YBa2Cu307 films in c-axis orientation on bicrystalline SrTiO3 substrates are investigated by TEM. The films and the substrates are examined in cross-section and in plane view. The grain boundary of the bicrystal substrate contains (110) faceted voids, but is otherwise straight on a nanometer scale. Contrary to this, the film grain boundary is not straight. The deviation from a straight grain boundary can be up to 100 nm for a 100 nm thick film. The deviation from the intended position of the YBCO grain boundary can already occur at the film/substrate interface where it can be as much as + 50 nm.

Low-temperature scanning laser microscopy has been used to investigate the spatial variation of the critical temperature Tc and critical current Ic in thin-film high-To multilayer structures that include dielectric layers. The method is described and measurements are presented on an YBa2Cu307_x-based multiturn coil with SrTiO3 insulating layer. We found that the critical temperature Tc of the YBa2Cu307_x tOp layer, from which the return strip of the coil is formed, is higher than that of the YBa2Cu307_x base layer. The critical current of the coil is limited by the quality of the YBa2Cu3OT_x base layer and not by the edges of the crossovers. 0921-4534/94/$07.00

Flat films, high quality insulating layers and adequately superconducting via contacts are basic elements for high T c device fabrication. We studied the influence of the process parameters of laser deposition on the occurrence of droplets and outgrowths in YBaCuO films. The droplet density is minimal when a laser fluence below about 1.0 J cm-2 is used. The outgrowth density decreases with increasing laser pulse rate or decreasing deposition temperature. High quality flat films were obtained with a rate of 10 Hz and at a temperature of 720 °C. Wet chemical etching and etching with an Argon ion source were used for structuring multilayers with SrTiO3 as an insulating layer. Smooth edges were obtained with an argon gun. Bromine and EDTA etching are not adequate techniques for fabricating controllable well-defined edges. Cross-overs, via contacts and coils were prepared.

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