Superconductor technology: apparatus – material – process – Processes of producing or treating high temperature... – Coating
Reexamination Certificate
2002-09-06
2004-12-28
McDonald, Rodney G. (Department: 1753)
Superconductor technology: apparatus, material, process
Processes of producing or treating high temperature...
Coating
C505S476000, C505S470000, C204S192240
Reexamination Certificate
active
06835696
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of forming a superconductor film composed of a compound of magnesium (Mg) and boron (B). More specifically, the ]present invention relates to a method of forming an as-grown film having a high critical temperature superconductor without being annealed.
2. Description of the Related Art
A MgB
2
compound features one of the highest transition temperatures of any superconductor. Additionally, a MgB
2
film can be integrated on a substrate to form an integrated circuit. Thus, the MgB
2
compound is expected to apply to electronics devices such as thin film devices.
It is reported that the coherent length &xgr;(0) of MgB
2
is 54, and the magnetic penetration depth is 140-180 nm. One well known method of making the superconductor of MgB
2
is to form a bulk of MgB
2
by compression molding of powder of mono-crystal MgB
2
, and then annealing the bulk at a high temperature. Another method of forming the superconductor of MgB
2
is to form a thin film of a MgB
2
compound by using PLD (pulse laser deposition), and then annealing the thin film of MgB
2
in the temperature range of 600° C.-1200° C. to make the film superconductive. The PLD method focuses a pulsed laser beam on a boron target to evaporate boron atoms and deposit the boron atoms on a substrate. The boron atoms on the substrate then react with magnesium atoms in high temperature magnesium vapor to form a MgB
2
film on the substrate. Further, the film is annealed at a high temperature, so as to become a superconductor. Another method of forming the superconductor film of a MgB
2
compound by using PLD is that which deposits magnesium and boron atoms on a substrate by laser deposition, and sets the substrate in magnesium vapor. The magnesium and boron on the substrate react in the magnesium vapor to form a thin film of the MgB
2
compound on the substrate. Annealing the MgB
2
film at a high temperature enables the film to have the features of a superconductor.
All prior art regarding fabrication of the superconductor of the MgB
2
compound requires high temperature annealing, in the range of 600° C.-1200° C. The necessity of the annealing process of the MgB
2
film to produce features of a superconductor makes fabrication of a device such as a thin film integrated circuit on a substrate difficult. Further, it has not been known that an as-grown film of MgB
2
on a substrate which is made by simultaneous magnesium and boron sputtering, using a sputtering apparatus, has characteristics of a superconductor without annealing the as-grown film.
SUMMARY OF THE INVENTION
The present invention features a method of forming a superconductor film of MgB
2
without annealing the as-grown film.
The present invention provides a method of forming an as-grown film of a superconductor composed of the MgB
2
compound made with magnesium and boron ejected from a magnesium target and a boron target, respectively, in a simultaneous sputtering process. The as-grown film composed of the compound of magnesium and boron can be a superconductor without being annealed. The as-grown film can be composed of a MgB
2
compound, or the film can be composed of one or more compounds of magnesium and boron different from the MgB
2
compound, or a magnesium element and a boron element in addition to the MgB
2
compound.
As mentioned above, a superconductor film of MgB
2
made using the present invention has features of a superconductor without being annealed, and its critical temperature is in the range of about 6K-29K. The present invention can be applied to fabricate an integrated circuit of a superconductor film, because the high temperature annealing process is not needed to make the as-grown film of the MgB
2
compound having features of a superconductor.
The objects, advantages and features of the present invention will be more clearly understood by referencing the following detailed disclosure and the accompanying drawings.
REFERENCES:
patent: 4629547 (1986-12-01), Honda et al.
patent: 6626995 (2003-09-01), Kim et al.
Atsushi Saito, et al., “Fabrication of Josephson Junctions As-Grown MgB2Thin Films,” The Japan Society of Applied Physics, No. 49, Mar., 2002, Abstract 28a-ZB-3.
Atsushi Saito, et al., “Low Temperature Fabrication of As-Grown MgB2Thin Films by Carrousel-Type Sputtering Apparatus”, The Japan Society of Applied Physic, No. 62, Sep. 12, 2002, Abstract 12p-M-9.
Jun Nagamatsu, et al., “Superconductivity at 39K in Magnesium Diboride,” Nature, vol. 410, p63-64, Mar. 2001.
Dave H. Blank, et al., “Superconducting Mg-B Films by Pulsed-Laser Deposition in an In Situ Two-Step Process Using Multicomponent Targets,” Applied Physics Letters, vol. 79, No. 3, Jul. 16, 2001, pp 394-396.
S.R. Shinde, et al., “Superconducting MgB2 Thin Films by Pulsed Laser Deposition,” Applied Physics Letters, vol. 79, No. 2, Jul. 9, 2001, pp 227-229.
Atsushi Saito, et al., “As-Grown Deposition of Superconducting MgB2Thin Films by Multiple-Target Sputtering System”, (1) Jpn.J.Appl.Phys.vol. 41 (2002)pp. L127-129 Part 2, No. 2A, Feb. 1, 2002,
Atsushi Saito, et al., “As-Grown Deposition of MgB2Thin Film and Fabrication of Josephson Junctions”, The Institute of Electronics, Information and Communication Engineers, Technical Report of IEICE.SCE2002-2, MW2002-2 (200-04).
Atsushi Saito, et al., “As-Grown MgB2Thin Films Deposited On Al2O3Substrates With Different Crystal Plane,” International Conference on Electronics Materials, Jun. 12, 2002, Abstract.
Atsushi Saito, et al., “As-Grown MgB2Thin Film Deposited On Al2O3Substrates With Different Crystal Plane,” Super Conductor Science and Technology 15 (2002) 1-5, Received Jun. 24, 2002.
Atsushi Saito, et al., “Fabrication of Josephson Junctions As-Grown MgB2Thin Films,” Applied Superconductivity Conference Aug. 8, 2002 Abstract (4EG11).
Kawakami Akira
Saito Atsushi
Shimakage Hisashi
Wang Zhen
Communications Research Laboratory Independent Administrative In
McDonald Rodney G.
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