High quality fully in-situ MgB2 thin films obtained by DC magnetron sputtering

MgB2 thin films were grown in-situ at INFM- University of Naples by a magnetron sputtering technique in a UHV system (10(-7) Pa) equipped with 3 focused 2" magnetron sources (a stoichiometric MgB2 and metallic Mg and B targets by Superconducting Components Inc.). The substrates (sapphire or MgO) were placed "on axis" at 7 cm from the target surface on the surface of a molybdenum heater that could be operated up to 1000degreesC under vacuum. Best results were obtained codepositing MgB2 and Mg at equal sputtering power (500W) for 10min on cold substrates, resulting in a Mg rich Mg-B precursor film. The films were then annealed in-situ at 830degreesC for 10 min in a In sealed Nb box in presence of saturated Mg vapor. The process is highly reproducible and can be easily scaled to produce large area films. The resulting films were about 1 mum thick, with 100nm surface roughness as measured by AFM Resistive transition showed a maximum T-c of 35K and a transition width lower than 0.5K. The residual resistivity ratio was 1.6 for the best sample. Resistivity measurements in external magnetic field up to 8 T have been performed both in parallel and perpendicular configuration. The upper critical magnetic field vs. temperature behavior has been determined from the experimental data and the superconducting anisotropy has been calculated for samples with different T-c.