A low-temperature argon ion milling process has been used to induce growth of c-oriented YBa2Cu3O7 on (001) MgO substrates with the in-plane film axes rotated 45° with respect to those of the substrate, and with respect to those of films grown on untreated regions of the substrate. This process is compatible with standard photolithographic processing, and has been used to produce defined areas of the two orientations on the same substrate. Josephson junctions and dc SQUIDs have been fabricated using the resulting grain boundaries.

Epitaxial thin films of YBa2Cu3O7 have been grown in situ by evaporation onto (001) MgO substrates. The composition was varied systematically to investigate the effects of changes in Cu content and Ba/Y ratio on the film properties. The results demonstrate that deviations from stoichiometry at the limit of resolution of most analytic techniques can have a large effect on structural and transport properties, as well as causing marked changes in surface morphology. The best properties (Jc≳3×106 A/cm2 at 77 K) are only found for a narrow range of compositions, which can be readily identified from the surface morphology.

The growth and characterisation of YBa2Cu3O7 thin films are reviewed. The discussion of growth is limited to the physical vapour deposition techniques of laser ablation, sputtering and evaporation. Emphasis is placed on the practical problems of growing epitaxial films in situ and characterising them.

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