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Applied Superconductivity, IEEE Transactions on

Issue 1  Part 1 • Date March 2001

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Displaying Results 1 - 25 of 331
  • The 2000 Applied Superconductivity Conference

    Publication Year: 2001 , Page(s): c3 - c29
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  • Low-voltage negative-resistance mixers of nano-meter SNS junctions

    Publication Year: 2001 , Page(s): 191 - 195
    Cited by:  Papers (2)  |  Patents (2)
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    The current carried by the bound quasi-particles in the N region of a mesoscopic SNS junction has dc and cosine components. The dc current component is carried by the pair charge (-2e) transferred by a couple of Andreev reflections at both of the NS interfaces. The pair-charge transfers decrease due to reduction of the allowed number, 2/spl Delta//V, of Andreev reflections when the voltage, V, increases. Therefore, the low-voltage negative-differential-resistance is observed on the I-V curves of mesoscopic SNS junction, when the junction is driven by the low impedance voltage-bias source. The supercurrent carried by the quasi-particle in the N-region is sensitive to the external high-frequency fields. In a mixer experiment using the nano-meter SNS junctions of NbN, prominent IF signal peaks are observed at low bias voltage. Each IF signal peak corresponds to the negative differential resistance region at low bias voltage. View full abstract»

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  • Properties of asymmetric high critical temperature dc SQUIDs

    Publication Year: 2001 , Page(s): 908 - 911
    Cited by:  Papers (2)
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    Asymmetries between the two Josephson junctions of a dc-SQUID have always been considered undesirable spurious effects, responsible for the degradation of the device performance. However, it was recently demonstrated that a suitable choice of the asymmetric configuration can lead to magnetic flux noise values lower than symmetric ones. The numerical analysis was performed by using parameters typical of low-Tc SQUIDs, operating at the liquid helium temperature. In this paper, the analysis has been extended to high critical temperature dc SQUIDs, operating at the liquid nitrogen temperature. Also in this case, asymmetric SQUIDs show the best performance in terms of both flux to voltage transfer coefficient V/sub /spl Phi// and magnetic flux noise S/sub /spl Phi//. In order to optimize the device performance, the dependence of SQUID properties on damping resistance and normalized SQUID inductance has been computed for both symmetric and asymmetric configurations. View full abstract»

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  • Jim Zimmerman and the SQUID

    Publication Year: 2001 , Page(s): 1026 - 1031
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    The career of Jim Zimmerman, beginning with a solid foundation in electronics and cryogenics, reached a turning point in 1965 when he became coinventor of the rf SQUID (Superconducting QUantum Interference Device), while working at the Scientific Laboratory of the Ford Motor Company in Dearborn, Michigan. Recognizing the exquisite sensitivity of the SQUID as an amplifier and magnetometer, Zimmerman devoted the remainder of his career, at Ford and later at the National Bureau of Standards, to the further development of the SQUID and its applications. In 1969, Zimmerman also helped found SHE Corporation, which marketed the first commercially successful SQUID. While at NBS, Zimmerman introduced two variations, the SQUID gradiometer and the fractional-turn SQUID, to enhance the sensitivity of SQUIDs in special situations. He also developed an improved understanding of SQUID dynamics by exploring the pendulum analog using carefully made models, work that has benefited a generation of students. Putting the SQUID to work, Zimmerman investigated applications in metrology, biomagnetism, and geophysics. Notably, he participated in collaborations that recorded the first magnetocardiogram made with a SQUID and the first magnetoencephalogram of an evoked auditory response. Later, Zimmerman explored closed-cycle refrigeration as a means of making SQUIDs more useful outside the laboratory environment, and in 1977 he demonstrated an operating SQUID cooled to 8.5 K by a Stirling-cycle refrigerator made largely of plastic. Zimmerman is remembered for his keen physical insight, the elegance and simplicity of his experiments, and his willingness to question conventional wisdom in all aspects of life. View full abstract»

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  • Conference author index

    Publication Year: 2001 , Page(s): 1402 - 1419
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  • Noise properties of YBa2Cu3O7-x step-edge junction dc SQUID magnetometers prepared on sapphire substrates

    Publication Year: 2001 , Page(s): 1355 - 1358
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    Step-edge YBa2Cu3O7-x (YBCO) dc SQUID magnetometers on sapphire substrates have been fabricated. CeO2 buffer layers and YBCO films were deposited in situ on the low angle (~35°) steps formed on the sapphire substrates with various thickness ratio of YBCO thin film to step height. Noise properties of the magnetometer exhibit quite different behavior according to the thickness ratio. The field noise of the dc SQUID magnetometer was measured to be 100~300 fT/√Hz at 100 Hz and about 1.5 pT/√Hz at 1 Hz with a dc bias method, and 450 fT/√Hz at 1 Hz with an ac bias method View full abstract»

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  • SINIS process development for integrated circuits with characteristic voltages exceeding 250 μV

    Publication Year: 2001 , Page(s): 1070 - 1073
    Cited by:  Papers (6)
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    At PTB, the fabrication process in Nb-Al/AlxOy /Al/AlxOy/Al-Nb SINIS multilayer technology has been improved to raise the characteristic voltage of SINIS two-tunnel Josephson junctions up to VC=ICRn =245 μV. The process has been realized in LTS implementation. Various sets of the test wafers and wafers containing dc/SFQ and SFQ/dc converters, Josephson transmission lines, and T-flipflop circuits were fabricated and measured. The critical current densities of the junctions have been varied in the range from 70 A/cm2 to 2.2 kA/cm2 with corresponding characteristic voltages of VC =55 μV and 245 μV at the temperature of 4.2 K. The junctions show nearly hysteresis-free behaviour (less than 15%), the intra-wafer parameter spread is smaller than ±10%. RSFQ circuits have been realized with operation margins of the bias currents larger than ±20% View full abstract»

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  • Performance of high-Tc dc SQUID magnetometers with resistively shunted inductances compared to “unshunted” devices

    Publication Year: 2001 , Page(s): 916 - 919
    Cited by:  Papers (5)
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    We have investigated resistively shunted direct-coupled high-Tc dc SQUID magnetometers with different inductances. At T=77 K, good quantitative agreement was observed between the measured maximum voltage modulation depth and calculated values based on the theoretical predictions by Enpuku et al. (1995) whereas the white magnetic flux noise at 10 kHz of all four devices was found to be a factor of 2.3 higher than predicted. The lowest white magnetic field noise of 153 fT/Hz1/2 was obtained for the magnetometer with an inductance of 100 pH and an outer dimension of the pickup loop of just 3 mm. The combined theoretical and experimental results suggest that although similar magnetic field noise values can he obtained for inductances up to 200 pH, the minimum value of the unshunted case cannot be improved upon. However, the maximum voltage modulation depth could be increased significantly at little cost to the noise compared to an unshunted device View full abstract»

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  • High-Tc SQUID magnetometers for use in moderate magnetically-shielded room

    Publication Year: 2001 , Page(s): 1323 - 1326
    Cited by:  Papers (5)
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    We have fabricated and characterized high-Tc planar SQUID magnetometers and first derivative gradiometers with directly-coupled pickup loops. The devices were made from single layer of YBa2Cu3O7-δ thin film on LSAT bicrystal substrate with 30° or 24° misorientation angle. Magnetic properties were investigated by applying a magnetic field B0 for the SQUID magnetometer patterned with holes to reduce the maximum structural width. We found an increasing low frequency noise with cooling fields B0 larger than 1.5 μT. This value consists with the threshold field estimated from the maximum structural width. A magnetic field noise level of 500 fT/Hz1/2 at 10 Hz was observed by using FLL electronics with a bias current reversal in a moderate magnetically-shielded room consisting of only two 1 mm thick layers of permalloy. Measurements of magnetocardiograms demonstrate the suitability of this magnetometer for biomagnetic applications. On the other hand, the gradiometer with two symmetric pickup loops was operated without any shielding. The performance obtained was a field gradient resolution of about 1 pT/cmHz1/2 at 1 kHz and 10 pT/cmHz1/2 at 1 Hz, with a baseline of 4 mm. The imbalance of this gradiometer was around 0.7%, limited by the sensitivity to homogeneous field of the SQUID itself View full abstract»

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  • Defect detection and classification using a SQUID based multiple frequency eddy current NDE system

    Publication Year: 2001 , Page(s): 1032 - 1037
    Cited by:  Papers (10)
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    The probability of detection (POD) of hidden fatigue defects in riveted multilayer joints, e.g. aircraft fuselage, can be improved by using sophisticated eddy-current systems which provide more information than conventional NDE equipment. In order to collect this information, sensor arrays or multi-frequency excitation schemes can be used. We have performed simulations and measurements with an eddy current NDE system based on a SQUID magnetometer. To distinguish between signals caused by material defects and those caused by structures in the sample, such as bolts or rivets, a high signal-to-noise ratio is required. Our system provides a large analog dynamic range of more than 140 dB/√Hz in unshielded environment, a digital dynamics of the ADC of more than 25 bit (>150 dB) and multiple frequency excitation. A large number of stacked aluminum samples resembling aircraft fuselage were measured, containing titanium rivets and hidden defects in different depths in order to obtain sufficient statistical information for classification of the defect geometry. We report on flaw reconstruction using adapted feature extraction and neural network techniques View full abstract»

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  • Nonlinear simulation and characterization of devices with HTS transmission lines using harmonic balance algorithms

    Publication Year: 2001 , Page(s): 1396 - 1399
    Cited by:  Papers (12)
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    This work presents the use of Harmonic Balance to simulate the nonlinear behavior of HTS transmission lines. Good agreement with theoretical cross-checks is found. We also show the use of this algorithm to fit the model of HTS lines from experimental measurements. We illustrate this by fitting several types of experimental data, and discuss how to avoid ambiguity in this fitting View full abstract»

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  • Cross-coupled band-pass filter using HTS microstrip resonators

    Publication Year: 2001 , Page(s): 485 - 488
    Cited by:  Papers (4)
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    We have fabricated microstrip band-pass filters based on the quadruplet geometry using high-temperature superconductor. Every half-wavelength resonator in the filter consists of a loop-like inductor and two patch capacitors at both ends. The inductive coupling in between the loop-like inductors of non-adjacent resonators produces transmission zeros in the frequency response. The transmission zero can be allocated by changing the polarity and the strength of the cross coupling. We have designed a 9-pole filter for personal communication services (PCS) application using combination of a CAD tool and a full-wave analysis EM simulator. We have fabricated filters using double-sided YBa2Cu3O7-δ (YBCO) thin films on LaAlO3 substrates. The filter has 1.784 GHz center frequency, 11 MHz 3-dB bandwidth, and 0.8 dB insertion loss at 60 K. Due to the transmission zeros near the passband, the steep skirt characteristic is exhibited. The attenuation at 1 MHz away from the edge of the passband is -34 dB View full abstract»

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  • Superconducting second-order sigma-delta modulators utilizing multi-flux-quantum generators

    Publication Year: 2001 , Page(s): 554 - 557
    Cited by:  Papers (2)
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    We have been developing a superconducting second-order sigma-delta analog-to-digital converter with a large bandwidth and a large dynamic range for software radio applications. In a superconducting second-order sigma-delta modulator utilizing a passive integrator and single-flux-quantum (SFQ) feedback, gain to compensate the large attenuation in the passive integrator of the modulator is required to obtain a large dynamic range. In this paper, a second-order modulator utilizing multi-flux-quantum (MFQ) generators creating the needed gain is reported and the design and experimental test results of the elementary circuits including a comparator, a first-order modulator, and the MFQ generator are described. The digital outputs of the comparator and the first-order modulator were experimentally evaluated, where the input dependence of the comparator switching probability and the noise-shaping properties of the modulator were clearly observed. The low speed operation of the MFQ generator creating three SFQ pulses was experimentally confirmed. The other circuits were also tested at low frequencies View full abstract»

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  • A compact HTS filter subsystem

    Publication Year: 2001
    Cited by:  Papers (1)
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    Summary form only given, as follows. We describe a compact, long-life High-Temperature Superconducting (HTS) filter subsystem for mobile telecommunication base stations. This system consists mainly of a HTS filter and a low-noise amplifier (LNA), which are cooled by a Stirling pulse tube type cryocooler. The cooler is compact and has a service life of more than 5 years, theoretically, because its head has no moving parts. The 13-pole HTS filter, which as a 20 MHz bandwidth at 1.955 GHz, is made using a YBCO HTS thin film, and has a minimum insertion loss of less than 0.2 dB at 70 K. The HTS filter and LNA are packaged in a vacuum chamber, which can retain vacuum for more than 5 years operated under constant temperature-controlled conditions View full abstract»

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  • Characterization of X-band filter of double-sided Y-Ba-Cu-O film on MgO substrate

    Publication Year: 2001 , Page(s): 119 - 122
    Cited by:  Papers (1)
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    We investigated the pulsed laser deposition process of double-sided Y-Ba-Cu-O thin films on MgO substrates, the critical current density (Jc) distribution and the microwave surface impedance (Rs) of the films, and the power handling capability by third-order intermodulation distortion (IMD3) measurements using 40 W high power microwave measurement system. A clean flat MgO surface was important for Y-Ba-Cu-O deposition and successfully obtained by three-hour pre-annealing at 1000°C in air. To confirm the film process, we designed, fabricated and measured the 11 GHz band-pass 7-pole Y-Ba-Cu-O filter. We also found that the outskirts of the Y-Ba-Cu-O film on MgO substrate were particularly important in Jc quality because the biggest microwave power in filter circuit is allocated in the outskirts of Y-Ba-Cu-O film area View full abstract»

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  • High-temperature superconducting edge-type Josephson junctions with modified interface barriers

    Publication Year: 2001 , Page(s): 770 - 775
    Cited by:  Papers (10)
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    This paper describes recent results on the fabrication, electrical characteristics, and microstructure of high-temperature superconducting edge-type Josephson junctions with modified interface barriers. The barriers are formed by surface modification of the YBa2Cu3O7-δ base layer. This process involves structural and chemical modification by ion irradiation and crystallization by annealing. The junctions showed resistively and capacitively shunted junction-like current-voltage characteristics and excellent uniformity. The spread in the critical current for one hundred junctions was smaller than 1σ=10% at 4.2 K. The uniformity is now approaching 1σ=5%. The junction characteristics have remained the same after two-year room-temperature storage. They also showed no change after high-temperature processing at about 700°C. High-resolution transmission electron microscopy revealed that both the crystal structure and chemical composition in relatively thick barriers are different from those of YBa2Cu3O7-δ View full abstract»

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  • Microwave responses of an insular intrinsic Josephson junction stack fabricated from Bi-Sr-Ca-Cu-O single crystal

    Publication Year: 2001 , Page(s): 1199 - 1202
    Cited by:  Papers (6)
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    The conventional c-axis intrinsic Josephson junction (IJJ) stack is usually fabricated from a piece of single crystal in such a way that it looks like a small mesa sitting on a big pedestal. In some cases the effects of this pedestal should be taken into account in order to explain the experimental observations. To avoid this problem we have developed a novel technique by which we are able to remove a small sample from the single crystal and place it on a substrate with low microwave loss. This enable us to couple it to other microwave devices such as antenna etc. This small sample, or junction stack, measures a few micrometers by a few micrometers in the a-b plane and a few hundred angstroms along the c-axis and is plated with normal metal on both the top and the bottom. To distinguish the structure from the conventional one, we call it an insular intrinsic Josephson junction stack. We carefully study current-voltage characteristics, microwave responses, frequency mixing properties, and discuss the possible applications View full abstract»

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  • Circuit improvements for a voltage multiplier

    Publication Year: 2001 , Page(s): 550 - 553
    Cited by:  Papers (9)
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    A voltage (or flux) multiplier is a device which multiplies applied SFQ pulses. Due to the quantum nature of an SFQ pulse the device can be used as a voltage (or flux) amplifier with a fundamentally accurate (integer) gain. Earlier we showed that the device can be used for improvement of dc and ac voltage standards. Recently we have found that a long voltage multiplier can display complex dynamic behavior, which can lead to undesirable collective oscillations. This report is devoted to theoretical optimization and experimental investigation of long voltage multipliers connected in series for dc current. Experimentally we have obtained accurate current steps with about 0.1 V voltage drop for a 5 mm×5 mm chip fabricated in Nb technology and tested at 4 K View full abstract»

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  • Effect of a static magnetic field on a slotted high-Tc SQUID magnetometer without a flux dam

    Publication Year: 2001 , Page(s): 1335 - 1338
    Cited by:  Papers (5)
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    A direct-coupling-type high-critical-temperature (high-Tc ) SQUID magnetometer with two pickup loops per SQUID on a bicrystal substrate has been fabricated. To avoid flux trapping, the superconducting films of the pickup loops have slits with a separation of 5 μm. To suppress flux entry into the pickup loops, there are no weak links on the pickup loops, i.e., no flux dams. In field cooling, noise did not substantially increase in the low frequency region unless the field reached around 100 μT. Regardless of whether the magnetometer was previously zero-field cooled or field-cooled, the flux did not enter the pickup loop until the changing field exceeded about 10 μT. The magnetometer cooled under geomagnetic- and environmental-field noise could work in an unshielded environment. A gradiometer was made by connecting the feedback coils of two magnetometers in series. The environmental field noise was reduced by the gradiometer by about 35 dB View full abstract»

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  • Fabrication and characterization of hot-electron bolometers for THz applications

    Publication Year: 2001 , Page(s): 566 - 569
    Cited by:  Papers (1)
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    Superconducting properties of Nb and NbN thin films for application in diffusion and phonon cooled Hot-Electron Bolometers have been systematically investigated. The materials were sputtered on fused quartz substrates in a wide thickness range. DC-measurements of the Nb films allow us to predict the intermediate frequency bandwidth of a hot-electron bolometer mixer device for a given design. To improve the characteristics of the NbN thin films, we used a 15 nm MgO seed layer View full abstract»

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  • Random telegraph voltage noise in a Bi2Sr2CaCu2O8+x intrinsic Josephson junction

    Publication Year: 2001 , Page(s): 304 - 307
    Cited by:  Papers (7)
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    Low frequency noise properties have been investigated in mesa-type Bi2Sr2CaCu2O8+x (BSCCO) intrinsic Josephson junction. The junction area for this mesa was 160 μm×40 μm. The mesa showed highly hysteretic current-voltage characteristic at low temperatures, and had seven discrete-resistive-branches. For the noise measurements only at T~36 K, we observed a rapid increase in the noise voltage spectrum over our entire bandwidth. Large random telegraph voltage noises (RTVN) were only detected for low bias current region of the BSCCO mesa for current biased on the 4th (Ib=6.0 mA) and 5th (Ib=5.0 mA) resistive-branches, and also not observed for all of voltage region at 4.2 K and low bias voltage region, from 1st to 3rd resistive-branches, at 36 K. The measured Sv(f) had the Lorentzian frequency dependence, as expected from the Machlup formula for random telegraph signal. The possible origin of the large RTVN may be thermal fluctuation of the “switchback” voltage Vmin View full abstract»

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  • Demonstration of chip-to-chip propagation of single flux quantum pulses

    Publication Year: 2001 , Page(s): 337 - 340
    Cited by:  Papers (2)  |  Patents (1)
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    We report experimental results on chip-to-chip transfer of single-flux-quantum (SFQ) pulses using an active multichip module (MCM). Josephson transmitters and receivers are integrated on both a chip and an MCM substrate. An MCM consisting of a 4.8-mm chip and an 8.2-mm MCM substrate was fabricated using a 1.6-kA/cm2 Nb-trilayer process and a solder-bumped flip-chip bonding technology. The correct operation of the circuit was confirmed by low-speed testing. Bit-error rate (BER) of the circuit was measured down to 10-5, and extrapolation of the error-function fits suggested a very small BER, lower than 10-200, at the optimum bias point. Experimental margins on the bias voltage were as large as ±34% View full abstract»

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  • Enhanced microwave power from triangular arrays of small Josephson junctions

    Publication Year: 2001 , Page(s): 454 - 458
    Cited by:  Papers (1)
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    We report on high frequency measurements of underdamped Josephson junction arrays consisting of two rows of parallel biased cells. The rf voltage generated on the junctions transverse to the bias current (horizontal junctions) is detected by a room temperature receiver in the W-band. In order to enhance the emitted power, it has been proposed (S.P.Y.) that the single horizontal junction in each cell be replaced by two (or more) horizontal junctions. This geometry has been proven to have better high frequency performance. Here we present comparative measurements of the output power from two row arrays of different geometries. Among the studied configurations, larger power is obtained from an array with square cells and two horizontal Junctions. In this array, the measured output power is up to about 2 times larger than that in the array with only one horizontal junction, and up to 20 times larger with respect to the array with conventional triangular cells. Experimental data are in good qualitative agreement with numerical simulations View full abstract»

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  • Imaging sub-millimeter waves in planar cryoelectronic circuits by scanning laser microscopy

    Publication Year: 2001 , Page(s): 716 - 720
    Cited by:  Papers (2)
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    Low temperature scanning laser microscopy (LTSLM) is demonstrated to be capable of imaging sub-THz electromagnetic fields in cryoelectronic integrated structures. This method allows one to evaluate the spatial distribution of time-averaged field amplitudes with a resolution of about one micrometer for samples with characteristic dimensions of order millimeters. Using LTSLM, cryoelectronic devices with both passive and active superconducting elements can be characterized. Local heating of superconducting structures by a laser beam introduces extra loss for the propagating and standing sub-millimeter waves. We present LTSLM images of two-dimensional 400 to 500 standing GHz wave patterns in integrated superconducting receiver chips View full abstract»

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  • Nb-based SIS mixer in the 800 GHz band

    Publication Year: 2001 , Page(s): 167 - 170
    Cited by:  Papers (2)
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    We have built a waveguide SIS mixer with Nb-based parallel-connected twin junctions at 800 GHz which is above the gap frequency of Nb (690 GHz). Heterodyne mixing was performed at 810 GHz and a receiver noise temperature of 580 K (DSB), which includes noise contributions due to a vacuum window and a beam splitter, was achieved using Nb/AlOx/Nb junctions with Nb striplines. The performance of this mixer is quite good and it is shown that efficient mixing in Nb-based SIS junctions is still possible above the gap frequency, SIS mixers with Al striplines have also been fabricated and good DC I-V characteristics have been observed. Heterodyne measurements of these mixers are now under preparation View full abstract»

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

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