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Gol'tsman, G. N., Vachtomin, Y. B., Antipov, S. V., Finkel, M. I., Maslennikov, S. N., Smirnov, K. V., et al. (2005). NbN phonon-cooled hot-electron bolometer mixer for terahertz heterodyne receivers. In Proc. SPIE (Vol. 5727, pp. 95–106).
Abstract: We present the results of our studies of NbN phonon-cooled HEB mixers at terahertz frequencies. The mixers were fabricated from NbN film deposited on a high-resistivity Si substrate with an MgO buffer layer. The mixer element was integrated with a log-periodic spiral antenna. The noise temperature measurements were performed at 2.5 THz and at 3.8 THz local oscillator frequencies for the 3 x 0.2 μm2 active area devices. The best uncorrected receiver noise temperatures found for these frequencies are 1300 K and 3100 K, respectively. A water vapour discharge laser was used as the LO source. The largest gain bandwidth of 5.2 GHz was achieved for a mixer based on 2 nm thick NbN film deposited on MgO layer over Si substrate. The gain bandwidth of the mixer based on 3.5 nm NbN film deposited on Si with MgO is 4.2 GHz and the noise bandwidth for the same device amounts to 5 GHz. We also present the results of our research into decrease of the direct detection contribution to the measured Y-factor and a possible error of noise temperature calculation. The use of a square nickel cell mesh as an IR-filter enabled us to avoid the effect of direct detection and measure apparent value of the noise temperature which was 16% less than that obtained using conventional black polyethylene IR-filter.
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Vahtomin, Y. B., Finkel, M. I., Antipov, S. V., Voronov, B. M., Smirnov, K. V., Kaurova, N. S., et al. (2002). Gain bandwidth of phonon-cooled HEB mixer made of NbN thin film with MgO buffer layer on Si. In Harvard university (Ed.), Proc. 13th Int. Symp. Space Terahertz Technol. (pp. 259–270). Cambridge, MA, USA.
Abstract: We present recently obtained values for gain bandwidth of NbN HEB mixers for different substrates and film thicknesses and for MgO buffer layer on Si at LO frequency of 0.85-1 THz. The maximal bandwidth, 5.2 GHz, was achieved for the device on MgO buffer layer on Si with a 2 nm thick NbN film. Functional devices based on NbN films of such thickness were fabricated for the first time due to an improvement of superconducting properties of NbN film deposited on MgO buffer layer on Si substrate.
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Finkel, M., Vachtomin, Y., Antipov, S., Drakinski, V., Kaurova, N., Voronov, B., et al. (2003). Gain bandwidth and noise temperature of NbTiN HEB mixer. In Proc. 14th Int. Symp. Space Terahertz Technol. (pp. 276–285).
Abstract: We have determined that the gain bandwidth of phonon-cooled HEB mixer employing NbTiN films deposited on MgO layer over Si substrate is limited b y the escape of phonons to the substrate. The cut-off frequencies of 1 um long devices operating at T 71, based on 3.5 nm. 4 nm and 10 nm thick films amount to 400 Mk. 300 MHz, and 100 MHz, respectivel y . The gain bandwidth of 0.13 . um long devices fabricated from 3.5 nm thick film is larger and amounts to 0.8 GIL; at the optimal operating point and to 1.5 GIL: at larger bias. The increase of the gain bandwidth from 400 MHz up to 1.5 GH: with the change of bridge length is attributed to diffusion cooling. A double sideband noise temperature of 4000 K was obtained for heterodyne receiver utilizing pilot NbTiN HEB mixer (not optimized for normal state resistance) operating at the local oscillator frequency of 2.5 THz.
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Goltsman, G. N., Vachtomin, Y. B., Antipov, S. V., Finkel, M. I., Maslennikov, S. N., Polyakov, S. L., et al. (2005). Low-noise NbN phonon-cooled hot-electron bolometer mixers for terahertz heterodyne receivers. In Proc. 9-th WMSCI (Vol. 9, pp. 154–159). International Institute of Informatics and Systemics.
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Kawamura, J., Blundell, R., Tong, C. - Y. E., Papa, D. C., Hunter, T. R., Gol'tsman, G., et al. (1998). First light with an 800 GHz phonon-cooled HEB mixer receiver. In Proc. 9th Int. Symp. Space Terahertz Technol. (pp. 35–43). Pasadena, California, USA.
Abstract: Phonon-cooled superconductive hot-electron bolometric (HEB) mixers are incorporated in a waveguide receiver designed to operate near 800 Gliz. The mixer elements are thin-film nio- bium nitride microbridges with dimensions of 4 nm thickness, 0.2 to 0.3 p.m in length and 2 jun in width. At 780 GHz the best receiver noise temperature is 840 K (DSB). The mixer IF bandwidth is 2.0 GHz, the absorbed LO power is —0.1 1.1W. A fixed-tuned version of the re- ceiver was installed at the Submillimeter Telescope Observatory on Mt. Graham, Arizona, to conduct astronomical observations. These observations represent the first time that a receiver incorporating any superconducting HEB mixer has been used to detect a spectral line of celes- tial origin.
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