OXYGEN ANNEALING OF EX-SITU YBCO AG THIN-FILM INTERFACES/

The resistivity of YBCO/Ag interfaces has been measured for different oxygen annealing temperatures for a series of ex-situ fabricated thin- film contacts having sizes ranging from 16 mu m x 16 mu m down to 4 mu m x 4 mu m. The interface resistivity began to decrease after anneali ng at 300 degrees C for 10 minutes in one atmosphere oxygen. After ann ealing at 400 degrees C, the contact resistivity decreased by several orders of magnitude to the 10(-7) Omega-cm(2) range. The 500-nm thick Ag layer showed massive surface diffusion and agglomeration for anneal ing temperatures above 400 degrees C; this temperature thus represents a practical limit for oxygen annealing the YBCO/Ag interface system f or more than 10 minutes. Rapid cooling of the chip after annealing led to a severe loss of critical current density in the YBCO layer, which could be restored by reannealing and cooling at a slower rate of 50 d egrees C/min. The relative shape of the conductance-vs.-voltage charac teristics of the YBCO/Ag interface were essentially unaltered by oxyge n annealing; the overall parabolic shape, scattering zero bias anomaly remained constant, even though the contact conductance increased by s everal orders of magnitude. These data suggest that the main reduction in interface resistivity arises from an enhancement of the effective contact area, not from a change in interface conduction mechanism.