Lobanov, Y. V., Tong, C. - Y. E., Hedden, A. S., Blundell, R., Voronov, B. M., & Gol'tsman, G. N. (2011). Direct measurement of the gain and noise bandwidths of HEB mixers. IEEE Trans. Appl. Supercond., 21(3), 645–648.
Abstract: The intermediate frequency (IF) bandwidth of a hot electron bolometer (HEB) mixer is an important parameter of the mixer, in that it helps to determine its suitability for a given application. With the availability of wideband low noise amplifiers, it is simple to measure the performance of an HEB mixer over a wide range of IF at a fixed LO frequency using the standard Y-factor method. This in-situ method allows us to measure both the gain and noise bandwidths simultaneously. We have also measured mixer output impedance with a vector network analyser. Intrinsic time constant has been extracted from the impedance data and compared to the mixer's bandwidths determined from receiver Y-factor measurement.
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Trifonov, A., Tong, C. - Y. E., Blundell, R., Ryabchun, S., & Gol'tsman, G. (2015). Probing the stability of HEB mixers with microwave injection. IEEE Trans. Appl. Supercond., 25(3), 2300404 (1 to 4).
Abstract: Using a microwave probe as a tool, we have performed experiments aimed at understanding the origin of the output-power fluctuations in hot-electron-bolometer (HEB) mixers. We use a probe frequency of 1.5 GHz. The microwave probe picks up impedance changes of the HEB, which are examined upon demodulation of the reflected wave outside the cryostat. This study shows that the HEB mixer operates in two different regimes under a terahertz pump. At a low pumping level, strong pulse modulation is observed, as the device switches between the superconducting state and the normal state at a rate of a few megahertz. When pumped much harder, to approximate the low-noise mixer operating point, residual modulation can still be observed, showing that the HEB mixer is intrinsically unstable even in the resistive state. Based on these observations, we introduced a low-frequency termination to the HEB mixer. By terminating the device in a 50-Ω resistor in the megahertz frequency range, we have been able to improve the output-power Allan time of our HEB receiver by a factor of four to about 10 s for a detection bandwidth of 15 MHz, with a corresponding gain fluctuation of about 0.035%.
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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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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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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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