Stock material or miscellaneous articles – Composite – Of inorganic material
Patent
1996-09-23
1999-06-29
Yamnitzky, Marie
Stock material or miscellaneous articles
Composite
Of inorganic material
428701, 428702, 428930, 2525191, 25251913, 505120, 505121, 505125, 505190, 505191, 505210, B32B 900, H01L 3912
Patent
active
059166975
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a superconducting material in the form of a film consisting of monomolecular layers superposed with one another on a substrate, including at least one first assembly of layers which constitutes an electric charge reservoir, and at least one second assembly of layers which forms a superconducting cell and which consists of a certain number n of superconducting layers, separated from one another by intermediate layers, the charge reservoir and the superconducting cell being adjacent in the stack of layers.
As used in this context, the term "monomolecular layer" indicates a layer consisting of a single thickness of the atoms or molecules constituting said layer.
A material as defined above is disclosed, for example, in document EP-A-0 305 292. However, in view of the method for obtaining the material which is disclosed in this document, it is probable that its layers are not strictly monomolecular and have numerous aggregates in which the species constituting the layers are distributed over a plurality of thicknesses (three-dimensional aggregates).
Furthermore, in several known examples of superconducting materials, the superconducting layers consist of a planar copper oxide, in general CuO.sub.2, often referred to as cuprate.
Known superconducting materials have a critical temperature of no more than 135K at atmospheric pressure, and 155K under very high pressure.
In other words, known superconducting materials must be cooled to below 135K at atmospheric pressure in order to become superconductors, which leads to very high operating costs and great technical difficulties.
The object of the present invention is to overcome this drawback.
To this end, according to the present invention, a superconducting material of the type in question is essentially characterized in that n is an integer at least equal to 4 and in that the intermediate layers have the chemical formula Ca.sub.1-x M.sub.x and are free of strontium, x being a real number at least equal to 0 and at most equal to 0.2, M being an element having an ionic radius close to that of the Ca.sup.2+ ion, and the intermediate layers being optionally complete.
By virtue of these arrangements, the critical temperature of the superconducting material is very greatly increased and, in at least one example, reaches 250K.
To achieve such results, it is essential that the growth mechanism of the layers is strictly monomolecular (atomic layer after atomic layer) in order to avoid mixing by thermal diffusion of the layers already deposited.
In advantageous embodiments, one and/or other of the following arrangements are employed: calcium oxide, which are separated by at least one layer composed of at least one metal oxide; Bi, Hg, Tl and Cu; charge reservoirs.
A further subject of the present invention is components comprising a material as defined above, in particular components employing the resistance, which is close to zero, of superconducting materials, such as interconnections, fast transistors and microwave components, or else components using Josephson junctions, such as superconducting quantum interference devices ("SQUIDs") and fast memory or switching devices for digital electronics.
Other characteristics and advantages of the material according to the invention, as well as the method for obtaining this material, will emerge during the following description of a preferred embodiment, given by way of nonlimiting example with reference to the appended drawings.
In the drawings:
FIG. 1 is a schematic sectional view representing a superconducting material according to a preferred embodiment of the invention;
FIG. 2 is a schematic view of an apparatus making it possible to fabricate the material according to the invention, and
FIG. 3 is a view representing the change over time of the intensity of an RHEED electron diffraction line during the deposition of a monomolecular layer.
In the particular embodiment represented in FIG. 1, the superconducting material according to the invention is in the form of a multilayer film deposited
REFERENCES:
patent: 5084265 (1992-01-01), Harada et al.
patent: 5264413 (1993-11-01), Bozovic et al.
CRC Handbook of Chemistry and Physics, 71st ed. (1990), CRC Press, Inc., p. 12-1.
"Low-Temperature Annealing Effect on Bi--Sr--Ca--Cu--O Thin Films Prepared by Layer-By-Layer Deposition", A. Tsukamoto, et al, Japanese Journal of Applied Physics, vol. 30, No. 5A, May 1991, pp. L830-L833, Tokyo, Japan.
"Hoch-T.sub.c -Supraleiter: Wie steht es mit den Anwendungen?", R. Hott, Phys Bl, 48 (1992) No. 5, pp. 355-358.
"Superconductivity of Bi.sub.2 -Sr.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.y (N=2, 3, 4, and 5) thin films prepared in situ by molecular-beam epitaxy technique", Y. Nakayama et al, J. Appl. Phys. 70(8), Oct. 15, 1991, pp. 4371-4377.
Lagues Michael
Lewiner Jacques
Ufinnova
Yamnitzky Marie
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