JPH02149403A - Process for preparing oxide superconductor and heat-treating apparatus of the superconductor - Google Patents

Abstract

PURPOSE:To obtain an oxide superconductor having superior characteristics consisting of satisfactorily oriented crystal structure by heat-treating an oxide superconductor or a precursor thereof while generating a temp. gradient in the superconductor or the precursor. CONSTITUTION:A substrate 20 is extended over supporting members 6, 7 after forming a thin film of a precursor of an oxide superconductor on the substrate 20. The supporting member 6 is heated at a desired temp. and an end side of the substrate 20 held in contact with the supporting member 6 is heated uniformly through the supporting member 6 at an almost same temp. as the supporting member 6. On one hand, the supporting member 7 is cooled through a heat transmitting body 9 with a cooling device 8, and another end side of the substrate 20 held in contact with the supporting member 7 is cooled. By heat-treating a thin film of an oxide superconductor or a precursor thereof while generating a temp. gradient in the thin film, a thermal stress exerts on the thin film due to the temp. gradient, but crystals of the thin film tend to transfer to an energetically stable state by reducing the thermal stress. Thus, orientation characteristics of the crystals are improved, and an oxide superconducting thin film having superior critical current characteristics is formed.

Description

Detailed Description of the Invention "Field of Industrial Application" The present invention relates to a method for producing an oxide superconductor that can obtain an oxide superconductor with good crystal orientation, and a heat treatment apparatus used in this production method. Regarding.

``Prior Art J'' In recent years, oxide superconductors with critical temperatures exceeding liquid nitrogen temperatures have been discovered one after another, but the oxide superconductors currently available contain impurities inside. Due to factors such as poor crystal orientation, this type of oxide superconductor has the disadvantage of poor critical current characteristics.In particular, this type of oxide superconductor exhibits anisotropy that allows electricity to flow easily in a specific direction of the crystal. In order to improve the critical current characteristics of oxide superconductors, it is necessary to improve crystal orientation to produce oxide superconductors with a well-organized crystal structure.

Against this background, in order to obtain an oxide superconductor with a well-ordered crystal structure, 2. Oxide superconductors have been manufactured by applying various thin film manufacturing techniques such as sputtering, CVD (chemical vapor deposition), MBE (molecular beam epitaxy), and laser evaporation.

However, most of the thin films produced by the above-mentioned method are in an amorphous state.1. Since the superconducting properties are also low, the thin film is usually crystallized by heat treatment after film formation to obtain an oxide superconducting thin film with good properties. To perform the heat treatment, an electric heater is provided near the sample inside the processing device, or an electric furnace equipped with an electric heater is used, and these electric heaters are activated to heat the sample. It is carried out in

``Problem to be Solved by the Invention'' However, when an electric heater is placed near a sample or when placed in the same processing container, components of the constituent materials of the electric heater evaporate and cause damage to the inside of the processing container. There is a problem in that these components can affect the superconducting thin film and deteriorate the properties of the superconducting thin film. Further, when the electric heater is energized, the electric heater generates noise, and this noise may become a noise source for the control device of the processing device and affect the control device.

Even when oxide superconductors are manufactured by applying the various film formation techniques and heat treatment techniques mentioned above, there are currently difficulties in achieving sufficient crystal orientation. It is difficult to obtain oxide superconductors that exhibit high critical current values.

The present invention has been made to solve the above problems, and therefore,
The object of the present invention is to provide a method and a heat treatment apparatus for producing a high-performance oxide superconductor having a crystal structure with good orientation.

[Means for solving the problem] In order to solve the problem, the invention described in claim 1 has the following features:
When heat treating an oxide superconductor or its precursor,
The oxide superconductor or its precursor is heat-treated under a temperature gradient.

In order to solve the above problems, the invention described in claim 2 includes: a hollow processing container; a support member provided in the processing container to support an oxide superconductor or its precursor;
A heating device that partially heats the oxide superconductor or its precursor by irradiating the oxide superconductor or its precursor supported by the support member or the support member with light, and increases the temperature of a portion other than the heated portion. It also includes a cooling means for suppressing this.

"Operation" Since heat treatment is performed with a temperature gradient applied to the oxide superconductor or its precursor, M stress is generated inside the oxide superconductor or its precursor during heat treatment, which causes the oxide superconductor to Alternatively, the precursor crystal attempts to reduce thermal stress and become an energetically stable single crystal state. Therefore, the heat treatment causes the crystals to be uniformly oriented, producing an oxide superconductor with a well-ordered crystal structure and good critical current characteristics.

Also, if a part of the precursor is heated with light and the pond part is cooled with a cooling device, 1. The oxide superconductor or its precursor is heat-treated under a temperature gradient. moreover,
By appropriately adjusting the output of the heating device and the output of the cooling device, a desired temperature gradient can be provided to the oxide superconductor or its precursor.

``Example'' Figure 1 shows an example of an apparatus used to carry out the method of the present invention. It is configured to include a heating device 2 connected thereto.

The processing container l is connected to a vacuum exhaust device 3 through an exhaust hole 1a formed in its side wall, and is connected to an inlet pipe 5.
It is connected to the reaction gas supply source 4 via. The introduction pipe 5 passes through the side wall of the processing container 1 and extends to the center of the processing container l.

The evacuation device 3 is capable of evacuating the inside of the processing container 1, and the reaction gas supply source 4 is used to supply pure oxygen gas or an inert gas containing oxygen gas to the inside of the processing container 1. be.

Further, in the center of the processing container 1, support members 6.7 of type 11 made of a metal material with good thermal conductivity such as stainless steel or copper are installed spaced apart from each other. These supporting members 6 and 7 are used to support the precursor of the oxide superconductor described later inside the processing container, so the supporting members 6 and 7 are made of materials that can withstand high temperatures during the heat treatment described later. It is preferable to form it from a metal material with good conductivity. In addition,
The shape of the support member 6.7 is not limited to the side face IJ type shown in the drawings, but may be any shape as long as it can support the precursor described later. Therefore, a chuck-like material that can hold the precursor is sufficient.

On the other hand, a cooling device 8 such as a cryostat is installed above the support member 7 on the right side of FIG. ing. The cooling bag @8 is formed so that a refrigerant such as liquid nitrogen can be housed or circulated therein. In this example, the cooling device 8 and the support member 7 are installed separately, but the cooling device 8 may be provided in direct contact with the support member 7 and the heat transfer member 9 may be omitted.

Further, a shutter plate lO is installed below the support member 6.7 and apart from the support member 6.7, and a shutter plate lO is installed on the side of the processing container l. An adjustment knob 11 connected to the shutter plate IO is formed.

The shutter plate 10 is provided with an aperture hole 10a below the support member 6, and by rotating the adjustment knob 11, the opening area of the aperture hole 10a can be adjusted to 11 sections.

On the other hand, a heating device 2 is connected to the bottom of the processing container l. This heating device 2 includes a reflection box 14 equipped with a heat source lamp 13 such as an infrared lamp inside, and a light guide 1 such as a quartz rod attached to the reflection box 14.
It is mainly composed of 5. The reflection box 14
A curved reflection mirror 16 is formed on the inner surface of the light guide 1. One end of the light guide 15 is attached to the reflection box 14 so as to face the heat source lamp 13.
The tip end of 5 passes through the bottom wall 11 of the processing container 1 and is close to the throttle hole 10a of the shutter plate 10.

Note that the light guide 15 guides light incident from one end to the other end. In this example, a quartz rod is used for the light guide 15, but this light guide 15 has a structure that guides light. Any type of fiber may be used, so a single-core fiber or a fiber with a bundle structure may be used.

Next, a case will be described in which the method of the present invention is implemented using the apparatus having the above structure.

Prior to carrying out the method of the present invention, a precursor of an oxide superconductor is produced using a conventionally known method.

In this example, since a film-like oxide superconductor is used, M
A substrate 20 made of gO or S rT io , etc.
A precursor thin film of an oxide superconductor is formed thereon using a method such as a CVD method, an MOCVD method, a laser evaporation method, a sputtering method, or an MBE method.

This precursor thin film is then heat treated.

Once the oxide superconductor precursor thin film has been formed on the substrate 20 by the method described above, the substrate 20 is placed so as to straddle the support member 6.7 as shown in FIG. Note that what is installed on the support member 6.7 in this manner may be a thin film of an oxide superconductor that exhibits superconducting properties and is manufactured by the film forming method described above.

Next, the inside of the processing container 1 is evacuated, and oxygen gas or an inert gas containing oxygen gas is supplied into the processing container 1 from the introduction pipe 5. In this case, the inside of the processing container 1 may be evacuated.

Next, the heat source lamp 13 is energized to emit light, and this light is reflected by the reflecting mirror 16 and sent to the light guide 15, and further sent to the inside of the processing container l via the light guide 15, and is supported. The lower surface of the member 6 is irradiated with focused light.

Here, the adjustment knob 11 is turned to adjust the opening area of the shutter plate IO, and the light irradiated from the light guide 15 to the lower surface of the support member 6 is adjusted.

By the above operations, the support member 6 can be heated to a desired temperature, and one end side of the substrate 20 that is in contact with the support member 6 via the support member 6 can be uniformly heated to the same temperature as the support member 6. Be able to do it. On the other hand, the support member 7 is cooled by the cooling device 8 via the heat transfer body 9, and the other end side of the substrate 20 that is in contact with the support member 7 is cooled. Therefore, the part of the substrate 20 that is in contact with the support member 6 is heated to a high temperature, for example, T2°C as shown in FIG. It is heat treated in a heated state.

Note that the heat treatment temperature is appropriately set depending on the type of precursor thin film of the oxide superconductor formed on the substrate. That is, the temperature on the high temperature side of the sample 20 needs to be lower than the melting temperature or decomposition temperature of the oxide superconductor.
The temperature on the low temperature side needs to be higher than the crystallization temperature of the oxide superconductor. Therefore, the temperature on the high temperature side is Y
- When using a precursor thin film of a BaCu-0 based oxide superconductor, the temperature is preferably below the temperature at which the oxide superconductor may decompose, that is, below 950°C;
In the precursor thin film of Ca-Cu-0 based oxide superconductor, the temperature is below the temperature at which the oxide superconductor may melt, that is,
The temperature is preferably 870°C or lower. Moreover, the temperature on the low-temperature side is preferably 400° C. or higher in any system.

Furthermore, although it is preferable that the temperature gradient given during the heat treatment be large, since the maximum temperature on the high temperature side and the minimum temperature on the low temperature side are regulated as described above, it is set within the range resulting from these regulations. Further, since it is necessary to achieve sufficient crystal orientation, the heat treatment time is preferably about 2 to 3 hours or longer, but may be several tens of minutes or more.

As explained above, if a thin film of an oxide superconductor or its precursor is heat-treated while applying a temperature gradient, thermal stress acts on the thin film due to the lAλ degree gradient, and the crystals of the thin film reduce this thermal stress and generate energy. attempts to move to a stable state. Therefore, the crystals in the thin film tend to transition to an energetically stable single crystal state, improving crystal orientation and producing an oxide superconducting thin film with excellent critical current characteristics.

Furthermore, since oxygen gas is supplied through the inlet pipe 5 during the crystal alignment, oxygen deficiency will not occur when the crystals of the oxide superconductor transform from tetragonal to orthorhombic crystals after heat treatment. A thin film of a superconductor with a sufficiently high critical temperature can be obtained.

Note that the apparatus having the above structure has a structure in which the substrate 20 is heated by light energy from the outside, and there is no contamination source such as an electric heater inside the processing chamber 1, so that heat treatment can be performed without contaminating the oxide superconducting thin film. . Furthermore, since the structure is such that light is guided into the processing container 1 by the light guide 15, the substrate 20 inside the processing container 1 can be heated using optical energy even if the side wall of the processing container is not transparent. Further, although the light guide 15 is provided to penetrate the side wall of the processing container 1, the processing container 1 can be easily made into a sealed structure by making the portion through which the light guide 15 passes through an airtight structure.

In addition, in the crystal of the oxide superconductor, the current flows along the direction parallel to the plane formed by the Cu atoms and the zero atoms (that is, the plane parallel to the plane formed by the a-axis and b-axis of the crystal of the oxide superconductor). It is known that the axes perpendicular to the a and b axes,
That is, since the crystal is oriented with the C-axis of the crystal perpendicular to the substrate, the direction in which current can easily flow is parallel to the substrate.

By the way, in the apparatus shown in FIG. 1, the support member 6 is heated to indirectly heat one end side of the substrate 20.
The configuration may be such that the position of a is changed so that one end of the substrate 20 can be directly heated with light.

Further, when a temperature gradient is created on a substrate using the apparatus shown in FIG. 1, a case in which the temperature gradient is controlled and grasped will be described below.

To control the temperature gradient in iQ, attach thermocouples to the back side of the board at the positions shown by symbols A, B, C, and D in FIG. All you have to do is adjust it.

Using an infrared lamp as the heat source lamp and attaching a thermocouple as shown in Figure 3, the substrate temperature was measured. By setting the infrared lamp current to 3 A, 6 A, and 8 A, As shown in Fig. 4, we can demonstrate that it is possible to give a sentence gradient in parts 8, C, and D.

"Production example" Using high frequency sputtering equipment, MgO or S
rT io s, width 10 mm, length 10 mm.

BizP b was sputtered onto a 0.5 mm substrate with a diameter of 17 mm under a pressure of 1 O-3 torr.
o, asryCas Cu30X composition, or Y, Ba, Cu307-8 thickness 2μ
A precursor thin film of an oxide superconductor of m was prepared.

Next, these substrates are heat-treated with a temperature difference such that the right end becomes TloC and the left end becomes T2°C, as shown in Figure 2, to create oxide superconductivity. A thin film was obtained. In addition, as a first comparison, an oxide superconducting thin film was manufactured by heat treatment at T, = T2 without operating the cooling device.

In the above heat treatment, the Bi-based precursor thin film was heated for 3 hours in an Ar gas atmosphere containing 7% O and gas in the inside of the processing container.
The precursor thin film of the system was heat-treated in an O2 gas atmosphere at a pressure of 1 atm for 3 hours.

Table 1 shows the critical current density at 77 K of the oxide superconducting thin film obtained after the heat treatment, the values of the heating temperatures T + and T *, and the temperature difference ΔT between T and T.

(Hereinafter, blank space) From the results shown in Table 1, it is clear that the critical current density is higher for the Y-based thin film and the Bi-based thin film that were heat-treated with a temperature gradient applied to both. It was found that the larger the gradient, the greater the effect of improving the critical current density.

"Effects of the Invention" As explained above, the method of the present invention heat-treats the oxide superconductor or its precursor with a temperature gradient. Since thermal stress acts on the crystals and the crystals are oriented to eliminate this thermal stress, an oxide superconductor having a crystal structure with good orientation can be obtained. Therefore, an excellent oxide superconductor with a high critical current density can be obtained. Also,
By adjusting the rate of temperature gradient, it is possible to obtain an oxide superconductor with a desired crystal orientation.

Further, by using the apparatus of the present invention, an oxide superconductor or its precursor can be heat-treated with a temperature gradient applied to it, making it possible to obtain an excellent oxide superconductor with a high critical current density. Further, by adjusting the output of the heating device and the output of the cooling device, heat treatment can be performed while providing a desired temperature difference. Furthermore, since the oxide superconductor or its precursor can be heated without providing a contamination source such as an electric heater inside the processing container, there is an effect that heat treatment can be performed without contaminating the precursor with atoms of the electric heater.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram showing an embodiment of the device of the present invention, Fig. 2 is a plan view showing the board, Fig. 3 is a plan view showing the position of the thermocouple attached to the back of the board, and Fig. 4 is the thermocouple. FIG. 3 is a diagram showing the relationship between the temperature of each part of the board to which the infrared lamp is attached and the infrared lamp current.・Processing container, exhaust device, ・・support member, heat transfer member, Oa・・throttle hole, 5・・light guide, 6・・reflection mirror heating device, ・・reactive gas supply source, cooling device, 0... Nyatter temporary, 3... Heat source lamp, 20... Board.

Claims (2)

[Claims] (1) A method for producing an oxide superconductor, which comprises heat-treating the oxide superconductor or its precursor in a state where a temperature gradient is applied to the oxide superconductor or its precursor. (2) A hollow processing container, a support member provided in the processing container to support the oxide superconductor or its precursor, and the oxide superconductor or its precursor supported by the support member, or the support An oxide comprising: a heating device that partially heats an oxide superconductor or its precursor by irradiating the member with light; and a cooling means that suppresses a temperature rise in a portion other than the heated portion. Heat treatment equipment for superconductors.