Fabrication of Al/AlO<sub><italic>x</italic></sub>/Al Josephson junctions on silicon and sapphire substrates using a cold-development technique

Wei Chen; JiaZheng Pan; ZuYu Xu; YangYang Lv; XianJing Zhou; XueCou Tu; Jun Li; GuoZhu Sun; HuaBing Wang

doi:10.1007/s11433-018-9298-3

SCIENCE CHINA Physics, Mechanics & Astronomy

SCIENCE CHINA Physics, Mechanics & Astronomy, Volume 62, Issue 6: 067011(2019) https://doi.org/10.1007/s11433-018-9298-3

Fabrication of Al/AlO_x/Al Josephson junctions on silicon and sapphire substrates using a cold-development technique

Wei Chen, JiaZheng Pan, ZuYu Xu, YangYang Lv, XianJing Zhou, XueCou Tu^*, Jun Li, GuoZhu Sun, HuaBing Wang^*

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ReceivedAug 4, 2018
AcceptedSep 4, 2018
PublishedDec 11, 2018

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Abstract

In order to obtain high-quality superconducting qubits, we employed a cold-development technique, using temperatures down to ?20°C, to fabricate Al/AlO_x/Al Josephson junctions. Cold development greatly reduced the sensitivity of the electron-beam resist to the developer, eliminated molecules of the electron-beam resist at trench edges, and improved the repeatability and reliability of the nanopatterning process. The fabricated samples have well-defined geometries and increased dose margins, with lateral sizes of 100?nm×100?nm on both silicon and sapphire substrates. Together with the bridge-free fabrication method we used in these experiments, we believe that the cold-development technique can play an important role in quantum information technology that employs superconducting qubits.

Funded by

the National Natural Science Foundation of China(Grant,Nos.,61727805,61771234,61501220,61611130069,61521001)

the National Key Research and Devlopment Programme of China(Grant,No.,2016YFA0301802)

Jiangsu Provincial Natural Science Fund(Grant,Nos.,BK20150561,BK20160635)

the Fundamental Research Funds for the Central Universities

and Nanjing University Innovation and Creative Program for PhD candidate(Grant,No.,CXCY17-15)

Acknowledgment

This work was supported by the National Natural Science Foundation of China (Grant Nos. 61727805, 61771234, 61501220, 61611130069, and 61521001), the National Key Research and Devlopment Programme of China (Grant No. 2016YFA0301802), Jiangsu Provincial Natural Science Fund (Grant Nos. BK20150561, and BK20160635), the Fundamental Research Funds for the Central Universities, and Nanjing University Innovation and Creative Program for PhD Candidate (Grant No. CXCY17-15). We thank Haifeng Yu for his valuable discussion.

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Figure 1
(Color online) (a) Schematic view of the double-angle aluminium-deposition process using a bridge-free technique. (b) The cross-shaped gap after development. (c) Bottom layer of Al deposited at an angle θ₁, covered with an in-situ oxidized layer. (d) Top Al layer deposited at an angle θ₂. (e) The as-prepared Al/AlO_x/Al Josephson junction after lift-off of the resist.
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Figure 2
(Color online) (a) Optical image of a 3D transmon qubit. (b) Optical microscope image of the microwave antenna integrated with the Josephson junction. (c) Scanning electron microscope (SEM) image of the Josephson junction with the size of 246?nm×275?nm.
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Figure 3
(Color online) Time-domain measurement of the coherence of a 3D transmon qubit. (a) Rabi oscillation and (b) relaxation from the first excited state |1>.
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Figure 4
(Color online) (a) SEM images of four typical Al/AlO_x/Al Josephson junctions on silicon substrates. The four figures correspond to the same exposure dose (3500?μC/cm²) but to the different development temperatures of 22, 6, ?10, and ?20°C, respectively. (b) Dependence of the normalized junction area on the development temperature. The dotted horizontal line represents the nominal area of 100?nm×100?nm. (c) The acceptable dose windows at different development temperatures for the junctions on silicon substrates.
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Figure 5
(Color online) (a) SEM images of four typical Al/AlO_x/Al Josephson junctions on sapphire substrates. The four figures correspond to the same exposure dose of 3500?μC/cm² but to the different development temperatures of 22, 6, ?10, and ?20°C, respectively. (b) Dependence of the normalized junction area on the development temperature. The dotted horizontal line represents the nominal area of 100?nm×100?nm. (c) The acceptable dose windows at different development temperatures for the junctions on sapphire substrates.

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85.25.Cp	Josephson devices
85.30.Mn	Junction breakdown and tunneling devices (including resonance tunneling devices)
03.65.Yz	Decoherence; open systems; quantum statistical methods (see also 03.67.Pp in quantum information; for decoherence in Bose-Einstein condensates, see 03.75.Gg)
03.67.-a	Quantum information (see also 42.50.Dv Quantum state engineering and measurements; 42.50.Ex Optical implementations of quantum information processing and transfer in quantum optics)