Nanoribbon Field-effect Transistors Research Articles

Edge-Passivated Monolayer WSe2 Nanoribbon Transistors.

The ongoing reduction in transistor sizes drives advancements in information technology. However, as transistors shrink to the nanometer scale, surface and edge states begin to constrain their performance. 2Dsemiconductorsliketransition metal dichalcogenides (TMDs)have dangling-bond-free surfaces, hence achieving minimal surface states. Nonetheless, edge state disorder still limits the performance of width-scaled 2D transistors. This work demonstrates a facile edge passivation method to enhance the electrical properties of monolayer WSe2 nanoribbons, by combining scanning transmission electron microscopy, optical spectroscopy, and field-effect transistor (FET) transport measurements. Monolayer WSe2 nanoribbons are passivated with amorphous WOxSey at the edges, which is achievedusing nanolithography and a controlled remote O2 plasma process. The same nanoribbons, with and without edge passivation are sequentially fabricated and measured. The passivated-edge nanoribbon FETs exhibit 10 ± 6 times higher field-effect mobility than the open-edge nanoribbon FETs, which are characterized with dangling bonds at the edges. WOxSey edge passivation minimizes edge disorder and enhances the material quality of WSe2 nanoribbons. Owing to its simplicity and effectiveness, oxidation-based edge passivation could become a turnkey manufacturing solution for TMD nanoribbons in beyond-silicon electronics and optoelectronics.

A comprehensive analysis of ultra low power GNRFET based 20T hybrid full adder for computing applications

In an era where energy efficiency is as important as computational speed, this paper introduces a new full adder circuit design that effectively integrates dynamic power gathering (DPG) power conservation benefits with XOR-XNOR pass-transistor logic (PTL) area and performance efficiencies using graphene nanoribbon field-effect transistors. GNRFETs are useful for digital logic due to their high carrier mobility and tunable bandgap. The paper describes the circuit’s seamless transition full adder response, demonstrating the tri-mode dynamic power gating strategy capacity to reduce static power depletion. The proposed hybrid full adder performs well with 7.76 nW power consumption, 481 ps latency, and 3.73 aJ PDP. This reduces power consumption by 99.9%, delay by 99.0%, and PDP by 99.8% compared to other adders. The effects of temperature, voltage, Noise immunity and Carry Forward Adders integration on power, delay, and PDP are also analysed, proving the design’s robustness. The adaptability of our full adder architecture allows its implementation in more complicated arithmetic and logic units, indicating a scalable and energy-efficient paradigm for future integrated circuits.

H/O edge passivated B/N co-doped armchair graphene nanoribbon field-effect transistors, based on first principles

This study employs the nonequilibrium Green’s function method in conjunction with density functional theory to fabricate and analyze a Graphene Nanoribbon Field-Effect Transistor (GNRFET). The co-doping of B and N creates built-in electric fields, thereby reducing leakage current. The results demonstrate effective control performance of planar gates, as evidenced by an increase in IDS with rising gate voltage. Furthermore, a negative differential conductance phenomenon is observed at bias voltages exceeding 0.7 V, exhibiting correlation with transmission spectra and energy band structures. To precisely illustrate the electron distribution within the doped scattering region, calculations involving transport paths, the molecular projection self-consistent Hamiltonian (MPSH), and the emission eigenvalues and eigenstates of the device are conducted. This research provides a reference for exploring and developing smaller and more energy-efficient AGNR field effect transistor designs and implementations. The principal objective of this paper is to investigate the potential applications of these smaller, more energy-efficient devices.

Design and Simulation of New High Speed, Low Power D-Flip-Flops, Implemented Using Graphene Nanoribbon and Carbon Nanotube Field Effect Transistors

Design and Simulation of New High Speed, Low Power D-Flip-Flops, Implemented Using Graphene Nanoribbon and Carbon Nanotube Field Effect Transistors

Phosphorene nanoribbon field effect transistor with a dual material gate

In this paper, we present a dual-material gate phosphorene nanoribbon field-effect transistor (DMG-PNRFET) that combines the advantages of a PNRFET with a DMG configuration. In this structure, the difference in the work function creates an extra barrier for band-to-band tunneling from the valence band (VB) to the conduction band (CB) inside the channel leading to lower off-currents. An illustration for transmission coefficients with relevant band diagrams is included to demonstrate energy-resolved current spectrum and tunneling emissions within the transport window for both on and off-states. Results also show that DMG-PNRFET possesses a higher ION/IOFF ratio, delay, and power delay product (PDP) compared to a conventional PNRFET. Hence, the DMG-PNRFET is better suited for digital applications. Our simulations rely on combining the density functional-based tight binding method with the non-equilibrium Green’s function.

Area-energy optimized ternary multiplier usingefficient design approaches in GNRFET technology

The semiconductor industry has long benefited from CMOS transistors in realizing advanced VLSI circuits. However, achieving area-energy optimization in CMOS-based VLSI circuits has become increasingly challenging due to short-channel effects. Another obstacle in manufacturing these transistors is the adoption of body-biasing techniques to adjust the threshold voltage (Vth) for developing ternary logic-based circuits. Researchers are now exploring emerging devices like graphene nanoribbon field-effect transistors (GNRFET) as potential candidates for future electronics. GNRFET devices not only leverage graphene’s remarkable properties but also benefit from the ability to achieve distinct Vth through tuning the width of graphene nanoribbons. This paper focuses on using tri-state 32-nm GNRFET devices to implement a novel area-energy optimized ternary multiplier circuit. To attain a logic ‘1′ in the proposed circuit, a power-efficient voltage division technique is employed. Additionally, efficient design approaches are used to reduce the critical path length and decrease the number of necessary transistors. Simulation results using HSPICE demonstrate that the proposed design reduces energy consumption by a minimum of 6.75% and up to 37.50% compared to other state-of-the-art 32-nm GNRFET-based TMUL circuits. Furthermore, the proposed design decreases both the area and complexity by utilizing a single-VDD and incorporating 24 transistors.

Design of power efficient and reliable hybrid inverter approach based 11 T SRAM design using GNRFET technology

Designing a power efficient and high-speed static random-access memory (SRAM) cell with improved noise stability using traditional complementary metal oxide semiconductor (CMOS) devices is an arduous task. Owing to balanced electrical properties of graphene nanoribbon field-effect transistor (GNRFET), its capability to realize high performance SRAM cells need a keen exploration. This article proposes an 11-transistor GNRFET SRAM cell which deploys hybrid inverter scheme. The hybrid inverter scheme encompasses two distinct inverters, based on stacked transistors and Schmitt trigger (ST) techniques. The simulations conducted using 16 nm GNRFET model in HSPICE simulator show that proposed SRAM cell has write power, hold power, read power, write static noise margin, hold static noise margin, read static noise margin, write delay and read delay of 0.445 nW, 0.978 µW, 1.8 nW, 225 mV, 222.8 mV, 225.1 mV, 24 pS and 49.6 pS, respectively. The results obtained for proposed SRAM cell have been found to be encouraging in contrast to previously reported SRAM cells implemented using 16 nm GNRFET model. Besides this, the effect of variation in various parameters of GNRFET on performance of proposed SRAM cell has been investigated in this article. The outstanding performance results of SRAM makes its suitable for developing high performance memories devices for biomedical digital gadgets, internet of things (IoT), artificial intelligence (AI) and smart agricultural applications.

Tri-state GNRFET-based fast and energy-efficient ternary multiplier

As silicon field-effect transistors encounter increasing scaling challenges, digital system designers are shifting their attention towards multi-valued logic (MVL), specifically ternary logic. The graphene nanoribbon field-effect transistor (GNRFET) emerges as a compelling alternative among post-MOSFET technologies for the implementation of ternary logic. This paper delves into the computational intricacies of ternary logic, underscores the outstanding features of GNRFET technology, and introduces a novel GNRFET-based 1-trit ternary multiplier (TMUL) requiring only 26 transistors. The performance of the design is assessed using the Synopsis HSPICE simulator with a 32-nm GNRFET model file operating at VDD = 0.9 V. The proposed TMUL surpasses existing designs due to its efficient paths with a minimal number of transistors for each output transition, a singular power supply voltage, and an extended voltage division scheme. In comparison to other contemporary TMUL designs, the proposed design exhibits a notable enhancement, showcasing a 21.42 % reduction in delay, a 33.11 % decrease in power-delay-product (PDP), and a 58.17 % decrease in energy-delay-product (EDP). Additionally, the design is subjected to thorough testing under diverse conditions including process, voltage, temperature (PVT) fluctuations, and load variations, validating its reliability and robustness.

Ballistic performance and overshoot effects in gallenene nanoribbon field-effect transistors

Gallenene is a novel metallic 2D material that can provide a semiconducting counterpart if patterned into quasi-one-dimensional (quasi-1D) nanostructures, i.e., gallenene nanoribbons (GaNRs). We investigate semiconducting GaNRs as a potential channel material for future ultrascaled field-effect transistors (FETs) by employing quantum transport simulations based on Green's functions and tight-binding Hamiltonians with the orbital resolution calibrated on ab initio calculations. The impact of GaNR width downscaling from ∼6 nm down to ∼0.2 nm on the electronic, transport, and ballistic device properties is investigated for the FET channel length of 15 nm. We report current enhancement and injection velocity overshoot effects for sub-1.2 nm-wide nFETs and pFETs, with a maximum current increase of 53% in the 1.2 nm-wide GaNR pFET in comparison to the widest device. In addition, promising current-driving capabilities of n- and p-channel GaNR FETs are observed with top ballistic currents of more than 2.2 mA/μm and injection velocities of up to 2.4 × 107 cm/s. The reported data are explained by analyzing the evolution of band structure and related parameters such as injection velocity, quantum capacitance, effective transport mass etc., with increasing quantum confinement effects in ultranarrow GaNRs. Generally, we find that quasi-1D gallenene is a promising channel material for future nanoscale FETs, especially for transistor architectures based on stacked nanosheets.

An energy-efficient design of ternary SRAM using GNRFETs

ABSTRACT The primary requirement of internet-of-things (IoT) applications is to have an energy-efficient design that extends the battery life for long-term operation. To achieve energy efficiency, one can employ multiple-valued logic (MVL) instead of binary logic and utilise graphene nanoribbon field-effect transistors (GNRFETs) as variable-threshold voltage (V th ) capable devices. The implementation of an MVL system enhances data transferability and reduces the number of interconnections, resulting in improved energy consumption compared to a binary system. In such systems, static random access memory (SRAM), which serves as a crucial component of very large-scale integrated (VLSI) chips, dominates energy consumption. This research paper introduces an energy-efficient ternary SRAM using GNRFETs. We propose a standard ternary inverter based on GNRFET devices, which serves as the fundamental building block of a storage cell. Simulation results conducted on a 32-nm GNRFET with a 0.9 V supply voltage demonstrate that the proposed design achieves energy consumption improvements ranging from 46.39% to 98.16% compared to the most recent ternary SRAMs. Furthermore, the SRAM cell is evaluated under various processes and environmental parameter variations.

Non-fourier phonon heat transport in graphene nanoribbon field effect transistors based on modified phonon hydrodynamic lattice Boltzmann method

Graphene, with its exceptional thermal conductivity and electron mobility, is widely recognized as a potential candidate for next-generation transistor materials. Despite the lack of pronounced phonon hydrodynamic phenomena at room temperature in graphene materials, momentum-conserving phonon normal scattering predominantly drives phonon hydrodynamic transport. Current methodologies, including the Single Mode Relaxation Time (SMRT) approximation and Fourier's law, inadequately capture phonon transport within the ballistic and hydrodynamic regimes of graphene. In light of these limitations, this study introduces a Non-gray phonon hydrodynamic lattice Boltzmann method in combination with the Temperature Jump Boundary Condition to provide a more accurate depiction of phonon heat transport in graphene nanoribbon field-effect transistors (GNRFETs) spanning these regimes. The findings reveal that our proposed model significantly mitigates heat transfer errors in GNRFETs, primarily driven by ballistic transport compared to the SMRT model. This suggests that the model's applicability extends beyond scenarios dominated by phonon hydrodynamics and is effective even in cases dominated by ballistic transport. In conclusion, our study emphasizes the impact of hydrodynamic transport on heat transfer in GNRFETs and underscores the importance of adjusting parameters related to the heating zone width and specular parameter to enhance thermal stability.

Graphene & its applications as field effect transistors

Graphene, owing to its excellent physical, mechanical, and electrical properties, as well as its outstanding optoelectronic properties, has garnered significant attention. Consequently, it has opened numerous opportunities for various types of future devices and systems. Graphene, a one-atom-thick layer of carbon atoms forming a honeycomb 2D crystal lattice, stands out as one of the most promising candidates in the field of nano- and microelectronics. This review provides an introduction to graphene, detailing its properties and its applications, particularly focusing on its utilization in the realm of Field Effect Transistors (FETs). Specifically, an analytical device model of heterostructure-based FETs is presented, which essentially comprises an array of nano ribbons clad. The model for Graphene Nano Ribbon (GNR) FETs includes Poisson's equation and can be employed to calculate the current-voltage characteristics and spatial distribution of electric potential along the channel.

On the grain boundary charge transport in p-type polycrystalline nanoribbon transistors.

Grain boundaries (GB) profoundly influence charge transport, and their localized potential barrier with a high density of defect states plays a crucial role in polycrystalline materials. There are a couple of models to estimate the density of states (DoS) of nanostructured materials in field-effect transistors (FETs) that probe interface traps between the semiconductor and dielectric but not at the grain boundaries. Here, we report on utilizing Levinson's and Seto's models of grain boundary transport and correlate them with the temperature-dependent hopping transport in copper iodide (CuI) polycrystalline nanoribbon (PNR) FETs. Experimentally, PNRs are obtained by e-beam lithography and thermal evaporation of CuI. To investigate the impact of GB, the devices are fabricated with different channel aspect ratios by varying widths (80, 260, and 570 nm) and lengths (20 to 90 μm). Owing to the high hole concentration, PNR FETs operate in depletion mode at 300 K. At various low temperatures (80-300 K), the figures-of-merits of FETs are estimated to understand device performance. We determine GB barrier heights, activation energy, and density of GB trap states and find equivalence between the two models. Furthermore, we calculate temperature-dependent hopping and trap-limited transport parameters to obtain DoS at the Fermi energy, trapped and free charge carrier density, localization length, hopping distance, hopping energy, etc. at various channel lengths. Based on this quantitative analysis, we propose a channel length-dependent GB barrier height variation due to the in-plane electric field and elucidate CuI energy band levels.

Exploring the Surface Oxidation and Environmental Instability of 2H-/1T'-MoTe2 Using Field Emission-Based Scanning Probe Lithography.

An unconventional approach for the resistless nanopatterning 2H- and 1T'-MoTe2 by means of scanning probe lithography is presented. A Fowler-Nordheim tunneling current of low energetic electrons (E = 30-60eV) emitted from the tip of an atomic force microscopy (AFM) cantilever is utilized to induce a nanoscale oxidation on a MoTe2 nanosheet surface under ambient conditions. Due to the water solubility of the generated oxide, a direct pattern transfer into the MoTe2 surface can be achieved by a simple immersion of the sample in deionized water. The tip-grown oxide is characterized using Auger electron and Raman spectroscopy, revealing it consists of amorphous MoO3 /MoOx as well as TeO2 /TeOx . With the presented technology in combination with subsequent AFM imaging it is possible to demonstrate a strong anisotropic sensitivity of 1T'-/(Td )-MoTe2 to aqueous environments. Finally the discussed approach is used to structure a nanoribbon field effect transistor out of a few-layer 2H-MoTe2 nanosheet.

Characterisation of graphene nano-ribbon field effect transistor and design of high performance PPN 12T GNRFET Full adder

Owing to the balanced electrical properties of graphene nanoribbon field effect transistors (GNRFETs), they are suitable next-generation devices for designing high performance circuits. However, as the fabrication for GNRFETs is at premature stage the performance of GNRFET device need to be explored with variation in its parameters. This article comprehensively analyses the impact of variations in GNRFET parameters on its threshold voltage, subthreshold swing and I ON /I OFF ratio. As an application example high performance PPN 12 T full adder is proposed using GNRFET device. The proposed full adder circuit shows dynamic power, propagation delay, low power-delay product and unity noise gain of 43.3 nW, 0.47 pS, 0.02 × 10−18 J and 0.46 respectively using supply voltage of 0.7 V. The performance of proposed full adder is compared with five previously proposed full adders using 16 nm GNRFET model in HSPICE simulation tool. Further, the impact of the GNRFET parameters on performance of proposed FA is investigated. A study of this nature is expected to improve performance of computing systems used in internet of things (IoT)-based infrastructure and health industry which demand for high performance next generation devices-based circuits.

Modulation of ballistic injection velocity in phosphorene nanodevices by bias and confinement effects

Atomistic quantum transport simulations are employed to study the electron injection velocity (vinj) and ballistic performance of phosphorene nanoribbon (PNR) field-effect transistors (FETs). We show that PNR bandstructure is immune to quantum confinement effects, which is seen in a rather constant vinj≈2.1 × 107cm/s down to the PNR width of 1.5 nm. Moreover, we demonstrate that the modulation of vinj by gate bias is available only for PNRs wider than 2.1 nm, with the maximum enhancement being 33%. Finally, it is reported that PNR FETs combine high cut-off frequencies above 526 GHz with acceptable bandgap that ranges from 0.7 eV to 1.6 eV in the examined PNR width range, which proves the plausibility of PNRs as channel material for future ultra-scaled high-speed FETs.

An unbalanced ternary multiplier cell based on graphene nanoribbon field-effect transistors for PVT-tolerant low-energy portable applications

The potential benefits of using multiple-valued logic (MVL), especially ternary logic, which includes less interconnections, quicker response times, and smaller chip sizes, has gained the interest of designers of digital systems. A practical solution for achieving circuits with multiple thresholds in an efficient manner is through using graphene nanoribbon field-effect transistors (GNRFETs) that have modifiable threshold voltage values by adjusting the width of graphene nanoribbon. This article leverages the unique characteristics of GNRFETs and proposes a new design for a single-trit ternary multiplier (TMUL) circuit. The proposed TMUL uses two supply voltages to block direct current paths from high-to-low voltage levels, resulting in power and energy savings. Additionally, unary operators such as negative and positive ternary inverters and the complement of decisive literal are used to reduce transistor count and improve circuit performance. To thoroughly evaluate the performance of the proposed GNRFET-based TMUL circuit, extensive simulations are performed using Synopsis HSPICE tool and 32-nm channel length GNRFET devices, while taking into account the influences of process-voltage-temperature variations (PVT). The simulation results confirm the robustness and reliability of the proposed design, exhibiting reductions in power consumption by 71.18% to 76.36%, and energy consumption by 67.78% to 86.54%, when compared to other state-of-the-art TMUL circuits available in literature. Moreover, Monte-Carlo simulations have been performed to demonstrate that the suggested design exhibits reduced sensitivity towards significant process variations. As a result, the presented TMUL design can be a good choice for use in low-energy battery-operated portable multimedia device.

The understanding of the impact of efficiently optimized underlap length on analog/RF performance parameters of GNR-FETs

The aim of this study is to examine the analog/RF performance characteristics of graphene nanoribbon (GNR) field-effect transistors (FETs) using a novel technique called underlap engineering. The study employs self-consistent atomistic simulations and the non-equilibrium Green's function (NEGF) formalism. Initially, the optimal underlap length for the GNR-FET by device has been determined evaluating the ON-current (ION) to OFF-current (IOFF) ratio, which is a critical parameter for digital applications. Subsequently, the impact of underlap engineering on analog/RF performance metrics has been analyzed and conducting a comprehensive trade-off analysis considering parameters such as intrinsic-gain, transistor efficiency, and device cut-off frequency. The results demonstrate that the device incorporating the underlap mechanism exhibits superior performance in terms of the ION/IOFF ratio, transconductance generation factor (TGF), output resistance (r0), intrinsic gain (gmr0), gain frequency product (GFP), and gain transfer frequency product (GTFP). However, the device without the underlap effect demonstrates the highest transconductance (gm) and cut-off frequency (fT). Finally, a linearity analysis has been conducted to compare the optimized GNR-FET device with the conventional GNR-FET device without the underlap effect.

Investigation of Single-Event Upset in Graphene Nano-Ribbon FET SRAM Cell.

In recent years, graphene has received so much attention because of its superlative properties and its potential to revolutionize electronics, especially in VLSI. This study analyzes the effect of single-event upset (SEU) in an SRAM cell, which employs a metal-oxide semiconductor type graphene nano-ribbon field effect transistor (MOS-GNRFET) and compares the results with another SRAM cell designed using a PTM 10 nm FinFET node. Our simulations show that there is a change in the data stored in the SRAM after a heavy ion strike. However, it recovers from radiation effects after 0.46 ns for GNRFET and 0.51 ns for FinFET. Since the degradation observed in Q and Qb of GNRFET SRAM are 2.7X and 2.16X as compared to PTM nano-MOSFET, we can conclude that GNRFET is less robust to single effect upset. In addition, the stability of SRAM is improved by increasing the supply voltage VDD.

Spin Transport in ScSe2 Nanoribbon Field Effect Transistor

Spin Transport in ScSe₂ Nanoribbon Field Effect Transistor