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Koshelets, V. P., Shitov, S. V., Ermakov, A. B., Filippenko, L. V., Koryukin, O. V., Khudchenko, A. V., et al. (2005). Superconducting integrated receiver for TELIS. IEEE Trans. Appl. Supercond., 15(2), 960–963.
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Koshelets, V. P., Dmitriev, P. N., Ermakov, A. B., Sobolev, A. S., Torgashin, M. Y., Kurin, V. V., et al. (2005). Optimization of the phase-locked flux-flow oscillator for the submm integrated receiver. IEEE Trans. Appl. Supercond., 15(2), 964–967.
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Kroug, M., Cherednichenko, S., Merkel, H., Kollberg, E., Voronov, B., Gol'tsman, G., et al. (2001). NbN hot electron bolometric mixers for terahertz receivers. IEEE Trans. Appl. Supercond., 11(1), 962–965.
Abstract: Sensitivity and gain bandwidth measurements of phonon-cooled NbN superconducting hot-electron bolometer mixers are presented. The best receiver noise temperatures are: 700 K at 1.6 THz and 1100 K at 2.5 THz. Parylene as an antireflection coating on silicon has been investigated and used in the optics of the receiver. The dependence of the mixer gain bandwidth (GBW) on the bias voltage has been measured. Starting from low bias voltages, close to operating conditions yielding the lowest noise temperature, the GBW increases towards higher bias voltages, up to three times the initial value. The highest measured GBW is 9 GHz within the same bias range the noise temperature increases by a factor of two.
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Larrey, V., Villegier, J. - C., Salez, M., Miletto-Granozio, F., & Karpov, A. (1999). Processing and characterization of high Jc NbN superconducting tunnel junctions for THz analog circuits and RSFQ. IEEE Trans. Appl. Supercond., 9(2), 3216–3219.
Abstract: A generic NbN Superconducting Tunnel Junctions (STJ) technology has been developed using conventional substrates (Si and SOI-SIMOX) for making THz spectrometers including SIS receivers and RSFQ logic gates. NbN/MgO/NbN junctions with area of 1 /spl mu/m/sup 2/, Jc of 10 kA/cm/sup 2/ and low sub-gap leakage current (Vm>25 mV) are currently obtained from room temperature sputtered multilayers followed by a post-annealing at 250/spl deg/C. Using a thin MgO buffer layer deposited underneath the NbN electrodes, ensures lower NbN surface resistance values (Rs=7 /spl mu//spl Omega/) at 10 GHz and 4 K. Epitaxial NbN [100] films on MgO [100] with high gap frequency (1.4 THz) have also been achieved under the same deposition conditions at room temperature. The NbN SIS has shown good I-V photon induced steps when LO pumped at 300 GHz. We have developed an 8 levels Al/NbN multilayer process for making 1.5 THz SIS mixers (including Al antennas) on Si membranes patterned in SOI-SIMOX. Using the planarization techniques developed at the Si-MOS CEA-LETI Facility, we have also demonstrated on the possibility of extending our NbN technology to high level RSFQ circuit integration with 0.5 /spl mu/m/sup 2/ junction area, made on large area substrates (up to 8 inches).
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Lindgren, M., Currie, M., Zeng, W. - S., Sobolewski, R., Cherednichenko, S., Voronov, B., et al. (1998). Picosecond response of a superconducting hot-electron NbN photodetector. Appl. Supercond., 6(7-9), 423–428.
Abstract: The ps optical response of ultrathin NbN photodetectors has been studied by electro-optic sampling. The detectors were fabricated by patterning ultrathin (3.5 nm thick) NbN films deposited on sapphire by reactive magnetron sputtering into either a 5×10 μm2 microbridge or 25 1 μm wide, 5 μm long strips connected in parallel. Both structures were placed at the center of a 4 mm long coplanar waveguide covered with Ti/Au. The photoresponse was studied at temperatures ranging from 2.15 K to 10 K, with the samples biased in the resistive (switched) state and illuminated with 100 fs wide laser pulses at 395 nm wavelength. At T=2.15 K, we obtained an approximately 100 ps wide transient, which corresponds to a NbN detector response time of 45 ps. The photoresponse can be attributed to the nonequilibrium electron heating effect, where the incident radiation increases the temperature of the electron subsystem, while the phonons act as the heat sink. The high-speed response of NbN devices makes them an excellent choice for an optoelectronic interface for superconducting digital circuits, as well as mixers for the terahertz regime. The multiple-strip detector showed a linear dependence on input optical power and a responsivity =3.9 V/W.
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