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Zhang, W.; Miao, W.; Yao, Q. J.; Lin, Z. H.; Shi, S. C.; Gao, J. R.; Goltsman, G. N. |
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Title |
Spectral response and noise temperature of a 2.5 THz spiral antenna coupled NbN HEB mixer |
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2012 |
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Phys. Procedia |
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Phys. Procedia |
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36 |
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334-337 |
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NbN HEB mixer |
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We report on a 2.5 THz spiral antenna coupled NbN hot electron bolometer (HEB) mixers, fabricated with in-situ process. The receiver noise temperature with lowest value of 1180 K is in good agreement with calculated quantum efficiency factor as a function of bias voltage. In addition, the measured spectral response of the spiral antenna coupled NbN HEB mixer shows broad frequency coverage of 0.8-3 THz, and corrected response for optical losses, FTS, and coupling efficiency between antenna and bolometer falls with frequency due to diffraction-limited beam of lens/antenna combination. |
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1875-3892 |
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1381 |
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Gao, J. R.; Hajenius, M.; Baselmans, J. J. A.; Klapwijk, T. M.; de Korte, P. A. J.; Voronov, B.; Gol'tsman, G. |
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NbN hot electron bolometer mixers with superior performance for space applications |
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Conference Article |
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2004 |
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Proc. Int. workshop on low temp. electronics |
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Proc. Int. workshop on low temp. electronics |
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11-17 |
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NbN HEB mixers, applications |
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Noordwijk |
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Armandillo, E.; Leone, B. |
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International workshop on low temperature electronics- WOLTE 6 - Noordwijk |
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1496 |
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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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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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Noise performance of NbN hot electron bolometer mixers at 2.5 THz and its dependence on the contact resistance |
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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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11-19 |
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NbN HEB mixers |
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NbN hot electron bolometer mixers (HEBM) are at this moment the best heterodyne receivers 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. The result is a low transparency interface between the bolometer itself and the contact/antenna structure. In this paper we report a detailed experimental study on a novel idea to increase the transparency of this interface. This leads to a record sensitivity and more reproducible performance. We compare identical bolometers, coupled with a spiral antenna, with different NbN bolometer-contact pad interfaces. We find that cleaning the NbN interface alone results in an increase in the noise temperature. However, cleaning the NbN interface and adding a thin additional superconductor prior to the gold contact deposition improves the noise temperature of the HEBm with more than a factor of 2. A device with a contact pad on top of an in-situ cleaned NbN film consisting of 10 nm of NbTiN and 40 nm of gold has a DSB noise temperature of 1050 K at 2.5 THz. |
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1497 |
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Baselmans, J. J. A.; Hajenius, M.; Gao, J. R.; Baryshev, A.; Kooi, J.; Klapwijk, T. M.; de Korte, P. A. J.; Voronov, B.; Gol’tsman, G. |
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Hot electron bolometer mixers with improved interfaces: sensitivity, LO power and stability |
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Conference Article |
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2004 |
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Proc. 15th Int. Symp. Space Terahertz Technol. |
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Proc. 15th Int. Symp. Space Terahertz Technol. |
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17-24 |
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NbN HEB mixers |
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We study twin slot antenna coupled NbN hot electron bolometer mixers with an improved contact structure and a small volume, ranging from 1 µm × 0.1 µm to 2 × 0.3 µm. We obtain a DSB receiver noise temperature of 900 K at 1.6 THz and 940 K at 1.9 THz. To explore the practical usability of such small HEB mixers we evaluate the LO power requirement, the sensitivity and the stability. We find that the LO power requirement of the smallest mixers is reduced to about 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. The stability of these receivers is characterized using a measurement of the Allan Variance. We find an Allan time of 0.5 sec. in an 80 MHz bandwidth. A small increase in stability can be reached by using a higher bias at the expense of a significant amount of sensitivity. The stability is sufficient for spectroscopic applications in a 1 MHz bandwidth at a 1 Hz chopping frequency. |
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1491 |
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Hajenius, M.; Baselmans, J. J. A.; Gao, J. R.; Klapwijk, T. M.; de Korte 2, P. A. J.; Voronov, B.; Gol’tsman, G. |
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Increased bandwidth of NbN phonon cooled hot electron bolometer mixers |
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Conference Article |
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2004 |
Publication |
Proc. 15th Int. Symp. Space Terahertz Technol. |
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Proc. 15th Int. Symp. Space Terahertz Technol. |
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381-386 |
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NbN HEB mixers, IF bandwidth |
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We study experimentally the IF gain bandwidth of NbN phonon-cooled hot-electron-bolometer (HEB) mixers for a set of devices with different contact structures but an identical NbN film. We observe that the IF bandwidth depends strongly on the exact contact structure and find an IF gain bandwidth of 6 GHz for a device with an additional superconducting layer (NbTiN) in between the active NbN film and the gold contact to the antenna. These results contradict the common opinion that the IF bandwidth is determined by the phonon-escape time between the NbN film and the substrate. Hence we calculate the IF gain bandwidth of a superconducting film using a two-temperature model. We find that the bandwidth increases strongly with operating temperature and is not limited by the phonon escape time. This is because of strong temperature dependence of the phonon specific heat in the NbN film. |
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1494 |
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Baselmans, J.; Kooi, J.; Baryshev, A.; Yang, Z. Q.; Hajenius, M.; Gao, J. R.; Klapwijk, T. M.; Voronov, B.; Gol’tsman, G. |
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Full characterization of small volume NbN HEB mixers for space applications |
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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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457-462 |
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NbN HEB mixers |
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NbN phonon cooled HEB’s are one of the most promising bolometer mixer technologies for (near) future (space) applications. Their performance is usually quantified by mea- suring the receiver noise temperature at a given IF frequency, usually around 1 – 2 GHz. However, for any real applications it is vital that one fully knows all the relevant properties of the mixer, including LO power, stability, direct detection, gain bandwidth and noise bandwidth, not only the noise temperature at low IF frequencies. To this aim we have measured all these parameters at the optimal operating point of one single, small volume quasioptical NbN HEB mixer. We find a minimum noise temperature of 900 K at 1.46 THz. We observe a direct detection effect indicated by a change in bias current when changing from a 300 K hot load to a 77 K cold load. Due to this effect we overestimate the noise temperature by about 22% using a 300 K hot load and a 77 K cold load. The LO power needed to reach the optimal operating point is 80 nW at the receiver lens front, 59 nW inside the NbN bridge. However, using the isothermal technique we find a power absorbed in the NbN bridge of 25 nW, a difference of about a factor 2. We obtain a gain bandwidth of 2.3 GHz and a noise bandwidth of 4 GHz. The system Allan time is about 1 sec. in a 50 MHz spectral bandwidth and a deviation from white noise integration (governed by the radiometer equation) occurs at 0.2 sec., which implies a maximum integration time of a few seconds in a 1 MHz bandwidth spectrometer. |
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Göteborg, Sweden |
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363 |
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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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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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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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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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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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