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Y. Fujii, M. Kroug,
K. Kaneko,
A. Gonzalez,
Y. Uzawa,
T. Kojima,
K. Kuroiwa,
A. Miyachi,
K. Makise,
Zhen Wang,
Wenlei Shan
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ABSTRACT: We have developed a dual polarization prototype model of the Atacama Large Millimeter/submillimeter Array (ALMA) Band 10 (787-950 GHz) receivers. The front-end optics comprises a pair of ellipsoidal mirrors, a wire grid, and two corrugated feed horns. A waveguide mixer block is attached to each feed horn in which a mixer chip employing Nb/AlOx/Nb juncions and NbTiN/SiO<sub>2</sub>/Al microstrip tuning circuits is mounted to a WR-1.2 full-height waveguide. A local oscillator (LO) signal receiving horn and a waveguide 10-dB LO coupler are integrated in the block to provide the LO signal to the mixer chip. A fixed-tuned multiplier with a diagonal horn located at the 110-K stage is used to transmit the LO power. The LO signal is then quasi-optically coupled to the mixer receiving horn. A very wide intermediate frequency (IF) system with a bandwidth of 4-12 GHz is employed. The receiver demonstrated double sideband (DSB) noise temperatures of about 160 K (4 h ν/ k <sub>B</sub>) without any correction for loss in front of the receiver at the LO frequency of 834 GHz at an operating physical temperature of 4 K.
IEEE Transactions on Appiled Superconductivity 07/2011; · 1.04 Impact Factor
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ABSTRACT: We have developed a single polarization engineering model of the Atacama Large Millimeter/Submillimeter Array (ALMA) Band 10 (0.78–0.95 THz) receivers. The front-end optics comprises a pair of ellipsoidal mirrors and a corrugated feed horn. A waveguide mixer block is attached to the feed horn in which an NbTiN-based superconductor–insulator–superconductor (SIS) mixer chip, which uses a quartz substrate, is mounted onto a WR-1.2 full-height waveguide. The SIS mixer employs two Nb/AlOx/Nb junctions and an NbTiN/SiO2/Al microstrip tuning circuit. A very wide intermediate frequency (IF) system with a bandwidth of 4–12 GHz is employed. The receiver demonstrated double-sideband (DSB) noise temperatures of below 240 K at local oscillator (LO) frequencies ranging from 792 to 945 GHz, without any correction for loss in front of the receiver. The lowest DSB receiver noise temperature, 179 K, was obtained at the center frequency of the designed band, which corresponds to about 4 quanta. These results represent state-of-the-art sensitivity for a receiver at an operating physical temperature of 4 K.
Superconductor Science and Technology 10/2009; 22(11):114002. · 2.66 Impact Factor
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ABSTRACT: We report on the mixing properties of waveguide SIS mixers with epitaxial NbN/AlN/NbN junctions and NbN/SiO<sub>2</sub>/NbTiN microstrips on MgO substrates. The superconducting transition temperature and 20-K resistivity of NbTiN film on the SiO<sub>2</sub> dielectric were 14.7 K and 175 muOmega cm, respectively. The junction tuning circuit was composed of an NbN/SiO<sub>2</sub>/NbTiN microstrip and two parallel-connected NbN/AlN/NbN junctions 0.9 mum in diameter. The critical current density and normal-state resistance of the fabricated NbN junction were 13 kA/cm<sup>2</sup> and 22 Omega, respectively. The heterodyne response was measured using 295- and 77-K blackbody sources, a local oscillator (LO) source, and a 25-mum-thick Kapton film as a beam splitter. An intermediate frequency (IF) amplifier with a bandwidth of 4-12 GHz was used in the measurements. The receiver noise temperature corrected for losses in the beam splitter and in the vacuum window of the cryocooler was 370 K at 860 GHz and was comparable to that of all-NbN mixes with NbN/MgO/NbN microstrips.
IEEE Transactions on Appiled Superconductivity 07/2009; · 1.04 Impact Factor
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ABSTRACT: Band10 of the Atacama Large Millimeter Array (ALMA) is a planned heterodyne receiver covering the frequency range 790 GHz-950 GHz. The waveguide mixers are superconductor insulator superconductor (SIS) Nb/Al-AlO<sub>x</sub>/Nb junctions integrated with NbTiN/SiO<sub>2</sub>/Al tuning circuits. Our junction definition process has been greatly simplified by introducing an inductively-coupled-plasma (ICP) etcher to the fabrication. The etching process, which employs a low-pressure CF<sub>4</sub>/O<sub>2</sub> plasma, allows to remove the entire Nb/Al-AlO<sub>x</sub>/Nb tri-layer in a single step. SIS mixers with current densities up to 10 kA/cm<sup>2</sup> and quality factor above 15 have been fabricated with good reproducibility. Minimum receiver noise temperature, corrected for optical losses, is 210 K at 860 GHz. With the goal to further improve the performance, optimization of circuit design and fabrication technology are discussed.
IEEE Transactions on Appiled Superconductivity 07/2009; · 1.04 Impact Factor
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ABSTRACT: We have designed, fabricated, and tested terahertz waveguide superconductor-insulator-superconductor (SIS) mixers with Nb/AlO<sub>x</sub>/Nb junctions and NbN/SiO<sub>2</sub>/Al microstriplines. The NbN ground plane used was an epitaxial film grown on a single-crystal MgO substrate. A two-junction tuning circuit, which was directly placed at the feed point of a bow-tie waveguide probe without impedance transformers, was used. A full-height waveguide, hammer-type choke filter, and zero-depth backshort were adopted for the design of the microstrip-waveguide transition structure. The Nb junctions in which the current density was 6.5 kA/cm<sup>2</sup> showed good I-V characteristics, yielding a subgap-to-normal-state resistance ratio greater than 20. The results obtained for the mixer performance showed a receiver noise temperature of 440 K (DSB) at 1 THz; the results were corrected for losses in the beam splitter and the vacuum window. A detailed analysis of the mixers suggested that the waveguide mixers composed of epitaxial NbN films and Nb junctions were effective in the terahertz band.
IEEE Transactions on Appiled Superconductivity 07/2009; · 1.04 Impact Factor
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ABSTRACT: We are developing the Atacama large millimeter/submillimeter array (ALMA) band 10 (787-950 GHz) receiver cartridge. The double-side-band (DSB) mixer consists of a corrugated feed horn, a full-height waveguide mixer block and a Nb(Ti)N-based superconductor-insulator-superconductor (SIS) mixer chip. The IF system uses a 4-12-GHz cooled low-noise InP-based MMIC amplifier and a 4-12-GHz isolator. Heterodyne sensitivity tests showed the mixer noise temperature of about 200 K in the 800 GHz band at an operating temperature of 4 K. This result is comparable to the state-of-the-art mixer performance at this frequency range.
Infrared, Millimeter and Terahertz Waves, 2008. IRMMW-THz 2008. 33rd International Conference on; 10/2008
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ABSTRACT: Nb/Al–AlNx/Nb SIS junctions have been fabricated by various RF plasma nitridation techniques. The reproducibility of the RNAproduct from batch to batch was improved by diluting the N2 plasma with He or Ar. For the He+N2 process, a power-law relation between the RNA product and the nitridation time was found to hold along 100-106Ω μm2, which implies that the thickness of the barrier grows logarithmically during the time it is exposed to the plasma. By applying a pulse-time-modulated RF power, we were able to slow down the nitridation significantly. Finally, we present the results of preliminary RF measurements. The Nb/Al–AlNx/Nb SIS mixers were tested at around 150GHz and 350GHz, and showed noise performances comparable to those of Nb/Al–AlOx/Nb SIS mixers.
Journal of Physics Conference Series 03/2008; 97(1):012251.
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ABSTRACT: We have investigated the current density dependence of subharmonic gap structures in NbN tunnel junctions. Using multiple Andreev reflection theory for a homogeneous barrier, we evaluated barrier transparency for junctions with various current densities ranging from 4 to 20 kA/cm<sup>2</sup> by observing the current step height at a voltage of 2Delta/ne for n = 1, 2, and 3. The results suggest that the tunnel barrier in NbN junctions is inhomogeneous due to a small number of "thinner" regions with high transparency. This transparency is still in the low transmission regime and is independent of the current density. This evaluation method should be useful for understanding the nature of tunnel barriers.
IEEE Transactions on Appiled Superconductivity 07/2007; · 1.04 Impact Factor
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ABSTRACT: The performance of a hot-electron bolometric (HEB) mixer based on NbN from 0.9 to 2.5 THz was investigated using a quasi-optical receiver configuration. An HEB mixer is an ultra-thin superconducting NbN strip located at the feed point of a thick normal conducting Au spiral antenna on a high-resistivity Si substrate. The active area of the mixer was 3 nm thick, 0.4 μm long and 4 μm wide. The quasi-optics consisted of an MgO hyperhemisphere with anti-reflection caps made of Kapton-JP polyimide film and an offset parabola to reduce input losses. The frequency dependence of the double-sideband receiver noise temperature was investigated at several frequencies by using a backward wave oscillator or an optically pumped far-infrared laser as the local oscillator. Results demonstrated low-noise and wide-band characteristics, below 1 K GHz−1 over the measured frequency range. At 917 GHz, the measured receiver noise temperature was 550 K across a 500 MHz intermediate-frequency bandwidth centred at 1.5 GHz, which is slightly better than that of other HEB mixers at around this frequency. This paper was presented at the 8th International Superconductive Electronics Conference, Osaka, Japan, 19–22 June 2001.
Superconductor Science and Technology 12/2001; 15(1):141. · 2.66 Impact Factor
