JPH0662359B2 - Manufacturing method of superconducting material - Google Patents

Description

The present invention relates to a method for manufacturing an oxide superconducting (also referred to as superconducting but also referred to as superconducting here) material.

The present invention intends to improve particularly important physical properties in the vicinity of a surface of a thin film type oxide superconducting material or a device using the surface of an oxide superconducting material. Furthermore, it is intended to stabilize the oxide superconducting material which is intended to be applied to the superconducting magnet etc. using bulk (internal), in particular, to stabilize the oxygen vacancy.

"Prior Art" Recently, oxide superconducting materials have been attracting attention. This is IBM
It originated in the development of Ba-La-Cu-O-based oxide superconducting materials at the Zurich Institute. In addition to this, yttrium-based oxide superconducting materials are also known, and the possibility of application to solid-state electron devices at liquid nitrogen temperature was clarified.

On the other hand, superconducting materials using metals such as Nb ₃ Ge have been well known so far. Attempts have been made to construct solid-state electronic devices such as Josephson devices using this metallic superconducting material. The Josephson device using this metal has been put to practical use almost for decades of research. However, this superconductor has a Tco (temperature at which electrical resistance becomes zero) of 2
It is extremely low at 3K and requires liquid helium, which is not practical.

On the other hand, recently, oxide superconducting materials represented by YBa ₂ Cu ₃ O ₆ to ₈ are known. This is a material with Tco of 90 to 100K, which is several tens of K higher than before.

“Conventional problems” However, this oxide superconducting material, which has recently received attention,
When the characteristics are investigated, in addition to Tco at 90 to 100K, the electric conductivity may change in the range of 150 to 270K.

The cause is that the oxide superconducting material has a modified triple perovskite structure, and has a structure with a small atomic density and filled with gaps. Therefore, oxygen is easily degassed, and when heated at 250 to 500 ° C in vacuum, oxygen vacancy (holes where atoms at the atomic level escape from the regular arrangement are called voids or vacancy) is generated more than necessary. It turned out to be lost. That is, whether the oxygen is in the ideal state or in the insufficient state is a fundamental problem for the material to have the superconducting property or the normal conducting property. found.

Therefore, according to the present invention, an element of Group VIIa of the Periodic Table of Elements (referred to as a filling element) is added to unnecessary vacancy of the oxide superconducting material to have an ideal oxygen vacancy concentration, heat resistance, and resistance. It is designed to have processability (such as being stable even when stored in a vacuum). It was found that the addition of the filling element to the vacancy thus strengthens the oxide superconducting material mechanically and makes it possible to increase the Tco to 100K or higher even in the thin film structure. In particular, when formed by a sputtering method, it is generally dense and cracks are likely to occur due to a difference in thermal expansion coefficient between the substrate and the substrate. And it is difficult to have the necessary orthorhombic form that causes superconductivity. For this reason, even if the structure is sufficiently dense, in order to cause superconductivity, the method of filling the oxygen vacancy with another filling material and the copper that is easy to form this vacancy are replaced with other elements so that oxygen vacancy is not generated. There are possible ways to do this. Group VIIa, especially manganese, of the periodic table of the present invention has a valence of +1 to +7, that is, it can be +2 valence, +4 valence, -1 valence, and -2 valence, and is effective for any of the above. Therefore, it became possible to form a dense thin film having heat resistance and process resistance by adding it to the target.

"Means for Solving the Problem" The present invention, when forming a film of an oxide superconducting material,
Using the sputtering method, an element of Group VIIa of the periodic table of elements is added during the process, and a part or all of the oxygen vacancy is filled to make a balance with this vacancy. Alternatively, part of copper is replaced with manganese or the like so that this oxygen vacancy does not occur. In particular, by adding an element of Group VIIa such as manganese to the vacancy and having a high superconducting property of Tco, the pervskite structure of this molecule is more stable. It is possible to as a result,
It has heat resistance and process resistance, and is particularly effective for thin film materials having a large surface area. In the present invention, when a target is hit by a sputtering method to fly an oxide superconducting material to form it on a surface to be formed, in addition to an inert gas which is a gas hitting the target, a gas containing a necessary amount of oxygen is added. Enclosed at the same time.

Here, as an example of the components of the oxide superconducting material, (A _1-x B
x) yCuzOwXv (x = 0 to 1, y = 2.0 to 4.0, preferably 2.5 to 3.5,
z = 1 to 4 preferably 1.5 to 3.5, w = 4 to 10 preferably 6
.About.8, v = 0.01 to 3). A is Y (yttrium), Gd (gadolinium), Yb (ytterbium), Eu (europium), Tb (terbium), Dy (dysprosium), Ho
(Holmium), Er (erbium), Tm (thulium), Lu (lutetium), Sc (scandium) or another element selected from one or more kinds of group IIIa of the periodic table. B is Ra
(Radium), Ba (Barium), Sr (Strontium), Ca
(Calcium), Mg (magnesium), Be (beryllium) are selected from Group IIa of the periodic table. X is the Periodic Table of the Elements VI
It is selected from Group Ia, that is, Mn (manganese), Tc (technetium), and Rc (rhenium). Manganese (using manganese oxide) whose price is low and whose compound is easily available is easy to handle. As a specific example, (YBa ₂ ) Cu ₃ O ₆ ~ ₈ X ₂ ~ _0.01
Was used. As A, a lanthanide element other than the above-mentioned elements in the periodic table of elements can be used.

In the present invention, an element of Group VIIa of the Periodic Table of Elements is added to the above-mentioned oxide superconducting material at a concentration of 1/100 to 200% compared to the concentration of vacancy in the case of no addition, and heat resistance and process resistance are improved. To improve.

That is, according to the present invention, after forming a thin film of the superconducting ceramic material to which the Group VIIa element is added by a sputtering method, a heat treatment is performed in air or oxygen at 600 to 950 ° C., for example 800 ° C. for 2 to 50 hours, for example, 15 Give time. By doing this,
In addition to manganese added to ceramics, added oxygen can be arranged in an appropriate coordination, and the surface can be a stable superconducting material. And I got 190K as Tco. After that, even if this measurement was repeated from the high temperature side to the low temperature side and from the low temperature side to the high temperature side, there was no particular change. When the temperature is set to a relatively low temperature in this way, deoxidation is more likely to occur than in the superconducting material at such a low temperature, and thus a vacancy that allows oxygen to escape is more likely to occur. It is presumed that the present invention could prevent such metamorphic changes by adding manganese. In addition, the periodic table of elements in this specification is based on a dictionary of physics and chemistry (Iwanami Shoten, published April 1, 1963).

"Function" As described above, the problem of deterioration of reliability in which the superconducting state disappears due to unknown reasons for oxide superconducting materials has disappeared, and the superconducting state can be preserved stably for a long time.

Further, by uniformly adding even to the inside, the superconducting properties obtained before that can be fixed.

As the superconducting property, it is important that it can be used in a state where Tco is higher and current density is higher.
However, even if such a sufficiently high Tco and current density are obtained, deterioration will occur until now by leaving in vacuum or continuing to flow a large current. (A _1-x Bx) yCuzOwX shown in the present invention
v However, x = 0.1 to 10, y = 2.0 to 4.0, z = 1.0 to 4.0, w = 4.0 to 1
0.0, v = 0.01 to 3.0 Tco could be stabilized by adding it to such an extent that it stabilizes at the atomic position where oxygen vacancy exists. Further, the current density capable of sustaining superconductivity was 1.5 × 10 ³ to 2 × 10 ⁵ A / cm ² , which was 50 times higher than the current density without addition, and could be preserved.

The present invention will be described below with reference to the drawings.

[Example 1] Fig. 1 shows an outline of a sputtering apparatus for producing the superconducting material of the present invention.

In FIG. 1, it has a target (1), a reaction chamber (4), a doping system (10) and an exhaust system (30).

The doping system is a gas containing argon (5), oxygen (6) and a halogen element (here, nitrogen fluoride (NF ₃ ) is used) (7)
Have been introduced. The exhaust system (30) is a turbo pump (8),
It consists of a pressure control valve (9) and a rotary pump (11).
The substrate (2) is arranged on a holder (3) which also serves as a heater, and is heated from room temperature to a temperature of up to 900 ° C.

The film formation was performed at room temperature. The distance between the target (1) and the formation surface of the substrate (2) is 2 to 15 cm.

Target (1) is (A _1-x Bx) yCuzOwXv x = 0.1 to 1.0, y = 2.
The oxide superconducting material represented by 0-4.0, z = 2.0-4.5, w = 4.0-8.0, v = 0.01-3.0 is provided by pressing. After this target is formed, the amount of copper is increased by about 20% to match the stoichiometric ratio. This so-called target (12)
The back side of the packing plate (13), magnet (1
4), cooling water inlet (15), cooling water outlet (16), shield plate
It consists of (17). These are electrically separated from the main body of the sputtering apparatus by the Teflon insulator (18). Then, a high negative voltage is applied to the current introduction terminal (20) for this target (1).

When performing the DC (direct current) sputtering method, this target is negatively applied and the substrate is at ground potential.

When the AC (alternating current) sputtering method is used, the substrate is used as an electrically floating state.

As "Experimental Example 1" target _{(12), YBa 2 Cu 3} ~ 3.6 O 6 ~ 8, Mn 0.01 ~ 2
Was used. The distance between the target and the substrate was 10 cm. Argon pressure is 4 × 10 ^-1 Pa, oxygen amount is 5 × 10 ^-3 Pa, NF ₃ 8 ×
It was set to 10 ^-4 Pa. The output of DC sputter was set to 500W and 1KW. This target had a diameter of 20 cm. The substrate (2) was kept at room temperature, and the holder (3) was rotated so as to have a uniform thickness. Such conditions were created, and this was annealed at 650 to 950 ° C. (8 hours), and then gradually cooled. In particular, this annealing is important for stably replacing or filling manganese. It was possible to make 126K Tco as an oxide superconducting material.

Part of NF ₃ may be introduced at the same time in this experiment. In this case, fluorine, which is a halogen element, is added to the film, and fluorine is added to the atomic positions where the oxygen vacancy remaining during the process should be constituted by the subsequent slow heating (thermal annealing), and structurally stable. Therefore, it is presumed that Tco can be greatly improved.

“Experimental example 2” As a target, Y _0.5 Yb _0.5 Ba ₂ Cu ₃ to ₄ O ₆ to ₈ X ₂ to _0.01
Was used. In this case, manganese was previously added as X. Argon is set to 4 × 10 ^-1 Pa and introduction of oxygen and
No NF ₃ was introduced. Finished film (thickness 2
thermal annealing at 800 ° C. for 5 hours in the atmosphere. As a result, the superconducting material formed on the formation surface has a Tco of 118K.
Got

“Effect” As shown in the present invention, +1 is added to the produced oxide superconducting material.
Valence to +7 valency, that is, -7 valency to -1 valency was scattered and added. Furthermore, it was extremely effective to subject this to gradual heat treatment in order to improve Tco and heat resistance.

As a result, the manganese-added oxide superconducting material was left in vacuum at 300 ° C. for 5 hours. However, in the manganese-added coating of the present invention, Tco is 100 to 150 K.
Stable superconductivity was maintained at a predetermined temperature of.

In the present invention, the term "oxide superconducting material" is used. However, as a result, it is clear from the technical idea of the present invention that the structure may be polycrystalline or single crystal.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a sputtering apparatus used in the present invention.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H01L 39/24 ZAA B 9276-4M

Claims (3)

[Claims] (1) (A _1-x Bx) yCuzOwXv, x = 0.1 to 10, y = 2.0 to
4.0, z = 2.0 to 4.5, w = 4.0 to 8.0, v = 0 to 3.0, A is an element selected from one or more members of Group IIIa of the Periodic Table of Elements, and B is an element of Periodic Table IIa. Element selected from one or more kinds of group, X is an element selected from one or more kinds of group VIIa of the periodic table of elements, and a gas containing oxygen and an inert gas is provided on the target. Sputter the target in (A _1-x Bx) yCuzOwX on the surface to be formed.
v, x = 0.1 to 10, y = 2.0 to 4.0, z = 1.0 to 4.0, w = 4.0 to 8.0, v
= 0.01 to 3.0, a method for producing a superconducting material, which comprises forming an oxide superconducting material and subjecting it to heat treatment. 2. The superconducting material according to claim 1, wherein the inert gas is argon and X is selected from Mn (manganese), Tc (technetium) and Re (rhenium). Manufacturing method. 3. The heat treatment according to claim 1
A method for producing a superconducting material, which comprises performing the treatment at a temperature of 600 to 950 ° C. and then gradually cooling it with a temperature gradient of 1 ° C./minute or less.