Epitaxial Growth of Sr x TiO y and Fabrication of EuBa 2 Cu 3 O 7-δ /Sr x TiO y /Pb Tunnel Junctions

Thin films deposited from a SrTiO 3 (STO) target using rf magnetron sputtering were examined. The Sr 1.6 TiO y films with perovskitelike structure grew epitaxially at substrate temperatures above 500°C. The trilayered films of EuBa 2 Cu 3 O 7 (EBCO)/STO/EBCO were deposited eptaxially on STO(110) substrates, but partial polycrystal growth in the EBCO film of the third layer was observed. In view of this result, EBCO(110)/STO(110)/Pb tunnel junctions were produced on STO(110) substrates. The I-V characteristics of junctions with an R nn of 10 Ω showed a gap opening at a bias voltage of about 10 mV, a clear gap structure at 2.5 mV and R j / R nn =12.4 below 2.5 mV. The low-energy gap below 2.5 mV was caused by the deterioration of the EBCO base electrodes due to the junction fabrication process. The large R j / R nn suggests that an STO epitaxial ultrathin film can be a good low-leakage barrier. On the other hand, lower resistance junctions showed the development of a supercurrent at zero bias.