Meledin, D., Pavolotsky, A., Desmaris, V., Lapkin, I., Risacher, C., Perez, V., et al. (2009). A 1.3-THz balanced waveguide HEB mixer for the APEX telescope. IEEE Trans. Microw. Theory Techn., 57(1), 89–98.
Abstract: In this paper, we report about the development, fabrication, and characterization of a balanced waveguide hot electron bolometer (HEB) receiver for the Atacama Pathfinder EXperiment telescope covering the frequency band of 1.25–1.39 THz. The receiver uses a quadrature balanced scheme and two HEB mixers, fabricated from 4- to 5-nm-thick NbN film deposited on crystalline quartz substrate with an MgO buffer layer in between. We employed a novel micromachining method to produce all-metal waveguide parts at submicrometer accuracy (the main-mode waveguide dimensions are 90×180 μm). We present details on the mixer design and measurement results, including receiver noise performance, stability and “first-light†at the telescope site. The receiver yields a double-sideband noise temperature averaged over the RF band below 1200 K, and outstanding stability with a spectroscopic Allan time more than 200 s.
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Cherednichenko, S., Drakinskiy, V., Berg, T., Kollberg, E. L., & Angelov, I. (2007). The direct detection effect in the hot-electron bolometer mixer sensitivity calibration. IEEE Trans. Microw. Theory Techn., 55(3), 504–510.
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Burke, P. J., Schoelkopf, R. J., Prober, D. E., Skalare, A., Karasik, B. S., Gaidis, M. C., et al. (1999). Mixing and noise in diffusion and phonon cooled superconducting hot-electron bolometers. J. Appl. Phys., 85(3), 1644–1653.
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Gao, J. R., Hajenius, M., Yang, Z. Q., Baselmans, J. J. A., Khosropanah, P., Barends, R., et al. (2007). Terahertz superconducting hot electron bolometer heterodyne receivers. IEEE Trans. Appl. Supercond., 17(2), 252–258.
Abstract: We highlight the progress on NbN hot electron bolometer (HEB) mixers achieved through fruitful collaboration between SRON Netherlands Institute for Space Research and Delft University of Technology, the Netherlands. This includes the best receiver noise temperatures of 700 K at 1.63 THz using a twin-slot antenna mixer and 1050 K at 2.84 THz using a spiral antenna coupled HEB mixer. The mixers are based on thin NbN films on Si and fabricated with a new contact-process and-structure. By reducing their areas HEB mixers have shown an LO power requirement as low as 30 nW. Those small HEB mixers have demonstrated equivalent sensitivity as those with large areas provided the direct detection effect due to broadband radiation is removed. To manifest that a HEB based heterodyne receiver can in practice be used at arbitrary frequencies above 2 THz, we demonstrate a 2.8 THz receiver using a THz quantum cascade laser (QCL) as local oscillator.
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Ryabchun, S., Tong, C. - Y. E., Blundell, R., & Gol'tsman, G. (2009). Stabilization scheme for hot-electron bolometer receivers using microwave radiation. IEEE Trans. Appl. Supercond., 19(1), 14–19.
Abstract: We present the results of a stabilization scheme for terahertz receivers based on NbN hot-electron bolometer (HEB) mixers that uses microwave radiation with a frequency much lower than the gap frequency of NbN to compensate for mixer current fluctuations. A feedback control loop, which actively controls the power level of the injected microwave radiation, has successfully been implemented to stabilize the operating point of the HEB mixer. This allows us to increase the receiver Allan time to 10 s and also improve the temperature resolution of the receiver by about 30% in the total power mode of operation.
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