JP2016054050A - Superconducting wire rod - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a superconducting wire rod on which, a protection layer is formed on a superconducting material, capable of easily making the protection layer thinner.SOLUTION: A superconducting wire rod 10 comprises: a substrate 1; a superconducting material layer 3 formed on the substrate 1; and a protection layer 4 formed on the superconducting material layer 3. The superconducting material layer 3 comprises plural salient parts on a surface facing the protection layer 4. A minimum interval between adjacent salient parts is equal to or less than 5 μm.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a superconducting wire, and more particularly to a superconducting wire in which a protective layer is formed on a superconducting material layer.

  In recent years, development of superconducting wires in which a superconducting layer is formed on a substrate has been underway. Among these, an oxide superconducting wire provided with a superconducting layer made of an oxide superconductor, which is a high-temperature superconductor having a transition temperature equal to or higher than the liquid nitrogen temperature, has attracted attention.

  As a structure of such an oxide superconducting wire, a structure in which a highly conductive protective layer made of Ag (silver) or an Ag alloy is formed on an oxide superconducting layer is widely known (for example, JP-A-2014-120383). Publication (refer patent document 1)). The protective layer functions as a bypass through which the current flowing through the oxide superconducting layer commutates when the oxide superconducting layer attempts to transition from the superconducting state to the normal conducting state. Note that Ag is used as a protective layer because the Ag layer has the property of impervious to oxygen at room temperature and permeate oxygen at high temperature. Therefore, when manufacturing an oxide superconducting wire, oxygen is passed through the Ag layer. This is because oxygen can be stably supplied to the oxide superconducting layer by performing oxygen annealing treatment in an atmosphere.

  On the other hand, since Ag is relatively expensive, it has been studied to further reduce the thickness of the protective layer containing Ag from the conventional thickness of about 2 to 10 μm. However, as described in Patent Document 1, when the protective layer containing Ag is thinned, when the protective layer is heated in the oxygen annealing treatment, Ag atoms locally aggregate on the surface of the superconducting layer and are isolated. It has been reported that a problem of becoming an aggregate of a plurality of dispersed Ag particles occurs. As a result, pinholes are formed in the protective layer and the oxide superconducting layer is exposed, so that the protection performance of the main surface of the oxide superconducting layer is deteriorated. Further, when oxygen escapes from the exposed portion, the crystal structure of the oxide superconducting layer may change, and the superconducting characteristics may deteriorate.

  Regarding such a defect, Patent Document 1 has found the knowledge that by smoothing the surface of the oxide superconducting layer, Ag aggregation in the process of oxygen annealing can be suppressed in the protective layer on the oxide superconducting layer. Yes. Specifically, in Patent Document 1, the arithmetic average roughness Ra (JIS B0601: 2001) of the surface of the oxide superconducting layer is set to 20 nm or less, or the maximum height Rz (JIS B0601: 2001) is set to 60 nm or less. Thus, it is shown that Ag aggregation can be suppressed even when the thickness of the protective layer is 50 to 2000 nm, which is thinner than the conventional one.

JP 2014-120383 A

  In Patent Document 1, an oxide superconducting layer is formed by a pulse laser deposition (PLD) method. In Patent Document 1, in order to keep the arithmetic average roughness and maximum height of the surface of the oxide superconducting layer within the above ranges, the temperature of the heating temperature of the substrate is increased and the film forming process is performed under the film forming conditions in the PLD method. The idea is to reduce the partial pressure of oxygen in the vacuum chamber.

  On the other hand, in the formation of an oxide superconducting layer using the PLD method, an attempt has been made to increase the thickness of the oxide superconducting layer in order to improve the critical current value (Ic). However, when the thickness of the oxide superconducting layer is increased, there is a problem that the crystallinity (crystal orientation) of the oxide superconducting layer is lowered. This is because, in the PLD method, the deposition material is normally deposited while heating the substrate from the surface (back surface) opposite to the surface (front surface) on which the film is formed. This is because the heating efficiency to the film-forming surface side decreases as the thickness increases.

  Such a problem can occur in Patent Document 1 as well. Therefore, in Patent Document 1, it is expected that the control of film forming conditions in the PLD method becomes more difficult as the thickness of the oxide superconducting layer is increased. As a result, as the oxide superconducting layer becomes thicker, it becomes difficult to form an oxide superconducting wire excellent in superconducting characteristics.

  An object of one embodiment of the present invention is to provide a superconducting wire in which a protective layer is formed on a superconducting material layer, and a configuration capable of easily realizing a thinner protective layer.

  A superconducting wire according to one embodiment of the present invention includes a substrate, a superconducting material layer formed on the substrate, and a protective layer formed on the superconducting material layer. The superconducting material layer has a plurality of convex portions on the surface facing the protective layer. The minimum interval between adjacent convex portions is 5 μm or less.

  According to the above, in the superconducting wire in which the protective layer is formed on the superconducting material layer, it is possible to easily realize the thinning of the protective layer.

It is a cross-sectional schematic diagram which shows the structure of the superconducting wire which concerns on embodiment of this invention. It is a schematic sectional drawing which shows a part of superconducting wire which concerns on this Embodiment. It is a schematic plan view which shows a part of superconducting wire which concerns on this Embodiment. It is a front view of the film-forming apparatus used for film-forming of the superconducting material layer concerning this Embodiment. It is a side view of the film-forming apparatus shown in FIG. 2 is an SEM image of a main surface of a superconducting material layer of Sample 1. 3 is a SEM image of a main surface of a superconducting material layer of Sample 2. 3 is a measurement result of a surface shape of a main surface of a superconducting material layer of Sample 1. FIG. 3 is a measurement result of a surface shape of a main surface of a superconducting material layer of Sample 2. FIG.

[Description of Embodiment of the Present Invention]
First, embodiments of the present invention will be listed and described.

  (1) A superconducting wire 10 according to one aspect of the present invention includes a substrate 1, a superconducting material layer 3 formed on the substrate 1, and a protective layer 4 formed on the superconducting material layer 3. The superconducting material layer 3 has a plurality of convex portions 20 on the surface facing the protective layer 4. The minimum interval between adjacent convex portions is 5 μm or less.

  As a result of intensive studies on a method for suppressing Ag aggregation in the course of oxygen annealing treatment, the present inventors have obtained the following knowledge and found the present invention.

  In the superconducting wire manufacturing process, a superconducting material layer is first formed on a substrate using a vapor phase method such as a PLD method, and then a protective layer is formed on the superconducting material layer and then oxygen annealing is performed in an oxygen atmosphere. Processing is performed. According to the study by the present inventors, when the superconducting material layer is formed, a large number of convex portions made of granular crystals are formed on the surface of the superconducting material layer. This convex portion becomes larger and larger as the thickness of the superconducting material layer increases. Then, the inventors increase the density of the convex portions on the surface of the superconducting material layer and reduce the minimum distance between the adjacent convex portions, so that Ag is locally present on the surface of the superconducting material layer during the oxygen annealing process. It was found that agglomeration can be suppressed.

  Furthermore, the present inventors have intensively studied to what extent the minimum distance between adjacent convex portions can be reduced to suppress Ag aggregation. As a result, it was found that Ag aggregation of the protective layer in the course of the oxygen annealing treatment can be suppressed by reducing the minimum distance between adjacent convex portions to 5 μm or less.

  Thereby, according to the superconducting wire according to one aspect of the present invention, even if the thickness of the protective layer is made thinner than the conventional one, the superconducting material layer is not exposed from the protective layer. Deterioration of superconducting characteristics can be prevented.

  Furthermore, according to the superconducting wire according to one aspect of the present invention, Ag aggregation can be suppressed if the minimum distance between adjacent convex portions is 5 μm or less. Therefore, it is not necessary to perform complicated control of the film forming conditions in order to improve the surface smoothness of the superconducting material layer, so that the protective layer can be easily made thinner.

  (2) Preferably, in the superconducting wire according to (1) above, the thickness of the superconducting material layer 3 is 1.5 μm or more. According to this, on the surface of the superconducting material layer 3, the minimum interval between adjacent convex portions can be set to 5 μm or less. Therefore, Ag aggregation of the protective layer during the oxygen annealing process can be suppressed.

  (3) Preferably, in the superconducting wire according to the above (1) or (2), the thickness of the protective layer 4 is 2 μm or less. Thereby, since the protective layer can be further reduced from the conventional thickness of about 2 to 10 μm, the superconducting wire can be reduced in price.

  (4) In the superconducting wire according to any one of (1) to (3), preferably, the protective layer 4 is made of silver (Ag) or an Ag alloy. According to this, in the superconducting wire provided with the protective layer containing Ag, the protective layer can be easily thinned, so that the superconducting wire can be made inexpensive.

[Details of the embodiment of the present invention]
Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the same or corresponding parts are denoted by the same reference numerals, and the description thereof will not be repeated.

<Configuration of superconducting wire>
FIG. 1 is a schematic cross-sectional view showing a configuration of a superconducting wire according to an embodiment of the present invention. FIG. 1 shows a cross section cut in a direction crossing the extending direction of the superconducting wire 10 according to the present embodiment. For this reason, the direction intersecting the paper surface is the longitudinal direction of the superconducting wire 10, and the superconducting current of the superconducting material layer 3 flows along the direction intersecting the paper surface. In addition, in the schematic cross-sectional view of FIG. 1, in order to make the drawing easier to see, the length in the vertical direction (hereinafter also referred to as “thickness direction”) and the horizontal direction (hereinafter also referred to as “width direction”) in the rectangular cross section. Although the difference in thickness is reduced, the length in the thickness direction of the cross section is actually sufficiently smaller than the length in the width direction. As shown in FIG. 1, the width direction of the superconducting wire 10 is the x-axis direction, the longitudinal direction is the y-axis direction, and the thickness direction is the z-axis direction.

  Referring to FIG. 1, superconducting wire 10 according to the present embodiment has an elongated shape (tape shape) having a rectangular cross section, and here, a relatively large surface extending in the longitudinal direction of the elongated shape. Is the main surface. Superconducting wire 10 includes substrate 1, intermediate layer 2, superconducting material layer 3, protective layer 4, and stabilization layer 6.

  The substrate 1 is preferably made of, for example, metal and has a long shape (tape shape) having a rectangular cross section. In order to wind around a coil, it is preferable that the board | substrate 1 is lengthened to about 2 km.

  The substrate 1 is more preferably an oriented metal substrate. The oriented metal substrate means a substrate having a uniform crystal orientation with respect to the biaxial direction in the plane of the substrate surface. Examples of the oriented metal substrate include Ni (nickel), Cu (copper), Cr (chromium), Mn (manganese), Co (cobalt), Fe (iron), Pd (palladium), Ag (silver), and Au ( An alloy composed of two or more metals among (gold) is preferably used. These metals can be laminated with other metals or alloys. For example, an alloy such as SUS, which is a high-strength material, can be used. In addition, the material of the board | substrate 1 is not specifically limited to this, For example, you may use materials other than a metal.

  The length of superconducting wire 10 in the width direction (x-axis direction in the figure) is, for example, about 4 mm to 10 mm. In order to increase the current density flowing in the superconducting wire 10, it is preferable that the cross-sectional area of the substrate 1 is small. However, if the thickness of the substrate 1 (in the y-axis direction in the figure) is made too thin, the strength of the substrate 1 may deteriorate. Therefore, the thickness of the substrate 1 is preferably about 0.1 mm, for example.

The intermediate layer 2 is formed on one main surface of the substrate 1. The superconducting material layer 3 is formed on the main surface of the intermediate layer 2 opposite to the main surface facing the substrate 1 (upper main surface in FIG. 1). The material constituting the intermediate layer 2 is preferably YSZ (yttria stabilized zirconia), CeO ₂ (cerium oxide), MgO (magnesium oxide), Y ₂ O ₃ (yttrium oxide), SrTiO ₃ (strontium titanate), or the like. . These materials have extremely low reactivity with the superconducting material layer 3 and do not deteriorate the superconducting characteristics of the superconducting material layer 3 even at the interface in contact with the superconducting material layer 3. In particular, when a metal is used as the material constituting the substrate 1, the difference in orientation between the substrate 1 having crystal orientation on the surface and the superconducting material layer 3 is relaxed, and the superconducting material layer 3 is formed at a high temperature. At this time, it can play a role of preventing the outflow of metal atoms from the substrate 1 to the superconducting material layer 3. In addition, the material which comprises the intermediate | middle layer 2 is not specifically limited to this.

  Moreover, the intermediate | middle layer 2 may be comprised by the some layer. When the intermediate layer 2 is composed of a plurality of layers, the layers constituting the intermediate layer 2 may be composed of different materials or parts of the same material.

The superconducting material layer 3 is a thin film layer through which a superconducting current flows in the superconducting wire 10. The superconducting material is not particularly limited. For example, it is preferable to use a RE-123 oxide superconductor. Note that the RE-123 series oxide superconductor is REBa ₂ Cu ₃ O _y (y is 6 to 8, more preferably 6.8 to 7, RE is a rare earth such as yttrium or Gd, Sm, or Ho. Means a superconductor expressed as). In order to improve the critical current value Ic, the thickness of the superconducting material layer 3 is preferably about 0.5 to 10 μm. Furthermore, in order to suppress Ag aggregation in the protective layer 4 covering the main surface of the superconducting material layer 3, the thickness of the superconducting material layer 3 is more preferably 1.5 μm or more. A suitable thickness of the superconducting material layer 3 will be described later.

  The protective layer 4 is formed on the main surface of the superconducting material layer 3 opposite to the main surface facing the intermediate layer 2 (upper main surface in FIG. 1). The protective layer 4 is made of Ag or an Ag alloy. The thickness of the protective layer 4 is preferably 2 μm or less, more preferably 0.05 μm or more and 2 μm or less.

  A laminate 5 is formed by the substrate 1, the intermediate layer 2, the superconducting material layer 3 and the protective layer 4 described above. A stabilization layer 6 is disposed so as to cover the periphery of the laminate 5. In the present embodiment, the stabilization layer 6 is disposed so as to cover the outer periphery of the stacked body 5, that is, to cover almost the entire outermost surface of the stacked body 5. However, the “periphery of the laminated body” of the present invention is not limited to the entire circumference, and may include at least the upper main surface and the side surface of the laminated body.

  The stabilization layer 6 is made of a foil or a plating layer of a highly conductive metal material. The stabilization layer 6 functions as a bypass along with the protective layer 4 when the superconducting material layer 3 transitions from the superconducting state to the normal conducting state. The stabilization layer 6 further has a function of protecting the stacked body 5 from external force and moisture. The material constituting the stabilization layer 6 is preferably, for example, Cu (copper) or Cu alloy. Although the thickness of the stabilization layer 6 is not specifically limited, It is preferable that it is 10 micrometers-500 micrometers from a viewpoint of protecting the protective layer 4 and the superconducting material layer 3 physically.

<Thinning of protective layer and its problems>
In the superconducting wire having the above-described configuration, it has been studied to further reduce the thickness of the protective layer containing Ag from the conventional thickness of about 2 to 10 μm from the viewpoint of cost reduction. However, on the other hand, when the thickness of the protective layer is reduced, Ag atoms locally aggregate on the surface of the superconducting material layer when the protective layer is heated in the oxygen annealing process performed after the protective layer is formed. A problem has been reported that an aggregate of a plurality of isolated and dispersed Ag particles is formed. Thereby, pinholes are formed in the protective layer and the superconducting material layer is exposed, so that the protection performance of the main surface of the superconducting material layer is lowered. Further, when oxygen escapes from the exposed portion, the crystal structure of the oxide superconducting layer may change, and the superconducting characteristics may deteriorate.

  The present inventors have obtained the following findings as a result of intensive studies on a method of suppressing Ag aggregation in the course of the oxygen annealing treatment.

  In the superconducting wire manufacturing process, first, a PLD method, a sputtering method, a metal organic chemical vapor deposition (MOCVD) method, a molecular beam epitaxy (MBE) method, etc. are applied on a substrate. A superconducting material layer is formed using a phase method, and after that, after forming a protective layer on the superconducting material layer, an oxygen annealing process is performed in an oxygen atmosphere. According to the study by the present inventors, when the superconducting material layer is formed, a large number of convex portions made of granular crystals are formed on the surface of the superconducting material layer. This convex portion becomes larger and larger as the thickness of the superconducting material layer increases. Then, the inventors increase the density of the convex portions on the surface of the superconducting material layer and reduce the minimum distance between the adjacent convex portions, so that Ag is locally present on the surface of the superconducting material layer during the oxygen annealing process. It was found that the agglomeration can be suppressed and the present invention has been completed.

<Overview>
Hereinafter, the detailed structure of the superconducting wire 10 according to the present embodiment will be described.

  FIG. 2 is a schematic cross-sectional view showing a part of superconducting wire 10 according to the present embodiment. FIG. 3 is a schematic plan view showing a part of superconducting wire 10 according to the present embodiment. FIG. 2 shows an enlarged cross-sectional structure near the superconducting material layer 3 in the superconducting wire 10. FIG. 3 shows an enlarged plan structure of the superconducting material layer 3 shown in FIG.

  2 and 3, a plurality of convex portions 20 are formed on the main surface (upper main surface in FIG. 1) of the superconducting material layer 3 opposite to the main surface facing the intermediate layer 2. Has been. The plurality of convex portions 20 are crystal grains formed when the superconducting material layer 3 is formed using a vapor phase method such as a PLD method.

  Crystal grains having various shapes, large and small, are formed on the main surface of the superconducting material layer 3. In the present embodiment, among the plurality of crystal grains, the height H from the main surface of the superconducting material layer 3 is 0.1 μm or more and the minimum width W is 0.1 μm or more. It will be defined as 20. Specifically, the height H of the convex portion 20 is measured by obtaining a difference in height between the height of the reference point and the height of the apex of the convex portion 20 using an arbitrary surface position of the superconducting material layer 3 as a reference point. The The height H of the convex portion 20 can be measured by, for example, an optical interference type surface shape measuring instrument or a stylus type surface shape measuring instrument (so-called step gauge).

  The minimum width W of the convex part 20 is the minimum width in the whole convex part 20 in planar view, as shown in FIG. The minimum width W of the convex portion 20 is measured by observing the main surface of the superconducting material layer 3 with, for example, a scanning electron microscope (SEM) or a transmission electron microscope (TEM). can do.

  The minimum distance L between adjacent convex portions corresponds to the shortest distance from one end surface of the adjacent convex portion 20 to the other end surface. The minimum distance L between the convex portions can be measured from, for example, an image (two-dimensional planar projection image) obtained with an electron microscope.

  On the main surface of the superconducting material layer 3, it is preferable that the minimum interval L between adjacent convex portions is narrow. As described above, since the plurality of convex portions 20 are provided close to each other on the main surface of the superconducting material layer 3, Ag aggregation in the course of the oxygen annealing treatment can be suppressed. Specifically, the minimum distance L between the convex portions is preferably 5 μm or less. It is considered that the Ag aggregation is suppressed because the convex portions 20 are arranged densely to prevent the movement of Ag atoms during heating. According to this, even when the thickness of the protective layer 4 is 2 μm or less, the superconducting material layer 3 is not exposed from the protective layer 4.

  As a countermeasure against Ag aggregation, the conventional technique takes an approach of smoothing the surface of the superconducting material layer (see Patent Document 1). Specifically, it has been proposed that the calculated average roughness Ra of the superconducting material layer is 20 nm or less, or the maximum height Rz is 60 nm or less. On the other hand, this embodiment suppresses Ag aggregation by narrowing the interval between the convex portions (crystal grains) formed on the surface of the superconducting material layer, and the surface smoothness of the superconducting material layer. This is different from the prior art in that it is not required. In other words, according to the present embodiment, even if the surface smoothness of the superconducting material layer is low, aggregation of Ag is suppressed if the minimum distance between adjacent convex portions is 5 μm or less. Therefore, it is not necessary to perform complicated control of the film forming conditions in order to improve the surface smoothness of the superconducting material layer, so that the protective layer can be easily made thinner.

  Here, the height H and the minimum width W of the protrusion 20 change in accordance with the film thickness T of the superconducting material layer 3. Therefore, the minimum distance L between adjacent convex portions also varies depending on the film thickness T of the superconducting material layer 3. Specifically, as the film thickness T of the superconducting material layer 3 is increased, the density of the protrusions 20 increases, thereby narrowing the minimum interval L between adjacent protrusions. In order to set the minimum distance L between adjacent convex portions to 5 μm or less, the film thickness T of the superconducting material layer 3 is preferably 1.5 μm or more. The upper limit value of the film thickness T is not particularly limited, but is preferably 10 μm or less in consideration of productivity.

<Method for manufacturing superconducting material layer>
Next, as a specific example of the method for manufacturing a superconducting material layer according to the present embodiment, a method for forming a superconducting material layer using the PLD method will be described as an example.

  FIG. 4 is a front view of a film forming apparatus used for forming a superconducting material layer according to the present embodiment. FIG. 5 is a side view of the film forming apparatus shown in FIG.

  4 and 5, the film forming apparatus according to the present embodiment includes a heater 22 for heating the back surface of the substrate W and a radiation plate 21 for heating the surface of the long substrate W. Prepare. The film forming apparatus further includes a deposition preventing plate 23 and a laser irradiation apparatus (not shown). The code | symbol T in FIG. 4 has shown the raw material target, and the code | symbol P has shown the laser plume. Further, the arrows in FIG. 5 indicate the transport direction of the substrate W.

  Note that the film forming apparatus is disposed in a chamber (not shown), and the atmospheric pressure and gas atmosphere in the chamber can be appropriately adjusted by supplying a predetermined gas into the chamber.

  As the substrate W on which the superconducting material layer is formed, a substrate formed of an oriented metal substrate on which an intermediate layer is formed is used. The heater 22 is wider than the substrate W and is disposed on the back side of the substrate W. Thereby, the substrate W can be uniformly heated in the width direction (y-axis direction) during film formation. The heater 22 is, for example, a lamp heater.

  The deposition preventing plate 23 is disposed between the heater 22 and the substrate W. The deposition preventing plate 23 prevents the deposited material from entering the substrate W and contaminating the heater 22.

  The two radiation plates 21 are arranged on the surface side of the substrate W so as to face the heater 22. Each of the radiation plates 21 is further arranged so as not to overlap the substrate W in a plan view of the surface of the substrate W. The two radiation plates 21 store the heat from the heater 22 and radiate the stored heat toward the film formation surface F of the substrate W, thereby heating the surface side of the substrate W. The radiation plate 21 is made of a material excellent in heat resistance and heat storage property, and for example, a stainless steel plate (SUS) is preferably used.

  As shown in FIG. 4, the two radiation plates 21 sandwich the substrate W in the width direction of the substrate W, and each have a predetermined inclination angle θ with respect to the direction perpendicular to the heater 22 around the film formation surface F. It is preferable that they are arranged in a state having (that is, a reverse C shape). Thus, by providing the radiation plate 21 with a predetermined inclination angle θ, the film formation surface F from the surface side of the substrate W can be efficiently heated. The inclination angle θ can be appropriately set in consideration of the structure of the entire apparatus, the line width of the substrate W, and the like, but it is generally preferable to set the inclination angle θ to about 25 to 50 ° with respect to the substrate 1.

  The raw material target T is a disk-shaped member disposed so as to face the film formation surface F of the substrate W. The raw material target T can be appropriately changed according to the type of the superconducting material layer formed on the substrate W. Superconducting material layers made of oxide superconducting materials require growth at high temperatures. According to the film forming apparatus of this embodiment, the oxide superconducting material layer can be particularly appropriately formed.

  The laser irradiation mechanism is arranged so that the surface of the raw material target T arranged so as to face the substrate W can be irradiated with laser light. A laser plume P is generated from the raw material target T by the irradiation of the laser beam. For example, an excimer laser is preferably used as the laser light. The laser light is incident on the surface of the raw material target T at an angle of 25 to 50 °.

Next, a method for forming a superconducting material layer using the film forming apparatus will be described.
First, the raw material target T is disposed so as to face the film formation surface F of the substrate W, and the inside of the chamber is set to an oxygen gas atmosphere of about 10 to 70 Pa. Then, a long substrate W having a length of several kilometers is conveyed at a predetermined speed between a supply reel and a take-up reel (both not shown).

  Next, the heater 22 is operated at a predetermined set temperature to heat the back side of the substrate W. The set temperature of the heater 22 is set, for example, to be about 1000 to 1500 ° C. at the heater internal temperature. At this time, heat that has not been irradiated to the back side of the substrate W is irradiated to the radiation plate 21 and accumulated. The heat accumulated in the radiation plate 21 is radiated toward the surface side of the substrate W to heat the film formation surface F.

  Subsequently, a laser plume P is generated by irradiating the raw material target T with laser light. Thus, the superconducting material sublimated from the raw material target T is attached to the surface of the substrate W, and a superconducting material layer is formed on the film formation surface F.

  According to the method of manufacturing a superconducting material layer according to the present embodiment, even if the heating efficiency from the back side of the substrate W is reduced due to the progress of film formation and the increase in the thickness of the superconducting material layer, the radiation is reduced. The film formation surface F of the substrate W is appropriately heated by the plate 21. Thereby, even if the film thickness is increased, a superconducting material layer with little variation in the surface state of the superconducting material layer can be formed.

  That is, by heating from the surface of the substrate W as well, the film formation surface F is sufficiently heated to suppress a decrease in heating efficiency to the film formation surface F accompanying the increase in the thickness of the superconducting material layer. Can do. As a result, it is possible to accurately manufacture the superconducting material layer in which the minimum distance L between the convex portions on the surface is controlled to 5 μm or less. As a result, Ag aggregation in the process of oxygen annealing can be reliably suppressed in the protective layer on the superconducting material layer.

  Furthermore, according to this embodiment, since the control of the film forming conditions does not become complicated even if the thickness of the superconducting material layer is increased, it is possible to easily realize a thin protective layer. Become.

  Hereinafter, although this Embodiment is described in detail using an Example, this Embodiment is not limited to this.

<Deposition of superconducting material layer>
A superconducting material layer is formed on the substrate W by the above-described superconducting material layer manufacturing method, the main surface of the superconducting material layer is observed using an SEM, and the surface shape of the main surface is measured using a stylus profilometer. It was measured.

As the substrate W (FIG. 4), an intermediate layer of a three-layer structure formed in the order of CeO ₂ / YSZ / CeO ₂ on a clad type metal substrate made of Ni—W alloy base material, SUS or the like as a base metal. An alignment substrate on which is formed is used.

On the film-forming surface F of the substrate W, the atmosphere in the chamber is set to an oxygen gas atmosphere of 16 Pa, and the heating temperature by the heater 22 is set to 800 to 950 ° C., so that GdBCO (GdBa ₂ Cu ₃ O _7-x A superconducting material layer was formed.

  At this time, in Sample 1, a superconducting material layer having a thickness of 0.94 μm was formed by performing film formation eight times at a predetermined repetition rate. On the other hand, in sample 2, a superconducting material layer having a film thickness of 3.4 μm was formed by performing film formation 30 times at the same repetition frequency as in sample 1.

  Next, in each of Samples 1 and 2, an Ag protective layer having a thickness of 2 μm was formed on the superconducting material layer by sputtering, and oxygen annealed in an oxygen atmosphere at a maximum temperature of 650 ° C. for 12 hours to obtain a laminate. Got.

<Evaluation>
1. SEM Observation In each sample, the main surface of the superconducting material layer was observed using a scanning electron microscope (SEM). FIG. 6 is a photograph of the main surface of the superconducting material layer of Sample 1 observed by SEM. FIG. 7 is a photograph of the main surface of the superconducting material layer of Sample 2 observed by SEM. 6 (a) and 7 (a) are photographs obtained by photographing the main surface of the superconducting material layer of the corresponding sample at a magnification of 5000 times, and FIGS. 6 (b) and 7 (b) correspond. It is the photograph which image | photographed the main surface of the superconducting material layer of the sample at 20000 times the magnification.

  In Sample 1, crystal grains having a size of about several μm are formed on the main surface of the superconducting material layer. On the other hand, in sample 2, crystal grains having a size of several tens of μm are formed. As the film thickness of the superconducting material layer increases, the size of the crystal grains formed on the main surface of the superconducting material layer increases and the number increases. Therefore, it can be seen that as the film thickness of the superconducting material layer increases, the interval between adjacent crystal grains becomes narrower.

2. Measurement of surface shape of main surface In each sample, the surface shape of the main surface of the superconducting material layer was measured. The measurement is performed using a stylus surface shape measuring instrument (device name: DEKTAK 3030, manufactured by Bruker Nano) on the main surface of the superconducting material layer in the longitudinal direction (y-axis direction) and the width direction (y-axis direction) within a range of 100 μm square. This was performed by tracing in the x-axis direction).

  FIG. 8 shows the measurement result (roughness curve) of Sample 1, and FIG. 9 shows the measurement result of Sample 2. 8A and 9A show the surface shape in the longitudinal direction of the main surface of the superconducting material layer of the corresponding sample, and FIGS. 8B and 9B show the superconductivity of the corresponding sample. The surface shape in the width direction of the main surface of a material layer is shown.

  In each of Sample 1 and Sample 2, irregularities appear on the surface by forming a plurality of crystal grains on the main surface of the superconducting material layer. Sample 1 has a height difference of about 0.4 μm at the maximum, whereas sample 2 has a maximum height difference of about 0.8 μm, which is almost twice as large as that of sample 1.

  As shown in FIGS. 2 and 3, in the present embodiment, among the plurality of crystal grains, the height from the main surface of the superconducting material layer is 0.1 μm or more, and the minimum width is 0.2 mm. The thing of 1 micrometer or more is defined as a convex part. If a convex part is extracted from the measurement result of each sample based on this, in sample 1, the part where the space between adjacent convex parts exceeds 10 μm is included. On the other hand, in sample 2, the interval between the adjacent convex portions is within 5 μm. When the surface of the laminated body after the oxygen annealing was observed, it was confirmed in Sample 1 that Ag of the protective layer was locally aggregated and a portion where the superconducting material layer was exposed was formed. On the other hand, in sample 2, Ag aggregation of the protective layer was suppressed, and it was confirmed that the superconducting material layer was not exposed.

  The embodiments and examples disclosed herein are illustrative in all respects and should not be construed as being restrictive. The scope of the present invention is shown not by the embodiments and examples described above but by the scope of claims, and is intended to include meanings equivalent to the scope of claims and all modifications within the scope.

DESCRIPTION OF SYMBOLS 1 Substrate 2 Intermediate layer 3 Superconducting material layer 4 Protective layer 5 Laminate 6 Stabilization layer 10 Superconducting wire 20 Convex part 21 Radiation plate 22 Heater 23 Depositing plate W Substrate T Raw material target P Laser plume

Claims (4)

A substrate,
A superconducting material layer formed on the substrate;
A protective layer formed on the superconducting material layer,
The superconducting material layer has a plurality of convex portions on the surface facing the protective layer,
A superconducting wire in which a minimum interval between adjacent convex portions is 5 μm or less.   The superconducting wire according to claim 1, wherein the superconducting material layer has a thickness of 1.5 μm or more.   The superconducting wire according to claim 1, wherein the protective layer has a thickness of 2 μm or less.   The superconducting wire according to any one of claims 1 to 3, wherein the protective layer is made of silver or a silver alloy.