Graphene Nanoribbon Tunnel Field Effect Research Articles

Modelling of Cut-off Frequency of Armchair Graphene Nanoribbon Tunnel Field Effect Transistor Using Transfer Matrix Method

Graphene is considered as a promising two-dimensional material for electronic device applications due to its high charge carrier mobility and it is extremely thin in size. As a material, graphene has great potential for the development of high-speed nano electric devices. Graphene can be used as a channel material in Tunnel Field Effect Transistor (TFET). In this study, the cut-off frequency of the armchair graphene nanoribbon tunnel field effect transistor (AGNR-TFET) device was modelled quantum mechanically. The solution of the Dirac-like Hamiltonian and Poisson equations self-consistently is used to determine the potential profile of device and the transmittance is calculated using the transfer matrix method (TMM). The Landauer formulation with the help of Gauss Legendre Quadrature Method (GLQM) is used to calculate the tunnelling current and the cut-off frequency of AGNR-TFET. The calculation results showed that the cut-off frequency increased as the drain voltage increased, while the increase in channel length and the N-index graphene made the cut-off frequency decreased. Moreover, the thicker the oxide layer could increase the cut-off frequency and the higher the temperature on the device would reduce the cut-off frequency.

Electrostatically Doped Junctionless Graphene Nanoribbon Tunnel Field-Effect Transistor for High-Performance Gas Sensing Applications: Leveraging Doping Gates for Multi-Gas Detection.

In this paper, a new junctionless graphene nanoribbon tunnel field-effect transistor (JLGNR TFET) is proposed as a multi-gas nanosensor. The nanosensor has been computationally assessed using a quantum simulation based on the self-consistent solutions of the mode space non-equilibrium Green's function (NEGF) formalism coupled with the Poisson's equation considering ballistic transport conditions. The proposed multi-gas nanosensor is endowed with two top gates ensuring both reservoirs' doping and multi-gas sensing. The investigations have included the IDS-VGS transfer characteristics, the gas-induced electrostatic modulations, subthreshold swing, and sensitivity. The order of change in drain current has been considered as a sensitivity metric. The underlying physics of the proposed JLGNR TFET-based multi-gas nanosensor has also been studied through the analysis of the band diagrams behavior and the energy-position-resolved current spectrum. It has been found that the gas-induced work function modulation of the source (drain) gate affects the n-type (p-type) conduction branch by modulating the band-to-band tunneling (BTBT) while the p-type (n-type) conduction branch still unaffected forming a kind of high selectivity from operating regime point of view. The high sensitivity has been recorded in subthermionic subthreshold swing (SS < 60 mV/dec) regime considering small gas-induced gate work function modulation. In addition, advanced simulations have been performed for the detection of two different types of gases separately and simultaneously, where high-performance has been recorded in terms of sensitivity, selectivity, and electrical behavior. The proposed detection approach, which is viable, innovative, simple, and efficient, can be applied using other types of junctionless tunneling field-effect transistors with emerging channel nanomaterials such as the transition metal dichalcogenides materials. The proposed JLGNRTFET-based multi-gas nanosensor is not limited to two specific gases but can also detect other gases by employing appropriate gate materials in terms of selectivity.

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).

Simulation insights of a new dual gate graphene nano-ribbon tunnel field-effect transistors for THz applications

This paper introduces a dual gate Graphene Nano-Ribbon Tunnel Field Effect Transistor (DG GNR TFET) structure and its performance characteristics are analysed. Technology Computer-Aided Design (TCAD) tool is used to simulate this novel non-silicon GNR TFET and to characterize various parameters of the device. A DG GNR TFET shows better device performance in terms of its surface potential, electric field and ON current (ION). The simulation results show that the proposed structure exhibits better ION/IOFF (109), average sub-threshold swing (43.16 mv/Dec) and threshold (0.3 V) when compared to a conventional Silicon TFET. Design parameters for the device such as dielectric thickness, body thickness, work function, source doping concentration, and channel length are analysed to deduce the fact that GNR can be used as an effective material in TFETs for low power electronics applications. Moreover, key parameters such as transconductance, transconductance generation efficiency and cut-off frequency (THz) are greatly improved in this proposed structure, which is highly desirable for analog/RF applications.

Design of bilayer graphene nanoribbon tunnel field effect transistor

PurposeThe purpose of this paper is to design novel tunnel field effect transistor (TFET) using graphene nanoribbons (GNRs).Design/methodology/approachTo design the proposed TFET, the bilayer GNRs (BLGNRs) have been used as the channel material. The BLGNR-TFET is designed in QuantumATK, depending on 2-D Poisson’s equation and non-equilibrium Green’s function (NEGF) formalism.FindingsThe performance of the proposed BLGNR-TFET is investigated in terms of current and voltage (I-V) characteristics and transconductance. Moreover, the proposed device performance is compared with the monolayer GNR-TFET (MLGNR-TFET). From the simulation results, it is investigated that the BLGNR-TFET shows high current and gain over the MLGNR-TFET.Originality/valueThis paper presents a new technique to design GNR-based TFET for future low power very large-scale integration (VLSI) devices.

Model of Tunneling Current on Bilayer Armchair Graphene Nanoribbon Tunnel Field Effect Transistor Using Transfer Matrix Method

Model of Tunneling Current on Bilayer Armchair Graphene Nanoribbon Tunnel Field Effect Transistor Using Transfer Matrix Method

Influence of defects on dissipative transport in graphene nanoribbons tunnel field-effect transistor

The influence of point defects on the dissipative carrier transport of armchair graphene nanoribbon (GNR) tunnel field effect transistor (TFET) is studied by solving the self-consistent Born approximation problem using the extended lowest order expansion method. The simulation results show that by introducing point defects to the channel region of the armchair GNR-TFET, the OFF state phonon contribution to the carrier transport changes significantly compared with that of the pristine device. The presence of defect would introduce additional optical phonon mode of much higher energy, which facilitates the OFF state phonon-assisted band-to-band tunneling process in a broader energy range and contribute to the dissipative carrier transport. In the ON-state, where the direct source to drain tunneling is at maximum, the electron–phonon interaction has a negligible effect, which is similar to that of the pristine device. Moreover, different defect types and locations are examined, their influence on hole and electron transport are reported.

Modeling of Armchair Graphene Nanoribbon Tunnel Field Effect Transistors for Low Power Applications

Modeling of Armchair Graphene Nanoribbon Tunnel Field Effect Transistors for Low Power Applications

Comparison of tunneling currents in graphene nanoribbon tunnel field effect transistors calculated using Dirac-like equation and Schrödinger's equation

The tunneling current in a graphene nanoribbon tunnel field effect transistor (GNR-TFET) has been quantum mechanically modeled. The tunneling current in the GNR-TFET was compared based on calculations of the Dirac-like equation and Schrödinger's equation. To calculate the electron transmittance, a numerical approach-namely the transfer matrix method (TMM)-was employed and the Launder formula was used to compute the tunneling current. The results suggest that the tunneling currents that were calculated using both equations have similar characteristics for the same parameters, even though they have different values. The tunneling currents that were calculated by applying the Dirac-like equation were lower than those calculated using Schrödinger's equation.

Sub-thermal switching of ultra-narrow graphene nanoribbon tunnel field effect transistors

In this paper, we study the device performance of the graphene nanoribbon tunnel field effect transistors in the sub 0.5V bias voltage range by non-equilibrium Green's function calculation. The ON/OFF ratio is found to increases with decreasing bias voltage, as the improved current suppression in the OFF state at low bias is more effective than the reduction of carriers in the ON state. Abrupt increase of the subthreshold slope (SS) from sub-thermal ∼30 mV/dec to 60 mV/dec below VBias of 0.1 V is observed. SS relates to the occupancy of carriers at the threshold energy of band-to-band tunneling. We furthermore discuss the constant potential barrier scaling of the graphene channel width and length.

Graphene Nanoribbon Tunnel Field-Effect Transistor via Segmented Edge Saturation

In this paper, segmented edge saturation (SES) is proposed as a novel method to design high-performance tunnel FETs (TFETs) using smooth graphene nanoribbon (GNR). When the edges of a smooth GNR are saturated by different elements in its different segments, the energy gaps ( ${E}_{g})$ of these segments can be tuned. Therefore, the tunneling and blocking effects are achieved simultaneously by reducing and enlarging the ${E}_{g}$ of GNR in its specific regions. Both high on-to-off current ( ${I}_{ \mathrm{\scriptscriptstyle ON}}/{I}_{ \mathrm{\scriptscriptstyle OFF}})$ ratio and large ${I}_{ \mathrm{\scriptscriptstyle ON}}$ are obtained. Simulation results show that the $\mathrm {I}_{ \mathrm{\scriptscriptstyle OFF}}$ of the SES GNR TFET is below $1 \times 10^{-4} ~\mu \text{A}/\mu \text{m}$ and the ${I}_{{ \mathrm{\scriptscriptstyle ON}}}$ reaches 2000 $\mu \text{A}/\mu \text{m}$ at 0.4-V supply voltage. Detailed transport mechanisms of this TFET are investigated in comparisons with its uniform saturation counterparts. Dynamic performance and scaling ability analyzes are also carried out. The largest intrinsic delay and switching energy are only 0.17 ps and 0.09 fJ/ $\mu \text{m}$ . Meanwhile, it can maintain high ${I}_{{ \mathrm{\scriptscriptstyle ON}}}/{I}_{ \mathrm{\scriptscriptstyle OFF}}$ ratios when the channel length is scaled down to several nanometers. The discussions on GNR edge roughness suggest that the roughness should be avoided for better ${I}_{ \mathrm{\scriptscriptstyle ON}}$ behaviors. The good performance of the TFET highlights the capabilities of SES in the developments of GNR tunnel devices.

Analytical Current Transport Modeling of Graphene Nanoribbon Tunnel Field-Effect Transistors for Digital Circuit Design

A semi-classical and a semi-quantum current transport model for p-i-n n-type armchair graphene nanoribbon tunnel field effect transistor (TFET) are studied analytically. The results are compared with the numerical quantum transport simulation method using an atomistic Schrodinger–Poisson solver within the non-equilibrium Green function (NEGF) formalism. The channel length and width are 20 and 4.9 nm and a-GNR band gap is 0.289 eV. Current ratio ${\rm I_{ON}}/{\rm I_{OFF}}$ at 0.1 V supply voltage is calculated as follows: 122, 16.3 and 116 with a subthreshold slopes 26, 69 and 27.4 mV/decade from semi-classical, semi-quantum and NEGF simulation, respectively. Performance of a-GNR TFET is also studied analytically and numerically considering a-GNR width variation. Voltage transfer characteristics of a-GNR TFET inverter are computed for 0.1 V and 0.2 supply voltages using three current transport models which are in close agreement.

Simulation of Dirac Electron Tunneling Current in Armchair Graphene Nanoribbon Tunnel Field-Effect Transistors Using a Transfer Matrix Method

We simulate quantum mechanical tunneling current in armchair graphene nanoribbon tunnel field-effect transistors (AGNR-TFETs). The relativistic Dirac equation is used to determine electron wave functions in the AGNRs, while the potential profile is solved by the Poisson equation. We use a transfer matrix method (TMM) to calculate the electron transmittance and the Dirac electron tunneling current in the AGNR-TFETs. The results show that the Dirac electron tunneling current increases with increasing the drain and gate voltages. Moreover, the AGNR width and the thickness of insulator affect the characteristics of the Dirac electron tunneling currents.

Graphene nanoribbon tunnel field effect transistor with lightly doped drain: Numerical simulations

By inserting a lightly doped region between the highly doped drain and the intrinsic channel of a graphene nanoribbon tunnel field effect transistor (GNR-TFET), we propose a new lightly doped drain (LDD)-GNR-TFET. Transport characteristics of the proposed transistor is numerically simulated, employing the third-nearest-neighbor tight-binding approximation in mode space non-equilibrium Green’s function formulism (NEGF), in ballistic regime. Simulations show, in comparison with a conventional GNR-TFET of the same dimensions, the proposed LDD-GNR-TFET exhibits a 102–103 times smaller OFF-current, an up to 105 times larger ON/OFF ratio, a shorter time delay, a smaller power-delay product (PDP) and a less drain induced barrier thinning (DIBT), besides preserving the subthreshold swing.

A Theoretical Model of Band-to-Band Tunneling Current in an Armchair Graphene Nanoribbon Tunnel Field-Effect Transistor

Tunneling current in an armchair graphene nanoribbon (AGNR) tunnel field-effect transistor (TFET) was modeled. A linear equation was employed in describing a potential distribution within the AGNR due to its simplicity. A parabolic dispersion and an electron effective mass obtained by approximating kx 0 to the parabolic dispersion were applied to AGNR. In order to obtain electron transmittance, electron wavefunctions in AGNR were based on Airy functions. The obtained transmittance was then applied to calculate the tunneling current by employing the Landauer formula. The calculated results showed that the tunneling current increases with the AGNR width. It was also shown that the tunneling current increases as temperature decreases. In addition, the gate voltage influences the saturation condition of tunneling current in AGNR TFETs.

Graphene nanoribbon tunneling field effect transistors

The electron-hole symmetry characteristic of graphene nanoribbons (GNRs) gives rise to the electron (hole) tunneling through valence (conduction) band states. By employing this property we have numerically investigated GNR field effect transistors with p+-type source and drain in the presence of a gate voltage-induced n-type channel using the non-equilibrium Green's function formalism.For long channels, the traditional FET-like I-V behavior is achieved, but at short channels, the sub threshold current opens up an oscillatory dependence on the gate voltage with a considerable amount of current of over 10−6A. This is the characteristic current behavior of resonant tunneling transistors that exhibit regions of negative differential resistance. The calculated discrete density of states in the channel attributes this behavior to the constructed n-type channel island between p-type source and drain with thin barriers formed by the energy gap.

Graphene Nanoribbon Tunneling Field-Effect Transistors With a Semiconducting and a Semimetallic Heterojunction Channel

We present a computational study of the device performance of graphene nanoribbon tunneling field-effect transistors (TFETs) with a heterogeneous channel. By varying the length and the energy bandgap (EG) of the heterogeneous region, the on- and off-state currents (ION and IOFF) can be effectively optimized independently. Both semiconducting and semimetallic heterogeneous regions are studied to understand the effects of EG engineering on device behaviors. In addition, the effect of gate coverage (GC) over the heterogeneous region is also investigated. We found that device performance is greatly affected by the positioning of the gate to modify the region where band-to-band tunneling occurs. For a given ION/IOFF of eight orders, our results show that, for the semiconducting heterojunction, a higher ION can be obtained by having the gate partially covering the heterogeneous region. This is due to a combination of a short tunneling length and resonant states, which leads to an increase in carrier concentration for the tunneling mechanism. On the other hand, for the semimetallic case, a similar ION/IOFF is only attainable when the heterogeneous region is not covered by the gate. A large IOFF is observed for even small GC due to the valence electrons from the source traveling to the conduction bands of the semimetallic region, enhancing the carrier transport toward the drain. Our study highlights the device design consideration required when optimizing the device performance of heterojunction TFETs.

Modeling and simulation of uniaxial strain effects in armchair graphene nanoribbon tunneling field effect transistors

In this paper, we perform a modeling and simulation study on strained armchair graphene nanoribbon (AGNR). Two uniaxial strain models based on a tight binding method are compared with results from first-principles calculation. Tunneling field effect transistors (TFETs) with channels made of strained AGNR of different widths are modeled and simulated by a ballistic quantum transport model based on nonequilibrium Green’s function and nonparabolic effective mass approximation. Compared with TFETs with narrow AGNR, those with strained wide AGNR can achieve better device performance.

Effect of Ribbon Width and Doping Concentration on Device Performance of Graphene Nanoribbon Tunneling Field-Effect Transistors

The device performance of graphene nanoribbon (GNR) tunneling field-effect transistor (TFET) is studied using the self-consistent non-equilibrium Green's function (NEGF) and quasi-two dimensional Poisson solver based on the Dirac equation model. The effects of different GNR widths and doping concentrations at the source and drain on the device characteristics are investigated and the electronic property of the GNR TFET is found to be strongly dependent on its width. A comprehensive characterization of this dependence is expected to be crucial to the designs and fabrications of GNR TFETs. Furthermore, the doping concentrations at the source and drain is found to play a crucial role on the ON- and OFF-state currents (ION and IOFF) respectively. Therefore, the ability to control the doping concentrations allows the tailoring of the drive current, the ION/IOFF ratio and the subthreshold swing of GNR TFETs to meet different design requirements.