JPH04214098A - Manufacture of oxide superconducting thin film - Google Patents

Abstract

PURPOSE:To efficiently execute film forming and to permit the formation of a dense oxide superconducting thin film having higher current density in the method for manufacturing an oxide superconducting thin film using laser ablation. CONSTITUTION:A target 7 having <=10% porosity is irradiated with a laser beam 8 to generate ablation in the irradiated part of te laser beam 8, by which grains splashed from the target 7 are deposited so that an oxide superconducting thin film 11 will is formed on a substrate 10.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing an oxide superconducting thin film using laser ablation.

0002

2. Description of the Related Art When a target is irradiated with a laser beam, ablation occurs in the irradiated portion of the laser beam, and particles of a substance constituting the target are scattered by this ablation. The scattered particles are deposited on a substrate placed to face the target, thereby forming a thin film of the substance constituting the target on the substrate.

[0003] Such a laser ablation method has recently attracted attention as a method for forming oxide superconducting thin films. According to the laser ablation method, oxide superconducting thin films can be manufactured at relatively low temperatures and high speeds. Therefore, by using, for example, a long body with appropriate flexibility as a substrate, it becomes possible to efficiently manufacture an oxide superconducting wire in which an oxide superconducting thin film is formed on the surface of the long body. .

In the laser ablation method, the composition of the target is reflected in the composition of the oxide superconducting thin film formed on the substrate with good reproducibility, so the target is usually a sintered body containing a component of an oxide superconducting substance. is used.

[0005]

[Problems to be Solved by the Invention] In the laser ablation method, particles scattered from the surface of the target by laser ablation are scattered mainly in a direction approximately perpendicular to the surface of the target, and the scattering direction of the particles is determined by the direction of the laser beam directed toward the target. is known to be almost independent of the angle of incidence. Therefore, if the substrate is placed directly in front of the portion of the target surface irradiated with the laser beam, the most efficient film formation can be achieved.

However, when the inventor of the present invention conducted repeated experiments, it was found that in most cases, when a target made of a normal sintered body was used, it was not possible to form a thin film at the theoretical or planned film formation rate. A dense thin film could not be obtained, and the critical current density of the obtained oxide superconducting thin film was not very high.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a method for manufacturing an oxide superconducting thin film that can be formed efficiently, is dense, and has a higher current density.

[0008]

[Means for Solving the Problems] The present inventor has discovered that the above-mentioned problems regarding the efficiency of film formation, the density and critical current density of the obtained oxide superconducting thin film are related to the properties of the target. They discovered this and came up with this invention.

[0009] In the present invention, the above-mentioned technical problem is solved by paying particular attention to the porosity of the target and setting it to 10% or less.

0010

[Operation] A target made of a sintered body produced by ordinary sintering has a relatively large porosity of more than 10%, for example 15%. As shown in FIG. 2, such a conventional target 1 has a high porosity, so even if it is polished, it inevitably forms an uneven surface 2 caused by the pores. Therefore, when the target 1 is irradiated with the laser beam 3, even though particles are scattered mainly in the direction perpendicular to the surface of the target 1 according to laser ablation, such particles are scattered from the uneven surface 2. Therefore, the scattered particles are directed in all directions, as shown by arrow 4. Therefore, such particles do not reach the substrate 5 efficiently, the deposition rate of the oxide superconducting thin film 6 becomes low, and the denseness and critical current density of the oxide superconducting thin film 6 are not so high. No.

On the other hand, as shown in FIG. 1, when a target 7 with a porosity of 10% or less is used according to the present invention, particles scattered from the target 7 due to the irradiation of the laser beam 8 are shown by the arrows. As shown at 9, it is directed within a more limited range and efficiently reaches the substrate 10. Therefore, the oxide superconducting thin film 11 is formed on the substrate 10 at a high deposition rate, and the denseness and critical current density of the obtained oxide superconducting thin film 11 are increased.

0012

As described above, according to the present invention, by using a dense target with a porosity of 10% or less, an oxide superconducting thin film can be formed at a high deposition rate. Furthermore, the obtained oxide superconducting thin film is dense and exhibits a high critical current density.

Therefore, the present invention is particularly useful in situations where film formation must be carried out efficiently, such as when forming an oxide superconducting thin film on a long substrate to produce an oxide superconducting wire. It is valid.

[0014]

[Example] Examples and comparative examples of the present invention will be described below. The porosity of the target used in each of these examples and comparative examples depends on the pressure applied in the sintering process to obtain the target and Adjustments were made by controlling the sintering time.

Example 1 A Y1 Ba2 Cu3 OY target with a porosity of 3% was irradiated with excimer laser light using KrF, and Mg
An oxide superconducting thin film was formed on an O(100) single crystal substrate. The film forming conditions were as follows: substrate temperature was 725°C, oxygen pressure in the film forming chamber was 100 mTorr, and substrate-target distance was 50 mTorr.
mm, the energy density of the laser beam was 2 J/cm2, and the repetition frequency of the laser beam was 5 Hz.

The film forming operation as described above was carried out for about 17 minutes to obtain an oxide superconducting thin film having a thickness of 5000 angstroms. The film formation rate at this time was approximately 300 angstroms/min.

When the surface of the obtained oxide superconducting thin film was observed with a scanning electron microscope, it was confirmed that it had a smooth surface, and when the critical current density of the oxide superconducting thin film was measured, it was found to be 77. At 3K, 2.8×106 A/
cm2.

Example 2 An oxide superconducting thin film was formed under the same film forming conditions as in Example 1, except that a target with a porosity of 6% was used.

The film forming operation was carried out for about 20 minutes, and the thickness was 500 mm.
A 0 angstrom oxide superconducting thin film was obtained. The film formation rate at this time was approximately 250 angstroms/min.

In this case as well, the oxide superconducting thin film has a smooth surface, and when its critical current density is measured, it is 7.
At 7.3K, it was 2.5×106 A/cm2.

Example 3 An oxide superconducting thin film was formed under the same film forming conditions as in Example 1, except that a target with a porosity of 9% was used.

[0022] The film forming operation was carried out for about 25 minutes, and the thickness was 500 mm.
A 0 angstrom oxide superconducting thin film was obtained. The film forming rate at this time was approximately 200 angstroms/min.

In this case as well, the oxide superconducting thin film has a smooth surface, and when its critical current density is measured, it is 7.
At 7.3K, it was 2.3×106 A/cm2.

Comparative Example 1 An oxide superconducting thin film was formed under the same film forming conditions as in Example 1, except that a target with a porosity of 15% was used. - The film forming operation was carried out for about 50 minutes, and an oxide superconducting thin film with a thickness of 5000 angstroms was obtained. The film formation rate at this time was about 100 angstroms/min.

When the surface of the obtained oxide superconducting thin film was observed with a scanning electron microscope, it was found that there were severe irregularities, and when the critical current density of the oxide superconducting thin film was measured, it was 5.0×10 5 A at 77.3 K. /cm2.

Other Examples and Comparative Examples Y1 Ba2
As a target consisting of Cu3OY, 3%, 6
%, 9%, and 15% porosity,
MgO (10
0) An oxide superconducting thin film was formed on a single crystal substrate. The energy density of the laser beam is set to 1.5 J/1 on the target surface.
The same film forming conditions as in Experimental Example 1 were adopted, except that the film thickness was set to cm2.

Table 1 below shows the critical current density (Jc) [A/cm2] and critical temperature (T
c) [K] is shown.

[0028]

[Table 1] As shown in Table 1, the effect of using a target with a porosity of 10% or less was remarkable.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a state in which the method for manufacturing an oxide superconducting thin film according to the present invention is being carried out.

FIG. 2 is an explanatory diagram showing a state in which a method for producing an oxide superconducting thin film is being carried out using a target with a high porosity.

[Explanation of symbols]

7 Target 8 Laser light 9 Arrow indicating the scattering direction of particles 10　Substrate 11 Oxide superconducting thin film

Claims (1)

[Claims] 1. A method for producing an oxide superconducting thin film using laser ablation, the method comprising using a target having a porosity of 10% or less.