Frequency Dependence Of Capacitance Research Articles

Involvement of protons in the ion transport cycle of Na+,K+-ATPase

The effect of pH on electrogenic sodium transport by the Na+ ,K+ -ATPase has been studied. Experiments were carried out by admittance recording in a model system consisting of a bilayer lipid mem­ brane with adsorbed membrane fragments containing purified Na+ ,K+ -ATPase. Changes in the membrane admittance (capacitance and conductance increments in response to photo-induced release of ATP from caged ATP) were measured as function of AC voltage frequency, sodium ion concentration, and pH. In solu­ tions containing 150 m M Na+, the frequency dependence of capacitance increments was not significantly dependent on pH in the range between 6 and 8. At a low NaCl concentration (3 mM), the capacitance incre­ ments at low frequencies decreased with the increasing pH. In the absence ofNaCl, the frequency-dependent capacitance increment at low frequencies was similar to that measured in the presence of 3 mM NaCI. These results may be explained by involvement of protons in the Na+, K+ -ATPase pump cycle, i.e., electroneutral exchange of sodium ions for protons under physiological conditions, electrogenic transport of sodium ions at high pH, and electrogenic transport of protons at low concentrations (and in the absence) of sodium ions.

Electrical equivalent circuit of an ion-exchange membrane system

Usually, the current flowing through an electrochemical cell is divided into the faradaic current going to an electrochemical interface reaction, and the current charging electric double layer (EDL). This division leads to the Randles–Ershler equivalent circuit with an EDL capacitance in one branch, and the faradaic impedance in the other, specific for each particular system. However, the physics of the separation of the impedance into faradaic and capacitive components for different electrochemical systems is not sufficiently clear. The most of derivations resulting in the formal construction of the Randles–Ershler or similar equivalent circuits are based on the a priori separation of the electroneutral and the double-layer regions. In this paper, we derive an equation for the impedance of a three-layer system consisted of an ion-exchange membrane and two adjoining diffusion boundary layers (DBL) starting from the Poisson equation. The system is polarized by a constant electric current over which a small sinusoidal signal is applied. The equation shows that the impedance of the considered system can be formally interpreted via an equivalent circuit with a frequency dependent capacitance in one branch and a finite-length Warburg-type impedance in the other. To take into account this dependence, the impedance of the system may be presented as a series connection of five circuits. Three of them are consisted of a geometric capacitance connected in parallel with an ohmic resistance, respectively, for both diffusion layers and for the membrane bulk; the two others being the double-layer capacitance in parallel with the finite-length Warburg impedance for the left and the right interfaces, respectively. The comparison of the impedance spectra calculated within our analytical approach with those obtained by the full numerical solution of the Nernst–Planck–Poisson (NPP) equations shows a good agreement. Different possible situations, which might arise in real systems (different stationary current densities, different thicknesses of the left-hand and right-hand DBLs), are analysed when applying the approximate solution.

Current transport mechanisms and trap state investigations in (Ni/Au)–AlN/GaN Schottky barrier diodes

The current transport mechanisms in (Ni/Au)–AlN/GaN Schottky barrier diodes (SBDs) were investigated by the use of current–voltage characteristics in the temperature range of 80–380 K. In order to determine the true current transport mechanisms for (Ni/Au)–AlN/GaN SBDs, by taking the J s(tunnel), E 0, and R s as adjustable fit parameters, the experimental J– V data were fitted to the analytical expressions given for the current transport mechanisms in a wide range of applied biases and at different temperatures. Fitting results show the weak temperature dependent behavior in the saturation current and the temperature independent behavior of the tunneling parameters in this temperature range. Therefore, it has been concluded that the mechanism of charge transport in (Ni/Au)–AlN/GaN SBDs, along the dislocations intersecting the space charge region, is performed by tunneling. In addition, in order to analyze the trapping effects in (Ni/Au)–AlN/GaN SBDs, the capacitance–voltage ( C– V) and conductance–voltage ( G/ω– V) characteristics were measured in the frequency range 0.7–50 kHz. A detailed analysis of the frequency-dependent capacitance and conductance data was performed, assuming the models in which traps are located at the heterojunction interface. The density ( D t ) and time constants ( τ t ) of the trap states have been determined as a function of energy separation from the conduction-band edge ( E c − E t ) as D t ≅ ( 5 – 8 ) × 10 12 eV - 1 cm - 2 and τ t ≅ ( 43 – 102 ) μ s , respectively.

Combined IV and CV Analysis of Laser Annealed Carbon and Boron Implanted SiGe Epitaxial Layers

SiGe epitaxial layers receiving sub-melt laser annealing after Carbon and Boron co-implantations are investigated. Their electrical properties have been evaluated in the reverse bias region of the IV and CV characteristics of SiGe/Si diode structures. Large dc leakage currents and frequency-dependent capacitance dispersions are observed. They are indicating the presence of electrically active defects in the studied devices. Combined IV and CV analysis suggests that the defectivity of the B-induced end-of-range defects can be enhanced by the laser treatment. This laser-driven enhancement can be suppressed by the C co-implantations. Experimental results also indicate that this C treatment is strongly affected by the laser annealing conditions.

Investigation of Trap States in AlInN/AlN/GaN Heterostructures by Frequency-Dependent Admittance Analysis

We present a systematic study on the admittance characterization of surface trap states in unpassivated and SiN x -passivated Al0.83In0.17N/AlN/GaN heterostructures. C–V and G/ω–V measurements were carried out in the frequency range of 1 kHz to 1 MHz, and an equivalent circuit model was used to analyze the experimental data. A detailed analysis of the frequency-dependent capacitance and conductance data was performed, assuming models in which traps are located at the metal–AlInN surface. The density (D t) and time constant (τ t) of the surface trap states have been determined as a function of energy separation from the conduction-band edge (E c − E t). The D st and τ st values of the surface trap states for the unpassivated samples were found to be $$ D_{\rm{st}} \cong (4 - 13) \times 10^{12} $$ $$ {\hbox{eV}}^{ - 1} {\hbox{cm}}^{ - 2} $$ and τ st ≈ 3 μs to 7 μs, respectively. For the passivated sample, D st decreased to $$ 1.5 \times 10^{12} $$ $$ {\hbox{eV}}^{ - 1} {\hbox{cm}}^{ - 2} $$ and τ st to 1.8 μs to 2 μs. The density of surface trap states in Al0.83In0.17N/AlN/GaN heterostructures decreased by approximately one order of magnitude with SiN x passivation, indicating that the SiN x insulator layer between the metal contact and the surface of the Al0.83In0.17N layer can passivate surface states.

Impedance and barrier capacitance of silicon diodes implanted with high-energy Xe ions

Abstract Characteristics of Si p + n diodes with non-uniformly distributed compensating defects, which were introduced by implantation with Xe 23+ ions, have been studied. The layer with the maximum concentration of the compensating defects was located in the vicinity of the metallurgical p – n junction. It is found that the presence of the defect layer results in non-monotonic dependences of the imaginary part of impedance (− Z ″) and differential conductance ( G = −d I /d U ) of the implanted diodes on reverse bias voltage U . An equivalent circuit of the irradiated diode is proposed, which allows us to approximate the measured frequency dependences of capacitance and conductance of the irradiated diodes and to determine values of diode barrier capacitance C pn at different reverse bias voltages.

A Thermal Model for Pulsed EM Field Exposure Effects in Cells at Nonthermal Levels

The thermal response of an isolated cell under pulsed electric field exposure is studied, including a frequency-dependent membrane capacitance model. The possibility of a fast localized membrane heating up to physiologically significant levels is suggested, without sensible increase in the cytoplasmic temperature.

On the interface properties of ZnO/Si electroluminescent diodes

ZnO layers grown on n−-Si(100), n+-Si(100), and n−-Si(111) substrates by pulsed-laser deposition were found to give electroluminescence. Light emission was observed in the form of discrete spots for currents over 1 mA with a white appearance to the naked eye. The intensity of these spots showed an erratic behavior over time, appearing and disappearing at random, while showing an associated random telegraph noise in the current signal. Regardless the substrate used, the electroluminescence spectra had a main broadband emission centered at about 600 nm and a relatively small peak at around 380 nm which corresponds to the energy of ZnO near band edge emission. Furthermore, the devices exhibited rectifying characteristics, whose current blocking direction depended on the substrate orientation. Optimization of ZnO conductivity and performing sample growth in N2 ambient were found to be critical to enhance the emission intensity. Rutherford backscattering characterization revealed the existence of an intermixed region at the interface between ZnO and Si. To study the electronic properties at the interface, frequency dependent capacitance measurements were carried out. The junction capacitance became frequency dependent at the bias voltages at which light emission occurs due to the relatively slow trapping and generation processes at deep centers. These centers are believed to play an important role in the mechanism of light emission.

Preparation and characterization of BiFeO 3/LaNiO 3 heterostructure films grown on silicon substrate

BiFeO 3/LaNiO 3 (BFO/LNO) heterostructure films are fabricated directly on Si (1 0 0) substrate. The LaNiO 3 layer, which is prepared by chemical solution deposition, is used both as the seed layer to improve the quality of BiFeO 3 layer, and as the bottom electrode for the electrical measurement. The BiFeO 3 layer, which is fabricated by pulsed laser deposition, presents compact microstructure with grain size about 100 nm. Saturated hysteresis loops of polarization vs. applied voltage have been measured at the frequency of 1 kHz. The value of remnant polarization is about 40 μC/cm 2. The frequency dependence of capacitance and loss tangent of the heterostructure is also studied. All the results of the electrical measurements indicate that the effect of leakage current has been suppressed in the BFO/LNO heterostructure. The results are significative for the application of BiFeO 3 films in microelectronic devices.

Poly(aniline) doped with 5-formyl-2-furansulfonic acid: A humidity memory

We present a new concept for a humidity sensor based on doped poly(aniline) that shows irreversible changes of its sheet resistance and capacitance upon exposure to humid conditions, i.e. a humidity memory. Therein humidity triggers an irreversible dedoping process, which results in a phase separation and crystallization of the hydrated form of its protonating agent, as suggested by combining FT-IR and UV–Vis-NIR spectroscopies, optical microscopy, dc-conductivity, and frequency dependent capacitance measurements. We also introduce a simple concept to activate the sensor and to monitor it through non-contact capacitance measurements. We anticipate that the proposed concept could be implemented for functional packaging to qualitatively detect whether their contents have been exposed to humidity during their transportation and storage history.

Electrical Characteristics of PbSe Nanoparticle/Si Heterojunctions

I-V characteristics of PbSe nanoparticle/single crystal Si heterojunctions prepared by chemical bath deposition method show a rectifying behavior. With decrease in average PbSe grain size between 72 nm and 9 nm currents decrease for forward and reverse bias. C-V characteristics indicate that the junctions transform into that of a metal insulator semiconductor (MIS) as the PbSe nanoparticle size decreases from 72 nm to 9 nm. This insulator like behavior of the small PbSe nanoparticle films is attributed to the highly resistive grain boundaries. Cole-Cole plots demonstrate that on decrease of grain size, the grain boundary contribution increases and grain contribution to the overall impedance decreases. Frequency dependence of capacitance proves space charge polarization in larger grains, which recedes with decrease in average grain size proving insulator like behavior of small PbSe nanoparticles.

Trap behaviors in AlGaN–GaN heterostructures by C–V characterization

Trap behaviors in AlGaN–GaN heterostructures were characterized by the means of mercury-probe capacitance–voltage (C–V) technique for samples grown on sapphire and SiC substrates. The effective trap density was determined by a simplified model to give a schematic explanation for the capacitance dispersion. Fluorine plasma treatment was carried out with appropriate time and power for further identification. The V Ga-related defects in (Al)GaN bulk layers were responsible for the frequency-dependent capacitance dispersion in pinch-off region, while the surface status influenced the capacitance dispersion in pinch-on region directly.

Dispersive capacitance and conductance across the phase transition boundary in metal-vanadium oxide-silicon devices

Utilizing metal-vanadium oxide (VO2)-semiconductor capacitor device structures, we have investigated the temperature- and frequency-dependent dielectric and ac conductance responses of vanadium oxide thin films that undergo metal-insulator transition (MIT). In both metallic and insulating regimes, VO2-based devices showed large tunabilities as high as ∼95% and ∼42%–54%, respectively. The frequency dependence of capacitance and ac conductance displays power-law behavior with respect to temperature and applied voltage over a broad range. Low-frequency dispersion in dielectric properties was also observed and their onset frequency varies across the MIT from ∼0.5 MHz in insulating state to ∼50 kHz in metallic state. The results are of potential relevance to utilizing functional oxides in electronic devices.

Atomistic Electrodynamics Model for Optical Properties of Silver Nanoclusters

In this work we have presented an atomistic electrodynamics model for describing the optical properies of silver clusters in the size range of 1−5 nm. The model consists of interacting atom-type capacitances and polarizabilities that combined describe the total response of the nanoclusters. A double Lorentzian oscillator is used to describe the frequency-dependent atomic polarizabilities, while a single Lorentzian oscillator is used to describe the frequency-dependent atomic capacitances. All atomic parameters have been optimized using reference data obtained from time-dependent density functional theory (TDDFT) calculations. As a comprehensive test of our model, we have studied the frequency-dependent polarizabilities of quasi-spherical silver nanoclusters having different structural motifs, i.e., icosahedra, truncated Ino and Marks decahedra, and regular truncated octahedra and cubocahedra. We have shown that clusters in all five structural motifs exhibit a strong absorption peak in the spectral region ...

Room-temperature interface state analysis of Au/Poly(4-vinyl phenol)/p-Si structure

The Poly(4-vinyl phenol) insulator layer was grown by spin coating technique onto p-Si substrate. Diode ideality factor (n), insulator layer thickness (δ), space charge region width (WD), interface state density (Nss), series resistance (Rs), acceptor concentration (NA) of the Au/Poly(4-vinyl phenol)/p-Si structure have been extracted from the current–voltage (I–V), frequency dependent capacitance–voltage (C–V) and conductance–voltage (G–V) measurements. It is pointed out that the interface states lead to deviation of the ideality factor value from 1 and frequency dispersion of the C–V characteristics. Nss profiles as a function of (Ess−Ev) obtained using I–V and low frequency C–V measurements are in good agreement. Nss values varying between 1012 and 1013eV−1cm−2 mean that Poly(4-vinyl phenol) is a candidate for insulator layer forming on Si as powerful as SiN4, SnO2, TiO2.

Frequency dependent capacitance and plasmon excitations in a coherent parallel-plate capacitor

We report the theoretical investigations of frequency-dependent capacitance in a coherent parallel-plate capacitor. It is found that the capacitance strongly depends on frequency and is complex at finite frequency. An interesting result is that in the frequency dependence of capacitance, a peak in the imaginary part of capacitance corresponds to the minimum of the real part and is related to a plasmonlike excitation, which is of damping and has a short lifetime. We also discussed the size effect of the capacitor and find that the capacitance approaches geometric capacitance when the distance between two plates of the capacitor is very large.

Capacitance and conductance characteristics of silicon nanocrystal metal–insulator–semiconductor devices

Metal–insulator–semiconductor (MIS) devices featuring silicon (Si) nanocrystals (NCs) embedded in a silicon dioxide (SiO 2) insulating layer have been fabricated by radio frequency magnetron sputtering. Capacitance–voltage ( C– V) curves of the Si:NC-MIS devices were found to exhibit deep depletion regions and frequency-dependent capacitance peaks at two values of bias voltage. Corresponding peaks were also identified in the conductance–voltage ( G– V) curves of the Si:NC-MIS devices. The peaks are attributable to (i) the small signal response of interface states at the interface of the insulating layer and the Si substrate, and (ii) external inversion layer coupling in the transition region between the modes of tunnel-limited and semiconductor-limited electron current.

Performance and Stability Characterization of Bottom Gated Amorphous Indium Gallium Zinc Oxide Thin Film Transistors Grown by RF and DC Sputtering

In this paper, the performance and the gate bias stability of amorphous indium gallium zinc oxide (a-IGZO) thin film transistors (TFTs) with different channel sputtering conditions, RF and DC are studied. DC devices show excellent electrical characteristics but larger charge trapping and slower detrapping in relaxation period under the same gate bias stress. To understand the cause of stress behavior, traps are extracted by subthreshold slop and low-high frequency dependent capacitance measurement and compared before and after gate bias stress. The extracted trap densities well explain the process-dependent device properties like as threshold voltage, mobility and on/off current ratio, but are not dependent on bias stress. From current–voltage (I–V) and capacitance–voltage (C–V) measurement, we can conclude that the threshold voltage instability arises due to the process of temporary charge trapping which is dominant only at gate bias stress and the trapping/detrapping behavior is strongly dependent on the channel layer deposition condition.

J0405-1-4 全面くし型電極を用いたVaRTMフローコントロール(知的材料・構造システム(1) 複合材料関連)

Since a fiber reinforced plastic structure is complicated in the adoption of integral molding for the reduction of structure weight, VaRTM (Vacuum assisted Resin Transfer Molding) is used widely for making a complicated structure easily. But local molding fault such as dryspot is liable to occur in VaRTM. To solve this problem, the impregnated area in the entire structure needs to be measured. In the present study, we measure the impregnated area using a smart film covering the entire structure. If a dryspot is likely to occur, the resin is heated by dielectric heating. Since the viscosity of resin is lower, the flow speed is faster. As a result, dielectric heating prevents a dryspot from occurring. Moreover, we confirmed the temperature of resin from measuring the frequency dependence of capacitance. We established the smart flow system of controlling impregnated are or temperature in VaRTM.

Five-element circuit model using linear-regression method to correct the admittance measurement of metal-oxide-semiconductor capacitor

The authors present a linear-regression method based on a five-element circuit model to correct measured capacitance-voltage and conductance-voltage curves. This model explains the effects of series resistance and parasitic capacitance/inductance on the frequency dispersion of measured capacitance and the magnification of measured conductance. These extracted parasitic components show significant dependencies on the geometry of capacitor structure, thereby causing different frequency-dependent capacitance characteristics in measurements.