JPH01201008A - Production of thin film of oxide superconductor - Google Patents

Abstract

PURPOSE:To obtain the title thin film of high critical temperature and excellent properties, by applying a voltage to a base material which emits heat by application of electricity to form a thin film of oxide superconductor on the base plate with high-temperature heating and temperature controlling facilitated. CONSTITUTION:A base plate of a nickel-based alloy such as stainless steel or hastelloy is coated with MgO or ZrO and heated in vacuum by applying a voltage (for example up to 600-1,000 deg.C). Then, a thin film of oxide superconductor such as Y-Ba-Cu-O is formed on the base plate, e.g., by the sputtering method, the electricity is stopped to cool down the base plate. Or an infrared lamp may be used to heat the base plate up to the prescribed temperature to form the superconductive layer, instead, then, the heating method may be switched to the voltage application to prepare the crystal structure of the superconductor film and adjust the oxygen content.

Description

DETAILED DESCRIPTION OF THE INVENTION "Industrial Application Field" The present invention relates to a method for producing an oxide superconducting thin film that can be used as a superconducting device such as a Josephson element or a superconducting memory element, or as a superconducting conductor.

"Conventional technology" In recent years, the critical temperature at which the normal conducting state transitions to the superconducting state (
An oxide-based superconductor has been discovered that exhibits a high value of Tc) exceeding the temperature of liquid nitrogen.

Conventionally, methods for producing thin films made of this type of oxide superconductor include, for example, vacuum evaporation, sputtering,
Six types of film forming methods are known, including the M I3 E (molecular beam epitaxy) method, the CVD (chemical vapor deposition) method, and the IV l) (ionic vapor deposition) method. These film forming methods are all performed under low pressure of 1 Torr or less, and in order to supply oxygen into the thin film, the atmosphere is an oxygen gas atmosphere or an oxygen gas atmosphere and an inert atmosphere. A gas atmosphere, such as a gas atmosphere, is used.

However, in the conventional method described above, since the partial pressure of oxygen in the atmosphere is low, it is difficult to introduce the desired amount of oxygen into the crystal of the film formed on the substrate, and the crystal composition differs from the stoichiometric composition. There was a problem of misalignment, and a film body with low superconducting properties such as critical current density tended to be produced.

Conventionally, during or after film formation, the film body is heated to about 600 to 1 OOO'C in an oxygen atmosphere to adjust the crystal structure of the film body, and the oxygen concentration is adjusted to improve the film body. Treatment is being carried out to improve superconducting properties.

To perform the above-mentioned heat treatment, for example, as shown in FIG.
The heater 3 is configured to be able to heat the substrate 4 mounted on the substrate 4, and the film body is heated via the substrate 4 by the heater 3.

In addition, as another method of performing multiple heat treatment, a substrate is placed inside a vacuum chamber, and the film body on this substrate is
There are methods that heat the film body by irradiating infrared rays from outside the vacuum chamber through a transparent window installed in the vacuum chamber, or methods that heat the film body with an infrared lamp provided inside the vacuum chamber. It is being

[Problems to be Solved by the Invention] In the conventional method using the heater 3, there is a problem that the life of the heater 3 is shortened because the heater 3 is used in an atmosphere without oxygen. In addition, in order to heat the substrate to a sufficiently high temperature, it is necessary to use a heater 3 with a large heat capacity, but if the heat capacity claw of the heater 3 is large, it will be difficult to cool down the superconducting thin film after heating. There was a problem in that the cooling rate could not be increased because the heater 3 continued to generate residual heat even after the electricity was turned off, and the superconducting properties tended to deteriorate after film formation. For this reason, conventionally, after forming a superconducting thin film, it was necessary to subject the superconducting thin film to heat treatment in a separate process to adjust the crystal structure of the superconducting thin film and adjust the oxygen concentration. Furthermore, when heating is performed using the heater 3, there is a problem that a part of the constituent material of the heater 3 evaporates during heating and mixes into the superconducting thin film on the substrate 4 as an impurity, deteriorating the superconducting properties of the superconducting thin film. Ta.

On the other hand, in the conventional method of heating using infrared rays,
Since the membrane body is irradiated with infrared rays through a transparent window formed in the vacuum chamber, the irradiation range is limited by the dimensions of the transparent window, making it difficult to heat the membrane body to a sufficiently high temperature. In particular, when the irradiation range of infrared rays is narrow, there is a problem that uniform heating cannot be achieved. Furthermore, since a transparent window is formed in the vacuum chamber, it is not possible to increase the degree of vacuum inside the vacuum chamber, and in some cases, the transparent window causes the problem that the degree of vacuum in the vacuum chamber decreases.

Note that when heating an infrared lamp inside a vacuum chamber, there is a limit to the size of the infrared lamp that can be installed due to the limited space inside the vacuum chamber, which causes the maximum temperature that can be heated to be reached. There is a problem in that there is a limit and heating cannot be done to the desired temperature.

The present invention has been made to solve the above problems,
Oxide superconducting thin films that can be heated to a high enough temperature to adjust the crystal shape and improve superconducting properties, are easy to control temperature, can be rapidly cooled, and do not contain impurities. The purpose is to provide a manufacturing method.

[Means for solving the problem] In order to solve the problem, the first invention uses a base material, at least a part of which is made of a conductive IX material that generates heat when energized, and the base material is heated by energizing the base material. An oxide superconducting thin film is formed on a base material in a heated state, and after the formation of the oxide superconducting thin film, electricity to the base material is stopped and the base material is cooled.

In order to solve the above problem, the second invention uses a base material at least partially made of a conductive material that generates heat when energized,
An oxide superconducting thin film is formed on this base material, and then electricity is applied to the base material to cause the base material to generate heat to heat the oxide superconducting thin film, and after heating for a required time, the current supply to the base material is stopped and the base material is heated. It cools the material.

"Action" jIl, material a71! The superconducting thin film is heated by heating to adjust the crystal structure of the superconducting thin film and adjust the oxygen m in the superconducting thin film. Furthermore, there is no need to provide a heater with a large heat capacity near the base material in order to generate heat in the base material itself, and it becomes possible to rapidly cool the superconducting thin film after heating. Furthermore, since there is no need to provide a heater near the base material, there is no need for impurities to be mixed into the superconducting thin film.

The present invention will be explained in more detail below.

FIG. 1 shows an example of an apparatus used when forming an oxide superconducting thin film by applying the sputtering method using an ion source to form an oxide superconducting thin film. A plate-shaped base material to be formed is shown.

As shown in FIG. 2, this base material 11 includes a plate-shaped main body 12 made of a metal material such as stainless steel, a nickel-based alloy such as Hastelloy, and superalloy, and an MgO layer formed on the upper surface of this main body 12. It is composed of a coating layer 13 made of ZrO, B aT io 3, etc. Note that the constituent material of the coating layer 13 reacts with the constituent elements of the oxide superconducting thin film formed on the base material l, as will be described later. A chemically stable material with low resistance is selected, and the coating layer 13 is formed on the upper surface of the main body portion 12 by a film forming method such as a cylindrical frequency magnetron sputtering method. Further, at least one of the main body portion 12 and the covering layer 13 is made of a material that can be energized and generates heat when energized. Note that the shape of the base material 11 is not limited to a plate shape, and any shape such as a linear shape, a tape shape, or a cylindrical shape can be used.

On the other hand, the oxide superconducting thin film formed on the base material 11 is specifically A-B-C-D (where A is S
c, Y, L a, Ce, P r, Nd, P m, S
m, E u, G d, 'l'' b.

Represents one or more elements of group 111a of the periodic table such as Dy, Ho, Er, 'l'm, Yb, Lu, etc., and B represents Sr, B
a, Ca, f3e.

Indicates one or more elements from group 11a of the periodic table, such as Mg and Ra, and C represents elements of group 1b1 of the periodic table, such as Cu, Ag, and Au.
Of the human element and Nb, D represents Cu or two or more elements including Cu, and D represents elements of group V+b of the periodic table such as O, S, Se, Te, and Po, and elements of group V+b of the periodic table such as F, I3r, I, and At. Indicates two or more elements containing 0 or O among the elements of group IIb of the periodic table. ) series are used.

The composition ratio of each constituent element of this oxide-based superconductor is, for example, in the case of a Y-Ba-Cu-0-based superconductor, Y
:Ba:Cu:0=l:(2~3):(3~
4)+(7-δ) is preferable, and δ is preferably in the range of 0 to 5.

Note that methods for forming the superconducting thin film on the substrate 11 include vacuum evaporation, sputtering, MBE (molecular beam epitaxy), CVD (chemical vapor deposition), and IVD (
Although various film forming methods such as ion vapor phase epitaxy (ion vapor phase epitaxy) and cluster ion beam method can be applied, in this example, a sputtering method using an ion source is used.

In the apparatus shown in FIG. 1, a base material 11 and a target 15 are arranged facing each other inside a vacuum container, and a first ion source 16 is provided on the side of the base material II so as to face the target 15. A second ion tube 17 is provided on the side of the target 15 so as to face the base material 11, and a power source 18 is further connected to the base material If, so that the base material 11 can be energized.

The target layer 15 is made of a material containing the elements constituting the oxide superconductor described above. Therefore A -I3-C
A target made of a superconductor of the A-I3-C-D system, which is produced by calcining and sintering a mixed powder containing each element of the -D system, or a he element, a B element, a C element, and a D element. It is possible to use an oxide target containing a predetermined ratio of .

The first ion source 16 irradiates the target 15 with accelerated ions to knock out the constituent atoms of the target 15, and the base material l! This is an apparatus for depositing a film on top of the film.

The second ion source 17 is a device that irradiates the base material 11 with oxygen in the form of ions, atoms, molecules, etc. In addition,
These ions ill 6. +7 is configured to include an ion generator and an ion extraction electrode, and is configured so that the ions generated by the ion generator can be accelerated by the extraction electrode and irradiated.

Next, a case in which an oxide superconducting thin film is manufactured using the apparatus shown in FIG. 1 will be described.

To manufacture an oxide superconducting thin film using the apparatus shown in FIG. Do not turn on the ion source 16.17 after bringing it to pressure. Further, the base material It is energized from the power source 18 to
to a temperature of about 600 to 1000°C.

Through the above operations, the ion source 16 irradiates the target I5 with ions and performs sputtering to generate a film made of an A-+3-C-D system oxide superconductor on the base (I!1). Simultaneously with the sputtering, the ion source 17 is operated to irradiate the base material 11 with oxygen ions.

By this oxygen ion irradiation, sufficient free oxygen can be supplied to the superconducting thin film, and an oxide superconducting thin film can be generated.

Once a thin film of a predetermined thickness is formed on the substrate If, the ion source 16. , +7 is stopped, and immediately after film formation or after a predetermined period of time has elapsed, electrical heating of the base material 11 is stopped to cool the base material 11.

Note that if the oxygen ion irradiation from the oxygen ion source I7 is not performed, there is a risk that oxygen will be insufficient inside the crystals of the produced thin film, resulting in a thin film that deviates from the desired chemical composition. A thin film lacking oxygen in this manner has the disadvantage of poor superconducting properties.

In this respect, if oxygen ions are supplied from the ion source 17, a thin film with excellent properties and a desired composition matching the stoichiometric composition can be obtained.

Further, in order to form the oxide superconducting thin film while heating the base material 11 with electricity, it is effective to be able to heat the superconducting thin film to a sufficiently high temperature. Furthermore, when cooling the superconducting thin film after electrical heating, compared to the conventional method in which heating is performed using a heater with a large heat capacity, since there is no member with a large heat capacity in the vicinity of the base material 11, the base material 11 can be easily cooled. It can be rapidly cooled. Therefore, the crystal structure of the formed superconducting thin film can be adjusted, and the proportion of oxygen in the crystal can be set to a desired value, which has the effect of producing an oxide superconducting thin film with excellent characteristics such as a high critical temperature. .

Furthermore, since there is no need to use the heater used in the conventional method, there is no need to introduce impurities into the superconducting thin film. Note that since there is no need to use infrared rays to heat the superconducting thin film, there is no need to provide a transparent window for transmitting infrared rays on the outer wall of the vacuum container, and the vacuum degree of the vacuum container does not decrease.

On the other hand, in the second invention, after forming the superconducting thin film 1, the Jk material 11 is heated by electrical heating to achieve the purpose 4.
It's true.

That is, in a state where electrical heating is stopped, a superconducting thin film 1 is formed by heating the base material 11 to a required temperature with a heating device such as an infrared lamp, and forming a superconducting thin film 11.
After forming the superconducting thin film 1-1, heating with an infrared lamp or the like is stopped, and then the base material 11 is electrically heated to a required temperature to adjust the crystal structure of the superconducting thin film H and adjust the oxygen content m.

In the above example, the vacuum container may be provided with an infrared lamp for preheating the superconducting thin film, and it is of course also possible to provide a temperature control device to adjust the overall temperature inside the vacuum container. be.

"Example" Using a device with the configuration shown in Figure 1, a stainless steel
+nn+, a tape-shaped base material formed by forming a 1 μm-thick coating layer on a tape-shaped body part with a thickness of 0.5 a + m is prepared, and on this base material, a sputtering method using an ion source is applied. The elements constituting the oxide superconductor represented by Y-B a-Cu-0 are sputtered, and at the same time oxygen ions are irradiated, a voltage of 25 V is applied to the substrate and the substrate is heated to 700 ° C. A superconducting thin film was formed. At this time, the ion acceleration voltage of the ion source was set to 100OV.
, the ion current is 100, and the vacuum degree of A1 atmosphere is 5XIO.
-'I'a.

After sputtering was performed for 4 hours under the above conditions, sputtering and current supply were stopped, and the substrate was cooled to obtain a superconducting thin film. In this case, the substrate temperature should be increased from 700℃ to 100℃.
The time required to prevent the temperature from dropping to 0.1 and the critical temperature (Tc) of the formed superconducting thin film were measured and shown in Table 1 below.

In addition, using a device configured by adding an ion source to the conventional device shown in Fig. 3, a Y-B a-Cu-0 sputtering target was used, and the substrate was heated to 700°C with a heater. , ion sputtering and oxygen ion irradiation were performed simultaneously under the same conditions as in the previous example to form an oxide superconducting thin film, and after the film was formed, power to the heater was stopped and the substrate was cooled to obtain an oxide superconducting thin film. Ta.

In this case, the time required to lower the temperature of the substrate from 700°C to 100°C and the critical temperature of the formed oxide superconducting thin film were measured and are shown in Table 1.

Table 1 As is clear from Table 1, when the substrate is heated by electrical heating, the cooling time can be significantly shortened compared to when it is heated using a heater, and rapid cooling processing is possible. It turned out that. It has also been found that the production efficiency of superconducting thin films is improved because the cooling time can be significantly shortened. It has also been found that oxide superconducting thin films produced by heating by electrical heating and then rapidly cooling have a high critical temperature.

``Effects of the Invention'' As explained hereinafter, the present invention is capable of heating the superconducting thin film to a sufficiently high temperature in order to heat the oxide superconducting thin film by electrically heating the base material. In this case, compared to the conventional method in which heating is performed using a heater with a large heat capacity, the base material can be rapidly cooled because there is no member with a large heat capacity in the vicinity of the base material. Therefore, the shape of the crystal of the oxide superconducting thin film can be adjusted and the amount of oxygen in the crystal can be adjusted, so that an oxide superconducting thin film with excellent characteristics such as a high critical temperature can be manufactured. Also,
Since there is no need to use a heater, there is no need for impurity elements to enter the superconducting thin film from the atmosphere.Furthermore, since there is no need to use infrared rays to heat the superconducting thin film, there is no need to There is no need to provide a transparent window, the degree of vacuum in the vacuum container does not decrease, and a film can be formed at the required pressure.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an example of an apparatus used to carry out the method of the present invention, FIG. 2 is a sectional view showing an example of a weir plate used to carry out the method of the present invention, and FIG. FIG. 2 is a configuration diagram for explanation. 11 - Base material, 12... Main body part, 13... Covering layer,
15... Target, 16... First ion source,
17...Second ion source, 18...Power source, 1■ - Superconducting thin film.

Claims (2)

[Claims] (1) Using a base material at least partially made of a conductive material that generates heat when energized, an oxide superconducting thin film is formed on the base material while heating the base material by supplying current to the base material, and A method for producing an oxide superconducting thin film, which comprises cooling the base material by stopping current supply to the base material after forming the superconducting thin film. (2) Using a base material at least partially made of a conductive material that generates heat when energized, forming an oxide superconducting thin film on this base material, and then energizing the base material to cause the base material to generate heat. A method for producing an oxide superconducting thin film, which comprises heating the oxide superconducting thin film, heating it for a required period of time, and then stopping current supply to the base material to cool the base material.