New deposition method of MgB2 thin film with thermal evaporation of Mg and sputtering of B

We are now developing a new in-situ deposition process for MgB2 film as a candidate method to mass-produce MgB2 thin film superconducting tape. In the new method, a MgB2 film is deposited on a heated metal substrate by a hybrid deposition method, which consists of thermal evaporation of magnesium and sputtering of boron. By using the hybrid deposition method, the substrate temperature can raise from 250 to 350°C, while its fluctuation is kept less than 1°C, which will improve the quality and reproducibility of MgB2 film in mass production. The Jc of MgB2 film deposited by the hybrid deposition method at 20 K and self-field was more than 30,000 A/mm2, which was better than the results reported by the two-step in-situ process using DC sputtering and 830°C high-temperature post annealing [17] or by the as-grown depostion using sputttering targets of Mg and B [18]. Although we obtained better Jc than other deposition methods that use sputtering process, the Jc is still lower than the value we obtained by using a co-evaporation method with electron beam (EB). We investigated the film structure and Jc-B-T properties of the film made by the hybrid deposition method and compared them with those of the film made by co-evaporation. From the analysis results, we think the reasons for the lower Jc are the larger amount of heterogeneous phases such as magnesium oxides in the film and the amorphous B phase under the MgB2. We expect to improve the the crystal qualities and superconductivities of the MgB2 film deposited by the new method by removing impurities in Ar gas during sputtering and thinning the B amorphous phase by increasing the Mg deposition rate in the initial stage of deposition.