Superconducting Properties of Single-crystal NbN Thin Films Deposited at Ambient Substrate Temperature

Wang, Zhen; Kawakami, Akira; Uzawa, Yoshinori; Komiyama, Bokuji

doi:10.1007/978-4-431-68535-7_225

Cited by 4 publications

(5 citation statements)

References 13 publications

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“…We have measured several films for both types which showed the same behavior. It should be noted that an epitaxial NbN film (without Ti) on an MgO substrate shows even larger ratios of about 4.2 [17]. Thus, it is concluded that the content of Ti in the NbTiN films may lower the superconducting gap energy of the film and the resistivity simultaneously.…”

Section: B Conductivity Of Nbtin Films At DC and Rfmentioning

confidence: 90%

Tuning Circuit Material for Mass-Produced Terahertz SIS Receivers

Uzawa

Fujii

González

et al. 2015

IEEE Trans. Appl. Supercond.

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A total of 73 dual polarization superconductorinsulator-superconductor (SIS) receivers for the Atacama Large Millimeter/submillimeter Array (ALMA) have been successfully produced to observe astronomical signals in the frequency band of 787-950 GHz. For the mass production of waveguide SIS mixer chips used in the receivers, we have tested two different compositions of Nb 1−x Ti x N thin films for use in the mixer's superconductor low-loss transmission lines. These components are being fabricated for mass-produced waveguide SIS mixer chips in receivers. One composition was prepared by employing a sputtering target with 20 wt.% Ti and 80 wt.% Nb (x = 0.2), and the other was prepared with a target composed of 30 wt.% Ti and 70 wt.% Nb (x = 0.3). Both films are deposited using dc magnetron sputtering on quartz substrates. We found that the ratio between the superconducting energy gap and the critical temperature (2Δ/k B T C ) of the Nb 0.8 Ti 0.2 N films is larger than that of the Nb 0.7 Ti 0.3 N films. Since we obtained better sensitivities in the SIS mixers using the Nb 0.8 Ti 0.2 N films, they were used to produce all the receivers. These showed excellent performance complying with the stringent ALMA specifications.

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Section: B Conductivity Of Nbtin Films At DC and Rfmentioning

confidence: 90%

Tuning Circuit Material for Mass-Produced Terahertz SIS Receivers

Uzawa

Fujii

González

et al. 2015

IEEE Trans. Appl. Supercond.

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“…The barrier height φ is estimated to be about 0.3 eV from the slope of the thickness dependence of critical current I c shown in figure 5. This value is smaller than that of MgO [11] or AlN [12].…”

Section: Underdamped Nbn/a-nbn X /Nbn Junctionsmentioning

confidence: 58%

Fabrication of all-NbN Josephson junctions using semiconductive amorphous barriers

Yamamori¹,

Yoshizawa²,

Fujimaki³

et al. 1996

Supercond. Sci. Technol.

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Both underdamped junctions and overdamped junctions utilizing semiconductive amorphous a-NbN x barriers have been fabricated by controlling the partial pressure of N 2 when the a-NbN x barrier is sputtered. While a NbN film is generally used as a superconductive electrode, we have used NbN films for both electrodes and barriers to fabricate overdamped junctions. The NbN x films for the barrier are an amorphous semiconductor and have high density of localized states. Typical overdamped junctions have J c of more than 50 kA cm −2 and I c R N products of 0.5 mV. On the other hand, typical underdamped junctions have critical current density of 0.5 kA cm −2 to 20 kA cm −2 and I c R N products of about 1.5 mV. The barrier height of the a-NbN x barrier is estimated to be about 0.3 eV from the slope of the barrier thickness dependence of critical current I c . Then, stacked double barrier junctions have been also fabricated.

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“…To understand the difference in the noise temperature between the two films, we investigated the complex conductivity,  1 ()-i 2 (), in the superconducting state of a 40-nm thick Nb 1-x Ti x N film with x = 0.2 (T C of 12 K) and a 45-nm thick film with x = 0.3 (T C of 13 K) by using a transmission-type terahertz time-domain spectroscopy system [41], which revealed that the derived 2/k B T C (the ratio between the superconducting gap energy and critical temperature) of the Nb 0.7 Ti 0.3 N and Nb 0.8 Ti 0.2 N films was approximately 3.6 and 4.0, respectively. It should be noted that an epitaxial NbN film (without Ti) on an MgO substrate shows an even larger ratio of approximately 4.2 [44]. Since our Nb 1-x Ti x N films with x = 0.2 and 0.3 show almost same T C for thick films, it can be concluded that the Ti content in the NbTiN films may reduce the superconducting gap energy of the film and the resistivity simultaneously.…”

Section: Mixer Performancementioning

confidence: 66%

Development of Superconducting Devices Supporting Radio Astronomy

Uzawa¹,

Kroug

Kojima³

et al. 2021

IEICE Trans. Electron.

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This paper describes the development of superconductorinsulator-superconductor (SIS) mixers for the Atacama Large Millimeter/submillimeter Array (ALMA) from the device point of view. During the construction phase of ALMA, the National Astronomical Observatory of Japan (NAOJ) successfully fabricated SIS mixers to meet the stringent ALMA noise temperature requirements of less than 230 K (5 times the quantum noise) for Band 10 (787-950 GHz) in collaboration with the National Institute of Information and Communications Technology. Band 10 covers the highest frequency band of ALMA and is recognized as the most difficult band in terms of superconducting technology. After the construction, the NAOJ began development studies for ALMA enhancement such as wideband and multibeam SIS mixers according to top-level science requirements, which are also presented.

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Superconducting Properties of Single-crystal NbN Thin Films Deposited at Ambient Substrate Temperature

Cited by 4 publications

References 13 publications

Tuning Circuit Material for Mass-Produced Terahertz SIS Receivers

Tuning Circuit Material for Mass-Produced Terahertz SIS Receivers

Fabrication of all-NbN Josephson junctions using semiconductive amorphous barriers

Development of Superconducting Devices Supporting Radio Astronomy

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