Search

A new alumina substrate with an extremely smooth surface was developed. This new alumina substrate includes Cr203and MgO as the additives. Reliability data and characteristics of tantalum nitride or tantalum and tantalum oxide films on the new substrate were compared with those on the glazed alumina.

For want of better electrical insulators in general and capacitor insulations in particular, especially in the realm of extra high voltage stress areas, work has been done by many pioneers toward this end, first in the materials provided by nature and then in the field of synthetics limited only by man's imagination. One of the newest and seemingly most practical glimpses of light, especially in the field of capacitor dielectrics, is the use of polypropylene films. A considerable amount of work has been done. The work involved is directed only to the particular interest of capacitor engineering and application. It was limited to the area of two most important requirements for capacitors used in the communication and control industries, namely, temperature coefficient and capacitance stability or retrace under temperature variation and cycling. Several types of construction and treatment are reviewed and results are presented for general evaluation. The main purpose of this paper is, of course, to reveal some pertinent experimental data and to limit the comment to a minimum. No claim is laid as to the ultimate superiority of polypropylene film capacitors, but the facts are presented and can be judged by their own merit. Some apparent highlights, such as the exceptionally good retrace, of course, have been pointed out, but in general the paper is intended to be an unbiased evaluation.

The statistical nature of time-dependent dielectric breakdown characteristics in MOS capacitors was evidenced by testing large numbers of capacitors fabricated on single wafers. A multi-point probe and automatic electronic visual display technique are introduced that will yield statistical results which are necessary for the investigation of temperature, electric field, thermal annealing, and radiation effects in the breakdown characteristics, and an interpretation of the physical mechanisms involved. It is shown that capacitors of area greater than 2 × 10 −3 cm 2 may yield worst-case results, and that a multi-point probe of capacitors of smaller sizes can be used to obtain a profile of non-uniformities in the SiO 2 films.

The possibility was examined of improving paper capacitors by the applications of new types of impregnants. The tests proved that the paper capacitors impregnated with the various new impregnants can be improved to such an extent that they are as good as plastic film condensers in stability, heat resistance, and temperature coefficients. In addition, paper capacitors are far smaller than plastic film dielectric capacitors. The research work undertaken showed that one way to develop the capacitors lies in research into impregnants, especially heat-resisting casting resins.

Recent application of capacitors as energy-storage devices for low-impedance loads, such as short-duration light sources and electric detonators, has emphasized the importance of examination of capacitor efficiency from this standpoint. Ballistic measurements, using a vacuum thermocouple and galvanometer, are shown to afford the desired evaluation.

The use of thin layers of organic material as capacitor dielectric is of considerable interest in connection with miniaturization techniques. A technique has been established for the manufacture of capacitors, employing aluminium foil coated with lacquer on both sides; edge insulation is achieved by etching away the exposed metal at one edge, and the second electrode is of evaporated metal. Using a 3?m coating of polyisocyanate lacquer, miniature capacitors, having a performance at 50 V and 50° C equal to that of paper capacitors, can be manufactured with an improvement in space factor of at least six. The etching technique is shown to have no adverse effect on life characteristic and enables small capacitors to be made with good high-frequency characteristics.

Coupling to high-voltage transmission lines for purposes of carrier-current communication was first. universally made by means of coupling wires. This type of coupling usually required high-power transmitting equipment, but when coupling capacitors were substituted it was possible to reduce the carrier input to the line without affecting the received signal strength. The paper gives an approximate method for determining the effectiveness of coupling wires and coupling capacitors. No attempt is made at refinements in calculations as it is only desired to show the effect of stray capacity. Curves show the change in practise from coupling wires to coupling capacitors. It is estimated that by the early part of 1928 the total number of the two types of coupling will be equal. The electrical characteristics for different types of insulation used in coupling capacitors, based on test results is given. Some important points of design for the new cable capacitor are included.

DIELECTRIC amplifiers are circuits which utilize the nonlinear characteristics of capacitors made with so-called ferroelectric materials as dielectrics. To predict the performance of a dielectric amplifier, the behavior of the nonlinear capacitor must be determined and some means of representing it analytically must be devised. The purpose of this paper is to investigate the behavior of a commonly used nonlinear capacitor under conditions encountered in dielectric amplifier circuits, to provide a basis for an analytical representation.

The response of unbiased tantalum capacitors to ionizing radiation has been measured for both small and large dose rates. The results have been analyzed using a two‐trap model for the Ta2O5 dielectric and an equivalent circuit model is presented. A significant reduction in the response of slug capacitors can be achieved by connecting two capacitors in the back‐to‐back or inverted‐parallel configuration.

Experience from experiments with a sample and hold circuit showed that dielectric absorption constitutes a fundamental limitation of the accuracy in analog memories. To gain more insight into the problem several materials commonly used as dielectrics in capacitors have been investigated. The theory of dielectric absorption is discussed. Results from measurements on capacitors with paper, cellulose acetate, parylene, polyester, polycarbonate, and polystyrene dielectrics are reported. The components in Dow's model, which describes the dielectric absorption, are calculated for the polycarbonate dielectric. A compensation circuit is suggested, which considerably reduces the effect of dielectric absorption in analog memories and electronic integrators.

The suitability of plastics as capacitor dielectrics is dependent on a variety of considerations, both electrical and mechanical, but primarily on their ability to be formed into thin uniform continuous films, whether unsupported or supported by a substrate. How far the expected advantages have been realized from the use of ‘tailored’ synthetic materials, instead of naturally occurring dielectric materials, is discussed in the light of the properties of capacitors made from some plastic films of established utility such as polystyrene, polyethylene terephthalate, polytetrafluoroethylene and polycarbonate [poly-bis (2-phenyl) propane carbonate]. Miniaturization can be achieved by the usual techniques of depositing surface films of metal of negligible thickness, and also by coating suitable substrates with films of plastic dielectric too thin to be self-supporting.

Capacitor improvements over the years have been largely identified with progress in dielectric materials. In this paper, emphasis is placed on miniaturization, especially as it relates to capacitor dielectrics. Modern capacitors can be divided into two general types: bulk capacitor types, most often used as discrete elements; and film capacitor types, which to date are exclusively single-layered and most useful in integrated thin-film networks. In bulk capacitor types, one strives for minimum volume, and the major volume factor is often the dielectric itself. A dielectric volume efficiency factor can be defined as eS2, where e is the dielectric constant and S is the permissible working stress. In some instances, as in electrolytic capacitors, electrode volume can also be appreciable. For film capacitor types, the area must be minimized and an area efficiency factor equal to eS is important. Consideration is given to contamination control, packaging, and novel structures.

An apparatus to measure the dispersion characteristics of thin film capacitors at extremely low frequencies, even below 0.01 Hz, is described. This makes it possible to study the slow motion of mobile ions in the dielectric. The apparatus runs completely automatically.

Feedthrough capacitors built of a multiplicity of stacked disks are practically useless filter elements because they behave essentially like tubular feedthrough capacitors, namely exhibiting pronounced parallel resonances. However, if washers of suitable, lossy ferrite are interspaced in the structure, the effective coupling impedance for the lower frequencies is identical with the 1/?C, whereas at medium and higher frequencies the effective coupling impedance is reduced by a factor of 1,000 to 10,000 or more, as compared with the best discoidal feedthrough capacitors available now. In fact, the effective coupling impedance is so low that resonances of the disks (even large ones) themselves become negligible. The advantage of the discussed structures is the absence of dc losses. The mathematical theory for all cases above is developed by matrix algebra and verified by experiments. The selection of the correct ferrite is analyzed. The practical significance of this development for extremely effective miniaturized low-pass filters is presented.

Metallized paper capacitors are being introduced into telephone apparatus wherever size is of prime importance. It is shown that low-voltage metallized paper capacitors with about half the volume of a foil-paper capacitor of conventional design have about the same characteristics as the latter. Performance data are discussed which indicate that such capacitors will give long service when used within their voltage rating and when well-protected against moisture. It is pointed out that this type of capacitor should be used within its voltage rating if sparking with its attendant circuit noise is to be avoided. When sparking does occur due to abnormal voltage conditions no permanent damage results.

By means of coupling capacitors connected to high voltage power transmission lines, high frequency carrier currents in different frequency channels may be transmitted over the power lines for supplementary services such as relaying, control, and communication. A new design of coupling capacitor has been made which, by combining 1, 2, 3, or 4 units in series, may be used on 69, 138, 230, or 287 kv circuits. Capacitors of the latter rating are being used on the Boulder Dam line of the city of Los Angeles.

Ever since the introduction of solid tantalum electrolytic capacitors, attempts have been made to replace the relatively expensive tantalum with other materials. Several patent applications indicate that aluminum, in the form of wire or sintered slugs, has been investigated in this connection. Attempts with aluminum foil are scarcely known, but a British patent, No. 845 698 (patent holder: U. S. Secretary of the Army), indicates that some preliminary work has been done in this line. In the meantime etched aluminum foils of high purity and surface gain have become commercially available, and forming methods resulting in highly stable aluminum oxide layers are now known, so that the successful construction of solid aluminum electrolytic capacitors seemed feasible. A series of experiments were therefore carried on in the laboratories of the Aluminium-Walzwerke Singen, to determine the usefulness of etched aluminum foils in solid aluminum capacitors. Preliminary results indicate that such capacitors can definitely be made with etched aluminum foils.

The large signal step response of a junction capacitor has been analyzed. Both abrupt and graded junctions have been considered. The analysis covers the charging and discharging of such capacitors through a linear resistance and through a battery. Expressions for the various responses have been derived. The results show that the charging and discharging waveforms are quite different as compared with the simple exponential rise and decay of linear capacitor. The analysis is utilized to study the operation of a cross-coupled multivibrator.

In recent months design engineers have been interested in capacitors with extremely high values of insulation resistance not normally achieved in the common one- or two-minute electrification period. After long periods of electrification, insulation resistance values in the order of 100-million megohm microfarads and more can be achieved with some types of capacitors. Such high values can be accurately measured by the special measuring technique described in this paper, which also discusses the interpretation of test data taken at various temperatures and voltages on some typical Mylar capacitors. The concepts of instantaneous and equivalent parallel insulation resistance are developed and their significance discussed.

Miniaturization of capacitors in America comprises a large effort and a wide variety of techniques and materials. In ceramics, major programmes directed toward reducing film thickness are approaching the 1 mil range. Thin-film studies are contributing evaporated dielectrics and the basis for anodic-film printed capacitors. A thermal oxide with excellent properties can be grown on silicon. Silicon nitride and reactively sputtered dielectrics are in the exploratory stage. Extension of solid-electrolytic capacitor designs is providing relatively large capacitance in small volume, both for the micro-module programme and as hearing-aid types. Progress is being made in realizing the intrinsic capability of organic polymers.The future holds promise of significant accomplishments both by application of ingenuity to the older materials and by realizing the potential of thin-film technology.

The high short-time stresses and discharges to which a series capacitor is exposed demand special design of the capacitor unit. The elements of such a design are reviewed, and two Swedish installations, one now in operation and the other under construction, are described.

Efforts made towards miniaturization in the field of Ceramic Capacitors have resulted in Barrier Layer Ceramic Capacitors. The highest known dielectric constant of the order of 100000 has been achi...

A process has been developed to produce A1-Al 2 0 3 -Al capacitors with good yields and suitable properties for use in thin-film circuitry. Tests were conducted to determine the effects that a number of variables have on production yields and capacitor characteristics. This paper reports the optimum found for each variable. The largest improvement inyields was brought about by following proper cleaning procedures and controlling dust on the substrate prior to insertion in the vacuum system and during pumpdown.

A survey of thin film dielectric materials is given and their application in capacitors is discussed. The dielectrics are considered in terms of the method of preparation, physico-chemical structure and general electrical properties.

A new type of electrolytic capacitor has been developed which provides a valuable supplement to the capacitors previously available to the circuit designer. In these new capacitors, a solid semi-conductor replaces the usual aqueous electrolyte. Because the materials are all inorganic nonvolatile solids, no hermetic seal is required for ordinary applications. Compared to other electrolytics, these capacitors are superior in low temperature characteristics and in shelf-aging. Their small size makes them especially suitable for transistor circuitry. They are in limited commercial production and are being used in a new rural carrier system.

Ruggedness, wide capacitance range, high volumetric efficiency, and relatively attractive cost have been the main reasons for the popularity of ceramic chip capacitors. Continuing improvements in most of these categories promise to keep the ceramic chip in its present position of prominence. This article considers multilayer, single-layer, and screened-on configurations. In addition, relationships between size, capacitance, and cost are covered for three common ceramic formulations (NPO, W5R, and Z5U).

It is shown in this paper that by an appropriate cleaning and forming procedure titanium metal can be anodically oxidized to a low leakage current, which makes it possible to use this material for capacitor fabrication. Experimental data are given for the metal/oxide/metal thin-film capacitor. A new "printing" technique especially suited for the fabrication of film capacitors in printed microminiaturized electronic circuits is described for the forming of the dielectric oxide layer.

CONSIDERABLE information has been published on the properties of ferroelectric materials1?4 and their use in digital memory devices has been described.5,6 It is the purpose of this paper to discuss the output signals from switched and unswitched ferroelectric storage capacitors, to treat the storage capacitor as a circuit element by the introduction of an equivalent circuit, and to present methods and several circuits by which the inherent signal-to-noise ratio can be improved.

A thorough analysis is made of geometrical effects on the capacity and dissipation factor of gold and thermally anodized tantalum interdigitated thin film capacitors. These capacitors are realized by deposition of a thin film conductor over a substrate with a medium dielectric constant. A series of evaluation tests under several environmental conditions and for both the deposited layers is given, together with a report of the behavioural analysis of the parameters which characterize the capacitors at different working frequencies. Examples of applications at both high and low frequencies with considerations about stability for the two types of conductor materials and choice criteria are then presented for the range of values from 1 to 30 pF, which are those in practical use.

Practical properties of thin film capacitors such as dielectric loss, temperature coefficient of capacitance and breakdown voltage have been related to such fundamental quantities as atomic numbers and permittivities. This permits estimation of the properties of “new” dielectrics in thin film form and short lists of the best materials for “low loss” and “high capacitance” capacitors are drawn up.

Direct-current capacitors of the impregnated-paper type play an important role in electronic equipment required by the Armed Services. In some of these applications good performance is required over very wide temperature ranges. A new chlorinated-hydrocarbon composition which maintains reasonable capacitance constancy over a wide temperature range is described. The properties of this liquid are compared with conventional chlorinated impregnants. Since some alternating voltages usually accompany the direct voltages applied to capacitors, the alternating-current behavior over wide temperature and frequency ranges is described for capacitors impregnated with three different liquids. The effect of voltage and temperature on the resistance of capacitors is discussed. Considerable attention is devoted to the life behavior of capacitors impregnated with chlorinated liquids under direct-current stresses at high temperatures. A life-testing procedure is described which has yielded very satisfactory results on capacitors of varying sizes and ratings. A means for prolonging the life of capacitors impregnated with chlorinated impregnants involving the addition of stabilizers is discussed. Data showing effect of a number of stabilizers are presented. Finally, some data are presented showing the effect of voltage on the life of direct-current capacitors.

The protracted contest between solid-state and thin-film microcircuitry proponents appears to be subsiding, due to the recognition that the two techniques really complement each other. Microcircuit manufacturers and users look to hybrid circuits as a good way to achieve Iow-cost, high-performance circuits. The technique, termed "reactive sputtering" of preparing thin films ranging from conductors to resistive films and even to dielectric films, by sputtering from a tantalum cathode in the presence of an oxygen partial pressure has been developed to deposit resistors and capacitors onto oxidized silicon substrates. Reactively sputtered resistive films of tantalum/tantalum oxide offer sheet resistivities of 27 to 25,400 ohms/square and TCR values of -3 to -1,280 ppm/°C. Their stability during 1000 hours at +125°C and 2 watts/inch2is about ±2 per cent. Dielectric films of reactively sputtered tantalum oxide have been prepared which offer 0.30 to 3.16 pF/mil2and Vbd of 82 to 8 volts respectively, and TCC values of +129 to +269 ppm/°C. Capacitors have been llfe tested for 1000 hours at +125°C at a conservative rating of 60 per cent of Vbd, and show excellent stability. Reactive sputtering variables, including time, current, gas flow, pressure, and substrate temperature and their relation to resistive and dielectric film properties are reported.

The capacitance, dissipation factor, resistivity, and dielectric strength of dried anodized aluminum films are discussed. A miniature non polar self healing capacitor using metalized anodic films is described. Construction techniques, performance, and ratings are presented.

Microminiature circuits can be made from thin films of insulating, resistive or conductive materials, which may be deposited on to suitable substrates by means of evaporation. This article describeu the making of such films and of components such as resistors and capacitors from them. Nickel chromium is used for resistors and silicon monoxide for capacitors; the conductors are made from gold or manganese-copper alloy. The aim has been to produce deposited circuit elements into which semiconductors will later be integrated; the resulting substrates are then to be made into fully sealed modules containing complete functional circuits. Before incorporating into sealed modules the individual components must be stable and resistant to ordinary climatic conditions likely to be met during manufacture, storage and assembly.

Tantalum oxide possesses several outstanding characteristics as a dielectric for thin-film capacitors: a relatively high dielectric strength, a high capacitance-to-area ratio, and good mechanical and electrical stability. The high capacitance density, however, becomes a disadvantage for capacitors in the range of about 100 pF and below. Silicon oxide has been widely investigated as a dielectric for low value capacitors, but it is limited by pinhole defects. By depositing SiO on Ta 2 O 5 to form a duplex dielectric structure, low value capacitors and large area distributed RC networks can be realized and incorporated into tantalum integrated circuitry. Because of the small probability of alignment between defects in the two dielectrics, high initial yields and improved long-term reliability have been obtained. Duplex dielectric capacitors were prepared on glass substrates by anodization of sputtered beta tantalum electrodes and vacuum sublimation of bulk silicon monoxide. Variables studied were silicon oxide thickness and gold versus nichrome-gold counterelectrodes. Comparative evaluations were made by leakage current tests and life tests at several voltages and temperatures. A 75-volt dc leakage current criterion indicates that high initial capacitor yields of 98-100 percent can be obtained with 130-volt anodic Ta 2 O 5 , either 2800 .A or 5000 A of silicon oxide, and both types of counterelectrode. These capacitors perform reliably at 50 volts and 85°C. Capacitors with gold counterelectrodes and the thicker films of silicon oxide exhibited a lower failure rate at the higher life test voltages and temperatures

This paper reports the second phase of our programme to indigenously develop hybrid integrated circuits based on tantalum thin films. (Report on the first phase, viz. development of resistors, has appeared in the September 1971 issue.) These IC's provide quality performance for linear applications right from audio/radio to microwave frequencies and are increasingly incorporated in recent versions of communication and radar equipment.A tantalum film capacitor is fabricated by anodizing the upper portion of the film to serve as a dielectric, the lower portion serving as a bottom electrode. Gold layer deposited on the dielectric constitutes the top electrode. The presence of pinholes, however, does not permit one to adopt such a simple approach. The problem has been successfully solved by adopting ‘a double layer approach’. It consists in once again depositing tantalum on the anodized film and anodizing it completely. Since the probability of pinholes in the two layers coinciding is very rare, this approach ...

A method is presented for the measurement of the variation of capacitance with voltage in gas-dielectric capacitors. It consists of applying to the capacitor a direct voltage and using a small alternating voltage to measure the capacitance variation. The direct voltage coefficient obtained in this manner differs from that obtained with alternating voltage, and this relationship is studied theoretically and verified experimentally. High-voltage compressed gas capacitors can have appreciable voltage coefficients because of eccentricity in their electrode structure. A method is presented for detecting and correcting such eccentricity without opening the capacitor. The voltage coefficients of a few solid dielectric capacitors were measured by comparison with a known air-dielectric capacitor and the results reported.

This paper describes a method of utilizing the voltage tuning characteristics of ferroelectric capacitors in a wide range, superheterodyne, dielectric-tuned, panoramic receiver. Continuous tuning over a 2:1 frequency band is obtained in frequency ranges up to 110 mc. Some of the problems encountered in this application are described, and a method of optimizing the parameters of specific materials is discussed. No detailed technical discussion is presented. The application of these capacitors to various types of circuitry is briefly indicated.

A capacitor has been developed which is superior to previously reported duplex capacitors. The dielectric consists of anodic tantalum oxide overlaid with silicon dioxide deposited by RF sputtering. This capacitor proved usefuI as a low-valued capacitor Of capacitance density ranging from 150 pF/mm2to 20 pF/mm2, corresponding to a thickness range of a silicon dioxide film from 0.2 µ/m to 2.0µm. The capacitor can be produced with very high yield Of approximately 100%, due to the defect-free anodic oxide film diminishing the importance of defects inevitably induced in the RF sputtered silicon dioxide film. The silicon dioxide film can be deposited without causing any deterioration of the anodic film of tantalum oxide by Control of the RFsputtering conditions. The capacitor remained stable with no failures occurring when aged under various conditions of voltage, temperature, and humidity. The capacitor can be processed in a manner compatible with the manufacturing process of the TM or TMM capacitor.

Metallized capacitor paper is attracting widespread interest as a way of reducing capacitor size. In metallized paper capacitors, the usual metal foil is replaced by a thin layer of metal evaporated onto the surface of the paper. Lacquering the paper prior to metallizing increases the dielectric strength and insulation resistance, reduces atmospheric corrosion of the metal, and diminishes the rate of loss of electrode metal by electrolysis. Owing to the extreme thinness of the metal layer, metallized paper capacitors are subject to a type of failure not ordinarily found in conventional capacitors. This type of failure consists of the loss of electrode by electrolysis and occurs under dc potential when the ionic conductivity is high, as results, for example, from the presence of moisture. For this reason, it is recommended that special precautions be taken to keep the ionic conductivity low, in particular with respect to thorough and effective drying and sealing of the capacitor units.

It has been found that under proper conditions thin dielectric films on the electrodes of certain types of cylindrical cross capacitors tend only to produce equal and opposite contributions to the phase angles of the two cross capacitances. To a lesser degree, this same type of cancellation effect has been found to be associated with toroidal cross capacitors.

This paper discusses the low frequency (less than 1 cps) and long time constant applications and testing of capacitors as used in analog control systems. Emphasis is placed on tantalum electrolyric types, as they provide the necessary volume efficiency for airborne systems. The effective capacitance is always larger at the low frequencies than at normal capacitance bridge measuring frequencies. The amount and predictability of the change varies with the rate of charge, the dielectric material and, in the case of tantalums, with the electrolytic system. The polar characteristics of tantalum capacitors introduce other problems, such as doubling the effective capacitance during the first cycle of applied voltage, and hybrid charging curves as voltage levels change. The cause of the increase in charge or discharge time with low rates of change applied is not known. It is apparently allied with the characteristic of dielectric absorption (voltage recovery after shorting the electrodes) in that those capacitors exhibiting the least dielectric absorption also show the least low-frequency sensitivitye Polarization of molecules or molecular chains in the dielectric and/or electrolyte is the probable cause.

THE LOAD capability and performance of high-voltage transmission lines can be improved by the installation of series capacitors. Some reasons for the application of series capacitors to transmission circuits are: 1. To effect the desired load division between parallel circuits. 2. To increase the load capacity of a transmission line by a nominal amount (0 to 50 per cent). 3. To provide increased line capacity so that the system can handle short-time emergency loads. 4. To increase the transient stability limits of a system. 5. To improve voltage regulation and power factor for a given load condition by reducing the operating angle of the line.