JPH0517272A - Deterioration preventive film for oxide superconducting material - Google Patents

Abstract

PURPOSE:To prevent the phenomenon that oxygen is removed from the inside of a superconducting material and the superconducting material is made nonsuperconducting by adding a halogen element into the superconducting material to reform the material to the material from which the oxygen is hardly removable and coating this material onto an oxide superconducting material. CONSTITUTION:The halogen element (e.g. fluorine) is added into the oxide superconducting material (e.g.: YBa2Cu3O6-8) by an ion implantation method, etc. The superconducting material is otherwise reformed to the material from which the oxygen is hardly removable by a method of previously adding a halogen compd. (e.g.: YF3) to the starting material of the oxide superconducting material to produce the oxide superconducting material. The adequate amt. of the halogen element to be added is the amt. to attain 1/100 to 200% concn. of the oxygen vacancy contained in the oxide superconducting material. The reformed superconducting material obtd. in such a manner is then coated as the deterioration preventive film on the oxide superconducting material. The oxide superconducting material which can maintain high reliability stably over a long period of time is thereby obtd.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a deterioration preventing film for 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 the surface of a device using the surface of an oxide superconducting material. Furthermore, it aims to stabilize the oxide superconducting material that is intended to be applied to the superconducting magnet etc. using bulk (internal), especially for the oxygen vacancy.

The periodic table of the elements in this specification is based on the dictionary of physics and chemistry (Iwanami Shoten, published April 1, 1963).

[0003]

2. Description of the Related Art Recently, oxide superconducting materials have attracted attention. This is a Ba done at the IBM Zurich Institute
-La-Cu-O-based oxide superconducting material has its origin in the development. In addition to this, an yttrium oxide superconducting material is also known, and the possibility of application of a solid-state electron device at liquid nitrogen temperature has been 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 by 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 very low Tco (temperature at which the electric resistance becomes zero) of 23K, and a liquid helium must be used, which is not practical.

On the other hand, in this metallic superconducting material, since all of the materials are metals, the components of the material can be made to be quite uniform both on the surface and inside (bulk).

[0006]

However, when the characteristics of the oxide superconducting material, which has been attracting attention recently, is investigated,
It was found that the characteristics (deterioration of reliability) near the surface (depth up to about 200 Å from the surface) are more likely to deteriorate than in the inside.

As a cause of this, it has been found that oxygen in the oxide superconducting material is extremely easily degassed in the vicinity of the surface. Furthermore, when heated at 250 to 500 ° C in vacuum, even the internal oxygen is easily degassed, and oxygen vacancy (a hole where atoms at the atomic level escape from the regular arrangement is called a void or vacancy) is generated more than necessary. It has been found. The ideal or deficient state of this oxygen proved to be a fundamental issue for the material, whether it could have superconducting properties or just normal conducting properties. .

Therefore, according to the present invention, the superconducting property is provided on the surface of the oxide superconducting material, in the vicinity of the surface thereof, and in the inside thereof, and further, it has an oxygen vacancy concentration of an ideal state, heat resistance and process resistance. It is designed to have properties (such as being stable even when stored in a vacuum).

[0009]

According to the present invention, a halogen element is added to an oxide superconducting material to fill a part or all of oxygen vacancies to make a counterbalance. In particular, by adding a halogen element such as fluorine to this vacancy while having a certain degree of this oxygen vacancy and having the highest superconducting property of Tco, this molecule can make the perovskite structure more stable. Is.
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, a halogen element, particularly fluorine, is added by a method such as an ion implantation method, and at the same time, the whole of them is heat-treated so that the added fluorine is arranged in an appropriate atomic arrangement.

The present invention is effective for any of oxide superconducting materials having a tablet structure and a thin film structure. In particular, in the case of having a thin film structure among these, the oxide superconducting material is
It is formed by using a printing method, a sputtering method, an MBE (molecular beam epitaxial) method, a CVD (vapor phase reaction) method, an optical CVD method, or the like.

As an example of the components of the oxide superconducting material, (A _1-x Bx) yCuzOw (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
-10, preferably 6-8). A is Y (yttrium), Gu (gadolinium), Yb (ytterbium), Eu
(Europium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium),
Lu (lutetium), Sc (scandium) or other elements are selected from one or more of the group 3a of the periodic table. B
Is Ra (Radium), Ba (Barium), Sr (Strontium),
Ca (calcium), Mg (magnesium), Be (beryllium)
Is selected from Group 2a of the Periodic Table of Elements. Especially used as a specific example _{(YBa 2) Cu 3 O 6} ~ 8. Further, as A, a lanthanide element or actinide element other than the above-mentioned elements in the periodic table can be used. In the present invention, a halogen element such as fluorine is added to the above oxide superconducting material at a concentration of 1/100 to 200% of vacancy to improve heat resistance and process resistance. A deterioration prevention film (passivation film) is formed on this surface in order to prevent degassing of oxygen that should originally exist in the material.

If the thickness of the insulating film is such that a tunnel current of 5 to 50 Å can flow, another superconducting material can be disposed on the upper surface of this insulating film to form a Josephson element.

Further, as a passivation film, 100-
With a thickness of 20000 Å, it can also be used as a deterioration preventing film.

That is, according to the present invention, after a halogen element such as fluorine is added to the oxide superconducting material, these are heated in an inert gas, air or oxygen at 250 to 500 ° C., for example 500 ° C., for 2 to 50 hours. For example, it is applied for 5 hours. By doing so, fluorine added by the ion implantation method or oxygen added in addition to fluorine can be arranged in an appropriate coordination, and the surface can be a stable superconducting material. The reason why the temperature is set to a relatively low temperature as described above is that deoxidization is more likely to occur than in the superconducting material at such a low temperature, and fluorine is more likely to be disposed in the void (vacancy) through which oxygen escapes. As a result, when kept at the liquid nitrogen temperature, the oxygen concentration on this surface can also keep an ideal state. That is, a passivation film can be made.

[0015]

[Operation] As described above, there is no problem of reliability deterioration that the superconducting state disappears near the surface of the oxide superconducting material for unknown reasons, and it becomes possible to effectively use the superconducting state for a long period of time. It was

At present, it is possible to obtain a high Tco and a high current density, but until now, deterioration occurs due to being left in a vacuum or continuing to flow a large current. The degree to which the halogen element shown in the present invention offsets the oxygen vacancy (
It was possible to stabilize Tco inside by forming a deterioration prevention film with a halogen element added to the concentration of 1/100 to 200% of vacancy).

As a result, it has become possible to operate a superconducting device, particularly a superconducting magnet, stably for a long period of time with high reliability.

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

[0019]

【Example】

Example 1 FIG. 1 shows the relative characteristics of the oxygen concentration distribution relating to the manufacturing process of the example of the present invention.

FIG. 1A shows YBa ₂ Cu ₃ O ₆ to ₈ as an example of the oxide superconducting material. The copper composition can be 3 or less. Such a superconducting material was formed on a tablet or a thin film so as to have a single crystal or polycrystal structure and used as a starting material (FIGS. 1 (A) (1)).

When this is held in a vacuum apparatus and the atmosphere is evacuated, oxygen in the vicinity of the surface (1 ') is degassed, and the atmosphere is reduced to about 200
The electrical characteristics in the range up to Å will deteriorate. That is, the oxygen concentration corresponding to FIG. 1 (A) is shown in FIG. 1 (D). In the figure, region (1) has a normal oxygen concentration. The area (1 ') indicates an insufficient area. This depth depends on the type, structure, and density of the superconducting material, but is 50 to 1000Å, generally about 200Å.

5 to 50Å, for example, 20Å for example, a silicon nitride film is formed on the upper surface of the silicon nitride film by the photo-CVD method (reactive gas is excited by light using ultraviolet light or laser light to form a film on the surface to be formed). Formed to a thickness of. Furthermore, ion implantation was performed on this. The accelerating voltage was weakened to 10 to 30 KV and added so that the oxygen concentration became constant. Here, heat treatment was performed at 350 ° C. for 2 hours. Further, the accelerating voltage of fluorine, which is a halogen element of the present invention, is varied from 10 to 500 KV, and the average addition concentration is 1/100 to 200% of the oxygen vacancy, for example, 3 × 10 ²¹ cm ^-3 d
I pushed.

Furthermore, the whole of these is 250 to 500 in oxygen.
The heat treatment was carried out at ℃, for example 350 ℃ for about 30 minutes.

By performing such heat treatment, FIG.
As shown in (E), it was possible to prevent oxygen from escaping, and it was possible to make structural deterioration of the oxide superconducting material having this perovskite structure less likely to occur inside.

The sample prepared in this example was taken out of the heated state and stored again in vacuum at 350 ° C. for 5 hours.
Then, by adding this fluorine, oxygen was not deficient near the surface of the superconducting material and in the bulk, and a highly reliable element could be manufactured.

[0026]

As shown in the present invention, the surface of the produced oxide superconducting material has extremely microscopic recesses in terms of an electron microscope, and the recesses have voids inside. Therefore, the surface becomes apparently very large. In order to passivate the surface, it was extremely effective to coat the surface with fluorine, which has the highest electronegativity, in a single layer or in a scattered manner to improve the heat resistance.
In addition, halogen elements can be filled on these surfaces and on the microscopic vacancy. The method of closely modifying the superconducting material was extremely effective because the manufacturing process could be simplified.

As a result, the bulk oxide superconducting material whose periphery is coated with the fluorine-containing deterioration preventing film for oxide superconducting material is heated at 300 ° C. for 5 hours in vacuum.
Left for hours. In the oxide material not coated with the deterioration preventing film, the superconducting property was completely lost. However, in the fluorine-containing coating of the present invention, the superconductivity was stably maintained with Tco of 79K.

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

In the examples of the present invention, fluorine was used as the halogen element. However, iodine and bromine may be added in the same manner as fluorine.

Heretofore, oxygen has been injected into the superconducting material by an ion implantation method or the like after forming the film. However, conversely, oxygen is previously added to the surface of the superconducting material or its vicinity by an ion implantation method, etc., then a film is formed, and the oxygen added by the heat oxidation treatment is suitable for atomic coordination to constitute superconductivity. It is also effective to arrange them in the.

In the present invention, an example has been shown in which fluorine is newly added to a material that has already been formed. However, when manufacturing this superconducting material, generally, fine grain materials of yttrium oxide, barium carbonate, and copper oxide are used, which are blended and repeatedly fired to form tablets. In the case of forming a thin film, this tablet is formed on the surface to be formed as a sputtering target. However, YF ₃ , YbF ₃ , TbF ₃ , and LaF ₃ may be partially or entirely used in the starting material and fluorine may be added in advance. Further, chloride or bromide may be used instead of the fluoride.

[Brief description of drawings]

FIG. 1 shows a manufacturing method of the present invention and an oxygen concentration distribution.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical display location H01B 13/00 565 D 8936-5G H01L 39/02 ZAA B 8728-4M

Claims (3)

[Claims] 1. A deterioration preventive film for an oxide superconducting material, which comprises substantially the same main component as that of the oxide superconducting material, wherein a halogen element is added to the same material as the constituent material of the oxide superconducting material. A featured deterioration prevention film for oxide superconducting materials. 2. The deterioration preventing film for an oxide superconducting material according to claim 1, wherein the halogen element is fluorine. 3. The halogen element according to claim 1, wherein the oxygen vacancy contained in the oxide superconducting material is 1/100 to 200%.
A film for preventing deterioration of an oxide superconducting material, which is added at a concentration of 10%.