Buffer layers and articles for electronic devices

Details Buffer layers and articles for electronic devices Buffer layers and articles for electronic devices

2002-12-19

2004-07-20

Stein, Stephen (Department: 1775)

Stock material or miscellaneous articles

Composite

Of metal

C428S697000, C428S699000, C428S701000, C428S702000, C505S237000, C505S238000, C505S239000

Reexamination Certificate

active

06764770

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to materials and methods for depositing buffer layers on biaxially textured and untextured metallic and metal oxide substrates for use in the manufacture of superconducting and other electronic articles, and more particularly to substrates comprising RMnO
3
, R
1−x
A
x
MnO
3
, and combinations thereof wherein R comprises an element selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y, and A comprises an element selected from the group consisting of Be, Mg, Ca, Sr, Ba, and Ra.
BACKGROUND OF THE INVENTION
One standard architecture for the ion-beam assisted deposition (IBAD) based Y—Ba
2
—Cu
3
—O
x
(YBCO) coated conductors utilizing CeO
2
, yttria stabilized zirconia (YSZ), and MgO is YBCO/CeO
2
/YSZ/MgO(BAD)/Ni-alloy. Since very thin MgO (IBAD) layers are sufficient to get the necessary biaxial texture, it is essential to provide a simplified buffer layer architecture to grow YBCO films. Thinner buffers are needed to increase the engineering critical current density of the YBCO coated conductors. Another alternative architecture utilizing inclined substrate deposition (ISD) deposition is YBCO/CeO
2
/YSZ/MgO(ISD)/Ni-alloy. The reaction of the CeO
2
with YBCO always results in the formation of BaCeO
3
at the buffer/YBCO interface. From previous demonstrations of the growth of YBCO films on LaMnO
3
-buffered Ni substrates, we expected that the interface between LaMnO
3
(LMO) and YBCO should be perfect.
The fabrication of YBCO coated conductors requires an economic and robust process to produce the YBCO superconductor layer. The BaF
2
ex situ (BF) method requires two distinct processing steps whereby first a non-superconducting precursor layer is deposited onto the substrate and this precursor layer is subsequently annealed in a furnace to form the superconducting YBCO. The two steps may facilitate economic scale-up for long length coated conductor fabrication. On a suitable substrate or buffer layer, using the BF method, the YBCO can be grown as an epitaxial layer with high critical current density (J
c
). However, many buffer layer materials or substrates exhibit a deleterious chemical reactivity toward the precursor layer during the ex situ anneal to the extent that a high-J
c
epitaxial YBCO film cannot be obtained. Previously, a suitable buffer layer had been identified in the form of thin ceria, CeO
2
. This material exhibits a moderate reactivity toward the precursor layer (leading to the reaction product barium cerate, BaCeO
3
). The use of CeO
2
as a single buffer layer on metallic substrates is restricted to metal (Ni) diffusion through the CeO
2
into the YBCO. LMO appears to exhibit a reduced reactivity toward the BF precursor during the ex situ anneal, making it easier to form epitaxial, high-J
c
YBCO layers. It has also been demonstrated that LMO provides a barrier against Ni diffusion and can be used as a single buffer layer. Previously, a layer of YSZ was used to provide a diffusion barrier. On this YSZ, a thin layer of CeO
2
was required to enable compatibility with the BF ex situ process. A single LMO layer was expected to replace both the YSZ and CeO
2
layers and possibly even the first seed layers.
LaMnO
3
perovskite (LMO) has been extensively studied in the past years, since it is the parent compound of the family of oxides La
1−x
A
x
MnO
3
(A may be any alkaline earth metal), showing interesting properties such as colossal magnetoresistance or charge-ordering. In this family, the replacement of La for divalent A cations, oxides Mn
3+
to Mn
4+
, introducing holes in the Mn3d band and gives rise to metallic and/or ferromagnetic behavior. Even in the absence of chemical doping, LaMnO
3
shows the ability to accommodate the so-called oxidative-nonstoichiometry, which also involves the partial oxidation of Mn
3+
to Mn
4+
cations in samples of global composition LaMnO
3+8
. In fact the insertion of oxides is not possible in the perovskite structure, and the nonstoichiometry is incorporated via cation vacancies.
Recent work has demonstrated that LaMnO
3
and (La,Sr)MnO
3
perovskites are good buffer layers for growth of superconductors such as YBCO. This work suggests that LMO could be used as a single buffer layer on Ni and Ni—W substrates for growth of YBCO by either pulsed laser ablation or the ex-situ BF technique. It was also demonstrated that LMO could be grown epitaxially on MgO single crystal. This is important since it enables growth of such buffer layers on ion-beam assisted deposition (IBAD) or (ISD) produced, biaxially textured MgO on untextured metal substrates. However the YBCO films grown in these demonstrations on LMO buffers were very thin—only 0.2 &mgr;m to 0.3 &mgr;m. What would happen when thicker films, several microns in thickness are grown was desired to be known. Especially for techniques such as the ex-situ BF technique, where incipient liquid phases are involved, substitution of La into the YBCO was of interest. Also, whether LMO buffers would work with every deposition process and superconductor-type such as REBCO or Ti-based or Hg-based superconductors was of interest. It had long been desired to exploit the relative chemical inertness of LMO buffer layers and the possibility of obtaining electrically conducting buffer layers by doping of the La site in a very flexible and broad manner. The present invention provides this much-needed flexibility.
The following U.S. Patents and U.S. Patent Application(s) contain information which is relevant to the present invention, and the disclosure of each is hereby incorporated by reference: U.S. Pat. No. 5,739,086 to Goyal et al. dated Apr. 14, 1998, U.S. Pat. No. 5,741,377 to Goyal et al. dated Apr. 21, 1998, U.S. Pat. No. 5,898,020 to Goyal et al. dated Apr. 27, 1999, U.S. Pat. No. 5,958,599 to Goyal et al. dated Sep. 28, 1999, U.S. Pat. No. 5,944,966 to Suetsugu et al. dated Aug. 31, 1999, U.S. Pat. No. 5,968,877 to Budai et al. dated Oct. 19, 1999, U.S. Pat. No. 6,296,701 B1 to Christen et al. dated Oct. 2, 2001, U.S. Pat. No. 5,972,847 to Feenstra et al. dated Oct. 26, 1999, U.S. Pat. No. 6,150,034 to Paranthaman et al. dated Nov. 21, 2000, U.S. Pat. No. 6,156,376 to Paranthaman et al. dated Dec. 5, 2000, U.S. Pat. No. 6,159,610 to Paranthaman et al. dated Dec. 12, 2000, U.S. Pat. No. 6,270,908 B1 to Williams et al. dated Aug. 7, 2001, U.S. Pat. No. 6,399,154 B1 to Williams et al. dated Jun. 4, 2002, and U.S. patent application Ser. No. 09/563,665 by Goyal et al. filed May 2, 2000.
OBJECTS OF THE INVENTION
Accordingly, it is an object of the present invention to provide new and improved materials and methods for depositing buffer layers on biaxially textured and untextured metallic and metal oxide subsumes for use in the manure of superconducting and other electronic articles. It is a further object to provide new and improved materials and methods for depositing buffer layer substrates comprising RMnO
3
, R
1−x
A
x
MnO
3
, and combinations thereof, wherein R is an element selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Y, and A is an element selected from the group consisting of Be, Mg, Ca, Sr, Ba, and Ra.
Further and other objects of the present invention will become apparent from the description contained herein.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, the foregoing and other objects are achieved by a buffered substrate for electronic devices which comprises a substrate selected from the group consisting of biaxially textured metals, biaxially textured metal alloys, and biaxially textured metal oxides, the substrate having at least one surface, and a buffer layer deposited epitaxially upon a surface of the substrate, the buffer layer being selected from the group consisting of RMnO
3
, R
1−x
A
x
MnO
3
, and combinations thereof, wherein R is an element selected from the group consisting of La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er,

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