JP3634078B2 - Oxide superconducting conductor - Google Patents

Oxide superconducting conductor Download PDF

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JP3634078B2
JP3634078B2 JP21480696A JP21480696A JP3634078B2 JP 3634078 B2 JP3634078 B2 JP 3634078B2 JP 21480696 A JP21480696 A JP 21480696A JP 21480696 A JP21480696 A JP 21480696A JP 3634078 B2 JP3634078 B2 JP 3634078B2
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thin film
intermediate thin
polycrystalline
oxide superconducting
orientation
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JPH09120719A (en
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隆 齊藤
康裕 飯島
真理子 保坂
伸行 定方
宰 河野
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Fujikura Ltd
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    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
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    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E40/00—Technologies for an efficient electrical power generation, transmission or distribution
    • Y02E40/60—Superconducting electric elements or equipment; Power systems integrating superconducting elements or equipment

Description

【０００１】
【発明の属する技術分野】
本発明は、超電導発電機用マグネット、磁気浮上列車用マグネット等に利用される酸化物超電導導体に係わり、オーバーオール（酸化物超電導導体全断面積）あたりの臨界電流密度が優れるという特性と、基材の長さ方向に対する超電導特性が安定した酸化物超電導層が形成されるという特性のうち少なくとも一方の特性を備えた酸化物超電導導体に関する。
【０００２】
【従来の技術】
近年になって発見された酸化物超電導体は、液体窒素温度を超える臨界温度を示す優れた超電導体であるが、現在、この種の酸化物超電導体を実用的な超電導体として使用するためには、種々の解決するべき問題点が存在している。その問題点の１つが、酸化物超電導体の臨界電流密度が低いという問題である。
【０００３】
前記酸化物超電導体の臨界電流密度が低いという問題は、酸化物超電導体の結晶自体に電気的な異方性が存在することが大きな原因となっており、特に酸化物超電導体はその結晶軸のａ軸方向とｂ軸方向には電気を流し易いが、ｃ軸方向には電気を流しにくいことが知られている。このような観点から酸化物超電導体を基材上に形成してこれを超電導体として使用するためには、基材上に結晶配向性の良好な状態の酸化物超電導体を形成し、しかも、電気を流そうとする方向に酸化物超電導体の結晶のａ軸あるいはｂ軸を配向させ、その他の方向に酸化物超電導体のｃ軸を配向させる必要がある。
【０００４】
【発明が解決しようとする課題】
ところで、酸化物超電導体を導電体として使用するためには、テープ状などの長尺の基材上に結晶配向性の良好な酸化物超電導層を形成する必要がある。ところが、金属テープなどの基材上に酸化物超電導層を直接形成すると、金属テープ自体が多結晶体でその結晶構造も酸化物超電導体と大きく異なるために、結晶配向性の良好な酸化物超電導層は到底形成できないものである。しかも、酸化物超電導層を形成する際に行なう熱処理によって金属テープと酸化物超電導層との間で拡散反応が生じるために、酸化物超電導層の結晶構造が崩れ、超電導特性が劣化する問題がある。
【０００５】
そこで本発明者らは、図１４に示すようなハステロイテープなどの金属テープからなる基材１の上にイットリウム安定化ジルコニア（ＹＳＺ）などの多結晶中間薄膜２を形成し、この多結晶中間薄膜２上に、酸化物超電導体の中でも臨界温度が約９０Ｋであり、液体窒素（７７Ｋ）中で用いることができる安定性に優れたＹ１Ｂａ２Ｃｕ３Ｏｘ系の超電導層３を形成することで超電導特性の優れた超電導導体１０を製造する試みを種々行なっている。
このような試みの中から本発明者らは先に、結晶配向性に優れた中間薄膜を形成するために、あるいは、超電導特性の優れた超電導テープを得るために、特願平３ー１２６８３６号、特願平３ー１２６８３７号、特願平３ー２０５５５１号、特願平４ー１３４４３号、特願平４ー２９３４６４号などにおいて特許出願を行なっている。
【０００６】
これらの特許出願に記載された技術によれば、ハステロイテープなどの金属テープの基材の片面にスパッタ装置により多結晶中間薄膜を形成する際に、スパッタリングと同時に基材成膜面の斜め方向からイオンビームを照射しながら多結晶中間薄膜を成膜する方法（イオンビームアシストスパッタリング法）により、結晶配向性に優れた多結晶中間薄膜を形成することができるものである。
この方法によれば、多結晶中間薄膜を形成する多数の結晶粒のそれぞれの結晶格子のａ軸あるいはｂ軸で形成する粒界傾角を３０度以下に揃えることができ、結晶配向性に優れた多結晶中間薄膜を形成することができる。そして更に、この配向性に優れた中間薄膜上にＹＢａＣｕＯ系の超電導層をレーザー蒸着法等により成膜するならば、酸化物超電導層の結晶配向性も優れたものになり、これにより、結晶配向性に優れ、７７Ｋで臨界電流密度が１０５Ａ／ｃｍ２以上と高い酸化物超電導層を形成することができる。
【０００７】
ところが前記特許出願に係る方法にあっては、基材の片面にイオンビームアシストスパッタリング法により多結晶中間薄膜を成膜すると圧縮応力により歪みが生じ、基材に反りが生じてしまう。酸化物超電導層の蒸着する際には、超電導特性が均質な酸化物超電導層を形成するために基材の表面温度を一定に保つ必要があるが、基材に反りがあると、基材表面を均一に加熱することが困難で基材の表面の温度分布にムラが生じてしまい、その結果、基材の長さ方向に対する超電導特性が不安定な酸化物超電導層が得られてしまうという問題があった。
さらにまた、前記特許出願に係る方法にあっては、得られる酸化物超電導層の膜厚が数μｍであるため、金属テープからなる基材の数１００μｍの厚さに比べて薄く、オーバーオール（酸化物超電導導体全断面積）あたりの臨界電流密度としては高くならないという問題があった。そこで、オーバーオールあたりの臨界電流密度を向上させるために、基材となる金属テープの厚さを薄くし、該基材の片面にイオンビームアシストスパッタリング法により多結晶中間薄膜を形成した後、この多結晶中間薄膜上にレーザ蒸着法等により酸化物超電導層を形成すると、酸化物超電導層の蒸着時に高温雰囲気によって基材が熱膨張し、該基材に反りやねじれなどの歪みが生じ、該基材上に形成されている多結晶中間薄膜にも歪みが生じてしまう。このような歪みが多結晶中間薄膜にあると、該多結晶中間薄膜上に形成される酸化物超電導層の結晶配向性が不良となり、目的とする超電導特性が得られない。
【０００８】
本発明は前記課題を解決するためになされたもので、多結晶中間薄膜の形成時の圧縮応力によって基材に反りが生じることなく、基材の長さ方向に対する超電導特性が安定した酸化物超電導層が形成されるという特性と、厚さの薄いテープ状の基材が用いられていても、酸化物超電導層の蒸着時の高温雰囲気によって上記基材に歪みが生じることが少なく、オーバーオールあたりの臨界電流密度が向上するという特性のうち少なくとも一方の特性を備えた酸化物超電導導体を提供することを目的とする。
【０００９】
【課題を解決するための手段】
請求項１記載の発明は前記課題を解決するために、テープ状の基材と、この基材の一方の面上に形成されて多数の結晶粒が結合されてなる配向制御多結晶中間薄膜と、上記基材の他方の面上に形成された多結晶中間速成薄膜と、上記配向制御多結晶中間薄膜上に形成された酸化物超電導層を具備してなるものである。
【００１０】
請求項２記載の発明は前記課題を解決するために、テープ状の基材と、この基材の両面上にそれぞれ形成されて多数の結晶粒が結合されてなる多結晶速成中間薄膜と、これら多結晶速成中間薄膜のうち一方の多結晶速成中間薄膜上に形成された配向制御多結晶中間薄膜と、この配向制御多結晶中間薄膜上に形成された酸化物超電導層を具備してなるものである。
【００１１】
請求項３記載の発明は前記課題を解決するために、テープ状の基材と、この基材の両面上にそれぞれ形成されて多数の結晶粒が結合されてなる多結晶速成中間薄膜と、これら多結晶速成中間薄膜上にそれぞれ形成された配向制御多結晶中間薄膜と、これら配向制御多結晶中間薄膜上にそれぞれ形成された酸化物超電導層を具備してなるものである。
【００１２】
請求項４記載の発明は前記課題を解決するために、請求項１〜３のいずれかに記載の酸化物超電導導体の配向制御多結晶中間薄膜を形成する多数の結晶粒のそれぞれの粒界傾角が３０度以下とするものである。請求項５記載の発明は前記課題を解決するために、請求項１〜４のいずれかに記載の酸化物超電導導体の中間薄膜がイットリウム安定化ジルコニアからなるものである。請求項６記載の発明は前記課題を解決するために、請求項１〜５のいずれかに記載の酸化物超電導導体において、配向制御多結晶中間薄膜がイオンビームアシストスパッタリング法により形成されたものである。
【００１３】
【発明の実施の形態】
以下、図面を参照して本発明の例について説明する。
図１は、本発明に係る酸化物超電導導体の第１の例を示すものであり、この例の酸化物超電導導体２０は、テープ状の基材２１の上面上に多数の結晶粒が結合されてなる配向制御多結晶中間薄膜２２が形成され、上記基材２１の下面上に多結晶速成中間薄膜２３が形成され、上記配向制御多結晶中間薄膜２２上に酸化物超電導層２４が形成されてなるものである。
【００１４】
前記基材２１の構成材料としては、ステンレス鋼、銅、または、ハステロイなどのニッケル合金などの合金各種金属材料から適宜選択される長尺の金属テープを用いることができる。この基材２１の厚みは、０．０１〜０．５ｍｍ、好ましくは０．０２〜０．１５ｍｍとされる。
基材２１の厚みが０．５ｍｍを超えると、後述する酸化物超電導層２４の膜厚に比べて厚く、オーバーオール（酸化物超電導導体全断面積）あたりの臨界電流密度としては低下してしまう恐れがある。一方、基材２１の厚みが０．０１ｍｍ未満であると、著しく基材の強度が低下し、超電導体の補強効果を消失してしまう恐れがある。
【００１５】
前記配向制御多結晶中間薄膜２２は、立方晶系の結晶構造を有する結晶の集合した微細な結晶粒が多数相互に結晶粒界を介して接合一体化されてなり、各結晶粒の結晶軸のｃ軸は基材２１の上面（成膜面）に対してほぼ直角に向けられ、各結晶粒の結晶軸のａ軸どうしおよびｂ軸どうしは、互いに同一方向に向けられて面内配向されている。各結晶粒の結晶のａ軸（あるいはｂ軸）どうしは、それらのなす角度（粒界傾角Ｋ）を３０度以内にして接合一体化されているのが好ましい。この配向制御多結晶中間薄膜２２の厚みは、０．１〜１．０μｍ、好ましくは０．３〜０．７μｍとされる。配向制御多結晶中間薄膜２２の厚みを１．０μｍを超えて厚くしてもももはや効果の増大は期待できず、経済的にも不利となる。一方、配向制御多結晶中間薄膜２２の厚みが０．１μｍ未満であると、薄すぎて基材２１を十分支持できず、後述する酸化物超電導層２４の蒸着時に高温雰囲気によって基材２１に歪みが生じる恐れがあり、また、熱処理時に酸化物超電導層２４の元素を基材２１側に拡散させてしまう恐れがあり、酸化物超電導層２４の成分組成が崩れる恐れがあるからである。
【００１６】
前記多結晶速成中間薄膜２３は、立方晶系の結晶構造を有する結晶の集合した微細な結晶粒が多数相互に結晶粒界を介して接合一体化されてなるものである。この多結晶速成中間薄膜２３の厚みは、０．１〜１．０μｍ、好ましくは０．３〜０．７μｍとされる。多結晶速成中間薄膜２３の厚みを１．０μｍを超えて厚くしてもももはや効果の増大は期待できず、経済的にも不利となる。一方、多結晶速成中間薄膜２３の厚みが０．１μｍ未満であると、薄すぎて基材２１を十分支持できず、後述する酸化物超電導層２４の蒸着時に高温雰囲気によって基材２１に歪みが生じる恐れがあるからである。
【００１７】
前記酸化物超電導層２４は、Ｙ１Ｂａ２Ｃｕ３Ｏｘ、Ｙ２Ｂａ４Ｃｕ８Ｏｘ、
Ｙ３Ｂａ３Ｃｕ６Ｏｘなる組成、（Ｂｉ，Ｐｂ）２Ｃａ２Ｓｒ２Ｃｕ３Ｏｘ、
（Ｂｉ，Ｐｂ）２Ｃａ２Ｓｒ３Ｃｕ４Ｏｘなる組成、
あるいはＴｌ２Ｂａ２Ｃａ２Ｃｕ３Ｏｘ、Ｔｌ１Ｂａ２Ｃａ２Ｃｕ３Ｏｘ、
Ｔｌ１Ｂａ２Ｃａ３Ｃｕ４Ｏｘなる組成などに代表される臨界温度の高い超電導材料からなるものである。この酸化物超電導層２４の厚みは０．５〜５μｍ程度とされる。
【００１８】
次に、前記配向制御多結晶中間薄膜２２と多結晶速成中間薄膜２３を製造する装置と製造方法について説明する。
図２は、前記多結晶速成中間薄膜２３を製造する装置の一例を示すものであり、この例の装置は、高周波スパッタ装置である。
本例の装置は、基材２１を保持する基材ホルダ３１と、この基材ホルダ３１の上方に所定間隔をもって対向配置された板状のターゲット３２を主体として構成されている。また、図中符号３３は、ターゲット３２を保持したターゲットホルダを示し、このターゲットホルダ３３は高周波電源３４に接続され、この高周波電源３４と前述の基材ホルダ３１はそれぞれ接地されている。また、図中符号３５は、テープ状の基材２１の送出装置、３６は基材２１の巻取装置を示し、この送出装置３５から連続的に基材ホルダ３１上に基材２１を送り出し、続いて巻取装置３６で巻き取ることで基材２１上に連続成膜することができるようになっている。
【００１９】
また、基材ホルダ３１、ターゲットホルダ３３は図示略の真空容器に収納されていて、基材ホルダ３１とターゲットホルダ３３の周囲を真空雰囲気に保持できるようになっている。更に前記真空容器には、ガスボンベなどの雰囲気ガス供給源が接続されていて、必要に応じて真空容器の内部を真空などの低圧状態で、かつ、アルゴンガスあるいはその他の不活性ガス雰囲気または酸素を含む不活性ガス雰囲気にすることができるようになっている。
以上の構成により、真空容器の内部を減圧してから高周波電源３４を作動させることによって基材２１の上方空間にプラズマを発生させることができ、このプラズマの作用によりターゲット３２の粒子をスパッタして基材２１側に向けて飛ばすことができるようになっている。
【００２０】
前記基材ホルダ３１は内部に加熱ヒータを備えて構成され、基材ホルダ３１上に配置された基材２１を必要に応じて所望の温度に加熱できるようになっている。
前記ターゲット３２は、目的とする多結晶速成中間薄膜２３を形成するためのものであって、目的の組成の多結晶中間薄膜と同一組成あるいは近似組成のものなどが用いられる。ターゲット３２として具体的には、ＭｇＯあるいはＹ２Ｏ３で安定化したジルコニア（ＹＳＺ）、ＭｇＯ、ＳｒＴｉＯ３などを用いることができるがこれらに限るものではなく、形成しようとする多結晶速成中間薄膜２３に見合うターゲットを適宜用いれば良い。
【００２１】
次に前記構成の装置を用いて基材２１上にＹＳＺの多結晶速成中間薄膜２３を形成する場合について説明する。
基材２１上に多結晶速成中間薄膜２３を形成するには、ＹＳＺのターゲットを用いるとともに基材２１を収納している真空容器の内部を真空引きして減圧雰囲気とする。そして、高周波電源３４を作動させる。これによりターゲット３２の構成粒子がスパッタされて基材２１上に飛来する。この粒子を所用時間かけて堆積させるならば、基材２１上に所望の厚さの多結晶速成中間薄膜を形成することができる。
このようにして得られた多結晶速成中間薄膜２３を構成する多数の結晶粒の結晶軸のａ軸とｂ軸とｃ軸は、いずれも任意な方向を向いていても良いし配向性があるものでも良い。
【００２２】
次に、図３は前述の配向制御多結晶中間薄膜２２を製造する装置の一例を示すものであり、この例の装置は、イオンビームスパッタ装置にイオンビームアシスト用のイオンガンを設けた構成となっている。
本例の装置は、基材２１を保持する基材ホルダ４５と、この基材ホルダ４５の斜め上方に所定間隔をもって対向配置された板状のターゲット４６と、前記基材ホルダ４５の斜め上方に所定間隔をもって対向され、かつ、前記ターゲット４６と離間して配置されたイオンガン４７と、前記ターゲット４６の斜め下方においてターゲット４６の下面に向けて配置されたスパッタビーム照射装置４８を主体として構成されている。また、図中符号４９は、ターゲット４６を保持したターゲットホルダを示している。また、図中符号５５は、テープ状の基材２１の送出装置、５６は基材２１の巻取装置を示し、この送出装置５５から連続的に基材ホルダ４５上に基材２１を送り出し、続いて巻取装置５６で巻き取ることで基材２１上に連続成膜することができるようになっている。
【００２３】
また、本の例の装置は図示略の真空容器に収納されていて、基材２１の周囲を真空雰囲気に保持できるようになっている。更に前記真空容器には、ガスボンベなどの雰囲気ガス供給源が接続されていて、真空容器の内部を真空などの低圧状態で、かつ、アルゴンガスあるいはその他の不活性ガス雰囲気または酸素を含む不活性ガス雰囲気にすることができるようになっている。
【００２４】
前記基材ホルダ４５は内部に加熱ヒータを備え、基材ホルダ４５の上に位置された基材２１を必要に応じて所望の温度に加熱できるようになっている。また、基材ホルダ４５の底部には角度調整機構Ｄが付設されている。この角度調整機構Ｄは、基材ホルダ４５の底部に接合された上部支持板６０と、この上部支持板６０にピン結合された下部支持板６１と、この下部支持板６１を支持する基台６２を主体として構成されている。前記上部支持板６０と下部支持板６１とはピン結合部分を介して互いに回動自在に構成されており、基材ホルダ４５の傾斜角度を調整できるようになっている。
なお、本例の装置では基材ホルダ４５の角度を調整する角度調整機構Ｄを設けたが、角度調整機構Ｄをイオンガン４７の支持部分に取り付けてイオンガン４７の傾斜角度を調整し、イオンビームの入射角度を調整するようにしても良い。また、角度調整機構は本の例の構成に限るものではなく、種々の構成のものを採用することができるのは勿論である。
【００２５】
前記ターゲット４６は、目的とする配向制御多結晶中間薄膜を形成するためのものであり、目的の組成の配向制御多結晶中間薄膜と同一組成あるいは近似組成のものなどを用いる。ターゲット４６として具体的には、ＭｇＯあるいはＹ２Ｏ３で安定化したジルコニア（ＹＳＺ）、ＭｇＯ、ＳｒＴｉＯ３などを用いるがこれに限るものではなく、形成しようとする配向制御多結晶中間薄膜に見合うターゲッを適宜用いれば良い。
【００２６】
前記イオンガン４７は、容器の内部に、蒸発源を収納し、蒸発源の近傍に引き出し電極を備えて構成されている。そして、前記蒸発源から発生した原子または分子の一部をイオン化し、そのイオン化した粒子を引き出し電極で発生させた電界で制御してイオンビームとして照射する装置である。粒子をイオン化するには直流放電方式、高周波励起方式、フィラメント式、クラスタイオンビーム方式などの種々のものがある。フィラメント式はタングステン製のフィラメントに通電加熱して熱電子を発生させ、高真空中で蒸発粒子と衝突させてイオン化する方法である。また、クラスタイオンビーム方式は、原料を入れたるつぼの開口部に設けられたノズルから真空中に出てくる集合分子のクラスタを熱電子で衝撃してイオン化して放射するものである。
本の例においては、図４に示す構成の内部構造のイオンガン４７を用いる。このイオンガン４７は、筒状の容器６５の内部に、引出電極６６とフィラメント６７とＡｒガスなどの導入管６８とを備えて構成され、容器６５の先端からイオンをビーム状に平行に照射できるものである。
【００２７】
前記イオンガン４７は、図３に示すようにその中心軸線Ｓを基材２１の上面（成膜面）に対して入射角度θ（基材２１の垂線（法線）と中心線Ｓとのなす角度）でもって傾斜させて対向されている。この入射角度θは５０〜６０度の範囲が好ましいが、５５〜６０度の範囲が最も好ましい。従ってイオンガン４７は基材２１の上面に対して入射角度θでもってイオンビームを照射できるように配置されている。
なお、前記イオンガン４７によって基材２１に照射するイオンビームは、
Ｈｅ＋、Ｎｅ＋、Ａｒ＋、Ｘｅ＋、Ｋｒ＋などの希ガスのイオンビーム、あるいは、それらと酸素イオンの混合イオンビームなどで良い。だだし、形成しようとする配向制御多結晶中間薄膜の結晶構造を整えるためには、ある程度の原子量が必要であり、あまりに軽量のイオンでは効果が薄くなることを考慮すると、Ａｒ＋、Ｋｒ＋などのイオンを用いることが好ましい。
前記スパッタビーム照射装置４８は、イオンガン４７と同等の構成をなし、ターゲット４６に対してイオンビームを照射してターゲット４６の構成粒子を基材２１に向けて叩き出すことができるものである。
【００２８】
次に前記構成の装置を用いてテープ状の基材２１の他方の面（多結晶速成中間薄膜２３が形成されていない側の面）上にＹＳＺの配向制御多結晶中間薄膜２２をイオンビームアシストスパッタリング法により形成する場合について説明する。
基材２１の多結晶速成中間薄膜２３が形成されていない側の面上に配向制御多結晶中間薄膜２２を形成するには、ＹＳＺのターゲットを用いるとともに、角度調整機構Ｄを調節してイオンガン４７から照射されるイオンビームを基材２１の上面に５０〜６０度の範囲の角度で照射できるようにする。次に基材２１を収納している容器の内部を真空引きして減圧雰囲気とする。この際の真空容器内の圧力は、イオンビームを使用する関係から図２に示す高周波スパッタ装置の真空容器内の圧力よりも低い値となる。そして、イオンガン４７とスパッタビーム照射装置４８を作動させる。
【００２９】
スパッタビーム照射装置４８からターゲット４６にイオンビームを照射すると、ターゲット４６の構成粒子が叩き出されて基材２１上に飛来する。そして、基材２１上に、ターゲット４６から叩き出した構成粒子を堆積させると同時にイオンガン４７からＡｒイオンと酸素イオンの混合イオンビームを照射して所望の厚みの配向制御多結晶中間薄膜２２を形成する。
このイオン照射する際の入射角度θは、５０〜６０度の範囲が好ましく、５５〜６０度の範囲が最も好ましい。ここでθを９０度とすると、多結晶中間薄膜２２のｃ軸は基材２１上の成膜面に対して直角に配向するものの、基材２１の成膜面上に（１１１）面が立つので好ましくない。また、θを３０度とすると、多結晶中間薄膜２２はｃ軸配向すらしなくなる。前記のような好ましい範囲の角度でイオンビーム照射するならば多結晶中間薄膜２２の結晶の（１００）面が立つようになる。
【００３０】
このような入射角度でイオンビーム照射を行ないながらスパッタリングを行なうことで、基材２１上に形成されるＹＳＺの配向制御多結晶中間薄膜２２の結晶軸のａ軸とｂ軸とを配向させることができるが、これは、堆積されている途中のスパッタ粒子に対して適切な角度でイオンビーム照射されたことによるものと思われる。
【００３１】
なお、この配向制御多結晶中間薄膜２２の結晶配向性が整う要因として本発明らは、以下のことを想定している。
ＹＳＺの配向制御多結晶中間薄膜２２の結晶の単位格子は、図５に示すように立方晶系であり、この結晶格子においては、基板法線方向が＜１００＞軸であり、他の＜０１０＞軸と＜００１＞軸はいずれも図５に示す方向となる。これらの方向に対し、基板法線に対して斜め方向から入射するイオンビームを考慮すると、図５の原点Ｏに対して単位格子の対角線方向、即ち、＜１１１＞軸に沿って入射する場合は５４．７度の入射角度となる。
【００３２】
ここで、前記のように入射角度５０〜６０度の範囲内でイオンビームを照射する際に最も良好な結晶配向性を示すということは、イオンビームの入射角度が前記５４．７度と一致するかその前後になった場合、イオンチャンネリングが最も効果的に起こり、基材２１上に堆積しつつある結晶において、基材２１の上面で前記角度に一致する配置関係になった原子のみが選択的に残り易くなり、その他の乱れた原子配列のものは斜め方向からのイオンビームのスパッタ効果によりスパッタされて除去される結果、配向性の良好な原子の集合した結晶のみが選択的に残って堆積してゆくことによるものと推定している。
ただし、このように堆積された結晶のうち、乱れた原子配列のものをイオンビームで除去しながら成膜するので、成膜レートは悪くなり、成膜速度は通常のスパッタリングで成膜するよりも遅くなる。
【００３３】
図６に、前記の方法で基材２１の一方の面上にＹＳＺの配向制御多結晶中間薄膜２２が形成され、基材２１の他方の面上に多結晶速成中間薄膜２３が形成された薄膜積層体２５を示す。なお、図６では結晶粒２７が１層のみ形成された状態を示しているが、結晶粒２７を多層構造としても差し支えないのは勿論である。
【００３４】
以上のように構成された薄膜積層体２５にあっては、更にその上に酸化物超電導層を形成することで実用に供される。そして、薄膜積層体２５の最上部には配向制御多結晶中間薄膜２２が形成されているので、この上に成膜される酸化物超電導層は結晶配向性に優れたものとなり、これにより超電導特性が向上する。
【００３５】
次に、前記薄膜積層体２５の上に酸化物超電導層を形成して酸化物超電導導体を製造する装置と製造する方法について説明する。
図７は酸化物超電導層を成膜法により形成する装置の一例を示すもので、図７はレーザ蒸着装置を示している。
この例のレーザ蒸着装置７０は、処理容器７１を有し、この処理容器７１の内部の蒸着処理室７２に薄膜積層体２５とターゲット７３を設置できるようになっている。即ち、蒸着処理室７２の底部には基台７４が設けられ、この基台７４の上面に薄膜積層体２５を設置できるようになっているとともに、基台７４の斜め上方に支持ホルダ７３ａによって支持されたターゲット７３が傾斜状態で設けられている。また、図中符号７５は薄膜積層体２５の送出装置、７６は薄膜積層体２５の巻取装置を示し、この送出装置７５から連続的に基台７４上に薄膜積層体２５を送り出し、続いて巻取装置７６で巻き取ることで薄膜積層体２５上に連続成膜することができるようになっている。また、処理容器７１は、排気孔７７ａを介して真空排気装置７７に接続されて蒸着処理室７２を所定の圧力に減圧できるようになっている。
【００３６】
前記ターゲット７３は、形成しようとする酸化物超電導層と同等または近似した組成、あるいは、成膜中に逃避しやすい成分を多く含有させた複合酸化物の焼結体あるいは酸化物超電導体などの板体からなっている。
従ってターゲット７３は、Ｙ１Ｂａ２Ｃｕ３Ｏｘ、Ｙ２Ｂａ４Ｃｕ８Ｏｘ、
Ｙ３Ｂａ３Ｃｕ６Ｏｘなる組成、（Ｂｉ，Ｐｂ）２Ｃａ２Ｓｒ２Ｃｕ３Ｏｘ、
（Ｂｉ，Ｐｂ）２Ｃａ２Ｓｒ３Ｃｕ４Ｏｘなる組成、
あるいはＴｌ２Ｂａ２Ｃａ２Ｃｕ３Ｏｘ、Ｔｌ１Ｂａ２Ｃａ２Ｃｕ３Ｏｘ、
Ｔｌ１Ｂａ２Ｃａ３Ｃｕ４Ｏｘなる組成などに代表される臨界温度の高い酸化物超電導層を形成するために使用するので、これと同一の組成か近似した組成のものを用いることが好ましい。
前記基台７４は加熱ヒータを内蔵したもので、薄膜積層体２５を必要に応じて所望の温度に加熱できるようになっている。
【００３７】
一方、処理容器７１の側方には、レーザ発光装置７８と第１反射鏡７９と集光レンズ８０と第２反射鏡８１とが設けられ、レーザ発光装置７８が発生させたレーザビームを処理容器７１の側壁に取り付けられた透明窓８２を介してターゲット７３に集光照射できるようになっている。レーザ発光装置７８はターゲット７３から構成粒子を叩き出すことができるものであれば、ＹＡＧレーザ、ＣＯ２レーザ、エキシマレーザなどのいずれのものを用いても良い。
【００３８】
次に前記ＹＳＺの配向制御多結晶中間薄膜２２の上に、酸化物超電導層２４を形成する方法について説明する。
まず、薄膜積層体２５をこれの配向制御多結晶中間薄膜２２側を上にして図７に示すレーザ蒸着装置７０の基台７４上に設置し、蒸着処理室７２を真空排気装置７７で減圧する。ここで必要に応じて蒸着処理室７２に酸素ガスを導入して蒸着処理室７２を酸素雰囲気としても良い。また、基台７４の加熱ヒータを作動させて薄膜積層体２５を所望の温度に加熱しても良い。
【００３９】
次にレーザ発光装置７８から発生させたレーザビームを蒸着処理室７２のターゲット７３に集光照射する。これによってターゲット７３の構成粒子がえぐり出されるか蒸発されてその粒子が配向制御多結晶中間薄膜２２上に堆積する。ここで構成粒子の堆積の際に配向制御多結晶中間薄膜２２が予めｃ軸配向し、ａ軸とｂ軸でも配向しているので、配向制御多結晶中間薄膜２２上に形成される酸化物超電導層２４の結晶のｃ軸とａ軸とｂ軸も配向制御多結晶中間薄膜２２に整合するようにエピタキシャル成長して結晶化する。これにより結晶配向性の良好な酸化物超電導層２４が得られる。なお、成膜後に必要に応じて酸化物超電導層２４の結晶構造を整えるための熱処理を施しても良い。
上述の方法により薄膜積層体２５の上に酸化物超電導層２４を形成すると、図１に示すような第１の例の酸化物超電導導体２０が得られる。
前記配向制御多結晶中間薄膜２２上に形成された酸化物超電導層２４は、多結晶状態となるが、この酸化物超電導層２４の結晶粒の１つ１つにおいては、基材２１の厚さ方向に電気を流しにくいｃ軸が配向し、基材２１の面方向にａ軸どうしあるいはｂ軸どうしが配向した結晶配向性が良好なものとなる。従って得られた酸化物超電導層２４は結晶粒界における量子的結合性に優れ、結晶粒界における超電導特性の劣化が少ないので、基材２１の面方向に電気を流し易く、臨界電流密度の優れたものが得られる。
【００４０】
第１の例の酸化物超電導導体２０にあっては、前述の構成としたことにより、テープ状の基材２１の厚さが薄くても、該基材２１が両面の配向制御多結晶中間薄膜２２と多結晶速成中間薄膜２３で支持されるので、酸化物超電導層２４の蒸着時に高温雰囲気によって基材２１に歪みが生じることが抑制される。これによって基材２１上の配向制御多結晶中間薄膜２２に歪みが生じることも少なくなり、配向制御多結晶中間薄膜２２の表面の平面性が向上するので、配向制御多結晶中間薄膜２２上に形成される酸化物超電導層２４の結晶配向性が良好となり、臨界電流密度が優れたものとなる。従って、この第１の例の酸化物超電導導体２０にあっては、厚みの薄いテープ状の基材２１が用いらているので、酸化物超電導導体の厚みが薄くなり、オーバーオール（酸化物超電導導体全断面積）あたりの臨界電流密度を向上させることができ、電流容量の大きい長尺の酸化物超電導導体を容易に提供することができる。
【００４１】
また、この第１の例の酸化物超電導導体２０は、基材２１の下面に形成された多結晶速成中間薄膜２３が絶縁層として機能するので、酸化物超電導層２４側のみさらに絶縁層を形成すればよく、また、マグネット等として用いる場合は、絶縁層を形成することなくそのまま巻き込むことが可能である。
また、配向制御多結晶中間薄膜２２を形成する多数の結晶粒のそれぞれの粒界傾角を３０度以下としたものにあっては、配向制御多結晶中間薄膜２２上に成膜された酸化物超電導層２４の結晶配向性がより良好になるので、より優れた超電導特性を示すものとなる。
上記第１の例の酸化物超電導導体２０にあっては、多結晶速成中間薄膜２３を高周波スパッタにより形成される場合について説明したが、ＣＶＤ法、真空蒸着法、電子ビーム蒸着法、レーザ蒸着法などの圧縮応力が入るプロセスで多結晶速成中間薄膜を成膜する必要があり、また、高エネルギープラズマによりアシストが必要であり、通常、Ａｒ等の希ガスが膜中にトラップされることが必要であるのでＰＶＤ法が好ましい。
【００４２】
また、上記第１の例の酸化物超電導導体２０にあっては、基材２１の下面に形成される中間薄膜が多結晶速成中間薄膜２３である場合について説明したが、この多結晶速成中間薄膜２３の代わりに配向制御多結晶中間薄膜２２が形成されていてもよく、すなわち図１０に示すような基材２１の両面上に多数の結晶粒が結合されてなる配向制御多結晶中間薄膜２２，２２が形成されたものであってもよい。基材２１の両面上に配向制御多結晶中間薄膜２２，２２を形成する場合、各配向制御多結晶中間薄膜２２はそれぞれイオンビームアシストスパッタリング法により形成されたものであることが好ましい。
図１０のような基材２１の両面上に配向制御多結晶中間薄膜２２，２２がイオンビームアシストスパッタリング法により形成された薄膜積層体２５にあっては、圧縮応力が入っているものの両面の配向制御多結晶中間薄膜２２，２２によって圧縮応力が打ち消されるため基材２１に反りが生じることを防止でき、さらに、基材２１の下面（加熱される面）にも配向制御多結晶中間薄膜２２が形成されているので、基材３１の酸化が防止される。これによって、配向制御多結晶中間薄膜２２上に酸化物超電導層２４を蒸着する時に薄膜積層体２５表面を均一に加熱し易くなり、薄膜積層体２５表面の温度分布にムラが生じることが殆どなく、薄膜積層体２５の温度が安定するので、基材２１の長さ方向に対する超電導特性が安定した酸化物超電導層２４を形成することができる。
従って、図１０に示した酸化物超電導導体２０にあっては、配向制御多結晶中間薄膜の形成時の圧縮応力によって基材に反りが生じることなく、基材の長さ方向に対する超電導特性が安定した酸化物超電導層が形成されるという特性と、厚さの薄いテープ状の基材が用いられていても、酸化物超電導層の蒸着時の高温雰囲気によって上記基材に歪みが生じることが少なく、オーバーオールあたりの臨界電流密度が向上するという特性の両方を備えているいう利点がある。
【００４３】
図８は、本発明に係る酸化物超電導導体の第２の例を示すものである。
この第２の例の酸化物超電導導体９０は、テープ状の基材２１の両面上にそれぞれ多結晶速成中間薄膜２３ａ，２３ｂが形成され、これら多結晶速成中間薄膜２３ａ，２３ｂのうち一方の多結晶速成中間薄膜２３ｂ上に配向制御多結晶中間薄膜２２ｂが形成され、この配向制御多結晶中間薄膜２２ｂ上に酸化物超電導層２４が形成されてなるものである。
【００４４】
この例の多結晶速成中間薄膜２３ａ，２３ｂは、先に説明した第１の例の多結晶中間速成薄膜２３と同等に多数の結晶粒が結合されてなるものであり、先に説明した方法とほぼ同様にして図２の高周波スパッタ装置を用いて形成でき、また、多結晶速成中間薄膜２３ｂの各結晶粒の結晶軸においてａ軸とｂ軸は特別には配向されていないが、ｃ軸は基材２１の上面（成膜面）に対してほぼ直角に向けられていることが好ましい。
この配向制御多結晶中間薄膜２２ｂは、先に説明した方法とほぼ同様にして、図３のイオンビームスパッタ装置にイオンビームアシスト用のイオンガンを備えた装置を用いて形成できるが、先の例のものと異なるところは、多結晶速成中間薄膜２３ｂ上に形成されている点である。
【００４５】
基材２１に対して上側の中間薄膜の厚みの合計、すなわち配向制御多結晶中間薄膜２２ｂと多結晶速成中間薄膜２３ｂとの厚みの合計は、０．１〜１．０μｍとされる。上側の中間薄膜の厚みの合計を１．０μｍを超えて厚くしてもももはや効果の増大は期待できず、経済的にも不利となる。一方、上側の中間薄膜の厚みの合計が０．１μｍ未満であると、薄すぎて基材２１を十分支持できず、後述する酸化物超電導層２４の蒸着時に高温雰囲気によって基材２１に歪みが生じる恐れがあり、また、熱処理時に酸化物超電導層２４の元素を基材２１側に拡散させてしまう恐れがあり、酸化物超電導層２４の成分組成が崩れる恐れがあるからである。
また、基材２１に対して下側の中間薄膜の厚み、すなわち多結晶速成中間薄膜２３ｂの厚みは、前記第１のの例の多結晶速成中間薄膜２３と同様の理由から０．１〜１．０μｍとされる。
【００４６】
この第２の例のように基材２１に対して上側の中間薄膜を多結晶速成薄膜２３ｂと配向制御多結晶薄膜２２ｂとの二層から構成するならば、多結晶速成中間薄膜２３ｂと配向制御多結晶中間薄膜２２ｂとを合わせた膜厚分を全て配向制御多結晶中間薄膜とするよりも短時間で成膜処理できるようになる。その理由は、第１の例のようにイオンビームを斜め方向から照射しながらスパッタリングすることによって基材２１に対して上側の中間薄膜である配向制御多結晶中間薄膜２２を形成する場合、その成膜速度は通常のイオンビームスパッタや高周波スパッタリングによって多結晶速成中間薄膜を形成する場合に比べて低下することになる。例えば、高周波スパッタリングによれば、通常、０．５μｍ／時間程度の速度で成膜処理できるが、斜め方向からイオンビームを照射しながらのスパッタリングによれば、０．１μｍ／時間程度の速度での成膜処理となる。
【００４７】
従って、第２の例の酸化物超電導導体９０にあっては、特に中間薄膜を多結晶速成薄膜と配向制御多結晶薄膜との二層から構成したことにより、多結晶速成中間薄膜２３ｂと配向制御多結晶中間薄膜２２ｂとを合わせた膜厚分を全て配向制御多結晶中間薄膜とするよりも、成膜に時間のかかる配向制御多結晶中間薄膜の部分が少なくなるうえ、多結晶速成中間薄膜部分は成膜速度が早いので、成膜時間が短縮される。
また、多結晶速成中間薄膜２３ｂと配向制御多結晶中間薄膜２２ｂを同一材料から構成すると、両薄膜２３ｂ、２２ｂの接合性は良好になり、両者の接合強度も十分に高いものとなる。
【００４８】
図９は、本発明に係る酸化物超電導導体の第３の例を示すものである。
この第３の例の酸化物超電導導体１００は、テープ状の基材２１の両面上にそれぞれ多数の結晶粒が結合されてなる多結晶速成中間薄膜２３ａ，２３ｂが形成され、これら多結晶速成中間薄膜２３ａ，２３ｂ上にそれぞれ配向制御多結晶中間薄膜２２ａ，２２ｂが形成され、これら配向制御多結晶中間薄膜２２ａ，２２ｂ上にそれぞれ酸化物超電導層２４ａ、２４ｂが形成されてなるものである。
【００４９】
この第３の例の酸化物超電導導体１００が、先に説明した第２の例の酸化物超電導導体９０と異るところは、基材に対して下側の多結晶速成中間薄膜２３ａ上にも配向制御多結晶中間薄膜２２ａが形成され、さらに該配向制御多結晶中間薄膜２２ａ上に酸化物超電導層２４ａが形成されている点である。
この例の多結晶速成中間薄膜２３ａは、先に説明した第１の例の多結晶中間速成薄膜２３と同等に多数の結晶粒が結合されてなるものであり、先に説明した方法とほぼ同様にして図２の高周波スパッタ装置を用いて形成でき、また、多結晶速成中間薄膜２３ａの各結晶粒の結晶軸においてａ軸とｂ軸は特別には配向されていないが、ｃ軸は基材２１の上面（成膜面）に対してほぼ直角に向けられていることが好ましい。
また、この配向制御多結晶中間薄膜２２ａは、先に説明した方法とほぼ同様にして、図３のイオンビームスパッタ装置にイオンビームアシスト用のイオンガンを備えた装置を用いて形成できる。
基材２１の両面上に多結晶速成中間薄膜２３ａ，２３ｂを介して形成される配向制御多結晶中間薄膜２２ａ，２２ｂは、それぞれイオンビームアシストスパッタリング法により形成されたものであることが好ましい。このように配向制御多結晶中間薄膜２２ａ，２２ｂがイオンビームアシストスパッタリング法により形成された薄膜積層体２５にあっては、圧縮応力が入っているものの両面の配向制御多結晶中間薄膜２２ａ，２２ｂによって圧縮応力が打ち消されるため基材２１に反りが生じることを防止でき、さらに、基材２１の下面（加熱される面）にも多結晶速成中間薄膜２３ａや配向制御多結晶中間薄膜２２ａが形成されているので、基材３１の酸化が防止される。これによって、配向制御多結晶中間薄膜２２ａ，２２ｂ上に酸化物超電導層２４ａ，２４ｂを蒸着する時に薄膜積層体２５表面を均一に加熱し易くなり、薄膜積層体２５表面の温度分布にムラが生じることが殆どなく、薄膜積層体２５の温度が安定するので、基材２１の長さ方向に対する超電導特性が安定した酸化物超電導層２４ａ，２４ｂを形成することができる。
【００５０】
基材２１に対して下側の中間薄膜の厚みの合計、すなわち配向制御多結晶中間薄膜２２ａと多結晶速成中間薄膜２３ａとの厚みの合計は、前記第２の例の配向制御多結晶中間薄膜２２ｂと多結晶速成中間薄膜２３ｂと同様の理由から０．１〜１．０μｍとされる。
酸化物超電導層２４ａは、先に説明した方法とほぼ同様にして、図７のレーザ蒸着装置を用いて形成でき、その厚みは前記第１の例の酸化物超電導層２４と同様に０．５〜５μｍ程度とされる。
【００５１】
第３の例の酸化物超電導導体１００にあっては、特に基材２１の両面上に中間薄膜を介して酸化物超電導層が形成されているので、オーバーオール（酸化物超電導導体全断面積）あたりの臨界電流密度が第１の例の酸化物超電導導体２０や第２の例の酸化物超電導導体９０の約２倍程度となり、オーバーオールあたりの臨界電流密度が大きくなり、電流容量のより大きい長尺の酸化物超電導導体を容易に提供することができるという利点がある。
さらに、第３の例の酸化物超電導導体１００において、配向制御多結晶中間薄膜２２ａ，２２ｂをそれぞれイオンビームアシストスパッタリング法により形成したものにあっては、配向制御多結晶中間薄膜の形成時の圧縮応力によって基材２１に反りが生じることなく、基材２１の長さ方向に対する超電導特性が安定した酸化物超電導層が形成されるという特性も備えているいう利点がある。
【００５２】
（本発明の作用）
本発明においては、テープ状の基材の両面上にそれぞれ中間薄膜を形成し、さらにこれら中間薄膜のうち配向制御多結晶中間薄膜上に酸化物超電導層を形成したことにより、テープ状の基材の厚さが薄くても、該基材が両面の中間薄膜で支持されるので、酸化物超電導層の蒸着時に高温雰囲気によって基材に歪みが生じることが抑制される。これによって基材上の中間薄膜に歪みが生じることも少なくなり、中間薄膜の表面の平面性が向上するので、配向制御多結晶中間薄膜上に形成される酸化物超電導層の結晶配向性が良好となる。
【００５３】
また、中間薄膜を多結晶速成薄膜と配向制御多結晶薄膜との二層から構成したことにより、多結晶速成中間薄膜と配向制御多結晶中間薄膜とを合わせた膜厚分を全て配向制御多結晶中間薄膜とするよりも、成膜に時間のかかる配向制御多結晶中間薄膜の部分が少なくなるうえ、多結晶速成中間薄膜部分は成膜速度が早いので、成膜時間が短縮される。
また、粒界傾角を３０度以下とした配向制御多結晶薄膜上に成膜された酸化物超電導層は結晶配向性がより良好になるので、より優れた超電導特性を示す。 さらに、基材の両面上の配向制御多結晶中間薄膜をイオンビームアシストスパッタリング法により形成したことにより、圧縮応力が入っているものの両面の配向制御多結晶中間薄膜によって圧縮応力が打ち消されるため基材に反りが生じることを防止でき、さらに、基材の下面（加熱される面）にも多結晶速成中間薄膜や配向制御多結晶中間薄膜が形成されているので、基材の酸化が防止される。これによって、配向制御多結晶中間薄膜上に酸化物超電導層を蒸着する時に薄膜積層体表面を均一に加熱し易くなり、薄膜積層体表面の温度分布にムラが生じることが殆どなく、薄膜積層体の温度が安定する。
【００５４】
【実施例】
（実施例１）
図２に示す構成の高周波スパッタ装置を使用し、この装置の真空容器の内部を真空ポンプで真空引きして１×１０−３トールに減圧した。基材として、幅１０ｍｍ、厚さ０．１ｍｍ、長さ１０ｃｍのハステロイＣ２７６テープを使用した。ターゲットはＹＳＺ（安定化ジルコニア）製のものを用い、スパッタ電圧３００Ｖ、スパッタ電流１００ｍＡに設定し、スパッタリングを１時間行なって基材の一方の面（下面）上に厚さ０．５μｍの膜状のＹＳＺの多結晶速成中間薄膜を形成した。
【００５５】
次に、図３に示す構成のイオンビームスパッタ装置を使用し、この装置を収納した真空容器内部を真空ポンプで真空引きして３．０×１０−４トールに減圧した。ターゲットはＹＳＺ（安定化ジルコニア）製のものを用い、スパッタ電圧１０００Ｖ、スパッタ電流１００ｍＡ、イオン源のビームの入射角度を５５度に各々設定し、イオン源のアシスト電圧を３００Ｖに、イオンビームの電流密度を２０μＡ／ｃｍ２にそれぞれ設定して基材の他方の面（上面）上にスパッタリングと同時にイオン照射を行なって５時間成膜処理することで厚さ０．５μｍのＹＳＺ配向制御多結晶中間薄膜を形成し、図６と同様の薄膜積層体を得た。なお、前記イオンビームの電流密度とは、試料近くに接地した電流密度計測装置の計測数値によるものである。
【００５６】
次に、前記配向制御多結晶中間薄膜上に図７に示す構成のレーザ蒸着装置を用いて厚さ１．０μｍの酸化物超電導層を形成し、図１と同様の酸化物超電導導体を作製した。ターゲットとして、Ｙ０．７Ｂａ１．７Ｃｕ３．０Ｏ７−ｘなる組成の酸化物超電導体からなるターゲットを用いた。蒸着処理室の内部を１×１０−６トールに減圧した後、内部に酸素を導入し２×１０−３トールとした後、レーザ蒸着を行なった。ターゲット蒸発用のレーザとして波長１９３ｎｍのＡｒＦレーザを用いた。この成膜後、４００゜Ｃで６０分間、酸素雰囲気中において薄膜を熱処理した。ここでの蒸着および熱処理の際、上記基材には歪みが生じなかった。以上の処理で得られた酸化物超電導導体は、厚さ１０２．０μｍ、 幅１０ｍｍ、長さ１０ｃｍのものである。
【００５７】
この酸化物超電導導体を冷却し、臨界電流密度の測定を行なった結果、臨界電流密度＝５．１×１０５Ａ／ｃｍ２（７７Ｋ、０Ｔ）を示し、オーバーオールあたりの臨界電流密度＝５，０００Ａ／ｃｍ２（７７Ｋ、０Ｔ）を示し、極めて優秀な超電導特性を発揮することを確認できた。
よって得られた酸化物超電導導体は、厚さが０．１ｍｍと薄い基材を用いても、酸化物超電導層の蒸着時に高温雰囲気によって上記基材に歪みが生じることがなく、オーバーオールあたりの臨界電流密度が向上することが明らかになった。
【００５８】
（実施例２）
基材として、幅１０ｍｍ、厚さ０．０５ｍｍ、長さ１０ｃｍのハステロイテープを用いた以外は、前記実施例１と同様にして酸化物超電導導体を作製した。ここでの酸化物超電導導体は、厚さ５２．０μｍ、幅１０ｍｍ、長さ１０ｃｍのものである。
この酸化物超電導導体を冷却し、臨界電流密度の測定を行なった結果、臨界電流密度＝４．８×１０５Ａ／ｃｍ２（７７Ｋ、０Ｔ）を示し、オーバーオールあたりの臨界電流密度＝９．２×１０３Ａ／ｃｍ２を示し、極めて優秀な超電導特性を発揮することを確認できた。
よって得られた酸化物超電導導体は、厚さが０．０５ｍｍと薄い基材を用いても、酸化物超電導層の蒸着時に高温雰囲気によって上記基材に歪みが生じることがなく、オーバーオールあたりの臨界電流密度が向上することが明らかになった。
【００５９】
（比較例１）
基材として、幅１０ｍｍ、厚さ０．５ｍｍ、長さ１０ｃｍのハステロイテープを用い、かつ該基材の下面に多結晶速成中間薄膜を形成しない以外は、前記実施例１と同様にして酸化物超電導導体を作製した。ここでの酸化物超電導導体は、厚さ５０１．５μｍ、幅０．５ｍｍ、長さ１０ｃｍのものであった。
この酸化物超電導導体を冷却し、臨界電流密度の測定を行なった結果、臨界電流密度＝５．２×１０５Ａ／ｃｍ２（７７Ｋ、０Ｔ）を示したが、オーバーオールあたりの臨界電流密度＝１．０×１０３Ａ／ｃｍ２と低いものであった。
【００６０】
（比較例２）
基材の下面に多結晶速成中間薄膜を形成しない以外は、前記実施例１と同様にして酸化物超電導導体を作製した。ここでの酸化物超電導導体は、厚さ１０１．５μｍ、幅１０ｍｍ、長さ１０ｃｍのものであった。
この酸化物超電導導体を冷却し、臨界電流密度の測定を行なった結果、臨界電流密度＝１．１×１０４Ａ／ｃｍ２（７７Ｋ、０Ｔ）を示し、オーバーオールあたりの臨界電流密度＝１×１０２Ａ／ｃｍ２と低いものであった。また、この酸化物超電導導体は、酸化物超電導層の蒸着時に高温雰囲気によって上記基材に歪みが生じた。
【００６１】
（実施例３）
図７に示す構成のレーザ蒸着装置を使用し、幅１０ｍｍ、厚さ０．２ｍｍ、長さ１０ｃｍのハステロイＣ２７６テープからなる基材の両面上にそれぞれ厚さ０．５μｍの膜状のＹＳＺの多結晶速成中間薄膜を形成した。ターゲットとして、ＹＳＺ（安定化ジルコニア）室温にてレーザ蒸着を行なった。ターゲット蒸発用のレーザとして波長１９３ｎｍのＡｒＦレーザを用いた。ここで基材の片面に厚さ０．５μｍの多結晶速成中間薄膜を成膜するのに要した時間は１０分であり、従って両面に多結晶速成中間薄膜を成膜するのに要した時間は２０分であった。次に、図３に示す構成のイオンビームスパッタ装置を使用し、この装置を収納ターゲットはＹＳＺ（安定化ジルコニア）製のものを用い、スパッタ電圧１０００Ｖ、スパッタ電流１００ｍＡ、イオン源のビームの入射角度を５５度に各々設定し、イオン源のアシスト電圧を３００Ｖに、イオンビームの電流密度を２０μＡ／ｃｍ２にそれぞれ設定して前記基材の両面に形成された多結晶速成中間薄膜のうち、一方の多結晶速成中間薄膜上にスパッタリングと同時にイオン照射を行なうイオンビームアシストスパッタリング法により１時間成膜処理することで厚さ０．１μｍのＹＳＺ配向制御多結晶中間薄膜を形成した。
【００６２】
ここで前述の多結晶速成中間薄膜は、厚さ０．５μｍのものを１０分で成膜したが、配向制御多結晶中間薄膜は、厚さ０．１μｍのものを１時間成膜できたので、レーザ蒸着により多結晶速成中間薄膜を形成する方が、イオンビームアシストを適用したスパッタリングで配向制御多結晶中間薄膜を製造するよりも５倍程度の速度で成膜できることが明かになった。
【００６３】
次に、前記配向制御多結晶中間薄膜上に図７に示すレーザ蒸着装置を用いて前記実施例１と同様にして厚さ１．０μｍの酸化物超電導層を形成し、図８と同様の酸化物超電導導体を作製した。ここでの熱処理の際、上記基材には歪みが生じなかった。以上の処理で得られた酸化物超電導導体は、厚さ２０２．１μｍ、幅１０ｍｍ、長さ１０ｃｍのものである。
【００６４】
この酸化物超電導導体を冷却し、臨界電流密度の測定を行なった結果、臨界電流密度＝５．２×１０５Ａ／ｃｍ２（７７Ｋ、０Ｔ）を示し、オーバーオールあたりの臨界電流密度＝２．５×１０３Ａ／ｃｍ２（７７Ｋ、０Ｔ）を示し、極めて優秀な超電導特性を発揮することを確認できた。
よって得られた酸化物超電導導体は、厚さが０．２ｍｍと薄い基材を用いても、酸化物超電導層の蒸着時に高温雰囲気によって上記基材に歪みが生じることがなく、オーバーオールあたりの臨界電流密度が向上することが明かになった。
【００６５】
（比較例３）
基材の下面に多結晶速成中間薄膜を形成しない以外は、前記実施例３と同様にして酸化物超電導導体を作製した。ここでの酸化物超電導導体は、厚さ２０１．６μｍ、幅１０ｍｍ、長さ１０ｃｍのものであった。
この酸化物超電導導体を冷却し、臨界電流密度の測定を行なった結果、臨界電流密度＝２．３×１０４Ａ／ｃｍ２（７７Ｋ、０Ｔ）を示したが、オーバーオールあたりの臨界電流密度＝１．１×１０２Ａ／ｃｍ２と低いものであった。また、この酸化物超電導導体は、酸化物超電導層の蒸着時に高温雰囲気によって上記基材に歪みが生じた。
【００６６】
（実施例４）
前記実施例３と同様にして基材の両面に多結晶速成中間薄膜を形成した。
次に、図３に示す構成のイオンビームスパッタ装置を使用し、前記実施例３と同様にして基材の両面に形成された多結晶速成中間薄膜のうち、一方の多結晶速成中間薄膜上にスパッタリングと同時にイオン照射を行なって１時間成膜処理することで厚さ０．１μｍのＹＳＺ配向制御多結晶中間薄膜を形成した。この後、他方の多結晶速成中間薄膜上に前述の方法と同様にして厚さ０．１μｍのＹＳＺ配向制御多結晶中間薄膜を形成した。
【００６７】
次に、基材の両側の前記配向制御多結晶中間薄膜上に図７に示す構成のレーザ蒸着装置を用いて前記実施例１と同様にして厚さ１．０μｍの酸化物超電導層をそれぞれ形成し、図９と同様の酸化物超電導導体を作製した。ここでの熱処理の際、上記基材には歪みが生じなかった。以上の処理で得られた酸化物超電導導体は、厚さ２０３．２μｍ、幅０．５ｍｍ、長さ１０ｃｍのものである。
【００６８】
この酸化物超電導導体を冷却し、臨界電流密度の測定を行なった結果、臨界電流密度＝４．８×１０５Ａ／ｃｍ２（７７Ｋ、０Ｔ）を示し、オーバーオールあたりの臨界電流密度＝４．７×１０３Ａ／ｃｍ２（７７Ｋ、０Ｔ）を示し、極めて優秀な超電導特性を発揮することを確認できた。
よって得られた酸化物超電導導体は、厚さが０．２ｍｍと薄い基材を用いても、酸化物超電導層の蒸着時に高温雰囲気によって上記基材に歪みが生じることがなく、オーバーオールあたりの臨界電流密度が実施例３の酸化物超電導導体の約２倍程度と大きいことが明かになった。
【００６９】
（実施例５）
基材として幅１０ｍｍ、厚さ０．２ｍｍ、長さ８０ｃｍのハステロイテープを用い、基材の上面上に形成するＹＳＺ配向制御多結晶中間薄膜の厚みを０．７μｍとし、基材の下面上に厚さ０．７μｍのＹＳＺ配向制御多結晶中間薄膜をイオンビームアシストスパッタリング法により形成した以外は実施例１と略同様にして薄膜積層体を得た。
ついで、一方の配向制御多結晶中間薄膜上に図７に示す構成のレーザ蒸着装置を用いて厚さ１．０μｍの酸化物超電導層を形成し、図１０と同様の酸化物超電導導体を作製した。
【００７０】
（比較例４）
基材の下面に配向制御多結晶中間薄膜を形成しない以外は前記実施例５と同様にして積層体を得た。
ついで、基材の上面に形成された厚さ０．７μｍのＹＳＺ配向制御多結晶中間薄膜上に図７に示す構成のレーザ蒸着装置を用いて厚さ１．０μｍの酸化物超電導層を形成し、図１４と同様の酸化物超電導導体を作製した。
【００７１】
前記実施例５で得られた薄膜積層体ならびに比較例４で得られた積層体を
９００〜９５０℃で加熱し、１ｍ／ｈで移動させたときの幅方向に沿った表面形状を測定することにより、反り状態を調べた。図１１に実施例５で得られた薄膜積層体の表面形状のプロファイルを示す。また、図１２に比較例４で得られた積層体の表面形状のプロファイルを示す。図１１、図１２中、横軸は幅方向の長さ（μｍ）であり、縦軸は厚み方向の高さ（オングストローム）である。
【００７２】
表面形状のプロファイルから反りの曲率半径は以下の式（Ｉ）により算出することができる。
Ｒ＝（Ｘ２＋Ｙ２）／２Ｙ ・・・（Ｉ）
式Ｉ中、Ｒは曲率半径、Ｘは表面形状のプロファイル中の高さがピークのときの幅方向の長さ（μｍ）、Ｙは表面形状のプロファイル中の高さがピークのときの厚み方向の高さ（オングストローム）を表す。
【００７３】
実施例５の薄膜積層体は図１１よりＸ＝４５００（μｍ）、
Ｙ＝｜−１００，０００｜（オングストローム）であるから、これらをＩ式に代入するとＲ＝９６４（ｃｍ）であった。
これに対して比較例４の積層体では図１２よりＸ＝４５００（μｍ）、
Ｙ＝４００，０００（オングストローム）であるから、これらをＩ式に代入するとＲ＝２５．３（ｃｍ）である。これより実施例５で得られた薄膜積層体（基材の両面に配向制御多結晶中間薄膜を形成したもの）は、比較例４で得られた積層体（基材の片面のみに配向制御多結晶中間薄膜を形成したもの）に比べて曲率半径が大きく、反り量が小さいことが分った。
【００７４】
実施例５ならびに比較例４で得られた酸化物超電導導体を、それぞれ酸化物超電導導体の中央部分側に対し、スパッタ装置によりＡｇコーティングを施し、更に両端部側にそれぞれＡｇの電極を形成し、Ａｇコーティング後に純酸素雰囲気中にて５００℃で２時間熱処理を施して測定試料とした。
そして、これら試料を液体窒素で７７Ｋに冷却し、外部磁場０Ｔ（テスラ）の条件で各試料における長さ方向ごとの臨界電流（Ｉｃ）を測定した結果を図１３に示す。図１３中、実線▲１▼は実施例５で得られた酸化物超電導導体の長さ方向の位置ごとの臨界電流を示すものであり、破線▲２▼は比較例４で得られた酸化物超電導導体の長さ方向の位置ごとの臨界電流を示すものである。
【００７５】
図１３から明らかなように、比較例４で得られた酸化物超電導導体は、長さ方向の臨界電流がいずれの箇所においても１５Ａ以下の値を示しており、基材の長さ方向に対して超電導特性が不良な酸化物超電導薄膜が形成されていることが分る。これに対して実施例５で得られた酸化物超電導導体は、長さ方向の臨界電流がいずれの箇所においても１８Ａ以上の特性が得られており、さらに、この実施例５の酸化物超電導導体の臨界電流の平均値は、比較例４のものの約２倍であり、従って基材の長さ方向に対して超電導特性が良好な酸化物超電導薄膜が形成されていることが分る。
【００７６】
【発明の効果】
以上説明したように本発明の酸化物超電導導体は、テープ状の基材の両面上にそれぞれ中間薄膜が形成され、さらにこれら中間薄膜のうち配向制御多結晶中間薄膜上に酸化物超電導層を形成されたものであるので、テープ状の基材の厚さが薄くても、該基材が両面の中間薄膜で支持されるので、酸化物超電導層の蒸着時に高温雰囲気によって基材に歪みが生じることが抑制される。これによって基材上の中間薄膜に歪みが生じることも少なくなり、配向制御多結晶中間薄膜の表面の平面性が向上するので、配向制御多結晶中間薄膜上に形成される酸化物超電導層の結晶配向性が良好となり、臨界電流密度が優れたものとなる。従って、本発明の酸化物超電導導体にあっては、厚みの薄いテープ状の基材が使用できるので、酸化物超電導導体の厚みを薄くすることができ、オーバーオール（酸化物超電導導体全断面積）あたりの臨界電流密度を向上させることができ、電流容量の大きい長尺の酸化物超電導導体を容易に提供することができるという利点がある。また、本発明の酸化物超電導導体は、基材の両面に形成された中間薄膜が絶縁層として機能するので、酸化物超電導層側のみさらに絶縁層を形成すればよく、また、マグネット等として用いる場合は、絶縁層を形成することなくそのまま巻き込むことが可能である。
【００７７】
また、特に中間薄膜を多結晶速成薄膜と配向制御多結晶薄膜との二層から構成した酸化物超電導導体にあっては、多結晶速成中間薄膜と配向制御多結晶中間薄膜とを合わせた膜厚分を全て配向制御多結晶中間薄膜とするよりも、成膜に時間のかかる配向制御多結晶中間薄膜の部分が少なくなるうえ、多結晶速成中間薄膜部分は成膜速度が早いので、成膜時間が短縮される。
【００７８】
また、基材の両面上に中間薄膜を介して酸化物超電導層が形成された酸化物超電導導体にあっては、オーバーオール（酸化物超電導導体全断面積）あたりの臨界電流密度が基材の一方の面上だけに酸化物超電導層が形成された酸化物超電導導体の約２倍程度となり、オーバーオールあたりの臨界電流密度が大きく、電流容量のより大きい長尺の酸化物超電導導体を容易に提供することができるという利点がある。
また、配向制御多結晶中間薄膜を形成する多数の結晶粒のそれぞれの粒界傾角を３０度以下としたものにあっては、配向制御多結晶中間薄膜上に成膜された酸化物超電導層の結晶配向性がより良好になるので、より優れた超電導特性を示すものとなる。
【００７９】
さらに、基材の両面上の配向制御多結晶中間薄膜をイオンビームアシストスパッタリング法により形成したものにあっては、圧縮応力が入っているものの両面の配向制御多結晶中間薄膜によって圧縮応力が打ち消されるため基材に反りが生じることを防止でき、しかも、基材の下面（加熱される面）にも多結晶速成中間薄膜や配向制御多結晶中間薄膜が形成されているので、基材の酸化が防止される。これによって、配向制御多結晶中間薄膜上に酸化物超電導層を蒸着する時に薄膜積層体表面を均一に加熱し易くなり、薄膜積層体表面の温度分布にムラが生じることが殆どなく、薄膜積層体の温度が安定するので、基材の長さ方向に対する超電導特性が安定した酸化物超電導層を形成することができる。
従って、本発明の酸化物超電導導体によれば、配向制御多結晶中間薄膜の形成時の圧縮応力によって基材に反りが生じることなく、基材の長さ方向に対する超電導特性が安定した酸化物超電導層が形成されるという特性と、厚さの薄いテープ状の基材が用いられていても、酸化物超電導層の蒸着時の高温雰囲気によって上記基材に歪みが生じることが少なく、オーバーオールあたりの臨界電流密度が向上するという特性の少なくとも一方の特性を備えた酸化物超電導導体を提供することができる。
【図面の簡単な説明】
【図１】本発明に係る酸化物超電導導体の第１の例を示す断面図である。
【図２】本発明に係る酸化物超電導導体の製造に好適に用いられる、基材上に多結晶速成中間薄膜を形成する高周波スパッタ装置の一例を示す構成図である。
【図３】本発明に係る酸化物超電導導体の製造に好適に用いられる、基材上に配向制御多結晶中間薄膜を形成するイオンビームスパッタ装置の一例を示す構成図である。
【図４】図３に示す装置に用いられるイオンガンの一例を示す断面図である。
【図５】イオンビーム照射とともに成膜処理を行う場合に、イオンビームの入射角度と立方晶系の結晶格子との角度関係を示す説明図である。
【図６】本発明に係る酸化物超電導導体の薄膜積層体を示す構成図である。
【図７】本発明に係る酸化物超電導導体の製造に好適に用いられる、配向制御多結晶中間薄膜上に酸化物超電導層を形成するための装置の一例を示す構成図である。
【図８】本発明に係る酸化物超電導導体の第２の例を示す断面図である。
【図９】本発明に係る酸化物超電導導体の第３の例を示す断面図である。
【図１０】本発明に係わる酸化物超電導体のその他の例を示す断面図である。
【図１１】実施例５で得られた薄膜積層体の表面形状のプロファイルである。
【図１２】比較例４で得られた積層体の表面形状のプロファイルである。
【図１３】実施例５、比較例４で得られた酸化物超電導導体の長さ方向の位置ごとの臨界電流を示すグラフである。
【図１４】従来の酸化物超電導導体の例を示す断面図である。
【符号の説明】
２０、９０、１００・・・酸化物超電導導体、
２１・・・基材、
２２、２２ａ、２２ｂ…配向制御多結晶中間薄膜、
２３、２３ａ、２３ｂ・・・多結晶速成中間薄膜、
２４、２４ａ、２４ｂ…酸化物超電導層。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an oxide superconducting conductor used for a magnet for a superconducting generator, a magnet for a magnetic levitation train, etc. The present invention relates to an oxide superconducting conductor having at least one of the characteristics that an oxide superconducting layer having stable superconducting characteristics in the length direction is formed.
[0002]
[Prior art]
The oxide superconductor discovered in recent years is an excellent superconductor exhibiting a critical temperature exceeding the liquid nitrogen temperature, but at present, to use this kind of oxide superconductor as a practical superconductor. There are various problems to be solved. One of the problems is that the critical current density of the oxide superconductor is low.
[0003]
The problem that the critical current density of the oxide superconductor is low is largely due to the presence of electrical anisotropy in the oxide superconductor crystal itself. In particular, the oxide superconductor has its crystal axis. It is known that electricity can easily flow in the a-axis direction and b-axis direction, but it is difficult to flow electricity in the c-axis direction. From this point of view, in order to form an oxide superconductor on a substrate and use it as a superconductor, an oxide superconductor with a good crystal orientation is formed on the substrate, It is necessary to orient the a-axis or b-axis of the oxide superconductor crystal in the direction in which electricity is to flow and to orient the c-axis of the oxide superconductor in the other direction.
[0004]
[Problems to be solved by the invention]
By the way, in order to use an oxide superconductor as a conductor, it is necessary to form an oxide superconducting layer with good crystal orientation on a long substrate such as a tape. However, when an oxide superconducting layer is formed directly on a base material such as a metal tape, the metal tape itself is polycrystalline and its crystal structure is significantly different from that of an oxide superconductor. The layer cannot be formed at all. In addition, since a diffusion reaction occurs between the metal tape and the oxide superconducting layer due to the heat treatment performed when forming the oxide superconducting layer, there is a problem that the crystal structure of the oxide superconducting layer breaks down and the superconducting characteristics deteriorate .
[0005]
Accordingly, the present inventors formed a polycrystalline intermediate thin film 2 such as yttrium-stabilized zirconia (YSZ) on a base material 1 made of a metal tape such as a Hastelloy tape as shown in FIG. 2 and Y1Ba which has a critical temperature of about 90K among oxide superconductors and has excellent stability that can be used in liquid nitrogen (77K). 2 Cu 3 Various attempts have been made to produce the superconducting conductor 10 having excellent superconducting characteristics by forming the Ox-based superconducting layer 3.
In order to form an intermediate thin film excellent in crystal orientation or to obtain a superconducting tape excellent in superconducting characteristics, the present inventors firstly applied Japanese Patent Application No. 3-126636 to such an attempt. Patent applications have been filed in Japanese Patent Application No. 3-126837, Japanese Patent Application No. 3-205551, Japanese Patent Application No. 4-13443, Japanese Patent Application No. 4-293464, and the like.
[0006]
According to the techniques described in these patent applications, when a polycrystalline intermediate thin film is formed on one side of a base material of a metal tape such as a Hastelloy tape by a sputtering apparatus, simultaneously with sputtering, from the oblique direction of the base material film formation surface. A polycrystalline intermediate thin film having excellent crystal orientation can be formed by a method of forming a polycrystalline intermediate thin film while irradiating an ion beam (ion beam assisted sputtering method).
According to this method, the grain boundary inclination angle formed by the a-axis or b-axis of each crystal lattice of a large number of crystal grains forming the polycrystalline intermediate thin film can be made to be 30 degrees or less, and the crystal orientation is excellent. A polycrystalline intermediate thin film can be formed. Further, if a YBaCuO-based superconducting layer is formed on the intermediate thin film having excellent orientation by a laser vapor deposition method or the like, the crystal orientation of the oxide superconducting layer will be excellent, and thereby the crystal orientation Excellent at a critical current density of 10 at 77K 5 A / cm 2 A high oxide superconducting layer as described above can be formed.
[0007]
However, in the method according to the patent application, if a polycrystalline intermediate thin film is formed on one side of the substrate by ion beam assisted sputtering, distortion occurs due to compressive stress, and the substrate is warped. When depositing an oxide superconducting layer, it is necessary to keep the surface temperature of the substrate constant in order to form an oxide superconducting layer with uniform superconducting properties. It is difficult to uniformly heat the substrate, resulting in uneven temperature distribution on the surface of the substrate, resulting in an oxide superconducting layer with unstable superconducting properties in the length direction of the substrate. was there.
Furthermore, in the method according to the patent application, since the thickness of the obtained oxide superconducting layer is several μm, it is thinner than the thickness of several hundreds of μm of the base material made of metal tape, and the overall (oxidation) There was a problem that the critical current density per unit superconducting conductor was not high. Therefore, in order to improve the critical current density per overall, the thickness of the metal tape as the base material is reduced, and a polycrystalline intermediate thin film is formed on one side of the base material by ion beam assisted sputtering. When an oxide superconducting layer is formed on a crystal intermediate thin film by a laser vapor deposition method or the like, the base material thermally expands due to a high temperature atmosphere during the deposition of the oxide superconducting layer, causing distortion such as warping or twisting, and the base The polycrystalline intermediate thin film formed on the material is also distorted. When such a strain is present in the polycrystalline intermediate thin film, the crystal orientation of the oxide superconducting layer formed on the polycrystalline intermediate thin film becomes poor, and the desired superconducting characteristics cannot be obtained.
[0008]
The present invention has been made in order to solve the above-described problems, and the oxide superconductivity has stable superconducting characteristics in the length direction of the base material without causing warpage of the base material due to compressive stress during the formation of the polycrystalline intermediate thin film. Even when a thin tape-like base material is used, the above base material is less likely to be distorted by the high temperature atmosphere during vapor deposition of the oxide superconducting layer, An object of the present invention is to provide an oxide superconductor having at least one of the characteristics that the critical current density is improved.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, the invention according to claim 1 is a tape-shaped base material, and an orientation-controlled polycrystalline intermediate thin film formed on one surface of the base material and bonded with a large number of crystal grains. And a polycrystalline intermediate rapid-forming thin film formed on the other surface of the base material, and an oxide superconducting layer formed on the orientation-controlled polycrystalline intermediate thin film.
[0010]
Claim 2 In order to solve the above-mentioned problems, the invention described in the specification is a tape-shaped base material, a polycrystalline rapid-growing intermediate thin film formed on both surfaces of the base material and bonded with a large number of crystal grains, and The intermediate controlled thin film includes an orientation controlled polycrystalline intermediate thin film formed on one polycrystalline fast-growing intermediate thin film, and an oxide superconducting layer formed on the orientation controlled polycrystalline intermediate thin film.
[0011]
Claim 3 In order to solve the above-mentioned problems, the invention described in the specification is a tape-shaped base material, a polycrystalline rapid-growing intermediate thin film formed on both surfaces of the base material and bonded with a large number of crystal grains, and It comprises an orientation control polycrystalline intermediate thin film formed on each of the intermediate thin films, and an oxide superconducting layer formed on each of these orientation control polycrystalline intermediate thin films.
[0012]
Claim 4 In order to solve the above problems, the invention described in claims 1 to 3 The grain boundary inclination angle of each of a large number of crystal grains forming the orientation-controlled polycrystalline intermediate thin film of the oxide superconducting conductor according to any one of the above is 30 ° or less. Claim 5 In order to solve the above problems, the invention described in claims 1 to 4 The intermediate thin film of the oxide superconducting conductor described in any of the above is made of yttrium-stabilized zirconia. Claim 6 In order to solve the problems, the invention described in the claims 1 to 5 In the described oxide superconducting conductor, an orientation-controlled polycrystalline intermediate thin film is formed by an ion beam assisted sputtering method.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, examples of the present invention will be described with reference to the drawings.
FIG. 1 shows a first example of an oxide superconducting conductor according to the present invention. The oxide superconducting conductor 20 of this example has a large number of crystal grains bonded on the upper surface of a tape-like substrate 21. An orientation-controlled polycrystalline intermediate thin film 22 is formed, a polycrystalline rapid-forming intermediate thin film 23 is formed on the lower surface of the substrate 21, and an oxide superconducting layer 24 is formed on the orientation-controlled polycrystalline intermediate thin film 22. It will be.
[0014]
As the constituent material of the base material 21, a long metal tape appropriately selected from various metal materials such as stainless steel, copper, or nickel alloys such as hastelloy can be used. The base material 21 has a thickness of 0.01 to 0.5 mm, preferably 0.02 to 0.15 mm.
If the thickness of the base material 21 exceeds 0.5 mm, it is thicker than the film thickness of the oxide superconducting layer 24 described later, and the critical current density per overall (oxide superconducting conductor total cross-sectional area) may be reduced. There is. On the other hand, when the thickness of the base material 21 is less than 0.01 mm, the strength of the base material is remarkably reduced, and the reinforcing effect of the superconductor may be lost.
[0015]
The orientation-controlled polycrystalline intermediate thin film 22 is formed by joining and integrating a large number of fine crystal grains in which crystals having a cubic crystal structure are joined together via a crystal grain boundary. The c-axis is oriented substantially perpendicular to the upper surface (deposition surface) of the substrate 21, and the a-axis and the b-axis of each crystal grain are oriented in the same plane in the same direction. Yes. It is preferable that the a-axis (or b-axis) of the crystals of each crystal grain be joined and integrated with an angle formed between them (grain boundary inclination angle K) within 30 degrees. The orientation controlled polycrystalline intermediate thin film 22 has a thickness of 0.1 to 1.0 μm, preferably 0.3 to 0.7 μm. Even if the thickness of the orientation-controlled polycrystalline intermediate thin film 22 exceeds 1.0 μm, the effect cannot be expected anymore, which is disadvantageous economically. On the other hand, if the thickness of the orientation controlled polycrystalline intermediate thin film 22 is less than 0.1 μm, the substrate 21 is too thin to support the substrate 21 sufficiently, and the substrate 21 is distorted by a high temperature atmosphere during the deposition of the oxide superconducting layer 24 described later. This is because the element of the oxide superconducting layer 24 may be diffused to the substrate 21 side during heat treatment, and the component composition of the oxide superconducting layer 24 may be destroyed.
[0016]
The polycrystalline rapid-forming intermediate thin film 23 is formed by joining and integrating a large number of fine crystal grains in which crystals having a cubic crystal structure are gathered together via a crystal grain boundary. The thickness of the polycrystalline rapid-forming intermediate thin film 23 is 0.1 to 1.0 μm, preferably 0.3 to 0.7 μm. Even if the thickness of the polycrystalline rapid-growing intermediate thin film 23 exceeds 1.0 μm, an increase in the effect can no longer be expected, which is economically disadvantageous. On the other hand, if the thickness of the polycrystalline rapid-forming intermediate thin film 23 is less than 0.1 μm, the substrate 21 is too thin to support the substrate 21 sufficiently, and the substrate 21 is distorted by a high-temperature atmosphere during the deposition of the oxide superconducting layer 24 described later. This is because it may occur.
[0017]
The oxide superconducting layer 24 is Y 1 Ba 2 Cu 3 Ox, Y 2 Ba 4 Cu 8 Ox,
Y 3 Ba 3 Cu 6 Composition of Ox, (Bi, Pb) 2 Ca 2 Sr 2 Cu 3 Ox,
(Bi, Pb) 2 Ca 2 Sr 3 Cu 4 Ox composition,
Or Tl 2 Ba 2 Ca 2 Cu 3 Ox, Tl 1 Ba 2 Ca 2 Cu 3 Ox,
Tl 1 Ba 2 Ca 3 Cu 4 It is made of a superconducting material having a high critical temperature typified by a composition such as Ox. The oxide superconducting layer 24 has a thickness of about 0.5 to 5 μm.
[0018]
Next, an apparatus and a manufacturing method for manufacturing the orientation-controlled polycrystalline intermediate thin film 22 and the polycrystalline rapid-forming intermediate thin film 23 will be described.
FIG. 2 shows an example of an apparatus for producing the polycrystalline rapid-growing intermediate thin film 23. The apparatus of this example is a high-frequency sputtering apparatus.
The apparatus of the present example is mainly configured by a base material holder 31 that holds the base material 21 and a plate-like target 32 that is disposed to face the base material holder 31 with a predetermined interval. Reference numeral 33 in the figure denotes a target holder that holds the target 32. The target holder 33 is connected to a high-frequency power source 34, and the high-frequency power source 34 and the substrate holder 31 are grounded. Reference numeral 35 in the figure denotes a feeding device for the tape-like base material 21, and 36 denotes a winding device for the base material 21. The base material 21 is continuously fed from the feeding device 35 onto the base material holder 31, Subsequently, the film can be continuously formed on the substrate 21 by being wound by the winder 36.
[0019]
The base material holder 31 and the target holder 33 are housed in a vacuum container (not shown) so that the periphery of the base material holder 31 and the target holder 33 can be maintained in a vacuum atmosphere. Further, an atmospheric gas supply source such as a gas cylinder is connected to the vacuum container, and the inside of the vacuum container is in a low-pressure state such as a vacuum and an argon gas or other inert gas atmosphere or oxygen is supplied as necessary. An inert gas atmosphere can be provided.
With the above configuration, it is possible to generate plasma in the upper space of the base material 21 by operating the high frequency power supply 34 after depressurizing the inside of the vacuum vessel, and by the action of this plasma, the particles of the target 32 are sputtered. It can fly toward the base material 21 side.
[0020]
The base material holder 31 includes a heater inside, and the base material 21 disposed on the base material holder 31 can be heated to a desired temperature as required.
The target 32 is used to form the target polycrystalline rapid-forming intermediate thin film 23, and the target 32 has the same composition as the polycrystalline intermediate thin film having the target composition or an approximate composition. Specifically, the target 32 is MgO or Y 2 O 3 Stabilized zirconia (YSZ), MgO, SrTiO 3 However, the present invention is not limited to these, and a target suitable for the polycrystalline rapid-forming intermediate thin film 23 to be formed may be used as appropriate.
[0021]
Next, the case where the YSZ polycrystalline rapid-growing intermediate thin film 23 is formed on the substrate 21 using the apparatus having the above-described configuration will be described.
In order to form the polycrystalline rapid-growing intermediate thin film 23 on the base material 21, a YSZ target is used, and the inside of the vacuum vessel containing the base material 21 is evacuated to form a reduced pressure atmosphere. Then, the high frequency power supply 34 is activated. Thereby, the constituent particles of the target 32 are sputtered and fly onto the substrate 21. If these particles are deposited over a required time, a polycrystalline rapid-growing intermediate thin film having a desired thickness can be formed on the substrate 21.
The a-axis, b-axis, and c-axis of the crystal grains of the large number of crystal grains constituting the polycrystalline rapid-generating intermediate thin film 23 thus obtained may all be oriented in any direction and have orientation. Things can be used.
[0022]
Next, FIG. 3 shows an example of an apparatus for manufacturing the above-described orientation-controlled polycrystalline intermediate thin film 22, and the apparatus of this example has a configuration in which an ion gun for ion beam assist is provided in an ion beam sputtering apparatus. ing.
The apparatus of this example includes a base material holder 45 that holds the base material 21, a plate-like target 46 that is disposed diagonally above the base material holder 45 with a predetermined interval, and an oblique upper side of the base material holder 45. It is mainly configured by an ion gun 47 opposed to the target 46 with a predetermined interval and spaced apart from the target 46, and a sputter beam irradiation device 48 disposed obliquely below the target 46 toward the lower surface of the target 46. Yes. Reference numeral 49 in the figure denotes a target holder that holds the target 46. Reference numeral 55 in the figure denotes a feeding device for the tape-like base material 21, and 56 denotes a winding device for the base material 21. The base material 21 is continuously fed out from the feeding device 55 onto the base material holder 45, Subsequently, the film can be continuously formed on the substrate 21 by being wound by the winder 56.
[0023]
The apparatus of this example is housed in a vacuum container (not shown) so that the periphery of the base material 21 can be maintained in a vacuum atmosphere. Further, an atmospheric gas supply source such as a gas cylinder is connected to the vacuum container, the inside of the vacuum container is in a low pressure state such as a vacuum, and an inert gas containing argon gas or other inert gas atmosphere or oxygen. The atmosphere can be changed.
[0024]
The base material holder 45 includes a heater inside, and the base material 21 positioned on the base material holder 45 can be heated to a desired temperature as required. An angle adjustment mechanism D is attached to the bottom of the base material holder 45. The angle adjusting mechanism D includes an upper support plate 60 joined to the bottom of the substrate holder 45, a lower support plate 61 pin-coupled to the upper support plate 60, and a base 62 that supports the lower support plate 61. Is the main constituent. The upper support plate 60 and the lower support plate 61 are configured to be rotatable with respect to each other via a pin coupling portion, and the inclination angle of the base material holder 45 can be adjusted.
Although the angle adjusting mechanism D for adjusting the angle of the base material holder 45 is provided in the apparatus of this example, the angle adjusting mechanism D is attached to the support portion of the ion gun 47 to adjust the inclination angle of the ion gun 47, and the ion beam The incident angle may be adjusted. In addition, the angle adjusting mechanism is not limited to the configuration of the present example, and it is needless to say that various configurations can be adopted.
[0025]
The target 46 is used to form a target orientation controlled polycrystalline intermediate thin film, and the target 46 has the same composition as the orientation controlled polycrystalline intermediate thin film having the target composition or an approximate composition. Specifically, the target 46 is MgO or Y 2 O 3 Stabilized zirconia (YSZ), MgO, SrTiO 3 However, the present invention is not limited to this, and a target suitable for the orientation controlled polycrystalline intermediate thin film to be formed may be used as appropriate.
[0026]
The ion gun 47 houses an evaporation source inside a container, and includes an extraction electrode in the vicinity of the evaporation source. In this apparatus, a part of atoms or molecules generated from the evaporation source is ionized, and the ionized particles are controlled by an electric field generated by an extraction electrode and irradiated as an ion beam. There are various types of ionization of particles such as a direct current discharge method, a high frequency excitation method, a filament method, and a cluster ion beam method. The filament type is a method in which a tungsten filament is energized and heated to generate thermoelectrons and collide with evaporated particles in a high vacuum to be ionized. In the cluster ion beam system, clusters of aggregate molecules coming out in a vacuum from a nozzle provided in an opening of a crucible containing raw materials are bombarded with thermal electrons and ionized to be emitted.
In this example, an ion gun 47 having an internal structure shown in FIG. 4 is used. This ion gun 47 is configured to include an extraction electrode 66, a filament 67, and an introduction tube 68 for Ar gas or the like inside a cylindrical container 65, and can irradiate ions in parallel in a beam shape from the tip of the container 65. It is.
[0027]
As shown in FIG. 3, the ion gun 47 has its central axis S with respect to the upper surface (film formation surface) of the substrate 21 and an incident angle θ (an angle formed between the perpendicular (normal) of the substrate 21 and the center line S). ) It is inclined to face each other. The incident angle θ is preferably in the range of 50 to 60 degrees, and most preferably in the range of 55 to 60 degrees. Accordingly, the ion gun 47 is arranged so as to be able to irradiate an ion beam at an incident angle θ with respect to the upper surface of the substrate 21.
The ion beam applied to the substrate 21 by the ion gun 47 is
He + , Ne + , Ar + , Xe + , Kr + An ion beam of a rare gas such as, or a mixed ion beam of them and oxygen ions may be used. However, in order to arrange the crystal structure of the orientation-controlled polycrystalline intermediate thin film to be formed, a certain amount of atomic weight is required, and considering that the effect is reduced with too light ions, Ar + , Kr + It is preferable to use ions such as
The sputter beam irradiation device 48 has the same configuration as the ion gun 47, and can irradiate the target 46 with the ion beam to strike out the constituent particles of the target 46 toward the substrate 21.
[0028]
Next, the YSZ orientation-controlled polycrystalline intermediate thin film 22 is ion beam assisted on the other surface of the tape-shaped substrate 21 (the surface on which the polycrystalline rapid-growing intermediate thin film 23 is not formed) using the apparatus having the above configuration. The case of forming by sputtering will be described.
In order to form the orientation controlled polycrystalline intermediate thin film 22 on the surface of the substrate 21 where the polycrystalline rapid intermediate film 23 is not formed, a YSZ target is used and the angle adjustment mechanism D is adjusted to adjust the ion gun 47. The ion beam irradiated from the upper surface of the substrate 21 can be irradiated at an angle in the range of 50 to 60 degrees. Next, the inside of the container containing the base material 21 is evacuated to create a reduced pressure atmosphere. At this time, the pressure in the vacuum container is lower than the pressure in the vacuum container of the high-frequency sputtering apparatus shown in FIG. Then, the ion gun 47 and the sputter beam irradiation device 48 are operated.
[0029]
When the target 46 is irradiated with an ion beam from the sputter beam irradiation device 48, the constituent particles of the target 46 are knocked out and fly onto the substrate 21. Then, the constituent particles knocked out from the target 46 are deposited on the base material 21 and at the same time, a mixed ion beam of Ar ions and oxygen ions is irradiated from the ion gun 47 to form the orientation controlled polycrystalline intermediate thin film 22 having a desired thickness. To do.
The incident angle θ at the time of ion irradiation is preferably in the range of 50 to 60 degrees, and most preferably in the range of 55 to 60 degrees. Here, when θ is 90 degrees, the c-axis of the polycrystalline intermediate thin film 22 is oriented at right angles to the film formation surface on the substrate 21, but the (111) plane stands on the film formation surface of the substrate 21. Therefore, it is not preferable. When θ is 30 degrees, the polycrystalline intermediate thin film 22 does not even have c-axis orientation. If the ion beam irradiation is carried out at an angle within a preferable range as described above, the (100) plane of the polycrystalline intermediate thin film 22 will stand.
[0030]
By performing sputtering while irradiating an ion beam at such an incident angle, the a-axis and b-axis of the YSZ orientation control polycrystalline intermediate thin film 22 formed on the substrate 21 can be aligned. It is possible that this is due to the ion beam being irradiated at an appropriate angle with respect to the sputtered particles being deposited.
[0031]
In addition, the present inventors assume the following as a factor which the crystal orientation of this orientation control polycrystal intermediate | middle thin film 22 arranges.
The unit cell of the crystal of the YSZ orientation-controlled polycrystalline intermediate thin film 22 is a cubic system as shown in FIG. 5. In this crystal lattice, the substrate normal direction is the <100> axis, and other <010> Both the> axis and the <001> axis are in the directions shown in FIG. In consideration of an ion beam incident from a direction oblique to the substrate normal with respect to these directions, when entering along the diagonal direction of the unit cell, that is, along the <111> axis with respect to the origin O in FIG. The incident angle is 54.7 degrees.
[0032]
Here, as described above, the best crystal orientation is exhibited when the ion beam is irradiated within the range of the incident angle of 50 to 60 degrees, which means that the incident angle of the ion beam coincides with the above 54.7 degrees. Or before and after that, ion channeling occurs most effectively, and in the crystal that is being deposited on the base material 21, only the atoms that are in a positional relationship that matches the angle on the upper surface of the base material 21 are selected. As a result, other disordered atomic arrangements are sputtered and removed by the sputtering effect of the ion beam from an oblique direction, so that only crystals with well-oriented atoms remain selectively left. Presumed to be due to accumulation.
However, since the film is deposited while removing the disordered atomic arrangement of the crystals deposited in this way with an ion beam, the film formation rate is deteriorated, and the film formation rate is higher than the film formation by normal sputtering. Become slow.
[0033]
FIG. 6 shows a thin film in which a YSZ orientation-controlled polycrystalline intermediate thin film 22 is formed on one surface of a base material 21 and a polycrystalline rapid-forming intermediate thin film 23 is formed on the other surface of the base material 21 by the method described above. The laminated body 25 is shown. 6 shows a state in which only one crystal grain 27 is formed, it is needless to say that the crystal grain 27 may have a multilayer structure.
[0034]
The thin film laminate 25 configured as described above is put to practical use by further forming an oxide superconducting layer thereon. Since the orientation controlled polycrystalline intermediate thin film 22 is formed on the uppermost portion of the thin film laminate 25, the oxide superconducting layer formed thereon is excellent in crystal orientation, thereby superconducting characteristics. Will improve.
[0035]
Next, an apparatus and method for manufacturing an oxide superconducting conductor by forming an oxide superconducting layer on the thin film laminate 25 will be described.
FIG. 7 shows an example of an apparatus for forming an oxide superconducting layer by a film forming method, and FIG. 7 shows a laser deposition apparatus.
The laser deposition apparatus 70 of this example has a processing container 71, and the thin film stack 25 and the target 73 can be installed in a deposition processing chamber 72 inside the processing container 71. That is, a base 74 is provided at the bottom of the vapor deposition chamber 72, and the thin film laminate 25 can be installed on the upper surface of the base 74, and supported by the support holder 73 a obliquely above the base 74. The target 73 is provided in an inclined state. In the figure, reference numeral 75 denotes a delivery device for the thin film laminate 25, and 76 denotes a take-up device for the thin film laminate 25. The thin film laminate 25 is continuously delivered from the delivery device 75 onto the base 74. The film can be continuously formed on the thin film stack 25 by being wound by the winder 76. The processing vessel 71 is connected to the vacuum exhaust device 77 through the exhaust hole 77a so that the vapor deposition processing chamber 72 can be depressurized to a predetermined pressure.
[0036]
The target 73 has a composition equivalent to or close to that of the oxide superconducting layer to be formed, or a composite oxide sintered body or oxide superconductor plate containing a large amount of components that easily escape during film formation. It consists of a body.
Therefore, the target 73 is Y 1 Ba 2 Cu 3 Ox, Y 2 Ba 4 Cu 8 Ox,
Y 3 Ba 3 Cu 6 Composition of Ox, (Bi, Pb) 2 Ca 2 Sr 2 Cu 3 Ox,
(Bi, Pb) 2 Ca 2 Sr 3 Cu 4 Ox composition,
Or Tl 2 Ba 2 Ca 2 Cu 3 Ox, Tl 1 Ba 2 Ca 2 Cu 3 Ox,
Tl 1 Ba 2 Ca 3 Cu 4 Since it is used to form an oxide superconducting layer having a high critical temperature typified by a composition such as Ox, it is preferable to use a composition having the same composition or an approximate composition.
The base 74 has a built-in heater so that the thin film stack 25 can be heated to a desired temperature as required.
[0037]
On the other hand, a laser light emitting device 78, a first reflecting mirror 79, a condenser lens 80, and a second reflecting mirror 81 are provided on the side of the processing container 71, and the laser beam generated by the laser light emitting device 78 is processed into the processing container. The target 73 can be focused and irradiated through a transparent window 82 attached to the side wall 71. As long as the laser emitting device 78 can knock out the constituent particles from the target 73, a YAG laser, CO 2 Any laser, excimer laser, or the like may be used.
[0038]
Next, a method of forming the oxide superconducting layer 24 on the YSZ orientation-controlled polycrystalline intermediate thin film 22 will be described.
First, the thin film stack 25 is placed on the base 74 of the laser vapor deposition apparatus 70 shown in FIG. 7 with the orientation-controlled polycrystalline intermediate thin film 22 side up, and the vapor deposition chamber 72 is decompressed by the vacuum exhaust apparatus 77. . Here, oxygen gas may be introduced into the vapor deposition chamber 72 as necessary to make the vapor deposition chamber 72 an oxygen atmosphere. In addition, the thin film laminate 25 may be heated to a desired temperature by operating the heater of the base 74.
[0039]
Next, the laser beam generated from the laser light emitting device 78 is focused and applied to the target 73 in the vapor deposition processing chamber 72. As a result, the constituent particles of the target 73 are extracted or evaporated, and the particles are deposited on the orientation controlled polycrystalline intermediate thin film 22. Here, since the orientation-controlled polycrystalline intermediate thin film 22 is preliminarily c-axis oriented during the deposition of the constituent particles and is also oriented along the a-axis and b-axis, the oxide superconductivity formed on the orientation-controlled polycrystalline intermediate thin film 22 The c-axis, a-axis, and b-axis of the crystal of the layer 24 are epitaxially grown and crystallized so that the alignment controlled polycrystalline intermediate thin film 22 is also aligned. As a result, an oxide superconducting layer 24 with good crystal orientation is obtained. Note that heat treatment for adjusting the crystal structure of the oxide superconducting layer 24 may be performed as necessary after film formation.
When the oxide superconducting layer 24 is formed on the thin film laminate 25 by the above-described method, the oxide superconducting conductor 20 of the first example as shown in FIG. 1 is obtained.
The oxide superconducting layer 24 formed on the orientation controlled polycrystalline intermediate thin film 22 is in a polycrystalline state. In each of the crystal grains of the oxide superconducting layer 24, the thickness of the base material 21 is changed. The c-axis in which electricity is difficult to flow in the direction is oriented, and the crystal orientation in which the a-axis or the b-axis is oriented in the plane direction of the base material 21 is good. Therefore, the obtained oxide superconducting layer 24 is excellent in quantum connectivity at the crystal grain boundary and has little deterioration in superconducting characteristics at the crystal grain boundary, so that electricity can easily flow in the plane direction of the base material 21 and has an excellent critical current density. Can be obtained.
[0040]
The oxide superconducting conductor 20 of the first example has the above-described configuration, so that even if the thickness of the tape-like base material 21 is thin, the base material 21 has a double-sided orientation controlled polycrystalline intermediate thin film. 22 and the polycrystalline rapid-growing intermediate thin film 23, it is possible to suppress the substrate 21 from being distorted by the high temperature atmosphere during the deposition of the oxide superconducting layer 24. This reduces distortion in the orientation-controlled polycrystalline intermediate thin film 22 on the substrate 21 and improves the planarity of the surface of the orientation-controlled polycrystalline intermediate thin film 22, so that it is formed on the orientation-controlled polycrystalline intermediate thin film 22. As a result, the crystal orientation of the oxide superconducting layer 24 is improved and the critical current density is excellent. Therefore, in the oxide superconducting conductor 20 of the first example, since the thin tape-like base material 21 is used, the thickness of the oxide superconducting conductor is reduced, and the overall (oxide superconducting conductor) is reduced. The critical current density per total cross-sectional area) can be improved, and a long oxide superconductor having a large current capacity can be easily provided.
[0041]
Further, in the oxide superconducting conductor 20 of the first example, since the polycrystalline rapid-forming intermediate thin film 23 formed on the lower surface of the base material 21 functions as an insulating layer, an insulating layer is further formed only on the oxide superconducting layer 24 side. In addition, when it is used as a magnet or the like, it can be wound as it is without forming an insulating layer.
Further, in the case where the grain boundary inclination angle of each of a large number of crystal grains forming the orientation controlled polycrystalline intermediate thin film 22 is 30 degrees or less, the oxide superconductivity formed on the orientation controlled polycrystalline intermediate thin film 22 Since the crystal orientation of the layer 24 becomes better, more excellent superconducting characteristics are exhibited.
In the oxide superconducting conductor 20 of the first example, the case where the polycrystalline rapid-growing intermediate thin film 23 is formed by high-frequency sputtering has been described. However, the CVD method, the vacuum evaporation method, the electron beam evaporation method, the laser evaporation method are used. It is necessary to form a polycrystalline rapid-growing intermediate thin film by a process that includes compressive stress such as high-energy plasma, and it is usually necessary to trap a rare gas such as Ar in the film. Therefore, the PVD method is preferable.
[0042]
Further, in the oxide superconducting conductor 20 of the first example, the case where the intermediate thin film formed on the lower surface of the base material 21 is the polycrystalline rapid-growing intermediate thin film 23 has been described. An orientation-controlled polycrystalline intermediate thin film 22 may be formed instead of 23, that is, an orientation-controlled polycrystalline intermediate thin film 22 in which a large number of crystal grains are bonded on both surfaces of a base material 21 as shown in FIG. 22 may be formed. When the orientation controlled polycrystalline intermediate thin films 22 and 22 are formed on both surfaces of the substrate 21, each orientation controlled polycrystalline intermediate thin film 22 is preferably formed by an ion beam assisted sputtering method.
In the thin film laminated body 25 in which the orientation control polycrystalline intermediate thin films 22 and 22 are formed on both surfaces of the base material 21 as shown in FIG. 10 by the ion beam assisted sputtering method, both surfaces are oriented although compressive stress is applied. Since the compressive stress is canceled by the controlled polycrystalline intermediate thin films 22, 22, it is possible to prevent the substrate 21 from warping, and the orientation controlled polycrystalline intermediate thin film 22 is also formed on the lower surface (heated surface) of the substrate 21. Since it is formed, oxidation of the base material 31 is prevented. This makes it easier to uniformly heat the surface of the thin film stack 25 when depositing the oxide superconducting layer 24 on the orientation-controlled polycrystalline intermediate thin film 22, and the temperature distribution on the surface of the thin film stack 25 is hardly uneven. Since the temperature of the thin film laminate 25 is stabilized, the oxide superconducting layer 24 having stable superconducting characteristics with respect to the length direction of the substrate 21 can be formed.
Therefore, in the oxide superconducting conductor 20 shown in FIG. 10, the superconducting characteristics with respect to the length direction of the base material are stable without causing the base material to be warped by the compressive stress during the formation of the orientation controlled polycrystalline intermediate thin film. Even when a thin tape-like substrate is used, the substrate is less likely to be distorted by the high temperature atmosphere during the deposition of the oxide superconducting layer. , There is an advantage of having both of the characteristics that the critical current density per overall is improved.
[0043]
FIG. 8 shows a second example of the oxide superconducting conductor according to the present invention.
In the oxide superconducting conductor 90 of this second example, polycrystalline fast-growing intermediate thin films 23a and 23b are formed on both surfaces of a tape-like base material 21, respectively. An orientation controlled polycrystalline intermediate thin film 22b is formed on the rapid crystallizing intermediate thin film 23b, and an oxide superconducting layer 24 is formed on the orientation controlled polycrystalline intermediate thin film 22b.
[0044]
The polycrystalline rapid-growing intermediate thin films 23a and 23b of this example are formed by combining a large number of crystal grains in the same way as the polycrystalline intermediate rapid-growing thin film 23 of the first example described above. 2 can be formed using the high-frequency sputtering apparatus of FIG. 2, and the a-axis and the b-axis are not particularly oriented in the crystal axes of each crystal grain of the polycrystalline rapid-growing intermediate thin film 23b. It is preferable that the substrate 21 is oriented substantially at right angles to the upper surface (film formation surface) of the substrate 21.
The orientation-controlled polycrystalline intermediate thin film 22b can be formed by using an apparatus provided with an ion gun for ion beam assist in the ion beam sputtering apparatus of FIG. 3 in substantially the same manner as described above. The difference from this is that it is formed on the polycrystalline rapid-forming intermediate thin film 23b.
[0045]
The total thickness of the intermediate thin film on the upper side with respect to the base material 21, that is, the total thickness of the orientation-controlled polycrystalline intermediate thin film 22b and the polycrystalline rapid growth intermediate thin film 23b is 0.1 to 1.0 μm. Even if the total thickness of the upper intermediate thin film exceeds 1.0 μm, the effect can no longer be expected, which is disadvantageous economically. On the other hand, if the total thickness of the upper intermediate thin film is less than 0.1 μm, the substrate 21 is too thin to support the substrate 21 sufficiently, and the substrate 21 is distorted by the high temperature atmosphere during the deposition of the oxide superconducting layer 24 described later. This is because there is a risk that the element of the oxide superconducting layer 24 may be diffused to the substrate 21 side during the heat treatment, and the component composition of the oxide superconducting layer 24 may be destroyed.
Further, the thickness of the intermediate thin film on the lower side with respect to the base material 21, that is, the thickness of the polycrystalline rapid-growing intermediate thin film 23b is 0.1 to 1 for the same reason as the polycrystalline rapid-growing intermediate thin film 23 of the first example. 0.0 μm.
[0046]
If the intermediate thin film on the upper side with respect to the base material 21 is composed of two layers of the polycrystalline rapid growth thin film 23b and the orientation control polycrystalline thin film 22b as in the second example, the polycrystalline rapid growth intermediate thin film 23b and the orientation control are performed. The total film thickness including the polycrystalline intermediate thin film 22b can be formed in a shorter time than using the orientation controlled polycrystalline intermediate thin film. The reason is that when the orientation controlled polycrystalline intermediate thin film 22 which is the upper intermediate thin film with respect to the base material 21 is formed by sputtering while irradiating an ion beam from an oblique direction as in the first example, the formation is performed. The film speed is reduced as compared with the case where a polycrystalline rapid-growing intermediate thin film is formed by normal ion beam sputtering or high-frequency sputtering. For example, with high frequency sputtering, film formation can usually be performed at a speed of about 0.5 μm / hour, but with sputtering while irradiating an ion beam from an oblique direction, the film can be processed at a speed of about 0.1 μm / hour. The film forming process is performed.
[0047]
Therefore, in the oxide superconducting conductor 90 of the second example, the intermediate thin film is composed of two layers of the polycrystalline rapid-forming thin film and the orientation-controlled polycrystalline thin film. Compared with the case where all the film thicknesses including the polycrystalline intermediate thin film 22b are made the orientation controlled polycrystalline intermediate thin film, the portion of the orientation controlled polycrystalline intermediate thin film that takes a long time for film formation is reduced, and the polycrystalline rapid growing intermediate thin film portion Since the film formation speed is high, the film formation time is shortened.
Further, when the polycrystalline rapid-forming intermediate thin film 23b and the orientation-controlled polycrystalline intermediate thin film 22b are made of the same material, the bonding properties of both the thin films 23b and 22b are improved, and the bonding strength between them is sufficiently high.
[0048]
FIG. 9 shows a third example of the oxide superconducting conductor according to the present invention.
In the oxide superconducting conductor 100 of this third example, polycrystalline fast-growing intermediate thin films 23a and 23b each formed by bonding a large number of crystal grains are formed on both surfaces of a tape-like substrate 21, and these polycrystalline fast-growing intermediate thin films 23a and 23b are formed. Orientation controlled polycrystalline intermediate thin films 22a and 22b are formed on the thin films 23a and 23b, respectively, and oxide superconducting layers 24a and 24b are formed on the orientation controlled polycrystalline intermediate thin films 22a and 22b, respectively.
[0049]
The oxide superconducting conductor 100 of the third example is different from the oxide superconducting conductor 90 of the second example described above, on the polycrystalline rapid-forming intermediate thin film 23a below the base material. An orientation control polycrystalline intermediate thin film 22a is formed, and an oxide superconducting layer 24a is further formed on the orientation control polycrystalline intermediate thin film 22a.
The polycrystalline rapid-growing intermediate thin film 23a in this example is formed by combining a large number of crystal grains in the same manner as the polycrystalline intermediate rapid-growing thin film 23 in the first example described above, and is almost the same as the method described above. 2 can be formed using the high-frequency sputtering apparatus of FIG. 2, and the a-axis and the b-axis are not particularly oriented in the crystal axes of each crystal grain of the polycrystalline rapid-growing intermediate thin film 23a, but the c-axis is a base material. It is preferable that it is directed substantially perpendicular to the upper surface (film formation surface) of 21.
Further, the orientation-controlled polycrystalline intermediate thin film 22a can be formed using an apparatus provided with an ion beam assist ion gun in the ion beam sputtering apparatus of FIG. 3 in substantially the same manner as described above.
The orientation-controlled polycrystalline intermediate thin films 22a and 22b formed on both surfaces of the substrate 21 via the polycrystalline rapid-forming intermediate thin films 23a and 23b are preferably formed by ion beam assisted sputtering. Thus, in the thin film laminated body 25 in which the orientation control polycrystalline intermediate thin films 22a and 22b are formed by the ion beam assisted sputtering method, although the compressive stress is applied, both sides of the orientation control polycrystalline intermediate thin films 22a and 22b are used. Since the compressive stress is canceled, it is possible to prevent the base material 21 from being warped. Further, the polycrystalline rapid-growing intermediate thin film 23a and the orientation controlled polycrystalline intermediate thin film 22a are also formed on the lower surface (heated surface) of the base material 21. Therefore, the oxidation of the base material 31 is prevented. This makes it easier to uniformly heat the surface of the thin film stack 25 when depositing the oxide superconducting layers 24a and 24b on the orientation-controlled polycrystalline intermediate thin films 22a and 22b, resulting in uneven temperature distribution on the surface of the thin film stack 25. Since the temperature of the thin film laminate 25 is stabilized, the oxide superconducting layers 24a and 24b having stable superconducting characteristics in the length direction of the substrate 21 can be formed.
[0050]
The total thickness of the intermediate thin film on the lower side with respect to the base material 21, that is, the total thickness of the orientation-controlled polycrystalline intermediate thin film 22a and the polycrystalline rapid-forming intermediate thin film 23a is the orientation-controlled polycrystalline intermediate thin film of the second example. For the same reason as 22b and the polycrystalline rapid-forming intermediate thin film 23b, the thickness is set to 0.1 to 1.0 μm.
The oxide superconducting layer 24a can be formed using the laser vapor deposition apparatus of FIG. 7 in substantially the same manner as described above, and the thickness thereof is 0.5 like the oxide superconducting layer 24 of the first example. ˜5 μm.
[0051]
In the oxide superconducting conductor 100 of the third example, since the oxide superconducting layer is formed on both surfaces of the base material 21 through the intermediate thin film, the total per oxide (total cross-sectional area of the oxide superconducting conductor) The critical current density is about twice that of the oxide superconducting conductor 20 of the first example and the oxide superconducting conductor 90 of the second example, the critical current density per overall is increased, and the long current capacity is larger. There is an advantage that the oxide superconducting conductor can be easily provided.
Furthermore, in the oxide superconducting conductor 100 of the third example, in the case where the orientation controlled polycrystalline intermediate thin films 22a and 22b are formed by ion beam assisted sputtering, respectively, compression during the formation of the orientation controlled polycrystalline intermediate thin film is performed. There is an advantage that an oxide superconducting layer having stable superconducting characteristics with respect to the length direction of the base material 21 is formed without warping the base material 21 due to stress.
[0052]
(Operation of the present invention)
In the present invention, an intermediate thin film is formed on both surfaces of a tape-shaped substrate, and an oxide superconducting layer is further formed on an orientation-controlled polycrystalline intermediate thin film among these intermediate thin films. Even if the thickness of the substrate is thin, since the substrate is supported by the intermediate thin films on both sides, the substrate is prevented from being distorted by a high temperature atmosphere during the deposition of the oxide superconducting layer. This reduces distortion in the intermediate thin film on the substrate and improves the flatness of the surface of the intermediate thin film, so that the crystal orientation of the oxide superconducting layer formed on the orientation controlled polycrystalline intermediate thin film is good. It becomes.
[0053]
In addition, since the intermediate thin film is composed of two layers, a polycrystalline rapid-growing thin film and an orientation-controlled polycrystalline thin film, the total film thickness of the polycrystalline fast-growing intermediate thin film and the orientation-controlled polycrystalline intermediate thin film is all controlled by the orientation-controlled polycrystalline. Compared to the intermediate thin film, the portion of the orientation controlled polycrystalline intermediate thin film, which takes longer to form the film, is reduced. In addition, the film forming time is shortened in the polycrystalline fast-growing intermediate thin film portion, so that the film forming time is shortened.
In addition, the oxide superconducting layer formed on the orientation-controlled polycrystalline thin film having a grain boundary tilt angle of 30 degrees or less exhibits better superconducting characteristics because the crystal orientation becomes better. Furthermore, since the orientation control polycrystalline intermediate thin film on both sides of the base material is formed by the ion beam assisted sputtering method, the compressive stress is canceled by the orientation control polycrystalline intermediate thin film on both sides although it contains compression stress. In addition, since the polycrystalline rapid growth intermediate thin film and the orientation controlled polycrystalline intermediate thin film are formed on the lower surface (the surface to be heated) of the base material, the base material is prevented from being oxidized. . This makes it easier to uniformly heat the surface of the thin film stack when depositing the oxide superconducting layer on the orientation controlled polycrystalline intermediate thin film, and the temperature distribution on the surface of the thin film stack is hardly uneven, and the thin film stack The temperature is stabilized.
[0054]
【Example】
(Example 1)
A high frequency sputtering apparatus having the configuration shown in FIG. 2 is used, and the inside of the vacuum vessel of this apparatus is evacuated by a vacuum pump to 1 × 10 -3 Depressurized to tall. As the substrate, Hastelloy C276 tape having a width of 10 mm, a thickness of 0.1 mm, and a length of 10 cm was used. A target made of YSZ (stabilized zirconia) is used, a sputtering voltage is set to 300 V, a sputtering current is set to 100 mA, and sputtering is performed for 1 hour to form a film having a thickness of 0.5 μm on one surface (lower surface) of the substrate. A YSZ polycrystalline fast-growing intermediate thin film was formed.
[0055]
Next, an ion beam sputtering apparatus having the configuration shown in FIG. 3 is used, and the inside of the vacuum vessel containing the apparatus is evacuated with a vacuum pump to 3.0 × 10 × 10. -4 Depressurized to tall. The target is YSZ (stabilized zirconia), the sputtering voltage is set to 1000 V, the sputtering current is set to 100 mA, the incident angle of the ion source beam is set to 55 degrees, the assist voltage of the ion source is set to 300 V, and the ion beam current is set. Density 20μA / cm 2 And forming a YSZ orientation-controlled polycrystalline intermediate thin film with a thickness of 0.5 μm by performing ion irradiation simultaneously with sputtering on the other surface (upper surface) of the substrate and performing film formation for 5 hours. 6 was obtained. Note that the current density of the ion beam is based on a numerical value measured by a current density measuring device grounded near the sample.
[0056]
Next, an oxide superconducting layer having a thickness of 1.0 μm was formed on the orientation-controlled polycrystalline intermediate thin film using a laser vapor deposition apparatus having the structure shown in FIG. 7, and an oxide superconducting conductor similar to that in FIG. 1 was produced. . Y as target 0.7 Ba 1.7 Cu 3.0 O 7-x A target made of an oxide superconductor having the following composition was used. 1 × 10 inside the vapor deposition chamber -6 After depressurizing to tall, oxygen was introduced into the interior to 2 × 10 -3 After forming torr, laser deposition was performed. An ArF laser having a wavelength of 193 nm was used as a target evaporation laser. After this film formation, the thin film was heat-treated at 400 ° C. for 60 minutes in an oxygen atmosphere. During the vapor deposition and heat treatment here, the substrate was not distorted. The oxide superconducting conductor obtained by the above treatment has a thickness of 102.0 μm, a width of 10 mm, and a length of 10 cm.
[0057]
As a result of cooling this oxide superconductor and measuring the critical current density, critical current density = 5.1 × 10 6. 5 A / cm 2 (77K, 0T), critical current density per overall = 5,000 A / cm 2 (77K, 0T) was shown, and it was confirmed that extremely excellent superconducting properties were exhibited.
Therefore, the obtained oxide superconducting conductor has a critical thickness per overall without any distortion occurring in the high temperature atmosphere during the deposition of the oxide superconducting layer even when a thin substrate having a thickness of 0.1 mm is used. It became clear that the current density improved.
[0058]
(Example 2)
An oxide superconducting conductor was prepared in the same manner as in Example 1 except that a Hastelloy tape having a width of 10 mm, a thickness of 0.05 mm, and a length of 10 cm was used as the substrate. The oxide superconducting conductor here has a thickness of 52.0 μm, a width of 10 mm, and a length of 10 cm.
As a result of cooling this oxide superconductor and measuring the critical current density, the critical current density = 4.8 × 10 6. 5 A / cm 2 (77K, 0T), critical current density per overall = 9.2 × 10 3 A / cm 2 It was confirmed that it exhibited extremely excellent superconducting properties.
Therefore, the obtained oxide superconducting conductor has a critical thickness per overall without any distortion occurring in the high temperature atmosphere during the deposition of the oxide superconducting layer even when using a thin base with a thickness of 0.05 mm. It became clear that the current density was improved.
[0059]
(Comparative Example 1)
Oxide in the same manner as in Example 1 except that a Hastelloy tape having a width of 10 mm, a thickness of 0.5 mm, and a length of 10 cm was used as the base material, and a polycrystalline rapid-growing intermediate thin film was not formed on the lower surface of the base material. A superconducting conductor was produced. The oxide superconducting conductor here had a thickness of 501.5 μm, a width of 0.5 mm, and a length of 10 cm.
As a result of cooling this oxide superconductor and measuring the critical current density, critical current density = 5.2 × 10 6. 5 A / cm 2 (77K, 0T), but critical current density per overall = 1.0 × 10 3 A / cm 2 It was low.
[0060]
(Comparative Example 2)
An oxide superconducting conductor was produced in the same manner as in Example 1 except that the polycrystalline rapid-growing intermediate thin film was not formed on the lower surface of the substrate. The oxide superconducting conductor here had a thickness of 101.5 μm, a width of 10 mm, and a length of 10 cm.
As a result of cooling this oxide superconductor and measuring the critical current density, critical current density = 1.1 × 10 4 A / cm 2 (77K, 0T), critical current density per overall = 1 x 10 2 A / cm 2 It was low. In addition, in the oxide superconducting conductor, the base material was distorted by a high temperature atmosphere during the deposition of the oxide superconducting layer.
[0061]
(Example 3)
Using a laser vapor deposition apparatus having the structure shown in FIG. 7, a multi-layer film of YSZ having a thickness of 0.5 μm is formed on both surfaces of a base material made of Hastelloy C276 tape having a width of 10 mm, a thickness of 0.2 mm, and a length of 10 cm. A rapid crystallizing intermediate thin film was formed. As a target, laser deposition was performed at a room temperature of YSZ (stabilized zirconia). An ArF laser having a wavelength of 193 nm was used as a target evaporation laser. Here, the time required to form the polycrystalline rapid-growing intermediate thin film having a thickness of 0.5 μm on one surface of the substrate is 10 minutes, and therefore the time required to form the polycrystalline rapid-growing intermediate thin film on both surfaces. Was 20 minutes. Next, an ion beam sputtering apparatus having the configuration shown in FIG. 3 is used, and this apparatus is housed using a YSZ (stabilized zirconia) target, a sputtering voltage of 1000 V, a sputtering current of 100 mA, and an incident angle of the ion source beam. Are set to 55 degrees, the assist voltage of the ion source is set to 300 V, and the current density of the ion beam is set to 20 μA / cm. 2 In the polycrystalline fast-growing intermediate thin film formed on both surfaces of the base material, the film is formed for one hour by ion beam assisted sputtering, in which ion irradiation is performed simultaneously with sputtering on one polycrystalline fast-growing intermediate thin film. Thus, a YSZ orientation controlled polycrystalline intermediate thin film having a thickness of 0.1 μm was formed.
[0062]
Here, the above-described polycrystalline rapid-growing intermediate thin film was formed with a thickness of 0.5 μm in 10 minutes, but the orientation-controlled polycrystalline intermediate thin film was formed with a thickness of 0.1 μm for 1 hour. It has been clarified that it is possible to form a polycrystalline rapid-growing intermediate thin film by laser vapor deposition at a rate about 5 times faster than the production of an orientation-controlled polycrystalline intermediate thin film by sputtering using ion beam assist.
[0063]
Next, an oxide superconducting layer having a thickness of 1.0 μm is formed on the orientation controlled polycrystalline intermediate thin film using the laser deposition apparatus shown in FIG. A superconducting conductor was prepared. During the heat treatment here, the substrate was not distorted. The oxide superconducting conductor obtained by the above treatment has a thickness of 202.1 μm, a width of 10 mm, and a length of 10 cm.
[0064]
As a result of cooling this oxide superconductor and measuring the critical current density, critical current density = 5.2 × 10 6. 5 A / cm 2 (77K, 0T), critical current density per overall = 2.5 × 10 3 A / cm 2 (77K, 0T) was shown, and it was confirmed that extremely excellent superconducting properties were exhibited.
Therefore, the obtained oxide superconducting conductor does not cause distortion in the above-mentioned base material due to a high temperature atmosphere during the deposition of the oxide superconducting layer, even when a thin base material having a thickness of 0.2 mm is used. It became clear that the current density was improved.
[0065]
(Comparative Example 3)
An oxide superconducting conductor was produced in the same manner as in Example 3 except that the polycrystalline rapid-growing intermediate thin film was not formed on the lower surface of the substrate. The oxide superconducting conductor here had a thickness of 201.6 μm, a width of 10 mm, and a length of 10 cm.
As a result of cooling this oxide superconductor and measuring the critical current density, the critical current density = 2.3 × 10. 4 A / cm 2 (77K, 0T), but critical current density per overall = 1.1 x 10 2 A / cm 2 It was low. In addition, in the oxide superconducting conductor, the base material was distorted by a high temperature atmosphere during the deposition of the oxide superconducting layer.
[0066]
(Example 4)
In the same manner as in Example 3, a polycrystalline rapid-growing intermediate thin film was formed on both surfaces of the substrate.
Next, using the ion beam sputtering apparatus having the configuration shown in FIG. 3, on one of the polycrystalline rapid-growing intermediate thin films formed on both surfaces of the substrate in the same manner as in Example 3, A YSZ orientation controlled polycrystalline intermediate thin film having a thickness of 0.1 μm was formed by performing ion irradiation simultaneously with sputtering and performing a film forming process for 1 hour. Thereafter, a YSZ orientation controlled polycrystalline intermediate thin film having a thickness of 0.1 μm was formed on the other polycrystalline rapid-growing intermediate thin film in the same manner as described above.
[0067]
Next, an oxide superconducting layer having a thickness of 1.0 μm is formed on the orientation controlled polycrystalline intermediate thin film on both sides of the base material in the same manner as in Example 1 using a laser deposition apparatus having the configuration shown in FIG. Then, an oxide superconducting conductor similar to that shown in FIG. 9 was produced. During the heat treatment here, the substrate was not distorted. The oxide superconducting conductor obtained by the above treatment has a thickness of 203.2 μm, a width of 0.5 mm, and a length of 10 cm.
[0068]
As a result of cooling this oxide superconductor and measuring the critical current density, the critical current density = 4.8 × 10 6. 5 A / cm 2 (77K, 0T), critical current density per overall = 4.7 × 10 3 A / cm 2 (77K, 0T) was shown, and it was confirmed that extremely excellent superconducting properties were exhibited.
Therefore, the obtained oxide superconducting conductor does not cause distortion in the above-mentioned base material due to a high temperature atmosphere during the deposition of the oxide superconducting layer, even when a thin base material having a thickness of 0.2 mm is used. It was revealed that the current density was about twice as large as that of the oxide superconducting conductor of Example 3.
[0069]
(Example 5)
Using a Hastelloy tape with a width of 10 mm, a thickness of 0.2 mm, and a length of 80 cm as the base material, the thickness of the YSZ orientation control polycrystalline intermediate thin film formed on the top surface of the base material is 0.7 μm, and on the bottom surface of the base material A thin film laminate was obtained in substantially the same manner as in Example 1 except that a 0.7 μm thick YSZ orientation controlled polycrystalline intermediate thin film was formed by ion beam assisted sputtering.
Next, an oxide superconducting layer having a thickness of 1.0 μm was formed on one orientation controlled polycrystalline intermediate thin film using a laser vapor deposition apparatus having the configuration shown in FIG. 7, and an oxide superconducting conductor similar to FIG. 10 was produced. .
[0070]
(Comparative Example 4)
A laminate was obtained in the same manner as in Example 5 except that no orientation-controlled polycrystalline intermediate thin film was formed on the lower surface of the substrate.
Next, an oxide superconducting layer having a thickness of 1.0 μm is formed on the YSZ orientation control polycrystalline intermediate thin film having a thickness of 0.7 μm formed on the upper surface of the substrate by using a laser vapor deposition apparatus having the configuration shown in FIG. An oxide superconductor similar to that shown in FIG. 14 was produced.
[0071]
The thin film laminate obtained in Example 5 and the laminate obtained in Comparative Example 4
The state of warping was examined by measuring the surface shape along the width direction when heated at 900 to 950 ° C. and moved at 1 m / h. FIG. 11 shows a profile of the surface shape of the thin film laminate obtained in Example 5. FIG. 12 shows a profile of the surface shape of the laminate obtained in Comparative Example 4. 11 and 12, the horizontal axis represents the length in the width direction (μm), and the vertical axis represents the height in the thickness direction (angstrom).
[0072]
The curvature radius of curvature can be calculated from the profile of the surface shape by the following formula (I).
R = (X 2 + Y 2 ) / 2Y (I)
In formula I, R is the radius of curvature, X is the length in the width direction (μm) when the height in the profile of the surface shape is a peak, and Y is the thickness direction when the height in the profile of the surface shape is a peak. Represents the height of angstrom.
[0073]
The thin film laminate of Example 5 is X = 4500 (μm) from FIG.
Since Y = | −100,000 | (angstrom), when these were substituted into the formula I, R = 964 (cm).
On the other hand, in the laminate of Comparative Example 4, X = 4500 (μm) from FIG.
Since Y = 400,000 (angstrom), when these are substituted into the formula I, R = 25.3 (cm). Thus, the thin film laminate obtained in Example 5 (in which the orientation control polycrystalline intermediate thin film was formed on both surfaces of the base material) was the laminate obtained in Comparative Example 4 (only one side of the base material was controlled in orientation control). It was found that the radius of curvature was large and the amount of warpage was small compared to the case where a crystal intermediate thin film was formed.
[0074]
The oxide superconducting conductors obtained in Example 5 and Comparative Example 4 were each subjected to Ag coating on the central portion side of the oxide superconducting conductor by a sputtering device, and further, Ag electrodes were formed on both end sides, respectively. After the Ag coating, heat treatment was performed at 500 ° C. for 2 hours in a pure oxygen atmosphere to obtain a measurement sample.
And these samples were cooled to 77K with liquid nitrogen, and the result of having measured the critical current (Ic) for every length direction in each sample on the conditions of external magnetic field 0T (Tesla) is shown in FIG. In FIG. 13, the solid line (1) indicates the critical current for each position in the length direction of the oxide superconducting conductor obtained in Example 5, and the broken line (2) indicates the oxide obtained in Comparative Example 4. It shows the critical current for each position in the length direction of the superconducting conductor.
[0075]
As is clear from FIG. 13, the oxide superconducting conductor obtained in Comparative Example 4 has a critical current in the length direction of 15 A or less at any location, with respect to the length direction of the substrate. It can be seen that an oxide superconducting thin film having poor superconducting properties is formed. On the other hand, the oxide superconducting conductor obtained in Example 5 has a characteristic in which the critical current in the length direction is 18 A or more at any location. Furthermore, the oxide superconducting conductor of Example 5 The average value of the critical current is about twice that of Comparative Example 4, and thus it can be seen that an oxide superconducting thin film having good superconducting characteristics in the length direction of the base material is formed.
[0076]
【The invention's effect】
As described above, the oxide superconducting conductor of the present invention has an intermediate thin film formed on both sides of a tape-like substrate, and an oxide superconducting layer is formed on an orientation-controlled polycrystalline intermediate thin film among these intermediate thin films. Therefore, even if the thickness of the tape-shaped substrate is thin, the substrate is supported by the intermediate thin films on both sides, and thus the substrate is distorted by the high temperature atmosphere during the deposition of the oxide superconducting layer. It is suppressed. This reduces distortion in the intermediate thin film on the substrate and improves the planarity of the surface of the orientation controlled polycrystalline intermediate thin film. Therefore, the oxide superconducting layer crystals formed on the orientation controlled polycrystalline intermediate thin film The orientation is good and the critical current density is excellent. Therefore, in the oxide superconducting conductor of the present invention, since a thin tape-like base material can be used, the thickness of the oxide superconducting conductor can be reduced, and overall (total cross-sectional area of oxide superconducting conductor) The critical current density can be improved, and there is an advantage that a long oxide superconductor having a large current capacity can be easily provided. In the oxide superconducting conductor of the present invention, since the intermediate thin film formed on both surfaces of the base material functions as an insulating layer, it is sufficient to form an insulating layer only on the oxide superconducting layer side, and it is used as a magnet or the like. In such a case, the film can be wound as it is without forming an insulating layer.
[0077]
In particular, in the case of an oxide superconducting conductor in which the intermediate thin film is composed of two layers of a polycrystalline rapid-growing thin film and an orientation-controlled polycrystalline thin film, the combined thickness of the polycrystalline rapid-growing intermediate thin film and the orientation-controlled polycrystalline intermediate thin film Compared to using an orientation-controlled polycrystalline intermediate thin film as a whole, the portion of the orientation-controlled polycrystalline intermediate thin film that takes a long time to deposit is reduced, and the polycrystalline rapid-growing intermediate thin film portion has a higher film forming speed, so the film forming time Is shortened.
[0078]
In the case of an oxide superconducting conductor in which an oxide superconducting layer is formed on both sides of the base material via an intermediate thin film, the critical current density per overall (total cross-sectional area of the oxide superconducting conductor) is one of the base materials. The oxide superconducting conductor in which the oxide superconducting layer is formed only on the surface of the oxide superconducting conductor is about twice as large, and the critical current density per overall is large, and a long oxide superconducting conductor having a larger current capacity is easily provided. There is an advantage that you can.
In addition, in the case where each grain boundary inclination angle of a large number of crystal grains forming the orientation controlled polycrystalline intermediate thin film is 30 degrees or less, the oxide superconducting layer formed on the orientation controlled polycrystalline intermediate thin film Since the crystal orientation becomes better, more excellent superconducting properties are exhibited.
[0079]
Furthermore, in the case where the orientation controlled polycrystalline intermediate thin film formed on both surfaces of the substrate is formed by ion beam assisted sputtering, the compressive stress is canceled by the orientation controlled polycrystalline intermediate thin film on both sides, although compressive stress is included. Therefore, it is possible to prevent the base material from being warped, and the polycrystalline fast-growing intermediate thin film and the orientation controlled polycrystalline intermediate thin film are also formed on the bottom surface (heated surface) of the base material. Is prevented. This makes it easier to uniformly heat the surface of the thin film stack when depositing the oxide superconducting layer on the orientation controlled polycrystalline intermediate thin film, and the temperature distribution on the surface of the thin film stack is hardly uneven, and the thin film stack Therefore, an oxide superconducting layer having stable superconducting characteristics in the length direction of the substrate can be formed.
Therefore, according to the oxide superconducting conductor of the present invention, the superconducting property with respect to the length direction of the base material is stable without causing warpage of the base material due to compressive stress during the formation of the orientation controlled polycrystalline intermediate thin film. Even when a thin tape-like base material is used, the above base material is less likely to be distorted by the high temperature atmosphere during vapor deposition of the oxide superconducting layer, An oxide superconductor having at least one of the characteristics that the critical current density is improved can be provided.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a first example of an oxide superconducting conductor according to the present invention.
FIG. 2 is a configuration diagram showing an example of a high-frequency sputtering apparatus for forming a polycrystalline rapid-growing intermediate thin film on a substrate, which is preferably used for manufacturing an oxide superconducting conductor according to the present invention.
FIG. 3 is a configuration diagram showing an example of an ion beam sputtering apparatus for forming an orientation-controlled polycrystalline intermediate thin film on a substrate, which is preferably used for manufacturing an oxide superconductor according to the present invention.
4 is a cross-sectional view showing an example of an ion gun used in the apparatus shown in FIG.
FIG. 5 is an explanatory diagram showing an angular relationship between an incident angle of an ion beam and a cubic crystal lattice when a film forming process is performed together with ion beam irradiation.
FIG. 6 is a structural diagram showing a thin film laminate of oxide superconducting conductors according to the present invention.
FIG. 7 is a configuration diagram showing an example of an apparatus for forming an oxide superconducting layer on an orientation-controlled polycrystalline intermediate thin film, which is preferably used for manufacturing an oxide superconducting conductor according to the present invention.
FIG. 8 is a cross-sectional view showing a second example of the oxide superconducting conductor according to the present invention.
FIG. 9 is a cross-sectional view showing a third example of the oxide superconductor according to the present invention.
FIG. 10 is a cross-sectional view showing another example of the oxide superconductor according to the present invention.
11 is a profile of the surface shape of the thin film laminate obtained in Example 5. FIG.
12 is a profile of the surface shape of the laminate obtained in Comparative Example 4. FIG.
13 is a graph showing the critical current at each position in the length direction of the oxide superconducting conductor obtained in Example 5 and Comparative Example 4. FIG.
FIG. 14 is a cross-sectional view showing an example of a conventional oxide superconducting conductor.
[Explanation of symbols]
20, 90, 100 ... oxide superconductor,
21 ... base material,
22, 22a, 22b ... Oriented controlled polycrystalline intermediate thin film ,
23, 23a, 23b ... Polycrystalline rapid intermediate film ,
24, 24a, 24b ... oxide superconducting layers.

Claims (6)

テープ状の基材と、この基材の一方の面上に形成されて多数の結晶粒が結合されてなる配向制御多結晶中間薄膜と、上記基材の他方の面上に形成された多結晶速成中間薄膜と、前記配向制御多結晶中間薄膜上に形成された酸化物超電導層を具備してなることを特徴とする酸化物超電導導体。Tape-shaped base material, orientation-controlled polycrystalline intermediate thin film formed on one surface of the base material and bonded with a large number of crystal grains, and polycrystal formed on the other surface of the base material An oxide superconducting conductor comprising a rapid-forming intermediate thin film and an oxide superconducting layer formed on the orientation-controlled polycrystalline intermediate thin film. テープ状の基材と、この基材の両面上にそれぞれ形成されて多数の結晶粒が結合されてなる多結晶速成中間薄膜と、これら多結晶速成中間薄膜のうち一方の多結晶速成中間薄膜上に形成された配向制御多結晶中間薄膜と、この配向制御多結晶中間薄膜上に形成された酸化物超電導層を具備してなることを特徴とする酸化物超電導導体。A tape-like base material, a polycrystalline fast-growing intermediate thin film formed on both surfaces of the base material and bonded with a large number of crystal grains, and one of these polycrystalline fast-growing intermediate thin films An oxide superconducting conductor comprising: an orientation-controlled polycrystalline intermediate thin film formed on the surface; and an oxide superconducting layer formed on the orientation-controlled polycrystalline intermediate thin film. テープ状の基材と、この基材の両面上にそれぞれ形成されて多数の結晶粒が結合されてなる多結晶速成中間薄膜と、これら多結晶速成中間薄膜上にそれぞれ形成された配向制御多結晶中間薄膜と、これら配向制御多結晶中間薄膜上にそれぞれ形成された酸化物超電導層を具備してなることを特徴とする酸化物超電導導体。Tape-shaped substrate, polycrystalline fast-growing intermediate thin film formed by bonding a large number of crystal grains formed on both surfaces of this base material, and orientation-controlled polycrystal formed on each of these polycrystalline rapid-growing intermediate thin films An oxide superconducting conductor comprising an intermediate thin film and an oxide superconducting layer formed on each of the orientation-controlled polycrystalline intermediate thin films. 請求項１〜３のいずれかに記載の酸化物超電導導体において、上記配向制御多結晶中間薄膜を形成する多数の結晶粒のそれぞれの粒界傾角が３０度以下であることを特徴とする酸化物超電導導体。The oxide superconducting conductor according to any one of claims 1 to 3 , wherein a grain boundary inclination angle of each of a large number of crystal grains forming the orientation controlled polycrystalline intermediate thin film is 30 degrees or less. Superconducting conductor. 請求項１〜４のいずれかに記載の酸化物超電導導体において、中間薄膜がイットリウム安定化ジルコニアからなることを特徴とする酸化物超電導導体。In the oxide superconductor according to any one of claims 1-4, oxide superconductor, wherein an intermediate thin film is made of yttrium stabilized zirconia. 請求項１〜５のいずれかに記載の酸化物超電導導体において、配向制御多結晶中間薄膜がイオンビームアシストスパッタリング法により形成されたものであることを特徴とする酸化物超電導導体。 6. The oxide superconductor according to claim 1, wherein the orientation controlled polycrystalline intermediate thin film is formed by an ion beam assisted sputtering method.
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