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Atomic structure and oxygen deficiency of the ultrathin aluminium oxide barrier in Al/AlOx/Al Josephson junctions.

Zeng L, Tran DT, Tai CW, Svensson G, Olsson E - Sci Rep (2016)

Bottom Line: The nanoscale dimension and disordered nature of the barrier oxide have been challenges for the direct experimental investigation of the atomic structure of the tunnel barrier.In the interior of the barrier, the oxide resembles the atomic structure of bulk aluminium oxide.Atomic defects such as oxygen vacancies at the interfaces can be the origin of the two-level systems and contribute to decoherence and noise in superconducting quantum circuits.

View Article: PubMed Central - PubMed

Affiliation: Department of Applied Physics, Chalmers University of Technology, 41296, Göteborg, Sweden.

ABSTRACT
Al/AlOx/Al Josephson junctions are the building blocks of a wide range of superconducting quantum devices that are key elements for quantum computers, extremely sensitive magnetometers and radiation detectors. The properties of the junctions and the superconducting quantum devices are determined by the atomic structure of the tunnel barrier. The nanoscale dimension and disordered nature of the barrier oxide have been challenges for the direct experimental investigation of the atomic structure of the tunnel barrier. Here we show that the miniaturized dimension of the barrier and the interfacial interaction between crystalline Al and amorphous AlOx give rise to oxygen deficiency at the metal/oxide interfaces. In the interior of the barrier, the oxide resembles the atomic structure of bulk aluminium oxide. Atomic defects such as oxygen vacancies at the interfaces can be the origin of the two-level systems and contribute to decoherence and noise in superconducting quantum circuits.

No MeSH data available.


Related in: MedlinePlus

Structure of an Al/AlOx/Al junction from scanning transmission electron microscopy (STEM) imaging and electron energy loss spectroscopy (EELS) analysis.(a) A cross-sectional ADF STEM image showing different layers in a typical Al/AlOx/Al Josephson junction with AlOx formed by thermal oxidation directly on the bottom Al electrode. (b) A high resolution ADF STEM image of a junction area showing the tunnel barrier. Lattice fringes and atomic columns from crystalline Al region are visible. (c) Al-L23 EELS line-profile obtained across the tunnel junction, from top Al electrode, aluminium oxide tunnel barrier to bottom Al electrode. The inset shows the Al-L23 ELNES signal from the centre of the barrier after subtracting the contribution from the Al electrode.
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f1: Structure of an Al/AlOx/Al junction from scanning transmission electron microscopy (STEM) imaging and electron energy loss spectroscopy (EELS) analysis.(a) A cross-sectional ADF STEM image showing different layers in a typical Al/AlOx/Al Josephson junction with AlOx formed by thermal oxidation directly on the bottom Al electrode. (b) A high resolution ADF STEM image of a junction area showing the tunnel barrier. Lattice fringes and atomic columns from crystalline Al region are visible. (c) Al-L23 EELS line-profile obtained across the tunnel junction, from top Al electrode, aluminium oxide tunnel barrier to bottom Al electrode. The inset shows the Al-L23 ELNES signal from the centre of the barrier after subtracting the contribution from the Al electrode.

Mentions: The Al/AlOx/Al Josephson junction used in this study is fabricated on SiO2/Si substrate (Fig. 1a). The mean tunnel barrier thickness in the junction is around 1.8 nm with a standard deviation of the thickness distribution less than 0.5 nm, as presented in a previous study23. The areas between the crystalline Al electrodes do not show long-range ordered features (e.g. Fig. 1b), indicating a disordered structure in the barrier layer. The amorphous structure of the barrier oxide was confirmed and investigated by EELS and electron diffraction, which will be presented in the following sections.


Atomic structure and oxygen deficiency of the ultrathin aluminium oxide barrier in Al/AlOx/Al Josephson junctions.

Zeng L, Tran DT, Tai CW, Svensson G, Olsson E - Sci Rep (2016)

Structure of an Al/AlOx/Al junction from scanning transmission electron microscopy (STEM) imaging and electron energy loss spectroscopy (EELS) analysis.(a) A cross-sectional ADF STEM image showing different layers in a typical Al/AlOx/Al Josephson junction with AlOx formed by thermal oxidation directly on the bottom Al electrode. (b) A high resolution ADF STEM image of a junction area showing the tunnel barrier. Lattice fringes and atomic columns from crystalline Al region are visible. (c) Al-L23 EELS line-profile obtained across the tunnel junction, from top Al electrode, aluminium oxide tunnel barrier to bottom Al electrode. The inset shows the Al-L23 ELNES signal from the centre of the barrier after subtracting the contribution from the Al electrode.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4940733&req=5

f1: Structure of an Al/AlOx/Al junction from scanning transmission electron microscopy (STEM) imaging and electron energy loss spectroscopy (EELS) analysis.(a) A cross-sectional ADF STEM image showing different layers in a typical Al/AlOx/Al Josephson junction with AlOx formed by thermal oxidation directly on the bottom Al electrode. (b) A high resolution ADF STEM image of a junction area showing the tunnel barrier. Lattice fringes and atomic columns from crystalline Al region are visible. (c) Al-L23 EELS line-profile obtained across the tunnel junction, from top Al electrode, aluminium oxide tunnel barrier to bottom Al electrode. The inset shows the Al-L23 ELNES signal from the centre of the barrier after subtracting the contribution from the Al electrode.
Mentions: The Al/AlOx/Al Josephson junction used in this study is fabricated on SiO2/Si substrate (Fig. 1a). The mean tunnel barrier thickness in the junction is around 1.8 nm with a standard deviation of the thickness distribution less than 0.5 nm, as presented in a previous study23. The areas between the crystalline Al electrodes do not show long-range ordered features (e.g. Fig. 1b), indicating a disordered structure in the barrier layer. The amorphous structure of the barrier oxide was confirmed and investigated by EELS and electron diffraction, which will be presented in the following sections.

Bottom Line: The nanoscale dimension and disordered nature of the barrier oxide have been challenges for the direct experimental investigation of the atomic structure of the tunnel barrier.In the interior of the barrier, the oxide resembles the atomic structure of bulk aluminium oxide.Atomic defects such as oxygen vacancies at the interfaces can be the origin of the two-level systems and contribute to decoherence and noise in superconducting quantum circuits.

View Article: PubMed Central - PubMed

Affiliation: Department of Applied Physics, Chalmers University of Technology, 41296, Göteborg, Sweden.

ABSTRACT
Al/AlOx/Al Josephson junctions are the building blocks of a wide range of superconducting quantum devices that are key elements for quantum computers, extremely sensitive magnetometers and radiation detectors. The properties of the junctions and the superconducting quantum devices are determined by the atomic structure of the tunnel barrier. The nanoscale dimension and disordered nature of the barrier oxide have been challenges for the direct experimental investigation of the atomic structure of the tunnel barrier. Here we show that the miniaturized dimension of the barrier and the interfacial interaction between crystalline Al and amorphous AlOx give rise to oxygen deficiency at the metal/oxide interfaces. In the interior of the barrier, the oxide resembles the atomic structure of bulk aluminium oxide. Atomic defects such as oxygen vacancies at the interfaces can be the origin of the two-level systems and contribute to decoherence and noise in superconducting quantum circuits.

No MeSH data available.


Related in: MedlinePlus