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In this paper, we develop fabrication technology and study aluminum films intended for superconducting quantum nanoelectronics using AFM, SEM, XRD, HRXRR. Two-temperature-step quasiepitaxial growth of Al on (111) Si substrate provides a preferentially (111)-oriented Al polycrystalline film and reduces outgrowth bumps, peak-to-peak roughness from 70 to 10 nm, and texture coefficient from 3.5 to 1.7, while increasing hardness from 5.4 to 16 GPa. Future progress in superconducting current density, stray capacitance, relaxation time, and noise requires a reduction in structural defect density and surface imperfections, which can be achieved by improving film quality using such quasiepitaxial growth techniques.

Josephson junctions (JJs) with non-hysteretic I-V characteristic and high critical parameters are required for many applications; in particular, they are needed to create tunable THz range oscillators. We fabricated and studied shunted superconductor-insulator-superconductor (SIS) Nb-AlOx-Nb tunnel junctions with an area of about 1m2, estimated their parameters, and compared them with theoretical models. To assess the performance of shunted junctions in the terahertz range, their characteristics were studied under the influence of a high-frequency signal; the estimated value of the characteristic voltage for the shunted junction at a high frequency is about 1 mV. To improve the circuit parameters, a new type of the shunting based on application of NIS junctions was proposed, which reduces the influence of parasitic inductance, expands the frequency range of the generator, and decreases the size of the structure. The JJs with a new type of shunting have been fabricated and studied. The niobium integrated circuits intended for matching the superconducting oscillator and an SIS junction as a microwave detector were designed, fabricated, and tested. Such structures are required for studying the spectral characteristics and analyzing the operation of the oscillator. The developed circuits have demonstrated efficient operation at frequencies from 300 to 700 GHz; the experimental results are in good agreement with the simulated characteristics. The results obtained will be implemented for further development of the THz range oscillators.

The surface of thin films of Nb, Al, NbTiN, SiO2, Al2O3 is investigated in this work. These films are necessary for the fabrication of high-sensitive devices of THz range. The fabrication processes of such devices are described briefly. All films were fabricated using a Kurt J. Lesker magnetron sputtering system. The study of the film surface roughness was carried out using a Bruker Ikon atomic force microscope. The surface quality of films is determined not only deposition mode, but plasma etching process also. The best values of the root-mean-square deviation of the surface profile Rq = 2 nm were obtained for the used NbTiN film with a thickness of 325 nm. Thin Al-layers that is used for tunnel barrier formation is studied. It is shown than Al films with a thickness of more than 6 nm are already continuous. The surface roughness of the single-layer and multilayer films has been studied.

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.

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 d I /d P = e/kT in quantum gain bolometer case, contrary to photon counter mode with quantum efficiency of n = 1 and responsivity d I /d P = 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 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.

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/cm(2) 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.

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.

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.

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.

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.

—Arrays of planar annular antennas in the 345 GHz range with integrated superconductor–insulator–normal metal–insulator–superconductor (SINIS) bolometers have been developed, fabricated, and experimentally investigated. To increase the absorption efficiency, the source signal was matched with the array using a back-to-back horn and a counter-reflector. The efficiency of the receiving structure was studied depending on the direction of irradiation—through the substrate and from the antenna—as well as on the thickness of the substrate. The methods for normalizing a received signal using a reference channel outside and inside a cryostat is described. The best results were obtained by irradiating the array from the antenna with a substrate thickness equivalent to a quarter wavelength in the dielectric and sputtering of the rear side with a gold film (counterreflector). The effective matching band in the main range was more than 50 GHz; the volt–watt sensitivity reaches 109 V/W.

Samples of superconductor–insulator–superconductor (SIS) and normal metal–insulator–superconductor (NIS) junctions with superconducting aluminum of different thickness were fabricated and experimentally studied, starting from conventional shadow evaporation with a suspended resist bridge. We also developed alternative fabrication by magnetron sputtering with two-step direct e-beam patterning. We compared Al film grain size, surface roughness, resistivity deposited by thermal evaporation and magnetron sputtering. The best-quality NIS junctions with large superconducting electrodes approached a resistance R(0)/R(V2Δ) factor ratio of 1000 at 0.3 K and over 10,000 at 0.1 K. At 0.1 K, R(0) was determined completely by the Andreev current. The contribution of the single-electron current dominated at V > VΔ/2. The single-electron resistance extrapolated to V = 0 exceeded the resistance R(V2Δ) by 3 × 109. We measured the influence of the magnetic field on NIS junctions and described the mechanism of additional conductivity due to induced Abrikosov vortices. The modified shape of the SINIS bolometer IV curve was explained by Joule overheating via NIN (normal metal–insulator–normal metal) channels.

Mixers based on superconductor–insulator–superconductor (SIS) tunnel junctions are the best input devices at frequencies from 0.1 to 1.2 THz. This is explained by both the extremely high nonlinearity of such elements and their extremely low intrinsic noise. Submicron tunnel junctions are necessary to realize the ultimate parameters of SIS receivers, which are used as standard devices on both ground and space radio telescopes around the world. The technology for manufacturing submicron Nb–AlN–NbN tunnel junctions using electron-beam lithography was developed and optimized. This article presents the results on the selection of the exposure dose, development time, and plasma chemical etching parameters to obtain high-quality junctions (the ratio of the resistances below and above the gap Rj/Rn). The use of a negative-resist ma-N 2400 with lower sensitivity and better contrast in comparison with a negative-resist UVN 2300-0.5 improved the reproducibility of the structure fabrication process. Submicron (area from 2.0 to 0.2 µm2) Nb–AlN–NbN tunnel junctions with high current densities and quality parameters Rj/Rn > 15 were fabricated. The spread of parameters of submicron tunnel structures across the substrate and the reproducibility of the cycle-to-cycle process of tunnel structure fabrication were measured.

Microwave detectors of the Metal-Insulator-Metal-Insulator-Metal (MIMIM) structure and the Superconductor-Insulator-Metal-Insulator-Superconductor (SIMIS) structure have been designed, fabricated and investigated. The difference of such samples was in external electrodes, MIMIM uses copper external electrodes, while SIMIS uses aluminum. Identical in dimensions MIMIM and SIMIS samples have been fabricated and experimentally studied in the temperature range of 0.1–2.7 K. Voltage and current response were measured at 300 GHz external irradiation using Backward Wave Oscillator (BWO). According to our estimates, the MIMIM current responsivity is 1.1·103 A/W in the case of a photon response and 4·104 A/W in the case of a bolometric response. The estimated noise equivalent power is in the range 2.5·10 18 W/ √ Hz to 1.2·10−19 W/√Hz.

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.

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.

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.

We present experimental results on the testing of cold-electron bolometer (CEB) detectors comprised of a thin Ti film absorber and two SIN junctions integrated with a planar antenna. The CEB performance was tested in a He 3 sorption cryostat HELIOX-AC-V at bath temperatures of 280‐305 mK. The optical response was measured using the hot/cold load method by flipping a Cu reflector opposite a blackbody surface inside a 3 K shield and using a thermal source with variable temperature. In the first experiment, the detector chip was mounted in an optical sample-holder whose aperture was switched towards or away from a blackbody source changing the incident radiation temperature from 3 K to 270 mK. As a result, we measured the optical response to a 3 K=270 mK radiation temperature change. The measured voltage response value for the detector integrated in a double-dipole antenna was 1VoutD 120 V. This corresponds to a noise equivalent power of NEPD Vn=.dV=dP/D 3:5 10 17 W Hz 1=2 , where dV=dP is the voltage to power response obtained from the incoming power estimation based on the Planck formula. (Some figures may appear in colour only in the online journal)