| 1. |
- Antipov, Sergey, et al.
(författare)
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Gain bandwidth of NbN HEB mixers on GaN buffer layer operating at 2 THz local oscillator frequency
- 2017
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Ingår i: 28th International Symposium on Space Terahertz Technology, March 13-15, 2017.
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Konferensbidrag (refereegranskat)abstract
- In this paper, we present IF bandwidth measurement results of NbN HEB mixers, which are employing NbN thin films grown on a GaN buffer-layer. The HEB mixers were operated in the heterodyne regime at a bath temperature of approximately 4.5 K and with a local oscillator operating at a frequency of 2 THz. A quantum cascade laser served as the local oscillator and a reference synthesizer based on a BWO generator (130-160 GHz) and a semiconductor superlattice (SSL) frequency multiplier was used as a signal source. By changing the LO frequency it was possible to record the IF response or gain bandwidth of the HEB with a spectrum analyzer at the operation point, which yielded lowest noise temperature. The gain bandwidth that was recorded in the heterodyne regime at 2 THz amounts to approximately 5 GHz and coincides well with a measurement that has been performed at elevated bath temperatures and lower LO frequency of 140 GHz. These findings strongly support that by using a GaN buffer-layer the phonon escape time of NbN HEBs can be significantly lower as compared to e.g. Si substrate, thus, providing higher gain bandwidth.
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| 2. |
- Baubert, Jean, 1976, et al.
(författare)
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IF Gain Bandwidth of membrane-based NbN Hot Electron Bolometers for SHAHIRA
- 2005
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Ingår i: IEEE Applied Superconductivity. ; 15:2, s. 505-510
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Tidskriftsartikel (refereegranskat)abstract
- SHAHIRA (Submm Heterodyne Array for HIghspeedRadio Astronomy) is a project supported by the EuropeanSpace Agency (ESA) and is designed to fly on the SOFIA observatory.A quasi-optic design has been chosen for 2.5/2.7 THz and4.7 THz, for hydroxyde radical OH, deuterated hydrogen HD andneutral atomic oxygen OI lines observations. Hot electron bolometers(HEBs) have been processed on 1 um thick SiO2 Si3N4stress-less membranes. In this paper we analyse the intermediatefrequency (IF) gain bandwidth from the theoretical point of view,and compare it to measurements.
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| 3. |
- Cherednichenko, Serguei, 1970, et al.
(författare)
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2.5THz multipixel heterodyne receiver based on NbN HEB mixers
- 2006
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Ingår i: Proc.SPIE. - 081946340X ; 6275, s. 62750I-1
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Tidskriftsartikel (refereegranskat)abstract
- A 16 pixel heterodyne receiver for 2.5 THz has been developed based on NbN superconducting hot-electron bolometer (HEB) mixers. The receiver uses a quasioptical RF coupling approach where HEB mixers are integrated into double dipole antennas on 1.5m thick Si3N4/ SiO2 membranes. Spherical mirrors (one per pixel) and backshort distance from the antenna have been used to design the output mixer beam profile. The camera design allows all 16 pixel IF readout in parallel. The gain bandwidth of the HEB mixers on Si3N4/ SiO2 membranes was found to be 0.70.9 GHz, which is much smaller than for similar devices on silicon. Application of buffer layers and use of alternative types of membranes (e.g. silicon-on-insulator) is under investigation.
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| 4. |
- Cherednichenko, Serguei, 1970, et al.
(författare)
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Gain bandwidth of NbN hot-electron bolometer terahertz mixers on 1.5 um Si3N4 /SiO2 membranes
- 2007
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Ingår i: Journal of Applied Physics. ; 101:12, s. 124508-1-(6)-
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Tidskriftsartikel (refereegranskat)abstract
- The gain bandwidth of NbN hot-electron bolometer terahertz mixers on electrically thin Si3N4 /SiO2 membranes was experimentally investigated and compared with that of HEB mixers on bulk substrates. A gain bandwidth of 3.5 GHz is achieved on bulk silicon, whereas the gain bandwidth is reduced down to 0.6–0.9 GHz for mixers on 1.5 um Si3 N4 /SiO2 membranes. We show that application of a MgO buffer layer on the membrane extends the gain bandwidth to 3 GHz. The experimental data were analyzed using the film-substrate acoustic mismatch approach.
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| 5. |
- Krause, Sascha, 1989, et al.
(författare)
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Reduction of Phonon Escape Time for NbN Hot Electron Bolometers by Using GaN Buffer Layers
- 2017
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Ingår i: IEEE Transactions on Terahertz Science and Technology. - 2156-342X .- 2156-3446. ; 7:1, s. 53-59
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we investigated the influence of the GaN buffer-layer on the phonon escape time of phonon-cooled hot electron bolometers based on NbN material and compared our findings to conventionally employed Si substrate. The presented experimental setup and operation of the HEB close to the critical temperature of the NbN film allowed for the extraction of phonon escape time in a simplified manner. Two independent experiments were performed at GARD/Chalmers and MSPU on a similar experimental setup at frequencies of approximately 180 and 140 GHz, respectively, and have shown reproducible and consistent results. By fitting the normalized IF measurement data to the heat balance equations, the escape time as fitting parameter has been deduced and amounts to 45 ps for the HEB based on Si substrate as in contrast to a significantly reduced escape time of 18 ps for the HEB utilizing the GaN buffer-layer under the assumption that no additional electron diffusion has taken place. This study indicates a high phonon transmissivity of the NbN-to-GaN interface and a prospective increase of IF bandwidth for HEB made of NbN on GaN buffer layers, which is desirable for future THz HEB heterodyne receivers.
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| 6. |
- Krause, Sascha, 1989, et al.
(författare)
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Study of IF bandwidth of NbN hot electron bolometers on GaN buffer layer using a direct measurement method
- 2016
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Ingår i: 27th International Symposium on Space Terahertz Technology, ISSTT 2016, Nanjing, China. ; , s. 3-
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Konferensbidrag (refereegranskat)abstract
- In this paper, we present a reliable measurement method to study the influence of the GaN buffer layer on phonon-escape time in comparison with commonly used Si substrates and, in consequence, on the IF bandwidth of HEBs. One of the key aspects is to operate the HEB mixer at elevated bath temperatures close to the critical temperature of the NbN ultra-thin film, where contributions from electron-phonon processes and self-heating effects are relatively small, therefore IF roll-off will be governed by the phonon-escape.Two independent experiments were performed at GARD and MSPU on a similar experimental setup at frequencies of approximately 180 and 140 GHz, respectively, and have shown reproducible and consistent results. The entire IF chain was characterized by S-parameter measurements. We compared the measurement results of epitaxial NbN grown onto GaN buffer-layer with Tc of 12.5 K (4.5 nm) with high quality polycrystalline NbN films on Si substrate with Tc of 10.5 K (5 nm) and observed a strong indication of an enhancement of phonon escape to the substrate by a factor of two for the NbN/GaN material combination.
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| 7. |
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| 8. |
- Wild, W., et al.
(författare)
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Millimetron—a large Russian-European submillimeter space observatory
- 2009
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Ingår i: Experimental Astronomy. - : Springer Science and Business Media LLC. - 0922-6435 .- 1572-9508. ; 23:1, s. 221-244
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Tidskriftsartikel (refereegranskat)abstract
- Millimetron is a Russian-led 12 m diameter submillimeter and far-infrared space observatory which is included in the Space Plan of the Russian Federation for launch around 2017. With its large collecting area and state-of-the-art receivers, it will enable unique science and allow at least one order of magnitude improvement with respect to the Herschel Space Observatory. Millimetron will be operated in two basic observing modes: as a single-dish observatory, and as an element of a ground-space very long baseline interferometry (VLBI) system. As single-dish, angular resolutions on the order of 3 to 12 arc sec will be achieved and spectral resolutions of up to a million employing heterodyne techniques. As VLBI antenna, the chosen elliptical orbit will provide extremely large VLBI baselines (beyond 300,000 km) resulting in micro-arc second angular resolution.
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| 9. |
- Zichi, Julien, 1990-
(författare)
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NbTiN for improved superconducting detectors
- 2019
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The physics of single photons is fascinating, by manipulating them we can observe and probe quantum effects. Doing so requires the fabrication and utilization of single photon sources, of which many types have been developed including quantum dots, trapped atoms and ions, and color centers. On the other end of the experiments, single photon detectors play a role of utmost importance, and while several types of detectors exist, superconducting nanowire single photon detectors are now the state-of-the-art technology. By offering near unity detection efficiency from the ultra-violet to the mid-infrared light spectrum, with negligible noise and excellent time resolution, they made possible many experiments that were previously technologically unfeasible. The same appealing characteristics have found a use in applications outside of the quantum optics framework, with notably light detection and ranging, biomedical imaging or CMOS circuits testing.In this thesis a controlled growth method for tailoring the characteristics of niobium titanium nitride in the framework of superconducting nanowire single photon detectors was developed. Reactive co-sputter deposition of niobium titanium nitride was shown to be a versatile method, both in terms of the degree of control over the material composition, and in the choice of substrates that it allows. Unity internal detection efficiency of detectors at telecom wavelengths was achieved by optimizing the niobium content in the material. The influence of lattice matching on the critical temperatures of films deposited at room temperature was investigated. The fabrication of superconducting nanowire single photon detectors on aluminum nitride-on-sapphire, on lithium niobate nano-waveguides, on gallium arsenide, and the integration on SiN waveguides was achieved. The material was used to fabricate detectors with optimized response for any linear polarization of the incoming photons by using a fractal architecture. Another method was proposed to achieve the same results by encapsulating meandering detectors in a high index dielectric material, resulting in a decrease of the permittivity mismatch between the nanowire material and its surrounding and therefore optimizing the efficiency for both orthogonal linear polarizations.Finally, detectors were fabricated from films developed in this work, and were operated to enable the implementation of polarization-based entanglement distribution in optical fibers in a real-conditions scenario, over a record distance of 96 km. This paves the way for the development of quantum communication networks using existing optical fiber links.
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