Structure and formation mechanism of interface-modified layer in ramp-edge Josephson junctions with La-doped 123-type superconducting electrodes

Ramp-edge-type Josephson junctions (JJ) with interface-modified barriers were fabricated. Yb/sub 0.9/La/sub 0.2/Ba/sub 1.9/Cu/sub 3/O/sub y/ and Y/sub 0.9/La/sub 0.2/Ba/sub 1.9/Cu/sub 3/O/sub y/ were used for the counter- and base-electrodes, respectively. Reliable junctions with I/sub c//spl sime/1 mA and 1/spl sigma/=6.5-8.0% for 25-100 JJ arrays were reproducibly obtained. For the junctions, the structure and composition of the barrier were investigated using a transmission electron microscope. A rather homogeneous layer with a thickness of a few nm was observed in the barrier region. The layer had a cubic lattice with a/spl sime/0.39/spl times/0.40 nm/sup 2/ and its cationic composition was Ba:La:(Y+Yb):Cu=38:10:20:32. It implies that the barrier consists of a thin layer of a cubic perovskite (Ba,La)(Y,Yb,Cu)O/sub 3/. The existence of La seems to stabilize the cubic perovskite and improve homogeneity of the barrier layer.