Use Of Capacitors Research Articles

Evaluation of process variants during the proposal preparation

AbstractThere are many important factors for small and medium sized enterprises (SME), especially individual customer demands, price pressure and the probability to deliver at the required date. Companies which want to be supplier for larger companies have to look carefully about these factors already during the proposal preparation. They are often in the branch of single-part or small-series production.One possibility to increase known factors is to consider different variants of manufacturing a product and the premature investigation of resources and there capacities. Therefore, this paper is introducing a conceptional framework for the evaluation of different process variants to manufacture a product. We want to optimise and evaluate process variants including the necessary resources and their capacitive use in an evaluated period. For this evaluation we use a genetic algorithm.Within this paper we define and classify a scheduling problem to map our requirements. Afterwards we explain the necessary information about a genetic algorithm that suites us for the solution of our problem.

The use of capacitance–resistance models for rapid estimation of waterflood performance and optimization

The capacitance–resistance model (CRM) offers the promise of rapid evaluation of waterflood performance. This semianalytical modeling approach is a generalized nonlinear multivariate regression technique that is rooted in signal processing. Put simply, a rate variation at an injector introduces a signal, with the corresponding response felt at one or more producers. CRM uses production and injection rate data and bottomhole pressure, if available, to calibrate the model against a specific reservoir. Thereafter, the model is used for predictions. We focused on three different control volumes for CRMs: the volume of the entire field, the drainage volume of each producer, and a drainage volume between each injector/producer pair. Unlike the numerical simulation approach, the CRMs use only production/injection data to predict performance, which provides simplicity and speed of calculation. Once the CRM is calibrated with historical production/injection data, we use an optimization technique to maximize the amount of oil produced by reallocating water injection rates. To verify CRM predictions, the models were tested against numerical flow-simulation results. Two case studies showed that the CRMs are able to successfully history match, and maximize the amount of oil produced by just reallocating water injection. This study introduces analytical solutions to the fundamental differential equations of the capacitance model based on superposition in time. In so doing, this approach adds flexibility, simplicity, and computational speed to the work presented previously.

Understanding the origins of the intrinsic dead layer effect in nanocapacitors

Thin films of high-permittivity dielectrics are considered ideal candidates for realizing high charge-density nanosized capacitors for use in next generation energy storage and nanoelectronic applications. The experimentally observed capacitance of such film nanocapacitors is, however, 1 order of magnitude lower than expected. This dramatic drop in capacitance is attributed to the so-called ``dead layer''---a low-permittivity layer at the metal-dielectric interface in series with the high-permittivity dielectric. The exact nature of the dead layer and the reasons for its origin still remain somewhat unclear. Based on insights gained from recently published ab initio work on ${\text{SrRuO}}_{3}{/\text{SrTiO}}_{3}{/\text{SrRuO}}_{3}$ and our first-principles simulations on Au/MgO/Au and Pt/MgO/Pt nanocapacitors, we construct an analytical model that isolates the contributions of various physical mechanisms to the intrinsic dead layer. In particular we argue that strain-gradients automatically arise in very thin films even in absence of external strain inducers and, due to flexoelectric coupling, are dominant contributors to the dead layer effect. Our theoretical results compare well to existing as well as our own ab initio calculations and suggest that inclusion of flexoelectricity is necessary for qualitative reconciliation of atomistic results. Our results also hint at some remedies for mitigating the dead layer effect.

Evaluating the suitability of thick-film TiO 2 capacitors for use in a wireless pressure measurement system

In this work, screen-printing onto glass and polymer substrates was used to form capacitors with an active area of 2 × 3 mm 2. The dielectric was formed using a polymer paste with TiO 2 as the functional ingredient. Devices prepared on glass substrates were tested as strain gauges. Their GF was measured to be 30. This is higher than the standard values (3–15) recorded for gauges based on oxide materials. It is thought that the higher sensitivity is a result of the preparation method and small crystallite size of the TiO 2 powder. After quantifying the materials sensitivity, the sensors on polymer substrates were attached to planar and cylindrical surfaces. They were then incorporated into a wireless pressure measurement system, consisting of a small size interface circuit and a transmitter. The receiver outputs a voltage reading corresponding to the sensor capacitance. Each device was placed in a liquid environment so that it could be exposed to hydrostatic pressure. A high sensitivity to pressure changes with low hysteresis was observed. It is thought that this system could be used to wirelessly monitor pressure changes in a variety of difficult to reach environments.

Lateral Size of Self-Patterned Nanostructures Controlled by Multi-Step Deposition

Self-patterning presents an appealing alternative to lithography for the production of arrays of nanoscale ferroelectric capacitors for use in high density non-volatile memory devices. Recently a self-patterning method, based on the use of the instability of ultrathin films during hightemperature treatments, was used to fabricate nanosized ferroelectrics. This paper reports the use of the method for the preparation of PZT nanoislands on different single crystalline substrates - SrTiO3, MgO and LaAlO3. Moreover, a multi-step deposition procedure in order to control lateral the dimension of the crystals was introduced. The nanostructures obtained were studied by atomic force microscopy, scanning electron microscopy and X-ray diffraction.

Investigation of TiO 2 thick film capacitors for use as strain gauge sensors

In this work the strain sensing properties of interdigitated and sandwich thick film capacitors, using titanium dioxide as the dielectric, are investigated. By pre-firing the TiO 2 powder and forming a polymer thick film paste the use of expensive paste ingredients, such as ruthenium or palladium oxide, was avoided. After firing, XRD was used to verify the composition and crystallite size of the TiO 2 powder, while SEM allowed the particle sizes of the powder to be examined. It was found that the powder has a crystallite and particle size, which is less than 1 μm. Following this, the sensors were fabricated by screen-printing onto glass substrates and placed in a cantilever beam arrangement so that the change in their capacitance with strain could be measured. The gauge factor, which demonstrates the devices sensitivity, was found by dividing the fractional change in capacitance by the applied strain. A gauge factor of 5 and 30 was recorded for interdigitated and sandwich capacitors, respectively. In the case of sandwich capacitors, this gauge factor is higher than normally achieved using oxide films (3–15). Furthermore, the sensors showed a high degree of linearity with low hysteresis. The TCC has been measured for temperatures ranging from 25 to 70 °C so that the effect of temperature on the devices is known. Values, typical of thick film capacitors (876–2834 ppm/°C) have been recorded for temperatures up to 60 °C. Finally, ac electrical measurements have been used to shown that tunnelling is the dominant conduction mechanism within the TiO 2 film.

A surface forces platform for dielectric measurements

Methods are described to implement dielectric spectroscopy (frequency range 10−1–106 Hz) within a surface forces apparatus by using as electrodes silver sheets on the backside of mica. These methods are applied to study the competitive effects of surface alignment, confinement, and shear field on 5CB (5-cyanobiphenyl), a nematic liquid crystal at the experimental temperature of 25 °C. In the planar orientation, films could be squeezed to a minimum thickness of ≈5 Å, the molecule’s thickness. In the perpendicular (homeotropic) orientation, films could be squeezed to ≈25 Å, the expected thickness of the head-to-tail 5CB dimer. It was difficult to discuss responses at f>105 Hz quantitatively because the peak was not visible in the experimental frequency window. Nonetheless, the onset of the relaxation mode for the planar oriented molecules appears at higher frequency than for the homeotropic orientation. A slower relaxation mode, peaked at f≈10 Hz, was assigned to electrode polarization due to the mobility of trace ions within the 5CB samples although these samples were >99.7% pure. The peak frequency was a factor of 3 slower with homeotropic than planar alignment and, in both cases, independent of film thickness except when the film thickness exceeded 10 μm. This was explained using a simple model based on the assumption that trace ions move to oppositely charged electrodes to form electric double layers. A small influence of shear on the dielectric response was observed but only when the dielectric response was measured at the same frequency as the large-amplitude shear deformation. Also described is the use of capacitance to measure force–distance profiles.

A study of the high frequency performance of thin film capacitors for electronic packaging

The provision of adequate decoupling capacitance in the power distribution system for integrated circuits (ICs) is an increasing concern. As clock rates and the IC gate density increase, discrete chip capacitors do not satisfy the decoupling requirements for high current switching at very high frequencies. Thin film capacitors not only exhibit better high frequency performance than discrete ceramic capacitors, but also provide the possibility for passive component integration. In this work, the high frequency performance of thin film capacitors was investigated using Maxwell Eminence, a high frequency structure simulator based on the finite element method. Good agreement between the calculated impedance and experimental results was obtained. At high frequencies, the performance of thin film capacitors is related to contact configurations, dielectric and metal layer thicknesses, and capacitor shapes. The influence of these factors on the impedance behavior was examined. Equivalent circuits of a thin film capacitor for use in a circuit simulator at high frequencies are discussed.

Modeling the effects of nonlinear materials in ceramic chip capacitors for use in digital and analog applications

This paper describes a physics-based numerical approach to building circuit models for electronic components that are made of nonlinear dielectrics. The resulting models are intended for use in time-domain circuit simulators to assess the effects of material nonlinearity on the electrical performance of such components as discrete de-coupling and filter capacitors that are used in digital and analog circuits. A 3-D electrostatic field solver is modified to take into account the nonlinear field dependence of the dielectric material and is employed to calculate the Q-V curve for any capacitive structure. Subsequently, a time integration method (similar to that used in SPICE) is utilized to devise an appropriate time-stepping algorithm for the current-charge relationship of a nonlinear capacitor that can be used to simulate its time-domain electrical characteristics. Sample results are provided to illustrate the methodology and the effects of the material nonlinearity on the performance of the capacitor.

Use of Capacitance To Measure Surface Forces. 2. Application to the Study of Contact Mechanics

We performed capacitance measurements between silver layers on the back side of thin (<1 μm) mica substrates in surface force apparatus to determine the contact area with very high precision (<0.1% of the total area) and at a rate that is faster (∼1 kHz) than that in more traditional methods based on interferometry. To demonstrate the capabilities of the technique, we measured the adhesion and adhesion hysteresis between two mica surfaces. A peculiar discontinuous decrease in contact area, with decreasing load, between two dry mica surfaces is observed. We also studied the possible effect of shear forces on the value of the contact area due to adhesive forces, as in JKR theory.

Materials specification for MCM-D decoupling capacitors using PZ, PZT, PLZT and BST dielectrics

The desired electrical properties of decoupling capacitors for use in an existing MCM-D process have been defined. Two types of dielectric have been investigated, sol-gel deposited P(L)ZT and dual ion beam sputtered (DIBS) BST. Their electrical properties have been measured and compared against this target. Decoupling capacitors have been fabricated and integrated with an MCM-D process, the resulting processing issues are discussed.

Use of Capacitance to Measure Surface Forces. 1. Measuring Distance of Separation with Enhanced Spatial and Time Resolution

We describe a simple method to measure the separation and forces between two macroscopic surfaces mounted in a crossed cylinder arrangement. It is shown that by measuring the capacitance between silver layers deposited on the backside of thin mica substrates, it is possible to achieve spatial resolution of less than 0.1 nm and time resolution of 1 ms. The growth of capacitance with decreasing distance of separation follows the predicted dependence for an ideal sphere and plate capacitor. To demonstrate the capability of obtaining force−distance profiles with this technique, octamethylcyclotetrasiloxane (OMCTS) has been confined between the mica sheets. We find that the process of collapse of the confined liquid, from four molecular layers to three, occurs more rapidly than 1 ms. This technique is also shown to give excellent results for opaque surfaces used in the surface forces apparatus (SFA), and we show that the adhesion energy between two surfaces of oxidized silicon is 3 mJ/m2. Applications of this ...

The use of capacitance in the measurement of angular and linear displacement

This paper describes the use of capacitor bridges in instrumentation for the measurement of relatively large angular and linear displacements. The particular feature of interest lies in the use of printed circuit board technology which allows repeatability at low cost associated with a rugged overall structure. Two possible electronic configurations are described, one being direct and the other using feedback in which the output depends only on the ratio of the capacitances. Experimental results are given for examples of angular and linear devices. They show that this approach readily yields devices with an accuracy of /spl plusmn/1% and indicates that results considerably better than this are ultimately possible. >

Characterization and modelling of thin-film ferroelectric capacitors using C-V analysis

Advances have been made in the electronic characterization and analysis of thin-film ferroelectric (FE) memory capacitors using capacitance vs. voltage (C-V) measurements. A mathematical model of the small-signal electrical behavior of the FE capacitor has been developed. This analysis shows that the small-signal characteristics of the FE capacitor are largely determined by the space charge concentrations at the ferroelectric to contact interface. These space charge regions have an adverse effect on the permittivity, coercivity and switching characteristics of the ferroelectric capacitor. These results will contribute to improving ferroelectric processing, appraising the quality of ferroelectric devices, and developing device models of the ferroelectric memory capacitors for use in circuit design.

Ferroelectrics for nonvolatile RAMs

The structure and operation of ferroelectric thin-film memory capacitors for use in nonvolatile random-access memory applications are described. The search for the ideal ferroelectric material for ferro-electronic memory applications is examined. Possible military and nonmilitary applications of these memories are noted. >

A low-loss SAW-TV-IF filter with an extended impedance matching range

A novel low-loss SAW (surface acoustic wave) filter for an intermediate frequency (IF) circuit in a color TV receiver has been developed. It consists of an apodized bidirectional and an unapodized group-type unidirectional transducer. The unidirectional transducer is designed to use different numbers of finger pairs in sending and reflecting electrodes for extension of the impedance-matching range. A thin-film capacitor for use as a phase shifter is monolithically fabricated on a 128 degrees Y-X LiNbO(3) substrate. A low insertion loss (11.3 dB) and impedance matching without adjustment are achieved at the same time without increasing the device chip size or number of electrical parts.

Tantalum oxide capacitors for GaAs monolithic integrated circuits

The performance of a high-yield tantalum oxide capacitor for use in GaAs monolithic microwave integrated circuits is described. The integral metal-insulator-metal sandwich structure is reactively sputter-deposited at low temperatures, compatible with a photoresist lift-off process, on semi-insulating GaAs substrate. Dielectric constants of 20-25 were achieved in the capacitors fabricated. An initial application of this process as an interstage coupling capacitor for a two-stage preamplifier is given.

Modification of grain boundaries in polycrystalline silicon with fluorine and oxygen

Hydrogen plasmas have been shown to significantly reduce barrier heights and recombination center densities in the grain boundaries in polycrystalline silicon. These results have stimulated interest in the use of other modifying agents. We demonstrate here that the exposure of n-type polycrystalline silicon to fluorine and oxygen in molecular and atomic forms can result in increased potential barrier heights. This has implications for the development of silicon varistors and capacitors for use in integrated circuits.

Capacitor-coupled logic using GaAs depletion-mode f.e.t.s

A new method of interconnecting depletion-mode GaAs f.e.t. logic stages, using capacitive coupling, eliminates the need for a negative power supply and is more tolerant of processing spreads, particularly of pinch-off voltage. The technique may be combined with conventional level shifting, operating at very low current. The use of capacitance may be extended to achieve clocked dynamic data storage with very low power dissipation.

Permanent-magnet a.c. generators

The development of permanent-magnet generators is reviewed and a novel multistacked form described. This machine is ideally suited to the production of a high airgap field from ceramic magnets, but polymer-bonded rare-earth magnets may also be used to advantage. A damping device can be incorporated to minimise load-angle oscillation. The use of capacitance to improve regulation and increase output is discussed. It is shown that the performance of the generator can be predicted with reasonably good accuracy by a simple computer program.