Mode space approach for tight-binding transport simulations in graphene nanoribbon field-effect transistors including phonon scattering

In this paper, we present a mode space method for atomistic non-equilibrium Green's function simulations of armchair graphene nanoribbon FETs that includes electron-phonon scattering. With reference to both conventional and tunnel FET structures, we show that, in the ideal case of a smooth electrostatic potential, the modes can be decoupled in different groups without any loss of accuracy. Thus, inter-subband scattering due to electron-phonon interactions is properly accounted for, while the overall simulation time considerably improves with respect to real-space, with a speed-up factor of 40 for a 1.5-nm-wide device. Such factor increases with the square of the device width. We also discuss the accuracy of two commonly used approximations of the scattering self-energies: the neglect of the off-diagonal entries in the mode-space expressions and the neglect of the Hermitian part of the retarded self-energy. While the latter is an acceptable approximation in most bias conditions, the former is somewhat inaccurate when the device is in the off-state and optical phonon scattering is essential in determining the current via band-to-band tunneling. Finally, we show that, in the presence of a disordered potential, a coupled mode space approach is necessary, but the results are still accurate compared to the real-space solution.Comment: 10 pages, 12 figures. Copyright (2013) American Institute of Physics. This article may be downloaded for personal use only. Any other use requires prior permission of the author and the American Institute of Physic

Boosting the voltage gain of graphene FETs through a differential amplifier scheme with positive feedback

We study a possible circuit solution to overcome the problem of low voltage gain of short-channel graphene FETs. The circuit consists of a fully differential amplifier with a load made of a cross-coupled transistor pair. Starting from the device characteristics obtained from self-consistent ballistic quantum transport simulations, we explore the circuit parameter space and evaluate the amplifier performance in terms of dc voltage gain and voltage gain bandwidth. We show that the dc gain can be effectively improved by the negative differential resistance provided by the cross-coupled pair. Contact resistance is the main obstacle to achieving gain bandwidth products in the terahertz range. Limitations of the proposed amplifier are identified with its poor linearity and relatively large Miller capacitance.Comment: 19 pages, 10 figure

Semianalytical quantum model for graphene field-effect transistors

We develop a semianalytical model for monolayer graphene field-effect transistors in the ballistic limit. Two types of devices are considered: in the first device, the source and drain regions are doped by charge transfer with Schottky contacts, while, in the second device, the source and drain regions are doped electrostatically by a back gate. The model captures two important effects that influence the operation of both devices: (i) the finite density of states in the source and drain regions, which limits the number of states available for transport and can be responsible for negative output differential resistance effects, and (ii) quantum tunneling across the potential steps at the source-channel and drain-channel interfaces. By comparison with a self-consistent non-equilibrium Green's function solver, we show that our model provides very accurate results for both types of devices, in the bias region of quasi-saturation as well as in that of negative differential resistance.Comment: 10 pages, 14 figure

Graphene Base Transistors: A Simulation Study of DC and Small-Signal Operation

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3D TCAD modeling of NO2CNT FET sensors

A new approach for TCAD modeling of CNT FET gas sensors is presented, whose key feature is the use of an effective Gaussian DOS to mimic the 1D CNT DOS. The TCAD procedure has been applied to the simulation of a suspended CNT FET for NO2sensing. Our results indicate that the model is able to provide I-V characteristics in excellent agreement with the experimental data, both before and after gas exposure

Characterization of dielectric properties and conductivity in encapsulation materials with high insulating filler contents

The properties of different molding-compound materials with high filler contents have been investigated in order to assess their electrical properties. The experimental part of the present work has been focused on dielectric spectroscopy and steady-state conduction measurements. The results have been used to investigate the electrical properties of the materials at different frequencies, temperatures and electric fields. Differences in the relaxation kinetics with increasing filler content have been found, which can be ascribed to the larger interface regions between the filler particles. In addition, the extracted conductivities show a hopping transport and different activation energies on the temperature range from 20 °C to 190 °C

Cyclosporine A in Ullrich Congenital Muscular Dystrophy: Long-Term Results

Six individuals with Ullrich congenital muscular dystrophy (UCMD) and mutations in the genes-encoding collagen VI, aging 5–9, received 3–5 mg/kg of cyclosporine A (CsA) daily for 1 to 3.2 years. The primary outcome measure was the muscle strength evaluated with a myometer and expressed as megalimbs. The megalimbs score showed significant improvement (P = 0.01) in 5 of the 6 patients. Motor function did not change. Respiratory function deteriorated in all. CsA treatment corrected mitochondrial dysfunction, increased muscle regeneration, and decreased the number of apoptotic nuclei. Results from this study demonstrate that long-term treatment with CsA ameliorates performance in the limbs, but not in the respiratory muscles of UCMD patients, and that it is well tolerated. These results suggest considering a trial of CsA or nonimmunosuppressive cyclosporins, that retains the PTP-desensitizing properties of CsA, as early as possible in UCMD patients when diaphragm is less compromised

Comprehensive comparison and experimental validation of band-structure calculation methods in III\u2013V semiconductor quantum wells

We present and thoroughly compare band-structures computed with density functional theory, tight-binding, k p and non-parabolic effective mass models. Parameter sets for the non-parabolic C, the L and X valleys and intervalley bandgaps are extracted for bulk InAs, GaAs and InGaAs. We then consider quantum-wells with thickness ranging from 3 nm to 10 nm and the bandgap dependence on film thickness is compared with experiments for In0:53Ga0:47As quantum-wells. The impact of the band-structure on the drain current of nanoscale MOSFETs is simulated with ballistic transport models, the results provide a rigorous assessment of III\u2013V semiconductor band structure calculation methods and calibrated band parameters for device simulations

Atrasentan and renal events in patients with type 2 diabetes and chronic kidney disease (SONAR): a double-blind, randomised, placebo-controlled trial

Background: Short-term treatment for people with type 2 diabetes using a low dose of the selective endothelin A receptor antagonist atrasentan reduces albuminuria without causing significant sodium retention. We report the long-term effects of treatment with atrasentan on major renal outcomes. Methods: We did this double-blind, randomised, placebo-controlled trial at 689 sites in 41 countries. We enrolled adults aged 18–85 years with type 2 diabetes, estimated glomerular filtration rate (eGFR)25–75 mL/min per 1·73 m 2 of body surface area, and a urine albumin-to-creatinine ratio (UACR)of 300–5000 mg/g who had received maximum labelled or tolerated renin–angiotensin system inhibition for at least 4 weeks. Participants were given atrasentan 0·75 mg orally daily during an enrichment period before random group assignment. Those with a UACR decrease of at least 30% with no substantial fluid retention during the enrichment period (responders)were included in the double-blind treatment period. Responders were randomly assigned to receive either atrasentan 0·75 mg orally daily or placebo. All patients and investigators were masked to treatment assignment. The primary endpoint was a composite of doubling of serum creatinine (sustained for ≥30 days)or end-stage kidney disease (eGFR <15 mL/min per 1·73 m 2 sustained for ≥90 days, chronic dialysis for ≥90 days, kidney transplantation, or death from kidney failure)in the intention-to-treat population of all responders. Safety was assessed in all patients who received at least one dose of their assigned study treatment. The study is registered with ClinicalTrials.gov, number NCT01858532. Findings: Between May 17, 2013, and July 13, 2017, 11 087 patients were screened; 5117 entered the enrichment period, and 4711 completed the enrichment period. Of these, 2648 patients were responders and were randomly assigned to the atrasentan group (n=1325)or placebo group (n=1323). Median follow-up was 2·2 years (IQR 1·4–2·9). 79 (6·0%)of 1325 patients in the atrasentan group and 105 (7·9%)of 1323 in the placebo group had a primary composite renal endpoint event (hazard ratio [HR]0·65 [95% CI 0·49–0·88]; p=0·0047). Fluid retention and anaemia adverse events, which have been previously attributed to endothelin receptor antagonists, were more frequent in the atrasentan group than in the placebo group. Hospital admission for heart failure occurred in 47 (3·5%)of 1325 patients in the atrasentan group and 34 (2·6%)of 1323 patients in the placebo group (HR 1·33 [95% CI 0·85–2·07]; p=0·208). 58 (4·4%)patients in the atrasentan group and 52 (3·9%)in the placebo group died (HR 1·09 [95% CI 0·75–1·59]; p=0·65). Interpretation: Atrasentan reduced the risk of renal events in patients with diabetes and chronic kidney disease who were selected to optimise efficacy and safety. These data support a potential role for selective endothelin receptor antagonists in protecting renal function in patients with type 2 diabetes at high risk of developing end-stage kidney disease. Funding: AbbVie