Capacitance Relaxation Research Articles

Slowly relaxing charge in lead borosilicate glass passive coatings studied by isothermal capacitance relaxation

The effective surface charge density in passive lead borosilicate glass coatings on a semiconductor surface was determined by the isothermal capacitance relaxation measurements. It was found that an increase in the temperature of coating formation is accompanied by increase in the effective surface charge density. This relationship is explained by the growth in concentration of the charge trapping centers with increasing content of a crystalline phase in the bulk of glass.

CAMP Activation of Apical Membrane Cl − Channels: Theoretical Considerations for Impedance Analysis

Transepithelial electrical impedance analysis provides a sensitive method to evaluate the conductances and capacitances of apical and basolateral plasma membranes of epithelial cells. Impedance analysis is complicated, due not only to the anatomical arrangement of the cells and their paracellular shunt pathways, but also in particular to the existence of audio frequency-dependent capacitances or dispersions. In this paper we explore implications and consequences of anatomically related Maxwell-Wagner and Cole-Cole dielectric dispersions that impose limitations, approximations, and pitfalls of impedance analysis when tissues are studied under widely ranging spontaneous rates of transport, and in particular when apical membrane sodium and chloride channels are activated by adenosine 3′,5′-cyclic monophosphate (cAMP) in A6 epithelia. We develop the thesis that capacitive relaxation processes of any origin lead not only to dependence on frequency of the impedance locus, but also to the appearance of depressed semicircles in Nyquist transepithelial impedance plots, regardless of the tightness or leakiness of the paracellular shunt pathways. Frequency dependence of capacitance precludes analysis of data in traditional ways, where capacitance is assumed constant, and is especially important when apical and/or basolateral membranes exhibit one or more dielectric dispersions.

Slow capacitance relaxation in (BaSr)TiO3 thin films due to the oxygen vacancy redistribution

Capacitance relaxation in Ba0.8Sr0.2TiO3 thin film structures has been investigated. Slow decrease of the capacitance after a bias voltage switching on is explained by suppressing the film dielectric permittivity by the field of a p-n junction originated as a result of the oxygen vacancy migration in the bias field. After the bias switching off, the p-n junction gradually disappears due to the vacancy diffusion, and the capacitance increases. The relation determining capacitance increase after the bias switching off has been obtained in agreement with experimental data. The proposed relaxation mechanism is considered as a certain type of the size effect when the p-n junction depleted region spreads over the film thickness.

Carrier transport in amorphous SiC/crystalline silicon heterojunctions

Charge carrier transport in chemical vapor-deposited amorphous SiC/p-type crystalline Si heterostructures has been studied over the temperature range 80–400 K, using current–voltage (I–V), current–temperature (I–T), capacitance–voltage (C–V), and capacitance relaxation (C–t) characteristics. These heterojunctions exhibit high breakdown voltages (230 V) and a diode rectification ratio of 103 at ±0.5 V. At low temperatures (80–120 K) the a-SiC behaves like a dielectric, and the interface built-in voltage can be determined from the capacitance–voltage plot. The corresponding low forward bias current flow is limited by variable-range electron hopping conductivity at Fermi level in the a-SiC layer. At increasing temperature and forward bias voltage, an additional hole current component is found with the transport governed by a multistep tunneling hole emission process through the a-SiC/c-Si heterobarrier. At still higher forward bias voltages (>0.8 V), space-charge-limited hole conduction in the presence of traps in the a-SiC bulk limits transport.

Crossover from space-charge-limited to recombination-limited transport in polymer light-emitting diodes

By performing admittance spectroscopy as a function of frequency on polymer light-emitting diodes, inductive and capacitive charge-relaxation processes with different characteristic time scales are separated. The inductive contributions arise from the finite transit time of injected carriers, while the capacitive contributions stem from dielectric redistribution of charge density in the device. The crossover from inductive charge relaxation at low bias to capacitive charge relaxation at high bias marks the transition from space-charge-limited to recombination-limited current flow. This unexpected result shows that, while the individual carrier mobilities are strongly enhanced by the applied field, the recombination mobility remains unaffected.

Deep level transient spectroscopy characterization of InAs self-assembled quantum dots

Deep level transient spectroscopy (DLTS) was used to obtain the energy level and the capture characteristics of InAs self-assembled quantum dots embedded in GaAs. A specially designed structure was used for the DLTS measurement for enhanced resolution. This structure allows us to detect capacitance relaxation signal from a single layer of quantum dots and to separate this signal from those of the DX centers inside the structure. The DLTS spectra with different filling pulses and different rate windows provide clear information on the energy level and the capture characteristics of the quantum dots.

A comprehensive model of backgate impedance dispersions in GaAs isolation structures

A comprehensive model explains low frequency reactive, resonant and negative resistance effects in backgate current flow in monolithic GaAs integrated circuits. In a sister paper experimental comparisons were made between structures prepared by MBE on undoped buffer layers at high and low temperatures and by ion implantation. The study employed GaAs MESFETs which were similarly prepared on the three substrates. These observations provide the basis for the model. In the case of the ion implanted and normally buffered structures the form of the susceptance frequency spectra depended on cathode size, dc bias and temperature and could include capacitive relaxation as well as inductive and capacitive behaviors separated by a resonance. The form of the variation of the conductance was closely associated and frequently included a frequency region within which there was negative small signal resistance. All of these effects have been explained in terms of electron trapping at trap planes located at the interface between the n-type active region and the isolation material. In the case of inductive and capacitive relaxations a single trapping process was sufficient but the negative resistance behavior makes the additional requirement that charge should be trapped sequentially at least twice. Mathematical modeling and computational simulations have been used to give support to the physical models. In the case of the ion implanted structures it was possible to demonstrate reasonable quantitative agreement between the model and experiment using trap DLTS data.

Minority-Carrier Generation at the Interface between Silicon and Lead Borosilicate Glass

The generation rate of minority carriers at the interface between a silicon substrate and a layer of lead borosilicate glass is evaluated experimentally by the method of capacitance relaxation. It is shown that an increase in the fire-polishing temperature of the glass results in a higher generation rate, due to an increased density of surface states at the interface. The lifetime of minority carriers in the interface layer of the substrate is determined. Deep generation centers are discovered in the bulk of the substrate. They are defects caused by a rise in substrate temperature during the fabrication of the specimen.

Observations of backgate impedance dispersion in GaAs isolation structures

Low frequency reactive, resonant and negative resistance effects have been observed in backgate current flow in monolithic GaAs integrated circuits. Comparisons have been made between structures prepared by MBE on undoped buffer layers at high and low temperatures and by ion implantation. The study employed GaAs MESFETs which were similarly prepared on the three substrates. Backgate admittance spectroscopy measurements were performed between adjacent isolated n-type mesa structures on the different isolation materials in the range 10 Hz to 10 kHz, at temperatures ranging from 80 K to 340 K. In the case of the ion implanted and normally buffered structures the form of the susceptance frequency spectra depended on cathode size, dc bias and temperature and could include capacitive relaxation as well as inductive and capacitive behaviors separated by a resonance. The form of the variation of the conductance was closely associated and frequently included a frequency region within which there was negative small signal resistance. These effects were not present when the buffer layer was prepared at low temperatures. The results are summarized to make explicit the requirements of an explanatory model.

Nonequilibrium processes in capacitive sensors based on porous silicon

The response of a capacitive sensor of the Al/por-Si/n-Si type to the presence of ammonia and water vapor in the gas phase was studied. It was found that illumination affects the process of capacitance relaxation.

The Changes in Dynamics of Solid Supported Lipid Films Following Hybridization of Short Sequence DNA

The methods of conductance and capacitance relaxation were used to monitor hybridization of short sequences of DNA on the surface of lipid membranes (s-BLM) supported on thin platinum or gold layers covered by 1-dodecanethiol. The 15-mer-5′-hexadecyl-deoxythymidylic modified by palmitic acid (C16pdT15) was used as a DNA sensor that was incorporated into the BLM by the C16 chain. The interaction of C16pdT15 with s-BLM resulted in decrease membrane capacitance and conductance. The DNA hybridization on s-BLM surface resulted in an increase of s-BLM conductance, however, interaction of s-BLM modified by C16pdT15 with noncomplementary oligonucleotide did not change membrane conductance. The capacitance relaxation following symmetrical voltage jumps allowed us to study the dynamics of the reorientation dipole moments of the membrane. The unmodified s-BLM were characterized by two relaxation components: fast τ1=20.3±0.2 µs and slow τ2=590.3±175 µs. Modification of the lipid layer by C16pdT15 resulted in a decrease of amplitude of the slower component below detectable limit, while hybridization resulted in recovery of two relaxation times. Similar behavior was characterized for the free standing BLM. The changes of relaxation times might be due to the influence of the hybridization process on the two-dimensional architecture of the phospholipid layer, for example on the size of the lipid clusters.

Regular relief on a silicon surface as a structural defect getter

An investigation was made to determine how a regular relief on the silicon surface influences gettering in silicon-silicon-dioxide structures. The regular relief was created by a photolithographic technique before oxidation and comprised an orthogonal network of overlapping bands. The gettering was determined from the isothermal relaxation of the capacitance of a silicon-silicon-dioxide structure after switching from strong inversion to even stronger inversion. It is shown that a regular relief at the silicon-silicon-dioxide interface is an effective getter at a depth of several hundred micron.

Frequency-Dependent Capacitance of the Apical Membrane of Frog Skin: Dielectric Relaxation Processes

Impedance analysis of the isolated epithelium of frog skin (northern Rana pipiens) was carried out in the frequency range between 0.1 Hz and 5.5 kHz while Na + transport was abolished. Under these conditions, the impedance is determined almost completely by the dielectric properties of the apical membranes of the cells and the parallel shunt resistance. The modeling of the apical membrane impedance function required the inclusion of dielectric relaxation processes as originally described by Cole and Cole (1941. J. Chem. Phys. 9:341–351), where each process is characterized by a dielectric increment, relaxation frequency, and power law dependence. We found that the apical plasma membrane exhibited several populations of audio frequency dielectric relaxation processes centered at 30, 103, 2364, and 6604 Hz, with mean capacitive increments of 0.72, 1.00, 0.88, and 0.29 μF/cm 2, respectively, that gave rise to dc capacitances of 1.95 ± 0.06 μF/cm 2 in 49 tissues. Capacitance was uncorrelated with large ranges of parallel shunt resistance and was not changed appreciably within minutes by K + depolarization and hence a decrease in basolateral membrane resistance. A significant linear correlation existed between the dc capacitance and Na + transport rates measured as short-circuit currents ( C a dc = 0.028 I sc + 1.48; I sc between 4 and 35 μA/cm 2) before inhibition of transport by amiloride and substitution of all Na + with NMDG ( N-methyl- d-glucamine) in the apical solution. The existence of dominant audio frequency capacitive relaxation processes complicates and precludes unequivocal interpretation of changes of capacitance in terms of membrane area alone when capacitance is measured at audio frequencies.

Kinetics of electric field screening in a space-charge region with a leakage channel and low-temperature conductance of surface channels in high-resistivity n-Si

The kinetics of electric field screening in a space-charge region with a leakage channel is considered on the basis of an experimental study of the conductance of surface channels in n-Si. The characteristic times of the fast and slow stages of space-charge relaxation at the channel boundary after switching of the reverse bias are estimated. The proposed channel-current relaxation mechanism can account for the observed large radio-frequency conductance of surface channels in n-Si and the formation of capacitance relaxation spectra similar to those traditionally associated with the charge exchange of deep centers. The nature of the surface donor centers responsible for the formation of conducting layers at the Si-SiO2 interface near 90 K is discussed.

Affinity biosensors based on solid supported lipid membranes. Their structure, physical properties and dynamics

The paper describes results of study of physical properties of novel affinity biosensor based on self-assembled metal supported systems of biotinylated bilayer lipid membranes (s-BLM). In this biosensor, avidin modified monoclonal antibody originating from E2/G2 clone (A-MAb) was used as the antibody and 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide as the antigen (Ag) to provide an immunological interaction that could be transduced by the presented s-BLM sensor. An increase of membrane conductance, κ, an increase of elasticity modulus in the direction perpendicular to the membrane plane, E ⊥ and decrease of membrane capacitance, C, were experimentally proved by the addition of Ag to the s-BLM and used as a sensor response. The analysis of experimental results showed that interaction of Ag with the A-MAb resulted in changes of membrane mechanical properties, which might be connected with the induction of conformational changes in the A-MAb complex after binding with Ag. Binding of A-MAb to the free standing BLM as well as interaction of 2,4-D with A-MAb modified BLM resulted in increase of relaxation times of dipole moments reorientation as revealed from capacitance relaxation experiments. The physical properties of the s-BLM depend on the metal support on which the membrane is formed. This has been proved by comparison of the properties of s-BLM formed on the tip of freshly cut polymer coated stainless steel wire and on thin gold layer.

The electrostriction, surface potential and capacitance relaxation of bilayer lipid membranes induced by tetracaine

The interaction of local anesthetic tetracaine (TTC) with planar bilayer lipid membranes (BLM) of egg PC and cholesterol was studied by the measurement of elasticity modulus perpendicular to the plane of the membrane, surface potential difference, electrical capacitance and capacitance relaxation following the voltage jump (yielding relaxation times for molecular dipoles or dipolar domains). Addition of TTC to one side of the BLM in the concentration range 0.3–33 μM leads to a more positive membrane surface potential, to slight increase of membrane capacitance, while elasticity modulus minimally changes. The surface potential increased with increasing concentration of TTC and was higher for less charged form of local anaesthetics (at pH 9) than that for more charged one (pH 6). This proves that the main contribution to the change of surface potential comes from the dipole potential of membrane surface. The 33 μM TTC concentration induced changes of dipole potential about 5.3±2.0 mV and 29.8±3.0 mV at pH 6 and pH 9, respectively, which corresponds to the change of surface dipole moment of 8.1±3.0 and 34.0±3.5 Debye, respectively. Unmodified BLMs were characterized by a singe relaxation time of about 5 μs corresponding to reorientation of molecular dipoles. Addition of TTC (final concentration 0.1 mM) resulted in appearance of additional slower relaxation component of 50 μs at electrolyte pH 9, while at pH 6 no changes of relaxation time occurred. We assume that due to more neutral form (at pH 9), TTC penetrates deeper into the lipid bilayer. Interaction of TTC with BLM probably induces phase separation of phospholipids and the perturbation of the bilayer dynamic.

Dielectric relaxation of Ba0.7Sr0.3TiO3 thin films from 1 mHz to 20 GHz

The dielectric relaxation of Ba0.7Sr0.3TiO3 thin films was investigated up to K band (20 GHz) using time domain and frequency domain measurements. Our results show that from 1 mHz to 20 GHz, the dielectric relaxation of the complex capacitance of Ba0.7Sr0.3TiO3 thin films can be understood in terms of a power law dependence known as the Curie–von Schweidler law. The small dispersion (less than 7% decrease in capacitance from 1 mHz to 20 GHz) and low loss (loss angle less than 0.006 at 20 GHz) measured in Ba0.7Sr0.3TiO3 thin films indicate that these films are applicable to device application up to at least K band.

Glucose minisensor based on self-assembled biotinylated phospholipid membrane on a solid support and its physical properties

We have developed a glucose minisensor based on a biotinylated, supported phospholipid membrane (s-BLM). We immobilized glucose oxidase (GOX) by coupling an avidin-GOX complex to a phospholipid bilayer formed from biotinylated crude ox brain extract (COB). The bilayer was supported on the free metal tip of a Teflon-coated stainless steel wire (diameter, 0.33 mm). The determination of glucose was based on detection of enzymatically generated hydrogen peroxide at a potential of +670 mV. We found an almost linear increase of membrane current with increasing glucose concentration up to 10 mM and a saturation effect above 30 mM glucose. A lower voltage for detection of glucose was made possible by modification of the membrane by the electron carrier TCNQ. Several methods have been used to study the physical properties of native and modified s-BLM and conventional BLM. With the electrostriction method we showed that addition of avidin-GOX complex to the electrolyte in which the biotinylated s-BLM was formed resulted in a decrease of membrane capacitance and a decrease of membrane compressibility perpendicular to the bilayer surface. The capacitance relaxation method was used to determine the changes of dielectric relaxation times (reorientation of dipole moments of polar groups of individual lipid molecules or lipid clusters) following addition of avidin-GOX. Native BLM formed from COB extract (2% solution in n-decane: butanol (8:1 v/v) exhibited one relaxation time of (5 ± 1) μs. Additional relaxation components (115 ± 27 μs and 26 ± 1 μs) appeared in BLM modified by biotin. Addition of the avidin-GOX complex to the biotinylated BLM resulted in the appearance of a slow component 505 ± 16 m ̊ s . These results clearly document the interaction of the strongly immobilized enzyme with the bilayer.

Analysis of the temporal instability of the parameters of an insulator/III–V compound by the isothermal capacitance relaxation method

Existing diagnostic techniques used to evaluate the temporal instability of the parameters of a semiconductor-insulator interface with deep-level centers are analyzed. A method is proposed for evaluating temporal instability according to the long-term isothermal transient behavior of the capacitance of a metal-insulator-semiconductor structure. The energy spectrum of the effective density of surface states is determined for n-type InP-SiO2-Al structures prepared by chemical vapor deposition. The variation of the capacitance during long-term isothermal relaxation provides a criterion of temporal instability of a semiconductor-insulator interface.

Analysis of the rate of change of inversion charge in thin insulator p-type Metal-Oxide-Semiconductor structures

A model of the rate of change of inversion charge has been used to investigate the capacitance relaxation associated with Fowler-Nordheim tunneling current in thin insulator p-type Metal-Oxide-Semiconductor (MOS) structures. In this model, the rate of change of inversion charge is taken to be equal to the difference between the generation current in the space charge region of Si and the Fowler-Nordheim tunneling current through the oxide. Using a step voltage, analytical expression for high frequency capacitance relaxation is obtained, the experimental results are consistent with model calculations.