JPH03183601A - Production of oxide superconducting film - Google Patents

Abstract

PURPOSE:To obtain a high performance superconducting device utilizing the advantages of an oxide superconducting film by forming an oxide superconducting film on an MgO (110) single crystal substrate, coating the surface of the film with an MgO (110) single crystal and carrying out heat treatment. CONSTITUTION:A thin Bi-Sr-Ca-Cu oxide film 2 is deposited on a mirror pol ished MgO (110) single crystal substrate 1 by a vapor growth method or other method. The surface of the film 2 is coated with a mirror polished MgO (110) single crystal sheet 3 and heat treatment is carried out in an oxygen atmosphere. After this heat treatment, the sheet 3 is removed. The film 2 is converted into an oxide superconducting film for a superconducting device.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for manufacturing an oxide superconducting film, which is a basic component of a compact, ultra-sensitive, ultra-high speed, and highly efficient superconducting device. be.

(Conventional technology) Devices using superconductivity include (1) cavities;
Superconducting high frequency components such as filters, (2) SQ
There are superconducting sensors such as υI[). For example, two-dimensional thin film devices such as filters and coils are required to have superconducting properties in the same direction in the plane, and at the same time, it is desirable to have equivalent superconducting properties in the thickness direction in the signal line connection region. Furthermore, a tunnel junction region used in a superconducting sensor requires a long coherence length in the thickness direction. Fifth
The figure shows the relationship between the crystal unit cell and crystal orientation in a Bi25r2Ca2Cu30x superconducting film. Although oxide superconducting films have the advantage of having a significantly higher critical temperature than metal-based superconducting films, they have the problem that their superconducting properties vary greatly depending on the crystal orientation because they have a layered structure as shown in Figure 5. . For example, the coherence length within the layer plane (a, b axis direction) is as long as 33-4n, allowing superconducting current to flow easily, but on the other hand, the coherence length in the layer perpendicular direction (c axis direction) is 0.2
It is short at -0.5 nm, making it difficult for superconducting current to flow. Therefore, thin film devices that require an in-plane method are based on a crystal oriented film (referred to as a C-axis oriented film) with the C-axis in the film thickness direction, but when considering signal line connections and tunnel junctions, It is desirable to have an oxide superconducting film in which fine crystals with a- and b-axes in the film thickness direction coexist at a certain ratio and have electrical properties that are isodirectional both in the film plane and in the film thickness direction. Therefore, in manufacturing superconducting thin film devices, it is important to have a method for manufacturing oxide superconducting films that allows control of crystal orientation.

Methods for manufacturing oxide superconducting films that constitute superconducting devices include physical vapor phase growth represented by vacuum evaporation and sputtering methods, and chemical vapor phase growth using chemical decomposition represented by MO-CVD method. There is a way to grow. In order to develop superconducting properties in oxide films grown by these methods, there are two methods: (1) heat-treating the grown film after deposition; (2) heat-treating the grown film by growing it while increasing the substrate temperature. There is a method of developing superconducting properties without the use of superconducting materials.

Currently, the main method used to control crystal orientation is to grow a film while increasing the substrate temperature, and the substrate material, its crystal plane orientation, and substrate temperature are important for controlling orientation. . This method is effective in the combination of a 5rTi03 single crystal substrate, which has a large dielectric loss in the high frequency signal region, and a Y-Ba-Cu-0 based superconducting film. However, although the dielectric loss is small, Y-Ba-Cu-0 and B1-3r-Ca-
There was a problem in that it could not be applied to an MgO single crystal substrate, which has poor lattice matching with a Cu-0 based superconducting film. Also,
The crystal orientation control method of growing a film while increasing the substrate temperature is close to epitaxial film growth, so in an oriented film where the film thickness direction is the a-axis or b@, a specific direction in the film plane becomes the c-axis, and the strong Anisotropy occurs within the membrane plane. This has caused a problem in that in-plane isotropy required for thin film devices cannot be guaranteed. On the other hand, in the post-deposition heat treatment, a special annealing process [Japanese Patent Application No. 1-2067261] is performed to form a B1-
Although a 5r-Ca-Cu-0 based superconducting film can be obtained, C
There was a problem in that orientation control other than the axis was difficult.

(Problems to be Solved by the Invention) As described above, since superconducting thin film devices whose main components are oxide superconducting films whose properties differ depending on crystal orientation are two-dimensional devices, in-plane isotropy is guaranteed. The base is a superconducting film that can be formed, that is, a C-axis oriented film. Furthermore, in the signal line connection region and tunnel junction region of device components, superconducting properties are required to be approximately the same in the film thickness direction as in the in-plane direction. Therefore, it is desirable to have a C-axis oriented film which is sufficiently smaller than these regions and which also contains a certain proportion of crystals including the a-axis or the b-axis in the film thickness direction. Conventionally, in Y-Ba-Cu-0 based superconducting films, the orientation has been controlled by the surface orientation of 5rTi(h) and the substrate temperature, but
There was a problem that the combination of the 0-based superconducting film and the MgO substrate could not be controlled.

The present invention provides a superconducting device having an oxide superconducting film as a basic element, by realizing an oxide superconducting film having isodirectional superconducting properties both in the plane and in the thickness direction.
The aim is to realize and provide high-performance superconducting devices without sacrificing the advantages of oxide superconducting films.

[Means to solve the problem]

The present invention provides Bi, S on the (110) crystal plane of MgO single crystal.
r.

It is characterized by imparting superconductivity to the oxide film by depositing an oxide film consisting of Ca, Cu, and O, and heat-treating the surface of the film while covering it with a (100) crystal plane of an MgO single crystal. do.

(Function) In the present invention, B 1- which constitutes a superconducting device
5r-(:a-Cu-0 based oxide film with Mg0(110)
By forming a crystal on a single crystal substrate and heat-treating the surface while covering it with an MgO (100) single crystal, a crystal with the C axis in the film thickness direction and a crystal with the a and b axes in the film thickness direction can be formed. The main feature is that they are mixed at a certain ratio. With conventional technology, it is difficult to obtain isotropic superconducting properties in the plane and in the film thickness direction, which are necessary for high-performance superconducting devices, that is, B1-
It has been difficult to control the crystal orientation of 5r-Ca-Cu-0 based superconducting films. In the present invention, since crystals with the C axis in the film thickness direction and crystals with the a and b axes in the film thickness direction can coexist at a certain ratio, superconducting properties are isotropic in the plane and in the film thickness direction. This method is significantly different from conventional technology in that it provides the following.

〔Example〕

FIG. 1 shows an embodiment of the invention. Figure 1(a) shows Mg0
(110) A cross-sectional view of a ll 1-5r-Ca-Cu-0-based film deposited on a substrate, FIG. 1(b) is a B 1-5r-
FIG. 2 is a cross-sectional view of a state in which the outermost surface of a Ca-Cu-0-based film is covered with a Mg0 (100) single crystal plate. 1 is Mgo (no)
The substrate 2 was formed by a vapor phase growth method such as sputtering [1i-
5 "-Ca-Cu-0 series oxide film, 3 is a MgO (100) single crystal plate for surface coating used during heat treatment. 1st
As shown in Figure (a), an oxide thin film 2 is deposited on a mirror-polished MgO (110) single crystal substrate 1 by vapor phase growth or the like. Next, as shown in FIG. 1(b), the outermost surface of the oxide thin film is coated with a mirror-polished MgO (100) single crystal plate 3 and heat-treated in an oxygen atmosphere. After the heat treatment, the coated MgO (100) single crystal plate is removed to obtain an oxide superconducting film for a superconducting device.

Figure 2 shows the B1-5r-Ca-
FIG. 2 is a schematic diagram of the surface of a Cu-0-based oxide superconducting film. 4 is a flat crystal whose C axis is in the vertical direction of the flat plate, and 5 is a needle crystal with a length of 4 to 5 μm in which the flat crystal stands upright. By forming the B1-5r-Ca-f:u-0 based oxide film by the method described in FIG. 1, a film state in which the tabular crystals 4 and many needle-like crystals 5 are mixed can be realized.

MgO (B 1-5r-Ca- on 1001 single crystal substrate
When a Cu-0 based film is deposited, covered with an MgO (100) single crystal plate, and heat treated, a superconducting film composed only of the tabular crystals 4 is obtained. MgO(110)! - When coated with a crystal plate and heat-treated, a small number of needle-like crystals 5 are present in addition to the plate-like crystals 4. On the other hand, when a B1-5r-Ca-Cu-0-based film is deposited on a Mg0 (110) single crystal substrate, coated with an MgO (100) single crystal plate, and heat treated,
and in the case of heat treatment without coating, tabular crystals 4
In addition, a small number of needle-like crystals 5 are mixed. Among them, in order to increase the proportion of needle-like crystals 5, a B 1-5r-f;a-Cu-0-based film is deposited on a Mg0 (110) single crystal substrate,
Mg0(100)! #The method of coating with a crystal plate and heat treatment was the most effective.

As an example, Fig. 3 shows Bi25r2CaCu20 deposited on a Mg0 (110) single crystal substrate and then heat treated.
Figure 3 shows the X-ray diffraction pattern of the x film. (a) is MgO(10
0) Film coated with a single crystal plate and heat treated, (b) is MgO (
110) 11 is an X-ray diffraction pattern of a film coated with a crystal plate and heat-treated. (c) is an X-ray diffraction pattern of a film heat-treated without surface coating.

All samples have a film thickness of approximately 1 μm. (a).

Although (b) and (C) show typical diffraction patterns with C-axis orientation, the C-axis orientation is further emphasized by performing the coating heat treatment. Here, MgO(too
) Bi25r2CaCu2 coated with a single crystal plate and heat treated
In the 0x film [FIG. 3(a)], a strong (2200) X-ray diffraction peak is present in addition to the typical C-axis orientation pattern. That is, the needle crystal 5 in which the flat plate crystal stands up is composed of (2200) crystal planes, which means that the needle crystal is an oriented crystal that includes the a and b axes in the film thickness direction. are doing.

The present invention is based on Bi25r2CaCu20. B other than 1-
It can also be applied to 5r-Ca-Cu-0 based superconducting oxide films.

FIG. 4 schematically shows oriented crystals that can be realized by forming a B 1-5r-Ca-Cu-0 film using the present invention. 6 is an Mg0 (110) single crystal substrate, 7 is a crystal corresponding to a- and b-axis orientation, and 8 is a crystal corresponding to C-axis orientation.

As described above, B1-
Deposit 5r-Ca-Cu-0 based film, MgO(100)
By covering with a crystal plate and performing heat treatment, it is possible to realize an oxide superconducting film in which a C-axis oriented flat crystal and a large number of a- and b-axis oriented needle-like crystals coexist. Therefore, the C-axis oriented crystal can ensure the in-plane method, and moreover, a large number of a, b
By using @-oriented crystals, the superconducting properties in the film thickness direction in the signal line connection having a size of more than 10-odd μm and in the tunnel junction region can be made closer to the in-plane properties, without compromising the advantages of oxide superconducting films. It is characterized by the ability to realize high-performance superconducting devices without any problems.

〔Effect of the invention〕

As explained above, by performing the heat treatment according to the present invention, it is possible to control the orientation of the oxide superconducting film, which is a basic component of superconducting devices. It is also possible to guarantee isotropic superconducting properties. Therefore, there is an advantage that a high-performance superconducting device that takes advantage of the advantages of an oxide superconducting film is possible.

[Brief explanation of drawings]

FIG. 1 is a diagram explaining the present invention in detail. FIG. 2 is a schematic diagram of the surface of a superconducting film formed according to the present invention. FIG. X after heat treatment of membrane
Line diffraction pattern. Figure 4 is a schematic diagram of a superconducting crystal grown on a Mg0 (110) substrate. Figure 5 is a diagram showing the relationship between the crystal unit cell and crystal orientation in a Bi25r2Ca2Cu, OX superconducting film. . ...Mg0 (lto) single crystal substrate, -Bi-5r-Ca-Cu-0 based oxide thin film,...
Single crystal plate for surface coating, ... tabular crystal, ... needle-like crystal, ... outermost surface of Mg0 (110) substrate, ... a, b
@oriented crystal, ... C-axis oriented crystal.

Claims (1)

[Claims] 1) Bi, Sr,
It is characterized by imparting superconductivity to the oxide film by depositing an oxide film consisting of Ca, Cu, and O, and heat-treating the surface while covering the (100) crystal plane of MgO single crystal. A method for producing an oxide superconducting film.