In situ noble metal YBa2Cu3O7 thin-film contacts

Thin-film contacts to YBa2Cu3O7 have been fabricated by an in situ noble-metal process and patterned down to 2×2 μm2; at this small size, the contacts carry transport current over 106 A/cm2 while maintaining a specific contact resistivity ρc in the 10−8 to 10−9 Ω cm2 range. No oxygen annealing was used in the processing, thus avoiding the problem of silver or gold agglomeration, as well as preserving a sharp interface for Josephson-device applications. ρc was measured to increase only ∼25% as temperature was increased from 4 to 90 K. The measurements were carried out on a series of film morphologies using both superconductor-normal metal and superconductor-normal metal-superconductor test structures; a carefully designed test pattern was used to correct for spreading conduction in the noble-metal contact layer. The contacts were ohmic with voltage-current characteristics that were linear over more than four orders of magnitude.