Wafer-scale Al junction technology for superconducting quantum circuits

• Published in: IEEE transactions on applied superconductivity 2024-05, Vol.34 (3), p.1-5
• Main Authors: Schmelz, M., Mutsenik, E., Bravin, S., Sultanov, A., Ziegler, M., Hubner, U., Peiselt, K., Mechold, S., Oelsner, G., Kunert, J., Stolz, R.
• Format: Article
• Language: English
• Subjects: Al Josephson junctions; circuits fabrication; Critical current (superconductivity); deep sub-micrometer junctions; Fabrication; Homogeneity; Integrated circuits; Josephson junctions; Junctions; Low temperature; Manhattan junction technology; Micrometers; Parameters; Parametric amplifiers; Qubit; Qubits (quantum computing); Resistance; Resists; Room temperature; superconducting qubits; Superconductivity; Temperature measurement; transmon qubit; Traveling waves; Tunnel junctions
• ISSN: 1051-8223; 1558-2515
• DOI: 10.1109/TASC.2024.3350580

Josephson tunnel junctions represent a key element in superconducting electronics and quantum circuits. For many years, shadow evaporation by means of Dolan-type bridges has been the state-of-the-art for deep sub- micrometer sized structures. Increasing demand in the number of Josephson junctions, e.g. in qubit circuits and travelling wave parametric amplifiers, requests for a wafer-scale fabrication process with precise control of junction parameters and have led to an advanced lift-off technique called Manhattan-type junction technology in recent years. Herein, we report on the development of a 100 mm wafer-scale fabrication technology for deep sub-micrometer sized Al Josephson junctions with linear dimensions down to 180 nm. The critical current I C of the junctions ranges from about 10 to 120 nA scaling with their linear dimensions. Low temperature transport measurements as well as room-temperature characterization has been used for I C and process homogeneity determination of series arrays of up to 50 Josephson junctions. We discuss technology parameters such as yield, on-chip and on-wafer reproducibility of the junction's critical currents as well as main process limitations. Moreover, we present experimental results on the characterization of first transmon-type qubits fabricated using this technology.