Superconductor technology: apparatus – material – process – Processes of producing or treating high temperature... – Process of making wire – tape – cable – coil – or fiber
Reexamination Certificate
2002-03-19
2003-12-30
Dunn, Tom (Department: 1725)
Superconductor technology: apparatus, material, process
Processes of producing or treating high temperature...
Process of making wire, tape, cable, coil, or fiber
C505S470000, C505S472000, C505S739000, C427S528000, C427S531000, C148S096000, C205S157000, C205S170000, C205S333000, C156S150000
Reexamination Certificate
active
06670308
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
FIELD OF THE INVENTION
The invention relates generally to epitaxial layers on biaxially textured surfaces and articles made therefrom. More specifically, the invention relates to a process for depositing epitaxial layers on biaxially textured substrates and associated articles.
BACKGROUND OF THE INVENTION
Many device applications require control of the grain boundary character of polycrystalline materials which form part of the device. For example, in high temperature superconductors grain boundary characteristics are important. The significant effect of grain boundary characteristics on current transmission across superconductor grain boundaries has been clearly demonstrated for Y123. For clean, stoichiometric boundaries, the grain boundary critical current J
c
(gb) appears to be determined primarily by the grain boundary misorientation. The dependence of J
c
(gb) on misorientation angle has been determined by Dimos et al. [1] in Y123 for several grain boundary types, which can be formed in epitaxial films on bicrystal substrates. These include [001] tilt, [100] tilt, and [100] twist boundaries [1]. In each case, high angle grain boundaries were found to be weak-linked. The J
c
value decreases exponentially with increasing grain boundary misorientation angle in artificially fabricated bicrystals of YBCO films [1]. The low J
c
observed in randomly oriented polycrystalline Y123 can be explained by the small percentage of low angle boundaries, the high angle grain boundaries impeding long-range current flow.
Recently, the Dimos experiment has been extended to artificially fabricated [001] tilt bicrystals in Tl
2
Ba
2
CaCu
2
O
8
[2], Tl
2
Ba
2
Ca
2
Cu
3
O
x
[3], TlBa
2
Ca
2
Cu
2
O
x
[4] and Nd
1.85
Ce
0.15
CuO
4
[3]. In each case it was found that, as in Y123, J
c
depends strongly on the distribution of grain boundary misorientation angles. Although no such measurements have yet been made on Bi-2223, data on current transmission across artificially fabricated grain boundaries in Bi-2212 indicates that most large angle [001] tilt [3] and twist [5,6] grain boundaries are weak links, with the exception of some coincident site lattice (CSL) related boundaries [5,6]. It is likely that the variation in J
c
with grain boundary misorientation in Bi-2212 and Bi-2223 will be similar to that observed in the well characterized cases of Y123 and Tl-based superconductors. Hence in order to fabricate high temperature superconductors with very high critical current densities, it is necessary to biaxially align the grains to produce a high percentage of low angle grain boundaries. This has been shown to result in significant improvement in the superconducting properties of YBCO films [7-10].
A simple method to fabricate long lengths of textured substrates with primarily low-angle grain boundaries for epitaxial deposition of high temperature superconducting (HTS) materials was proposed by Goyal et al. [10]. This method is known as Rolling-Assisted-Biaxially-Textured-Substrates (RABiTS). Four U.S. patents have been issued on this process and related process variants (U.S. Pat. Nos. 5,739,086, 5,741,377, 5,898,020 and 5,958,599). In the RABiTS method, the substrate formed has primarily low angle grain boundaries. A patent has also been issued on the fabrication of biaxially textured alloy substrates by Goyal et al. (U.S. Pat. No 5,944,966). An important issue in the successful use of alloy substrates in many applications is the ability to deposit high quality epitaxial buffer layers on the substrate.
References Cited:
1. D. Dimos, P. Chaudhari, J. Mannhart, and F. K. LeGoues, Phys. Rev. Lett. 61, 219 (1988); D. Dimos, P. Chaudhari, and J. Mannhart, Phys. Rev. B 41, 4038 (1990).
2. A. H. Cardona, H. Suzuki, T. Yamashita, K. H. Young and L. C. Bourne, Appl. Phys. Lett., 62 (4), 411, 1993.
3. M. Kawasaki, E. Sarnelli, P. Chaudhari, A. Gupta, A. Kussmaul, J. Lacey and W. Lee, Appl Phys. Lett., 62(4), 417 (1993).
4. T. Nabatame, S. Koike, O B. Hyun, I, Hirabayashi, H. Suhara and K. Nakamura, Appl. Phys. Lett. 65 (6), 776 (1994).
5. N. Tomita, Y. Takahashi and Y. Ishida, Jpn. J. Appl. Phys., 29 (1990) L30; N. Tomita, Y. Takahashi, M. Mori and Y. Ishida, Jpn. J. Appl. Phys., 31, L942 (1992).
6. J. L. Wang, X. Y. Lin, R. J. Kelley, S. E. Babcock, D. C. Larbalestier, and M. D. Vaudin, Physica C, 230,189 (1994).
7. Y. lijima, K. Onabe, N. Futaki, N. Sadakata, O. Kohno and Y. Ikeno, J. of Appl. Phys., 74, 1905 (1993).
8. R. P. Reade et al., Appl. Phys. Lett., 61, 2231 (1992).
9. X. D. Wu, S. R. Foltyn, P. Arendt, J. Townsend, C. Adams, I. H. Campbell, P. Tiwari, Y. Coulter and D. E. Peterson, Appl. Phys. Lett., 65, 1961 (1994).
10. A. Goyal, D. P. Norton, D. M. Kroeger, D. K. Christen, M. Paranthaman, E. D. Specht, J. D. Budai, Q. He, B. Saffian, F. A. List, D. F. Lee, E. Hatfield, P. M. Martin, C. E. Clabunde, J. Mathis and C. Park,
Special
10
th anniversary on High Temperature Superconductors of J. of Materials Research
, vol. 12, pgs. 2924-2940, 1997.
SUMMARY OF THE INVENTION
This invention provides a method for electrochemical deposition of epitaxial layers and formation of epitaxial articles. The method provides an inexpensive, non-vacuum technique that can proceed at a very high rate.
An epitaxial article is formed where at least one layer of the article is deposited using an electrochemical process. A substrate is provided having a biaxially textured surface. A substantially single orientation epitaxial layer deposited by an electrochemical process is disposed on and in contact with the biaxially textured surface.
A substantially single orientation epitaxial layer, as used herein, refers to a single orientation epitaxial layer having only one epitaxial crystallographic relationship with the surface in question. The substantially single orientation epitaxial layer preferably provides both in-plane texture and out-of-plane texture of less than 15 degrees FWHM, more preferably being less than 10 degrees FWHM.
The substrate can be a rolled and annealed biaxially-textured substrate having a biaxially textured metal surface. Textured metal surfaces can include Cu, Ag, Ni, Fe, Pd, Pt, Al, and alloys thereof. The substrate can also be a single crystal substrate. The substrate can be Si or GaAs, these substrates preferably being single crystal substrates.
The substantially single orientation epitaxial layer can be a metal or metal alloy layer, the metal or metal alloy layer selected from Cu, Ag, Ni, Fe, Pd, Pt and Al, and alloys thereof. The substantially single orientation epitaxial layer can provide both in-plane texture and out-of-plane texture of less than 10 degrees FWHM. At least one epitaxial buffer layer can be disposed on the substantially single orientation epitaxial layer.
The article can include an epitaxial electromagnetically active layer, such as a superconducting layer, disposed on and in contact with the epitaxial buffer layer. The superconductor layer can be an oxide superconductor. The oxide superconductor is preferably selected from REBa
2
Cu
3
O
7
where RE is a rare earth element, and (Bi, Pb)
1
Sr2Ca
n−1
Cu
n
O
2n+2
, where n is an integer between 1 and 4, (Tl, Pb)
1
Ba
2
Ca
n−1
Cu
n
O
2n+2
, where n is an integer between 1 and 4, and (Hg, Tl, Pb)
1
Ba
2
Ca
n−1
Cu
n
O
2n+2
, where n is an integer between 1 and 4. It is noted that (Bi, Pb) and (Tl, Pb) and (Hg, Tl, Pb) as used above imply any amount of doping of Pb, in (Tl, Pb) and (Bi, Pb) compounds and any amount of doping of Tl and Pb in (Hg, Tl, Pb) compounds. Furthermore, doping of Ca in RE for the REBa
2
Cu
3
O
7
compound is also possible.
A method for electrochemically depositing epitaxial layers on substrates includes the step of providing a substrate with a textured surface. A substantially single orientation epitaxial layer is electrochemically deposited on the textured surface.
Akerman & Senterfitt
Cooke Colleen P
Dunn Tom
UT-Battelle LLC
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