JPH0761817A - Method for forming oxide superconducting film by laser ablation method - Google Patents

Abstract

(57) [Summary] [Object] To provide a method for forming a Y ₁ Ba ₂ Cu ₃ O _7-X superconducting film having a high critical current density on a polycrystalline substrate by a laser ablation method. [Configuration] By irradiating the target with a laser,
A method of depositing a substance scattered from a target surface on a polycrystalline substrate to form a Y ₁ Ba ₂ Cu ₃ O _7-X superconducting film, wherein the target contains 6% by weight or more and 20% by weight or more.
It is characterized by containing the following Ag.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION This invention relates to laser ablation.
The present invention relates to a method for forming an oxide superconducting film by the
, Especially on polycrystalline substrates by laser ablation
To Y₁Ba ₂Cu₃O_7-XRegarding superconducting film formation method
It is something.

[0002]

2. Description of the Related Art In recent years, the development of a laser device has been remarkable, and film formation by a laser ablation method using it has been actively performed. In the laser ablation method, by irradiating the target with a laser, the particles of the substance constituting the target are scattered in the state of atoms and molecules from the irradiation part of the target, and these scattered particles reach the substrate, and onto the substrate. A film is formed.

The film formation by the laser ablation method has a very high film formation rate as compared with other vapor phase methods such as the sputtering method, the vacuum vapor deposition method and the CVD method, and therefore the production rate can be industrially increased. it can. Further, the film formation by the laser ablation method is suitable for film formation of oxides, nitrides, etc. because the film formation atmosphere can be changed relatively freely as compared with other vapor phase methods.

For these reasons, the laser ablation method has recently been very often used for industrial production.

[0005]

Problem to be Solved by the Invention Laser ablation
On the substrate using the method₁Ba₂Cu₃O_7-XOf superconducting film
When forming a film, the film is grown in an oxygen atmosphere of several hundred mTorr.
Y in the membrane chamber₁Ba₂Cu ₃O_7-XComposition or a group close to it
Irradiate excimer laser on target
Atoms, molecules, or those that are scattered from
Particles are deposited on the substrate, and Y₁Ba₂Cu₃O
_7-XA superconducting film is obtained.

In the formation of such a Y ₁ Ba ₂ Cu ₃ O _7-X superconducting film, when the substrate is a single crystal substrate such as MgO, the formed film becomes a single crystal or a state close to it, and a crystal is formed. It is not affected by the grain boundaries or is extremely reduced. Therefore, the critical current density of the obtained superconducting film also becomes very high, and the liquid nitrogen temperature is 1 × 10 ⁶ A /
A value of cm ² or more can be easily obtained.

However, in order to obtain a superconducting wire used for superconducting applications such as superconducting magnets, superconducting power transmission, and superconducting fault current limiters, hastelloy, silver, or YSZ.
It is necessary to form a Y ₁ Ba ₂ Cu ₃ O _7-X superconducting film on a polycrystalline substrate such as. When the substrate is polycrystalline as described above, the formed film is also polycrystalline and is affected by the crystal grain boundaries. Therefore, the critical current density of the superconducting film formed on the polycrystalline substrate is much lower than the critical current density of the superconducting film formed on the single crystal substrate, which is 4 × 10 ⁴ A / cm ² I could only get a low value.

An object of the present invention is to solve the above-mentioned problems and to provide a liquid crystal on a polycrystalline substrate at a temperature of 1 × 10 ⁵ A / c
Y ₁ Ba ₂ Cu ₃ having a high critical current density of m ² or more
An object of the present invention is to provide a method capable of forming an O _{7 -X} superconducting film by a laser ablation method.

[0009]

The oxide superoxide according to the present invention
The method of forming the conductive film is to irradiate the target with a laser.
With, the substances scattered from the target surface are
Accumulate on a plate, Y ₁Ba₂Cu₃O_7-XSuperconducting film
A method for forming a film, wherein 6% by weight or more is contained in the target.
It is characterized by containing 20% by weight or less of Ag.

[0010]

According to the present invention, the Y ₁ Ba ₂ Cu ₃ O _7-X superconducting film is formed on the polycrystalline substrate by the laser ablation method using the target containing Ag. Therefore, the crystal grains of the formed Y ₁ Ba ₂ Cu ₃ O _7-X superconducting film become large, and the influence of the crystal grain boundaries during current application is reduced. Therefore, the critical current density is improved.

As described above, in the case of a single crystal superconducting film,
A critical current density of 1 × 10 ⁶ A / cm ² or more can be obtained, but in the case of a polycrystalline superconducting film, it is on the order of 10 ⁴ A / cm ² . The reason why the critical current density of the polycrystalline superconducting film becomes low in this way is that the existence of crystal grain boundaries causes the precipitation of insulators at the grain boundaries and the crystal orientations between the crystals are inclined to each other. It is because the superconducting current becomes difficult to flow because of the existence of Therefore, the larger the crystal grain size, the smaller the influence of the grain boundaries, and the higher the grain boundary current density.

Also, a target using Ag is used.
And the deposited Y₁Ba₂Cu₃O _7-XCrystal of superconducting film
Suppresses the precipitation of Y, Ba, and Cu compounds at the grain boundaries
To be Therefore, reduction of the critical current density can be prevented.
Since the compound that usually precipitates is an insulator,
Insulators are deposited on the area corresponding to 80% of the grain boundary area.
Then, the critical current density is lower than that when the insulator is not deposited.
Will be 20%. However, target using Ag
Insulators that precipitate at the grain boundaries are
Since the grain boundary area is suppressed to 10% or less, the critical current density is reduced.
It is possible to prevent a decrease in degree.

Further, according to the present invention, Ag may be deposited instead of depositing the insulator at the grain boundaries. In this case, since the specific resistance of Ag is small and the area of the grain boundary is larger than the thickness of the precipitated Ag, the resistance becomes negligibly small.

In general, in the Y-Ba-Cu-O superconducting film, when the crystal orientations at the crystal grain boundaries are inclined to each other, it becomes difficult for the superconducting current to flow, so that the insulator does not precipitate at the crystal grain boundaries. However, a phenomenon occurs that the critical current density of the polycrystalline film decreases. However, according to the present invention, the precipitation of Ag causes a current to flow from the superconducting film to Ag having an extremely low resistance, and further a current to the superconductor, so that the crystal orientations of the crystals are tilted as described above. The phenomenon that the superconducting conductive current becomes difficult to flow due to this is eliminated. Actually, due to the precipitation of Ag, a current flows through a superconductor → a normal conductor → a superconductor, but the resistance of Ag is so low that the resistance can be ignored. Rather A
By depositing g, it is possible to prevent a decrease in the critical current density due to the inclination of the crystal orientation between the crystals due to the presence of the low-resistance normal-conducting layer.

Further in accordance with the present invention, Y ₁ Ba ₂ Cu
Ag or an oxide of Ag of 1 μm or less is precipitated in the crystal of the ₃ O _{7 -X} superconducting film. Therefore, this precipitate serves as a pinning point to improve the critical current density.

[0016]

EXAMPLE A film having a composition of Y ₁ Ba ₂ Cu ₃ O _7-X was formed by a laser ablation method so that Ag was changed to be contained between 5 and 25% by weight. An excimer laser having a wavelength of 248 nm using KrF as an excitation gas was used as the laser, and the repetition frequency was 50 Hz. The film forming atmosphere at this time was an oxygen gas pressure of 300 mTorr. The distance between the target and the substrate was 50 mm. By film formation for 10 minutes,
A 0.5 μm film was obtained.

Y-Ba-Cu-obtained in this way
The critical current density of the O-based oxide superconducting film was measured in liquid nitrogen by the 4-terminal method. The result is shown in FIG. In FIG. 1, the horizontal axis represents Ag contained in the target.
(% By weight), and the vertical axis represents the critical current density (× 10 ⁵ A / cm ² ) at 77.3K.

As is apparent from FIG. 1, when the amount of Ag contained in the target is 6% by weight or more and 20% by weight or less, a superconducting film having a high critical current density is obtained, and particularly, 9% by weight of Ag is obtained. It can be seen that the superconducting film having the highest critical current density can be obtained by forming the film using the target containing the film. Further, when the average size of crystal grains of the film formed by using the target containing 9% by weight of Ag and the film formed by using the target containing no Ag was measured to be 3 μm each. And 0.2 μm
Met.

[0019]

As described above, according to the present invention, Y ₁ B having a high critical current density is formed on a polycrystalline substrate.
The a ₂ Cu ₃ O _7-X superconducting film can be formed by the laser ablation method.

[Brief description of drawings]

FIG. 1 Amount of Ag contained in a target and 77.3K
It is a figure which shows the relationship with the critical current density in.

Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number in the agency FI Technical display location H01L 39/24 ZAA B 9276-4M // H01B 12/06 ZAA 7244-5G (72) Inventor Hayashi Kenki Osaka 1-3-3 Shimaya, Konohana-ku, Yokohama, Osaka, Ltd. (72) Inventor, Gozo Fujino 1-3-3 Shimaya, Konohana-ku, Osaka (72) Invention, Osaka Tatsushi Hara 2-4-1, Nishi-Atsujigaoka, Chofu-shi, Tokyo Inside TEPCO Ltd. Technical Research Institute (72) Inventor Hideo Ishii 2-4-1 Nishi-Atsujigaoka, Chofu-shi, Tokyo Inside TEPCO Technical Research Institute

Claims (1)

[Claims] 1. A method for forming a Y ₁ Ba ₂ Cu ₃ O _{7 -X} superconducting film by irradiating a target with a laser to deposit a substance scattered from the target surface on a polycrystalline substrate. In the target, 6% by weight or more and 20% by weight or less of A
A method for forming an oxide superconducting film by a laser ablation method, which comprises g.