Regensburg 2025 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 11: Superconductivity: Poster

TT 11.28: Poster

Monday, March 17, 2025, 15:00–18:00, P4

Chemical-mechanical polishing process for the fabrication of cross-type Nb/Al-AlOx/Nb Josephson tunnel junctions — •A. Stoll, N. Fiedler, L. Münch, D. Hengstler, A. Reifenberger, A. Fleischmann, and C. Enss — KIP, Heidelberg University

Josephson tunnel junctions (JJs) are the basic elements of many superconducting electronic devices such as qubits or superconducting quantum interference devices (SQUIDs). Since many applications demand numerous JJs, a reliable wafer-scale fabrication process yielding reproducible, high-quality junctions is essential.

We present the microfabrication process of cross-type Nb/Al-AlOx/Nb Josephson tunnel junctions, emphasizing chemical-mechanical polishing (CMP) for planarization within SiO₂. A layer of SiO₂ is deposited over the structured trilayer, and CMP is used to polish away excess SiO₂, resulting in a planar, smooth, and uniform surface that enhances the accuracy and reliability of the junctions. Quality checks were conducted on junctions of various sizes, as well as the influence of support-like structures around junctions, to evaluate performance and scalability. Electrical characterizations demonstrate high-quality superconducting properties, validating the efficacy of CMP in the planarization of Josephson junction trilayers

This method enhances the scalability and integration of Josephson junctions in complex superconducting circuits, contributing to advancements in quantum computing and superconducting electronics.

Keywords: Josephson junctions; CMP