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Shurakov, A., Tong, C. - Y. E., Blundell, R., Kaurova, N., Voronov, B., & Gol'tsman, G. (2013). Microwave stabilization of a HEB mixer in a pulse-tube cryocooler. IEEE Trans. Appl. Supercond., 23(3), 1501504.
Abstract: We report the results of our study of the stability of an 800 GHz hot electron bolometer (HEB) mixer cooled with a pulse-tube cryocooler. Pulse-tube cryocoolers introduce temperature fluctuations as well as mechanical vibrations at a frequency of ~1 Hz, both of which can cause receiver gain fluctuations at that frequency. In our system, the motor of the cryocooler was separated from the cryostat to minimize mechanical vibrations, leaving thermal effects as the dominant source of the receiver gain fluctuations. We measured root mean square temperature variations of the 4 K stage of ~7 mK. The HEB mixer was pumped by a solid state local oscillator at 810 GHz. The root mean square current fluctuations at the low noise operating point (1.50 mV, 56.5 μA) were ~0.12 μA, and were predominantly due to thermal fluctuations. To stabilize the bias current, microwave radiation was injected to the HEB mixer. The injected power level was set by a proportional-integral-derivative controller, which completely compensates for the bias current oscillations induced by the pulse-tube cryocooler. Significant improvement in the Allan variance of the receiver output power was obtained, and an Allan time of 5 s was measured.
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Trifonov, A., Tong, C. - Y. E., Grimes, P., Lobanov, Y., Kaurova, N., Blundell, R., et al. (2017). Development of a silicon membrane-based multipixel hot electron bolometer receiver. IEEE Trans. Appl. Supercond., 27(4), 1–5.
Abstract: We report on the development of a multipixel hot electron bolometer (HEB) receiver fabricated using silicon membrane technology. The receiver comprises a 2 × 2 array of four HEB mixers, fabricated on a single chip. The HEB mixer chip is based on a superconducting NbN thin-film deposited on top of the silicon-on-insulator (SOI) substrate. The thicknesses of the device layer and handling layer of the SOI substrate are 20 and 300 μm, respectively. The thickness of the device layer is chosen such that it corresponds to a quarter-wave in silicon at 1.35 THz. The HEB mixer is integrated with a bow-tie antenna structure, in turn designed for coupling to a circular waveguide, fed by a monolithic drilled smooth-walled horn array.
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Trifonov, A., Tong, C. - Y. E., Grimes, P., Lobanov, Y., Kaurova, N., Blundell, R., et al. (2017). Development of A Silicon Membrane-based Multi-pixel Hot Electron Bolometer Receiver. In IEEE Trans. Appl. Supercond. (Vol. 27, 6).
Abstract: We report on the development of a multi-pixel
Hot Electron Bolometer (HEB) receiver fabricated using
silicon membrane technology. The receiver comprises a
2 × 2 array of four HEB mixers, fabricated on a single
chip. The HEB mixer chip is based on a superconducting
NbN thin film deposited on top of the silicon-on-insulator
(SOI) substrate. The thicknesses of the device layer and
handling layer of the SOI substrate are 20 μm and 300 μm
respectively. The thickness of the device layer is chosen
such that it corresponds to a quarter-wave in silicon at
1.35 THz. The HEB mixer is integrated with a bow-tie
antenna structure, in turn designed for coupling to a
circular waveguide,
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Kawamura, J., Blundell, R., Tong, C. - Y. E., Gol'tsman, G., Gershenzon, E., & Voronov, B. (1995). NbN hot-electron mixer measurements at 200 GHz. In Proc. 6th Int. Symp. Space Terahertz Technol. (pp. 254–261).
Abstract: We present noise and gain measurements of resistively driven NbN hot-electron mixers near 200 GHz. The device geometry is chosen so that the dominant cooling process of the hot-electrons is their interaction with the lattice. Except for a single batch, the intermediate frequency cut-off of these mixer elements is – 3 700 MHz, and has shown little variation among other batches of devices. At 100 MHz we measured intrinsic mixer losses as low as —3 dB. We measured the noise temperatures at several intermediate frequencies, and for the best de- vice at 137 MHz with 20 MHz bandwidth, we measured 2000 K; using a low-noise first- stage amplifier at 1.5 GHz with 200 MHz bandwidth, the receiver noise temperature measured 2800 K. We estimate that the noise contribution from the mixer is 500 K and the total losses are —15 dB at 137 MHz.
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Ryabchun, S., Tong, C. - Y. E., Blundell, R., Kimberk, R., & Gol'tsman, G. (2007). Study of the effect of microwave radiation on the operation of HEB mixers in the terahertz frequency range. IEEE Trans. Appl. Supercond., 17(2), 391–394.
Abstract: We have investigated the effect of injecting microwave radiation, with a frequency much lower than that corresponding to the energy gap of the superconductor, on the performance of the hot-electron bolometer mixer incorporated into a THz heterodyne receiver. More specifically, we show that exposing the mixer to microwave radiation does not cause a significant rise of the receiver noise temperature and fall of the mixer conversion gain so long as the microwave power is a small fraction of local oscillator power. The injection of a small, but controlled amount of microwave power therefore enables active compensation of local oscillator power and coupling fluctuations which can significantly degrade the gain stability of hot electron bolometer mixer receivers.
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