JPH09310169A - Dispersed grain oxide thin film containing rare earth element and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an oxide thin film having excellent characteristics by incorporating rare earth elements and copper and allowing it to exist on the surface of a substrate in a state in which grains are dispersed. SOLUTION: As a substrate, though limitation is not placed in particular, quartz glass or the like are suitably used. For producing an oxide thin film on this substrate by sputtering, at first, with rare earth elements as a target, sputtering is executed using Ar ions. Next, with a copper element as a target, sputtering is similarly executed to form a metallic multilayer film on the surface of the substrate. The formed thin film is subjected to thermal oxidation treatment in an oxidizing atmosphere such as air in an electric furnace. This heat treatment is executed generally at about <=1200 deg.C. In this way, the dispersed grains are formed at uniform density on the surface of the substrate with the (c) axis orientated vertically to the substrate. Moreover, the grai size and grain density can be regulated by changing the molar ratio of the rare earth elements to the copper element. Thus, they are suitable as the pinning points for a superconductive thin film or as the active points for carriers and catalysts uniformly distributed over the substrate.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing a particle-dispersed oxide thin film containing a rare earth element. More specifically, the present invention is a particle containing a rare earth element useful for a magnetic sensor, an infrared detector, an electromagnetic wave detector or an ultra-high speed computer element, as well as a petroleum refining catalyst, an automobile exhaust gas purification catalyst or a gas sensor utilizing a catalytic action. The present invention relates to a method for manufacturing a dispersed oxide thin film.

[0002]

2. Description of the Related Art Conventionally, as a practical superconducting material, a material made of an element such as Nb or Ge or a metal such as an Nb-Ge alloy has been known. However, although these conventional superconducting materials are high in density and rich in extensibility, they have a low critical temperature Tc of 23 K or less. Therefore, when they are used, it is necessary to use a large amount of expensive liquid helium as a coolant. However, there has been a problem that the superconducting machine and the sensor using them are large and expensive.

On the other hand, in recent years, a critical temperature Tc is Y-Ba-Cu-O based on liquid nitrogen temperature or higher, Bi-Pb-Sr-.
Oxide superceramics such as Ca-Cu-O have been found, and the development of superconductivity application technology has been activated. However, since these oxides are only hole-doped (p-type superconductor), they are greatly restricted when forming an electronic device.

Further, how much a superconducting current can flow in a superconductor in a magnetic field is important for application, but this depends on how many pins can strongly pin the quantized magnetic flux. . However, at present, the precipitates in the superconductor, the grain boundaries, or the lattice defects due to ion irradiation play a role of pinning, but it is difficult to uniformly introduce pinning points to the superconductor.

In such a situation, including rare earth,
Application of so-called (Ln) ₂ CuO ₄ type oxide (Ln: rare earth element) is expected. Among the superconducting oxides having a high critical temperature Tc and containing copper, the (Ln) ₂ CuO ₄ type has a general formula of (Ln1, Ln2, A) CuO _4-Z (where Ln1 and Ln2 are rare earth elements). , A is an alkali or alkaline earth element). Its crystal structure has the simplest structure in which only one layer of Cu—O is contained in the unit cell. The critical temperature Tc is 20 to 40K, which is lower than that of Y-based or Bi-based superconducting oxides, but is superior to that of metallic superconductors.

There are three types of compounds represented by this general formula. The first one is a K ₂ NiF ₄ type (T type) with a Cu coordination number of 8, and (La, Ba) ₂ CuO ₄ belongs to this, and is a superconductor using holes as carriers. is there. The second one is called T'type and has a Cu coordination number of 4
This is also called an electron-doped type, and is a superconductor having electrons as carriers. The third type is called a T ″ type, which has a coordination number of Cu of 5 and is a superconductor having holes as carriers.

As described above, the above (Ln) ₂ CuO ₄
The type crystal has a critical temperature Tc of a metal or alloy superconductor.
Higher, electron-doped (n-type) and hole-doped (p
There are two types), and by combining both,
It has an advantage that the number of types of electronic devices is doubled. However, unlike the metal-based superconducting material, the (Ln) ₂ CuO ₄ type oxide needs to be oriented with respect to the substrate because the flowing direction of superconducting electrons has a specific relationship with the crystal plane. . Further, in order to prevent the deterioration of superconductivity due to the influence of the magnetic field, it is necessary to introduce uniform pinning points in the superconductor. Furthermore, although such oxides are expected to be used as catalysts or sensors, in actual use, for example, in order to increase the frequency of contact with gas, it is necessary to increase the specific surface area. There were also problems.

The present invention has been made in view of the above circumstances and has a high orientation, a pinning point is uniformly introduced into a thin film, and is strong against a magnetic field and has a high critical current density. It is an object of the present invention to provide a method for producing a conductive oxide thin film, and a new oxide thin film for producing a catalyst, a sensor element, and the like which can control the activity and reaction rate on a carrier or a substrate.

[0009]

In order to solve the above-mentioned problems, the present invention contains one or more kinds of rare earth elements and copper and exists as a thin film in a state of particles dispersed on a substrate surface. A heterostructured superconducting thin film, characterized in that a particle-dispersed oxide thin film containing a rare earth element (claim 1) and a superconducting oxide film are disposed and integrated on the oxide thin film. (Claim 2) is provided.

Further, according to the present invention, a sputtering apparatus is used to target rare earth elements and copper elements,
A method for producing a particle-dispersed oxide thin film containing a rare earth element, characterized in that a metal multi-layer is formed on a substrate by sequentially sputtering these, and then thermal oxidation is performed in an oxidizing atmosphere. ) And a superconducting oxide film is formed on the thin film, and a method for producing a heterostructure superconducting thin film (claim 7) is provided.

Further, according to the present invention, in the above-mentioned method for producing an oxide thin film, a multi-step thermal oxidation treatment is performed at a temperature of 1200 ° C. or lower (claim 4), and further 600 to 850.
Controlling the particle size and particle density of dispersed particles by heat treatment at 90 ° C. and then thermal oxidation at 900 to 1200 ° C. (claim 5) and by controlling the molar ratio of rare earth element and copper element to be sputtered. (Claim 6) and the like are also provided.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, the substrate is not particularly limited, but quartz glass, alumina, zirconia,
Stabilized zirconia, magnesia (MgO), strontium titanate (SrTiO3) and the like are suitable. However, in order to obtain an oriented or single crystal thin film, a single crystal of MgO or SrTiO ₃ having a specific crystal plane cut out is preferable.

Similarly, although the kind of the rare earth element is not particularly limited, Nd, Pr, Sm, La and the like are exemplified from the viewpoint of manufacturing a heterostructure superconducting thin film. When the oxide thin film of the present invention is manufactured by sputtering, the procedure is as follows. First, sputtering is performed using Ar ions with a rare earth element as a target. Next, similarly sputter with a copper element as a target,
A metal multilayer film is formed on the substrate. Alternatively, the copper element may be sputtered first, and then the rare earth element may be sputtered. The sputter conditions are not particularly limited, but generally, the degree of vacuum is 10 ⁻⁵ to 10 ⁻² Pa, and the substrate temperature is from room temperature to 70.
0 ° C. is appropriate.

The thin film produced under the above conditions is subjected to oxidation treatment in an electric furnace in an oxidizing atmosphere such as air. The heat treatment is generally performed at a temperature of about 1200 ° C. or lower. And in this case, from the beginning a high temperature, for example 90
When performed at 0 to 1100 ° C., it is feared that the metal film may evaporate and disappear.
For example, it is desirable to carry out in at least two stages. That is, since heat treatment at a temperature of less than 600 ° C. does not easily oxidize and diffuse and does not easily crystallize, 60
After oxidizing the metal film by oxidation at a relatively low temperature of 0 to 850 ° C. for 5 to 20 hours, a temperature range higher than 900 to 1
Heat treatment is performed at 200 ° C. for 1 to 3 hours in the same atmosphere to disperse the metal film into particles. In the heat treatment at a temperature of 900 to 1200 ° C., the CuO layer becomes a liquid phase, and this liquid phase causes the orientation of the film.

The atmosphere for the thermal oxidation treatment may be an appropriate atmosphere such as air or oxygen. For example, the c-axis of the dispersed particles produced by the above embodiment is oriented perpendicular to the substrate, and is formed on the substrate with a uniform density. The crystal grain size and grain density can be controlled by changing the molar ratio of the rare earth element and the copper element. Therefore, it is suitable as a pinning point of a superconducting thin film containing a rare earth element having a high critical current density in a magnetic field, or as an active point of a catalyst uniformly distributed on a carrier or a substrate.

In order to obtain a superconducting material that is strong against a magnetic field, the particle-dispersed oxide film alone does not function. Therefore, a continuous film is additionally formed on the system consisting of the substrate and dispersed particles by a physical or chemical vapor phase method to form a superconductor-normal conductor (here, particle dispersed system) heterostructure. In this structure, the normal conductor (particle dispersion system) functions as a pinning point and becomes a superconducting material that is strong against magnetic fields. The heterostructure is a structure in which two or more kinds of materials having different functions exist in the same material, and the functions (impacts) which cannot be achieved by a simple substance (material) constituting the structure are exhibited. That is, a superconducting film alone is weak against a magnetic field, but by forming a heterostructure by interspersing normal conducting materials as pinning points there,
It becomes a material that is strong against magnetic fields. As a physical vapor phase method, MBE
(Molecular beam epitaxy) method, sputtering method, vapor deposition method, etc.
As the chemical vapor deposition method, a CVD method (chemical vapor deposition method), MOCVD (organic metal CVD method), or the like is used.

In producing a superconducting film having a pinning point that is strong against a magnetic field, the particle dispersion system must be a normal conducting substance. In the case of a rare earth oxide containing Cu, it does not exhibit superconductivity and is a normal conductive material, and a rare earth high temperature superconducting oxide also contains an oxygen content (for example, (N
It does not exhibit superconductivity depending on y) in d, Ce) ₂ CuO _y . Further, since the critical temperature Tc of the rare earth high temperature superconducting oxide is at most about 40K, a superconducting oxide having a higher critical temperature, for example, YBa ₂ Cu ₃ O.
_When combined with _x (Tc = 90K), the rare earth high temperature superconducting oxide also functions as a normal conducting material depending on the use temperature of the material (40 to 90K).

The composition of the film to be added later to the particle dispersion system which functions as a pinning point is Cu.
All high temperature oxide superconductors including are applicable. For example, Y-based (YBa ₂ Cu ₃ O _x ) and Bi-based (Bi-Pb)
-Sr-Ca-Cu-O), and high temperature oxide superconductors containing rare earths ((Nd, Ce) ₂ CuO _x etc.). Examples will be shown below, and the method for producing a particle-dispersed oxide thin film containing a rare earth element of the present invention will be described in more detail.

[0019]

EXAMPLES Example 1 A three-pole DC magnetron sputtering apparatus was used,
An oxide thin film of Nd ₂ CuO ₄ composition, which is a matrix of a superconducting oxide of d _0.85 , Ce _0.15 ) ₂ CuO ₄ composition, was prepared.

The conditions for forming the thin film were a vacuum of 10 ^-4 Pa, an emitter current of 40 A, a plasma current of 4.0 A, and a target voltage of 100 to 200V. Nd for target
Metal and copper metal, SrTiO3 (100 faces) for the substrate
It was used. First, from one sputter particle source, Nd
Was sputtered to form a metal film on the substrate, and then Cu was sputtered thereon to form a metal multilayer film. Further, this film was subjected to a two-step oxidation treatment. As a first step, the above film was oxidized in air at 800 ° C. for 10 hours, and as a second step, heat treatment was performed in air at 1100 ° C. for 1 hour to improve the crystallinity of the film crystal. An oxide thin film having a composition of ₂ CuO ₄ was obtained. X-ray diffraction analysis was performed in order to analyze the structure of Nd ₂ CuO ₄ thus obtained.

FIG. 1 of the accompanying drawings shows the result of an X-ray diffraction analysis of Nd ₂ CuO ₄ produced according to the present invention. As shown in FIG. 1, it can be seen that Nd ₂ CuO ₄ produced according to the present invention has a high c-axis orientation. Nd _1.83 Ce _0.17 CuO formed by the sputtering method based on the above Nd ₂ CuO ₄ film
The heterostructure film of _X / YBa ₂ Cu ₃ O _7- δ had Jc = 1.1 × 10 ⁷ A / cm ² at 77K in zero magnetic field. Example 2 As in Example 1, one sputtered particle source
d was sputtered to form a metal film on the substrate, and Cu was sputtered thereon to form a metal multilayer film.

Further, this film was subjected to a two-step oxidation treatment. As a first step, the above film was placed in air at 800 ° C.
Then, as a second step, a particle-dispersed thin film of Nd ₂ CuO ₄ composition was obtained by heat treatment in air at 1100 ° C. for 1 hour. X-ray diffraction analysis was performed to analyze the structure of the dispersed particles thus obtained. FIG. 2 of the accompanying drawings shows that Nd ₂ C produced according to the present invention.
2 shows the result of X-ray diffraction analysis of a particle-dispersed thin film having a uO ₄ composition.

Nd ₂ C prepared as shown in FIG.
It can be seen that the particle-dispersed thin film of uO ₄ composition has a high c-axis orientation. FIG. 3 of the accompanying drawings shows an SEM photograph of a particle-dispersed thin film of Nd ₂ CuO ₄ composition prepared according to the present invention. As shown in FIG. 3, in the produced particle-dispersed thin film of Nd ₂ CuO ₄ composition, the dispersed particles are uniformly distributed on the substrate. Example 3 Using the same apparatus as in Example 1, the sputtering time was adjusted to change the molar ratio of Nd and Cu to prepare a metal multilayer film, and this film was subjected to a two-step heat treatment. As a first step, the above membrane was exposed to air at 800 ° C for 1 hour.
Oxidation was performed for 0 hours, and as a second step, heat treatment was performed in air at 1100 ° C. for 1 hour to obtain a particle dispersion type thin film.

FIG. 4 of the accompanying drawings shows the relationship between the molar ratio of sputtered Nd and Cu and the particle size of the particle-dispersed thin film of Nd ₂ CuO ₄ composition prepared according to the present invention. Shows the relationship between the molar ratio of Nd and Cu and the particle density. As shown in FIGS. 4 and 5, Cu
When the deposition amount of is increased, the size of dispersed particles becomes larger,
It can be seen that the grain density decreases.

[0025]

As described in detail above, according to the present invention, it is possible to easily prepare a system in which highly oriented crystal grains of a superconducting oxide containing a rare earth element are uniformly dispersed on a substrate. That is, it is useful for producing a superconducting oxide thin film in which a normal conducting substance is dispersed as a pinning point in a superconducting thin film and which has a high current density that is strong against a magnetic field.

By changing the molar ratio of the rare earth element and the copper element, the grain size and grain density of the crystal grains can be easily controlled, and it is useful for producing a catalyst whose activity and reaction rate can be controlled.

[Brief description of drawings]

FIG. 1 is a diagram showing a result of an X-ray diffraction analysis of a continuous thin film having a composition of Nd ₂ CuO ₄ produced according to the present invention.

FIG. 2 is a diagram showing a result of an X-ray diffraction analysis of a particle-dispersed thin film having a Nd ₂ CuO ₄ composition produced according to the present invention.

FIG. 3 is an electron microscope (SEM) replacing the drawing of a particle-dispersed thin film of Nd ₂ CuO ₄ composition prepared according to the present invention.
It is a photograph.

FIG. 4 is a diagram showing a relationship between a sputtered Nd-Cu molar ratio and a particle size of a particle-dispersed thin film having an Nd ₂ CuO ₄ composition manufactured by the present invention.

FIG. 5 is a diagram showing a relationship between a molar ratio of Nd and Cu and a grain density.

Claims (7)

[Claims] 1. Containing one or more rare earth elements and copper,
A particle-dispersed oxide thin film containing a rare earth element, which is present as a thin film in which particles are dispersed on the surface of a substrate. 2. A heterostructure superconducting thin film, wherein a superconducting oxide film is disposed and integrated on the oxide thin film of claim 1. 3. A metal multilayer film is formed on a substrate by sequentially sputtering a rare earth element and a copper element as targets with a sputter device, and then performing thermal oxidation treatment in an oxidizing atmosphere. A method for producing a particle-dispersed oxide thin film containing a rare earth element. 4. The production method according to claim 3, wherein the thermal oxidation treatment is carried out in multiple stages at a temperature of 1200 ° C. or lower. 5. The method according to claim 3, wherein the heat treatment is performed at 600 to 850 ° C., and the thermal oxidation treatment is then performed at 900 to 1200 ° C. 6. The method according to claim 3, wherein the particle diameter and particle density of the dispersed particles are controlled by controlling the molar ratio of the rare earth element and copper element to be sputtered. 7. A heteroconductive film characterized in that a superconducting oxide is physically or chemically formed on a particle-dispersed oxide thin film containing a rare earth element, which is produced by the method according to any one of claims 3 to 6. Method for manufacturing structural superconducting thin film.