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 massproduce 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.

High-temperature post-annealing to improve Jc -B-T properties of MgB2 thin film synthesized via hybrid deposition combining thermal evaporation of magnesium and sputtering of boron

“…It is necessary to develop a deposition technique suitable for incorporation in a reel-to-reel machine that is used for the synthesis of long MgB 2 -thin-film superconducting tapes. 17) The synthesis process for these machines involves the deposition of magnesium and boron on a heated long-tape substrate passed between the reels while taking up the substrate by the reels. Here, several magnesium and boron evaporation sources are arranged in line or in a matrix.…”

“…The technique comprises the thermal evaporation of magnesium and sputtering of boron. 17) The J c of the MgB 2 film deposited via this technique was 31 000 A mm −2 at 20 K under a self-field (0 T). However, the MgB 2 film exhibited a low J c of 380 A mm −2 at 20 K under a magnetic field of 1 T applied parallel to the film, and it is necessary to significantly increase the obtained J c under these conditions.…”

“…In this study, the J c -B-T properties of a MgB 2 film deposited by the proposed hybrid deposition are improved by high-temperature postannealing, and the change of MgB 2 film structure is investigated. conditions for the MgB 2 films, including those of sample (a) deposited in a previous study, 17) are listed in Table I. Sample (a) was obtained via deposition of a MgB 2 film on a 200 nm thick titanium film formed on a copper substrate.…”

Tunable p- and n-Type Tellurium-Free Mg3Bi2 Thermoelectric Thin Films by Thermal Coevaporation

“…31 The reliability of thermal evaporation of Mg is supported by other studies focusing on the coevaporation of Mg and B to form MgB thin films. 32,33 These considerations make thermal coevaporation of said constituents a promising technique to fabricate Mg x Bi y thin films.…”

“…However, already in 1979 Long et al had reported on the thermal coevaporation of Mg and Bi and the formation of a two-component alloy in which the compositional variations were below 0.5% . The reliability of thermal evaporation of Mg is supported by other studies focusing on the coevaporation of Mg and B to form MgB thin films. , These considerations make thermal coevaporation of said constituents a promising technique to fabricate Mg x Bi y thin films.…”