the ballistic limits. The dielectric and work function modulation techniques are used for the electrical detection of DNA and gas molecules, respectively. The behaviors of both the sensors have been investigated, and the impacts of variation in geometrical and electrical parameters on the sensitivity of sensors have also been studied. In comparison to other FET-based sensors, the proposed sensors provide not only higher sensitivity but also better electrical and scaling performances. The obtained results make the proposed DG-GNRFET-based sensors as promising candidates for ultra-sensitive, small-size, low-power and reliable CMOS-based DNA, and gas sensors.

Double gate graphene nanoribbon field effect transistor with electrically induced junctions for source and drain regions

In this paper a novel graphene nanoribbon transistor with electrically induced junction for source and drain regions is proposed. An auxiliary junction is used to form electrically induced source and drain regions beside the main regions. Two parts of same metal are implemented at both sides of the main gate region. These metals which act as side gates are connected to each other to form auxiliary junction. A fixed voltage is applied on this junction during voltage variation on other junctions. Side metals have smaller workfunction than the middle one. Tight-binding Hamiltonian and nonequilibrium Green's function formalism are used to perform atomic scale electronic transport simulation. Due to the difference in metals workfunction, additional gates create two steps in potential profile. These steps increase horizontal distance between conduction and valance bands at gate to drain/source junction and consequently lower band to band tunneling probability. Current ratio and subthreshold swing improved at different channel lengths. Furthermore, device reliability is improved where electric field at drain side of the channel is reduced. This means improvement in leakage current, hot electron effect behavior and breakdown voltage. Application to multi-input logic gates shows higher speed and smaller power delay product in comparison with conventional platform.

Double gate graphene nanoribbon field effect transistor with single halo pocket in channel region

A new structure for graphene nanoribbon field-effect transistors (GNRFETs) is proposed and investigated using quantum simulation with a nonequilibrium Green's function (NEGF) method. Tunneling leakage current and ambipolar conduction are known effects for MOSFET-like GNRFETs. To minimize these issues a novel structure with a simple change of the GNRFETs by using single halo pocket in the intrinsic channel region, “Single Halo GNRFET (SH-GNRFET)”, is proposed. An appropriate halo pocket at source side of channel is used to modify potential distribution of the gate region and weaken band to band tunneling (BTBT). In devices with materials like Si in channel region, doping type of halo and source/drain regions are different. But, here, due to the smaller bandgap of graphene, the mentioned doping types should be the same to reduce BTBT. Simulations have shown that in comparison with conventional GNRFET (C-GNRFET), an SH-GNRFET with appropriately halo doping results in a larger ON current (Ion), smaller OFF current (Ioff), a larger ON–OFF current ratio (Ion/Ioff), superior ambipolar characteristics, a reduced power–delay product and lower delay time.

Theoretical analysis of a novel dual gate metal–graphene nanoribbon field effect transistor

A new double gate graphene nanoribbon field effect transistor with dual material for gate namely DMG-GNRFET is proposed. DMG-GNRFET includes a gate which is divided to the left and right side materials with different work functions. The left side metal (the source side) has lower work function than the right side one. This difference creates a step in potential profile which decreases band to band tunneling. Due to this step, the proposed structure has lower subthreshold swing, higher saturation current, lower leakage current and consequently higher current ratio than conventional structure. These advantages make DMG-GNRFET more suitable for digital applications. Transport properties of the proposed structure are compared to conventional GNRFET. The devices have been simulated based on self-consistent solution of Poisson and Schrodinger equations within non-equilibrium Green׳s function formalism. The effects of third nearest neighbor, dangling bands, and edge roughness have been included in the procedure to obtain more reliable simulations.

Investigation of the novel attributes of a double-gate graphene nanoribbon FET with AlN high-κ dielectrics

The use of high-κ dielectrics is an inevitable requirement to continue the historical performance scaling trend. Recently, the electrical transport characteristics of graphene FET on an aluminum nitride (AlN) substrate in spite of other common dielectric materials indicate significant improvement of carrier mobility. This paper proposes a novel double-gate graphene nanoribbon field-effect transistor (GNRFET) on AlN dielectric substrates. More studies exploring device characteristics are included to assess the performance over the conventional SiO2-based one. It is found that the high-κ GNRFET affords larger on current, on–off ratio, transconductance and intrinsic gain. The high-κ structure also provides further immunity against short-channel effects including drain-induced barrier-lowering and subthreshold swing.

Electrically-activated source extension graphene nanoribbon field effect transistor: Novel attributes and design considerations for suppressing short channel effects

In this paper a double gate graphene nanoribbon field effect transistor with electrically-activated source extension is proposed. Source region of the proposed structure includes two sections, an electrically-activated extension and a doped section. The electrically extension, which is located between doped source section and gate region, is biased independent of the gate to form a virtual extension for source. The electrically-activated extension creates a step in potential profile which increases the horizontal distance between conduction and valance bands at channel to source junction. This step reduces the probability of band to band tunneling, lowers the leakage current and improves drain induced barrier lowering. The devices have been simulated based on self consistent solution of Poisson and Schrodinger equations within non-equilibrium Green’s function formalism. In addition, the effects of the edge and third nearest neighbor are included for more accurate outcomes. Simulations show that the proposed structure is a more reliable device because of its higher ON/Off current ratio, shorter delay time, and smaller power delay product beside lower subthreshold swing than conventional graphene nanoribbon field effect transistor.

A computational study of gate and channel engineering for GNRFETs performance enhancement

In this article, the effects of single-material-gate (SMG), halo doping (HALO), triple-material-gate (TMG) and triple-material halo doping (TMG-H) structures on electrical characteristics have been investigated for double gate graphene nanoribbon field-effect transistors (GNRFETs) using a full quantum transport simulation. The simulations are based on non-equilibrium Green’s functions (NEGF) solved self-consistently using 3D-Poisson’s equations. The results reveal that a larger difference between the work functions of gate metals of TMG structure will result in increasing the on–off current ratio in GNRFETs. HALO structure reduces the leakage current and alleviates the short channel effects (SCEs) like drain-induced barrier-lowering. Because of the perceivable steps in surface potential profile, which leads to additional lateral electric field peak along the channel, TMG and TMG-H structures have a larger average lateral electric field along the channel, which significantly promotes the transport efficiency and thus improves the subthreshold characteristics of devices.

Analytical modeling of uniaxial strain effects on the performance of double-gate graphene nanoribbon field-effect transistors

The effects of uniaxial tensile strain on the ultimate performance of a dual-gated graphene nanoribbon field-effect transistor (GNR-FET) are studied using a fully analytical model based on effective mass approximation and semiclassical ballistic transport. The model incorporates the effects of edge bond relaxation and third nearest neighbor (3NN) interaction. To calculate the performance metrics of GNR-FETs, analytical expressions are used for the charge density, quantum capacitance, and drain current as functions of both gate and drain voltages. It is found that the current under a fixed bias can change several times with applied uniaxial strain and these changes are strongly related to strain-induced changes in both band gap and effective mass of the GNR. Intrinsic switching delay time, cutoff frequency, and Ion/Ioff ratio are also calculated for various uniaxial strain values. The results indicate that the variation in both cutoff frequency and Ion/Ioff ratio versus applied tensile strain inversely corresponds to that of the band gap and effective mass. Although a significant high frequency and switching performance can be achieved by uniaxial strain engineering, tradeoff issues should be carefully considered.

Modelling and simulation of saturation region in double gate graphene nanoribbon transistors

Novel analytical models for surface field distribution and saturation region length for double gate graphene nanoribbon transistors are proposed. The solutions for surface potential and electric field are derived based on Poisson equation. Using the proposed models, the effects of several parameters such as drain-source voltage, oxide thickness and channel length on the length of saturation region and electric field near the drain are studied.

A model for length of saturation velocity region in double-gate Graphene nanoribbon transistors

Length of saturation region (LVSR) as an important parameter in nanoscale devices, which controls the drain breakdown voltage is in our focus. This paper presents three models for surface potential, surface electric field and LVSR in double-gate Graphene nanoribbon transistors. The Poisson equation is used to derive surface potential, lateral electric field and LVSR. Using the proposed models, the effect of several parameters such as drain–source voltage, oxide thickness, doping concentration and channel length on the LVSR is studied.

Numerical study of quantum transport in the double-gate graphene nanoribbon field effect transistors

The ballistic performance of armchair graphene nanoribbon (GNR) field effect transistors (FET) with doped source and drain at different lengths of the channel are studied by self-consistently solving the non-equilibrium Green's Function (NEGF) transport equation in an atomistic basis set with a 3-D Poisson equation. The I– V characteristics of the simulated model manifests the ballistic top of the barrier and tunneling under the barrier currents in different lengths of the intrinsic channel for two different doping of the source and drain extensions of the device. The length-dependent maximum cut-off frequency is derived.