Characterization of superconducting single-electron transistors with small Al/AlO$_{x}$/V Josephson junctions

Shimada, Hiroshi; Miyawaki, Kazuhiro; Hagiwara, Ayano; Takeda, Kouichi; Mizugaki, Yoshinao

doi:10.1088/0953-2048/27/11/115015

Cited by 4 publications

(6 citation statements)

References 51 publications

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“…Similar conclusions have been reached by other groups, either for somewhat similar Al-AlOx-Nb devices as here [19] or for Al-AlOx-V devices [23]. In both those cases, as in this study, the higher T C material (Nb or V) was evaporated on top of the tunneling barrier.…”

Section: Discussionsupporting

confidence: 91%

“…We find that although the Nb quality is high right at the junction as judged by the high ∆, we observe excess sub-gap current in the NIS state which cannot be explained by the simplest theories of broadening of the superconducting density of states [20,21,22]. This result is in agreement with previous studies in Al/AlOx/Nb [19] and in Al/AlOx/V [23] junctions, but in contrast with our previous work with Nb-Al-AlOx-Cu [24] or other similarly fabricated NIS junctions of NbN [25] or TaN [26], where the simple Dynes broadening [20,21] does explain the data. We comment at the end on the possible explanations for this difference.…”

Section: Introductionsupporting

confidence: 92%

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Applications and non-idealities of submicron Al–AlOx–Nb tunnel junctions

Julin¹,

Maasilta²

2016

Supercond. Sci. Technol.

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We have developed a technique to fabricate sub-micron, 0.6µm×0.6µm Al-AlOx-Nb tunnel junctions using a standard e-beam resist, angle evaporation and double oxidation of the tunneling barrier, resulting in high quality niobium, as determined by the the high measured values of the critical temperature T C ∼ 7.5 K and the gap ∆ ∼ 1.3 meV. The devices show great promise for local nanoscale thermometry in the temperature range 1 -7.5 K. Electrical characterization of the junctions was performed at sub-Kelvin temperatures both with and without an external magnetic field, which was used to suppress superconductivity in Al and thus bring the junction into a normal-metal-insulator-superconductor (NIS) configuration. We observed excess sub-gap current, which could not be explained by the standard tunneling theory. Evidence points towards materials science issues of the barrier or Nb/AlOx interface as the culprit.

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Section: Discussionsupporting

confidence: 91%

Section: Introductionsupporting

confidence: 92%

Applications and non-idealities of submicron Al–AlOx–Nb tunnel junctions

Julin¹,

Maasilta²

2016

Supercond. Sci. Technol.

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“…In particular the origin of such large conductance is likely related to the presence of vanadium. Similar high subgap conductances have been observed in several occasions in V-based tunnel junctions 40 – 44 , as well as in Nb-based tunnel junctions 45 .…”

Section: Resultssupporting

confidence: 86%

High operating temperature in V-based superconducting quantum interference proximity transistors

Ligato

Marchegiani

Virtanen

et al. 2017

Sci Rep

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Here we report the fabrication and characterization of fully superconducting quantum interference proximity transistors (SQUIPTs) based on the implementation of vanadium (V) in the superconducting loop. At low temperature, the devices show high flux-to-voltage (up to 0.52 mV/Φ0) and flux-to-current (above 12 nA/Φ0) transfer functions, with the best estimated flux sensitivity ~ 2.6 μΦ0/(Hz)1/2 reached under fixed voltage bias, where Φ0 is the flux quantum. The interferometers operate up to T bath 2 K, with an improvement of 70% of the maximal operating temperature with respect to early SQUIPTs design. The main features of the V-based SQUIPT are described within a simplified theoretical model. Our results open the way to the realization of SQUIPTs that take advantage of the use of higher-gap superconductors for ultra-sensitive nanoscale applications that operate at temperatures well above 1 K.

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“…A similar differential conductance characteristic with a double gap structure has been observed in a V/AlO x /Al/AlO x / V SET with the superconductivity of Al suppressed with a magnetic field. 66 It is known that a finite density of states (DOS) of quasiparticles remains in the superconducting gap even in the superconducting state of vanadium. 66,67 It is the reason why we observed a finite conductance in the gap range, and the observed Coulomb gap is regarded as that for the quasiparticles.…”

Section: Resultsmentioning

confidence: 99%

“…66 It is known that a finite density of states (DOS) of quasiparticles remains in the superconducting gap even in the superconducting state of vanadium. 66,67 It is the reason why we observed a finite conductance in the gap range, and the observed Coulomb gap is regarded as that for the quasiparticles. Thus, at V CG /2 < |V| < V G /2, the sequential tunneling of quasiparticles inside the superconducting gap occurs and gives a finite conductance.…”

Section: Resultsmentioning

confidence: 99%

Nanoscale Tunnel Junctions and Metallic Single-Electron Transistors via Shadow Evaporation and In Situ Atomic Layer Deposition of Tunnel Barriers

Shimada

Koike

Kikkawa

et al. 2021

ACS Appl. Nano Mater.

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Nanoscale metallic tunnel junctions are important elements of state-of-the-art technologies including superconducting qubits, single electronics, nanospintronics, and caloritronics. The most widely used versatile method of their fabrication is shadow evaporation through bilayer-resist masks patterned using electron-beam lithography. However, useable materials for the electrodes of junctions in this method were limited thus far because of the difficulty in forming good-quality tunnel barriers on them during the process. In this work, we have developed a process for fabricating nanoscale tunnel junctions in which the shadow evaporation method is combined with an atomiclayer-deposition (ALD)-grown Al 2 O 3 tunnel barrier formed in situ. To realize this process, we constructed a vacuum evaporator in which the sample chamber is equipped with a room-temperature remote-plasma ALD apparatus. This method enables control of the thickness of the tunnel barrier with the precision of the order of 0.1 nm. We successfully fabricated nanoscale Ni/Al tunnel junctions and a Ni/Al/Ni single-electron transistor, both having Ni bottom electrodes, as well as nanoscale V/V double superconducting tunnel junctions using the developed process. This process extends the applicability of the shadow evaporation technique for fabricating nanoscale tunnel junctions in various metals for bottom electrodes, with tunnel barriers of good quality. As specific applications, it will improve the controllability of nanoscale tunnel spin injectors for spintronics, increase the design freedom of caloritronic devices, and introduce a possibility to use various superconducting metals in superconducting quantum circuits.

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Characterization of superconducting single-electron transistors with small Al/AlO$_{x}$/V Josephson junctions

Cited by 4 publications

References 51 publications

Applications and non-idealities of submicron Al–AlOx–Nb tunnel junctions

Applications and non-idealities of submicron Al–AlOx–Nb tunnel junctions

High operating temperature in V-based superconducting quantum interference proximity transistors

Nanoscale Tunnel Junctions and Metallic Single-Electron Transistors via Shadow Evaporation and In Situ Atomic Layer Deposition of Tunnel Barriers

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