Patent Application
20090260851
The present invention relates to a superconductive thin film material and a manufacturing method of the superconductive thin film material, and for example to a superconductive thin film material which is superior in superconductivity and a manufacturing method of the superconductive thin film material.
Conventionally, as shown in
Above-mentioned Patent Document 1 discloses a method in which an intermediate layer is formed on a substrate with a crystal orientation on its surface, followed by a superconductive layer further formed thereon, in order to improve the orientation of the superconductive layer.
However, with the oriented polycrystalline base material disclosed in above-mentioned Patent Document 1, an element diffusion reaction may occur, i.e., constituent elements of the superconductive layer may diffuse out to the substrate side while constituent elements of the substrate may diffuse out to the superconductive layer side, because the superconductive layer is deposited by utilizing a thermal reaction. When the constituent elements of the substrate reach the superconductive layer beyond the intermediate layer, they tend to react with the superconducting elements of which the superconductive layer is composed, leading to a problem of lower superconductivity.
Hence the present invention was made to solve the above problem, and an object of the present invention is to provide a superconductive thin film material achieving superior superconductivity by preventing the element diffusion reaction and a manufacturing method of such a superconductive thin film material.
The inventors found out that the thickness of the intermediate layer accounts for the problem of developing the element diffusion reaction in the superconductive thin film material. The constituent elements of the substrate reach the superconductive layer beyond the intermediate layer to cause the problem of the element diffusion reaction therebetween if the intermediate layer has an insufficient thickness. The inventors have worked out wholeheartedly to prevent such an element diffusion reaction and consequently found out the film thickness of the intermediate layer required to prevent the element diffusion reaction.
The superconductive thin film material according to the present invention is provided with a substrate, an intermediate layer, and a superconductive layer. One or at least two layers constitute the intermediate layer, formed on the substrate, with a thickness of not less than 0.4 μm. The superconductive layer is formed on the intermediate layer.
According to the superconductive thin film material of the present invention, the element diffusion between the substrate and the superconductive layer can be prevented by providing the intermediate layer of not less than 0.4 μm in thickness. Thus the degradation of superconductivity of the formed superconductive layer can be prevented, making it possible to provide the superconductive thin film material with good superconductivity.
A material for forming the intermediate layer in the above-mentioned superconductive thin film material is preferably an oxide having a crystal structure which is at least one of a halite type, a fluorite type, a perovskite type, and a pyrochlore type.
These material for the intermediate layer tend to develop less element diffusion reactions with the superconductive layer, even if the intermediate layer is in contact with the superconductive layer, because they have very low reactivity with a superconductive layer.
Preferably, the material for forming the substrate in the above-mentioned superconductive thin film material is an oriented metal while the material for forming the intermediate layer includes at least one of yttria-stabilized zirconia, cerium oxide, magnesium oxide, and strontium titanate.
Thus the element diffusion reaction between the substrate and the superconductive layer can be suppressed when an oriented metal with excellent property is used for a substrate.
A manufacturing method of a superconductive thin film material according to the present invention is directed to a method of manufacturing the above-mentioned superconductive thin film including the steps of preparing a substrate, forming an intermediate layer constituted of one layer or at least two layers on the substrate, and forming a superconductive layer. In the step of forming the superconductive layer, the superconductive layer is formed on the intermediate layer by at least one of vapor and liquid deposition methods.
According to the manufacturing method of the superconductive thin film material of the present invention, the superconductive layer with its surface being excellent in the crystal orientation as well as smoothness can be formed in the step of forming the superconductive layer. Therefore, the superconductive thin film material with good superconductivity showing a large critical current value and large critical current density can be manufactured.
According to the superconductive thin film material of the present invention, providing an intermediate layer of not less than 0.4 μm in thickness, which is sufficient to prevent an element diffusion reaction, achieves superior superconductivity.
10 superconductive thin film material, 11 substrate, 12 intermediate layer, 12a first layer, 12b second layer, 12c third layer, 13 superconductive layer.
An embodiment of the present invention will be described hereinafter with reference to the drawings. The same or corresponding elements have the same reference characters allotted. Their label and function are also identical. Therefore, detailed description thereof will not be repeated.
As shown in
More specifically, the material forming substrate 11 is preferably metal. More preferably, substrate 11 is an oriented metal substrate. Note that an oriented metal substrate means a substrate in which the crystal orientation is uniform with respect to biaxial directions within the plane on the substrate surface. An alloy which is composed of two or more metals among the following, for example, may be suitably used as an oriented metal substrate: Ni (nickel), Cr (chromium), Mn (manganese), Co (cobalt), Fe (iron), Pd (palladium), Cu (copper), Ag (silver) and Au (gold). Such metals can also be laminated with other metals or alloys. For example alloys such as SUS, which is a high-strength material, can also be used. Note that the material of substrate 11 is not particularly limited to the above and materials other than metal, for example, may be used as well.
Substrate 11 may be 50-200 μm thick and have a lengthy belt-like shape.
A thickness x of intermediate layer 12 is not less than 0.4 μm. Thickness x is preferably not less than 0.8 μm, more preferably not less than 1.1 μm. If a thickness y of intermediate layer 102 is as small as in the conventional superconductive thin film material 100 shown in
The material for forming intermediate layer 12 is preferably an oxide having a crystal structure which is at least one of a halite type, a fluorite type, a perovskite type, and a pyrochlore type. Examples of the oxide that has such a crystal structure include: rare earth element oxides such as cerium oxide (CeO2), holmium oxide (Ho2O3), yttrium oxide (Y2O3), and ytterbium oxide (Yb2O3); yttria-stabilized zirconia (YSZ); magnesium oxide (MgO); strontium titanate (SrTiO3); BZO (BaZrO3); aluminum oxide (Al2O3); and Ln-M-O compound (Ln is one or more lanthanoid elements, M is one or more element chosen from Sr, Zr, and Ga, and O is oxygen). In particular, yttria-stabilized zirconia (YSZ), cerium oxide (CeO2), magnesium oxide (MgO), strontium titanate (SrTiO3) and the like may be suitably used as a material for forming intermediate layer 12 from a viewpoint of the crystal constant and crystal orientation. These materials have very low reactivity with superconductive layer 13 such that they do not degrade superconductivity of superconductive layer 13 even at the interface at which the intermediate layer 12 with these materials contacts with superconductive layer 13. In particular, in the case where metal is used as a material for forming substrate 11, the difference between substrate 11 which has a crystal orientation on its surface and superconductive layer 13 is reduced and the metal atoms are prevented from outflowing from substrate 11, which is composed of oriented metal with a crystal orientation on its surface, to superconductive layer 13, when superconductive layer 13 is formed at a high temperature. Note that the material for forming intermediate layer 12 is not limited to the above-mentioned material.
Moreover, intermediate layer 12 has preferably a good crystal orientation. The above-mentioned materials are examples of such materials which have a good crystal orientation.
Intermediate layer 12 may be constituted of a plurality of layers as shown in
When intermediate layer 12 is constituted of a plurality of layers, each layer constituting intermediate layer 12 may be formed from different materials. For example as shown in
Intermediate layer 12 is not particularly limited as above, but may be of any number of layers, for example two, not less than four, or one layer as shown in
Note that the lattice mismatching rate between intermediate layer 12 and superconductive layer 13 is preferably not more than 10%, and the lattice mismatching rate between intermediate layer 12 and substrate 11 is not more than 10%.
It is preferred that the surface of intermediate layer 12 on which superconductive layer 13 is formed is flat. For example, intermediate layer 12 has preferably surface roughness of 10 nm or less.
Although the material for forming superconductive layer 13 is not particularly limited, it is preferable to use for example an RE-123 superconductor. Note that the RE-123 superconductor refers to a superconductor expressed as REBa2Cu3Oy (y is between 6 and 8, more preferably approximately 7, RE is a rare earth element such as yttrium, Gd, Sm, or Ho). Thus forming intermediate layer 12 and superconductive layer 13 on substrate 11, which is composed of a flexible metal, can achieve the superconductive thin film material which shows a large critical current value and critical current density. The thickness of superconductive layer 13 may be for example between 0.2 μm and 5 μm.
When using the superconductive thin film material for example as a superconducting wire material, Ag (silver) stabilized layer or Cu (copper) stabilized layer may be formed on superconductive layer 13 as a surface protecting layer or a stabilized layer (not shown) in order to protect the surface of superconductive layer 13.
Now with reference to
As shown in
Subsequently, a step of forming intermediate layer 12 (S20) is performed. At this step (S20), intermediate layer 12 is formed on prepared substrate 11 so that its thickness is not less than 0.4 μm. The oxide which has a crystal structure such as a halite type, fluorite type, perovskite type and pyrochlore type, for example, can be used as intermediate layer 12. At the step (S20), any deposition method such as a physical deposition method including a pulsed laser deposition method (PLD method) and the like, can be used.
Note that at the step (S20), first layer 12a is formed on substrate 11 for example by the physical deposition method, second layer 12b is formed on first layer 12a for example by the physical deposition method, and third layer 12c is formed on second layer 12b for example by the physical deposition method, in the same way as described above, even when intermediate layer 12 is constituted of multiple layers as shown in
Next, a step of forming superconductive layer 13 on the surface of intermediate layer 12 is performed (S30). At this step (S30), superconductive layer 13 is formed by either vapor or liquid deposition method.
Specifically, the laser deposition method, the sputtering method, the electron beam deposition method and the like may be mentioned, for example, as the vapor deposition method. The organic metal deposition method and the like, for example, are mentioned as the liquid deposition method. If superconductive layer 13 is formed by at least one of the laser deposition method, the sputtering method, the electron beam method, and organic metal deposition method, the layer can be provided with the surface with the superior crystal orientation as well as smoothness.
In the step (S30), in forming superconductive layer 13, a temperature from 600° C. to 900° C. is preferably set. Even when superconductive layer 13 is thus formed under such a high temperature, the atomic diffusion reaction is hardly generated between superconductive layer 13 and substrate 11, because intermediate layer 12 is sufficiently thick.
Note that a planarization step of planarizing the surfaces of substrate 11, intermediate layer 12 and superconductive layer 13 may be performed following steps (S10, 20, 30). The planarization step can be carried out by any method such as CMP (Chemical Mechanical Polishing) method, wet etching method, mechanical polishing method, and the like.
Superconductive thin film material 10 can be manufactured by carrying out steps (S10-S30) described above.
Moreover, when using the superconductive thin film material as a superconducting wire material, for example, another step of forming a surface protecting layer (not shown) on the surface of superconductive layer 13 may be further provided. At this step, for example, a surface protecting layer, which is an Ag stabilized layer, is formed on superconductive layer 13.
Superconductive thin film material 10 according to the embodiment of the present invention prevents the element diffusion reaction in which the constituent elements of substrate 11 move towards superconductive layer 13 and the constituent elements of superconductive layer 13 move towards substrate 11, because intermediate layer 12 has a thickness of not less than 0.4 μm, as described above. Moreover, superconductive thin film material 10 according to the embodiment serves to provide a good crystal orientation as well as to prevent the element diffusion reaction. Thus, superconductive thin film material 10 can achieve excellent superconductivity because the property of superconductive layer 13 is not degraded.
The following experiments were conducted in order to confirm the effect of the superconductive thin film material according to the present invention. That is, the superconductive thin film materials with the intermediate layer of thickness shown in Table 1 according to examples 1-3 and comparative examples 1 and 2 were prepared and their critical current values were measured. The film thickness of the intermediate layer of each superconductive thin film material and the measured value of the critical current are shown in Table 1.
In example 1, the superconductive thin film material was manufactured basically according to the manufacturing method of the above-mentioned embodiment. Specifically, a Ni alloy substrate was first prepared at the step of preparing a substrate (S10). Then at the step of forming an intermediate layer (S20), the intermediate layer composed of metal oxide was formed on the substrate by the vapor deposition method. Specifically, the intermediate layer was constituted of three layers and cerium oxide was formed to a thickness of 0.1 μm as a seed crystal layer (a first layer) for growing crystals on the substrate. Then YSZ was formed to a thickness of 0.2 μm as a diffusion preventing layer (a second layer) on the seed crystal layer, and cerium oxide was formed to a thickness of 0.1 μm as a lattice matching layer (a third layer). Then at the step of forming a superconductive layer (S30), HoBa2Cu3Ox (HoBCO) was deposited as a superconductive layer by the laser deposition method so that it has a film thickness of 0.8 μm. The superconductive thin film material according to example 1 was thus obtained.
Note that the film thickness of the intermediate layer in Table 1 shows the total thickness of the first, second and third layers.
The superconductive thin film material in example 2 was basically provided with the same structure as in example 1 except that the intermediate layer in example 2 had a film thickness of 0.8 μm. Specifically, the intermediate layer of the superconductive thin film material in example 2 had the seed crystal layer (first layer) of 0.1 μm thick, the diffusion preventing layer (second layer) of 0.6 μm thick, and the lattice matching layer (third layer) of 0.1 μm thick.
The superconductive thin film material in example 3 was basically provided with the same structure as in example 1 except that the intermediate layer in example 3 had a film thickness of 1.1 μm. Specifically, the intermediate layer of the superconductive thin film material in example 3 had the seed crystal layer (first layer) of 0.1 μm thick, the diffusion preventing layer (second layer) of 0.9 μm thick, and the lattice matching layer (third layer) of 0.1 μm thick.
The superconductive thin film material in comparative example 1 was basically provided with the same structure as in example 1 except that the thickness of the intermediate layer in comparative example 1 had a film thickness of 0.2 μm. Specifically, the intermediate layer of the superconductive thin film material in comparative example 1 had the seed crystal layer (first layer) of 0.1 μm thick, the diffusion preventing layer (second layer) of 0 μm thick and the lattice matching layer (third layer) of 0.1 μm thick.
The superconductive thin film material in comparative example 2 was basically provided with the same structure as in example 1 except that the intermediate layer in comparative example 2 had a film thickness of 0.3 μm. Specifically, the intermediate layer of the superconductive thin film material in comparative example 2 had the seed crystal layer (first layer) of 0.1 μm thick, the diffusion preventing layer (second layer) of 0.1 μm thick and the lattice matching layer (third layer) of 0.1 μm thick.
(Measurement Result)
The results of measurement, as described above, of the critical current values for the superconductive thin film material in examples 1-3 and comparative examples 1 and 2 are presented in
As shown in Table 1 and in
According to the examples of the present invention, it was found that the superconductive thin film material of the present invention could improve the superconductive layer properties such as the critical current value by making the intermediate layer not less than 0.4 μm in thickness.
The embodiments and examples disclosed herein should not be taken by way of limitation but illustrative in all respects. It is intended that the scope of the present invention be expressed by the terms of the appended claims, rather than by the above-mentioned description, and all the modifications within the meaning and scope of the claims and their equivalents be included.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-139262 | May 2006 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2007/058656 | 4/20/2007 | WO | 00 | 10/30/2008 |
