| Records |
| Author |
Ryabchun, Sergey; Tong, Cheuk-yu Edward; Blundell, Raymond; Kimberk, Robert; Gol’tsman, Gregory |
Title  |
Stabilisation of a terahertz hot-electron bolometer mixer with microwave feedback control |
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Conference Article |
| Year |
2007 |
Publication |
Proc. 18th Int. Symp. Space Terahertz Technol. |
Abbreviated Journal |
Proc. 18th Int. Symp. Space Terahertz Technol. |
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Pages |
193-198 |
| Keywords |
waveguide NbN HEB mixers, Allan variance, stability |
| Abstract |
We report on implementation of microwave feedback control loop to stabilise the performance of an HEB mixer receiver. It is shown that the receiver sensitivity increases by a factor of 4 over a 16-minute scan, and the corresponding Allan time increases up to 10 seconds, as opposed to an open loop value of 1 second. Our experiments also demonstrate that the receiver sensitivity is limited by the intermediate frequency chain. |
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1421 |
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Kooi, J. W.; Baselmans, J. J. A.; Baryshev, A.; Schieder, R.; Hajenius, M.; Gao, J.R.; Klapwijk, T. M.; Voronov, B.; Gol’tsman, G. |
| Title |
Stability of heterodyne terahertz receivers |
Type |
Journal Article |
| Year |
2006 |
Publication |
J. Appl. Phys. |
Abbreviated Journal |
J. Appl. Phys. |
| Volume |
100 |
Issue |
6 |
Pages |
064904 (1 to 9) |
| Keywords |
NbN HEB mixers |
| Abstract |
In this paper we discuss the stability of heterodyne terahertz receivers based on small volume NbN phonon cooled hot electron bolometers (HEBs). The stability of these receivers can be broken down in two parts: the intrinsic stability of the HEB mixer and the stability of the local oscillator (LO) signal injection scheme. Measurements show that the HEB mixer stability is limited by gain fluctuations with a 1∕f spectral distribution. In a 60MHz noise bandwidth this results in an Allan variance stability time of ∼0.3s. Measurement of the spectroscopic Allan variance between two intermediate frequency (IF) channels results in a much longer Allan variance stability time, i.e., 3s between a 2.5 and a 4.7GHz channel, and even longer for more closely spaced channels. This implies that the HEB mixer 1∕f noise is strongly correlated across the IF band and that the correlation gets stronger the closer the IF channels are spaced. In the second part of the paper we discuss atmospheric and mechanical system stability requirements on the LO-mixer cavity path length. We calculate the mixer output noise fluctuations as a result of small perturbations of the LO-mixer standing wave, and find very stringent mechanical and atmospheric tolerance requirements for receivers operating at terahertz frequencies. |
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0021-8979 |
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1444 |
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Beebe, M. R.; Beringer, D. B.; Burton, M. C.; Yang, K.; Lukaszew, R. A. |
| Title |
Stoichiometry and thickness dependence of superconducting properties of niobium nitride thin films |
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Journal Article |
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2016 |
Publication |
Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films |
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Journal of Vacuum Science & Technology A: Vacuum, Surfaces, and Films |
| Volume |
34 |
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2 |
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021510 (1 to 4) |
| Keywords |
potential plagiarism, possible plagiarism, NbN films |
| Abstract |
The current technology used in linear particle accelerators is based on superconducting radio frequency (SRF) cavities fabricated from bulk niobium (Nb), which have smaller surface resistance and therefore dissipate less energy than traditional nonsuperconducting copper cavities. Using bulk Nb for the cavities has several advantages, which are discussed elsewhere; however, such SRF cavities have a material-dependent accelerating gradient limit. In order to overcome this fundamental limit, a multilayered coating has been proposed using layers of insulating and superconducting material applied to the interior surface of the cavity. The key to this multilayered model is to use superconducting thin films to exploit the potential field enhancement when these films are thinner than their London penetration depth. Such field enhancement has been demonstrated in MgB2 thin films; here, the authors consider films of another type-II superconductor, niobium nitride (NbN). The authors present their work correlating stoichiometry and superconducting properties in NbN thin films and discuss the thickness dependence of their superconducting properties, which is important for their potential use in the proposed multilayer structure. While there are some previous studies on the relationship between stoichiometry and critical temperature TC, the authors are the first to report on the correlation between stoichiometry and the lower critical field HC1. |
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0734-2101 |
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Potential plagiarism for 1503 |
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1504 |
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Krause, S.; Mityashkin, V.; Antipov, S.; Gol'tsman, G.; Meledin, D.; Desmaris, V.; Belitsky, V.; Rudzinski, M. |
| Title |
Study of IF bandwidth of NbN hot electron bolometers on GaN buffer layer using a direct measurement method |
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Conference Article |
| Year |
2016 |
Publication |
Proc. 27th Int. Symp. Space Terahertz Technol. |
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30-32 |
| Keywords |
NbN HEB, GaN buffer layer |
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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 (4.5nm) with high quality polycrystalline NbN films on Si substrate with Tc of 10.5K (5nm) 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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1202 |
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| Author |
Ryabchun, S.; Tong, C.-Y. E.; Blundell, R.; Kimberk, R.; Gol'tsman, G. |
| Title |
Study of the effect of microwave radiation on the operation of HEB mixers in the terahertz frequency range |
Type |
Journal Article |
| Year |
2007 |
Publication |
IEEE Trans. Appl. Supercond. |
Abbreviated Journal |
IEEE Trans. Appl. Supercond. |
| Volume |
17 |
Issue |
2 |
Pages |
391-394 |
| Keywords |
NbN HEB mixers |
| Abstract |
We have investigated the effect of injecting microwave radiation, with a frequency much lower than that corresponding to the energy gap of the superconductor, on the performance of the hot-electron bolometer mixer incorporated into a THz heterodyne receiver. More specifically, we show that exposing the mixer to microwave radiation does not cause a significant rise of the receiver noise temperature and fall of the mixer conversion gain so long as the microwave power is a small fraction of local oscillator power. The injection of a small, but controlled amount of microwave power therefore enables active compensation of local oscillator power and coupling fluctuations which can significantly degrade the gain stability of hot electron bolometer mixer receivers. |
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1051-8223 |
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1427 |
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