VERY THIN YBA2CU3O7 STEP-EDGE JOSEPHSON-JUNCTIONS

Step-edge Josephson junctions were fabricated from 20 and 10 nm thick epitaxial YBa2Cu3O7 films on SrTiO3 substrates. The junction cross sec tions were in the 10(-8) cm2 range; similar to those in standard 200-3 00 nm thick junctions. The current-voltage characteristics, with and w ithout microwave irradiation, were of resistively-shunted-junction (RS J) type. The junction resistivities were in the range 10(-8)-10(-7) OM EGA cm2 range, up to two orders of magnitude higher than in standard j unctions, while the I(c) R(n)s were comparable. This behaviour was exp lained by a strong decrease in the number of parallel point-contact-ty pe connections with the junction thickness. The junctions deteriorated quickly upon thermal cycling.