Method of forming a superconductor

Details Method of forming a superconductor Method of forming a superconductor

1999-05-06

2001-09-11

Nelms, David (Department: 2818)

Semiconductor device manufacturing: process

Coating with electrically or thermally conductive material

To form ohmic contact to semiconductive material

C438S226000, C257S033000, C505S330000

Reexamination Certificate

active

06287969

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to superconductor materials.
2. Description of the Related Art
Superconductor materials are gaining ever increasing attention for their ability to carry significantly large currents without resistance. Even at high frequencies well into the microwave regime and at large current levels, these materials can exhibit negligible dissipation. The so-called high temperature superconductors are especially important for many applications because they can exhibit such properties at temperatures of 77 K or higher. One promising application for these materials is in the form of epitaxially grown superconductor this films for use in wireless communication systems, both satellite and ground based.
The high temperature superconductors are generally anisotropic oxide materials. In a crystal of a typical high temperature superconductor, say YBa
2
Cu
3
O
7-8
, currents are readily carried in the ‘a’ or ‘b’ crystallographic directions while the ‘c’ direction can only sustain a small current without significant dissipation. Many other high temperature superconductor materials are even more anisotropic. As a result, optimal current-carrying capacity in a film requires an orientation of the ‘c’ axis everywhere perpendicular to the substrate. This geometry enables the current to flow in the ‘a’ and ‘b’ directions only. Even with the proper alignment of the ‘c’ axis, the alignment of the ‘a’ and ‘b’ directions is relevant for the current-carrying capacity. In some applications, it may be preferable for the ‘a’ and ‘b’ directions to be consistent throughout the film, although for YBa
2
CU
3
O
7-8
, and many other high temperature superconductors, this may lead to different properties in the ‘a’ and ‘b’ directions. Large currents can also be carried if the ‘a’ and ‘b’ directions occasionally interchange via a mechanism called “twinning”. It is generally considered not desirable to have other relative orientations of the ‘a’ and ‘b’ directions in different parts of the film since these lead to large angle grain boundaries which are found to decrease the current carrying capacity of the film.
Typically, as these films are grown their outer surface tends to roughen. This can be due to particulates attaching to the film during growth or the nucleation of undesired orientations. Even if such difficulties are avoided the surface will tend to roughen as it grows and can be characterized by a series of peaks and valleys. This is usually attributed to a “spiral growth mode” known to be typical for these materials. In such films, regardless of the height of the peaks, the current is limited by the thickness in the valleys. Further, any current carried or induced near the surface of a peak must necessarily travel in the ‘c’ axis direction to pass through a valley.
Moreover, attempts to continue the growth process and increase the useful thickness have progressively diminishing returns thereon since the peaks tend to gain height at the expense of the valleys. In other words, the valleys do not see a commensurate increase in height.
In addition to reducing the current carrying capacity, rough films have other undesirable properties. These include increased microwave surface resistance and increased electrical noise. Such defects in the films will also make patterning the film difficult and hamper the film development of more complicated multi-layer structures on top of the superconducting film.
It is an object of the present invention to provide novel superconductors.
SUMMARY OF THE INVENTION
Briefly stated, the invention involves a method of forming a superconductor, comprising the steps of:
providing a substrate;
exposing the substrate to a first atmosphere, including precursors to form a first epitaxial layer segment,
exposing the first layer segment to a second atmosphere, including precursors to form a second epitaxial layer segment, and
exposing the second layer segment to a third atmosphere including precursors to form a third epitaxial layer segment,
wherein each of the first and third layer segments are each formed from a superconductor material and the second layer segment is formed from a material different from the first and third layer segments,
wherein the first, second and third layer segments have a collective thickness, the third layer segment having an outer surface with a roughness which is less than that of a single layer of the superconductor material with a thickness equal to the collective thickness.
In another embodiment, there is provided a composite superconductor film applied to a substrate, the film having a thickness of at least 5000 Angstroms and an outer surface having an average roughness not exceeding 250 Angstroms.
In another aspect of the present invention, there is provided a layer of superconductor materials, the layer having a current carrying capacity and an inner discontinuous epitaxial region formed in the presence of dielectric precursor materials and at a concentration so as not to substantially reduce the current carrying capacity.


REFERENCES:
patent: 4486464 (1984-12-01), Young
patent: 4728626 (1988-03-01), Tu
patent: 5030613 (1991-07-01), Chai
patent: 5236896 (1993-08-01), Nakamura
patent: 5322526 (1994-06-01), Nakamura
patent: 5326988 (1994-07-01), Ishada
patent: 5347086 (1994-09-01), Potter
patent: 5388068 (1995-02-01), Ghosal
patent: 5399546 (1995-03-01), Nakamura
patent: 5407903 (1995-04-01), Nakamura
patent: 5413982 (1995-05-01), Inada
patent: 5416072 (1995-05-01), Inada
patent: 5420101 (1995-05-01), Copetti
patent: 5434127 (1995-07-01), Nakamura
patent: 5439875 (1995-08-01), Tanaka
patent: 5446015 (1995-08-01), Nakamura
patent: 5466664 (1995-11-01), Inada
patent: 5506197 (1996-04-01), Nakamura
patent: 5547923 (1996-08-01), Nakamura
patent: 5906965 (1999-05-01), Rao
patent: 5985404 (1999-11-01), Yano et al.
patent: 6023072 (2000-02-01), Silver
patent: DE 196 34 463 A1 (1996-08-01), None
Whorls Upon Whorls L. Garwin Nature vol. 350 Mar. 28, 1991 p.277—1 page .
Screw Dislocations in High-T Films C.Garber et al Nature vol. 350 Mar. 28, 1991-13 2 pages.
Molecular beam . . . surface roughness—W.Schindler et al Thin Solid Films, 250 (1994) Elsevier Sci. S.A. 6 pages.
Internet U.S. Patent 5,589,284, Summerfelt et al. Dec. 31, 1996—5 pages.
Internet U.S. Patent 5,585,330, Cadotte, Jr. et.al. Dec. 17, 1996—2 pages.
Internet U.S. Patent 5,585,300, Summerfelt Dec. 17, 1996—4 pages.
Internet U.S. Patent 5,538,941, Findikoglu, et.al. Jul. 23, 1996—2 pages.
Internet U.S. Patent 5,449,659, Garrison, et.al. Sep. 12, 1995—2 pages.
Internet U.S. Patent 5,219,827,Higaki, et.al. Jun. 15, 1993—2pages.
Internet U.S. Patent 5,098,178, Ortbasi Mar. 24, 1992—4 pages.
Database Search Jan. 29, 1997 16:18:59 5 pages.
Database Search Jan. 29, 1997 17:20:20 5 pages.
3.2.2 Growth Mechanism, Internet, T. Shimizu—4 pages.
High Temperature Superconductors, Internet—5 pages.
High Quality Y . . . films . . . vapor deposition H.Busch et al. J.Appl.Phys.70(4).Aug. 15,1991—3 pages.
New Research Opp.in Supercond IV* B.J.Batlogg et al. Jnl.of Superconductivity V.10 No.6 1997—39 pages.
Dependence of Crystalline . . . laser ablated . . . A.H.Carim et al,Appl.Phys.Lett.58(8) Feb. 25, 1991—3 pages.
Surface Mechanics—Chapter 8 p.173-191 F.Fongsulung Ref. Thode TA 418.7.L55—18 pages.
Growth Mechanism . . . Tunneling Microscopy M.Hawley et al.Reports:Sci.vol.251 Mar. 29, 1991—3 pages.
Measurements . . . Superconductors—A.Kapitulnik & K.Char IBM J.Res.Develop. vol. 33 No.3 May 1989—10 pages.
The formation . . . surface resistance—S.F.Karmanenot et al.Supercond.Sci Technol.6 (1993) 23-29 7 pages.
Substrate temperature . . . pulsed-laser ablation B.L.Low et al.Supercond.Sci Technol.10 (1997) 6 pages.
Reproducible sputtering . . . various thicknesses F.E.Luborsky et al.J.Appl.Phys.64(11)Dec. 1,1988—4 pages.
Handbook of Thin Film Technology—Maissel & Glang McGraw Hill p.6-13 to 6-17 Ref TK.7821.15.T5H34—6 pages.
Metalorganic Chemical . . . superconducting films S.Matsuno et al Appl.Phys Lett.60(19)May 11,1992—3 pages.
Topical Revie

Affiliated with

Also associated with

Rating

Method of forming a superconductor does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Method of forming a superconductor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of forming a superconductor will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2450708