Superconductor-insulator-normal Metal-insulator-superconductor Research Articles

Microwave Receiving System Based on Cryogenic Sensors for the Optical Big Telescope Alt-Azimuth.

This article presents the results of evaluating the possibility of conducting radio astronomy studies in the windows of atmospheric transparency ~100, ~230, and ~350 GHz using the optical Big Telescope Alt-Azimuthal (BTA) of the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS). A list of some promising astronomical tasks is proposed. The astroclimat conditions at the BTA site and possible optical, cryogenic, and mechanical interfaces for mounting a superconducting radio receiver at the focus of the optical telescope are considered. As a receiving system, arrays of detectors cooled to ~0.3 K based on the superconductor-insulator-normal metal-insulator-superconductor (SINIS) structure are proposed. The implementation of the project will make it possible to use the BTA site of the SAO RAS not only to solve some astronomical problems (it is possible to consider the implementation of a single observatory, the VLBI (very-long-baseline interferometry) mode in the Suffa, EHT (Event Horizon Telescope), and Millimetron projects), but it will also be used to test various cryogenic detectors in a real observatory.

Arrays of electrically small antennas with SINIS detectors for SubTHz astronomy and atmosphere propagation research

An overview of different arrays of electrically small annular antennas of 350 GHz band with integrated superconductor-insulator-normal metal-insulator-superconductor (SINIS) detectors is presented in this paper. Arrays developed for both astronomical observations on the BTA 6 m telescope and measurements there of test sources for investigation of atmospheric turbulence to estimate its influence on the data rate of subTHz telecommunication channels. It is shown both numerically and experimentally that to simulate the electrodynamics of such non-phased antenna arrays it is necessary to investigate the whole array, not a single cell with Floquet ports. The first results of studying of superconducting antennas are also presented in this paper.

Arrays of Sub-Terahertz Cryogenic Metamaterial

Integrated quasi-optical cryogenic terahertz receivers contain arrays of detectors, quasi-optical filters, interferometers, and other metamaterials. Matrices of quasi-optical band-pass, low-pass, and high-pass filters, Fabry–Perot grid interferometers, and arrays of half-wave and electrically small antennas with superconductor-insulator-normal metal-insulator-superconductor (SINIS) sub-terahertz wavelength range detectors were fabricated and experimentally studied on the same computational, technological, and experimental platform. For the design of the filters, we used the periodic frequency-selective surfaces (FSS) approach, contrary to detector arrays that can be presented in a model of distributed absorbers. The structures were fabricated using direct electron beam lithography, thermal shadow evaporation, lift-off, alternatively magnetron sputtering, and chemical and plasma etching. The numerical simulation methods of such structures are sufficiently different: for the reactive matrices with low losses, the approximation of an infinite structure with periodic boundary conditions is applicable, and for the arrays of detectors with dissipative elements of absorbers, a complete analysis of the finite structure with hundreds of interacting ports is applicable. The difference is determined by the presence of dissipation in the detector arrays, the phase of the reflected or re-emitted signal turned out to be undefined and the Floquet periodic boundary conditions are correct only for a phased array antenna. The spectral characteristics of the created filters, interferometers, and antenna arrays were measured in the frequency range 50–600 GHz.

A 90 GHz SINIS Detector With 2 GHz Readout

A superconductor-insulator-normal metal-insulator-superconductor (SINIS) detector integrated in a planar 90 GHz band twin-slot antenna with a 2 GHz superconducting resonator readout was fabricated and experimentally studied. In order to achieve high pixel count, the traditional dc readout of the SINIS detector is replaced by NbN coplanar 13.850 mm long superconducting resonator. SINIS detectors have traditionally dc Junction Field Effect Transistor (JFET) room-temperature readout. Such readout requires individual wiring for each pixel, while the microwave readout is far less cluttered as only one coaxial line is needed for hundreds of devices. Such readout operates similar to frequency domain multiplexing (FDM) for microwave kinetic inductance detectors (MKID). The planar twin slot antenna has two parallel slots in a metal ground plane which are excited coherently by short sections of a coplanar waveguide (CPW) line with a SINIS detector at the center. One section of the CPW is extended past the slot in a long superconducting section which functions as a quarter wavelength resonator. This resonator is short circuited to the ground plane at the far end, with the expected open circuited end terminated by the SINIS detector in the antenna. We measured the response of sample to black body radiation temperatures 6 K and 9 K. The corresponding dynamic resistance maximum drops from 50 kΩ down to 30 kΩ. An RF readout channel comprising a coplanar coupler and a coplanar resonator has a resonant frequency of 1.8 GHz. Unloaded Q factor (without incoming irradiation) is 200. The signal spectral characteristics and the response to the black body radiation have shown design values as expected.

Non-Thermal Absorption and Quantum Efficiency of SINIS Bolometer

We study mechanisms of absorption in two essentially different types of superconductor-insulator-normal metal-insulator-superconductor (SINIS) bolometers with absorber directly placed on Si wafer and with absorber suspended above the substrate. The figure of merit for quantum photon absorption is quantum efficiency equal to the number of detected electrons for one photon. The efficiency of absorption is dramatically dependent on phonon losses to substrate and electrodes, and electron energy losses to electrodes through tunnel junctions. The maximum quantum efficiency can approach <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">n</i> = <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">hf/kT</i> = 160 at f = 350 GHz T = 0.1 K, and current responsivity d <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> /d <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> = <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e/kT</i> in quantum gain bolometer case, contrary to photon counter mode with quantum efficiency of n = 1 and responsivity d <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I</i> /d <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">P</i> = <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e/hf</i> . In experiments, we approach intrinsic quantum efficiency up to n = 80 electrons per photon in bolometer with suspended absorber, contrary to quantum efficiency of about one for absorber on the substrate. In the case of suspended Cu and Pd absorber, Kapitsa resistance protect from power leak to Al electrodes.

Spectral Response of Arrays of Half-wave and Electrically Small Antennas with SINIS Bolometers

Two types arrays of annular half-wave and electrically small antennas with typical sizes of the elements corresponding to 1/10 of the wavelength at SubTHz band with integrated superconductor-insulator-normal metal-insulator-superconductor (SINIS) bolometers have been developed, fabricated and experimentally studied. We performed numerical modeling of the full structure and use additional reference channels in experimental studies to enhance the accuracy of the spectral response estimations of receiving arrays. In experiments three reference channels were used for normalization of the spectral response: a pyroelectric detector outside the cryostat, and two cold channels-a RuO(2)bolometer and on-chip thermometer comprising series array of NIS-junctions.

Quantum Response of a Bolometer Based on the SINIS Structure with a Suspended Absorber

Bolometers based on the superconductor–insulator–normal-metal–insulator–superconductor (SINIS) structure with an absorber suspended above the substrate are developed, fabricated, and experimentally studied in the terahertz frequency range. In contrast to the previously studied bolometers with an absorber located directly on the substrate, the real bolometric mode of operation is achieved, i.e., there is more than one excited electron per quantum of electromagnetic radiation (the quantum efficiency is larger than 1). A quantum efficiency of fifteen electrons per quantum of radiation with a frequency of 350 GHz was achieved in the studied bolometers.

СИНИС-болометр с микроволновым считыванием

We have designed, fabricated, and experimentally studied a Superconductor-Insulator-Normal Metal-Insulator-Superconductor (SINIS) bolometer integrated in a twin-slot antenna with central frequency of 90 GHz and connected to a superconducting coplanar readout resonator. Such single pixel is intended for multichannel matrix of high-sensitive receiver for radioastronomy, in which readout of many channels is arranged via single coaxial cable instead of separate wires and separate amplifiers for each channel.

Arrays of Annular Antennas With SINIS Bolometers

For improving the dynamic range and sensitivity at high power load, we have integrated superconductor-insulator-normal metal-insulator-superconductor (SINIS) bolometers with a frequency selective surface (FSS)-based distributed absorber formed by a series and parallel array consisting of 25 annular antenna elements, each containing two SINIS bolometers. By using a design with 50 bolometers, we reduce incident power load on each bolometer, increase sensitivity and saturation power which is important for ground-based and balloon-borne telescopes with high background power loads. Our main detector pixel is optimized for a frequency band centered at 345GHz. The detectors are matched to incoming telescope beam by a back-to-back horn with a back reflector. Such a configuration improves both the efficiency and the bandwidth of the receiver. Measured voltage responsivity approaches 210(9) VW with an amplifier-limited voltage noise of 20nVHz(12), which corresponds to a NEP 10(-17) WHz(12). The linear voltage response for incoming power is observed for absorbed power of about 5 pW. The current responsivity for parallel array is 210(4) AW and the shot noise limited intrinsic noise equivalent power is NEP 510(-18)WHz(12). The noise equivalent temperature difference is NETD 100 KHz(12) at 2.7-K background radiation temperature.

Annular antenna array metamaterial with SINIS bolometers

We fabricated and experimentally studied a wideband metamaterial comprising a 2D array of annular antennas with Superconductor-Insulator-Normal metal-Insulator-Superconductor (SINIS) bolometers. The annular antenna array metamaterial was designed for a frequency range of 300–450 GHz and consists of periodically arranged electrically small rings, each containing two or four SINIS bolometers connected in series or parallel. These periodic structures with a unit cell size of about one-tenth of a wavelength act as a distributed absorber and receive two orthogonal polarizations. The unit’s small cell size provides a higher density of bolometers and therefore increases the bandwidth and the dynamic range of a single pixel. Theoretical estimates at a central frequency of 345 GHz yield absorption efficiencies of over 80% of the incident RF power within the 300–450 GHz frequency range. The average absorption by the metamaterial matrix in the given frequency band is at least twice as high in comparison to the half-wave circle matrix. We measured the optical response at sample temperatures as low as 100 mK using a quasi-optical setup that consisted of an immersion sapphire lens, bandpass mesh filters, and a variable temperature cryogenic blackbody radiation source. The measured series array voltage responsivity was 1.3 × 109 V/W for radiation temperatures ranging from 2 K to 7.5 K. The current responsivity for the parallel array was 2.4 × 104 A/W at a bath temperature of 100 mK. The spectral response was measured in a 240–370 GHz range with a Backward Wave Oscillator radiation source. The measured equivalent temperature sensitivity could be reduced to 100 μK/Hz1/2 at a 2.7 K radiation temperature level, a value that is suitable for anisotropy measurements in cosmic microwave background radiation.

SINIS bolometer with a suspended absorber

We have developed a Superconductor-Insulator-Normal Metal-Insulator-Superconductor (SINIS) bolometer with a suspended normal metal bridge. The suspended bridge acts as a bolometric absorber with reduced heat losses to the substrate. Such bolometers were characterized at 100-350 mK bath temperatures and electrical responsivity of over 109 V/W was measured by dc heating the absorber through additional contacts. Suspended bolometers were also integrated in planar twin-slot and log-periodic antennas for operation in the submillimetre-band of radiation. The measured voltage response to radiation at 300 GHz and at 100 mK bath temperature is 3*108 V/W and a current response is 1.1*104 A/W which corresponds to a quantum efficiency of ~15 electrons per photon. An important feature of such suspended bolometers is the thermalization of electrons in the absorber heated by optical radiation, which in turn provides better quantum efficiency. This has been confirmed by comparison of bolometric response to dc and rf heating. We investigate the performance of direct SN traps and NIS traps with a tunnel barrier between the superconductor and normal metal trap. Increasing the volume of superconducting electrode helps to reduce overheating of superconductor. Influence of Andreev reflection and Kapitza resistance, as well as electron-phonon heat conductivity and thermal conductivity of N-wiring are estimated for such SINIS devices.

Temperature dependence of single-electron pumping using a SINIS turnstile

A quantum electric current standard is the last missing piece of the quantum metrology triangle. A suitable candidate for realizing this quantum current standard is a single-electron pumping device based on a superconductor/insulator/normal metal/insulator/superconductor (SINIS) turnstile. Here, we show the temperature dependence of the single-electron pumped current of a SINIS turnstile. As the operating temperatures are increased, the current plateaus of the single-electron pumping tilt because of increased back tunneling, which originates from the thermal broadening of energy levels in the normal metal island of the SINIS turnstile. Hence, we find that to use a SINIS turnstile for the current standard at more than 300mK, it is necessary to increase the superconducting energy gaps of the lead material and the charging energy of the island.

Cold-electron bolometer arrays

Superconductor bolometers such as transition edge sensors, hotelectron bolometers, bolometers on the kinetic inductance of a superconductor, and cold� electron bolometers are the most sensitive receivers for the submillimeter band. The radiation power in such bolometers is absorbed in an absorber made of a thin normalmetal film connected to superconductor- insulator-normal metal (SIN) tunnel junctions. These SIN junctions serve for electron cooling (simi� larly to the Peltier effect in semiconductors) and the output signal proportional to the absorbed power is measured on them. The maximum electron cooling and maximum current response are observed in a bias region somewhat lower than the energy gap of the superconductor in the region of the maximum nonlin� earity of the current-voltage characteristic. Electron cooling makes it possible not only to improve the sen� sitivity, but also to expand the dynamic range due to an increase in the saturation power, because the absorbed power is removed from the absorber by a cooling cur� rent. However, for applications in atmospheric radio astronomy, the power of cosmic microwave back� ground radiation is usually higher than the saturation power of a single bolometer of a superconductor- insulator-normal metal-insulator-superconductor (SINIS) structure, where the normal metal is an absorber film at whose edges SIN junctions are formed. When arrays of such structures are used, the signal power is distributed between individual bolom� eters; this makes it possible to expand the dynamic range in proportion to the number of bolometers in an array. To improve electron cooling, expand the dynamic range, and match the input and output impedances, series/parallel arrays of coldele ctron bolometers have been developed, manufactured, and measured at temperatures from 50 to 350 mK. The bolometers are integrated into crossslot antennas to analyze the polarization of cosmic microwave background radiation at a frequency of 345 GHz. The maximum tem� perature response is 6.5 µV/mK. The noiseequivalent electric powe r at a temperature of 300 mK is 1.2 × 10 -17 W/Hz 1/2 .

Synthesis of Precision Waveforms Using a SINIS Josephson Junction Array

A synthesizer of precision ac waveforms based on a binary superconductor insulator-normal metal-insulator-superconductor (SINIS) Josephson junction array has been developed. The array segments are individually biased using a high-speed bias source which gives a switching time of approximately 250 ns between voltage steps. The accuracy limitations of the system due to limited risetime and bandwidth are discussed. Comparisons between the synthesizer and a planar multijunction thermal converter (PMJTC) indicate that it is possible to synthesize sine waves with known rms value having an accuracy in the range of 1 part in 10/sup 7/.

Terahertz spectroscopy with a Josephson oscillator and a SINIS bolometer

The voltage response of a thin-film normal-metal hot-electron bolometer based on a SINIS (superconductor-insulator-normal metal-insulator-superconductor) structure to the radiation of a high-temperature Josephson junction in the terahertz frequency region was measured. Bolometers were integrated with planar log-periodic and double-dipole antennas, and Josephson junctions were integrated with log-periodic antennas. Measurements showed that the Josephson junction at a temperature of 260 mK was overheated by the transport current, so that its electron temperature exceeded 3 K at a bias voltage of 1 mV. The maximum response of a bolometer with a double-dipole antenna was observed at a frequency of 300 GHz, which agreed well with the calculated value. The Josephson radiation was observed at frequencies up to 1.7 THz. The voltage response of a bolometer reached 4×108 V/W, and the total noise-equivalent power reached 1.5×10−17 W/Hz1/2.

Margins of junction parameter spread for non-hysteretic Josephson junction arrays

The programmable Josephson voltage standard shows robust step stability and is convenient for many metrological applications. The advantages of the programmable Josephson voltage standard are due to the array of non-hysteretic Josephson junctions with very high uniformity. We have numerically investigated the non-hysteretic Josephson junction arrays: externally shunted SIS (superconductor-insulator-superconductor) junctions and SINIS (superconductor-insulator-normal metal-insulator-superconductor) junction array. For the externally shunted SIS junction, we found the existence of an optimal range of the shunt inductance. For the SINIS junction array, the maximum tolerable nonuniformity of the junction parameters and the microwave power could be derived according to a tolerance criterion given in terms of the step width of the first Shapiro step. The simulation was also compared with an experimental observation for 1 V SINIS array with 8192 junctions.

Characterization of binary josephson series arrays of different types at bnm-lne and comparisons with conventional sis arrays

Three 1-V binary Josephson arrays developed by the NIST, the PTB, and the VTT, and using, respectively, superconductor-normal metal-superconductor (SNS), superconductor-insulator-normal metal-insulator-superconductor (SINIS), and externally shunted superconductor-insulator-superconductor (es-SIS) Josephson junctions, have been tested at BNM-LNE. The arrays have been found to work properly. Results from direct comparisons with conventional SIS arrays show a good agreement with deviations of less than 0.5 nV at any nominal voltage between 41 mV and 1.3 V.

Application of Josephson series arrays to a DC quantum voltmeter

Josephson series arrays with a binary sequence of nonhysteretic superconductor-insulator-normal metal-insulator-superconductor (SINIS) junctions have been realized. The arrays of up to 8192 junctions (14 bits) are operated at microwave frequencies of about 70 GHz with low microwave power. An electronic system was built to drive an automated dc quantum voltmeter. Two electrically isolated quantum voltmeters (QVMs) in the same cryoprobe and driven by one frequency have been used for calibrating resistive dividers with the intention of demonstrating some advantages of these instruments.

10 V SINIS Josephson junction series arrays for programmable voltage standards

A programmable dc voltage standard for output voltages of up to 10 V has been realized. The series arrays, consisting of about 69120 overdamped superconductor/insulator/normal metal/insulator/superconductor (SINIS) Josephson junctions, have been fabricated using the reliable Nb-Al/Al/sub 2/O/sub 3/ technology. The arrays can be operated in conventional Josephson voltage standards at microwave frequencies from 70 GHz to 75 GHz. Steps of constant voltage are observed at very low microwave power levels, since the major part of the microwave power is generated by the junctions themselves. The operation of the arrays and the formation of Shapiro steps are discussed.

High-frequency performance of RSFQ circuits realized in SINIS technology

The paper presents the determination of the high-frequency performance of Rapid Single Flux Quantum (RSFQ) circuits fabricated in superconductor-insulator-normal metal-insulator-superconductor (SINIS) technology. Circuits of different designs have been realized and were experimentally investigated, including specially designed T flip-flop (TFF) structures and circuits consisting of a switch terminated in Josephson transmission lines. For TFF circuits, the operational functionality was investigated in the frequency range from dc up to nearly 200 GHz. Two frequency domains were found. In the first domain, ranging up to frequencies of 80 GHz (f/sub C//spl cong/Y/sub C///spl Phi//sub 0/), correct digital operation of the device was ascertained. Beyond this range a second domain was found, ranging to nearly 200 GHz, for which quasi-analog frequency dividing is assumed. The bias current margins are /spl plusmn/30% at 40 GHz and /spl plusmn/15% between 130 GHz and 200 GHz. For circuits consisting of a switch, the operational functionality was proved in the frequency range from dc up to 50 GHz, with bias current margins of more than /spl plusmn/20%. The critical current density of the circuits is j/sub C//spl cong/750 A/cm/sup 2/. The smallest junction area is about A=12 /spl mu/m/sup 2/, and the characteristic voltage is V/sub C/=170 /spl mu/V.