JPH02260672A - Superconductive member - Google Patents

Abstract

PURPOSE:To enhance a critical current and its density by a method wherein an oxide superconductor oriented layer, an oxide superconductor layer, and a normal conductor layer are successively formed in lamination on a base to form a laminated unit, and a superconductive member of this design is composed of two or more laminated units. CONSTITUTION:An oxide superconductor oriented layer 2 is formed on a base 1, an oxide superconductor layer 3 is deposited thereon, and a normal conductor layer 4 which functions as the pinning center of the superconductor layer 3 is formed thereon to form a superconductive member 5. The layer 4 is formed on a metal thin film of Fe, Ni, Co, Ag, Au, Pt, Pd, Mo, Ta, W, or the like or ally thin film of them. On the other hand, a unit is formed of a three-layered laminated body of the layers 2-4 and two or more units are successively stacked up to constitute a superconductive member 11. The oxide superconductor layers 3 separated by the layers 2 and 4 serve as current paths separately.

Description

Detailed Description of the Invention [Object of the Invention] (Industrial Application Field) The present invention relates to a superconducting member using an oxide superconductor.

(Prior art) Since it was announced in 1986 that Ba-La-Cu-0-based layered perovskite oxides have a high critical temperature of over 40, oxide-based superconductors have attracted attention. , research in the search for new materials is being actively conducted.

Among them, defective perovskite-type oxide superconductors represented by the Y-Ba-Cu-0 system, which have a high critical temperature higher than the liquid nitrogen temperature, the B1-3r-Ca-Cu-0 system and the Tl-Ba- Ca-Cu-0-based oxide superconductors have important industrial value because inexpensive liquid nitrogen can be used as a coolant instead of expensive liquid helium. Research into these applications is also being actively conducted, and a large number of applications are being considered, including ultra-high-speed superconducting devices, SQUID sensors, superconducting wiring, superconducting coils, and power transmission lines.

For example, if superconductors are used as wiring for various electronic devices, signal delays caused by the wiring will be reduced, making it possible to speed up signal processing or calculations. When considering the application of oxide superconductors to such superconducting wiring, it is advantageous to use a thin film whose critical current density is one order of magnitude higher than that of a bulk material. Oxide superconductor thin films with such excellent superconducting properties are achieved by using single crystal substrates such as MgO and 5rTiJ, which have similar coefficients of thermal expansion and lattice constants to those of oxide superconductors, as substrates. By using oriented oxide superconductor thin films formed on these single crystal substrates by sputtering, vapor deposition, etc., it has become possible to obtain critical current densities exceeding 10'' A/+j.

In addition, attempts have been made to form oxide superconductor thin films on bendable metal tapes, etc., and by taking advantage of this property that they can be easily bent, they can be used for superconducting coils. Attempts have also been made to make wire rods.

By the way, as mentioned above, it is known that the critical current density of an oxide superconductor thin film is more than an order of magnitude higher than that of a bulk material, but this is just a current density. However, the critical current does not necessarily increase in proportion to it, but remains at a certain value. This is considered to be due to the skin effect that occurs even in the superconducting state. However, the maximum current required for the wiring actually exceeds the critical current value of the oxide superconductor thin film. ' Therefore, in order to flow a sufficient current, a superconducting interconnection has been proposed in which boundaries are provided between oxide superconductor layers using a normal conductive material or an insulator to form multiple current paths (Japanese Patent Laid-Open No. 6
4-3908, 64-28844, etc.).

In addition, as a method to improve the critical current density of an oxide superconductor, a ferromagnetic metal layer is interposed between the oxide superconductor layers as a pinning center, and multiple current paths are provided to improve the maximum current and reduce the magnetic flux. It has been proposed to improve the critical current density by suppressing the invasion (see Japanese Patent Application Laid-open No. 318014/1983, etc.).

(Problem to be solved by the invention) It is known that the critical current density of an oxide superconductor can be improved by aligning the crystal orientation in a certain direction. However, in the above-mentioned multilayer structure of oxide superconductors with a normal conducting material layer or insulating layer interposed, each oxide superconducting layer is placed on a normal conducting material layer or an insulating layer. This makes it difficult to control the crystal orientation of the oxide superconductor, which is expected to reduce the critical current density of each oxide superconductor layer itself. There was a problem in that the effect of intervening the center could not be fully utilized.

The present invention has been made to address the problems of the prior art, and aims to improve the critical current value obtained by providing multiple current paths and the critical current density by introducing a pinning center. The purpose of this invention is to provide a superconducting member that is fully utilized by maintaining the orientation of the physical superconductor layer.

[Structure of the Invention] (Means for Solving the Problems) That is, the superconducting member of the present invention is a superconducting member in which a superconducting conductor layer containing a substance exhibiting superconducting transition is formed on a base, wherein the superconducting conductor layer is oxidized. It is characterized by being composed of a laminated unit consisting of an oriented layer of a physical superconductor, an oxide superconductor layer formed on this oriented layer, and a normal conductive material layer formed on this oxide superconductor layer. In particular, it is characterized in that a plurality of laminated units are formed in order in the thickness direction.

(Function) In the superconducting member of the present invention, the superconducting conductor layer is composed of an orientation layer of an oxide superconductor made of MgO, 5rTj01, etc./an oxide superconductor layer/a normal conductive material layer as one laminated unit. The crystal orientation of the oxide superconductor layer is always constant due to the presence of the orientation layer. Further, the normal conductive material layer formed on the oxide superconductor layer functions as a pinning center, and suppresses the intrusion of magnetic flux lines into the inside of the oxide superconductor.

These can improve superconducting properties such as critical current density. By sequentially laminating a plurality of the above laminated units, each oxide superconductor layer whose crystal orientation is aligned due to the presence of the orientation layer acts as a current path, and the superconductor layer flows in proportion to the number of units. The maximum current that can flow increases.

(Example) Next, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view showing the structure of a superconducting member according to an embodiment of the present invention. In the same figure, 1 is an St single crystal substrate, an Mg
O5SrTi03, Al103, Y stabilized Zr0z
The substrate is made of various materials and shapes such as oxide substrates such as (YSZ) and metal tapes, and on this substrate 1 is an alignment layer 2 of an oxide superconductor layer with a thickness of about 10 to 3000 layers.
is formed. This alignment layer 2 is made of, for example, MgO,
5rT103, A1203, Y-stabilized Zr02 (YS
Z), etc., and a material with a lattice constant and thermal expansion coefficient similar to those of the oxide superconductor is used, which aligns the crystal orientation of the oxide superconductor layer formed on the orientation layer in a certain direction. , which ensures the superconducting properties inherent to oxide superconductors. Note that the alignment layer 2 is used as the substrate 1.
If the same material is used, the formation of this first alignment layer can be omitted.

An oxide superconductor layer 3 having a thickness of about 500 to 5μ is formed on the alignment layer 2F, and examples of this oxide superconductor include perovskite-type oxide superconductors containing rare earth elements, 3r-Ca-Cu-0 based oxide superconductor, Tl-Ba-Ca-Cu-0 based oxide superconductor, etc. are applied.

The oxide superconductor containing a rare earth element and having a perovskite structure may be one that can realize a superconducting state, for example, REMCuO-based 237-δ (RE is Y s LaS ScS Nd,
Ss, Eu% Gd, Dy,, Ho5Ers
At least one element selected from rare earth elements such as Tm, Yb, and Lu, at least 18 elements selected from old tBaSSr and Ca, δ represents an oxygen defect, usually a number of 1 or less, and a part of Cu. is TI, vSCrs M
11%Can be replaced with Fe, Co, old, Zn, etc. ) are exemplified. Note that rare earth elements are defined in a broad sense and include 5cSY and La-based elements.

In addition, the B1-8r-Ca-Cu-0-based oxide superconductor has the chemical formula: Bi25r2Ca2 Cu30x
・-(1): B12 (Sr, Ca) 3cu20x
-(II) (in the formula, a part of Bl can be replaced with pb etc.), and is represented by TI-Ha-Ca-C
The u-0 based oxide superconductor has the chemical formula: T12 Ba2 Ca2 Cu30x
=---(m): T12(Ba, Ca)3Cu20x
.;...(IV) etc.

A normal conducting material layer 4 functioning as a pinning center for the oxide superconductor is formed on the oxide superconductor layer 3 to constitute a superconducting member 5. The normal conductive material layer 4 which becomes this pinning center is composed of Pe5Ni, Co5
Ag5Au-Pt5Pd%No, Ta.

Each metal thin film such as V and these alloy thin films can be made to a thickness of 50 people or more.
It was formed to a thickness of about 2,000 people.

The superconducting member 5 of this embodiment having the above-mentioned configuration is manufactured, for example, as follows.

First, the alignment layer 2 is formed on the surface of the substrate 1 by sputtering, CVD, or
It is formed by ion cluster beam evaporation method, molecular beam epitaxy method, etc. In particular, a thin film with good crystallinity can be obtained by ion cluster beam evaporation.

Next, an oxide superconductor layer 3 is similarly formed on the alignment layer 2 by a sputtering method, a CVD method, an ion cluster beam evaporation method, or the like.

For example, when forming the oxide superconductor layer 3 by sputtering, the target may be a sintered body of each oxide superconductor, or a compound containing the constituent elements of the oxide superconductor may be used individually. Good too. When using a sintered body of oxide superconductor as a target, the composition of the obtained film and the target composition may not necessarily match.
It is preferable to analyze the obtained film and make the target contain more of the missing element, or to further install a target containing the missing element and control it independently. Note that when forming the oxide superconductor layer 3 by sputtering, heat treatment may be performed while introducing oxygen in a vacuum chamber as necessary, or oxygen may be removed by heat treatment in an oxygen stream after removal from the vacuum chamber. A high-quality film with fewer defects can be obtained, and the transition temperature can be improved.

Further, in the ion cluster beam evaporation method, raw materials containing each constituent element are individually heated and evaporated to be deposited, and the composition can be controlled for each element. Also,
Unlike normal vapor deposition methods, after the evaporated atoms fly out of the nozzle, they are rapidly cooled by adiabatic expansion, aggregate to form clusters, and are further ionized and accelerated, which reduces the migration effect on the deposition surface. It has the advantage that significantly larger and more oriented films can be obtained at relatively low temperatures compared to other methods. However, when forming a thin film of an oxide, the melting point of the oxide is generally high and it is difficult to evaporate the oxide itself, so each element is evaporated in an oxygen atmosphere and the film is formed without reacting. Therefore, the method of supplying oxygen is an important factor. Oxygen can be supplied by being ionized by electron cyclotron resonance (P, CR), by forming oxygen radicals by high frequency, microwave, light, etc., or by heating and activating.
It is preferable to supply oxygen in an active state, which provides a greater effect than simply spraying oxygen onto the surface to be deposited. In addition to oxygen, it is also effective to convert oxygen into ozone using silent discharge. Furthermore, oxygen-containing gases such as N20 and Go have weak bonding energy with other atoms, and can more easily form oxygen radicals by electric discharge such as high-frequency electric power than from molecular oxygen.

Thereafter, a normal conductive material layer 4 is similarly formed on the oxide superconductor layer 3 by sputtering, vacuum evaporation, ion cluster beam evaporation, etc., thereby obtaining the superconducting member 5 shown in FIG. .

Next, an example in which a superconducting member was specifically manufactured according to the above manufacturing method will be described.

Example 1 First, an Sl single crystal substrate was set in a substrate holder equipped with a heating mechanism placed in a vacuum container, and a 5rT1
03 was placed as a target. Then, Ar gas and 02 gas were added to the vacuum container at 108ec! 4, and the inside of the vacuum container is lXl0-"T.

After reducing the pressure to rr pressure, sputtering was performed by supplying R1 force of lkV to the target while heating the Sl single crystal substrate to 450'C, and sputtering was performed to form a 5rTi03 film with a thickness of 1000 mm.
The film was formed as an alignment layer.

Next, the target has a YBa Cu O composition of 2
The sintered body was replaced with a sintered body of an oxide superconductor having a diameter of 37-δ, and a Y-Ba-Cu-0 based oxide superconductor film having a thickness of 5,000 wafers was formed under the following conditions.

Sputtering gas: Ar gas-108108CC gas-10
3CCM Vacuum container internal pressure 1 x 10' Torr Substrate temperature -650°C Supply type crab RF electric car 1 kV Note that after film formation by sputtering, heat treatment was performed at 800°C for 10 minutes while introducing oxygen gas.

Thereafter, an Ag film with a thickness of 1,000 thick was formed on the Y-Da-Cu-0 based oxide superconductor thin film under the following conditions.

Sputtering gas: Ar gas - 10 secM Vacuum container internal pressure I
When the transition temperature of a superconducting member having a laminated unit of uO-based oxide superconductor film/Ag film was measured, it was 80, and when the critical current density was measured in a high magnetic field of 5 T, it was 10' A/cd. A good value exceeding . This is because the 5rTI(h film enhances the orientation of the Y-Da-Cu-0 based oxide superconductor film, and the Ag film serves as a pinning center for magnetic flux.

Example 2 A 31 single crystal substrate was set in a substrate holder with a heating mechanism placed in a vacuum container, and 02 gas was poured into the vacuum container.
While supplying at 0300M, the inside of the vacuum container was
' After reducing the pressure to Torr, the Sl single crystal substrate was heated to 300 Torr.
The S' and Ti clusters were evaporated from separate ion guns while heating to 1000 °C to form a 5r
A T1(h film was formed as an alignment layer. The ionization current was 0.5 A, and the acceleration voltage was 1 kV.

Next, Y, Ba and Cu were evaporated onto the 5rT103 film from separate ion guns, and excited by ECR while supplying oxygen at 10900M.
A Y-Ba-Cu-0 based oxide superconductor film with a thickness of 5000 was formed.

The individual conditions are as follows.

Y: Evaporation rate -15 people/+u+ s Acceleration voltage -1 kV.

Ionization current - 0.5A Ba: Evaporation rate - 40 people 1■, acceleration voltage - 1kV, ionization current - 0.5A Cu: Evaporation rate - 10 people 1■, acceleration voltage - 1kV.

Ionization current - 0.5 A ECR conditions: Atmospheric pressure - LX 10' Torr, Microwave power - 200 W, Magnetic field - g 75 G, Substrate temperature - 400°C The Y-Ba-Cu-0 based oxidation obtained in this way When the transition temperature and critical current density of the superconductor film were determined at 1lFI, Tc -80K, Jc -105A
A good value of /c (237-δ) was obtained. Also, when X-ray diffraction was performed, it was confirmed that the YBa Cu O film had excellent orientation. According to the method, a high-quality oxide superconductor film can be obtained at a low substrate temperature.

Thereafter, an Ag film with a thickness of 1,000 thick was formed on the Y-Ba-Cu-0 based oxide superconductor film under the following conditions.

Evaporation source 2Ag Vacuum container internal pressure LX 10' Torr Acceleration voltage: lkV Ionization current 20, 3A 5rT103 film thus obtained/Y-Ba-
When the superconducting properties of a superconducting conductor having a stacked unit of Cu-0 based oxide superconductor film/Ag film were determined in 2-1,
The transition temperature was 80, and the critical current density in a high magnetic field of 5 T also showed a good value exceeding IO'A/cj.

In addition, by installing a coil directly under the substrate and applying high-frequency waves to it, oxygen was blown out through a hole in the coil to form plasma, resulting in a high-quality film with fewer oxygen deficiencies. . Furthermore, it was confirmed that the film quality was further improved by post-treatment in a vacuum container or in an oxygen atmosphere using a furnace.

In addition, according to this ion cluster beam method, since it is possible to control each single element, it is possible to control even B1-8r-Ca-Cu-0 system and Tl-Ba-Ca-Cu-0 system oxide superconductor films. , a film exhibiting a high transition temperature was obtained.

Example 3.4 Thickness as substrate 0. A copper tape with a width of 10 nm was prepared, and 5rTI (h film/Y-Ba-Cu-0 based oxide superconductor film/8g film) was deposited on this copper tape under the same conditions as in Examples 1 and 2. A laminated unit was fabricated.

When the critical current density of the tape-shaped superconducting conductor obtained in this way was measured under 5T, it was found that each
^/C? Good values were obtained, and when superconducting coils were fabricated using this tape-shaped superconducting conductor and the magnetic field strength was measured, it was confirmed that each of them exhibited sufficient magnetic force for practical use.

In addition, as such a linear substrate, Pe1SO3%A
Similar effects were obtained using tape materials and wire materials such as g and ^l.

Next, other embodiments of the present invention will be described.

FIG. 2 is a sectional view showing the structure of a superconducting conductor according to another embodiment of the present invention. As shown in the figure, the superconducting member 11 of this example has an alignment layer 2 on the base 1 as in the above example.
, an oxide superconductor layer 3 and a normal conductive material layer 5 are formed in order, and a plurality of units are formed in order with this three-layer stack as a unit. Each of the oxide superconductor layers 3 partitioned by the oxide superconductor layer 3 constitutes an individual current path.

Next, an example in which a superconducting member having the above structure was specifically manufactured will be described.

Example 5.6 S l under the same conditions as Examples 1 and 2! 5rTI (h film/Y-Ba-Cu-0
A laminated unit of oxide superconductor film/Ag film was prepared,
Further, each of these laminated units was made into one unit and 10 layers were laminated under the same conditions to produce superconducting members.

When the maximum current value that can be passed through the superconducting member having a plurality of current paths thus obtained was measured, good values of 50 A or more were obtained for each.

In addition, as a comparison with these examples, a superconducting member was fabricated under the same conditions as the above examples, including the number of laminated layers, except that only an Ag film was formed between the oxide superconductor layers, and the maximum current value was measured. Met.

In this way, in conventional superconducting members having multiple current paths, as the number of layers increases, the orientation of the oxide superconductor layers deteriorates, and the superconducting properties of each oxide superconductor layer deteriorates, making it difficult to maintain sufficient No effect can be obtained. On the other hand, in the superconducting member of the present invention, each oxide superconductor layer is formed on an orientation layer, so it is possible to stack multiple layers without losing the orientation, thereby creating multiple current paths. This makes it possible to fully obtain the effects of introducing the pinning center and the effects of introducing the pinning center.

[Effects of the Invention] As explained above, the superconducting member of the present invention has a constant crystal orientation of the oxide superconductor layer by the orientation layer and a magnetic flux pinning effect by the normal conductive material layer, so that the superconducting member of the present invention Improve the superconducting properties of the layer. becomes possible. By stacking these in order, it is possible to create multiple current paths without impairing their excellent superconducting properties, making it possible to flow a practically sufficient current, and providing a practical superconducting member. .

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view schematically showing the structure of a superconducting member according to one embodiment of the present invention, and FIG. 2 is a cross-sectional view schematically showing the structure of another embodiment of the present invention. 1... Base body, 2... Orientation layer, 3...
...Oxide superconductor layer, 4...Normal conductive material layer, 5.11...Superconducting member. Applicant: Toshiba Corporation

Claims (2)

[Claims] (1) In a superconducting member in which a superconducting conductor layer containing a substance exhibiting superconducting transition is formed on a substrate, the superconducting conductor layer includes an oriented layer of an oxide superconductor and an oxide superconductor formed on the oriented layer. 1. A superconducting member comprising a laminated unit including a body layer and a normal conductive material layer formed on the oxide superconductor layer. (2) The superconducting member according to claim 1, wherein a plurality of the laminated units are formed in order in the thickness direction.