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arXiv:1706.06397 · Superconductor Science and Technology

Side-wall spacer passivated sub-μm Josephson junction fabrication process

Leif Grönberg, M. Kiviranta, Visa Vesterinen, Janne Lehtinen, Slawomir Simbierowicz, Juho Luomahaara, Mika Prunnila, Juha Hassel

Published Oct 17, 2017• 36 citations
arXivHTMLPDF

Abstract

We present a structure and a fabrication method for superconducting tunnel junctions down to the dimensions of 200 nm using i-line UV lithography. The key element is a sidewall-passivating spacer structure (SWAPS) which is shaped for smooth crossline contacting and low parasitic capacitance. The SWAPS structure enables formation of junctions with dimensions at or below the lithography-limited linewidth. An additional benefit is avoiding the excessive use of amorphous dielectric materials which is favorable in sub-Kelvin microwave applications often plagued by nonlinear and lossy dielectrics. We apply the structure to niobium trilayer junctions, and provide characterization results yielding evidence on wafer-scale scalability, and critical current density tuning in the range of 0.1–3.0 kA cm −2 . We discuss the applicability of the junction process in the context of different applications, such as SQUID magnetometers and Josephson parametric amplifiers.

DOI
10.1088/1361-6668/aa9411

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We present a structure and a fabrication method for superconducting tunnel junctions down to the dimensions of 200 nm using i-line UV lithography. The key element is a sidewall-passivating spacer structure (SWAPS) which is shaped for smooth crossline contacting and low parasitic capacitance. The SWAPS structure enables formation of junctions with dimensions at or below the lithography-limited linewidth. An additional benefit is avoiding the excessive use of amorphous dielectric materials which is favorable in sub-Kelvin microwave applications often plagued by nonlinear and lossy dielectrics. We apply the structure to niobium trilayer junctions, and provide characterization results yielding evidence on wafer-scale scalability, and critical current density tuning in the range of 0.1–3.0 kA cm −2 . We discuss the applicability of the junction process in the context of different applications, such as SQUID magnetometers and Josephson parametric amplifiers.
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