A cryogenic bolometer has been fabricated using a bundle of single-walled carbon nanotubes as absorber. A bolometric response was observed when the device was exposed to radiation at 110GHz. The temperature response was 0.4mV∕K, with an intrinsic electrical responsivity at low frequency up to 109V∕W and noise equivalent power of 3×10−16W∕Hz1∕2 at 4.2K. The response is largest at input power levels of a few femtowatts and decreases inversely proportional to the input power. Low frequency noise shows a 1∕f dependence.

Two series/parallel arrays of ten cold-electron bolometers with superconductor-insulator-normal tunnel junctions were integrated in orthogonal ports of a cross-slot antenna. To increase the dynamic range of the receiver, all single bolometers in an array are connected in parallel for the microwave signal by capacitive coupling. To increase the output response, bolometers are connected in series for dc bias. With the measured voltage-to-temperature response of 8.8 µV/mK, absorber volume of 0.08 µm 3 , and output noise of about 10 nV/Hz 1/2 , we estimated the dark electrical noise equivalent power (NEP) as NEP = 6 * 10 −18 W/Hz 1/2 . The optical response down to NEP = 2 * 10 −17 W/Hz 1/2 was measured using a hot/cold load as a radiation source and a sample temperature down to 100 mK. The fluctuation sensitivity to the radiation source temperature is 1.3 * 10 −4 K/Hz 1/2 . A dynamic range over 43 dB was measured using a backward-wave oscillator, a variable polarization grid attenuator, and cold filters/attenuators.

Superconducting Josephson junctions with high characteristic voltages (I c R n larger than 4 mV at 4.2 K) are fabricated by depositing YBa 2 Cu 3 O 7−x on tilted sapphire bicrystal substrates, where the tilting axis is along the grain boundary. The good junction quality and low microwave losses in sapphire gave high frequency response well into the THz region. High quality YBa 2 Cu 3 O 7−x epitaxial films were deposited on tilted sapphire substrates with CeO 2 buffer layers by pulsed laser deposition. YBaCuO films have smaller tilt angles, from 1.0°up to 10.3°, compared to inclination angles of the substrates from 1.5°to 13.6°. X-ray diffraction shows only a single orientation of the films in the a-b plane, as well as an absence of a-axis particles and outgrowths. Critical temperatures as high as T c = 88.5− 89.0 K and ⌬T c ഛ 1.5 K were obtained in all films. The grain boundary in a common high-T c superconducting junction is usually much less straight than in the in-plane rotated bicrystal substrate, depressing Josephson currents. The waviness of the artificial grain boundary in a tilted bicrystal film is three times less than in an in-plane (untilted) bicrystal. Tilted Josephson junctions of widths from 1.5 to 6 µm were tested at temperatures from 0.26 to 77 K. I c R n products as high as 4.5 mV were observed at T = 4.2 K. Shapiro steps were observed at voltages over 3 mV under 300 GHz irradiation. Josephson radiation from the tilted junction was measured at frequencies up to 1.7 THz by a cryogenic bolometer. Suppressing the critical current with a magnetic field can separate Josephson radiation and thermal radiation. A parabolic dependence of the response on bias voltage for thermal radiation corresponds to an increase of junction temperature from 260 mK at zero bias to 3 K at 1 mV bias.

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We report on the optimization of electron cooling by SIN tunnel junctions due to the advanced geometry of superconducting electrodes and very effective normal metal traps for more efficient removal of quasiparticles at temperatures from 25 to 500 mK. The maximum decrease in electron temperature of about 200 mK has been observed at bath temperatures 300-350 mK. We used four-junction geometry with Al-AlO x-Cr/Cu tunnel junctions and Au traps. Efficient electron cooling was realized due to the improved geometry of the cooling tunnel junctions (quadrant shape of the superconducting electrode) and optimized Au traps just near the junctions (≈0.5 µm) to reduce reabsorption of quasiparticles after removing them from normal metal. The maximum cooling effect was increased from a temperature drop of dT = −56 mK (ordinary cross geometry) to −130 mK (improved geometry of superconducting electrodes) and to dT = −200 mK (improved geometry of superconducting electrodes and effective Au traps). The heating peak (instead of cooling) near the zero voltage across cooling junctions has been observed in practice for all samples at temperatures below 150 mK. For higher cooling voltages close to the superconducting gap, the heating was converted to cooling with decreased amplitude. The leakage resistance of the tunnel junctions gives a reasonable explanation of the heating peak. The phonon reabsorption due to the recombination of quasiparticles in superconducting electrodes gives an additional improvement in the theoretical fitting but could not explain the heating peak. An anomalous zero-bias resistance peak has been observed for all tested structures. The peak is explained by Coulomb blockade of tunnelling in transistor-type structures with relatively small tunnel junctions. The work on electron cooling is devoted to the development of a cold-electron bolometer (CEB) with capacitive coupling by SIN tunnel junctions to the antenna for sensitive detection in the terahertz region. Direct electron cooling of an absorber plays a crucial role in supersensitive detection in the presence of a realistic background power load.