Vertically-stacked Josephson junctions using YbBa/sub 2/Cu/sub 3/O/sub 7-x/ as a counter electrode for improving uniformity

We have fabricated vertically-stacked interface-treated Josephson junctions using YbBa/sub 2/Cu/sub 3/O/sub 7-x/ (YbBCO) as a counter electrode for improving the uniformity. We used YBCO for the base electrode. Most of the junctions fabricated on one chip exhibited resistively-shunted-junction (RSJ) characteristics. The properties of the junctions at 4.2 K were as follows: J/sub c/=1.0/spl times/10/sup 3/ A/cm/sup 2/ with a 1/spl sigma/ spread of 6.9%, and I/sub c/R/sub n/=0.5 mV with a 1/spl sigma/ spread of 5.4%. These spreads were improved compared with those of junctions with YBCO as a counter electrode. Furthermore, the normal conductance G/sub n/ of the junctions with the YbBCO counter electrode was independent of the temperature. Such characteristics have not been obtained for YBCO vertically-stacked interface-treated junctions. We speculate that this difference is attributed to the lattice mismatch between base-and counter-electrodes.