Oxide superconducting wire, connecting structure, method for manufacturing oxide superconducting wire, and method for manufacturing connecting structure

Abstract

To provide an oxide superconducting wire that can reduce an interface resistance between a superconductive layer and a protective layer, and a connection structure including the oxide superconducting wire, and to provide a method for producing the oxide superconducting wire, and a method for producing a connection structure including the oxide superconducting wire.SOLUTION: An oxide superconducting wire includes a substrate 10, a superconductive layer 12, and a protective layer 13. The protective layer 13 is in contact with the superconductive layer 12 and contains silver. The superconductive layer 12 includes a first region 12F and a second region 12S.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to oxide superconducting wires, connecting structures, methods for manufacturing oxide superconducting wires, and methods for manufacturing connecting structures. [Background technology]

[0002] Patent Document 1 discloses a tape-shaped oxide superconducting wire comprising a substrate, an intermediate layer, a superconducting layer formed of an oxide superconductor, and a protective layer formed of silver. The protective layer is formed on the superconducting layer. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2017-010833 [Overview of the project] [Problems that the invention aims to solve]

[0004] In the configuration described in Patent Document 1, an oxide superconductor and silver, which are made of different materials, are joined at the interface between the superconducting layer and the protective layer. In this case, there is a problem that the interfacial resistance between the superconducting layer and the protective layer is high. When the interfacial resistance between the superconducting layer and the protective layer is high, there is a problem that the connection resistance in the connection structure where the two oxide superconducting wires are connected becomes high.

[0005] In the method for manufacturing tape-shaped oxide superconducting wires described in Patent Document 1, a superconducting layer is formed on top of the substrate by the PLD method, and then silver is directly formed on the superconducting layer by the sputtering method. After forming the protective layer, heat treatment (oxygen annealing) is performed in an oxygen atmosphere to introduce oxygen into the superconducting layer.

[0006] As a result of diligent study of oxide superconducting wires manufactured by this method, the inventors have obtained the following findings: Due to the oxygen annealing treatment, oxygen is removed from the oxide superconductor constituting the superconducting layer, forming a high-resistance layer in the superconducting layer. As a result, the interfacial resistance between the superconducting layer and the protective layer increases.

[0007] Furthermore, the inventors have focused on the fact that even in a connection structure in which tape-shaped oxide superconducting wires are connected to each other, the interfacial resistance between the superconducting layer and the protective layer becomes high. Specifically, to manufacture a connection structure connecting two tape-shaped oxide superconducting wires, the ends of two oxide superconducting wires are generally overlapped in the thickness direction of the wires and connected via solder. In a connection structure between oxide superconducting wires, the superconducting layer of one oxide superconducting wire, the silver protective layer of one oxide superconducting wire, and solder are layered in that order, followed by the silver protective layer of the other oxide superconducting wire and the superconducting layer of the other oxide superconducting wire.

[0008] Regarding the manufacture of such a connection structure, the inventors measured the connection resistance by changing the temperature of the heat treatment (connection heat treatment) used to melt the solder, without changing conditions such as the connection area and solder thickness between two oxide superconducting wires. As a result, the inventors confirmed that the connection resistance fluctuates depending on the temperature of the connection heat treatment. The inventors gained the insight that the interfacial resistance between the superconducting layer and the protective layer may fluctuate due to the temperature of the connection heat treatment used to manufacture the connection structure.

[0009] The present invention has been made in consideration of these circumstances and aims to provide an oxide superconducting wire that reduces interfacial resistance between a superconducting layer and a protective layer, and a connecting structure equipped with this oxide superconducting wire. Furthermore, the present invention aims to provide a method for manufacturing this oxide superconducting wire and a method for manufacturing a connecting structure equipped with this oxide superconducting wire. [Means for solving the problem]

[0010] To solve the above problems, an oxide superconducting wire according to one aspect of the present invention includes a tape-shaped base material, a superconducting layer provided above the base material and composed of an oxide superconductor, and a protective layer provided on the superconducting layer, contacting the superconducting layer and containing silver. The superconducting layer is composed of a second region formed on the side of the base material in the thickness direction and a first region formed on the side of the protective layer. The oxide superconductor in the second region has a predetermined oxygen concentration, the oxide superconductor in the first region has an oxygen concentration lower than that of the oxide superconductor in the second region, and the thickness of the first region is 100 nm or less.

[0011] According to the oxide superconducting wire according to one aspect of the present invention, the superconducting layer is composed of a second region formed on the side of the base material in the thickness direction and a first region formed on the side of the protective layer. The oxide superconductor in the second region has a predetermined oxygen concentration, the oxide superconductor in the first region has an oxygen concentration lower than that of the oxide superconductor in the second region, and the thickness of the first region is 100 nm or less. Thereby, the thickness of the first region with a low oxygen concentration becomes small. That is, the thickness of the high-resistance layer formed in the superconducting layer becomes small. Therefore, the interface resistance between the superconducting layer and the protective layer can be reduced, and the problems in the oxide superconducting wire can be solved.

[0012] In the oxide superconducting wire according to one aspect of the present invention, the oxide superconductor in the second region has a uniform oxygen concentration distribution, and the oxide superconductor in the first region has a concentration gradient in which the oxygen concentration decreases in the direction from the base material to the protective layer.

[0013] In the oxide superconducting wire according to one aspect of the present invention, the interface resistance between the superconducting layer and the protective layer is 1×10

[0012] Ωcm 2 ~1×10 -9 Ωcm 2 and may be within the range.

[0014] In the oxide superconducting wire according to one aspect of the present invention, the protective layer may contain silver oxide.

[0015] In an oxide superconducting wire according to one aspect of the present invention, the protective layer comprises a silver oxide layer and a silver layer, and the silver oxide layer may be located between the silver layer and the superconducting layer.

[0016] To solve the above problems, a connection structure according to one aspect of the present invention is a connection structure in which a first oxide superconducting wire and an object to be connected are connected, wherein the first oxide superconducting wire and the object to be connected partially overlap in the thickness direction of the first oxide superconducting wire, the first oxide superconducting wire comprises a tape-shaped base material, a superconducting layer provided above the base material and composed of an oxide superconductor, and a protective layer provided on the superconducting layer, in contact with the superconducting layer and containing silver, the superconducting layer is composed of a second region formed on the base material side in the thickness direction and a first region formed on the protective layer side, the oxide superconductor in the second region has a predetermined oxygen concentration, the oxide superconductor in the first region has a lower oxygen concentration than the oxide superconductor in the second region, and the thickness of the first region is 100 nm or less.

[0017] According to one aspect of the present invention, the superconducting layer is composed of a second region formed on the substrate side in the thickness direction and a first region formed on the protective layer side, the oxide superconductor in the second region has a predetermined oxygen concentration, the oxide superconductor in the first region has a lower oxygen concentration than the oxide superconductor in the second region, and the thickness of the first region is 100 nm or less. This reduces the thickness of the first region with low oxygen concentration. In other words, it reduces the thickness of the high-resistance layer formed in the superconducting layer. Therefore, it is possible to reduce the interfacial resistance between the superconducting layer and the protective layer, thereby solving problems in the connection structure.

[0018] In one aspect of the present invention, the connecting structure has an oxide superconductor in the first region having a concentration gradient in which the oxygen concentration decreases in the direction from the substrate toward the protective layer.

[0019] A connection structure according to one aspect of the present invention has an interfacial resistance between the superconducting layer and the protective layer of 1 × 10 -11 Ωcm 2 ~1 × 10 -9 Ωcm 2 It may be within the range of [a certain limit].

[0020] In a connecting structure according to one aspect of the present invention, the protective layer may contain silver oxide.

[0021] In a connection structure according to one aspect of the present invention, the protective layer comprises a silver oxide layer and a silver layer, and the silver oxide layer may be located between the silver layer and the superconducting layer.

[0022] To solve the above problems, a method for manufacturing an oxide superconducting wire according to one aspect of the present invention involves forming a superconducting layer made of an oxide superconductor on a substrate, forming a protective layer containing silver oxide directly above the superconducting layer, and heating the superconducting layer and the protective layer to reduce the silver oxide contained in the protective layer to silver, and introducing the oxygen produced by the reduction into the superconducting layer.

[0023] According to one embodiment of the present invention, a method for manufacturing an oxide superconducting wire involves heating a protective layer containing silver oxide and a superconducting layer to reduce the silver oxide to silver, and introducing the oxygen produced by the reduction into the superconducting layer. Therefore, even if oxygen is removed from the superconducting layer by oxygen annealing, the portion where oxygen was removed is replenished by the oxygen produced by the reduction. Consequently, the thickness of the high-resistance layer is reduced, and the problem of high interfacial resistance between the superconducting layer and the protective layer can be solved.

[0024] In one aspect of the present invention, when forming the protective layer containing silver oxide directly on the superconducting layer, a silver oxide layer constituting a part of the protective layer may be formed directly on the superconducting layer, then a silver layer constituting a part of the protective layer may be formed on the silver oxide layer, and the superconducting layer and the protective layer may be heated to reduce the silver oxide layer contained in the protective layer to silver, and the oxygen produced by the reduction may be introduced into the superconducting layer.

[0025] In one aspect of the present invention, when forming the protective layer containing silver oxide directly on the superconducting layer, a silver layer constituting a part of the protective layer may be formed directly on the superconducting layer, then a silver oxide layer constituting a part of the protective layer may be formed on the silver layer, and the superconducting layer and the protective layer may be heated to reduce the silver oxide layer contained in the protective layer to silver, and the oxygen produced by the reduction may be introduced into the superconducting layer.

[0026] To solve the above problems, a method for manufacturing a connection structure according to one aspect of the present invention involves preparing an oxide superconducting wire formed by forming a superconducting layer made of oxide superconductor on a substrate and forming a protective layer containing silver oxide directly above the superconducting layer, preparing an object to be connected to the oxide superconducting wire, partially overlapping the protective layer and the object to be connected, and heating the oxide superconducting wire and the object to be connected so that the silver oxide contained in the protective layer is reduced to silver at a position corresponding to the overlapping portion of the protective layer and the object to be connected when viewed in the thickness direction of the oxide superconducting wire, and the oxygen produced by the reduction is introduced into the superconducting layer.

[0027] To solve the above problems, a method for manufacturing a connection structure according to one aspect of the present invention involves preparing an oxide superconducting wire formed by forming a superconducting layer made of oxide superconductors on a substrate and forming a protective layer containing silver oxide directly on the superconducting layer, preparing an object to be connected to the oxide superconducting wire, partially overlapping the protective layer and the object to be connected, and heating the oxide superconducting wire and the object to be connected so that the silver oxide contained in the protective layer is reduced to silver at a position corresponding to the overlapping portion of the protective layer and the object to be connected when viewed in the thickness direction of the oxide superconducting wire, and introducing the oxygen produced by the reduction into the superconducting layer.

[0028] According to a method for manufacturing a connection structure according to one aspect of the present invention, the protective layer containing silver oxide and the superconducting layer are heated to reduce the silver oxide to silver, and the oxygen produced by the reduction is introduced into the superconducting layer. Therefore, even if oxygen is removed from the superconducting layer by the connection heat treatment, the portion where oxygen has been removed is replenished by the oxygen produced by the reduction. Consequently, the thickness of the high-resistance layer is reduced, and the problem of high interfacial resistance between the superconducting layer and the protective layer can be solved.

[0029] A method for manufacturing a connection structure according to one aspect of the present invention may involve defining a first portion corresponding to the overlapping portion on the surface of the superconducting layer, forming the protective layer containing silver oxide directly above the superconducting layer, forming a silver oxide layer constituting a part of the protective layer on the first portion of the superconducting layer, overlapping the silver oxide layer formed on the first portion in the thickness direction with the object to be connected, and heating the oxide superconducting wire and the object to be connected to reduce the silver oxide contained in the silver oxide layer of the protective layer to silver, and introducing the oxygen produced by the reduction into the superconducting layer.

[0030] A method for manufacturing a connection structure according to one aspect of the present invention may involve defining a first portion corresponding to the overlapping portion on the surface of the superconducting layer, forming the protective layer containing silver oxide directly on the superconducting layer, forming a silver oxide layer constituting a part of the protective layer on the first portion of the superconducting layer, then forming a silver layer constituting a part of the protective layer on the silver oxide layer, overlapping the silver layer formed on the first portion in the thickness direction with the object to be connected, and heating the oxide superconducting wire and the object to be connected to reduce the silver oxide contained in the silver oxide layer of the protective layer to silver, and introducing the oxygen produced by the reduction into the superconducting layer.

[0031] A method for manufacturing a connection structure according to one aspect of the present invention may involve defining a first portion corresponding to the overlapping portion on the surface of the superconducting layer, forming the protective layer containing silver oxide directly on the superconducting layer, forming a silver layer constituting a part of the protective layer on the first portion of the superconducting layer, then forming a silver oxide layer constituting a part of the protective layer on the silver layer in the first portion, overlapping the silver oxide layer formed on the first portion in the thickness direction with the object to be connected, and heating the oxide superconducting wire and the object to be connected to reduce the silver oxide contained in the silver oxide layer of the protective layer to silver, and introducing the oxygen produced by the reduction into the superconducting layer.

[0032] In one aspect of the present invention, a method for manufacturing a connection structure may be used to join the oxide superconducting wire and the object to be connected by overlapping them with solder interposed in the thickness direction. [Effects of the Invention]

[0033] According to the above aspects of the present invention, it is possible to provide an oxide superconducting wire that reduces interfacial resistance between a superconducting layer and a protective layer, and a connecting structure equipped with this oxide superconducting wire. According to the above aspects of the present invention, it is possible to provide a method for manufacturing this oxide superconducting wire and a method for manufacturing a connecting structure equipped with this oxide superconducting wire. [Brief explanation of the drawing]

[0034] [Figure 1] This is a schematic enlarged cross-sectional view showing an oxide superconducting wire according to the first embodiment of the present invention. [Figure 2] This is an enlarged cross-sectional view showing an oxide superconducting wire according to a modified example of the first embodiment of the present invention. [Figure 3] This is an enlarged cross-sectional view schematically showing a connection structure according to a second embodiment of the present invention. [Figure 4] This is an enlarged cross-sectional view schematically showing a connection structure according to a modified example of the second embodiment of the present invention. [Figure 5]This is an enlarged cross-sectional view schematically showing a connecting structure according to a second embodiment of the present invention, and is a diagram illustrating a method for manufacturing the connecting structure. [Figure 6] This is an enlarged cross-sectional view schematically showing a connection structure according to a third embodiment of the present invention, and is a diagram illustrating a method for manufacturing the connection structure. [Figure 7] This is an enlarged cross-sectional view schematically showing a connection structure according to a fourth embodiment of the present invention, and is a diagram illustrating a method for manufacturing the connection structure. [Figure 8] This is an enlarged cross-sectional view schematically showing a connection structure according to a fifth embodiment of the present invention, and is a diagram illustrating a method for manufacturing the connection structure. [Figure 9] This graph illustrates the comparative example. [Figure 10] This is a graph illustrating an embodiment of the present invention. [Figure 11] This figure illustrates an embodiment of the present invention, and is a structural graph showing oxide superconducting wires connected in a bridge configuration. [Modes for carrying out the invention]

[0035] Hereinafter, an oxide superconducting wire, a connecting structure, a method for manufacturing the oxide superconducting wire, and a method for manufacturing the connecting structure according to embodiments of the present invention will be described in detail with reference to the drawings. For convenience, in order to make the features of the present invention easier to understand, the drawings used in this description may show enlarged versions of key parts, and the dimensional ratios of each component may not be the same as in reality.

[0036] In the drawings referenced in the following description, the X, Y, and Z directions, corresponding to a three-dimensional Cartesian coordinate system, are shown (symbols X, Y, and Z). The X direction corresponds to the width direction of the oxide superconducting wire. The Y direction corresponds to the extension direction of the oxide superconducting wire. The Z direction corresponds to the thickness direction of the oxide superconducting wire or the thickness direction of the connecting structure.

[0037] (First Embodiment) (Composition of oxide superconducting wire 1) An oxide superconducting wire according to the first embodiment will be described with reference to Figure 1. The oxide superconducting wire 1 according to this embodiment comprises a base material 10, an intermediate layer 11 provided on the base material 10, a superconducting layer 12 provided on the intermediate layer 11, a protective layer 13 provided on the superconducting layer 12, and a stabilizing layer 14 provided on the protective layer 13. The oxide superconducting wire 1 may also include an insulating coating layer covering the base material 10, the intermediate layer 11, the superconducting layer 12, the protective layer 13, and the stabilizing layer 14.

[0038] The height of the oxide superconducting wire 1, that is, the length from the bottom surface of the substrate 10 to the top surface of the protective layer 13 (length in the Z direction in Figure 1), is, for example, 80 μm. The width of the oxide superconducting wire 1, that is, the length from the left end to the right end of the oxide superconducting wire 1 (length in the X direction in Figure 1), is, for example, 12 mm.

[0039] (Base material 10) The base material 10 is a tape-shaped metal substrate. Specific examples of metals that make up the metal substrate include nickel alloys such as Hastelloy (registered trademark), stainless steel, and oriented Ni-W alloys in which a texture is introduced into a nickel alloy.

[0040] (Intermediate layer 11) The intermediate layer 11 may have a multilayer structure, and for example, it may have a diffusion prevention layer, a bed layer, an orientation layer, a cap layer, etc., in the order from the substrate 10 toward the superconducting layer 12. In a structure in which these multiple layers are provided in the intermediate layer 11, the number of each layer is not limited to one. Some of these multiple layers constituting the intermediate layer 11 may be omitted. Furthermore, a structure in which two or more layers of the same type are repeatedly laminated may be adopted. The intermediate layer 11 may also be a metal oxide. By forming a superconducting layer 12 on an intermediate layer 11 with excellent orientation, it becomes easy to obtain a superconducting layer 12 with excellent orientation.

[0041] (Superconducting layer 12) The superconducting layer 12 has the function of conducting electric current when in a superconducting state. The superconducting layer 12 is composed of an oxide superconductor and is provided so as to be in contact with the protective layer 13. Specifically, the material used for the superconducting layer 12 is not particularly limited. For example, an RE-Ba-Cu-O based oxide superconductor (REBCO based oxide superconductor) represented by the general formula REBa2Cu3O X (RE123) can be mentioned. Examples of the rare earth element RE include one or more of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Among them, one of Y, Gd, Eu, and Sm or a combination of two or more of these elements is preferable. Generally, X is 7-x (oxygen deficiency amount x: about 0 to 1).

[0042] The matrix material of this oxide superconductor is an insulator, but by taking in oxygen through oxygen annealing treatment, it becomes an oxide superconductor and has the property of exhibiting superconducting characteristics.

[0043] The superconducting layer 12 is composed of two layers, a second region 12S formed on the substrate 10 side and a first region 12F formed on the protective layer side, in the thickness direction of the superconducting layer 12. The oxide superconductor of the second region 12S and the oxide superconductor of the first region 12F each have a specific oxygen concentration, and the oxide superconductor of the second region 12S has a predetermined oxygen concentration. On the other hand, the oxygen concentration of the oxide superconductor in the first region 12F is lower than the oxygen concentration of the oxide superconductor in the second region 12S.

[0044] In the oxygen concentration profile of the superconducting layer 12 in the thickness direction, the oxide superconductor in the second region 12S has a uniform and consistent oxygen concentration distribution regardless of the position in the thickness direction. On the other hand, the oxide superconductor in the first region 12F has a concentration gradient in which the oxygen concentration gradually decreases from the substrate 10 side to the interface BF between the superconducting layer 12 and the protective layer 13. For example, if the oxygen concentration in the second region 12S is 100%, then in the thickness direction of the first region 12F, the oxygen concentration at the boundary with the second region 12S is approximately the same as the oxygen concentration in the second region 12S (≒100%), and the oxygen concentration near the interface BF with the protective layer 13 is approximately 20%. The thickness of the first region SF is preferably 100 nm or less, and may be 50 nm or 20 nm. The interfacial resistance at the interface BF between the superconducting layer 12 and the protective layer 13 is 1 × 10⁻⁶ -11 Ωcm 2 ~1 × 10 -9 Ωcm 2 It should be within the range.

[0045] (Protective layer 13) The protective layer 13 is provided on the superconducting layer 12 and is in contact with the superconducting layer 12. The protective layer 13 functions as a current path that acts as a bypass path for overcurrents generated due to some kind of accident when current is supplied to the oxide superconducting wire 1. The protective layer 13 is made of silver (Ag) or a silver alloy.

[0046] Regarding the composition of the protective layer 13, the silver oxide content in the protective layer 13 changes before and after oxygen annealing (heat treatment in an oxygen atmosphere) is performed on the oxide superconducting wire 1 in an oxygen atmosphere. Specifically, in this embodiment, in the manufacturing method of the oxide superconducting wire 1, a superconducting layer 12 is formed on top of the substrate 10, and then a protective layer 13 containing silver oxide is directly formed on the superconducting layer 12 by sputtering. Subsequently, the oxide superconducting wire 1 is subjected to oxygen annealing in an oxygen atmosphere to introduce oxygen into the superconducting layer 12.

[0047] At this time, a reduction reaction occurs in which the silver oxide in the protective layer 13, which was in the state before oxygen annealing, is reduced to silver. Some or all of the oxygen produced by the reduction reaction is introduced into the superconducting layer 12 during the oxygen annealing treatment. In other words, in the state after oxygen annealing, not all of the silver oxide in the protective layer 13 may be reduced to silver, and silver oxide may remain in the protective layer 13. On the other hand, in the state after oxygen annealing, all of the silver oxide in the protective layer 13 may be reduced to silver, so no silver oxide may remain in the protective layer 13.

[0048] (Stabilization layer 14) The material for the stabilization layer 14 can be selected from copper, copper alloys such as Cu-Zn alloy (brass) and Cu-Ni alloy, aluminum, aluminum alloy, stainless steel, and other materials. The stabilizing layer 14 may be composed of multiple layers. Furthermore, the stabilizing layer 14 may be formed by metal plating, or it may have a structure in which the entire laminate, including the layers from the substrate 10 to the protective layer 13, is covered with a plating layer.

[0049] (Method for manufacturing oxide superconducting wire 1) First, a base material 10, which is a tape-shaped metal substrate, is prepared. Next, an intermediate layer 11 is formed on the base material 10. For example, the IBAD film deposition method is used to form the intermediate layer 11. Furthermore, a superconducting layer 12 composed of oxide superconductors is formed on the intermediate layer 11. For example, the PLD method is used to form the superconducting layer 12.

[0050] Next, a protective layer 13 is formed directly above the superconducting layer 12. In this invention, a sputtering method using a silver oxide target is used to form the protective layer 13. Examples of silver oxide include AgO, Ag2O, and a mixture of AgO and Ag2O. In this embodiment, Ag2O is used. The content (concentration) of silver oxide in the protective layer 13 is adjusted by selecting from several types of silver oxide targets.

[0051] Subsequently, the intermediate layer 11, superconducting layer 12, and protective layer 13 laminated on the substrate 10 are subjected to oxygen annealing (heat treatment in an oxygen atmosphere) in an oxygen atmosphere. Through oxygen annealing, oxygen permeates through the protective layer 13 and is introduced into the superconducting layer 12. In addition, during oxygen annealing, the silver oxide in the protective layer 13 is reduced to silver, and the oxygen produced by this reduction is also introduced into the superconducting layer 12. Through the above manufacturing method, the oxide superconducting wire 1 shown in Figure 1 is obtained. Oxygen annealing can be carried out by heating at 300 to 1000°C in an oxygen atmosphere or in air.

[0052] In the oxygen annealing process, with regard to the reduction reaction from silver oxide to silver, all of the silver oxide in the protective layer 13 may be reduced to silver, or only a portion of the silver oxide in the protective layer 13 may be reduced to silver. With regard to the introduction of oxygen from silver oxide to the superconducting layer 12, all of the oxygen from the silver oxide in the protective layer 13 may be introduced into the superconducting layer 12, or only a portion of the oxygen from the silver oxide in the protective layer 13 may be introduced into the superconducting layer 12.

[0053] The amount of oxygen introduced from silver oxide into the superconducting layer 12, and the control of the reduction reaction from silver oxide to silver, can be achieved, for example, by adjusting the silver oxide content in the protective layer 13 or by adjusting the oxygen annealing treatment conditions. Furthermore, by adopting a laminated structure for the protective layer 13 consisting of a silver layer with a low silver oxide content or no silver oxide content and a silver oxide layer containing silver oxide, the amount of oxygen introduced from silver oxide into the superconducting layer 12 can be adjusted, and the reduction reaction from silver oxide to silver can be controlled.

[0054] With this method of manufacturing oxide superconducting wire 1, the oxygen concentration in the first region 12F is lower than the oxygen concentration in the second region 12S of the superconducting layer 12, and the thickness of the first region 12F is 100 nm or less. Furthermore, in the first region 12F, an oxygen concentration profile is obtained in which the oxygen concentration gradually decreases from the substrate 10 side to the interface BF between the superconducting layer 12 and the protective layer 13. The interfacial resistance at interface BF is 1 × 10⁻⁶ -11 Ωcm 2 ~1 × 10 -9 Ωcm2 It falls within the range.

[0055] Next, the operation and effects of the oxide superconducting wire 1 configured as described above will be explained. According to this embodiment, instead of simply laminating the silver layer constituting the protective layer 13 onto the superconducting layer 12 and subjecting it to oxygen annealing, the protective layer 13 containing silver oxide is laminated onto the superconducting layer 12 and then subjected to oxygen annealing. This reduces the silver oxide to silver, and the oxygen produced by the reduction can be introduced into the superconducting layer 12. Therefore, even if oxygen is removed from the superconducting layer by the oxygen annealing process, the areas where oxygen has been removed are replenished by the oxygen produced by the reduction of silver oxide. Furthermore, since the thickness of the first region 12F is 100 nm or less, the thickness of the high-resistance layer is reduced, contributing to a reduction in the interfacial resistance between the superconducting layer 12 and the protective layer 13.

[0056] In the oxide superconducting wire 1 according to this embodiment, the interfacial resistance between the superconducting layer 12 and the protective layer 13 is 1 × 10⁻⁶ -11 Ωcm 2 ~1 × 10 -9 Ωcm 2 Since it falls within this range, a low-resistance oxide superconducting wire 1 can be realized.

[0057] (Modification of the first embodiment) In the following descriptions of multiple modifications of the first embodiment, the same reference numerals are used for the same components as in the description of the first embodiment, and their descriptions are omitted or simplified. Furthermore, the descriptions of the same manufacturing processes as those described in the first embodiment are omitted or simplified.

[0058] (Modification 1 of the first embodiment) A modified example of the first embodiment of the oxide superconducting wire will be described with reference to Figure 2. The oxide superconducting wire 1A shown in Figure 2 has the same configuration as the base material 10, intermediate layer 11, superconducting layer 12, and stabilizing layer 14 that constitute the oxide superconducting wire 1. The oxide superconducting wire 1A differs from the oxide superconducting wire 1 in terms of the structure of the protective layer 13.

[0059] The protective layer 13 shown in Figure 2 contains silver oxide. In other words, the protective layer 13 has a structure in which silver oxide remains due to the manufacturing method of the oxide superconducting wire 1 described above. Specifically, the protective layer 13 has a silver oxide layer 13F and a silver layer 13S. The silver oxide layer 13F is located between the silver layer 13S and the superconducting layer 12. In other words, the silver oxide layer 13F, which has a higher silver oxide content than the silver layer 13S, is adjacent to the superconducting layer 12 via the interface BF.

[0060] Here, the silver layer 13S may contain silver oxide formed by spontaneous oxidation, such as a surface oxide film.

[0061] In other words, in Figure 2, some of the oxygen from the silver oxide in the protective layer 13 of the oxide superconducting wire 1 before oxygen annealing is introduced into the superconducting layer 12 during the oxygen annealing process, causing a partial reduction reaction from silver oxide to silver, and resulting in silver oxide remaining in the protective layer 13 after the oxygen annealing process. Even with the oxide superconducting wire 1A having such a configuration, the same effects as the oxide superconducting wire 1 according to the first embodiment described above can be obtained.

[0062] (Modification 2 of the first embodiment) In the manufacturing method of the oxide superconducting wire 1 described above, a protective layer 13 containing silver oxide was formed directly on the superconducting layer 12, and then an oxygen annealing treatment was performed to introduce oxygen from the silver oxide into the superconducting layer 12, thereby reducing the silver oxide to silver. The modification 2 of the first embodiment described below differs from the above manufacturing method in terms of the formation of the protective layer 13.

[0063] First, an intermediate layer 11 and a superconducting layer 12 are sequentially laminated on a substrate 10. Next, a protective layer 13 containing silver oxide is formed directly above the superconducting layer 12. When forming the protective layer 13, first, as a first step, a silver oxide layer containing silver oxide, which constitutes part of the protective layer 13, is formed directly above the superconducting layer 12. Then, as a second step, a silver layer, which constitutes part of the protective layer 13, is formed on the silver oxide layer. Next, by heating the superconducting layer 12 and the protective layer 13, oxygen from the silver oxide in the protective layer 13 is introduced into the superconducting layer 12, and the silver oxide in the protective layer 13 is reduced to silver.

[0064] In the first step of forming a silver oxide layer containing silver oxide directly above the superconducting layer 12, after forming the silver oxide layer over the entire surface of the superconducting layer 12, the silver oxide layer may be partially peeled off from the superconducting layer 12, thereby patterning the layer so that a portion of the silver oxide layer remains on the superconducting layer 12. This forms a silver oxide layer with a desired pattern on the superconducting layer 12. In the second step, silver is formed directly above the patterned silver oxide layer and directly above the superconducting layer 12. Alternatively, by using a known mask having an aperture pattern, patterning may be performed so that a silver oxide layer remains on the superconducting layer 12 at a position corresponding to the aperture pattern.

[0065] In this modification 2 of the first embodiment, the same effects as those of the oxide superconducting wire 1 described above can be obtained. Furthermore, a silver oxide layer having a desired pattern can be formed on the superconducting layer 12.

[0066] (Modification 3 of the first embodiment) Modification 3 of the first embodiment, described below, differs from the manufacturing method according to the first embodiment described above in terms of the formation of the protective layer 13.

[0067] First, an intermediate layer 11 and a superconducting layer 12 are sequentially laminated on a substrate 10. Next, a protective layer 13 containing silver oxide is formed directly above the superconducting layer 12. When forming the protective layer 13, first, as a first step, a silver layer constituting part of the protective layer 13 is formed directly above the superconducting layer 12. Then, as a second step, a silver oxide layer constituting part of the protective layer 13 is formed on the silver layer. Next, by heating the superconducting layer 12 and the protective layer 13, oxygen from the silver oxide in the protective layer 13 is introduced into the superconducting layer 12, and the silver oxide in the protective layer 13 is reduced to silver.

[0068] In the first step of forming a silver layer with a lower silver oxide content than the silver oxide layer directly above the superconducting layer 12, after forming the silver layer over the entire surface of the superconducting layer 12, the silver layer may be partially peeled off from the superconducting layer 12, thereby patterning the silver layer so that it partially remains on the superconducting layer 12. This forms a silver layer with a desired pattern on the superconducting layer 12. In the second step, the silver oxide layer is formed directly above the patterned silver layer and directly above the superconducting layer 12. Alternatively, by using a known mask having an aperture pattern, patterning may be performed so that a silver layer remains on the superconducting layer 12 at a position corresponding to the aperture pattern.

[0069] In this modification 3 of the first embodiment, the same effects as those of the oxide superconducting wire 1 described above can be obtained. Furthermore, a silver layer having a desired pattern can be formed on the superconducting layer 12.

[0070] (Second Embodiment) (Configuration of connection structure 3) Next, the oxide superconducting wire according to the second embodiment will be described with reference to Figure 3. In Figure 3, the same reference numerals are used for components identical to those in the first embodiment, and their descriptions are omitted or simplified.

[0071] The connection structure 3 according to this embodiment has a structure in which a first oxide superconducting wire 1 (oxide superconducting wire) and a second oxide superconducting wire 2 (object to be connected) are connected. The connection structure 3 has an overlapping portion 16 in which the first oxide superconducting wire 1 and the second oxide superconducting wire 2 partially overlap in the Z direction. In other words, a part of the first oxide superconducting wire 1 and a part of the second oxide superconducting wire 2 overlap such that the second oxide superconducting wire 2 protrudes from the end of the first oxide superconducting wire 1 in the extending direction (Y direction). In this embodiment, the first oxide superconducting wire 1 and the second oxide superconducting wire 2 are connected via solder 15 at the overlapping portion 16.

[0072] (Composition of the first oxide superconducting wire 1) The first oxide superconducting wire 1 comprises a base material 10A, an intermediate layer 11A provided on the base material 10A, a superconducting layer 12A provided on the intermediate layer 11A, and a protective layer 13A provided on the superconducting layer 12A. Each of the base material 10A and intermediate layer 11A constituting the first oxide superconducting wire 1 is, for example, the same as the base material 10 and intermediate layer 11 described in the first embodiment above.

[0073] (Superconducting layer 12A) The superconducting layer 12A has a superconducting portion 52 that overlaps the overlapping portion 16 in the Z direction. The superconducting portion 52 has a first region 12F having a concentration gradient in which the concentration of oxygen contained in the superconducting portion 52 decreases in the direction toward the substrate 10A from the interface BF1 between the superconducting portion 52 and the protective layer 13A. The superconducting portion 52 has a second region 12S that is spaced apart from the first region 12F in the direction toward the substrate 10A from the interface BF1, and in which the concentration of oxygen contained in the superconducting portion 52 is substantially constant.

[0074] In the oxygen concentration profile in the thickness direction of the superconducting portion 52, the oxide superconductor in the second region 12S has a uniform and consistent oxygen concentration distribution regardless of the position in the thickness direction. On the other hand, the oxide superconductor in the first region 12F has a concentration gradient in which the oxygen concentration gradually decreases from the substrate 10A side to the interface BF1 between the superconducting portion 52 and the protective layer 13A. For example, if the oxygen concentration in the second region 12S is 100%, then in the thickness direction of the first region 12F, the oxygen concentration at the boundary with the second region 12S is approximately the same as the oxygen concentration in the second region 12S (≒100%), and the oxygen concentration near the interface BF1 with the protective layer 13A is approximately 20%. The thickness of the first region SF is preferably 100 nm or less, and may be 50 nm or 20 nm. The interfacial resistance at the interface BF1 between the superconducting portion 52 and the protective layer 13A is 1 × 10⁻⁶ -11 Ωcm 2 ~1 × 10 -9 Ωcm 2 It should be within the range.

[0075] (Protective layer 13A) The protective layer 13A is provided on the superconducting layer 12A, is in contact with the superconducting layer 12A, and contains silver. The protective layer 13A has the same configuration as the protective layer 13 in the first embodiment described above. At the overlapping portion 16, the protective layer 13A faces the protective layer 23 of the second oxide superconducting wire 2. In this embodiment, the protective layer 13A is in contact with the solder 15.

[0076] (Composition of the second oxide superconducting wire 2) The second oxide superconducting wire 2 comprises a base material 20, an intermediate layer 21 provided on the base material 20, a superconducting layer 22 provided on the intermediate layer 21, and a protective layer 23 provided on the superconducting layer 22. Each of the components constituting the second oxide superconducting wire 2—the base material 20, the intermediate layer 21, the superconducting layer 22, and the protective layer 23—has a conventionally known configuration. Alternatively, it may have the same configuration as the oxide superconducting wire described in the first embodiment described above.

[0077] (Manufacturing method for the connecting structure 3) Referring to Figure 5, the manufacturing method of the connection structure 3 according to the second embodiment will be described. First, the first oxide superconducting wire 1 and the second oxide superconducting wire 2, which constitute the connection structure 3, are prepared. The first oxide superconducting wire 1 is formed in the same manner as in the first embodiment described above, by forming a superconducting layer 12A made of oxide superconductors on top of the base material 10A, and forming a protective layer 13A containing silver oxide directly above the superconducting layer 12A. Then, the first oxide superconducting wire 1 is formed by performing an oxygen annealing treatment in an oxygen atmosphere. The second oxide superconducting wire 2 is formed by a similar method.

[0078] When manufacturing the first oxide superconducting wire 1, the surface area of ​​the superconducting layer 12A on which the protective layer 13A is formed is defined. Specifically, on the surface of the superconducting layer 12A, a first portion 12P corresponding to the overlapping portion 16 and a second portion 12Q corresponding to the portion other than the first portion 12P are defined. The first portion 12P is the region including the end of the first oxide superconducting wire 1 in the extending direction. The first portion 12P is the portion opposite to the region including the end of the second oxide superconducting wire 2 in the extending direction.

[0079] Next, a protective layer 13A containing silver oxide is formed directly above the superconducting layer 12A. At this time, a silver oxide layer 13H, which constitutes part of the protective layer 13A and contains silver oxide at a high concentration, is formed on the first portion 12P of the superconducting layer 12A. A silver layer 13L, which constitutes part of the protective layer 13A and has a lower silver oxide content than the silver oxide layer 13H, is formed on the second portion 12Q.

[0080] The methods for forming the silver oxide layer 13H and the silver layer 13L will be explained in detail. First, a silver oxide layer 13H is formed over the entire surface of the superconducting layer 12A by sputtering. Next, the silver oxide layer 13H formed on the second portion 12Q is peeled off while leaving the silver oxide layer 13H formed on the first portion 12P. This exposes the second portion 12Q of the superconducting layer 12A. Next, a silver layer 13L is formed on the second portion 12Q. As a result, as shown in Figure 5, a silver oxide layer 13H and a silver layer 13L are formed on the upper surface of the superconducting layer 12A.

[0081] After the silver oxide layer 13H and silver layer 13L are formed on the upper surface of the superconducting layer 12A in this manner, the protective layer 13A of the first oxide superconducting wire 1 and the second oxide superconducting wire 2 are partially overlapped. Specifically, the silver oxide layer 13H formed on the first portion 12P is overlapped with the second oxide superconducting wire 2 when viewed in the Z direction. In this embodiment, solder 15 is interposed between the first oxide superconducting wire 1 (protective layer 13A) and the second oxide superconducting wire 2 (protective layer 23). Furthermore, to obtain a connection structure using solder 15, for example, a connection heat treatment at approximately 200°C is applied, causing the solder to melt and connecting the first oxide superconducting wire 1 and the second oxide superconducting wire 2.

[0082] By performing this connection heat treatment, the silver oxide contained in the silver oxide layer 13H of the protective layer 13A is reduced to silver in the silver oxide layer 13H formed in the first portion 12P, at a position corresponding to the overlap 16 between the protective layer 13A and the second oxide superconducting wire 2 when viewed in the Z direction. The oxygen produced by the reduction is introduced into the superconducting layer 12A. Through the manufacturing method described above, the connection structure 3 shown in Figure 3 or Figure 4 is obtained.

[0083] Regarding the introduction of oxygen from silver oxide to the superconducting layer 12A, either all of the oxygen from the silver oxide in the silver oxide layer 13H may be introduced into the superconducting layer 12A, or some of the oxygen from the silver oxide in the silver oxide layer 13H may be introduced into the superconducting layer 12A. Regarding the reduction reaction from silver oxide to silver, either all of the silver oxide in the silver oxide layer 13H may be reduced to silver, or some of the silver oxide in the silver oxide layer 13H may be reduced to silver.

[0084] The amount of oxygen introduced from silver oxide into the superconducting layer 12A, and the control of the reduction reaction from silver oxide to silver, can be achieved, for example, by adjusting the silver oxide content in the silver oxide layer 13H or by adjusting the connection heat treatment conditions.

[0085] With this manufacturing method for the connection structure 3, the oxygen concentration in the first region 12F is lower than that in the second region 12S of the superconducting layer 12A, and the thickness of the first region 12F is 100 nm or less. Furthermore, in the first region 12F, an oxygen concentration profile is obtained in which the oxygen concentration gradually decreases from the substrate 10A side to the interface BF1 between the superconducting layer 12A and the protective layer 13A. The interfacial resistance at interface BF1 is 1 × 10⁻⁶ -11 Ωcm 2 ~1 × 10 -9 Ωcm 2 It falls within the range.

[0086] Next, the operation and effects of the connection structure 3 configured as described above will be explained. According to this embodiment, the silver oxide contained in the silver oxide layer 13H can be reduced to silver, and the oxygen produced by the reduction can be introduced into the superconducting layer 12A. Therefore, even if oxygen is removed from the superconducting layer by the connection heat treatment, the portion where oxygen has been removed is replaced by the oxygen produced by the reduction of silver oxide. This makes it possible to reduce the thickness (depth from the interface) of the portion where oxygen has been removed from the superconducting layer 12A. Consequently, the size of the high-resistance layer formed in the superconducting layer 12A is reduced, contributing to a reduction in the interfacial resistance between the superconducting layer 12A and the protective layer 13A.

[0087] In the connection structure 3 according to this embodiment, the interfacial resistance between the superconducting layer 12A and the protective layer 13A is 1 × 10 -11 Ωcm 2 ~1 × 10 -9 Ωcm 2 Since it is within the range, a connection structure 3 equipped with a low-resistance oxide superconducting wire 1 can be realized.

[0088] In the manufacturing method of the connection structure 3 described above, the order in which the silver oxide layer 13H and the silver layer 13L are formed is not limited to the above method. For example, the following method may be used. First, the silver layer 13L is formed on the entire surface of the superconducting layer 12A by sputtering. Next, the silver layer 13L formed on the first part 12P is peeled off while leaving the silver layer 13L formed on the second part 12Q. This exposes the first part 12P of the superconducting layer 12A. Next, the silver oxide layer 13H is formed on the first part 12P. As a result, the silver oxide layer 13H and the silver layer 13L are formed on the upper surface of the superconducting layer 12A, as shown in Figure 5.

[0089] Alternatively, a silver oxide layer 13H may be formed on the superconducting layer 12 corresponding to the first portion 12P by using a known mask having an aperture pattern corresponding to the first portion 12P. Similarly, a silver layer 13L may be formed on the superconducting layer 12 corresponding to the second portion 12Q by using a known mask having an aperture pattern corresponding to the second portion 12Q.

[0090] (Modified version of the second embodiment) The following describes a modified example of the second embodiment of the connecting structure 3 with reference to Figure 4. For modifications of the second embodiment, the same reference numerals are used for the same components as those used in the description of the first and second embodiments, and their descriptions are omitted or simplified. Furthermore, the descriptions of the same manufacturing processes as those described in the first and second embodiments are omitted or simplified.

[0091] The structure of the connecting structure 3 and protective layer 13A shown in Figure 4 differs from that of the second embodiment. The protective layer 13A shown in Figure 4 contains silver oxide. In other words, the protective layer 13A has a structure in which silver oxide remains due to the manufacturing method of the connecting structure 3 described above. Specifically, the protective layer 13A has a silver oxide layer 13F and a silver layer 13S with a lower silver oxide content than the silver oxide layer 13F. The silver oxide layer 13F is located between the silver layer 13S and the superconducting layer 12A. In other words, the silver oxide layer 13F, which has a higher silver oxide content than the silver layer 13S, is adjacent to the superconducting layer 12A via the interface BF1.

[0092] In other words, in Figure 4, some of the oxygen from the silver oxide contained in the silver oxide layer 13H of the protective layer 13A of the oxide superconducting wire 1, prior to the connection heat treatment, is introduced into the superconducting layer 12A during the connection heat treatment, causing a partial reduction reaction from silver oxide to silver, and resulting in silver oxide remaining in the protective layer 13A after the connection heat treatment. Even with a connection structure 3 having such a configuration, the same effects as the connection structure 3 according to the second embodiment described above can be obtained.

[0093] (Third embodiment) (Manufacturing method for the connecting structure 3) Referring to Figure 6, the manufacturing method of the connection structure 3 according to the third embodiment will be described. In the following description, the differences between the third embodiment and the second embodiment will be explained. The same reference numerals will be used for the same components used in the descriptions of the first and second embodiments, and their descriptions will be omitted or simplified. Furthermore, the descriptions of the same manufacturing processes as those described in the first and second embodiments will be omitted or simplified.

[0094] First, similar to the second embodiment described above, the first portion 12P and the second portion 12Q are defined on the surface of the superconducting layer 12A. Next, a protective layer 13A containing silver oxide is formed directly above the superconducting layer 12A. In this process, the silver oxide layer 13H is first formed on the first portion 12P of the superconducting layer 12A. Subsequently, the silver layer 13L is formed on the silver oxide layer 13H and on the second portion 12Q of the superconducting layer 12A. In other words, unlike the method shown in Figure 5, the silver oxide layer 13H and the silver layer 13L are sequentially laminated on the first portion 12P.

[0095] As a method for forming the silver oxide layer 13H on the first portion 12P of the superconducting layer 12A, a method is used in which the silver oxide layer 13H is formed on the entire surface of the superconducting layer 12A by sputtering, and then the silver oxide layer 13H formed on the second portion 12Q is peeled off while leaving the silver oxide layer 13H formed on the first portion 12P. Alternatively, the silver oxide layer 13H may be formed on the superconducting layer 12 corresponding to the first portion 12P by using a known mask having an opening pattern corresponding to the first portion 12P.

[0096] After the silver oxide layer 13H and silver layer 13L are formed on the upper surface of the superconducting layer 12A in this manner, the protective layer 13A of the first oxide superconducting wire 1 and the second oxide superconducting wire 2 are partially overlapped. Specifically, the silver layer 13L formed on the first portion 12P is overlapped with the second oxide superconducting wire 2 when viewed in the Z direction. In this embodiment, solder 15 is interposed between the first oxide superconducting wire 1 (protective layer 13A) and the second oxide superconducting wire 2 (protective layer 23). Furthermore, similar to the second embodiment, the first oxide superconducting wire 1 and the second oxide superconducting wire 2 are connected by performing a connection heat treatment.

[0097] By performing this connection heat treatment, the silver oxide contained in the silver oxide layer 13H of the protective layer 13A is reduced to silver in the silver oxide layer 13H formed in the first portion 12P, at a position corresponding to the overlap 16 between the protective layer 13A and the second oxide superconducting wire 2 when viewed in the Z direction. The oxygen produced by the reduction is introduced into the superconducting layer 12A. Through the manufacturing method described above, the connection structure 3 shown in Figure 3 or Figure 4 is obtained.

[0098] As described above, the same effects as those of the connection structure 3 according to the second embodiment can be obtained in the third embodiment as well. That is, even if a first oxide superconducting wire 1 is used which has a configuration in which a silver oxide layer 13H and a silver layer 13L are sequentially laminated on the first portion 12P of the superconducting layer 12A before the connection heat treatment, it is possible to reduce the interfacial resistance at the interface BF1 between the superconducting layer 12A and the protective layer 13A.

[0099] (Fourth Embodiment) (Manufacturing method for the connecting structure 3) Referring to Figure 7, the manufacturing method of the connection structure 3 according to the fourth embodiment will be described. In the following description, the differences between the fourth embodiment and the second embodiment will be explained. The same reference numerals will be used for the same components used in the descriptions of the first and second embodiments, and their descriptions will be omitted or simplified. Furthermore, the descriptions of the same manufacturing processes as those described in the first and second embodiments will be omitted or simplified.

[0100] First, similar to the second embodiment described above, the first portion 12P and the second portion 12Q are defined on the surface of the superconducting layer 12A. Next, a protective layer 13A containing silver oxide is formed directly above the superconducting layer 12A. In this process, a silver layer 13L is first formed on the first portion 12P and the second portion 12Q of the superconducting layer 12A. Subsequently, a silver oxide layer 13H is formed on the silver layer 13L in the first portion 12P. In other words, unlike the method shown in Figure 5, the silver layer 13L and the silver oxide layer 13H are sequentially laminated on the first portion 12P.

[0101] As a method for forming the silver oxide layer 13H on the first portion 12P of the superconducting layer 12A, a silver layer 13L is formed over the entire surface of the superconducting layer 12A by sputtering, and then the silver oxide layer 13H is laminated onto the silver layer 13L in the first portion 12P. Alternatively, the silver oxide layer 13H may be formed on the superconducting layer 12 corresponding to the first portion 12P by using a known mask having an opening pattern corresponding to the first portion 12P.

[0102] After the silver oxide layer 13H and silver layer 13L are formed on the upper surface of the superconducting layer 12A in this manner, the protective layer 13A of the first oxide superconducting wire 1 and the second oxide superconducting wire 2 are partially overlapped. Specifically, the silver oxide layer 13H formed on the first portion 12P is overlapped with the second oxide superconducting wire 2 when viewed in the Z direction. In this embodiment, solder 15 is interposed between the first oxide superconducting wire 1 (protective layer 13A) and the second oxide superconducting wire 2 (protective layer 23). Furthermore, similar to the second embodiment, the first oxide superconducting wire 1 and the second oxide superconducting wire 2 are connected by performing a connection heat treatment.

[0103] By performing this connection heat treatment, the silver oxide contained in the silver oxide layer 13H of the protective layer 13A is reduced to silver in the silver oxide layer 13H formed in the first portion 12P, at a position corresponding to the overlap 16 between the protective layer 13A and the second oxide superconducting wire 2 when viewed in the Z direction. The oxygen produced by the reduction is introduced into the superconducting layer 12A. Through the manufacturing method described above, the connection structure 3 shown in Figure 3 or Figure 4 is obtained.

[0104] As described above, the same effects as those of the connection structure 3 according to the second embodiment can be obtained in the fourth embodiment as well. In other words, even if a first oxide superconducting wire 1 is used which has a configuration in which a silver layer 13L and a silver oxide layer 13H are sequentially laminated on the first portion 12P of the superconducting layer 12A before the connection heat treatment, it is possible to reduce the interfacial resistance at the interface BF1 between the superconducting layer 12A and the protective layer 13A.

[0105] (Fifth embodiment) (Method of manufacturing a connecting structure) Referring to Figure 8, a method for manufacturing the connection structure according to the fifth embodiment will be described. In the following description, the differences between the fifth embodiment and the second embodiment will be explained. The same reference numerals will be used for the same components as those used in the descriptions of the first and second embodiments, and their descriptions will be omitted or simplified. Furthermore, the descriptions of the same manufacturing processes as those described in the first and second embodiments will be omitted or simplified.

[0106] As shown in Figure 8, the connection structure according to the fifth embodiment joins the first oxide superconducting wire 1 and the second oxide superconducting wire 2 without using solder 15. Specifically, as explained with reference to Figure 5, a silver oxide layer 13H is formed on the surface of the superconducting layer 12A in the first portion 12P, and a silver layer 13L is formed in the second portion 12Q. Next, the protective layer 23 of the second oxide superconducting wire 2 and the silver oxide layer 13H are superimposed. In this state, the first oxide superconducting wire 1 and the second oxide superconducting wire 2 are subjected to a connection heat treatment. The temperature of the connection heat treatment is, for example, about 200°C. As a result, the silver oxide layer 13H containing silver and the silver protective layer 23 containing silver are bonded together.

[0107] By performing this connection heat treatment, the silver oxide contained in the silver oxide layer 13H of the protective layer 13A is reduced to silver in the silver oxide layer 13H formed in the first portion 12P, at a position corresponding to the overlap 16 between the protective layer 13A and the second oxide superconducting wire 2 when viewed in the Z direction. The oxygen produced by the reduction is introduced into the superconducting layer 12A.

[0108] As described above, the fifth embodiment also provides the same effects as the connection structure 3 according to the second embodiment described above. It is possible to reduce the interfacial resistance at the interface BF1 between the superconducting layer 12A and the protective layer 13A without using solder 15.

[0109] Although not shown in Figures 3 to 8, each end of the two oxide superconducting wires 1 and 2 is connected to another oxide superconducting wire. In other words, a long oxide superconducting wire is obtained in which multiple oxide superconducting wires are soldered together along the direction of extension of the oxide superconducting wire. With this configuration, it is possible to manufacture a long oxide superconducting wire with reduced connection resistance.

[0110] Preferred embodiments of the present invention have been described above, and it should be understood that these are illustrative examples of the invention and should not be considered as limiting. Additions, omissions, substitutions, and other modifications can be made without departing from the scope of the invention. Accordingly, the invention should not be considered limited by the foregoing description, but rather limited by the claims.

[0111] In the embodiments described above, a structure in which an intermediate layer is arranged between the substrate and the superconducting layer was described. In the present invention, it is sufficient for the superconducting layer to be provided above the substrate, the superconducting layer may be provided on the substrate, or the superconducting layer 12 may be in direct contact with the substrate.

[0112] In the embodiments described above, an example was given in which a second oxide superconducting wire 2 was used as the object to be connected, but electrodes may also be used as the object to be connected. [Examples]

[0113] Next, we will compare the embodiments of the present invention with comparative examples and specifically describe the embodiments of the present invention.

[0114] (Oxygen concentration profile at the interface between the superconducting layer and the silver protective layer) Figures 9 and 10 show the oxygen concentration profiles in the region near the interface between the superconducting layer (REBCO layer) and the silver protective layer (Ag layer) that constitute the oxide superconducting wire. Figure 9 is a graph illustrating a comparative example, showing experimental results when the silver protective layer does not contain silver oxide. Figure 10 is a graph illustrating an example, showing experimental results when the silver protective layer contains silver oxide. An energy-dispersive X-ray spectrometer (EDS) was used as the measuring instrument.

[0115] In the comparative example, a silver protective layer was formed directly above the superconducting layer by a sputtering method using a known silver target. Note that the silver protective layer may contain silver oxide formed by spontaneous oxidation, such as a surface oxide film. Therefore, in the comparative example, "the silver protective layer does not contain silver oxide" means that silver oxide was not intentionally introduced into the protective layer. In the examples, a silver protective layer was formed directly above the superconducting layer by sputtering using a silver oxide target. In both the comparative examples and the examples, a superconducting layer having the same composition was used. In the following description, the "interface between the superconducting layer and the silver protective layer" may be simply referred to as the "interface."

[0116] In Figures 9 and 10, the horizontal axis represents the depth in the direction from the interface toward the superconducting layer. The "0" on the horizontal axis indicates the position of the interface. The range "0 to -700" on the horizontal axis, i.e., the range to the left of "0" in Figures 9 and 10, represents the depth within the superconducting layer, starting from the interface. Conversely, the range "0 to 100" on the horizontal axis, i.e., the range to the right of "0" in Figures 9 and 10, represents the depth within the silver protective layer, starting from the interface. The vertical axis represents the energy intensity measured by an energy-dispersive X-ray spectrometer.

[0117] The experimental results shown in Figures 9 and 10 revealed the following: [1] As shown in the comparative example, the oxygen concentration gradually increased within the range of 0 to 280 nm from the interface inside the superconducting layer. At depths greater than 280 nm, the oxygen concentration did not increase, remained constant, and stabilized. It became clear that a low-oxygen region with a low oxygen concentration was formed in the superconducting layer within the range of 0 to 280 nm. In this low-oxygen region, the superconducting properties were low, and the interfacial resistance between the superconducting layer and the silver protective layer increased. [2] As shown in the examples, the oxygen concentration increased within the range of 0 to 50 nm from the interface inside the superconducting layer. At depths greater than 50 nm, the oxygen concentration did not increase, remained constant, and stabilized. It was found that a low-oxygen region with a low oxygen concentration was formed in the superconducting layer within the range of 0 to 50 nm. In the examples, the low-oxygen region, that is, the range from 0 to 50 nm in depth from the interface, is a region where a concentration gradient occurs in which the oxygen concentration decreases from the substrate side to the interface, and corresponds to the "first region" of the present invention. Furthermore, in the examples, the region where the oxygen concentration is approximately constant and stable, that is, the region with a depth of 50 nm or more, is the oxygen concentration stable region and corresponds to the "second region" of the present invention. [3] Comparing the comparative example with the example, the oxygen concentration increased gradually from the interface in the comparative example. On the other hand, the oxygen concentration increased sharply from the interface in the example. The depth of the low-oxygen region in the comparative example was 280 nm, while the depth of the low-oxygen region in the example was 50 nm, indicating that the depth of the low-oxygen region in the example was smaller (thinner) than that of the comparative example. Therefore, compared to the comparative example, the interface resistance between the superconducting layer and the silver protective layer can be reduced in the example. [4] Further detailed analysis of the examples revealed that the point where the oxygen concentration in the low-oxygen region becomes 50% of the oxygen concentration in the stable oxygen concentration region (intensity approximately 580) (intensity approximately 290) is located within 100 nm of the interface. Furthermore, the low-oxygen region in the example is located between a point 280 nm away from the interface and the interface. The low-oxygen region in the example is located between a point 100 nm away from the interface and the interface. The low-oxygen region in the example is located between a point 50 nm away from the interface and the interface.

[0118] (Relationship between silver oxide film thickness and connection resistance in connection structures) Oxide superconducting wires 100 and 200 were prepared, each containing a silver protective layer 400 with silver oxide film thicknesses of 0 nm, 5 nm, 10 nm, 100 nm, 200 nm, 500 nm, and 1000 nm. As shown in Figure 11, two oxide superconducting wires 100 and 200 were connected using a bridge section 300 to prepare seven types of connection structures (connection structures A to G).

[0119] Solder 500 is interposed between each of the two oxide superconducting wires 100 and 200 and the bridge section 300. By applying a connection heat treatment at approximately 200°C, the solder 500 is melted, and each of the two oxide superconducting wires 100 and 200 is connected to the bridge section 300. Subsequently, the connection resistance of each of the seven types of connection structures was measured. The experimental results are as follows. Regarding the evaluation results listed in Table 1, "Unacceptable" indicates a connection resistance of 10 -8 Ωcm 2 This indicates that it is a unit, and "OK" means the connection resistance is 10 -9 Ωcm 2 This indicates that it is a unit, and "Good" means the connection resistance is 10 -9 Ωcm 2 This indicates the following cases:

[0120] [Table 1]

[0121] The results shown in Table 1 clearly indicate that connection resistance deteriorates when the silver oxide film thickness is 0 nm (i.e., the silver protective layer does not contain silver oxide) (evaluation result: "Unacceptable"). It was found that when the silver oxide film thickness was between 5 nm and 1000 nm, the evaluation result was either "acceptable" or "good." Furthermore, it was revealed that the evaluation result was "good" when the silver oxide film thickness was between 10 nm and 500 nm. [Explanation of Symbols]

[0122] 1…Oxide superconducting wire (first oxide superconducting wire), 1A…Oxide superconducting wire, 2…Oxide superconducting wire (second oxide superconducting wire), 3…Connecting structure, 10, 10A, 20…Substrate, 11, 11A, 21…Intermediate layer, 12, 12A, 22…Superconducting layer, 12F…First region, 12P…First part, 12Q…Second part, 12S…Second region, 13, 13A, 23…Protective layer, 13F, 13H…Silver oxide layer, 13L, 13S…Silver layer, 14…Stabilizing layer, 15…Solder, 16…Overlap portion, 52, 62…Superconducting portion

Claims

1. A tape-shaped base material, A superconducting layer, made of an oxide superconductor, is provided above the aforementioned substrate, A protective layer is provided on the superconducting layer, is in contact with the superconducting layer, and contains silver. Equipped with, The superconducting layer is composed of a second region formed on the substrate side in the thickness direction and a first region formed on the protective layer side. The oxide superconductor in the second region has a predetermined oxygen concentration. The oxide superconductor in the first region has a lower oxygen concentration than the oxide superconductor in the second region. The thickness of the first region is 100 nm or less. The protective layer contains silver oxide, The protective layer comprises a silver oxide layer and a silver layer. The silver oxide layer is located between the silver layer and the superconducting layer. Oxide superconducting wire.

2. The oxide superconductor in the second region has a uniform oxygen concentration distribution, and the oxide superconductor in the first region has a concentration gradient in which the oxygen concentration decreases in the direction from the substrate toward the protective layer. The oxide superconducting wire according to claim 1.

3. The interfacial resistance between the superconducting layer and the protective layer is 1 × 10 －１１ Ωcm ２ ~1 x 10 －９ Ωcm ２ It is within the range. The oxide superconducting wire according to claim 1 or claim 2.

4. A method for manufacturing an oxide superconducting wire, comprising: forming a superconducting layer composed of an oxide superconductor on a substrate; forming a protective layer containing silver oxide directly above the superconducting layer; and heating the superconducting layer and the protective layer to reduce the silver oxide contained in the protective layer to silver, and introducing the oxygen produced by the reduction into the superconducting layer, When forming the protective layer containing silver oxide directly above the superconducting layer, a silver oxide layer constituting a part of the protective layer is formed directly above the superconducting layer, and then a silver layer constituting a part of the protective layer is formed on the silver oxide layer. By heating the superconducting layer and the protective layer, the silver oxide layer contained in the protective layer is reduced to silver, and the oxygen produced by the reduction is introduced into the superconducting layer.

5. A method for manufacturing an oxide superconducting wire, comprising: forming a superconducting layer composed of an oxide superconductor on a substrate; forming a protective layer containing silver oxide directly above the superconducting layer; and heating the superconducting layer and the protective layer to reduce the silver oxide contained in the protective layer to silver, and introducing the oxygen produced by the reduction into the superconducting layer, When forming the protective layer containing silver oxide directly above the superconducting layer, a silver layer constituting a part of the protective layer is formed directly above the superconducting layer, and then the silver oxide layer constituting a part of the protective layer is formed on the silver layer. By heating the superconducting layer and the protective layer, the silver oxide layer contained in the protective layer is reduced to silver, and the oxygen produced by the reduction is introduced into the superconducting layer. A method for manufacturing oxide superconducting wires.

6. An oxide superconducting wire is prepared by forming a superconducting layer composed of oxide superconductors on top of a substrate, and forming a protective layer containing silver oxide directly above the superconducting layer. Prepare the object to be connected to the oxide superconducting wire, The protective layer and the object to be connected are partially overlapped, A method for manufacturing a connection structure, comprising heating the oxide superconducting wire and the object to be connected, thereby reducing the silver oxide contained in the protective layer to silver at a position corresponding to the overlapping portion of the protective layer and the object to be connected, viewed in the thickness direction of the oxide superconducting wire, and introducing the oxygen produced by the reduction into the superconducting layer, On the surface of the superconducting layer, a first portion corresponding to the overlapping portion is defined, When forming the protective layer containing silver oxide directly above the superconducting layer, the silver oxide layer constituting a part of the protective layer is formed on the first portion of the superconducting layer. Subsequently, a silver layer constituting a part of the protective layer is formed on the silver oxide layer. When viewed in the thickness direction, the silver layer formed on the first portion and the object to be connected are superimposed. By heating the oxide superconducting wire and the object to be connected, the silver oxide contained in the silver oxide layer of the protective layer is reduced to silver, and the oxygen produced by the reduction is introduced into the superconducting layer. A method for manufacturing a connecting structure.

7. An oxide superconducting wire is prepared by forming a superconducting layer made of oxide superconductors on a substrate and forming a protective layer containing silver oxide directly above the superconducting layer. Prepare the object to be connected to the oxide superconducting wire, The protective layer and the object to be connected are partially overlapped, A method for manufacturing a connection structure, comprising heating the oxide superconducting wire and the object to be connected, thereby reducing the silver oxide contained in the protective layer to silver at a position corresponding to the overlapping portion of the protective layer and the object to be connected, viewed in the thickness direction of the oxide superconducting wire, and introducing the oxygen produced by the reduction into the superconducting layer, On the surface of the superconducting layer, a first portion corresponding to the overlapping portion is defined, When forming the protective layer containing silver oxide directly above the superconducting layer, a silver layer constituting a part of the protective layer is formed on the first portion of the superconducting layer. Subsequently, a silver oxide layer constituting a part of the protective layer is formed on the silver layer. The silver oxide layer formed on the first portion and the object to be connected are superimposed when viewed in the thickness direction. By heating the oxide superconducting wire and the object to be connected, the silver oxide contained in the silver oxide layer of the protective layer is reduced to silver, and the oxygen produced by the reduction is introduced into the superconducting layer. A method for manufacturing a connecting structure.

8. An oxide superconducting wire is prepared by forming a superconducting layer made of oxide superconductors on a substrate and forming a protective layer containing silver oxide directly above the superconducting layer. Prepare the object to be connected to the oxide superconducting wire, The protective layer and the object to be connected are partially overlapped, A method for manufacturing a connection structure, comprising heating the oxide superconducting wire and the object to be connected, thereby reducing the silver oxide contained in the protective layer to silver at a position corresponding to the overlapping portion of the protective layer and the object to be connected, viewed in the thickness direction of the oxide superconducting wire, and introducing the oxygen produced by the reduction into the superconducting layer, In the superconducting layer, a first portion corresponding to the overlapping portion is defined on the surface of the superconducting layer, and when forming the protective layer containing silver oxide directly above the superconducting layer, a silver layer constituting a part of the protective layer is formed on the first portion of the superconducting layer, and then a silver oxide layer constituting a part of the protective layer is formed on the silver layer in the first portion, and the silver oxide layer formed on the first portion and the object to be connected are superimposed as viewed in the thickness direction, and the oxide superconducting wire and the object to be connected are heated to reduce the silver oxide contained in the silver oxide layer of the protective layer to silver, and the oxygen produced by the reduction is introduced into the superconducting layer. A method for manufacturing a connecting structure.

9. In the thickness direction, the oxide superconducting wire and the object to be connected are joined by overlapping them with solder in between. A method for manufacturing a connecting structure according to any one of claims 6 to 8.

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