A side-wall spacer passivated fabrication process of niobium Josephson junctions

This work presents the latest refinements of our fabrication process for Nb/Al-AlO_x/Nb Josephson junctions. A key element is a side-wall spacer passivated structure, which is effective in the formation of junctions with sizes down to the sub-micrometer range. The multi-layer process is carried out on 150 mm wafers with UV lithography.  Critical current density tuning is achieved in the range of 0.1-3 kA cm^-2, which supports a multitude of applications.  We are continuously validating the process quality by characterizing cryogenic devices with relevance for quantum computing. These include Josephson parametric amplifiers including traveling wave parametric amplifiers, Josephson oscillators, and an emerging category of single-flux quantum circuits