Superconductor technology: apparatus – material – process – High temperature devices – systems – apparatus – com- ponents,... – Measuring or testing system or device
Reexamination Certificate
1999-03-23
2001-07-17
Beck, Shrive (Department: 1762)
Superconductor technology: apparatus, material, process
High temperature devices, systems, apparatus, com- ponents,...
Measuring or testing system or device
C505S238000, C505S701000, C427S062000, C428S930000, C257S033000
Reexamination Certificate
active
06263219
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
1. Field of the Invention
The present invention relates to a SQUID. The present invention is related to a configuration of a SQUID and a method for manufacturing the same. More specifically, the present invention is related to a SQUID formed of an oxide superconducting thin film on a sapphire substrate.
2. Description of Related Art
Generally, a SQUID comprises a circular current road for superconducting current, including one or two Josephson junctions. The SQUID related to the present invention is a SQUID formed of an oxide superconducting thin film, in particular one that has the composition “RBa
2
Cu
3
O
7−x
(“R” indicates a rare earth element chosen among a group formed a Yb, Er, Ho, Y, Dy, Gd, Eu, Sm and Nd)”. The oxide superconducting thin film of this kind has high critical temperature and is to be effective by cooling by liquid nitrogen.
However, a specified crystal structure is required so that the oxide thin film obtains a superconducting state. Accordingly, in most case, an oxide superconducting thin film is fonned on a MgO single crystal substrate or SrTiO
3
single crystal substrate. These substrate materials have well matching of cell to the oxide superconducting thin film and preferable arrangement of crystal is provided.
However, MgO single crystal substrate and SrTiO
3
single crystal substrate are very expensive, and, these substrates having a large area are hard to obtain. As the result, SQUID formed of an oxide superconducting thin film tends to be expensive.
On the other hand, Si single crystal substrate or sapphire substrate is obtained easily and cheap. However, an oxide superconducting thin film is hard to be formed on them.
SUMMARY OF THE INVENTION
The problems mentioned above are solved by the present invention. In a manufacture method of the present invention, sapphire substrate is used as a substrate material and oxide superconducting thin film of high quality is formed at the same time.
A characteristic of the present invention is not simple displacement of substrate material. Namely, when a SrTiO
3
film is formed directly on a sapphire substrate, SrTiO
3
film (
100
) is never formed. However, the method according to the present invention is obtained by a 3-phase production process.
As the first process, a CeO
2
(
100
) film is formed on the sapphire substrate. As the second process forms, a RBa
2
Cu
3
O
7−x
(
001
) film (“R” indicates a rare earth element chosen among a group formed of Yb, Er, Ho, Y, Dy, Gd, Eu, Sm and Nd) is formed oil the CeO
2
(
100
) film. As the third process, SrTiO
3
(
100
) film is formed on the RBa
2
Cu
3
O
7−x
(
001
) film. At last, the oxide superconducting thin film to be a SQUID is formed on this SrTiO
3
(
100
) film.
Such processes bring the following effect.
Each film sticks well mutually. The oxide superconducting thin film can be formed on a SrTiO
3
film that is oriented (
100
). Accordingly, high quality oxide superconducting thin film is provided on a sapphire substrate. The quality of the oxide superconducting thin film is equal to the one of an oxide superconducting thin film on MgO substrate or SrTiO
3
substrate. Acquisition of a sapphire substrate is easy, as opposed to MgO substrate or SrTiO
3
substrate.
Furthermore, an advantage is not simply confined to reduction of material cost. A sapphire substrate having a large area is readily available. Accordingly, several SQUIDs can be formed on one substrate and production of SQUID becomes possible in large quantities.
In other words, high performance and inexpensive SQUID can be supplied by the present invention.
The above and other objects, features and advantages of the present invention will be apparent from the following description of preferred embodiments of the invention with reference to the accompanying drawings.
REFERENCES:
patent: 0 545 815 A2 (1993-06-01), None
Boikov et al, J. Appl. Phys. 81(7) pp. 3232-3236, Apr. 1997.*
Kotelyanski et al, Inst. Phys. Conf. Ser. 148 vol. 2, no page numbers (Abstract), 1995.*
Laibowitz et al, Appl. Phys. lett. 64(2), pp. 247-249, Jan. 1994.*
Yuan C. W. et al. “Step edge YBa/sub 2/Cu/sub 3/O/sub 7- delta/DC SQUIDs on sapphire substrates”,Applied Physics Letters, May 18, 1992, USA, vol. 60, No. 20, pp. 2552-2554.
Beck Shrive
Chen Bret
Foley & Lardner
Sumitomo Electric Industries Inc.
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