FOCUSED ION-BEAM FABRICATION OF SINGLE GRAIN BI2SR2CA1CU2OX SUBMICRON BRIDGES

Superconducting microbridges have been patterned by direct milling of the Bi2Sr2Ca1Cu2O(x) polycrystalline thin films using focused ion beam. Several single grain and multigrain bridges of sizes as small as 0.3-mu-m have been fabricated. Single grain microbridges exhibit a linear temperature dependence of the critical current density with J(c) = 10(6) A/cm2 at 8 K, and zero magnetic field. Larger 50-100-mu-m bridges show lower critical current densities of J(c) = 10(4)-10(5) A/cm2. The current-voltage (I-V) and the J(c) vs T characteristics show two qualitatively different types of superconducting weak links. The single grain microbridges behave as homogeneous superconductors with transport exhibiting flux creep and flux flow. The large bridges can be characterized as granular superconductors with weakly connected grains, and their I-V and the J(c) vs T characteristics are dependent on processing conditions.