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Baselmans JJA, Hajenius M, Gao J, de Korte P, Klapwijk TM, Voronov B, et al. Doubling of sensitivity and bandwidth in phonon-cooled hot-electron bolometer mixers. In: Zmuidzinas J, Holland WS, Withington S, editors. Proc. SPIE. Vol 5498. SPIE; 2004. p. 168–76.
Abstract: NbN hot electron bolometer (HEB) mixers are at this moment the best heterodyne detectors for frequencies above 1 THz. However, the fabrication procedure of these devices is such that the quality of the interface between the NbN superconducting film and the contact structure is not under good control. This results in a contact resistance between the NbN bolometer and the contact pad. We compare identical bolometers, with different NbN – contact pad interfaces, coupled with a spiral antenna. We find that cleaning the NbN interface and adding a thin additional superconductor prior to the gold contact deposition improves the noise temperature and the bandwidth of the HEB mixers with more than a factor of 2. We obtain a DSB noise temperature of 950 K at 2.5 THz and a Gain bandwidth of 5-6 GHz. For use in real receiver systems we design small volume (0.15x1 micron) HEB mixers with a twin slot antenna. We find that these mixers combine good sensitivity (900 K at 1.6 THz) with low LO power requirement, which is 160 – 240 nW at the Si lens of the mixer. This value is larger than expected from the isothermal technique and the known losses in the lens by a factor of 3-3.5.
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Gao JR, Hajenius M, Baselmans JJA, Klapwijk TM, de Korte PAJ, Voronov B, et al. NbN hot electron bolometer mixers with superior performance for space applications. In: Armandillo E, Leone B, editors. Proc. Int. workshop on low temp. electronics. Noordwijk; 2004. p. 11–7.
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Gao JR, Hajenius M, Baselmans JJA, Yang ZQ, Baryshev AM, Barends R, et al. Twin-slot antenna coupled NbN hot electron bolometer mixers for space applications. In: Proc. 9-th WMSCI. Vol 9. International Institute of Informatics and Systemics; 2005. p. 148–53.
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Hajenius M, Baselmans JJA, Gao JR, Klapwijk TM, de Korte PAJ, Voronov B, et al. Low noise NbN superconducting hot electron bolometer mixers at 1.9 and 2.5 THz. Supercond Sci Technol. 2004;17(5):S224–S228.
Abstract: NbN phonon-cooled hot electron bolometer mixers (HEBs) have been realized with negligible contact resistance between the bolometer itself and the contact structure. Using a combination of in situ cleaning of the NbN film and the use of an additional superconducting interlayer of a 10 nm NbTiN layer between the Au of the contact structure and the NbN film superior noise temperatures have been obtained as low as 950 K at 2.5 THz and 750 K at 1.9 THz. Here we address in detail the DC characterization of these devices, the interface transparencies between the bolometers and the contacts and the consequences of these factors on the mixer performance.
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Gao GR, Hovenier JN, Yang ZQ, Baselmans JJA, Baryshev A, Hajenius M, et al. A novel terahertz heterodyne receiver based on a quantum cascade laser and a superconducting bolometer. In: Proc. 16th Int. Symp. Space Terahertz Technol. Göteborg, Sweden; 2005. p. 19–23.
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Baselmans JJA, Baryshev A, Reker SF, Hajenius M, Gao JR, Klapwijk TM, et al. Direct detection effect in small volume hot electron bolometer mixers. Appl Phys Lett. 2005;86(16):163503 (1 to 3).
Abstract: We measure the direct detection effect in a small volume (0.15μm×1μm×3.5nm)(0.15μm×1μm×3.5nm) quasioptical NbN phonon cooled hot electronbolometermixer at 1.6THz1.6THz. We find that the small signal sensitivity of the receiver is underestimated by 35% due to the direct detection effect and that the optimal operating point is shifted to higher bias voltages when using calibration loads of 300K300K and 77K77K. Using a 200GHz200GHzbandpass filter at 4.2K4.2K the direct detection effect virtually disappears. This has important implications for the calibration procedure of these receivers in real telescope systems.
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Hajenius M, Baselmans JJA, Baryshev A, Gao JR, Klapwijk TM, Kooi JW, et al. Full characterization and analysis of a terahertz heterodyne receiver based on a NbN hot electron bolometer. J. Appl. Phys.. 2006;100(7):074507.
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Hajenius M, Baselmans JJA, Gao JR, Klapwijk TM, de Korte PAJ, Voronov B, et al. Improved NbN phonon cooled hot electron bolometer mixers. In: Proc. 14th Int. Symp. Space Terahertz Technol. Tucson, USA; 2003. p. 413–23.
Abstract: NbN phonon-cooled hot electron bolometer mixers (HEBs) have been realized with negligible contact resistance to Au pads. By adding either a 5 nm Nb or a 10 nm NbTiN layer between the Au and NbN, to preserve superconductivity in the NbN under the Au contact pad, superior noise temperatures have been obtained. Using DC I,V curves and resistive transitions in combination with process parameters we analyze the nature of these improved devices and determine interface transparencies.
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Baselmans JJA, Hajenius M, Gao JR, Klapwijk TM, de Korte PAJ, Voronov B, et al. Doubling of sensitivity and bandwidth in phonon cooled hot electron bolometer mixers. Appl Phys Lett. 2004;84(11):1958–60.
Abstract: We demonstrate that the performance of NbN lattice cooled hot electron bolometer mixers depends strongly on the interface quality between the bolometer and the contact structure. We show experimentally that both the receiver noise temperature and the gain bandwidth can be improved by more than a factor of 2 by cleaning the interface and adding an additional superconducting interlayer to the contact pad. Using this we obtain a double sideband receiver noise temperature TN,DSB=950 K
at 2.5 THz and 4.3 K, uncorrected for losses in the optics. At the same bias point, we obtain an IF gain bandwidth of 6 GHz.
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Floet DW, Baselmans JJA, Klapwijk TM, Gao JR. Resistive transition of niobium superconducting hot-electron bolometer mixers. Appl Phys Lett. 1998;73(19):2826.
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