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We report the preparation of Tc-optimized Bi2Sr2Ca1Cu2O8+δ thin films on SrTiO3 substrates using a planar dc-sputtering method. The oxygen content of these films is adjusted in situ by controlling the oxygen flow during sputtering. The oxygen content can be varied continuously from the overdoped state (Tc=72 K) to the condition with optimum oxygen content (Tc=88 K), and further, to the underdoped state (Tc=76 K). The oxygen content is determined by x-ray measurements of the c-axis lattice parameter.

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We demonstrate that the surface morphology of 20–200-nm-thick magnetron-sputtered Y1Ba2Cu3O7 films can be optimized by careful control of the plasma current. The optimization can be performed at different substrate temperatures allowing us to maximize the transition temperature Tc and the homogeneity of the films independently from the optimization of the surface morphology. This sequence allows us to retain the characteristic high Tc values (Tc≳90 K, Jc≳106 A/cm2 at 77 K). To obtain very thin films (<40 nm) with similar superconducting properties, the deposition temperature has to be ramped during the sputter process.

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