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| 1996 Part 3 |
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Front Cover (1996 - Part
3)
No author information
available
Summary: Not
available |
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Table
of Contents (1996 - Part 3)
No
author information available
Summary: Not
available |
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Superconducting
direct digital synthesizer
A.
Spooner, Binneg Lao, D. Rowe, C. Harper, S. Schwarzbek, D.J.
Durand, L. Eaton and A.D. Smith
Summary:
Communications transmitters, receivers, radar
applications, and related test equipment require precise
control over generated frequencies which can be provided by
digital synthesis. Superconductivity technology offers to
greatly improve the operational frequency range at a tiny
fraction of the power of present GaAs and Si digital frequency
synthesizers, an important consideration for systems with
multiple receiver elements and satellite applications. We
designed, fabricated, and tested a digital superconducting
frequency synthesizer on a 1-cm square substrate in niobium
technology and tested at 4 Kelvin. The chip contains a 12-bit
pipelined MVTL incremental phase accumulator (simple expansion
to 32 bits achieves one part in 4.3/spl times/10/sup 9/
frequency resolution). The most significant 10-bits of the
accumulated phase proceed to a Sine ROM which is based on
SQUID cells and employs data compression to minimize circuit
size. An 8-bit ROM output word proceeds to a superconducting
D/A converter to construct the analog output waveform which
updates each clock cycle. We have operated the entire
superconducting synthesizer above 1 GHz. Our performance goal
with present fabrication technology is /spl ges/4 GHz
operation. |
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Contention
solver for a superconducting packet
switch
M. Hosoya, S. Kominami, W.
Hioe and T. Nishino
Summary: The paper
describes the architecture of a contention solver (CS) to be
used in a superconducting packet switch prototype, and the
design and tests of 2/spl times/2 switching elements which
compose the CS. The contention solver is based on a Batcher
sorter, in which switching elements check for contention
between input packets. A priority port is used to guarantee
correct operation of the sorter even if a packet is
invalidated during the sorting process. A 2/spl times/2 CS
switching element with 2-bit data-width was designed in
dual-rail logic. It was fabricated using three-junction SQUID
gates by a standard Nb tri-layer process, and consists of 102
OR-equivalent gates in an area of 1.2 mm x 1.8 mm. Its correct
operation was confirmed completely. |
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Circuits
for chip-to-chip transportation of bits from single flux
quantum circuits
A.H. Miklich,
A.H. Worsham, D.L. Miller and J.X. Przbysz
Summary:
We have designed circuits to transmit and receive bits
generated by Single-Flux-Quantum (SFQ) circuits. Our circuits
were fabricated using shunted Nb-AlOx-Nb junctions. The
transmitter is a series array of dc SQUIDs driven into the
voltage state in response to an input SFQ pulse. The receiver
circuit is inductively coupled to the transmitter. Current
from the transmitter biases a junction race in the receiver
such that a clock pulse either passes (a '1' bit) or does not
(a '0' bit). We have measured a maximum peak-to-peak amplitude
from the transmitter of 296 /spl mu/V at a clock rate of 2.5
GHz, and 187 /spl mu/V at 5 GHz. |
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A
vortex transitional memory cell for 1-Mbit/cm/sup 2/ density
Josephson RAMs
H. Numata, S.
Nagasawa and S. Tahara
Summary: We developed
an 8.5 /spl mu/m/spl times/11.5 /spl mu/m vortex transitional
(VT) memory cell. The memory cell is the smallest Josephson
memory cell ever reported. The cell was fabricated by electron
cyclotron resonance plasma etching and bias-sputtering
planarization. This is also the first Josephson circuit
fabricated with sub-micron minimum feature size. Proper
nondestructive read-out operation was verified even after
half-selected conditions. An operating margin of /spl
plusmn/14% was obtained for control currents I/sub X/ and
I/sub Y/. These results are promising for developing a
1-Mbit/cm/sup 2/ density Josephson RAM. |
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New
multi-flux-quantum logic
family
V.K. Kaphmenko and E.
Wikborg
Summary: We report on a voltage-state
logic family based on shunted Josephson junctions and on the
Rapid Single Flux Quantum (RSFQ) concept. Storing information
in a voltage-state form makes this Multi-Flux-Quantum Logic
(MFQL) easier to match to complementary metal-oxide
semiconductor (CMOS) circuits. The switching of MFQL element
between the voltage and zero-voltage states takes a minimum of
two SFQ pulses, and the switching time of this logic is
comparable to that of RSFQ logic. The key logic element is an
inverter in the form of an asymmetric interferometer, and the
underlying idea is to use a separate superconducting wire to
supply a standard dc output voltage for the elements. The
asymmetric interferometer, directly coupled to the other
elements, is actually a Josephson junction based
three-terminal device or transistor. Elements such as NOT, OR,
NOR, XOR, XNOR, a toggle flip-flop, and an RS trigger have
been simulated, and show margins better than /spl plusmn/24%.
The performance of this logic with current circuit fabrication
technologies is also discussed. |
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High-T/sub
c/ superconductor oversampled delta modulator for
analog-to-digital converters
Y.M.
Zhang, N. Dubash, U. Ghoshal and K. Char
Summary:
Based on a single-level YBCO thin film topology and
seven bicrystal grain-boundary junctions, a high temperature
superconductor delta modulator for analog-to-digital
converters has been designed, fabricated, and tested. A single
bit quantizer based on a quantum flux parametron (QFP)
comparator is used for the modulator. A large superconducting
inductor is used both for the signal input and for the
feedback. A small resistor is chosen for connecting the
comparator to the read-out section. The oversampling provides
large input signal bandwidth with high dynamic range. Circuit
simulations prove the concept of the design. The effective LSB
and MSB of the modulator are discussed in terms of input
inductance, junction critical current, and QFP noise current.
The density of latched output pulses is proportional to the
change of input amplitude. Au wires were employed to make
crossover of bias lines. Although this modulator did not
function as expected for low-speed measurements, it shows the
proper latching behaviour of the output section at 4.2 K and
35 K. |
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Fabrication
and characterization of YBa/sub 2/Cu/sub 3/O/sub 7-/spl
delta///SrTiO/sub 3//Ag trilayer films on SrTiO/sub 3/
bicrystal substrates
H. Haensel,
C. Hoefener, D. Koelle and R. Gross
Summary:
We have fabricated YBa/sub 2/Cu/sub 3/O/sub 7-/spl
delta///SrTiO/sub 3//Ag trilayer thin films on bicrystal
SrTiO/sub 3/ substrates for electric field effect three
terminal devices. For the electrical transport measurements
the samples were patterned using optical lithography and wet
or ion beam etching. The dielectric properties of the
SrTiO/sub 3/ barrier layer were analyzed by measuring the
temperature and voltage dependence of the relative dielectric
constant /spl epsiv//sub r/ and the resistivity /spl rho//sub
iso/. By optimization of the deposition process, /spl rho//sub
iso/=2/spl times/10/sup 10/ /spl Omega/m and a breakdown
voltage E/sub bd/=1/spl times/10/sup 7/ V/m were obtained at
4.2 K. For /spl epsiv//sub r/ a maximum value of 460 was
observed around 75 K. By the deposition of the trilayer
structure on bicrystal substrates, gated grain boundary
Josephson junctions (GBJs) were fabricated. High quality GBJs
have been obtained covered by a SrTiO/sub 3/ gate insulator
with a maximum change in the polarization of 0.08 C/m/sup
2/. |
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Josephson
properties of Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub y/ bicrystal
junctions grown by a sequential deposition technique using
molecular beam epitaxy
Kiejin
Lee, I. Iguchi, T. Ishibashi, K. Sato, H. Soutome and M.
Kawabe
Summary: We report Josephson and
crystallographic properties of the Bi/sub 2/Sr/sub 2/CaCu/sub
2/O/sub y/ junctions fabricated on MgO(100) bicrystal
substrates by a molecular-beam-epitaxy method incorporating
co-evaporation and sequential deposition techniques. With the
sequential deposition technique which has the advantage of
promoting the surface diffusion of adatoms, we obtained the
highly growth-controlled films without precipitation of any
second impurity phases. During the film growth, the sharp
reflection high-energy electron diffraction (RHEED) patterns
were also observed. However, the RHEED patterns showed the a-b
twin structures due to the lattice mismatch, which influenced
the Josephson transport properties at the junction boundary.
The normal resistance of the bicrystal junction was 1.5 /spl
Omega/ and the I/sub c/R/sub n/ product was 0.75 mV at 4.2 K.
The Shapiro steps under millimeter-wave irradiation were
clearly observed up to 65 K. The Josephson microwave
self-radiation spectra at receiving frequency f/sub REC/=22
GHz. The observed Josephson transport properties are discussed
in relation to the microscopic crystallographic
properties. |
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Conduction
mechanisms in c-axis oriented YBCO based trilayer junctions
with ferromagnetic A/sub 0.7/B/sub 0.3/MnO/sub 3/ manganite
barriers
M.A. Bari, O. Cabeza, L.
Capogna, P. Woodall, C.M. Muirhead and M.G.
Blamire
Summary: The mixed-valence manganites
(A/sub 0.7/B/sub 0.3/)MnO/sub 3/ are prospective barrier
materials for high-T/sub c/ junctions. They exhibit colossal
magnetoresistance (CMR) and are chemically and structurally
compatible with YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO). The
resistivity can be varied by an impressive 11 orders of
magnitude upon substitution of the cations A and B. We have
studied the magnetisation and resistivity of La/sub 0.7/Ca/sub
0.3/MnO/sub 3/ (LCMO) thin films in grown epitaxially with
YBCO by pulsed-laser deposition. We report here on the
fabrication of c-axis oriented YBCO trilayer junctions
employing LCMO as a barrier material. The crystal structure
and surface morphology of a series of heterostructures has
been studied using XRD and atomic force microscopy. The
current-voltage characteristics have been measured as a
function of temperature and magnetic field. In contrast to
previously reported results the resulting devices exhibit no
supercurrents. We propose the Glazman-Matveev inelastic
tunnelling via localised states as a possible conduction
mechanism for quasiparticle transport through the manganite
barrier. |
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Edge-like
planar sandwich-type junctions using a-axis oriented YBa/sub
2/Cu/sub 3/O/sub 7-x//insulator/YBa/sub 2/Cu/sub 3/O/sub 7-x/
trilayers
Gun Yong Sung and Jeong
Dae Suh
Summary: We have fabricated the
in-plane aligned a-axis oriented YBa/sub 2/Cu/sub 3/O/sub
7-x//LaSrGaO/sub 4//YBa/sub 2/Cu/sub 3/O/sub 7-x/
(YBCO/LSGO/YBCO) heteroepitaxial trilayers on LSGO (100)
substrates. A LSGO insulating barrier and top YBCO layer were
grown on the ion-beam etched in-plane aligned, a-axis oriented
YBCO bottom layer. Superconductor-insulator-superconductor
edge-like planar sandwich-type junctions using these a-axis
oriented YBCO/LSGO/YBCO trilayers had a superconducting
transition temperature of 84 K and revealed flux-flow type I-V
characteristics. |
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Magnetic
field modulation of critical currents in YBaCuO co-planar
Josephson junctions using focused ion
beam
Y. Soutome and Y.
Okabe
Summary: The YBa/sub 2/Cu/sub 3/O/sub
7-/spl delta// co-planar Josephson junctions by Focused Ion
Beam were fabricated by changing the width and the thickness
of a YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin film. The
magnetic properties of the junctions were measured at
different temperatures. In the junction with 300 nm thickness,
the magnetic field modulation of the critical current at 4.2 K
was not observed. Near the critical temperature of the
junction, the magnetic modulation curve was similar to that of
a dc-SQUID. From the SEM observation, some microshorts were
observed on the junction. In the junction with 200 nm
thickness, the I-V curve was changed from flux-flow junction
type to RSJ type. The magnetic modulation curve of the 7 /spl
mu/m wide junction at 4.2 K was similar to a Fraunhofer
pattern. Thus it is considered that the coupling region was
changed from a microshort to weak coupling region, when the
thickness of the YBaCuO film was decreased from 300 nm to 200
nm. |
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Nondestructive
detection of dislocations in steel using a SQUID
gradiometer
N. Kasai, N.
Ishikawa, H. Yamakawa, K. Chinone, S. Nakayama and A.
Odawara
Summary: We have developed a magnetic
flux imaging system. The magnetic flux image (MFI) shows the
distribution of magnetic flux density over a plate like
specimen. The change of the pattern in the MFI by tensile
deformation has been investigated in a carbon steel without
applying magnetic field using the system. A clear striped
pattern appeared after deformation by fine plastic strain
between 0.2 and 1.0% before strain-hardening. Luders bands,
which are groups of slip bands, appeared on the plate surface
and were observed at the corresponding locations of the
stripes in the MFIs. This shows that the fine deformation is
nondestructively detected using the MFI. |
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Materials
issues related to the fabrication of HTS
SQUIDs
S.G. Haupt, D.K. Lathrop,
R. Matthews, S.L. Brown, R. Altman, W.J. Gallagher, F.
Milliken, J.Z. Sun and R.H. Koch
Summary: A
number of materials related problems have hindered the
development of a reproducible process for the fabrication of
high-quality SQUIDs and magnetometers. In this paper we
discuss the use of GdBa/sub 2/Cu/sub 3/O/sub 7/ and YBa/sub
2/Cu/sub 3/O/sub 7/ thin films for the fabrication of
step-edge and bicrystal magnetometers and how materials
selection can influence issues such as reproducibility, yield
and noise performance. Magnetometers with noise performance as
low as 63 fT//spl radic/Hz have been made with variations in
junction parameters (I/sub c/ and R/sub n/) that are as low as
25% on-chip and 57% from chip-to-chip. |
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Wideband
front end for high-frequency SQUID
electronics
R.D. Penny, D.K.
Lathrop, B.D. Thorson, B.R. Whitecotton, R.H. Koch and J.R.
Rosen
Summary: We report the development of a
wide-bandwidth, low-noise front end to facilitate the high
frequency operation of both LTS and HTS DC SQUIDs. A
transformer of novel design non-resonantly matches the dynamic
impedance of the SQUID through a twisted pair to a
room-temperature amplifier. The amplifier uses active feedback
techniques to flatten the response of the signal path. When
operated in conjunction with the high frequency SQUID feedback
electronics (developed by IBM T.J. Watson Labs) with a
modulation frequency of 16 MHz, and a Quantum Design DC SQUID,
the system achieved a slew rate of 1.9/spl times/10/sup 6/
/spl Phi//sub 0/ s/sup -1/, a closed-loop performance of 5 MHz
and a noise level of 5.5 /spl mu//spl Phi//sub 0//(Hz)/sup
1/2/. The response from SQUID input to amplifier output was
relatively flat from 2 MHz to 25 MHz, with usable signal to 45
MHz. We believe the performance is limited by cabling and
expect significant improvements in miniaturized
design. |
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SQUID
gradiometers for a fundamental study of underwater magnetic
detection
M. Hirota, K. Nanaura,
Y. Teranishi and T. Kishigami
Summary: An LTS
SQUID gradiometer measuring six elements of first order
magnetic gradient was produced for a fundamental study of
magnetic detection and localization under water. It was
installed at the sea bottom shallower than 30 m and we
measured magnetic noise which might degrade its detecting
performance. Noise caused by the imbalance of the gradiometer
pickup coils was suppressed by using an auxiliary three-axis
SQUID magnetometer output. The imbalance parameters were
determined by measuring geomagnetic variations surrounding the
sea bottom. A test for the trial detection of an iron boat was
conducted with the use of this gradiometer. The results
obtained showed a high signal-to-noise ratio for the
gradiometer. |
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Angular
dependence of the symmetry of the order parameter in YBa/sub
2/Cu/sub 3/O/sub 7-/spl
delta//
Y. Gim, A. Mathai, R.
Black, A. Amar and F.C. Wellstood
Summary:
Using a 4.2 K scanning SQUID microscope, we examined
twinned thin-film YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//
(YBCO)-Ag-PbIn SQUIDs and measured the phase of the order
parameter in the YBCO for 13 different tunneling angles. We
have found that the order parameter in YBCO is time-reversal
symmetric and shows a d(x/sup 2/-y/sup 2/)-pairing symmetry,
provided the junctions are properly made. Detailed analysis of
our data reveals that any time-reversal breaking component is
less than 5%, which rules out states such as d(x/sup 2/-y/sup
2/)+ is or d(x/sup 2/-y/sup 2/)+ id/sub xy/. |
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HTSC
Josephson junctions and dc SQUIDs on SrTiO/sub 3/ bicrystal
substrates grown by floating zone
method
A.M. Balbashov, I.Yu.
Parsegov, E.K. Kovev, I.I. Vengrus, M.Yu. Kupriyanov, S.N.
Polyakov and O.V. Snigirev
Summary: A new
approach to the fabrication of a SrTiO/sub 3/ bicrystal
substrates, based on floating zone growth of natural SrTiO/sub
3/ bicrystals with misorientation angles 24/spl deg/ and
37/spl deg/, has been developed. Thin film YBCO Josephson
junctions and dc SQUIDs on SrTiO/sub 3/ bicrystal substrates
were fabricated and studied at T=77 K. The critical current
density j/sub c/ and I/sub c/R/sub n/ product for the
junctions with misorientation angle /spl alpha/=24/spl deg/
were close to 2/spl times/10/sup 4/ A/cm/sup 2/ and 190-260
/spl mu/V, respectively, while for /spl alpha/=37/spl deg/ it
was found that j/sub c//spl ap/2/spl times/10/sup 3/ A/cm/sup
2/ and I/sub c/R/sub n//spl ap/90-120 /spl mu/V. The dc SQUIDs
were made with typical inductances 20-80 pH, critical currents
of 20-150 /spl mu/A and resulting voltage modulation 10-40
/spl mu/V. Noise measurements performed at 77 K revealed low
1/f noise with cut-off frequency about 10 Hz. |
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Tunable
YBCO resonators on YIG
substrates
D.E. Oates, A. Pique,
K.S. Harshavardhan, J. Moses, F. Yang and G.F.
Dionne
Summary: A tunable stripline resonator
has been fabricated from YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO)
films deposited on single-crystal Y/sub 3/Fe/sub 5/O/sub 12/
(YIG) substrates. The films were deposited by laser ablation
and employ buffer layers for epitaxial growth. The surface
resistance of the YBCO on YIG has been measured independently
and is 5/spl times/10/sup -4/ /spl Omega/ at 10 GHz and 77 K.
The resonator is tuned with an external field that changes the
permeability of the YIG. At 77 K we have observed tunablity of
the fundamental (approximately 1.7 GHz in zero applied field)
and the overtone resonances of the stripline. A mode of
resonance frequency of 12 GHz has demonstrated tuning of 500
MHz for 500 Oe external field without appreciable degradation
of the Q which is about 1200. For 2 kOe the tuning range is
approximately 1 GHz. For higher applied fields the Q of the
resonance degrades significantly presumably because of
degradation of the surface resistance of the YBCO due to the
applied field. The measured Q in zero applied field is about a
factor of two to four lower than expected from the surface
resistance of the film indicating that losses in the YIG may
be affecting the performance. |
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Numerical
characterization of impedance transformers consisting of
vertically stacked superconducting transmission
lines
S. Kohjiro, T. Kikuchi, S.
Kiryu and A. Shoji
Summary: A novel coupling
configuration between an SIS mixer, an antenna, and a local
oscillator has been numerically characterized for an
integrated receiver operated in the sub-THz region. The
configuration consists of two vertically stacked
superconducting striplines, where the thickness of their
common electrode t/sub 2/ is of the order of its magnetic
penetration depth /spl lambda//sub 2/. It has been found that
the coupling efficiency between the antenna and the mixer
decreases with decrease of t/sub 2///spl lambda//sub 2/, while
that between the mixer and the local oscillator has a local
maximum. It is also shown that the coupling efficiencies
increase with decrease of Q/sub A/, the Q-factor due to the
tunneling loss in the mixer. For Q/sub A/=5.0 and 16, 75-85%
of the available signal power and sufficient power from the
local oscillator can be absorbed in the tunnel conductance of
the mixer at 1 THz. This coupling efficiency is equal to or
larger than that of a conventional planar
coupler. |
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Superconductor
ferrite phase shifters and
circulators
D.E. Oates, G.F.
Dionne, D.H. Temme and J.A. Weiss
Summary: We
have previously demonstrated high-T/sub c/
superconductor/ferrite nonreciprocal microwave phase shifters
that avoid dc magnetic-flux penetration of the superconductor
through a novel design of the magnetic circuit, and thus
operate with very low loss. Recently, a simplified magnetic
structure has been introduced, and devices with approximately
0.1 dB insertion loss with 500 degrees of phase shift (figure
of merit 5000 deg/dB) at 10 GHz and 77 K using YBCO have been
demonstrated. The same operating principles have been applied
to the design and fabrication of circulators. By combining
three low-loss phase shifters and three T junctions on a
ferrite substrate in a configuration with three-fold symmetry,
a three-port switching circulator has been demonstrated using
niobium at 4 K. The insertion loss is less than 1 dB, the
isolation greater than 20 dB, and switching time less than 1
/spl mu/s. The switching circulator can serve as a low-loss,
high-speed rf switch. Extension of this design to YBCO is
discussed. Higher performance, reduced weight and volume, as
well as lower cost are anticipated for microwave systems that
can benefit from such circulators and phase
shifters. |
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Full-wave
modeling of HTS dual-mode patch filters and staggered
coupled-line filters
A. Flores,
C. Collado, C. Sans, J. O'Callaghan, R. Pous and J.
Fontcuberta
Summary: In order to obtain
high-power handling, dual-mode patch HTS filters have been
analyzed through Green's function and desegmentation
techniques. A precise circuit model has been obtained and
applied to the filter design process, and useful design curves
relating filter parameters and physical dimensions of the
square patch have been plotted. Several designs have been made
using them and then optimized with the Method of Moments in
the Spectral Domain. For higher order circuits, staggered
coupled-line HTS filters have been considered. The designs
have been made using the method of moments to compute the
coupling capacitances, and then optimized with the Method of
Moments in the Spectral Domain. One dual-mode patch filter and
one staggered coupled-line filter have been fabricated on a
YBCO film. Measurements agree well with
simulations. |
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Influence
and evaluation of parasitic inductance in shunted Josephson
junctions
A.B. Cawthorne, C.B.
Whan and C.J. Lobb
Summary: The shunt
resistors used in many Josephson junction circuits contain an
inductive component that can significantly degrade
high-frequency performance. Numerical simulations reveal
complex dynamical behaviour, including relaxation
oscillations, period-doubling sequences, and chaos, all of
which are serious problems for applications as high-frequency
sources and detectors. This complex AC behaviour creates
features in the simulated DC current-voltage characteristics.
Since these simulations closely match experimental data, they
can be used to investigate the high-frequency AC behaviour of
real junctions. Thus, we are able to use simple DC
measurements to observe evidence of complex high-frequency
dynamics. The inductance of the shunt branch can be accurately
determined by comparing simulations to measurements.
Simulations also allow us to map regions of the parameter
space which exhibit complicated behaviour. These regions
should be avoided when a nearly sinusoidal voltage waveform is
desired, as is the case for Josephson junction-based
oscillators. |
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125%
bandwidth superconducting chirp
filters
H.C.H. Cheung, M.
Holroyd, F. Huang, M.J. Lancaster, B. Aschermann, M. Getta, G.
Muller and H. Schlick
Summary: A
previously-presented synthesis procedure is employed to design
ultra-wide bandwidth linear chirp (quadratic phase) filters.
The synthesis procedure eliminates the harmonic responses,
theoretically permitting a bandwidth close to 200% (i.e. the
frequency band zero to twice centre frequency) without
aliasing problems. It can also be configured so that the chirp
Fresnel ripples are relegated to the time domain. (This avoids
a large frequency domain ripple which in a low-loss device
would create the inadmissible requirement that gain at the
peak of the ripple be greater than unity.) The design
procedure is equally suitable for single and dual delay line
implementations. Measurements to be presented will be on
superconducting single-track coplanar and microstrip filters,
patterned from epitaxial YBCO films sputtered onto 2-inch
diameter LaAlO/sub 3/ substrates. They have a centre frequency
of 8 GHz, bandwidth of 10 GHz (125%), and a TB product of
80. |
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Optimization
of SrTiO/sub 3/ for applications in tunable resonant
circuits
R.E. Treece, J.B.
Thompson, C.H. Mueller, T. Rivkin and M.W.
Cromar
Summary: A series of SrTiO/sub 3/
(STO) films have been grown at a wide range of deposition
conditions in order to determine the optimal growth parameters
to maximize ferroelectric tuning while maintaining the lowest
dielectric losses. The deposition pressure of the ambient
O/sub 2/ (40 mTorr
a(bulk) at
higher pressures (P(dep)>65 mTorr). The dielectric constant
(/spl epsiv//sub r/) and loss tangent (tan/spl delta/) were
determined as a function of applied field at room temperature
(300 K) and at liquid nitrogen temperature (77 K). The low
frequency dielectric properties of the STO films were found to
be a weak function of the strain of the ferroelectric
film. |
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Bolometric
response of optically thick superconducting
films
J.D. Chern, H.C. Yang, Z.D.
Genchev, H.E. Horng and D. Dew-Hughes
Summary:
A one-dimensional heat conduction model is established
to interpret the chopping frequency dependence of the
bolometric response of optically thick superconducting films.
The key feature of this model is that it takes into account
the thermal boundary conductance of both the film/substrate
and the substrate/heat-sink interfaces. The model is found to
be suitable for both the strong and weak thermal coupling
cases. By comparing the results with a simplified bolometric
model, explicit expressions of the thermal conductance,
thermal capacitance, radiation absorption efficiency and
response time constant of the bolometric system have been
deduced, where the influences of the film, substrate and the
heat conduction boundaries are all considered. |
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High
T/sub c/ GdBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//
superconducting thin film
bolometers
Hong-Cheng Li,
Rui-Lang Wang, Fa-Bao Wan, Yi-Mei Ping, Guang-Sheng He and
Ming-Xiang Yu
Summary: Single element and
2/spl times/2 array bolometers have been prepared with
GdBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// superconducting thin
films on Zr(Y)O/sub 2/ single crystal substrates. The
bolometers are meander type with line width and distance of 10
/spl mu/m, the effective area is /spl phi/ 0.8 mm or 0.8/spl
times/0.8 mm/sup 2/. The resistance transition temperature of
the films is higher than 90 K and the transition width is less
than 2 K, after patterning by photolithography and wet
etching. The substrate was ground and polished to about 0.05
mm in thickness for reducing heat capacitance and increasing
the responsivity. The performances of the bolometers are NEP
of 3.8/spl times/10/sup -12/ WHz/sup -1/2/, normalized
detectivity D* of 1.7/spl times/10/sup 10/ cmHz/sup 1/2//W and
responsivity Rv of 3300 V/W. These properties did not degrade
after the bolometers were stored for 20 months under more than
40 warm-cold cycles. The properties of each element in the
2/spl times/2 array are comparable within 8%. |
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Response
of YBCO devices to mid-infrared
radiation
S.T. Ruggiero, C.
Zhong, K.J. Rennert, L.R. Vale and D.A.
Rudman
Summary: We present results on the
responsivity of YBCO thin-film devices to mid-infrared (25
/spl mu/m) radiation. Light is generated by pulsed diode-laser
sources monitored by a calibrated HgCdTe detector. For the
sample geometry studied here, we estimate an upper limit to
the low-frequency responsivity, R of /spl sim/1000
V/W. |
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Voltage-biased
high-T/sub c/ superconducting infrared bolometers with strong
electrothermal feedback
A.T. Lee,
J.M. Gildemeister, Shih-Fu Lee and P.L.
Richards
Summary: In the current generation
of high-T/sub c/ bolometers the thermal conductance is often
chosen for a short time-constant rather than for optimal
sensitivity. We describe a novel bolometer bias and readout
scheme that promises to relax this constraint. Voltage bias of
the superconductor results in strong negative electrothermal
feedback that greatly reduces the time-constant of the
bolometer. We estimate that a decrease of more than one order
of magnitude in time-constant should be possible with existing
high-T/sub c/ thermometers. We give theoretical estimates of
the performance gain with voltage bias for several bolometers
that have been reported in the literature. We find cases where
the sensitivity can be greatly improved (by changing the
thermal conductance) while holding the time constant fixed and
others where the bolometer can be made much faster while
maintaining the sensitivity. |
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Suspended
epitaxial YBaCuO bolometers on silicon and SIMOX
substrates
L. Mechin, J.-C.
Villegier and D. Bloyet
Summary: Suspended
epitaxial YBaCuO bolometers were successfully fabricated by
two silicon micromachining techniques. The first one used the
RIE (Reactive Ion Etching) of Si substrates and the second one
the etching of the SiO/sub 2/ layer in SIMOX (Separated by
IMplanted OXygen) substrates. Thermal conductances and time
constants of different suspended bridges fabricated by RIE
were measured as functions of length and width. The influence
of the materials constituting the membrane was discussed by
comparing a "RIE bridge" to a similar "SIMOX bridge". All
measurements were consistent with calculations from thermal
model. Experimental results and model lead to the optimization
of a 100/spl times/100 /spl mu/m/sup 2/ IR detector. Its
detectivity D*, measured at 85 K under irradiation from a
blackbody, was 2.5 10/sup 9/ cm/spl radic/(Hz)/W, with a time
constant of 564 /spl mu/s. These performances are among the
best reported for YBaCuO bolometers. |
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Antireflective
coating for BiPbSrCaCuO
sensors
S.N. Qiu, L.N. Phong and
I. Shih
Summary: The applications of high
T/sub c/ superconductors as transition edge bolometers or room
temperature thermopiles appear most promising at the long
infrared wavelengths. However, the sensor performance at these
wavelengths is impeded by the large reflectance of
superconductor films. In this work, effects of antireflective
coating on the performance of BiPbSrCaCuO sensors were
investigated. Thermal evaporation was used to deposit
semiconductor CdS onto sputtered BiPbSrCaCuO films. It was
found that, in order to achieve transparent and uniform CdS
coating, it was necessary to maintain the substrate
temperature at 180/spl deg/C during the evaporation. The
superconductivity of BiPbSrCaCuO appeared to be not degraded
by the deposition of CdS. After the deposition of CdS with a
nearly optimum thickness, the reflectance of BiPbSrCaCuO
sensor was reduced from 0.8 to below 0.4 for wavelengths above
10 /spl mu/m. In addition, the temperature coefficient of the
film resistance was seen to increase in the transition region.
The increases of film absorptance and resistance were
consistent with the change of bolometric responsivity of the
coated sensor. The use of Ge semiconductor for antireflective
coating was also studied. A reflectance of 0.16 was achieved
at wavelengths near 10 /spl mu/m on Ge coated sensors. This
small reflectance was in good agreement with predictions
derived from the computed optical constants of BiPbSrCaCuO
films. |
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High
frequency operation of Josephson vortex flow transistor with a
controlled damping
J.-C.
Villegier, S. Nicoletti, M.-C. Cyrille and R.
Chicault
Summary: Both HTS and LTS junctions,
respectively YBaCuO grain boundary junctions made on MgO
24/spl deg/ [001] tilted bicrystals and shunted Nb/AlOx-Al/Nb
"SNOP" tunnel junctions deposited on sapphire have been used
in asymmetrically biased Josephson vortex flow transistors
(JVFT). As shown previously by Gross et al. (1995), we verify
that the self field effect induced by current bias in
asymmetrically designed JVFT with large screening parameter
/spl beta//sub L/ can be used for increasing the current gain.
Gain of about 10 up to 77 K are obtained with practical YBaCuO
devices. High frequency operation of the devices has been
experimentally verified up to the MHz range and extrapolated
to GHz by using the control input gate coupled in a coplanar
configuration to the vortex flow SQUID array, while reasonable
values of transresistance, bandwidth and dynamical range are
observed. Influence of the damping on the JVFT performances
has been also studies experimentally by varying the subgap
resistance of the Nb tunnel junctions. Amplifiers made of
asymmetrical HTS JVFT may be competitive with SQUID or FET
amplifiers for NMR, Electromagnetic Compatibility or Infrared
imaging applications. |
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Transient
response of Josephson-coupled
multilayers
S. Lomatch and E.D.
Rippert
Summary: We investigate the response
of a Josephson-coupled multilayer to an ultra-short voltage
pulse. The response is understood in terms of the dynamics of
the phase differences across the layers, calculated from both
the microscopic theory and the resistively shunted junction
(RSJ) model. We discuss how such response might play a role in
novel multilayered switching devices for use in electronics
applications, such as flux quantum digital
circuitry. |
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New
vortex flow transistors made of YBa/sub 2/Cu/sub 3/O/sub y/
thin films
A. Fujimaki, M.
Kusunoki, M. Kito, S. Yoshida, H. Andoh and H.
Hayakawa
Summary: We have investigated the
performances of several types of vortex flow transistors
including nanobridge vortex flow transistors (NBVFTs) based on
a parallel array of nanobridges, planar Josephson vortex flow
transistors (planar JVFTs) based on a parallel array of grain
boundary Josephson junctions, and new JVFTs with a stacked
structure (stacked JVFTs). Considering the integration and the
reduction of the L/R time constant, the areas of the
transistors were restricted to less than 350 /spl mu/m/sup 2/.
A NBVFT showed a flux-to-voltage transfer function of 2.6
mV//spl Phi//sub 0/, which was one order of magnitude larger
than that of the other transistors. In contrast, the NBVFTs
showed a very small current gain due to a large kinetic
inductance of a nanobridge, while the NBVFT had the smallest
area among the three. A planar JVFT with asymmetric geometry
was easy to fabricate and showed a current gain of 2.2 at 4.2
K. However, the planar JVFT requires a large area, leading to
a long response time other than the internal delay time. A
stacked JVFT also showed a current gain of 2.5 at 4.2 K. A
layered structure yielded a strong coupling between the body
of the JVFT and the control line. Due to this strong coupling,
the response time of the stacked JVFT was considerably
improved compared to that of the planar JVFT. |
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A
new three terminal vortex flow device
[YBCO]
A. Davidson and N.F.
Pedersen
Summary: Part of the reason for the
failure of magnetically controlled Abrikosov vortex flow
devices has been low magnetic coupling coefficients, combined
with pinning: control currents tend to drive the control
electrode normal before sufficient flux is coupled to the flux
flow channel to overcome pinning. We have observed that
interesting devices may use direct injection of flux, without
an isolated control electrode. Experimental studies using
opposite polarity currents show dramatic effects in device
characteristics; simulations show that these effects are
manifestations of vortex interactions. |
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Design
and implementation of a dual-control active device using YBCO
grain-boundary junctions
T.
Nguyen, B.A. Davidson, G.A. Daniels, J.B. Beyer and J.E.
Nordman
Summary: We propose a dual-control
active device based on overdamped long junctions. In analogy
to the semiconductor dual-gate field effect transistor which
can be considered a cascode (output terminals in series) of
two single-gate FETs, the dual-control device consists of two
single devices in parallel at the outputs. The transresistance
of one device is shown to be a linear function of the second
control current over a sizable range. This unique feature
makes the dual-control device highly desirable for
applications such as gain control and mixing, Active devices
have been fabricated using arrays of YBCO bi-crystal
grain-boundary junctions. Tight coupling of the control fields
to the array was achieved by injecting the control current
into an "ear" structure at one end of the array. The
large-signal current gain, however, is less than 1 due to the
asymmetric bias and end injection. Improved current gain with
tight coupling to the entire array is necessary for a
practical dual-control device. |
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Mutual
phase-locking of fluxons in stacked long Josephson junctions:
simulations and experiments
G.
Carapella, G. Costabile, G. Filatrella, M.H. Manscher, J.
Mygind, M.A. Nordahn, N.F. Pedersen and A.
Petraglia
Summary: We report on the
experimental observation of reciprocal phase-locking in
stacked Nb-AlO/sub x/-Nb Josephson junctions having overlap
geometry. When the junctions are independently biased in zero
external magnetic field, they each exhibit several Zero Field
Steps. Biasing both the junctions on the Zero Field Steps, one
with constant current while the other is swept along the step,
we have observed phase-locking between the fluxons in the two
junctions and measured the phase-locking range. We have found
that the bound state can be very stable, and that the stack
exhibits the same features reversing either the polarity of
the bias current or the role of the junctions. An analogous
investigation of the effect of the magnetic field on the
stability of the bound state has been performed. Numerical
simulations have shown that the underlying dynamics
corresponding to this situation is a bound state of a
fluxon-antifluxon pair. Finally, the effect of rf radiation on
the junctions has been investigated. |
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Electronic
cooling in Nb/AlO/sub x//Al/AlO/sub x//Nb double tunnel
junctions
L. Capogna, G. Burnell
and M.G. Blamire
Summary: Several recent
papers have predicted the feasibility of superconducting
tunnel junction-based electronic cryocooler devices operating
in the temperature range 0.1-4 K. We have extended previous
work in stacked Nb/AlO/sub x/ devices to investigate the
nonequilibrium effects in them and to examine the influence of
barrier conductance and layer thickness on the electronic
cooling achievable by this technique. We have also analysed
the maximum cooling possible with junctions of our present
conductance. |
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Analysis
of the interfaces of stacked Josephson junctions by atomic
force microscopy
V. Lacquaniti,
S. Maggi, E. Monticone and R. Steni
Summary:
The surface properties of vertical stacks of
Nb/(Al-AlO/sub x//Nb)/sub n/ Josephson junctions have been
investigated by Atomic Force Microscopy (AFM). The results
indicate that the roughness of the AlO/sub x/ layers is nearly
constant and independent of the surface features of the
underlaying Nb films. The superposition of several Nb and
Al-AlO/sub x/ films has an overall smoothing effect on their
surfaces, as indicated by the strong reduction of the rms
roughness in a stack of junctions with respect to that of the
base Nb film. The height-height correlation function shows
that the rms roughness increases on small sampling lengths
l(l<20 mm) as l/sup /spl alpha// with /spl alpha//spl
ap/0.85 for both Nb and AlO/sub x/. The interface profiles
between the Al-AlO/sub x/ and Nb electrodes have been
reconstructed from AFM data, and a reasonable agreement with
anodization spectroscopy profiles has been
found. |
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Stacked
niobium Josephson junction arrays under x-band
irradiation
A.M. Klushin, S.
Schornstein, H. Kohlstedt, G. Wende, F. Thrum and H.-G.
Meyer
Summary: Stacked Josephson junction
arrays located at the rf current antinodes of a
superconducting microstripline resonator were investigated.
The circuits were designed to obtain highly accurate voltages
at cm-waveband microwave driving and low rf-power level.
Nb-Al/AlO/sub x/-Nb Josephson junctions with tunneling area of
60 /spl mu/m/spl times/300 /spl mu/m and critical current
density up to 7 A/cm/sup 2/ were used. We compared the average
voltages of the rf induced maximal current steps in arrays
with up to three junctions per stack. Quantized current steps
up to 300 mV were observed under microwave irradiation at
frequency of 19.20 GHz in circuits with 384 three-junction
stacks. The dynamics of stacked tunnel junctions in the
presence of rf-currents will be discussed with respect to
application as voltage standards. |
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Fabrication
and characteristics of vertically stacked NbCN/MgO/NbCN
Josephson junctions with thin intermediate
electrodes
T. Kikuchi, S. Kiryu,
S. Kohjiro, Q. Wang, A. Shoji, S. Sato and S.
Nagao
Summary: Vertically stacked
NbCN/MgO/NbCN Josephson junctions with thin intermediate
electrodes (2 nm-11 nm) have been fabricated on a wafer in a
computer-controlled sputtering. The tunneling characteristics
of fabricated junctions have been evaluated as functions of
the number of stacks and thickness of intermediate electrodes
d. As a result, it has been found that the energy gap for
intermediate electrodes reduced with d linearly depending on
1/d. The junction quality parameter R/sub SG//R/sub N/
gradually decreased with d. |
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Magnetic
field dependence of thermal excitations in Josephson
junctions
M.G. Castellano, G.
Torrioli, C. Cosmelli, F. Chiarello, M. Cirillo, P. Carelli
and G. Rotoli
Summary: We have measured the
rate of escape out of the zero-voltage state in Josephson
tunnel junctions as a function of the applied magnetic field.
A marked difference is found in the behaviour of long and
small junctions. In all cases, the statistical distribution of
the switching currents can be described using a Kramers model
for the escape process, where the barrier to be overcome is
the Josephson barrier and the activation energy is due to an
effective temperature T/sub e/. For small junctions T/sub e/
coincides, as expected, with the thermodynamic temperature,
regardless of the applied magnetic field. For long junctions
instead it is found that the escape temperature depends
markedly on the magnetic field and on the junction geometry
(inline or overlap), suggesting a close relationship with the
magnetic field distribution inside the junction. |
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Constant-voltage
steps in arrays of Nb-PdAu-Nb Josephson
junctions
S.P. Benz and C.J.
Burroughs
Summary: Design and fabrication of
Nb-PdAu-Nb trilayer Josephson junctions are described. The
microwave response of an array of 1000 of these junctions was
measured, and constant-voltage step heights mere characterized
as a function of the microwave amplitude and frequency.
Experimental results fit well to point-junction simulations at
the 3 GHz design frequency of the microwave distribution
network. The observed step height of 3.8 mA shows that the
array and microwave distribution are sufficiently uniform for
application in programmable Josephson voltage
standards. |
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Shot
noise properties of superconducting quasiballistic
contacts
Y. Misaki, A. Saito, S.
Anezaki and K. Hamasaki
Summary: Experiment
and analysis have been done to show that the low frequency
voltage noise properties of a current-biased
Nb-(constrictions)-NbN (S-c-S') contacts is well described by
existing theories of a mesoscopic two-terminal conductor. The
quasiparticle characteristics of the S-c-S' which has
adjustable current-voltage curve is also well analyzed using
the theory based on the single Andreev reflection model
without heating. In the clean S-c-S' contacts, there is no
measurable excess noise contribution associated with the
Andreev reflection itself. |
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Magnetic
field behavior of vertical stacks of Josephson junctions with
large idle regions
D. Andreone,
V. Lacquaniti, S. Maggi, E. Monticone and R.
Steni
Summary: We report first measurements
of the magnetic field dependence of the critical currents of
vertical stacks of two Nb/Al-AlO/sub x//Nb Josephson junctions
with large idle regions. We kept constant the width of the
lateral idle region and changed the ratio of the longitudinal
idle part to the junction length. To provide a close coupling
of the two junctions of the stack, the thickness of the
intermediate Nb electrode was smaller than the London
penetration depth. The effect of the idle region on the
magnetic behavior of the stack is discussed. In same
experiments, a clear and nearly periodic current locking
effect has been observed, that was independent of the
dimensions of the idle region. |
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Power
handling capability improvement of high-temperature
superconducting microwave
circuits
Zhi-Yuan Shen, C.
Wilker, P. Pang, D.W. Face, C.F. Carter III and C.M.
Harrington
Summary: The focus of High
Temperature Superconducting (HTS) microwave circuit
development has now shifted to improving the high power
handling capability. This paper reviews our latest results in
this area including: HTS material improvement; new concepts
and rules for HTS high power circuit design; and the latest
high power filter test results. For HTS materials, the surface
resistance versus rf magnetic field test results and the third
harmonic test results for both YBa/sub 2/Cu/sub 3/O/sub 7/ and
Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub 8/ thin films are
presented. For HTS microwave circuits, novel design concepts
and rules for high power HTS filters are discussed. Several
compact planar HTS filters were designed, fabricated, packaged
and tested. The performance of a 3-pole, 1.3% equal-ripple
bandwidth planar HTS filter showed no measurable degradation
for transmitted power levels up to 74 watts at 77 K. The
performance of a 2-pole, 1% equal-ripple bandwidth planar HTS
filter showed no measurable degradation for transmitted power
levels up to 115 watts at 77 K. To our knowledge, these test
results represent the highest power handling of compact planar
HTS filters operating at 77 K, sufficient for use in
telecommunication transmitters. |
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Optically
tuned propagation delay in Y-Ba-Cu-O superconducting delay
lines
Shinho Cho and H.R.
Fetterman
Summary: An optoelectronic
technique was used to study the optical tuning of electrical
picosecond pulses propagation in YBa/sub 2/Cu/sub 3/O/sub 7-x/
superconducting delay lines. The propagation time through the
delay lines was monitored as a function of the optical pulse
energy incident on the superconducting thin film. The optical
excitation consists of two 70 ps laser pulse trains at a 76
MHz repetition rate, generated by a mode-locked laser. One
pulse train was used to pump a dye laser, while the second was
used to illuminate the superconducting delay lines. The
measured propagation time is well described by a squared
dependence on the applied optical pulse energy. In addition,
optically induced changes in the resonant frequency were
investigated by using a resonator technique in the frequency
domain. |
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HTS/ferroelectric
devices for microwave
applications
S.S. Gevorgian, E.F.
Carlsson, S. Rudner, U. Helmersson, E.L. Kollberg, E. Wikborg
and O.G. Vendik
Summary: High Temperature
Superconducting (HTS, e.g. YBCO) microwave devices based on
bulk or thin film ferroelectrics (e.g. Strontium Titanate-STO)
are studied theoretically and experimentally. YBCO/STO/YBCO
parallel-plate resonators and based on bulk single crystal STO
are for electrically tunable high power filters, phase
shifters and other devices in the frequency band 0.5-2.0 GHz
of advanced microwave communication systems. Thin film
YBCO/STO Inter-digital Capacitors (IDC), Coplanar Waveguides
(CPW) phase shifters/delay lines are also designed and studied
experimentally for low microwave power applications. Modelling
problems of these devices and microwave losses in
ferroelectrics are also discussed. |
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Wideband
compressive receiver based on advanced superconductor and
semiconductor circuits
W.G.
Lyons, D.R. Arsenault, C.L. Keast, D.C. Shaver, R. Berger,
A.C. Anderson, P.G. Murphy, T.C.L.G. Sollner and R.W.
Ralston
Summary: A novel compressive
cryoreceiver architecture has been proposed combining analog
HTS, cryoelectronic, and advanced high-speed GaAs and
high-speed/low-power SOI CMOS semiconductor technologies. The
proposed receiver will rival the sensitivity of narrowband
receivers while providing unprecedented wideband instantaneous
frequency coverage with very small size, weight, and power
requirements. Future developments will extend the bandwidth
capability. HTS tapped-delay-line chirp filters are the
enabling technology for instantaneous bandwidths greater than
1 GHz. The filters support dispersive delays as long as 40 ns
and time-bandwidth products in excess of 100 using a
bonded/thinned-wafer technique to fabricate YBa/sub 2/Cu/sub
3/O/sub 7-/spl part// stripline structures on 125-/spl
mu/m-thick, 5-cm-diam LaAlO/sub 3/ substrates. The filters
have produced better than -18-dB error sidelobes in a receiver
configuration. Preliminary work toward SOI CMOS receiver ASICs
is reported. These ASICs will perform pulse data thinning, and
binary integration functions. Requirements for A/D converters
are discussed. |
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An
SFQ digital to analog
converter
R.D. Sandell, B.J.
Dalrymple and A.D. Smith
Summary: We have
developed and demonstrated a digital to analog converter DAC
which uses an SFQ counter to precisely divide an input
reference oscillator to produce a set of binary
frequencies/voltages. The binary input gates the output SFQ
pulses of the counter flip flops to a passive summing network,
producing an analog output current. The DAC is asynchronous
(no clock to reset latching circuits), low power, and requires
only N equal matched resistors. We have built and tested a
4-bit Nb DAC with data clocking rates up to 1 GHz. Using the
DAC we have generated arbitrary wave forms including ramps and
sine waves. By measuring the harmonic content of sine wave
outputs, we deduce values for the DAC linearity. |
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SNS
programmable voltage
standard
C.A. Hamilton, S.P.
Benz, C.J. Burroughs and T.E. Harvey
Summary:
Superconductor-Normal-Superconductor (SNS) junctions
have been used in the design and fabrication of a 1-V rapidly
programmable voltage standard. The superconducting circuit is
a series array of 32 768 Nb-PdAu-Nb junctions with taps that
divide the array into a binary sequence of smaller array
segments with a minimum segment size of 128 junctions. The
16-GHz drive frequency is set by the characteristic frequency
of the junctions. A computer-controlled 8-channel bias system
controls the current in each segment and allows the rapid
selection of any one of 513 discrete voltage levels. The
system is designed for fast dc measurements and the synthesis
of precise ac waveforms. |
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Single
flux quantum circuits for 2.5 Gbps data
switching
A. Hodge Worsham, A.H.
Miklich, D.L. Miller, Joonhee Kang and J.X.
Przybysz
Summary: We have designed and
measured single flux quantum (SFQ) circuits for data switching
at 2.5 Gbps. A fully functional 2/spl times/2 switching node
is presented. The node can be used to form a larger switching
fabric (4/spl times/4, 8/spl times/8, etc.). The node accepts
data streams at either or both inputs, routing the data based
on address bits present in the data stream. This approach
allows the data to be self-routing and the switch to be
self-synchronous. In addition, the switch can route data
correctly on an active input line if the other is
idle. |
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Decimation
filter with novel MVTL XOR
gate
Y.P. Xie and T. Van
Duzer
Summary: A single-rail Modified
Variable Threshold Logic (MVTL) decimation filter is designed
by employing a novel XOR gate, which overcomes the difficulty
of the lack of a good inverter in the MVTL logic family. A
10-bit deep-pipelined decimation filter consisting of about
700 junctions in a 5 mm/spl times/5 mm chip with power
consumption of 0.4 mW is designed. |
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Multi-gigahertz
operation of 3-junction-interferometer-based Josephson
latching logic circuits
W. Hioe,
M. Hosoya, S. Kominami, H. Nagaishi and T.
Nishino
Summary: Josephson latching logic
gates require an ac power supply for correct operation. Owing
to the difficulty in fabricating Josephson regulators for
large power currents, multi-phase sinusoidal power supply is
the preferred method for multi-gigahertz operation. However,
the inherently variable ac power reduces device margin for
covering process variations. As a result, there exists a
strong relationship between circuit size, maximum operating
frequency and circuit throughput for a given available margin.
The trade-offs between these performance criteria are analyzed
for 3-junction-interferometer-based logic gates. Experimental
evaluation of the multi-gigahertz operation of small circuits
showed that careful design of power supply networks that
reduce power supply fluctuations will be needed to maximize
performance. Simulation and experimental results are
discussed. |
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Mixed
analog-digital niobium superconductive circuits for a
2-gigachip-per-second spread-spectrum
modem
J.P. Sage and D.A.
Feld
Summary: This paper describes the
architecture and operation of a superconductive programmable
matched filter that provides rapid synchronization information
and data demodulation for a 2-GHz spread-spectrum modem.
Results are reported for the first circuit fabrication runs
using a new doubly planarized process. With the exception of
circuits containing layout errors, all circuits have performed
as intended and with characteristics that match well the
predictions of JSIM simulations. The MVTL digital components
and the buffer between the digital and analog circuits have
been demonstrated for the first time. The seven-stage MVTL
shift register in a complete prototype filter was operated at
1 GHz. In addition, combinations of (1) the MVTL digital shift
register and the buffer and (2) the buffer and the T/H cell
have been operated successfully, demonstrating that all of the
components in the filter core will work
together. |
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Asymmetric
YBaCuO interferometers and SQUIDs made with focused
electron-beam irradiation
junctions
D.F. Moore, A.J. Pauza,
W.E. Booij, M.G. Blamire, K. Herrmann, F. Baudenbacher, T.
Harnisch, J.F. Walker, N. Cade and D.
Jedamzik
Summary: We report the fabrication
and testing of compact interferometers operating at
temperatures up to 60-80 K. Focused electron-beam irradiation
Josephson junctions are made in YBaCuO, and a focused ion beam
is used for precise etching of the tracks of superconductor.
The SQUID characteristics and the properties of coupled
superconducting loops are promising for applications such as
comparators for analog/digital converters. Focused ion beam
trimming of circuit elements is particularly useful for
prototyping devices and for defining the small inductors
required in circuits for high temperature
operation. |
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Tl/sub
2/Ba/sub 2/CaCu/sub 2/O/sub 8/ films: Growth and applications
in dc SQUIDs and microwave
devices
Y.F. Chen, Z.G. Ivanov,
L.-G. Johansson, R.I. Kojouharov, I.M. Angelov, E. Olsson,
V.A. Roddatis, E.A. Stepantsov, A.Y. Tzalenchuk, A.L. Vasiliev
and T. Claeson
Summary: Tl-2212 thin films
were grown ex situ in a two step process on a variety of
substrates, including ones with artificially introduced high
angle steps. Grain boundary weak links were formed on
LaAlO/sub 3/ substrates with steps and on bicrystal substrates
and were employed in dc SQUIDs. The white noise level of the
SQUIDs was 50/spl mu//spl Phi//sub 0///spl radic/(Hz) at 77 K.
A 12.5 GHz HEMT oscillator stabilized with a Tl-2212 resonator
gave 8-10 dB lower phase noise than using a gold
resonator. |
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High-T/sub
c/ superconductor-normal-superconductor junctions with
polyimide-passivated ambient-temperature edge
formation
J.B. Barner, A.W.
Kleinsasser and B.D. Hunt
Summary:
Superconductor-Normal-Superconductor (SNS) edge
Josephson Junctions (JJs) continue to be a focus of high-T/sub
c/ superconductor (HTS) electronics development. The ability
to form clean edges in HTS materials is essential for
successful SNS edge JJs as well as crossovers and via
contacts. We report a novel SNS JJ fabrication process in
which a YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta///SrTiO/sub 3/
base electrode/insulator bilayer coated with a polyimide
passivation layer is rotated during Ar ion milling through a
reflowed photoresist mask to form omnidirectional edges. No
sample cooling is used during milling. YBa/sub 2/Cu/sub
2.8/Co/sub 0.2/O/sub 7-/spl delta// normal layers and YLa/sub
0.05/Ba/sub 2/Cu/sub 3/O/sub 7-/spl delta// counter-electrodes
completed the SNS JJ's. Devices fabricated using this
polyimide passivation layer have significantly smaller spreads
in critical current and resistance than those processed
without it. |
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Ba/sub
1-x/K/sub x/BiO/sub 3/ thin films and grain boundary junctions
prepared on MgO substrates
S.
Imaeda, M. Inoue, A. Fujimaki and H.
Hayakawa
Summary: We have made grain boundary
junctions of Ba/sub 1-x/K/sub x/BiO/sub 3/ thin film deposited
on MgO bicrystal substrate. A high initial deposition
temperature yielded superconductive Ba/sub 1-x/K/sub x/BiO/sub
3/ films from powder targets. We observed clear energy gap
structure in the current-voltage characteristics of these
junctions. In the high frequency radiation (10.5 GHz), Photon
Assisted Tunneling was observed. |
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Improvement
of junction properties of YBaCuO/PrBaCuO/YBaCuO trilayer
Josephson junctions
H. Sato, S.R.
Gjoen, H. Akoh, N. Nakamura and K. Hara
Summary:
We have demonstrated improvement of junction properties
for YBaCuO/PrBaCuO/YBaCuO trilayer junctions, using a backing
plate of Al and Cu stacked foils between substrate and sample
holder to ensure uniform substrate temperature during
deposition of trilayer films, and by controlling film
composition precisely to reduce the precipitated particles on
the surface of the films. All junctions with a barrier
thickness of 35 nm and dimensions of less than 10 /spl
mu/m/spl times/10 /spl mu/m showed RSJ-like current-voltage
characteristics with some excess currents at 4.2 K. Typical
values of Josephson critical current density J/sub c/ as
measured using a magnetic modulation of total critical current
density, and normalized junction resistance R/sub n/A were
2.4/spl times/10/sup 3/A/cm/sup 2/ and 1.8/spl times/10/sup
-7//spl Omega/cm/sup 2/ at 4.2 K, respectively. For the 88
junctions on the substrate, the 1-/spl sigma/ spreads of J/sub
c/ and R/sub n/A were obtained to be 34% and 25%,
respectively. |
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Size,
order, and interface effects on PrBa/sub 2/Cu/sub 3/O/sub 7/
barriers
M.I. Faley, U. Poppe,
C.L. Jia and K. Urban
Summary: The
artificially varied structural quality of interfaces
significantly affects the transport properties of YBa/sub
2/Cu/sub 3/O/sub 7/-PrBa/sub 2/Cu/sub 3/O/sub 7/-YBa/sub
2/Cu/sub 3/O/sub 7/ junctions. The mechanism of conductivity
changes from a semiconducting-like to a metal-like one with an
improvement of the interface quality, the microstructure of
the materials and the reduction of the barrier thickness. The
proposed model including a carrier induced superconductivity
and a bending of the electronic bands at the interfaces gives
a satisfactory explanation of the experimental
results. |
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High-resistivity
SNS Josephson junctions scribed in YBa/sub 2/Cu/sub 3/O/sub
7-/spl delta// by electron
irradiation
B.A. Davidson, B.
Hinaus, M. Rzchowski, K. Siangchaew, M. Libera and J.E.
Nordman
Summary: We demonstrate that the
behavior of Josephson junctions scribed in YBa/sub 2/Cu/sub
3/O/sub 7-/spl delta// (YBCO) with a high-brightness electron
source are described well by conventional
superconductor-normal-superconductor (SNS) theory. These
junction characteristics include a fully normal interlayer
(T/sub cN/=0), intermediate length (L//spl xi//sub n/(T/sub
c/)/spl ap/8-10), and a reduced order parameter at the SN
interface. Consistent application of this model of diffusive
transport across a metallic interlayer in the dirty limit
requires a reduced carrier concentration in the irradiated
region, a junction length L/spl ap/5 nm, and a normal
resistivity near the metallic limit. I/sub c/R/sub n/ products
higher than 3 mV at low temperatures are
observed. |
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A
high-T/sub c/ Josephson junction on a narrow tungsten line
formed by focused ion beam-chemical vapor deposition [of
NdBaCuO]
S. Morohashi, T. Utagawa
and Y. Enomoto
Summary: We have fabricated
two types of high-T/sub c/ Josephson junctions using a focused
ion beam technique. High-T/sub c/ junctions fabricated using a
narrow-focused Ga-ion beam to damage a substrate, resulting in
a geometrical defect prior to high-T/sub c/ layer deposition,
show flux flow-like characteristics for the SrTiO/sub 3/
substrate. The current-voltage characteristics of the
junctions which are fabricated on a narrow tungsten (W) metal
layer deposited on both MgO and SrTiO/sub 3/ substrates using
a focused ion beam chemical vapor deposition technique are
qualitatively consistent with a resistively shunted junction
model and show Shapiro steps under microwave
irradiation. |
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A
61-channel SQUID system for MEG measurement cooled by a GM/JT
cryocooler
K. Sata, S. Fujimoto,
N. Fukui, E. Haraguchi, T. Kido, K. Nishiguchi and Y.M.
Kang
Summary: A SQUID-based MEG measurement
system cooled by a GM/JT cryocooler have been developed. The
system consists of 61 channels of axial gradiometers arranged
on a spherical surface, and thus can conform to a human head.
The white noise level of the system is in a range between 12
and 18 fT/Hz/sup 1/2/. The noise from the cryocooler
controlled to a level of 15 pT by several improvements to the
cryostat (e.g., using low electrical conductivity material).
Since the latter noise have a periodic characteristics, it can
be reduced by using a "noise template" (i.e., a digital
process using a computer). The system is described here, and
its performance demonstrated by using it to measuring the
faint biomagnetic fields from a human brain. |
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The
properties of HTS Josephson junctions and DC SQUIDs fabricated
on MgO bicrystals
E.J. Romans,
T.G. Henrici, C. Carr, J.C. MacFarlane, C.M. Pegrum and G.B.
Donaldson
Summary: We have fabricated HTS
Josephson Junctions and DC SQUIDs using MgO bicrystals and
YBCO thin films grown by PLD. The electrical and noise
properties of the junctions have been measured. The SQUIDs
have been designed and fabricated for use in our NDE
programme. For this reason, their performance in unshielded
environments is discussed here. |
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Optimization
of a SQUID system for space
J.M.
Lockhart, B. Muhlfelder, G.M. Gutt, M. Luo, R.C. Clappier,
T.R. McGinnis and G.R. Smith
Summary: We have
optimized a sensitive SQUID measurement system for use in a
space flight experiment in the presence of significant
interference from other sub-systems and the perturbing effects
of EMI and thermal fluctuations. We will describe developments
including a sapphire carrier for the SQUID chip, a precision
temperature controller for the SQUID, control electronics with
high bandwidth and enhanced thermal stability, and special
shielding and filtering techniques used to increase EMI
resistance. |
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Tightly
coupled dc SQUIDs with resonance
damping
R.H. Ono, J.A. Koch, A.
Steinbach, M.E. Huber and M.W. Cromar
Summary:
We have reduced the effect of resonances on washer
style dc SQUIDs coupled to input flux transformers and
analyzed our damping structures using a distributed circuit
model. A resistance of 1/spl Omega/ is placed across each turn
of a 137-turn coil coupled to a planar washer dc SQUID
reducing the structure in the voltage-flux curve thus
extending the range of current biases over which the device
operates. The energy sensitivity of the SQUID is predicted to
not be degraded by the intracoil resistors. |
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A
dc SQUID-based magnetic microscope study of the magnetic
properties of the Ni thin
films
S.A. Gudoshnikov, N.N.
Ukhansky, I.I. Vengrus, K.E. Andreev, A.M. Tishin and O.V.
Snigirev
Summary: We have applied a developed
HTS dc SQUID based magnetic microscope for study of the
magnetic properties of ultrathin Ni films. A magnetic moment
sensitivity close to 10/sup -15/ A.m/sup 2//Hz/sup 1/2/ has
been obtained at 77 K. The space resolution was determined at
level of 100 /spl mu/m by the separation between the SQUID and
the studied film surface. One-domain structure, in-plane
orientation of magnetic moment and ferromagnetic-like ordering
in 26 /spl Aring/ thick film were found. An absolute value of
the film magnetic moment has been estimated. |
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Multichannel
heart scanner based on high-T/sub c/
SQUIDs
H.J.M. ter Brake, N.
Janssen, J. Flokstra, D. Veldhuis and H.
Rogalla
Summary: A 7-channel magnetometer for
magnetocardiography based on high-T/sub c/ SQUIDs has been
realized. This magnetometer is used for test experiments in
the development of a multichannel high-T/sub c/ SQUID based
heart-scanner for clinical applications. The intrinsic noise
level of the channels in the 7-channel system is typically 120
fT//spl radic/(Hz) down to 1 Hz. Magnetocardiograms were
recorded inside a magnetically shielded room. Introductory
experiments were performed on the suppression of noise by
combining magnetometers to form planar gradiometers. The noise
suppression that can be established appeared to be limited by
the imbalance of the gradiometric configuration, which is
roughly 2%. This relatively poor balance of the system is
caused by inaccuracies in the transfer functions of the
individual SQUID magnetometers, and by deviations from the
planar geometry. |
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Magnetic
hysteresis in YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//
magnetometer sense loops
J.W.
Purpura and R.F. Wiegert
Summary: We have
measured the magnetic hysteresis of a YBa/sub 2/Cu/sub 3/O/sub
7-/spl delta// thin-film magnetometer test sample at 77 K for
applied magnetic field ramp amplitudes up to 1 mT. The test
sample was designed with two distinct SQUID magnetometer input
sense loops connected in series with each other and also with
an output washer located outside of the magnetic field
application region. In addition to permitting fields to be
applied to the input loops in the same direction, as in a
conventional magnetometer arrangement, this sample design
allowed opposing fields to be applied to the loops, providing
a measure of hysteresis behavior expected for a gradiometer
loop. The fractional hysteresis in the loops for field
excursions of 100 /spl mu/T, as encountered for rotation in
the Earth's field, was 2.1/spl times/10/sup -5/ for the
gradiometer mode measurement, and 3.5/spl times/10/sup -4/ for
a magnetometer measurement. We found that hysteresis measured
with the sample cooled down in a 50 /spl mu/T field was
identical to that measured with the sample cooled in "zero
field". |
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Power
dependence of microwave Z/sub s/ in high-T/sub c/ Josephson
junctions: Measurements and
modeling
Y.M. Habib, D.E. Oates,
G. Dresselhaus and M.S. Dresselhaus
Summary:
The nonlinear power dependence of the microwave
frequency surface impedance of high-T/sub c/ superconductors
remains inadequately understood, thus limiting device
applications. It is believed that weak links, grain
boundaries, and other material defects exhibiting Josephson
junction behavior are a source of the nonlinear behavior.
Using a stripline-resonator technique, we have performed
microwave measurements of the resistive and reactive
components of the impedance as a function of input power,
frequency, temperature, and dc applied magnetic field. The
results are compared to a resistively shunted junction (RSJ)
model that yields excellent agreement at low and intermediate
values of the input current. The values of I/sub c/ and R/sub
n/ from dc transport measurements are compared to the rf
values obtained from fitting data using the RSJ
model. |
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Characteristic
impedance of a microwave transmission line using a Tl/sub
2/Ba/sub 2/CaCu/sub 2/O/sub x/ superconductor on a MgO
substrate
K. Shimaoka, M. Nemoto,
S. Yoshikawa, I. Yoshida and Y. Yoshisato
Summary:
Characteristic impedance of microstrip lines having a
Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub x//MgO/Au structure is
measured using a low-temperature vector network measuring
system. A small test fixture for the superconducting
microstrip lines is fabricated and mounted on a cryocooler. A
correction method is applied to the data at low temperatures
and the characteristic impedance of the superconducting
microstrip lines is determined from the corrected data at 80
K. |
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Magnetic
shielding effect of multiple-layer thin superconducting plates
by T-method
A. Kamitani, M.
Shibata and S. Ohshima
Summary: The magnetic
shielding effect of superconducting plates is investigated by
means of the numerical simulation. Shielding plates are
assumed to have a multiple-layer structure and each layer is
assumed to be thin enough. As the critical state model of the
superconductor, a modified Bean model is adopted so that the
current density may not exceed the critical one. Under these
assumptions, the governing equation of the shielding current
is expressed in terms of the normal component of the current
vector potential. A two-dimensional numerical code to
integrate the equation has been developed and the time
evolution of the shielding currents is followed by use of the
code. The results of computations show that the shielding
currents concentrate extremely in the vicinity of the
boundary. This is mainly because the effective conductivity of
the superconductor becomes sufficiently large that the problem
constitutes a singular perturbation problem. In addition, It
turns out that the shielding coefficients depend on neither
time nor frequency of the imposed magnetic
fields. |
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Analysis
of Nb superconductor-insulator-superconductor tunnel junctions
with Al striplines for THz radiation
detection
P. Dieleman, T.M.
Klapwijk, J.R. Gao and H. van de Stadt
Summary:
We study the gain and noise of a receiver consisting of
a niobium junction embedded in an aluminum impedance matching
circuit. The junction is operated in a waveguide mount with an
adjustable backshort. The uncorrected double side band noise
temperatures are 940 K to 1388 K for 820 to 980 GHz
respectively. The total optical loss is obtained from the
losses of the individual components, the losses in the
stripline are calculated using the Reuter-Sondheimer equation
in the extreme anomalous limit. The embedding impedance
follows from the pumped curves and the Tucker equations which
are also used to determine the noise and gain of the junction.
The main limitation to the receiver sensitivity is shown to be
the loss in the aluminum circuit. |
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Twin-junction
SIS mixer with an inductance made of a coplanar
stripline
T. Noguchi, H. Iwashita
and Sheng-Cai Shi
Summary: We propose to use
a coplanar waveguide as an inductance instead of the
micro-stripline in the parallel-connected twin-junction SIS
mixer to achieve an ideal tuning bandwidth which is determined
by the inverse of the /spl omega/R/sub N/C/sub J/ product of
the twin-junction circuit. We have designed and made a
parallel-connected twin-junction SIS mixer employing an
inductance made of a coplanar waveguide at 100 GHz band. The
resonance frequencies of the parallel-connected twin-junction
device and its scaled devices are in fairly good agreement
with the expected resonance frequencies. The performance of
the parallel-connected twin-junction mixer with an inductance
made of the coplanar waveguide is as good as those of
conventional SIS mixers. This result suggests that the
parallel-connected twin-junction SIS mixer employing the
coplanar waveguide is one of the most promising candidates for
fixed-tuned (or tunerless) SIS mixers. |
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Quasi-optical
NbN/AlN/NbN mixers in submillimeter wave
band
Y. Uzawa, Z. Wang and A.
Kawakami
Summary: We have designed,
fabricated and evaluated a quasi-optical SIS receiver with
NbN/AlN/NbN tunnel junctions in the submillimeter-wave region.
The receiver consists of a planar self-complementary
log-periodic antenna and MgO hyperhemispherical lens with an
anti-reflection cap for RF optics, NbN SIS junctions and a
radial short stub tuner to resonate out its capacitance for RF
matching. The prepared NbN SIS junction has a current density
of 20 kA/cm/sup 2/ and is about 1 /spl mu/m in diameter,
supplying a small /spl omega/C/sub J/R/sub N/ product (/spl
omega/C/sub J/R/sub N/=3 at 300 GHz). From 297 to 356 GHz the
average double sideband (DSB) receiver noise temperature
measured by using the standard Y-factor method was about 200
K. The lowest receiver noise temperature, 167 K (DSB), was
obtained at around 303 GHz. These results suggest that our NbN
SIS junctions can be used for terahertz mixer elements instead
of Nb SIS junctions. |
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Observed
photon-assisted process in mesoscopic SNS
mixers
T. Matsui and H.
Ohta
Summary: The trajectory of
quasiparticles in mesoscopic SNS weak-links is similar to the
electron of hydrogen atoms. SNS weak-links are characterized
by the Zener break down (tunneling) induced across the phase
difference /spl phi/=/spl pi/ at large voltages. When the weak
links are connected to a voltage bias source with zero output
impedance, subharmonic gap structures are observed as a large
dynamic resistance area or negative-differential conductance
area at the voltage of V/sub n/=2/spl Delta//ne on the I-V
curve. Where n=1,2,3..., strong structures are caused by
resonance effect in between the energy gap and the multiple
Andreev reflections that are present whenever there is a
spatial inhomogeneity of pair potential. The enhanced IF
signal peaks and their periodic modulation of voltage interval
/spl planck//spl omega//e are observed around the subgap
voltages. These results show rough profile of the density of
states and a quantum structure due to photon-assisted process
with the resonance effect in between the energy gap and the
multiple Andreev reflections in SNS weak-links. |
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Low
noise broadband fixed tuned SIS waveguide mixers at 660 and
800 GHz
C.E. Honingh, S. Haas, D.
Hottgenroth, K. Jacobs and J. Stutzki
Summary:
We present measurements and simulations of mixer
performance around 660 GHz and around 800 GHz. We use
Nb-Al/sub 2/O/sub 3/-Nb tunnel junctions with areas of 0.9
/spl mu/m/sup 2/ and 0.7 /spl mu/m/sup 2/, and RA-products of
14.5 /spl Omega/(/spl mu/m)/sup 2/ and 13 /spl Omega/(/spl
mu/m)/sup 2/ for 660 GHz and 800 GHz. Both junctions have an
integrated tuning structure made of niobium that consists of a
series resonant stub and a quarter lambda transformer. The
waveguide mixerblock has no additional adjustable tuning
elements. It contains just a waveguide cavity and a substrate
channel across it. A horn is carefully adjusted to the cavity
and flanged to the block. The measured receiver noise
temperatures from 630-690 GHz are below 190 K with a best
value of 120 K at 655 GHz. From 780-820 GHz they are below 950
K with a best value of 780 K at 792 GHz. When the operating
temperature is reduced from 4.2 K to 2.5 K, a reduction in
noise temperature from 830 K to 660 K is observed at 810 GHz.
The mixer performance is simulated using the quantum theory of
mixing. The simulated performance shows a fairly good
agreement with the measured one. |
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Development
of a 500-GHz band SIS
mixer
Sheng-Cai Shi, T. Noguchi
and J. Inatani
Summary: This paper presents
detailed experimental and analytical results for a 500-GHz
tuneless waveguide SIS mixer, which is incorporated with
parallel-connected twin junctions. The 500-GHz SIS mixer
exhibits as low an overall receiver noise temperature as 176 K
at 482 GHz, despite relatively poor quality of the SIS
junction. The effect of the junction subgap leakage is
therefore investigated. The experimental results are finally
compared to those simulated by the quantum theory of
mixing. |
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Active
components for high-T/sub c/ Josephson
receivers
St. Beuven, O. Harnack,
L. Amatuni, H. Kohlstedt and M. Darula
Summary:
We present results of a systematic work towards
components for an integrated high-T/sub c/ receiver. As a
local oscillator, which is necessary for heterodyne detection,
the array type of the multi junction superconducting loop
(MSL) was investigated. We observed the phase locking of all
junctions by means of dc-measurements. At the same time the
radiation of the array was detected using a detector junction
coupled to the array. Phase locking of all junctions was
achieved up to nearly 1 THz. Furthermore, the results of
heterodyne mixing experiments in the W-band using single
high-T/sub c/ grain boundary junctions are presented. The
possible integration of Josephson oscillator and mixer into a
single circuit is discussed. |
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Noise
temperature measurement of YBCO Josephson mixers in millimeter
and submillimeter waves
H.
Shimakage, Y. Uzawa, M. Tonouchi and Z.
Wang
Summary: We have investigated YBCO
step-edge Josephson junctions as millimeter and submillimeter
wave mixers. These mixers were integrated with an Au thin-film
log-periodic antenna designed for broadband coupling of the
radiation. We estimated the noise temperature of the mixer
using conventional hot/cold blackbody irradiation techniques
in the 100- and 300-GHz bands. We found that the Au thin-film
antenna yielded about 5 dB higher coupling efficiency than
that of YBCO thin film antenna, and the noise temperature
decreased from 2,800 K to 1,800 K. The best receiver noise
temperature, 1,200 K, was achieved in the 300-GHz band through
improvement in impedance matching. |
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Epitaxial
YBa/sub 2/Cu/sub 3/O/sub 7/(7-x) thin films on CeO/sub 2/
buffered sapphire for optical
mixers
F. Ronnung, M. Danerud, M.
Lindgren and D. Winkler
Summary: Optical
mixers based on YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) thin
films deposited on CeO/sub 2/ thin film buffered sapphire
substrates were developed and used for photoresponse
measurements. Firstly, a 50 nm CeO/sub 2/ thin film was laser
deposited on sapphire at a substrate temperature (T/sub s/) of
760/spl deg/C and an oxygen pressure (p/sub O2/) of 1.0/spl
times/10/sup -2/ mbar, followed by an annealing for 15 min at
850/spl deg/C. Subsequently, a /spl sim/50 nm thick YBCO layer
was laser deposited at T/sub s/=760/spl deg/C and p/sub
O2/=1.0 mbar. Finally, a 150 nm thick Au film for contacts was
laser deposited in situ. X-ray diffraction and /spl phi/-scan
showed a high degree of c-axis and in-plane orientation. The
critical temperature was 89 K and the critical current, j/sub
c//spl sim/2.10/sup 6/ A/cm/sup 2/ at 77 K. Two diode lasers
(/spl lambda/=1.56 /spl mu/m) were coupled into a single mode
fiber, which was centered at a patterned mixer structure in
the YBCO film. Optical mixing was detected up to 7 GHz at a
temperature of 77 K. |
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NbN-MgO-NbN
junctions prepared on room-temperature quartz substrates for
quasiparticle mixers
B. Plathner,
M. Schicke, T. Lehnert, K.H. Gundlach, H. Rothermel, M. Aoyagi
and S. Takada
Summary: NbN tunnel junctions
are of great interest for THz heterodyne receivers because
their large gap voltage of 5 mV yields an upper frequency
limit of 4/spl Delta//h=2.4 THz for quasiparticle mixing. AC
losses in NbN films, however, imply that a NbN matching
circuit can be used at most to the NbN gap frequency, 2/spl
Delta//h=1.2 THz. Another issue is the poor thermal
conductivity of NbN films which complicates heat extraction
from the junction. One solution to these problems are hybride
mixer chips in which NbN junctions are integrated into
appropriate superconducting or normal metal matching circuits.
Both for waveguide mixers and quasioptical mixers quartz
substrates are the first choice. We report on a
room-temperature process for NbN-MgO-NbN junction fabrication
which permits the realization of hybride mixer chips on quartz
substrates. Appropriate plasma conditions for NbN film
deposition are created by employing a second Nb target as a
selective nitrogen pump. NbN films on quartz substrates
without and with intermediate layers of Nb, Al, Al/SiO/sub 2/,
and Nb/SiO/sub 2/ have critical temperatures above 15 K and
normal state resistivities from 100 to 130 /spl mu//spl
Omega/cm. In the first step, NbN junctions with nominal areas
of 0.36 /spl mu/m/sup 2/ and current densities of 10 kA/cm/sup
2/ at 5.5 mV were integrated into Nb films forming the tuning
circuit and a dipole antenna. The lowest receiver noise
temperature in the 350 GHz range was 245 K double side
band. |
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Terahertz
response for bicrystal YBCO Josephson
junctions
K. Nakajima, Jian Chen,
H. Myoren, T. Yamashita and Peiheng Wu
Summary:
The high-frequency response of bicrystal YBa/sub
2/Cu/sub 3/O/sub 7-/spl delta// Josephson junctions for far
infrared laser irradiation is presented. The junctions on
silicon and MgO substrates exhibit a remarkable first order
Shapiro step for the methanol line at 1.76 THz. dV/dI
measurements reveal several steps corresponding to the
methanol lines at 1.48, 1.76 and 2.53 THz. The line width of
Josephson oscillation at these frequencies is estimated from
the width of the Shapiro steps. It is suggested that the
excess shot noise broadens the line width. |
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Optimization
of high-T/sub c/ Josephson fluxon-antifluxon transistors based
on numerical simulation
Y.M.
Zhang, E. Terzioglu and M.R. Beasley
Summary:
A Josephson fluxon-antifluxon transistor (JFAT) can be
constructed utilizing high-T/sub c/ bicrystal or SNS long
junctions with a control line on top of the junction, This
device can be modeled numerically by solving the perturbed
sine-Gordon equation. A JFAT has a higher current gain and a
faster transient response compared to a conventional Josephson
flux-flow transistor which has a U-shaped control line on top
of the long junction. Dependences of the control
characteristics on the width and the location of the control
line, as well as on the junction length are calculated. The
influence of a superconducting ground plane on device
characteristics are also discussed. These results are
important to the design of high-T/sub c/ digital circuits
based on JFATs. |
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Effect
of a uniform magnetic field on the I-V curves of
SFFTs
P. Bernstein, C. Picard,
J.F. Hamet, C. Prouteau, J.P. Contour and M.
Drouet
Summary: The connection between the
effect of a uniform magnetic field on the I-V curves measured
on the microbridges of superconducting flux flow transistors
and the vortex dynamics is studied with the help of a model
assuming that the motion of the vortices is due to a diffusion
process. It is shown that the application of the field results
in a critical current reduction which depends on the amplitude
of the field and the thickness of the film only. As a
consequence the effective thickness of the superconducting
layer of the studied microbridges can be estimated from I-V
measurements carried out with and without applied
field. |
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Development
of 3 terminal devices based on asymmetric, long, YBCO
Josephson junctions
S.P. Isaac,
E.J. Tarte, F.J. Baudenbacher and M.G.
Blamire
Summary: The critical current of
long, asymmetric Josephson junctions, I/sub c/, is highly
dependent on the applied magnetic field and the geometry.
Nearby currents are able to significantly modulate I/sub c/,
leading to many possible devices. We have fabricated
asymmetric long junctions (1-32 /spl mu/m) in YBCO thin films
deposited on SrTiO/sub 3/ bicrystals that show improved
sensitivity to control fields compared with symmetrically
biased structures. The effect of the size and shape of the
structures has been investigated in order to optimise the gain
and critical current. We have compared our results to
simulations. |
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Josephson
flux-flow resonances and transistors based on YBa/sub 2/Cu/sub
3/O/sub 7/ step edge
junctions
H.R. Yi, D. Winkler and
T. Claeson
Summary: The flexibility of step
edge junctions is very attractive for device applications.
With an improved process based on an amorphous carbon mask
technique and electron beam lithography, we were able to
fabricate high quality YBa/sub 2/Cu/sub 3/0/sub 7/ long
Josephson junctions across sharp and straight step edges on
(001) LaAIO/sub 3/ substrates. Flux-flow resonances were
observed in the current-voltage curves for some long Josephson
junctions. The resonance voltage can linearly be tuned by an
applied magnetic field. Asymmetric in-line type Josephson
flux-flow transistors were fabricated based on the long
Josephson junctions. The critical current I/sub c/, and the
response voltage V at a fixed bias current Ib, were measured
as a function of the control current I/sub cr/ through a
control line inductively coupled to the junction. A maximum
current gain of g=17, and a corresponding transresistance of
r/sub m/=9 /spl Omega/, were achieved at 4.2 K. |
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Superconductive
multi-chip module process for high speed digital
applications
L.A. Abelson, R.N.
Elmadjian, G.L. Kerber and A.D. Smith
Summary:
We report on the development of a superconducting
multi-chip module (MCM) process for high speed digital
packaging applications, which allows superconducting
microstrip connections of superconducting chips with
impedances up to 50 /spl Omega/. The MCM process uses a low
temperature polymer, benzocyclobutene (BCB) dielectric, which
has excellent planarization properties (>90%). The six mask
MCM process uses three Nb wire layers, two BCB layers, and
Ti/Pd/Au for the pad metallization. To maximize yield of 32 mm
square MCM die, we optimized Nb deposition and BCB curing
parameters to minimize stress-induced failures and reduce
defect density. Current-carrying capabilities of signal lines
and vias (5 /spl mu/m minimum design rule) are in excess of 20
mA//spl mu/m linewidth. We discuss successful packaging of
superconducting chips, demonstrating error-free operation up
to 5 Gbit/s, and other process improvements, such as the use
of NbN wiring for 10 K operation. |
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Robust
superconducting die attach
process
K.E. Yokoyama, G.
Akerling, A.D. Smith and M. Wire
Summary: As
complexity of superconducting digital systems increase, the
need for multi-chip modules and a reliable, high bandwidth
attachment scheme for superconducting die becomes more and
more critical. We have developed a flip chip die attach
process for Low Temperature Superconducting (LTS) chips using
InSn reflow soldering. Using standard reflow techniques, we
create highly reproducible, uniform 14 micron-high solder
bumps on gold-defined pad regions. Subsequent alignment,
compression, and reflow soldering produce reliable, low
inductance connections with high yield. The short interconnect
distance of 5-7 /spl mu/m results in low enough inductance to
support multi-GHz chip interconnect at low impedance. We have
successfully tested and thermally cycled flip chipped die over
many temperature cycles to liquid helium temperatures with no
failures. We will report on successful attachment, testing,
and rework of superconducting circuit chips. Specifically, we
present data on solder bump uniformity, yield, electrical and
thermal characteristics, reworkability, and reliability under
repeated thermal cycling. |
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S-N-S
weaklink junctions fabricated by nanometer
lithography
N. Hirose, H. Ohta,
T. Matsui and M. Fukuda
Summary: It is well
known that the dimensions of the weak-link is the most
important factor of its characteristics. However, the
relationship between the dimensions and the characteristics of
the weak-links are not clarified, because the geometrical
dimensions are usually different from the effective
dimensions, To clarify this relationship, we fabricated S-N-S
(niobium as the superconductor and gold as the normal metal)
weak-link junctions using electron beam lithography (EBL),
reactive ion etching (RIE) and lift-off. The dimensions of the
weak-links were controllable and the minimum width and length
were 30 nm and 40 nm, respectively,. |
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An
improved NbN integrated circuit process featuring thick NbN
ground plane and lower parasitic circuit
inductances
G.L. Kerber, L.A.
Abelson, R.N. Elmadjian, G. Hanaya and E.G.
Ladizinsky
Summary: We report on the
development of a 10 K, NbN superconductive integrated circuit
(IC) technology that utilizes an improved SiO/sub 2/
interlevel dielectric (ILD) deposition process and a thick NbN
ground plane layer to reduce parasitic circuit inductances.
The ILD process uses a novel low frequency (40 kHz) substrate
bias during sputter deposition of SiO/sub 2/, which produces
very smooth oxide films having a roughness less than 0.1 nm
(rms) as measured by atomic force microscopy (AFM).
Bias-sputtered SiO/sub 2/ is used to planarize and to smooth
the surface of the NbN ground plane layer in preparation for
fabrication of NbN/MgO/NbN tunnel junctions. High current
density tunnel junctions ranging from 1000 A/cm/sup 2/ to 5000
A/cm/sup 2/, fabricated over NbN ground planes up to 1 /spl
mu/m thick, exhibit low subgap leakage (V/sub m//spl sim/15 mV
at 10 K) and high subgap voltage (V/sub g/=4.4 mV at 10 K).
Typical wiring inductance over ground plane has been reduced
by 25% compared to our present NbN foundry
process. |
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Fabrication
of submicron Nb/AlO/sub x//Nb Josephson junctions using ECR
plasma etching technique
M.
Aoyagi, M. Maezawa, H. Nakagawa and I.
Kurosawa
Summary: It is important to develop
a high-yielding and reproducible fabrication process of
submicron Nb/AlO/sub x//Nb Josephson junctions to improve the
integration level and the operating speed of Josephson LSI
circuits. For this purpose, we have developed a junction
fabrication process by introducing an electron cyclotron
resonance (ECR) plasma etching technique with CF/sub 4/ gas.
In the ECR plasma etching technique, highly anisotropic
etching of Nb was achieved. Over-etching was reduced by 86%.
We have successfully fabricated Nb/AlO/sub x//Nb junctions
with critical current density of 10/sup 4/ A/cm/sup 2/ using
the cross-line patterning (CLIP) method and the electron beam
(EB) lithography technique, where the size of the junctions
was varied from 2 /spl mu/m to 0.5 /spl mu/m at 0.1 /spl mu/m
intervals. High-quality submicron junctions for integrated
circuits with small spread of critical current Ic was
obtained. High uniformity of Ic was achieved. The
characteristics of the fabricated junctions are discussed and
compared with the junctions fabricated by RIE
technique. |
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High
resolution ADC system
S.V. Rylov,
L.A. Bunz, D.V. Gaidarenko, M.A. Fisher, R.P. Robertazzi and
O.A. Mukhanov
Summary: We have developed and
verified experimentally a novel high-resolution
superconducting ADC architecture based on phase
modulation/demodulation principle and implemented in RSFQ
logic. We have demonstrated an ADC chip providing full
implementation of this architecture, including on-chip
decimation filter and multiple-channel synchronizer. We have
also developed a digital ADC evaluation system consisting of
an interface electronics block converting the low-voltage ADC
output to standard TTL form at multi-MHz sampling rate, and a
computerized test station performing data acquisition,
processing and display in real time. Using this system we have
demonstrated that for low-frequency (kHz) signals our ADC
chips possess linearity in excess of 16 bits with Spur-Free
Dynamic Range over 108 dB, which is an important benchmark for
any high-resolution ADC technology. |
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Operating
margins for a pulse-driven programmable voltage
standard
S.P. Benz, C.J.
Burroughs and C.A. Hamilton
Summary: We have
designed and fabricated a Josephson voltage standard where the
voltage can be rapidly and continuously programmed by changing
the repetition frequency of a pulse drive. Simulations are
made to optimize the operating margins of the circuit for
different pulse waveforms. The response of a 1000-junction
array of Nb-PdAu-Nb junctions is measured, and
constant-voltage step heights are characterized as a function
the pulse amplitude, pulse width, frequency. A DC bias range
of 0.62 mA is demonstrated over a continuous voltage-tunable
range from -6.2 mV to +6.5 mV. |
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Interface
circuits for chip-to-chip data transfer at GHz
rates
J.X. Przybysz, D.L. Miller,
S.S. Martinet, Joonhee Kang, A. Hedge Worsham and M.L.
Farich
Summary: Interface circuits for the
transfer of data between Single Flux Quantum (SPQ) circuits
have been designed, fabricated, and operated at speeds up to 3
Gigabits per second. The circuit employed an improved version
of the SFQ/Latch converter, a Modified Variable Threshold
Logic (MVTL) OR/AND gate, a 3/spl times/ latching amplifier,
and a 3/spl times/-to-10/spl times/ latching amplifier. The
amplifier circuits employed stacks of latching junctions.
Resistors between the parallel stacks of junctions damped
residual currents to prevent flux trapping during reset.
Tolerance to critical current variations in the series stacks
of junctions was provided by inductive chokes on the input
junction shunting resistors. Microwave modeling programs were
used to ensure proper distribution of the applied current to
all of the latching elements. The circuit transferred data at
3 Gigabits per second from one SFQ circuit up to room
temperature and back to another SFQ circuit through 3.4 meters
of 50-ohm cable. |
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Error
rate of RSFQ circuits:
theory
Q.P. Herr and M.J.
Feldman
Summary: For the first time, the
bit-error rate of an active SFQ experiment is compared to
theoretical prediction. The theory of thermally induced errors
is developed using the Fokker-Planck equation. The equivalent
noise temperature of the experiment is found to be 11.0 K. The
error rate vs. bias current follows an error function
dependence and extrapolates to vanishingly small error rate at
optimal bias. |
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Experimental
demonstration of complementary output switching logic
approaching 10 Gb/s clock
frequencies
M. Jeffery, W. Perold
and T. Van Duzer
Summary: We have proposed a
new type of voltage-state logic called Complementary Output
Switching Logic (COSL). The COSL circuits were optimized for
5-10 GHz operation using a Monte Carlo method. Here we present
experimental test results of the basic COSL gates in the
frequency range 1-10 GHz, and discuss bit error rate
measurements at 2-5 Gb/s. |
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Time-to-digital
converters based on RSFQ digital
counters
O.A. Mukhanov and S.V.
Rylov
Summary: We have designed, fabricated,
and successfully tested a Time-to-Digital converter (TDC). The
TDC circuit consists of superconductive counters based on
toggle flip-flops with destructive readout, shift registers,
parallel-to-serial converters, and pulse detectors. The value
of the counter is latched while the counter is operating at
full speed. The TDC resolution is directly determined by the
maximum counter speed, or 50 ps for an available 20 GHz clock
rate. The circuits are implemented in HYPRES' standard Nb
process with a critical current density of 1.0 kA/cm/sup 2/
using HYPRES' library of standard RSFQ cells. |
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3.69
GHz single flux quantum pseudorandom bit sequence generator
fabricated with Nb/AlO/sub
x//Nb
J.H. Kang, J.X. Przybysz,
S.S. Martinet, A.H. Worsham, D.L. Miller and J.D.
McCambridge
Summary: A 4 bit 15 sequence SFQ
(Single Flux Quantum) pseudorandom bit sequence generator was
built with an eight-level Nb/AlO/sub x//Nb Josephson junction
integrated circuit process. An SFQ circuit was built into the
code generator to enable a rapid restart. The test results
showed that the circuit operated correctly at the seed of 3.69
GHz. The XNOR gate and shift register worked correctly at 5
GHz. However, the back delay was longer than 200 psec and the
generator acted as a 5 bit 21 sequence code generator at this
frequency. At 200 MHz, the code generator was operated
continuously to observe its stability. Over the course of two
and one half hours, the circuit made only five code errors,
indicating a bit error rate of 3/spl times/10/sup -12/. At 2
GHz we collected 10 million samples on the 4023rd bit of the
sequence. No wrong signal values were observed, indicating the
bit error rate is less than 5/spl times/10/sup -11/ at this
frequency. |
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A
comparison of two types of single flux quantum comparators for
a flash ADC with 10 GHz input
bandwidth
P.D. Bradley and S.V.
Rylov
Summary: We compare the SQUID
wheel/Quantum Flux Parametron (QFP) comparator to a new Rapid
Single Flux Quantum (RSFQ) compatible design. Both have been
simulated to demonstrate /spl sim/0.5 ps threshold accuracy
which would permit the construction of a flash
analog-to-digital converter with six effective bits of
resolution at 10 GHz input bandwidth, over three times better
than the best performance demonstrated with any technology, At
lower input frequencies, both designs have demonstrated that a
10-bit flash ADC is possible. Although simulations of the
QFP-based design are more accurate at high signal slew rates
due to its symmetry, the RSFQ-based design has a better
signal-to-noise ratio and a faster and more flexible clocking
scheme which ultimately prove to be more
important. |
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SFQ
data communication switch
N.B.
Dubash, Perng-Fei Yuh, V.V. Borzenets, T. Van Duzer and S.R.
Whiteley
Summary: A new SFQ data
communication switch has been designed and tested. Complete
operation of a 4/spl times/4 switch circuit has been
demonstrated with address decoding at low-speed. Transmission
through a given path in the switch has been demonstrated for
data rates up to 4 Gb/s. Circuit simulations show operation of
the switch cells up to 30 Gb/s. The circuit was fabricated
using HYPRES's standard 1 kA/cm/sup 2/ niobium process. The
switch has a crossbar architecture with an RF SQUID based
switch cell at each crosspoint. The address is decoded by
means of RSFQ shift registers which are integrated into the
switch matrix. The design enables high bit-rate, low
crosstalk, non-blocking architecture, NRZ or RZ data format,
and self routing of variable length data
packets. |
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PSCAN'96:
new software for simulation and optimization of complex RSFQ
circuits
S. Polonsky, P.
Shevchenko, A. Kirichenko, D. Zinoviev and A.
Rylyakov
Summary: The first version of PSCAN
program (Personal Superconductor Circuit ANalyzer) was
introduced in 1991. The program is a general purpose
superconductor circuit simulator with an emphasis on the
design of Rapid Single-Flux-Quantum (RSFQ) circuits. In the
intervening years a number of new features were gradually
added to the program. In particular, verification of the
correct circuit behavior was enhanced using a special
hierarchical Single-Flux-Quantum Hardware Description Language
(SFQHDL). Next, a fast heuristic algorithm for margin
optimization was introduced, which increased the number of
parameters that can be simultaneously optimized in reasonable
CPU times. Finally, recently we improved the numerical
algorithm used for the simulation by using sparse symmetric
positive definite matrices (instead of general structure band
matrices as before). As a result, simulation speed has
increased almost tenfold. Now it takes about 30 seconds of a
CPU time on HP716/100 workstation to run a 2000 ps simulation
of a 120-Josephson-junction circuit, and about a week to
optimize all parameters of a two hundred Josephson junction
circuit. We have merged all these improvements in a new
version of our simulator, PSCAN'96. |
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A
single-flux-quantum
demultiplexer
D.L. Miller, J.X.
Przybysz, A.H. Worsham and Joonhee Kang
Summary:
Many applications of Single-Flux-Quantum (SFQ) circuits
will rely on the transfer of multi-Gigabit per second data
streams from SFQ logic to semiconductor logic for further
processing. The low output voltages of superconducting
circuits currently limit the data rate per channel to a few
GHz. We have designed and fabricated an SFQ demultiplexer to
reduce data transfer clock rates. The demultiplexer uses
clocked data distribution through a binary tree architecture.
The circuit was fabricated using an eight level Nb/AlO/sub
x//Nb process and tested at 4.2 K. |
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Multi-Gb/s
operation of flipped chip MVTL
circuits
B.J. Dalrymple, M.
Leung, R.D. Sandell, J.W. Spargo, Thi Pham and A.
Spooner
Summary: Development of a reliable
flipped chip mounting technique enables demonstration of high
speed, complex digital circuits. Flip chip mounting has
greatly reduced parasitic inductance compared to conventional
wire bonding, and permits remounting of known good die onto
multi-chip modules. Superconductive digital circuits have
operated to 4.3 Gb/s in our custom test station. The circuit
and carrier are fabricated using TRW's foundry process. The
chips are flipped onto a superconducting coplanar carrier
using a low temperature solder reflow process reported on at
this conference. Testing is performed in a multi-GHz, flip
contact, variable temperature probe. This test facility is
capable of testing circuits to 12 Gb/s. We will describe the
operation and performance of our circuits at high bit rates,
and design improvements intended to facilitate operation at
higher bit rates with improved yield. In addition, we will
discuss the use of a logic simulation tool to analyze the
output words, and pinpoint the gate or gates that failed to
operate properly. |
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RSFQ
microprocessor: new design
approaches
P. Bunyk, A.Yu.
Kidiyarova-Shevchenko and P. Litskevitch
Summary:
We present a revised version of our previous RSFQ
(Rapid Single Flux Quantum) microprocessor architecture and
discuss approaches that we are using in the design of its
functional units. In particular, the data processing pipeline
built of D/sup 2/ cells, a 16-bit pipelined register block and
an all-RSFQ self-reset decoder suitable for pipelined
implementation are described in detail. Methods of VHDL
description and verification of RSFQ circuitry are also
discussed. |
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Rapid
single-flux-quantum dual-rail logic for asynchronous
circuits
M. Maezawa, I. Kurosawa,
M. Aoyagi, H. Nakagawa, Y. Kameda and T.
Nanya
Summary: Dual-rail logic circuit
elements based on rapid single-flux-quantum (RSFQ) technology
have been designed and simulated. The proposed circuits can
operate asynchronously, since dual-rail data include timing
information in themselves. Therefore dual-rail logic scheme
has a possibility of solving some problems of RSFQ circuits
with flow clocking, which would become more serious as
operating speed and complexity of the circuit increase.
Implementation of RSFQ dual-rail AND and XOR cells is
described. A scheme of transfer-ring data from a flow-clocked
circuit to a parallel dual-rail circuit is also proposed,
which a fully asynchronous dual-rail
demultiplexer. |
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New
design of single-bit all-digital RSFQ
autocorrelator
A.V.
Rylyakov
Summary: We present a new design of
a Rapid Single-Flux-Quantum (RSFQ) all-digital one-bit
autocorrelator for submillimeter spectrometry applications,
featuring 4 GHz input signal bandwidth, double oversampling
quantizer, and 16 Mbps-per-channel output rate. The delay line
of the autocorrelator is based on a circular shift register
with XOR gates performing multiplication of the delayed and
undelayed single-bit signals at every stage. The
multiplication results are accumulated by room-temperature
electronics after being prescaled in on-chip binary counters
consisting of 10 T flip-flops per stage. We report results of
experimental testing of a 16-stage autocorrelator delay line
with multiplication and for a linear array of 8 low-power T
flip-flop binary counters, all fabricated in HYPRES' standard
3.5 /spl mu/m 1000 A/cm/sup 2/ Nb-trilayer process. We also
discuss physical and technical limits of the minimal power
dissipation in RSFQ circuits. |
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Planar
HTS device process using ion
implantation
Q.Y.
Ma
Summary: A planar inhibiting fabrication
technique of HTS electronic devices has been developed in
recent years and is summarized. A systematic study of the
properties of ion inhibited HTS films is presented. The
inhibition of superconductivity is carried out by the
implantation of reactive ions such as Al, B, Ca, and Si into
YBCO epitaxial films. The inhibited films are characterized
using resistivity, susceptibility, SIMS, XRD, XPS, and SEM
measurements. The results indicate that the implanted ions
react strongly with oxygen, which turn the films resistive,
and even insulative without altering the overall crystalline
structure of the films. The effect of ion diffusion is also
investigated. Ion gettering phenomenon is observed in Si
implanted films. Those effects define the pattern resolution
of the planar inhibiting fabrication process. The ion
implantation process is applied to the fabrication of HTS
single layer devices. These devices include Josephson
junctions, DC SQUIDs, RF coils, and microwave waveguides.
Operational step-edge junctions and DC SQUIDs with a minimum
width of 2 /spl mu/m were formed and tested at 77 K. Passive
devices such as low loss waveguides (1-25 GHz) and high Q
resonators (33 MHz) were demonstrated. The performance of
these devices, in general, is better than or at least equal to
that of dry etched devices. However, the new process offers
two major advantages. first, the patterned device is planar,
which allows a multilayer device to be built, and second,
there is little or no chemical contamination of the patterned
devices. To demonstrate the viability of this technique for
the fabrication of multilayer devices, simple YBCO/STO/YBCO
tri-layer structures (such as crossover and a parallel-plate
capacitor), with two implantations were
fabricated. |
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Low
frequency voltage noise in high temperature superconductor
Josephson junctions
A. Marx, L.
Alff and R. Gross
Summary: We have performed
detailed measurements of 1/f voltage noise in a variety of
bicrystal grain boundary Josephson junctions and in ramp edge
junctions with artificial barriers. Fluctuations of the
junction critical current I/sub c/ and the normal state
resistance R/sub n/ were found to fully account for the
measured 1/f noise. For the normalized fluctuations S/sub I/
and S/sub R/, which were found to be independent of
temperature, a linear scaling with R/sub n/ has been observed.
Correlation experiments proved that the fluctuations of I/sub
c/ and R/sub n/ are anti-phase correlated. The ratio S/sub
I//S/sub R/ of the normalized fluctuations is in close
agreement with the scaling of the I/sub c/R/sub n/-product
indicating a common underlying physical mechanism. Our
analysis strongly supports the Intrinsically Shunted Junction
(ISJ) model based on an insulating grain boundary containing a
high density of localized defect states with fluctuating
electron occupation causing 1/f noise. The effective charge
trapping time within single traps shows thermally activated
behavior and was found to decay exponentially with increasing
bias voltage. |
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High
frequency applications of intrinsic Josephson junctions in
mesa structures on Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8+y/
single crystals
G. Hechtfischer,
W. Walkenhorst, G. Kunkel, K. Schlenga, R. Kleiner, P. Muller
and H.L. Johnson
Summary: We report on high
frequency experiments with mesa structures patterned on Bi/sub
2/Sr/sub 2/CaCu/sub 2/O/sub 8+y/ single crystals (BSCCO). Due
to the intrinsic Josephson effect between adjacent CuO/sub 2/
bilayers these mesas form stacks of 100 to 500 Josephson
junctions. The ac-Josephson effect was investigated in the
frequency range between 6 GHz and 120 GHz. We focus our
interest on possible applications of intrinsic Josephson
junctions as flux-flow oscillators and high-frequency mixers.
These components form the essential parts of an integrated
mm-wave receiver in BSCCO technology. |
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Investigations
on the c-axis transport properties of YBa/sub 2/Cu/sub 3/O/sub
7-/spl delta///PrBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin
film superlattices
A. Schattke,
G. Jakob, J.C. Martinez and H. Adrian
Summary:
In this paper we report on the c-axis transport
properties of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta///PrBa/sub
2/Cu/sub 3/O/sub 7-/spl delta// superlattices. We describe the
preparation, characterisation and patterning of thin film
superlattices into suitable mesa structures via standard
photolithography. Resistive measurements were carried out
which point towards an inhomogenous current distribution in
the normal state resistance. Below T/sub c/, the c-axis
properties determine the temperature dependent resistance.
Resonant tunneling is observed with no Josephson
current. |
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Material
aspects for preparing HTS quasiparticle injection
devices
C.W. Schneider, R.
Moerman, F.J.G. Roesthuis, R.G. Wichern, G.J. Gerritsma and H.
Rogalla
Summary: Quasiparticle (QP) injection
devices based on HTS could play an important role in future
superconducting applications if material aspects can be better
controlled. One reason why this kind of device received little
attention in the past is the lack of an appropriate barrier
for QP tunnelling. In a series of experiments, we used
different barriers to test if they are suitable, i.e. if a
current and possibly a voltage gain can be achieved. We
improved the performance of planar YBCO/natural barrier/Au
devices and a current gain of more than 6 at 40 K was
observed. Most devices, however, showed signs of heating
effects. Another barrier material was SrTiO/sub 3/ with layers
of 5-6 nm thickness. Current-voltage characteristics showed
that the barriers were continuous and we observed current
gains of up to 3 at 60 K. PrBa/sub 2/Cu/sub 3/O/sub 7-x/ is an
interesting candidate if one could overcome the problem of
resonant inelastic tunnelling for QP. In a series of
experiments we demonstrated that, even for 3 Mn thin PBCO
barriers on a- and c-axis oriented YBa/sub 2/Cu/sub 3/O/sub
7-x/, most devices showed at best a current gain of 1.
However, we have indications that a current gain of 10 could
be possible with unity voltage gain. |
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Control
and reproducibility of c-axis
microbridges
S.W. Goodyear, R.G.
Humphreys, J.S. Satchell, N.G. Chew, M.J. Wooliscroft and K.
Lander
Summary: Vertical c-axis microbridges,
with dimensions comparable to the penetration depth (/spl
lambda//sub c/), have been investigated experimentally and
theoretically. Josephson-like effects are observed due to
coherent motion of vortices across the bridge. Both the
on-chip and chip to chip reproducibility has been improved
from previous reports by process optimisation. Within an array
it is highly dependent on the oxygenation state and the
temperature of the sample. Although the spread in parameters
within an array of standard junctions is almost good enough to
fabricate many circuits of interest, the I/sub c/ is too high
and the R/sub n/ too low for many logic applications. In an
attempt to reduce the coupling strength, the growth
temperature of a region of the material in the microbridge has
been varied. Initial results suggest I/sub c/ can be reduced
and R/sub n/ increased to a level which, with further
optimisation, might be useful for logic applications, while
the reproducibility was not adversely affected. |
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Microwave
coupling of the Josephson junction arrays with an external
source
Insang Song, Yunsung Huh,
Gwangseo Park, E.-H. Lee, J.-W. Lee, S. Kwok and Joonhee
Kang
Summary: We have fabricated a YBa/sub
2/Cu/sub 3/O/sub y/ (YBCO) array of five Josephson junctions
designed with additional inductive coupling lines (AICLs). The
junctions in this array were dc-biased in parallel to
oscillate coherently in-phase and integrated with AICLs to
improve the impedance matching between this array and external
circuits such as a waveguide. The effect of AICLs was
investigated by studying its influence on the current-voltage
characteristics of the Josephson junction array (JJA) under
external microwave irradiations with frequency of 22 GHz. The
experimental results show that the behavior of the
Shapiro-steps depends upon the effective inductance of AICLs
which affects the total impedance and microwave coupling. We
were able to obtain an oscillation frequency of about 73% of
the maximum available frequency calculated from the
characteristic voltage of the Josephson junctions in the array
at a temperature of 12 K. By calculating the total impedance
of the array, we obtained the suitable parameters of the array
for microwave coupling with waveguide for various values of
inductance, ac frequencies and number of Josephson
junctions. |
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35
/spl planck/ two-stage SQUID system for gravity wave
detection
I. Jin, A. Amar, T.R.
Stevenson, F.C. Wellstood, A. Morse and W.W.
Johnson
Summary: We have designed, built and
tested a two-stage SQUID measuring system which is primarily
intended for use in a 50 mK omnidirectional gravity wave
detection system. We fabricated three Nb-Al/AlO/sub x/-Nb
trilayer SQUIDs on a single chip: there is one sensor SQUID
and two readout SQUIDs which amplify the output of the sensor
SQUID. At a temperature of 90 mK, we measured an intrinsic
energy sensitivity of the sensor SQUID of /spl epsi//sub
v/=S/sub /spl Phi///(2L)=35/spl planck/ at 1 kHz, of which
24/spl planck/ is white noise and 11/spl planck/ is 1/f
noise. |
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Experimental
digital SQUID with integrated feedback
circuit
U. Fath, R. Hundhausen,
T. Fregin, P. Gerigk, W. Eschner, A. Schindler and F.H.
Uhlmann
Summary: A digital SQUID with the
feedback loop closed on chip was simulated, designed,
fabricated and tested. The basic architecture of a delta
modulator A/D converter with coarse quantization was
implemented using a latching comparator and a write gate which
acts in conjunction with the pickup loop as an integrator. The
digital data stream was amplified at 4.2 K using a current
amplifier stage, a voltage driver gate and a GaAs FET
impedance transformer. The analog input signal was
reconstructed at room temperature by integrating the data
stream using a 17 bit up/down counter at a clock frequency of
about 10 MHz. Noise measurements of the D/A converted signal
have been taken indicating that bit errors cause a 1/f/sup 2/
like excess noise. Numerical simulations have been performed
in parallel to the design and experimental verification.
Operation margins of all gates, except for the voltage driver
have been estimated using a circuit-orientated simulator.
Models to estimate noise and linearity of the feedback loop
arrangement have been developed. |
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A
compact planar gradiometer system for measuring tangential
components of biomagnetic
fields
Y.H. Lee, H.C. Kwon, J.M.
Kim, Y.K. Park and J.C. Park
Summary:
Presents a compact and reliable planar gradiometer for
a multichannel system measuring tangential components of
biomagnetic fields. The readout electronics was simplified by
using a double relaxation oscillation SQUID (DROS) which
provides very large flux-to-voltage transfer of typically 3
mV//spl Phi//sub 0/, enabling direct readout by a DC
preamplifier with modest voltage noise. The DROS was made from
hysteretic Nb/AlO/sub x//Nb junctions. To realize a compact
and reliable gradiometer, the planar pickup coil is integrated
on the same wafer with the SQUID. The planar pickup coil
consists of two 10 mm/spl times/10 mm coils connected in
series to form a first-order gradiometer and has a baseline of
30 mm. The field gradient noise is 9 fT/cm/spl radic/Hz at 1
Hz inside a magnetically shielded room. The gradiometers were
arranged to measure simultaneously x and y components of
biomagnetic fields. |
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High-T/sub
c/ DC-SQUID system for nondestructive
evaluation
F. Schmidl, S.
Wunderlich, L. Dorrer, H. Specht, S. Linzen, I. Schneidewind
and P. Seidel
Summary: We developed different
types of thin film high temperature superconductor (high-T/sub
c/) DC-SQUID magnetometers and gradiometers for application in
a nondestructive testing system. We used these sensors in a
liquid nitrogen dewar mounted above a computer controlled x-y
table within a compact /spl mu/-metal shielded chamber. The
planar galvanically coupled gradiometers based on step-edge or
bicrystal Josephson junctions were investigated in shielded
and unshielded environment. We discuss the influence of
junction type and SQUID parameters depending on the device
geometry on the sensitivity of our complete testing system.
Our interest is focused in particular on the noise properties
and magnetic field resolution at 77 K. Measurements of ac and
dc current distributions will be shown as well as measurements
of magnetic moments of different samples. |
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Tesla/volt
calibration method for integrated planar SQUID
gradiometers
A.C.
Bruno
Summary: A calibration method for
integrated planar SQUID gradiometers is proposed based on a
spatial Fourier technique and on the fact that each
gradiometer design has its own theoretical spatial transfer
function. The calibration consists in scanning the gradiometer
over a known input field source and measuring the output
voltage values. The measured transfer function is the result
of the division of the Fourier transform of the output signal
by the Fourier transform of the input signal. The calibration
factor is obtained by fitting the measured transfer function
with the theoretical one. The experimental procedure was
simulated and calibration factors with imprecision of about
0.2% are expected in actual measurements. |
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Properties
of YBaCuO nanobridges and
dc-SQUIDs
M.V. Pedyash, D.H.A.
Blank, J.H. de Muijnck and H. Rogalla
Summary:
YBaCuO nanobridges and inductively shunted dc-SQUIDs
have been patterned by direct Focused Ion Beam milling.
Nanobridges manifest true Josephson effect, which can be
explained by coherent motion of Abrikosov vortices in the
bridge. An enhancement of this effect is proposed to be due to
local suppression of the superconducting properties within the
nanobridge area. This leads to a transition from SNS to SS'S
type behavior of the nanobridge with decreasing temperature.
Temperature dependence of the critical current, dynamic
resistance, and SQUID voltage-flux modulation is discussed.
The flux noise level of the nanoSQUID is measured to be about
6.5 /spl mu//spl Phi//sub 0///spl radic/Hz at 62.7
K. |
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Large
area flux transformers and passivation for flip-chip
magnetometers
C. Francke, L. Mex,
A. Kramer, B. Meyer and J. Muller
Summary: We
have fabricated thin-film flux transformers prepared from
heteroepitaxially grown, highly c-axis oriented YBa/sub
2/Cu/sub 3/O/sub 7/-SrTiO/sub 3/-YBa/sub 2/Cu/sub 3/O/sub
7/-trilayers. Crossovers and vias as well as complete test
coils exhibit critical temperatures around 85 K with critical
current densities of j/sub c/=1.5/spl times/10/sup 6/ A/cm/sup
2/ at 77 K. AFM and TEM investigations showed that only convex
edges enable highly c-axis oriented films on the beveled edges
with the CuO-planes aligning themselves parallel to the
substrate surface. The fabricated flux transformers yield a
gain of more than 43. To protect devices against their
environment and prevent oxygen losses we have developed a
passivation layer deposited by polymerization of the
silicon-organic compound hexamethyldisilazane (HMDS-N) in a
plasma enhanced chemical vapor deposition process. The 150 nm
thick films exhibit excellent passivation properties without
substantial interference with device properties. The films can
be used as the isolation and scratch protection between SQUIDs
and thin-film flux transformers in flip-chip
magnetometers. |
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Low
excess flux noise in YBa/sub 2/Cu/sub 3/O/sub 7-x/ dc SQUIDs
cooled in static magnetic
fields
E. Dantsker, S. Tanaka,
P.A. Nilsson, R. Kleiner and J. Clarke
Summary:
We have investigated the effect of device geometry on
the excess low frequency 1/f noise of thin-film YBCO dc SQUIDs
cooled in static magnetic fields. The key factor in
eliminating this noise is the reduction of the linewidth of
the SQUID loop to a value below the average separation of the
flux vortices. The spectral density of the flux noise in these
devices was independent of cooling field up to 33 /spl mu/T in
the best case. Estimates indicate that incorporating this
device into a directly-coupled magnetometer would not increase
the noise further. |
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Inductance
estimation for complicated superconducting thin film
structures with a finite segment
method
B. Guan, M.J. Wengler, P.
Rott and M.J. Feldman
Summary: A scheme for
computing inductances in complex superconducting thin film
microcircuits, using the method of finite segments, is
presented. The goal is to obtain more accurate inductance
estimation as is required in a layout design of high speed
superconducting digital circuit investigations. A variety of
geometric structures such as short stripline, corner, tee
connection and Josephson junction via are discussed.
Simulation results for these common inductance elements are
given for the HYPRES fabrication process requirements. The
database created during these simulations has been used in the
development of high speed RSFQ digital devices. |
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Microwave
characterization of coplanar waveguide transmission lines
fabricated by ion implantation patterning of YBa/sub 2/Cu/sub
3/O/sub 7-/spl delta//
J.C.
Booth, J.A. Beall, D.C. DeGroot, D.A. Rudman, R.H. Ono, J.R.
Miller, M.L. Chen, S.H. Hong and Q.Y. Ma
Summary:
We report on the application of Si and Al
ion-implantation patterning to the fabrication of low-loss
microwave transmission lines in high-temperature
superconductor (HTS) thin films. Using this technique, we have
fabricated coplanar waveguide (CPW) transmission lines in
YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) thin films
deposited on LaAlO/sub 3/ substrates. We have used both
resonant and broadband measurements in order to characterize
the performance of the resulting transmission line structures.
For the broadband measurements, on-wafer calibrations were
used to obtain accurate S-parameters and transmission line
propagation constants up to 25 GHz. The propagation constants
of the ion-implanted transmission lines do not differ
significantly from those of lines patterned using conventional
ion milling over the frequency range studied, with a value for
the attenuation constant of approximately 0.03-0.04 dB/cm at
50 K and 10 GHz. The relatively low losses of the
ion-implanted devices demonstrate the effectiveness of this
method of patterning for HTS microwave device
fabrication. |
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Resonators
for a 2 pole filter fabricated from YBCO coated LaAlO/sub 3/
cylinders
H. Kittel, M. Klauda,
C. Neumann, J. Dutzi, Y.R. Li, R. Smithey, E. Brecht, R.
Schneider, J. Geerk, J. Keppler and K.
Klinger
Summary: We prepared and tested
dielectric resonators designed for a two pole filter. These
resonators were LaAlO/sub 3/ single crystalline cylinders
which were covered on the end faces by about 350 nm YBa/sub
2/Cu/sub 3/O/sub 7-/spl delta// thin films and on the
cylindrical surface by 4 /spl mu/m gold films. The YBa/sub
2/Cu/sub 3/O/sub 7-/spl delta// films were c-axis oriented
with mosaic spreads of about 0.3/spl deg/. The inductive
transition temperatures were above 90 K. The HF properties
were characterized by evaluation of the H/sub 011/ mode at
8.05 GHz, and by measuring the surface resistance at 18.9 GHz.
At 77 K the Q-value of this resonance was typically 12000,
which is about a factor of 2 higher than the Q-value of 6560
found for end faces covered with pure copper. From these
resonators two-pole bandpass filters were constructed that at
77 K showed an insertion loss of -0.26 dB at their center
frequency of 6.3 GHz. |
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An
electrically tunable high-T/sub c/ microwave bandpass
filter
D.S. Mallory and A.M.
Kadin
Summary: A prototype superconducting
microwave bandpass filter whose center frequency can be tuned
electrically is designed, modeled, fabricated, and tested. The
tuning is accomplished via self-heating of a superconducting
control line located next to a superconducting resonating
element. Both the single-pole microstrip filter and the
control line are patterned from a single thin-film layer of
YBa/sub 2/Cu/sub 3/O/sub 7/. When the critical current of the
control line is exceeded, at an operating temperature of 77 K
and below, the center frequency of 13 GHz shifts down by as
much as 50 MHz, with only a modest increase of insertion loss.
This performance is successfully modeled in terms of the
change in the kinetic inductance of the filter element caused
by heating the control line. Switching speeds in excess of 1
kHz are demonstrated. Implications of these results for the
design of an improved tunable high-temperature superconducting
filter are discussed. |
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Microstrip
disk resonators for filters fabricated from TBCCO thin
films
A.P. Jenkins, K.S. Kale,
D.J. Edwards, D. Dew-Hughes, A.P. Bramley, C.R.M. Grovenor and
S.V. Kale
Summary: Microstrip disk type
resonators have been designed and tested. These have been
fabricated from TBCCO 2212 thin films deposited by DC
sputtering onto 2 cm square LaAlO/sub 3/ substrates. The R/sub
s/ of such large area films has been measured at 40 GHz using
a copper end wall replacement cavity and shown to be less than
200 /spl mu//spl Omega/ scaled to 10 GHz and at 80 K. Q values
of 2 to 6 GHz disk resonators have demonstrated considerable
improvements when compared to both linear HTS microstrip
resonators and comparable copper disk resonators.
Additionally, preliminary results for the performance of such
disk resonators as a function of microwave power will be
presented for application in high power filters. |
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High
current density NbN/AlN/NbN tunnel junctions for submillimeter
wave SIS mixers
Z. Wang, Y. Uzawa
and A. Kawakami
Summary: We report on the
fabrication and properties of high current density NbN/AlN/NbN
tunnel junctions for the application of superconducting SIS
mixers in the submillimeter wave regions. Junctions having
current densities as high as 50 kA/cm/sup 2/ exhibited a good
Josephson tunneling behaviour, excellent terahertz response,
and sensitive heterodyne mixing properties. Accurate values of
junction capacitance were estimated by measuring dc-SQUID
resonant steps for the design of tuning circuits. The measured
specific capacitance gives values in the range of 20-200
fF//spl mu/m/sup 2/ for the current density range of 1-100
kA/cm/sup 2/. The NbN/AlN/NbN tunnel junctions were integrated
with a NbN thin film antenna to investigate the terahertz
responses and mixing tests in a quasi-optical testing system.
Photon-assisted tunneling steps were clearly observed on the
I-V curve with irradiation up to 1.02 THz, and a low-noise
heterodyne mixing was demonstrated in the 300-GHz
band. |
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Preparation
of NbC/sub x/N/sub 1-x/ Josephson junctions with TiN/sub x/
barriers
Qian Wang, T. Kikuchi,
S. Kohjiro and A. Shoji
Summary: This paper
presents the preparation process and the characteristics of
titanium nitride films and nonhysteretic NbC/sub
x/N/sub1-x//TiN/sub x//NbC/sub x/N/sub 1-x/ SNS junction,s
using TiN/sub x/ as the barrier material. Structural studies
show that TiN/sub x/ films prepared by rf sputtering at room
temperature have a preferential orientation of TiN(111) phase,
while those grown at higher ,substrate temperatures are
(200)-oriented. Resistivilies of the TiN, films range from
45/spl mu//splOmega//spl middot/cm to 110/spl mu/spl
Omega//spl middot/cm, depending on the values of N/sub 2/
partial pressure. Polycrystalline NbC/sub x/N/sub 1-x/ films
with high T/sub c/ have been grown on TiN, films by rf
sputtering. NbC/sub x/C/sub x/N/sub 1-x//TiN/sub x//NbC/sub
x/N/sub 1-x/ trilayer junctions with various dimensions and
TiN/sub x/ thicknesses have been fabricated. Current-voltage
characteristics of the junction with a 130nm-thick TiN/sub x/
barrier show nonhysteiretic behavior and strong critical
current modulatilon with applied magnetic field, suggesting
the characteristics of a Josephson SNS large junction. The
I/sub c/R/sub N/ product and the critical current density
J/sub c/ of a 5/spl mu/mx5/spl mu/m junction at 4.2K are
estimated to be 30/spl mu/V and 36kA/cm/sup 2/,
respectively. |
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Characterization
of NbN/AlN/NbN tunnel junctions fabricated without intentional
heating
N.N. Iosad, D.V.
Balashov, M.Yu. Kupriyanov, S.N. Polyakov and V.V.
Roddatis
Summary: We have fabricated by SNEP
process Nb/Al/NbN/AlN/NbN Josephson junctions with the gap
voltage V/sub g/=2/spl Delta//e/spl ap/4.0 mV, subgap leakage
R/sub sg//R/sub n//spl ap/6.0, current density measured at the
gap current rise J/sub g//spl ap/1.5 kA/cm/sup 2/. The
(111)-textured NbN with transition temperature T/sub c//spl
ap/16 K have been deposited at ambient substrate temperature.
Phase composition and structure of the NbN films were
investigated by X-ray diffraction analysis (XRD). It was found
that the films have a structure close to the cubic /spl
delta/-NbN (JCPDS card N38-11556) and the phase composition
and intrinsic stress in NbN depend on Ar and N/sub 2/ partial
pressure during DC magnetron sputtering. Cross-sectional TEM
analysis showed that in-situ deposition of thin Al layer in
the base Nb/Al/NbN electrode provides effective planarization
of its surface and the result in improvement of tunnel
junction parameters. |
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Superconductor-semiconductor-superconductor
planar junctions of aluminium on /spl delta/-doped
gallium-arsenide
R. Taboryski, T.
Clausen, J. Kutchinsky, C.B. Sorensen, P.E. Lindelof, J.B.
Hansen and J.L. Skov
Summary: We have
fabricated and characterized planar
superconductor-semiconductor-superconductor (S-Sm-S) junctions
with a high quality (i.e. low barrier) interface between an
n/sup ++/ modulation doped conduction layer in MBE grown GaAs
and in situ deposited Al electrodes. The Schottky barrier at
the S-Sm interface was compensated by inserting several Si
/spl delta/-doped layers above the conduction layer and close
to the surface of the GaAs heterostructure. Below 1.2 K, the
transition temperature of Al, the dc I-V curves of such S-Sm-S
junctions with a wide and short GaAs channel exhibited the
classic features of S-N-S junctions including subharmonic
energy gap structure (SGS) and excess current (EC) due to
Andreev reflections at the interfaces. |
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Nanometer
SNS junctions as quantum-well
devices
H. Ohta and T.
Matsui
Summary: SNS junctions as
electron-wave devices are studied both theoretically and
experimentally. At zero bias voltage, the trajectory of
quasiparticles bound in the well of pair potential is closed
in the position-momentum space (x, p) and the area enclosed by
the trajectory is an adiabatic invariant to be quantized. A
very general program is developed to draw multiple Andreev
reflections automatically in SNS structures at arbitrary bias
voltages. The program teaches characteristics of the junctions
are very sensitive to bias voltages especially across the
subgap voltages V=2/spl Delta//ne. |
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Towards
broadband communications between RSFQ
chips
S. Polonsky and D.
Schneider
Summary: We have investigated the
applicability of Single Flux Quantum (SFQ) and Multiple Flux
Quanta (MFQ) approaches to communications between RSFQ
logic/memory chips. SFQ pulses can be transmitted between
chips if inductive discontinuity L lies below 3-5 pH. For
larger L one can employ MFQ pulses which have the same width
as the SFQ pulses, but M times larger amplitude. For example,
for L=20 pH, M=4 is sufficient. We have developed an MFQ
driver and a receiver capable of transmitting the data in
10-20 Gbps/pin range for the use in simple flip-chip MCM
packages based on Si substrates. |
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Real-time
digital error correction for flash analog-to-digital
converter
S.B. Kaplan, S.V. Rylov
and P.D. Bradley
Summary: We have designed,
fabricated and successfully tested digital error-correction
circuits to improve the performance of superconductive flash
analog-to-digital converters (ADCs). The comparators coding
the most significant bits (MSBs) are the least sensitive to
the input signal, and therefore have the most threshold errors
due to jitter and threshold misplacement. These errors are
completely eliminated by implementing an ADC architecture
using two comparators per bit, and employing logic to encode
bit N by looking back to the state of the (N-1) bit. In this
way, all code transitions are derived from the least
significant bit (LSB) comparators. The MSB comparators are
used only to encode the LSB data. |
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Josephson
output interfaces for RSFQ
circuits
O.A. Mukhanov, S.V.
Rylov, D.V. Gaidarenko, N.B. Dubash and V.V.
Borzenets
Summary: We have developed and
demonstrated high bandwidth Josephson circuits to interface
the output of RSFQ circuits to room temperature electronics.
Asynchronous dc powered voltage driver circuits have been
designed to amplify RSFQ signal levels to voltage outputs in
the 2-4 mV range, in a wide bandwidth. These driver circuits
have been characterized and tested for data rates up to 8
Gb/s. The bit error rate for one of these drivers has been
measured up to 7 Gb/s for a (2/sup 31/-1) bit long
pseudo-random bit sequence (PRBS). In order to match the data
rate of Josephson circuits to slower room temperature
electronics, we have developed clock-controlled shift
registers which allow shift-in and shift-out of data at
different frequencies. Complete functionality of these
circuits integrated with the drivers has been demonstrated at
low speed. Shift registers integrated with the voltage driver
circuits have been tested at high-speed for data rates up to 6
Gb/s. |
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RSFQ
circular shift registers
C.A.
Mancini, N. Vukovic, A.M. Herr, K. Gaj, M.F. Bocko and M.J.
Feldman
Summary: The circular shift register
is a versatile building block for RSFQ digital circuits. It
can be used for local memory and it is essential for the
proposed implementation of residue number system arithmetic.
It is surprising that the successful recurrent operation of
such a shift register has never been reported m the RSFQ
literature. Circular shift registers have a design constraint
that is unusual in RSFQ circuits-the requirement of zero
overall clock skew. We propose and analyze three novel designs
and compare their simulated parameter margins as well as their
maximum operating frequencies, latencies and areas. These
designs differ in the topology of the clock distribution
network as well as the type of storage element employed in the
data path. Two designs show satisfactory parameter margins and
large maximum clock frequency. |
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a-axis
YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta///Au interface
conductance-voltage
characteristics
Yizi Xu, J.W.
Ekin, S.E. Russek, R. Fiske, C.C. Clickner, I. Takeuchi, Z.
Trajanovic, T. Venkatesan and C.T. Rogers
Summary:
Conductance-voltage characteristics of interfaces
between a-axis YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO)
thin films and gold are presented. When the gold counter
electrode is deposited in-situ, the junctions have a specific
interface resistivity in the 10/sup -9/ /spl Omega/-cm/sup 2/
range, about an order of magnitude lower than nominal in-situ,
c-axis YBCO/noble-metal junctions. As with nominal c-axis
YBCO/noble-metal junctions, there is clear evidence at T=4 K
for a peak in the conductance at low bias. In addition, a dip
in the the middle of the broad peak structure was resolved. It
appears to be a feature unique to the a-axis YBCO/Au
interface. |
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Magnetic
field and microwave effects on critical current fluctuations
in HTS grain-boundary Josephson
junctions
Ling Hao, J.C.
MacFarlane, C.M. Pegrum, G.J. Sloggett and C.P.
Foley
Summary: The excess noise levels in HTS
grain boundary Josephson junctions, when expressed as critical
current fluctuations |/spl delta/I/sub c/|, vary linearly with
I/sub c/ as the temperature changes. By contrast, when the
critical current is suppressed by an external magnetic field,
the measured fluctuations |/spl delta/I/sub c/| remain nearly
constant while L itself undergoes order-of-magnitude changes.
This effect, which does not seem to have been widely
recognized, is examined with respect to the spatial modulation
of the critical current density within the junction.
Calculations based on this model are in good agreement with
our experimental measurements. In related studies, we measure
the excess noise levels between Shapiro steps in a
microwave-irradiated junction, and find them to agree with a
modified version of the Likharev-Semenov equation for thermal
noise. |
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Correlation
between ramp morphology and properties of ramp-type
junctions
C. Horstmann, P.
Leinenbach, R. Dittmann, U. Memmert, U. Hartmann and A.I.
Braginski
Summary: The correlation between
the morphology of ramps in YBa/sub 2/Cu/sub 3/O/sub 7-/spl
delta// thin films prepared by ion-beam etching and the
properties of ramp-type junctions was investigated in detail.
Ramp-type junctions were fabricated using PrBa/sub 2/Cu/sub
2.9/Ga/sub 0.1/O/sub 7-/spl delta// as the barrier material.
We examined the influence of different fabrication parameters
on the ramp properties by Atomic Force Microscopy (AFM).
Properties of junctions, which were fabricated by employing a
post-baking of the etching mask, were compared with those of
junctions prepared without any special treatment. Junctions
containing the improved ramps showed I-V characteristics and a
temperature dependence of the normal resistance R/sub N/
typical for resonant tunneling. The other junctions, having
also an order of magnitude lower values of R/sub N/, exhibited
a metallic temperature dependence of R/sub N/, which can be
possibly explained by contributions from metallic channels in
the PrBa/sub 2/Cu/sub 2.9/Ga/sub 0.1/O/sub 7-/spl
delta//-barrier. |
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Deposition
and tunneling phenomena of dc sputtered BiSrCaCuO-based
heterostructures
A.M. Cucolo, R.
Di Leo, A. Nigro, P. Romano, E. Bacca, W. Lopera, M.E. Gomez
and P. Prieto
Summary: We have produced
Bi/sub2/Sr/Sub 2/CaCu/sub 2/O/sub /spl delta/+/spl delta///
Bi/sub2/Sr/Sub 2/YCu/sub 2/O/sub /spl delta/+/spl delta///
Bi/sub2/Sr/Sub 2/CaCu/sub 2/O/sub /spl delta/+/spl delta//
heterostructures using a high pressure dc sputtering
technique. The films have been deposited in situ at high
oxygen pressure on (001) SrTi0/sub 3/ substrates. X-ray
diffraction and high resolution transmission electron
microscopy (HRTEM) showed highly c-axis oriented trilayers.
TEM analysis showed sharp interfaces between the
superconducting films and the barrier, without intermediate
amorphous regions. The Bi/sub2/Sr/Sub 2/CaCu/sub 2/O/sub /spl
delta/+/spl delta// layers had superconducting transition
temperatures of 87 K , with /spl tri/T/sub c//spl les/1 K
while the barrier layers showed a semiconductor-like behavior
explained in terms of variable range hopping process. At low
temperatures the conductance versus voltage characteristics
exhibit peaks indicative of gaplike structures a t about /spl
plusmn/30 mV, finite conductances at zero bias and flat
backgrounds for energies higher than 30 mV. |
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Doped-type
coplanar junctions in the Bi/sub 2/Sr/sub 2/Ca/sub 1/Cu/sub
2/O/sub 8+/spl delta//
system
A.C. Meltzow, S. Hu, J.
Hollkott, J. Auge, B. Spangenberg, H. Kurz, N.D. Zakharov and
D. Hesse
Summary: We report on a vertical
Josephson junction in the Bi/sub 2/Sr/sub 2/Ca/sub 1/Cu/sub
2/O/sub 8+/spl delta// (BSCCO) system, based on a bilayer
structure. A highly resistive bottom layer of Bi/sub 2/Sr/sub
2/(Ca/sub 1-z/Gd/sub z/)Cu/sub 2/O/sub 8+/spl delta// is
deposited by DC-sputtering and covered by an undoped BSCCO
layer with a T/sub c/ of typically 90 K. Junctions are formed
by trenches patterned through the top layer into the resistive
bottom layer. We found that the critical current I/sub c/ of
the junctions is determined by the width of the grooves.
Josephson coupling is demonstrated by Shapiro-like steps in
the I-V curve up to a width of 0.8 /spl mu/m. |
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Improvements
in the properties of electron beam damage YBa/sub 2/Cu/sub
3/O/sub 7-/spl delta//
junctions
M.G. Blamire, W.E.
Booij, A.J. Pauza, E.J. Tarte and D.F.
Moore
Summary: We have considerably improved
the properties of our electron beam damage junctions by using
a smaller condenser aperture. The better defined beam results
in a more concentrated damage profile. Consequently, the
junctions have a more resistive barrier and higher current
density compared to junctions fabricated with a large
aperture. We can now obtain an I/sub c/R/sub n/ value of 2 mV
up to a temperature of 50 K. The improved junctions have
barriers with T/sub cn/=0 K, and consequently operate over a
much wider temperature range. Using the small aperture we have
varied the length of the barrier while keeping its resistivity
constant. The exponential variation of the critical current of
these junctions with length shows that they have an
SNS-character with the decay length varying between 3 and 4
nm. |
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HTS
SQUID system with Joule-Thomson cryocooler for eddy current
nondestructive evaluation of aircraft
structures
R. Hohmann, H.-J.
Krause, H. Soltner, H. Zhang, C.A. Copetti, H. Bousack, A.I.
Braginski and M.I. Faley
Summary: For the
detection of deep-lying flaws in aircraft structures, an eddy
current system in conjunction with a planar SQUID gradiometer
is being developed. The need for a mobile system imposes
additional requirements on cooling regarding mobility,
operation independent of spatial orientation, and handling. We
present results on the operation of HTS SQUIDs with the
commercial Joule-Thomson-cryocooler KC 100 ("cryotiger") by
APD and report on cooler characteristics and system
performance. Magnetometers and gradiometers of both rf and dc
type have been integrated with the cryocooler. Noise spectra
both in unshielded and shielded environments have been shown
to be orientation independent. Compared to stationary
operation, the system sensitivity is reduced by additional
noise generated by the movement. With an improved integration
scheme, this motion-related noise is nearly eliminated. The
system was equipped with a differential eddy current
excitation and a synchronized digital lock-in detection.
Two-dimensional scans are presented that illustrate the
system's capability to find fatigue cracks and corrosion pits
hidden below several layers of aluminum. |
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Planar
HTS gradiometers with large
baseline
Y. Zhang, H. Soltner,
H.-J. Krause, E. Sodtke, W. Zander, J. Schubert, M. Gruneklee,
D. Lomparski, M. Banzet, H. Bousack and A.I.
Braginski
Summary: We have designed an HTS
single-layer planar rf double-hole gradiometer with long and
well defined baseline up to 5 mm and small washer areas. We
measured a gradient field resolution of about 1 pT/(cm/spl
middot//spl radic/Hz) above 10 Hz in an unshielded
environment. The gradiometer could be operated placed on a
swinging pendulum in the geomagnetic field. This permitted a
simple demonstration of a movable SQUID system. We placed a
SQUID system on a scanning table and performed two-dimensional
eddy-current nondestructive evaluation measurements on
realistic samples. |
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HTS
rf SQUIDs with fully integrated planar tank
circuits
Y. Zhang, H. Soltner, N.
Wolters, W. Zander, J. Schubert, M. Banzet and A.I.
Braginski
Summary: For the optimization of
the operation of rf-SQUIDs, a high pumping frequency f/sub 0/
and a high quality factor Q of the tank circuit are desirable.
For this purpose we used a washer rf SQUID or a
current-injection loop SQUID integrated with a modified planar
hairpin resonator around the SQUID. On LaAlO/sub 3/
substrates, we measured f/sub 0/ at resonance in the range of
about 550 MHz to 1.1 GHz and unloaded quality factors Q/sub 0/
from 4000 to about 6000 using several layouts with different
diameters. We found that the coupling coefficient k between
the SQUID and the resonator can be estimated from the
geometrical parameters of the layout. The requirement k/sup
2/Q>1 can easily be met with our design. Our layouts are
very flexible, as they make possible the implementation of
various single and multilayer antennas. Using a single layer
flux transformer, 13 mm in outer diameter, together with a
SQUID in the flip chip technique, we obtained a white flux
noise of 50 fT//spl radic/Hz for a 150 pH SQUID. |
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Eddy-current
nondestructive material evaluation by high-temperature SQUID
gradiometer using rotating magnetic
fields
A. Haller, Y. Tavrin and
H.-J. Krause
Summary: To exploit the
sensitivity offered by HTS SQUID systems for detection of deep
faults inside conductive samples, a new approach was taken to
avoid additional noise sources typical of scanning
measurements. The excitation fields are rotated by electronic
control which permits one to keep the sample and the system
stationary during measurements. Flaws of 10 mm and 40 mm
length were detected under 12 mm thick covers of aluminum. The
orientation of the flaws was mapped by taking advantage of the
anisotropic excitation of eddy currents by the chosen
differential coils. This approach is particularly promising
for ferromagnetically contaminated samples and radially
oriented defects, e.g. originating from rivets. |
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Operation
of HTS SQUIDs with a portable cryostat: a SQUID system in
conjunction with eddy current technique for non-destructive
evaluation
M.L. Lucia, R.
Hohmann, H. Soltner, H.-J. Krause, W. Wolf, H. Bousack, M.I.
Faley, G. Sporl and A. Binneberg
Summary: We
present a new design of a portable nitrogen cryostat for
operation of moving SQUIDs. A mixture of liquid and gaseous
nitrogen fills a reservoir in direct contact with a copper
part for the SQUID integration. The temperature at the SQUID
position is 77.8 K or 78.8 K depending on orientation, and
varies within /spl plusmn/10 mK during lateral movement. The
cryostat can operate as a portable system for 7 hours without
refilling. Washer rf SQUIDs and dc gradiometers were
integrated with the cryostat. We proved the operation of the
system as a moving magnetometer in an unshielded laboratory
environment. Noise spectra in shielding and outside were
independent of orientation. The system was equipped with a
differential eddy current excitation. We show the first
non-destructive material evaluation results for fatigue crack
detection on stationary samples with moving SQUID
sensors. |
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Excess
low-frequency flux noise in dc
SQUIDs
M.E. Huber, M.W. Cromar
and R.H. Ono
Summary: We have fabricated dc
superconducting quantum interference devices (SQUIDs)
incorporating Nb/Al-oxide/Nb Josephson junctions in both
stripline and washer geometries. Low-frequency noise in excess
of that predicted by the resistively-shunted junction model is
present in both geometries and is demonstrated to be flux
noise. This flux noise is not environmental. Improvements in
fabrication processing over the past four years have reduced
the level of this flux noise. SQUIDs are now fabricated with
PdAu resistors, Nb wiring layers, and SiO/sub 2/ interlayer
dielectric. In our best well-coupled SQUIDs, the white-noise
energy sensitivity is 5/spl times/10/sup -31/ J/spl middot/s,
with a 1/f knee below 0.1 Hz. We believe further reduction in
the flux noise might be obtained with the use of on-chip flux
shielding and/or trapping structures. |
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NDT
of high speed fine particles by high Tc
SQUID
T. Nagaishi, H. Kugai, H.
Toyoda and H. Itozaki
Summary: We detected
moving magnetized fine particles with high Tc SQUIDs. The
output signals of SQUIDs were investigated with various
particle speeds. It was found that the signal decreases less
than 20% with an increase of particle speed from 10 to 500
m/min. An iron particle of 50 /spl mu/m diameter could be
detected by the SQUID. The high Tc SQUID had a trilayered
15-turn flux transformer. It has a magnetic field resolution
of 48 fT Hz/sup -1/2/ at white noise level and a magnetic
field capture area of 2.7 mm/sup 2/. |
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Reduction
of ambient magnetic field noise for high-T/sub c/ SQUID
applications
N. Tralshawala, J.R.
Claycomb and J.H. Miller Jr.
Summary: We
discuss results of our investigations on ambient noise
reduction using localized high-T/sub c/ (HTS) passive magnetic
shields. We have quantified our results in terms of shielding
factors for ambient noise, and signal-to-noise improvement
ratio (SNIR) for source fields. Issues such as the critical
fields of our HTS shields and their flux noise are also
discussed. The relative merits of this and other noise
reduction techniques are discussed vis-a-vis
magnetocardiography (MCG) and nondestructive testing (NDT) of
materials in an unshielded environment. |
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Control
of chaos in discrete Josephson transmission
lines
I.L. Atkin and E.
Abraham
Summary: We have simulated the
control of chaos by chaos in discrete Josephson transmission
lines to obtain periodic outputs of selected frequency. Our
system consists of an underdamped 1-D parallel array of 11
small Josephson junctions in the presence of an externally
applied magnetic field. Control of chaos is achieved by a
delayed feedback mechanism which selects one of the unstable
periodic orbits embedded within the associated strange
attractor. Although the dimensionality of our system is
relatively large (22), control was achieved by applying the
delayed feedback to a single boundary junction resulting in
the above stable oscillatory output. The essence of our work
shows that unwanted chaotic signals could be turned into
useful applications such as microwave oscillators of variable
frequency, without modifying the original
system. |
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A
novel phase-locked state in discrete Josephson
oscillators
A.E. Duwel, T.P.
Orlando, S. Watanabe and H.S.J. Van der
Zant
Summary: We have measured a novel
phase-locked state in discrete parallel arrays of Josephson
junctions which can be used for oscillator applications.
Previous Josephson junction oscillators have been based on the
Eck step, where a large-amplitude wave of nearly a single
harmonic travels through the system. Multi-row systems biased
on the Eck step could improve the output power, but their
in-phase oscillations are difficult to stabilize. A new
in-phase state which is very stable has been measured as a
step in the dc I-V characteristic of one and two row systems.
Simulations show that large-amplitude oscillations of two
harmonics characterize the state. The rows are phase-locked
and in-phase for the higher harmonic. We present an analytic
expression for the oscillation frequencies and their magnetic
tunability. |
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Experimental
study of flux flow and resonant modes in multi-junction
Josephson stacks
N. Thyssen, H.
Kohlstedt and A.V. Ustinov
Summary: Magnetic
field dependence of current-voltage characteristics of 7-layer
stacked Nb/Al-AlO/sub x//Nb long Josephson junctions are
investigated experimentally. The magnetic coupling between the
junctions is provided by their common superconducting
electrodes of the thickness smaller than the London
penetration depth. The current-voltage characteristics clearly
display collective flux-flow behaviour of Josephson vortices
(fluxons) which simultaneously move in up to 5 layers of the
stack under the influence of the bias current. The flux-flow
behaviour is modulated by a complicated structure of
cavity-like resonances which show a broad range of
characteristic frequencies. Our observations can be
qualitatively explained as the interplay between the Fiske
modes and the two-dimensional resonances in these stacks. For
the intermediate magnetic field range, we find pronounced
resonant modes with large voltage spacing which indicates
mutually coherent operating junctions. |
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Linewidth
of frequency locked flux flow oscillators for sub-mm wave
receivers
V.P. Koshelets, S.V.
Shitov, A.V. Shchukin, L.V. Filippenko and J.
Mygind
Summary: Presently Flux Flow
Oscillators (FFOs) are being developed for integration with
superconductor-insulator-superconductor (SIS) mixers intended
for submillimeter wave integrated receivers. Here we report on
a detailed study of the dc and microwave properties of
Nb-AlO/sub x/-Nb FFOs. A model based on the Josephson
self-pumping effect is proposed for explanation of the
experimentally measured dc I-V curves (IVC). Extensive
measurements of the spectral linewidth of the radiation
emitted from a FFO have been performed up to 600 GHz using a
new reliable technique based on harmonic mixing. The results
are compared to recent theoretical predictions. |
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Ultrafast
photoexcited quasiparticle dynamics in YBCO films observed by
THz emission
M. Hangyo, S.
Tomozawa, Y. Murakami, M. Tonouchi, M. Tani, Z. Wang and K.
Sakai
Summary: We observed a femtosecond
time-transient nonequilibrium state in optically excited YBCO
thin films for the first time. Ultrashort electromagnetic
pulses were radiated from the films by an ultrafast
supercurrent modulation with fs laser pulse irradiation.
Quasiparticle dynamics was characterized by the analysis of
the emission waveforms based on Rothwarf-Taylor rate
equations. |
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Enhanced
THz radiation from YBCO thin film bow-tie antennas with
hyper-hemispherical MgO lens
M.
Tonouchi, M. Tani, Z. Wang, K. Sakai, M. Hangyo, N. Wada and
Y. Murakami
Summary: We demonstrate power
enhancement of terahertz (THz) radiation from YBCO thin films.
An ultra-wide-band electromagnetic pulse, which contains
frequency components over 3 THz, was excited by ultrafast
supercurrent modulation with femtosecond optical pulse
irradiation. The maximum THz radiation power emitted into free
space was achieved up to 0.5 /spl mu/W with the combination of
a bow-tie antenna and an MgO hyper-hemispherical lens. We
discuss the radiation power dependence on temperature,
excitation power, and bias supercurrent. |
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Effect
of intense proton irradiation on properties of Josephson
devices
S. Pagano, R. Cristiano,
L. Frunzio, V.G. Palmieri, G. Pepe, R. Gerbaldo, G. Ghigo, L.
Gozzelino, E. Mezzetti and R. Cherubini
Summary:
We have experimentally investigated the effects of
intense proton beam irradiation (up to 10/sup 15/ p/cm/sup 2/)
on Josephson junctions and junction arrays. The devices we
have studied were realized using state of the art full-Nb
technology, employing same materials and thicknesses of common
Josephson digital circuit designs. We have analysed in detail
the magnetic field dependence of the junction critical
current, and the quasiparticle tunneling current, in order to
observe possible occurrence of permanent changes produced by
the ionizing particles. No evidence of radiation induced
damage on the properties of the junctions has been
found. |
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InAs-inserted-channel
InAlAs/InGaAs inverted HEMTs with superconducting
electrodes
T. Akazaki, H.
Takayanagi, J. Nitta and T. Enoki
Summary: We
investigate the device characteristics of
InAs-inserted-channel In/sub 0.52/Al/sub 0.48/As/In/sub
0.53/Ga/sub 0.47/As inverted high electron mobility
transistors (HEMTs) with superconducting Nb electrodes. In
these transistors, the ohmic contact between Nb and the
two-dimensional electron gas formed in the InAs layer is
obtained by contact with the Nb-InAs direct, instead of with
an alloyed normal metal and semiconductor as in a conventional
HEMT. The contact resistance of 0.15 /spl Omega/mm between the
Nb ohmic electrodes and the channel decreased by a factor of 3
compared with that when a conventional AuGe/Ni alloyed ohmic
contact is used. For a 0.5-/spl mu/m-gate device, the maximum
extrinsic transconductance at 4.2 K was 1 S/mm, even at a very
low drain voltage of 0.2 V. These results indicate that this
ohmic contact formation will allow us to utilize in this
device both the improved HEMT characteristics and the superior
performance of superconducting electrodes. |
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Superconductor/nonlinear-dielectric
bilayers for tunable and adaptive microwave
devices
A.T. Findikoglu, Q.X. Jia
and D.W. Reagor
Summary: Microwave devices
using coplanar waveguide (CPW) structures which incorporate
bilayers of superconducting YBa/sub 2/Cu/sub 3/O/sub 7-x/ and
nonlinear dielectric SrTiO/sub 3/ on 1 cm/spl times/1 cm/spl
times/0.5 mm LaAlO/sub 3/ substrates. The microwave devices
include voltage-tunable phase shifters and delay lines,
voltage-tunable mixers, and voltage-tunable and adaptive
bandpass filters. Under dc voltage bias, these compact CPW
devices exhibit more than 360/spl deg/ relative phase shift at
2 GHz, more than 30 dB tunability in mixed microwave power
between 0.7 GHz and 5.9 GHz, and fine-tunable symmetric filter
profile at around 2.5 GHz with less than 2% bandwidth and more
than 15% adaptive range. |
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Physics
and technology of high temperature superconducting Josephson
junctions
R. Gross, L. Alff, A.
Beck, O.M. Froehlich, D. Koelle and A. Marx
Summary:
The controllable fabrication of reliable HTS Josephson
junctions with sufficiently small spread of their
characteristic parameters has not yet been achieved and
prevents the successful use of HTS Josephson junctions in
complex integrated circuits. The problems in HTS junction
fabrication certainly are related to the specific properties
of the cuprate superconductors, which make the fabrication of
high quality interfaces in HTS junctions employing artificial
barrier layers extremely difficult. Therefore, several types
of HTS Josephson junctions make use of so-called intrinsic
interfaces originating from grain boundaries or the intrinsic
layer structure of the cuprates. Beyond the fabrication
technology, the physics of HTS Josephson junctions is not well
understood. In particular, the detailed mechanisms of charge
transport in the various junctions types and the impact of an
unconventional symmetry of the superconducting order parameter
are unsettled issues. We summarize the key issues regarding
the physics and technology of HTS Josephson junctions and
discuss possible routes to a useful HTS junction
technology. |
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High-T/sub
c/ SNS edge junctions with integrated YBa/sub 2/Cu/sub 3/O/sub
x/ groundplanes
B.D. Hunt, M.G.
Forrester, J. Talvacchio, R.M. Young and J.D.
McCambridge
Summary: We have fabricated
high-T/sub c/ SNS weak links in an edge geometry with
integrated YBa/sub 2/Cu/sub 3/O/sub x/ (YBCO) groundplanes and
SrTiO/sub 3/ insulators, using a process which incorporates
six epitaxial layers, including a Co-doped-YBCO normal-metal
interlayer. The SNS edge junctions were produced using films
deposited by both off-axis sputtering and pulsed laser
deposition. These devices exhibit tight J/sub c/ spreads and
high I/sub c/R/sub n/ products in a current density regime
well-suited for SFQ circuit fabrication. We also describe
results on SNS junctions fabricated in a novel "slot"
geometry, designed to reduce junction and interconnect
inductances. |
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A
low-inductance, low-I/sub c/ HTS junction
process
J.M. Murduck, J. Burch,
R. Hu, C. Pettiette-Hall, J.A. Luine, S.M. Schwarzbek, M.
Sergant and H. Chan
Summary: One of the
challenges In fabricating digital circuitry with high
temperature superconductors (HTS) is in developing a reliable
junction process. The requirements of this junction process
include: low-parasitic inductance, well-targeted and
reproducible total inductance, uniformity in I/sub c/ and
R/sub n/, and also well-targeted I/sub c/ and I/sub c/R/sub n/
product greater than 300 /spl mu/V at 65 K. Junction
inductance can be greatly reduced by fabrication above a
groundplane. Yet the addition of a groundplane introduces
fabrication issues such as film smoothness and maintenance of
epitaxy through the multiple layers necessary. Step-edge
junctions and SNS edge junctions with groundplanes are
examined and compared through a Taguchi experimental design
series. Process equipment modifications in our HTS foundry
necessary to reach our fabrication goals are
outlined. |
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Fabrication
of superconductor-normal metal-superconductor Josephson
junctions with integrated high-T/sub c/
groundplanes
W.H. Mallison, S.J.
Berkowitz and A.S. Hirahara
Summary: We
describe the fabrication of superconductor-normal
metal-superconductor YBa/sub 2/Cu/sub 3/O/sub x/ (YBCO) edge
junctions with a cobalt-doped YBCO barrier. The process
includes an integrated high-T/sub c/ groundplane with a low
/spl epsiv//sub r/ interlevel dielectric layer of Sr/sub
2/AlNbO/sub 6/ (SAN). We have used groundplanes of both
sputtered YBCO and YBCO and NdBa/sub 2/Cu/sub 3/O/sub x/
(NBCO) deposited by thermal coevaporation. Junction to
groundplane isolations of >3.5/spl times/10/sup 8/ /spl
Omega//spl middot/cm have been measured with a groundplane
T/sub c/ as high as 90 K. The proper functioning of the
groundplane was verified by measuring the inductance of
identical SQUIDs on and off the groundplane. The SQUID
inductance on the groundplane was as low as 1.2 pH//spl
square/ at 70 K. The spreads in the junction critical currents
are comparable for devices on and off the groundplane
Groundplane and junction uniformity issues such as film
morphology, and edge and barrier formation will be
discussed. |
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Electrical
properties of YBCO/Ca-YBCO/YBCO trilayer Josephson junctions
using c-axis oriented films
J.Q.
Wang, M. Muruyama, T. Ota, H. Terai, M. Inoue, A. Fujimaki and
H. Hayakawa
Summary: We have studied
electrical properties of YBCO/Y/sub 0.7/Ca/sub 0.3/Ba/sub
2/Cu/sub 3/O/sub 7-x/ (Ca-YBCO)/YBCO trilayer junctions using
c-axis oriented films. The Ca-YBCO films used here are the
overdoped version of YBCO and show transition temperatures
around 55 K. All of the junctions show RSJ-like
current-voltage characteristics in a certain temperature
range, though the range decreases with the Ca-YBCO interlayer
thickness. For an applied magnetic field, the junctions show
Fraunhofer pattern, indicating a Josephson coupling through
the interlayers. The normal resistance of the junctions is
proportional to the thickness of the interlayer, suggesting
little interface resistance. The exponential dependence of the
critical current on temperature and that on the interlayer
thickness mean that the junctions behave as SNS junctions.
These experimental results imply the proximity effect along
c-axis in high temperature superconductors. |
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C-axis
transport properties and intrinsic Josephson effect in YBa/sub
2/Cu/sub 3/O/sub 7/-films
W.
Prusseit, M. Rapp and R. Semerad
Summary: We
have developed a standard photolithographic process to
fabricate intrinsic Josephson effect (IJE) devices on the
basis of thin films. In this way the dimensions of the
structures could be reduced into the micron range which turned
out to be essential to observe IJE signatures. Another key
point was a reduction of the interlayer coupling in YBa/sub
2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) which could be realized
by removal of chain oxygen. The enhanced anisotropy led to
RSJ-like current-voltage characteristics as well as microwave
emission at 11 GHz and 24 GHz up to temperatures slightly
below T/sub c/ demonstrating intrinsic Josephson coupling in
YBCO for the first time. |
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Tunneling
characteristics of Bi-Sr-Ca-Cu-O intrinsic Josephson
junctions
M. Suzuki, K. Tanabe,
S. Karimoto and Y. Hidaka
Summary:
Tunneling-type current-voltage (I-V) characteristics
with a clear energy gap structure have been observed for very
thin intrinsic Josephson junction stacks fabricated on the
surface of underdoped Bi/sub 2/Sr/sub 2/CaCu/sub 2/O/sub 8/
single crystals with the CuO/sub 2/ bilayer numbers of 27, 18,
and 9. It is found that the nonequilibrium heating effect is
significant in this layered material, and that an increase in
the number of CuO/sub 2/ bilayers or a decrease in the c-axis
resistivity leads to significant gap suppression and negative
resistance. The tunneling properties are characterized by the
three points: (1) the energy gap suppression by the
nonequilibrium superconductivity effect, (2) a large subgap
conductance, and (3) an extraordinarily small maximum
Josephson current compared with the BCS value. Numerical
calculation shows that the observed I-V curves are consistent
with the two-dimensional d-wave order parameter with the gap
suppression due to the nonequilibrium effect. |
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Electrical
and noise properties of YBa/sub 2/Cu/sub 3/O/sub 7/ ramp-type
Josephson junctions
M.
Schilling
Summary: Josephson junctions with
PrBa/sub 2/Cu/sub 3/O/sub 7/ barriers are used in integrated
magnetometers, where for biomagnetic applications the noise at
low frequencies should be as low as possible. The 1/f-noise
contribution close to the critical current is governed by
critical current fluctuations. We measure the electrical and
noise properties of our ramp-type Josephson junctions and
interpret them in a model of resonant tunneling through the
PrBa/sub 2/Cu/sub 3/O/sub 7/ barrier. We find that the
critical current fluctuations /spl delta/I/sub c//I/sub c/
scale with the temperature dependent critical current. The
consequences for the noise properties of integrated
magnetometers are discussed. |
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High-T/sub
c/ SNS Josephson junctions: moving beyond
adolescence
A.W. Kleinsasser and
K.A. Delin
Summary: Attempts to develop high
temperature superconductor (HTS) microelectronics have been
limited by the immature nature of HTS circuit technology. Much
of the present effort worldwide is based on
superconductor-normal-superconductor (SNS) Josephson junctions
(JJ's). Only within the past three years have SNS junctions
been fabricated which can be interpreted with conventional
proximity effect theory. We discuss the history and present
status of HTS SNS devices and the prospects for producing a
mature technology for practical applications. |
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Single
flux quantum crossbar switch
Qing
Ke, B.J. Dalrymple, D.J. Durand and J.W.
Spargo
Summary: A crossbar switch has been
designed using Single Flux Quantum (SFQ) gates exclusively for
all internal functions. A 4/spl times/4 prototype has been
fabricated in our Nb process foundry with J/sub c/ of 2000
A/cm/sup 2/. We report on the design and performance of the
switch and of an individual crosspoint element at high data
rates (/spl ges/1 Gbps). A novel design of a
double-edge-triggered dc/SFQ converter is discussed. The
requirements for output amplification and on-chip versus
off-chip amplifier issues will be presented. |
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An
optically coupled superconducting analog to digital
converter
L.A. Bunz, R.
Robertazzi and S. Rylov
Summary: A
superconducting analog-to-digital converter has been coupled
with a laser diode also operating at 4.2 K to provide a serial
output data stream via an optical fiber. The optical signal is
converted to a room temperature electrical signal using
standard optical fiber receiver techniques. After
amplification these signals are fed into a fast comparator
circuit. The output of the comparator is a TTL level signal
suitable for connection to conventional electronic
equipment. |
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High
speed testing of a four-bit RSFQ decimation digital
filter
Q.P. Herr, K. Gaj, A.M.
Herr, N. Vukovic, C.A. Mancini, M.F. Bocko and M.J.
Feldman
Summary: We have developed a high
speed test scheme for RSFQ circuits, in order to measure the
maximum clock frequency of a four-bit RSFQ decimation digital
filter (simulated to be 11 GHz). Our high speed test requires
only a low speed interface and standard low-cost measurement
equipment. Three auxiliary test units built of simple RSFQ
circuits are used. A circular JTL structure generates an
on-chip high speed clock with frequency adjustable from 4 to
16 GHz. A pseudo-random number generator with period 64 clock
cycles provides parallel input to the filter. Finally, 12
four-bit acquisition shift registers collect output data. We
have integrated all the above units on a single chip. The chip
is initialized at low speed, run at high speed, and read out
at low speed. Our testing scheme is superior to previously
reported high-speed tests in the area of the added circuitry,
in the requirements on high-speed input/output, in control,
and in the parameters of the measurement equipment. The scheme
can be easily adapted to test various RSFQ
circuits. |
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A
novel Josephson ternary
multiplier
M. Morisue, J. Endo,
T. Morooka, Y. Kogure and A. Kanasugi
Summary:
A novel Josephson ternary logic circuit to perform
multiplication is proposed. The fundamental circuit of the
multiplier is based on Josephson complementary ternary logic
circuit (JCTL). In this paper the principle of the ternary
multiplier is described. We have fabricated the multiplier
using SQUIDs which were made of Nb/AlOx/Al/Nb junctions, and
measurements of the logic operation of the circuit were
carried out. The results showed satisfactory operation of the
multiplier, which agreed well with the results of simulation.
The advantages of the proposed ternary multiplier are
capability of ultra-high speed computation, low power
consumption and very simple construction with less number of
elements to perform a ternary multiplication. |
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A
low power 12 bit flux shuttle shift register with Nb
technology
R. Lochschmied, R.
Herwig, M. Neuhaus and W. Jutzi
Summary: A 12
bit Flux Shuttle shift register with a new write and readout
gate has been simulated and fabricated using Nb/Al/sub 2/O/sub
3//Nb Josephson junctions. Write, shift and read operations
have been tested successfully at 4.2 K. Drive currents are
independent from input bit sequence. Although measurements
were disturbed by trapped flux, minimum margins are /spl
Delta/I=/spl plusmn/10%. The power dissipation of a shift
register cell is 9 nW/GHz. Total power losses caused by
terminating resistors are 70 /spl mu/W. The minimum line width
may be scaled down to 0.5 /spl mu/m, because power losses per
unit area of long Flux Shuttle shift registers are extremely
low. |
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A
high-T/sub c/ 4-bit periodic threshold analog-to-digital
converter
G.J. Gerritsma, A.J.
Verhoeven, R.J. Wiegerink and H. Rogalla
Summary:
Using ramp-type Josephson junctions a 4-bit periodic
threshold ADC has been designed, fabricated and tested.
Practical design constraints will be discussed in terms of
noise immunity, flux flow, available technology, switching
speed etc. In a period of four years we fabricated about 100
chips in order to bring the technology to an acceptable level
and to test various designs and circuit layouts. This resulted
in a basic comparator that is rather insensitive to the stray
field generated by the analog input signal or variations in
mask alignment during fabrication. The input signal is fed
into the comparators using a resistive divider network. Full
functionality at low frequencies has been
demonstrated. |
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Low
resistance metal contacts to TlBaCaCuO thin
films
L.S. Weinman, M.L. Chen, K.
Viggiano, S.H. Hong and Q.Y. Ma
Summary:
Stable low resistance contacts to TlBaCaCuO (2212)
films using single layer and trilayer metal contacts were
fabricated ex-situ. For single layer contacts, Au contacts
were evaporated on either large (unpatterned) or small
(patterned) contact pads through a shadow mask or a
photoresist mask. Prior to the metal deposition, the air
exposed films were cleaned by oxygen plasma. Rapid Thermal
Annealing (RTA) was performed on single layer contact samples
at 450-600/spl deg/C for 30 seconds. The contact resistivities
of the samples were measured using a cryogenic Kelvin probe at
78 K and 300 K. The large contacts showed the best contact
resistivity of 1.4/spl times/10/sup -8/ /spl Omega/cm/sup 2/
at 78 K, which is the lowest value ever reported for ex-situ
contacts. The films were patterned using chemical etching or
ion implantation with a minimum line width of 2 /spl mu/m.
Contact resistivity of 1.5/spl times/10/sup -8/ /spl
Omega/cm/sup 2/ at 78 K for the small contacts was obtained.
Au/Ni/Au (3000/2000/3000 /spl Aring/) trilayer contacts were
made by RF sputtering. The contact resistivities of trilayer
metal contacts were measured and showed the lowest value of
7.4/spl times/10/sup -7/ /spl Omega/cm/sup 2/ at 78 K. Such
low resistance contacts allow a supercurrent of 200 mA or a
current density of 3/spl times/10/sup 5/ A/cm/sup 2/ to cross
the metal-HTS film interface without dissipating electric
power. We have also showed that the contact resistivity values
remain the same after several thermal cycling
processes. |
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Laser
trimming of Y-Ba-Cu-O step-edge Josephson
junctions
R. Adam, W. Kula, R.
Sobolewski, J.M. Murduck and C.
Petriette-Hall
Summary: We report our studies
on the laser-induced permanent changes in electrical transport
of YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) step-edge Josephson
junctions. The junctions were fabricated from 200-nm-thick
YBCO films deposited by laser ablation onto 300-nm-high steps
etched in LaAlO/sub 3/ substrates. Laser annealing was
performed in-situ by illuminating the junctions at 50 K with a
focused Ar-ion laser beam of the intensity up to 10/sup 5/
W/cm/sup 2/. Under optimal irradiation, we observed up to 50%
increase of the junction critical current. The modified
critical currents were stable and did not change with time or
during the helium-to-room-temperature thermal cycling. The
annealed junctions exhibited RSJ-like current-voltage
characteristics and an enhancement of the I/sub c/R/sub n/
product of up to 50%. The I/sub c/(B) characteristics of the
illuminated junctions showed up to 10% shift of the first
minima, indicating changes in the junction-barrier area. The
I/sub c/(B) simulations, based on the Yanson model of large
junction-barrier fluctuations, demonstrated that laser
treatment improved barrier homogeneity. We believe that upon
laser irradiation, photo-assisted thermal oxygen reordering
takes place in the vicinity of the junction barrier,
consequently leading to grain boundaries with increased oxygen
content and improved junction dc characteristics. An
illumination power exceeding 10/sup 5/ W/cm/sup 2/ resulted in
oxygen out-diffusion from the junction area and loss of the
Josephson-like properties. |
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Study
of in-situ prepared high-temperature superconducting edge-type
Josephson junctions
T. Satoh, M.
Hidaka and S. Tahara
Summary: High-T/sub c/
edge-type Josephson junctions usually have ex-situ interfaces,
that probably contain damaged layers caused by etching process
and/or by exposure to air. The ex-situ interface layer may be
an origin of poor reproducibility and uniformity of the device
characteristics, as well as an excess interface resistance and
a suppression of the critical current. We have developed an
in-situ edge preparation process to improve the uniformity and
electrical characteristics of the edge junctions. In our
in-situ process, the base YBaCuO electrode edge is not exposed
to air after the preparation of the edge and subsequently
followed by the deposition of a barrier layer and a counter
electrode. The in-situ YBaCuO/PrBaCuO/YBaCuO junctions showed
larger critical current density (J/sub c/) and normal state
conductance (G/sub n/) than the ex-situ junctions. In
addition, smaller J/sub c/ and G/sub n/ spreads have been
obtained for the in-situ junctions. |
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Characterization
of ramp edge-geometry Ag:YBa/sub 2/Cu/sub 3/O/sub
7-x//PrBa/sub 2/Cu/sub 3/O/sub 7-x//Ag:YBa/sub 2/Cu/sub
3/O/sub 7-x/ junctions and dc
SQUIDs
Q.X. Jia, D. Reagor, X.D.
Wu, C. Mombourquette and S.R. Foltyn
Summary:
High-temperature superconducting Josephson junctions
and dc SQUIDs were fabricated using a ramp edge-geometry SNS
configuration. Ag-doped YBa/sub 2/Cu/sub 3/O/sub 7-x/ was used
as electrodes and PrBa/sub 2/Cu/sub 3/O/sub 7-x/ as barrier.
The I/sub c/R/sub n/ value of the junctions was in excess of
120 /spl mu/V at 75 K. The dc SQUIDs showed a flux modulation
depth, /spl part/V//spl part//spl Phi/, over 150 /spl
mu/V//spl Phi/, at 75 K. The flux noise of the devices,
measured with dc bias currents operated at 75 K, showed a 1/f
dependence at low frequency having values below 100 /spl
mu//spl Phi//sub 0/Hz/sup - 1/2 / (the best values in the
range of 30/spl sim/40 /spl mu//spl Phi//sub 0/Hz/sup - 1/2 /)
at 1 Hz and less than 5 /spl mu//spl Phi//sub 0/Hz/sup - 1/2 /
in the white noise region. The voltage modulation and magnetic
field noise were 37 /spl mu/V and /spl sim/2 pTHz/sup - 1/2 /
at 1 kHz for the directly-coupled dc SQUID magnetometers (with
a pick-up loop 6 mm/spl times/ 3.5 mm) based on the ramp
edge-geometry SNS configuration. |
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Fabrication
and characterization of YBa/sub 2/Cu/sub 3/O/sub 7-x/
grain-boundary Josephson junctions on [110] NdGaO/sub 3/
bicrystal and single-twin
substrates
H. Schulz, U. Poppe,
N. Klein, K. Urban, Y.Y. Divin and I.M.
Kotelyanskii
Summary: To meet the
requirements of high-frequency applications, we have
fabricated YBa/sub 2/Cu/sub 3/O/sub 7-x/ grain-boundary
junctions on 2/spl times/12/spl deg/ [110] NdGaO/sub 3/
bicrystal substrates. Compared to reference junctions made on
(100) SrTiO/sub 3/ bicrystals, the specific resistances R/sub
n/A of the junctions on NdGaO/sub 3/ were usually several
times higher. Furthermore, they showed RSJ-like behavior in a
more limited temperature range, which might be due to weak
links in the YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin film formed on
twin boundaries of the NdGaO/sub 3/ bicrystal substrate. The
electrical properties of these additional weak links have been
studied by preparing YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin-film
bridges crossing a single twin boundary of a NdGaO/sub 3/
substrate. The critical current densities j/sub c/ were found
to be on the order of 1/spl times/10/sup 6/ A/cm/sup 2/.
Therefore, even for the smallest twin boundary junctions, a
pronounced flux-flow-behavior is observed. |
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Impedance
control of Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub x/ Josephson
junctions on MgO substrates for millimeter wave
sensing
S. Yoshikawa, M. Nemoto,
K. Shimaoka, K. Niki, I. Yoshida and Y.
Yoshisato
Summary: SIS-type
(Superconductor-Insulator-Superconductor) intrinsic stacked
Josephson junctions (ISJJs) and SNS-type
(Superconductor-Normal conductor-Superconductor) step-edge
Josephson junctions (SEJJs) have been successfully fabricated
using anisotropic Tl/sub 2/Ba/sub 2/CaCu/sub 2/O/sub x/ thin
films on MgO substrates. In order to apply them to millimeter
wave receivers, their normal resistance (Rn) was controlled,
which determines the impedance matching for millimeter wave
signals. For electrical transport along the c-axis, the Rn of
a single unit ISJJ with a 5 /spl mu/m-square mesa was
estimated to be 580 /spl Omega/. For electrical transport
parallel to the ab-plane, the R/sub n/ of series connected six
SEJJs (6-SEJJs) with the gentle slope of 28/spl deg/ was 2.0
to 3.8 /spl Omega/. Since their responsivities as millimeter
wave detectors were two to three orders of magnitude larger
than those of single SEJJs, efficient IF (intermediate
frequency) output of fundamental mixing with LO (local
oscillation) power of a few microwatts was observed up to 95
K. |
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Growth
and properties of NdBa/sub 2/Cu/sub 3/O/sub 7-/spl
delta///PrBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//
quasi-homostructures for the fabrication of electronic
devices
G.A. Alvarez, J.G. Wen,
F. Wang, T. Utagawa and Y. Enomoto
Summary:
We report on well-characterized c-axis
quasi-homoepitaxial multilayers made of NdBa/sub 2/Cu/sub
3/O/sub 7-/spl delta// (NBCO) and PrBa/sub 2/Cu/sub 3/O/sub
7-/spl delta// (PBCO) films with very smooth surface
morphology and high crystallinity, grown on SrTiO/sub 3/
substrates by pulsed laser deposition (PLD). X-ray diffraction
(XRD), transmission electron microscopy (RBS) and Rutherford
backscattering spectrometry (RBS) analyses provide evidence of
long-range crystalline perfection, and a well-equilibrated and
relaxed crystal. Furthermore, high quality junctions were
fabricated from c-axis-oriented NBCO/PBCO/NBCO multilayers.
The current-voltage characteristics (CVC) exhibit supercurrent
and quasi-particle tunneling that is commonly observed for
superconductor-insulator-superconductor (SIS) junctions. Our
results show the importance of using barrier layer materials
of PBCO sandwiched between NBCO electrodes for the fabrication
of electronic devices. |
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Resonant
Josephson current through a long SIS
junction
I.A. Devyatov, M.Yu.
Kupriyanov and G. Wendin
Summary: We have
considered the resonant Josephson tunneling in SIS junctions
with a localized state in the interlayer for an arbitrary
relation between the width of the resonant level and the
superconducting gap and for arbitrary barrier thickness. The
analysis was carried out in the framework of the Bogolubov-de
Gennes equations. For the case of short junctions and high
barriers our results coincide with the results of Beenakker
and van Houten theory. The obtained results can be applied for
explanations of the properties of HTS Josephson
junctions. |
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Electrodynamics
of closely coupled YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//
junctions
W.E. Booij, A.J. Pauza,
D.F. Moore, E.J. Tarte and M.G. Blamire
Summary:
Direct electron-beam irradiation of high-T/sub c/ thin
films has been used to create closely spaced Josephson
junctions which operate at temperatures of 60-80 K. The
electrodynamics of two junctions have been investigated by
studying the dependence of the critical current on an applied
magnetic field. The junctions spaced between 50 and 150 nm
could be measured independently by using a narrow third
electrode. Closely spaced junctions with moderate critical
currents showed a strong divergence of I/sub c/s when a
magnetic field was applied. We show that these results
correspond with simulations of two junctions coupled by a
redistribution current. At higher critical currents the same
junctions show locking of their I/sub c/s. We propose a three
terminal device based on these closely-spaced multiple
junctions. |
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Plastic-molded
LTS DC-SQUIDs for multichannel biomagnetic measurement
systems
Y. Utaka, T. Kido and K.
Kudo
Summary: A plastic molding technique for
SQUIDs has been developed to protect the chip from moisture
damage. A 1.5-mm-thick layer of molding compound (epoxy resin,
elastic resin, and silica powder) was poured over Ketchen-type
DC-SQUID that has Nb/AlO/sub x//Nb Josephson junctions. The
moisture resistance of these plastic-molded SQUIDs was
examined by subjecting them to temperature and humidity
storage tests (60/spl deg/C, 90% relative humidity, 1,000
hours), and then measuring their performance characteristics.
The results showed that the plastic packaging protected the
chip from moisture damage, while not affecting the noise
performance of the SQUIDs. The plastic molding therefore
improved reliability and ease in handling of such
SQUIDs. |
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A
low-noise, two-stage DC SQUID amplifier with high bandwidth
and dynamic range
R. Cantor, L.P.
Lee, A. Matlashov and V. Vinetskiy
Summary:
We describe a low-noise, two-stage dc Superconducting
QUantum Interference Device (SQUID) amplifier that is designed
for applications requiring high bandwidth and dynamic range.
The output signal of a low-noise SQUID in the input stage
coherently modulates a series array of identical SQUIDs in the
output stage via a common modulation line. The input stage is
designed so its output signal does not produce multiple
modulation periods in the output stage. The output stage is
designed to have sufficient gain so the output noise is
dominated by the amplified noise of the input SQUID and
exceeds the noise of a preamplifier in the room temperature
readout electronics. The SQUID amplifier may therefore be
operated without flux modulation or any impedance matching
network, resulting in a large dynamic range and high
bandwidth. |
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Integrated
low-temperature superconductor SQUID gradiometers for
nondestructive evaluation
U.
Klein, M.E. Walker, C. Carr, D.M. McKirdy, C.M. Pegrum, G.B.
Donaldson, A. Cochran and H. Nakane
Summary:
We describe an eddy current nondestructive evaluation
system using a low-temperature superconductor magnetic field
sensor in an electromagnetically unshielded environment. The
sensor comprises a niobium dc superconducting quantum
interference device (SQUID) integrated with a first-order
gradiometric pickup coil to reject spatially uniform
interference fields but remain sensitive to flaw induced
fields. We demonstrate its use in locating and mapping
subsurface flaws in a multilayered aluminum structure using an
eddy current excitation field at a frequency of 70 Hz, with no
magnetic shielding around the specimen or
cryostat. |
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Development
of a heart monitoring system based on thin film high-T/sub c/
DC-SQUIDs
P. Seidel, F. Schmidl,
R. Weidl, S. Brabetz, F. Klemm, S. Wunderlich, L. Dorrer and
H. Nowak
Summary: Our aim is to built up an
one-channel heart monitoring system to achieve fast and
reliable information about the patients condition as well in
emergency cases as in serial examinations by a non-invasive
and touchless method. Step-edge and bicrystal junctions were
used to prepare planar galvanically coupled thin film
gradiometers and magnetometers. These sensors were used to
carry out measurements in well-shielded and weak disturbed
environment and we compared the different noise properties and
field gradient resolutions. The influence of antenna
configuration, SQUID parameter, cooling conditions, and
different kinds of signal analysis will be
discussed. |
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77
K SQUIDs operating in the Earth's magnetic
field
G.J. Sloggett, C.P. Foley,
S. Lam, R.A. Binks and D.L. Dart
Summary:
Weak magnetic fields like the Earth's field (/spl
sim/50 /spl mu/T) can adversely affect the operation of 77 K
thin-film high-T/sub c/ SQUIDs through flux penetration into
either the junction or the body of the SQUID. Josephson vortex
penetration into the junction causes suppression of the
critical current, increased white noise and possible cessation
of normal SQUID operation. We have used various techniques to
overcome this problem, including development of narrow (/spl
sim/1 /spl mu/m wide) step-edge junctions with high critical
current density. The adverse effects of Abrikosov vortex
penetration into the SQUID include magnetic hysteresis and
increased low-frequency noise. Film quality (J/sub c/) is
found to be important In minimising these
effects. |
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HTS
SQUID magnetometers with intermediate flux
transformers
M.N. Keene, N.J.
Exon, J.S. Satchell, R.G. Humphreys, N.G. Chew and K.
Lander
Summary: We have modeled and
fabricated a novel HTS magnetometer with a d.c. SQUID which
couples to an on-chip flux transformer via an intermediate
flux transformer. This configuration allows high efficiency
coupling between a 65 mm/sup 2/, 28 nH pickup loop and a low
inductance (<15 pH) SQUID. The small SQUID inductance is
required for low noise and high /spl part/V//spl part//spl
Phi/ so that direct readout schemes may be used. The
intermediate flux transformer was flip-chipped with a
sub-micron separation to the main substrate. The magnetometer
makes use of CAM junction technology, double thickness (/spl
ap/0.7 /spl mu/m) YBa/sub 2/Cu/sub 3/O/sub 7/ layers, and a
groundplaned SQUID slot. The measured responsivity at 77 K was
0.57 mm/sup 2/ (3.6 nT//spl Phi//sub 0/) with /spl part/V//spl
part//spl Phi/=98 /spl mu/V//spl Phi//sub 0/ which is close to
that predicted by our model. No resonances, which degrade the
performance of similarly configured LTS devices, were
observed. We attribute this to the use of PrBa/sub 2/Cu/sub
3/O/sub 7/ as the isolation barrier. Excess white noise,
probably due to Johnson noise from the PrBa/sub 2/Cu/sub
3/O/sub 7/, limited the sensitivity in our first device to 33
fT//spl radic/Hz at 77 K. |
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A
computationally efficient approach to microwave circuit
modeling of complex high temperature superconductor
circuits
J.M.
Pond
Summary: A computationally efficient
approach to modeling complex high temperature superconductor
(HTS) microwave circuits is described which combines
two-dimensional electromagnetic solutions of microwave
transmission lines, incorporating a phenomenological
description of HTS behavior, with conventional commercially
available microwave-circuit computer-aided-design software.
Internal inductance effects are known to have a substantial
impact on the design and implementation of narrowband HTS
circuits. Phase velocities and characteristic impedances can
be well modeled using a phenomenological description of HTS
superconductivity along with a generalized approximate
boundary condition and a two dimensional electro-magnetic
solution to the waveguiding structure. Resultant parameterized
design equations can then be incorporated into standard
commercially available microwave-circuit computer-aided-design
software. The test case examined in detail was the
superconducting channelized receiver delivered by the Naval
Research Laboratory to Phase II of the High Temperature
Superconducting Space Experiment. Excellent agreement was
obtained between measurements made on the demultiplexer and
this HTS microwave circuit modeling approach. |
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Demonstration
of a 20 GHz phase shifter using high-temperature
superconducting SNS
junctions
S.J. Berkowitz, C.F.
Shih, W.H. Mallison, D. Zhang and A.S.
Hirahara
Summary: We have achieved a
figure-of-merit of 90/spl deg//dB from a Co-doped
Superconductor-Normal-Superconductor junction series array
phase shifter, with 300 junctions The maximum observed phase
shift was 25/spl deg/ from a 900 junction array. The entire
device fits on a die size of 0.5/spl times/0.5 cm/sup 2/,
which is suitable for integration into a phased array.
However, the performance of this high-temperature
superconductor device is still below the 150/spl deg//dB for a
conventional shifter. In simulations, we see that an improved
performance of 150-200/spl deg//dB is possible. If this
performance can be achieved, the reduced base loss in addition
to the reduction in loss from the antennas and feed lines in
an integrated antenna array would lead to a system-wide
performance advantage for a superconducting
system. |
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Design
and fabrication of YBCO patch
antennas
S. Ohshimas, T.
Ogasawara and K. Ehata
Summary: We designed
superconducting rectangular patch antennas which have a
resonance frequency of 5 GHz and an input-impedance of 50 /spl
Omega/. We used the transmission line model and the moment
method to determine this patch antenna's geometric form. We
also fabricated the superconducting patch antennas of
YBa2C3O7-y (YBCO) thin films and Cu films. The YBCO films were
prepared by Helicon sputtering method. The input impedance and
return loss of the YBCO patch antennas at 19 K were 50 /spl
Omega/ and -35 dB, respectively. The return loss of the YBCO
patch antenna was smaller than that of Cu patch antenna with
the same geometry. |
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HTS
cavities for low phase noise oscillator
applications
T.W. Button, P.A.
Smith, N.M. Alford, R.B. Greed, M.J. Adams and B.F.
Nicholson
Summary: The origins of phase noise
in oscillator systems are reviewed. A simple, self-excited 7.5
GHz oscillator incorporating either a conventional metal
cavity resonator or a high temperature superconducting (HTS)
cavity has been produced. Comparative measurements made at 77
K demonstrate significant improvements in the close-to-carrier
noise performance of the oscillator incorporating the HTS
cavity; 10 dB at a 10 kHz offset rising to more than 25 dB at
a 10 Hz offset. The unloaded Q of the HTS cavity doubled to
>10/sup 6/ on cooling from 77 K to 64 K suggesting that
further improvements in noise performance could be
achieved. |
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A
hybrid superconductive/semiconductive microwave
receiver
A. Romano, R.R. Mansour
and F. Thomson
Summary: A 6 GHz hybrid
superconductive/semiconductive microwave receiver (HSSMR) has
been developed. It consists of an HTS microstrip preselect
filter, a cryogenic LNA, a commercially available
off-the-shelf mixer, and a superconducting local oscillator
(LO). The operating bandwidth is 500 MHz, which is centered at
an RF frequency of 5.9 GHz and a corresponding IF frequency of
4.483 GHz. Downconversion is facilitated by a 10.383 GHz LO.
The oscillator incorporates an HTS/sapphire resonator with a
measured unloaded Q of 98100, at 77 K. The entire receiver is
cooled to an operating temperature of 77 K. The measured
performance is given for each of the components and for the
overall receiver. The resultant receiver conversion gain is
27.5 dB and the associated noise figure is less than 0.7
dB. |
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Low
phase noise microwave oscillators based on HTS shielded
dielectric resonators
I.S. Ghosh,
N. Tellmann, D. Schemion, A. Scholen and N.
Klein
Summary: To meet the specifications of
future radar and communication systems we developed a low
phase noise microwave oscillator. This feedback oscillator
consists of a commercial MESFET-amplifier at room temperature
and a LaAlO/sub 3/ dielectric resonator with high temperature
superconducting (HTS) shielding at 63 K. The resonator
operating at a resonance frequency of 5.6 GHz showed unloaded
quality factors in the 10/sup 5/ to 10/sup 6/ range. By means
of a strong resonator coupling (|S/sub 21/|=6 dB) and an
amplifier gain of 20 dB we obtained an output power of +15
dBm. The phase noise L(f/sub m/) of the oscillator was below
the detection limit for offset frequencies beyond 10 kHz. For
offset frequencies below 5 kHz measurements revealed perfect
L(f/sub m/)/spl prop/f/sub m//sup .3/-behaviour according to
the Leeson model. The phase noise was -110 dBc/Hz at 1 kHz
offset and -130 dBc/Hz at 10 kHz. This phase noise performance
is superior to state of the art SAW- or quartz oscillators for
f/sub m/>10 kHz. To further reduce the phase noise
performance close to the carrier we investigated the
implementation of a phase locked loop (PLL). The long term
temperature stability of the oscillator frequency can be
enhanced by introducing a central cylinder made from rutile
(TiO/sub 2/). We present numerical and experimental results on
this compensation. |
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Narrow-band
HTS microstrip combiner
technology
R.G. Humphreys, C.P.
Barrett, N.G. Chew, S.J. Hedges, R.B. Greed, B.D. Hunt, B.F.
Nicholson, S. Hensen and G. Muller
Summary:
Contiguous 7-pole filters centred at 7.97 and 8.00 GHz
have been made by co-evaporation of YBa/sub 2/Cu/sub 3/O/sub
x/ thin films on MgO substrates. The 0.3% bandwidth filters
make stringent demands on the design and fabrication
processes. Good control of the centre frequency and bandwidth,
sharp cut-offs and high linearity have been achieved. A pair
of filters has been assembled as a layer of a combiner
circuit, and its characteristics studied. Although the
individual filters have been successfully made to high
accuracy, the extreme precision required by a combiner circuit
would require some tuning for high performance, at least at
the present state of the technology. |
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Magnetometry
based on sharpened high T/sub c/ GBJ Fraunhofer
patterns
V. Martin, M.L.C. Sing,
D. Robbes, J. Certenais, N. Quellec and D.
Crete
Summary: At EUCAS'95, we reported on
the large enhancement of the sharpness of the diffraction
pattern exhibited by YBCO grain boundary junctions on
bicrystal substrates. This effect results from large focusing
effects of the superconducting electrodes; the geometry used
is a small square washer (630/spl times/630 /spl mu/m/sup 2/)
with the junction in the center. For such devices, the
Fraunhofer pattern is contracted around the value B/sub n//spl
ap/0 where B/sub n/ is the perpendicular magnetic field
applied to the washer. A FWHM of the Fraunhofer pattern of 155
mG has been observed leading to a field response of 176 A/T or
50 V/T corresponding to voltage and current biasing modes
respectively. A white noise level of 3 pT//spl radic/Hz mas
measured. Although a field modulation was applied to remove
some of the "1/f" noise, an unusual telegraphic noise
appearing as jumps of about 20 nT still remained. This is
probably associated to vortex hopping between pinning sites in
the vicinity of the junction. We propose a possible way for
removing such large perturbations. These devices are to be
used in active shielding systems and will be very useful in
SQUID systems to be operated in an open
environment. |
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Influence
of phonon trapping on the performance of NbN kinetic
inductance detectors
A.D.
Semenov, M.A. Heusinger, K.F. Renk, E. Menschikov, A.V.
Sergeev, A.I. Elant'ev, I.G. Goghidze and G.N.
Gol'tsman
Summary: Voltage and microwave
photoresponse of NbN thin films to modulated and pulsed
optical radiation reveals, far below the superconducting
transition, a response time consistent with the lifetime of
nonequilibrium quasiparticles. We show that even in 5 nm thick
films at 4.2 K the phonon trapping is significant resulting in
a quasiparticle lifetime of a few nanoseconds that is an order
of magnitude larger than the recombination time. Values and
temperature dependence of the quasiparticle lifetime obey the
Bardeen-Cooper-Schrieffer theory and are in quantitative
agreement with the electron-phonon relaxation rate determined
from the resistive response near the superconducting
transition. We discuss a positive effect of the phonon
trapping on the performance of kinetic inductance
detectors. |
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A
high stability temperature controller based on a
superconducting high-T/sub c/
sensor
M.L.C. Sing, E. Lesquey,
C. Dolabdjian and D. Robbes
Summary: An
analysis is given of a temperature control scheme described
previously (1995), showing its intrinsic noise limitations.
This scheme made good use of YBCO microbridges as temperature
sensors. We find that high temperature to voltage transfer
coefficient values (/spl Gt/1 V/K) are required in order to
reach fluctuation levels well below 100 /spl mu/K/sub pp/.
Consequently, a new design of the circuit has been made by
introducing a current pre-biasing technique of the microbridge
and allowing very large offset compensations. A transfer
coefficient value of 441 V/K was used to obtain a temperature
control with fluctuations less than 1.6 /spl mu/K/sub pp/ over
a 2 hour recording time. Such high stability temperature
controllers leading to fluctuation levels in the /spl mu/K/sub
p/ range can prove to be very useful for high-T/sub c/ SQUID
systems working at 77 K and in high-T/sub c/ bolometer
applications. |
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Noise
from YBCO films: size and substrate
dependence
D.G. McDonald, R.J.
Phelan Jr., L.R. Vale, R.H. Ono, J.P. Rice, L. Borcherdt, D.A.
Rudman, J. Cosgrove and P. Rosenthal
Summary:
Electrical noise measurements at 10 Hz are reported for
YBCO films at the resistive edge. Results are given for films
with widths of 0.1, 1, and 5 mm that were deposited
simultaneously on the same substrate, for three different
substrate materials. The NET improves by approximately a
factor of 10 as the thermometer area is increased by a factor
of 2500, with fixed bias current, At temperatures giving
maximum dR/dT and with nominally 19 mA bias currents, the 5 mm
samples have very low noise equivalent temperatures of 3.1,
3.5, and 4.4 nK//spl radic/Hz for LaAlO/sub 3/, Al/sub 2/O/sub
3/, and Si substrates, respectively. These are the lowest
values reported up to the present time. Surprisingly, noise
from the sample on Si is consistent with pure Johnson noise
even with bias Current as large as 5 mA (0.28/spl times/10/sup
4/ A/cm/sup 2/). For YBCO thicknesses no greater than 50 nm
excellent thermometers can be made on any of these substrates
in spite of the mechanical strains produced in the films by
the substrate. |
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Possible
three terminal HTS transistor
device
A.M. Gulian and D. Van
Vechten
Summary: A non-zero, gauge invariant
potential /spl mu/ has been recognized since 1972 to occur in
superconductors in various non-equilibrium circumstances. It
is central to the description of the time dependent
properties. Non-zero values of this potential cause gap
suppression. Thus if the local value of the potential /spl mu/
can be made sufficiently large, the material can be locally
switched into the normal state. Superfluid flow would no
longer exist and a voltage would be required to sustain a
preexisting current. The S to N switching time is expected to
be sub-picosecond for Nb and faster for the HTS materials. The
time scale for the restoration of superconductivity will be
set by the dynamic branch mixing time, sub-nanosecond for Nb.
Thus the main difficulty in designing a superconducting
transistor analog using this effect is in producing a
sufficiently large value of /spl mu/. We suggest that an
appropriate mechanism is provided by the injection of a
current of predominantly electron- or hole-like character from
a doped non-degenerate semiconductor into a thin, current
carrying superconducting film. |
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Single-electron
transistors based on Al/AlO/sub x//Al and Nb/AlO/sub x//Nb
tunnel junctions
K. Bluthner, M.
Gotz, A. Hadicke, W. Krech, T. Wagner, H. Muhlig, H.-J. Fuchs,
U. Hubner, D. Schelle, E.-B. Kley and L.
Fritzsch
Summary: As an alternative to the
shadow evaporation method for the preparation of ultrasmall
tunnel junctions we have established the so-called
self-aligned in-line technique. It was applied to the
fabrication of common Al/AlO/sub x//Al-type and, for the first
time, Nb/AlO/sub x//Nb-based single-electron transistors. The
characterization of the samples at temperatures in the range
of a few hundred millikelvins reveals charging effects
(Coulomb blockade and gate modulation) of the quasiparticle
current. |
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Intrinsic
phase-locked state in two-dimensional Nb Josephson
arrays
E. Trias, M. Barahona,
T.P. Orlando and H.S.J. Van der Zant
Summary:
We present experimental results and numerical
simulations of a new phase-locked state in two-dimensional
arrays when nearly fully frustrated and driven by a dc
current. In this state, all the rows of the array act
coherently and phase-lock at a voltage that depends on the
geometric loop inductance and junction capacitance. We also
experimentally observe the resonance in one-dimensional ladder
arrays, implying that two-dimensional arrays have inter-row
phase-locking mechanisms. The horizontal junctions also appear
to play a role in the dynamics. Two-dimensional arrays have
been proposed as tunable microwave oscillators. |
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Off-chip
detection of radiation from a linear array oscillator with a
spiral antenna
S. Kiryu, Wenxing
Zhang, Siyuan Han, S. Deus and J.E. Lukens
Summary:
Radiation from a linear array oscillator with a spiral
antenna has been measured using an off-chip coupled bolometer.
The array oscillator has a distributed array structure with
300 resistively shunted junctions which are placed in the
groups of 6 junctions. The array oscillator was fabricated on
a Si wafer with a two-arm spiral antenna. The chip was
attached to a Si lens with an anti-reflection coating. Rather
large power (>100 nW) was detected at a number of array
bias voltages V/sub bias/ from 115 mV to 196 mV, which
correspond from 185 GHz to 315 GHz. The maximum measured power
was 550 nW at V/sub bias/=125 mV (200 GHz). |
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Phase-locked
one- and two-dimensional Josephson-junction arrays as
millimeter and submillimeter wave
generators
V.K. Kornev, A.V.
Arrmanov, A.D. Mashtakov and G.A.
Ovsyannikov
Summary: The results of numerical
simulations of phase-locked 1D and 2D Josephson-junction
arrays are reported. It is shown that the multi-junction
structures with non-local junction interaction provide
phase-locked oscillation state within wide critical current
margins /spl Delta/I/sub c/ up to 40...50%. The effective
non-local interaction in 2D structure based on 4-junction
interferometer cell can be provided by the regular single flux
quantum array flow across it. The wide tolerable spread in
/spl Delta/I/sub c/ allows one to realize both (i)
phase-locked 2D high-T/sub c/ Josephson-junction array with
the oscillation frequency F close to characteristic value
F/sub c/ and (ii) based on Nb tunnel Josephson-junction
technology 1D array with the voltage-controlled phase-locked
oscillation frequency within wide frequency band from 0.4
F/sub c/ to 1.2 F/sub c/. |
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Generation
of mode locked pulses using 2D triangular-Josephson junction
arrays
S.P. Yukon and N.C.H.
Lin
Summary: We have numerically investigated
the behavior of 2D triangular Josephson junction arrays
(TJJAs) employed as rf sources. Each array is driven by
(vertical) DC forcing currents at a carrier frequency /spl
omega//sub 0/ and the rf output of each horizontal array
junction is assumed to be coupled to an antenna and quasi
optically summed in the far field. By superimposing (vertical)
differential forcing currents that have constant increments
from row to row, or that are applied to the outermost columns
of the array, it is possible to, respectively, create
mode-locked pulses above the array or steer the antenna array
beam. By breaking the symmetry of the array from row to row it
is possible to phase lock the array to create a monochromatic
source. |
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The
observation of subharmonic peculiarities of I-V characteristic
of edge-type Josephson junction chains placed in microwave
resonator
A.P. Lipatov, V.A.
Ilyin and A.A. Verevkin
Summary: The
spectrums of own Josephson radiation and I-V characteristics
of one-dimensional chains of edge-type Nb Josephson junction
placed into microwave resonator have been studied. The
interaction with the external resonator caused synchronization
of junctions forming the chain. This effect was detected
experimentally. In the hysteresis region of I-V characteristic
we have found the presence of own radiation area. Its bounds
are determined by the value of junction characteristic voltage
and are practically independent from the value of chain bias
voltage. The studies of negative differential resistance
region of I-V characteristic shows the presence of thin
structure which may be interpreted as a set of subharmonic
steps caused by the coupling of Josephson junction own
radiation with external microwave resonator. |
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Josephson
array oscillators with microstrip
resonators
A. Kawakami, Y. Uzawa
and Z. Wang
Summary: Interaction between two
Josephson junctions and a microstrip resonator is investigated
using a resonator shunted junction (RLCSJ) model. A sharp
current step resulting from coupling with the resonator is
observed in simulated I-V characteristics. There is strong
phase-locking and decreasing of dynamic resistance at the
current step. We design and fabricate two types of Josephson
array oscillators using these effects to obtain stable phase
locking and narrow linewidth for the oscillation. The
fabricated oscillators are formed with nine shunted Nb/AlOx/Nb
tunnel junctions and Nb microstrip resonators. The power of
the oscillator delivered to the load resistor was estimated to
be about 3.6 /spl mu/W at 330 GHz. A composite linewidth of
the oscillators is also measured at about 19 MHz at 4.2 K
using two oscillators with a log-periodic antenna and a SIS
detector. |
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Theory
of phase locking in simple two-dimensional Josephson junction
arrays with small inductances
M.
Basler, W. Krech and K.Yu. Platov
Summary:
Several elementary two-dimensional Josephson junction
arrays have been investigated mainly analytically with the
special emphasis on phase locking. For this purpose, a novel
perturbation scheme appropriate for the handling of small loop
inductances has been developed and applied to (i) a single
SQUID cell, (ii) two cells coupled by an inductive line, and
(iii) an externally loaded two-cell configuration with more
general internal shunt. While internal in-phase locking within
the cells can easily be achieved as long as the normalized
ring inductances are small compared to unity, the inter-cell
coupling tends to favor an antiphase regime. A mechanism is
proposed for circumventing this problem and the boundaries
separating both regimes are determined. The influence of an
external load is considered as well. |
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Magnetic
microscopy using SQUIDs
F.C.
Wellstood, Y. Gim, A. Amar, R.C. Black and A.
Mathai
Summary: SQUID-based magnetic
microscopy involves scanning a sample closely past a low-noise
SQUID. With the SQUID held in a flux-locked loop, a computer
records the feedback output as a function of sample position
and converts the resulting data into a false color image of
magnetic field strength. Present systems have achieved spatial
resolution down to about 5 /spl mu/m and flux resolution down
to about 1 /spl mu//spl Phi//sub 0//Hz/sup 1/2/. They have
been used to study the pairing symmetry of the high-T/sub c/
superconductors, for high-frequency imaging, and for a variety
of applications related studies. Recently, microscopes have
also been developed for high resolution magnetic imaging of
room-temperature samples. We briefly describe the design,
operation, and capabilities of these systems. |
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Miniature
vector magnetometer for scanning SQUID
microscopy
M.B. Ketchen, J.R.
Kirtley and M. Bhushan
Summary: We have
demonstrated a miniature vector magnetometer for imaging three
orthogonal components of the magnetic field in close proximity
to a planar sample. This magnetometer consists of three
separate SQUIDs fabricated adjacent to each other on a planar
substrate using a planarized, three-level-of-metal low-Tc
process with features as small as 0.8 /spl mu/m. The z-axis
SQUID has a conventional single square pick-up loop,
approximately 10 /spl mu/m in size, that connects to remotely
located tunnel junctions via a totally enclosed planar coaxial
lead structure. The x- and y-axis SQUIDs are of similar design
except that the pick-up structures are in the form of
multiple-turn planar solenoids about 10 /spl mu/m in size. In
this paper we will discuss the design, fabrication, and
characterization of the devices along with initial results of
the imaging of individual trapped flux quanta. |
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Self-oscillating
micro-SQUIDs for application in a scanning SQUID
microscope
J. Dechert, K.
Krischker, T. Goddenhenrich, M. Muck and C.
Heiden
Summary: The obtainable spatial
resolution of a scanning SQUID microscope depends among others
on the effective SQUID area. An effective area of only a few
/spl mu/m/sup 2/ is desirable as it allows for a spatial
resolution of a few /spl mu/m. SQUIDs with conventional tunnel
junctions are not suitable for this task, since tunnel
junctions usually have a relatively large area and are
therefore sensitive to magnetic fields themselves. A SQUID
with nanobridges as weak links provides very small junction
areas of below 0.1 /spl mu/m/sup 2/. When making use of the
thermal hysteresis in the I-V-characteristics of these
bridges, a SQUID relaxation oscillator can be realised. In
such a self-oscillating SQUID (SOS) the oscillation frequency
depends periodically on the applied magnetic flux. By reading
out the frequency change instead of a voltage change, a simple
and compact SQUID readout results. As a first application of
such micro-SQUIDs, a scanning SQUID microscope was built and
the magnetic field of a nickel tip with 100 nm apex radius was
measured. |
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High-T/sub
c/ SQUID microscope for room temperature
samples
T.S. Lee, Y.R. Chemla, E.
Dantsker and J. Clarke
Summary: A high-T/sub
c/ SQUID microscope has been constructed for imaging samples
at room temperature and atmospheric pressure. The SQUID is
mounted on the upper end of a sapphire rod, cooled to liquid
nitrogen temperature, below a 3-/spl mu/m thick silicon
nitride vacuum window. This arrangement yields a
SQUID-to-sample separation as low as 15 /spl mu/m. A sample
can be placed on the window or scanned over the SQUID to
produce magnetic images. |
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Functional
modeling of RSFQ circuits using Verilog
HDL
Kris Gaj, Chin-Hong Cheah,
E.G. Friedman and M.J. Feldman
Summary:
Circuit level simulation is too slow to be used for
verification of function and timing of large RSFQ circuits.
The alternative, known from semiconductor digital circuit
design, is simulating at the logic (gate) instead of the
circuit (transistor or junction) level. Using a hardware
description language (HDL) such as Verilog, it is possible to
write functional model of each of the RSFQ basic gates. A
large RSFQ circuit composed of hundreds gates and thousands
Josephson junctions can then be simulated using standard
semiconductor industry CAD tools. We have developed a library
of Verilog models for over 15 basic RSFQ gates. We describe in
detail our model for the DRO RSFQ cell. We show how this model
can be generalized for other more complex cells. Our library
has been verified by employing it in the design of timing for
three large RSFQ circuits. |
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Feasibility
study of RSFQ-based self-routing nonblocking digital
switches
D.Y. Zinoviev and K.K.
Likharev
Summary: This paper describes the
results of a preliminary analysis of ultra-fast low-power
superconductor digital switches based on Rapid
Single-Flux-Quantum (RSFQ) technology. In particular,
RSFQ-based crossbar, Batcher-banyan, and shared bus switching
cores have been considered, and the possible parameters of
these circuits have been estimated. The results show that the
proposed RSFQ digital switches with overall throughput of 7.5
Tbps operating at an internal clock frequency of /spl sim/60
GHz and dissipating very little power could effectively
compete with their semiconductor and photonic
counterparts. |
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Flux
trapping experiments in single flux quantum shift
registers
R.P. Robertazzi, I.
Siddiqi and O. Mukhanov
Summary: As the
integration level of superconducting digital circuits
increases, flux trapping in these devices becomes a serious
problem. High resolution A/D converters and other high speed
signal processing systems have been demonstrated with junction
counts well into the 10/sup 3/ range. Such large circuits
require special testing techniques to prevent flux trapping
within the gates, which can reduce bias margins and cause
malfunctions of these devices. We discuss the results of
experiments using single flux quantum shift registers in which
we have varied the ground plane hole pattern and magnetic
shield degaussing procedure to minimize flux trapping in these
circuits. The operating bias margins of the shift registers
have been measured as a function of different testing
procedures and ground plane hole designs. In situ degaussing
of the magnetic shields aids in the reduction of flux trapping
and gave the best results. Measurements of the permeability of
mu metal at 4.2 K are discussed. |
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Design
and low speed testing of a four-bit RSFQ
multiplier-accumulator
Q.P. Herr,
N. Vukovic, C.A. Mancini, K. Gaj, Qing Ke, V. Adler, E.G.
Friedman, A. Krasniewski, M.F. Bocko and M.J.
Feldman
Summary: We have designed and RSFQ
multiplier-accumulator, the central component of our
decimation digital filter. The circuit consists of 38
synchronous RSFQ cells of six types arranged into a
rectangular systolic array fed by one parallel input and one
serial input. Timing is based on counter-flow clock
distribution scheme with simulated maximum clock frequency of
11 GHz. The circuit, fabricated at Hypres, Inc., contains 1100
Josephson junctions, has power consumption less than 0.2 mW,
and area less than 2.5 mm/sup 2/. The multiplier-accumulator
has been tested at low frequency demonstrating full
functionality and stable operation over a 24 hour testing
period. This four-bit multiplier accumulator is one of the
largest reported RSFQ circuits verified experimentally to
date. |
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Design
and fabrication of an adder circuit in the extended phase-mode
logic
T. Onomi, T. Yamashita, Y.
Mizugaki and K. Nakajima
Summary: We present
the design and the fabrication of an adder circuit in the
extended phase-mode logic family. The phase-mode logic is a
single flux quantum (SFQ) logic which utilizes an SFQ as an
information bit carrier. The single-bit adder circuit is made
up of an INHIBIT gate which is the basic device of the
phase-mode logic. The circuit has been designed and fabricated
using Nb/AlO/sub x//Nb Josephson junctions with Josephson
critical current density of 1.0 kA/cm/sup 2/. In order to
confirm the circuit operation, the fabricated adder circuit
has been tested at low speed. For investigating the
possibility of a high-frequency operation, dc voltages
generated by fluxon pulse trains have been measured. From the
Josephson voltage-frequency relation, the result shows that
the circuit has potential to complete the carry operation
within 20 psec. |
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Single
flux quantum elements based on a single-layer of a high-T/sub
c/ superconductor
V.K.
Kaplunenko, E.A. Stepantsov, H.R. Yi, T. Claeson, H. Toepfer,
G. Hildebrandt, F.H. Uhlmann and E. Wikborg
Summary:
We have designed, fabricated and successfully tested
three SFQ elements: a toggle flip-flop, a SFQ voltage
amplifier, and an RS-flip-flop. The design uses a single
superconducting layer and it is optimized by repeated computer
simulations and repeated inductance calculations. The
inductances are made as narrow slits of 0.5 /spl mu/m width.
Their values are calculated numerically taking into account
material parameters derived from experiment. The YBCO
junctions are either of step edge type on LaAlO/sub 3/
substrates or located on two closely spaced bi-crystal grain
boundaries on a novel YSZ tricrystal substrate. Carbon masks
were used to form steps on LaAlO/sub 3/ substrates and for the
YBCO patterning. Voltage amplifier shows operation up to 60 K,
and both flip-flops were observed to operate at temperatures
up to 30 K with parameters close to the simulated values. The
operation frequency of a T-flip-flop cell of about 150 GHz was
achieved and a new measurement technique of the margins of an
RS trigger is suggested. |
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Analog
simulation on enhanced AC Josephson effect for a junction
driven by RF-current source
A.
Takada and T. Kikuchi
Summary: The ac
Josephson effect for a current-driven Josephson junction
enhanced by a non-monochromatic input signal is studied based
on an analog simulation. The obtained rf-induced step-height
in the current-voltage characteristic which is a measure of
this effect suggest that the use of either a pulse train or a
biharmonic consisting of fundamental and second harmonic
sinusoidal functions is effective for the enhancement, if
compared to a monochromatic signal drive. It is revealed that
the individual phase locking between the rf-signal and the
Josephson oscillation is much more stabilized by use of the
pulse train-like signal and can be explained qualitatively by
a pendulum motion, i.e., the relatively slow motion of the
pendulum near the position of rest. |
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The
effects of step angle on step edge Josephson junctions on
MgO
C.P. Foley, S. Lam, B.
Sankrithyan, Y. Wilson, J.C. MacFarlane and L.
Hao
Summary: We have fabricated step edge
junctions using MgO substrates and YBCO thin films. By varying
the angle of the step edge over a range of angles up to 45/spl
deg/, we have obtained 3 distinct step edge morphologies: a
deep trench junction, a double junction and a single junction.
We found that only the step angle and morphology affected the
critical current density (I/sub c/) and that the film
thickness-to-step height ratio had no effect over the range
0.2-1.1. Noise measurements indicated that the single junction
steps had the lowest level of critical current fluctuations
and the highest values of dynamic resistance. We have also
studied the variation of I/sub c/ with temperature and found
it follows the Ambergaokar-Baratoff model with a lower zero
energy gap. We use this information to confirm that the
junction parameters are affected by the c-axis tilt and the
in-plane orientations proposed by others and consider the
transport mechanisms across the junction. |
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Barrier
properties of grain boundary junctions in high-T/sub c/
superconductors
O.M. Froehlich,
P. Richter, A. Beck, D. Koelle and R. Gross
Summary:
We have measured the quasiparticle tunneling (QPT) in
grain boundary Josephson junctions for different high
temperature superconductors. The investigation of the
temperature and voltage dependence of the QPT in different
applied magnetic fields (from 0 to 12 T) over a wide voltage
range provided strong evidence for an insulating barrier with
a high density of localized states. The average barrier height
/spl phi/ and thickness d of the different materials was
extracted from the parabolic background conductance at high
voltages. In the low voltage regime we observed a zero-bias
conductance peak, that is discussed in terms of spin-flip and
Kondo-type scattering at the interface (Anderson-Appelbaum
model). |
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YBa/sub
2/Cu/sub 3/O/sub 7-x/ Josephson junctions on bicrystal Al/sub
2/O/sub 3/ and SrTiO/sub 3/
substrates
L.R. Vale, R.H. Ono
and D.A. Rudman
Summary: Bicrystal
grain-boundary junctions (bi-GBJs) have been reproducibly
fabricated on SrTiO/sub 3/ (STO) and r-plane Al/sub 2/O/sub 3/
(sapphire) bicrystal substrates. Sapphire bicrystals are
candidates for high-frequency applications due to their low
dielectric constant and loss tangent. The sapphire bi-GBJs
demonstrated resistively shunted junction (RSJ)-like current
voltage characteristics, with junction parameters comparable
to the STO bi-GBJs and critical current densities Jc/spl
sim/10/sup 5/ A/cm/sup 2/. Independent control of junction
resistance (R/sub N/) was demonstrated with the use of Au
shunt layers. In addition, overlayers such as Au or STO may
act to passivate the GBJs and improve long term
stability. |
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YBaCuO/TlBaCaCuO
epitaxial thin film superconducting multilayers-a novel
approach to intrinsic Josephson junction
devices
M. Veith, K. Kirsch, T.
Eick and E. Steinbeiss
Summary: Tl/sub
2/Ba/sub 2/CaCu/sub 2/O/sub 8/ (TBCCO) thin films have been
deposited on top of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//
(YBCO) thin films. Both layers are superconducting with T/sub
c/ values of 105 K and 75 K respectively and in
superconducting contact. XRD scans show the TBCCO film to grow
epitaxially and c-axis oriented on the YBCO ground layer.
Possible applications for such multilayers are novel concepts
for intrinsic Josephson arrays requiring well defined mesa
structures of TBCCO. |
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Orientation
effects in YBCO/PBCO/YBCO trilayer
junctions
F. Gire, D. Robbes, C.
Gonzalez, F.R. Ladan and J.P. Senateur
Summary:
We have completed a comparative study on
YBaCuO/PrBaCuO/YBaCuO trilayer junctions according to the
crystallographic orientation of the films used in order to
determine the best orientation to get a Josephson junction
working at 77 K. To this end, 100% a-axis, [110] and [103]
oriented samples have been deposited using the hollow cathode
method. In order to characterize our junctions, /spl Phi/
scan, resistivity and electrical measurements were made, None
of the a-axis junctions were able to work above 20 K, due to
the very large resistive transition of the base electrode. On
the other hand, the structures made with [110] films had good
superconducting properties and the barrier exhibited
superconducting transition beyond 80 K (J/sub c/(77 K)/spl
ap/5.10/sup 3/ A/cm/sup 2/), but no Josephson effects were
seen, Finally, we would stress the fact that almost all the
devices made with [103] oriented films exhibited clear Shapiro
steps at 77 K. The T/sub c/ and J/sub c/(77 K) of these
structures were respectively 82 K and 2.102 A/c cm/sup
2/. |
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Properties
of HTS step-edge SNS
junctions
A.A. Golubov, V.M.
Krasnov and M.Yu. Kupriyanov
Summary: The
critical current and current-voltage characteristics of
step-edge HTS SNS junctions are discussed theoretically. In
accordance with the experimental data it is assumed that the
current transport through both NS interfaces takes place in
ab-direction. In the bottom interface ((001) surface of YBCO)
the ab-coupling may occur due to atomic steps which play a
role of constrictions for the current flow. Therefore the
contact is modelled as SNS structure with system of
constrictions located at both interfaces. The L/sub c/R/sub N/
product and the excess current I/sub cx/ are calculated as a
function of temperature, interface transparency and N layer
thickness. It is shown that in accordance with the
experimental data the I/sub cx/ and I/sub c/ are of the same
order of magnitude in a broad parameter range. |
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Critical
currents, proximity effect, and Josephson penetration depth in
planar high-T/sub c/ Josephson
junctions
S.K. Tolpygo and M.
Gurvitch
Summary: We have studied the
temperature dependence of the critical current in planar
high-T/sub c/ Josephson junctions fabricated in YBa/sub
2/Cu/sub 3/O/sub 7/ thin films by focused electron
irradiation. We show that in the range of critical current
densities spanning more than five orders of magnitude and
temperature range 0.1 |
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A
tuned SQUID amplifier for MRI based on a DOIT flux locked
loop
H.C. Seton, J.M.S. Hutchison
and D.M. Bussell
Summary: We have developed a
4.2 K, flux locked, tuned d.c. SQUID amplifier to improve the
SNR of a low field MRI system operating at 0.01 T (425 kHz).
The flux locked loop, based on the Direct Offset Integration
Technique, has a noise level of 2.6 /spl mu//spl Phi//sub 0/
Hz/sup -1/2/ and a slew rate of 1.6/spl times/10/sup 6/ /spl
Phi//sub 0/ s/sup -1/ at 425 kHz when used with a commercially
obtained SQUID. The high intrinsic Q-factor of the MRI pick-up
coil is damped by the action of the loop and by an additional
feedback circuit to provide imaging bandwidths of up to 10
kHz. We have developed a special low noise liquid helium
cryostat so that the final system has a magnetic field
resolution of 0.08 fT Hz/sup -1/. This receiver was used in a
small scale MRI system to image non-conducting test objects
and the human arm. The images show significant improvements in
SNR over those obtained with an equivalent room temperature
receiver. |
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High
linear dynamic range magnetometer utilizing a large array of
serially connected SQUIDS
Kin Li
and S.P. Hubbell
Summary: A 7104-element
serially connected SQUID array magnetometer has been designed
and tested. The array had a measured magnetic field to voltage
transfer function dV/dB of 1.2/spl times/10/sup 5/ volt/Tesla
and a peak to peak modulation voltage of 0.6 volt. The
sensitivity of the array magnetometer is 105 fT/Hz/sup 1/2/ at
20 kHz, and is limited by the 1/f noise of SQUIDs. The
effective signal collection area of the array is 0.018 cm/sup
2/. The measured dynamic range of the array is 126
dB. |
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Spatial
response of symmetric and asymmetric planar SQUID
gradiometers
M.E. Walker, G.
Lang, U. Klein, C.M. Pegrum, G.B. Donaldson and S.
Cochran
Summary: First and second order
symmetric gradiometers, and first order singly and doubly
asymmetric gradiometers have been designed and fabricated
using a standard niobium thin-film process. Here we present
the results of our simulations of the effect of varying the
gradiometer geometry, order and symmetry. In particular, we
are interested in the spatial response of the gradiometer. We
compare the simulations with experimental data. |
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Noise
behaviour of the un SQUID studied by numerical
simulation
M. Kiviranta and H.
Seppa
Summary: The unshunted SQUID is a
magnetic flux sensor, whose Josephson junctions are damped in
a novel way. We have studied its dynamics with noise sources
by numerical simulation. Results suggest that its energy
resolution is at least 2 times better than that of a
conventional dc SQUID. |
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Direct-coupled
high T/sub c/ DC SQUID gradiometer with single layer YBa/sub
2/Cu/sub 3/O/sub 7/
Yunsung Huh,
Soon-Gul Lee, In-Seon Kim, Yong Ho Lee, Hyuk Chan Kwon, Yong
Ki Park, Jong-Chul Park, Insang Song and Gwangseo
Park
Summary: We have studied first
derivative high T/sub c/ dc SQUID (Superconducting QUantum
Interference Device) gradiometer from a single layer of Y/sub
1/Ba/sub 2/Cu/sub 3/O/sub 7/ thin film using pulsed laser
deposition (PLD) and argon ion beam etching method. The planar
gradiometer consists of two pickup loops coupled directly to
dc SQUID with an inductance of about 20 pH in the center of
the structure. The gradiometer contains step-edge type
junctions of 3 /spl mu/m width and is made on the SrTiO/sub 3/
substrate of 12/spl times/25 mm/sup 2/ in size. The SQUID
showed RSJ type junction I-V characteristics with T/sub c/ of
86 K and swing voltage of /spl sim/4 /spl mu/V at 79.3 K. The
magnetometer was sensitive only to the gradient of the
magnetic field with well balanced null response to uniform
fields. |
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Low-temperature
scanning electron microscopy for low noise studies of
high-T/sub c/ superconductors
R.
Gerber, T. Nissel, H.-G. Wener, A. Willmann, S. Keil, H.
Hansel, R.P. Huebener, D. Koelle and R.
Gross
Summary: Low-Temperature Scanning
Electron Microscopy (LTSEM) has been successfully applied to
the investigation of the local superconducting properties of
thin films and Josephson junctions as well as to the study of
more complex superconducting circuits. Since many
superconducting devices and circuits can be operated
successfully only in low ambient magnetic fields, we have
built a liquid nitrogen cooled low temperature stage with
improved magnetic shielding for the temperature range between
77 and 130 K. For effective magnetic shielding we use a
superconducting YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// tube
in addition to several Mumetall shields. We established
further improvements such as an in-vacuum motorized x-y-slide,
which allows us to shift the sample with a minimum step width
of 1.5 /spl mu/m. We present first test measurements of the
transport properties of a high T/sub c/ dc SQUID that
demonstrate the functionality of the new stage. |
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Magneto-optical
studies of high-T/sub c/ SQUID
circuits
S. Govorkov, A.A. Fife,
G. Anderson, V. Haid, Hu Zhou, B. Heinrich and J.
Chrzanowski
Summary: Magneto-optical studies
have been carried out on high-T/sub c/ thin film circuits such
as flux transformer coils and DC SQUIDs. The high resolution
magnetic field maps emphasize regions of high field and
localized defects. Observation of the flux transformer coil
response to an applied field allowed a determination of the
minimum critical current. An inversion procedure is also
described for calculation of the current distributions in the
patterned coil films. The images of DC SQUIDs fabricated on
bicrystal substrates show the effects of flux penetration
through the bicrystal boundary. The noise performance of the
coils while flip-chip coupled to the bicrystal DC SQUIDs is
also summarized. The research has provided information useful
for improvements to multi-level high-T/sub c/ circuit design
and fabrication. |
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Octopux:
an advanced automated setup for testing superconductor
circuits
D.Y. Zinoviev and Y.A.
Polyakov
Summary: An integrated multipurpose
setup for the automated testing of superconductor devices and
circuits has been designed, implemented, and installed in the
RSFQ Laboratory of the State University of New York at Stony
Brook. The extendable and modular design of the setup allows a
wide variety of low-frequency superconductor experiments to be
carried out including those that require immediate interaction
between the setup and the researcher. |
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Superconducting
generator of electromagnetic
pulses
A.N.
Lykov
Summary: An idea for the creation of
active devices is proposed, based on flux jumps in layered
superconductors. In a magnetic field slightly tilted to the
layers a system of kinks on vortex lines can arise in such
superconductors. Rotation of the sample leads to the existence
of a kink structure even in a parallel magnetic field, since
the planar pinning centers obstruct disappearance of the
kinks. This is confirmed by the existence of a perpendicular
component of the trapped magnetic field when the film is
parallel to the external field under rotation. The transition
of the lattice into the ground state with minimum energy
should lead to the generation of an electromagnetic pulse; its
output energy is equal to the sum of the energies of the
kinks, which can be a significant part of the energy of the
magnetic field in the sample. |
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Josephson
voltage standard microwave circuits fabricated in a modified
all-niobium technology for operation at low drive
frequencies
H.-G. Meyer, G.
Wende, L. Fritzsch, F. Thrum and H.-J.
Kohler
Summary: A resonant type of
cryoelectronic microwave circuit for the generation of
frequency-scaled Josephson voltages is presented. The circuits
consist of superconducting microstripline resonators with
series arrays of Josephson tunnel junctions located on the
microwave current antinodes. This microwave design was chosen
to obtain highly accurate Josephson voltages at low microwave
power levels and low drive frequencies. The resonator circuits
have been fabricated in both niobium-lead and all-niobium
technology. At present, we have observed long-term stable
Josephson voltages up to 0.75 V for niobium-lead circuits with
1320 junctions and 0.66 V for all-niobium circuits with 1456
junctions, respectively. |
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Superconductor-insulator-normal
tunnel junctions for on-chip measurement of the
temperature
M.G. Castellano, R.
Leoni, G. Torrioli, P. Carelli, A. Gerardino and F.
Melchiorri
Summary: We describe SIN
(superconductor-insulator-normal) tunnel junctions made by
thin-films of Nb/AlOx/Cu and we report on the measurements of
their I-V characteristics between 10 K and 0.3 K. The
junctions show a strong dependence of the subgap conductance
on the temperature, which makes them suitable for the on-chip
measurement of the temperature. In this paper we also describe
the design of an on-chip electronic refrigerator based on this
type of junction. |
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Color
selective optical sensors based on dye/superconductor
assemblies
J.T. McDevitt, D.C.
Jurbergs, S.J. Eames, S.M. Savoy and J.
Zhao
Summary: This paper describes the
design, construction and operation of hybrid
dye/superconductor optical sensors. A reflective mirror layer
positioned between the dye and superconductor components is
used as a means to reject light signals that are not absorbed
strongly by the dye. On resonance signals are shown to couple
effectively with the underlying superconductor where they
evoke measurable responses. These structures form the basis
for color selective optical sensors. |
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Maximum
theoretical bandwidth and slewrate of a dc SQUID feedback
system
R.H.
Koch
Summary: The maximum theoretical
bandwidth and slewrate for a dc SQUID when it is operated in a
flux locked loop is calculated. |
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Reduction
of low frequency excess noise and temperature drift of SQUIDs
by "degaussing" using high frequency magnetic
fields
M. Muck, S. Schone and C.
Heiden
Summary: We have investigated a
possible scheme to reduce 1/f noise generated by thermally
activated hopping of vortices in SQUIDs by trying to remove
vortices from the SQUID body, or at least move them to pinning
sites having a high pinning energy. This is accomplished by a
"demagnetisation" scheme using a high frequency magnetic
field. Niobium SQUIDs were carefully cooled in a magnetically
well shielded environment and then exposed to switching
transients. The thereby generated low frequency excess noise
or an increased white noise could substantially be reduced by
this demagnetisation process. The temperature dependence of
the flux signal of the flux locked SQUID and the magnetic
field dependence of this drift could also be reduced in cases
where the drift was caused by motion of trapped vortices. The
influence of frequency and amplitude of the demagnetisation
field on the amount of noise reduction was studied in some
detail. |
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The
development of a high-T/sub c/ magnetocardiography system for
unshielded environment
B. David,
O. Dossel, V. Doormann, R. Eckart, W. Hoppe, J. Kruger, H.
Laudan and G. Rabe
Summary: A modular,
9-channel high-T/sub c/ SQUID system for magnetocardiography
(MCG) was developed and tested in an unshielded environment.
Galvanically-coupled magnetometers made from Y-Ba-Cu-O films,
with intrinsic white noise levels as low as 70 fT//spl
radic/Hz, are used as SQUID sensors. In an unshielded
environment, a noise level of about 1 pT//spl radic/Hz for
each channel was achieved using an active noise compensation
system. A new digital planar gradiometer is proposed. First
magnetocardiograms recorded in an unshielded environment are
presented. |
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Scanning
DC-SQUID system with high spatial resolution for
NDE
K. Chinone, S. Nakayama, T.
Morooka, A. Odawara and M. Ikeda
Summary: We
have developed a scanning DC-SQUID system with a high spatial
resolution for NDE. The SQUID system is composed of a
concentric multiloop DC-SQUID gradiometer using Nb/AlOx/Nb
Josephson junction, a non-magnetic scanning stage, a cryostat
and a computer for gathering data and controlling the system.
We have developed the concentric multi-loop gradiometer (d/sup
2/Bz/dr/sup 2/, r/sup 2/=x/sup 2/+y/sup 2/) to have a higher
spatial resolution and reduce background noise. The
gradiometer was integrated on a single 3/spl times/3 mm/sup 2/
Si chip. To reduce the standoff distance between the specimen
and the pick-up coil, a cryostat with a thin bottom space was
developed. A scanning stage was made of nonmagnetic materials
and was driven by air pressure using a rod-less cylinder to
avoid making magnetic noise. |
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Electromagnetic
nondestructive evaluation: moving HTS SQUIDs, inducing field
nulling and dual frequency
measurements
C. Carr, D.McA.
McKirdy, E.J. Romans, G.B. Donaldson and A.
Cochran
Summary: We have previously shown
that simple, single layer HTS SQUIDs can be used effectively
in electromagnetic nondestructive evaluation (NDE) using eddy
current techniques in a magnetically unshielded environment.
HTS SQUID systems for NDE applications are expected to be
small and portable allowing non-stationary measurements to be
carried out in the Earth's field above a stationary sample.
Here we present application-oriented results showing the
ability of our HTS electronic gradiometer to cope with the
movement of the sensors above a series of simulated flaws in
aircraft grade aluminum samples. To permit the detection of
fine surface and subsurface structures we have applied active
field nulling to the two SQUIDs to increase the effective
signal to noise ratio. The excitation signal is applied via a
non-superconducting coil to provide a lower field environment
for each device. We also present results using a dual
frequency eddy current technique to allow depth profiling of
flaws in multilayer structures. |
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Experiments
on eddy current NDE with HTS rf
SQUIDS
M. v. Kreutzbruck, K.
Troll, M. Muck, C. Heiden and Y. Zhang
Summary:
HTS SQUIDs are promising sensors for applications in
eddy current NDE. Due to their high field sensitivity at low
frequencies, they are especially suitable for applications,
where a large penetration depth is required. We have set up
two SQUID systems for low frequency eddy current NDE. 3 GHz rf
SQUIDs made from YBCO are used as sensors with a field
resolution of about 1pT//spl radic/(Hz). One system, where the
SQUIDs are cooled by immersing them in liquid nitrogen, is
optimised for testing fellows of aircraft wheels. The fixed
cryostat is mounted close to the outer surface of the rotating
fellow. The second system uses a cryocooler for SQUID cooling.
A motorised x-y stage is used to move the SQUIDs above the
plane specimen to be tested. Due to the high slewrate of the
SQUID electronics, both systems can easily be operated in an
unshielded environment. A double-D shaped coil is used to
reduce the excitation field at the location of the SQUID. We
report on first results of measurements on aircraft
parts. |
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A
2-channel wideband SQUID system for high-frequency geophysical
applications
D. Drung, T. Radic,
H. Matz, H. Koch, S. Knappe, S. Menkel and H.
Burkhardt
Summary: A prototype radiomagnetic
sounding system for measuring the conductivity of the shallow
subsoil down to some 10 m depth was built. With this system,
the horizontal magnetic field and field gradient of radio
transmitters in the frequency range 10-2000 kHz are detected
in small bore-holes of /spl lsim/1 m depth using two wideband
SQUIDs. The SQUIDs are operated at 4.2 K in a flux-locked loop
having a bandwidth of 11 MHz, a white flux noise level of
1.6/spl times/10/sup -6/ /spl Phi//sub 0///spl radic/(Hz), a
feedback range of /spl plusmn/610 /spl Phi//sub 0/, and a
maximum slew rate of 2/spl times/10/sup 6/ /spl Phi//sub 0//s
above 500 kHz increasing to 5/spl times/10/sup 7/ /spl
Phi//sub 0//s at 13 kHz. The system was successfully tested in
a first field measurement under urban environmental
conditions. The system design allows one in principle to use
nitrogen-cooled sensors. |
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Advances
in sensor development and demonstration of superconducting
gradiometers for mobile
operation
T.R. Clem, M.C.
Froelich, D.J. Ovenvay, J.W. Purpura, R.F. Wiegert, R.H. Koch,
D.K. Lathrop, J. Rozen, J.H. Eraker and J.M.
Schmidt
Summary: During the 1980s a
SQUID-based superconducting gradiometer prototype utilizing
bulk niobium and wire superconducting components cooled by
liquid helium was developed by the US Navy. This sensor was
successfully utilized in demonstrations for sea mine
countermeasures and for the detection of UneXploded Ordnance
(UXO). Advances in this sensor technology are being pursued
for longer detection ranges and for more versatile operation.
An advanced sensor prototype using all thin film niobium
circuits and a new liquid helium cooling concept has been
built to provide significant increases in sensitivity. In
addition, a high Tc sensor concept using liquid nitrogen
refrigeration has been developed to reduce package size and to
simplify logistic and support requirements for field
operation. This paper will review the current status and plans
of this program, specifically describing the recent advances
in sensor development and results from the demonstration to
detect UXO. |
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A
Cadence-based design environment for single flux quantum
circuits
V. Adler, Chin-Hong
Cheah, K. Gaj, D.K. Brock and E.G. Friedman
Summary:
The semiconductor industry standard
computer-aided-design (CAD) tool Cadence has been calibrated
for a 3 /spl mu/m Niobium technology in order to design and
build superconductive single flux quantum (SFQ) circuits. The
top-down design methodology includes Verilog functional
simulation, schematic capture, graphic layout, functional
verification, design rule checking, electrical rule checking,
and layout-vs.-schematic verification. This design framework
has been used successfully at the University of Rochester in
designing more than 15 elementary SFQ cells and three large
scale digital and mixed-signal SFQ circuits, demonstrating
significant improvement in both design efficiency and
accuracy. |
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Counting
SFQ analog to digital converter
results
R.D. Sandell, D.J.
Durand, B.J. Dalrymple and T. Pham
Summary:
We have characterized Nb analog to digital converters
using a resistor-coupled SFQ flip flop counter and a latching
destructive readout (DRO). The counter used SFQ buffers
between bits to provide isolation during destructive readout.
We have measured parallel readout at sample rates up to 125
MSPS. We have also successfully operated an ADC which has
Josephson junction regulated flip flop gate and readout bias
busses. Using a self-resetting gate (SRG) at the carry out of
the counter, we have measured the bit error rates (BER) of the
counters. A two junction SQUID quantizer, biased in the
voltage state, was used to produce correlated SFQ pulses at
each junction. The SRG outputs of two 10 bit counters
connected to the two quantizer outputs were compared. We
measured a BER of /spl sim/5/spl times/10/sup -11/ with the
quantizer operating at 19 GHz. We believe the principle error
source is the latching SRG. |
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Optoelectronic
clocking system for testing RSFQ circuits up to 20
GHz
J.F. Buzacchelli, Hae-Seung
Lee, S. Alexandrou, J.A. Misewich and M.B.
Ketchen
Summary: Unlike coaxial cable,
optical fiber has a bandwidth commensurate with the clock
rates of even the fastest rapid single flux quantum (RSFQ)
circuits. Employing this advantage, we have developed an
optoelectronic clocking system, in which optical pulses from a
picosecond laser are delivered via fiber to a superconducting
chip, on which metal-semiconductor-metal (MSM) photodiodes
generate fast electrical pulses with subpicosecond timing
accuracy. An optical pulse splitter, constructed out of
beamsplitters, mirrors, and half-wave plates, permits
selection of pulse pattern and clock rate from 80.6 MHz up to
20.6 GHz. With a sampling oscilloscope, we have directly
observed optical triggering of an RSFQ T flip-flop at
frequencies up to 1.3 GHz with a variety of bit patterns.
Optical triggering of a Josephson transmission line (JTL) at
frequencies up to 20.6 GHz has been verified by precise
measurement of the Josephson voltage; this result represents
the highest clock rate ever reported for an optical interface
for RSFQ circuits. |
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Optimization
of hybrid JJ/CMOS memory operating
temperatures
D. Gupta, B.
Amrutur, E. Terzioglu, U. Ghoshal, M.R. Beasley and M.
Horowitz
Summary: A major drawback of present
superconducting electronics is the lack of suitable large
scale memory. One approach to circumvent this problem is to
use semiconducting CMOS memory in conjunction with the fast
Josephson junction (JJ) logic. This requires operating the
CMOS memory at cryogenic temperatures. The speed of CMOS
circuits has been shown to increase at cryogenic temperatures.
Further increase in speed can be obtained by using JJ sense
circuits in the CMOS memory. Preliminary results show that
access time of 1.5 ns should be possible with this hybrid
JJ/CMOS approach using 1.2 micron CMOS, and JJ sense and
interface circuits. We also report the results of an analysis
of the optimal operating temperature of such hybrid memories
in conjunction with refrigeration requirements in light of the
emerging cryocooler technologies. |
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New
SQUID gate and its implementation into logic
circuits
F. Furuta, S. Matsumoto,
H. Akaike, A. Fujimaki and H. Hayakawa
Summary:
We propose non-latching gates based on Superconducting
QUantum Interference Device (SQUID) and logic circuits based
on it. The gate consists of a 3-junction-SQUID coupled with an
RF-SQUID inductively. According to numerical simulation, the
wide bias margin reached /spl plusmn/52%. Adopting the
magnetic coupling to apply input signals, the fan-out larger
than unity was obtained without reducing signal current level.
These consequences enabled us to realize complicated logic
functions using this gate, The gate delay was 4.5ps at
Jc=10kA/cm/sup 2/. An EXOR gate composed of two gates had the
bias margin of /spl plusmn/35% and the delay time of 12ps. The
operation in non-latching mode is also suitable for digital
circuits based on HTS junctions. |
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Stochastic
simulation of SFQ logic
J.
Satchell
Summary: The high speed and low
power of Single Flux Quantum logic (SFQ) are extremely
attractive, and significant capabilities have been
demonstrated in Nb technology. However the burden of cooling
to 4.2K has been a barrier to its widespread implementation.
The advent of High Temperature Superconductors (HTS), raises
the prospect of more accessible temperatures. This paper
examines some theoretical constraints on the implementation of
SFQ in HTS, and derives some ideas about the parameters
required of any HTS SFQ technology. |
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Effect
of the cooling time in YBa/sub 2/Cu/sub 3/O/sub 7/(7-/spl
delta/) film-growth process on grain boundary Josephson
junctions for small-scale
circuits
T. Ogawa and M.
Koyanagi
Summary: We have studied the effect
of the cooling time of YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//
films on the properties of bicrystal Josephson junctions. In
the three regions of the cooling time as 5/spl sim/6, 10/spl
sim/20, and more than 30(min.), the junctions' Tc were above
87K, 50/spl sim/86K and above 86K, and the average value of
the IcRn products at 77K were 0.12mV, 50/spl mu/V, and 80/spl
mu/V, respectively. The junction's Tc, the I-V curves, and the
junction parameters were changed due to the change of the
cooling time. As a result, it was found that the cooling time
was very important factor to determine the junction
properties. |
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Characterization
of ramp-type YBa/sub 2/Cu/sub 3/O/sub 7/ junctions by
AFM
D.H.A. Blank, G.J.H.M.
Rijnders, R.M.H. Bergs, M.A.J. Verhoeven and H.
Rogalla
Summary: We studied the morphology of
ramps in REBa/sub 2/Cu/sub 3/O/sub 7/ (REBCO) epitaxial films
on SrTiO/sub 3/ substrates, fabricated by RF magnetron sputter
deposition and pulsed laser deposition (PLD), by Atomic Force
Microscopy (AFM) and High Resolution Electron Microscopy
(HREM). The ramps were fabricated by Ar ion beam etching using
different masks of standard photoresist and TiN. AFM-studies
on ramps in sputter deposited films show a strong dependence,
i.e., formation of facets and ridges, on the angle of
incidence of the ion beam with respect to the substrate
surface as well as the rotation angle with respect to the
crystal axes of the substrate. Ramps in pulsed laser deposited
films did not show this dependence. Furthermore, we studied
the effect of an anneal step prior to the deposition of
barrier layers (i.e. PrBa/sub 2/Cu/sub 3-x/Ga/sub x/O/sub 7/)
on the ramp. First results show a crystallization of the ramp
surface, resulting in terraces and a non-homogeneous growth of
the barrier material on top of it. The thickness variations,
for thin layers of barrier material, can even become much
larger than expected from the amount of deposited material and
are dependent on the deposition and anneal conditions. HREM
studies show a well-defined interface between barrier layer
and electrodes. The angle of the ramp depends on the etch rate
of the mask and REBCO and on the angle of incidence of the ion
beam. Hard masks, like TIN, have a much lower etch rate
compared to photoresist, resulting in an angle of the ramp
comparable to the angle of incidence and, subsequently, in a
low etching rate on the ramp. |
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YBa/sub
2/Cu/sub 3/O/sub 7-x/ grain boundary Josephson junctions with
a MgO seed layer
A. di Chiara, F.
Lombardi, F.M. Granozio, U.S. di Uccio, F. Tafuri and M.
Valentino
Summary: A YBa/sub 2/Cu/sub 3/O/sub
7-x/ artificial grain boundary Josephson junction mas
fabricated on to a [110] SrTiO/sub 3/ substrate employing a
MgO seed layer. YBa/sub 2/Cu/sub 3/O/sub 7-x/ grows mainly
oriented (103) on SrTiO/sub 3/ and [001] on the seed layer. An
artificial 45/spl deg/ a or b axis tilt or twist boundary can
occur according to the orientation of the MgO edge with
respect to the [001] in plane direction of the substrate.
Josephson junctions of good quality and excellent
reproducibility were obtained in microbridges patterned across
the grain boundary. Typical features of the phenomenology of
high critical temperature superconductor (HTCS) Josephson
junction were observed. The maximum value of the I/sub C/R/sub
N/ product is of the order of 2-3 millivolts at T=4.2 K and of
the order of 50 /spl mu/V at T=77 K respectively. The
modulation of the critical current with the external applied
magnetic field confirms the Josephson nature of the current in
the weak link. |
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Surface
depression of the order parameter and pair symmetry in the
Josephson critical current of high-T/sub c/ SIS' and SIS
junctions
R.S. Gonnelli, D.
Putterro, G.A. Ummarino and C. Bravi
Summary:
The Josephson critical current I/sub c/(T) in various
high-T/sub c/ SIS' and SIS junctions of different kind has
been analyzed, and its discrepancies with BCS s-wave
predictions are consistent with a model which takes into
account an intrinsic depression of the order parameter /spl
Delta/ at the interface between the superconductor and the
insulating layer as the cause of the reduced values of I/sub
c/(T)R/sub N/(T) and its behaviour vs. T up to T/sub c/.
Comparison with the fits obtained by a model based on s+id
pair symmetry with a dominant d-wave component shows that the
latter is unable to describe experimental results in shape
with an univocal ratio /spl Delta//sub d///spl Delta//sub s/
and, in magnitude, it often yields results two or three times
greater than those measured. On the contrary, our
gap-depressed model only fails to describe experimental data
when junctions' quality is rather poor, due to the fabrication
process and other reasons related to the quality of
interfaces. |
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Noise
characteristics of YBCO c-axis microbridge
junctions
T.G. Henrici, Ling Hao,
J.C. MacFarlane, C.M. Pegrum, S.W. Goodyear, J.S. Satchell and
R.G. Humphreys
Summary: We present
measurements of the noise properties of YBCO c-axis
Microbridge (CAM) Junctions. The junctions have been
characterised in terms of their electrical and noise
properties over range of temperature and frequency. The
methods used provide both very high sensitivity measurements
in a narrow frequency band (60 kHz), and moderate sensitivity
measurements in a broad band (0.01-10 kHz). The normalised
levels of critical current fluctuations and normal resistance
fluctuations are found to be comparable to earlier
measurements carried out on grain boundary junctions at both
100 Hz and 60 kHz. The 60 kHz results can be modelled
reasonably successfully with the same model developed to
describe grain boundary junctions. The frequency dependence is
close to 1/f, but has some Lorentzian shaped deviations
appearing for many of the junctions examined. These structures
are both temperature and bias current dependent. |
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Millimeter-wave
radiation in high-T/sub c/ Josephson
junctions
G. Kunkel, G.
Hechtfischer, M. Frommberger, K. Veit, R. Kleiner, P. Muller,
W. Prusselt, H. Kinder, L. Ferchland, G. Daalmans and R.H.
Ono
Summary: We have investigated
millimeter-wave radiation from single Josephson junctions and
small phase-locked Josephson junction arrays. Josephson
junctions were fabricated on sapphire bicrystal substrates.
Emission could be measured up to 110 GHz. Resonances in
ten-junction circuits yield linewidths narrower than 200 MHz.
This type of array might be useful for applications in
integrated receiver systems. |
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Low
noise LTS SQUIDs for application in gravitational
experiments
W. Vodel, H. Koch, S.
Nietzsche, J. V. Zameck Glyscinski, H. Dittus, S. Lochmann and
C. Mehls
Summary: The Weak Principle of
Equivalence (WEP) is proved up to now with an accuracy of
1/spl times/10/sup -12/. Short range free fall experiments
attained an accuracy of 5/spl times/10/sup -10/ only.
Microgravity facilities such as the "Drop Tower Bremen"
enables long range free fall experiments which may improve the
accuracy of free fall tests to <10/sup -12/ using high
performance SQUID measuring technique. In this review the
application of LTS DC SQUIDs with Nb-NbO/sub x/-Pb/In/Au
window-type Josephson junctions for gravitational experiments
is described. Under optimal conditions a noise limited
sensitivity of 1.4/spl times/10/sup -12/ m//spl radic/(Hz) for
the position detector was achieved corresponding to a flux
noise of the SQUID system of 2/spl times/10/sup -6/ /spl
Phi//sub 0///spl radic/(Hz). The contribution gives the design
of the DC SQUID position detector and summarizes recent
results of its application in gravitational
experiments. |
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Serial
array high T/sub c/ SQUID
magnetometer
Soon-Gul Lee,
Yunsung Huh, Gwang-Seo Park, In-Seon Kim, Yong Ki Park and
Jong-Chul Park
Summary: SQUID magnetometers
have been fabricated from series arrays of YBa/sub 2/Cu/sub
3/O/sub 7/ dc SQUIDs by pulsed laser film deposition and ion
mill patterning techniques. The array was designed either in
linear chain with flux focusers or in meander structure. The
arrays consisted of 50-130 step-edge junction SQUIDs and each
SQUID had inductance of 20-40 pH with 2-5 /spl mu/m junction
width. A linear array of 50 SQUIDs showed a modulation
amplitude of 150 /spl mu/V which corresponds to a gain of /spl
sim/10. One of 80 SQUID meander arrays had a gain of as high
as 50. These results provide feasibility of the series array
of SQUIDs in the direct readout SQUID amplifier circuitry with
wide bandwidth. Larger number SQUID arrays and processes to
increase the gain to the theoretical value need to be
studied. |
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Growth
of NdBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thin films and
fabrication of directly coupled dc SQUID
magnetometer
Yong Ki Park, Dong
Han Ha, In-Seen Kim, Jong-Chul Park and Yunsung
Huh
Summary: Thin films of NdBa/sub 2/Cu/sub
3/O/sub 7-/spl delta// were fabricated by off-axis rf
sputtering and pulsed laser deposition (PLD) methods. The
deposition parameters for thin film fabrication, such as gas
pressure, substrate temperature, annealing conditions, and rf
power or laser energy density were studied. Highly c-axis
oriented thin films with the maximum T/sub c/ (R=0) of 87 K
were obtained at the optimum deposition conditions of rf
sputtering. It, however, was more difficult to optimize the
PLD conditions. The directly coupled dc SQUIDs were fabricated
on SrTiO/sub 3/ bi-crystal substrates using single layer
NdBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// film grown by PLD
method. |
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Resonant
characteristics of high T/sub c/ DC SQUID caused by large
dielectric constant of SrTiO/sub
3/
K. Enpuku, T. Maruo and T.
Minotani
Summary: Dynamic behavior of a DC
SQUID coupled to a resonant circuit is studied with numerical
simulation. It is shown that large RF noise flux is caused by
the resonant circuit, and is added to the SQUID. This RF flux
affects considerably the SQUID characteristics, e.g.,
appearance of resonant behavior and the increase of noise. It
is also shown that a parasitic capacitance between the
resonant circuit and the ground of the SQUID changes the SQUID
characteristics. Therefore, it is important to suppress the RF
noise flux and decrease the parasitic in order to improve the
characteristics of the SQUID. |
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Superconducting
tunnel junctions as photon counting detectors in the infrared
to the ultraviolet
P. Verhoeve,
N. Rando, A. Peacock, A. van Dordrecht, A. Poelaert and D.J.
Goldie
Summary: Photon counting experiments
with Ta/Al superconducting tunnel junctions are presented.
Single photon detection is demonstrated in the wavelength
range /spl lambda/=200-2000 nn with a resolving power /spl
lambda///spl Delta//spl lambda/=22-4. The response of the
detector shows good linearity with photon
energy. |
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Inhomogeneous
response of superconducting tunnel junctions with a killed
electrode for X-ray
spectroscopy
M.L. van den Berg,
M.P. Bruijn, J. Gomez, F.B. Kiewiet, P.A.J. de Korte, H.L. van
Lieshout, O.J. Luiten, J. Martin, J.B. le Grand, T. Schroeder
and R.P. Huebener
Summary: Nb-based
superconducting tunnel junctions are being developed as high
energy resolution X-ray detectors. Unfortunately, loss of
excess quasiparticles at the edges, combined with lateral
diffusion, results in an inhomogeneous response. To study this
degradation of energy resolution, we manufactured detectors
with a Ta trap in the top or bottom electrode away from the
tunneling barrier. Excess quasiparticles in this so-called
killed electrode will be trapped effectively and thus removed
from the tunneling process. The X-ray spectra of the active
electrode can be fitted with a model based on classical
diffusion of quasiparticles. On junctions with a killed bottom
electrode also Low Temperature Scanning Electron Microscopy
(LTSEM) measurements have been performed. The X-ray spectra
and the LTSEM scans are consistent with each other and with
the model. The energy resolution of the junctions presented
here is limited by loss of quasiparticles at the
edges. |
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Technique
for fabricating tungsten thin film sensors with T/sub c/ /spl
les/100 mK on germanium and silicon substrates [dark matter
detectors]
B.A. Young, S.W. Nam,
P.L. Brink, B. Cabrera, B. Chugg, R.M. Clarke, A.K. Davies and
K.D. Irwin
Summary: Until recently, our work
on superconducting thin film phonon sensors for cryogenic
detector applications was limited to silicon substrates only.
We have now successfully extended low T/sub c/ (/spl les/100
mK) tungsten sensor technology and sensor fabrication
capability to include high purity germanium substrates as
well. Here, we describe a technique for fabricating low T/sub
c/ superconducting tungsten films on germanium, and we present
first results from cryogenic characterization experiments with
these films. We also summarize our work on the development of
a process to independently etch aluminum and tungsten films
deposited on the same germanium substrate. The capability to
selectively etch aluminum and tungsten films is critical for
the fabrication of our silicon and soon also germanium
detectors which utilize overlapping thin films of
superconducting tungsten and aluminum for the phonon sensors.
Due to the nature of their operation, we refer to these
sensors as W/Al Quasiparticle trap assisted-Electrothermal
feedback-Transition edge (QET) Sensors. |
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Characteristics
of large Nb-based tunnel junctions for X-ray
detection
K. Maehata, K.
Ishibashi, H. Nakagawa, H. Akoh, E. Joosse, S. Takada and M.
Katagiri
Summary: A high quality Nb-based
tunnel junction with a dimension of 200 /spl mu/m/spl
times/200 /spl mu/m was tested by irradiating with X-rays. Two
kinds of stable operation modes were observed by applying a
magnetic field with different ramping speeds. The junction
exhibited a good response to X-rays of 5.9 keV, and FWHM (full
width at half maximum) of 93 eV was obtained. |
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Empirical
characteristics of tunnel junctions for X-ray
detection
K. Ishibashi, T.
Kishimoto, K. Maehata, M. Hashimoto and Y.
Matsumoto
Summary: Superconducting tunnel
junctions show an excellent energy resolution in X-ray
detection. A simple procedure is employed to give an overview
of the detector characteristics regardless of superconductor
materials such as Al, Sn and Nb. By introducing an empirical
relationship between junction parameters, the detector
characteristics of signal magnitude and energy resolution are
reproduced to an acceptable degree. This method gives helpful
suggestion for understanding detector performance, and also
serves as a guide line for designing tunnel
junctions. |
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Proximity
effect and hot-electron diffusion in Ag/Al/sub 2/O/sub 3//Al
tunnel junctions
H. Netel, J.
Jochum, S.E. Labov, C.A. Mears, M. Frank, D. Chow, M.A.
Lindeman and L.J. Hiller
Summary: We have
fabricated Ag/Al/sub 2/O/sub 3//Al tunnel junctions on Si
substrates using a new process. This process was developed to
fabricate superconducting tunnel junctions (STJs) on the
surface of a superconductor. These junctions allow us to study
the proximity effect of a superconducting Al film on a normal
metal trapping layer. In addition, these devices allow us to
measure the hot-electron diffusion constant using a single
junction. Lastly these devices will help us optimize the
design and fabrication of tunnel junctions on the surface of
high-Z, ultra-pure superconducting crystals. |
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Single
photon imaging X-ray spectrometers using low noise current
preamplifiers with dc voltage
bias
S. Friedrich, K. Segall,
M.C. Gaidis, C.M. Wilson, D.E. Prober, P.J. Kindlmann, A.E.
Szymkowiak and S.H. Moseley
Summary: We have
developed superconducting single-photon imaging X-ray
detectors with an energy resolution of 54 eV at 6 keV and a
spatial resolution of 1 /spl mu/m over an effective length of
40 /spl mu/m. They utilize a current-sensitive low-noise
preamplifier with a dc voltage bias. It has a signal bandwidth
of 300 kHz, current noise of i/sub n/=0.26 pA//spl radic/(Hz)
and voltage noise of e/sub n/=0.5 nV//spl radic/(Hz) with an
input capacitance of 200 pF under operating conditions.
Injected pulses with a charge Q=3.7/spl middot/10/sup 6/
electrons have been measured with a standard deviation /spl
sigma/Q=3400 electrons, corresponding to an electronic noise
of 13 eV at 6 keV. |
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Superconducting
tunnel junctions on Nb- and Ta-single crystal substrates for
X-ray spectrometry
M.P. Bruijn,
F.B. Kiewiet, M.L. van den Berg, O.J. Luiten, P.A.J. de Korte,
C.G.S. Brons, A.W. Hamster and J. Flokstra
Summary:
We present the first high quality Nb/Al-based tunnel
junctions, fabricated with a superconducting interface onto
single crystal substrates of Nb and Ta. Current-voltage
measurements down to 1.4 K show a subgap current which is
dominated by thermal excitation of quasiparticles, no ohmic or
superconducting leakages could be observed. The fabrication
process and development steps, such as preparation of
ultra-smooth crystal surfaces are described. |
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Development
of a new superconducting detector for the ultra-violet and
soft X-ray regimes
D. Koller, D.
Van Vechten, M.G. Blamire, K.S. Wood, G.G. Fritz, J.S.
Horwitz, G.M. Daly, J.B. Thrasher, J.F. Pinto, A.L.
Gyulamiryan, V.H. Vartanyan, R. Akopyan and A.M.
Gulian
Summary: UV and X-ray astronomy need
hyperspectral imaging devices, i.e. large format (1000/spl
times/1000) arrays of pixels in which each single-photon event
is tagged with spectral information. Such devices permit
multicolor imagery and surveys to be obtained with a single
camera. Here we discuss the first-stage of development of a
new generation of UV/X-ray detectors that will provide
0.1-0.01% energy resolution in an array format. |
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Spiral
antenna NbN hot-electron bolometer mixer at submm
frequencies
S. Svechnikov, G.
Gol'tsman, B. Voronov, P. Yagoubov, S. Cherednichenko, E.
Gershenzon, V. Belitsky, H. Ekstrom, E. Kollberg, A. Semenov,
Y. Gousev and K. Renk
Summary: We have
studied the phonon-cooled hot-electron bolometer (HEB) as a
quasioptical mixer based on a spiral antenna designed for the
0.3-1 THz frequency band and fabricated on sapphire and high
resistivity silicon substrates. HEB devices were produced from
superconducting 3.5-5 nm thick NbN films with a critical
temperature 10-12 K and a critical current density of
approximately 10/sup 7/ A/cm/sup 2/ at 4.2 K. For these
devices we reached a DSB receiver noise temperature below 1500
K, a total conversion loss of L/sub t/=16 dB in the 500-700
GHz frequency range, an IF bandwidth of 3-4 GHz and an optimal
LO absorbed power of /spl sime/4 /spl mu/W. We experimentally
analyzed various contributions to the conversion loss and
obtained an RF coupling factor of about 5 dB, internal mixer
loss of 10 dB and IF mismatch of 1 dB. |
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Millimeter-wave
self-radiation from high-Tc Josephson junction
arrays
Kiejin Lee, I. Iguchi,
Jeha Kim, Seok-Kil Han and Kwang-Yong Kang
Summary:
We report the strong microwave Josephson radiation from
an array of high-T/sub c/ junctions on a MgO bicrystal
substrate from centimeter- to millimeter-wave ranges. The dc
bias current was fed to the junction array having parallel
geometry with the pair of junctions shunted by superconducting
loops. The configuration of bias leads was a series of
interlocking dc SQUID's geometry which guaranteed the
oscillation of all junctions at the same frequency. The phase
differences between adjacent junctions with different I/sub
c/R/sub n/ products could be controlled by an external small
magnetic field. For a five-junctions array, we observed the
coherent output power of about 13 pW without external magnetic
flux, which was nearly five times higher than that of a single
bicrystal junction. We observed the Josephson linewidth of the
self-radiation in the coherent state to be less than 1 GHz by
adjustment of the external flux. |
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High-frequency
properties of two-dimensional Josephson junction
arrays
A.B. Cawthorne, P. Barbara
and C.J. Lobb
Summary: Two-dimensional arrays
of Josephson junctions have been shown to operate in a state
in which the microwave oscillations of the junctions are
phase-coherent. However, the performance of an array is
strongly dependent on both the details of the load-coupling
circuit and the characteristic parameters of the junctions. We
have measured two-dimensional arrays of resistively shunted
Josephson tunnel junctions which are capacitively coupled to a
nearby detector junction. Changing the critical current of the
junctions in our arrays, while keeping the junction parasitics
and array coupling roughly the same, results in an unexpected
change in device operation. We have also investigated
variations of the coupling circuit. Numerical simulations of
the detection circuit enable us to estimate the power output
from the array and to optimize the parameters of the
system. |
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Detailed
investigation of two-dimensional Josephson junction array
circuits
M. Keek, T. Doderer, R.
Mueller, R. Pfeifer, A. Laub, R.P. Huebener, T. Traeuble, R.
Dolata, T. Weimann and J. Niemeyer
Summary:
We have investigated two-dimensional arrays of
overdamped Josephson junctions that have been fabricated in
Nb/Al/sub 2/O/sub 3//Nb-technology, together with microwave
coupling structures. Different arrays have shown to emit
coherent microwave radiation by using microwave-coupled
on-chip detectors. Low-temperature scanning electron
microscopy is used to study the coupling of the microwave
radiation to an on-chip load. From the appearance of Shapiro
steps in the current vs. voltage curves of detector junctions
for different degrees of disorder in the array-junctions,
margins of the spread in the critical currents of the
Josephson junctions for coherent oscillation can be
drawn. |
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Improved
1 V and 10 V Josephson voltage standard
arrays
J. Kohlmann, F. Muller, P.
Gutmann, R. Popel, L. Grimm, F.-W. Dunschede, W. Meier and J.
Niemeyer
Summary: 1 V and 10 V Josephson
voltage standard arrays are fabricated on the basis of an
improved design, using a modified technology. The Nb/Al/sub
2/O/sub 3//Nb trilayer is deposited directly on the Si wafer.
The edges of the base electrodes are insulated by an
anodization process. The maximum step voltage increases
linearly with the external microwave voltage. Switching
between different voltage levels is possible by simple
switching of the dc voltage bias. A laboratory-made, oversized
circular waveguide reduces the attenuation of the experimental
set-up. |
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High-resolution
superconducting X-ray spectrometers with an active area of 282
/spl mu/m/spl times/282 /spl
mu/m
C.A. Mears, S.E. Labov, M.
Frank, H. Netel, L.J. Hiller, M.A. Lindeman, D. Chow and A.T.
Barfknecht
Summary: Superconducting tunnel
junctions coupled to superconducting absorbers may be used as
high-resolution, high-efficiency X-ray spectrometers. We have
tested devices with niobium X-ray absorbing layers coupled to
aluminum layers that serve as quasiparticle traps. In this
work we measure the current pulses from a large-area tunnel
junction using an amplifier based on an array of 100 SQUIDs.
Using this amplifier and a 282 /spl mu/m/spl times/282 /spl
mu/m junction, we have measured an energy resolution of 19 eV
FWHM for 1.5 keV X-rays and 21 eV for 2.6 keV X-rays. The area
of this junction is eight times the area of any junction
previously measured to have such high energy
resolution. |
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High
energy photon absorption in superconductors results in branch
imbalance potential
D. Van
Vechten, K.S. Wood, D. Koller, A.M. Gulian and V.R.
Nikogosian
Summary: When a superconductor is
disturbed by a high energy deposition, an asymmetry in the
distributions of electron-like and hole-like excitations
results. This manifests itself as a voltage output, which can
be measured in different ways. Here we study the behavior of
this quantity using the kinetic equations to model the energy
cascade. Special attention is paid to the similarity and
differences between the behaviors of normal metals and
superconductors. The particular case of tantalum is considered
in the modeling. |
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YBa/sub
2/Cu/sub 3/O/sub 7-x/ thin-film picosecond photoresponse in
the resistive state
M. Lindgren,
M. Currie, C. Williams, T.Y. Hsiang, P.M. Fauchet, R.
Sobolewski, S.H. Moffat, R.A. Hughes, J.S. Preston and F.A.
Hegmann
Summary: Using a subpicosecond
electro-optic sampling technique, we have characterized the
photoresponse of current-biased YBa/sub 2/Cu/sub 3/O/sub 7-x/
(YBCO) photodetectors, designed as 5-/spl mu/m-wide and 7-/spl
mu/m-long microbridges patterned in 100-nm-thick, high-quality
epitaxial films grown on LaAlO/sub 3/ substrates by pulsed
laser deposition. The bridges were centered in a coplanar
waveguide structure, allowing the photogenerated pulses to be
measured 20 /spl mu/m from the detector. The experiments were
conducted in the temperature range between 20 and 80 K;
however, the bridges were biased in the switched (resistive)
state, which corresponded to a hot-spot formation at the
center of the microbridge. The photoresponse from 100-fs laser
pulses (395-nm wavelength) was measured to be in the form of a
single spike with the width as short as 1.3 ps. The physical
origin of this ultrafast response is attributed to
nonequilibrium electron heating, We extracted the intrinsic
temporal parameters of the YBCO response-the electron
thermalization time equal to 0.56 ps and electron-phonon
energy relaxation time equal to 1.1 ps, Our measurements
demonstrate that a simple YBCO microbridge can operate as a
>100-GHz bandwidth photodetector, e.g., as an
optical-to-electrical transducer for optoelectronic interface
in YBCO digital electronics. |
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Hilbert-transform
spectral analysis of millimeter- and submillimeter-wave
radiation with high T/sub c/ Josephson
junctions
Y.Y. Divin, V.V.
Pavlovskii, O.Y. Volkov, H. Schulz, U. Poppe, N. Klein and K.
Urban
Summary: We have demonstrated the first
applications of Josephson-effect-based Hilbert-transform
spectral analysis using high-T/sub c/ Josephson junctions.
YBa/sub 2/Cu/sub 3/O/sub 7-x/ grain-boundary Josephson
junctions have been fabricated on [110] NdGaO/sub 3/ bicrystal
substrates for these measurements. At first, spectra of
Josephson radiation have been measured by the
Hilbert-transform technique in the range 60-800 GHz. A
Lorentzian shape of the Josephson radiation and the
possibility to obtain a spectral resolution as low as 0.1
cm/sup -1/ in the submillimeter-wave range has been
demonstrated at liquid nitrogen temperature. Moreover, spectra
of high-harmonic content of the radiation coming from
commercial millimeter-wave oscillators have been measured in
the spectral range from 60 to 450 GHz. A comparison of
Hilbert-transform spectral analysis with conventional
techniques is given. |
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SQUID
based W-Al quasiparticle-trap assisted superconducting
transition edge sensor with position
resolution
Sae Woo Nam, P.L.
Brink, B. Cabrera, B. Chugg, R.M. Clarke, A.K. Davies and B.A.
Young
Summary: We have demonstrated a new
type of phonon sensor for cryogenic particle detectors with
high-bandwidth SQUID readout. Our Quasiparticle-trap assisted
Electrothermal feedback Transition edge sensor (QET) utilizes
aluminum quasiparticle traps attached to a tungsten
superconducting transition edge sensor patterned on a silicon
substrate. The tungsten lines are voltage biased and
self-regulate in the transition region. Phonons from particle
interactions in the silicon deposit energy into the creating
quasiparticles. The quasiparticles are trapped into the
tungsten and cause its electrical resistance to increase. The
resulting decrease in current through the sensor is measured
with a DC SQUID array. We have been able to demonstrate
xy-position resolution of /spl sim/0.3 mm for 6 keV X-rays
from an /sup 55/Fe source in a 2 cm/spl times/2 cm/spl times/4
mm (4 g) detector. We describe our optimizations of the sensor
design for improved energy and position. By simultaneously
measuring the ionization yield we have demonstrated
discrimination between electron and nuclear recoil events in a
100 g Si detector for the CDMS (Cryogenic Dark Matter Search)
experiment. |
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Design
centering methods for yield optimization of cryoelectronic
circuits
T. Harnisch, J. Kunert,
H. Toepfer and H.F. Uhlmann
Summary: We
present the results of comparison of different design
centering methods, e.g. simplicial approximation method and
centers-of-gravity method. The effectiveness of the proposed
yield optimization strategies is demonstrated by application
to various RSFQ circuits and analytical test functions. A
SPICE-type program which includes the possibilities of analog
behavior modeling and transient noise simulation was used for
circuit simulation. Based on these methods, an interactive
yield optimization framework for cryo-electronic circuits was
developed and tested. |
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Advanced
on-chip test technology for RSFQ
circuits
A.F. Kirichenko, O.A.
Mukhanov and A.I. Ryzhikh
Summary: We have
developed an advanced version of on-chip test system with new
high-speed clock generation and control. For high-speed clock
generation, a novel wide-bandwidth ring generator is designed
using circular Josephson transmission lines with an
inductively coupled trigger. The generator is capable of
producing SFQ clock pulses in the range of from 15 to 55 GHz
using a 1 kA/cm/sup 2/ Nb fabrication process. For clock
control, we have designed two different types of
clock-controller circuits based on programmable shift-register
and counter. Using the on-chip test system, we have
successfully tested a parallel multiplier module up to 15 GHz
with 16% dc bias margins. |
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A
multilayered superconducting neural network
implementation
E.D. Rippert and
S. Lomatch
Summary: We present the results of
numerical simulations of a novel neural networking
implementation utilizing multilayered Josephson junction (or
series array) based synaptic circuits with local memory. These
synaptic circuits utilize single flux quanta for both neural
information and synaptic weight programming, and we present a
simple circuit that can implement Hebbian learning at a
completely local level, with global control over the rates of
both learning and forgetting in synapses. |
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Design
and fabrication of QFP logic gates based on YBa/sub 2/Cu/sub
3/O/sub 7/ step-edge junctions
H.
Hasegawa, Y. Tarutani, U. Kabasawa, N. Sugii, T. Fukazawa and
K. Takagi
Summary: Quantum Flux Parametron
(QFP) logic gates were designed and fabricated from a single
layer of YBa/sub 2/Cu/sub 3/O/sub 7/ thin film based on
step-edge Josephson junctions. Self-inductance (L) of the QFP
loop, an important circuit parameter, as is critical current
(J/sub c/) of the Josephson junction, was determined by using
directly coupled dc superconducting quantum interference
devices (SQUIDs). Magnetically coupled dc SQUIDs were used to
detect the output signal from the QFP. Simulated waveforms
were used to identify the operation modes of the QFP as a
function of the circuit parameters. From examination of the
output waveforms of the QFP, operation in agreement with
simulations was confirmed. |
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Investigation
of the signal resolution of a high-T/sub c/ balanced
comparator
B. Oelze, B. Ruck, E.
Sodtke, T. Filippov, A. Kidiyarova-Shevchenko, M. Kupriyanov
and W. Prusseit
Summary: The use of
high-T/sub c/ Josephson junctions for digital applications
requires a careful study of the influence of thermal noise on
circuit performance. We investigated a balanced current
comparator, which contains a basic component of all RSFQ
circuits: two overdamped Josephson junctions connected in
series. The dependence of the dc-voltage across the Josephson
junctions on signal current was measured to determine the
threshold uncertainty of switching of the comparator. The
experimental data obtained at different sampling pulse
frequencies, in a temperature range from 10 to 50 K, were
compared with a theoretical model, taking into account the
influence of thermal noise as well as of sampling pulse
frequency. |
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Optimization
and magnetic field behavior of sputtered submicron YBa/sub
2/Cu/sub 3/O/sub 7/ step-edge
Josephson-junctions
M. Vaupel, G.
Ockenfuss and R. Wordenweber
Summary: YBa/sub
2/Cu/sub 3/O/sub 7/ step-edge junctions with widths down to
0.5 /spl mu/m are fabricated on SrTiO/sub 3/-substrates by Ar
ion-beam milling of the steps, high-pressure on-axis magnetron
sputtering and, finally, electron beam patterning and ion-beam
etching of the microbridge. For ratios of film thickness to
step height of about 1/2 the current-voltage characteristics
show Shapiro steps under microwave irradiation and RSJ
(resistively shunted junction)-like behavior. The periodic
dependence of the critical current upon the magnetic field
resembles a Fraunhofer-pattern. The period of the current
variation /spl Delta/B/sub 0/ depends upon the width w of the
junction according to the theoretical prediction for planar
thin Josephson junctions: /spl Delta/B/sub 0/=1.84/spl
phi//sub 0//w/sup 2/. Junctions with widths of 0.7 /spl mu/m
possess a large magnetic field stability with /spl Delta/B/sub
0//spl ap/100 G. Small junctions (w<1 /spl mu/m) exhibit
voltage jumps in the Fraunhofer pattern, which are explained
by flux penetration of single vortices into the
superconducting electrodes. |
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In-plane
anisotropic properties of (103)/(013) and 10/spl deg/ YBCO
thin films
S.M. Morley, R.P.
Campion, K. Horbelt, P.J. King, H.-U. Habermeier and B.
Leibold
Summary: There is much current
interest in fabricating structures including microbridges and
vortex flow devices from high T/sub c/ thin films with high
in-plane electrical anisotropy. Two types of film have been
studied, films grown on 10° vieinaliy cut SrTiO/sub 3/, and
(013)/(103) oriented films grown on (110) SrTiO/sub 3/
substrates in a two-temperature growth process. The 10° films
have a normal state anisotropy of 3-6 (100K) dependent on film
thickness . The l00nm (013)/(103) films have a normal state
anisotropy of 23 (1OOK). We report wide ranging I-V
measurements taken over a range of temperatures and applied
magnetic fields for both the normal and superconducting states
for these films. This data is used to investigate the
anisotropy below T/sub c/ both in the linear (flux-flow)
regime and in the non-linear (irreversibity) regime at lower
temperatures and higher currents. |
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Fabrication
of superconductor/semiconductor quasi-monolithic devices using
epitaxial liftoff
technology
Qixin Huang and K.
Hohkawa
Summary: This paper reports a study
on the fabrication technology of high performance functional
devices, where high temperature superconductor and compound
semiconductor devices are monolithically integrated on the
same substrate. We investigated optimal conditions for
epitaxial liftoff process and succeeded in fabricating HTS
device and GaAs MESFET on SrTiO/sub 3/ substrate without
degrading characteristics of superconductor and semiconductor
devices. We also carried out basic integrated circuit
fabrication processes such as patterning and etching for
quasi-monolithic structure. The results confirmed that
fabricating high performance functional devices is
feasible. |
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Comparability
of measurement results obtained with multi-SQUID-systems of
different sensor
configurations
M. Burghoff, U.
Steinhoff, W. Haberkorn and H. Koch
Summary:
Currently several brands of multichannel SQUID-systems
for application in biomagnetism are commercially available.
However, these devices are widely differing in SQUID
specifications, gradiometer construction, sensor configuration
and other parameters. The distortion of temporal recordings of
the magnetic field due to varying sensor constructions has
been evaluated. Examples of cardiac measurements show clearly
that such data differ from each other. Therefore, these data
cannot directly be compared in multicentric clinical studies.
This contribution presents a method for comparison of signals
recorded with different sensor systems. This method transforms
the recorded signals into signals of a reference system. The
recorded signals are modeled by means of a multipole virtual
generator, which is then used to compute the signals in the
reference system. The efficiency of the algorithm is
demonstrated for measurements of the heart magnetic
field. |
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The
use of (Double) relaxation oscillation SQUIDs as a
sensor
M.J. van Duuren, G.C.S.
Brons, H.E. Kattouw, J. Flokstra and H.
Rogalla
Summary: Relaxation Oscillation
SQUIDs (ROSs) and Double Relaxation Oscillation SQUIDs (DROSs)
are based on relaxation oscillations that are induced in
hysteretic dc SQUIDs by an external L-R shunt. The relaxation
frequency of a ROS varies with the applied flux /spl Phi/,
whereas the output of a DROS is a dc voltage, with a typical
flux-to-voltage transfer of /spl part/V//spl part//spl
Phi//spl ap/1 mV//spl Phi//sub 0/. The flux-to-frequency
response of several ROSs has been measured and compared with
theory for frequencies up to 7 GHz. Various DROS designs-a
multi-loop direct coupling DROS, a DROS with a washer type
signal SQUID and a DROS with gradiometric signal SQUID-will be
discussed in this paper. The integration of a DROS with a
digital flux locked loop ("Smart DROS") will also be
analyzed. |
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Integrated
SQUID gradiometers for measurement in disturbed
environments
V. Schultze, R.
Stolz, R. Ijsselsteijn, V. Zakosarenko, L. Fritzsch, F. Thrum,
E. Il'ichev and H.-G. Meyer
Summary: Planar
dc SQUID gradiometers with integrated antenna were designed
and investigated. With low-T/sub c/ superconductors they were
realized as washer type and as transformer type SQUID
gradiometers. With high-T/sub c/ superconductors we tested
galvanometer SQUIDs. Field gradient sensitivities of 32
fT/(cm/spl radic/(Hz)) could be achieved with low-T/sub c/
SQUIDs and of 520 fT/(cm/spl radic/(Hz)) with high-T/sub c/
SQUIDs, respectively. All types of gradiometers could work
stable in disturbed environments. The influence of the SQUID
gradiometer layout and the construction of the sample holder
on the degree of disturbance suppression is
shown. |
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Flux
to voltage transfer function and noise in double relaxation
oscillation SQUIDs
GengHua Chen,
HongYing Zhai and QianSheng Yang
Summary:
Under the low-damping limit, flux to voltage transfer
function and classical intrinsic noise expressions for both
thermal fluctuation and relaxation oscillation in double
relaxation oscillation SQUID(DROS)s can be obtained with
numerical calculation. The expressions show that the noise has
T/sup 6/5/ temperature dependence and that at low relaxation
oscillation frequencies, /spl omega//sub r/, the noise has a
1//spl omega//sub r/ behavior, and then turns up and gradually
saturates at very high frequencies comparable with the plasma
frequency. The upturn point, which gives the optimum energy
resolution, might be near 10 GHz for typical DROS circuit
parameters. |
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Design
and analysis of high-T/sub c/ SQUID current
amplifiers
G. Hildebrandt and
H.F. Uhlmann
Summary: SQUID preamplifiers are
very sensitive and have a low noise level. We present
simulation studies for asymmetric voltage biased SQUID current
amplifiers with one superconducting layer. For a simple SQUID
amplifier the gain has been calculated versus the loop and
noise parameter. An optimum of the gain versus the loop
parameter has been obtained. For a parallel SQUID array
amplifier a design rule has been derived. The possible margins
for the critical current have been calculated. The inductance
values used in the simulations have been calculated by a 3D
field program from an assumed layout. |
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A
new concept for integrated YBa/sub 2/Cu/sub 3/O/sub 7/
magnetometers
R. Scharnweber and
M. Schilling
Summary: We present an
integrated magnetometer concept that combines inductance
matching by a flux transformer with the low inductance of a
multiloop pick-up coil. Using ramp-type Josephson junctions
with PrBa/sub 2/Cu/sub 3/O/sub 7/ barriers, a 90 pH dc SQUID
together with a five turn flux transformer is coupled to a
multiloop pick-up coil. The dependence of the effective area
of the magnetometer on the temperature is investigated by
successively disconnecting the pick-up loops. The 1/f flux
noise of the integrated magnetometer is suppressed by
operation in a flux-locked loop mode with bias current
modulation. This results in a flux density noise of /spl
radic/(S/sub B/)(1 Hz,77 K)=100 fT//spl radic/(Hz). Using this
magnetometer, different biomagnetic measurements have been
performed. |
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High
T/sub c/ superconducting CPW bandstop filters for radio
astronomy front ends [YBa/sub 2/Cu/sub 3/O/sub 7/-LaAlO/sub
3/]
S. Wallage, J.L. Tauritz,
G.H. Tan, P. Hadley and J.E. Mooij
Summary:
We have designed and tested a superconducting coplanar
waveguide (CPW) bandstop filter consisting of 8 coupled line
sections at a center frequency of 1.53 GHz. A packaged 94.7%
bandwidth low pass Chebychev design yielded a filter with a
center frequency of 1.56 GHz, less than 1.2 dB insertion loss
in the passband and better than 28 dB rejection at 20 Kelvin.
With a skirt selectivity of 1.53(=BW/sub 1 dB//BW/sub -28 dB/)
and low insertion loss this filter is an excellent candidate
for suppressing contiguous spurious signals in cooled
low-noise receiving front ends. |
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Anomalous
current-dependence of kinetic inductance in ultrathin NbN
meander lines
M.W. Johnson and
A.M. Kadin
Summary: We have measured the rf
impedance of 10-nm thick superconducting granular NbN meander
lines between 5 /spl mu/m and 20 /spl mu/m wide. The complex
reflection coefficient was obtained directly using a vector
network analyzer. The impedance (at 10 MHz for a 5 /spl mu/m
wide line) is dominated by the large kinetic Inductance of the
film, with a sheet inductance of order 1 nH, giving a total
inductance of 400 nH for a 5 /spl mu/m/spl times/2 mm line.
The kinetic inductance diverges as T/spl rarr/T/sub c/=6.5 K,
as expected from Ginzburg-Landau theory (GL). Of particular
interest is a substantial decrease of measured inductance with
increasing dc current, contrary to the dependence expected
from GL. This anomalous current dependence is not well
understood, but may be related to vortex dynamics and
Josephson effects in these granular films, as supported by
preliminary Josephson array simulations. These results have
important implications for potential devices such as tunable
rf phase shifters and kinetic inductance
photodetectors. |
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A
dc SQUID based low-noise 4 GHz
amplifier
G.V. Prokopenko, S.V.
Shitov, V.P. Koshelets, D.B. Balashov and J.
Mygind
Summary: The dc SQUID based RF
amplifier (SQA) looks very attractive as an IF amplifier for
integration with a SIS mixer and a flux-flow oscillator (FFO)
in a fully superconducting submillimeter wave receiver
suitable for space applications. Important advantages of the
SQA are its low noise, extremely low power consumption, and
complete compatibility with the fabrication process currently
used for SIS mixers. Single stage amplifiers with a novel
signal coupling circuit have been developed and tested in the
frequency range 3.6-4.1 GHz. The 1 /spl mu/m/sup 2/ area
Nb-AlO/sub x/-Nb junctions shunted by Ti resistors are grouped
in a double washer dc SQUID. Two samples with slightly
different designs showed the following gain, noise temperature
and 3 dB bandwidth: 10.0/spl plusmn/1 dB, 5.0/spl plusmn/1.5
K, 3.86-3.90 GHz, and 6.8/spl plusmn/1 dB, 22/spl plusmn/7 K,
3.89-4.05 GHz, respectively. |
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High
Q dielectric resonators using YBa/sub 2/Cu/sub 3/O/sub x/
thick films and polycrystalline
dielectrics
S.J. Penn, N.McN.
Alford and T.W. Button
Summary: The
combination of high Q dielectric resonators and high
temperature superconducting (HTS) films offer many advantages
in the area of cellular and satellite communications. The high
cost of single crystal dielectrics and HTS thin films may be
unattractive in certain applications. Superconducting thick
films and polycrystalline ceramic dielectrics offer a high
performance, low cost alternative to high Q thin film/single
crystal dielectric resonators. Results on polycrystalline
dielectrics show that Q's well in excess of 10/sup 5/ at 10
GHz and 77 K can be achieved in a design made compact by the
use of a HTS thick film shield. |
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Frequency
stability of dielectric loaded HTS microwave
resonators
J. Gallop, L. Hao, F.
Abbas and C.D. Langham
Summary: High Q
dielectric loaded superconducting resonators have many
potential microwave applications. A key issue for many of
these is the stability with which the resonant frequencies of
such resonators may be realised, for use as frequency
references etc. We report experiments on a number of different
resonator geometries using YBCO thick films as planar shields
for composite dielectric structures. The experimental results
are analysed and surface impedance data as a function of
temperature and frequency is deduced for each superconductor
specimen as well as real and imaginary components of the
relative permittivity of each dielectric material involved in
the resonators. Using these parameters predictions are made
for the attainable stability in realistic resonator
structures. We compare these predictions with stability
requirements for a number of wide ranging and niche
applications. |
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Traveling-wave
type LiNbO/sub 3/ optical modulator with a superconducting
coplanar waveguide electrode
K.
Yoshida, A. Minami and Y. Kanda
Summary:
Microwave characteristics of a LiNbO/sub 3/ optical
modulator employing a superconductor electrode (Nb) as a
transmission line of a traveling signal has been studied
experimentally in the temperature range from 300 K to 4.2 K.
In the frequency range between dc and 26.5 GHz it is shown
that the obtained modulation depth is in good agreement with
the theoretically expected one. The present results
demonstrate the possible applications of superconducting
electrodes to high performance LiNbO/sub 3/ optical
modulators. |
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Tunable
SrTiO/sub 3/ varactors using parallel plate and interdigital
structures
C.H. Mueller, R.E.
Treece, T.V. Rivkin, F.A. Miranda, H.R. Moutinho, A.
Swartzlander-Franz, M. Dalberth and C.T.
Rogers
Summary: The dielectric properties of
SrTiO/sub 3/ (STO)/YBCO and STO films deposited on LaAlO/sub
3/ substrates were evaluated, for potential varactor
applications wherein the capacitance is altered via a dc
voltage applied across the STO film. The optimal growth
temperature for the STO films in the STO/YBCO structures was
800/spl deg/C; higher temperatures resulted in interfacial
degradation and poor film quality, and lower temperatures
resulted in films with lower dielectric constants (/spl
epsi//sub r/) and tunabilities. Interdigital varactors
comprised of STO films deposited directly on LaAlO/sub 3/
displayed higher tunabilities and significantly lower
losses. |
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Studies
of ferroelectric field effects in Pt/Pb(Zr/sub 0.5/Ti/sub
0.5/)O/sub 3//YBa/sub 2/Cu/sub 3/O/sub 7/
heterostructures
Z.W. Dong, Z.
Trajanovic, T. Boettcher, I. Takeuchi, V. Talyansky, C.-H.
Chen, R.P. Sharma, R. Ramesh and T.
Venkatesan
Summary: Pt/Pb(Zr/sub 0.5/Ti/sub
0.5/)O/sub 3//YBa/sub 2/Cu/sub 3/O/sub 7/ (Pt/PZT/YBCO)
heterostructures were made by pulsed laser deposition on (100)
SrTiO/sub 3/ or (100) LaSrGaO/sub 4/ substrates for studies of
ferroelectric field effects in high-T/sub c/ superconducting
thin films. X-ray diffraction data, including /spl Phi/ scans,
indicated that the PZT layer grew with c-axis orientation
epitaxially on top of the YBCO layers. Polarization
measurements at room temperature and 77 K showed similar
hysteretic loops in the PZT layer. The remanent polarization
field can induce as many as 10/sup 14/ carriers/cm/sup 2/ in
the bottom superconducting channel at the interface. Both
c-axis and in-plane-aligned a-axis-oriented YBCO films,
typically exhibiting zero resistance transition temperature of
/spl sim/85 K, were used as superconducting channels. By
polarizing the PZT film, a 2-5% change in both the channel
resistance and the critical current at 77-85 K was obtained in
/spl sim/100 nm thick films. Device operation at microsecond
speeds was observed. |
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Anomalous
dielectric effect of La/sub 2-x/Sr/sub x/CuO/sub
4/
M. Sugahara, S.-B. Wu, X.-Y.
Han, H.-F. Lu, N. Haneji, H. Kaneda and N.
Yoshikawa
Summary: The dielectric response of
c-axis oriented La/sub 2-x/Sr/sub x/CuO/sub 4/ film is
experimentally studied using Pd/La/sub 2-x/Sr/sub x/CuO/sub
4//(100)SrTiO/sub 3//Pd multi-layer structure. Anomalous
capacitance increase is observed at Sr doping level x/spl
ap/1/2/sup n/, where the drop of resistivity in bulk La/sub
2-x/Sr/sub x/CuO/sub 4/ in normal state has been
reported. |
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Modeling
and analysis of capacitances in metallic single electron
tunneling structures
M. Knoll,
H.F. Uhlmann, M. Gotz and W. Krech
Summary:
The calculation of the capacitances between
well-separated thin coplanar electrodes is of fundamental
importance in single charge electronics, e.g. for optimizing
the geometry of digital circuits with respect to desired
coupling as well as to parasitic cross-talk capacitances. We
are able to extract such capacitances from three-dimensional
numerical field computations basing on the boundary element
method. Our program yields relevant information about the
dependence of the capacitance on geometry as verified by
comparing calculated gate coupling capacitances of different
types of single electron transistors with values obtained from
the experiment. |
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Fabrication
of a high-T/sub c/ superconducting field effect transistor by
ion beam sputtering
T. Saito,
Xuyang Cai, K. Usami, T. Kobayashi and T.
Goto
Summary: We have fabricated Au/SrTiO/sub
3/(STO)/YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) trilayer
structures and superconducting field effect transistors
(SuFETs). Insulating STO films were deposited by the ion beam
sputtering (IBS) method at high oxygen pressure (/spl
sim/10/sup -2/ Torr). (l00) peaks were observed in the X-ray
diffraction (XRD) patterns of STO films deposited at
temperatures higher than about 400/spl deg/C. The leakage
current characteristics of a 400-nm-thick STO film were almost
symmetric at different polarities and low leakage current of
the order of 10/sup -9/ A was obtained up to around /spl
plusmn/25 V at 4.2 K. The dielectric constant electric field
product /spl epsiv//sub rS/E/sub BD/ of the STO film was
estimated to be about 2.2/spl times/10/sup 8/ V/cm. In the
SuFET fabrication process, a 10-nm-thick YBCO film covered
with the STO layer was hardly degraded. The modulation of the
normal state resistance of a sample almost corresponds to that
of the induced carrier at positive bias. When a voltage of +20
V was applied to the gate electrode at 4.2 K, the current
decreased by about 5% and the mutual conductance was 3.8 /spl
mu/S at a drain voltage of 10 mV. |
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Understanding
the behavior of superconducting Coulomb-blockade
electrometers
D. Song, A. Amar,
C.J. Lobb and F.C. Wellstood
Summary: We
report measurements and quantum mechanical simulations of the
behavior of superconducting two-junction Coulomb-blockade
electrometers biased near the superconducting gap. Our quantum
model allows coherent superpositions of states with different
number of charges on the island. It predicts maximum current
modulation /spl delta/I for devices with tunneling resistance
R/sub /spl Sigma///spl ap/64/spl pi//spl Delta//spl
planck//sup 2/C/sub /spl Sigma///sup 2//(e/sup 6//spl tau/),
where /spl tau/ is the time for which the system maintains
quantum coherence, C/sub /spl Sigma// is the total island
capacitance and /spl Delta/ is the superconducting energy gap.
For comparison, we built Al-AlO/sub x/-Al electrometers with
R/sub /spl Sigma// from 61 k/spl Omega/ to 1.7 M/spl Omega/
and C/sub /spl Sigma// ranging from 0.9 fF to 8 fF. We find
good agreement for /spl tau//spl ap/0.35 nsec. |
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Large
electric field effect on Al/BaTiO/sub 3//Y/sub 0.6/Pr/sub
0.4/Ba/sub 2/Cu/sub 3/O/sub 7-y/
structure
S. Hontsu, J. Ishii, M.
Nakamori, H. Tabata, T. Kawai and A.
Fujimaki
Summary: A superconducting field
effect transistor with Al/BaTiO/sub 3//Y/sub 0.6/Pr/sub
0.4/Ba/sub 2/Cu/sub 3/O/sub 7-y/ multistructures has been
fabricated by in situ pulsed laser deposition technique. The
BTO/YPBCO bilayers show well crystallized structures by X-ray
diffraction measurements. The relative dielectric constant
(/spl epsi//sub r/) of BTO is 170 at 77 K. The observed
relative change of the source-drain resistance (/spl
Delta/R/sub SD//R/sub SD/) is enhanced up to -17.2% by the
application of electric field. This value is 34 times as large
as calculated from the modulation of areal carrier of
field-induced charge density (/spl Delta/n/n). |
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Electric
field effect of SrTiO/sub 3//YBa/sub 2/Cu/sub 3/O/sub 7-x/
bi-layer grown by MBE and PLD
T.
Nakamura, H. Inada and M. Iiyama
Summary:
Oxygen content and interface properties in SrTiO/sub
3//YBa/sub 2/Cu/sub 3/O/sub 7-x/(STO/YBCO) bi-layer definitely
affect electric properties of superconducting field effect
transistor (SuFET). Good interface can be obtained by
molecular beam epitaxy (MBE). Deposition pressure of MBE is
too low to oxygenate the ultra-thin YBCO through STO. The
oxygen pressure of pulsed laser deposition (PLD) is high
enough to oxygenate the YBCO but YBCO film surface is degraded
by impurity gases because of its high oxygen pressure. We
successfully combined MBE and PLD methods to obtain STO/YBCO
bilayers with both good interface and electrical properties.
The transconductance of SuFET was 5mS/cm, which is higher than
SuFET grown by all-MBE and all-PLD. |
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Superconducting
Coulomb-Blockade electrometers with tunable Josephson
coupling
A. Amar, D. Song, C.J.
Lobb and F.C. Wellstood
Summary: We report
measurements made on superconducting Al-AlO/sub x/-Al
Coulomb-blockade electrometers with fixed gap /spl Delta/ and
charging energy E/sub c/, but tunable Josephson coupling E/sub
j/ via application of a magnetic field. This allows us to
investigate the effects of changing the E/sub j//E/sub c/
ratio on the device characteristics. We compare the observed
modulation with respect to magnetic field and gate voltage
with the theoretical predictions in the supercurrent
region. |
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2.5
THz NbN hot electron mixer with integrated tapered slot
antenna
S.I. Svechnikov, O.V.
Okunev, P.A. Yagoubov, G.N. Gol'tsman, B.M. Voronov, S.I.
Cherednichenko, E.M. Gershenzon, E. Gerecht, C.F. Musante, Z.
Wang and K.S. Yngvesson
Summary: A Hot
Electron Bolometer (HEB) mixer for 2.5 THz utilizing a NbN
thin film device, integrated with a Broken Linearly Tapered
Slot Antenna (BLTSA), has been fabricated and is presently
being tested. The NbN HEB device and the antenna were
fabricated on a SiO/sub 2/ membrane. A 0.5 micrometer thick
SiO/sub 2/ layer was grown by rf magnetron reactive sputtering
on a GaAs wafer. The HEB device (phonon-cooled type) was
produced as several parallel strips, 1 micrometer wide, from
an ultrathin NbN film 4-7 nm thick, that was deposited onto
the SiO/sub 2/ layer by dc magnetron reactive sputtering. The
BLTSA was photoetched in a multilayer Ti-Au metallization. In
order to strengthen the membrane, the front-side of the wafer
was coated with a 5 micrometer thick polyimide layer just
before the membrane formation. The last operation was
anisotropic etching of the GaAs in a mixture of HNO/sub 3/ and
H/sub 2/O/sub 2/. |
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Diffusion-cooled
superconducting hot electron bolometer heterodyne mixer
between 630 and 820 GHz
K.
Fiegle, D. Diehl and K. Jacobs
Summary: We
report on heterodyne mixing experiments between 630-820 GHz
using a diffusion-cooled superconducting hot electron
bolometer at intermediate frequencies from 1-2 GHz. The
niobium bolometer which is cooled by diffusion of the hot
electrons into a normal conductor has dimensions of 0.3 /spl
mu/m/spl times/0.15 /spl mu/m and was fabricated at KOSMA with
a two-step electron beam lithography process. The film
thickness of the device is 30 nm with T/sub c/ of 6.1 K and
/spl Delta/T/sub c/ of 0.7 K. The mixing experiments are
performed with a tunerless waveguide mixer block previously
used for very low-noise SIS receivers. At a physical
temperature of 2.2 K, receiver noise temperatures at 666 GHz
are 1500 K at 1.0 GHz intermediate frequency, increasing
rapidly above 1.5 GHz. The dissipated local oscillator power
is evaluated to be 65-90 nW. |
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Current
dependent noise in a YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta//
hot-electron bolometer
Yu.P.
Gousev, A.D. Semenov, I.G. Goghidze, E.V. Pechen, A.V.
Varlashkin, G.N. Gol'tsman, E.M. Gershenzon and K.F.
Renk
Summary: We investigated the output
noise of a YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO)
superconducting hot-electron bolometer (HEB) in a large
frequency range (10 kHz to 8 GHz); the bolometer either
consisted of a structured 50 nm thick YBCO film on LaAlO/sub
3/ or a 30 nm thick film on a MgO substrate. We found that
flicker noise dominated at low frequencies (below 1 MHz),
while at higher frequencies Johnson noise and a current
dependent noise were the main noise sources. |
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Fabrication
of a diffusion cooled superconducting hot electron bolometer
for THz mixing applications
B.
Bumble and H.G. LeDuc
Summary: Recent
interest in bolometers for heterodyne mixing applications has
prompted development of microbridges which are small enough to
allow electron diffusion to dominate over electron-phonon
interaction as a cooling mechanism. Prior results at 533 GHz
have demonstrated several GHz intermediate frequency (IF)
bandwidth. Here we describe our processing method in which the
bolometer element is a 10 nm thin film of niobium defined by
electron beam lithography down to dimensions of 80 nm. This
microbridge is embedded in a normal metal (Au) antenna
structure for 1.2 and 2.5 THz applications. |
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Fabrication
of high-T/sub c/ hot-electron bolometric mixers for terahertz
applications
M.J. Burns, A.W.
Kleinsasser, K.A. Delin, R.P. Vasquez, B.S. Karasik, W.R.
McGrath and M.C. Gaidis
Summary:
Superconducting hot-electron bolometers (HEB) represent
a promising candidate for heterodyne mixing at frequencies
exceeding 1 THz. Nb HEB mixers offer performance competitive
with tunnel junctions without the frequency limit imposed by
the superconducting energy gap. Although the performance of
YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// HEB mixers is not
projected to be superior to that of Nb devices, which operate
at low temperatures, they introduce the possibility of
sensitive, low power heterodyne detectors operating at
temperatures approaching 90 K for applications requiring
portability and closed-cycle refrigeration. We report on the
fabrication and characterization, both DC and RF, of
high-T/sub c/ mixers based on ultra-thin (/spl les/20 nm)
YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// films patterned to
micrometer dimensions and incorporated into 2.5 THz planar
mixer circuits. |
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Receiver
measurements at 1267 GHz using a diffusion-cooled
superconducting transition-edge
bolometer
A. Skalare, W.R.
McGrath, B. Bumble and H.G. LeDuc
Summary: We
report receiver noise temperature measurements using a
quasioptically coupled diffusion-cooled hot-electron bolometer
mixer at a local oscillator frequency of 1267 GHz, and an
intermediate frequency of 1.4 GHz. A best double-sideband
(DSB) receiver noise temperature of 1880 K was measured, with
an estimated mixer noise of 945 K (DSB), and a conversion
efficiency including coupling losses of -19 dB (DSB). The
coupled local oscillator power requirement for this device is
estimated at roughly 6 nW. The mixer noise temperature is less
than twice that measured earlier in a waveguide receiver at
530 GHz, which shows that the sensitivity of this type of
mixer does not degrade sharply with increasing frequency in
this regime. |
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Noise
characteristics of a NbN hot-electron mixer at 2.5
THz
A.D. Semenov, Y.P. Gousev,
K.F. Renk, B.M. Voronov, G.N. Gol'tsman, E.M. Gershenzon, G.W.
Schwaab and R. Feinaugle
Summary: The noise
temperature of a NbN phonon cooled hot-electron mixer has been
measured at a frequency of 2.5 THz for various operating
conditions. We obtained for optimal operation a double
sideband mixer noise temperature of /spl ap/14000 K and a
system conversion loss of /spl ap/23 dB at intermediate
frequencies up to 1 GHz. The dependences of the mixer noise
temperature on the bias voltage, local oscillator power, and
intermediate frequency were consistent with the
phenomenological description based on the effective
temperature approximation. |
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Noise
bandwidth of diffusion-cooled hot-electron
bolometers
R.J. Schoelkopf, P.J.
Burke, D.E. Prober, B. Karasik, A. Skalare, W.R. McGrath, M.C.
Gaidis, B. Bumble and H.G. LeDuc
Summary: We
present studies of the input and output noise of diffusion
cooled hot-electron bolometer mixers. By simultaneously
measuring the gain and noise (with a 14 GHz LO) as a function
of intermediate frequency for a 0.16 /spl mu/m diffusion
cooled Nb device, we show that the noise bandwidth (4 GHz) is
larger than the gain bandwidth (2.4 GHz). The output noise is
55 K, and the mixer noise is very low, 340 K DSB. This shows
that diffusion cooled devices have low noise over a broad
enough intermediate frequency band for practical applications
in THz receivers. |
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A
low-noise 2.5 THz superconductive Nb hot-electron
mixer
B.S. Karasik, M.C. Gaidis,
W.R. McGrath, B. Bumble and H.G. LeDuc
Summary:
We report on the development of a quasioptical Nb
hot-electron bolometer mixer for a 2.5 THz heterodyne
receiver. The devices are fabricated from a 12 nm thick Nb
film, and have a 0.30 /spl mu/m/spl times/0.15 /spl mu/m
in-plane size, thus exploiting diffusion as the electron
cooling mechanism. The rf coupling was provided by a twin-slot
planar antenna on an elliptical Si lens. A specially designed
2.5 THz system, using a CO/sub 2/-pumped FIR laser as local
oscillator (LO), with rf hot/cold loads enclosed in vacuum to
avoid atmospheric absorption, was used in the experiment. The
experimentally measured double sideband (DSB) noise
temperature of the receiver was as low as /spl les/3000 K,
with an estimated mixer noise temperature of /spl ap/750 K.
These results demonstrate the operation of the
diffusion-cooled bolometer mixer above 2 THz. |
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Quasi-optical
SIS mixers with normal metal tuning
structures
Mei Bin, M.C. Gaidis,
J. Zmuidzinas, T.G. Phillips and H.G. LeDuc
Summary:
We recently reported (1996) a quasi-optical SIS mixer
which used Nb/Al-oxide/Nb tunnel junctions and a normal-metal
(Al) tuning circuit to achieve an uncorrected receiver noise
temperature of 840 K (DSB) at 1042 GHz. Here we present
results on several different device designs, which together
cover the 300-1200 GHz frequency range. The mixers utilize an
antireflection-coated silicon hyper-hemispherical lens, a
twin-slot antenna, and a two-junction tuning circuit. The
broad-band frequency response was measured using Fourier
transform spectrometry (FTS), and is in good agreement with
model calculations. Heterodyne tests were carried out from 400
GHz up to 1040 GHz, and these measurements agree well with the
FTS results and with calculations based on Tucker's theory
(1985). |
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An
integrated 500 GHz receiver with superconducting local
oscillator
V.P. Koshelets, S.V.
Shitov, L.V. Filippenko, A.M. Baryshev, W. Luinge, H.
Golstein, H. van de Stadt, J.-R. Gao and T. de
Graauw
Summary: An integrated quasioptical
receiver consisting of a planar double-dipole antenna, SIS
mixer and superconducting Flux-Flow Oscillator (FFO) with
matching circuits has been designed, fabricated and tested in
the frequency range 420-530 GHz. The integrated receiver is
very suitable for space applications because of its low size,
mass and power consumption. All components of the receiver are
integrated on a 4 mm/spl times/4 mm/spl times/0.2 mm
crystalline quartz substrate using a single Nb-AlO/sub x/-Nb
trilayer. The successful operation of the integrated receiver
comprising a number of new crucial elements has been
demonstrated. A DSB noise temperature as low as 140 K at 500
GHz and a tuning range of more than 100 GHz have been
obtained. A comparison of the FFO with conventional external
LO has been performed. |
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Development
of a 3/spl times/3 micromachined millimeter wave SIS imaging
array
G. de Lange, A. Rahman, E.
Duerr, Qing Hu, H. Huang and A.W.
Lichtenberger
Summary: The design of, and
preliminary results from, a 3/spl times/3 micromachined
millimeter wave focal plane imaging array with superconducting
tunnel junctions as mixing elements are presented. The array
operates in the 175-205 GHz frequency range. Micromachined
horn antennas consist of a dipole antenna fabricated on a thin
dielectric membrane inside a pyramidal cavity etched in
silicon. The relative ease of fabricating arrays of
micromachined antennas make them of particular interest in the
development of imaging arrays. DC tests of the array show that
the junction characteristics are uniform across the array. The
devices are sufficiently cooled. Local oscillator power has
been coupled to the different elements in the
array. |
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Distributed
quasiparticle mixing in a non-linear transmission line at
sub-millimeter wavelengths
C.E.
Tong, R. Blundell, B. Bumble, J.A. Stern and H.G.
LeDuc
Summary: A new class of distributed
mixer based on the non-linear quasiparticle tunnel current in
a superconductor-insulator-superconductor transmission line
has been proposed and tested. The Nb/Al/AlOx/Nb junctions used
in our mixers are typically 200 nm wide and are between 1 and
2 guided wavelengths long. Compared with the traditional
sub-millimeter lumped element quasiparticle mixer, the
distributed mixer requires lower critical current densities,
lower magnetic field as well as simpler tuning circuitry.
Experiments have been performed in various sub-millimeter
frequency bands. Receiver noise temperatures of 66 K at 460
GHz, 210 K at 630 GHz and 600 K at 780 GHz have been measured.
These noise temperatures are comparable to or slightly better
than the noise temperatures of the corresponding lumped
element mixers. |
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On-chip
radiation detection from stacked Josephson flux-flow
oscillators
A.V. Ustinov, S.V.
Shitov, N. Iosad and H. Kohlstedt
Summary:
Radiation measurements with a double-junction stacked
Josephson flux-flow oscillator on-chip coupled to an SIS
detector are reported. Impedance matching between the
oscillator and the detector has been achieved using a broad
band coupling circuit. Radiation power in the detector up to
10 nW has been measured in the frequency range between 170 and
410 GHz. Coherent radiation from two stacked junctions has
been observed both at the fundamental Josephson frequency and
at its second harmonic. The distribution of the radiation
power between first two harmonics allows us to distinguish
between mutually coupled in-phase and out-of-phase flux-flow
modes in the junctions. Coherent operation of stacked
Josephson junction oscillators in the millimeter and
sub-millimeter wave band is demonstrated. |
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High-temperature
superconducting Josephson Vortex Flow Transistors: numerical
simulations and experimental
results
T. Bauch, S. Weiss, H.
Haensel, A. Marx, D. Koelle and R. Gross
Summary:
Josephson Vortex Flow Transistors (JVFTs) based on high
transition temperature superconductors (HTS) are promising
candidates for three-terminal devices, which may be used e.g.
at the interface between superconducting and semiconducting
electronics. We have investigated the performance of JVFTs
based on parallel arrays and on long HTS Josephson junctions,
both theoretically and experimentally. Our numerical
simulation results reveal the dependence of the current gain
on various device parameters, such as number of junctions,
loop size, and screening parameter /spl beta/=L/L/sub j/,
where L is the loop inductance and L/sub j/ the Josephson
inductance of a single junction. We have fabricated various
devices using symmetrically and asymmetrically injected bias
currents. The experimental results are in good agreement with
our simulation results and it is shown that for asymmetric
devices high values of the current gain above 20 can be
obtained for temperatures below 60 K. |
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Niobium
nitride/aluminium nitride superconductor/insulator multilayers
and tunnel junctions
Z.H. Barber
and M.G. Blamire
Summary: Niobium
nitride/aluminium nitride multilayers have been fabricated
using dc reactive magnetron sputter deposition. By careful
optimization a suitable set of deposition conditions has been
achieved under which both high quality superconducting and
insulating layers may be fabricated. This has allowed
automation of the deposition process to fabricate multilayers
by simple computer control of substrate position and
shuttering. Deposition onto a range of single crystal and
amorphous substrates has given a range of different crystal
structures. We have measured the transport properties of these
multilayers as a function of superconductor and insulator
layer thickness in order to study the interlayer coupling, and
have fabricated stacked
superconductor-insulator-superconductor
junctions. |
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Multilayer
edge SNS SQUIDs for digital
circuits
M.G. Forrester, B.D.
Hunt, J. Talvacchio, R.M. Young and J.D.
McCambridge
Summary: We have fabricated and
characterized direct-injection High Temperature
Superconducting (HTS) SQUIDs using a six-epitaxial-layer
process which integrates edge geometry
superconductor-normal-superconductor (SNS) junctions with an
HTS ground plane. The period of the SQUID threshold curves was
used to infer microstrip inductances of approximately 1
pH//spl square/ at 65 K. Total SQUID inductances as low as
/spl ap/5 pH were inferred from the measured critical current
modulation depth. A novel junction geometry was used in some
devices to reduce the parasitic inductances of the junction
leads by approximately 1 pH. Maintaining such low inductances
is particularly important for Single Flux Quantum digital
circuits. |
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SFQ
balanced comparators at a finite sampling
rate
V.K. Semenov, T.V. Filippov,
Yu.A. Polyakov and K.K. Likharev
Summary: We
have extended our previous study of SFQ balanced comparators
which use two overdamped Josephson junctions to (a) finite
sampling rate and (b) junctions with higher critical current
density. The effective width /spl Delta/I/sub x/ of the gray
zone of the comparators fabricated using the niobium-trilayer
technology of HYPRES, Inc. (j/sub c//spl ap/1 kA/cm/sup 2/)
and Stony Brook's domestic planarized process (j/sub c//spl
ap/5 kA/cm/sup 2/) has been measured as a function of the SFQ
pulse rate (from 2.5 to 55 GHz) and temperature (from 1.6 to
4.2 K), for various drivers which determine the SFQ pulse
shape and external impedance. The data have been compared with
available theories of Josephson junction dynamics in the
presence of thermal and quantum fluctuations. We have found
that /spl Delta/I/sub x/ can be substantially reduced by using
relatively broad ("soft") SFQ pulses. For high-j/sub c/
comparators fed by short (/spl sim/2-ps) SFQ pulses the
temperature dependence is practically negligible, indicating
the dominance of quantum fluctuations. |
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Multilayer
HTS SFQ analog-to-digital
converters
J.D. McCambridge, M.G.
Forrester, D.L. Miller, B.D. Hunt, J.X. Pryzbysz, J.
Talvacchio and R.M. Young
Summary: We have
fabricated and measured high T/sub c/ superconductor single
flux quantum 1-bit flux-counting analog-to-digital converters
(ADCs). The ADCs were made with a multilayer all-epitaxial
process which incorporates 10 edge SNS
(superconductor-normal-superconductor) or step-edge grain
boundary (SEGB) Josephson junctions with a YBa/sub 2/Cu/sub
3/O/sub 7-/spl delta// groundplane. The ADC consists of a
quantizer connected to a Toggle flip-flop through a
buffer-like stage. Direct readout of the flux state of the T
flip-flop was made with a Read SQUID inductively coupled
through a hole in the groundplane. The circuits were operated
at 65 K and low speeds. The SNS circuits outperformed the SEGB
circuits because of their higher readout voltages and tighter
critical current spreads. |
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Inductance
computation of microscopic superconducting
loop
T. Nakazato and Y.
Okabe
Summary: Aimed for the design of
superconducting digital circuits, a direct method is proposed
to estimate the inductance of three-dimensional microscopic
superconducting loop. This method directly computes
current-density distribution by using the Maxwell equations
and the expression of the momentum, which are both
discretized; without free-energy minimization technique, we
just solve a set of linear equations considering a
spatially-discrete model. Computer simulation was carried out
for various shapes of superconductors, and the simulated
results agreed well with the Chang's formula in a model which
can be regarded as two-dimensional. The magnetic field
distribution also agreed well with the theoretical
value. |
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Formal
description of the functional behavior of RSFQ logic circuits
for design and optimization
purposes
H. Toepfer, T. Harnisch,
J. Kunert, S. Lange and H.F. Uhlmann
Summary:
For being used in the design of Rapid Single Flux
Quantum (RSFQ) circuits in a multipurpose manner, we developed
a systematic and consistent approach for modeling the nominal
circuit behavior using hardware description languages. We are
presenting a method for establishing evaluation criteria for
the circuit's behavior which can directly be used in the input
for circuit simulation and serve as a behavioral reference in
yield-driven optimization cycles. Furthermore, this behavioral
modeling technique allows for mixed-mode simulation with its
advantages of both analysis speed-up and error localization.
Finally, we demonstrate the application in high-level circuit
synthesis which will be necessary to manage complex design
problems. |
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Data-driven
self-timed RSFQ digital integrated circuit and
system
Z.J. Deng, N. Yoshikawa,
S.R. Whiteley and T. Van Duzer
Summary: A
novel asynchronous timing scheme, data-driven self-timing
(DDST) is proposed and implemented in Rapid
Single-Flux-Quantum (RSFQ) superconductive integrated
circuits. In this asynchronous approach, the timing signals
are generated from the data and no global clock is needed to
drive the RSFQ circuit and system. The essence of the
self-timing scheme is to localize the system timing in order
to avoid the overhead of global clock distribution, and to
minimize the timing uncertainty. The DDST scheme has been
applied to the design of a shift register, a demultiplexor,
and a self-timed high speed digital test system. In this
paper, test results of a 4-bit DDST shift register and a high
speed on-chip clock generator will be presented to demonstrate
the successful DDST operation of RSFQ integrated circuits at a
rate of 20 Gb/s. |
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Prospects
for quantum coherent computation using superconducting
electronics
M.F. Bocko, A.M. Herr
and M.J. Feldman
Summary: We discuss the
prospects and challenges for implementing a quantum computer
using superconducting electronics. It appears that Josephson
junction devices operating at milli-Kelvin temperatures can
achieve a quantum dephasing time of milliseconds, allowing
quantum coherent computations of 10/sup 10/ or more steps.
This figure of merit is comparable to that of atomic systems
currently being studied for quantum computation. |
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Complementary
Josephson Junction circuits
E.
Terzioglu, D. Gupta and M.R. Beasley
Summary:
We present simple Complementary Josephson Junction
circuits using 1 kA/cm/sup 2/ Nb junctions. We use long,
sine-shaped junctions in order to achieve gain and suppressed
side lobes. We have simulated layout-extracted simple inverter
and ring oscillator circuits to evaluate the performance of
these circuits in 1 kA/cm/sup 2/ technology. Projected gate
delays with possible higher critical current density
technologies are also simulated. We have experimentally tested
the operation of inverter circuits. |
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A
4 bit YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// bicrystal
Josephson junctions flux shuttle shift
register
R. Koch, T. Scherer, M.
Winter and W. Jutzi
Summary: A flux shuttle
shift register with master and slave sections is implemented
with YBCO Josephson junctions along only one straight grain
boundary of a bicrystal substrate. The investigated prototype
comprises a write circuit, four master/slave shift register
cells and a dynamic read out circuit for single flux quanta.
The simulation results and the layout are
presented. |
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AFM
analysis of step-edge Josephson
junctions
J.B. Bulman, O.O.
Salazar and J.M. Murduck
Summary: We report
on an analysis of step-edge Josephson junctions with a variety
of different electrical behavior I/sub c/'s and IV curve
characteristic shapes. We investigated a correlation between
the shape of the IV curve and the morphology of the step-edge
YBCO film concentrating on the sharpness of the step. Using
Atomic Force Microscopy (AFM), determination of the film's
surface properties over the step were obtained. The steepness
of the angle of the film over the step correlated with the
behavior of the IV curve. When the average angle over the step
was >23/spl deg/ the IV curve exhibited the resistively
shunted junction [RSJ] shape. Less steep average angles
<23/spl deg/ corresponded to flux flow-like IV
curves. |
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Comparison
of effective noise temperatures in YBa/sub 2/Cu/sub 3/O/sub
7-/spl delta// junctions
G.M.
Fischer, J. Mygind and N.F. Pedersen
Summary:
The dc voltage response to 70 GHz radiation was
measured for YBCO bicrystal junctions, step edge junctions and
ramp edge junctions at temperatures from 4 K to 90 K.
Employing the RSJ-model and assuming thermal noise, the
Josephson radiation is about equal to the voltage difference
of the voltage response to the small signal microwave
irradiation. In the presence of excess noise, an effective
noise temperature can be defined and is used as a figure of
merit. In bicrystal grain boundary junctions with zero
magnetic field the effective noise temperature was determined
to be equal to the physical temperature within experimental
error. Bicrystal grain boundary junctions with non-zero
magnetic field, step edge junctions and ramp edge junctions
showed excess noise. The scaling of the noise temperature is
compared with the width of the junction in units of the
Josephson penetration depth. |
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Micro-Raman
spectroscopy studies of Co doped Y-Ba-Cu-O thin
films
D. Chamberlain, J.P. Sydow,
R.A. Buhrman, B.H. Moeckly and K. Char
Summary:
We report on the micro-Raman spectroscopy study of thin
films of YBa/sub 2/Cu/sub 3-x/Co/sub x/O/sub 7-/spl delta//
grown by laser ablation. Depending on the growth pressure, the
films are found to be either homogenous or inhomogeneous on a
scale /spl Gt/2 /spl mu/m. In either case the films are, on
average, oxygen deficient, but this deficit can be
substantially improved, yielding /spl delta/ less than zero in
thin film microstructures treated by oxygen electromigration.
This indicates that the Co addition to such films impedes, but
does not forbid the attainment of a relatively optimal degree
of occupancy of the dopant, chain oxygen sites. |
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The
capacitance of bicrystal Josephson junctions deposited on
SrTiO/sub 3/ substrates
E.J.
Tarte, G.A. Wagner, R.E. Somekh, F.J. Baudenbacher, P.
Berghuis and J.E. Evetts
Summary: We have
investigated the capacitance of grain boundary Josephson
junctions deposited on symmetric 24/spl deg/ misoriented
SrTiO/sub 3/ bicrystal substrates using hysteresis and Fiske
resonances in their current voltage characteristics. Our
measurements show that the total junction capacitance is
proportional to the junction area. The capacitance per unit
area is (140/spl plusmn/30) fF /spl mu/m/sup -2/ and this
implies that the main effect of the large relative
permittivity of the substrate is to scale-up the grain
boundary capacitance by a factor of around 10. We also find
that in the planar geometry of bicrystal grain boundary
junctions the velocity of light in the junction depends upon
film thickness. |
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Self-field
effects in intrinsic Josephson junction stacks in (Bi,Pb)/sub
2/Sr/sub 2/CaCu/sub 2/O/sub y/ single
crystals
G. Oya, M. Iwama and A.
Irie
Summary: We have studied the features of
intrinsic Josephson junction stacks in the c-axis direction in
highly Pb-substituted (Bi/sub 1-x/Pb/sub x/)/sub 2/Sr/sub
2/CaCu/sub 2/O/sub y/ (with x/spl ges//spl sim/0.2) single
crystals exhibiting multiple branches with hysteresis on the
I-J characteristics. For the mesa of the single crystal with
x=/spl sim/0.2, as the self-field effects on the fluxon motion
in the Intrinsic Josephson junctions, the flux flow branch and
the zero field step were successfully observed in addition to
the supercurrent at zero voltage and the multiple resistive
branches. Moreover, their ac Josephson effect was also
confirmed by observation of the microwave-induced Shapiro
step. These results imply the existence of intrinsic Josephson
effects in the single crystals with x/spl ges//spl
sim/0.2. |
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Influence
of d(x/sup 2/-y/sup 2/) symmetry on device applications of
high-T/sub c/ grain boundary
junctions
H. Hilgenkamp, J.
Mannhart, B. Mayer, C. Gerber, J.R. Kirtley and K.A.
Moler
Summary: Grain boundary junctions in
high-T/sub c/ thin films generally consist of facets with
typical dimensions below 100 nm. In combination with a d(x/sup
2/-y/sup 2/) symmetry component of the order parameter, this
faceting gives rise to an inhomogeneous critical current
density J/sub c/ along the grain boundary. The inhomogeneity
is most prominent for asymmetric 45/spl deg/ [001] tilt grain
boundaries. For a large fraction of the facets in these
boundaries the order parameter orientation gives rise to an
additional /spl pi/ phase difference, and therefore to a
'negative' critical current density. This leads to highly
anomalous magnetic field dependences of the critical current.
Direct imaging with scanning SQUID microscopy provides
evidence that magnetic flux is generated spontaneously in
these boundaries. These observations have several significant
implications, both for understanding the properties of grain
boundaries in high-T/sub c/ superconductors and for their
applications. |
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Josephson
junctions fabricated by oxygen ion irradiation of YBa/sub
2/Cu/sub 3/O/sub 7-x/ thin
films
J. Hollkott, S. Hu, C.
Becker, J. Auge, B. Spangenberg, H. Kurz, N.D. Zakharov, D.
Hesse and B. Hollander
Summary: Ion
irradiated microbridges are an interesting type of Josephson
junction, because their technological requirements can be very
low. In this paper a specialized fabrication process and the
electrical characterization of the fabricated devices are
reported on. The I/sub C/R/sub N/ product at 77 K is about 24
/spl mu/V. The phase coherence was proven by measurements on
DC-SQUIDs made of these junctions. To get a deeper insight of
the damage produced by ion irradiation, YBa/sub 2/Cu/sub
3/O/sub 7-x/, thin films have been investigated by high
resolution transmission electron microscopy (HRTEM) and
Rutherford backscattering spectroscopy (RBS). |
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SQUID
based remanence measurements for
immunoassays
R. Kotitz, H. Matz,
L. Trahms, H. Koch, W. Weitschies, T. Rheinlander, W. Semmler
and T. Bunte
Summary: The use of fine
magnetic particles as labels for antibodies and the
measurement of their remanent magnetization for the
preparation of immunoassays is presented. Antibodies were
coupled with magnetic nanoparticles and samples were prepared
by reaction of the magnetically labeled antibodies with their
solid phase adsorbed antigen. After exposing the samples to a
field of some mT a dc-SQUID system measures the remanent
sample magnetization in the absence of an external field. The
combination of high moment labels and SQUIDs yields
ultrasensitive immunoassays with a wide range of detectable
analyte concentrations. In contrast to most standard
techniques in our method the detected magnetic signal is
specific only for bound reaction partners, thus eliminating
the need for separation of unbound components. |
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High
sensitivity digital SQUID
magnetometers
M. Radparvar and
S.V. Rylov
Summary: A single-chip digital
SQUID magnetometer integrates a sensitive analog SQUID sensor
with a comparator gate and feedback circuitry on the same
chip. The comparator gate is an asymmetric SQUID gate driving
two DC-to-SFQ converters in series with the feedback coil. In
an optimized digital magnetometer chip, sensitivity and noise
level are determined by the input analog SQUID. The dynamic
range of such digital chips is extremely wide enabling them to
be operated in a relatively high magnetic field environment
without extensive magnetic shielding. Their slew rate is
determined by the frequency of an external two-phase clock.
This chip simplifies room temperature electronics and, due to
its digital output, can be easily multiplexed on-chip. In this
paper, we describe this digital SQUID magnetometer chip and
summarize our experimental results demonstrating a digital
SQUID chip with sensitivity of 20 /spl mu//spl Phi//sub
0///spl radic/(Hz) and a system slew rate of 5/spl
times/10/sup 6/ /spl Phi//sub 0//s at the pick up
coil. |
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Scanning
microwave microscopy of active superconducting microwave
devices
S.M. Anlage, C.P.
Vlahacos, S. Dutta and F.C. Wellstood
Summary:
We have developed a scanning microwave microscope which
can image features with 20 /spl mu/m spatial resolution. The
microscope consists of a section of open-ended coaxial cable
which is scanned over the surface of a planar sample. Images
can be made in either passive mode, in which the reflectivity
of the probe tip is measured as a function of position, or in
active mode, in which stray fields from the sample are picked
up by the scanning probe and measured with a vector
demodulation circuit. We have imaged reflectivity variations
of metallic and superconducting samples in passive mode to
determine the spatial resolution of the technique. Images are
also presented in active mode of a superconducting microwave
device taken at liquid nitrogen temperature. |
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Effects
of magnetic fields and microwave irradiation on step-edge and
bi-epitaxial YBa/sub 2/Cu/sub 3/O/sub y/
SQUIDs
H.E. Horng, J.H. Lu, J.M.
Wu, S.Y. Yang, H.C. Yang and J.D. Chern
Summary:
Current-voltage (I-V) curves of step-edge YBa/sub
2/Cu/sub 3/O/sub y/ junctions, SQUIDs, and Junctions in
parallel in a magnetic field and under microwave irradiation
were measured. I/sub c/-/spl Phi/ curves for a single
Josephson junctions show Fraunhofer diffraction pattern. The
voltage of SQUIDs and Josephson junctions in parallel at a
constant bias current is modulated by external magnetic
fields. In additional to integer Shapiro steps, non-integer
constant-voltage steps were observed under microwave
irradiation in bi-epitaxial SQUIDs. The non-integer voltage
steps can be modulated by the microwave power and the applied
magnetic field. |
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Directly
coupled DC-SQUIDs of YBCO step-edge junctions fabricated by a
chemical etching process operating at 77
K
Junho Gohng, Eun-Hong Lee,
I-Hun Song, Junghyun Sok, Sang-Jin Park, Jo-Won Lee and C.Y.
Dosquet
Summary: High T/sub c/ directly
coupled DC-SQUIDs have been successfully fabricated on
chemically etched MgO substrate steps. The chemical etching
was performed in a mixed acid solution of H/sub 3/PO/sub 4/
and H/sub 2/SO/sub 4/ for the best control of etched surface
and roughness. YBCO thin films were deposited epitaxially on
the step-edged MgO substrate by a KrF laser ablation method.
Characteristics of the directly coupled DC-SQUID have been
studied following the patterning and fabrication of the
device. The chemically etched steps show sharper edges at the
bottom of the step as well as the top unlike those made by ion
milling. AFM and Raman Spectroscopy studies on the YBCO thin
film deposited and patterned on chemically etched show no sign
of appreciable degradation. The result is a good quality
junction even at a relatively low step angle. Directly coupled
DC-SQUIDs that are fabricated with this process show sweeping
voltages of 160 /spl mu/V at 4.2 K, and 6 /spl mu/V at 77 K,
respectively. |
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Optimization
of large-area single-layer flux-transformers and concentrators
coupled to RF-SQUIDs in flip-chip
geometry
G.J. Ockenfuss, J.
Borgmann, M. Reese and R. Wordenweber
Summary:
The effect of layout modifications of large-area
single-layer YBa/sub 2/Cu/sub 3/O/sub 7/ flux transformers
onto the effective area and system noise has been investigated
systematically and the excellent performance of sputtered
large-area flux transformers is demonstrated. First, the gain
of sensitivity and noise contribution of the transformer
(coupled to a 8/spl times/8 mm/sup 2/ washer rf-SQUID) was
determined as a function of the line width of the YBa/sub
2/Cu/sub 3/O/sub 7/ pickup loop w/sub p/ ranging between 1 and
8.2 mm for 1" transformer (O=25.4 mm) and 1 and 19 mm for 2"
transformer (O=50.8 mm), respectively. Leaving the diameter of
the pickup coil (b/sub 1/=23 mm, b/sub 2/=46 mm) and the
coupling coil (d=6 mm, width=1.2 mm) unchanged, the gain in
sensitivity increases from 2.1 for w/sub p/=1 mm to 2.7 for
w/sub p//spl ges/6 mm in the case of 1" transformers and from
3.3 for w/sub p/=1 mm to 4.6 for w/sub p/=19 mm for 2"
transformers. No additional noise contribution of the
transformer could be observed, i.e. a flux noise of 70 /spl
mu//spl Phi//sub 0//spl radic/(Hz) was determined above 5 Hz
and at 77 K. The best values for the field-to-flux conversion
efficiency and the effective area were 0.74 nT//spl Phi//sub
0/ and 2.98 mm/sup 2/ for 1" and 0.43 nT//spl Phi//sub 0/ and
4.94 mm/sup 2/ for 2" transformers, respectively. The
comparison of the experimental data with the theory indicates,
that the expressions derived for low-T/sub c/ superconducting
planar devices have to be modified in the case of high-T/sub
c/ devices. Second, the performance of the sputter deposited
large-area devices is demonstrated for the case of an axial
gradiometer. The white noise level of the whole gradiometer
system in an unshielded environment was <100 fT//spl
radic/(Hz) for frequencies above 5 Hz and the common mode
rejection of the homogeneous field was measured to be better
than 10/sup 4/. Real-time magnetocardiographic signals
obtained via this gradiometer in a magnetically unshielded
environment show a large signal-to-noise ratio. |
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Dc-SQUID
magnetometers and gradiometers on the basis of quasiplanar
ramp-type Josephson
junctions
M.I. Faley, U. Poppe,
K. Urban, H.-J. Krause, H. Soltner, R. Hohmann, D. Lomparski,
R. Kutzner, R. Wordenweber, H. Bousack, A.I. Braginski, V.Yu.
Slobodchikov, A.V. Gapelyuk, V.V. Khanin and Yu.V.
Maslennikov
Summary: Nonaqueous Br-ethanol
chemical etching was successfully used for the preparation of
the Josephson junctions, vias and crossovers in magnetometers
including flux transformers. PrBa/sub 2/Cu/sub 3/O/sub 7-x/
thin films were used for the barrier layer in the Josephson
junctions of the SQUIDs and as an insulation in the junctions
and in the flux transformers. Dc-SQUID magnetometers with
small inductances and even without flux antennas were used for
NDE applications which mainly require a high dynamic range.
Highly sensitive devices were prepared with flip-chip flux
antennas. An ac-bias SQUID electronics significantly improves
the sensitivity of the magnetometers at low
frequencies. |
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Miniaturized
HTS/dielectric multilayer filters for satellite
communications
R.S. Kwok, S.J.
Fiedziuszko, F.A. Miranda, G.V. Leon, M.S. Demo and D.Y.
Bohman
Summary: Presently, most communication
satellites contain well over a hundred of filters in their
payload. Typical satellite multiplexers use dual mode cavity
or dielectric resonator filters which are large and heavy. As
future advanced electronic systems for satellite
communications become more complex, they will need even more
filters requiring filter miniaturization without performance
degradation. Therefore, any improvement in filter technology
consistent with this requirement could enhance satellite's
performance. To reduce the size, weight, and cost of the
multiplexers without compromising performance, we introduce a
new class of dual mode multilayer filters consisting of
YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// and LaAlO/sub 3/ thin
films. The multilayer configuration in C-band, for example,
occupies only 1% of the volume of its dielectric resonator
counterpart. Details of the design, fabrication, and testing
of these filters will be presented. |
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A
study of the applicability of high temperature superconducting
RF receive coils to the MRI
industry
D.G. Smith, P.S. Gerner
and C.P. Zuhoski
Summary: This paper
discusses the results of Booz/spl middot/Allen and Hamilton's
investigation of the market acceptance issues which would
influence the adoption of high temperature superconducting
(HTS) receiver coils for low-field MRI equipment. While HTS
receivers could bring distinct advantages in image quality or
imaging time, the changing healthcare marketplace, especially
for high-end diagnostic imaging equipment, makes adoption
problematic. In order to achieve commercial acceptance, HTS
coils would have to enable new capabilities or applications,
while not violating the marketplace requirements of ease of
use, safety, and high reliability. |
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Materials
for HTS-shielded dielectric
resonators
C. Zuccaro, I. Ghosh,
K. Urban, N. Klein, S. Penn and N.M. Alford
Summary:
The microwave properties of single crystalline
LaAlO/sub 3/, LSAT ((LaAlO/sub 3/)/sub 0.3/-(Sr/sub
2/AlTaO/sub 6/)/sub 0.7/), rutile (TiO/sub 2/), and
polycrystalline Al/sub 2/O/sub 3/ were investigated employing
dielectric resonator techniques. LaAlO/sub 3/ (/spl epsi//sub
r/=23.7) exhibits a frequency dependent maximum of tan/spl
delta/ at about 70 K, which can be explained by defect dipole
relaxation. This leads to a variation of tan/spl delta/ at 9
GHz and 77 K from 5/spl middot/10/sup -6/ to 2/spl
middot/10/sup -5/, the lowest values were achieved with
Verneuil grown crystals. LSAT (/spl epsi//sub r/=22.8)
exhibits an even more pronounced maximum with absolute values
in the 10/sup -4/ range. For rutile (/spl epsi//sub r/=108) we
measured a monotonous increase of tan/spl delta/ with
temperature, which can be explained by intrinsic losses due to
phonons. The loss tangent of Ti-doped polycrystalline,
sintered Al/sub 2/O/sub 3/ was found to be only 4/spl
middot/10/sup -6/ at 10 GHz and 77 K. Except LSAT the
materials investigated so far provide a large potential for
applications as dielectric resonators shielded by high
temperature superconducting (HTS) films. |
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Heterodyne
detector using a SNS
junction
A.M. Luiz, L.A.A.
Pereira and R. Nicolsky
Summary: We propose
new designs for millimeter-wave heterodyne detectors using the
negative differential resistance of SNS junctions. The SNS
junction may be used as the local oscillator in conventional
receivers or a single SNS junction may be simultaneously used
as the local oscillator and as the mixer itself, taking
advantage of the nonlinearity of the current-voltage
characteristic (CVC) of the junction. We calculate CVC curves
for high-Tc SNS junctions (YBCO-SNS junctions), which are
expressed as a function of T/Tc and other
parameters. |
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Ultrafast
optoelectronic switches based on high-T/sub c/
superconductors
C. Jaekel, H.G.
Roskos and H. Kurz
Summary: We present
measurements of the ultrafast reflectivity change of YBa/sub
2/Cu/sub 3/O/sub 7-/spl delta// thin films upon femtosecond
laser excitation. The response is attributed to the breaking
of Cooper pairs and the subsequent recombination of
quasiparticles. In a current-biased superconducting bridge,
these transient processes lead to the generation of picosecond
electromagnetic pulses, which can be directly detected by
measuring the emitted radiation from the bridge in a
quasi-optical setup. We show that the emitted pulse can be
calculated from the all-optical measurements. |
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Generation
and propagation of subpicosecond pulses in a photoconductive
GaAs switch integrated onto a gold/YBa/sub 2/Cu/sub 3/O/sub x/
coplanar transmission line
structure
B.H. Larsen, T. Holst,
Yueqiang Shen, T. Freltoft, C.J. Osbahr, R.H. Jacobsen and
S.R. Keiding
Summary: We present a new type
of photoconductive GaAs switch, which can be integrated
directly onto an already existing high-T/sub c/ circuit. Our
test circuit consists of two coupled coplanar transmission
lines made of gold on top of a YBa/sub 2/Cu/sub 3/O/sub x/
layer grown on a MgO substrate. When the photoconductive
switch is irradiated with femtosecond laser pulses,
subpicosecond (0.4 ps) electric pulses are created. These
pulses are capable of propagating more that 1 mm along the
transmission line. The pulses were detected with a
photoconductive sampling technique, and results are presented
at both room temperature and at 81 K. The photoconductive
switch is useful both as an optical trigger generating pulses
and in the sampling system detecting the pulses. This switch
can be used to characterize high-T/sub c/ circuits e.g. SFQ
logic in the subpicosecond time domain. |
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THz
emission from high-T/sub c/ superconductors by optical pulse
excitation
M. Hangyo, S.
Tomozawa, Y. Murakami, M. Tonouchi, M. Tani, Z. Wang and K.
Sakai
Summary: Emission of ultrashort
electromagnetic pulses from current-biased superconducting
YBCO films has been observed by exciting with femtosecond
laser pulses. The emission device is made of YBCO strip lines
with a bridge at their center on an MgO substrate. The
electric field of the pulse is detected by a photoconductive
switch made of LT-GaAs. The emitted pulse width is /spl
sim/0.5 psec and its Fourier component extends up to 2 THz.
Characteristics of the THz emission such as bias current, pump
power and temperature dependence are investigated in detail.
The emission mechanism is ascribed to the ultrafast
supercurrent modulation caused by the
photoexcitation. |
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Fast
NbN superconducting switch controlled by optical
radiation
M. Zorin, I.
Milostnaya, G.N. Gol'tsman and E.M.
Gershenzon
Summary: The switching time and
the optical control power of the NbN superconducting switch
have been measured. The device is based on the ultrathin film
5-8 nm thick patterned as a structure of several narrow
parallel strips (/spl sim/1 /spl mu/m wide) connected to wide
current leads. The current-voltage characteristic of the
switch at temperature 4.2 K demonstrated a hysteresis due to
DC current self-heating. We studied the
superconducting-to-resistive state transition induced by both
optical and bias-current excitations. The optical pulse
duration was /spl sim/20 ps and the rise time of the current
step was determined to be less than 50 ps. The optical pulse
was delivered to the switch by the semiconductor laser through
an optical fiber. We found that the measured switching time is
less than the duration of the optical excitation. The
threshold optical power density does not exceed 3/spl
middot/10/sup 3/ W/cm/sup 2/. The proposed device can be used
in the fiber input of LTS rapid single flux quantum
circuits. |
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Mature
SQUID-systems and their
application
H.
Koch
Summary: When commercializing
SQUID-technology, system aspects predominate, as the
SQUID-sensor itself is usually only a minor part of the whole
instrumentation. Unfortunately the diversity required by
customers and/or by special constraints of the particular
application necessitates in all but a few cases customs-made
SQUID-systems. The article underlines this fact with examples
of recent instrumentation solutions in the fields of
ultrasensitive measurement techniques, environmental
geophysics, biomagnetism, and biochemical analysis and
discusses some additional aspects where an end-user oriented
approach directly feeds back into the systems design phase. A
common trend in SQUID development required by all applications
mentioned is the need for higher slew-rates while keeping the
field sensitivity as good as possible. |
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Filter
subsystems for wireless
communications
M.J. Scharen, D.R.
Chase, A.M. Ho, A. O'Baid, K.R. Raihn and R.J.
Forse
Summary: Thin-film oxide superconductor
materials and advanced processing techniques have been used to
fabricate high-performance filters for cellular communications
base stations. Quasi-elliptic bandpass and band reject filters
were designed and realized using microstrips to approximate
lumped elements. These quasi-lumped resonators have achieved
unloaded Q's of more than 40,000. Precise system control
allows for high operating temperature (77 K), using either
Yttrium or Thallium high T/sub c/ compounds, compensating for
temperature dependence. Such filters have been successfully
integrated into a permanently evacuated dewar and cooled by a
miniature Stirling cycle cooler. The cooler and dewar were
integrated with control electronics which run off standard
cellular base station +27 V power sources. The system consumes
less than 100 W in operation, making it one of the most
efficient HTSC subsystems demonstrated to date. |
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Improved
sensitivity of NMR spectroscopy probes by use of
high-temperature superconductive detection
coils
H.D.W.
Hill
Summary: High resolution nuclear
magnetic resonance (NMR) spectroscopy is an important
technique for the determination of molecular structures and
physical properties of liquid samples. A major drawback is its
low signal-to-noise ratio compared with other spectroscopic
methods. The dominant source of noise in a spectrometer is
often Johnson noise in the detection coils. Conductus, a
leading manufacturer of superconductive electronics, and
Varian, a leading manufacturer of NMR spectrometers, have
successfully developed NMR sample probes using detection coils
fabricated from thin films of the high temperature
superconductor, YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO)
which reduce that noise and provide a sensitivity enhancement
of a factor of four compared with conventional coils. The
detection coils are maintained at about 25 K while the sample,
contained in a 5 mm diameter tube, is at room temperature. The
coils must carry high radio frequency currents during the
excitation phase of a pulsed NMR experiment and, in order to
maintain spectral quality, should cause little perturbation of
the polarizing magnetic field. Characteristics of these probes
and examples of spectra obtained are shown. |
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Josephson
voltage standard-a review
C.A.
Hamilton, C.J. Burroughs and S.P. Benz
Summary:
The unique ability of a Josephson junction to convert a
microwave frequency f into a voltage Nhf/2e with high accuracy
and the adoption of this phenomenon as the basis for the SI
Volt Realization have created a market for Josephson voltage
standards that is unassailable from any other technology. This
paper reviews the development of Josephson voltage standards
including the junction and array design, the microwave
circuit, and the system integration. With the dc Josephson
standard largely transferred to the commercial sector, NIST is
developing a new class of devices in which the output voltage
can be rapidly programmed either by digitally selecting the
quantum number N or by driving the Josephson array with a
variable frequency pulse train. These new devices will make
possible fast, high-accuracy characterizations of A/D and D/A
converters and the synthesis of ac waveforms. |
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Author
Index (1996 - Part 3)
No author
information available
Summary: Not
available |
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