Showing papers on "Capacitance published in 1997"

Self-capacitance of inductors

Abstract: A new method for predicting the stray capacitance of inductors is presented. The method is based on an analytical approach and the physical structure of inductors. The inductor winding is partitioned into basic cells-many of which are identical. An expression for the equivalent capacitance of the basic cell is derived. Using this expression, the stray capacitance is found for both single- and multiple-layer coils, including the presence of the core. The method was tested with experimental measurements. The accuracy of the results is good. The derived expressions are useful for designing inductors and can be used for simulation purposes.

A dynamic analysis of the Dickson charge pump circuit

Abstract: Dynamics of the Dickson charge pump circuit are analyzed. The analytical results enable the estimation of the rise time of the output voltage and that of the power consumption during boosting. By using this analysis, the optimum number of stages to minimize the rise time has been estimated as 1.4 N/sub min/, where N/sub min/ is the minimum value of the number of stages necessary for a given parameter set of supply voltage, threshold voltage of transfer diodes, and boosted voltage. Moreover, the self-load capacitance of the charge pump, which should be charged up at the same time as the output load capacitance of the charge pump, has been estimated as about one-third of the total charge pump capacitance. As a result, the equivalent circuit of the charge pump has been modified. The analytical results are in good agreement with simulation by the iteration method, typically within 10% for the rise time and within 2% for the power consumption. In the case of a charge pump with MOS transfer transistors, the analytical results of the rise time agree with the SPICE simulation within 10%.

Characterization of Electrical Materials, Especially Ferroelectrics, by Impedance Spectroscopy

Abstract: A review is given of some of the problems encountered in the analysis and interpretation of impedance data. The importance of choosing the correct equivalent circuit to represent the data is emphasized and it is shown how ferroelectric materials, with their characteristic temperature-dependent capacitance, are particularly suited to discriminating between plausible equivalent circuits. Results are discussed for two materials, LiTaO3 single crystal and BaTiO3 ceramics.

Scanning Single-Electron Transistor Microscopy: Imaging Individual Charges

Abstract: A single-electron transistor scanning electrometer (SETSE)—a scanned probe microscope capable of mapping static electric fields and charges with 100-nanometer spatial resolution and a charge sensitivity of a small fraction of an electron—has been developed. The active sensing element of the SETSE, a single-electron transistor fabricated at the end of a sharp glass tip, is scanned in close proximity across the sample surface. Images of the surface electric fields of a GaAs/AlxGa1−xAs heterostructure sample show individual photo-ionized charge sites and fluctuations in the dopant and surface-charge distribution on a length scale of 100 nanometers. The SETSE has been used to image and measure depleted regions, local capacitance, band bending, and contact potentials at submicrometer length scales on the surface of this semiconductor sample.

Differential Capacitance Measurements in Solvent-Free Ionic Liquids at Hg and C Interfaces

Abstract: Series-stacked, double-layer carbon capacitors are slated to be used in electric vehicles for power management as well as in consumer electronics for memory backup and burst power. Nonaqueous electrolytes are preferred over aqueous electrolytes, since a wider voltage window can be accessed in the former electrolytes, thereby requiring fewer cells in the series stack. However, it has historically been difficult to assess whether the organic solvent and/or the supporting electrolyte determine the anodic limit. We have eliminated this ambiguity by using solvent-free ionic liquids where the source of anodic oxidation may be ascribed to the anion alone. Even though the new ionic liquids manifested high oxidation limits, we found that when used in practical capacitors comprising high-surface-area carbon cloth electrodes, a much lower capacitance (compared to smooth electrodes) was achieved. To understand whether the observed decrease in capacitance might be due to the microporosity of the carbon cloth electrode or to practical limitation of the device itself. we first measured the differential capacitance (C dl ) at a Hg/1-ethyl-3-methyl imidazolium imide. The integral capacitance at the Hg interface was then calculated and compared with that of a smooth glassy carbon electrode, a carbon yarn, and a cloth electrode. In addition, the effect of (CF 3 SO 2 ) 3 C - , (CF 3 SO 2 ) 2 N - , CF 3 SO 3 - , an BF 4 - on C dl were interpreted based on existing theories of double-layer structure.

The Limitations of Energy Density for Electrochemical Capacitors

Abstract: Electrochemical capacitors can be divided into two types depending on whether the salt concentration in the electrolyte changes during charging and discharging. In the first type of capacitor, such as double-layer capacitors, the salt concentration in the electrolyte reduces during the charging of the capacitor. The maximum energy density of this type of capacitor will depend not only on the specific capacitance and the operating voltage, but also on the salt concentration of the electrolyte. In this paper, a formula describing the dependence of energy density on specific capacitance, operating voltage, and salt concentration is given based on the optimized weight (or volume) ratio of the electrode material and the electrolyte. It shows that for electrochemical capacitors using nonaqueous electrolytes, the maximum energy density of the capacitor will be limited mainly by the low salt concentrations of the electrolyte. The relationship between the energy density and the mass density of the electrode is also given. The optimum mass density of the electrode can be obtained based on the value of the theoretical energy density for capacitors with different electrolytes. In the second type of capacitor, such as pseudocapacitors with metal oxide electrodes, the salt concentration in the electrolyte remains constant during charging and discharging. The maximum energy density of this type of capacitor will be limited mainly by specific capacitance and operating voltage.

Stabilization of electrostatically actuated mechanical devices

Abstract: We show that the pull-in instability, which significantly limits the operation of electrostatically actuated devices, can be avoided by the simple addition of a series capacitance.

Mechanism of stress-induced leakage current in MOS capacitors

Abstract: Stress-induced leakage current (SILC) is examined both below and above the voltage at which the preexisting Fowler-Nordheim tunneling current dominates. Based on these results, it is argued that SILC is the result of inelastic rather than elastic trap-assisted tunneling. This clarification explains the well-known thickness dependence of the SILC at low fields that has identified it as a scaling limitation for nonvolatile memory tunnel oxide. It also explains a newly observed different thickness dependence at high fields and facilitates modeling of the electric field/voltage and trap density dependencies of the SILC.

Few-electron ground states of charge-tunable self-assembled quantum dots

Abstract: The few-electron ground states of self-assembled InAs quantum dots are investigated using high-resolution capacitance spectroscopy in magnetic fields up to 23 T. The level structure reveals distinct shells which are labeled as $s$-, $p$-, and $d$-like according to their symmetry. Our measurements enable us to resolve the single-electron charging not only of the lowest $(s)$ state with two electrons but also of the second lowest $(p)$ state with four electrons as pronounced maxima in the capacitance spectra. Furthermore, two peaks at higher energy can be attributed to charging of the $d$ shell with the first two electrons. We discuss the energy spectrum in terms of spatial quantization energy, Coulomb blockade, and many-particle effects. At around $B=15$ T we observe a magnetic-field-induced intermixing of the $p$ and $d$ shell. Additional fine structure in the capacitance spectra is observed and discussed both in terms of nearest-neighbor Coulomb interactions and monolayer fluctuations of the dot size.

Energy Storage Characteristics of a Piezo-Generator using Impact Induced Vibration

Abstract: This paper presents theoretical and experimental considerations of the energy storage characteristics of a piezoelectric generator developed previously by the authors. In this paper, the oscillating output voltage induced by mechanical impact via the piezoelectric effect is rectified, and the electrical energy is stored in a capacitor. The effect of the capacitance of the capacitor and the initial voltage is investigated using an equivalent circuit model. A maximum efficiency over 35% has been achieved with a prototype generator.

Impedance Spectroscopy of Self-Assembled Monolayers on Au(111): Evidence for Complex Double-Layer Structure in Aqueous NaClO4 at the Potential of Zero Charge

Abstract: The impedance of a Au(111) electrode modified by three different self-assembled monolayers has been studied over a wide frequency range in aqueous NaClO4 solutions. The impedance characteristics of the bare electrode are compared with those of the same electrode modified with decanethiol, ω-hydroxydecanethiol, and 4‘-hydroxy-4-mercaptobiphenyl. In the case of the decanethiol system the interfacial impedance can be represented as a capacitor due to the self-assembled monolayer in series with the solution resistance. However, for the latter two systems, the impedance behavior is more complex with a high resistance in the monolayer parallel to the expected capacitance. This behavior is quite different than that discussed to date in the literature and assumed in the interpretation of voltammetric data for modified electrodes. The parameters for these systems are reported here as a function of electrolyte concentration at the point of zero charge on the bare Au(111). The consequences of the present observation...

Novel fingerprint scanning arrays using polysilicon TFT's on glass and polymer substrates

Abstract: Novel fingerprint scanning arrays based upon capacitance sensing have been made Each sensor element consists of a capacitor electrode and two poly-Si thin film transistors for addressing and read out The devices were fabricated on glass, polyimide and polyethersulphone substrates using a low temperature (<250/spl deg/C) process

High Temperature Sensors Based on Metal–Insulator–Silicon Carbide Devices

Abstract: High temperature gas sensors based on catalytic metal-insulator-silicon carbide (MISiC) devices are developed both as capacitors and Schottky diodes. A maximum operation temperature of 1000 degrees C is obtained for capacitors based on 4H-SiC, and all sensors work routinely for several weeks at 600 degrees C. Reducing gases like hydrocarbons and hydrogen lower the flat band voltage of the capacitor and the barrier height of the diode. The time constants for the gas response are in the order of milliseconds and because of this good performance the sensors are tested for combustion engine control. For temperatures around 600 degrees C total combustion occurs on the sensor surface and the signal is high for fuel in excess and low for air in excess. At temperatures around 400 degrees C the response is more linear. The high temperature operation causes interdiffusion of the metal and insulator layers in these devices; and this interdiffusion has been studied. At sufficiently high temperatures the inversion capacitance shows different levels for hydrogen free and hydrogen containing ambients, which is suggested to be due to a reversible hydrogen annealing effect at the insulator-silicon carbide interface.

Low-Dielectric-Constant Materials for ULSI Interlayer-Dielectric Applications

Abstract: Continuing improvement of microprocessor performance historically involves a decrease in the device size. This allows greater device speed, an increase in device packing density, and an increase in the number of functions that can reside on a single chip. However higher packing density requires a much larger increase in the number of interconnects. This has led to an increase in the number of wiring levels and a reduction in the wiring pitch (sum of the metal line width and the spacing between the metal lines) to increase the wiring density. The problem with this approach is that—as device dimensions shrink to less than 0.25 μm (transistor gate length)—propagation delay, crosstalk noise, and power dissipation due to resistance-capacitance (RC) coupling become significant due to increased wiring capacitance, especially interline capacitance between the metal lines on the same metal level. The smaller line dimensions increase the resistivity (R) of the metal lines, and the narrower interline spacing increases the capacitance (C) between the lines. Thus although the speed of the device will increase as the feature size decreases, the interconnect delay becomes the major fraction of the total delay and limits improvement in device performance. To address these problems, new materials for use as metal lines and interlayer dielectrics (ILD) as well as alternative architectures have been proposed to replace the current Al(Cu) and SiO2 interconnect technology.

Plasma processing system

Abstract: A plasma processing system capable of carrying out a uniform processing is provided. According to the present invention, a substantially annular high-frequency antenna 156 of a predetermined number of turns, e.g., 1 turn, is provided in an opening 102b via a first shielding member 160 and a dielectric member 158. The capacitance of a variable capacitor 172 connected to ground is adjusted so that series resonance occurs at the mid point of the high-frequency antenna 156. With this construction, it is possible to form a desired electric field in a plasma producing space to produce a high-density plasma. In addition, a feeding member 126 is formed so that the substantially vertical cross-section thereof has a profile expressed by an exponential function r=f(L). Therefore, it is possible to supply a high-frequency power to an upper electrode without causing the electric breakdown and the damping of the high-frequency power.

Light-emitting diodes based on poly-p-phenylene-vinylene: II. Impedance spectroscopy

Abstract: Electrical impedance measurements on poly-p-phenylene-vinylene (PPV) light-emitting diodes in the frequency range between 100 Hz and 10 MHz are reported. A significant difference can be revealed between the device characteristics of light-emitting diodes eliminated on indium-tin-oxide (ITO) and those of other high-work-function metals (e.g., Au). Thermal conversion of the precursor polymer on ITO substrates results in a p-type doping of the conjugated polymer PPV. Hence, devices in the configuration ITO/PPV/Al display Schottky behavior, which can be modeled by a simple equivalent circuit of two RC elements in series, representing a bulk and a junction region. The low-frequency device capacitance displays a pronounced voltage dependence and, from a detailed analysis, the ionized acceptor concentration NA, the diffusion potential VD, and the width of the space charge region w can be obtained. Typical values for NA are 1016–1017 cm−3, and for VD within the range 1–1.5 V, resulting in a width w of the space c...

A novel analysis on the performance of an isolated self-excited induction generator

Abstract: This paper presents a novel approach based on eigenvalue and eigenvalue sensitivity analyses to predict both minimum and maximum values of capacitance required for the self-excitation of a three-phase induction generator. Numerous numerical methods based on steady-state equivalent circuit models have been proposed to find the minimum capacitance of self-excited induction generators by solving simultaneous nonlinear equations. Steady-state and sensitivity analyses of different capacitance values with respect to various system parameters are performed. Transient analyses of the studied induction generator under different loading conditions are also carried out. Experimental results obtained on a 1.1 kW induction machine confirm the feasibility and effectiveness of the proposed approach.

Fast controller design for single-phase power-factor correction systems

Abstract: A fast controller is presented for single-phase boost-type power factor correction circuits. The twice-line-frequency ripple component is removed from the measured output voltage with an adaptive estimator. This enables the closed-loop time constants and overshoots to be reduced by two orders of magnitude compared to traditional designs. The controller copes with considerable uncertainty in input voltage magnitude, line frequency and output capacitance. All sections of the control system are shown to be asymptotically stable. Experimental results are presented to verify the excellent dynamics and robust behavior of the design.

The Effect of Salt Concentration in Electrolytes on the Maximum Energy Storage for Double Layer Capacitors

Abstract: Double layer capacitors made with activated carbon electrodes and filled with nonaqueous electrolytes at different salt concentrations have been studied. It was found that the performance of the capacitor is strongly dependent on the salt concentration in the electrolyte. For electrolytes with high salt concentrations, the maximum energy stored in the capacitor is limited by the capacitance of the electrode material. For electrolytes with low salt concentrations, the maximum operating voltage as well as the maximum energy decreases with decreasing salt concentration. It has been demonstrated from ac impedance measurements that the decay of the maximum energy is due to the depletion of free ions in the electrolyte. The maximum energy storage in double layer capacitors with electrolytes at different salt concentrations was measured and was found to agree with the theory developed previously. From the study of dc charge and discharge cycles at different constant current rates, it was found that the power performance of the capacitor is also strongly dependent on the salt concentration in the electrolyte.

Regulating and equalizing DC capacitance voltages in multilevel STATCOM

Abstract: Because of the high MVA ratings, it would be expensive to provide independent, equal, regulated DC voltage sources to power the multilevel converters which are proposed for STATCOMs. DC voltage sources can be derived from the DC link capacitances which are charged by the rectified AC power. This paper addresses two control issues: (1) regulation of the DC capacitance voltages and (2) their equalization. Equalization is necessary (i) to ensure the even sharing of voltage stresses in the gate-turn-off thyristors (GTOs), and (ii) to prevent the degradation of total harmonic distortion (THD) factors, as all harmonic elimination strategies depend on equal voltages in their assumptions. The strategies considered are: (a) the fundamental frequency method, and (b) the sinusoidal pulse width modulation method. Digital simulations are used to confirm the feasibility of the control methods.

Capacitive sensitive switch method and system

Abstract: A touch sensor switch that responds to touching, or even to the proximity of an object, is disclosed. The switch includes a number of capacitance elements, or touch pads, that produce an effective capacitance dependent upon the physical proximity of the object. A microcontroller under control of a program stored in a read-only memory causes its I/O port to set a transient voltage on each capacitance element as a logic level. Each transient voltage is at variance with the capacitive element's preferred voltage level. The program then reads the I/O port, and hence the logic levels of the capacitance elements, as the capacitive elements revert to their preferred voltage levels, and calculates the proximity of the object, or touching, from relationships among recorded signals. The circuit may also be embodied in an application specific integrated circuit.

Method and apparatus for tuning a continuous time filter

Abstract: A tuning circuit for generating a digital code to be used to calibrate a capacitor array of the type used in active RC filters is comprised of a single-slope A/D converter with fixed reference voltages as inputs and an output value which is dependent on the RC product of a resistor and capacitor within the converter. A decoder converts the RC product as measured by the A/D converter into a digital code which, when applied to the appropriate capacitor array, sets the array capacitance to compensate for the difference between the measured RC product and the nominal design value.

Suspension with multi-layered integrated conductor trace array for optimized electrical parameters

Abstract: A head suspension has an integrated multi-layer trace conductor array for supporting and electrically interconnecting a read/write head to electronic circuitry in a disk drive. The electrical micro strip transmission line characteristics of the conductor array is controlled by the selective placement and connection of the trace paths within the multiple layers in order to control and balance electrical parameters including array inductance, inter-trace capacitance, and trace capacitance to a ground plane. The ground plane may further comprise a solid sheet of material or an arrangement of grounded traces disposed in proximity to signal-carrying traces of the micro strip transmission line in order to control and obtain desired electrical characteristics.

Floating inductance simulation based on current conveyors

Abstract: A basic floating inductance simulation circuit with grounded capacitance using only noninverting second-generation current conveyors as active elements is introduced. The circuit is modified by using current controlled conveyors, yielding electronically tunable inductances. Simulation results are also presented.

Characterization of sputtered barium strontium titanate and strontium titanate-thin films

Abstract: Sputtered Ba1−xSrxTiO3 (BST) and SrTiO3 (STO) films and capacitors made with these dielectrics have been characterized with respect to physical and electrical properties. Specific capacitance values included a high of 96 fF/μm2 for BST films deposited of 600 °C and a high of 26 fF/μm2 for STO films deposited at 400 °C. Leakage current densities at 3.3 V for the most part varied from mid 10−8 to mid 10−6 A/cm2. All of the dielectrics are polycrystalline, although the lowest temperature STO films have a nearly amorphous layer which impacts their capacitance. Grain size increases with deposition temperature, which correlates to higher dielectric constants. The lattice parameter of the BST films is larger than that of bulk samples. Capacitance, leakage, breakdown, and lifetime results are reported.

Tunability and Calculation of the Dielectric Constant of Capacitor Structures with Interdigital Electrodes

Abstract: The voltage dependence of the dielectric constant of ferroelectricmaterials makes them attractive for use as tuning elements in microwavecircuits. In this study, capacitance tuning and loss measurements wereperformed on ferroelectric materials prepared by the sol-gel process and RFmagnetron sputtering. We find that Pb(Zr,Ti)O3 (PZT) thinfilms with interdigital electrodes can be fabricated with reasonably lowloss to make them useful for room temperature tuning applications. Inaddition, it is found that high temperature post-deposition annealing ofboth sputtered SrTiO3 (ST) and sol-gel derivedBaTiO3 (BT) films markedly improves their tuning and lossfactor characteristics. By annealing the samples in the range of1000–1100°C, the tunability was increased by as much as a factorof seven, while the dissipation factors were decreased to values of0.3–0.5%. In addition, it is shown that the permittivity of thefilms in these interdigitated capacitor structures can be calculated usingan analytical model previously described by Farnell et al. [1].

A realistic large-signal MESFET model for SPICE

Abstract: A comprehensive large-signal MESFET model that provides a realistic description of measured characteristics over all operating regions is presented, It describes subthreshold conduction and breakdown. It has frequency dispersion of both transconductance and drain conductance, and derates with power dissipation. All derivatives are continuous for a realistic description of circuit distortion and intermodulation. The model has improved descriptions of capacitance and bias dependence. It has small-signal S-parameter accuracy extended to a wide range of operating conditions. The model is implemented with new techniques for continuity and dispersion. These provide accurate prediction of circuit performance and also improve simulation speed.