SELECTIVE EPITAXIAL-GROWTH FOR YBCO THIN-FILMS

A novel selective epitaxial growth (SEG) technique for YBa2Cu3O7-delta (YBCO) thin films is presented. The method involves the deposition of a thin (about 10 nm) metal layer, in the desired pattern, on a substr ate before the deposition of the superconducting thin film. During gro wth the metal reacts with the YBCO, forming locally an insulating comp ound. Best results are obtained with Ti or W, yielding structures with sharp boundaries and creating insulating areas with high resistivitie s. The technique has been analysed for the titanium case. It was found that during the YBCO growth the titanium layer reacts with the YBCO t o form an amorphous Ba-Ti-O compound. The YBCO cannot grow epitaxially on top of this layer, and a mainly amorphous YBCO film with insulatin g characteristics results. The resistivity of the insulating parts has been investigated as a function of the layer thicknesses of both the titanium and the YBCO. Both increasing the YBCO layer or a slight decr ease of the titanium layer thickness yields a strong decrease in the r esistivity. The SEG technique has been successfully applied to create submicron patterns, without any sign of degradation. Bridge structures with widths down to 200 nm could be prepared that still showed a T-c value of 89 K and J(c) values in excess of 2 x 10(6) A cm(-2) at 77 K.