A study was made of the properties of superconducting thin films deposited onto sapphire substrates by the radio-frequency magnetron co-sputtering of Mg and B. The effects of annealing temperature and Mg:B ratio upon the superconducting properties of the film were investigated. Films were prepared by the room-temperature co-deposition of Mg and B, using 2 guns, and were annealed in situ to form the superconducting phase. The Ar sputtering pressure was 20mtorr, with 5% of H to trap remnant O in the deposition chamber. The average rf power density of the Mg target was varied from 2 to 4W/cm2, with that of B fixed at 12W/cm2. An additional Mg layer was deposited on top, to compensate for Mg loss during in situ annealing. The films were heated to 500 to 750C, at a rate of 60C/min, annealed for 20min, and cooled naturally. The best results were obtained for films deposited with the rf power of the Mg target at 50W, with annealing at 700C. The mechanism of MgB2 formation in low-pressure annealing was believed to be that, during annealing, the local Mg vapour pressure within the film fell within the thermodynamic window.

Properties of MgB2 Thin Films made by Radio Frequency Magnetron Co-Sputtering. S.G.Lee, J.R.Ahn, Y.Kim, S.H.Moon, K.W.Lee, I.S.Kim, Y.K.Park: Superconductor Science and Technology, 2003, 16, 1550-3