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Zhang, W., Jiang, L., Lin, Z. H., Yao, Q. J., Li, J., Shi, S. C., et al. (2005). Development of a quasi-optical NbN superconducting HEB mixer. In Proc. 16th Int. Symp. Space Terahertz Technol. (pp. 209–213).
Abstract: In this paper, we report the performance of a quasi-optical NbN superconducting HEB (hot electron bolometer) mixer measured at 500 and 850GHz. The quasi-optical NbN superconducting HEB mixer is cryogenically cooled by a 4-K close-cycled refrigerator. Measured receiver noise temperature at 850 and 500GHz are 3000K and 2500K respectively with wire grid as beamsplitter, while the lowest receiver noise temperature is found to be approximately 1200K with Mylar film. The theoretical receiver noise temperature (taking into account the elliptical polarization of log-spiral antenna) is consistent with measured one. The receiver noise temperature and conversion gain with 15-μm Mylar film as the beamsplitter at 500GHz are thoroughly investigated for different LO pumping levels and dc biases. The stability of the mixer’s IF output power is also demonstrated.
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Yang, Z. Q., Hajenius, M., Baselmans, J. J. A., Gao, J. R., Klapwijk, T. M., Voronov, B., et al. (2005). Improved sensitivity of NbN hot electron bolometer mixers by vacuum baking. In Proc. 16th Int. Symp. Space Terahertz Technol. (pp. 222–225).
Abstract: We find that the sensitivity of heterodyne receivers based on superconducting hot-electron bolometer (HEB) in- creases by 25 − 30% after baking at 85 o C and in a high vacuum. The devices studied are twin-slot antenna coupled HEB mixers with a small NbN bridge of 1×0.15 μm 2 . The mixer noise temperature, gain, and resistance versus temperature curve of a HEB before and after baking are compared and analyzed. We show that baking reduces the intrinsic noise of the mixer by 37 % and makes the superconducting transition of the bridge and the contacts sharper. We argue that the reduction of the noise is due to the improvement of the transparency of the contact/film interface. 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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Loudkov, D., Tong, C. - Y. E., Blundell, R., Kaurova, N., Grishina, E., Voronov, B., et al. (2005). An investigation of the performance of the waveguide superconducting HEB mixer at different RF embedding impedances. In Proc. 16th Int. Symp. Space Terahertz Technol. (pp. 226–229).
Abstract: We have conducted an investigation of the performance of superconducting hot-electron bolometric (HEB) mixer at 800 GHz as a function of the embedding impedance of the waveguide embedding circuit. Using a single half-height mixer block, we have developed three different mixer chip configurations, offering nominal embedding resistances of 70, 35, and 15 Ohms. Both the High Frequency Structure Simulator (HFSS) software and scaled model impedance measurements were employed in the design process. Two batches of HEB mixers were fabricated to these designs using 3-4 nm thick NbN thin film. The mixers were characterized through receiver noise temperature measurements and Fourier Transform Spectrometer (FTS) scans. Briefly, a minimum receiver noise temperature of 440 K was measured at a local oscillator frequency 850 GHz for a mixer of normal state resistance 62 Ohms incorporated into a circuit offering a nominal embedding impedance of 70 Ohms. We conclude from our data that, for low noise operation, the normal state resistance of the HEB mixer element should be close to that of the embedding impedance of the mixer mount.
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Gao, J. R., Hajenius, M., Baselmans, J. J. A., Yang, Z. Q., Baryshev, A. M., Barends, R., et al. (2005). Twin-slot antenna coupled NbN hot electron bolometer mixers for space applications. In Proc. 9-th WMSCI (Vol. 9, pp. 148–153). International Institute of Informatics and Systemics.
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Jiang, L., Zhang, W., Yao, Q. J., Lin, Z. H., Li, J., Shi, S. C., et al. (2005). Characterization of a quasi-optical NbN superconducting hot-electron bolometer mixer. In Proc. PIERS (Vol. 1, pp. 587–590).
Abstract: In this paper, we report the performance of a quasi-optical NbN superconducting HEB (hot electron bolome-ter) mixer measured at 500 GHz. The quasi-optical NbN superconducting HEB mixer is cryogenically cooled bya 4-K close-cycled refrigerator. Its receiver noise temperature and conversion gain are thoroughly investigatedfor different LO pumping levels and dc biases. The lowest receiver noise temperature is found to be approxi-mately 1200 K, and reduced to about 445 K after correcting theloss of the measurement system. The stabilityof the mixer’s IF output power is also demonstrated.
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