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Baryshev, A.; Baselmans, J. J. A.; Reker, S. F.; Hajenius, M.; Gao, J. R.; Klapwijk, T. M.; Vachtomin, Yu.; Maslennikov, S.; Antipov, S.; Voronov, B.; Gol'tsman, G. |
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Title |
Direct detection effect in hot electron bolometer mixers |
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2005 |
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Proc. 16th Int. Symp. Space Terahertz Technol. |
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Proc. 16th Int. Symp. Space Terahertz Technol. |
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463-464 |
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NbN HEB mixers, effect of direct detection, direct detection effect |
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NbN phonon cooled hot electron bolometer (HEB) mixers are currently the most sensitive heterodyne detectors at frequencies above 1.2 THz. They combine a good sensitivity (8-15 times the quantum limit), an IF bandwidth of the order of 4-6 GHz and a wide RF bandwidth from 0.7-5.2 THz. However, for use in a space based observatory, such as Herschel, it is of vital importance that the Local Oscillator (LO) power requirement of the mixer is compatible with the low output power of present day THz LO sources. This can be achieved by reducing the mixer volume and critical current. However, the large RF bandwidth and low LO power requirement of such a mixer result in a direct detection effect, characterized by a change in the bias current of the HEB when changing the RF signal from a black body load at 300 K to one at 77 K. As a result the measured sensitivity using a 300 K and 77 K calibration load differs significantly from the small signal sensitivity relevant for astronomical observations. In this article we describe a set of dedicated experiments to characterize the direct detection effect for a small volume quasi-optical NbN phonon cooled HEB mixer. We measure the direct detection effect in a small volume (0.15 μm · 1 μm · 3.5 nm) quasi- optical NbN phonon cooled HEB mixer at 1.6 THz. We found that the small signal sensitivity of the receiver is underestimated by approximately 35% due to the direct detection effect and that the optimal operating point is shifted to higher bias voltages when using calibration loads of 300 K and 77 K. Using a 200 GHz wide band-pass filter at the 4.2 K the direct detection effect virtually disappears. Heterodyne response measurements using water vapor absorption line in a gas cell confirms the existence and a magnitude of a direct detection effect. We also propose a theoretical explanation using uniform electron heating model. This direct detection effect has important implications for the calibration procedure of these receivers in real telescope systems. We are developing Nb HEBs for a large-format, diffusion-cooled hot electron bolometer (HEB) array submillimeter camera. The goal is to produce a 64 pixel array together with the University of Arizona to be used on the HHT on Mt Graham. It is designed to detect in the 850 GHz atmospheric window. We have fabricated Nb HEBs using a new angle- deposition process, which had previously produced high quality Nb-Au bilayer HEB devices at Yale. [1] We have characterized these devices using heterodyne mixing at ~30 GHz to compare to 345 GHz tests at the University of Arizona. We can also directly compare our Nb HEB mixers to SIS mixers in this same 345 GHz system. This allows us to rigorously calibrate the system’s losses and extract the mixer noise temperature in a well characterized mixer block, before undertaking the 850 GHz system. Here we give a report on the initial devices we have fabricated and characterized. * Department of Applied Physics, Yale University ** Department of Astronomy, University of Arizona [1] Applied Physics Letters 84, Number 8; p.1404-7, Feb 23 (2004) |
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Hajenius, M.; Baselmans, J. J. A.; Gao, J. R.; Klapwijk, T. M.; de Korte, P. A. J.; Voronov, B.; Gol'tsman, G. |
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Title |
Low noise NbN superconducting hot electron bolometer mixers at 1.9 and 2.5 THz |
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2004 |
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Supercond. Sci. Technol. |
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Supercond. Sci. Technol. |
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17 |
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5 |
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S224-S228 |
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NbN HEB mixers |
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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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0953-2048 |
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558 |
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Hajenius, M.; Baselmans, J. J. A.; Gao, J. R.; Klapwijk, T. M.; de Korte, P. A. J.; Voronov, B.; Gol’tsman, G. |
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Improved NbN phonon cooled hot electron bolometer mixers |
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Conference Article |
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2003 |
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Proc. 14th Int. Symp. Space Terahertz Technol. |
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Proc. 14th Int. Symp. Space Terahertz Technol. |
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413-423 |
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NbN HEB mixers |
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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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Tucson, USA |
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337 |
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Gao, J. R.; Hajenius, M.; Tichelaar, F. D.; Klapwijk, T. M.; Voronov, B.; Grishin, E.; Gol’tsman, G.; Zorman, C. A.; Mehregany, M. |
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Monocrystalline NbN nanofilms on a 3C-SiC∕Si substrate |
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2007 |
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Appl. Phys. Lett. |
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Appl. Phys. Lett. |
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91 |
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6 |
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062504 (1 to 3) |
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NbN films, nanofilms |
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The authors have realized NbN (100) nanofilms on a 3C-SiC (100)/Si(100) substrate by dc reactive magnetron sputtering at 800°C. High-resolution transmission electron microscopy (HRTEM) is used to characterize the films, showing a monocrystalline structure and confirming epitaxial growth on the 3C-SiC layer. A film ranging in thickness from 3.4to4.1nm shows a superconducting transition temperature of 11.8K, which is the highest reported for NbN films of comparable thickness. The NbN nano-films on 3C-SiC offer a promising alternative to improve terahertz detectors. For comparison, NbN nanofilms grown directly on Si substrates are also studied by HRTEM.
The authors acknowledge S. V. Svetchnikov at National Centre for HRTEM at Delft, who prepared the specimens for HRTEM inspections. This work was supported by the EU through RadioNet and INTAS. |
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0003-6951 |
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1425 |
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Gao, J.R.; Hiajenius, M.; Yang, Z.Q.; Klapwijk, T.M.; Miao, W.; Shi, S. C.; Voronov, B.; Gortsman, G. |
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Direct comparison of the sensitivity of a spiral and a twin-slot antenna coupled HEB mixer at 1.6 THz |
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2006 |
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Proc. 17th Int. Symp. Space Terahertz Technol. |
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Proc. 17th Int. Symp. Space Terahertz Technol. |
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59-62 |
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NbN HEB mixers |
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To make a direct comparison of the sensitivity between a spiral and a twin slot antenna coupled HEB mixer, we designed both types of mixers and fabricated them in a single processing run and on the same wafer. Both mixers have similar dimensions of NbN bridges (1.5-2 pm x0.2 pm). At 1.6 THz we obtained a nearly identical receiver noise temperature from both mixers (only 5% difference), which is in a good agreement with the simulation based on semi analytical models for both antennas. In addition, by using a bandpass filter to reduce the direct detection effect and lowering the bath temperature to 2.4 K, we measured the lowest receiver noise temperature of 700 K at 1.63 THz using the twin-slot antenna mixer. |
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1436 |
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Baselmans, J. J. A.; Hajenius, M.; Gao, J. R.; Baryshev, A.; Kooi, J.; Klapwijk, T. M.; Voronov, B.; de Korte, P.; Gol'tsman, G. |
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Title |
NbN hot electron bolometer mixers: sensitivity, LO power, direct detection and stability |
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2005 |
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IEEE Trans. Appl. Supercond. |
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IEEE Trans. Appl. Supercond. |
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15 |
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2 |
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484-489 |
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HEB mixers, direct detection effect, stability, Allan variance |
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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. Both the receiver noise temperature and the gain bandwidth can be improved by 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 of 950 K at 2.5 THz and 4.3 K, using a 0.4/spl times/4 /spl mu/m HEB mixer with a spiral antenna. At the same bias point, we obtain an IF gain bandwidth of 6 GHz. To comply with current demands on THz mixers for use in space based receivers we reduce the device size to 0.15/spl times/1 /spl mu/m and use a twin slot antenna. We report measurements of the noise temperature, LO power requirement, stability and the direct detection effect, using a mixer with a 1.6 THz twin slot antenna and a 1.462 THz solid state LO source with calibrated output power. |
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1051-8223 |
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546 |
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Baselmans, J. J. A.; Hajenius, M.; Gao, J. R.; Klapwijk, T. M.; de Korte, P. A. J.; Voronov, B.; Gol'tsman, G. |
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Doubling of sensitivity and bandwidth in phonon cooled hot electron bolometer mixers |
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2004 |
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Appl. Phys. Lett. |
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Appl. Phys. Lett. |
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84 |
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11 |
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1958-1960 |
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NbN HEB mixers |
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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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352 |
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Yang, Z. Q.; Hajenius, M.; Baselmans, J. J. A.; Gao, J.R.; Klapwijk, T. M.; Voronov, B.; Gol’tsman, G. |
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Improved sensitivity of NbN hot electron bolometer mixers by vacuum baking |
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Conference Article |
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2005 |
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Proc. 16th Int. Symp. Space Terahertz Technol. |
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Proc. 16th Int. Symp. Space Terahertz Technol. |
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222-225 |
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NbN HEB mixer |
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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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1471 |
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Yang, Z. Q.; Hajenius, M.; Baselmans, J. J. A.; Gao, J. R.; Voronov, B.; Gol’tsman, G. N. |
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Reduced noise in NbN hot-electron bolometer mixers by annealing |
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2006 |
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Supercond. Sci. Technol. |
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Supercond. Sci. Technol. |
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19 |
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4 |
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L (9 to 12) |
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NbN HEB mixers |
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We find that the sensitivity of heterodyne receivers based on superconducting hot-electron bolometers (HEBs) increases by 25–30% after annealing at 85 °C in vacuum. The devices studied are twin-slot antenna coupled mixers with a small NbN bridge of 1 × 0.15 µm2. We show that annealing changes the device properties as reflected in sharper resistive transitions of the complete device, apparently reducing the device-related noise. 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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0953-2048 |
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Zhang, W.; Khosropanah, P.; Gao, J. R.; Kollberg, E. L.; Yngvesson, K. S.; Bansal, T.; Barends, R.; Klapwijk, T. M. |
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Quantum noise in a terahertz hot electron bolometer mixer |
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2010 |
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Applied Physics Letters |
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Appl. Phys. Lett. |
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96 |
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11 |
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111113-(1-3) |
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HEB mixer, quantum limit, quantum noise, vacuum box, THz, Terahertz |
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We have measured the noise temperature of a single, sensitive superconducting NbN hot electron bolometer (HEB) mixer in a frequency range from 1.6 to 5.3 THz, using a setup with all the key components in vacuum. By analyzing the measured receiver noise temperature using a quantum noise (QN) model for HEB mixers, we confirm the effect of QN. The QN is found to be responsible for about half of the receiver noise at the highest frequency in our measurements. The beta-factor (the quantum efficiency of the HEB) obtained experimentally agrees reasonably well with the calculated value. |
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