NbN multilayer technology on R-plane sapphire

Villegirr, J.-C.; Hadacek, N.; Monso, S.; Delnet, B.; Roussy, Agnès; Febvre, Pascal; Lamura, G.; Laval, J. Y.

doi:10.1109/77.919286

Cited by 42 publications

(24 citation statements)

References 12 publications

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“…For films with an intended thickness of 3.5 nm ͑not directly measured͒, the highest superconducting transition temperatures ͑T c ͒ are reported to be 9.5-11 K. 9 Among them, NbN films on MgO, MgO buffer layers and sapphire substrates have higher T c than NbN films on Si substrates. These substrates allow for epitaxial growth of the NbN films, [8][9][10] resulting in a monocrystalline structure. For HEB mixers, Si is a preferred substrate because of its low loss at terahertz frequencies, well-established processing technology, and inherent reliability.…”

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confidence: 99%

Monocrystalline NbN nanofilms on a 3C-SiC∕Si substrate

Gao

Hajenius

Tichelaar

et al. 2007

Applied Physics Letters

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The authors have realized NbN ͑100͒ nanofilms on a 3C-SiC ͑100͒/Si͑100͒ substrate by dc reactive magnetron sputtering at 800°C. High-resolution transmission electron microscopy ͑HRTEM͒ 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 3.4 to 4.1 nm shows a superconducting transition temperature of 11.8 K, 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. © 2007 American Institute of Physics. ͓DOI: 10.1063/1.2766963͔The ability to grow superconducting NbN films of several nanometer thick is of significant importance to the development of modern photon detector technology. Superconducting hot electron bolometer ͑HEB͒ mixers based on such nanofilms are the only sensitive heterodyne detectors for high-resolution spectroscopy at frequencies between 1.5 and 6 THz.1-4 These detectors will be used on the Herschel space telescope 5 and are required in various future conceptual space missions. 6 Another type of detector, the superconducting single photon detector ͑SSPD͒, 7 is based on similar films and is ultrafast and sensitive for the detection of both visible and infrared photons. SSPDs can perform high speed photon counting which has many applications, for example, optical communications and quantum information.To date, HEB mixers are based on ultrathin NbN films grown primarily on substrates such as Si with its native oxide, 2-4 MgO, 8 and Si with a buffering MgO film. 9 SSPDs are based on NbN films grown on sapphire substrates. For films with an intended thickness of 3.5 nm ͑not directly measured͒, the highest superconducting transition temperatures ͑T c ͒ are reported to be 9.5-11 K.9 Among them, NbN films on MgO, MgO buffer layers and sapphire substrates have higher T c than NbN films on Si substrates. These substrates allow for epitaxial growth of the NbN films, 8-10 resulting in a monocrystalline structure. For HEB mixers, Si is a preferred substrate because of its low loss at terahertz frequencies, well-established processing technology, and inherent reliability. However, the drawback to using Si in this case is the limited intermediate frequency bandwidth, which is set by the thermal time constant.In this letter, we demonstrate superconducting NbN nanofilms on a 3C-SiC buffered Si substrate. The films were characterized by high-resolution transmission electron microscopy ͑HRTEM͒. In addition, the superconducting properties were measured.The 3C-SiC buffer layers were heteroepitaxially grown on Si ͑100͒ substrates by atmospheric pressure chemical vapor deposition at 1280°C using a process described in detail elsewhere.11 To ensure reasonably good crystal quality near the top surface of the 3C-SiC layer given its lattice mismatch with Si, we choose a thickness of 1 m for 3C-SiC layer. As reported previously, 11 t...

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confidence: 99%

Monocrystalline NbN nanofilms on a 3C-SiC∕Si substrate

Gao

Hajenius

Tichelaar

et al. 2007

Applied Physics Letters

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“…We find that the resistivity ratio, which is smaller than 1, decreases almost linearly from 0.98 to 0.89 as N 2 flow rate is increased from 1.4 sccm to 2.9 sccm. This kind of temperature dependence is commonly observed in polycrystalline NbN films [1][2][3][4][5][6][7][8][9] and often interpreted as grain-boundary scattering effect [3,4]. T c and normal state resistivity for all the NbN thin films studied in this work are summarized in Fig.…”

Section: Resultsmentioning

confidence: 90%

“…To obtain high T c of around 16 K, NbN films were often deposited at elevated temperatures of around 300°C [7][8]. However, in the case of multilayers such as spin-switch devices, multilayers grown at elevated temperatures can be vulnerable to alloying of two different materials at interfaces.…”

Section: Introductionmentioning

confidence: 99%

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Transition temperatures and upper critical fields of NbN thin films fabricated at room temperature

Hwang¹,

Kim²

2015

Progress in Superconductivity and Cryogenics

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NbN thin films were deposited on thermally oxidized Si substrate at room temperature by using reactive magnetron sputtering in an Ar-N 2 gas mixture. Total sputtering gas pressure was fixed while varying N 2 flow rate from 1.4 sccm to 2.9 sccm. X-ray diffraction pattern analysis revealed dominant NbN(200) orientation in the low N 2 flow rate but emerging of (111) orientation with diminishing (200) orientation at higher flow rate. The dependences of the superconducting properties on the N 2 gas flow rate were investigated. All the NbN thin films showed a small negative temperature coefficient of resistance with resistivity ratio between 300 K and 20 K in the range from 0.98 to 0.89 as the N 2 flow rate is increased. Transition temperature showed non-monotonic dependence on N 2 flow rate reaching as high as 11.12 K determined by the mid-point temperature of the transition with transition width of 0.3 K. On the other hand, the upper critical field showed roughly linear increase with N 2 flow rate up to 2.7 sccm. The highest upper critical field extrapolated to 0 K was 17.4 T with corresponding coherence length of 4.3 nm. Our results are discussed with the granular nature of NbN thin films.

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“…NbN films were grown at CEA-DRFMC by DC magnetron sputtering of a Nb target in a Ar/N 2 plasma [10]. Very thin films were deposited at 600 °C substrate temperature and passivated by an AlN layer in-situ deposited at room temperature [11].…”

Section: Methodsmentioning

confidence: 99%