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 fabri cating crossovers, vias, YBCO/YBCO contacts, and multiple coverage of steps with trilayer structures of YBCO / epitaxial insulator / YBCO, T wo insulator materials were used, high-epsilon SrTiO3 and relatively l ow-epsilon Sr2AlTaO6 (SAT). The deposition conditions for both insulat ors had to be optimized to simultaneously obtain smooth surfaces, suff iciently high oxygen diffusion rates to re-oxidize underlying YBCO, an d resistivities in planar capacitor structures of > 10(9) Ohm-cm at 77 K. The particular process used to clean film surfaces after photolitho graphy and Ar ion milling was also critical in obtaining smooth surfac es for a subsequently deposited film layer, For the non-planar capacit or structures formed at crossovers, the effective resistivity of insul ators decreased as a function of linewidth, particularly for lines les s than 10 mu m wide, However, even for narrow lines patterned in the t op YBCO layer, critical current densities, J(c)(77K), exceeded 10(6) A /cm(2).