Critical current dependence on line width and long term stability of epitaxial YBa/sub 2/Cu/sub 3/O/sub 7-x/ thin film lines

We have investigated the line width dependence of the critical current density of epitaxial, ion beam etched YBCO lines of 1...20 /spl mu/m width and 10 /spl mu/m...10 cm length. The long term stability of superconducting parameters was studied over a period of several months. YBCO films with J/sub c/>1*10/sup 7/ A/cm/sup 2/ at 77 K can be fabricated using a variety of existing technologies. An increase of the critical current density of up to 40% has been observed if the line width decreases from w=20 /spl mu/m to w=1 /spl mu/m which corresponds to the width dependence of the current density distribution as is shown by FEM simulations. The J/sub c/ increase of narrower lines can be compromised by the degradation of the conductor edges. Based on values of the penetration depth obtained from phase velocity measurements, the simulation was used to extract values of the intrinsic critical current density and of the width of the degraded zone by fitting the J/sub c/(w) curves. Our measurements suggest the increase of the effective penetration depth of degraded lines. At present lines of width >=5 /spl mu/m can be fabricated which maintain at 77 K critical currents of about 5*10/sup 6/ A/cm/sup 2/. Over tens of centimeters line length. Degradation of the superconducting properties occurs during storage. It is accompanied by the disappearance of the J/sub c/ increase of narrower lines. Degradation is pronounced at narrow and long lines which points to defect and edge related oxygen.<
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