JPH04152685A - Superconducting element - Google Patents

Abstract

PURPOSE:To form the whole element integrally so as to enable it to be easily formed and stabilized in characteristic by a method wherein a layer of material which diffuses into an oxide superconductor to turn it into a non-superconductor is formed, and a non-superconducting layer is formed of an oxide superconductor which is turned non-superconductive by the diffusion of the material concerned. CONSTITUTION:A superconducting element is formed of an oxide superconducting thin film 10 provided onto a board 4 provided with an Si layer 40 on its surface. The oxide superconducting thin film 10 provided onto a part other than the Si layer 40 is formed into superconducting layers 1 and 2 made of crystal orientated in a C axis. Si atoms are diffused into the oxide superconducting thin film 10 adjacent to the Si layer 40 to partially turn the film 10 into a non-superconducting layer 3. The oxide superconducting thin film 10 is extremely small in thickness at a part 20 located on the side face of the Si layer 40, and the superconducting layers 1 and 2 are made to constitute a superconductive junction at the part 20 concerned. This superconducting element can be formed without laminating a non-superconducting thin film or the like on an oxide superconducting thin film. The superconducting element is formed of an oxide superconducting thin film originally formed in one piece, so that an interface between a superconducting layer and a non-superconducting layer can be formed very sharp.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to superconducting elements. More specifically, the present invention relates to a novel structure of a superconducting element comprising a superconducting layer made of an oxide superconductor and a non-superconducting layer adjacent to the superconducting layer.

BACKGROUND ART When using an oxide superconductor in a superconducting element, it is necessary to have a structure in which an oxide superconductor layer is laminated with a layer of a non-superconductor, a semiconductor, or the like. For example, when a superconducting junction called a tunnel Josephson junction is realized using an oxide superconductor, a first oxide superconductor layer, a non-superconductor layer, and a second oxide superconductor layer are sequentially formed. It shall be of laminated construction.

In the tunnel Josephson junction described above, the thickness of the non-superconductor layer is determined by the coherence length of the superconductor. Since an oxide superconductor has a very short coherence length, in a tunnel-type Josephson junction using an oxide superconductor, the thickness of the non-superconductor layer must be approximately several nanometers.

On the other hand, considering the characteristics of the device, each of the above layers must have good crystallinity. In other words, it is preferable that all the layers be formed of single crystal, and if there is a polycrystalline or amorphous layer, The performance of the Josephson element is not stable.

Not only the above-mentioned tunnel-type Josephson device, but also devices such as superconducting transistors that combine oxide superconductors and semiconductors are similarly required to have each layer composed of a single crystal.

Problems to be Solved by the Invention A conventional tunnel-type Josephson device using an oxide superconductor is produced by sequentially depositing a first oxide superconducting thin film, a non-superconducting thin film, and a second oxide superconducting thin film on a suitable substrate. This was achieved by layering. Therefore, in order to produce a device with excellent characteristics, it is necessary to form a single crystal non-superconducting thin film several nanometers thick on an oxide superconducting thin film.

However, it is difficult to produce a thin film of another material with good crystallinity on the oxide superconducting thin film, and therefore the crystallinity of the second oxide superconducting thin film laminated thereon is also poor.

Further, in the tunnel type Josephson junction of the conventional configuration produced by the above-mentioned conventional method, the interface between the oxide superconducting thin film and the non-superconducting thin film 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 element with a novel configuration that solves the problems of the prior art described above.

Means for Solving Problems According to the present invention, in a superconducting element having a superconducting layer made of an oxide superconductor formed on a substrate and a non-superconducting layer adjacent to the superconducting layer, one layer on the substrate is A layer of a substance that diffuses into the oxide superconductor and loses its superconductivity is formed in the oxide superconductor, and the non-superconducting layer is composed of an oxide superconductor in which the substance diffuses and loses its superconductivity. A superconducting element is provided.

Function: In the superconducting element of the present invention, a superconducting layer made of an oxide superconductor and a non-superconducting layer are arranged adjacent to each other on the same substrate. In the superconducting element of the present invention, a layer of a substance that easily diffuses into the oxide superconductor and causes the oxide superconductor to lose its superconductivity is formed on a portion of the substrate. Due to the substances diffused into the oxide superconducting thin film from this layer, a part of the oxide superconducting thin film turns into a non-superconducting layer. It is preferable that the above-mentioned substance is easily diffused to the extent that it is diffused into the oxide superconducting thin film during film formation. As such a substance, for example, Sl, Ge, AI, etc. are preferable.

The superconducting element of the present invention having the above-described configuration is originally composed of an oxide superconducting thin film formed integrally. Furthermore, the interface between the superconducting layer and the non-superconducting layer is formed to be very sharp.

When the superconducting element of the present invention described above is, for example, a Josephson element, it is preferable that the layer of the above-mentioned substance has a linear shape with a width of about 1 μm. Further, the thickness of the layer is preferably about 5Q nm. When manufacturing a Josephson device using an oxide superconductor, the thickness of the non-superconducting layer of the necessary tunnel barrier is about 5 nm. In the superconducting element of the present invention, since the non-superconducting layer is formed by diffusion as described above, the concentration of the diffusing substance decreases as the thin film grows. Therefore,
In the method of the present invention, the non-superconducting portion of the tunnel barrier is the edge portion 20 of the oxide superconducting thin film. Therefore, the thickness of the oxide superconducting thin film at the two edges is
It needs to be different.

Although any oxide superconductor can be used in the superconducting element of the present invention, Y2, Ba2Cu, and 07-8-based oxide superconductors are preferred because they can stably produce high-quality thin films with good crystallinity. Also, Bi25r2Ca, (:u, O
X-based oxide superconductors are particularly preferred because their superconducting critical temperature Tc is high.

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.

Embodiment FIG. 1 shows a schematic cross-sectional view of an example of a superconducting element of the present invention. The superconducting element in Figure 1 is a Josephson element,
It consists of an oxide superconducting thin film 10 formed on a substrate 4 having a Si layer 40 on its surface.

The oxide superconducting thin film 10 on the surface of the substrate 4 other than the vicinity of the S1 layer 40 is a superconducting layer 1 composed of C-axis oriented crystals.
．． 2. Furthermore, S1 atoms diffuse into the oxide superconducting thin film 10 near the S1 layer 40 on the surface of the substrate 4, forming a non-superconducting layer 3. The oxide superconducting thin film 10 is made of Si
The thickness of the portion 20 on the side surface of the layer 40 is extremely thin, and the superconducting layer 1.2 is superconductingly bonded in this portion 20.

Production Example 1 A superconducting element of the present invention was produced. An MgO single crystal substrate is used for the substrate, and Y1Ba2CU3Ch is used for the oxide superconductor.
-x was used. The manufacturing procedure will be described with full reference to FIGS. 2(a) to 2(C).

First, as shown in FIG. 2(a), a Mg0 (100) substrate 4
A Si layer 40 having a width of 1 μm and a thickness of 0.2 μm is formed by vacuum evaporation over the entire width of the device as shown in FIG. The vapor deposition conditions are shown below.

Substrate temperature 600℃ Pressure I X1O-6Torr Vapor deposition rate
As shown in FIG. 2(C), an oxide superconducting thin film was formed on a substrate 4 having a Si layer 40 on its surface. Using a sintered body containing Y, Ba, and [U in an atomic ratio of 1:2:4.5 as a target, C-axis orientation is formed on a portion of the surface of the substrate 4 other than the Si layer 40 by an oxidation sputtering method. The oxide superconducting thin film was grown to a thickness of 100 r+m. The reason why the off-axis sputtering method was used is to make the edges of the oxide superconducting thin film formed on the 81 layer 40 have different thicknesses.

In this example, the oxide superconducting thin film was formed so that the portion 20 on the side surface of the S1 layer 40 was extremely thin. The sputtering conditions are shown below.

Substrate temperature 630℃ Sputtering gas Ar 8SCCM024SCC
M Pressure 5 , Si is 2Qnm
It had spread to a certain extent. Furthermore, when it was cooled to 85K and microwaves with a frequency of 10 GHz and an output of 0.1 mW were applied, a Shapiro step was observed at a voltage point that is a multiple of 20.7 μV, confirming that Josephson coupling was realized. It was done.

Preparation Example 2 A superconducting element of the present invention shown in FIG. 1 was prepared in the same manner as in Preparation Example 1 using a Bi2Sr2Ca2Cu308 superconductor. A 5rTiO3 (100) substrate was used as the substrate. As in Preparation Example 1, a Si layer having a width of 1 μm and a thickness of 0.2 μm is formed over the entire width of the device on the surface of the substrate by vacuum evaporation. The vapor deposition conditions are shown below.

Substrate temperature: 600°C Pressure: I 8+2Sr by the ophaxis battering method used.
A 2Ca2Cu3ON oxide superconducting thin film was formed.

The sputtering conditions are shown below.

Substrate temperature 650℃ Sputtering gas Ar 83CCM○24SCC
M Pressure 5 X 10-2 Torr The oxide superconducting thin film formed under the above conditions is composed of C-axis oriented crystals except for the vicinity of the S1 layer on the substrate surface, and there are 20 layers of SL in the vicinity of the Si layer of the substrate. It had spread to a certain extent. Furthermore, when it was cooled to 90 K and microwaves with a frequency of 15 GHz and an output of 0.1 mW were applied, a Shapiro step was observed at a voltage point that is a multiple of 31 μV, confirming that Josephson coupling was realized.

As described in detail, the superconducting element of the present invention has a structure in which a part of the oxide superconducting thin film is replaced with a non-superconducting layer.

Therefore, it can be manufactured without laminating a non-superconducting thin film or the like on an oxide superconducting thin film as in the conventional case. When the superconducting element of the present invention is manufactured according to the method of the present invention, the entire element is integrally formed, so that it is not only easy to manufacture, but also has stable characteristics. Furthermore, since the non-superconducting layer is made of an oxide similar to an oxide superconductor, it does not have any adverse effects on various properties.

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

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of a superconducting element of the present invention, and FIG. 2 is a schematic diagram showing an example of a process for producing a superconducting element of the present invention. [Main reference numbers] 1.2...Superconducting layer, 3...Non-superconducting layer, -Substrate

Claims (1)

[Claims] In a superconducting element having a superconducting layer made of an oxide superconductor formed on a substrate and a non-superconducting layer adjacent to the superconducting layer, a portion of the substrate is diffused into the oxide superconductor and has superconductivity. 1. A superconducting element, characterized in that a layer of a substance that causes properties to be lost is formed, and the non-superconducting layer is composed of an oxide superconductor in which the substance has diffused and lost superconductivity.