SNS junction on Nb-Ti base for microwave circuits

Abstract

Superconductor -normal metal -superconductor (SNS) junctions a r e well-suited for large-scale integrated superconducting circuits. Potential applications a r e programmable voltage standards, digital-to-analog converters a n d large-scale RSFQ circuits. T h e application of SNS junctions provides some advantages, e.g. a simplified fabrication technology a n d reduced parasitic inductances. But it requires a technological process with dimensions down to the submicrometer region to achieve sufficiently high characteristic voltages IcRN.In our process the normal metal interlayer is titanium. Therefore the sidewall insulation of the junctions can be made by anodization, as it is known from the Nb-AI technology. NbTi-Nb Josephson junctions a n d junction a r r a y s were fabricated down t o the submicrometer range with I,R, values up to 87 microvolt depending on the titanium thickness. Their measured critical currents have a small spread of about 10 percent.Shapiro steps a r e observed under the influence of microwave irradiation. For the application of such junctions in a programmable Josephson voltage standard a new type of microwave circuit using coplanar strips is proposed a n d successfully tested in 10 V SIS circuits.

Miniaturization of Josephson Junctions for Digital Superconducting Circuits

“…However, this value of suppression parameter is difficult to implement. It is, for this reason, the experimentally obtained magnitudes of characteristic voltage is rather small [18,[44][45][46][47][48][49][50][51][52][53]. Note that a simple decrease in the N -layer thickness is not a solution of this problem.…”

Miniaturization of Josephson junction for digital superconducting circuits

“…However, this value of suppression parameter is difficult to implement. It is, for this reason, the experimentally obtained magnitudes of characteristic voltage is rather small [18,[45][46][47][48][49][50][51][52][53][54]. Note that a simple decrease in the N layer thickness is not a solution of this problem.…”

Josephson voltage standards

“…Intrinsically shunted junctions have the advantage that the fabrication process is easier and less space is required. Overdamped, intrinsically shunted junctions have been realized using SNS junctions (consisting, for example, of AuPd (Benz 1995), Ti (Schubert et al 2001a), or HfTi (Hagedorn et al 2001 as normal conductor) or SINIS junctions consisting of an Nb/Al 2 O 3 /Al/Al 2 O 3 /Nb multilayer (Schulze et al 1998). Kautz (1995) performed simulation calculations of Shapiro steps in SNS Josephson junctions.…”

“…They include 50 coplanar waveguides for SNS junctions and lowimpedance striplines for SINIS junctions. Recently, Schubert et al (2001aSchubert et al ( , 2001b proposed a new kind of 50 coplanar stripline which has also been applied to SINIS junctions.…”