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

Abstract

We are now developing a new in situ deposition process for MgB _2 film as a candidate method to mass-produce MgB _2 thin film superconducting tape. In the new method, a MgB _2 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 MgB _2 film in mass production. The J _c of MgB _2 film deposited by the hybrid deposition method at 20 K and self-field was more than 30,000 A mm ^−2 , which was better than the results reported by the two-step in situ process using DC sputtering and 830 °C high-temperature post annealing [ 1 ] or by the as-grown depostion using sputttering targets of Mg and B [ 2 ]. Although we obtained better J _c than other deposition methods that use sputtering process, the J _c is still lower than the value we obtained by using a co-evaporation method with electron beam (EB). We investigated the film structure and J _c –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 J _c are the larger amount of heterogeneous phases such as magnesium oxides in the film and the amorphous B phase under the MgB _2 . We expect to improve the the crystal qualities and superconductivities of the MgB _2 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.

Keywords

• superconductor
• MgB2
• thin film