Nanoribbon Tunnel Field Effect Transistor 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).

Graphene antidot nanoribbon tunnel field‐effect transistor

A graphene nanoribbon tunnel field-effect transistor (TFET) model is proposed, in which the antidot pattern is used to generate the heterojunction (HJ) band structure. The intrinsic strain at the HJ interface is absent naturally, greatly avoiding the tunnelling blocking effect of the interface states. The energy gap (Eg) of the graphene antidot nanoribbon (GANR) can be flexibly modulated through the antidot morphology, resulting in highly tunable device performance. Moreover, the stability of the TFET behaviours considering the patterning technology issue is studied. Simulation results indicate that the GANR is suitable for the TFET design in different application scenarios.

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.

Investigation of 6-armchair graphene nanoribbon tunnel FETs

A simulation-based study of an n-type six-dimer-line armchair graphene nanoribbon (6-AGNR) tunnel field-effect transistor with asymmetric reservoir doping density is carried out. Tunnel field-effect transistor (TFET) structures are proposed based on a detailed investigation of the device behavior for different applied voltages, channel lengths, temperatures, insulator thicknesses, dielectric constants, and source impurity molar fractions. By suppressing the tunneling transmission in the off-state, the channel length of the device using HfO2 can be scaled down to 5 nm without increasing the leakage current. When using a supply voltage of 0.4 V, the ION/IOFF ratio reaches a high value of 3.6 × 1010 for the device with a 5-nm channel. Besides, a subthreshold swing (SS) of 3.8 mV/dec is measured for the same GNR-TFET. The high-performance 10-nm-channel device, when supplied with 0.6 V, exhibits a boosted ION value of up to 4.3 × 103 µA/µm, with SS, gm, and Dini values of 28 mV/dec, 11 µS, and 11 fs, respectively. Nevertheless, conventional GNR-TFETs with various channel lengths exhibit rather outstanding characteristics. Such 6-AGNR TFETs display promising functionality for application in future digital and analog integrated circuits.

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.

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

A new ultra-scaled graphene nanoribbon junctionless tunneling field-effect transistor: proposal, quantum simulation, and analysis

In this paper, a new ultrascaled junctionless graphene nanoribbon tunnel field-effect transistor (JL GNRTFET) is proposed through a computational study. The quantum simulation approach is based on the resolution of the Schrodinger equation using the mode space non-equilibrium Green’s function formalism coupled self-consistently with a Poisson equation in the ballistic limit. The proposed nanodevice is endowed with ungated region between the auxiliary and control gates as well as with a laterally graded channel doping in order to improve the switching performance of the ultrascaled junctionless GNRTFET. The performance assessment has included the IDS–VGS transfer characteristics, subthreshold swing, current ratio, intrinsic delay, and power-delay product. It has been found that the proposed ultrascaled junctionless GNR tunneling FET can provide improved switching performance than its conventional counterpart. The proposed strategy can be applied to improve similar ultrascaled junctionless tunneling field-effect transistors for the future digital electronics, where the high-performance and the aggressive downscaling should be in agreement.

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

An analytical drain current model for graphene nanoribbon tunnel field-effect transistors

We develop a tunneling probability model based on a structure of p+-i-n+ of a graphene nanoribbon (GNR) tunnel field-effect transistors (TFETs), and present an analytical drain current model based on the tunneling probability model. Model results are compared with those in the literature, and good agreements are observed. With the drain current model, the output and transfer characteristics of currents in a GNR TFET can be obtained easily and quickly. Being in an explicit form, the drain current model can be embedded in the integrated circuit design simulation tools. We observe that low temperature favors both the GNR TFET’s drain current and subthreshold swing.

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.

Computational study of silicene nanoribbon tunnel field-effect transistor

Stable room temperature operation of field-effect transistor (FET) based on two-dimensional silicon (silicene) has recently been reported. Like graphene, silicene is a Dirac cone material. Silicene-based devices provide high off-state leakage current due to lack of a significant bandgap. However, quantum confined silicene nanoribbon (SiNR) shows observable bandgap which can be used for making switching transistors for digital integrated circuit design. Contrary to metal oxide semiconductor FET (MOSFET), tunnel field-effect transistor (TFET) overcomes the physical limit of scaling of supply voltage. In this work, we present structure and characteristics of SiNR TFET using atomistic simulation based on self-consistent solution of 3D Poisson and Schrodinger equations within the non-equilibrium Green’s function formalism. Performances are also compared with the International Technology Roadmap for Semiconductors projected high performance requirements of 2026 nMOSFETs.

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.

Performance Evaluation of Bilayer Graphene Nanoribbon Tunnel FETs for Digital and Analog Applications

The recent advancement in the fabrication of narrow graphene nanoribbon with smooth edges has catalyzed the growth of nanoribbon based transistors. Motivated by these advances, we suggest bilayer graphene nanoribbon tunnel field-effect transistors (BLGNR-TFETs) for low voltage digital and analog applications. The device performance is analyzed by quantum transport simulation, based on self-consistent solutions of two-dimensional Poisson's equation and nonequilibrium Green's function formalism. The results indicate that the use of BLGNR-TFET instead of monolayer graphene nanoribbon TFET with very narrow width, increases the ON current and reduces the intrinsic device delay without lowering the ON/OFF current ratio. The BLGNR-TFET for analog/RF applications has provided higher intrinsic gain at very narrow ribbon width; however, very narrow width reduces the cutoff frequency. Furthermore, RF figure of merits are investigated in the presence of external parasitics.

Silicene Nanoribbon Tunnel Field Effect Transistor

Scaling of metal oxide semiconductor field effect transistor (MOSFET) following the Moore’s law is approaching to its near end as the power dissipation at the chip level is becoming increasingly difficult to reduce [1]. The International Technology Roadmap for Semiconductors (ITRS) considers several non-classical devices as a future replacement of silicon-based MOSFETs among which tunnel field effect transistor (TFET) is found to be promising [2, 3]. Compared to bulk three dimensional material based TFETs, study of TFETs based on two dimensional atomically thick materials have shown potential to operate at low supply voltage with a low subthreshold slope (SS) compared to 60mV/decade in conventional MOSFETs [4]. Different forms of two dimensional materials are studied such as Dirac cone materials (graphene, silicene, gemanene, stanene), transition metal dichalcogenides (TMD), transition oxides (TO) and topological insulators (TI). Compared to the study of TFET based on other two dimensional materials, silicene TFET remained large unexplored. Silicene is the two dimensional atomically thick planer form of bulk silicon. Stable room temperature operation of FET based on silicene has recently been reported [5]. Like graphene, silicene is a Dirac cone material with devices which provide high off-state leakage current due to the lack of a significant bandgap. However, quantum confined silicene nanoribbon (SiNR) shows observable bandgap making it suitable for digital applications [6]. Moreover, being an allotrope of silicon, silicene is also expected to be suitable for fabrication technology. Here, we present our work on SiNR TFET using atomistic simulation based on self-consistent solution of the 3D Poisson and Schrödinger equations within the non-equilibrium Green’s function (NEGF) formalism. SiNR has two types of edges, armchair and zigzag. We have considered armchair configuration in our study for a channel length of 10nm of a double gate SiNR TFET. Source and drain are 10nm each. Our default SiNR width is ~4nm providing a band gap of 1.42eV. Top and bottom gate oxides of our studied TFET are 2nm of SiO2. The effective tight binding Hamiltonian is adopted from the work of Voon et al. [7] and is simulated using the simulation code proposed in [8] for Si-Si bond length of 2.25Å and hoping integral of -6.43eV with -1.12eV correction at the SiNR edges [7]. The n+-type source and p+-type drain are doped with a molecular fraction of 0.001. A drain source voltage (VDS) of 0.3V is considered in this work. The studied SiNR TFET provides an on/off current ratio of ~107 with an average steep subthreshold slope (SS) of 6mV/decade for VDS=0.3V. A record low ~0.75x10-11pW/μm off-state leakage power is estimated. We have found that the leakage level increases as the supply voltage increases. The off-state leakage current increases to 0.6pA/μm as VDS increases from 0.3V to 0.95V. As the width of SiNR increases and the corresponding band gap decreases, leakage current also increases at small band gap with a reduction in on/off current ratio. The steep subthreshold slope of our studied SiNR TFET suits low power operation. With a suitable high-k dielectric and low gate oxide thickness, on-state drive current can be improved. Performance of SiNR TFET is also compared with ITRS projected high performance (HP) requirements of 2026 nMOSFET where SiNR TFET exceeds the performance of 2026 nMOSFET by 1014 times less power dissipation at 103 times higher on/off current ratio. Acknowledgement: Part of the work is supported by the United States Air Force Research Laboratory under agreement number FA9453-10-1-0002. The U.S. Government is authorized to reproduce and distribute reprints for Government purposes notwithstanding any copyright notation thereon.

Silicene Nanoribbon Tunnel Field Effect Transistor

Stable room temperature operation of field effect transistor (FET) based on two-dimensional silicon (silicene) has recently been reported. Like graphene, silicene is a Dirac cone material. Silicene-based devices provide high off-state leakage current due to lack of a significant bandgap. However, quantum confined silicene nanoribbon (SiNR) shows observable bandgap which can be used for making switching transistors for digital integrated circuit design. Contrary to metal oxide semiconductor FET (MOSFET), tunnel field effect transistor (TFET) overcomes the physical limit of scaling of supply voltage. In this work, we present structure and characteristics of SiNR TFET using atomistic simulation based on self-consistent solution of 3D Poisson and Schrödinger equations within the non-equilibrium Green’s function (NEGF) formalism. Performances are also compared with the International Technology Roadmap for Semiconductors (ITRS) projected high performance requirements of 2026 nMOSFETs.