Josephson traveling wave parametric amplifiers can have high gain and wide frequency range, high sensitivity, and low noise, which makes them promising for quantum computing, array receiver readout systems, spectroscopy, single-photon detectors, etc. In this paper, the authors investigate samples of traveling wave parametric amplifiers based on a three-layer Nb/AlOx/Nb superconductor–insulator–superconductor (SIS) structure with a SNAIL (Superconducting Nonlinear Asymmetric Inductive Elements) series array. Each SNAIL cell consists of the kinetic inductance of four SIS junctions and the nonlinear inductance of a smaller SIS junction. The cells are alternately connected in antiphase with respect to the magnetic flux, which ensures a change in the sign of the Kerr nonlinearity and a reduction in the phase mismatch for the pump frequency, signal frequency, and idler frequency. The transmission spectra of the samples were measured at temperatures of 4.2 and 2.8 K in the frequency range of 0.1–6 GHz.

Comprehensive structural studies of thin island Al films with a thickness of 20–50 nm deposited by magnetron sputtering on Si(111) substrates in an argon plasma at a pressure of 6 × 10–3 mbar and a temperature ranging from 20 to 500°C are presented. The morphology and microstructure of the films are studied using XRD, SEM, EDS, and TEM methods. It is found that most of the islands are Al 001 and Al 111 crystallites with lateral sizes of 10–100 nm, differently conjugated with the Si(111) substrate. At room temperature of the substrate, only Al 001 crystallites are epitaxially formed on it. The epitaxial growth of Al 111 crystallites is predominant as the substrate temperature increases above 400°C. The influence of the temperature of the Si(111) substrate on the process of epitaxial growth of crystallites, the dynamics of their shape, and structural perfection is shown. It is found that crystallites epitaxially connected to the substrate experience deformation at ε = 7 × 10–3 and ε = –2 × 10–3 for Al 001 and Al 111, respectively. It is shown that for thin island Al films on Si(111), the dependence of the number of crystallization centers and the particle growth rate on the supercooling temperature is consistent with the band model of crystallization. At the same time, a shift in the characteristic temperatures for the zone boundaries is observed due to the properties of the substrate. This must be taken into account when engineering the surface morphology and structural perfection of crystallites in Al island magnetron films.

The results of complementary studies of Al films grown by magnetron sputtering at room temperature are presented. The films were obtained on standard Si(111) substrates without and with a ∼20 nm aluminum (homobuffer) layer preliminarily grown on their surface at 400°C. The interdependence of the morphology, microstructure, and hardness of Al films on the state of the substrate surface was studied by the HRXRR, XRD, SEM, EDS, AFM, and Nano Indenter (ASTM) methods. It is shown that the formation of homobuffer layers on the substrate surface makes it possible to control the structural and mechanical properties of thin aluminum films.

The article discusses the prospects for developing the observational base at the Special Astrophysical Observatory of the Russian Academy of Sciences (SAO RAS) for astrophysical research in the millimeter-wave range. As a first step, a project is proposed to create a set of sub-terahertz receiving equipment to operate at the optical BTA telescope. Additionally, the possibility of installing a new instrument to operate in the frequency range of up to 230 GHz ( λ=1.3 mm) at the Upper Research Site of SAO RAS is considered. Technical and operational characteristics of the instrument, site selection for the installation of a fully steerable millimeter-wave antenna, statistics of meteorological data and atmospheric absorption are discussed. A list of potential scientific tasks addressed by instruments of this class is provided.

The results of complementary studies of Al films grown by magnetron sputtering at room temperature are presented. The films were obtained on standard Si(111) silicon substrates without and with a ~20 nm aluminum (homobuffer) layer preliminarily grown on their surface at 400°C. The interdependence of the morphology, microstructure, and hardness of Al films on the state of the substrate surface was studied by the HRXRR, XRD, SEM, EDS, AFM, and Nano Indenter (ASTM) methods. It is shown that the formation of homobuffer layers on the substrate surface makes it possible to control the structural and mechanical properties of thin aluminum films.

A series of studies of the structure of aluminum films deposited on single-crystal silicon substrates in different temperature regimes has been carried out. The roughness and grain size of 20-nm thick films of nuclei deposited at elevated temperatures and also dusted over the nucleus layer at room temperature to a thickness of 150 nm was studied using an atomic force microscope. The film profile was measured in an electron microscope. It is found that films on a hot sublayer turn out to be smoother, more rigid (less friable), and make it possible to expect the creation of superconductor–insulator–superconductor and superconductor–insulator–normal metal transitions with a higher current density and lower capacitance, respectively.

Tunneling Josephson junctions of the superconductor-insulator-superconductor (SIS) type have a history of more than 50 years, and theoretical estimates of the ultimate parameters of devices for receiving and processing signals based on them look very promising. In practice, in many cases, the actually achieved parameters turn out to be much worse than the theoretical ones, so for niobium SQUIDs the characteristic voltage Vc=IcRn at best reaches 200 µV, and according to theory it should be up to 2 mV. For Terahertz SIS mixers and oscillators, the main problems are a large specific capacitance, hysteresis, and leakage currents. These problems may be related to the morphology and crystal structure of superconductor films. In practice, films are granular, tunnel barriers are nonuniform, the effective area is about 10% of geometric area, leakage currents, parasitic capacitances occur. The crystal structure determines fundamentally different properties of the same elements, for example, for carbon it is diamond, graphite, fullerenes, nanotubes. Important components of a promising superconducting technology are: the use of single-crystal substrates matched in lattice constant and orientation with the grown films, optimization of growth temperature conditions, controlled formation of an oxide or nitride tunnel barrier. One option is to use a Schottky barrier for the semiconductor interlayer instead of a dielectric or normal metal one. This review presents the results of studying films by X-ray diffraction diagnostics, atomic force microscopy, and electron microscopy, showing the main bottlenecks of the existing technology with the deposition of niobium, niobium nitride, and aluminum films on oxidized standard silicon substrates, as well as the results of quasi-epitaxial growth of films on single-crystal substrates at various temperature conditions. Reproducible manufacturing of high-quality tunnel junctions can be achieved by implementing atomically smooth surfaces of tunnel contacts, which will improve the signal and noise characteristics of superconducting devices for receiving and processing information.

The features of conductivity in aluminum films produced by various methods are described depending on the presence of impurities, film thickness, and deposition conditions. The results of measuring the surface properties and crystal structure of fabricated films of aluminum, aluminum oxide, and aluminum nitride by X-ray diffraction and atomic force microscopy are presented. SIS, SIN, NIN junctions based on aluminum were fabricated using both shadow evaporation and magnetron sputtering. The current-voltage characteristics were measured. The prospects for improving the characteristics of aluminum SIS junctions, SQUID amplifiers, and SINIS detectors operating at temperatures of about 100 mK are discussed. Keywords: aluminum thin films, surface roughness, atomically smooth films, tunnel junctions.

A detailed analysis of power flow in superconductor-insulator-normal metal-insulator-superconductor (SINIS) structures with aluminum superconducting electrodes and normal metal absorber made of aluminum with suppressed superconductivity is carried out. From a comparison with the experimental results of measuring the current-voltage characteristics at temperatures from 0.087 K to 0.3 K, it was concluded that the power of the electron-phonon interaction is proportional to the difference of sixth powers of the electron and phonon temperatures. The previously applied relation with the difference of fifth powers leads to an almost twofold error in determining the power of the electron-phonon interaction and an estimate of the electron temperature that is underestimated by about 40 mK.

We give a review of both our own original scientific results of the development of superconducting receivers for sub-terahertz astronomy and the main leading concepts of the global instrumentation. The analysis of current astronomical problems, the results of microwave astroclimate research, and the development of equipment for sub-terahertz radio astronomy studies justify the need and feasibility of a major infrastructure project in Russia to create a sub-terahertz telescope, as well as to enhance the implementation of the ongoing Millimetron and Suffa projects. The following results are discussed: i) superconducting coherent receivers and broadband subterahertz detectors for space, balloon, and ground-based radio telescopes have been developed and tested; ii) ultrasensitive receiving systems based on tunnel structures such as superconductor—insulator—superconductor (SIS) and superconductor—insulator—normal metal—insulator—superconductor (SINIS) have been created, fabricated, and examined; iii) a receiving array based on SINIS detectors and microwave readout system for such structures has been implemented; iv) methods for manufacturing high-quality tunnel structures Nb/AlOx/Nb and Nb/AlN/NbN based on niobium films with a current density of up to 30 kA/cm2 have been developed. Receivers operated at 200 to 950 GHz and having a noise temperature only a factor of 2 to 5 higher than the quantum limit have been created and tested.

Abstract Aim To evaluate long-term safety and efficacy of anatomically optimized distal renal denervation (RDN). Methods We assessed major adverse cardiovascular and renal events; changes in BP (office, ambulatory), and renal function (serum creatinine, eGFR) over 3 year follow-up extension of our double blind, randomized controlled study of the efficacy and safety of distal RDN versus conventional main trunk treatment in patients with true resistant hypertension (NCT02667912). Results Of 55 randomized patients (28/27, distal/main trunk RDN, respectively), 47 (23/24) were assessed at 1 year, and 39 (21/18) - at 3-year post-procedure. During 3-year follow-up 2 fatal and 2 non-fatal strokes were observed in distal RDN group versus one heart failure death and 2 non-fatal strokes in group of main trunk treatment. In distal RDN arm BP remained powerfully and significantly lowered both at 1 and 3 years post-procedure: −18.0 (95% CI −27.6; −8.5) and −16.9 (95% CI −27.3; −6.5) mmHg, 24h ambulatory systolic. During 1st year this potent BP lowering effect was accompanied by moderate eGFR decrease: −8.9 (95% CI −14.8; −3.1) ml/min/sq.m, however, this decrease was later reduced to non-significant −6.5 (95% CI −13.2; 0.3) ml/min/sq.m at 3 year post-procedure signaling some improvement in renal function after 1st year despite sustained strong BP lowering. In group of main trunk intervention BP only moderately decreased at 1 year −12.1 (95% CI −19.2; −5.0) mmHg, in parallel with small non-significant change in eGFR: −1.3 (95% CI −6.6; 4.0) ml/min/sq.m. Subsequently, BP lowering effect weakened and lost significance at 3 years post-procedure: −8.5 (95% CI −19.7; 2.2) mmHg. In contrast, eGFR continued to decline and reached significant −5.0 (95% CI −9.6; −0.3) ml/min/sq.m at the end of the study. Five patients developed new onset chronic kidney disease after main trunk RDN versus 3 patients – after distal RDN. The number of concomitant antihypertensive medications did not significantly changed in either group. Conclusion Our data demonstrate strong long-term BP lowering efficacy of distal RDN and, also, the potential of this procedure to prevent the decline of renal function in patients with resistant hypertension. Funding Acknowledgement Type of funding sources: None.

We designed, fabricated, and tested several prototypes of a Josephson Travelling Wave Parametric Amplifier (JTWPA) with aluminum SIS junctions integrated in series array of dc SQUIDs in the central line of coplanar waveguide. Three types of fabrication recipes were tested: two with shadow evaporation and one with magnetron sputtering and direct e-beam lithography. IV curves of SQUIDs were measured at bath temperature of 0.3 K. We developed a cryogenic setup for meas-urements of spectral characteristics of JTWPA comprising cold HEMT amplifier with circulator, cold attenuators and filters in signal and pump coaxial lines. Resonant characteristic of coplanar quarter-wave resonator with directional coupler intended for short JTWPA was measured.

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.

Superconductor–insulator–normal metal–insulator–superconductor (SINIS) detectors are developed with promising applications in two scheduled instruments of the space project of the Millimetron radio telescope, as well as ground-based high-altitude BTA (Big Telescope Alt-Azimuthal) and Suffa telescopes. For the multipixel imaging array, two matrix versions are developed: half-wave and electrically small antennas with series and parallel connection of elements in each pixel. In the former case, readout is performed using field-effect transistors; in the latter case, readout is performed using superconducting quantum interferometers (SQUIDs). For multipixel applications, a structure with frequency multiplexing of channels, in which each pixel represents a coplanar resonator connected to a common coplanar line and read using a cryogenic microwave amplifier is developed and fabricated for the first time. As such an amplifier, a prototype of the Josephson traveling-wave parametric amplifier (JTWPA) based on aluminum SIS junctions is developed and fabricated for the first time. Such a design provides fast readout of hundreds of channels over one coaxial line, noise removal with spectrum 1/ f in the readout channel due to an increase in the readout frequency to several gigahertz, as well as reduction of the heat load on a sorption refrigerator due to a decrease in the number of lead wires from several hundred to one coaxial cable.

Page 542, the sentence under Fig. 3 should read as follows: According to Fig. 3, the maximum radiation response is 2 × 109 V/W, which is 2.5 times greater than that at approximately the same power absorbed by the detector, but given in [3] at a substrate temperature of 0.2 K.

Prototypes of the design of Josephson traveling-wave parametric amplifier based on aluminum superconductor–insulator–superconductor junctions in the form of direct-current SQUIDs included in central conductor of coplanar line are developed, fabricated, and investigated. Three manufacturing methods for the fabrication of such devices are tested: two of them using shadow evaporation and one using magnetron sputtering and direct electron-beam lithography. Current–voltage characteristics of the junctions are measured at 0.3 K. A cryogenic setup for the measurement of spectral characteristics of such amplifier containing cold semiconductor amplifier with circulator and cooled attenuators of the channels of input signal and pump is developed. The absorption spectrum of coplanar directional coupler with a quarter-wave resonator dedicated for measurements of short chains from one to 27 SQUIDs is measured.

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 n = hf/kT = 160 at f = 350 GHz T = 0.1 K, and current responsivity dI/dP = e/kT in quantum gain bolometer case, contrary to photon counter mode with quantum efficiency of n = 1 and responsivity dI/dP = e/hf. 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.

A bolometer, which is based on a superconductor–insulator–normal metal–insulator–superconductor (SINIS) structure, integrated into a twin-slot antenna with a central frequency of 90 GHz, and connected with a superconducting microwave readout resonator, has been designed, fabricated, and experimentally studied. Such an elementary cell is designed for the multi-element array of a high-sensitive radioastronomic receiver, in which the readout from a great number of channels is performed by a single coaxial cable instead of separate wires and amplifier in each channel.

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 RuO2 bolometer and on-chip thermometer comprising series array of NIS-junctions.

Bolometers based on the structure of a superconductor - insulator - normal metal - insulator - superconductor with an absorber suspended above the substrate have been developed, manufactured, and experimentally investigated in the THz frequency range. In such structures, in contrast to the previously studied bolometers with an absorber located directly on the substrate, the bolometric mode of operation of the receiver is realized, i.e., more than one electron is excited per quantum of radiation (quantum efficiency greater than 1). In the studied bolometers, it was possible to achieve a quantum efficiency of 15 electrons per radiation quantum with a frequency of 350 GHz.