Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
1992-08-18
2001-06-26
Krynski, William (Department: 1774)
Stock material or miscellaneous articles
Composite
Of inorganic material
C428S689000, C428S930000, C505S121000, C505S125000, C505S126000, C505S220000, C505S234000, C505S235000, C505S236000, C505S238000, C505S239000
Reexamination Certificate
active
06251530
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a thin film of a high-temperature superconductor compound, and to a method for producing the thin film.
REFERENCES
Berkley, D. D., et al.,
Appl. Phys. Lett.
53:1973 (1988).
Bozovic, I., et al.,
Science and Technology of Thin Film Technology II
(R. McConnell, et al., eds.), Plenum, N.Y. p.267 (1990).
Bozovic, I., et al.,
Journal of Superconductivity
5:19 (1992).
Chakoumakos et al.,
Journal of Materials Research
4(4):767 (1989).
Eckstein, J. N., et al.,
Appl. Phys. Lett.
57:531 (1990).
Fujita et al.,
Applied Physics Letters
56(3):295-297 (1990).
Hor et al.,
Physical Review Letters
58(9):911-912 (1987).
Kawai, T., et al., to be published in
Proc. Mat. Res. Soc. Symp. S: Layered Superconductors: Fabrication, Properties and Applications
(D. T. Shaw, et al., eds.) (1992).
Klausmeier-Brown, M. E., et al., Appl. Phys. lett, 60:657 (1992).
Li, Q., et al.,
Phys. Rev. Lett.
64:3086 (1990).
Lowndes, D. H., et al.,
Rhys. Rev. Lett.
65:1160 (1990).
Moodenbaugh et al.,
Physical Review Letters
58(18):1885-1887 (1987).
Murphy et al.,
Physical Review Letters
58(18):1891-1894 (1987).
Nakayama et al.,
Japanese Journal of Applied Physics
28(10):L1809-L1811 (1989).
Phillips, J. C., “Physics of High-T
c
Superconductors”, Academic Press (1989).
Schlom et al.,
Journal of Crystal Growth
) (1989).
Siegrist, T., et al.,
Nature
334:231 (1988).
Tarascon et al.,
Physical Review B
38(13):8885-8892 (1988).
Thompson, L. F., et al., eds. “Introduction to Photolithography”, ACS Symposium Series, Washington, D.C., (1983).
Triscone, J. M., et al.,
Phys. Rev. Lett.
64:3086 (1990).
Wu et al.,
Physical Review Letters
58(9):908-910 (1987).
BACKGROUND OF THE INVENTION
High temperature superconducting (HTSC) compounds including mixed oxides of rare earth, alkaline earth and copper metals are known (e.g., Phillips). Wu et al., and Hor et al. have discussed Y—Ba—Cu—O compound systems as exhibiting HTSC. Moodenbaugh et al., Murphy et al., and Hor et al. disclose additional rare earth, alkaline earth, copper metal mixed oxide compounds exhibiting superconductive properties. Additional superconducting mixed metal oxide compounds of La—Sr—Cu—O, Bi—Sr—Ca—Cu—O and Tl—Ba—Ca—Cu—O have also been developed.
Tarascon et al. disclose Bi—Sr—Ca—Cu—O superconducting compounds of the formula Bi
2
Sr
2
Ca
n-1
Cu
n
O
y
wherein n=1, 2 or 3 which are prepared by firing at high temperatures stoichiometric amounts of Bi
2
O
3
, SrCO
3
or SrO
2
, and CuO powders. Similarly, Chakoumakos et al. have disclosed the preparation of Bi—Sr—Cu—O compounds, particularly Bi
2
Sr
2
CuO
6
compounds of the formula Bi
2
Sr
2
Ca
n-1
Cu
n
O
x
, where n is from 1 to 5 which are formed by molecular beam epitaxy of layered structures. Eckstein et al. have also disclosed the formation of thin films of perovskite-related high-temperature superconductors using atomic layer molecular beam epitaxy.
One of the major goals in the technology of thin high-temperature superconducting electronics is to fabricate trilayer SIS Josephson Junctions. The major obstacle to achieving this goal is the large anisotropy of cuprate superconductors of the type referenced above, which results in a very short coherence length in the direction perpendicular to the CuO
2
layers, as well as in generally small critical current, j
c
⊥, in that direction. The structural cause of at least a major part of this anisotropy is the existence of so-called “blocking layers” such as the Bi—O layer in Bi
2
Sr
2
CaCu
2
O
8
(e.g., Beyers)
It is for that reason that a substantial interest has been generated by the first successful synthesis of (Sr,Ca)CuO
2
. This so called “infinite layer” cuprate, also known as the “parent compound” of cuprate superconductors, was synthesized in 1988 at the AT&T Bell Laboratories (Siegrist). This compound has no “blocking layers”. However, its transport properties were disappointing, in that the material was found to be semiconducting and showed no traces of superconductivity.
Several Japanese groups have investigated this material, and there have been some reports of superconductivity in the material in the popular press. So far, the claims failed to be confirmed in other laboratories.
More recently, data on a (Sr,Ca)CuO
2
thin film which showed resistance that at first increased with decreasing temperature in a semiconducting like-manner, but then turned over to decrease below about 60-80 K, has been reported. However, conductor resistance never reached zero, i.e., the samples were not completely superconducting (Kawai). The composition of the presumed minority superconducting phase was not identified.
SUMMARY OF THE INVENTION
In one aspect, the present invention includes a thin film of a high-temperature superconducting compound having the formula M
1-x
CuO
2-y
, where M is one or more of the alkaline earth metals Ca, Sr, or Ba, x is 0.05 to 0.3, and x>y. The compound is characterized by zero resistivity at a temperature of at least 35 K. In a preferred embodiment, M is Ca and Sr, at a ratio of Ca to Sr between about 1:1 to 5:1.
The compound may be formed of alternating atomic monolayers of CuO
2-y
, and M, where the layer formed by M has between about 5-30% metal-atom vacancies, and substantially more such cation vacancies than oxygen-atom vacancies in the CuO
2-y
layers.
Also disclosed is a superconducting device composed of a substrate, and layered on the substrate, a thin film of a high-temperature superconducting compound of the type just described.
In another aspect, the invention includes a method of forming a superconducting device which includes a superconducting thin-film compound characterized by zero resistivity at a temperature of at least 35 K, and preferably higher, e.g., 40 K.
The method includes depositing on a substrate, by molecular beam epitaxy, successive atomic monolayers of Cu, and an alkaline earth metal M selected from one or more of Ca, Sr, and Ba, at a ratio of M:Cu of between 0.70-0.95:1. During the deposition step, a stream of ozone is directed against the deposited material on the substrate, thus forming alternate layers of CuO
2-y
and M, where the layer formed by M has between about 5-30% metal-atom vacancies, and substantially more vacancies than oxygen-atom vacancies in the CuO
2-y
layers. The layering steps are repeated until a desired film thickness is achieved.
These and other objects and features of the invention will be more fully understood when the following detailed description is read in conjunction with the accompanying drawings.
REFERENCES:
patent: 4983575 (1991-01-01), Komuro
patent: 5047390 (1991-09-01), Higashino
Berkley, D.D., et al., “In situ Formation of Superconducting YBa2Cu3O7-xThin Films Using Pure Ozone Vapor Oxidation”,Appl. Phys. Lett.,V. 53, No. 20, pp. 1973-1975, Nov. 1988.
Bozovic, I., et al., “In situ Growth of Superconducting Single Crystal Bi-Sr-Ca-Cu-O Thin Films by Molecular Beam Epitaxy”,Science and Technology of Thin Film Superconductors II,(R. McConnell, et al., eds.), Plenum, NY, pp. 267-272, 1990.
Bozovic, I., et al., Superconductivity in Epitaxial Bi2Sr2Cu06/Bi2Sr2CaCu208Superlattices: The Superconducting Behavior of Ultrathin Cuprate Slabs,Journal of Superconductivity,V. 5, No. 19, pp. 19-23, 1992.
Chakoumakos, B.C., et al., “Characterization and Superconducting Properties of Phases in the Bi-Sr-Cu-O System”,Journal of Materials Research,V. 4, No. 4, pp. 767-780, Jul./Aug. 1989.
Eckstein, J.N., et al., “Atomically Layered Heteroepitaxial Growth of Single-Crystal Films of Superconducting Bi2Sr2Ca2Cu3Ox”,Appl. Phys. Lett.,V. 57, pp. 931-933, Aug. 1990.
Fujita, J., et al., “In situ epitaxial Growth of Bi2(Sr,Ca)3Cu2OxFilms by Ion Beam Sputtering with an Atomic Oxygen Source”,Appl. Phys. Lett.,V. 56, No. 3, pp. 295-297, Jan. 1990.
Hor, P.H., et al., “High-Pressure Study of the New Y-Ba-Cu-0 Superconducting Compound System”,Physical Review Letters,V. 58, No. 9, pp. 911-912, Mar. 2, 1987.
Klausmeier-Brown, M. E., et al., “Accurate Measurement of Atomic Beam Flux by Pseudo-Double-Beam Atmo
Bozovic Ivan
Eckstein James N.
Krynski William
Varian Inc.
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