RAMP TYPE HTS JOSEPHSON-JUNCTIONS WITH PRBACUGAO BARRIERS

Ramp type Josephson junctions have been fabricated using DyBa2Cu3O7-de lta as electrode material and PrBa2Cu3-xGaxO7-delta with x=0, 0.10 and 0.40 as junction barriers. Barrier thickness lie between 6-30 nm. Sev eral junctions without barrier were made in order to find ways to mini mize the damage of the ramp interface. In total about 40 chips were fa bricated each containing several junctions and their I-V characteristi cs measured for various temperatures down to 4.2 K. Only those junctio ns showing clear RSJ-like curves were selected to be analyzed. In some cases we also measured I-c as a function of a small applied field and obtained a clear Fraunhofer pattern, but there is a tendency to flux trapping as evidenced by LTSEM. It was found at 4.2 K that the critica l current density J(c) scales with the specific resistance R(n)A as J( c)=C-bar(R(n)A)(-m) (m=1.8+/-0.5). The barrier material dependent cons tant C-bar increases with x, whereas, for a given d, J(c) is constant and R(n)A increases.