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Jiang, L., Miao, W., Zhang, W., Li, N., Lin, Z. H., Yao, Q. J., et al. (2006). Characterization of a quasi-optical NbN superconducting HEB mixer. IEEE Trans. Microwave Theory Techn., 54(7), 2944–2948.
Abstract: In this paper, the performance of a quasi-optical NbN superconducting hot-electron bolometer (HEB) mixer, cryogenically cooled by a close-cycled 4-K refrigerator, is thoroughly investigated at 300, 500, and 850 GHz. The lowest receiver noise temperatures measured at the respective three frequencies are 1400, 900, and 1350 K, which can go down to 659, 413, and 529 K, respectively, after correcting the loss and associated noise contribution of the quasi-optical system before the measured superconducting HEB mixer. The stability of the quasi-optical superconducting HEB mixer is also investigated here. The Allan variance time measured with a local oscillator pumping at 500 GHz and an IF bandwidth of 110 MHz is 1.5 s at the dc-bias voltage exhibiting the lowest noise temperature and increases to 2.5 s at a dc bias twice that voltage.
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Yang, Z. Q., Hajenius, M., Baselmans, J. J. A., Gao, J. R., Voronov, B., & Gol’tsman, G. N. (2006). Reduced noise in NbN hot-electron bolometer mixers by annealing. Supercond. Sci. Technol., 19(4), L (9 to 12).
Abstract: We find that the sensitivity of heterodyne receivers based on superconducting hot-electron bolometers (HEBs) increases by 25–30% after annealing at 85 °C in vacuum. The devices studied are twin-slot antenna coupled mixers with a small NbN bridge of 1 × 0.15 µm2. We show that annealing changes the device properties as reflected in sharper resistive transitions of the complete device, apparently reducing the device-related noise. The lowest receiver noise temperature of 700 K is measured at a local oscillator frequency of 1.63 THz and a bath temperature of 4.3 K.
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Jiang, L., Li, J., Zhang, W., Yao, Q. J., Lin, Z. L., Shi, S. C., et al. (2005). Characterization of NbN HEB mixers cooled by a close-cycled 4 Kelvin refrigerator. IEEE Trans. Appl. Supercond., 15(2), 511–513.
Abstract: It is quite beneficial to operate superconducting hot-electron-bolometer (HEB) mixers with a close-cycled 4 Kelvin refrigerator for real applications such as astronomy and atmospheric research. In this paper, a phononcooled NbN HEB mixer (quasioptical type) is thoroughly characterized under such a cooling circumstance. The effects of mechanical vibration, electrical interference, and temperature fluctuation of a two-stage Gifford-McMahon 4 Kelvin refrigerator upon the characteristics of the phononcooled NbN HEB mixer are investigated in particular. Detailed measurement results are presented.
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Vakhtomin, Y. B., Finkel, M. I., Antipov, S. V., Smirnov, K. V., Kaurova, N. S., Drakinskii, V. N., et al. (2003). The gain bandwidth of mixers based on the electron heating effect in an ultrathin NbN film on a Si substrate with a buffer MgO layer. J. of communications technol. & electronics, 48(6), 671–675.
Abstract: Measurements of the intermediate frequency band 900 GHz of mixers based on the electron heating effect (EHE) in 2-nm- and 3.5-nm-thick superconducting NbN films sputtered on MgO and Si substrates with buffer MgO layers are presented. A 2-nm-thick superconducting NbN film with a critical temperature of 9.2 K has been obtained for the first time using a buffer MgO layer.
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Kawamura, J., Tong, C. - Y. E., Blundell, R., Papa, D. C., Hunter, T. R., Patt, F., et al. (2001). Terahertz-frequency waveguide NbN hot-electron bolometer mixer. IEEE Trans. Appl. Supercond., 11(1), 952–954.
Abstract: We have developed a low-noise waveguide heterodyne receiver for operation near 1 THz using phonon-cooled NbN hot-electron bolometers. The mixer elements are submicron-sized microbridges of 4 nm-thick NbN film fabricated on a quartz substrate. Operating at a bath temperature of 4.2 K, the double-sideband receiver noise temperature is 760 K at 1.02 THz and 1100 K at 1.26 THz. The local oscillator is provided by solid-state sources, and power measured at the source is less than 1 /spl mu/W. The intermediate frequency bandwidth exceeds 2 GHz. The receiver was used to make the first ground-based heterodyne detection of a celestial spectroscopic line above 1 THz.
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Antipov, S. V., Svechnikov, S. I., Smirnov, K. V., Vakhtomin, Y. B., Finkel, M. I., Goltsman, G. N., et al. (2001). Noise temperature of quasioptical NbN hot electron bolometer mixers at 900 GHz. Physics of Vibrations, 9(4), 242–245.
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Svechnikov, S. I., Antipov, S. V., Vakhtomin, Y. B., Goltsman, G. N., Gershenzon, E. M., Cherednichenko, S. I., et al. (2001). Conversion and noise bandwidths of terahertz NbN hot-electron bolometer mixers. Physics of Vibrations, 9(3), 205–210.
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Gerecht, E., Musante, C. F., Zhuang, Y., Yngvesson, K. S., Gol’tsman, G. N., Voronov, B. M., et al. (1999). NbN hot electron bolometric mixerss—a new technology for low-noise THz receivers. IEEE Trans. Appl. Supercond., 47(12), 2519–2527.
Abstract: New advances in hot electron bolometer (HEB) mixers have recently resulted in record-low receiver noise temperatures at terahertz frequencies. We have developed quasi-optically coupled NbN HEB mixers and measured noise temperatures up to 2.24 THz, as described in this paper. We project the anticipated future performance of such receivers to have even lower noise temperature and local-oscillator power requirement as well as wider gain and noise bandwidths. We introduce a proposal for integrated focal plane arrays of HEB mixers that will further increase the detection speed of terahertz systems.
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Gol’tsman, G. N., & Gershenzon, E. M. (1999). Phonon-cooled hot-electron bolometric mixer: overview of recent results. Appl. Supercond., 6(10-12), 649–655.
Abstract: The paper presents an overview of recent results for NbN phonon-cooled hot electron bolometric (HEB) mixers. The noise temperature of the receivers based on both quasioptical and waveguide versions of HEB mixer has crossed the level of 1 K·GHz−1 at 430 GHz (410 K) and 600–650 GHz (480 K) and is close to this level at 820 GHz (1100 K) and 900 GHz (980 K). The gain bandwidth measured for quasioptical HEB mixer at 620 GHz reached 4 GHz and the noise temperature bandwidth was almost 8 GHz. Local oscillator power requirements are about 1 μW for mixers made by photolithography and are about 100 nW for mixers made by e-beam lithography. The studies in terahertz receivers based on HEB superconducting mixers now present a dynamic, rapidly developing field.
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Gerecht, E., Musante, C. F., Jian, H., Yngvesson, K. S., Dickinson, J., Waldman, J., et al. (1999). New results for NbN phonon-cooled hot electron bolometric mixers above 1 THz. IEEE Trans. Appl. Supercond., 9(2), 4217–4220.
Abstract: NbN Hot Electron Bolometric (HEB) mixers have produced promising results in terms of DSB receiver noise temperature (2800 K at 1.56 THz). The LO source for these mixers is a gas laser pumped by a CO/sub 2/ laser and the device is quasi-optically coupled through an extended hemispherical lens and a self-complementary log-periodic toothed antenna. NbN HEBs do not require submicron dimensions, can be operated comfortably at 4.2 K or higher, and require LO power of about 100-500 nW. IF noise bandwidths of 5 GHz or greater have been demonstrated. The DC bias point is also not affected by thermal radiation at 300 K. Receiver noise temperatures below 1 THz are typically 450-600 K and are expected to gradually approach these levels above 1 THz as well. NbN HEB mixers thus are rapidly approaching the type of performance required of a rugged practical receiver for astronomy and remote sensing in the THz region.
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