Properties of MgB₂thin films made by radio frequency magnetron co-sputtering

Abstract

We have studied properties of the superconducting MgB 2 thin films made on sapphire substrates by radio frequency (rf) magnetron co-sputtering of Mg and B. The effects of annealing temperature and Mg:B ratio on the superconducting properties of the film were investigated. Films were prepared by room-temperature co-deposition of Mg and B using two guns and annealed in situ to form the superconducting MgB 2 phase. Ar sputtering pressure was 20 mtorr with 5% of hydrogen gas to trap remnant oxygen gas in the deposition chamber. Average rf power density of Mg target was varied from 2 to 4 W cm −2 with that of B fixed at 12 W cm −2 . An additional Mg layer was deposited on top to make up for Mg loss during in situ annealing. Films were heated up to 500-750 • C at the rate of 60 • C min −1 , annealed for 20 min, and naturally cooled down by turning off the heater. The best results were obtained for films deposited with the rf power of Mg target at 50 W and annealed at 700 • C. The mechanism for MgB 2 formation in low-pressure annealing is believed to be that during annealing the local Mg vapour pressure inside the film falls within the thermodynamic window.

As-grown superconducting MgB2thin films prepared at extreme deposition conditions

“…The transition width T (=T on c −T 0 c ) is much larger for F2 ( T ≈ 8 K) than for F1 ( T ≈ 1 K). T reflects the degree of local inhomogeneity in T c [5], which, to our surprise, seems to be larger in sample F2 (which is of better structural quality) than in F1. Further studies are required to clarify this point.…”

“…The fabrication of SC MgB 2 thin films, junctions and heterostructures is appealing for technological device applications [2][3][4]. A vast amount of reports on MgB 2 thin film preparation methods exist in the literature [2], including those based on magnetron sputtering [5][6][7], pulsed laser deposition (PLD) [8][9][10], hybrid physical-chemical vapor deposition [11,12], precursor film post-processing [13][14][15], ion beam synthesis [16], and co-deposition combined with molecular beam epitaxy (MBE) [17][18][19][20][21][22][23][24][25].…”

An overview of progress in Mg-based hydrogen storage films*

“…There are a series of sputtering methods, for instance, according to the presence or absence of an applied magnetic field, sputtering is divided into magnetron sputtering and nonmagnetron sputtering; according to the type of current of power source, sputtering can be divided into direct current (DC) sputtering and radio frequency sputtering; according to the presence or absence of reactive gases during sputtering, sputtering is divided into reactive sputtering and non-reactive sputtering; according to the continuity of the current of power source, sputtering can be divided into continues sputtering and pulsed sputtering. [41][42][43][44][45][46][47][48][49][50][51] If the plasma is not generated by the bombardment of the particles, which are accelerated in the electric field, with the target, but by the interaction of pulsed laser with the target, then the deposition is called pulsed laser sputtering deposition or pulsed laser deposition (PLD). [52,53] For Mg-based thin films, hydrogenation can be achieved in two ways: air-exposed hydrogenation and plasma-based hydrogenation, which is realized in reactive sputtering.…”

Fabrication of Planar Sandwich Type Josephson Junctions Using ${\rm MgB}_{2}$ Thin Film With a Nb Counter Electrode

“…They are in-situ annealing of Mg-B film and ex-situ annealing of B precursor in Mg vapor. The in-situ annealing method has been reported previously [16].…”