JPH08109469A - Production of metallic oxide thin film - Google Patents

Abstract

PURPOSE: To provide a method in which an oxide superconducting film having the orientating properties of crystal axes close to single crystals can be deposited on a metallic substrate even if a metallic substrate of polycrystals is used. CONSTITUTION: Chemical species for constituting metallic oxides such as yttria stabilized zirconia, cerium oxide, magnesium oxide or the like are fed to the surface of a metallic substrate 4 by laser abrasion. At this time, while d.c. current is conducted to the metallic substrate 4 via an electrode 7a and 7b, a film of the metallic oxides in which the chemical species are deposited and the crystal axes are oriented is deposited. On the film of the metallic oxides obtd. as the same manner, a thin film constituted of an oxide superconductor is deposited.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a thin film of a metal oxide containing an oxide superconductor, and in particular, an intermediate layer is formed on a metal substrate and an oxide superconducting layer is formed thereon. For how to.

[0002]

2. Description of the Related Art A thin film made of an oxide superconductor is manufactured by RF sputtering, DC sputtering, ion beam sputtering,
It can be formed by a film forming method typified by a cluster ion beam method, a MOCVD method, an MBE method, a laser ablation method, or the like. Generally, oxide superconducting films produced by these methods have better crystallinity and excellent superconducting properties than oxide superconductors produced by other methods such as solid phase method and melt method. . For example, MgO,
Y ₂ O ₃ (0 to 8 mol%)-ZrO ₂ (YSZ), Sr
Y ₁ Ba ₂ Cu ₃ formed on a single crystal substrate of TiO _3, etc.
The O _x superconducting film has a characteristic of 10 ⁶ A / cm ² (7
A critical current density (Jc) of 7.3 K and a magnetic field of 0) or higher is obtained relatively easily. This Jc is 100 to 1000 times higher than that obtained by other methods.

When it is desired to form a single crystal thin film made of a different material on a substrate made of a specific material, a single crystal substrate having a lattice constant close to that of the thin film material to be formed is generally used. Then, on the single crystal substrate, vacuum deposition, CVD,
A single crystal thin film is grown by laser deposition or the like. This is a well-known technique as a heteroepitaxial growth method. The oxide superconducting film formed on the single crystal substrate according to such a technique can be epitaxially grown by reflecting the crystallinity of the substrate. Then, the oxide superconducting film on the single crystal substrate can grow into a substantially single crystal by growing with all the three crystal axes.

[0004]

On the other hand, when a thin film of an oxide superconductor is formed on a substrate to manufacture a superconducting wire, a tape-shaped elongated body is required as the substrate. If it is desired to epitaxially grow an oxide superconductor on a tape-shaped substrate according to the technique described above, it is necessary to prepare a single crystal tape. However, it is almost impossible to prepare a long tape-shaped single crystal substrate.

Therefore, using a long tape base material such as a polycrystalline metal, an intermediate layer for preventing diffusion of base material elements into a superconductor is first formed, and then an oxide superconducting layer is formed thereon. Attempts have been made to do so. However, the intermediate layer formed on the polycrystalline metal is almost polycrystalline, and the oxide superconductor deposited on it is also polycrystalline. The Jc of the oxide superconductor film formed in this way is reduced to about 1/100 of that when a single crystal substrate is used.

An object of the present invention is to solve the above problems and to provide a method of imparting crystal axis orientation close to that of a single crystal to an oxide superconducting film even when a polycrystalline metal substrate is used. is there.

[0007]

According to the present invention, there is provided a method for producing a metal oxide thin film, which method comprises a polycrystalline surface or an amorphous surface of a conductive substrate or a polycrystalline film formed on the conductive substrate. A method of depositing a thin film of metal oxide on an amorphous film, comprising:
The chemical species for forming the metal oxide are supplied in the gas phase in the direction of the substrate surface or a film formed on the substrate, and the chemical species are supplied to the conductive substrate while applying a direct current to the substrate surface or the substrate. It is characterized in that it is deposited on the film formed in 1.

In the present invention, the chemical species for forming the metal oxide can be supplied in a direction substantially perpendicular to the surface of the substrate or the film formed on the substrate. In this case, the direct current can flow in a fixed direction substantially parallel to the surface of the substrate or the surface of the film formed on the substrate. The species deposited on the substrate are preferably those capable of forming an electric dipole.

In the present invention, the metal oxide thin film is R
F sputtering method, DC sputtering method, ion beam sputtering method, cluster ion beam method, MOCVD method, MBE
Method, laser ablation method, or other vapor phase film forming method. The laser ablation method is preferable because it can form a high-quality film in a short time, and is more preferable especially when forming an oxide superconducting film. Excimer lasers are preferably used for laser ablation. As the excimer laser, a KrF excimer laser (wavelength 248 nm) and an ArF excimer laser (wavelength 193 nm) are preferably used.

The present invention finds particular application for forming thin films of oxide superconductors. In this case, a conductive material,
In particular, an oxide superconducting film is formed on a substrate made of metal via an intermediate layer. The intermediate layer is formed for the purpose of preventing the substrate element from diffusing into the oxide superconducting film. In this process, the invention can be applied first to form the intermediate layer. As an intermediate layer, a thin film of metal oxide can be formed on a conductive substrate according to the present invention. Next, an oxide superconducting film is formed on the intermediate layer made of metal oxide. When the intermediate layer is formed according to the present invention, the oxide superconducting film need not be formed by the method of the present invention. As shown below, it is possible to form an intermediate layer in which crystal axes are strongly oriented in a specific direction according to the present invention, and a film of a superconductor can be grown, preferably epitaxially grown according to the crystal structure of the intermediate layer. Because you can. The preferred metal oxide for the intermediate layer is yttria-stabilized zirconia (eg, Y ₂ O).
₃ (0 to 8 mol%)-ZrO ₂ ), cerium oxide (Ce
O ₂ ) and at least one selected from the group consisting of magnesium oxide (MgO).
Oxides capable of exhibiting a cubic system are preferable as the metal oxide of the intermediate layer.

On the other hand, a thin film made of an oxide superconductor can be formed according to the present invention. In this case, the intermediate layer may not be formed according to the present invention. Supplying a chemical species for forming an oxide superconductor in a vapor phase onto a polycrystalline, preferably amorphous intermediate layer, and depositing the chemical species on the intermediate layer while applying a direct current to a conductive substrate. This makes it possible to deposit an oxide superconducting film having crystal axes strongly oriented in a specific direction. The intermediate layer is, for example, the above-mentioned yttria-stabilized zirconia, cerium oxide,
Alternatively, it can be formed from magnesium oxide.

The oxide superconductors include yttrium-based, bismuth-based, thallium-based oxide superconductors, and the like. In the present invention, particularly, Y ₁ Ba ₂ Cu ₃ O _7-X (0≤X <1) is used. It is applied to form a thin film of yttrium-based oxide superconductor.

In the present invention, the thin film can be formed on a substrate having various materials, sizes and shapes. The substrate may be made of a single material or may be made of a composite material. A substrate having a surface coated with a specific material may be used. A metal tape can be preferably used as the substrate.
Preferred metals include Hastelloy, stainless steel, nickel and the like. When it is desired to form a thin film on a long metal tape, the chemical species can be deposited while moving the substrate in the longitudinal direction. Thereby, a thin film is formed along the longitudinal direction of the tape. A superconducting wire can be provided by forming a thin film of an oxide superconductor according to this method.

[0014]

In the present invention, when a direct current is applied to the conductive substrate, a static magnetic field is generated in a form surrounding the applied current according to Ampere's right-handed screw law. When a charged particle moves in this static magnetic field, the particle receives a Lorentz force perpendicular to the magnetic field direction and the moving direction of the particle.

Ceramic materials such as magnesium oxide, yttria-stabilized zirconia, and cerium oxide have a strong ionic bond property. For example, magnesium oxide contains Mg ²⁺ and O ^2−.
A molecule is formed by the Coulomb force between the ions of. This M
Although the gO molecule is neutral as a whole, when attention is paid to the constituent atoms, it can be said that particles having a positive charge and particles having a negative charge are connected to each other, forming an electric dipole.

Therefore, consider a case where MgO is to be deposited on a metal substrate by using, for example, a laser ablation method. When the MgO sintered body target is irradiated with a laser, the target is decomposed into atomic and molecular levels and scattered, and is deposited on the substrate arranged facing the target. At this time, when the MgO molecules enter into the static magnetic field generated by the current flowing through the metal substrate, they receive the Lorentz force as described above, but the Mg +
Since the electric charge and O have a negative electric charge, they receive forces in opposite directions. As a result, it is considered that the most stable state is when the Mg-O dipoles, that is, the MgO molecules, are aligned in the direction orthogonal to the magnetic field and the flight direction. By depositing MgO on the substrate in such a state, it becomes possible to give a specific orientation to the crystal axis of the obtained film.

It is considered that the mechanism described above works similarly for yttria-stabilized zirconia, cerium oxide, etc., and can give the orientation of crystal axes. Further, the oxide superconductor is also a substance having a strong ionic bond, and it is considered that the crystal axis can be oriented by the same mechanism.

[0018]

【Example】

 Example 1 As a material for the intermediate layer, MgO, as an oxide superconductor
Y₁Ba₂Cu₃O _XThe case of using will be described.

As a metal substrate, a size of 10 × 10 × 0.
A 5 mm Hastelloy c-276 was used and a film was formed thereon by laser ablation. FIG. 1 schematically shows an apparatus for film formation. In the apparatus, a target 1 made of a material for forming a metal oxide is irradiated with a laser beam 2, and a plasma (plume) 3 containing a chemical species for film formation is generated in a direction substantially perpendicular to the target 1. To do. The substrate 4 is provided in the direction in which the plume is generated, and the substrate 4 can be held at a predetermined temperature by the holder 5. Electrodes 7a and 7 are provided on both ends of the substrate 4, respectively.
b is attached so that the substrate can be energized from the DC power supply 6. In such an apparatus, the film forming conditions are as shown in Table 1.

[0020]

[Table 1]

First, an experiment was carried out by applying a direct current when forming the MgO intermediate layer. DC current is 1-10A
And MgO as a target by laser ablation while applying a current of each value to the substrate.
A film was formed. For comparison, film formation was performed without energization. The orientation of crystal axes (crystal planes) in the film was investigated by an X-ray diffraction method. Table 2 summarizes the relationship between the value of the energizing current and the crystal plane orientation in the formed MgO film.

[0022]

[Table 2]

From this result, it is understood that the crystal axis orientation of the MgO film is improved by passing a direct current, and one crystal axis is aligned perpendicular to the substrate surface. As described above, it is considered that the electric dipoles are most stable when they are aligned in the direction perpendicular to the magnetic field direction and the dipole motion direction. A magnetic field that is almost parallel to the substrate surface is generated by the applied current, and the motion direction of the electric dipole due to the Mg—O coupling is substantially perpendicular to the substrate surface. It is considered that crystals are formed so as to be (perpendicular to the magnetic field). If such crystallization progresses, the <100> crystal axis should grow perpendicular to the substrate surface in view of the MgO crystal structure, and the results shown in Table 2 are based on this assumption. It shows that it is correct. Moreover, as a result of the X-ray pole figure measurement, the samples of 3A to 10A are
It was found that the axes are also aligned in the plane parallel to the substrate surface.
In the sample of 1A, some crystallographic orientation was observed, but it was not clear.

Next, MgO was applied at a current of 0 and 7 A, respectively.
For the sample with the film formed, Y ₁ B
A film of a ₂ Cu ₃ O _x was formed. No current was applied when forming the superconductor film, and the film was deposited by laser ablation under the conditions shown in Table 1. Table 3 shows the critical current densities of the obtained superconducting films.

[0025]

[Table 3]

In the sample which was not energized during the MgO film formation, Y ₁ Ba ₂ Cu ₃ O _x had the c-axis oriented almost perpendicular to the substrate surface, but the remaining a and b axes had orientation. I couldn't do it. In the sample in which the oxide superconductor was deposited on the MgO film formed by applying a current of 7 A, the c-axis of the superconductor was oriented perpendicular to the substrate surface, and the a and b axes of the superconductor were also oriented in a specific direction. It was revealed that they were strongly oriented. As shown in Table 3, the oxide superconductor film deposited on the MgO film formed while energizing showed a high critical current density.

Example 2 MgO as an intermediate layer material and Y ₁ B as an oxide superconductor
a ₂ Cu ₃ O _x tape-shaped Hastelloy C having a width of 10 mm, a thickness of 0.5 mm and a length of 100 mm as a metal substrate
The case of using -276 will be described.

The film forming conditions are as shown in Example 1.
Was. Move the tape substrate at a constant speed when forming the film.
Was. This forms a thin film along the length of the tape.
Was done. The moving speed of the tape is 7 when the MgO film is formed.
mm / min, Y₁Ba₂Cu₃O _X3 mm when forming the film
/ Min.

FIG. 2 schematically shows an apparatus for energizing while moving the tape-shaped substrate. Referring to the figure, tape-shaped substrate 14 is moved in the direction of the arrow. The substrate 14 has a pair of electrodes 17a and 17a provided at a predetermined interval.
An electric current is passed through the lead wires 16a and 16b to the portion of the substrate which is in contact with the electrode b and which exists between the electrodes.
The substrate 14 can be held at a predetermined temperature by the holder 15. On the moving tape-like substrate 14, the chemical species in the plasma 13 generated by irradiating the target 11 with the laser beam 12 are sequentially deposited along the longitudinal direction of the tape, and a film is formed along the longitudinal direction of the tape. Will be done.

As a result of applying an electric current when forming the MgO film, the same results as in Example 1 were obtained regarding the crystallinity of MgO. No change in crystallinity due to the movement of the substrate was observed.

Next, as in the first embodiment, the energizing currents 0 and 7
For the tape-shaped sample on which the MgO film was formed in A,
Under the same conditions as in Example 1, a Y ₁ Ba ₂ Cu ₃ O _x film was continuously formed while moving the substrate by laser ablation. At this time, power is not supplied. The critical current density was measured over the entire length of each tape at a measurement interval of 70 mm. The results are summarized in Table 4. As in the case of Example 1, by conducting a direct current, good crystal axis orientation was obtained, and a high critical current density was shown for the superconducting film.

[0032]

[Table 4]

Example 3 A case where yttria-stabilized zirconia (YSZ) is formed on a metal substrate will be described. 1 for a metal substrate
Hastelloy c-276 of 0 × 10 × 0.5 mm was used. Table 5 shows the film forming conditions.

[0034]

[Table 5]

During film formation, a direct current of 0 to 10 A was passed through the metal substrate. When the X-ray diffraction measurement of the YSZ layer was performed, a continuous change in the orientation of crystal axes was observed according to the current value. Table 6 shows the intensity ratio of the diffraction peak of the (220) plane to the (200) plane. When not energized, (2
It can be seen that the orientation of the (00) plane is predominant, and the orientation of the (220) plane becomes stronger as the current value increases. As mentioned above, it is considered most stable that the electric dipoles are aligned in the direction perpendicular to the magnetic field direction and the dipole motion direction. In the case of the present embodiment, a magnetic field that is substantially parallel to the substrate surface is generated by the applied current, and the movement direction of the electric dipole due to the Zr-O coupling is substantially perpendicular to the substrate surface. Therefore, it is considered that the YSZ crystal is formed so that the Zr-O bonding direction is parallel to the substrate surface (perpendicular to the magnetic field). If crystallization proceeds in that way,
Considering the crystal structure of YSZ, the <110> crystal axis should grow perpendicular to the substrate surface, and the results shown in Table 6 show that this assumption is correct.

[0036]

[Table 6]

Example 4 Hastelloy c of 10 × 10 × 0.5 mm as a metal substrate
-276 was used to deposit CeO ₂ on this substrate. Table 7 shows the film forming conditions.

[0038]

[Table 7]

During film formation, a direct current of 0 to 10 A was passed through the metal substrate. When the crystallinity of the formed CeO ₂ film was measured by an X-ray diffraction method, a continuous change in the orientation of crystal axes was observed depending on the current value.
Table 8 shows the intensity ratio of the diffraction peak of the (220) plane to the (200) plane. When not energized, (200)
It can be seen that the orientation of the plane is mainly, and the orientation of the (220) plane becomes stronger as the current value increases. As mentioned above, it is considered most stable that the electric dipoles are aligned in the direction perpendicular to the magnetic field direction and the dipole motion direction. In the case of this embodiment, a magnetic field almost parallel to the substrate surface is generated by the applied current, and the movement direction of the electric dipole due to the Ce-O coupling is substantially perpendicular to the substrate surface. It is considered that the cerium oxide crystal grows so that the direction is parallel to the substrate surface (perpendicular to the magnetic field). If such crystallization proceeds,
Considering the crystal structure of cerium oxide, the <110> crystal axis should grow perpendicular to the substrate surface, and the results shown in Table 8 show that this assumption is correct.

[0040]

[Table 8]

Example 5 Y ₁ Ba ₂ Cu ₃ O was applied while applying a direct current to a metal substrate.
An example in which a film of an _X oxide superconductor is formed is shown. Hastelloy c-276 of 10 × 10 × 0.5 mm as a metal substrate
It was used. The basic film forming conditions for the oxide superconductor are as shown in Example 1. In addition, YSZ as an intermediate layer material
It was adopted. In this embodiment, an uncrystallized (amorphous) YSZ film is first deposited on a metal substrate,
An oxide superconducting film was deposited on it by laser ablation. The applied current when forming the oxide superconducting film was 0 to 10A.

The crystallinity of the sample on which the superconducting film was formed without passing an electric current was measured by X-ray diffraction. In this case, the c-axis was oriented perpendicular to the substrate surface, and the crystallinity of the superconducting film in this direction was good. The orientation of the c-axis of the oxide superconductor remained almost unchanged even when the applied current increased, and the c-axis showed good orientation at all current values. In addition, as a result of X-ray pole figure measurement, when the superconducting film was formed at a current value of 3 A or more,
It was found that the remaining two axes (a and b axes) were also strongly oriented in a particular direction. Table 9 shows the critical current densities of the obtained films.

[0043]

[Table 9]

The Y ₁ Ba ₂ Cu ₃ O _x superconductor is Y-
O, Cu-O, Ba-O, Cu-O, Ba-O, Cu-
It is a layered type material in which constituent elements are stacked in the order of O, YO, Cu-O .... It is considered that each layer forms an electric dipole as described above by the bond with oxygen atoms. It is considered that electric dipoles are most stable when they are aligned in a direction perpendicular to the magnetic field direction and the dipole motion direction. It is considered that the orientation of crystal axes in the plane of the substrate is improved by arranging the dipoles of each layer in a certain direction. The results shown in Table 9 show that the increase in the applied current improves the orientation of the crystal axes in the plane parallel to the substrate, and the inclination angle between the crystal grains is reduced, so that weak bonds between the crystal grains are reduced. Suggesting that

Example 6 An example of forming a Y ₁ Ba ₂ Cu ₃ O _x oxide superconductor film on a metal substrate will be described. As a metal substrate, width 10 mm,
A tape-shaped Hastelloy c-276 having a thickness of 0.5 mm and a length of 100 mm was used. The film forming conditions and the applied current were the same as in Example 5. In forming the oxide superconducting film, first, an uncrystallized (amorphous) YSZ film was formed on the substrate, and an oxide superconducting film was deposited thereon by laser ablation. The tape substrate was moved at a constant speed during the formation of the oxide superconductor film. Thereby, the oxide superconducting film was formed along the longitudinal direction of the tape. The moving speed of the tape was 3 mm / min.

In the oxide superconducting film, the change in the orientation of the crystal axes due to the applied current was almost the same as the result obtained in Example 5 from the X-ray diffraction method, the X-ray pole figure method, etc. No change was observed. Table 1 shows the results of measuring the critical current density at intervals of 70 mm over the entire length of the tape.
Sum up to 0.

[0047]

[Table 10]

In order to reduce the difference between the coefficient of thermal expansion of the intermediate layer material or the oxide superconductor and the coefficient of thermal expansion of the substrate, Hastelloy c is used as the metal substrate in the above embodiments.
-276 was used. However, in the present invention, the substrate is not limited to this material. In the above example,
Other metals or alloys having a small coefficient of thermal expansion difference from the deposited material can be used as the substrate with similar results.

[0049]

As described above, according to the present invention,
A single crystalline thin film can be formed on a polycrystalline or amorphous substrate by a simple process. As a base material
When a long metal tape is used, a single crystal thin film made of yttria-stabilized zirconia, magnesium oxide, cerium oxide, or the like can be formed on the long metal tape. By heteroepitaxially growing an oxide superconductor on this thin film, a superconductor having a high critical current density can be formed. Further, the present invention can be used for forming the oxide superconducting film itself to form a superconducting film having high single crystallinity and high critical current density. If the superconducting film is formed along the longitudinal direction of the tape,
It is also possible to obtain a superconducting wire. From this point, the present invention is useful in the manufacturing process of the oxide superconducting wire.

[Brief description of drawings]

FIG. 1 is a schematic diagram for explaining an example of a method according to the present invention.

FIG. 2 is a schematic diagram for explaining another example of the method according to the present invention.

[Explanation of symbols]

 1, 11 Target 2, 12 Laser beam 3, 13 Plasma 4, 14 Substrate 5, 15 Holder 7a, 7b, 17a, 17b Electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenki Hayashi 1-3-3 Shimaya, Konohana-ku, Osaka City Sumitomo Electric Industries, Ltd. Osaka Works

Claims (8)

[Claims] 1. A method of depositing a thin film of a metal oxide on a polycrystalline surface or an amorphous surface of a conductive substrate or on a polycrystalline film or an amorphous film formed on the conductive substrate, the method comprising: Chemical species for forming a substance, in the gas phase in the direction of the substrate surface or a film formed on the substrate, while supplying a direct current to the conductive substrate, the chemical species A method for producing a metal oxide thin film, which comprises depositing on a surface of the substrate or on a film formed on the substrate. 2. The chemical species are supplied in a direction substantially perpendicular to the substrate surface or a film formed on the substrate, and the direct current is substantially parallel to the substrate surface or a film surface formed on the substrate. Method according to claim 1, characterized in that the flow is in a constant direction. 3. The method of claim 1 or 2, wherein the chemical species is capable of forming an electric dipole. 4. The method according to claim 1, wherein the chemical species is deposited by laser ablation.
The method described in the section. 5. The metal oxide according to claim 1, wherein the metal oxide is at least one selected from the group consisting of yttria-stabilized zirconia, cerium oxide and magnesium oxide. the method of. 6. The conductive substrate is made of metal, and a thin film made of the metal oxide is deposited on the substrate while applying the direct current to the substrate, and then a thin film made of an oxide superconductor is formed thereon. The method according to claim 1, further comprising a step. 7. The method according to claim 1, wherein the metal oxide is an oxide superconductor. 8. The conductive substrate is a tape-shaped body, and the thin film is deposited on the surface of the tape-shaped body while moving the tape-shaped body in the longitudinal direction. 7. The method according to any one of 7.