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Proceedings of the IEEE

Issue 8 • Date Aug 1989

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Displaying Results 1 - 16 of 16
  • Potential methods for the fabrication of high-Tc superconductors for wires and cables

    Page(s): 1124 - 1131
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    Studies of practical properties, such as upper critical field (HC2) and critical-current density, of high-T c oxide superconductors of Y-Ba-Cu-O Bi-Sr-Ca-Cu-O, and Tl-Ba-Ca-Cu-O systems are reviewed. The Hc2 of these materials is much higher than that of conventional metallic superconductors, indicating a high potential for practical applications, even when they are used in liquid nitrogen. However, the HC2 of these materials is also highly anisotropic, as can be expected from an examination of their crystal structure. In addition to this anisotropy, the presence of weak links and a weak pinning force in this material limit the transport current density J3 to much lower levels than that required for practical applications. Recent fabrication processes that have good potential for producing wire or tape conductors or high-Tc oxide are reviewed. Some details are presented of the powder method and other fabrication processes using diffusion, solidification, and deposition techniques. For the Ag-sheathed oxide tapes, Jc values exceeding 10000 A/cm2 at 77 K and 0 T have been reported for both Bi and Tl oxide materials View full abstract»

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  • Principles and applications of SQUIDs

    Page(s): 1208 - 1223
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    An overview of the current status of DC and RF SQUIDs (superconducting quantum interference devices) is presented. Using Nb-based thin-film technology, a number of groups can now routinely fabricate DC SQUIDS with input circuits integrated on the same chip. At 4.2 K, the DC SQUID, which operates with a constant bias current, can detect signals with an equivalent energy per unit bandwidth of a few hundred h2π. RF SQUIDs, which operate with an RF flux bias, are usually machined from bulk Nb, and have a typical energy sensitivity per unit bandwidth of 105 to 106h2π. Both types of SQUID can be used in a wide variety of applications, including magnetometers, gradiometers, susceptometers, voltmeters, RF amplifiers, gravity-wave antennas, and gravity gradiometers. Both DC and RF SQUIDs have been fabricated from high-temperature superconductors and operated at temperatures of up to 77 K. These devices exhibit high levels of 1/f noise, which generally arises from the motion of trapped magnetic flux View full abstract»

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  • Superconducting magnets and their applications

    Page(s): 1132 - 1142
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    Superconducting magnets are now being used in such diverse applications as medical imaging, fusion research, and power conditioning. Steady improvement in the understanding of instability and quenching has allowed increases in current density and compactness of winding. The resulting reduction in winding size has allowed the construction of economical magnets for imaging, acceleration, and high-resolution spectrometers. Large magnets for fusion and energy applications have been made possible by composite conductors containing large amounts of copper or aluminum. It is noted that the advent of high-temperature superconductors may hold the promise of very-high-field magnets. Meanwhile, low-temperature superconductors capable of generating fields up to 30 T have been developed. In either case, structural materials of greater strength than are now available and novel construction techniques will be needed View full abstract»

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  • Application of superconductors to motors, generators, and transmission lines

    Page(s): 1143 - 1154
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    Two specific applications of superconductors are considered: electric machinery (motors and generators) and transmission lines. Development work carried out with respect to both types of equipment indicates that the use of superconductors is feasible, even if only liquid-helium-cooled superconductors are considered. The high-T c superconductors will have a beneficial impact on motors, generators, and transmission lines only if conductors with sufficient mechanical properties and current-carrying capabilities can be developed View full abstract»

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  • Flux transfer devices

    Page(s): 1280 - 1286
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    Flux transfer device theory is reviewed. In such devices, generalized magnetic flux, defined as the time integral of voltage, is used to describe the device characteristics. The Josephson junction and inductor are the main circuit elements in flux transfer devices, because they maintain a constant value for the time integral of voltage. Flux transfer devices are based on either an RF SQUID (superconducting quantum interference device) or a fluxon device. Four devices, including the parametric quantron and the quantum flux parametron, are reviewed as applications of the RF SQUID. The fluxon feedback oscillator and a soliton device are also reviewed as applications of fluxon devices. The quantum flux parametron is then described. The parametron principle and the fundamental properties of the quantum flux parametron such as gain, switching speed, and power dissipation are discussed. Logic circuits and a memory cell are also reviewed. A novel analog-to-digital converter is proposed as an application of the quantum flux parametron View full abstract»

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  • Superconductor-semiconductor hybrid devices, circuits, and systems

    Page(s): 1287 - 1301
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    The discovery of superconductors whose critical temperatures are above liquid nitrogen temperature has prompted considerable interest in hybrid superconducting-semiconducting electronics applications. The authors review the efforts to hybridize these technologies. Some of these efforts have already been demonstrated on a laboratory scale; others are at present just theoretical proposals. Hybridization is possible on the system, circuit, and device levels. The authors review studies of the applications of superconductors for interconnecting semiconductor systems and combining semiconductor and superconductor devices to enhance the performance of both digital and analog systems. Novel circuit combinations of superconducting and semiconducting devices are mentioned, as are proposals to combine these materials on the device level. It is noted that the use of hybrid combinations may permit some electronic functions to be performed better than either technology could perform separately View full abstract»

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  • High-temperature superconductive thin films

    Page(s): 1155 - 1163
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    The material and physical properties of the new high-temperature copper oxide superconductors relevant to electronic device applications are reviewed. The various approaches to their synthesis in useful thin-film form are discussed and the properties of films made by the various techniques are compared, as are results from the principal high-temperature superconductors. It is argued that, because of the strong anisotropy and poor conduction across grain boundaries typical of these materials, only well-textured films will generally be useful in electronic applications. The utility of the bulk critical current density as an entry-level figure of merit for any film is emphasized View full abstract»

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  • Digital logic circuits

    Page(s): 1177 - 1193
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    Recent progress in Josephson digital logic circuits is described. It is noted that changing the junction material from a lead alloy to niobium has dramatically improved process reliability, and that high-speed, low-power operations have been demonstrated at large-scale integrated-circuit levels. The first Josephson microprocessor, operated at 770 MHz, verified the potential of Josephson devices for future digital elements. The possibilities of the ultrafast Josephson computer, previously shelved because of a number of problems, are being actively reconsidered. The performance anticipated for Josephson digital circuits using high-temperature superconducting materials is also discussed View full abstract»

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  • Superconducting components for infrared and millimeter-wave receivers

    Page(s): 1233 - 1246
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    The superconducting components developed for infrared and millimeter-wave receivers are reviewed. A brief description is given of the scientific principles on which each device is based, followed by a discussion of the performance that has been achieved in terms of the appropriate figures of merit. Comments are made about the possibility that useful device performance can be achieved by using the new high-Tc oxide superconductors. The authors emphasize photon-assisted quasi-particle tunneling and the superconductor-insulator-superconductor (SIS) quasi-particle mixer, which is the only superconducting component to find substantial applications at infrared or millimeter wavelengths. Descriptions are given of the SIS quasi-particle direct detector, the Josephson effect oscillator, the Josephson effect parametric amplifier, and the various superconducting bolometers, for which practical applications appear possible. The less promising Josephson-effect detector and mixer and the various ideas for superconducting photon detectors are described because of the current interest in possible high-Tc versions of these devices View full abstract»

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  • Standards and high-speed instrumentation

    Page(s): 1224 - 1232
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    The authors review four applications of superconductivity of current interest in metrology. These applications are Josephson series-array voltage standards, cryogenic current comparators, a superconducting sampling oscilloscope, and a novel bolometer based on a kinetic inductance thermometer View full abstract»

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  • Josephson shift registers

    Page(s): 1274 - 1279
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    A review of Josephson shift-register circuits that have been designed, fabricated, or tested is presented with emphasis on work in the 1980s. Operating speed is most important, since it often limits system performance. Older designs used square-wave clocks, but most modern designs use offset sine waves, with either two or three phases. Operating margins and gate bias uniformity are key concerns. The fastest measured Josephson shift register operated at 2.3 GHz, which compares well with a GaAs shift register that consumes 250 times more power. The difficulties of high-speed testing have prevented many Josephson shift registers from being operated at their highest speeds. Computer simulations suggest that 30-GHz operation is possible with current Nb/Al 2O3/Nb technology. Junctions with critical current densities near 10 kA/cm2 would make 100-GHz shift registers feasible View full abstract»

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  • Niobium-based integrated circuit technologies

    Page(s): 1164 - 1176
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    Metallurgical and electrical properties of Nb and NbN films for use as Josephson junction electrodes and wiring layers are investigated. The crystallographic and superconducting properties necessary for Nb-based integrated circuit processes are clarified. Tunnel barrier structures of NbN-Nb oxide-NbN (Pb alloy) and Nb-Al oxide-Nb Josephson junctions have been analyzed and correlated with junction characteristics and critical current uniformity. It was found that the surface structure of a base electrode should be smooth to ensure that Josephson junctions have low leakage current and uniform critical current distribution. New types of Josephson junctions with artificial tunnel barriers such as amorphous Si or Mg oxide are reviewed. A variety of Josephson junction structures or processes have been developed for Nb-based Josephson integrated circuits in order to improve circuit performance. These include junction miniaturization, planarization, and stacked junction structures. These structures are mainly intended for Nb-Al oxide-Nb Josephson circuits. The Nb-Al oxide-Nb Josephson junction technology is by far the most advanced and has been used in logic and memory circuits, for example a 4-bit×4-bit parallel multiplier, a Josephson logic gate array, a 16-bit arithmetic logic unit, a 4-bit microprocessor, and 1-kb and 4-kb memory circuits View full abstract»

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  • Josephson memory technology

    Page(s): 1194 - 1207
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    Memory circuit architecture (decoder, cell, cell array, and sense circuit) is surveyed, with emphasis on implementing a memory with fast access and low power consumption. Recent progress in fabrication and circuit technology has improved memory performance. An AC powering scheme, instead of the earlier DC system, has been developed. The AC powering scheme eliminates complicated timing control, which restricts shortening access time, but introduces large power consumption and in-phase powering problems. A parallel decoding scheme that decreases the number of decoding stages is presented. It will decrease the decoding time and AND scheme decoder. An attractive OR-inverter scheme has been proposed for a decoder suitable for a memory with a large capacity. The chip performance strongly depends not only on whether the read mode is destructive or nondestructive but also on the cell connection method, which determines the line inductance. Because the cell input line inductance depends on layered construction of the lines, a planarizing technology for an Nb Josephson integrated circuit has been developed to reduce line inductance by thinning the insulators. Access time of less than 0.5 ns has been confirmed in 1-kb and 4-kb memories using the proposed memory architecture View full abstract»

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  • Superconductive A/D converters

    Page(s): 1264 - 1273
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    A number of superconductive A/D (analog/digital) converter designs that show promise for superiority in high-bandwidth or high-resolution applications are known. On the high-resolution side, counting-type converters appear quite attractive. Voltage-to-frequency and tracking A/D converters are reviewed in this category. On the ultra-high-bandwidth side (greater than about 1 GHz) the parallel-type A/D converters seem to be advantageous. A number of parallel periodic-threshold A/D converters that have been attempted over the years as well as a fully parallel (2N-1 comparators) A/D converter are reviewed View full abstract»

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  • Conventional wire and cable technology

    Page(s): 1110 - 1123
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    The present state of the art of practical bulk superconductors is reviewed. The recent developments in high-current density fine-filament NbTi conductors are dealt with at length. The improvements achieved can be applied to the full range of different product forms of monofilamentary NbTi. These are described together with the fabrication methods used to produce them. Three practical fabrication techniques for multifilamentary Nb3Sn are outlined and properties are compared and discussed. Reference is made to V3Ga, NbN, and Chevrel phases and the novel fabrication techniques used to produce these materials. It is pointed out that the lessons learned in the manufacture of these compound superconductors can be used to help in the development of the newer high-Tc materials View full abstract»

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  • Superconductive analog signal processing devices

    Page(s): 1247 - 1263
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    Real-time signal processing is important in many emerging applications in areas such as pulse-compression radar, spread-spectrum communications, and electronic warfare. The required digitally equivalent computational rate for these applications is on the order of 102 arithmetic operations per second and the required instantaneous bandwidths could approach 10 GHz. These exceed by nearly three orders of magnitude the capabilities projected for digital systems in the near future, and even exceed that of recently developed analog technologies such as surface-acoustic-wave (SAW) signal-processing devices. To meet anticipated future system needs, superconductive analog signal-processing components with bandwidths of 2 GHz have recently been realized, and the technology is being developed for the realization of 10-GHz bandwidths. Issues of fabrication technology and subsystem integration are examined for superconductive analog signal-processing devices View full abstract»

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North Carolina State University