Superconductor technology: apparatus – material – process – Processes of producing or treating high temperature... – Coating
Patent
1992-06-16
1994-05-17
King, Roy V.
Superconductor technology: apparatus, material, process
Processes of producing or treating high temperature...
Coating
505704, 505730, 505731, 505732, 505741, 505742, 505476, 505501, 427 62, 427 63, 4271263, 427282, B05D 512
Patent
active
053128036
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a superconducting film, and more particularly, to a process for producing a film of a bismuth based perovskite superconducting material containing lead.
A superconducting film wiring currently practicable in the art is a Bi-base superconducting film wiring.
Examples of the Bi-base superconducting film wiring realizable in the art include that comprising a 10 K phase having a superconducting transition temperature, i.e., a critical temperature, Tc, of 10 K at which a normal conducting phase is transferred to a superconducting phase, that comprising a 80 K phase having a critical temperature, Tc, of 80 K, and that comprising a 110 K phase having a critical temperature, Tc, of 110 K, but it is known in the art that it is very difficult to prepare a Bi-based superconducting film wiring of a 110 K phase.
In the superconductor field, however, since a high superconducting transition temperature greatly benefits the cooling, such as a reduction of size of the whole equipment through a simplification of a cooling device, a Bi-based superconducting wiring of a 110 K phase is required.
DESCRIPTION OF THE RELATED ART
In general, a Bi-based superconducting film has been produced by depositing a material film on a substrate by sputtering, vacuum evaporation or the like and subjecting the material film to a post-heat treatment to synthesize a superconducting film. In this case, the patterning is usually conducted either by using a mask in the deposition of the superconducting material film or by conducting etching after the deposition.
A very precise control of the temperature is necessary for producing a Bi-based superconducting film comprising a 110 K phase, and the formation of a single phase of a 110 K phase without the addition of Pb to the composition has been regarded as very difficult. As the present inventors have already reported (see "Appl. Phys. Lett., 54", pp. 1362-1364 (1989)), however, since Pb vigorously evaporates during sintering, the amount of Pb becomes insufficient even in the case of a film having wide pattern width, and thus it is not easy to form a Bi-based superconducting film comprising a 110 K phased.
The present inventors have succeeded in forming a Bi-based superconducting film having a single phase of a 110 K phase by adding Pb in a considerably higher concentration than that in the case of a bulk or the like (see "Appl. Phys. Lett., 55", pp. 1252-1254 (1989)).
In general, in a Bi-based superconducting film, there exists a superconducting phase wherein the critical temperature, Tc, varies depending upon the difference in the number of Cu-O planes contained in the unit cell. At the present time, in the Bi-based superconducting film represented by the formula Bi.sub.2 Sr.sub.2 Ca.sub.n-1 Cu.sub.n O.sub.x, three superconducting compounds are known, i.e., a phase having a Tc of 10 K wherein n is 1, a phase having a Tc of 80 K wherein n is 2, and a phase having a Tc of 110 K wherein n is 3.
The synthesis of a superconducting film comprising a 110 K phase having the highest critical temperature, Tc, is expected from the practical viewpoint, but as described above, even in the case of a film having a width pattern width, the Pb vigorously evaporates during sintering and reached a state such that the amount of Pb becomes insufficient. For this reason, a technique wherein a large amount of Pb is added has been developed. In this case, however, it has been found that the evaporation of Pb becomes more vigorous in the case of a pattern having a small line width, so that the proportion of the formation of the 110 K phase is decreased. When a larger amount of Pb is added to a pattern having a small line width, the superconducting material film partially melts during sintering to form a 110 K phase. The partial melting temperature is closely related to the proportion of Pb. Specifically, when the proportion of Pb is high, the superconducting material film unfavorably melts at a low temperature of about 840.degree. C. and the melting becomes
REFERENCES:
Nabatame et al, "Properties of Tl.sub.2 Ba.sub.2 Ca.sub.2 Cu.sub.3 O.sub.x thin films with a Critical Temperature of 122K Prepared by Excimer Laser Ablation", Jpn. J. Appl. Phys. vol. 29, No. 10, Oct. 1990, pp. L1813-L1815.
Ichikawa et al, "Highly Oriented Superconducting Tl-Ca-Ba-Cu Oxide Thin Films with 2-1-2-2 Phase", Appl. Phys. Lett. 53(10) Sep. 1988 pp. 919-921.
Lee et al, "Superconducting Tl-Ca-Ba-Cu-O Thin Films with Zero Resistance at Temperatures of up to 120K", Appl. Phys. Lett. 53(4) Jul. 1988 pp. 329-331.
A. Tanaka et al., "Pb-doped Bi-Sr-Ca-Cu-O thin films," Appl. Phys. Lett., vol. 54, No. 14, Apr. 3, 1989, pp. 1362-1364.
A. Tanaka et al., "Composition dependence of high T.sub.c phase formation in Pb-doped Bi-Sr-Ca-Cu-O thin films," Appl. Phys. Lett., vol. 55, No. 12, Sep. 18, 1989, pp. 1252-1254.
Kamehara Nobuo
Niwa Koichi
Tanaka Atsushi
Yamanaka Kazunori
Fujitsu Limited
King Roy V.
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