Reliable Preparation of High Quality Superconducting Thin MgB₂ Films for Application

Since the discovery of its superconductivity (J. Nagamatsu, N. Nakagawa, T. Muranka, et al., 2001, Nature, 410, 63), MgB₂ attracts considerable attention. A number of groups have intensively tried to fabricate high-quality MgB₂ films during the last years. However, the surface quality which is necessary for microelectronic device applications is still far from being achieved In this work we report the growth and the properties of high-quality films which are prepared in a two-step process: 1) deposition of the precursor films and 2) their annealing in Mg vapor with a specially designed, reusable reactor (C. B. Eom, et al., 2001, Nature, 411, 558). The films were grown on single crystal substrates of R-cut Al₂O₃ as well as of Al₂O₃ (100), (128° rot) LiNbO₃ and MgO (100). The highest value of T_c = 39.4 K was observed for films deposited at 770 K on sapphire and MgO and annealed at 1120 K for one hour. Our method allows also the growth of high-T_c smooth films with high reproducibility and opens perspectives for the use of MgB₂ films in microelectronics, especially for high-frequency applications.