SNS and SIS Josephson junctions with dimensions down to the submicron region prepared by a unified technology
Ludwig Fritzsch, H. Elsner, M. Schubert +1 more
Several applications of Josephson junctions (JJs) in low-temperature superconducting circuits such as programmable voltage standards and SFQ logical circuits or SQUID sensors require JJs with sub-µm dimensions. A method for preparing superconductor-isolator-superconductor (SIS) JJs as well as superconductor-normal metal-superconductor (SNS) JJs was developed which allows the preparation of both types of junctions by nearly the same technological process. Titanium is used as the normal metal for the SNS JJ. Ti can be anodically oxidized and a technology similar to the well-tried Nb-Al technology for SIS JJs can be applied to the SNS system, too. By electron-beam exposure of a negative deep UV photoresist (ma-N 2400) a stable resist mask is generated which has to withstand the following three self-aligned process steps: etching of the Nb counterelectrode by RIE, isolation by anodization and lifting of a SiO planarization layer. By this process SNS (Nb-Ti-Nb) and SIS (Nb-Al/AlO x -Nb) Josephson junctions with smallest junction areas of 0.49 µm 2 were prepared and characterized by dc measurements and under the influence of microwave irradiation. The Nb-Ti-Nb junctions have I c R n products of 87 µV. They can be used for programmable Josephson voltage standard circuits at frequencies of 70 GHz.
Superconductor Science and Technology•Nov 1, 1999•9 citations