Superconductor technology: apparatus – material – process – Processes of producing or treating high temperature... – Coating
Patent
1992-06-17
1994-04-26
King, Roy V.
Superconductor technology: apparatus, material, process
Processes of producing or treating high temperature...
Coating
505730, 505731, 505728, 505742, 505476, 427 62, 427 63, 20419224, B05D 512, C23C 1400
Patent
active
053067029
DESCRIPTION:
BRIEF SUMMARY
DESCRIPTION
1. Field of the Invention
The present invention relates to a superconducting film, and more particularly to a process for producing a film of a bismuth-base perovskite superconducting material containing lead.
A superconducting film wiring currently practically used in the art is a Bi-based superconducting film wiring.
Examples of the Bi-based superconducting film wiring used in the art include a film 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, a film comprising an 80 K phase having a critical temperature, Tc, of 80 K, and a film comprising a 110 K phase having a critical temperature, Tc, of 110 K. Nevertheless, 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 is greatly beneficial when cooling, i.e., allows a reduction of the size of the whole equipment through a simplification of a cooling device, a Bi-based superconducting wiring comprising a 110 K phase should be easily realized.
2. 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 accomplished by using either a mask in the deposition of the superconducting material film or by conducting an etching after the deposition.
A very precise control of the temperature is necessary for producing a Bi-based superconducting film of 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)), since Pb is easily evaporated during sintering, the amount of Pb becomes insufficient even in the case of a film having a wide width, and thus it is not easy to form a Bi-based superconducting film of a 110 K phase.
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)).
To improve the critical current density, Jc, of a Bi-based superconducting film having a single phase of a 110 K phase, it is necessary to get strong electrical couples across grain boundaries. The facilitation of the flow of a current by an improvement in the orientation of the crystal is considered effective for this purpose. In this case, it is important that the grain boundary per se be reduced by increasing the size of the crystal grain diameter, with an improvement in the orientation. In this case also, it is difficult to form a large crystal of a 110 K phase due to the rapid evaporation of Pb during sintering.
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. Currently, in the Bi-based superconducting film represented by the formula Bi.sub.2 Sr.sub.2 Cu.sub.n Cu.sub.n-1 O.sub.x, there are three known superconducting compounds, 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 of a 110 K phase having the highest critical temperature, Tc, is expected from a practical viewpoint. As described above, however, even in the case of film with a large width pattern, the Pb easily evaporates during sintering and thus the amount of Pb becomes insufficient. For this reason, a technique wherein a relatively large amount of Pb is added has been deve
REFERENCES:
Kao et al, "Transformation of Superconducting Phases in (Bi,Pb)-Sr-Ca-Cu-O during Post-Annealing", Jpn. J. Appl. Phys. 28(9) Sep. 1989, pp. L558-L560.
T. W. Clyne & P. J. Withers (Editors) `Proceedings of The Second European Conference on Advanced Materials and Processes` 24 Jul. 1991, The Institute of Materials, Oxford, UK "Is Texture Necessary to Obtain High Critical Currents in Superconducting Ceramics?", C. M. Grovenor et al. *p. 102, line 1-2, paragraph 3*.
A. Tanaka et al., "Pb-doped Bi-Sr-Ca-Cu-O thin films," Appl. Phys. Lett., vol. 54, No. 14, Apr. 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. 1989, pp. 1252-1254.
Kamehara Nobuo
Niwa Koichi
Tanaka Atsushi
Fujitsu Limited
King Roy V.
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