JPH04127484A - Superconducting junction - Google Patents

Abstract

PURPOSE:To easily manufacture and to obtain excellent characteristics by providing a nonsuperconducting layer formed of crystal of a-axis orientation of oxide having less number of oxygens than that of an oxygen superconductor, and a second superconducting layer formed equally to a first conducting layer formed on the nonsuperconducting layer. CONSTITUTION:A superconducting junction is formed of a crystal of a-axis orientation of oxide having less number of oxygens than that of oxide superconductor, having a superconducting layer formed of oxide superconductor crystal of a-axis orientation and containing component elements equal to those of the oxide superconductor for forming the superconducting layer and equal crystal structure in the nonsuperconducting layer. A first superconducting layer 1 formed on a substrate 4, a nonsuperconducting layer 3 formed in the vicinity of a center on the layer 1, and a superconducting layer 2 formed on the layer 3 are provided. The layers 1, 2 are formed of thin film of about 200-300nm thick formed of the same oxide superconductor crystal of a-axis orientation. The layer 3 is a thin film of about 10nm thick formed of a-axis oriented crystal of the oxide having equal component elements to those of the oxide superconductor for forming the layers 1, 2 and equal crystal structure.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to superconducting junctions. More specifically, the present invention relates to a novel superconducting junction using an oxide superconductor.

Although there are various configurations for realizing a superconducting junction, such as the conventional Josephson junction, the most preferred structure is a tunnel-type junction in which a thin non-superconductor is sandwiched between a pair of superconductors.

Generally, such a superconducting junction has a very fine structure, and the above-mentioned pair of superconductor and non-superconductor are so-called thin films.

For example, when realizing a tunnel-type superconducting junction using an oxide superconductor as a superconductor, a first oxide superconducting thin film, a non-superconducting thin film, and a second oxide superconducting thin film are laminated in order on a substrate. do.

Depending on the purpose, non-superconductors include insulators such as MgO,
Semiconductors such as No. 81 and metals such as No. 81 are used to construct superconducting junctions with different characteristics.

The thickness of the non-superconductor in a tunnel-type superconducting junction is determined by the coherence length of the superconductor.

Oxide superconductors have very short coherence lengths, so
In a tunnel-type superconducting junction using an oxide superconductor, the thickness of the non-superconductor must be on the order of several nanometers.

On the other hand, in consideration of the operating characteristics of a superconducting junction, each layer constituting the superconducting junction must have good crystallinity and be a single crystal or a polycrystal with an orientation very close to that of a single crystal.

Problems to be Solved by the Invention In the tunnel type superconducting junction described above, a first oxide superconducting thin film, a non-superconducting thin film, and a second oxide superconducting thin film each having good crystallinity must be laminated. It is difficult to stack a very thin non-superconducting thin film with good crystallinity on top of an oxide superconducting thin film, and it is difficult to form an oxide superconducting thin film with good crystallinity on top of this non-superconducting thin film. This is extremely difficult due to the characteristics of oxide superconductors.

Further, even if the above-described laminated structure was realized, the interface between the oxide superconductor and the non-superconductor was not in good condition, and desired characteristics could not be obtained.

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a superconducting junction with a novel configuration using an oxide superconductor, which solves the problems of the prior art described above.

Means for Solving the Problems According to the present invention, a first superconducting layer composed of C-axis oriented crystals of an oxide superconductor formed on a substrate, and the oxide superconductor formed on the superconducting layer. a non-superconducting layer formed of a C-axis oriented crystal of an oxide having the same constituent elements and crystal structure as the superconductor and having a smaller oxygen number than the oxide superconductor; A superconducting junction is provided, comprising a first superconducting layer and a second superconducting layer configured identically.

Function The superconducting junction of the present invention is characterized in that the superconducting layer is composed of C-axis oriented oxide superconductor crystals, the non-superconducting layer has the same constituent elements and the same crystal structure as the oxide superconductor constituting the superconducting layer, and Its main feature is that it is composed of C-axis oriented crystals of oxides with a smaller number of oxygen atoms than physical superconductors.

Oxide superconductors generally have anisotropy in their superconducting properties. That is, the critical current density and coherence length in the direction perpendicular to the C-axis of the crystal are both larger than those in the direction parallel to the C-axis of the crystal.

In the superconducting junction of the present invention, all layers are composed of oxide superconductor crystals with C-axis orientation or oxide superconductors with an equivalent crystal structure, so the main current flows in a direction perpendicular to the C-axis of the crystal. .

Therefore, the thickness of the non-superconducting layer can be made larger and the operating current is larger than that using an oxide superconducting thin film made of C-axis oriented crystals, so the restrictions on manufacturing conditions are relaxed.
It is also advantageous when used.

The above-mentioned superconducting bonding of the present invention can be performed by sputtering method, MBE
It can be manufactured using a vacuum evaporation method.

That is, the following procedure is used to produce the superconducting junction of the present invention.

First, a thin film is formed on a substrate heated to 561 to 580° C. using raw materials used for producing a thin film of an oxide superconductor. When a thin film is produced at this substrate temperature, an oxide superconducting thin film composed of C-axis oriented oxide superconducting crystals can be obtained.

Next, the substrate temperature is set to 540 to 560° C., and a thin film is formed on the C-axis oriented oxide superconducting thin film using the above raw materials. At this substrate temperature, a C-axis oriented crystal of an oxide having the same constituent elements and the same crystal structure as the oxide superconductor and having a small number of oxygen atoms can be obtained. As described below, this oxide exhibits semiconductor-like properties at low temperatures.

Finally, the substrate temperature is again raised to 561 to 580° C., and a C-axis oriented oxide superconducting thin film is produced to complete the superconducting junction of the present invention.

Each layer constituting the superconducting junction of the present invention is produced from the same raw material, and the production method is also basically the same.

Since each layer is successively formed using the same device, the interface between each layer exposed at each stage during fabrication will not deteriorate. In addition, in the superconducting junction of the present invention, both the superconducting layer and the non-superconducting layer differ only in the crystal direction and the number of oxygen atoms, but are basically composed of the same oxide, so even if the component elements diffuse, they will have an adverse effect on each other. It has no effect.

As described above, the non-superconducting layer of the superconducting junction of the present invention is composed of an oxide that has the same constituent elements and the same crystal structure as the oxide superconductor, and has a lower number of oxygen than the oxide superconductor. Furthermore, in the superconducting junction of the present invention, both the oxide superconductor crystal forming the superconducting layer and the oxide crystal forming the non-superconducting layer have an a-axis orientation in which the a-axis is perpendicular to the substrate.

Furthermore, the oxide constituting the non-superconducting layer of the superconducting junction of the present invention exhibits semiconductor-like behavior in which the resistivity increases as the temperature decreases when cooled.

In the superconducting junction of the present invention, any oxide superconductor can be used, but Y-8a-Cu-0-based oxide superconductors can stably yield high-quality thin films with good crystallinity. preferable. Further, B1-3r-Ca-Cu-0 based oxide superconductor is particularly preferable because its superconducting critical temperature Tc is high.

Further, the superconducting junction of the present invention includes MgO, 5rTiO+,
It is also preferable to fabricate on an oxide substrate such as YSZ. This is because it is easy to form an a-axis oriented thin film of an oxide superconductor on a specific surface of these substrates.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the following disclosure is merely an example of the present invention and does not limit the technical scope of the present invention in any way.

Example FIG. 1 shows a cross-sectional view of an example of the superconducting junction of the present invention.

The superconducting junction shown in FIG. 2 superconducting layers 2.

Superconducting layers 1 and 2 are thin films with a thickness of about 200 to 300 nm and made of oxide superconductor crystals with the same a-axis orientation. The non-superconducting layer 3 is a thin film with a thickness of about 10 nm and made of an a-axis oriented crystal of an oxide having the same constituent elements and the same crystal structure as the oxide superconductors forming the superconducting layers 1 and 2.

For example, superconducting layers 1 and 2 are Y + Ba2 with a-axis orientation
In the case of a Cu307-x superconducting thin film, the non-superconducting layer 3 is a-axis oriented Y1Ba2Cu3O7-Y (y>
) is composed of an oxide thin film shown in

Example 1 A superconducting junction of the present invention having the configuration shown in FIG. 1 was fabricated.

First, on the (100) plane of an MgO substrate, YIBa with a-axis orientation, which will become the first superconducting layer 1, is deposited by sputtering.
2CLl, C) An r-x superconducting thin film was formed.

The main film forming conditions are shown below.

Substrate temperature 570℃ Sputtering gas Ar 8sccM024SCC
M Pressure 5×10 Film thickness 300 nm Torr Next, an a-axis oriented YIBa2CuaOt-y (V > The main film forming conditions are shown below.

Substrate temperature 550℃ Sputtering gas Ar 8 SCCM024SC
CM Pressure 5
The superconducting thin film was also formed using the sputtering method.

The film forming conditions were the same as those under which the first superconducting layer 1 was formed.

The superconducting junction of the present invention produced as described above was processed into a device and its characteristics were measured. Cooled to 85K, frequency 14GH
z, applying microwaves with an output of 0.2 mW to the Tato roller, 2
A Shapiro step was observed at a voltage point that is a multiple of 8.9 μV, confirming that Josephson coupling was realized.

Example 2 A superconducting junction of the present invention having the configuration shown in FIG.
It was produced using a -Ca-Cu-0 based oxide superconductor. First, an a-axis oriented B layer, which will become the first superconducting layer 1, is deposited on the (100) plane of an MgO substrate by sputtering.
i, Sr, Ca2Cu30) I superconducting thin film was formed.

The main film forming conditions are shown below.

Substrate temperature 580℃ Sputtering gas Ar 8SCCMO□ 4S
CCM Pressure 5×10 Film thickness 300 nm Torr Next, a-axis oriented Bl, Sr2Ca2Cu30wl-y (y >
0) A thin film was formed by sputtering method. The main film forming conditions are shown below.

Substrate temperature 540℃ Sputtering gas Ar 8 SCCM024SC
CM Pressure: 5
The 08 superconducting thin film was also formed by the sputtering method.

The film forming conditions were the same as those under which the first superconducting layer 1 was formed.

The superconducting junction of the present invention produced as described above was processed into a device and its characteristics were measured. Cooled to 90K, frequency 9G&,
Output 0. When IW microwave was applied, 18.6
A Shapiro step was observed at a voltage point that is a multiple of μV, confirming that Josephson coupling was realized.

As described in detail, according to the present invention, a tunnel-type superconducting junction with a novel configuration can be realized using an oxide superconductor. The superconducting junction of the present invention is easy to manufacture because both the superconducting layer and the non-superconducting layer are composed of oxides having the same crystal structure and consisting of the same constituent elements, and it is easy to obtain one with excellent characteristics.

In addition, especially since all the layers are composed of a-axis oriented oxide superconductor crystals or oxide crystals having the same crystal structure, superconducting critical current density and coherence length are greatly advantageous.

The present invention further promotes the application of superconducting technology to electronic devices.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the superconducting junction of the present invention. [Main reference number] 1.2... superconducting layer, 3...Non-superconducting layer, 4... Board Patent applicant: Sumitomo Electric Industries, Ltd.

Claims (1)

[Claims] A first superconducting layer composed of a-axis oriented crystals of an oxide superconductor formed on a substrate, and having the same constituent elements and crystal structure as the oxide superconductor formed on the superconducting layer. , a non-superconducting layer made of an a-axis oriented crystal of an oxide having a smaller oxygen number than the oxide superconductor, and a second superconducting layer formed on the non-superconducting layer and made equal to the first superconducting layer. A superconducting junction characterized by comprising a superconducting layer and a superconducting layer.