The superconducting properties of ruthenium (Ru) thin films and microstructures are investigated. The microstructures are used as transition edge sensors (TES), working at He-3 evaporation cryostats’ temperatures. Ruthenium is substantially inert, and the critical temperature Tc for bulk Ru samples is known from state of art to be 0.40-0.51 K. We investigated magnetron sputtered Ru thin films with thicknesses 13-300 nm on a Si substrate and electron lithography fabricated TES samples, based on the thin-film Ru microstructures. It has been found, that the Tc for the Ru thin films is 0.55-0.70 K, and the width of the transition region is 1-5 mK, and for the Ru TES Tc = 0.55 and ΔT = 4 mK. Furthermore, it was established that lithography process had no significant influence on the properties of the TES samples, so we were able to get consistent properties for several fabrication sessions. Therefore ruthenium is concluded to be a desirable material for transition edge sensors working at He-3 cryostats’ temperatures.
The method of image reconstruction with sub-diffraction resolution in radio vision devices (RVD) of shortwave
millimeter and terahertz frequency range is proposed. The method is based on image scanning using two-dimensional
receiving element array of RVD when array and image move circularly in common plane relatively each to other
(rotating or not rotating) with small eccentricity between their centers. The results of scanning are signals reading out by
detectors of array receiving elements. Each signal is proportional to the integral of two functions product. One function is
a perfect image field distribution of the observed object received by RVD without diffraction distortion. Another one is
RVD optical (quasioptical) transfer function comprising beams delivering incident radiation to detectors of array. The
second function takes into account whole received radiation beam paths from RVD input to each detector including the
effect of diffraction and reciprocal circular scanning of array and image. The image of observed object itself can be
found solving inverse ill-posed problem determined by mentioned above integral relations. The estimation using
computer simulation has shown that proposed method permits to increase resolution up to ten times in comparison with
the case of diffraction restriction. The method is aimed at radioastronomy telescopes and RVD's for the security, medical
diagnostics and other systems.
Alexander Vystavkin, Alla Kovalenko, Sergey Shitov, Andrey Pestryakov, Sergey Bankov, Vladimir Zabolotny, Elena Frolova, Ilya Cohn, Oleg Koryukin, Artem Kuzmin, Anton Zubovich, Andrey Uvarov, Aleksey Il'in, Vladimir Trofimov, Alexander Chernikov, Vyacheslav Vdovin, Vladimir Perminov, Oleg Bol'shakov, Marat Mingaliev, Gregory Yakopov
We describe design of two-polarization imaging array of 7 antenna-coupled TES-bolometers. The fabrication procedure
involves both electron beam lithography and convenient optical lithography resulting in submicron definition of TES
absorber films (down to ~ 0.2 μm) integrated within planar submm-wave antenna. Concept of matching optics between
the long-focus optical telescope and lens-antenna TES bolometer array is described. Two-mirror short-focusing beam
concentrator in combination with image rotator provides signal coupling to immersion lenses of the array. Each TES
bolometer is coupled via microstrip transmission line to only one polarization of two-polarization crossed double-slot
lens-antenna. Design of cryogenic 0.3-K system accommodating the matching optics is presented. We describe
multiplexing readout scheme, which combines tomography, rotational scanning of the image and frequency domain
division methods that drastically reduce the amount of wiring and substantially increase the final image resolution,
especially for low-dimension arrays.
We present the results of experimental development of an ultrasensitive normal metal hot-electron microbolometer with Andreev mirrors and electronic cooling by superconductor- insulator-normal metal (SIN) tunnel junctions. A value NEP equals 5 (DOT) 10-18 W/Hz1/2 for the temperature fluctuations component of noise and the thermal time constant (tau) equals 0.2 microseconds at 300 mK have been estimated for one of the realized devices with thermal conductance G approximately equals 6 (DOT) 10-12 W/K. At 100 mK, the thermal conductance was decreased to G approximately equals 7 (DOT) 10-14 W/K, that gives NEP equals 2 (DOT) 10-19 W/Hz1/2 for the temperature noise component and a thermal time constant (tau) equals 5 microseconds. Such microbolometer is intended as a detector of millimeter and submillimeter wave radiation for space applications.
An integrated quasioptical receiver circuit comprising planar complementary log-periodic antenna, SIS mixer with microstrip matching transformers and parallel array of unshunted SIS junctions operating as a local oscillator has been designed, fabricated and tested. The array of parallel SIS junctions united in a microstrip transmission line can be described as a Josephson transmission line (JTL) with single flux quanta synchronously moving along the array of quantum interferometers. The JTL with 20 junctions each 4 micrometers in diameter has critical current 4.5 mA, normal resistance 0.3 (Omega) and a self-detection step at about 1.1 mV. The step width is over 1.5 mA in current scale and 50 (mu) V in voltage scale that corresponds to about 1 (mu) W oscillation power and 25 GHz tuning range with 550 GHz central frequency. A current applied along the top electrode of the JTL allows to vary the output power of such oscillator. The advantages of such oscillator in comparison with Flux-FLow Oscillator are higher impedance of microstrip line about 10 (Omega) that makes easier matching to SIS mixer, lower losses at frequencies about the energy gap for Nb, narrow linewidth and the possibility to tune output power. THe SIS junction IV curve shows current steps at about 1.2 mV that corresponds to the matching circuit central frequency about 600 GHz that is close to JTL central frequency.
A quasioptical Josephson detector with resistively shunted superconducting tunnel junctions of superconductor-insulator-superconductor (SIS) type and different integrated matching circuits for mm waveband region has been designed, fabricated and experimentally studied. A special quasioptical cryogenic probe has been designed and fabricated for measurements of microwave response of such integrated receiving structures. For low-frequency matching a cold transformer has been used at the output port. Many efforts have been made for reducing the external noise influence on Josephson junction IV curve. Quasioptical beamguide has been optimized and adjusted using Bi bolometers evaporated instead of Josephson junctions in the center of planar antenna. Beampatterns of several types of planar antennas, including self-complementary and non-complementary logarithmic spiral and log-periodic antennas, have been measured using the same technique.
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