Transport study of gate and channel engineering on the surrounding-gate CNTFETs based on NEGF quantum theory

In this paper, we comprehensively study the effects of gate and channel engineering on the performances of surrounding-gate CNTFETs using a quantum kinetic model, which is based on two-dimensional non-equilibrium Green functions (NEGF) solved self-consistently with Poisson’s equations. The iterative approach between Poisson equation and NEGF has been discussed. For the first time, the influences of double-material-gate and linear doping structures on the CNTFETs have been investigated. The calculated results show that double-material-gate CNTFETs with conventional doping (DMG-CNTFETs) can effectively suppress the drain-induced barrier lowering (DIBL), short-channel effects (SCEs), and achieve better sub-threshold property as compared with single-material-gate CNTFETs with conventional doping (SMG-CNTFETs). Compared with conventional doping, linear doping presents lower leakage current, higher I _on /I _off ratio, and lower sub-threshold swing, which means a better ability of gate controlling. In addition, we present a detailed discussion of the performances of scaling down, and conclude that DMG structure can meet the ITRS’10 requirements better than SMG, especially that the I _on /I _off ratio is two orders of magnitude higher than that of ITRS’10 requirements.     

Nanoscale circuit implementation using tri-metal gate engineered nanowire MOSFET with gate stack for analog/RF applications

In this work, the potential benefit of tri-metal gate engineered nanowire MOSFET with gate stack for analog/RF applications is developed and presented. A systematic, quantitative investigation of main figure of merit for the device is carried out to demonstrate its improved RF/analog performance. The results show an improvement in drain current, \(I_{\mathrm{on}} /I_{\mathrm{off}}\) ratio, transconductance, unity-gain frequency (\(f_{\mathrm{T}}\)), maximum oscillation frequency (\(f_{\mathrm{max}}\)) providing superior RF performance as compared to single and dual-metal gate stack nanowire MOSFET. The suitability of the device for analog/RF applications is also analyzed by implementing the device in a low-noise amplifier circuit, and the S-parameter values are estimated.     

Design and analysis of a gate-all-around CNTFET-based SRAM cell

This paper proposes a highly stable and low power 6-T static random access memory (SRAM) cell design using a gate-all-around carbon nanotube field effect transistor (GAA-CNTFET). The 6-T SRAM cell is designed and analyzed in HSPICE for different performance metrics viz. SNM, read SNM, write SNM, delay, and leakage power for both the top gate CNTFET and the GAA-CNTFET. The effect of variation of the power supply voltage on the leakage current is also presented, and it was found that the GAA-CNTFET accounts for low power dissipation at higher supply voltage. The 6-T SRAM cell is analyzed for different flat band conditions of the p-type CNTFET taking flatband of the n-type as constant, which is called a dual flat band voltage technique. Through simulations, it is found that by increasing the flatband voltage of a p-type CNTFET, the SRAM gives better performance. The dual flatband variation technique is compared with dual chirality technique, and it is observed that both techniques give the same results.     

Uncoupled mode space approach for analysis of nanoscale strained junctionless double-gate MOSFET

In this paper, we have analyzed the electrical characteristics of Strained Junctionless Double-Gate MOSFET (Strained JL DG MOSFET). A quantum mechanical transport approach based on non-equilibrium Green’s function (NEGF) method with the use of uncoupled mode space approach has been employed for this analysis. We have investigated the effects of high-\(\kappa \) materials as gate and spacer dielectrics on the device performance. Low OFF-state current, low DIBL, and low subthreshold slope have been obtained with increase in the gate and spacer dielectric constants. The electrical characteristics of strained JL DG MOSFET have also been compared with conventional JL DG MOSFET and Inversion Mode (IM) DG MOSFET. The results indicated that the Strained JL DG MOSFET outperforms the conventional JL and IM DG MOSFETs, yielding higher values of drain current.     

Accurate modeling of Metal/HfO<Subscript>2</Subscript>/Si capacitors

In this work, we study the differences caused in the Capacitance-Voltage (C-V) characteristics of MOS devices when SiO₂ is replaced by HfO₂ as the gate dielectric. A self-consistent Schrödinger-Poisson solver has been developed to include the effects of quantum confinement and the influence of different parameters such as the effective mass, barrier height, and dielectric constant (κ) of the gate insulator material. Two different devices are considered: A Double Gate MOSFET and a Surrounding Gate Transistor. The validity of the Equivalent Oxide Thickness (EOT) is studied.     

GaN-based double-gate (DG) sub-10-nm MOSFETs: effects of gate work function

Double-gate (DG) metal–oxide–semiconductor field-effect transistors (MOSFETs) with GaN channel material are very promising for use in future high-performance low-power nanoscale device applications. In this work, GaN-based sub-10-nm DG-MOSFETs with different gate work function, \(\varPhi \), were designed and their performance evaluated. Short-channel effects (SCEs) were significantly reduced by introduction of gates made of dual metals. Use of gold at the source side, having higher \(\varPhi \) (\(\varPhi _{\mathrm{Au}}=5.11\,\hbox {eV}\)) compared with aluminum (\(\varPhi _{\mathrm{Al}}=4.53\,\hbox {eV}\)), at the drain side enhanced the gate control over the channel and screened the effect of the drain on the channel. Dual-metal (DM) DG-MOSFETs showed better results in the nanoscale regime and were more robust to SCEs. Therefore, GaN-based sub-10-nm DM DG-MOSFETs are suitable candidates for use in future complementary metal–oxide–semiconductor (CMOS) technology.     

Toward Optimization of Insulation between Two Concentric Spheres

This article considers the problem of increasing the electric strength of a high-voltage structure corresponding to a segment of the concentric capacitor. In such a capacitor with radii r₀ and r _m > r₀ determining the insulation clearance with the value r _m –r₀ with dielectric capacity ε₀, the specified problem is solved using an additional insulation layer with the dielectric capacity ε > ε₀ limited by the radii r₀ and r_ε < r _m . A simple algorithm of calculation of the optimal thickness of this layer minimizing maximum intensity E _m in the function of radii r₀ and r _m and relative capacity ε/ε₀ > 2 is obtained. According to the calculations, the decrease of min E _m can achieve several tens of percent. The obtained algorithm is also transformed into a synthesis algorithm of the thickness of the aforementioned layer providing the predetermined value min E _m . The calculations of the optimal values of all dimensions of the capacitor in the function of the dielectric capacity of the layer and degree of intensity reduction E _m are given in a form appropriate for practical use.     

On optimization of the insulation of high-voltage coaxial bushing

This paper considers ways to improve the electric strength of a high-voltage bushing by decreasing the maximum electric intensity. For a coaxial cylindrical bushing with radii r₀ and r_m > r₀, which result in an insulation gap (r_m–r₀) with permittivity ε₀, this problem is solved with the use of an additional layer of insulation. This layer, with permittivity ε > ε₀, is limited by radii r₀ and r_ε < r_m. A simple algorithm to calculate an optimal thickness of this layer was obtained; the algorithm minimizes the maximum intensity as a function of radii r₀ and r_m and relative permittivity ε/ε₀ > 1.582. The algorithm is also transformed into an algorithm of synthesis of the noted layer thickness providing minimum intensity E_m. The optimal relative values of all the dimensions of a high-voltage bushing as a function of the layer permittivity and level of reduction in the intensity E_m are given in a form that is convenient for practical use.     

Parallel operation of triple- and double-wound transformers with difference transformation ratios

During the operation of electric-power systems, there is often a problem of splitting up the capacity of transformers installed on substations, which, as a rule, entails mounting two or more transformers in parallel instead of a single one, the total capacity of which is the same. In such replacement, there is a problem of uniform distribution of the load between transformers. When using transformers that have the same capacity and are structurally similar, uniformity of load distribution is reached achieved owing to symmetry of parallel circuits. However, if transformers with of different designs and various transformation ratios are connected, then uniformity of a capacity distribution between transformers is violated. With an increase in the total load current, in the case of double-wound transformer I and triple-wound transformer II connected in parallel, the secondary current of transformer I increases, as does its primary current, while the primary and secondary currents of transformer II decrease. In addition, the total current from the mains is less than the current of the primary winding of transformer I. With an increase in the loading current, the secondary current of transformer I increases and the secondary current of transformer II decreases. At the highest value of the secondary current of transformer II, the vector of primary current of this transformer advances the voltage vector by more than by 90°. In addition, the secondary winding of transformer II consumes active power from transformer I and returns it to its primary winding.     

DCE-MRI of hepatocellular carcinoma: perfusion quantification with Tofts model versus shutter-speed model—initial experience

Objective

To quantify hepatocellular carcinoma (HCC) perfusion and flow with the fast exchange regime-allowed Shutter-Speed model (SSM) compared to the Tofts model (TM).

Materials and methods

In this prospective study, 25 patients with HCC underwent DCE-MRI. ROIs were placed in liver parenchyma, portal vein, aorta and HCC lesions. Signal intensities were analyzed employing dual-input TM and SSM models. ART (arterial fraction), K ^trans (contrast agent transfer rate constant from plasma to extravascular extracellular space), v _e (extravascular extracellular volume fraction), k _ep (contrast agent intravasation rate constant), and τ _i (mean intracellular water molecule lifetime) were compared between liver parenchyma and HCC, and ART, K ^trans, v _e and k _ep were compared between models using Wilcoxon tests and limits of agreement. Test–retest reproducibility was assessed in 10 patients.

Results

ART and v _e obtained with TM; ART, v _e , k _e and τ _i obtained with SSM were significantly different between liver parenchyma and HCC (p < 0.04). Parameters showed variable reproducibility (CV range 14.7–66.5 % for both models). Liver K ^trans and v _e ; HCC v _e and k _ep were significantly different when estimated with the two models (p < 0.03).

Conclusion

Our results show differences when computed between the TM and the SSM. However, these differences are smaller than parameter reproducibilities and may be of limited clinical significance.

     

Quantum analysis based extraction of frequency dependent intrinsic and extrinsic parameters for GEWE-SiNW MOSFET

This paper examines the bias-independent and bias-dependent extrinsic and intrinsic parameters of the gate electrode workfunction engineered (GEWE) silicon nanowire (SiNW) metal–oxide–semiconductor field-effect transistor (MOSFET) by considering quantum effects. The results reveal that the effect of extrinsic parameters such as the resistance, capacitance, and inductance of the electrodes is less pronounced in the GEWE-SiNW compared with the conventional SiNW or conventional MOSFET. The intrinsic transconductance of the GEWE-SiNW device can be further improved by tuning the gate metal workfunction difference, which results in shorter time constant and lower parasitic capacitance, making it suitable for radiofrequency integrated circuit (RFIC) design. It is also observed that, in the saturation region, the device exhibits improved transconductance and noticeable reduction in \(C_{\mathrm{sdx}}\) [due to drain-induced barrier lowering (DIBL)] but the parasitic capacitance and time constant also reduce. In addition, a non-quasi-static small-signal model has been studied in terms of Z and Y parameters; the results show good agreement with the results of three-dimensional (3D) simulations at thousands of GHz.     

Multiferroic,magnetoelectric and magneto-impedance properties of NiFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/(Pb,Sr) TiO<Subscript>3</Subscript> bilayer films

We prepared NiFe₂O₄/(Pb, Sr)TiO₃ (NFO/PST) bilayer films by the chemical solution method and investigated their multiferroic, magnetoelectric and magneto-impedance properties. Multiferroic properties have been observed at room temperature. The bilayer films exhibit saturation polarization P _s ? 26.6 μC/cm² and saturation magnetization M _s ? 134 emu/cm³. With increasing Sr content, M _s. and P _s values of the NFO/PST bilayer films decrease. The variation may be ascribed to the influence of interfacial strain and decrease in tetragonality. High magnetoelectric coupling effect has been observed in the NFO/PST bilayer films with maximum value of α _E  = 6.35 Vcm^?1 Oe^?1 measured at H _DC  ~ 1 kOe and f ~ 10 kHz for Sr ~ 10% (NFO/PST10). The magneto-impedance measurements establish a strong dependence on magnetic field, further confirming magnetoelectric response in NFO/PST bilayer films. An alternative approach for impedance analysis of NFO/PST10 bilayer film provides direct evidence of strain mediated magnetoelectric coupling at room temperature. The results indicate that NFO/PST bilayer films can be considered as a potential multiferroic magnetoelectric material.     

Heterogate junctionless tunnel field-effect transistor: future of low-power devices

Gate dielectric materials play a key role in device development and study for various applications. We illustrate herein the impact of hetero (high-k/low-k) gate dielectric materials on the ON-current (\(I_{\mathrm{ON}}\)) and OFF-current (\(I_{\mathrm{OFF}}\)) of the heterogate junctionless tunnel field-effect transistor (FET). The heterogate concept enables a wide range of gate materials for device study. This concept is derived from the well-known continuity of the displacement vector at the interface between low- and high-k gate dielectric materials. Application of high-k gate dielectric material improves the internal electric field in the device, resulting in lower tunneling width with high \(I_{\mathrm{ON}}\) and low \(I_{\mathrm{OFF}}\) current. The impact of work function variations and doping on device performance is also comprehensively investigated.     

Quantitative effects of acquisition duration and temporal resolution on the measurement accuracy of prostate dynamic contrast-enhanced MRI data: a phantom study

Objectives

The aim of this study was to investigate the effect of the temporal resolution (T _res) and acquisition duration (AD) on the measurement accuracy of contrast concentration–time curves (CTCs), and derived phenomenological and pharmacokinetic parameter values, in a dynamic contrast-enhanced MRI experiment using a novel phantom test device.

Materials and methods

‘Ground truth’ CTCs were established using a highly precise optical imaging system. These precisely known CTCs were produced in an anthropomorphic environment, which mimicked the male pelvic region, and presented to the MRI scanner for measurement. The T _res was varied in the range [2–24.4 s] and the AD in the range [30–600 s], and the effects on the measurement accuracy were quantified.

Results

For wash-in parameter measurements, large underestimation errors (up to 40%) were found using T _res values ≥16.3 s; however, the measured wash-out rate did not vary greatly across all T _res values tested. Errors in derived K ^trans and v _e values were below 14 and 12% for acquisitions with {T _res ≤ 8.1 s, AD ≥ 360 s} and {T _res ≤ 16.3 s, AD ≥ 360 s}, respectively, but increased dramatically outside these ranges.

Conclusions

Errors in measured wash-in, wash-out, K ^trans, and v _e parameters were minimised using T _res ≤ 8.1 s and AD ≥ 360 s, with large errors recorded outside of this range.

     

Microwave dielectric properties of (1-<Emphasis Type="Italic">x</Emphasis>) BiVO<Subscript>4</Subscript>–<Emphasis Type="Italic">x</Emphasis>Ln<Subscript>2/3</Subscript>MoO<Subscript>4</Subscript> (Ln=Er,Sm, Nd,la) ceramics with low sintering temperatures

A series of microwave dielectric ceramics of (1-x) BiVO₄ -xLn_2/3MoO₄ (Ln = Er, Sm, Nd and La; x = 0.06, 0.08, 0.10) sintered below 900 °C were prepared via solid-state reaction. As the x values increase, the monoclinic scheelite continuously changes to a tetragonal structure at x = 0.10. The incorporation of Ln_2/3MoO₄ into the BiVO₄ matrix increases the product (Q × f) of quality factor (Q) and resonance frequency (f), and temperature coefficient (τ _f ), but lowers the dielectric constant (ε _r). Microwave dielectric ceramics with low sintering temperatures (<900 °C) are obtained: ε _r of ~71.1, 81.6, 75.6 and ~75.3; Q × f values of ~8292, 5508, 8695 and 9043 GHz; τ _f of ~ ?51, 134, 149 and 158 ppm/°C, for 0.94BiVO₄–0.06Er_2/3MoO₄, 0.92BiVO₄–0.08Sm_2/3MoO₄, 0.9BiVO₄–0.1Nd_2/3MoO₄ and 0.9BiVO₄–0.1La_2/3MoO₄ ceramics, respectively. Moreover, (1-x) BiVO₄ -xLn_2/3MoO₄ (Ln = Er, Sm, Nd and La; x = 0.06, 0.08 and 0.10) ceramics are chemically compatible with both Ag and Cu powders at their sintering temperatures. The series of microwave dielectric ceramics might be potential candidates for low temperature co-fired ceramics (LTCC) technology applications.     

Monte Carlo analysis of dynamic characteristics and high‐frequency noise performances of nanoscale double‐gate MOSFETs

In this paper, a full‐band Monte Carlo simulator is employed to study the dynamic characteristics and high‐frequency noise performances of a double‐gate (DG) metal–oxide–semiconductor field‐effect transistor (MOSFET) with 30 nm gate length. Admittance parameters (Y parameters) are calculated to characterize the dynamic response of the device. The noise behaviors of the simulated structure are studied on the basis of the spectral densities of the instantaneous current fluctuations at the drain and gate terminals, together with their cross‐correlation. Then the normalized noise parameters (P, R, and C), minimum noise figure (NF_min), and so on are employed to evaluate the noise performances. To show the outstanding radio‐frequency performances of the DG MOSFET, a single‐gate silicon‐on‐insulator MOSFET with the same gate length is also studied for comparison. The results show that the DG structure provides better dynamic characteristics and superior high‐frequency noise performances, owing to its inherent short‐channel effect immunity, better gate control ability, and lower channel noise. Copyright © 2012 John Wiley & Sons, Ltd.     

High-blocking-voltage UMOSFETs with reformed electric field distribution

A high-performance vertical GaN metal–oxide–semiconductor field-effect transistor (MOSFET) with a U-shaped gate (UMOSFET) and high blocking voltage is proposed. The main concept behind this work is to reform the electric field distribution to achieve high blocking voltage. The proposed structure includes p-regions in the drift region, which we call reformed electric field (REF) regions. Simulations using the two-dimensional SILVACO simulator reveal the optimum doping concentration, and width and height of the REF regions to achieve the maximum depletion region at the breakdown voltage in the drift region. Also, the electric field distribution in the REF-UMOSFET is reformed by producing additional peaks, which decreases the common peaks under the gate trench. We discuss herein the impact of the height, width, and doping concentration of the REF regions on the ON-resistance (R_ON) and blocking voltage. The blocking voltage, specific ON-resistance, and figure of merit \( \left( {{\text{FOM}} = \frac{{V_{{{\text{BR}}}}^{2} }}{{R_{{{\text{ON}}}} }}} \right) \) are 1140 V, 0.587 mΩ cm² (V_GS = 15 V, V_DS = 1 V), and 2.214 GW/cm², respectively. The blocking voltage and FOM are increased by about 72 % and 171 % in comparison with a conventional UMOSFET (C-UMOSFET).     

A first-principles study of the structural,elastic, electronic,vibrational, and optical properties of BaSe<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Te<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

The structural, elastic, electronic, vibrational, and optical properties of BaSe_1?xTe_x alloys are investigated by means of the full-potential linearized augmented plane wave method. The exchange–correlation effects are treated with the local density approximation, as well as the GGA-PBE, GGA-PBEsol, and GGA?+?mBJ schemes of the generalized gradient approximation. Ternary BaSe_1?xTe_x compounds have not yet been synthesized. Improved predictions of the structural parameters are obtained using the GGA-PBEsol approach. Calculations of the electronic and optical properties with the GGA?+?mBJ approach yield accurate results. Ternary BaSe_1?xTe_x alloys are wide-band-gap semiconductors with a direct gap Γ–Γ. The upper valence band is mainly due to Se p and Te p states, while the bottom of the conduction band results essentially from Ba d states. The dielectric function, refractive index, reflectivity, absorption coefficient, and energy-loss function are calculated in the range 0–35 eV. The increase in x gives rise to a redshift of the optical spectra. BaSe_1?xTe_x alloys exhibit reflective properties of metals in some energy ranges. The static dielectric constant ?₁(0) and the static refractive index n₀ are calculated. The investigation of the elastic and vibrational properties shows that ternary BaSe_1?xTe_x should be mechanically and dynamically stable, elastically anisotropic, brittle, and relatively soft.     

Rapid measurement of intravoxel incoherent motion (IVIM) derived perfusion fraction for clinical magnetic resonance imaging

Objective

This study aimed to investigate the reliability of intravoxel incoherent motion (IVIM) model derived parameters D and f and their dependence on b value distributions with a rapid three b value acquisition protocol.

Materials and methods

Diffusion models for brain, kidney, and liver were assessed for bias, error, and reproducibility for the estimated IVIM parameters using b values 0 and 1000, and a b value between 200 and 900, at signal-to-noise ratios (SNR) 40, 55, and 80. Relative errors were used to estimate optimal b value distributions for each tissue scenario. Sixteen volunteers underwent brain DW-MRI, for which bias and coefficient of variation were determined in the grey matter.

Results

Bias had a large influence in the estimation of D and f for the low-perfused brain model, particularly at lower b values, with the same trends being confirmed by in vivo imaging. Significant differences were demonstrated in vivo for estimation of D (P = 0.029) and f (P < 0.001) with [300,1000] and [500,1000] distributions. The effect of bias was considerably lower for the high-perfused models. The optimal b value distributions were estimated to be brain_500,1000, kidney_300,1000, and liver_200,1000.

Conclusion

IVIM parameters can be estimated using a rapid DW-MRI protocol, where the optimal b value distribution depends on tissue characteristics and compromise between bias and variability.

     

Structural and magnetic evolution of Fe-doped TiO<Subscript>2</Subscript> nanoparticles synthesized by sol-gel method

Nanocrystalline Ti_1-x Fe _x O₂ particles were fabricated via sol-gel method and their structures, morphology and magnetic properties were investigated. The structure of the Ti_1-x Fe _x O₂ nanospheres evolved from mixed anatase and rutile phases to pure anatase phase with increasing iron content. Additionally, it is found the evolution of magnetism: sample x = 3% shows room temperature ferromagnetism while the rests exhibit paramagnetism. The hysteresis loop of sample x = 3% is attributable to paramagnetic and ferromagnetic phase and the paramagnetic and ferromagnetic components are separated. The susceptibility of Ti_1-x Fe _x O₂ increases and then decreases with the increase of Fe content. The magnetism is explained by the BMP theory.