DC Behavior Research Articles

Implementation of nanoscale double-gate CMOS circuits using compact advanced transport models

In this paper we present the results of the implementation of a nanoscale double-gate (DG) MOSFET compact model, which includes hydrodynamic transport model, in Verilog-A in order to carry out circuit simulation. The model in Verilog-A is used with the SMASH circuit simulator for the analysis of the DC and transient behavior electrical CMOS circuits. Template devices representative for a downscaled symmetric double-gate MOSFET was used to validate the models for n-channel and p-channel. A CMOS inverter and a ring oscillator have been analyzed. Comparison of its performance between the drift-diffusion (DD) and hydrodynamic transport model within the practical range of bias voltages has been highlighted.

Characterization of DC, analog/RF, and low frequency noise in silicon-on-insulator nMOSFETs with different body-contact structures

This paper fabricated SOI nMOSFETs with floating body and different body-contact structures, including H-gate (HG), body-tied-to-source (BTS), and low-barrier-body-contact (LBBC), on the same SOI substrate. Through direct comparison of DC, analog, RF, and noise behaviors among these devices, the LBBC device has been found to show the best capability to suppress floating-body effects, superior output resistance, and low frequency noise characteristics. Although peak values of transconductance and cutoff frequency in the LBBC device are not so high as those in the HG or BTS device, weaker dependency on gate bias in the LBBC device makes choosing of work point more easy and flexible. Among these structures, the LBBC body contact structure could be a good candidate suitable to SOI nMOSFETs for analog/RF applications.

Anisotropic properties and conduction mechanism of TlInSe2 chain semiconductor

TlInSe2 chain crystals were prepared using the modification of the Bridgman technique. The grown crystals were identified by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDX), and X-ray diffraction (XRD). We investigate the anisotropy of transport properties for the first time for TlInSe2 crystals. Temperature dependence of the dc electrical conductivity, Hall coefficient, Hall mobility, and charge carrier concentration were investigated in the temperature range 184–455 K. The conduction mechanism of TlInSe2 crystals was studied, and measurements revealed that the dc behavior of the grown crystals can be described by Mott’s variable range hopping (VRH) model in the low temperature range, while it is due to thermoionic emission of charge carriers over the chain boundaries above 369 K. The Mott temperature, the density of states at the Fermi level, and the average hopping distance are estimated in the two crystallographic directions. The temperature dependence of the ac conductivity and the frequency exponent, s, is reasonably well interpreted in terms of the correlated barrier-hopping CBH model.

Intrinsic mixing behavior of superconducting NbTiN hot electron bolometer mixers based on in situ technique

In this paper, we present the comparison of measured and simulated results for 0.8 and 1.5THz waveguide NbTiN HEB mixers fabricated by in situ technique, with a relatively thick NbTiN film (10.8nm). The dimension of NbTiN HEB mixers are 1–1.5μm in width and 0.15–0.2μm in length respectively. The lowest receiver noise temperature is measured to be as low as 410K and reduced to 210K after the correction of the losses of quasi-optical path and IF amplifier chain at both 0.8 and 1.5THz. We adopt an optimized hot spot model to simulate the DC and RF behaviors of the NbTiN HEB mixer by combining phonon-cooling and diffusion-cooling mechanisms together. The measured and calculated current–voltage curves are in good agreement. The modeled lowest intrinsic mixer noise temperature are 85 and 100K at 0.8 and 1.5THz respectively, which are smaller than the measured results by factor of about 2times. The IF gain bandwidth are observed to be quite sensitive to the microbridge length, with 2.5GHz for 0.15-μm long device down to 1.9GHz for 0.2-μm length. The calculated and measured results show the two cooling mechanism work together to improve the performance of the waveguide NbTiN HEB mixers.

Attributes of Direct Current Aperiodic and Alternating Current Harmonic Components Derived From Large Amplitude Fourier Transformed Voltammetry Under Microfluidic Control in a Channel Electrode

The flow rate dependencies of the aperiodic direct current (dc) and fundamental to eighth alternating current (ac) harmonic components derived from large-amplitude Fourier transformed ac (FT-ac) voltammetry have been evaluated in a microfluidic flow cell containing a 25 μm gold microband electrode. For the oxidation of ferrocenemethanol ([FcMeOH]/[FcMeOH](+) process) in aqueous 0.1 M KNO(3) electrolyte, standard "Levich-like" dc behavior is observed for the aperiodic dc component, which enables the diffusion coefficient for FcMeOH to be obtained. In experimental studies, the first and second ac harmonic components contain contributions from the double layer capacitance current, thereby allowing details of the non-Faradaic current to be established. In contrast, the higher order harmonics and dc aperiodic component are essentially devoid of double layer capacitance contributions allowing the faradaic current dependence on flow rate to be studied. Significantly, flow rate independent data conforming to linear diffusion controlled theory are found in the sixth and higher ac harmonics at a frequency of 15 Hz and for all ac harmonics at a frequency of ≥ 90 Hz. Analysis of FT-ac voltammograms by theory based on stationary microband or planar electrode configurations confirms that stationary microband and planar electrode configurations and experimental data all converge for the higher order harmonics and establishes that the electrode kinetics are very fast (≥1 cms(-1)). The ability to locate, from a single experiment, a dc Faradaic component displaying Levich behavior, fundamental and second harmonics that contain details of the double layer capacitance, and Faradaic ac higher order harmonic currents that are devoid of capacitance, independent of the volume flow rate and also conform closely to mass transport by planar diffusion, provides enhanced flexibility in mass transport and electrode kinetic analysis and in understanding the performance of hydrodynamic electrochemical cells and reactors.

Enhanced DC model for GaN HEMT transistors with built-in thermal and trapping effects

This paper presents an enhanced DC model of a gallium nitride (GaN) high electron mobility transistor (HEMT) and the corresponding extraction procedure. This proposed model is based on new analytical equations that describe the DC behavior of the device, including thermal and trapping effects. A new analytical expression of thermal resistance that is considered to be temperature dependent is proposed. The trapping effect is modeled using an added term in the drain current expression with bias dependence. GaN HEMTs fabricated on a silicon wafer and also on a silicon carbide wafer are considered to validate the model. The thermal and trapping effects are characterized without using the pulsed measurement method which usually requires more complex measurements. Large-signal measurements are also used to assess further the validity of the DC model when it is integrated in and main part of a large-signal model used to design an inverse class-F amplifier.

Robust Simulation of Opto-Electronic Systems by Alternating Complex Envelope Representations

The increased use of optics in information processing and transmission systems motivates the development of self-consistent opto-electronic transient simulators. This letter presents a technique to significantly improve the DC and transient convergence behavior of a modified nodal analysis based optoelectronic simulation framework by allowing optical device models to be “switched” between a linear formulation using real and imaginary fields to a non-linear magnitude and phase representation. Configurable multilayer filters and optical ring modulators are used as examples to demonstrate the effectiveness of this approach in obtaining robust simulation convergence.

Test Results of Three Poloidal Field Superconducting Samples in SULTAN

Superconductors for the ITER Poloidal Field Coils are large cable-in-conduit conductors (CICC) made of NbTi strands encased in a round-in-square stainless steel jacket. Three prototype conductor sections for poloidal field coils PF1/6, PF2/3/4 and PF5 have been fabricated in collaboration of the domestic RF, CN and EU agencies and tested in SULTAN Test Facility at the nominal operating conditions. The test aimed to characterize the DC and AC behavior of the conductors. The DC test was focused on the current sharing temperature (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">cs</sub> ) at the nominal operating current and nominal operating background field. The take-off electric field at the nominal Helium mass flow rate was investigated versus the cable current density over a broad range of field and temperature. The AC loss measurement was performed before any electromagnetic loading and after a number of load cycles in order to define the impact of cyclic loads on the coupling currents constant of the cable. From the test results in SULTAN test facility, the margins in normal operation and the limits of the operation range of the ITER PF conductors are assessed.

Influence of the sintering temperature on the magnetic and electric properties of NiFe2O4 ferrites

This study evaluates the structural, microstructural, electric and magnetic properties of nickel ferrite samples prepared through the solid state reaction. It was observed that an increase in the sintering temperature produces a higher cation concentration in the A site when compared to the B site. The assessment of magnetic properties showed that an increase in grain size leads to a decrease in the coercive fields verging on superparamagnetic values, while the saturation magnetization increases up to 46.5 Am².kg-1 for samples sintered at 1200 ºC. The dc electric resistivity behavior of samples was attributed to the increase in the cross-sectional area of grains as well as the different oxidation states and distribution of cations amongst the lattice sites of the spinel structure.

Design of an Ultra-Low-Power Multi-Stage AC/DC Voltage Rectifier and Multiplier Using a Fully-Automated and Portable Design Methodology

A fully-automated and portable design methodology has been developed based on an efficient model and a gradient's method to optimize an ULP (Ultra Low Power) AC-DC multi-stage rectifier through the overall design window in a practical design time. Innovative ULP diodes featuring two CMOS transistors are modeled and used to reduce leakage. The diode model includes parasitic capacitances, thus taking into account DC and AC behavior for various frequencies and voltage amplitudes. A 3-stage rectifier taking a 1 Vpp input sinusoidal signal at 13.56 MHz and providing a 10 μA load current has been designed in 250 nm bulk CMOS technology with 72% power conversion efficiency and 1.99 V output voltage. Robust design decisions with respect to process corner variations have been reached with this methodology and are also presented.

Analysis of carrier dynamic effects in transistor lasers

We present an analytical model to analyze the influence of carrier dynamics on the static and dynamic responses of transistor laser (TL). Our analysis is based on solving the continuity equation and the rate equations which incorporate the virtual states as a conversion mechanism. We show that the details of the dc and small signal behavior of transistor lasers are strongly affected by the escape and capture times of carriers in quantum well (QW). Also, the effects of carrier recombination lifetime in the quantum well and base regions on the TL static and dynamic performances are investigated.

Analysis of limit cycle behavior in DC–DC boost converters

This paper deals with limit cycle behaviors in DC–DC boost converters with a proportional-integral (PI) voltage compensator, which is a popular design solution for increasing output voltage in power electronics. Extensive cycle-by-cycle numerical simulations are used to capture all limit cycle behaviors. It is found that there exist two types of limit cycle behaviors rather than only one type in a boost converter. For each type of limit cycle, its underlying mechanism is revealed by circuit analysis. Moreover, the critical condition is derived to predict the occurrence of the limit cycle behaviors in terms of Routh stability criterion, and the analytical expressions for the limit cycles I and II are given based on the averaged model approach. Finally, these theoretical results are verified by numerical simulations and circuit experiments.

Dendritic cells provide a potential link between smoking and inflammation in rheumatoid arthritis

IntroductionSmoking increases the risk of developing rheumatoid arthritis (RA) and affects the severity of established RA. Smoking can impact on Th17 lymphocyte differentiation and function through activation of the aryl hydrocarbon receptor (AHR), a process with implications for the pathogenic mechanisms in RA that involve the cytokine, interleukin (IL)-17A. The objective of this study was to establish any effect of smoking on the inflammatory tissue lesions of rheumatoid arthritis via the AHR and IL-17A.MethodsTwenty synovial and eighteen subcutaneous nodule tissue samples from 31 patients with RA were studied. Patient smoking status at the time of tissue collection was established. Expression of AHR, CYP1A1, AHRR, IL6, IL17A, IL17F, IL22, IL23, IL23R, IFNG, TBX21, IDO1 and FOXP3 genes were assessed in tissues and cultured cells using real-time PCR. Two-colour immunofluorescence was used to co-localise AHR and CYP1A1 protein in synovial tissues. The response of monocytes and monocyte-derived dendritic cells (mo-DCs) to the AHR agonist, benzo(a)pyrene (BaP) was compared in vitro.ResultsAHR gene expression was demonstrated in rheumatoid synovial tissues and nodules with significantly greater expression in synovia. Expression was not influenced by smoking in either tissue. Evidence of AHR activation, indicated by CYP1A1 and AHRR gene expression, was found only in synovia from patients who smoked. However, IL17A gene expression was lower in synovia from smokers. TBX21 and FOXP3 expression was not affected by smoking. Within the synovial tissues of smokers the principal cell type with evidence of AHR activation was a subset of synovial DCs. This observation was consistent with the sensitivity of human mo-DCs to BaP stimulation demonstrated in vitro. Exposure to BaP affected mo-DC function as demonstrated by decreased IL6 expression induced by PolyI:C, without affecting indoleamine 2,3 dioxygenase (IDO)1 expression.ConclusionOur findings show that one effect of smoking on inflamed rheumatoid synovial tissue involves activation of the AHR pathway. A subset of synovial DCs is important in the response to cigarette smoke. The potential for smoking to affect DC behaviour in joint tissues has relevance to both early and late phases of RA pathogenesis and warrants further investigation.

Finite Length Effects for Osmotic Pressures of PEG Polymers

Previously we derived a one-parameter scaling-law equation of state for the osmotic pressures of polyethylene glycol (PEG) polymers in water, applicable over a broad range of polymer sizes and concentrations (J. Phys. Chem. B, 2009, 113, 3709). The derived equation is a non-virial linear combination of a low-concentration van’t Hoff (vH) term and a higher-concentration des Cloizeaux (dC) term. A single parameter α locates the crossover from dilute vH to semidilute dC behavior. The value of α was determined by an empirical fit to the concentration-dependent data of Rand et al. (loc.cit.) for PEGs of molecular weights ranging from 300 to 20,000 daltons. Appropriate scaling collapsed all the data onto a single curve that was well fit by our equation of state with the single parameter α = 0.49 ± 0.01. Now, by fitting α to the scaled osmotic pressures of each polymer separately, we find a small but systematic dependence of α on polymer size. As the number of monomers N increases, α(N) decreases monotonically toward an asymptotic value that we call α∗. The interaction strength of shorter polymers is thus larger than that of longer polymers. Because scaling theories assume polymers of infinite length, α∗ can be viewed as the value of α in the scaling limit. A correction-to-scaling formula derived from renormalization group theory provides an excellent fit to α(N) for PEG polymers, yielding α∗ = 0.43 ± 0.02. The present formulation for α(N) further improves the accuracy of the osmotic pressures of PEG polymers calculated by our equation of state.

Explicit Drain Current, Charge and Capacitance Model of Graphene Field-Effect Transistors

This paper presents a compact physics-based model of the drain current, charge, and capacitance of graphene field-effect transistors, which is of relevance for the exploration of dc, ac, and transient behavior of graphene-based circuits. The physical framework is a field-effect model and drift-diffusion carrier transport incorporating saturation velocity effects. First, an explicit model has been derived for the drain current. Using it as a basis, explicit closed-form expressions for the charge and capacitances based on the Ward-Dutton partition scheme were derived, covering continuously all the operation regions. The model is of special interest for analog and radio-frequency applications where bandgap engineering of graphene is not needed.

Tuning A-site ionic size in R0.5Ca0.5MnO3 (R = Pr, Nd and Sm): robust modulation in dc and ac transport behavior

Structural investigations on Pr0.5Ca0.5MnO3, Nd0.5Ca0.5MnO3 and Sm0.5Ca0.5MnO3 display a systematic tuning in orthorhombic distortion which appears due to a change in A-site ionic size. Comprehensive investigations on dc conduction using various models indicate strong correlation with structural changes. Careful analysis of the ac conductivity mechanism as a function of frequency and temperature brings out a pronounced effect of structural modifications on the polaron conduction mechanism. Contrary to typical manifestations, dc conductivity and relaxation of charge carriers reveal non-Arrhenius behavior. This work provides a detailed and systematic addition to the phase diagram of electronic transport in the rare-earth manganite system doped with a divalent alkali atom.

Electrical conductivity, dielectric properties and optical absorption of organic based nanocrystalline sodium copper chlorophyllin for photodiode application

Sodium copper chlorophyllin (SCC) thin films were successfully prepared, using dip coating technique. Thermal gravimetric analysis (TGA) was performed for studying the thermal stability of SCC film. The surface morphology of thin films was studied by using scanning electron microscopy (SEM). The crystalline structural characteristics were undertaken with the aim of determining the lattice parameters together with a complete list of the Miller indices and interplanar spacing for SCC. The molecular structure and electronic transitions of SCC were investigated by Fourier-transform infrared (FTIR) and absorption spectrum, respectively. Temperature dependence of the DC electrical conductivity, ( σ DC) was investigated in the temperature range 289–373 K. Measurements revealed that the σ DC behavior of the films can be described by Mott's one-dimensional variable range hopping (VRH) model in the entire temperature range. The AC conductivity, ( σ AC( ω)) results were discussed in terms of the correlated barrier hopping (CBH) mechanism for charge carrier transport. The maximum barrier height and the hopping length were estimated. The temperature dependence of the σ AC( ω) shows Arrhenius type with one thermal activation energy for each frequency. The behavior of the real and imaginary parts of the dielectric constant as a function of both temperature and frequency were discussed. The energy band model was applied and the type of the optical transitions responsible for optical absorption was found to be direct allowed transition. Position dependent for SCC thin film photo-detector was studied by using laser diode source.

Backbone of conductivity in two-dimensional metal-insulator composites

In percolation theory, the backbone is defined by chopping off dangling ends from the percolating cluster. For structures with high degree of spatial correlation, as they are typical for porous thin films, trimming of the full structure to reveal the part determining the electrical conductivity is more subtle than the classic definition of the backbone. To expand the applicability of the concept, we present a purely geometric definition for the backbone of a two-dimensional percolating cluster. It is based on a sequence of image analysis operations defining the backbone in terms of an image filter. The change of both area fraction and effective conductivity induced by applying the backbone filter to various binary images and a two-parameter family of sets is assessed by numerical means. It is found that the backbone filter simplifies the geometry of complex microstructures significantly and at the same time preserves their electrical DC behavior. We conclude that the backbone will be useful as a first ingredient for a geometric estimator of the effective conductivity of metal-insulator composites.

Chaotic Behaviour of DC Drives

Chaotic dynamical behaviour of a chopper fed dc drive has been investigated. Bifurcation behaviour of the system is observed by varying system parameters. The route of transition from periodic behaviour to chaos has been investigated and quantified by maximum Lyapunov exponent.

The first non-acetato members of the bis(anion)octacarboxylatotetrakis{di-2-pyridyl-methanediolate(−2)}enneametal(II) family of complexes: Synthesis, X-ray structures and magnetism of [M 9(N 3) 2(O 2CCMe 3) 8{(py) 2CO 2} 4] (M = Co, Ni)

The combined use of di-2-pyridyl ketone [(py) 2CO] and azides (N 3 −) in nickel(II) and cobalt(II) pivalate chemistry has afforded complexes [Ni 9(N 3) 2(O 2CCMe 3) 8{(py) 2CO 2} 4] ( 1) and [Co 9(N 3) 2(O 2CCMe 3) 8{(py) 2CO 2} 4] ( 2), where (py) 2CO 2 2− is the gem-diolate(−2) form of (py) 2CO. The complexes are isostructural and crystallize in the monoclinic P2 1/ c space group. Their molecular structures consist of nine metal(II) ions, eight of which are arranged as two parallel squares flanking the ninth. DC magnetic susceptometry on powdered samples of 1 ( 1-p) reveal an overall antiferromagnetic behavior, leading to an S = 0 ground state. AC susceptometry reveals out-of-phase signals between 10 and 27 K, and ZFC and FC experiments show a divergence of the two curves below ∼27 K. Magnetization-decay and field-sweep experiments verify the relaxation behavior of the sample. Samples of the complex arising from carefully washed single crystals ( 1-cr) reveal a similar DC behavior, without however the appearance of cusps in the χ Μ Τ versus T curves, and no relaxation. The relaxation behavior has been assigned to NiO impurities. The results illustrate the extreme care that should be taken when examining the magnetic properties of apparently analytically pure materials obtained under heating. Complex 2 exhibits an overall antiferromagnetic behavior, without observation of any relaxation phenomena.