TRANSPORT CHARACTERISTICS OF TL2BA2CACU2O8 BICRYSTAL GRAIN-BOUNDARY JUNCTIONS AT 77-K

We report the fabrication and characterization of thin-film grain boundary junctions in TL-based superconductors on bicrystal substrates. Post-deposition processed TL2Ba2CaCu2O8 films were grown on bicrystal SrTiO3 substrates, with varying degrees of misorientation angle theta. Critical current densities and current-voltage curves had a strong dependence on theta. For theta greater-than-or-equal-to 10-degrees, there was a two-to-three order of magnitude reduction in critical current density, and for theta greater-than-or-equal-to 20-degrees, the current-voltage curves displayed resistively shunted junction behavior. These high angle grain boundary junctions have features at 77 K that are attractive for device applications, including sharp voltage onsets, well-behaved dc magnetic and rf field dependence, I(c)R(n) products as large as 300 muV, and low 1/f noise. Simple dc superconducting quantum interference devices fabricated with these junctions exhibited transfer functions of up to 30 muV/PHI0 at 77 K.