Stock material or miscellaneous articles – Composite – Of inorganic material
Reexamination Certificate
2001-12-20
2003-10-21
Dunn, Tom (Department: 1725)
Stock material or miscellaneous articles
Composite
Of inorganic material
C505S190000, C505S191000, C505S211000, C505S220000, C505S230000, C505S701000
Reexamination Certificate
active
06635368
ABSTRACT:
STATEMENT OF GOVERNMENT INTEREST
The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.
BACKGROUND OF THE INVENTION
The present invention relates to HTS (high-temperature superconductor) film-based electronic devices, more particularly to types and configurations of HTS films in such devices.
Thin film configurations and thin stripe (elongated thin film) configurations are at the core of all electronic HTS-based applications, such as magnetic-field SQUID (superconducting quantum interference device) sensors, frequency mixers, video-sensors and filters. These films and stripes are universally grown as “c-axis-aligned” HTS films (also referred to herein as “c-axis” HTS films); that is, the c-axis of the anisotropic HTS crystal structure is oriented normal to the substrate surface. Consequently, the superconductivity-sited planes (i.e., the planes which are believed to be the sites of superconductivity) in the HTS crystal structure lie in parallel to the substrate surface. Therefore, for the common configuration of an external magnetic field oriented normal to the film's surface, the associated vortices cut normal to and across all superconductivity-sited planes in the film.
Thermal random motion of such vortices is associated with the observed voltage noise in these films. In the alignment of vortices and the superconductivity-sited planes, it is difficult to arrest that random motion, since there are no intrinsic crystal defects parallel to the c-axis to “pin” it down. The ubiquitous extrinsic grain and twin boundaries pinning centers which do run parallel to the c-axis are too sparsely distributed to limit this random motion effectively. This is believed to qualitatively explain the observed white noise and the substantial low frequency 1/f-like (ELF, or extremely low frequency) noise in HTS-film based electronic apparatuses such as a SQUIDs. This noise, in turn, is a major sensitivity-limiting factor in SQUIDs and other electronic devices configured of stripes and thin films.
SUMMARY OF THE INVENTION
In view of the foregoing, it is an object of the present invention to provide method and apparatus for reducing the white and 1/f-like low-frequency (<100Hz) voltage-noise in High Temperature Superconductor (HTS) film-based electronic devices such as SQUIDs, mixers, video-sensors and filters.
The present invention provides the combination of a film and substrate wherein such combination is adaptable to use in (e.g., as included in or as part of) film-based HTS electronic apparatus so as to attribute such apparatus with low ELF noise and low white noise. The present invention also provides a high-temperature superconductor (HTS) film-based electronic device, which is inclusive of an inventive film-and-substrate combination and is consequently characterized by low extremely low frequency (ELF) noise and low white noise. According to many embodiments of this invention, the inventive film-based HTS so electronic device is a SQUID which is thus characterized by low ELF noise and low white noise.
In accordance with the present invention, “a-axis-aligned” HTS films (also referred to herein as “a-axis” HTS films) are used, instead of the conventionally used c-axis-aligned HTS films, in HTS-based electronic devices. The term “film,” as used herein, refers to a superconductive thin film of any outline shape, elongate (stripe-like) or otherwise. Some inventive embodiments provide a film-and-substrate combination wherein the entire HTS film is a-axis-aligned film configured in a homogenous manner. Other inventive embodiments provide a film-and-substrate combination wherein the HTS film is configured in a heterogeneous manner, referred to herein as “patterned.”
An inventively patterned HTS film can be an entirely a-axis-aligned film which is configured in at least two different ways; for instance, an inventively “intra-patterned” HTS film can include one or more a-axis-aligned film areas characterized by a first crystalline orientation relative to the substrate surface, and one or more a-axis-aligned areas characterized by a second crystalline orientation relative to the substrate surface. Alternatively, an inventively patterned HTS film can be partially a-axis-aligned film and partially c-axis-aligned film; for instance, an inventively “inter-patterned” HTS film can include one or more a-axis-aligned film areas and one or more c-axis-aligned areas. An inventively patterned HTS film can be both “intra-pattered” and “inter-patterned”; for instance, it is possible that two or more a-axis-aligned film areas differ from each other and/or two or more c-axis-aligned film areas differ from each other. Many inventively patterned HTS films adopt a preferred configuration whereby a-axis-aligned film is disposed along the film's periphery (or at least a portion thereof) so as to serve as a barrier to inward vortex advancement or penetration from the film's periphery.
In the realm of HTS-film-based electronic devices, the present invention's homogeneous a-axis film-and-substrate embodiments and patterned a-axis film-and-substrate embodiments (either a-axis-plus-a-axis embodiments or a-axis-plus-c-axis embodiments) are both advantageous as compared with c-axis film embodiments. Generally, in accordance with inventive practice of a-axis film, whether homogeneous or patterned, the vortex penetration and motion—both thermal and current-induced—is drastically impeded. It has been recognized early on in the superconductivity field that the a-b-planar Cu—O planes in the HTS crystal structure are characterized by superior pinning capacity (for vortices parallel to the a-b planes). However, according to conventional practice, the YBCO is used in a c-axis film capacity, so that the Cu—O planes are not brought to bear on the vortices.
In essence, the present invention effects a ninety-degree shift in orientation of the superconductor lattice relative to the substrate surface. This invention turns the YBCO molecules “on their side,” so to speak, in relation to the plane defined by the substrate surface; therefore, the a-b-planar Cu—O planes existing in the YBCO molecules will be rendered in such orientation relative to the substrate surface as to be brought to bear on the vortices.
It has been observed that the a-b planes quite densely populate the superconductor molecules, and hence the a-b planes potentially are especially effective inhibitors of vortex activity; indeed, the extremely high density of the a-b planes in the HTS layered structure renders them ideal vortex-motion inhibitors. The veracity of the observation that the a-b planes have great vortex-inhibitive efficacy has been recently reconfirmed in connection with “coated conductors,” the “second generation” HTS high-quality films. The present invention's a-aligned film automatically takes advantage of this fundamental property of a-b planes in association with the motion of vortices. Consequently, vortex penetration, transversal motion (to the current direction) and the associated thermal voltage noise are minimized to the maximum, or practically so, by inventive practice.
The following United States patents are incorporated herein by reference: Divin et al. U.S. Pat. No. 6,156,706 issued Dec. 5, 2000; Young et al. U.S. Pat. No. 6,083,884 issued Jul. 4, 2000; Matsunaga et al. U.S. Pat. No. 5,885,939 issued Mar. 23, 1999; Nishino et al. U.S. Pat. No. 5,729,046 issued Mar. 17, 1998; Kamamoto et al. U.S. Pat. No. 5,716,908 issued Feb. 10, 1998; Suh et al. U.S. Pat. No. 5,677,264 issued Oct. 14, 1997; Mukaida et al. U.S. Pat. No. 5,593,950 issued Jan. 14, 1997; Nakamura et al. U.S. Pat. No. 5,430,012 issued Jul. 4, 1995; Oishi et al. U.S. Pat. No. 5,420,103 issued May 30, 1995. Also incorporated herein by reference is Nakahara et al. U.S. Patent Application Publication US2001/0017220 A1 published Aug. 30, 2001.
According to frequent inventive practice, “patterned” film embodiments are
Cooke Colleen P.
Dunn Tom
Kaiser Howard
The United States of America as represented by the Secretary of
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