SKM 2023 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 57: Poster: Superconductivity I

TT 57.20: Poster

Donnerstag, 30. März 2023, 15:00–18:00, P2/OG2

Comparison of window-type and cross-type Nb/Al-AlO_x/Nb Josephson tunnel junctions — •Fabienne Bauer¹, Martin Neidig¹, Christian Enss², and Sebastian Kempf¹ — ¹Institute of Micro- and Nanoelectronic Systems, Karlsruhe Institute of Technology — ²Kirchhoff Institute of Physics, Heidelberg University

Josephson tunnel junctions (JJs) are the heart of numerous superconducting electronic devices such as SQUIDs, qubits or parametric amplifiers. Out of the multitude of junction variants, Nb/Al-AlO_x/Nb junctions have somehow become the state of the art as they are resilient to thermal cycling and additionally show a very high junction quality and reproducibility of characteristic junction properties. Against this background, we present two anodization-free fabrication processes for Nb/Al-AlO_x/Nb Josephson junctions. One is a variant of the selective niobium etching process (SNEP) for fabricating window-type junctions. The second is a process for producing self-aligning, low-capacitance cross-type Josephson junctions. For comparing both processes, we comprehensively characterized fabricated junctions by studying resonance phenomena in unshunted dc-SQUIDs to determine the intrinsic junction capacitance and determined characteristic junction figures of merit. We show that both of our processes yield very high quality JJs. However, our cross-type Josephson junctions turn out not only to greatly simplify the fabrication process and to provide much lower junction capacitance, but also to show a greatly improved homogeneity of critical current density distribution as determined by analysing the magnetic field dependence of the critical current.