Materials basis for a six-level epitaxial HTS digital circuit process

We have developed a process for fabrication of HTS single-flux-quantum logic circuits based on edge SNS junctions which requires six epitaxial film layers and six mask levels, The process was successfully applied to fabrication of small-scale circuits (less than or equal to 10 junctions), This paper examines the materials properties affecting the reproducibility of YBCO-based SNS junctions, the low inductance provided by an integrated YBCO ground plane, and electrical isolation by SrTiO3 or Sr2AlTaO6 ground-plane and junction insulator layers, Some of the critical processing parameters identified by electrical measurements, TEM, SEM, and AFM were control of second-phase precipitates in YBCO, oxygen diffusion, Ar ion-milling parameters, and preparation of surfaces for subsequent high-temperature depositions.