Abstract
We have developed a process for the fabrication of YBa/sub 2/Cu/sub 3/O/sub 7/ (YBCO) step edge junctions. This process greatly improved the uniformity of the step angles, the straightness and sharpness of the step edges on LaAlO/sub 3/ substrates. We used an electron beam lithography defined amorphous carbon film as an ion milling mask. By studying junctions made across straight and wavy step edges, we showed the importance of the straightness on the quality of YBCO junctions. Junctions fabricated across these improved step edges showed less j/sub c/ variations (a factor of 2-3 compared to >10 for standard step edge junctions) and improved current distribution. We increased the McCumber constant /spl beta//sub c/ by varying the step height and the YBCO film thickness (h and t). Hysteresis was observed in the I-V characteristics at 4.2 K for junctions with h=240 nm and t=180 nm. The capacitance per unit area was calculated to be 15 fF//spl mu/m/sup 2/. The magnetic field (H) dependence of the critical current (I/sub c/) showed well-defined periods with a main peak in the center. The I/sub c/ in the first minimum can be suppressed to 20-40% in most cases. For some junctions, I/sub c/ can also be suppressed to zero at higher temperatures. However, we did not observe a perfect Fraunhofer pattern in the I/sub c/ vs. H curve. The field period /spl Delta/H was found to have a w/sup -2/ dependence on the junction width (w). >
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
