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Applied Superconductivity, IEEE Transactions on

Issue 1 • Date March 2005

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Displaying Results 1 - 14 of 14
  • Table of contents

    Publication Year: 2005 , Page(s): c1
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  • IEEE Transactions on Applied Superconductivity publication information

    Publication Year: 2005 , Page(s): c2
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  • Output interface with latching driver for LTS-SFQ circuits

    Publication Year: 2005 , Page(s): 1 - 5
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (408 KB) |  | HTML iconHTML  

    We propose an output interface with a latching driver for single-flux-quantum (SFQ) circuits operating at 4.2 K. An optimum critical current density Jc of the latching driver was discussed, and a multichip module (MCM) structure with SFQ circuits and latching drivers was proposed for 40-Gb/s operation. To optimize Jc of the latching driver, we calculated the punchthrough probability of Nb-Al-AlOx-Nb junctions and high-temperature superconductor (HTS) junctions. The Nb junction with a Jc of 45 kA/cm2, which has a hysteresis of 44% for the latching operation, leads to a punchthrough probability lower than 10-15 for an ideal ac-bias of 40 GHz. On the other hand, ramp-edge-type interface-modified junctions based on YBa2Cu3O7-x have an optimum Jc of 60 kA/cm2 that gives the smallest punchthrough probability lower than 10-15 for an ideal ac-bias of 40 GHz without any shunt capacitance. Because the optimum Jc of 45 kA/cm2 for the latching driver is too large to fabricate large-scale integrated SFQ circuits with the Nb junction, the MCM structure consisting of SFQ circuits and latching drivers with the optimum Jc is important to prepare 40-Gb/s SFQ systems. The Jc of 60 kA/cm2 is a practical value for the HTS junctions, and use of the low-temperature superconductor (LTS)-HTS MCM structure is also one way to realize the high-speed SFQ systems. View full abstract»

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  • High-speed demonstration of single-flux-quantum cross-bar switch up to 50 GHz

    Publication Year: 2005 , Page(s): 6 - 10
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (464 KB) |  | HTML iconHTML  

    We have been developing a single-flux-quantum (SFQ) cross-bar switch, which is a main component of a network packet switch. We think that a network switch is an application in which the high speed of SFQ technology would be advantageous. Anticipating general and large-scale SFQ logic circuit design, we used the cell-based design method and the CONNECT standard SFQ cell library. The two-input and two-output cross-bar switch, a core switch component, consists of 13 logic cells connected by Josephson-transmission-line (JTL) cells. Because of the large size of JTL cells and the large delay in them, timing adjustment becomes more difficult as the operating speed and circuit size increase. After using a commercially available automatic router to find appropriate routes efficiently, we used a static timing analyzer for fine timing adjustment. Timing violations were fixed by changing JTL path delays using the tools we developed. The target operating frequency of the switch was 40 GHz, which corresponds to a clock period of 25 ps. Careful timing adjustment was necessary to ensure correct operations at such a high speed. The test chip was fabricated by using an NEC standard Nb process. The circuit, including on-chip test circuitry, was composed of about 1500 Josephson junctions. We confirmed its correct operations up to 50 GHz with a bias margin of ±20%. View full abstract»

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  • Limitation of DC currents by YBa2Cu3O7-δ-Au superconducting films

    Publication Year: 2005 , Page(s): 11 - 16
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (408 KB) |  | HTML iconHTML  

    The limitation of dc fault currents is one of the issues for the development of dc networks or links. This paper shows for the first time the high potential of YBa2Cu3O7-δ-Au bilayers for the design of dc current limiters. Such devices are based on the transition into the normal state of the superconducting YBa2Cu3O7-δ films above a current I*>Ic, where Ic is the critical current at the onset of dissipation. The study of the transition under current pulses shows that a thermally driven transition into the normal state can occur after a delay ttrans. This duration is defined by the amplitude of the current pulse. For I*≈3Ic, this delay is less than 10 μs. The abrupt transition into the normal state allows an efficient current limitation. A recovery of the superconducting state can also occur under current. This property can be extremely interesting for autonomous operation of a current limiter in an electrical network in case of transient over-currents coming from the starting of high-power devices. View full abstract»

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  • Finite-element method modeling of superconductors: from 2-D to 3-D

    Publication Year: 2005 , Page(s): 17 - 25
    Cited by:  Papers (29)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1144 KB) |  | HTML iconHTML  

    A three-dimensional (3-D) numerical modeling technique for solving problems involving superconducting materials is presented. The model is implemented in finite-element method software and is based on a recently developed 3-D formulation for general electromagnetic problems with solid conductors. It has been adapted for modeling of superconductors with nonlinear resistivity in 3-D, characterized by a power-law E-J relation. It has first been compared with an existing and verified two-dimensional (2-D) model: Compared are the current density distribution inside the conductors and the self-field ac losses for different applied transport currents. Second, the model has been tested for computing the current distribution with typical 3-D geometries, such as corner-shaped and twisted superconductors. Finally, it has been used with two superconducting filaments in the presence of external magnetic field for verifying the existence of coupling currents. This effect deals with the finite length of the conductors and cannot be taken into account by 2-D models. View full abstract»

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  • Analysis and simulation of the effects of distributed nonlinearities in microwave superconducting devices

    Publication Year: 2005 , Page(s): 26 - 39
    Cited by:  Papers (33)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (752 KB) |  | HTML iconHTML  

    This paper presents a comprehensive study of microwave nonlinearities in superconductors, with an emphasis on intermodulation distortion and third-harmonic generation. It contains the analysis of various resonant and nonresonant test devices and its validation using numerical simulations based on harmonic balance (HB). The HB simulations made on test devices show that the closed-form equations for intermodulation and third-harmonic generation are only valid at low power levels. The paper also contains examples of application of HB to illustrate that this technique is useful to simulate superconductive devices other than simple test devices, and that the validity of the simulations is not restricted to low drive power levels. Most of the analyses and simulations of this paper are based on electrical parameters that describe the nonlinearities in the superconducting material. These parameters are compatible with many existing models of microwave nonlinearities in superconductors. We discuss the particulars on how to relate these electrical parameters with one of the existing models that postulates that the nonlinear effects are due to a dependence of the penetration depth on the current density in the superconductor. View full abstract»

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  • High-Tc dc SQUID cooled by pulse-tube cooler and corrosion measurements

    Publication Year: 2005 , Page(s): 40 - 43
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB) |  | HTML iconHTML  

    We developed an YBCO high-Tc dc superconducting quantum interference device (SQUID) system cooled by a pulse-tube cooler. To stabilize and control the operating temperature of SQUID, a temperature controlling method, using dc SQUID itself as the temperature sensor, was developed. With the temperature controller, the temperature fluctuation could be reduced to about 50 mK and the dc SQUID magnetometer could keep locking for over 8 h. Using this dc SQUID magnetometer, we did some corrosion measurements in shielding. The field produced by the corrosion of aluminum plate with one side immersed in corrosion solution could be successfully detected. View full abstract»

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  • Fabrication of niobium titanium nitride thin films with high superconducting transition temperatures and short penetration lengths

    Publication Year: 2005 , Page(s): 44 - 48
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (592 KB) |  | HTML iconHTML  

    We report a systematic study of the superconducting and normal state properties of reactively sputtered Nb0.62Ti0.38N thin films deposited on thermally oxidized Si wafers. The superconducting transition temperature (Tc) was found to increase from 12 K for films prepared on unheated substrates to over 16 K for films prepared on substrates maintained at 450°C. A Nb buffer layer was found to improve Tc by ∼0.5 K for growths at lower substrate temperatures. The films fabricated at 450°C have an amply smooth surface (1.5±0.25 nm root mean square roughness), a sufficiently high Tc, and sufficiently small penetration depth (200±20 nm at 10 K) to be useful as ground planes and electrodes for current-generation 10 K rapid single-flux quantum circuit technology. View full abstract»

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  • RSFQ signed serial multiplier-accumulator

    Publication Year: 2005 , Page(s): 49 - 53
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (536 KB) |  | HTML iconHTML  

    We have designed and successfully tested at low speed a rapid single flux quantum signed serial multiplier-accumulator with target clock frequency 20 GHz. Each bit slice of the device consists of 106 Josephson junctions and 90 resistors. It consumes 22 mA of current and occupies 0.3 mm2. The accumulator of the developed multiplier makes two (rather than three) primitive operations per cycle without any additional overheads. This makes it fast and very robust. In particular, ±18% bias supply margins have been measured in a four-slice multiplier. This is our first device where superconductor microstrip lines (MSLs) have been routinely used. The MSL interfaces introduce some overhead but it is compensated by the simplicity of the design procedure. View full abstract»

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  • IEEE Member Digital Library

    Publication Year: 2005 , Page(s): 54
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  • IEEE copyright form

    Publication Year: 2005 , Page(s): 55 - 56
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  • IEEE Transactions on Applied Superconductivity upcoming special conference issues

    Publication Year: 2005 , Page(s): c3
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  • IEEE Transactions on Applied Superconductivity Information for authors

    Publication Year: 2005 , Page(s): c4
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Aims & Scope

IEEE Transactions on Applied Superconductivity contains articles on the applications of superconductivity and other relevant technology.

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Meet Our Editors

Editor-in-Chief
Britton L. T. Plourde
Syracuse University
bplourde@syr.edu
http://www.phy.syr.edu/~bplourde