High quality Nb/Al-AlOx/Nb Josephson junction

Morohashi, Shinichi; Shinoki, Fujitoshi; Shoji, Akira; Aoyagi, Masahiro; Hayakawa, Hisao

doi:10.1063/1.95696

Cited by 107 publications

(20 citation statements)

References 9 publications

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“…Specifically, the influence of temperature [25] and oxygen pressure during static oxidation [26][27][28] and both combined [29][30][31] were studied. Variations of the critical current are usually attributed to the variation of the AlOx-layer thickness [32,33].…”

Section: Introductionmentioning

confidence: 99%

Structural and nanochemical properties ofAlOxlayers inAl/AlOx/Al-layer systems

Fritz

Radtke

Schneider

et al. 2019

Phys. Rev. Materials

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The structural and nanochemical properties of thin AlOx layers are decisive for the performance of advanced electronic devices. For example, they are frequently used as tunnel barriers in Josephson junction-based superconducting devices. However, systematic studies of the influence of oxidation parameters on structural and nanochemical properties are rare up to now, as most studies focus on the electrical properties of AlOx layers. This study aims to close this gap by applying transmission electron microscopy in combination with electron energy loss spectroscopy to analyze the structural and nanochemical properties of differently fabricated AlOx layers and correlate them with fabrication parameters. With respect to the application of AlOx as tunnel barrier in superconducting Josephson junctions, Al/AlOx/Al-layer systems were deposited on Si substrates. We will show that the oxygen content and structure of amorphous AlOx layers is strongly dependent on the fabrication process and oxidation parameters.Dynamic and static oxidation of Al yields oxygen-deficient amorphous AlOx layers, where the oxygen content ranges from x = 0.5 to x = 1.3 depending on oxygen pressure and substrate temperature. Thicker layers of stoichiometric crystalline -Al2O3 layers were grown by electron-beam evaporation of Al2O3 and reactive sputter deposition.

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Section: Introductionmentioning

confidence: 99%

Structural and nanochemical properties ofAlOxlayers inAl/AlOx/Al-layer systems

Fritz

Radtke

Schneider

et al. 2019

Phys. Rev. Materials

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“…1 and Table I, the quality of our NbN/AlN/NbN junctions is not only better than that of all previously reported NbN tunnel junctions 9-12,15-17 but also comparable with or better than that of high-quality Nb tunnel junctions. [19][20][21] The controllability of J c is one of the important issues for junction applications. In this work, J c (i.e., the thickness of AlN barriers) is controlled by depositing time at a very low deposition rate of 0.05 nm/s.…”

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confidence: 99%

High-quality epitaxial NbN/AlN/NbN tunnel junctions with a wide range of current density

Wang

Terai

Qiu

et al. 2013

Applied Physics Letters

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“…In those applications, fairly large micron-scale junctions can typically be tolerated, and fabrication usually proceeds by the robust Nb/Al/AlOx/Nb trilayer deposition and etching techniques 12,13 , where Nb and Al are typically sputter deposited, and the high quality AlOx barrier is thermally grown on a thin < 10 nm Al layer. This process typically yields a high gap ∆ ∼ 1.3 mV and a near bulk T C ∼ 9 K 14,15 .…”

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confidence: 99%

Sub-micron normal-metal/insulator/superconductor tunnel junction thermometer and cooler using Nb

Nevala

Chaudhuri

Halkosaari

et al. 2012

Applied Physics Letters

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We have successfully fabricated Cu/AlOx-Al/Nb normal-metal/insulator/superconductor tunnel junction devices with a high value of the superconducting gap (up to ∼ 1 mV), using electron-beam lithography and angle evaporation techniques in the sub-micron scale. The subgap conductance of these junctions shows the expected strong temperature dependence, rendering them suitable for thermometry all the way from 100 mK to 6 K. In addition, some direct electronic cooling of the normal metal was also seen at bias values near the gap edge. The device performance was strongly influenced by the details of the Al layer geometry, with lateral spilling of the aluminium giving rise to strong extra subgap features, and the thickness of Al layer affecting the proximised superconducting gap value of the superconducting Al/Nb bilayer.Normal-metal-insulator-superconductor (NIS) tunnel junction devices have already proven as promising solid state coolers 1-4 , accurate low temperature thermometers and sensitive bolometers 2,5,6 , and near-ideal single electron transistors 7,8 . Some active research on such devices is aimed at enhancing the cooling power at sub-300 mK temperatures 9 , but increasing the operational range in temperature by changing the superconducting material (gap ∆) from the traditional aluminum has not been very successful yet, although a promising new alternative is to use SIS' structures, instead 10 .To extend the range of NIS devices beyond the operational range of Al, which has an upper limit for thermometry at T C ∼1.5 K and the maximum cooling power at T ∼ 300 mK, one should consider the elemental metal with highest gap, niobium (T C ∼ 9 K). It is already routinely used for SIS tunnel junction applications in SQUIDs, radiation detectors and digital electronics 11 . In those applications, fairly large micron-scale junctions can typically be tolerated, and fabrication usually proceeds by the robust Nb/Al/AlOx/Nb trilayer deposition and etching techniques 12,13 , where Nb and Al are typically sputter deposited, and the high quality AlOx barrier is thermally grown on a thin < 10 nm Al layer. This process typically yields a high gap ∆ ∼ 1.3 mV and a near bulk T C ∼ 9 K 14,15 .In contrast, for single-charge devices and for small thermometers and bolometers, sub-micron scale junctions are desired. They are easier to fabricate using angle-evaporation and lift-off 16 , although a successful but more complex sub-micron Nb trilayer Josephson junction process has also been demonstrated15 . The quality of evaporated Nb, unfortunately, has turned out to be quite sensitive to the exact chamber and substrate conditions, such as vacuum level, evaporation speed, substrate to Nb crucible distance and especially to the type of resist used [17][18][19][20][21][22] . Problems with standard polymer resists are typically attributed to decomposition and outgassing during Nb evaporation, leading to the suppression of T C and ∆.Here, we demonstrate that a fairly simple angleevaporation process can, nevertheless, be used to fabricate good...

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High quality Nb/Al-AlOx/Nb Josephson junction

Cited by 107 publications

References 9 publications

Structural and nanochemical properties ofAlOxlayers inAl/AlOx/Al-layer systems

Structural and nanochemical properties ofAlOxlayers inAl/AlOx/Al-layer systems

High-quality epitaxial NbN/AlN/NbN tunnel junctions with a wide range of current density

Sub-micron normal-metal/insulator/superconductor tunnel junction thermometer and cooler using Nb

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