Showing papers on "Capacitor published in 1998"

RF-MEMS switches for reconfigurable integrated circuits

Abstract: This paper deals with a relatively new area of radio-frequency (RF) technology based on microelectro-mechanical systems (MEMS). RF MEMS provides a class of new devices and components which display superior high-frequency performance relative to conventional (usually semiconductor) devices, and which enable new system capabilities. In addition, MEMS devices are designed and fabricated by techniques similar to those of very large-scale integration, and can be manufactured by traditional batch-processing methods. In this paper, the only device addressed is the electrostatic microswitch - perhaps the paradigm RF-MEMS device. Through its superior performance characteristics, the microswitch is being developed in a number of existing circuits and systems, including radio front-ends, capacitor banks, and time-delay networks. The superior performance combined with ultra-low-power dissipation and large-scale integration should enable new system functionality as well. Two possibilities addressed here are quasi-optical beam steering and electrically reconfigurable antennas.

Characterization of double-layer capacitors (DLCs) for power electronics applications

Abstract: The double-layer capacitor (DLC) for power applications is a new device. A simple resistive capacitive equivalent circuit is insufficient to characterize its terminal behavior. Based on physical reasoning, an equivalent circuit is proposed to provide the power electronics engineer with a model for the terminal behavior of the DLC. The equivalent circuit model consists of three RC branches, one of them with a voltage-dependent capacitance. A method to identify the circuit parameters is presented. Measurements of carbon-based DLC's for power applications are presented, analyzed, and the equivalent circuit response is compared with experimental results.

A high-efficiency CMOS voltage doubler

Abstract: A charge pump cell is used to make a voltage doubler using improved serial switches. A complete power efficiency theory is presented which fits the measurements. The importance of capacitors is shown with plots of power efficiency versus load and stray capacitors. Several problems arising at low voltage or high frequency are developed and some optimizations are presented. The substrate current is totally suppressed by the technique of bulk commutation. A power efficiency of 95% has been reached using external capacitors. A fully integrated charge pump is also presented and shows a maximum power efficiency of 75%.

Discovery of a useful thin-film dielectric using a composition-spread approach

Abstract: The continuing drive towards miniaturization of electronic devices1 is motivating the search for new materials. Consider, for example, the case of the much-used dynamic random-access memory. The minimum capacitance per cell that can be tolerated is expected2 to remain at 30–40 fF, but as the cell area decreases, the corresponding reduction in geometric capacitance has to be compensated for. So far, this has been achieved by resorting to complex non-planar structures and/or using much thinner films of the dielectric insulator, amorphous silicon dioxide (a-SiOx), although the latter approach is limited by the electric fields that can be supported by a-SiOx before its insulating properties break down. An alternative strategy is to develop thin-film insulators that have a dielectric constant significantly greater than that of a-SiOx, reducing the size of the fields required for device operation. Here we show that a composition-spread technique allows for the efficient evaluating of materials with both a high dielectric constant and a high breakdown field. We apply this approach to the Zr–Sn–Ti–O system, and we find that compositions close to Zr0.15Sn0.3Ti0.55O2−δ are better thin-film dielectrics than high-quality deposited a-SiOx. Although detailed tests of the performance of these materials have not yet been carried out, our initial results suggest that they are likely to be comparable to the best alternatives (such as (Ba, Sr)TiO3) currently being considered for integrated-circuit capacitors.

Characterization of ultra-thin oxides using electrical C-V and I-V measurements

Abstract: The measurement of electrical parameters from capacitance-voltage (C-V) and current-voltage (I-V) curves provides a fast means of characterizing oxides in MOS capacitors or transistor structures. For ultra-thin oxides (<2 nm), conventional, well-established techniques must be reconsidered and modified due to several increasingly important physical effects including polysilicon depletion and surface quantum mechanical effects. In this work these effects have been incorporated into a rapid analysis program for extracting ultra-thin oxide parameters from measured C-V and I-V data. The technique uses a physically based model of structure charge and potential combined with a non-linear least squares fitting technique to extract device parameters.

Failure prediction of electrolytic capacitors during operation of a switchmode power supply

Abstract: Electrolytic filter capacitors are frequently responsible for static converter breakdowns. To predict these faults, a new method to set a predictive maintenance is presented and tested on two types of converters. The best indicator of fault of the output filter capacitors is the increase of ESR (equivalent series resistance). The output-voltage ripple /spl Delta/V/sub o/ of the converter increases with respect to ESR. In order to avoid errors due to load variations, /spl Delta/V/sub o/ is filtered at the switching frequency of the converter. The problem is that this filtered component is not only dependent on the aging of the capacitors, but also on the ambient temperature, output current, and input voltage of the converter. Thus, to predict the failure of the capacitors, this component is processed with these parameters and the remaining time before failure is deduced. Software was developed to establish predictive maintenance of the converter. The method developed is as follows. First, a reference system including all the converter parameters was built for the converter at its sound state, i.e., using sound electrolytic filter capacitors. Then, all these parameters were processed and compared on line to the reference system, thereby, the lifetime of these capacitors was computed.

Capacitive distance sensor

Abstract: A distance sensor has a capacitive element in turn having a first capacitor plate which is positioned facing a second capacitor plate whose distance is to be measured. In the case of fingerprinting, the second capacitor plate is defined directly by the skin surface of the finger being printed. The sensor comprises an inverting amplifier, between the input and output of which the capacitive element is connected to form a negative feedback branch. By supplying an electric charge step to the input of the inverting amplifier, a voltage step directly proportional to the distance being measured is obtained at the output.

Micromachined electro-mechanically tunable capacitors and their applications to RF IC's

Abstract: Micromachined electro-mechanically tunable capacitors with two and three parallel plates are presented. Experimental devices have been fabricated using a standard polysilicon surface micromachining process. The two-plate tunable capacitor has a measured nominal capacitance of 2.05 pF, a Q-factor of 20 at 1 GHz, and achieves a tuning range of 1.5:1, The three-plate version has a nominal capacitance of 4.0 pF, a Q-factor of 15.4 at 1 GHz, and a tuning range of 1.87:1. The tuning ranges achieved here are near theoretical limits. Effects due to various physical phenomena such as temperature, gravity, and shock are examined in detail. An RF voltage-controlled oscillator with an integrated inductor and a micromachined tunable capacitor is also demonstrated. The active circuit and the inductor have been fabricated in a 0.5 /spl mu/m CMOS process. The voltage-controlled oscillator has been assembled by bonding together the CMOS and the micromachined parts. The 1.35 GHz voltage-controlled oscillator has a phase noise of -98.5 dBc/Hz at a 100 kHz offset from the carrier.

A shunt active filter based on voltage detection for harmonic termination of a radial power distribution line

Abstract: This paper focuses on a shunt active filter based on the detection of harmonic voltages at the point of installation. The objective of the active filter is to attenuate harmonic propagation resulting from series/parallel resonance between capacitors for power factor correction and line inductors in a power distribution line. The active filter acts as a low resistor to the external circuit for harmonic frequencies, and it is installed on the end bus of the power distribution line, just like a 50 /spl Omega/ terminator installed on the end terminal of a signal transmission line. Therefore, the function of the active filter is referred to as "harmonic termination" in this paper. Experimental results obtained from a laboratory system rated at 200 V and 20 kW verify that the active filter for the purpose of harmonic termination has the capability of harmonic damping throughout the power distribution line.

A new control approach to three-phase active filter for harmonics and reactive power compensation

Abstract: This paper deals with a new control scheme for a parallel 3-phase active filter to eliminate harmonics and to compensate the reactive power of the nonlinear loads. A 3-phase voltage source inverter bridge with a DC bus capacitor is used as an active filter (AF). A hysteresis based carrierless PWM current control is employed to derive the switching signals to the AF. Source reference currents are derived using load currents, DC bus voltage and source voltage. The command currents of the AF are derived using source reference and load currents. A 3-phase diode rectifier with capacitive loading is employed as the nonlinear load. The AF is found effective to meet IEEE-519 standard recommendations on the harmonics level.

Broad-band power amplifier using dielectric photonic bandgap structure

Abstract: Two class AB GaAs field-effect transistor (FET) power amplifiers have been designed and fabricated in the 4.4-4.8 GHz range. In the first case, a dielectric PBG line was incorporated in the design to tune the second harmonic. In the second case, a 50-/spl Omega/ line is used with no harmonic tuning. The PBG structure allows broad-band harmonic tuning and is inexpensive to fabricate. A 5% improvement in power-added efficiency was achieved at the design frequency of 4.5 GHz, in both simulation and measurement.

Vibration damping and control using shunted piezoelectric materials

Abstract: Research on shunted piezoelectric materials, conducted mainly over the past decade, provides new options to engineers who are responsible for solving structural vibration control problems. The general method is made possible by the relatively strong electromechanical coupling exhibited by modern piezoelectric materials. If a piezoelectric element is attached to a structure, it is strained as the structure deforms and converts a portion of the energy associated with vibration into electrical energy. The piezoelectric element (which behaves electrically as a capacitor), in combination with a network of electrical elements connected to it (a shunt network), comprises an electrical system that can be configured to accomplish vibration control through its treatment of electrical energy. Four basic kinds of shunt circuits are typically used: resistive, inductive, capacitive, and switched. Each of these kinds of shunts results in characteristically different dynamic behavior: a resistive shunt dissipates energy through Joule heating, which has the effect of structural damping. An inductive shunt results in a resonant LC circuit, the behavior of which is analogous to that of a mechanical vibration absorber (tuned mass damper). A capacitive shunt changes the effective stiffness of the piezoelectric element, which can be used to advantage in, for example, a tunable mechanical vibration absorber. A switched shunt offers the possibilities of controlling the energy transfer to reduce frequency-dependent behavior, or perhaps the conversion of energy to a usable form. This paper reviews recent research related to the use of shunted piezoelectric materials for vibration damping and control.

High-dielectric constant thin films for dynamic random access memories (dram)

Abstract: ▪ Abstract We discuss high-dielectric films, in general, oxide ferroelectrics based on simple perovskite structures and related Aurivillius-phase layered structure perovskites employed as thin-film capacitors in dynamic random access memories (DRAMs). Emphasis is on breakdown mechanisms and limits, leakage currents, electrodes and electrode interfaces, scaling to submicron geometries, and deposition techniques.

Fractal capacitors

Abstract: A linear capacitor structure using fractal geometries is described. This capacitor exploits both lateral and vertical electric fields to increase the capacitance per unit area. Compared to standard parallel-plate capacitors, the parasitic bottom-plate capacitance is reduced. Unlike conventional metal-to-metal capacitors, the capacitance density increases with technology scaling. A classic fractal structure is implemented with 0.6-/spl mu/m metal spacing, and a factor of 2.3 increase in the capacitance per unit area is observed. It is shown that capacitance boost factors in excess of ten may be possible as technology continues to scale. A computer-aided-design tool to automatically generate and analyze custom fractal layouts has been developed.

High efficiency power converter

Abstract: A power converter nearly losslessly delivers energy and recovers energy from capacitors associated with controlled rectifiers in a secondary winding circuit, each controlled rectifier having a parallel uncontrolled rectifier. First and second primary switches in series with first and second primary windings, respectively, are turned on for a fixed duty cycle, each for approximately one half of the switching cycle. Switched transition times are short relative to the on-state and off-state times of the controlled rectifiers. The control inputs to the controlled rectifiers are cross-coupled from opposite secondary transformer windings.

Fibril composite electrode for electrochemical capacitors

Abstract: Composite electrodes comprising carbon nanofibers (fibrils) and an electrochemically active material are provided for use in electrochemical capacitors. The fibril composite electrodes exhibit high conductivity, improved efficiency of active materials, high stability, easy processing, and increase the performance of the capacitor. A method for producing the composite electrodes for use in electrochemical capacitors is also provided.

Optimized frequency-shaping circuit topologies for LDOs

Abstract: Typical low drop-out (LDO) regulator architectures suffer from an inherent load regulation performance limitation. This limitation manifests itself through limited DC open-loop gain, and results from stringent closed-loop bandwidth requirements. The frequency response of the system is highly sensitive to the loading conditions, thereby making proper compensation a laborious endeavor. This paper discusses and addresses the limitation on regulating performance imposed by frequency compensation. Several LDO circuit topologies are subsequently developed to this end. They enhance load regulation performance by relaxing the DC open-loop gain restrictions. The circuit structures essentially alter the frequency response of the system via the error amplifier. A low drop-out regulator adopting an embodiment of the proposed technique was fabricated in the MOSIS 2-/spl mu/m process technology. The system, designed for an output capacitor of 4.7 /spl mu/F, was stable with an equivalent series resistance (ESR) ranging from 0 to 12 /spl Omega/, bypass capacitors ranging from 0 to 2.2 /spl mu/F, and a load current ranging from 0 to 50 mA.

AC powered light emitting diode array circuits for use in traffic signal displays

Abstract: An LED array circuit includes a number of series connected LED pairs, each pair including two parallel connected oppositely polarized LEDS. The array is coupled to a standard AC voltage source in series with an inductor L having Q>5 and a reactance which is equivalent to the resistance of a current limiting resistor. The use of an inductor in place of a resistor increases the efficiency of the array to approximately 80%. The efficiency of the array is increased even further by coupling a capacitor parallel to the array and by tuning the inductor and capacitor to the frequency of the AC voltage source. According to one embodiment of the invention, a somg;e retro-fittable unit is provided wherein an inductor, a capacitor, and an array of LEDs are contained in a housing having substantially the same size and shape as a standard incandescent bulb or the lens/filter used in a traffic signal display. According to another embodiment of the invention, a single module is provided with a plurality of LED arrays, with each LED array having its own capacitor coupled in parallel thereto, and its own series coupled switch. The module is coupled to and across the AC voltage source, with one node of the module coupled to the AC voltage source by an inductor.

Chip capacitors and chip capacitor electromagnetic interference filters

Abstract: An electromagnetic interference (EMI) filter capacitor assembly is provided for shielding and decoupling a conductive terminal pin or lead of the type used, for example, in an implantable medical device against passage of external interference signals. The EMI filter is constructed of relatively inexpensive ceramic chip capacitors which replace relatively expensive feedthrough capacitors as found in the prior art. The chip capacitors are mounted directly onto a hermetic feedthrough terminal in groups of two or more which vary in physical size, dielectric material and capacitance value so that they self-resonate at different frequencies. This "staggering" of resonant frequencies and direct installation at the hermetic terminal provides the EMI filter with sufficient broadband frequency attenuation. In one preferred form, multiple chip capacitor groupings are mounted onto a common base structure, with each capacitor grouping associated with a respective terminal pin. In another preferred form, a non-conductive substrate is provided with metalized circuit traces to better accommodate the mounting of the chip capacitors. Additionally, novel chip capacitor geometry/termination-metallization is provided which significantly reduces the internal inductance of the capacitor to improve its high frequency performance as an EMI filter. Such reduced inductance chip capacitor designs are readily adaptable to incorporate multiple electrically isolated active plate sets within a single monolithic casing.

Study of the ground bounce caused by power plane resonances

Abstract: We describe Delta-I noise caused by power plane resonances in multilayer boards. First, we study the effect of power plane resonances on the ground bounce of the system by performing finite-difference time-domain (FDTD) simulations. We simulate the voltage fluctuations at one point of the printed circuit board (PCB) due to a current surge between the power planes in a different point. Next, two methods to prevent this ground bounce effect are investigated. The first method consists of adding lumped capacitances to the design. The effect of one large capacitor is compared to the effect of adding a "wall" of smaller capacitors. A second approach is to isolate the chips by etching a slot around the sensitive integrated circuits (ICs) and connecting both sides by a small inductor. Both methods provide excellent protection against power plane resonances.

DC-to-DC converter with inductor current sensing and related methods

Abstract: A DC-to-DC power converter includes at least one power switch, a pulse width modulation circuit for generating control pulses for the at least one power switch, an output inductor connected to the at least one power switch, and a current sensor connected in parallel with the inductor for sensing current passing through the inductor. The current sensor preferably includes a resistor and a capacitor connected together in series. The current sensor is connected to a peak current control loop circuit cooperating with the pulse width modulation circuit for controlling the at least one power switch responsive to the current sensor. The resistor and capacitor preferably have respective values so that the current sensor is a substantially instantaneous current sensor. The output inductor has an inductance and a direct current (DC) resistance defining a first time constant. In one embodiment, the resistor and capacitor of the current sensor define a second time constant within a predetermined range of each other. In another embodiment, the resistor and capacitor of the current sensor define a second time constant substantially equal to the first time constant.

A feedback linearizing control scheme for a PWM converter-inverter having a very small DC-link capacitor

Abstract: This paper addresses a control method of reducing the size of the DC link capacitors of a power converter-inverter system. The main idea is to utilise the inverter operation status in the current control of the power converter. Specifically, information on the load power is incorporated in synthesizing the converter current control input so that a proper DC voltage level is maintained. The authors describe the dynamics of load current and apply feedback linearization theory to obtain an input output linearized system. Theoretically, this control strategy is effective in regulating the DC voltage level even though the DC link capacitor is arbitrarily small and load varies abruptly. The superior performance is demonstrated through simulation and experiment. Experiment was performed with a 9 kW PWM power converter-vector inverter system having a 75 /spl mu/F DC-link capacitor.

A unity power factor converter using half-bridge boost topology

Abstract: A single-phase high-efficiency near-unity power-factor (PF) half-bridge boost converter circuit, which has been proposed earlier by other researchers, is presented with detailed analysis. This converter is capable of operating under variable PF. However, the focus of this paper is in achieving unity PF operation only. The efficiency of this circuit is high because there is only one series semiconductor on-state voltage drop at any instant. The existence of an imbalance in the voltages of the two DC-link capacitors, which was noted before, is confirmed here. The cause for the imbalance is analyzed using appropriate models, and a control method to eliminate it is discussed in detail. Analysis and design considerations for the power circuit using the fixed-band hysteresis current control (HCC) technique are provided. The analytical results are verified through simulation using switched and averaged circuit models of the scheme and also through experimental work. At 90-V AC input and 300-W 300-V output, the experimental prototype demonstrates an efficiency of 96.23% and a PF of 0.998. This converter, with its relatively high DC-output voltage, is well suited for the 110-V utility supply system. A circuit modification for universal input voltage range operation is also suggested.

Modeled tunnel currents for high dielectric constant dielectrics

Abstract: The effect of dielectric constant and barrier height on the WKB modeled tunnel currents of MOS capacitors with effective oxide thickness of 2.0 nm is described. We first present the WKB numerical model used to determine the tunneling currents. The results of this model indicate that alternative dielectrics with higher dielectric constants show lower tunneling currents than SiO/sub 2/ at expected operating voltages. The results of SiO/sub 2//alternative dielectric stacks indicate currents which are asymmetric with electric field direction. The tunneling current of these stacks at low biases decreases with decreasing SiO/sub 2/ thickness. Furthermore, as the dielectric constant of an insulator increased, the effect of a thin layer of SiO/sub 2/ on the current characteristics of the dielectric stack increases.

Multilevel Power Conversion - An Overview Of Topologies And Modulation Strategies

Abstract: Multilevel power converters represent a potential breakthrou,qh in employing swirching converters to medium voltage applications (2-13 k w . This pciper summarizes the stat e of the art in this rapidly a'eveloping Jeld ofpower electronics.

Capacitors : Pulsed powder science and technology

Abstract: Over the last decade, significant increases in capacitor performance, especially in reliability and energy/power densities, have been achieved for energy discharge applications in plasma science and fusion research applications through a combination of advanced manufacturing techniques, new materials, and diagnostic methodologies to provide requisite life-cycle performance for high energy pulse applications. Recent innovations in analysis of aging are introduced for predicting component performance and fault tolerance, especially relevant for very high energy storage applications necessary for next generation simulators, electrically energized fusion research machines, and advanced high power electronics for commercial, industrial, and military applications. Included in this study will be developments in capacitor technologies for electronics filtering and resonant energy transfer applications, as well as multisecond energy reservoir applications for uninterruptible power sources and the like. Next generation power electronics, driven by advances in solid state switching technologies, will require reduced capacitor dissipation factor by 1/3 to 1/10 at the same cost, particularly for ac applications. In addition, higher power electronics will require robust high frequency mica capacitor technology for >300°C operation, up to 5 kV. The increasing expansion of the motor drive and industrial switched mode power supply (SMPS) market will be driven in cost by the availability of electrolytic capacitors of 750-850 Vdc ratings, at 450 Vdc cost and size. New formation processes and electrolytes are anticipated to be needed to achieve these extended performance levels. At higher frequencies, advanced power electronics drives the need for lower equivalent series resistance (ESR) « 0.1% to 100 MHz, multimicrofarad value solid tantalum capacitors, having fail-safe surface mount configurations. Emerging power electronics applications in the millisecond and longer time are projected to have a broad application need for electrochemical chemical double layer capacitors, especially for compact sizes as this technology has the potential of achieving energy densities of many 20 kJ/kg for discharge times of tens of seconds. The prismatic power conditioning system, designed to be compliant with the available volume and surfaces into which it is to be placed, is described in some detail. It permits flexibility for the design engineer to optimize the design without having to allocate a specific space for the power conditioning system or subcomponents. Such prismatic geometry power and power conditioning systems are becoming commercially feasible in the low power consumer and industrial regime because of dramatic advances in multichip module switching, energy storage, and planarized interconnections. This work builds on assessing the applicability of these technologies to the megawatt-class average power, power electronics regime. Higher power density prismatic power electronics enables a broad range of applications in the commercial arena in areas such as motor drives, inverters, power quality systems, and mobile power systems.

Thickness dependence of the effective dielectric constant in a thin film capacitor

Abstract: The static value of the effective dielectric constant in a thin film capacitor is simulated by means of the local field theory. The value of it shows a sharp decrease as the film thickness is decreased in an ultrathin film geometry. This phenomenon is due to the size effect intrinsic to a thin film structure and has nothing to do with the material aspect. The decrease is more remarkable for larger values of the bulk dielectric constant. It is recovered by inserting interface layers with larger atomic polarizability between the film and the capacitor electrode.

Perovskite thin films for high-frequency capacitor applications1

Abstract: ▪ Abstract Perovskite, ferroelectric and paraelectric, thin films exhibit outstanding dielectric properties, even at high frequencies (>1 GHz). This feature makes films such as (Ba,Sr)TiO3 and Pb(Zr,Ti)O3 ideally suited for a wide range of capacitor applications, particularly decoupling capacitors and tunable microwave capacitors; the latter application has been fueled by the recent explosion in wireless communications. The successful implementation of these materials as high-frequency dielectrics requires a detailed understanding of both their processing and materials properties.

Hermetically sealed EMI feedthrough filter capacitor for human implant and other applications

Abstract: An integrated hermetically sealed feedthrough capacitor filter assembly is provided for the shielding and decoupling of a conductive terminal pin or lead of the type used, for example, in an implantable medical device such as a cardiac pacemaker or cardioverter defibrillator against passage of external interference signals, such as caused by digital cellular phones The simplified feedthrough assembly described herein eliminates the traditional terminal pin subassembly In this novel approach, the ceramic feedthrough capacitor itself forms a hermetic seal with a conductive pacemaker housing to which it is mounted by welding or brazing The feedthrough capacitor is configured such that its internal electrodes are not exposed to body fluids, with capacitor electrode plate sets coupled respectively to a conductive ferrule, pin or housing (which may be grounded) and to the non-grounded, or active, terminal pin(s) by conductive adhesive, soldering, brazing, welding or the like In one preferred form, multiple feedthrough filter capacitors are provided in a substantially coplanar array within a common base structure, with each capacitor in association with a respective terminal pin