Dresden 2026 – scientific programme
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TT: Fachverband Tiefe Temperaturen
TT 28: Superconducting Electronics: SQUIDs and other Josephson Circuits and Components
TT 28.2: Talk
Tuesday, March 10, 2026, 09:45–10:00, CHE/0089
Chemical-mechanical polishing process for the fabrication of cross-type Nb/Al-AlOx/Nb Josephson tunnel junctions — •Alexander Stoll, Lukas Münch, Daniel Hengstler, Andreas Reifenberger, Andreas Fleischmann, and Christian Enss — Kirchhoff-Institute for Physics, Heidelberg University, Germany
The core elements at the frontier of superconducting electronic devices, such as qubits or superconducting quantum interference devices (SQUIDs), are the Josephson tunnel junctions (JJs). To enable scaling in production of these devices, good parameter control is required, including a uniform quality and reproducibility. We use a cross-type geometry for our JJs so that our junction area is not limited by alignment inaccuracies and, at the same time, parasitic capacitances and thus parasitic LC resonances can be avoided. A sputtered SiO2 layer used for the insulation of the structured Nb/Al-AlOx/Nb trilayer including its sidewalls usually requires a time-consuming lift-off and leaves behind undesired wings that can compromise the quality of subsequent layers. To mitigate these challenges, we introduced a chemical-mechanical polishing (CMP) step. We present our optimized fabrication process which achieves a well-embedded, smooth, and uniform post-CMP surface and substantially improves the reliability and yield of our JJs on 3 inch wafer-scale. A variety of tests to characterize the JJs based on their IV-characteristics and their Fraunhofer Patterns as well as the electrical properties of the superconducting Nb are discussed.
Keywords: Josephson tunnel junction; Nb/Al-AlOx/Nb trilayer; chemical-mechanical polishing; microfabrication; subgap leakage