Investigation of ErBa/sub 2/Cu/sub 3/O/sub 7//Cu/sub 2/ O/normal metal tunnel structures

Tunneling studies have been made using sputtered Cu/sub 2/O as an insulating barrier between an EBCO thin film and a normal metallic layer. Cu/sub 2/O was selected for its low potential for chemical reaction with the superconducting layer and for its photoconductive properties. Having a band gap in the visible (2 eV), Cu/sub 2/O is a suitable candidate for photosensitive tunneling experiments. EBCO thin films were deposited in situ onto MgO substrates using an off-axis sputtering technique. T/sub c/'s of as-deposited films were between 80 and 85 K. Inductively measured J/sub c/'s ranged between 10/sup 6/ and 10/sup 7/ A/cm/sup 2/ at 4 K. A 5-20-nm layer of Cu/sub 2/O was sputtered directly on top of the superconducting film. Room-temperature resistivities of the Cu/sub 2/O layer were typically greater than 10/sup 6/ Omega -cm. A normal metal layer (typically gold) was then deposited onto the Cu/sub 2/O layer. Transport properties of the structure were measured at temperatures ranging above and below the T/sub c/ of the superconducting layer. Measurements of structures fabricated to date showed no tunneling effects. Measurements of the I-V characteristic of a Cu/EBCO bilayer exhibited nonohmic behavior at 85 K and 4 K, indicating the existence of an extraneous interfacial layer. Preliminary results on one such structure indicate possible tunneling effects.