Observation of recrystallization process of interface-modified barrier and the properties of interface-modified ramp-edge junctions

摘要

We successfully observed RHEED patterns in recrystallization process of interfacemodified barrier by using a-axis oriented YBCO films. ECR ion bombardment was used for making an amorphous layer. RHEED patterns of a typical tri-layered perovskite structure was observed for as-deposited a-axis oriented YBCO films. A halo pattern showing the existence of an amorphous layer was changed to three types of patterns by changing the ECR and annealing conditions. The YBCO surface damaged at the higher ion acceleration voltage showed clear recrystallization to a-axis oriented YBCO after annealing. The surface damaged at lower voltages showed RHEED patterns different from that of a-axis oriented YBCO. In these cases, regions with a cubic or a psude-cubic structure were observed at the interface by TEM. YBCO ramp-edge Josephson junctions fabricated under optimum conditions exhibited resistively and capacitively shunted junction(RCSJ)-like I-V curves with a typical IcRn product at 4.2K of 1～3mV. I-V characteristics of a 25JJ series-array at 4.2K showed the Ic spread 1σas 13.5% for 25 junctions.