Vertically-stacked Josephson junctions using YbBa2Cu3O7-x as a counter electrode for improving uniformity

We have fabricated vertically-stacked interface-treated Josephson junctions using YbBa₂Cu₃O_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_c=1.0×10³ A/cm² with a 1σ spread of 6.9%, and I_cR_n=0.5 mV with a 1σ spread of 5.4%. These spreads were improved compared with those of junctions with YBCO as a counter electrode. Furthermore, the normal conductance G_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.