The effects of in situ annealing upon the superconducting properties of thin films were investigated for the purpose of obtaining high critical temperatures close to the bulk value. The MgB2 thin films were fabricated by rf magnetron sputtering onto c-plane sapphire substrates. Thin films were produced by simultaneously sputtering pure B and a Mg metal target. Sputtering deposition was followed by in situ annealing in a high vacuum. To prevent the evaporation of Mg from the film surface, 2-step annealing was adopted: the first step was the crystallization stage at low-temperature annealing and the next was an improvement of the superconducting properties by annealing at high temperature. In the optimal annealing process (a thin film was first heated at 600C for 2h and then 650C for 2h) thin films with a zero resistivity temperature of 29K were consistently obtained.

Two-Step in situ Annealing Effects on Sputter-Deposited MgB2 Thin Films. Z.Mori, T.Doi, K.Eitoku, Y.Ishizaki, H.Kitaguchi, M.Okada, K.Saitoh, Y.Hakuraku: Superconductor Science and Technology, 2004, 17, 47-50