JPH04151883A - Superconducting device - Google Patents

Abstract

PURPOSE:To make it possible to prepare a superconducting junction which is stabilized in performance and excellent in reproducibility by installing a specific junction layer which forces an oxide superconductor to produce a superconducting junction between a first superconducting layer and a second superconducting layer. CONSTITUTION:This device comprises an oxide superconducting thin film 10 formed on a substrate 4 having a PrO2 layer 40 on the surface as a material which deteriorates a crystalline orientation performance of an oxide superconducting thin film. The thin oxide superconducting film on such part which excludes the PrO2 layer 40 on the surface of the substrate 4, are turned in superconducting layers 1 and 2 consisting with c axial-oriented crystal while the thin oxide superconducting film on the PrO2 layer 40 on the surface of the substrate 4 is poor in terms of crystalline orientation performance and forms a junction layer 3. This construction makes it possible to form the whole device in one piece, facilitates the preparation and stabilizes its characteristics as well.

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 configuration of a superconducting element comprising first and second superconducting layers made of oxide superconductors and a bonding layer disposed between these superconducting layers.

BACKGROUND OF THE INVENTION Josephson devices are the most typical type of superconducting devices that utilize strong nonlinear current-voltage characteristics due to Josephson junctions. A Josephson junction is generally a pair of superconductors joined at a junction where a superconducting junction is realized. The most preferred structure of the Josephson junction is a tunnel-type junction in which a thin non-superconductor is sandwiched between a pair of superconductors. In this case, the joint consists of a thin insulator layer. However, there are weakly coupled superconducting junctions in which a pair of superconductors are weakly coupled, such as point-contact weakly coupled superconducting junctions where the junction is a tiny point, and microbridge-type weakly coupled superconducting junctions where the junction is a superconducting current path with a small cross-sectional area. Superconducting junctions also exhibit the Josephson effect, although the characteristics are different.

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

When realizing the Josephson device of the tunnel type Josephson junction described above using an oxide superconductor, the first oxide superconductor layer, the tunnel barrier insulator layer, and the second oxide superconductor layer are sequentially formed. It shall be of laminated construction.

In the above Josephson element, the thickness of the insulator layer is
Determined by the coherence length of the superconductor. Since oxide superconductors have a very short coherence length, in tunnel-type Josephson devices using oxide superconductors, the thickness of the insulator layer must be approximately several nm.

Furthermore, both point-contact type superconducting junctions and microbridge type superconducting junctions require very fine processing to achieve weak coupling between a pair of superconductors.

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 layers be formed of single crystal, and if there is a polycrystalline or amorphous layer, the performance of the Josephson element will not be 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 consists of sequentially laminating a first oxide superconducting thin film, an insulating thin film, and a second oxide superconducting thin film on a suitable substrate. This was accomplished by doing so. Therefore, in order to produce a device with excellent characteristics, it is necessary to form a single crystal insulator thin film several nanometers thick on the 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 insulating thin film was not in good condition, and desired characteristics could not be obtained.

On the other hand, the fine processing required to realize point-contact type superconducting junctions and micro-bridge type superconducting junctions is extremely difficult, and it has not been possible to produce superconducting junctions with stable performance with good reproducibility.

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 the Problems According to the present invention, first and second superconducting layers made of an oxide superconductor formed on a substrate, and the first and second superconducting layers constitute a superconducting junction. The first
and a bonding layer disposed between the second superconducting layer, wherein the bonding layer is disposed on a layer of a substance that deteriorates the crystal orientation of the oxide superconductor formed on the substrate. The constituent elements are the same as the oxide superconductor,
A superconducting element is provided, characterized in that it is made of an oxide having poorer crystal orientation than the oxide superconductor.

Function The superconducting element of the present invention is characterized in that the first and second superconducting layers made of oxide superconductors and the bonding layer that produces a superconducting bond between the first and second superconducting layers are adjacent to each other on the same substrate. It is located. Further, the bonding layer is composed of an oxide having the same constituent elements as the oxide superconductor constituting the superconducting layer, and having a worse crystal orientation than the oxide superconductor. Specifically, in terms of the manufacturing method, the superconducting element of the present invention is produced by forming an oxide superconducting thin film on a substrate partially formed with a layer of a substance that deteriorates the crystal orientation of the oxide superconductor. It has a bonding layer whose crystal orientation is disturbed by the material layer and which has lost superconductivity.

The superconducting element of the present invention having the above structure is originally composed of an oxide superconducting thin film formed integrally, and the constituent elements are the same in all parts. Further, the interface between the superconducting layer and the bonding layer is a grain boundary, and the bonding layer is formed as a weak bonding layer.

The superconducting element of the present invention described above can be manufactured by forming an oxide superconducting thin film on a substrate partially formed with a layer of a substance that deteriorates the crystal orientation of the oxide superconductor. The crystalline state of a thin film of an oxide superconductor is greatly influenced by the underlying substrate. For example, MgO, SrTiO3 (10
0) An oxide superconducting thin film consisting of a C-axis oriented single crystal can be easily grown on a substrate. However, even if films are formed under the same conditions, an oxide superconducting thin film with poor crystal orientation grows on, for example, PtO2, ZrO2, Y2O3, etc.

Therefore, the element of the present invention has pro2, Zr on a part of the surface.
It can be produced by forming an oxide superconducting thin film on a substrate on which a layer of O2, Y2O3, etc. is formed.

In addition to the above-mentioned PtO2, ZrO2, and Y2O3, substances that deteriorate the crystal orientation of the oxide superconducting thin film include Ba.
F2, CaF2, MgF2, etc. can be used.

For example, when manufacturing a Josephson device, the layer of the above-mentioned substance is preferably in the form of a line with a width of about 1 μm.

Further, the thickness of the layer is preferably about 50 nm,
The thickness of the bonding layer is approximately several hundred nm.

The part of an oxide superconducting thin film grown on a substrate directly above the substrate is greatly influenced by the substrate, but as it grows, the influence from other parts of the thin film increases.

Therefore, when forming a bonding layer several hundred nm thick in an oxide superconducting thin film, it is necessary to form a layer of the above-mentioned substance with a width of about 1 μm on the substrate surface.

Although any oxide superconductor can be used in the superconducting element of the present invention, y, ea2cu307-X-based oxide superconductors are preferred because they can stably yield high-quality thin films with good crystallinity. Furthermore, Bi25r2Ca2Cu308-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 pr02 layer 40 on its surface. The oxide superconducting thin film on the surface of the substrate 4 other than the 2102 layer 40 is
The superconducting layer 1.2 is composed of C-axis oriented crystals. Further, the oxide superconducting thin film on the Pr02 layer 40 on the surface of the substrate 4 has poor crystal orientation and becomes the bonding layer 3.

Production Example 1 A superconducting element of the present invention was produced. An MgO single crystal substrate is used as the substrate, and YIBa2CII30 is used as the oxide superconductor.
i-x was used. Referring to FIGS. 2(a) to (C),
The manufacturing procedure will be explained.

First, as shown in FIG. 2(a), a Mg0 (100) substrate 4
As shown in FIG. 2(b), a Pr02 layer 40 having a width of 1 μm and a thickness of 5 Qnm is formed by vacuum evaporation over the entire width of the device. At this time, it is necessary to perform epitaxial growth at a low deposition rate.

The vapor deposition conditions are shown below.

Substrate temperature 800℃ Pressure 5 X10-'Torr (02
) Vapor deposition rate IA/sec As shown in FIG. 2(C), an oxide superconducting thin film was formed on a substrate 4 having a Pr02 layer 40 on its surface. Y, Ba
Using a sintered body containing Cu and Cu in an atomic ratio of 1:2:4.5 as a target, a C-axis oriented oxide superconducting thin film is grown on the surface of the substrate 4 other than the Pr02 layer 40 by sputtering. The film was formed as follows. The sputtering conditions are shown below.

Substrate temperature 630℃ Suba Tsutaring gas 8r 3SCCU024SC
CM Pressure 5 It consisted of In addition, it is cooled to 85■ (frequency 10GHz,
When microwaves with an output of 0.1 mW were applied, 20.
A Shapiro step is observed at voltage points that are multiples of 7 μV,
It was confirmed that Josephson coupling was realized.

Preparation Example 2 B] Using 2Sr2Ca2CI+3011 superconductor,
A superconducting element of the present invention shown in FIG. 1 was produced by the same method as in Production Example 1. The substrate contains 5rTi03 (10
0) A substrate was used. Similarly to Preparation Example 1, Pr with a width of 1 μm and a thickness of 50 nm is placed on the surface of the substrate over the entire width of the device.
A Ch layer is formed by vacuum evaporation. At this time, it is necessary to perform epitaxial growth at a low deposition rate.

The vapor deposition conditions are shown below.

Substrate temperature 800℃ Pressure 5 XIO'Torr (02) Vapor deposition rate
B1, Sr, C
A Bi25r2Ca2Cu3Ch oxide superconducting thin film was formed by sputtering using a sintered body containing a and Cu in an atomic ratio of 2:2:2:3 as a target.

The sputtering conditions are shown below.

Substrate temperature 650℃ Sputtering gas 83CCMo24SCC
M Pressure 5
The Pr02 layer of the substrate was composed of polycrystals. Also, it was cooled to 90K and the frequency was 150I (z.

When microwaves with an output of 0.1 mW were applied, 31μ
A Shapiro step was observed at a voltage point that is a multiple of V, 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 bonding 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 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 bonding layer is made of an oxide having the same constituent elements as the oxide superconductor, it does not adversely affect 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. C Main reference numbers] 1.2...Superconducting layer, 3...Joining layer, 4...Substrate

Claims (1)

[Claims] The first layer is made of an oxide superconductor formed on a substrate.
and a superconducting element having a second superconducting layer and a bonding layer disposed between the first and second superconducting layers such that the first and second superconducting layers constitute a superconducting bond, An oxide having the same constituent elements as the oxide superconductor and having a worse crystal orientation than the oxide superconductor, the layer being disposed on a layer of a substance that deteriorates the crystal orientation of the oxide superconductor formed on the substrate. A superconducting element characterized by being composed of a material.