Effect of ozone anneals on YBa/sub 2/Cu/sub 3-x/Co/sub x/O/sub 2/ thin films

We report on the effect of 200-500C ozone anneals on the resistivity versus temperature (RT) and Raman spectra characteristics of YBa/sub 2/Cu/sub 3-x/Co/sub x/O/sub 2/ (Co-YBCO) thin films, with x=0.3, 0.5, 0.75, and 1.0. Cold wall anneals are conducted at /spl sim/1 aim. of a flowing O/sub 2//O/sub 3/ mixture with /spl sim/2% O/sub 3/ by weight. The enhanced partial pressure of atomic oxygen, relative to canonical O/sub 2/ anneals, provided by ozone to the surface of Co-YBCO films, leads to enhanced oxygenation. This is demonstrated by the observation of an increase in T/sub c/ (25 K to 75 K for x=0.3, 0 to 38 K for x=0.5, and 0 to a T/sub c/(onset) of 19 K for x=0.75) and improvement in Raman spectra data following ozone anneals. This high degree of oxygenation is unstable under O/sub 2/ anneals at temperatures as low as 200C. We attribute this to the fact that the partial pressure of oxygen above well oxygenated Co-YBCO is greater than 1 atm. at /spl sim/200C. We will discuss the implication of these results for the stability and uniformity of SNS ramp edge Josephson junctions which employ Co-YBCO N-layers.