Nanoribbon Field-effect Transistors Research Articles

Using Superlattice Structure in the Source of GNRFET to Improve Its Switching Performance

Our aim is to improve the switching performance of the graphene nanoribbon field-effect transistors (GNRFETs), exploiting the concept of energy filtering. Within the proposed scheme, a superlattice (SL) structure is used in the source of the transistor for filtering high-energy electron tail by engineering the density of states (DOS). According to simulation results, this can significantly decrease the OFF-current and the subthreshold swing (SS). A comparison of the proposed device with a conventional GNRFET and a graphene nanoribbon (GNR) tunneling field-effect transistor (GNRTFET) demonstrates a significant improvement. Therefore, a typical SL-GNRFET can reduce the average and the minimum of the SS to 44.6 and 12.5 mV/dec, respectively, at room temperature. Moreover, in order to optimize the proposed structure, the effects of the SL geometrical parameters on the transistor characteristics are numerically investigated.

Investigating electrical properties of controllable graphene nanoribbon field effect transistors

It is always an important issue to open the energy gap for graphene while retaining its high carrier mobility. Narrowing down large-area graphene into graphene nanoribbons (GNRs) is one of the ways to open the energy gap to achieve field-effect transistors (FET) suitable for logic circuits. But it has been a problem to obtain GNRs with controllable width and specific boundary structure. In this work, we proposed a simple high-precision preparation method for GNRs. In the process, GNRs with a width of 200 nm and smooth edges were prepared by a focused ion beam (FIB) etching process. Graphene nanoribbon field-effect transistors (GNR-FET) were fabricated by electron beam lithography (EBL). In this device, due to the proximity of the edge of the He+ during the FIB etching process, the carbon atom structure of the GNRs edge was changed, resulting in variations in electron transport properties. The electrical performance test demonstrated that the on/off current ratio of the GNR-FET device was up to 103 at room temperature. The structural defects of the GNRs caused the device carrier mobility down to 371.6 cm2V−1s−1. The structural defects in the GNRs edge introduced by FIB can improve the on/off current ratio of the device and hence enhanced its electrical regulation performance. Our work provides a simple method of making controllable GNRs to fabricate field effect transistors.

Single Gate Graphene Nanoribbon-on-Insulator (GNROI) FET as a Novel Strategy to Enhance Electrical Performance-Numerically RF and DC Characteristics Extraction

Graphene nanoribbon Field Effect Transistor (GNRFET) as a recently introduced interesting candidate has gotten a great deal of interest in many device fields. The paper has suggested a novel configuration in the case of only single gate on the top channel. The GNR is deposited on SiO2 considered as the thick buried oxide instead of SiC material in the single gate conventional GNRFET. This reformation is led to the gradual variation of the surface potential thus increasing the electric field and electron velocity. An increase in the drain current for the proposed device is the most important exploration in this work. The numerically extracted parameters by TCAD revealed the electrical performance improvement for both the DC and RF conditions in the cases of the ON current, sub-threshold swing, DIBL, Ion/Ioff, parasitic capacitances, transconductance, power gains, and output conductance. It is worth noting that the short channel effects are well controlled in the new proposed configuration. Also, the impact of different High-K dielectrics as the buried oxide on the electrical performance has been studied and the most suitable buried oxide has been selected to reach the best results.

Simulations of Graphene Nanoribbon Field Effect Transistor for the Detection of Propane and Butane Gases: A First Principles Study.

During the last few years graphene has emerged as a potential candidate for electronics and optoelectronics applications due to its several salient features. Graphene is a smart material that responds to any physical change in its surrounding environment. Graphene has a very low intrinsic electronic noise and it can detect even a single gas molecule in its proximity. This property of graphene makes is a suitable and promising candidate to detect a large variety of organic/inorganic chemicals and gases. Typical solid state gas sensors usually requires high operating temperature and they cannot detect very low concentrations of gases efficiently due to intrinsic noise caused by thermal motion of charge carriers at high temperatures. They also have low resolution and stability issues of their constituent materials (such as electrolytes, electrodes, and sensing material itself) in harsh environments. It accelerates the need of development of robust, highly sensitive and efficient gas sensor with low operating temperature. Graphene and its derivatives could be a prospective replacement of these solid-state sensors due to their better electronic attributes for moderate temperature applications. The presence of extremely low intrinsic noise in graphene makes it highly suitable to detect a very low concentration of organic/inorganic compounds (even a single molecule ca be detected with graphene). In this article, we simulated a novel graphene nanoribbon based field effect transistor (FET) and used it to detect propane and butane gases. These are flammable household/industrial gases that must be detected to avoid serious accidents. The effects of atmospheric oxygen and humidity have also been studied by mixing oxygen and water molecules with desired target gases (propane and butane). The change in source-to-drain current of FET in the proximity of the target gases has been used as a detection signal. Our simulated FET device showed a noticeable change in density of states and IV-characteristics in the presence of target gas molecules. Nanoscale simulations of FET based gas sensor have been done in Quantumwise Atomistix Toolkit (ATK). ATK is a commercially available nanoscale semiconductor device simulator that is used to model a large variety of nanoscale devices. Our proposed device can be converted into a physical device to get a low cost and small sized integrated gas sensor.

Theoretical Analysis of Tunneling GNRFET under Local Compressive Uniaxial Strain

By applying %3 compressive local uniaxial strain on 2.5 nm of source and 2.5 nm of channel regions of tunneling graphene nanoribbon field-effect transistor (T-GNRFET), we propose a new local-strained source and channel (LSSC) T-GNRFET. Quantum simulations of the proposed structure have been done in mode-space non-equilibrium Green’s function (NEGF) approach in ballistic regime. Simulation results show that in comparison with the conventional T-GNRFET of the same dimensions, the ON-current of the proposed structure has been improved considerably. Besides, the proposed structure enjoys better analog characteristics such as transconductance (gm) and unity-gain frequency (ft).

Design of Ternary Logic and Arithmetic Circuits Using GNRFET

Multiple valued logic (MVL) can represent an exponentially higher number of data/information compared to the binary logic for the same number of logic bits. Compared to the conventional and other emerging device technologies, Graphene Nano Ribbon Field Effect Transistor (GNRFET) appears to be very promising for designing MVL logic gates and arithmetic circuits due to some exceptional electrical properties of the GNRFET, e.g., the ability to control the threshold voltage by changing the width of the GNR. Variation of the threshold voltage is one of the prescribed techniques to achieve multiple voltage levels to implement the MVL circuit. This paper introduces a design approach for ternary logic gates and circuits using MOS-type GNRFET. The designs of basic ternary logic gates like inverters, NAND, NOR, and ternary arithmetic circuits like the ternary decoder, 3:1 multiplexer, and ternary half-adder are demonstrated using GNRFET. A comparative analysis of the GNRFET based ternary logic gates and circuits and those based on the conventional CMOS and CNTFET technologies is performed using delay, total power, and power-delay-product (PDP) as the metrics. The simulation and analysis are performed using the H-SPICE tool with a GNRFET model available on the Nanohub website.

Design of High-Performance 1-Bit Full Adder Cells Based on MOS-Type GNRFETs

In deep sub-micron technologies, conventional silicon-based transistors are faced main several problems related to the short-channel effects such as power dissipation, subthreshold leakage, and drain-induced barrier lowering (DIBL). Graphene nano-ribbon field-effect transistors (GNRFETs) have become a potential contender as a substitute for traditional silicon-based transistors in next generation nano-electronic devices. They exhibit fantastic properties such as high charge carrier mobility, mean free path of electrons, faster switching, and high ION/IOFF ratio. In order to prove the competences and superiority of these types of transistors, various circuits like full adder (FA) cells, which are the main building block of computational systems must be simulated and studied. This paper presents redesigning various 1-bit FA cells such as Complementary Metal-Oxide-Semiconductor (CMOS), Complementary Pass-Transistor Logic (CPL), Transmission-Gate (TG), Hybrid CMOS (HCMOS), and Transmission Function Adder (TFA) using MOS-GNRFET devices in 16nm technology node. Different HSPICE simulations are performed to obtain propagation delay, average power consumption, power-delay-product (PDP), and energy-delay-product (EDP) of FA cells and are compared with 16nm CMOS predictive technology model (PTM) at different supply voltages. The obtained results indicate that MOS-GNRFET based 1-bit FA cells have better performance than that of Si-CMOS one. The MOS-GNRFET based FA cells improve propagation delay and EDP at least 31.195% and 4.372%, respectively.

Local impact of Stone–Wales defect on a single layer GNRFET

In this work, a new structure of single layer armchair graphene nanoribbon field effect transistor with the Stone–Wales (SW) defect (SWGNRFET) is studied. The simulations are solved with Poisson–Schrödinger equation self-consistently by using Non-Equilibrium Green Function (NEGF) and in the real space approach. The energy band structure is obtained by approximation tight-binding method. The results show that displacement of a defect in the width of the channel of the new structure is led to 50% increase in ION/IOFF ratio only by rotating of a C–C (Carbon–Carbon) bond with similar behavior. But, a remarkable increase of 300% in ION/IOFF ratio is obtained by a “dual center” defect. The results show that structure with defects in the middle of the channel, has the best performance of SWGNRFET. On the other hand, ION/IOFF ratio decreases when the defect moves from middle to the “near the drain” and “source”.

Engineered Nanopores-Based Armchair Graphene Nanoribbon FET With Resonant Tunneling Performance

This article presents a novel armchair graphene nanoribbon (AGNR) field-effect transistor with engineered nanopores for resonant tunneling. Two rectangular nanopores are punched to create two potential barriers and one quantum well. Channel and source and drain contacts are AGNR, indicating structure homogeneity. Nonequilibrium Green’s function and Poisson’s equations are used for structural analysis. The input variables are well width (WW), drain voltage ( ${V}_{D}{)}$ , and barrier width (BW). The effects of repositioning nanopores and AGNR type (i.e., semiconductor and semimetal) are also studied. The impact of the parameters on the density of states, transmission probabilities, peak current ( ${I}_{P}{)}$ and its voltage ( ${V}_{P}{)}$ , valley current ( ${I}_{V}$ ) and its voltage ( ${V}_{{V}}{)}$ , and peak-to-valley ratio (PVR) are investigated. Simulation results show that in both AGNR types, a decrease in WW brings about higher ${I}_{P}$ , ${V}_{P}$ , and ${V}_{V}$ . Moreover, in the semimetal AGNR, the narrowest WW leads to the highest PVR value. Another key observation is that with a decrease in ${V}_{D}$ , the PVR increases, and negative gate transconductance (NGT) characteristics show better performance. In addition, in the semimetal AGNR, the highest PVR value and the best NGT characteristics occur at the highest BW. Furthermore, repositioning nanopores across the device width does not affect the energy of the first resonance level. Finally, the structure with the largest unobstructed width (i.e., the one with the least backscattering) has the highest PVR.

NDR Behavior of a Phosphorous-Doped Double-Gate MoS2 Armchair Nanoribbon Field Effect Transistor

This paper presents the negative differential resistance (NDR) behavior of an MoS2 armchair nanoribbon double-gate field effect transistor. The large peak-to-valley current ratio (PVCR) of 2.58 × 102 with a peak current value of − 0.8 μA is achieved with the presented device configuration. A 5-nm channel length device was considered for the study and an extended Huckel model with nonequilibrium Green’s function method is used for the simulation. A phosphorus atom is used as a substitutional dopant at the sulfur site of the MoS2 field effect transistor near the source and drain regions. The PVCR of the device can be controlled by applying a gate voltage. The achieved subthreshold slope of the device is 88 mV/decade with Ion/Ioff value of 1011 at 300 K. The other parameters such as peak current and NDR voltage window are analyzed. The proposed device configuration shows the potentiality of MoS2 armchair nanoribbon material for future small length scale electronic device applications.

Modeling of lightly-doped drain and source contact with boron and nitrogen in graphene nanoribbon

Graphene, a monolayer carbon atoms arranged in hexagonal honeycomb lattice possesses impressive electronic properties. It is utilized as channel, source and drain contact in graphene nanoribbon field-effect transistor (GNRFET). Zigzag graphene nanoribbon (ZGNR) is used as semi-metallic drain and source terminal to a pristine armchair graphene nanoribbon (AGNR) that acts as a semiconducting channel. In addition, a single dopant, either nitrogen or boron is added to create lightly-doped drain and source contact. The electronic properties of graphene nanoribbon (GNR) with lightly-doped drain and source contacts are obtained from tight-binding approach. With self-energy matrices, the lightly-doped contacts Hamiltonian matrices are combined with the pristine channel Hamiltonian matrix. The density of states (DOS) are simulated based on the non-equilibrium Green's Function (NEGF) formalism. Our findings are then compared with published research work. Furthermore, it is demonstrated that the DOS of the overall GNR structure still retain a small band gap and possess semiconducting properties when the channel is connected to semi-metallic contact at the drain and source terminal.

Fault Modeling of Graphene Nanoribbon FET Logic Circuits

Due to the increasing defect rates in highly scaled complementary metal–oxide–semiconductor (CMOS) devices, and the emergence of alternative nanotechnology devices, reliability challenges are of growing importance. Understanding and controlling the fault mechanisms associated with new materials and structures for both transistors and interconnection is a key issue in novel nanodevices. The graphene nanoribbon field-effect transistor (GNR FET) has revealed itself as a promising technology to design emerging research logic circuits, because of its outstanding potential speed and power properties. This work presents a study of fault causes, mechanisms, and models at the device level, as well as their impact on logic circuits based on GNR FETs. From a literature review of fault causes and mechanisms, fault propagation was analyzed, and fault models were derived for device and logic circuit levels. This study may be helpful for the prevention of faults in the design process of graphene nanodevices. In addition, it can help in the design and evaluation of defect- and fault-tolerant nanoarchitectures based on graphene circuits. Results are compared with other emerging devices, such as carbon nanotube (CNT) FET and nanowire (NW) FET.

Approach for MVL design based on armchair graphene nanoribbon field effect transistor and arithmetic circuits design

This paper presents the approach for multiple-valued logic (MVL) design and implementing the arithmetic circuit based on armchair graphene nanoribbon field effect transistors (GNRFETs). For this purpose, the values of the threshold voltages are obtained for GNRFETs for utilizing in MVL. The Id-Vgs curve is drawn for all n-type GNRFETs by Synopsys HSPICE tools. Moreover, the width variations and band gap energy are scrutinized. The value of threshold voltage for range of N ​= ​3p+1 is more than N ​= ​3p. These observations exhibit that variation of the threshold voltages can be utilized for a circuit design based on GNRFET. Furthermore, the sub-threshold swing is obtained. As a proof of the concept, the ternary arithmetic circuits based on GNR are designed with 0.5 ​V supply voltage. The computational results confirm the threshold voltages values as well as the suitable figure of merits of using GNRFETs in multiple-valued logic circuit design.

A computational study of short-channel effects in double-gate junctionless graphene nanoribbon field-effect transistors

As the channel length shrinks below the 10-nm regime, emerging materials, junctionless technology, and multiple-gate geometries provide an excellent combination to continue progress towards lower-cost high-performance ultrascaled devices. In this study, the double-gate junctionless (JL) graphene nanoribbon field-effect transistor (GNRFET) and its conventional counterpart (C-GNRFET) are compared in terms of short-channel effects (SCEs) using a quantum simulation. The computational approach is based on solving the Schrodinger equation using the mode-space nonequilibrium Green’s function formalism coupled self-consistently with a Poisson equation in the ballistic limit. The analysis of gate length downscaling shows that the JL GNRFET exhibits better leakage current, subthreshold swing (SS), drain-induced barrier lowering, and threshold voltage roll-off in comparison with the conventional GNRFET. In addition, we reveal that a decrease in the n-type doping concentration can enhance the above-mentioned characteristics of both devices. The results indicate that the JL GNRFET can mitigate critical issues and enhance the immunity to SCEs of the GNRFET, making it a promising candidate for high-performance ultrascaled (sub-5-nm) technology.

Smart Nanostructured Materials based on Self‐Assembly of Block Copolymers

AbstractNanoscale fabrication of smart materials relying on the molecular self‐assembly of block copolymers (BCPs) has been recognized as a valuable platform for various next‐generation functional structures. In this Progress Report, the recent advances in the BCP self‐assembly process, which has paved the way for viable applications of emerging nanotechnologies, are highlighted. Effective light‐induced self‐assembly based on photothermal annealing of high‐χ BCPs and conformal 3D surface nanopatterning exploiting chemically modified graphene flexible substrates are reviewed as the typical instances of advanced BCP‐based nanofabrication methodologies. Additionally, relevant potential application fields are suggested, namely, graphene nanoribbon field effect transistors, highly tunable refractive index metasurfaces for visible light, high‐sensitivity surface‐enhanced Raman spectroscopy, 2D transition metal dichalcogenide nanopatterning, sequential infiltration synthesis, and organic photovoltaics. Finally, the future research direction as well as innovative applications of these smart nanostructured materials is proposed.

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.