Abstract
We present a fabrication technology for nanoscale superconducting quantum interference devices (SQUIDs) with overdamped superconductor-normal metal-superconductor (SNS) trilayer Nb/HfTi/Nb Josephson junctions. A combination of electron-beam lithography with chemical-mechanical polishing and magnetron sputtering on thermally oxidized Si wafers is used to produce direct current SQUIDs with 100-nm-lateral dimensions for Nb lines and junctions. We extended the process from originally two to three independent Nb layers. This extension offers the possibility to realize superconducting vias to all Nb layers without the HfTi barrier, and hence to increase the density and complexity of circuit structures. We present results on the yield of this process and measurements of SQUID characteristics.
Highlights
Superconducting quantum interference devices (SQUIDs) are sensitive detectors of magnetic flux Φ, used in a large variety of applications [1,2]
We extended our fabrication technology for nanoSQUIDs with superconductor-normal metal-superconductor (SNS) Josephson junctions (JJs) from origiWe extended our fabrication technology for nanoSQUIDs with SNS JJs from originally two to three independent layers of Nb
Fabricating high aspect ratio interdigital capacitors (IDCs) was challenging due to the large area of the structures which must be fabricated without any defects, causing a reduced yield; still we demonstrate the possibility to obtain the capacitances very precisely in agreement with the capacitor design
Summary
Superconducting quantum interference devices (SQUIDs) are sensitive detectors of magnetic flux Φ, used in a large variety of applications [1,2]. Our fabrication technology, which is based on the combination of EBL and CMP, by contrast, offers the possibility to realize even smaller vias and JJs. In this paper we describe the extension of our Nb multilayer technology for nanoSQUIDs from originally two to three independent layers of Nb. In this paper we describe the extension of our Nb multilayer technology for nanoSQUIDs from originally two to three independent layers of Nb This allows to significantly increase the density of circuit structures. The possibility to realize direct vias between all independent Nb layers, i.e. directly connecting each Nb layer without the normal conducting HfTi barrier in-between (e.g., to realize purely superconducting bridges for coils), offers improved design flexibility. We demonstrate that the extension of our fabrication process does not influence the electric transport properties of our SQUIDs and can be used to further develop more complex nanoSQUID circuits
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