JP2955407B2 - Superconducting element - Google Patents
Superconducting elementInfo
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- JP2955407B2 JP2955407B2 JP3245537A JP24553791A JP2955407B2 JP 2955407 B2 JP2955407 B2 JP 2955407B2 JP 3245537 A JP3245537 A JP 3245537A JP 24553791 A JP24553791 A JP 24553791A JP 2955407 B2 JP2955407 B2 JP 2955407B2
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- Prior art keywords
- film
- superconducting
- oxide superconductor
- superconductor
- main electrode
- Prior art date
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Description
【０００１】[0001]
【産業上の利用分野】本発明は、酸化物超電導体を利用
した超電導素子に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting element using an oxide superconductor.
【０００２】[0002]
【従来の技術】従来から、超電導素子として、PbやNb等
の金属超電導体で超電導電子対がトンネルできる程度の
薄い絶縁層を挟み込んだ構成のトンネル型ジョセフソン
接合が知られている。このような従来のトンネル型ジョ
セフソン素子は、液体ヘリウム温度に近い極低温動作が
必要とされている。また、トンネル型ジョセフソン接合
に特有な、ヒステリシスを持つ電流−電圧特性を示すた
め、回路構成が複雑になる等の問題があり、広く実用に
供されるまでには至っていない。2. Description of the Related Art Conventionally, as a superconducting element, a tunnel-type Josephson junction having a structure in which a thin superconducting element can be tunneled by a metal superconductor such as Pb or Nb is sandwiched. Such a conventional tunnel-type Josephson device needs to operate at a very low temperature close to the temperature of liquid helium. In addition, since the current-voltage characteristic having hysteresis characteristic of a tunnel-type Josephson junction is exhibited, there is a problem that a circuit configuration is complicated and the like, and it has not yet been widely used.
【０００３】一方、金属超電導体を用いた、ヒステリシ
ス特性をもたないジョセフソン接合素子として、金属超
電導体からなる主電極間を、細くてかつ薄い金属で接続
した、いわゆるブリッジ型接合の開発も進められてき
た。このようなブリッジ型接合は、ブリッジ部の断面積
を電極部に比べて十分に小さくし、かつブリッジ部の長
さをコヒーレンス長と同程度に作製することができれ
ば、ヒステリシスの無い電流−電圧特性を有するジョセ
フソン接合となり、かつトンネル接合と同程度の高い出
力電圧が得られる可能性があるとして期待されてきた。
しかし、このようなブリッジ型接合を従来の金属超電導
体を用いて平面上に構成するには、 0.1μm程度の超微
細加工が必要であり、さらにブリッジ部に用いられる材
料が金属であるために、接合抵抗を十分に高められない
等の難点を有していることから、実用化するまでには至
っていない。また、上述したトンネル型接合の場合と同
様に、液体ヘリウム温度に近い極低温動作が必要である
という難点をも有していた。On the other hand, as a Josephson junction element using a metal superconductor and having no hysteresis characteristics, a so-called bridge type junction in which main electrodes made of a metal superconductor are connected with a thin and thin metal has also been developed. It has been advanced. If such a bridge-type junction has a cross-sectional area of the bridge portion sufficiently smaller than that of the electrode portion and the length of the bridge portion can be made substantially equal to the coherence length, current-voltage characteristics without hysteresis can be obtained. It has been expected that there is a possibility that a Josephson junction having the following characteristics will be obtained, and an output voltage as high as a tunnel junction may be obtained.
However, in order to construct such a bridge type junction on a plane using a conventional metal superconductor, ultra-fine processing of about 0.1 μm is required, and since the material used for the bridge part is metal, However, it has difficulties such as not being able to sufficiently increase the junction resistance, and thus has not been put to practical use. In addition, as in the case of the above-described tunnel junction, there is a disadvantage that an extremely low temperature operation close to the temperature of liquid helium is required.
【０００４】このような状況の下、最近、液体窒素温度
以上の温度で超電導特性を示す酸化物超電導体材料が発
見され、大きな注目を集めている。この酸化物超電導体
を用いて、良好なジョセフソン接合を作製することが可
能となれば、上記した従来の金属超電導体を用いて構成
したジョセフソン接合に比べ、少なくとも極低温動作の
必要がなくなることから、広範囲な応用が期待されてい
る。Under these circumstances, recently, oxide superconductor materials exhibiting superconductivity at a temperature equal to or higher than the temperature of liquid nitrogen have been discovered and have attracted much attention. If it becomes possible to produce a good Josephson junction using this oxide superconductor, there is no need for at least cryogenic operation as compared with the above-mentioned conventional Josephson junction using a metal superconductor. Therefore, a wide range of applications are expected.
【０００５】[0005]
【発明が解決しようとする課題】しかしながら、酸化物
超電導体材料は、その表面が大気中で容易に劣化し、ま
たコヒーレンス長が小さいという本質的な問題を有して
いるため、明確なジョセフソン特性を示す良好な接合は
得られていないのが現状である。つまり、臨界温度の高
い酸化物超電導体を用いたジョセフソン接合の開発は、
産業上大きく寄与するものと期待されているため、これ
を実用に供するための接合構造、ならびにその製造方法
の開発が課題とされていた。However, the oxide superconductor material has the essential problems that its surface is easily degraded in the atmosphere and its coherence length is small, so that a clear Josephson material is required. At present, good bonding showing characteristics has not been obtained. In other words, the development of Josephson junctions using oxide superconductors with high critical temperatures
Since it is expected to greatly contribute to the industry, development of a joining structure for making this practical and a method of manufacturing the same has been a challenge.
【０００６】本発明は、このような課題に対処してなさ
れたもので、良好なジョセフソン特性を示すと共に、制
御性に優れ、かつ大きな出力電圧が得られる、酸化物超
電導体を用いた超電導素子を提供することを目的とす
る。SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has a superconductivity using an oxide superconductor which exhibits good Josephson characteristics, is excellent in controllability, and can obtain a large output voltage. It is intended to provide an element.
【０００７】[0007]
【課題を解決するための手段】すなわち、本発明の超電
導素子は、酸化物超電導体からなる２つの主電極部と、
これら主電極部間に介在され、該主電極部間を電気的に
接続する接続部とを具備する超電導素子であって、前記
接続部は、前記酸化物超電導体と結晶構造が類似した非
超電導酸化物中に散在された複数の超電導電流経路を有
し、これらの超電導電流経路は前記接続部を構成する非
超電導酸化物の結晶粒界に沿って形成されていると共
に、その各断面積が前記主電極部の断面積に比べて十分
に小さいことを特徴としている。That is, the superconducting element of the present invention comprises two main electrode portions made of an oxide superconductor;
A superconducting element interposed between these main electrode portions and having a connection portion for electrically connecting the main electrode portions, wherein the connection portion has a non-superconducting structure similar in crystal structure to the oxide superconductor. It has a plurality of superconducting current paths scattered in the oxide , and these superconducting current paths are non-conductive
Both are formed along the grain boundaries of the superconducting oxide.
To its respective cross-sectional area is characterized by the go sufficiently small compared to the cross-sectional area of the main electrode portion.
【０００８】本発明の超電導素子における接続部は、上
述したように、非超電導体例えば絶縁体や常伝導体中に
埋め込まれて散在する、複数の超電導電流経路を有して
いる。このような超電導電流経路は、接続部を構成する
非超電導体の結晶粒界に沿って形成することにより、再
現性よく得ることができる。[0008] As described above, the connecting portion in the superconducting element of the present invention has a plurality of superconducting current paths embedded and scattered in a non-superconductor such as an insulator or a normal conductor. Such a superconducting current path can be obtained with good reproducibility by being formed along the crystal grain boundaries of the non-superconductor constituting the connection portion.
【０００９】例えば、酸化物超電導体と、これと結晶構
造の類似した非超電導体とを連続的に積層形成すると、
非超電導体中に存在する結晶粒界に沿って元素の高速な
拡散を生じ、結晶粒界の極く近傍の導電特性が大きく変
化する。一例として、 YBa2 Cu3 O 7 膜（以下、 Y-Ba-
Cu-O膜と記す）と、PrBa2 Cu3 O 7 膜（以下、Pr-Ba-Cu
-O膜と記す）とを積層形成すると、 Yが粒界に沿っての
み拡散し、本来は低温で絶縁体であるPr-Ba-Cu-O膜に、
金属的な伝導を担う部分を局所的に生じさせることがで
きる。一方、 Y-Ba-Cu-O膜とPr-Ba-Cu-O膜とは結晶構造
が同一であり、また格子定数も極めて近いために、結晶
粒界は Y-Ba-Cu-O膜とPr-Ba-Cu-O膜との界面で連続的に
繋がる。この結果、Y-Ba-Cu-O/Pr-Ba-Cu-O/Y-Ba-Cu-Oの
3層構造を作製すると、下部の Y-Ba-Cu-O膜からPr-Ba-
Cu-O膜を通して上部の Y-Ba-Cu-O膜まで、ほぼ直線的に
繋がった結晶粒界に沿って、金属的な伝導パスが形成さ
れる。この伝導パスが本発明における超電導電流経路と
なる。For example, when an oxide superconductor and a non-superconductor having a similar crystal structure to the oxide superconductor are continuously laminated,
High-speed diffusion of elements occurs along the grain boundaries existing in the non-superconductor, and the conductive properties in the immediate vicinity of the grain boundaries change significantly. As an example, a YBa 2 Cu 3 O 7 film (hereinafter, Y-Ba-
Cu-O film) and PrBa 2 Cu 3 O 7 film (hereinafter Pr-Ba-Cu
-O film), Y diffuses only along the grain boundaries, and the low-temperature Pr-Ba-Cu-O film is an insulator.
A portion that performs metallic conduction can be locally generated. On the other hand, the crystal structure of the Y-Ba-Cu-O film and that of the Pr-Ba-Cu-O film are the same, and the lattice constants are extremely close. It is continuously connected at the interface with the Pr-Ba-Cu-O film. As a result, Y-Ba-Cu-O / Pr-Ba-Cu-O / Y-Ba-Cu-O
When a three-layer structure is fabricated, Pr-Ba-
A metallic conduction path is formed along the almost linearly connected grain boundaries through the Cu-O film to the upper Y-Ba-Cu-O film. This conduction path is the superconducting current path in the present invention.
【００１０】また、このような結晶粒界を利用した超電
導電流経路は、 Y-Ba-Cu-O系酸化物超電導体とPr-Ba-Cu
-O系絶縁体とを組合せた場合に限らず、各種の酸化物超
電導体とそれと結晶構造が類似した非超電導体とを組合
せることによって形成することが可能である。A superconducting current path utilizing such a grain boundary is composed of a Y-Ba-Cu-O-based oxide superconductor and a Pr-Ba-Cu
The present invention is not limited to the case where the insulator is combined with an -O-based insulator, and can be formed by combining various oxide superconductors and a non-superconductor having a similar crystal structure to the oxide superconductor.
【００１１】このようにして得られる超電導電流経路
は、その断面積を主電極部のそれに比べて十分小さくす
ることができ、かつ超電導電流経路相互の間の距離を接
続部における磁界侵入深さより十分小さくすることがで
きる。よって、このような超電導電流経路を有する接続
部を用いることによって、ブリッジ型の接合を構成する
ことが可能となる。なお、本発明の超電導素子は、広い
意味で可変厚ブリッジ（バリアブル・シックネス・ブリ
ッジ：以下、ＶＴＢと記す）接合と見なすことができ
る。[0011] Thus a superconducting current path obtained, the cross-sectional area than that of the main electrode portion can be made sufficiently small, and Ri magnetic field penetration depth Saya the distance between the superconducting current path cross in the connecting portion It can be made sufficiently small. Therefore, it is possible to form a bridge-type junction by using a connection portion having such a superconducting current flow path. The superconducting element of the present invention can be regarded as a variable thickness bridge (Variable Thickness Bridge: VTB) junction in a broad sense.
【００１２】形成する超電導電流経路の密度や相互の間
隔は、接合の面積に応じて設定するものとする。この超
電導電流経路の密度や相互の間隔は、接続部を構成する
非超電導体の結晶粒の大きさを制御することにより、所
望の値とすることができる。この結晶粒の大きさは、薄
膜の形成条件を制御することで、種々の値を得ることが
できる。また、超電導電流経路の長さは、使用する酸化
物超電導体のコヒーレンス長に応じて設定するものと
し、接続部を構成する非超電導体の厚さを制御すること
によって、容易に所望の値とすることができる。The density of superconducting current paths to be formed and the distance between them are set in accordance with the area of the junction. The density and the distance between the superconducting current paths can be set to desired values by controlling the size of the crystal grains of the non-superconductor constituting the connection portion. Various values can be obtained for the size of the crystal grains by controlling the conditions for forming the thin film. In addition, the length of the superconducting current path is set according to the coherence length of the oxide superconductor to be used, and by controlling the thickness of the non-superconductor constituting the connection portion, the desired value can be easily obtained. can do.
【００１３】[0013]
【作用】本発明の超電導素子においては、非超電導体中
に埋め込まれて散在する複数の超電導電流経路を有する
接続部によって、ジョセフソン接合を構成している。上
記超電導電流経路は、例えば主電極部となる酸化物超電
導体と、接続部を構成する非超電導酸化物との結晶粒界
を利用して形成することができるため、超電電流経路の
各断面積を主電極部の断面積に比べて十分に小さくする
ことができると共に、超電導電流経路相互の間の距離を
接続部における磁界侵入深さより十分に小さくすること
ができる。また、超電導電流経路の密度や相互の間隔
は、例えば接続部を構成する非超電導酸化物の結晶粒の
大きさを制御することにより所望の値とすることができ
るため、所望の超電導電流密度を有する接合の作製が可
能となる。さらに、接続部を構成する非超電導酸化物の
厚さを所望の値とすることで、超電導電流経路を流れる
超電導電流がコヒーレントなジョセフソン応答を行う条
件を満たすことができる。これらによって、従来の平面
上に作製していたＶＴＢ接合の場合に要求された極微細
加工を行うことなく、積層構造の条件を制御するだけ
で、酸化物超電導体を用いた良好な特性を有するジョセ
フソン接合を得ることができる。In the superconducting element of the present invention, a junction having a plurality of superconducting current paths embedded and scattered in a non-superconductor forms a Josephson junction. The superconducting current path can be formed by using, for example, a crystal grain boundary between an oxide superconductor serving as a main electrode portion and a non-superconducting oxide forming a connection portion. it is possible to sufficiently smaller than the area to the cross-sectional area of the main electrode portion, it is possible to sufficiently reduce Ri magnetic field penetration depth Sayo at the connecting portion the distance between the superconducting current path other. Further, the density of the superconducting current paths and the distance between the superconducting current paths can be set to a desired value by controlling the size of the crystal grains of the non-superconducting oxide constituting the connection portion. Can be produced. Furthermore, by setting the thickness of the non-superconducting oxide constituting the connection portion to a desired value, it is possible to satisfy the condition that the superconducting current flowing through the superconducting current path performs a coherent Josephson response. With these, it is possible to obtain good characteristics using an oxide superconductor only by controlling the conditions of the laminated structure without performing the ultra-fine processing required in the case of a VTB junction manufactured on a conventional flat surface. A Josephson junction can be obtained.
【００１４】[0014]
【実施例】以下、本発明の超電導素子の実施例について
説明する。DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the superconducting element of the present invention will be described below.
【００１５】図１は、本発明をＹ−Ｂａ−Ｃｕ−Ｏ／Ｐ
ｒ−Ｂａ−Ｃｕ−Ｏ／Ｙ−Ｂａ−Ｃｕ−Ｏ積層構造を有
する超電導素子に適用した実施例の断面構造を示す図で
ある。図１において、１はＳｒＴｉＯ３（１００）基板
等の絶縁基板であり、このＳｒＴｉＯ３（１００）基板
１上には、下側の主電極部となるＹ−Ｂａ−Ｃｕ−Ｏ系
酸化物超電導体膜２が形成されている。このＹ−Ｂａ−
Ｃｕ−Ｏ系酸化物超電導体膜２上には、接続部を構成す
る非超電導体層として、Ｐｒ−Ｂａ−Ｃｕ−Ｏ系絶縁体
膜３が形成されている。このＰｒ−Ｂａ−Ｃｕ−Ｏ系絶
縁体膜３内には、Ｐｒ−Ｂａ−Ｃｕ−Ｏ結晶の結晶粒界
に沿って、図示を省略した複数の超電導電流経路が形成
されている。これらの超電導電流経路は、その各断面積
が主電極部の断面積に比べて十分小さく、かつ超電導電
流経路相互の間の距離が接続部における磁界侵入深さよ
り十分小さく設定されている。FIG. 1 shows that the present invention is applied to Y—Ba—Cu—O / P
It is a figure showing the section structure of the example applied to the superconducting element which has r-Ba-Cu-O / Y-Ba-Cu-O laminated structure. In FIG. 1, reference numeral 1 denotes an insulating substrate such as a SrTiO 3 (100) substrate, and on the SrTiO 3 (100) substrate 1, a Y—Ba—Cu—O-based oxide superconductor serving as a lower main electrode portion is provided. A body film 2 is formed. This Y-Ba-
On the Cu-O-based oxide superconductor film 2, a Pr-Ba-Cu-O-based insulator film 3 is formed as a non-superconductor layer constituting a connection portion. In the Pr-Ba-Cu-O-based insulator film 3, a plurality of superconducting current paths (not shown) are formed along the grain boundaries of the Pr-Ba-Cu-O crystal. These superconducting current paths have respective cross-sectional areas sufficiently smaller than the cross-sectional area of the main electrode portion, and the distance between the superconducting current paths is set sufficiently smaller than the magnetic field penetration depth at the connection portion. ing.
【００１６】このようなPr-Ba-Cu-O系絶縁体膜３上に
は、上側の主電極部となる Y-Ba-Cu-O系酸化物超電導体
膜４が形成されており、これら Y-Ba-Cu-O系酸化物超電
導体膜２/ Pr-Ba-Cu-O系絶縁体膜３/Y-Ba-Cu-O系酸化物
超電導体膜４による積層構造によって、ＶＴＢ接合が構
成されている。なお、上部 Y-Ba-Cu-O系酸化物超電導体
膜４上には、絶縁膜５を介して、上部 Y-Ba-Cu-O系酸化
物超電導体膜４への配線６が設けられている。On such a Pr-Ba-Cu-O-based insulator film 3, a Y-Ba-Cu-O-based oxide superconductor film 4 serving as an upper main electrode portion is formed. The VTB junction is formed by the laminated structure of the Y-Ba-Cu-O-based oxide superconductor film 2 / Pr-Ba-Cu-O-based insulator film 3 / Y-Ba-Cu-O-based oxide superconductor film 4. It is configured. On the upper Y-Ba-Cu-O-based oxide superconductor film 4, a wiring 6 to the upper Y-Ba-Cu-O-based oxide superconductor film 4 is provided via an insulating film 5. ing.
【００１７】このような構成の超電導素子は、例えば以
下のようにして製造される。なお、図２に上記超電導素
子の製造工程を示す。まず、 SrTiO3(100) 基板１上
に、マグネトロンスパッタ法等によって、下部Y-Ba-Cu-
O系酸化物超電導体膜２、Pr-Ba-Cu-O系絶縁体膜３およ
び上部 Y-Ba-Cu-O系酸化物超電導体膜４を順に積層形成
する（図２−ａ）。各層の膜厚は、この実施例では 300
nm、20nm、 200nmとした。The superconducting element having such a configuration is manufactured, for example, as follows. FIG. 2 shows a manufacturing process of the superconducting element. First, on the SrTiO 3 (100) substrate 1, the lower Y-Ba-Cu-
An O-based oxide superconductor film 2, a Pr-Ba-Cu-O-based insulator film 3, and an upper Y-Ba-Cu-O-based oxide superconductor film 4 are sequentially laminated (FIG. 2A). The thickness of each layer is 300 in this example.
nm, 20 nm, and 200 nm.
【００１８】この際に重要な事は、積層構造を同一装置
において連続的に形成し、大気に晒さないこと、ならび
に下部 Y-Ba-Cu-O系酸化物超電導体膜２の成膜時の基板
温度を、所定の超電導転移温度を維持し、かつ結晶粒が
所定の大きさになるよう設定することである。前者は Y
-Ba-Cu-O膜とPr-Ba-Cu-O膜との界面に結晶配列の乱れを
与えないためであり、後者は先に述べた所定の超電導ジ
ョセフソン電流の値を得るために不可欠である。すなわ
ち、下部 Y-Ba-Cu-O系酸化物超電導体膜２の結晶粒の大
きさによって、Pr-Ba-Cu-O系絶縁体膜３中の結晶粒の大
きさが決定されるためである。そして、このPr-Ba-Cu-O
系絶縁体膜３中の結晶粒の大きさにより、超電導電流経
路の密度や相互の間隔が決定される。これら超電導電流
経路の密度や相互の間隔は、前述したように接合の面積
に応じて設定するものとする。In this case, it is important that the laminated structure is formed continuously in the same apparatus and is not exposed to the atmosphere, and that the lower Y-Ba-Cu-O-based oxide superconductor film 2 is formed at the time of film formation. The purpose is to set the substrate temperature such that a predetermined superconducting transition temperature is maintained and crystal grains have a predetermined size. The former is Y
This is because the crystal arrangement is not disordered at the interface between the -Ba-Cu-O film and the Pr-Ba-Cu-O film, and the latter is indispensable for obtaining the above-mentioned predetermined superconducting Josephson current value. It is. That is, the size of the crystal grains in the Pr-Ba-Cu-O-based insulator film 3 is determined by the size of the crystal grains of the lower Y-Ba-Cu-O-based oxide superconductor film 2. is there. And this Pr-Ba-Cu-O
The density of the superconducting current paths and their mutual intervals are determined by the size of the crystal grains in the system insulator film 3. The density of these superconducting current paths and the distance between them are set in accordance with the area of the junction as described above.
【００１９】この実施例では、基板温度を 680℃に設定
して成膜した。この場合、下部Y-Ba-Cu-O系酸化物超電
導体膜２はａ軸配向となり、結晶粒の大きさは平均して
50nm程度であった。また、 Y-Ba-Cu-O膜２、４の超電導
転移温度（臨界温度）は 83Kであった。なお、臨界温度
が理想的な Y-Ba-Cu-O膜の 92Kに比べて低いのは、結晶
粒が設定した大きさとなるように、基板温度を低めに設
定したためである。結晶粒の大きさを変えずに臨界電流
を向上させるには、例えば SrTiO3 (100) 基板１上に、
予めPr-Ba-Cu-O膜を必要な結晶粒の大きさが得られる基
板温度で成膜し、次いで高い臨界温度が得られる基板温
度で、下部 Y-Ba-Cu-O系酸化物超電導体膜２を形成すれ
ばよい。この場合、結晶粒の大きさは下地のPr-Ba-Cu-O
膜で決まり、臨界温度は Y-Ba-Cu-O膜の成膜時の温度で
決まるためである。In this embodiment, the film was formed with the substrate temperature set at 680 ° C. In this case, the lower Y-Ba-Cu-O-based oxide superconductor film 2 has an a-axis orientation, and the size of crystal grains is on average.
It was about 50 nm. The superconducting transition temperature (critical temperature) of the Y-Ba-Cu-O films 2 and 4 was 83K. The reason why the critical temperature is lower than the ideal temperature of 92K of the Y-Ba-Cu-O film is that the substrate temperature is set lower so that the crystal grains have the set size. In order to improve the critical current without changing the crystal grain size, for example, on a SrTiO 3 (100) substrate 1,
In advance, a Pr-Ba-Cu-O film is formed at a substrate temperature at which the required crystal grain size can be obtained, and then at a substrate temperature at which a high critical temperature can be obtained, the lower Y-Ba-Cu-O-based oxide superconductor is formed. The body film 2 may be formed. In this case, the size of the crystal grain is Pr-Ba-Cu-O
This is because it is determined by the film, and the critical temperature is determined by the temperature at which the Y-Ba-Cu-O film is formed.
【００２０】このような条件の下で、 Y-Ba-Cu-O系酸化
物超電導体膜２/ Pr-Ba-Cu-O系絶縁体膜３/Y-Ba-Cu-O系
酸化物超電導体膜４の積層構造を連続成膜によって形成
することにより、この成膜の過程でPr-Ba-Cu-O系絶縁体
膜３の粒界に沿って Yが拡散し、本来絶縁体であるPr-B
a-Cu-O結晶の粒界近傍の伝導特性が大きく変化する。こ
れによって、図３に示すように、Pr-Ba-Cu-O系絶縁体膜
３の結晶粒界に沿って、超電導電流を流すための電流経
路７が複数形成される。なお、図３は接合部を拡大して
模式的に示す図であり、図中８はPr-Ba-Cu-O系絶縁体の
結晶粒を、９はY-Ba-Cu-O系酸化物超電導体の結晶粒を
示している。Under these conditions, the Y-Ba-Cu-O-based oxide superconductor film 2 / Pr-Ba-Cu-O-based insulator film 3 / Y-Ba-Cu-O-based oxide superconductor By forming the laminated structure of the body film 4 by continuous film formation, Y diffuses along the grain boundaries of the Pr—Ba—Cu—O based insulator film 3 in the process of this film formation, and is essentially an insulator. Pr-B
The conduction properties near the grain boundaries of a-Cu-O crystals change significantly. Thereby, as shown in FIG. 3, a plurality of current paths 7 for flowing a superconducting current are formed along the crystal grain boundaries of the Pr—Ba—Cu—O-based insulator film 3. FIG. 3 is a diagram schematically showing an enlarged view of the joint, in which 8 is a crystal grain of a Pr—Ba—Cu—O-based insulator, and 9 is a Y—Ba—Cu—O-based oxide. 2 shows crystal grains of a superconductor.
【００２１】このようにして、結晶粒界に沿って形成さ
れた超電導電流経路７は、その各断面積が主電極部２、
４の断面積に比べて十分小さく、かつ超電導電流経路７
の相互間の距離が接続部における磁界侵入深さより十分
小さくなる。このような超電導電流経路７の存在によっ
て、Ｙ−Ｂａ−Ｃｕ−Ｏ系酸化物超電導体膜２／Ｐｒ−
Ｂａ−Ｃｕ−Ｏ系絶縁体膜３／Ｙ−Ｂａ−Ｃｕ−Ｏ系酸
化物超電導体膜４による積層構造がＶＴＢ接合として機
能する。The superconducting current path 7 formed along the crystal grain boundary in this manner has a cross-sectional area of
4 and sufficiently smaller than the cross-sectional area of
Mutual distance of the magnetic field penetration depth Saya Ri sufficiently small at the connecting portion. Due to the existence of such a superconducting current path 7, the Y-Ba-Cu-O-based oxide superconductor film 2 / Pr-
The laminated structure of the Ba-Cu-O-based insulator film 3 / Y-Ba-Cu-O-based oxide superconductor film 4 functions as a VTB junction.
【００２２】積層膜形成後の加工工程は、通常の半導体
素子作製に用いられるものと同様である。まず、光学露
光法で接合部のパターンをレジスト膜に転写し、次いで
レジストをマスクとしてイオンミリング法等により、接
合の面積に合せて Y-Ba-Cu-O系酸化物超電導体膜２およ
びPr-Ba-Cu-O系絶縁体膜３をエッチングする（図２−
ｂ）。この実施例では、接合面積は10μm ×10μm とし
た。The processing steps after the formation of the laminated film are the same as those used for manufacturing a normal semiconductor device. First, the pattern of the bonding portion is transferred to the resist film by an optical exposure method, and then the Y-Ba-Cu-O-based oxide superconductor film 2 and Pr are adjusted to the bonding area by ion milling using the resist as a mask. -Ba-Cu-O-based insulator film 3 is etched (Fig. 2-
b). In this embodiment, the bonding area was 10 μm × 10 μm.
【００２３】次に、下部および上部 Y-Ba-Cu-O系酸化物
超電導体膜２、４への配線を互いに絶縁するための絶縁
膜５を積層形成し、この絶縁膜５を接合部上部のみを開
口させるよう加工する（図２−ｃ）。この絶縁膜５とし
ては、種々の材質を利用することができるが、この実施
例では工程を簡略化する目的でネガレジストを利用し
た。この後、上部 Y-Ba-Cu-O系酸化物超電導体膜４への
配線６を例えばAuによって形成する（図２−ｄ）ことに
よって、超電導素子が完成する。Next, an insulating film 5 for insulating the wirings to the lower and upper Y-Ba-Cu-O-based oxide superconductor films 2 and 4 from each other is formed in layers, and this insulating film 5 is Only the opening is made (FIG. 2-c). As the insulating film 5, various materials can be used. In this embodiment, a negative resist is used for the purpose of simplifying the process. Thereafter, the wiring 6 to the upper Y-Ba-Cu-O-based oxide superconductor film 4 is formed of, for example, Au (FIG. 2D), thereby completing the superconducting element.
【００２４】ここで述べた通り、本発明の超電導素子
は、通常の光学露光工程のみで作製することができ、極
端な微細加工は必要としない。この点は本発明の実際の
産業上の応用を考える上で重要である。As described herein, the superconducting element of the present invention can be manufactured only by a usual optical exposure step, and does not require extremely fine processing. This is important in considering the actual industrial application of the present invention.
【００２５】図４は、上記した実施例で得られた超電導
素子の液体ヘリウム温度における電流−電圧特性を示し
ている。臨界電流として 1.2mA、素子の出力電圧である
Ｉc ・Ｒn 積として 4mVが得られた。酸化物超電導体に
期待される出力電圧20mVに比べて低いのは、Pr-Ba-Cu-O
系絶縁体膜３の厚さ、すなわち超電導電流経路の長さが
最適化されていないためであり、Pr-Ba-Cu-O系絶縁体膜
３を薄くすることで、さらに良好な特性を得ることがで
きる。FIG. 4 shows a current-voltage characteristic at a liquid helium temperature of the superconducting element obtained in the above embodiment. 1.2mA as critical current, 4 mV was obtained as I c · R n product, which is the output voltage of the device. Compared to the expected output voltage of 20mV for oxide superconductors, Pr-Ba-Cu-O
This is because the thickness of the system-based insulator film 3, that is, the length of the superconducting current path has not been optimized, and even better characteristics can be obtained by making the Pr-Ba-Cu-O-based insulator film 3 thinner. be able to.
【００２６】また、図５はこの実施例の超電導素子が実
際に均一なジョセフソン特性を示すことを確認するため
に行った臨界電流の印加磁界依存性である。図５から分
かるように、作製した超電導素子は理想的なフラウンホ
ファーパターンを示した。このようなジョセフソン特性
は液体窒素温度でも確認され、本発明の素子が高温で動
作し得ることが検証できた。FIG. 5 shows the dependence of the critical current on the applied magnetic field, which was performed to confirm that the superconducting element of this embodiment actually showed uniform Josephson characteristics. As can be seen from FIG. 5, the produced superconducting element exhibited an ideal Fraunhofer pattern. Such Josephson characteristics were confirmed even at the temperature of liquid nitrogen, and it was verified that the device of the present invention can operate at a high temperature.
【００２７】なお、上記実施例においては、 Y-Ba-Cu-O
膜/ Pr-Ba-Cu-O膜/Y-Ba-Cu-O膜による積層構造に本発明
の超電導素子を適用した例について述べたが、本発明は
これに限定されるものでなく、他の酸化物超電導体材料
とそれと結晶構造が類似した非超電導体との組合せに適
用することも可能である。ただし、上記実施例による材
料の組合せによれば、中間層の結晶粒界の密度の制御な
らびに粒界に沿った元素拡散による導電性の変化の 2点
を、確実にかつ制御した形で提供できるため、特に本発
明を効果的に利用することができる。In the above embodiment, Y-Ba-Cu-O
Although the example in which the superconducting element of the present invention is applied to a laminated structure of a film / Pr-Ba-Cu-O film / Y-Ba-Cu-O film has been described, the present invention is not limited to this. It is also possible to apply the present invention to a combination of an oxide superconductor material and a non-superconductor having a similar crystal structure to the above oxide superconductor material. However, according to the combination of materials according to the above embodiments, two points, that is, control of the density of crystal grain boundaries of the intermediate layer and change in conductivity due to element diffusion along the grain boundaries can be provided in a reliable and controlled manner. Therefore, the present invention can be particularly effectively used.
【００２８】[0028]
【発明の効果】以上説明したように、本発明によれば、
酸化物高温超電導体を利用した高温で動作し得るジョセ
フソン接合素子を再現性よく、かつ極端な微細加工技術
を用いずに容易に得ることができる。本発明による超電
導素子は理想的なジョセフソン特性を有しながら、電流
−電圧特性にヒステリシスを示さず、かつ出力電圧が高
いため、ＳＱＵＩＤ（超電導磁束量子干渉計）の応用に
最適であると共に、非ラッチ型のジョセフソン集積回路
を実現する基本構成素子として好適である。かくして、
本発明の超電導素子は産業上多大の寄与をすることが期
待される。As described above, according to the present invention,
A Josephson junction device that can operate at a high temperature using an oxide high-temperature superconductor can be easily obtained with good reproducibility and without using an extremely fine processing technique. The superconducting element according to the present invention has ideal Josephson characteristics, shows no hysteresis in current-voltage characteristics, and has a high output voltage. It is suitable as a basic component for realizing a non-latch type Josephson integrated circuit. Thus,
The superconducting element of the present invention is expected to make a great contribution to industry.
【図１】本発明の一実施例による超電導素子の構成を示
す断面図である。FIG. 1 is a sectional view showing a configuration of a superconducting element according to one embodiment of the present invention.
【図２】図１に示す超電導素子の製造工程を示す断面図
である。FIG. 2 is a sectional view showing a manufacturing process of the superconducting element shown in FIG.
【図３】図１に示す超電導素子の接合部を拡大して模式
的に示す図である。FIG. 3 is an enlarged schematic view of a junction of the superconducting element shown in FIG. 1;
【図４】本発明の一実施例によって得られた超電導素子
の電流−電圧特性を示す図である。FIG. 4 is a diagram showing current-voltage characteristics of a superconducting element obtained according to one embodiment of the present invention.
【図５】本発明の一実施例によって得られた超電導素子
の臨界電流の印加磁界依存性を示す図である。FIG. 5 is a diagram showing the applied magnetic field dependence of the critical current of the superconducting device obtained according to one embodiment of the present invention.
１…… SrTiO3 (100) 基板 ２……下部 Y-Ba-Cu-O系酸化物超電導体膜 ３……Pr-Ba-Cu-O系絶縁体膜 ４……上部 Y-Ba-Cu-O系酸化物超電導体膜 ５……絶縁膜 ６……配線 ７……超電導電流経路1. SrTiO 3 (100) substrate 2. Lower Y-Ba-Cu-O-based oxide superconductor film 3. Pr-Ba-Cu-O-based insulator film 4. Upper Y-Ba-Cu- O-based oxide superconductor film 5: insulating film 6: wiring 7: superconducting current flow path
───────────────────────────────────────────────────── フロントページの続き (72)発明者 井上 眞司 神奈川県川崎市幸区小向東芝町１番地 株式会社東芝 総合研究所内 (72)発明者 砂井 正之 神奈川県川崎市幸区小向東芝町１番地 株式会社東芝 総合研究所内 (56)参考文献 特開 平２−39476（ＪＰ，Ａ) (58)調査した分野(Int.Cl.6，ＤＢ名) H01L 39/22 H01L 39/24 H01L 39/00 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shinji Inoue 1 Koga Toshiba-cho, Saisaki-ku, Kawasaki-shi, Kanagawa Prefecture Toshiba Research Institute Co., Ltd. No. 1 Toshiba Research Institute, Inc. (56) References JP-A-2-39476 (JP, A) (58) Fields investigated (Int. Cl. 6 , DB name) H01L 39/22 H01L 39/24 H01L 39 / 00
Claims (1)
と、これら主電極部間に介在され、該主電極部間を電気
的に接続する接続部とを具備する超電導素子であって、 前記接続部は、前記酸化物超電導体と結晶構造が類似し
た非超電導酸化物中に散在された複数の超電導電流経路
を有し、これらの超電導電流経路は前記接続部を構成す
る非超電導酸化物の結晶粒界に沿って形成されていると
共に、その各断面積が前記主電極部の断面積に比べて十
分に小さいことを特徴とする超電導素子。1. A superconducting element comprising: two main electrode portions made of an oxide superconductor; and a connection portion interposed between the main electrode portions and electrically connecting the main electrode portions, The connection portion has a crystal structure similar to that of the oxide superconductor.
A plurality of superconducting current paths scattered in the non-superconducting oxide , and these superconducting current paths constitute the connection portion.
Formed along the grain boundaries of the non-superconducting oxide
Both superconductive elements each of its cross-sectional area and wherein the go sufficiently small compared to the cross-sectional area of the main electrode portion.
Priority Applications (1)
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP3245537A JP2955407B2 (en) | 1991-09-25 | 1991-09-25 | Superconducting element |
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| Publication Number | Publication Date |
|---|---|
| JPH0590652A JPH0590652A (en) | 1993-04-09 |
| JP2955407B2 true JP2955407B2 (en) | 1999-10-04 |
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ID=17135174
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| GB2288094A (en) * | 1994-03-25 | 1995-10-04 | Secr Defence | Superconductive junction |
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