In situ noble metal YBa2Cu3O7 thin-film contacts

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Abstract
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.