JPH04111482A - Superconductive element and manufacture thereof - Google Patents

Abstract

PURPOSE:To manufacture the superconductive element without laminating an insulator film, etc., on an oxide superconductive film by putting it in such structure that one part of the superconductive film is replaced with an insulator layer, and forming the semiconductor layer and the superconductive layer so that they may stand in a line in the direction perpendicular to the c axis. CONSTITUTION:A Y1Ba2Cu3O7-X superconductive film 1, whose axis a is perpendicular (orientated in the direction of axis) to the surface of a substrate, is formed by sputtering method on the MgO (100) substrate 4. Subsequently, based on the results of measurement of crystal direction, the arrangement of each layer is decided so that each layer may stand in an line in the direction perpendicular to the c axes of the Y1Ba2Cu3O7-X crystals constituting the oxide superconductive film 1. Furthermore, based on the measurement of crystal direction, a semiconductor layer is formed at the end in the direction perpendicular to the c axes of Y1Ba2Cu3O7-X crystals constituting the oxide superconductive film 1. Y films 71 and 72 are formed, in the same thickness of 300nm as an Au film 5, on a photoresist 6 and the part where the oxide superconductive film is exposed, and further photoresists 61 and 62 are formed on the Au film 5 and the Y film 72.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a superconducting element and a method for manufacturing the same. More specifically, the present invention relates to a superconducting element having a novel configuration, including a superconductor layer made of an oxide superconductor and a semiconductor layer adjacent to the superconductor layer, and a method for manufacturing the same.

BACKGROUND ART When using an oxide superconductor in a superconducting element, it is necessary to have a structure in which the oxide superconductor layer is laminated with layers of an insulator, a semiconductor, etc. For example, a superconducting element called a superconducting base transistor, as shown in FIG. 1, has an emitter 21 made of a superconductor or a normal conductor, a tunnel barrier 22 made of an insulator, and a base made of a superconductor. 23, a semiconductor isolator 24 and a collector 25 made of a normal conductor are stacked.

The above superconducting base transistor achieves high-speed operation using a superconducting tunnel junction and a superconducting base.

The thickness of the tunnel barrier of a superconducting tunnel junction must be several times the coherence length of the superconductor. Since oxide superconductors have a very short coherence length, in superconducting tunnel junctions using oxide superconductors, the thickness of the tunnel barrier must be approximately several nm.

Further, in the above superconducting base transistor, electrons traveling through the superconducting base 23 may be reflected at the interface between the superconducting base 23 and the semiconductor isolator 24. Therefore, controlling the superconductor-semiconductor interface is also important.

On the other hand, in consideration of the characteristics as an element, each of the above layers must have good crystallinity. That is, 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 device will not be stable.

Problems to be Solved by the Invention Conventional superconducting base transistors using oxide superconductors have been realized by sequentially stacking the above-mentioned layers on a suitable substrate. Therefore, in order to produce an element with excellent characteristics, it is necessary to laminate a single crystal insulator thin film, an oxide superconducting thin film, and a semiconductor thin film several nanometers thick.

However, it is difficult to form a thin film of another material with good crystallinity on an oxide superconducting thin film, and there are also a limited number of base substrates on which an oxide superconducting thin film with good crystallinity can be formed.

Furthermore, in a superconducting base transistor having a conventional structure manufactured by the conventional method described above, the interface between the oxide superconducting thin film and the semiconductor thin film was not in good condition, and desired characteristics could not be obtained.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a superconducting element having a novel configuration and a method for manufacturing the same, which solves the problems of the prior art described above.

Means for Solving the Problems According to the present invention, in a superconducting element having a superconductor layer and a semiconductor layer adjacent to the superconductor layer, the superconductor layer and the semiconductor layer are arranged on the same substrate, and the superconductor layer and the semiconductor layer are arranged on the same substrate, The superconductor layer is made of an oxide superconductor, the semiconductor layer is made of the oxide superconductor containing impurities, and the C axis of each of the oxides is in a plane parallel to the substrate, and A superconducting element characterized by having an orientation perpendicular to the direction in which a main current flows is provided.

Further, in the present invention, as in the above superconducting element, a superconductor layer and an adjacent semiconductor layer are arranged, the superconductor layer is composed of an oxide superconductor, and the semiconductor layer is substantially the same as the oxide superconductor. The oxide superconductor is composed of oxides that are composed of the same constituent elements and whose composition ratio is different from that of the oxide superconductor, and the C-axis of each of the oxides is in a plane parallel to the substrate, and the main current is A superconducting element characterized by having an orientation perpendicular to a flowing direction is provided.

Furthermore, in the present invention, as a method for manufacturing each of the above-mentioned superconducting elements, an oxide superconducting thin film composed of oxide superconducting crystals having an orientation such that the C axis is in a plane parallel to the substrate is formed on a substrate. forming a film, and diffusing impurities into a part of the oxide superconducting thin film so that the layers constituting the superconducting element are arranged adjacently in parallel in a direction perpendicular to the C axis of the oxide superconducting crystal. A method for manufacturing a superconducting element is provided, which includes a step of forming a semiconductor layer. The present invention also includes a method for manufacturing a superconducting element that includes a step of forming the semiconductor layer by diffusing a portion of the elements constituting the oxide superconductor in excess instead of the impurities.

Function In the superconducting element of the present invention, a superconductor layer and a semiconductor layer made of an oxide superconductor are arranged adjacent to each other on the same substrate. In addition, the semiconductor layer is an oxide superconductor that constitutes the superconductor layer, and is an oxide that exhibits semiconducting characteristics by containing impurities or containing an excessive amount of a part of the elements that constitute the oxide superconductor. It is configured. In other words, particularly from the viewpoint of the manufacturing method, the superconducting element of the present invention is a semiconductor layer formed by "adding impurities" to a part of an oxide superconducting thin film formed on a substrate, or a superconducting layer forming "an oxide superconductor". The method includes a semiconductor layer formed with a portion of an element in excess.

In the superconducting element of the present invention, the oxides constituting the superconductor layer and the semiconductor layer have an orientation in which the C axis is parallel to the substrate, and the C axis is parallel to the direction in which the main current of the superconducting element flows. Preferably the axis is vertical. This is because the oxide superconductor has anisotropy in its superconducting properties, and particularly the critical current density and coherence length are large in the direction perpendicular to the C-axis.

The superconducting element of the present invention having the above structure is originally composed of an integrally formed oxide superconducting thin film, and the crystal structure is the same in all parts. Therefore, unlike conventional superconducting elements, all layers have good crystallinity.

In the superconducting element of the present invention described above, an oxide superconducting thin film is formed on a substrate, and impurities are diffused into this thin film over the entire width and thickness, or a part of the elements constituting the oxide superconductor is added in excess. It can be manufactured by forming a portion that is

This portion becomes a semiconductor layer, and this semiconductor layer and superconductor layer are formed so as to be aligned in a direction perpendicular to the C-axis.

Methods for diffusing impurities into an oxide superconducting thin film include a method in which a thin film containing the impurity to be diffused is laminated on an oxide superconducting thin film and then subjected to heat treatment, and a method in which ion implantation is performed. In particular, in oxide superconductors, impurities tend to diffuse in a direction perpendicular to the C axis of the crystal.

Therefore, by forming a thin film in which the C axis of the crystal is parallel to the substrate surface, that is, in the C axis or b axis orientation, forming a layer containing impurities on a part of this thin film, and performing heat treatment, the present invention can be realized. The superconducting element of the invention can be manufactured. It is also possible to make some of the elements constituting the oxide superconductor excessive by a similar method.

The impurity to be diffused into the oxide superconducting thin film is Si.
etc. are preferred. This is because when Sl is diffused into an oxide superconductor, it exhibits semiconductor-like characteristics. Therefore, the state of the semiconductor-oxide superconductor interface containing Si as an impurity is extremely good. On the other hand, elements used in excess to form a semiconductor layer include, for example, Y, Ba2Cu30, etc. for the oxide superconductor. -Y when using X
is preferred.

Although any oxide superconductor can be used in the superconducting element of the present invention, Y HBa2Cu+ 07-X based oxide superconductor is preferred because it can stably provide a high quality thin film with good crystallinity. Furthermore, Bi25r2Ca2Cu30X-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.

EXAMPLE A superconducting base transistor was fabricated as an example of a superconducting element of the present invention by the method of the present invention. An MgO single crystal substrate is used for the substrate, and Y and Ba2CU are used for the oxide superconductor.
307-x was used. The manufacturing procedure will be explained with reference to FIGS. 2(a) to (1).

First, a YIBa2Cu30t-x superconducting thin film 1 was formed on an MgO (100) substrate 4 by sputtering, as shown in FIG. 2(a), with the a-axis not perpendicular to the substrate surface but oriented along the a-axis. The main film forming conditions are shown below.

Substrate temperature 630℃ Sputtering gas Ar 90% 0210% Pressure 5 Xl0-2Torr film
Thickness: 400 nm After film formation under the above conditions, this oxide superconducting thin film 1
The crystal direction of the YIBa2Cu30t-x crystal constituting the was measured by electron beam diffraction.

Next, as shown in FIG. 2(b), a 300 nm thick Au thin film 5 was formed on this oxide superconducting thin film 1 by vacuum evaporation.

Next, the semiconductor layer and insulating layer constituting the superconducting transistor are built into the oxide superconducting thin film 1. At this time, based on the results of the crystal orientation measurements made earlier, each layer is made into the oxide superconducting thin film 1. 1 consists of Y, Ba2Cu
, ○? The arrangement of each layer is determined so that they are aligned in a direction perpendicular to the a-axis of the -X crystal. In this example, Fig. 2 (C) to (2)
Up to Y1Ba2, which constitutes the oxide superconducting thin film 1
It is assumed that the a-axis of the Cu307-X crystal is perpendicular to the plane of the paper.

Based on the above measurement of the crystal direction, a semiconductor layer is formed at the end of the Y lBa2Cu30 q-8 crystal constituting the oxide superconducting thin film 1 in the direction perpendicular to the a-axis. The left side of the Au thin film 5 was covered with a photoresist 6 as shown in FIG. 2(C). As shown in FIG. 2(d), etching was performed by Ar ion milling until the right side of the oxide superconducting thin film 1 was exposed. The exposed portion of this oxide superconducting thin film 1 is a portion that will become a semiconductor layer.

On the exposed parts of the photoresist 6 and the oxide superconducting thin film 1, Y thin films 71 and 72 are formed by sputtering to form the same thickness as the Au thin film 5, as shown in FIG. 2(e).
It is formed to a thickness of 0 nm. Photoresist 6 and Y thin film 71 are removed by a lift-off method, and photoresists 61 and 62 are formed on Au thin film 5 and Y thin film 72 as shown in FIG. 2(f). In this case, the photoresists 61 and 62 are placed as close as possible, and the gap between them is formed so as to be on the Au thin film 5.

Etching is performed again by Ar ion milling, and
The thin film 5 is divided into 51 and 52 as shown in FIG.
Thin films 81 and 82 are deposited. By the lift-off method, photoresists 61 and 6 are removed as shown in FIG. 2(i).
2. Remove excess portions of the Au thin film 81 and the Au thin film 82.

The thus processed thin film is heat-treated in a high vacuum. The heat treatment conditions are shown below.

Pressure (degree of vacuum) I Xl0-'Torr substrate temperature
After heat treatment at 700°C for 3 minutes, the Y thin film 72 is removed by Ar ion milling, and the Au thin film 53 is replaced with the Au thin film 5 as shown in FIG. 2(j).
Form separately from 2. By the above heat treatment, the Au thin film 5
The part of the oxide superconducting thin film 1 in the gap between 1 and 82 becomes an insulator 3 as oxygen in the crystal escapes, and the Au thin film 5 becomes an insulator 3.
The lower part of 1 is the first superconductor layer 11 and the Au thin film 5
The lower portion of 2 becomes the second superconductor layer 12.

Furthermore, Y is diffused into the portion of the oxide superconducting thin film 1 below the Y thin film 72 to become the semiconductor layer 2 .

Finally, as shown in Figure 2 (2), the insulator film 91,92,9
3 and 94, and the wiring metal film 101, 102 and 1
03 to complete the superconducting element of the present invention.

After completion, the crystallinity of the first and second superconductor layers 11 and 12 and the semiconductor layer 2 was examined, and it was found that they were all good, almost single crystals. Further, the superconducting critical temperatures of the first and second superconductor layers 11 and 12 were both 88.

In this example, the semiconductor layer 2 was formed by laminating the Y thin film 72 on the oxide superconducting thin film 1 and heat-treating it, but the oxide superconducting thin film 1 was exposed in the state shown in FIG. It is also possible to form a semiconductor layer by implanting Y ions into the portion.

Further, in the method of the present embodiment, since the semiconductor layer 2 and the insulator layer 3 are formed at the same time, a superconducting base transistor can be manufactured very efficiently.

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 an insulating layer. Therefore, it can be manufactured without stacking an insulator 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 produced according to the method of the present invention, the whole is formed in one piece, so it is not only easy to produce, but also has good crystallinity in each part and stable characteristics. Furthermore, since the insulator layer is composed of an oxide with the same crystal structure and the same constituent elements as the oxide superconductor, the insulator that makes up the insulator layer has an adverse effect on various properties of the oxide superconductor thin film. I have nothing to give.

Furthermore, in the superconducting element of the present invention, the direction in which current related to the operation of the element flows is perpendicular to the C-axis of the oxide superconductor crystal, so that various characteristics are excellent.

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

[Brief explanation of drawings]

FIG. 1 is a conceptual diagram of a superconducting base transistor, and FIG. 2 is a schematic diagram showing steps for manufacturing a superconducting element of the present invention by the method of the present invention. [Main reference numbers] 1... Superconductor thin film, 2... Semiconductor layer, 3... Insulator layer, 4... Substrate, 5... Au thin film, 6... Photoresist EB BC

Claims (4)

[Claims] (1) In a superconducting element having a superconductor layer and a semiconductor layer adjacent to the superconductor layer, the superconductor layer and the semiconductor layer are arranged on the same substrate, and the superconductor layer is an oxide superconductor. wherein the semiconductor layer is composed of the oxide superconductor containing impurities, and the c-axis of each of the oxides is in a plane parallel to the substrate and perpendicular to the direction in which the main current flows. A superconducting element characterized by having orientation. (2) In a superconducting element having a superconductor layer and a semiconductor layer adjacent to the superconductor layer, the superconductor layer and the semiconductor layer are arranged on the same substrate, and the superconductor layer is an oxide superconductor. wherein the semiconductor layer is composed of an oxide having substantially the same constituent elements as the oxide superconductor and whose composition ratio is different from that of the oxide superconductor, and each of the oxides has a c-axis. A superconducting element, characterized in that the superconducting element has an orientation that is in a plane parallel to the substrate and perpendicular to the direction in which the main current flows. (3) A superconductor layer on a substrate and made of an oxide superconductor, and a semiconductor layer on the substrate adjacent to the superconductor layer and made of the oxide superconductor containing impurities. In a method for producing a superconducting element, an oxide superconducting thin film composed of oxide superconducting crystals having an orientation in which the c-axis is in a plane parallel to the substrate is formed on a substrate, and the oxide superconducting thin film is forming the semiconductor layer by diffusing impurities into a portion of the oxide superconducting thin film so that the layers constituting the superconducting element are adjacent and parallel in a direction perpendicular to the c-axis of the crystal; A method for producing a superconducting element characterized by: (4) a superconductor layer on a substrate made of an oxide superconductor; and a superconductor layer on the substrate adjacent to the superconductor layer made of substantially the same constituent elements as the oxide superconductor; In a method for producing a superconducting element having a semiconductor layer made of an oxide having a composition ratio different from that of the oxide superconductor, an oxide having an orientation such that the c-axis lies in a plane parallel to the substrate on the substrate. An oxide superconducting thin film composed of superconducting crystals is formed, and the oxide superconducting thin film is formed such that each layer constituting the superconducting element is adjacently arranged in parallel in a direction perpendicular to the c-axis of the oxide superconducting crystal. A method for manufacturing a superconducting element, comprising the step of forming the semiconductor layer by diffusing a part of the elements constituting the body in excess.