Chemistry of inorganic compounds – Rare earth compound
Reexamination Certificate
2000-05-08
2001-12-11
Wilson, Allan R. (Department: 2815)
Chemistry of inorganic compounds
Rare earth compound
C257S033000, C423S592100, C505S239000
Reexamination Certificate
active
06328942
ABSTRACT:
RELATED APPLICATION
U.S. patent application Ser. No. 09/337,724, entitled “Rare Earth Metal Compounds For Use In High Critical Temperature Thin Film Superconductors, Ferroelectrics, Pyroelectrics, Piezoelectrics, and Hybrids,” assigned U.S. patent application No. 08/502,739, entitled “Compounds in the Series A
2
MeSbO
6
for Use as Substrates, Barrier-Dielectric Layers and Passivating Layers in High Critical Temperature Superconducting Devices,” which have both been partially assigned to the same assignee, have been filed in the United States Patent and Trademark Office and are related to this application. U.S. patent application Ser. No. 08/502,739 was issued as U.S. Pat. No. 5,814,584 on Apr., 29, 1998, and is incorporated herein by reference.
FIELD OF INVENTION
The invention relates in general to dielectric substrates and barriers to be used in High Critical Temperature Superconducting microwave and millimeterwave devices, and in particular to new and useful compounds of the general formula A
4
MeSb
3
O
12
where A is either barium (Ba) or strontium (Sr) and Me is an alkali metal ion selected from the group consisting of lithium (Li), sodium (Na) and potassium (K).
BACKGROUND OF THE INVENTION
Heretofore, the best superconducting electronic devices have been fabricated as thin film epitaxial structures deposited on dielectric substrates or buffer layers, and the best substrate or barrier dielectric in thin film superconductor technology has been LaAlO
3
. Dielectric substrates and buffer layers for microwave devices and growth of high quality HSTC films must meet stringent requirements, including being a member of a cubic crystal system, exhibiting no twinning or strain and a close fit to the HTSC lattice parameters. They must also have a comparable temperature coefficient of expansion; a low isotropic dielectric constant; a low dielectric loss and no chemical reaction with HTSC and they must be mechanically strong. There have been problems with the use of LaAlO
3
. For one, its dielectric constant is too high, meaning that at high frequencies device features become unmanageably small. Another drawback of LaAlO
3
is its anisotropic dielectric constant which creates very difficult device fabrication. It also undergoes a phase transition leading to twinning and stress.
Many of these problems were overcome by the above-referenced U.S. patent application Ser. No. 09/337,724, but the rare earth metal compounds of that invention are magnetic, particularly at low temperatures, and losses may arise from the use of rare earth metals in those compounds. Magnetic losses were overcome by the above-referenced U.S. Pat. No. 5,814,584 which also disclosed lattice parameters in the A
2
MeSbO
6
compounds that provided a comparable or better fit to YBa
2
Cu
3
O
7-&dgr;
(YBCO) than the compounds disclosed in U.S. patent application Ser. No. 09/337,724.
One unsolved problem remains ionic diffusion, which can occur across the boundary between the substrate/barrier and the YBCO, scandium (Sc), indium (In) and gallium (Ga) compounds disclosed in U.S. Pat. No. 5,814,584, issued on Apr. 29, 1998, which may diffuse across and substitute for copper (Cu
2+
). This diffusion will reduce both the critical temperature, or T
c
, and the critical current density, or J
c
, while increasing the surface resistance, or R
s
, all of which are detrimental to microwave device operation. In order to overcome the drawbacks and limitations of past devices utilizing LaAlO
3
or MgO substrates and buffered YSZ or sapphire, as well as the tendency for ions to diffuse across the boundary between the substrate/barrier and the YBCO, antimonates with ordered perovskite structures have been investigated because these materials provide a relatively low dielectric loss of approximately 1×10
−3
and provide isotropic dielectric constants. The term “low dielectric loss,” as used throughout this disclosure, is defined as any dielectric loss lower than 1×10
−2
. The term “low dielectric constant,” as used throughout this disclosure, is defined as any dielectric constant lower than 26, and, in this invention ranges from 9-16.2, within an experimental error of ±5%.
The present invention solves the barrier diffusion problem by deposition of thin film compounds by pulsed laser deposition in the system A
4
MeSb
3
O
12
where A is either barium (Ba) or strontium (Sr) and Me is an alkali metal ion selected from the group consisting of lithium (Li), sodium (Na) and potassium (K) in which these ions may diffuse across the substrate/film interface without adversely impacting the T
c
, and J
c
characteristics, without the drawbacks and limitations of previous compounds. The ions of the compounds of the present invention may also diffuse across the interface between the substrate/barrier and YBCO, except that these ions, depending upon which YBCO ions they substitute for, may increase T
c
and J
c
for small concentrations, and suffer from none of the disadvantages and drawbacks of the compounds utilizing LaAlO
3
or MgO substrates and buffered YSZ or sapphire.
Crystal structures of the compounds in the system Ba
4
MeSb
3
O
12
, where Me is Li and Na have been previously determined by x-ray and neutron diffraction and both of these compounds were found to be cubic, to belong to space group Im3m, to be perovskites and to exhibit an Me:Sb ordering of 1:3 on B sites. Also, Sr
4
NaSb
3
O
12
has been reported in the literature as being monoclinic space group P2
1
as determined from x-ray and neutron diffraction studies. The inventors herein have made different findings. Further, the prior art does not disclose uses of these compounds in HTSC and hybrid microwave devices made herein.
The following references and publications, describe the prior art in this area:
A. Tauber, et. al., abstract entitled “Sr
2
ReSbO
6
; Re=Rare Earth, Barrier/Dielectric Layers and Substrates for Thin Film High T
c
Superconductors for Microwave Applications,” published in Abstracts of Materials Research Society 1994 Fall Meeting, p.292, Nov. 27-Dec. 2, 1994, Boston, Mass.;
S. C. Tidrow, et. al., paper entitled “HTSC Substrate and Buffer Compounds, A
2
MeSbO
6
Where A=Ba, Sr and Me=Sc, In and Ga,” published in
Physica C
, presented at 1995 Material Research Society's Spring Meeting held in San Francisco, Calif.;
A. J. Jacobsen, et. al., 30
Acta Crystalligrahica
, 1705-1711 (1974);
J. A. Alonso, et. al., 22
Materials Research Bulletin
, 69-74 (1987);
K. P. Reis, et. al., preprinted in Texas Center for Superconductivity at University of Houston and printed at 49
Acta Crystalligrahica
, 1585-1588 (1993);
J. A. Alonso, et. al., 84
Journal of Solid State Chemistry
, 16-22 (1990);
P. Woodward, et. al., 9
Journal of Material Research
, 2118-2126 (1994);
R. D. Shannon et al “Dielectric constants of yttrium and rare-earth garnets, the polarizability of gallium oxide and the oxide additivity rule,” (1990); and
R. D. Shannon “Dielectric polarizabilities of ions in oxides and fluorides,” (1993).
SUMMARY OF THE INVENTION
The general object of this invention is to provide materials that can be used as a substrate or barrier dielectric in thin film superconductor technology that can overcome the shortcomings of LaAlO
3
. A more particular object of the invention is to provide a substrate or barrier dielectric with a low dielectric constant, a low dielectric loss and a material that does not undergo a phase transition that leads to twinning and stress. A further object of this invention is to provide compounds having alkali metal ions which will possess none of the disadvantages of utilizing rare earth metal which can have magnetic losses at low temperature. In addition, alkali metal ions may diffuse across the interface between the substrate/barrier and the YBCO with no detrimental effect on, or may slightly increase, T
c
and J
c
for small concentrations, depending upon the crystallographic sites to which the ions diffuse.
It has now been found that the aforementioned objects can be attained using a compoun
Finnegan Robert D.
Tauber Arthur
Tidrow Steven C.
Wilber William D.
Tereschuk George B.
The United States of America as represented by the Secretary of
Wilson Allan R.
Zelenka Michael
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