Ultrahigh ON/Off Current Ratio γ-Graphyne-1 Nanotube Based Sub 10 nm TFET Modeling and Simulation

Utilizing γ-graphyne-1 nanotubes (GyNTs) in the Tunneling Field Effect Transistors (TFETs) suppresses ambipolarity and enhances subthreshold swing (SS) of TFETs which is because of large energy band gap and high electron effective mass of GyNTs. In this research analysis of structural, electronic and thermoelectric properties of γ-graphyne-1 family under the deformation potential (DP) approach reveals that electron-phonon mean free path (MFP) of an Armchair GyNT (3AGyNT) and Zigzag GyNT (2ZGyNT) are 45 and 290 nm, respectively. Therefore, ballistic transport of sub 10 nm 3AGyNT-TFETs and 2ZGyNT-TFETs in different channel lengths are investigated utilizing Non-Equilibrium Green’s Function (NEGF) formalism in the DFTB platform. Ultrahigh Current Ratio (OOCR) value of 1.6 x 1010 at VDD = 0.2 V and very low point SS of 5 mV/dec are belonged to the 3AGyNT-TFET with channel length of 9.6 nm. 2ZGyNT-TFETs shows higher on-state current and SS as well as lower OOCR than those of 3AGyNT-TFETs. A linear relationship between channel length and logarithmic off-state current is reported that is consistent with WKB approximation. The obtained results along with the ultralow power consumption of the suggested GyNT-TFETs, make them as replacement of digital silicon MOSFETs in the next generation nanoelectronic devices.

Leakages suppression by isolating the desired quantum levels for high-temperature terahertz quantum cascade lasers

The key challenge for terahertz quantum cascade lasers (THz-QCLs) is to make it operating at room-temperature. The suppression of thermally activated leakages via high lying quantum levels is emphasized recently. In this study, we employ the advanced self-consistent method of non-equilibrium Green’s function, aiming to reveal those kinds of leakages in the commonly used THz-QCL designs based on 2-, 3- and 4-quantum well. At the high temperature of 300 K, if all the confined high lying quantum levels and also the continuums are included within three neighboring periods, leakages indeed possess high fraction of the total current (21%, 30%, 50% for 2-, 3- and 4-quantum well designs, respectively). Ministep concept is introduced to weaken those leakage channels by isolating the desired levels from high lying ones, thus the leakages are well suppressed, with corresponding fractions less than 5% for all three designs.

Theoretical limit of how small we can make MoS2 transistor channels

As the size of electronic devices is reduced below 3 nanometers, contact resistance and tunnel leakage current have become crucial factors affecting device performance. The 2D material MoS2 is a potential semiconductor to substitute conventional silicon. In this work, the density functional theory combined with the non-equilibrium Green's function was used to simulate the transport properties of 2H semiconductor phase MoS2 connected to 1T metal phase MoS2 lead. It is found that when the channel length is greater than or equal to 2.736nm, the leakage current can be negligible, marking this length as miniaturization limit for a conventional transistor or diodes. When the channel length is smaller than 2.736nm, the transport are dominated by the direct tunneling. The junctions can be used to design the devices based on the tunneling effect.

Creation and Annihilation of Magnetic Skyrmions for Neuromorphic Computing Applications

In this work we present the creation, annihilation and dynamics of a topologically protected magnetic structure, a skyrmion, for neuromorphic computing application. We study the effect of Dzyaloshinskii Moriya interaction (DMI) and surface anisotropy on the skyrmion density. The relation between skyrmion annihilation threshold anisotropy Kth and DMI coefficient is evaluated. Furthermore, the skyrmion diameter dependence on these two parameters is studied. Using MOKE analysis we study the effect of external magnetic field on the skyrmion density and predict the threshold magnetic field for the transition of magnetic texture from Labriynth domains to skyrmions. These results are further supported by the MuMax simulations. The spin orbit torque SOT manipulation of skyrmion size and density is also presented for skyrmion applications in the race-track memory and neuromorphic computing. Motivated by the results, we propose a Skyrmionic neuromorphic device and using SOT switching mechanism, show its applicability as spintronic synapse and neuron. The MuMax simulations are coupled to the Non- Equilibrium Green’s Function formalism to model the neuron and synapse behavior. Finally, we conclude with the possibility of using these devices for pattern recognition and other unconventional computing paradigms.

Creation and Annihilation of Magnetic Skyrmions for Neuromorphic Computing Applications

In this work we present the creation, annihilation and dynamics of a topologically protected magnetic structure, a skyrmion, for neuromorphic computing application. We study the effect of Dzyaloshinskii Moriya interaction (DMI) and surface anisotropy on the skyrmion density. The relation between skyrmion annihilation threshold anisotropy Kth and DMI coefficient is evaluated. Furthermore, the skyrmion diameter dependence on these two parameters is studied. Using MOKE analysis we study the effect of external magnetic field on the skyrmion density and predict the threshold magnetic field for the transition of magnetic texture from Labriynth domains to skyrmions. These results are further supported by the MuMax simulations. The spin orbit torque SOT manipulation of skyrmion size and density is also presented for skyrmion applications in the race-track memory and neuromorphic computing. Motivated by the results, we propose a Skyrmionic neuromorphic device and using SOT switching mechanism, show its applicability as spintronic synapse and neuron. The MuMax simulations are coupled to the Non- Equilibrium Green’s Function formalism to model the neuron and synapse behavior. Finally, we conclude with the possibility of using these devices for pattern recognition and other unconventional computing paradigms.

Simulation and fabrication of an ammonia gas sensor based on PEDOT:PSS

Purpose The purpose of this study is use to density functional theory (DFT) to investigate the molecular adsorption by PEDOT:PSS for different doping levels. DFT calculations are performed using the SIESTA code. In addition, the non-equilibrium Green’s function method is used within the TranSIESTA code to determine the quantum transport properties of molecular nanodevices. Design/methodology/approach Density functional theory (DFT) is used to investigate the molecular adsorption by PEDOT:PSS for different doping levels. DFT calculations are performed using the SIESTA code. In addition, the non-equilibrium Green’s function method is used within the TranSIESTA code to determine the quantum transport properties of molecular nanodevices. Findings Simulation results show very good sensitivity of Pd-doped PEDOT:PSS to ammonia, carbon dioxide and methane, so this structure cannot be used for simultaneous exposure to these gases. Silver-doped PEDOT:PSS structure provides a favorable sensitivity to ammonia in addition to exhibiting a better selectivity. If the experiment is repeated, the sensitivity is increased for a larger concentration of the applied gas. However, the sensitivity will decrease at a higher ratio than smaller concentrations of gas. Originality/value The advantages of the proposed sensor are its low-cost implementation and simple fabrication process compared to other sensors. Moreover, the proposed sensor exhibits appropriate sensitivity and repeatability at room temperature.

Modeling Nanoscale III–V Channel MOSFETs with the Self-Consistent Multi-Valley/Multi-Subband Monte Carlo Approach

We describe the multi-valley/multi-subband Monte Carlo (MV–MSMC) approach to model nanoscale MOSFETs featuring III–V semiconductors as channel material. This approach describes carrier quantization normal to the channel direction, solving the Schrödinger equation while off-equilibrium transport is captured by the multi-valley/multi-subband Boltzmann transport equation. In this paper, we outline a methodology to include quantum effects along the transport direction (namely, source-to-drain tunneling) and provide model verification by comparison with Non-Equilibrium Green’s Function results for nanoscale MOSFETs with InAs and InGaAs channels. It is then shown how to use the MV–MSMC to calibrate a Technology Computer Aided Design (TCAD) simulation deck based on the drift–diffusion model that allows much faster simulations and opens the doors to variability studies in III–V channel MOSFETs.

Electronic, Magnetic and Spin-polarized Transport Properties of the Zigzag-Zigzag Penta-graphene Nanoribbon

Electronic, magnetic and spin-polarized transport properties of the zigzag-zigzag pentagraphene nanoribbon are investigated theoretically within the framework of density functional theory combined with non-equilibrium Green’s function formalism. It is found that the spinunpolarized ZZ-PGNR behaves as metal. However, the spin-polarized ZZ-PGNRs show to be the magnetic semiconductor properties. More importantly, for the ZZ-PGNRs based device, the spin-filtering effect occurs strongly near Fermi level. Our findings suggest that ZZ-PGNRs might hold a significant promise for developing spintronic devices.