YBa/sub 2/Cu/sub 3/O/sub 7-x/ Josephson junctions on bicrystal Al/sub 2/O/sub 3/ and SrTiO/sub 3/ substrates

Bicrystal grain-boundary junctions (bi-GBJs) have been reproducibly fabricated on SrTiO/sub 3/ (STO) and r-plane Al/sub 2/O/sub 3/ (sapphire) bicrystal substrates. Sapphire bicrystals are candidates for high-frequency applications due to their low dielectric constant and loss tangent. The sapphire bi-GBJs demonstrated resistively shunted junction (RSJ)-like current voltage characteristics, with junction parameters comparable to the STO bi-GBJs and critical current densities Jc/spl sim/10/sup 5/ A/cm/sup 2/. Independent control of junction resistance (R/sub N/) was demonstrated with the use of Au shunt layers. In addition, overlayers such as Au or STO may act to passivate the GBJs and improve long term stability.