Regensburg 2019 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 55: Superconductivity: Tunneling and Josephson Junctions

TT 55.2: Vortrag

Donnerstag, 4. April 2019, 09:45–10:00, H23

Fabrication and characterization of cross-type Nb/Al-
AlO_x/Nb Josephson junctions — •Fabienne Bauer, Christian Enss, and Sebastian Kempf — Kirchhoff-Institute for Physics, Heidelberg University, Im Neuenheimer Feld 227, 69120 Heidelberg, Germany.

Josephson tunnel junctions are the basic element of numerous superconducting electronic devices such as SQUIDs or qubits. The performance and sensitivity of many of those devices depend on and particularly improve with decreasing junction capacitance. The latter depends on the material and the thickness of the tunnel barrier, the junction area as well as the overlap of different wiring layers adding parasitic capacitance. Therefore, the junction capacitance can be reduced by avoiding parasitic overlaps as well as by optimizing the oxidation parameters and the junction area.

Within this context, we present an anodization-free fabrication process for cross-type Nb/Al-AlO_x/Nb Josephson junctions. They are built by the overlap of two perpendicular superconducting stripes with the tunnel barrier in between eliminating any parasitic capacitance and making a reduced junction area easily possible. As a further advantage, restrictions in alignment accuracy do not limit the junction size. We will show that our cross-type tunnel junctions have a smaller capacitance compared to our window-type junctions and that they exhibit a reproducible high quality. In addition, we discuss the performance of dc-SQUIDs based on cross-type junctions to demonstrate the profit resulting from this new fabrication process.