This invention relates in general to superconductors, and in specific to methods and systems for quality testing of superconductor material.
Electrical resistance in metals arises because electrons that are propagating through the solid are scattered because of deviations from perfect translational symmetry. These deviations are produced either by impurities or the phonon lattice vibrations. The impurities form the temperature independent contribution to the resistance, and the vibrations form the temperature dependent contribution.
Electrical resistance, in some applications, is very undesirable. For example, in electrical power transmission, electrical resistance causes power dissipation, i.e. loss. The power dissipation grows in proportion to the square of the current, namely P=I2R in normal wires. Thus, wires carrying large currents dissipate large amounts of energy. Moreover, the longer the wire used in either larger transformers, bigger motors or larger transmission distances, the more dissipation, since the resistance in a wire is proportional to its length. Thus, as wire lengths increase more energy is lost in the wires, even with relatively small currents. Consequently, electric power plants produce more energy than that which is used by consumers, since a portion of the energy is lost due to wire resistance.
In a superconductor that is cooled below its transition temperature Tc, there is no resistance because the scattering mechanisms are unable to impede the motion of the current carriers. The current is carried, in most known classes of superconductor materials, by pairs of electrons known as Cooper pairs. The mechanism by which two negatively charged electrons are bound together is described by the BCS (Bardeen Cooper Schrieffer) theory. In the superconducting state, i.e. below Tc, the binding energy of a pair of electrons causes the opening of a gap in the energy spectrum at Ef, which is the Fermi energy or the highest occupied level in a solid. This separates the pair states from the “normal” single electron states. The size of a Cooper pair is given by the coherence length which is typically 1000 Å, although it can be as small as 30 Å in the copper oxides. The space occupied by one pair contains many other pairs, which forms a complex interdependence of the occupancy of the pair states. Thus, there is insufficient thermal energy to scatter the pairs, as reversing the direction of travel of one electron in the pair requires the destruction of the pair and many other pairs due to the complex interdependence. Consequently, the pairs carry current unimpeded. For further information on superconductor theory please see “Introduction to Superconductivity,” by M. Tinkham, McGraw-Hill, New York, 1975.
Many different materials can become superconductors when their temperature is cooled below Tc. For example, some classical type I superconductors (along with their respective Tc's in degrees Kelvin (K)) are carbon 15K, lead 7.2K, lanthanum 4.9K, tantalum 4.47K, and mercury 4.47K. Some type II superconductors, which are part of the new class of high temperature superconductors (along with their respective Tc's in degrees K), are Hg0.8Tl0.2Ba2Ca2Cu3O8.33 138K, Bi2Sr2Ca2Cu3O10 118 k, and YBa2Cu3O7-x 93K. The last superconductor is also well known as YBCO superconductor, for its components, namely Yttrium, Barium, Copper, and Oxygen, and is regarded as the highest performance and highest stability high temperature superconductor, especially for electric power applications. YBCO has a Perovskite structure. This structure has a complex layering of the atoms in the metal oxide structure.
A problem with YBCO superconductors specifically, and the oxide superconductors in general, is that they are hard to manufacture because of their oxide properties, and are challenging to produce in superconductor form because of their complex atomic structures. The smallest defect in the structure, e.g. a disordering of atomic structure or a change in chemical composition, can ruin or significantly degrade their superconducting properties. Defects may arise from many sources, e.g. impurities, wrong material concentration, wrong material phase, wrong processing temperature, poor atomic structure, and improper delivery of materials to the substrate, among others.
Thin film YBCO superconductors can be fabricated in many ways including pulsed laser deposition, sputtering, metal organic deposition, physical vapor deposition, and chemical vapor deposition. Two typical ways for the deposition of thin film YBCO superconductors are described here as example. In the first way, the YBCO is formed on a wafer substrate in reaction chamber 200, as shown in
In the second way depicted in
Neither of the above described methods for forming thin film high temperature superconductors can produce a long length tape or ribbon of YBCO which can be used to replace copper (or other metal) wires in electric power applications. The first way only allows for the production of small pieces of superconductor material on the wafer, e.g. a batch process. The second way can only be used to make tape that is a few feet in length and uses multiple passes to generate a superconductor film of several microns thickness. The second way has a practical limitation of about 5 feet. Larger pieces of tape would require a larger heating chamber. A larger heating roller will also be needed. The tape will cool down after leaving roller 302, and thus will need more time to heat back up to the required temperature. Heating on one side of the chamber, with a cool down on the other side of the chamber may also induce thermal cracks into the YBCO layer and other layers formed on the metal substrate. The smaller pieces of tape produced by the second method may be spliced together to form a long length tape, but while the pieces may be superconducting, splice technology is not yet at the point of yielding high quality high temperature superconductor splices. Consequently, current arrangements for forming superconductors cannot form a long, continuous tape of superconductor material.
The present invention is directed to a system and method which imparts quality control testing to a reel-to-reel superconductor manufacturing line. The manufacturing line uses a pay-out reel to dispense the tape substrate. The manufacturing line includes various stages to form the superconductor layer onto the tape substrate, including an initialization stage, a deposition stage, and an anneal stage. The manufacturing line includes a take-up reel to spool the superconductor tape.
The quality testing may be performed in a separate stage before the initialization stage, after the initialization stage, after the deposition stage and/or after the anneal stage, or combinations thereof. The quality control testing will ensure the characteristics of the final superconductor tape, as well as the tape under process. The quality control testing may be used to control and/or change production parameters (e.g. temperature, pressure, gas concentrations, precursor amounts, etc). The quality testing may be incorporated into one or more of the initialization stage, the deposition stage, and the anneal stage. For example, the deposition stage may comprise one or more reactors, and quality control testing system(s) may be built into one or more of the reactors. As another example, transition chambers are used between each stage and between each reactor, and quality control testing system(s) may be built into one or more of the transition chambers. Note that quality control testing may be performed separately from the production line.
The quality control may incorporate direct or indirect measurement of superconductor properties including atomic order, temperature, reflectivity, surface morphology, thickness, microstructure, Tc, Jc, microwave resistivity, etc., or the direct or indirect measurement of the properties of the buffer layers or the coating layers of the tape including atomic order, temperature, reflectivity, surface morphology, thickness, microstructure, etc, as well as measurements of the tape substrate.
One embodiment of the invention may use a microwave measurement system to determine the surface resistance and/or dielectric properties of the tape substrate, a buffer layer, and/or the superconductor layer. This system may include a quarter wave coaxial resonator or a far field resonator. This system may be located in a transition chamber, a reactor, or in a separate testing chamber.
Another embodiment uses an ion scattering system to determine the atomic order and/or composition of the tape substrate, a buffer layer, and/or the superconductor layer. This system may use a time-of-flight detector to determine the composition of the layer under test. This system may also use one or more detectors set at predetermined angles to detect scattered ions to determine the atomic order of the layer under test.
The foregoing has outlined rather broadly the features and technical advantages of the present invention in order that the detailed description of the invention that follows may be better understood. Additional features and advantages of the invention will be described hereinafter which form the subject of the claims of the invention. It should be appreciated by those skilled in the art that the conception and specific embodiment disclosed may be readily utilized as a basis for modifying or designing other structures for carrying out the same purposes of the present invention. It should also be realized by those skilled in the art that such equivalent constructions do not depart from the spirit and scope of the invention as set forth in the appended claims. The novel features which are believed to be characteristic of the invention, both as to its organization and method of operation, together with further objects and advantages will be better understood from the following description when considered in connection with the accompanying figures. It is to be expressly understood, however, that each of the figures is provided for the purpose of illustration and description only and is not intended as a definition of the limits of the present invention.
For a more complete understanding of the present invention, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:
System 400 uses pay-out reel 401 to dispense tape 408, which is a ribbon of substrate at this point in the process, at a constant rate. The system then uses initialization stage 402 to pre-heat and/or pre-treat tape 408 before growing the superconductor layer and any buffer layers) thereon. Pre-heating may be desirable to lessen thermal shock of the substrate. Pre-treating may also be desirable to reduce contaminants from the substrate before growing the superconductor layer. The system then uses deposition stage 403 that has at least one reactor or reaction chamber 490 to deposit one or more materials onto tape 408 that is used to form the superconductor layer. The number of reactors needed may depend upon a number of factors, including the type of superconductor material that is being formed, the type and number of buffer layers that are needed (if any) between the superconductor material and the substrate, and the type of substrate that is used to support the superconductor material. The system uses anneal stage 404 to finalize the superconductor layer and cool down the superconductor tape. The system uses take-up reel 406 to spool the superconductor tape.
System 400 may include one or more transition chambers 491 between initialization stage 402 and the reaction chambers, between the reaction chamber and anneal stage 404, and between reaction chambers if more than one reaction chamber is used. Additional reaction chambers or reactors may be used to provide buffer layers between substrate 408 and the high temperature superconductor (HTS) film, or coating layers on top of or in between layers of the HTS film. The transition chambers isolate each stage or reactor from the other stages and/or reactors, and thereby prevent cross-contamination of materials from one stage or reactor to another stage or reactor.
The system may be used to form superconductor tape from different superconductor materials, including, but not limited to YBa2Cu3O7-x, YBCO, NdBa2Cu3O7-x, LaBa2Cu3O7-x, Bi2Sr2Ca2Cu3Oy, Pb2-xBixSr2Ca2Cu3Oy, Bi2Sr2CaCu2Oz, Tl2Ba2CaCu2Ox, Tl2Ba2Ca2Cu3Oy, TlBa2Ca2Cu3Oz, Tl1-x BixSr2-yBayCa2Cu4Oz, TlBa2Ca1Cu2Oz, HgBa2CaCu2Oy, HgBa2Ca2Cu3Oy, MgB2, copper oxides, rare earth metal oxides, and other high temperature superconductors. Furthermore, embodiments may operate for many different thin film deposition processes, including but not limited to metalo-organic chemical vapor deposition (MOCVD), pulsed laser deposition, DC/RF sputtering, metal organic deposition, molecular beam epitaxy, and sol gel processing.
System 400 includes quality control testing to ensure the proper characteristics of the final superconductor tape, as well as the tape under process. The quality control testing may be incorporated at any of reactors 490, in any of transition chambers 491, and/or at pre-treat 402 or post-anneal stages 404. The quality control testing may be located in a separate stage, e.g. testing stage 418. The quality control testing may incorporate direct or indirect measurement of YBCO properties including atomic order, temperature, reflectivity, surface morphology, thickness, microstructure, Tc, Jc, microwave resistivity, etc., or the direct or indirect measurement of the properties of the buffer layers or the coating layers of the tape including atomic order, temperature, reflectivity, surface morphology, thickness, microstructure, etc. Note that Jc is the critical current density, i.e, the maximum amount of current that the wire can handle before breakdown. Some superconductor elements may have a Jc of 100,000 amps/cm2 or greater. Good superconductor elements may have a Jc of 500,000 amps/cm2 or greater.
There is a useable correlation between the surface resistance at high temperature (e.g. 600 degrees C.) and the superconducting quality of the tape at superconducting temperatures (e.g. liquid nitrogen temperature). Thus, the lower the resistance at high temperature, the better the superconductor layer.
System 501 includes microwave emitter/receiver 502 and quarter wave coaxial resonator 503 that surrounds tape 408. Such resonators are commercially available from a number of sources (e.g. Integrated Microwave, Mite Q, etc). Microwaves are emitted from emitter 502 and are directed to coaxial resonator 503 that includes tape 408. Tape 408 affects the microwave energy, and a portion of the energy is reflected back to receiver 502. The surface resistance of tape 408, as well as, the dielectric properties then can be determined through known methods
System 501 may provide a high resolution measurement for a small area of tape 408. The measurements may be taken continuously, as tape 408 moves through system 501. Any changes to quality are usually be detected quickly, thus allowing the production process to be changed to correct for any error. Note that a plurality of these systems may be used, each of which may be deployed across the width of tape 408 (orthogonal to the direction of movement), and, thus, each measuring a different strip of the tape.
Note that system 501 may use far-field resonator 501 instead of a quarter wave resonator 503. A far-field resonator may allow for a larger area of tape 408 to be measured (e.g. 5 mm square), but while providing a lower resolution measurement than quarter wave resonator 503. The far field resonator may also be useful in measuring the dielectric constant of tape 408. From the dielectric constant, the thickness and quality of the layer of interest (either buffer or superconductor) may be determined. The dielectric constant may be a good indicator of, for example, the quality of the one or more buffer layers by indicating thickness and purity.
Such far-field resonators are commercially available from a number of sources (e.g. Integrated Microwave, Mite Q, etc). In such a system, microwaves are emitted from emitter 502 and are directed to a coaxial resonator, which may be similar to resonator 503, that includes tape 408. Tape 408 affects the microwave energy, and a portion of the energy is reflected back to the receiver 502. The surface resistance of the tape, as well as the dielectric properties, then can be determined through known methods. It should be noted that the material used to construct a quality testing system, such as system 501, should be constructed such that parts exposed to the inside of system 400 are appropriately stable. For example, parts that are exposed in one of reactors 490 or transition chambers 491 should be high-temperature stable because of the heat in those areas.
Detector 703 may be a time-of-flight detector. This type of detector allows for the determination of mass resolution of the dislodged material so that the composition of the surface can be determined. Note that the ion density is low so that very little material is dislodged, which will not affect the properties of the layer being examined. Thus, either the substrate layer, a buffer layer, or the superconductor layer may be examined to ensure that the stoichiometry is correct.
Note that with multiple detectors, one (or more) of the detectors may be a time-of-flight detector to determine the composition based on dislodged material of the layer, and the others may be set to receive properly scattered ions to determine atomic ordering of the layer.
This quality system may be preferably located in one of transition chambers 491, since this type of testing usually needs to be conducted in a high vacuum, e.g. 10−3 Torr or lower, and with little or no background gas. The measurements may be taken continuously, as the tape moves through system 701. Any changes to quality would be detected quickly, and allow the production process to be changed to correct for any error.
Note that as a further alternative arrangement, the quality testing system may be located in a separate stage, e.g. testing stage 418. Note that multiple instantiations of the testing systems of
Further note that any combination of testing systems of
Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps.
This application claims priority to U.S. Provisional Patent Application No. 60/538,849, the disclosure of which is hereby incorporated herein by reference. This application is related to co-pending and commonly assigned U.S. patent applications Ser. No. 10/206,123, entitled “METHOD AND APPARATUS FOR FORMING SUPERCONDUCTOR MATERIAL ON A TAPE SUBSTRATE,” filed Jul. 26, 2002, to co-pending and commonly-assigned U.S. patent application Ser. No. 10/206,900, entitled “SUPERCONDUCTOR MATERIAL ON A TAPE SUBSTRATE,” filed Jul. 26, 2002, and concurrently filed and commonly assigned U.S. patent application Ser. No. 10/206,783, entitled “METHOD AND APPARATUS FOR FORMING A THIN FILM ON A TAPE SUBSTRATE,” filed Jul. 26, 2002, to U.S. patent application Ser. No. ______ [attorney docket no. 5837-P001CP1-10311280] filed concurrently herewith and entitled “METHOD AND APPARATUS FOR FORMING SUPERCONDUCTOR MATERIAL ON A TAPE SUBSTRATE,” to U.S. patent application Ser. No. ________ [attorney docket no. 5837-P004US-10311281] filed concurrently herewith and entitled “SYSTEM AND METHOD FOR PROVIDING PRECURSORS,” and to U.S. patent application Ser. No. ______ [attorney docket no. 5837-P005US-10311282] filed concurrently herewith and entitled “SYSTEM AND METHOD FOR JOINING SUPERCONDUCTIVITY TAPE,” the disclosures of which are hereby incorporated herein by reference.
Number | Date | Country | |
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60538849 | Jan 2004 | US |