Aspects of low-temperature annealing YBa2Cu3O7-δ thin films

We describe a simple post-deposition annealing technique for crystallizing very smooth (10 nm rms surface roughness) thin films of YBa2Cu3O7-δ (123) on SrTiO3 at low temperatures. The method does not rely on matching oxygen partial pressures and maximum annealing temperatures to particular points on the 123 critical stability line. Zero resistances in the range 89-94 K and critical current densities up to 2 MA cm-2 (at 77 K) are readily achieved for stoichiometric films. The various stages of our procedure are analysed in detail from the viewpoint of film-oxidation. By reference to film chemistry and oxygen stoichiometries, interesting similarities and differences between the present process and the so-called BaF2 method have been identified. We discuss evidence gathered from the literature, which suggests that in films annealed by the BaF2 method the position of the critical stability line of partially fluorinated 123 depends on the degree of fluorination. Heat treatments are described which allow crystallographic orientation to be modified in a predictable way and which may be useful in producing high-angle grain boundary Josephson junctions. (orig.)