JP7716751B2 - Multi-core thin film superconducting wire and its manufacturing method - Google Patents

Description

The present invention relates to a multi-core thin-film superconducting wire and its manufacturing method.

REBa ₂ Cu ₃ O _7-d (REBCO, RE = rare elements such as Y, Eu, Gd, and Sm, with a composition ratio of RE:Ba:Cu = 1:2:3), a type of high-temperature superconductor, is a material that can be applied to superconducting magnets and power-saving electric equipment. For application in superconducting magnets, it is essential to reduce AC losses and the effects of shielding magnetic fields. Meanwhile, the so-called thin-film superconducting wires expected for these applications can only be fabricated as thin tapes, providing materials with high critical current densities.

When considering applying these wires to existing power systems, including AC, a thinning process is necessary to ensure stable current flow, prevent AC losses, and reduce shielding magnetic fields. Until now, thinning required mechanical cutting or post-processing, such as creating multiple grooves with a laser, a method known as laser scribing.

In recent years, a thinning process that does not require post-processing has been developed (see, for example, Patent Document 1). Patent Document 1 discloses that a superconducting wire substrate used in the manufacture of superconducting wire by a coating pyrolysis method, in which a metal organic compound solution is applied and then a specified heat treatment is performed to form a thin oxide superconducting film, has at least one or more non-coating portions along the length and width of the superconducting wire substrate to prevent the formation of a coating of the metal organic compound solution.

According to Patent Document 1, in order to utilize the liquid repellency of the non-coated areas, the formation of oxide superconducting thin films is limited to thermal decomposition using a solution. Therefore, heat treatment is required to remove the non-coated areas and form the oxide.

JP 2011-124167 A

Based on the above, the objective of the present invention is to provide a multi-core thin-film superconducting wire that can be manufactured without post-processing, and a method for manufacturing the same.

A multi-core thin film superconducting wire according to the present invention comprises a substrate, a plurality of non-superconducting layers disposed on the substrate, and a rare earth oxide thin film disposed on the substrate and the plurality of non-superconducting layers, wherein the rare earth oxide thin film contains a doped or undoped rare earth element (RE), barium (Ba), copper (Cu) and oxygen (O) and satisfies the general formula REBa ₂ Cu ₃ O _7-d (where 0≦d≦0.8), and the substrate is a textured substrate for the rare earth oxide thin film, thereby solving the above-mentioned problems.
The rare earth oxide thin film located on the plurality of non-superconducting layers may have lower crystallinity than the rare earth oxide thin film located on the substrate.
The rare earth oxide thin film located on the plurality of non-superconducting layers may further contain an impurity phase.
The impurity phase may be copper oxide and/or Y ₂ BaCuO _x (4≦x≦6).
The plurality of non-superconducting layers may be made of a metal material or an oxide material that does not have superconductivity.
The metallic or oxide material may have a melting point above 800°C.
The metallic material may be selected from the group consisting of zirconium (Zr), silver (Ag), niobium (Nb), gold (Au), hafnium (Hf), cobalt (Co), germanium (Ge), platinum (Pt), and silicon (Si).
The oxide may be a barium composite oxide (BaMO ₃ , where M is selected from the group consisting of zirconium (Zr), hafnium (Hf), niobium (Nb) and tin (Sn)).
The oxide may be selected from the group consisting of aluminum oxide (Al ₂ O ₃ ), silicon oxide (SiO ₂ ), titanium oxide (TiO ₂ ), zinc oxide (ZnO), cerium oxide (CeO ₂ ), zirconium oxide (ZrO ₂ ), and hafnium oxide (HfO ₂ ).
The width of the plurality of non-superconducting layers may be in the range of 100 nm to 20 μm.
The width of the plurality of non-superconducting layers may be in the range of 1 μm to 20 μm.
The thickness of the plurality of non-superconducting layers may be in the range of 100 nm to 1 μm.
The thickness of the rare earth oxide thin film may be in the range of 100 nm to 500 nm.
The substrate may be made of any of a variety of materials, including magnesium oxide (MgO), strontium titanate (SrTiO ₃ ), lanthanum aluminate (LaAlO ₃ ), strontium aluminum tantalate (SAT; Sr ₂ AlTaO ₆ ), yttria-stabilized zirconia (YSZ), lanthanum gallate (LaGaO ₃ ), neodymium gallate (NdGaO ₃ ), praseodymium gallate (PrGaO ₃ ), yttrium aluminate (YAlO ₃ ), barium stannate (BaSnO ₃ ), barium zirconate (BaZrO ₃ ), neodymium barium tantalate (Ba ₂ NdTaO ₆ ), strontium stannate (SrSnO ₃ ), calcium stannate (CaSnO ₃ ), and strontium lanthanum gallate (LaSrGaO _{4 )} . ), lanthanum strontium aluminate (LaSrAlO ₄ ), cerium oxide (CeO ₂ ), yttrium oxide (Y ₂ O ₃ ), (LaAlO ₃ ) _0.3 -(SrAl _0.5 Ta _0.5 O ₃ ) _0.7 (LSAT), magnesium oxide (MgO), and sapphire.
The substrate may be a biaxially textured substrate.
The rare earth oxide thin film may be doped with nanorods made of a material selected from the group consisting of barium zirconate ( _BaZrO3 ), barium stannate ( _BaSnO3 ), barium hafnate ( _BaHfO3 ), and gold (Au).
The spacing between the plurality of non-superconducting layers may be in the range of 100 nm to 1 mm.
The method for manufacturing the above-mentioned multi-core thin film superconducting wire according to the present invention includes forming a plurality of non-superconducting layers on a substrate using lithography or printing technology, and forming a rare earth oxide thin film on the substrate and the plurality of non-superconducting layers, thereby solving the above-mentioned problem.
Forming the plurality of non-superconducting layers may occur at room temperature.
The rare earth oxide thin film may be formed by a method selected from the group consisting of physical vapor deposition, chemical vapor deposition, and liquid phase deposition.

A multi-core thin-film superconducting wire according to the present invention comprises a substrate, a plurality of non-superconducting layers disposed thereon, and a rare earth-based oxide thin film disposed on the substrate and the plurality of non-superconducting layers, the rare earth-based oxide thin film containing a doped or undoped rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O) and satisfying the general formula REBa ₂ Cu ₃ O _7-d (where 0≦d≦0.8). Because the substrate is an orientation substrate for rare earth-based oxide thin films, the rare earth-based oxide thin film disposed on the substrate is oriented relative to the substrate and exhibits excellent superconductivity. Meanwhile, the crystallinity of the rare earth-based oxide thin film disposed on the plurality of non-superconducting layers is lower than that of the rare earth-based oxide thin film disposed on the substrate. This disturbance in crystal orientation makes it difficult for superconducting current to flow through the rare earth-based oxide thin film disposed on the plurality of non-superconducting layers. As a result, the wire exhibits superconductivity, and alternates between regions where superconducting current easily flows and regions where superconducting current does not easily flow, and can function as a multi-core thin film superconducting wire.

The method for manufacturing multi-core thin-film superconducting wire according to the present invention involves forming multiple non-superconducting layers on a substrate using lithography or printing techniques, and then forming a rare earth oxide thin film on the substrate and the multiple non-superconducting layers. Because it is simply a matter of forming a rare earth oxide thin film on a substrate containing multiple non-superconducting layers, there is no need to remove the multiple non-superconducting layers, and no post-processing is required.

Schematic diagram showing a multi-core thin-film superconducting wire according to the present invention. Schematic diagram showing details of a multi-core thin-film superconducting wire according to the present invention. Flowchart showing the manufacturing process of the multi-core thin film superconducting wire according to the present invention Procedure showing the steps for manufacturing multifilamentary thin film superconducting wires of Examples 1 to 3 FIG. 1 shows an optical microscope image of the surface of an STO substrate having multiple non-superconducting layers used in Examples 1 and 2. FIG. 1 shows an SEM image of the surface of an STO substrate having multiple non-superconducting layers used in Examples 1 and 2. FIG. 1 shows a laser microscope image of the surface of an STO substrate having multiple non-superconducting layers used in Examples 1 and 2. 1 shows SEM images of the surfaces of the multi-core thin film superconducting wires of Examples 1 to 3. FIG. 1 shows an XRD pattern of the surface of the multi-core thin film superconducting wire of Example 1. FIG. 1 is a diagram showing the temperature dependence of the electrical resistance of the multi-core thin-film superconducting wire of Example 1. 1 shows a magnetic deflection image of the multi-core thin-film superconducting wire of Example 1. STEM image of the cross section of the multifilamentary thin-film superconducting wire of Example 1 TEM image of the cross section of the multi-core thin film superconducting wire of Example 1 EBSD image of the surface of the multifilamentary thin-film superconducting wire of Example 1 FIG. 15 is a diagram showing the distribution of the inclination of the crystal orientation calculated from the EBSD image of the rare earth oxide thin film on the Zr film in FIG. 14. EDX mapping of the cross section of the multifilamentary thin film superconducting wire of Example 1

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that like elements are designated by like numbers and their description will be omitted.
FIG. 1 is a schematic diagram showing a multi-core thin film superconducting wire according to the present invention.
2 is a schematic diagram showing details of a multi-core thin film superconducting wire according to the present invention.

The multi-core thin film superconducting wire 100 of the present invention comprises a substrate 110, a plurality of non-superconducting layers 120 disposed on the substrate 110, and a rare earth-based oxide thin film 130 disposed on the substrate 110 and the non-superconducting layer 120. The rare earth-based oxide thin film 130 contains a doped or undoped rare earth element (RE), barium (Ba), copper (Cu), and oxygen (O), and has the general formula REBa ₂ Cu ₃ O _7-d (where 0≦d≦0.8). Furthermore, since the substrate 110 is a textured substrate for the rare earth-based oxide thin film 130, the rare earth-based oxide thin film 130 on the substrate 110 is textured with respect to the substrate 110.

A rare earth oxide thin film expressed by the general formula REBa ₂ Cu ₃ O _7-d (where 0≦d≦0.8) has an oxygen-deficient layered perovskite structure, and is composed of an alternating stack of superconducting layers consisting of RE and CuO ₂ planes above and below it that exhibit superconductivity, and block layers consisting of BaO planes and CuO chains, and has a perovskite structure, and is known as a superconducting material.

The rare earth element RE is preferably at least one selected from the group consisting of lutetium (Lu), ytterbium (Yb), thulium (Tm), erbium (Er), holmium (Ho), dysprosium (Dy), gadolinium (Gd), europium (Eu), and samarium (Sm). The critical temperature Tc can be changed depending on the rare earth element RE selected, so it should be selected according to the application.

The rare earth-based oxide thin film 130 may have nanorods as pinning centers to improve the superconducting current. Such nanorods are preferably made of a material selected from the group consisting of barium zirconate ( _BaZrO3 ), barium stannate ( _BaSnO3 ), barium hafnate ( _BaHfO3 ), and gold (Au). Among these, barium zirconate is preferred because it has the same perovskite structure as the rare earth-based oxide thin film 130 and therefore does not deteriorate the superconducting properties.

The doping amount of such nanorods is preferably in the range of 5 mol% to 15 mol%. This range maintains the crystal structure of the rare earth oxide thin film 130 and improves the superconducting current without reducing superconductivity.

In this way, the rare earth-based oxide thin film 130 located on the substrate 110 is oriented relative to the substrate 110 and exhibits excellent superconductivity. On the other hand, the rare earth-based oxide thin film 130 located on multiple non-superconducting layers 120 is less likely to allow superconducting current to flow and is less likely to exhibit superconductivity. As a result, regions where superconducting current flows easily and regions where superconducting current does not flow easily are repeated without physically cutting the rare earth-based oxide thin film 130, allowing it to function as a multi-core, thin-wired multi-core thin-film superconducting wire.

The substrate 110 is not particularly limited as long as it is a substrate that orients the rare earth oxide thin film 130, but examples thereof include magnesium oxide (MgO), strontium titanate ( _SrTiO3 ), lanthanum aluminate ( _LaAlO3 ), strontium aluminum tantalate (SAT; _Sr2AlTaO6 ), _yttria -stabilized zirconia (YSZ), lanthanum gallate ( _LaGaO3 ), neodymium gallate ( _NdGaO3 ), praseodymium gallate ( _PrGaO3 ), yttrium aluminate (YAlO3), barium stannate ( _BaSnO3 ), barium zirconate ( _BaZrO3 ), neodymium barium tantalate ( _Ba2NdTaO6 ), strontium stannate ( _SrSnO3 ), calcium stannate (CaSnO3 ₎ , and _{the like} . ), lanthanum strontium gallate (LaSrGaO ₄ ), lanthanum strontium aluminate (LaSrAlO ₄ ), cerium oxide (CeO ₂ ), yttrium oxide (Y ₂ O ₃ ), (LaAlO ₃ ) _0.3 -(SrAl _0.5 Ta _0.5 O ₃ ) _0.7 (LSAT), magnesium oxide (MgO), and sapphire. These are known as texture substrates for the rare earth-based oxide thin film 130.

For example, when using MgO as the substrate, the rare earth-based oxide thin film 130 can be c-axis oriented by using an MgO single crystal substrate with a {100} plane orientation. The rare earth-based oxide thin film 130 is not limited to a c-axis orientation as long as it is oriented. Those skilled in the art can appropriately select a single crystal substrate made of the oxides described above and an s-plane orientation to match the crystal orientation of the rare earth-based oxide thin film 130.

Alternatively, the substrate 110 may be a biaxially textured substrate. A biaxially textured substrate is a substrate in which an in-plane textured intermediate layer is formed on a metal substrate, and is known to be used for the rare earth oxide thin film 130.

For ease of understanding, hereafter, the rare earth-based oxide thin film 130 located on the substrate 110 will be simply referred to as the rare earth-based oxide thin film 210 (Figure 2), and the rare earth-based oxide thin film 130 located on the multiple non-superconducting layers 120 will be simply referred to as the rare earth-based oxide thin film 220 (Figure 2).

The crystallinity of the rare earth-based oxide thin film 220 is preferably lower than that of the rare earth-based oxide thin film 210. The difference in crystallinity is due to a disorder in the crystal orientation. A rare earth-based oxide thin film 220 with a disordered crystal orientation has a lower tendency to allow superconducting current to flow than an oriented rare earth-based oxide thin film 210. This disorder in crystal orientation, i.e., a difference in crystallinity, can be confirmed by electron backscatter diffraction (EBSD) using a scanning electron microscope; it is sufficient if the rare earth-based oxide thin film 220 has a plane with a crystal orientation different from that of the rare earth-based oxide thin film 210. By referring to the EBSD image, the difference can be distinguished simply by the difference in color.

There are no particular limitations as long as there is a difference between the crystallinity of the rare earth-based oxide thin film 210 and that of the rare earth-based oxide thin film 220, but preferably, if the average tilt of adjacent crystal orientations in the ab plane in the rare earth-based oxide thin film 220 is 4° or more, superconducting current will be less likely to flow and multifilamentary wire can be facilitated. In this specification, the tilt of the crystal orientation is defined as the average of the tilt of the crystal orientations of adjacent crystal grains calculated for 100 crystal grains.

Simply put, the average tilt can be considered to be 4° or greater if, per 100 crystal grains, the rare earth-based oxide thin film 220 contains 10% to 80% crystal grains that have a crystal orientation different from the main crystal orientation of the crystals of the rare earth-based oxide thin film 210. More preferably, the rare earth-based oxide thin film 220 only needs to contain 35% to 45% crystal grains per 100 crystal grains that have a crystal orientation different from the main crystal orientation of the crystals of the rare earth-based oxide thin film 210.

The rare earth-based oxide thin film 220 preferably contains an impurity phase 230. The impurity phase 230 contained in the rare earth-based oxide thin film 220 does not exhibit superconductivity. Therefore, regions that exhibit superconductivity and regions that do not exhibit superconductivity/are unlikely to exhibit superconductivity are repeated without physically cutting the rare earth-based oxide thin film 130, allowing it to function as a multi-core thin film superconducting wire.

Such impurity phase 230 is preferably copper oxide and/or Y ₂ BaCuO _x (4≦x≦6). Neither of these exhibits superconductivity. The content of the impurity phase 230 may preferably be in the range of 5 vol % or more and less than 100 vol %. Within this range, the impurity phase 230 does not exhibit superconductivity, thereby facilitating multifilamentary wire formation. The presence of the impurity phase 230 can be determined by elemental mapping or the like attached to a scanning electron microscope or the like. Even if the rare earth-based oxide thin film 220 is largely made up of the impurity phase, the proportion of the rare earth-based oxide thin film 220 in the entire rare earth-based oxide thin film 130 is extremely small. Therefore, according to X-ray diffraction, the entire rare earth-based oxide thin film 130 can be said to satisfy the general formula REBa ₂ Cu ₃ O _7-d (where 0≦d≦0.8), and the present invention also includes such a case. The content of the impurity phase 230 may more preferably be in the range of 5 vol % to 20 vol %. A small amount of impurities allows for multifilamentary wire.

The ratio of the width of the rare earth-based oxide thin film 210 to the width of the rare earth-based oxide thin film 220 is preferably 1 or more and 1000 or less. This allows the wire to function as a multi-core thin-film superconducting wire. The ratio of the width of the rare earth-based oxide thin film 210 to the width of the rare earth-based oxide thin film 220 may more preferably be 10 or more and 500 or less.

The multiple non-superconducting layers 120 may be made of any material that does not have superconductivity, but are preferably made of a metal or oxide material that does not have superconductivity.

The non-superconducting metal or oxide material is preferably made of a material with a melting point above 800°C. This prevents the rare earth oxide thin film 130 from reacting with the non-superconducting layer 120 during the manufacturing process described below. There is no particular upper limit to the melting point, but it may be, for example, 2000°C or lower for metal materials and 3000°C or lower for oxide materials.

The non-superconducting metal material is illustratively selected from the group consisting of zirconium (Zr), silver (Ag), niobium (Nb), gold (Au), hafnium (Hf), cobalt (Co), germanium (Ge), platinum (Pt), and silicon (Si). These metal materials can be deposited on a substrate at room temperature and have melting points above 800°C. If deposited on these metal materials, the rare earth oxide thin film 230 will either become polycrystalline or, if oriented, will have low orientation.

An example of an oxide material that does not have superconductivity is barium composite oxide ( _BaMO3 , where M is selected from the group consisting of zirconium (Zr), hafnium (Hf), niobium (Nb), and tin (Sn). This composite oxide can be formed into a film on a substrate at room temperature and has a melting point exceeding 800°C. Such a composite oxide has low reactivity with rare earth-based oxide thin films, and therefore promotes the formation of the rare earth-based oxide thin film 230.

Alternatively, the non-superconducting oxide material may be selected from the _group consisting of aluminum oxide ( _Al2O3 ), silicon oxide ( _SiO2 ), titanium oxide ( _TiO2 ), zinc oxide (ZnO), cerium oxide ( _CeO2 ), zirconium oxide ( _ZrO2 ), and hafnium oxide ( _HfO2 ). These oxides can be deposited on a substrate at room temperature and have melting points above 800°C. If deposited on these oxides, the rare earth-based oxide thin film 220 will be polycrystalline or will be poorly oriented, if at all.

There are no particular restrictions on the width of the non-superconducting layer 120, as long as it is possible to form the rare earth oxide thin film 220 described above, but it is preferable that it be in the range of 100 nm to 20 μm. A width of 100 nm or more is preferable because it allows the use of the lithography or printing techniques described above. Considering the size of the wire, it is best to set the upper limit at 20 μm.

The width of the non-superconducting layer 120 more preferably falls within the range of 1 μm to 20 μm. Within this range, the rare earth oxide thin film 220 on the non-superconducting layer 20 will have low crystallinity and may contain impurity phases 230.

The spacing between the non-superconducting layers 120 preferably falls within the range of 100 nm to 1 mm. This allows the wire to function as a multi-core thin-film superconducting wire. The spacing between the non-superconducting layers 120 more preferably falls within the range of 10 μm to 500 μm. The spacing between the non-superconducting layers 120 is even more preferably within the range of 30 μm to 100 μm. This allows the wire to efficiently suppress AC losses and reduce the effects of shielding magnetic fields.

The thickness of the non-superconducting layer 120 is not particularly limited, but is preferably in the range of 100 nm to 1 μm. Within this range, the rare earth oxide thin film 220 on the non-superconducting layer 20 will have low crystallinity and may contain an impurity phase 230. The thickness of the non-superconducting layer 120 is more preferably in the range of 100 nm to 500 nm.

The multi-core thin-film superconducting wire 100 of the present invention is made by multi-cored rare earth oxide thin films without physically cutting them, which suppresses AC loss and reduces shielding magnetic fields. Such multi-core thin-film superconducting wire 100 is applicable to electric power equipment, medical accelerators, nuclear fusion reactors, etc.

Next, a method for manufacturing the multi-core thin film superconducting wire 100 of the present invention will be described.
FIG. 3 is a flow chart showing the manufacturing process of a multi-filamentary thin film superconducting wire according to the present invention.

The multi-core thin film superconducting wire 100 of the present invention includes the following manufacturing steps.
Step S310: Forming a plurality of non-superconducting layers on a substrate using lithography or printing techniques.
Step S320: forming a rare earth-based oxide thin film on the substrate and the plurality of non-superconducting layers.

In this way, the multi-core thin-film superconducting wire of the present invention can be manufactured simply by forming multiple non-superconducting layers on a substrate and then forming a rare earth oxide thin film on top of them, without the need for post-processing such as physical cutting of the rare earth oxide thin film, and without the need to remove the non-superconducting layers.

Each step will be described in detail. Note that the substrate, non-superconducting layer, and rare earth oxide thin film are as described with reference to Figures 1 and 2, so their description will be omitted.

In step S310, resist is patterned on the substrate using lithography or printing technology. The resist may be a composition whose solubility in a developer changes when exposed to light or an electron beam. Multiple linear patterns are drawn on the resist in the longitudinal direction of the substrate using, for example, a laser exposure device, and when developed, only the irradiated areas are removed.

The lithography technology can be either the existing photolithography or electron beam lithography. The printing technology can be the existing nanoimprint technology.

A non-superconducting layer is formed on a substrate with a patterned resist by physical vapor deposition (vacuum deposition, molecular beam deposition, PLD (Physical Laser Deposition) using laser ablation, molecular beam epitaxy, various sputtering methods, etc.). Considering the process using resist, the non-superconducting layer is formed at room temperature (between 8°C and 35°C). The resist is then removed using a solvent or other method, forming multiple non-superconducting layers on the substrate in the longitudinal direction.

In step S320, a rare earth oxide thin film is formed on the substrate on which multiple non-superconducting layers have been formed by the above-mentioned physical vapor deposition method, chemical vapor deposition method (such as MOCVD and various CVD methods including flash CVD), chemical liquid phase deposition method (such as the sol-gel method or metal organic decomposition (MOD) method), or liquid phase mist deposition (such as the LSMCD method).

In step S320, simply forming a rare earth-based oxide thin film on a substrate with multiple non-superconducting layers formed thereon causes the rare earth-based oxide thin film directly above the substrate to grow oriented relative to the substrate due to the orientation substrate, and the rare earth-based oxide thin film directly above the non-superconducting layer may have low crystallinity and may contain impurity phases. As a result, the multi-core thin film superconducting wire 100 of the present invention shown in Figures 1 and 2 is obtained.

The present invention will now be described in detail using specific examples, but please note that the present invention is not limited to these examples.

[Examples 1 to 3]
In Examples 1 to 3, multi-core thin-film superconducting wires were fabricated using photolithography. The substrate was a (001) STiO3 _single crystal substrate (STO substrate), the non-superconducting layers were Zr or Ag _films , and the rare earth oxide thin films were 10% _BaZrO3 nanorod-doped or undoped _{YBa2Cu3O7 films} .

Figure 4 shows the procedure for manufacturing the multi-core thin-film superconducting wires of Examples 1 to 3.

A resist 420 (OFPR800LB, manufactured by Tokyo Ohka Kogyo Co., Ltd.) was applied to an STO substrate 410 (5 mm x 5 mm), and the resist 420 was patterned using a maskless exposure system (DL-1000, manufactured by Nano System Solutions Co., Ltd.). This removed the exposed portions of the resist, leaving multiple linear resists 420a extending along the length of the STO substrate 410.

For ease of understanding, Figure 4 shows three equally spaced linear resists 420a, but in reality there were five linear resists, spaced apart in the order of 2 μm, 5 μm, 10 μm, and 15 μm.

Next, a non-superconducting layer 430, which was a Zr film (300 nm) or an Ag film (300 nm), was formed using an RF magnetron sputtering device (Shibaura Mechatronics Corporation, CFD-4EP-LL (4G)). The sputtering conditions are shown in Table 1.

The substrate was then immersed in a resist remover (Remover PG, manufactured by MicroChem) to remove the resist 420a. This resulted in the formation of multiple linear non-superconducting layers 430a on the STO substrate 410.

The resulting non-superconducting layer 430a on the STO substrate 410 was observed using an optical microscope (Keyence Corporation, VHX-1000), a scanning electron microscope (SEM, Hitachi High-Tech Corporation, SU-70), and a laser microscope (Keyence Corporation, VK-X1100). The results are shown in Figures 5 to 7.

_A rare earth oxide thin film 440, which was undoped or 10% BaZrO _nanorod -doped _{YBa2Cu3O7 ,} was formed on an STO substrate 410 with multiple non-superconducting layers 430a using a pulsed laser deposition system (manufactured by ULVAC). The PLD conditions are shown in Table 2. The target was obtained from TEP.

For simplicity, the experimental conditions for the multi-core thin film superconducting wires of Examples 1 to 3 are shown in Table 3.

The surfaces of the multi-core thin-film superconducting wires of Examples 1 to 3 obtained in this manner were observed using an SEM. The results are shown in Figure 8. X-ray diffraction was performed on the rare earth oxide thin films of the multi-core thin-film superconducting wires of Examples 1 to 3 using an X-ray diffractometer (TRY-HA, manufactured by TRY SE). The results are shown in Figure 9. The temperature dependence of electrical resistance was measured on the rare earth oxide thin films of the multi-core thin-film superconducting wires of Examples 1 to 3. The results are shown in Figure 10.

The surfaces of the multicore thin-film superconducting wires of Examples 1 to 3 were observed using a magnetic deflection observation device. The results are shown in Figure 11. The cross-sectional appearances of the multicore thin-film superconducting wires of Examples 1 to 3 were observed using a scanning transmission electron microscope (STEM, JEOL, JEM-ARM200F-G) equipped with an energy dispersive X-ray spectrometer (EDX). These results are shown in Figures 12 and 13. EBSD images of the surfaces of the multicore thin-film superconducting wires of Examples 1 to 3 were examined using the SEM described above. The results are shown in Figures 14 and 15. Furthermore, detailed elemental analysis of the multicore thin-film superconducting wires of Examples 1 to 3 was performed using EDX. The results are shown in Figure 16.

The above results will be summarized.
FIG. 5 shows an optical microscope image of the surface of the STO substrate having multiple non-superconducting layers used in Examples 1 and 2.
FIG. 6 shows an SEM image of the surface of the STO substrate having multiple non-superconducting layers used in Examples 1 and 2.
FIG. 7 shows a laser microscope image of the surface of the STO substrate having multiple non-superconducting layers used in Examples 1 and 2.

In Figure 5, the dark grayscale areas are non-superconducting layers made of Zr films, and it was confirmed that multiple linear non-superconducting layers were formed on the STO substrate. From the left in Figure 5, the widths of the non-superconducting layers were 2 μm, 5 μm, 10 μm, and 15 μm.

Figure 6 shows an enlarged view of the non-superconducting layer, a 15 μm-wide Zr film. Lithography technology clearly defined the boundary of the non-superconducting layer. Figure 7(B) is a measurement image of the surface irregularities of the main image (Figure 7(A)) of the non-superconducting layer, a 15 μm-wide Zr film. In Figure 7(B), the dark grayscale area corresponds to a height of 300 nm, and the thickness of the non-superconducting layer, a Zr film, was 300 nm. Although not shown, the non-superconducting layer, an Ag film, of Example 3 also exhibited a similar appearance and was 300 nm thick.

Figure 8 shows SEM images of the surfaces of the multi-core thin-film superconducting wires of Examples 1 to 3.

Figures 8(A) to (C) show the surfaces of the multi-core thin-film superconducting wires of Examples 1 to 3, respectively, and for ease of understanding, the areas corresponding to the non-superconducting layers are indicated by dotted lines.

Figures 8(A) and (B) show that both the rare earth oxide thin film directly on the STO substrate and the rare earth oxide thin film directly on the non-superconducting layer were uniform in appearance. The presence of nanorods was confirmed in Figure 8(B). On the other hand, Figure 8(C) shows that the rare earth oxide thin film directly on the STO substrate and the rare earth oxide thin film directly on the non-superconducting layer appear differently, due to the different number of integration times.

Figure 9 shows the XRD pattern of the surface of the multi-core thin-film superconducting wire of Example 1.

9, only the diffraction peak of 00L was observed, and the rare earth oxide thin film was identified as c-axis oriented YBa ₂ Cu ₃ O ₇ as a whole. Although not shown, it was also confirmed in Examples 2 and 3 that the thin films were c-axis oriented 10% BaZrO ₃ nanorod-doped YBa ₂ Cu ₃ O ₇ or undoped YBa ₂ Cu ₃ O ₇ .

Figure 10 shows the temperature dependence of the electrical resistance of the multi-core thin-film superconducting wire of Example 1.

10, it was found that the rare earth oxide thin film of undoped YBa ₂ Cu ₃ O ₇ of Example 1 became superconducting at a critical temperature Tc of 85.9 K. This critical temperature was similar to the critical temperature previously reported for YBa ₂ Cu ₃ O _7. Although not shown, it was also found that the rare earth oxide thin films of Examples 2 and 3 became superconducting in a similar manner.

Figure 11 shows a magnetic deflection image of the multi-core thin-film superconducting wire of Example 1.

11, it was found that the regions were clearly magnetically divided along the four bright grayscale lines, and that the rare earth oxide thin film was multifilamentary. These four lines are non-superconducting Zr films, suggesting that superconducting current does not easily flow in YBa ₂ Cu ₃ O ₇ on the Zr film. Although not shown, the multifilamentary thin film superconducting wires of Examples 2 and 3 also showed similar magnetic deflection images.

From the above, it has been shown that if a multi-core thin-film superconducting wire is provided with a substrate, a plurality of non-superconducting layers located on the substrate, and a rare earth-based oxide thin film located thereon, the rare earth-based oxide thin film containing a doped or undoped rare earth element (RE), barium (Ba), copper (Cu) and oxygen (O) and satisfying the general formula REBa ₂ Cu ₃ O _7-d (where 0≦d≦0.8), and the substrate is an orientation substrate for the rare earth-based oxide thin film, the rare earth-based oxide thin film can be multi-cored without physical cutting.

FIG. 12 is an STEM image of a cross section of the multi-core thin film superconducting wire of Example 1.
FIG. 13 is a TEM image of a cross section of the multi-core thin film superconducting wire of Example 1.

12 and 13, a region in which a non-superconducting layer, which is a Zr film, is on the STO substrate and a rare earth oxide thin film, which is _YBa2Cu3O7 , is on top of that, and a region in which a rare _earth oxide thin film, which is _{YBa2Cu3O7 ,} is on top of _{the STO} substrate, were confirmed.

Figure 14 is an EBSD image of the surface of the multi-core thin-film superconducting wire of Example 1.

Figure 14 shows the image in grayscale, but it is actually a color image, with the same brightness indicating the same crystal orientation. In Figure 14, the crystal orientation of the rare earth oxide thin film 210 directly on the STO substrate was essentially aligned in the 100 direction. On the other hand, the crystal orientation of the rare earth oxide thin film 220 directly on the Zr film was clearly random. This indicates that the crystallinity of the rare earth oxide thin film 220 directly on the Zr film was lower than that of the rare earth oxide thin film 210 directly on the STO substrate. Although not shown, the cross sections of the multi-core thin film superconducting wires of Examples 2 and 3 also had a similar appearance.

Figure 15 shows the distribution of crystal orientation tilt calculated from the EBSD image of the rare earth oxide thin film on the Zr film in Figure 14.

Figure 15 shows that in the rare earth oxide thin film 220 on the Zr film, over 60% of the crystal grains have the same crystal orientation, but the remaining 40% of the crystal grains have varying crystal orientations, with a wide distribution of inclinations from 5° to 80° relative to the main crystal orientation. Although not shown, the inclination of adjacent crystal orientations within the ab plane of the rare earth oxide thin film 210 directly on the STO substrate is 2° or less, meaning that essentially 100% of the crystal grains have the same crystal orientation, the same as the aforementioned 60% of the crystal grains.

Figure 16 shows EDX mapping of the cross section of the multi-core thin-film superconducting wire of Example 1.

FIG. 16(A) shows EDX mapping of YBa ₂ Cu ₃ O ₇ directly on the Zr film, and FIG. 16(B) shows EDX mapping of YBa ₂ Cu ₃ O ₇ directly on the STO substrate. Comparing FIG. 16(A) and FIG. 16(B) reveals differences in the compositions of Y, Ba, and Cu, among others. This also suggests that the crystallinity of the rare earth oxide thin film directly on the Zr film may be lower than that of the rare earth oxide thin film directly on the STO substrate, and that it may contain impurity phases. Furthermore, EDX mapping revealed that the rare earth oxide thin film directly on the Zr film contains copper oxide (CuO) as an impurity phase, with a content of 5 vol% or more. Even if the measurement area is simply converted to the entire rare earth oxide thin film directly on the Zr film, the content of the impurity phase is considered to be 20 vol% or less. Although not shown, the cross sections of the multicore thin film superconducting wires of Examples 2 and 3 also had similar appearances.

The manufacturing method for multi-core thin-film superconducting wire of the present invention is advantageous for practical use because it allows for multi-core formation without post-processing. The multi-core thin-film superconducting wire of the present invention is thinned without physical cutting, thereby suppressing AC loss and reducing shielding magnetic fields. Such multi-core thin-film superconducting wire is applicable to electric power equipment, medical accelerators, nuclear fusion reactors, etc.

100 Multi-core thin film superconducting wire 110 Substrate 120, 430, 430a Non-superconducting layer 130, 210, 220, 440 Rare earth oxide thin film 230 Impurity phase 410 STO substrate 420, 420a Resist

Claims (15)

A substrate;
a plurality of linear non-superconducting layers positioned on the substrate;
a rare earth oxide thin film disposed on the substrate and the plurality of non-superconducting layers;
The rare earth oxide thin film contains a doped or undoped rare earth element (RE), barium (Ba), copper (Cu) and oxygen (O), and satisfies the general formula REBa ₂ Cu ₃ O _7-d (where 0≦d≦0.8);
the substrate is a substrate for texture of the rare earth oxide thin film,
The plurality of non-superconducting layers are made of a metal material selected from the group consisting of zirconium (Zr), silver (Ag), niobium (Nb), gold (Au), hafnium (Hf), cobalt (Co), germanium (Ge), platinum (Pt), and silicon (Si), or an oxide material that is barium composite oxide ( _BaMO3 , where M is selected from the group consisting of zirconium (Zr), hafnium (Hf), niobium (Nb), and tin (Sn)). The multi-core thin-film superconducting wire of claim 1, wherein the crystallinity of the rare earth oxide thin film located on the plurality of non-superconducting layers is lower than that of the rare earth oxide thin film located on the substrate. The multi-core thin-film superconducting wire according to claim 1 or 2, wherein the rare earth oxide thin films located on the plurality of non-superconducting layers further contain an impurity phase. 4. The multi-core thin film superconducting wire according to claim 3, wherein the impurity phase is copper oxide and/or _Y2BaCuOx ( _4≤x≤6 ). A multi-core thin-film superconducting wire according to any one of claims 1 to 4, wherein the widths of the multiple non-superconducting layers are in the range of 100 nm to 20 μm. The multi-core thin-film superconducting wire of claim 5, wherein the widths of the multiple non-superconducting layers are in the range of 1 μm to 20 μm. A multi-core thin-film superconducting wire according to any one of claims 1 to 6, wherein the thicknesses of the multiple non-superconducting layers are in the range of 100 nm to 1 μm. A multi-core thin-film superconducting wire according to any one of claims 1 to 7, wherein the thickness of the rare earth oxide thin film is in the range of 100 nm to 500 nm. The substrate may be made of any of a variety of materials, including magnesium oxide (MgO), strontium titanate (SrTiO ₃ ), lanthanum aluminate (LaAlO ₃ ), strontium aluminum tantalate (SAT; Sr ₂ AlTaO ₆ ), yttria-stabilized zirconia (YSZ), lanthanum gallate (LaGaO ₃ ), neodymium gallate (NdGaO ₃ ), praseodymium gallate (PrGaO ₃ ), yttrium aluminate (YAlO ₃ ), barium stannate (BaSnO ₃ ), barium zirconate (BaZrO ₃ ), neodymium barium tantalate (Ba ₂ NdTaO ₆ ), strontium stannate (SrSnO ₃ ), calcium stannate (CaSnO ₃ ), and strontium lanthanum gallate (LaSrGaO _{4 )} . 9. The multi-core thin film superconducting wire according to claim 1, wherein the oxide is selected from the group consisting of lanthanum strontium aluminate (LaSrAlO ₄ ), cerium oxide (CeO ₂ ), yttrium oxide (Y ₂ O ₃ ), (LaAlO ₃ ) _0.3 -(SrAl _0.5 Ta _0.5 O ₃ ) _0.7 (LSAT), magnesium oxide (MgO), and sapphire. A multi-core thin-film superconducting wire according to any one of claims 1 to 9, wherein the substrate is a biaxially oriented substrate. The multi-core thin film superconducting wire according to any _{one of claims 1 to 10, wherein the rare earth oxide thin film is doped with nanorods made of a material selected from the group consisting of barium zirconate (BaZrO 3 )} , barium stannate (BaSnO ₃ ), barium hafnate (BaHfO 3 ), and gold (Au). A multi-core thin-film superconducting wire according to any one of claims 1 to 11, wherein the spacing between the multiple non-superconducting layers is in the range of 100 nm to 1 mm. forming a plurality of linear non-superconducting layers on a substrate using a lithography technique or a printing technique;
forming a rare earth oxide thin film on the substrate and the plurality of non-superconducting layers;
13. The method for manufacturing a multi-core thin film superconducting wire according to claim 1, wherein the plurality of non-superconducting layers are made of a metal material selected from the group consisting of zirconium (Zr), silver (Ag), niobium (Nb), gold (Au), hafnium (Hf), cobalt (Co), germanium (Ge), platinum (Pt), and silicon (Si), or an oxide material that is barium composite oxide (BaMO ₃ , where M is selected from the group consisting of zirconium (Zr), hafnium (Hf), niobium (Nb), and tin (Sn)). The method of claim 13, wherein forming the plurality of non-superconducting layers is performed at room temperature. 15. The method according to claim 13, wherein the rare earth-based oxide thin film is formed using a technique selected from the group consisting of physical vapor deposition, chemical vapor deposition, and liquid phase deposition.