JPH0577317B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Application of the Invention The present invention relates to a method for producing a solid-state device, particularly a Josephson type device, using a ceramic superconducting material.

The present invention is intended to improve the particularly important physical properties near the surface of a device using the surface of an oxide superconducting material, thereby increasing the reliability of surface-based devices.

"Prior Art" Ceramic superconducting materials have recently attracted attention. This has its origins in the development of Ba-La-Cu-O based oxide superconducting materials at the IBM Zurich Research Institute. In addition to this, yttrium-based superconducting ceramics are also known.
The potential applications of solid-state electronic devices at liquid nitrogen temperatures have been revealed.

On the other hand, superconducting materials using metals such as Na ₃ Ge are well known. Attempts have been made to construct solid-state electronic devices such as Josephson devices using this metallic superconducting material.

After more than ten years of research, Josephson devices using this metal are almost ready for practical use. However, this superconductor has a Tco (temperature at which electrical resistance becomes zero)
The temperature is extremely low at 23K, and liquid helium must be used, so it is not practical.

In this metallic superconducting material, since all of the material is metal, the components of the material can be made uniform both on the surface and in the interior (bulk).

``Conventional Problems'' However, when investigating the properties of oxide ceramic superconducting materials, which have been attracting attention recently, it has been found that the surface and vicinity (approximately 200 Å depth from the surface) are compared to the interior (bulk). It was found that characteristics deteriorated (reliability decreased).

For this reason, even when attempts were made to create Josephson devices, the characteristics of the ceramics, which were normal in the early stages, deteriorated.

It was experimentally confirmed that the cause of this is that oxygen in oxide ceramics is extremely easily degassed near the surface.
It turns out that whether this oxygen is in ideal or deficient conditions presents a fundamental problem for the material: whether it has superconducting properties or only normal conducting properties. did.

For this reason, the present invention aims to provide superconducting properties at or near the surface of this oxide ceramic, by having a thickness sufficient to enable tunnel junctions on the surface, and which is thinner than oxides or other materials. In addition to forming a coating that has a blocking effect against oxygen degassing, oxygen is added to the ceramics that tend to become oxygen-deficient on the inside, so that the near surface has superconducting properties as well as the interior. The purpose is to provide a method.

"Means for Solving the Problem" The present invention forms a film on the surface of superconducting ceramics to make it a more complete blocking layer, and in the case of metals or semiconductors, oxidizes this film and transforms it into an insulating film. Furthermore, by performing solid phase-solid phase diffusion (diffusion of oxygen from the solid coating into another solid ceramic), the oxygen in this coating is diffused into a region on or near the surface, generally to a depth of approximately 200 Å. The aim is to optimize the oxygen concentration of

The film used for this purpose may be an oxide insulating film of aluminum oxide, tantalum oxide, titanium oxide, or the like.

Further, as this film, a metal or a semiconductor which becomes an oxide insulating film after oxidation treatment can also be used. Namely, metals include aluminum, titanium, tantalum, copper, barium, and yttrium, and semiconductors include silicon or germanium. These are aluminum oxide by oxidation,
It can be titanium oxide, tantalum oxide, copper oxide, barium oxide, or ytrium oxide.
Further, silicon may be replaced with silicon oxide, and germanium may be replaced with germanium oxide.

In the present invention, screen printing method, sputtering method,
MBE (Molecular Beam Epitaxial)
A superconducting material is formed using a method such as a method or a CVD (vapor phase reaction) method. As an example of this, (A _1-x BX)
yCuzOw, x=0~1, y=2.0~4.0 preferably
2.5-3.5, z=1-4 preferably 1.5-3.5, W=
4 to 10, preferably 6 to 8. A is Y (yztrium), Gu (gadolinium), Yb (yzterubium), Eu (europium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Lu (lutetium) ), Sc (scandium), or one or more of the other elements in group a of the periodic table. B is Ra (radium), Ba (bariyum),
Sr (strontium), Ca (calcium), Mg
(magnesium) and Be (beryllium) from group a of the periodic table. In particular _, ( _YBa2 ) _Cu3O6-8 was used as _a specific example. Further, as A, a lanthanide element or an actinide element other than the above-mentioned elements in the periodic table of elements can be used.

In the present invention, the insulating film formed by this oxidation heat treatment has a thickness that allows a tunnel current of 5 to 50 Å to flow. Then, another superconducting material is disposed on the upper surface of this insulating film to construct a Josephson element as shown in FIG. 2A.

That is, after a film is formed on superconducting ceramics, this film can be made into a complete insulating film by subjecting it to heat treatment in air or oxygen at 400 to 1000°C, for example, 600°C, for 1 to 100 hours, for example, 5 hours. . Furthermore, at such high temperatures, oxygen in this insulating film diffuses into the ceramics (solid phase-solid phase diffusion).
However, oxygen can be supplied to the oxygen-deficient state at or near this surface, and superconducting properties can be sufficiently maintained at or near this surface. As a result, we confirmed the Josephson effect by maintaining the temperature at liquid nitrogen, and as a result, we were able to obtain the performance shown in FIG. 2B as its characteristics.

``Operation'' By doing this, the problem of reduced reliability, where the superconducting state disappears for unknown reasons near the surface of oxide superconducting ceramics, is eliminated.
It has now become possible to effectively utilize the superconducting state of the surface in a stable manner for a long period of time.

As a result, it has become possible to operate devices using this surface, particularly Josephson devices, stably and with high reliability for a long period of time.

The present invention will be explained below with reference to the drawings.

Example 1 FIG. 1 shows the manufacturing process of an example of the present invention and the relative characteristics of the oxygen concentration distribution related thereto.

Figure 1A shows superconducting ceramics, e.g.
_{YBa2Cu3O6-8 . _ _} The copper content can be 3 or less. Such a superconducting ceramic was formed on a tablet or a thin film to have a single crystal or polycrystalline structure, and was used as a starting material (A1 in FIG. 1).

When this is held in a vacuum device and the atmosphere is evacuated, the oxygen near the surface 1' is degassed, and approximately 200
Deterioration occurs in the electrical characteristics in the range up to 100 Å.

That is, the oxygen concentration corresponding to Figure 1A is shown in Figure 1D.
Shown below. In the figure, region 1 has normal oxygen concentration. Furthermore, area 1' indicates a shortage area. This depth depends on the type, structure, and density of the superconducting material, but is generally about 50 to 1000 Å, and generally about 200 Å.

Aluminum 2 was formed on the upper surfaces of these to a thickness of 30 Å by vacuum evaporation.

Further, the whole was heat-treated in oxygen at 400 to 1000°C, for example, 600°C, for 1 to 100 hours, for example, 5 hours. This heat treatment is preferably performed under atmospheric pressure or under increased pressure, rather than under reduced pressure.

By performing heat treatment in such an oxidizing atmosphere for a long time, this metal 2 is oxidized and transformed into aluminum oxide 3. Furthermore, oxygen diffuses into the superconducting material from the aluminum oxide. As a result, as shown in FIG. 1E, it was possible to make the concentration of oxygen the same as that inside.

The sample made in this example was removed from the heated state and stored again in a vacuum. This blocking layer 3 prevents oxygen from being depleted on or near the surface of the superconducting material, making it possible to produce a highly reliable device.

This insulating film was extremely effective as a passivation film.

Example 2 In this example, a Josephson junction type superconducting element was manufactured based on the facts of Example 1.

According to Example 1, oxide insulator 3 was formed to a thickness of 20 Å. After this, other superconducting material 4 is applied to this upper surface.
was selectively formed by methods such as sputtering, CVD, MBE, and screen printing. Alternatively, a method may be used in which the superconducting material is formed on the entire surface and then the superconducting material is selectively formed.

In this way, a tunnel junction type Josephson junction device is obtained, and an example of its characteristics is shown in FIG. 2B. As is clear from the drawings, two stable points are created with the same current due to the Josefson effect, and it has been found that the present invention can be applied to logic circuit elements and memory elements.

Example 3 The production process of this example is shown in FIG. That is, the superconducting material 1 is formed as a thin film on the base 10 having a non-superconducting surface.

A silicon oxide film 6 was formed on this superconducting material to a thickness of 0.5 μm by CVD.

Furthermore, as shown in FIG. 3B, this silicon oxide film was photo-etched to form holes 7 only in the region where Josephson junctions were to be formed.

Thereafter, Example 1 was carried out to form an insulating film 3 on the entire surface through which a tunnel current could flow. Furthermore, another superconducting ceramic 4 was formed on the upper surface by sputtering method or the like.

Next, this ceramic 4 was selectively removed by photoetching, and a plurality of Josephson junction elements 20, 20', 20'' were provided.

They are the lower superconducting material 1, the bonding coating 3',
3″, 3 Further upper superconducting material 4′, 4″, 4
It is composed of:

In addition, in the drawing, if unnecessary parts of the lower superconducting material are selectively removed as shown in Figure 1A to form a plurality of island-like regions, a so-called integrated Josephson junction device can be created. .

"Effect" As shown in the present invention, an oxide superconductor is produced,
By forming a passivation film on the surface and further densifying or oxidizing it,
The method of fabricating highly reliable Jofson devices by making this film more perfect and at the same time modifying the superconducting material in close contact with it is extremely effective because it simplifies the manufacturing process. .

In the present invention, the term superconducting ceramics is used. However, this is due to the fact that the superconducting material is an oxide. It is clear from the technical concept of the present invention that the crystal structure may be polycrystalline or single crystalline. In particular, in the case of a single crystal structure, when using a superconducting material, epitaxial growth may be performed on the substrate.

[Brief explanation of the drawing]

FIG. 1 shows the manufacturing method and impurity concentration of the present invention. FIGS. 2 and 3 show the Josephson junction superconducting device of the present invention and its characteristics.

Claims (1)

[Claims] 1. A step of forming an insulating film or a metal or semiconductor that will become an insulating film after oxidation on the upper surface of superconducting ceramics, and heat-treating the entirety in an oxidizing atmosphere to eliminate oxygen depletion in the upper part of the ceramics. 1. A method for manufacturing a Josephson-type device, comprising the steps of removing the superconducting material, and, after the step, disposing another superconducting material on the coating. 2. A method for manufacturing a Josephson type device according to claim 1, wherein the other superconducting material is made of superconducting ceramics. 3. The method of manufacturing a Josephson type device according to claim 1, wherein the film is formed of a metal or a semiconductor and is transformed into an insulating film by heat treatment in an oxidizing atmosphere.