PROPERTIES OF PASSIVE STRUCTURES FOR MULTILAYER HTS DIGITAL CIRCUITS

The passive structures required for HTS digital circuits that must be formed at high temperature (650-750 degrees C) were evaluated by fabricating crossovers, vias, YBCO/YBCO contacts, and multiple coverage of steps with trilayer structures of YBCO / epitaxial insulator / YBCO, Two insulator materials were used, high-epsilon SrTiO3 and relatively low-epsilon Sr2AlTaO6 (SAT). The deposition conditions for both insulators had to be optimized to simultaneously obtain smooth surfaces, sufficiently high oxygen diffusion rates to re-oxidize underlying YBCO, and resistivities in planar capacitor structures of > 10(9) Ohm-cm at 77K. The particular process used to clean film surfaces after photolithography and Ar ion milling was also critical in obtaining smooth surfaces for a subsequently deposited film layer, For the non-planar capacitor structures formed at crossovers, the effective resistivity of insulators decreased as a function of linewidth, particularly for lines less than 10 mu m wide, However, even for narrow lines patterned in the top YBCO layer, critical current densities, J(c)(77K), exceeded 10(6) A/cm(2).