High-current-density superconductor thin films and methods for their production

Claim 2

Thin-film, high current density superconductor device characterized by high critic temperatures, which device comprises: a) a substrate, on which the following are deposited in succession: b) a layer formed by a polycrystalline alloy; c) a polycrystalline layer formed by metal oxides; d) a superconductor layer; - with said (b) crystalline layer being a polycrystalline layer of a homogeneous binary alloy of two elements having melting points different from each other, and having a polycrystalline structure with a preferential orientation; -with said (c) polycrystalline layer being a layer formed by metal oxides, used as crystalline buffers, having a structure compatible with the superconductor film; - with said (d) superconductor film being a film of a material of the type of YBa₂Cu₃O 7-x having a polycrystalline structure with a preferential orientation.

Claim 3

Device according to claim 1, endowed with good characteristics of superconductivity at temperature higher than or equal to 77°K.

Claim 4

Device according to claim 1, characterized in that the (a) substrate indifferently is either an amorphous substrate, or a crystalline substrate.

Claim 5

Device according to claim 1, characterized in that the binary alloy of the (b) layer is preferably formed by a pair of metals, the components of which are selected from the following metals: copper, silver and gold.

Claim 6

Device according to claim 1, characterized in that the crystals of the (b) layer show a preferential orientation.

Claim 7

Device according to claim 1, characterized in that said (c) polycrystalline layer is a layer formed by metal oxides compatible with the (d) superconductor layer, preferably SrTiO₃ or ZrO₂, used as crystalline buffers for the superconductor films.

Claim 8

Device according to claim 1, characterized in that said (d) superconductorlayer is a layer of YBa₂Cu₃O 7-x with 0 < x < 0.5 having a polycrystalline structure lacking oxygen as compared to the stoichiometric amounts.

Claim 9

Device according to claim 1, characterized in that the crystals of the (d) superconductor layer show a preferential orientation, thus enabling a higher J c to be achieved.

Claim 10

Process for preparing the superconductor device according to claims from 1 to 8, characterized in that: - a first element is deposited, by means of the technique of heat-evaporation under vacuum, or of sputtering, in the form of an either amorphous or microcrystalline layer, on the (a) substrate; - on the so-formed first layer, a second element is deposited by means of the same deposition techniques, which has a lower melting temperature than the first element, and is capable of forming a homogeneous solid solution with said first element, by operating under a constant temperature higher than the melting temperature of the second element, and close to, but lower than, the melting temperature of the first element, so as to cause the first element to gradually melt in the form of a liquid alloy with the second element, and it to crystallize in the form of a solid, binary ad homogeneous alloy, with a (b) polycrystalline layer being formed; - on the so-formed (b) polycrystalline layer, a (c) polycrystalline layer formed by metal oxides is deposited by means of the technique of sputtering, or of heat-evaporation under vacuum, and said (c) layer is grown in epitaxial or quasi-rheotaxial growing mode, in the form of a polycrystalline layer of metal oxides; - the device is completed by means of the further deposition of the superconductor layer, by means of a process of sputtering combined with conditions of epitaxy or of quasi-rheotaxy, so as to duplicate the morphology of the underlying layer in the superconductor layer under way of formation.

Claim 11

Process for the preparation of the superconductor device according to claims from 1 to 8, characterized in that the superconducting phase is evidenced after an annealing of the film under an O₂ atmosphere at a temperature of about 800°C.

Claim 12

Process according to claim 10, characterized in that in the formation of the (b) layer, the process is carried out with two metals, the melting points of which are different from each other by at least 50°C, and the deposition of the second element is carried out at a temperature lower than the melting temperature of the first element.