JPH0590652A - Superconducting device - Google Patents
Superconducting deviceInfo
- Publication number
- JPH0590652A JPH0590652A JP3245537A JP24553791A JPH0590652A JP H0590652 A JPH0590652 A JP H0590652A JP 3245537 A JP3245537 A JP 3245537A JP 24553791 A JP24553791 A JP 24553791A JP H0590652 A JPH0590652 A JP H0590652A
- Authority
- JP
- Japan
- Prior art keywords
- superconducting
- film
- superconductor
- cross
- oxide superconductor
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Granted
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Abstract
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 insulating layer capable of tunneling a superconducting conductor pair is sandwiched between metal superconductors such as Pb and Nb is known. Such a conventional tunnel type Josephson element is required to operate at an extremely low temperature close to the temperature of liquid helium. Further, since it exhibits a current-voltage characteristic having a hysteresis peculiar to the tunnel type Josephson junction, there is a problem that the circuit configuration becomes complicated, and it has not been widely put into practical use.
【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 having no hysteresis characteristic, a so-called bridge type junction in which main electrodes made of a metal superconductor are connected by a thin and thin metal is also developed. It has been advanced. Such a bridge-type junction has a current-voltage characteristic without hysteresis as long as the cross-sectional area of the bridge portion can be made sufficiently smaller than that of the electrode portion and the length of the bridge portion can be made approximately equal to the coherence length. It has been expected that it will be possible to obtain a Josephson junction having a high output voltage and to obtain an output voltage as high as that of a tunnel junction.
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 necessary, and the material used for the bridge part is metal. However, since it has a drawback that the junction resistance cannot be sufficiently increased, it has not been put to practical use. Further, as in the case of the tunnel type junction described above, there is also a drawback that a cryogenic 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, an oxide superconductor material exhibiting superconducting properties at a temperature of liquid nitrogen or higher has been discovered and has attracted great attention. If it becomes possible to fabricate a good Josephson junction using this oxide superconductor, at least cryogenic operation will be unnecessary compared to the Josephson junction constructed using the conventional metal superconductor described above. 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, since the oxide superconductor material has the essential problems that the surface thereof is easily deteriorated in the atmosphere and the coherence length is small, a clear Josephson material is obtained. At present, a good bond showing the characteristics is not obtained. In other words, the development of Josephson junction using oxide superconductor with high critical temperature is
Since it is expected to make a large contribution to the industry, the development of a joining structure and its manufacturing method for practical use has been an issue.
【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。The present invention has been made in response to such a problem, and shows superconductivity using an oxide superconductor which exhibits good Josephson characteristics, is excellent in controllability, and can obtain a large output voltage. The purpose is to provide a device.
【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、非超電導体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、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く、かつ該
超電導電流経路相互の間の距離が前記接続部における磁
界侵入深さおよび該接続部の断面積より十分に小さいこ
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,
What is claimed is: 1. A superconducting element, comprising: a connecting part interposed between these main electrode parts and electrically connecting the main electrode parts, wherein the connecting parts are a plurality of superconducting flow paths scattered in a non-superconductor. 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 such that the magnetic field penetration depth at the connection portion and It is characterized by being sufficiently smaller than the cross-sectional area of the connecting 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。As described above, the connecting portion in the superconducting element of the present invention has a plurality of superconducting current flow paths embedded and scattered in a non-superconductor such as an insulator or a normal conductor. Such a superconducting flow path can be obtained with good reproducibility by being formed along the crystal grain boundaries of the non-superconductor forming 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 crystal structure similar to that of the oxide superconductor are continuously laminated,
High-speed diffusion of the element occurs along the grain boundaries existing in the non-superconductor, and the conductivity characteristics in the immediate vicinity of the grain boundaries change significantly. As an example, 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 Pr-Ba-Cu-O film, which is originally an insulator at low temperature,
It is possible to locally generate a portion responsible for metallic conduction. On the other hand, since the Y-Ba-Cu-O film and the Pr-Ba-Cu-O film have the same crystal structure and the lattice constants are very close, the crystal grain boundary is similar to that of the Y-Ba-Cu-O film. 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 formed, the Pr-Ba-
A metallic conduction path is formed along the grain boundaries that are almost linearly connected to the upper Y-Ba-Cu-O film through the Cu-O film. This conduction path serves as the superconducting current flow 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。Further, a superconducting current flow path utilizing such grain boundaries is used in Y-Ba-Cu-O-based oxide superconductors and Pr-Ba-Cu.
The present invention is not limited to the case of combining with an -O insulator, but can be formed by combining various oxide superconductors and a non-superconductor having a crystal structure similar to that of 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および接続部の断面積より十
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。The superconducting current paths thus obtained can have a sufficiently small cross-sectional area as compared with that of the main electrode portion, and the distance between the superconducting current paths can be determined by the magnetic field penetration depth and It can be made sufficiently smaller than the cross-sectional area of the connection portion. Therefore, by using the connecting portion having such a superconducting current flow path, it is possible to form a bridge type junction. The superconducting element of the present invention can be regarded as a variable thickness bridge (variable thickness bridge: hereinafter referred to as 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 the superconducting current flow paths to be formed and the distance between them are set according to the area of the junction. The density of the superconducting current paths and the distance between them can be set to desired values by controlling the size of the crystal grains of the non-superconductor forming 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 forming the connection portion, it is possible to easily obtain a desired value. 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体との結晶粒界を利
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および接続部の断面積より十分
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
導体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, the Josephson junction is constituted by the connecting portions having a plurality of superconducting current flow paths which are embedded in the non-superconductor and scattered. The superconducting current path can be formed, for example, by utilizing the crystal grain boundaries of the oxide superconductor serving as the main electrode portion and the non-superconductor forming the connecting portion, and therefore each cross-sectional area of the superconducting current path is Can be made sufficiently smaller than the cross-sectional area of the main electrode portion, and the distance between the superconducting current flow paths can be made sufficiently smaller than the magnetic field penetration depth in the connection portion and the cross-sectional area of the connection portion. Further, the density of the superconducting current paths and the mutual spacing can be set to desired values by controlling the size of the crystal grains of the non-superconductor forming the connecting portion, and thus the desired superconducting current density is obtained. It is possible to manufacture a joint. Furthermore, by setting the thickness of the non-superconductor forming the connection portion to a desired value, it is possible to satisfy the condition that the superconducting current flowing through the superconducting current path makes a coherent Josephson response. Due to these, it is possible to obtain good characteristics using an oxide superconductor simply by controlling the conditions of the laminated structure without performing the ultrafine processing required in the case of the VTB junction which has been conventionally formed on a plane. Josephson junctions 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。EXAMPLES Examples of the superconducting device of the present invention will be described below.
【００１５】図１は、本発明をY-Ba-Cu-O/Pr-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 SrTiO
3 (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
入深さおよび接続部の断面積より十分小さく設定されて
いる。FIG. 1 shows the present invention as Y-Ba-Cu-O / Pr-Ba-Cu-O / Y.
It is a figure which shows the cross-section of the Example applied to the superconducting element which has a -Ba-Cu-O laminated structure. In FIG. 1, 1 is SrTiO
This is an insulating substrate such as a 3 (100) substrate, and this SrTiO 3 (100)
On the substrate 1, a Y-Ba-Cu-O-based oxide superconductor film 2 to be the lower main electrode portion is formed. On this Y-Ba-Cu-O-based oxide superconductor film 2, a Pr-Ba-Cu-O-based insulator film 3 is formed as a non-superconductor layer that constitutes a connection part.
In the Pr-Ba-Cu-O-based insulator film 3, a plurality of superconducting current flow paths (not shown) are formed along the crystal grain boundaries of the Pr-Ba-Cu-O crystal. The cross-sectional area of each of these superconducting current paths is sufficiently smaller than the cross-sectional area of the main electrode part, and the distance between the superconducting current paths is sufficiently smaller than the magnetic field penetration depth at the connection part and the cross-sectional area of the connection part. It is set.
【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 is formed a Y-Ba-Cu-O-based oxide superconductor film 4 which serves as an upper main electrode portion. Due to 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, VTB bonding is achieved. It is configured. Wiring 6 to the upper Y-Ba-Cu-O-based oxide superconductor film 4 is provided on the upper Y-Ba-Cu-O-based oxide superconductor film 4 via the 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 structure is manufactured, for example, as follows. In addition, the manufacturing process of the said superconducting element is shown in FIG. First, on the SrTiO 3 (100) substrate 1, a lower Y-Ba-Cu- layer was formed by a magnetron sputtering method or the like.
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. 2-a). 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。At this time, it is important that the laminated structure is continuously formed 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. The substrate temperature is set so that a predetermined superconducting transition temperature is maintained and the crystal grains have a predetermined size. The former is Y
This is because the disorder of the crystal arrangement is not given to the interface between the -Ba-Cu-O film and the Pr-Ba-Cu-O film, and the latter is indispensable for obtaining the predetermined superconducting Josephson current value described above. 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 in the lower Y-Ba-Cu-O-based oxide superconductor film 2. is there. And this Pr-Ba-Cu-O
The size of the crystal grains in the system insulator film 3 determines the density of the superconducting current paths and the distance between them. The density of these superconducting current flow 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 example, the substrate temperature was set to 680 ° C. to form the film. In this case, the lower Y-Ba-Cu-O-based oxide superconductor film 2 has an a-axis orientation, and the average crystal grain size is
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 that of the ideal Y-Ba-Cu-O film of 92K is that the substrate temperature is set low so that the crystal grains have the set size. To improve the critical current without changing the size of the crystal grains, for example, on the SrTiO 3 (100) substrate 1,
A Pr-Ba-Cu-O film was formed in advance at a substrate temperature at which the required crystal grain size was obtained, and then at the substrate temperature at which a high critical temperature was obtained, the lower Y-Ba-Cu-O-based oxide superconducting The body film 2 may be formed. In this case, the crystal grain size 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 such conditions, Y-Ba-Cu-O-based oxide superconductor film 2 / Pr-Ba-Cu-O-based insulator film 3 / Y-Ba-Cu-O-based oxide superconducting film By forming the laminated structure of the body film 4 by continuous film formation, Y is diffused 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 characteristics near the grain boundary of a-Cu-O crystal change greatly. As a result, 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. Note that FIG. 3 is an enlarged schematic view of the joint portion, in which 8 is crystal grains of a Pr—Ba—Cu—O based insulator and 9 is a Y—Ba—Cu—O based oxide. The crystal grains of the superconductor are shown.
【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および接
続部２の断面積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。In this way, the superconducting current path 7 formed along the crystal grain boundaries has a cross-sectional area of the main electrode portion 2,
4 is sufficiently smaller than the cross-sectional area and the superconducting current flow path 7
The distance between the two is sufficiently smaller than the magnetic field penetration depth at the connection portion and the cross-sectional area of the connection portion 2. Due to the existence of such a superconducting flow path 7, the Y-Ba-Cu-O-based oxide superconductor film 2 / Pr-Ba-Cu-O-based insulator film 3 / Y-Ba-Cu-O-based oxide superconducting film The laminated structure of the body 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 in the usual production of semiconductor elements. First, the pattern of the junction is transferred to the resist film by the optical exposure method, and then the Y-Ba-Cu-O-based oxide superconductor film 2 and Pr are adjusted according to the area of the junction by the ion milling method using the resist as a mask. -Ba-Cu-O-based insulator film 3 is etched (Fig. 2-
b). In this example, 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 laminated and formed. Process so that only the opening is opened (Fig. 2-c). Although various materials can be used for the insulating film 5, in this embodiment, a negative resist is used for the purpose of simplifying the process. After that, the wiring 6 to the upper Y-Ba-Cu-O-based oxide superconductor film 4 is formed of, for example, Au (FIG. 2D) to complete 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 above, the superconducting element of the present invention can be manufactured only by the ordinary optical exposure process, and does not require extreme fine processing. This point 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 current-voltage characteristics at the 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. Pr-Ba-Cu-O is lower than the output voltage of 20 mV expected for oxide superconductors.
This is because the thickness of the system insulator film 3, that is, the length of the superconducting current path is not optimized. By making the Pr-Ba-Cu-O system insulator film 3 thinner, better characteristics can be obtained. 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 to confirm that the superconducting element of this example actually exhibits uniform Josephson characteristics. As can be seen from FIG. 5, the manufactured superconducting device showed an ideal Fraunhofer pattern. Such Josephson characteristics were confirmed even at liquid nitrogen temperature, and it was verified that the device of the present invention could operate at 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
The example in which the superconducting element of the present invention is applied to the laminated structure of the film / Pr-Ba-Cu-O film / Y-Ba-Cu-O film has been described, but the present invention is not limited to this and other It is also possible to apply to the combination of the above oxide superconductor material and a non-superconductor having a similar crystal structure. However, according to the combination of the materials according to the above-mentioned examples, it is possible to provide the two points of the control of the density of the crystal grain boundary of the intermediate layer and the change of the conductivity due to the element diffusion along the grain boundary in a reliable and controlled manner. Therefore, the present invention can be effectively utilized.
【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,
It is possible to easily obtain a Josephson junction device using an oxide high temperature superconductor that can operate at high temperature with good reproducibility and without using an extremely fine processing technique. The superconducting element according to the present invention is ideal for application of SQUID (superconducting magnetic flux quantum interferometer) because it has ideal Josephson characteristics, but does not exhibit hysteresis in current-voltage characteristics and has a high output voltage. It is suitable as a basic constituent element for realizing a non-latch type Josephson integrated circuit. Thus,
The superconducting element of the present invention is expected to make a great contribution in 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 structure of a superconducting element according to an 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 cross-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 joint portion of the superconducting element shown in FIG.
【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 device obtained according to an example 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 applied magnetic field dependence of a critical current of a superconducting device obtained according to an example of the present invention.
【符号の説明】 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[Explanation of symbols] 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 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 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Shinji Inoue, 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki City, Kanagawa Prefecture, Toshiba Research Institute Co., Ltd. Town No. 1 Incorporated company Toshiba Research Institute
Claims (2)
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、非超電導体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、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く、か
つ該超電導電流経路相互の間の距離が前記接続部におけ
る磁界侵入深さおよび該接続部の断面積より十分に小さ
いことを特徴とする超電導素子。1. A superconducting element comprising: two main electrode parts made of an oxide superconductor; and a connecting part interposed between the main electrode parts and electrically connecting the main electrode parts. The connection portion has a plurality of superconducting flow paths scattered in a non-superconductor, and each of these superconducting flow paths has a cross-sectional area that is sufficiently smaller than the cross-sectional area of the main electrode section, and A superconducting element, characterized in that the distance between the superconducting current paths is sufficiently smaller than the magnetic field penetration depth in the connecting portion and the cross-sectional area of the connecting portion.
体材料の結晶粒界に沿って形成されていることを特徴と
する超電導素子。2. The superconducting element according to claim 1, wherein the superconducting current flow path is formed along a crystal grain boundary of the non-superconducting material forming the connecting portion.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP3245537A JP2955407B2 (en) | 1991-09-25 | 1991-09-25 | Superconducting element |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP3245537A JP2955407B2 (en) | 1991-09-25 | 1991-09-25 | Superconducting element |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH0590652A true JPH0590652A (en) | 1993-04-09 |
| JP2955407B2 JP2955407B2 (en) | 1999-10-04 |
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5710437A (en) * | 1993-03-05 | 1998-01-20 | Nippon Steel Corporation | Radiation detecting device using superconducting tunnel junction and method of fabricating the same |
| US5821556A (en) * | 1994-03-25 | 1998-10-13 | The Secretary Of State For Defence In Her Britannic Majesty's Government Of The United Kingdom Of Great Britain And Northern Ireland | Superconductive junction |
-
1991
- 1991-09-25 JP JP3245537A patent/JP2955407B2/en not_active Expired - Fee Related
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5710437A (en) * | 1993-03-05 | 1998-01-20 | Nippon Steel Corporation | Radiation detecting device using superconducting tunnel junction and method of fabricating the same |
| US5821556A (en) * | 1994-03-25 | 1998-10-13 | The Secretary Of State For Defence In Her Britannic Majesty's Government Of The United Kingdom Of Great Britain And Northern Ireland | Superconductive junction |
Also Published As
| Publication number | Publication date |
|---|---|
| JP2955407B2 (en) | 1999-10-04 |
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