JP2899285B2 - Superconductor - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a superconductor. In particular, it relates to a compound thin film superconductor.

As a conventional art high-temperature superconductor, but such niobium nitride (NbN) and germanium niobium (Nb ₃ Ge) is known as A15 type binary compounds, superconducting transition temperatures of these materials are met at most 24 ° K Was. On the other hand, a perovskite-based ternary compound is expected to have a higher transition temperature, and a Ba-La-Cu-O-based transition temperature of 90 K class high-temperature superconductor has been proposed [JGBendo
rz and KAMuller, Zetshrift frphysik B-Condensed Matt
er 64,189-193 (1986)].

Furthermore, it has been discovered that Bi-Sr-Ca-Cu-O-based materials exhibit a transition temperature of 100K or more.

Although the details of the superconducting mechanism of this type of material are not clear, the transition temperature may be higher than room temperature, and more promising properties are expected as a high-temperature superconductor than conventional binary compounds.

Problems to be Solved by the Invention However, Bi-Sr-Cu-O-based materials can be formed only in the process of sintering with the current technology, and thus can be obtained only in the form of ceramic powder or blocks.
On the other hand, when this kind of material is put into practical use, it is strongly demanded to make it thinner or linear, but it is extremely difficult with conventional techniques.

The present inventors have found that a thin-film high-temperature superconductor is formed by using a thinning method such as a sputtering method with this kind of material, and invented a novel superconductor configuration based on this. .

Means for Solving the Problems The superconductor of the present invention is characterized in that the main component is Bi-Sr-Ca
-In a superconductor having a Cu-O coating adhered thereon, the buffer film is made of calcium fluoride, barium fluoride, CaF2 type crystal material such as strontium fluoride, or BaTiO3, CaT
Perovskite crystal materials such as iO3, CdTiO3, PbZrO3, and PbHfO3, or ZnO-type crystal materials such as ZnS, Zn, ZnSe, and CdS, or materials composed of any of alumina, strontium titanate, steatite, forsterite, beryllia, and spinel It is characterized by being constituted by.

The superconductor according to the present invention has a great feature in that the superconductor is formed as the compound thin film. Since the material of the superconductor is decomposed into ultrafine particles called atomic state and then deposited on the substrate, the composition of the formed superconductor is essentially homogeneous compared to conventional sintered bodies, When bismuth is included, low-temperature formation becomes possible, and a very high-precision superconductor is realized by the present invention using the buffer film.

The present invention will be described with reference to the drawings.

In FIG. 1, a quaternary compound coating 12 of Bi-Sr-Ca-Cu-O is formed on a substrate 11 by, for example, a sputtering method.
In this case, the base 11 is intended to hold the ternary compound coating 12 exhibiting superconductivity. Furthermore, a major feature of the present invention is that a buffer layer 15 is provided at the interface between the base 11 and the compound coating 12. Therefore, the superconductor of the present invention essentially has a layered structure.

When a semiconductor such as silicon, germanium, gallium arsenide, gallium nitride, gallium phosphide, indium phosphide, indium arsenide, zinc sulfide, zinc selenide, and cadmium sulfide is used as the base 11 in FIG. 1, superconductivity and the functions of the semiconductor are integrated. Thus, a new functional element is formed. The present inventors have discovered that when the quaternary compound film 12 is formed directly on the substrate 10, these semiconductor constituent elements often diffuse into the quaternary compound film 12 and deteriorate the superconductivity of the quaternary compound film. did. Therefore, the present invention has found that a buffer film is formed in order to prevent these characteristics from deteriorating.

Furthermore, it has been found that there is an optimal buffer film for forming a quaternary compound film 12 having a high crystallinity on the surface 13 of the substrate 11.

That is, as the buffer film 15, the main components are platinum, gold, silver,
The present inventors have confirmed that good superconducting characteristics can be obtained by using a film made of a metal such as rhodium or an alloy thereof.

Furthermore, the present inventors have found that as the buffer film, magnesium oxide, spinel, strontium titanate, zirconium oxide or _{BaF 2, CaF 2, SrF 2} CaF 2 type material such as, or ZnS, ZnO, ZnSe, etc. Cds, ZnO type material or Ba
It has been confirmed that good superconducting properties can be obtained even when a crystalline thin film of a material having a perovskite structure such as Tio ₃ , CaTiO ₃ , CdTiO ₃ , PdZrO ₃ , PbHfO ₃ is used.

Furthermore, when the buffer film is made of porcelain such as alumina, magnesium oxide, zirconium oxide, steatite, forsterite, beryllia, spinel, or quartz,
The present inventors have found that good superconductivity can be obtained even when formed on high silicate glass, borosilicate glass, soda glass, aluminum oxide glass, zirconia glass, silicon nitride glass, or silicon oxynitride glass film. Confirmed.

Here, as the substrate 11 on which these buffer films are formed, silicon, germanium, gallium arsenide, gallium nitride,
Good results were obtained using single crystals of gallium phosphide, indium phosphide, indium arsenide, zinc sulfide, zinc selenide or cadmium sulfide, but when a crystalline thin film was formed on these single crystal substrates 11, The inventors have confirmed that a buffer layer 15 having a good quality can be obtained.

Furthermore, as shown in FIG. 2, the present inventors formed a buffer layer 15 in which at least the A layer and the B layer were sequentially laminated, and covered the substrate surface 13 with this multilayer buffer layer. Arsenic, gallium nitride, gallium phosphide,
It was confirmed that a better superconducting material could be obtained by using a substrate 11 made of indium phosphide, indium arsenide, zinc sulfide, zinc selenide, cadmium sulfide, or the like. Where A
Layer, B layer is a glass layer such as quartz, silicon oxide, high silicate glass, borosilicate glass, CaF ₂ type crystal layer such as calcium fluoride, barium fluoride, strontium fluoride, platinum,
It is obtained by a combination of two kinds of metal layers such as gold and silver, zirconium oxide, aluminum oxide and magnesium oxide.

Hereinafter, in order to further understand the contents of the present invention, specific examples will be described.

(Specific Example 1) Using a gallium arsenide single crystal plane as a substrate 11, a buffer layer 15 made of a platinum thin film having a thickness of 0.1 μm was provided by high frequency planar magnetron sputtering, and Bi- (Sr / Ca) _2-
A layer structure 10 was formed by depositing a Cu ₂ -O coating 12. In this case, the Ar gas pressure is 0.5 Pa and the sputtering power is 150
W, the sputtering time was 10 hours, the film thickness was 6 μm, and the substrate temperature was 500 ° C. The formed layered structure was further heat treated in air at 800 ° C. for 1 hour.

The coating had a room temperature resistivity of 100 μΩcm and a superconducting transition temperature of 80K.

(Specific Example 2) Using a gallium arsenide single crystal plane as the substrate 11, a 1 μm-thick quartz thin film and a 0.1 μm-thick platinum thin film were sequentially formed by high-frequency planar magnetron sputtering to form an A layer and a B layer of the buffer layer 15. the provided further _{Bi- (Sr / Ca) 2 -Cu} 2 -O coating 1
2 was deposited to form a layered structure 10. In this case, the pressure of the Ar gas was 0.5 Pa, the sputtering power was 150 W, the sputtering time was 10 hours, the film thickness was 6 μm, and the substrate temperature was 500 ° C. The formed layered structure is further heated in air at 800 ° C, 1
Heat treated for hours.

The coating had a room temperature resistivity of 100 μΩcm and a superconducting transition temperature of 80K.

Quaternary compound superconductor effects of this type of invention _{Bi- (Sr / Ca) 2 -Cu} 2 -O
The details of the change in the superconducting characteristics due to the change in the composition ratio of the constituent elements of the above are not clear. However, even if the ratio of Bi, Sr / Ca, and O ₂ is changed, as long as Ca is included, the superconducting transition temperature does not change the essential characteristics of the layered structure of the invention.

In particular, the superconductor according to the present invention has a great feature in that a high-quality superconductor can be thinned at a low temperature. That is, the conventional high-temperature superconducting material requires 600 ° C.
A substrate temperature of 00 ° C. was required. However, Bi-containing materials can be cooled down in comparison with a conventional sintered body.

Further, as described above, the feature of the low-temperature synthesis of the present invention can be used for integration with a device such as Si or GaAs, and can be used as a material for various superconducting devices such as a Josephson device. In particular, there is a possibility that the transition temperature of this type of compound superconductor may be room temperature, so that the conventional practical range is wide, and the industrial value of the present invention is high.

[Brief description of the drawings]

FIG. 1 and FIG. 2 are block diagrams of a superconductor substrate according to an embodiment of the present invention. 11: Base, 12: Ternary compound coating. 15 ... buffer layer.

 ──────────────────────────────────────────────────の Continuing on the front page (72) Inventor Hiroshi Ichikawa 1006 Kazuma Kadoma, Osaka Pref. Matsushita Electric Industrial Co., Ltd. (72) Inventor Shinichiro Hatta 1006 Kadoma Kadoma Kadoma, Osaka Matsushita Electric Industrial Co., Ltd. (72) Inventor Kumiko Hirochi 1006 Kazuma Kadoma, Osaka Prefecture Inside Matsushita Electric Industrial Co., Ltd. (72) Inventor Kiyotaka Wasa 1006 Odaka Kazuma Kadoma, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (56) Reference Literature The Nikkan Kogyo Shimbun, January 22, 1988, 14th edition, No. 14776, page 1, Appl. Phys. Lett. 51 (25) pp. 2164-2166 IEEE Trans. on Mag netics. Vol. MAG-23, no. 2 pp. 1674-1677

Claims (2)

(57) [Claims] 1. A superconductor having a main component of Bi-Sr-Ca-Cu-O coated on the buffer film of a substrate having at least one surface coated with the buffer film. CaF2 type crystal material such as calcium, barium fluoride, strontium fluoride, or BaTiO3, CaTiO3, CdTiO
3, composed of a perovskite crystal material such as PbZrO3 or PbHfO3, or a ZnO-type crystal material such as ZnS, ZnO, ZnSe, CdS, or a material composed of any of alumina, strontium titanate, steatite, forsterite, beryllia, and spinel. A superconductor characterized by the following. 2. The buffer film is made of a glass layer of quartz, silicon oxide, high silicate glass, borosilicate glass or the like, a CaF ₂ type crystal material such as calcium fluoride, barium fluoride or strontium fluoride, platinum or gold. 2. The superconductor according to claim 1, wherein the superconductor is constituted by a combination of two kinds of metals, such as silver, silver, and aluminum oxide.