JPH0350192A - Production of superconducting film and its device - Google Patents

Abstract

PURPOSE:To form the multi-component oxide superconducting film having a high critical temp. and large critical current density by a spray pyrorinse method by atomizing a raw material soln. having a specific compsn. by means of ultrasonic oscillation and passing the raw material together with oxygen as a carrier gas through the surface of a perpendicularly held high temp. substrate. CONSTITUTION:A device having a flexible film 8 consisting of vinyl, etc., in the bottom is immersed into water 10 in a water tank 9 having an ultrasonic oscillator 11 in the bottom. The raw material soln. 2 of, for example, a Bi-Sr-Ca-Cu system, is put into the device and a narrow and rectangular film forming chamber 3 is provided above the device and a raw material atomizing chamber 2 below the same. The substrate 6 consisting of an MgO single crystal, etc., is mounted in the film forming chamber 3 and is heated by a heater 7 to 450 to 800 deg.C. The raw material soln. 1 is atomized by the ultrasonic oscillation generated by the ultrasonic oscillator 11 and gaseous O2 as the carrier gas is supplied from a gas introducing port 4 and is risen as the gaseous mixture with the atomized raw materials in the region within 10mm from the surface of the substrate 6, by which the superconducting film consisting of the multi component oxide of the B-Sr-Ca-Cu-O system having a high critical temp. and a large critical current density is formed on the surface of the substrate 6.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing a superconducting film and an apparatus therefor. More specifically, the present invention provides a method for producing a superconducting film with excellent characteristics with a thickness of approximately 0.5 μm to 1000 μm by a spray pyrolysis method, and a novel configuration of an apparatus used to carry out this method. Regarding.

Conventional technology Complex oxide superconducting materials discovered in recent years are
Since it has an extremely high superconducting critical temperature compared to other superconducting materials, various research is being conducted in various fields toward the practical application of superconducting technology.

It is known that superconducting materials manufactured by powder metallurgy, which is the most common manufacturing method for composite oxide-based superconducting materials, have a low superconducting critical current density, which decreases extremely in the presence of a magnetic field. In contrast, high critical current densities have been observed in superconducting materials fabricated as thin films from an early stage, and efforts are being made to further improve this.

Sputtering, electron beam evaporation, and the like are known as representative methods for forming composite oxide superconducting thin films. It is known that these methods can produce superconducting thin films with excellent crystal orientation, and can produce conductive thin films having high critical temperatures and high critical current densities.

However, these methods require complicated vacuum equipment and its operation, and generally have extremely slow film formation speeds, so they cannot be said to be methods suitable for practical use.

Therefore, it has been proposed to fabricate a superconducting film by a method called spray pyrolysis. This spray pyrolysis method is a method of forming a film on a heated substrate by spraying a solution of raw materials such as nitrate, acetate, chloride, etc. It has excellent characteristics.

■No vacuum equipment is required, making it easy to expand the area.

■Fast film formation speed.

(2) Since the raw material reaches the deposition surface or its vicinity in a solution state, composition control can be performed accurately, especially in the deposition of multi-element thin films.

■It is generally possible to form films with excellent crystallinity.

Regarding the preparation of superconducting thin films by the spray pyrolysis method, please refer to the Japanese Journal of
Applied Physics Vol, 27 (198
8), Nα Hada pp, L1669, ■ High Temperature Superconductivity Data Book supervised by Maruzen Publishing/New Technology Development Corporation, page 26, etc.

Problems to be Solved by the Invention The superconducting film produced by the spray pyrolysis method described in the above-mentioned literature shows good C-axis orientation by selecting an appropriate substrate, and can be used at relatively high temperatures. It has been confirmed that it exhibits effective superconducting properties.

However, currently implemented methods, e.g.
There is a clear difference in the superconducting critical temperature between 94K, the temperature at which the resistance begins to decrease, and 89K, the temperature at which the resistance becomes unmeasurable. Moreover, high critical current density has not yet been achieved in superconducting films obtained by conventional methods.

Therefore, the purpose of the present invention is to solve the above-mentioned problems of the prior art and provide a new method for producing a superconducting film exhibiting better characteristics by basically adopting the spray pyrolysis method. It is said that

Another object of the present invention is to provide a novel film forming apparatus for carrying out the method provided by the present invention.

Means for Solving the Problems According to the present invention, there is a method of forming a film made of an oxide superconducting material on a substrate by a spray pyrolysis method, the underlying substrate being heated at a temperature in the range of 450 to 800°C. An oxide film is formed on the substrate by heating it to a temperature of A method for manufacturing a superconducting film is provided, the method comprising the steps of:

Furthermore, according to the present invention, as an apparatus for carrying out the method for producing a superconducting film according to the present invention, a means for holding the substrate so that the film-forming surface of the substrate is perpendicular, and a means for holding the substrate so that the film-forming surface of the substrate is vertical, an atomizing means for atomizing a liquid raw material containing constituent elements; a means for supplying a carrier gas for conveying the atomized raw material gas generated by the atomizing means; and a carrier gas supplied by the supplying means. The atomized raw material being conveyed is
A superconducting film manufacturing apparatus is provided, comprising: a source gas guiding means configured to flow from below to above on the film forming surface of the substrate in parallel with the film forming surface. .

Function: One of the main features of the method for manufacturing a superconducting film according to the present invention is that the substrate temperature during film formation is limited to 450 to 800°C.

That is, a detailed study of the process of manufacturing a superconducting film using the conventional spray pyrolysis method revealed that in the conventional method, the substrate temperature during film formation was set at around 400°C. However, it was found that when the film was formed at this substrate temperature, the inside of the Mi conductive film was not dense, and therefore a high critical current density could not be achieved. Therefore, as a result of examining various substrate temperatures, it was found that the above range is preferable for producing a dense superconducting film.

Here, if the substrate temperature is lower than the above range, a dense superconducting film cannot be obtained as described above, and excellent characteristics such as critical current density cannot be achieved. On the other hand, when the substrate temperature is higher than the above range, thermal convection generated near the film forming surface due to the heat of the substrate inhibits the adhesion of the raw material components contained in the raw material gas to the film forming surface.

In addition, in the film forming method according to the present invention, since the substrate temperature is higher than that in the conventional method, it is more disadvantageous than the conventional method in terms of the effect of thermal convection on film forming as described above.

Therefore, as a second main feature of the method according to the present invention,
It is proposed to form a superconducting film while controlling the flow of source gas so that it flows in a region within 10 mm from the film-forming surface of the substrate.

That is, by limiting the flow path of the source gas, it is possible to prevent the source gas from separating from the film forming surface due to thermal convection.

The reason why the flow range of the source gas was set within 1Q mm from the film forming surface is as follows. That is, in the film forming process using the spray pyrolysis method, since atomized water droplets transport the raw material components, it is advantageous to set conditions such that the water droplets reach the vicinity of the substrate by turbulent airflow. For this purpose, it is effective to make the flow path thinner so that the laminar flow of the source gas becomes thinner. As will be specifically described later, the range in which such an effect becomes significant is 1Q mm or less in terms of the thickness of the flow path with respect to the substrate.

In addition, when atomized raw material gas enters the narrow flow path of the film forming chamber, there is a phenomenon in which the laminar flow of the raw material gas becomes thinner in the vicinity of the population.
This is known as the "demographic effect."

According to a preferred embodiment of the present invention, it is advantageous to make use of such a "Purro effect", and specifically, the substrate during film formation is placed within 100 mm from the inlet of the raw material gas. It is preferable.

In addition, in order to prevent the source gas from separating from the film-forming surface of the substrate due to thermal convection as described above, the film-forming chamber should be arranged vertically so that convection occurs parallel to the film-forming surface. is also advantageous.

Furthermore, the present invention proposes an apparatus for carrying out the method for producing a superconducting film according to the present invention as described above.

This apparatus is the same as an apparatus for carrying out a conventional spray pyrolysis method in that it includes means for atomizing the raw material and means for guiding the raw material gas to the film-forming surface of the substrate. That is, the main feature of this device, as will be specifically described later, is that it is configured to limit the flow path of the source gas flowing on the film-forming surface to a range within 1Q mm from the film-forming surface of the substrate. That's true.

By adopting such a configuration, in this device, even if the substrate temperature is set to a high temperature of 450° C. or higher, drifting of the raw material gas is not inhibited by thermal convection.

Furthermore, according to one of the preferable features of the present invention, by holding the substrate vertically and flowing the source gas from below to above in parallel with the substrate, the source gas near the film forming surface can be favorably replaced. At the same time, the influence of thermal convection can be effectively eliminated.

The characteristics of the spray pyrolysis method described above are very advantageous for producing multi-element thin films or thick films such as composite oxide superconducting materials, and the method and apparatus of the present invention as described above can be used. By using this, a dense composite oxide film can be obtained. By heat-treating such a composite oxide film according to a conventional method, a thickness of 0.5
A high-quality superconducting film having a wide range of thickness from about μm to 1000 μm can be obtained.

In addition, the method according to the present invention can be applied to the known La-3r-Cu system,
Any of these can be applied to the production of thin films using composite oxide superconducting materials such as Y--Ba--Cu, but particularly advantageous is the number that satisfies the following formula: % formula %. ] A composite oxide-based superconducting material having a composition that satisfies the following is mentioned. This composite oxide superconducting material has a critical temperature of 10
It has advantageous features such as a very high G value of 0 or more, and less G deterioration after fabrication. Further, as a base substrate that can be advantageously used in the method of the present invention, MgO1SrTiO
s, Y S Z, etc.

Hereinafter, the present invention will be described in more detail with reference to the drawings, but the following disclosure is only one embodiment of the present invention, and does not limit the technical scope of the present invention in any way.

Embodiment FIG. 1 is a diagram schematically showing a configuration example of a film forming apparatus that can be used when carrying out the method for producing a superconducting film by spray pyrolysis according to the present invention.

As shown in FIG. 1, this apparatus is mainly composed of an atomization chamber 2 containing a raw material solution 1 and a film forming chamber 3 communicating with the atomization chamber 2. The atomization chamber 2 is provided with a supply hole 4 through which carrier gas is supplied, and the atomization chamber 2 of the film forming chamber 3 is provided with a supply hole 4 through which a carrier gas is supplied.
A carrier gas discharge hole 5 is provided on the opposite side. Further, the film forming chamber has a side wall having a width larger than the substrate 6 used for film forming, and a side wall having a width of 3 mm to 3 Q mm as described later.
It has a substantially rectangular cross section defined by a side wall configured such that the width can be changed up to 100 mm, and a substrate holder for holding the substrate 6 and a heater for heating the substrate 6 are mounted on the side wall. 7.

Further, the bottom of the atomization chamber 2 is closed with a flexible membrane 8 made of vinyl or the like to prevent the raw material solution 1 from flowing out. The bottom of the atomization chamber 2 is immersed in water 10 contained in a water tank 9, and an ultrasonic vibrator 11 is placed directly below the atomization chamber 2.

The film forming apparatus configured as described above is used as follows.

First, the raw material solution 1 is stored inside the atomization chamber 2, and
The substrate 6 is fixed in the film forming chamber 3. After the substrate 6 is heated to a desired substrate temperature by the heater 7, the ultrasonic transducer 11 is operated while supplying the carrier gas through the supply hole 4. The ultrasonic waves generated by the ultrasonic transducer 11 are transmitted to the water 10 and the membrane 8.
The raw material solution 1 is atomized through. The atomized raw material solution 1 flows into the film forming chamber 3 as a raw material gas together with the carrier gas. In the film forming chamber 3, part of the source gas adheres to the surface of the substrate 6, forming a thin film having a composition based on the composition of the source gas.

The reason why the superconducting oscillator 11 is placed through water and a vinyl film is to prevent the superconducting oscillator 11 from being corroded by the nitrate aqueous solution.

Fabrication Example 1 A superconducting film was fabricated according to the film forming method according to the present invention using the film forming apparatus configured as described above.

First, a raw material solution was prepared. In this production example, the water is 400m
j! For this, a solution of was used. On the other hand, as a substrate, MgO
A single-crystal substrate was used, and its (001) plane was the film-forming surface.

As the ultrasonic transducer 11, CF manufactured by Sanyo Electric Co., Ltd.
The model K-8450F humidifier was used.

02 gas is used as carrier gas, 1000cc/min
was supplied at a flow rate of

Films were formed using the apparatus described above under various conditions as shown in Table 1 below. In this manufacturing example, the width from the film forming surface of the substrate to the film forming chamber wall opposite to the film forming surface is lQm.
Film formation was performed with the setting at m.

After film formation, each superconducting film sample produced in this way was heat-treated at 930°C for 4 hours in zero air flow, and then the superconducting critical temperature Tc (the temperature at which electrical resistance becomes unmeasurable) was 77, 3. Critical current density Jc at K
was measured and evaluated. These evaluation results are also shown in Table 1.

Table 1 As can be seen from Table 1, when the substrate temperature is 600°C,
The highest critical temperatures and critical current densities are achieved.

Production Example 2 Using the same raw materials and substrates as in Production Example 1, superconducting films were produced under various flow conditions of the raw material gas.

The manufacturing conditions are as shown in Table 2 below.

Note that the substrate temperature was 600°C. In addition, each of the fabricated superconducting film samples was heated at 930°C in zero air flow after film formation.
After performing heat treatment for an hour, each superconducting critical temperature T
c (temperature at which electrical resistance becomes unmeasurable) and 77,3
The critical current density Jc at K was measured and evaluated. These evaluation results are also shown in Table 2.

As can be seen from Table 2, the highest critical temperature and critical current density are achieved when the channel width is 5 mm. Also,
When the channel width exceeds 1Qmm, the obtained film does not exhibit effective superconducting properties.

DETAILED DESCRIPTION OF THE INVENTION As described in detail, according to the present invention, a high-quality superconducting film exhibiting a high critical temperature and high critical current density can be fabricated by a spray pyrolysis method having a number of excellent features.

As mentioned above, the spray pyrolysis method has a very high film formation rate compared to other film formation methods, so
It is also possible to produce a thick film of about m to 1000 μm. Therefore, the superconducting film produced by this method can also be applied as a wiring material or a magnetic shielding material.

[Brief explanation of drawings]

FIG. 1 is a diagram schematically showing the configuration of a film forming apparatus that can be used when carrying out the method for producing a superconducting film according to the present invention. [Main reference numbers] 1... Raw material solution, 2... 3... Film forming chamber, 4... 5... Carrier gas exhaust hole, 7... Heater, 8... 9... Water tank , 11... Atomization chamber, carrier gas supply hole, ... Substrate, membrane, ultrasonic vibrator

Claims (2)

[Claims] (1) A method of forming a film made of an oxide superconducting material on a substrate by spray pyrolysis, in which the underlying substrate is heated to a temperature in the range of 450 to 800°C, and the desired oxide superconducting film is formed. A superconducting film comprising the step of forming an oxide film on the substrate by flowing a mist of raw material gas containing the constituent elements in an area within 10 mm from the film-forming surface of the substrate. Fabrication method. (2) An apparatus for carrying out the method according to claim 1, comprising means for holding the substrate so that the film-forming surface of the substrate is vertical, and a liquid containing constituent elements of the target oxide superconducting material. an atomizing means for atomizing the raw material; a means for supplying a carry-in gas for carrying in the atomized raw material gas generated by the atomizing means; and the mist carried in by the carrier gas supplied by the supply means. Preparation of a superconducting film characterized in that the method includes a source gas guiding means configured such that the raw material flows from below to above on the film forming surface of the substrate in parallel with the film forming surface. Device.