JP2703227B2 - Superconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a superconductor device using a thin film of a perovskite-type oxide superconductor. (Prior Art) In recent years, since it was announced that Ba-La-Cu-O-based layered perovskite-type oxides may have a high critical temperature, research on oxide superconductors has been carried out in various places. (Z.Phys.B Condensed Matter 64,189-193 (198
6)). Among them, a defect perovskite type (ABa ₂ Cu ₃ O) having an oxygen defect typified by a Y—Ba—Cu—O system
_7-δ type) (A is an element selected from Y, Yb, Ho, Dy, Eu, Er, Tm, and Lu, and δ is a number of 1 or less; the same applies hereinafter). It has been drawing attention as a very promising material because its critical temperature Tc is as high as 90 K or higher and higher than liquid nitrogen (Phys. Rev. Lett. Vol. 58 No. 9, 908-910). When such an oxide superconductor is used as a conducting wire, it is conceivable to enclose it in a metal tube or to attach it in a pattern on a substrate, but in the latter case, the superconductor is used. Since the linear expansion coefficient is 18 × 10 ⁻⁶ / K, which is 2 to 3 times larger than that of ordinary ceramics such as alumina, there is a problem that cracks are generated and adhesion is poor when the thermal cycle is repeated. (Problems to be Solved by the Invention) As described above, when the oxide superconductor is used in the form of a thin film adhered on a substrate, the linear expansion coefficient of the superconductor is large, and furthermore, the temperature is reduced to a critical temperature. When the thermal cycle is repeated, there is a possibility that cracks may be generated to deteriorate the characteristics or to be separated from the substrate. The present invention has been made in order to solve such conventional difficulties, and it is an object of the present invention to provide a superconductor device formed by forming a perovskite-type superconductor thin film on a substrate and having no risk of deterioration in characteristics due to a thermal cycle. And Superconductor device of the configuration of the invention] (Means for Solving the Problems) Thus, the present invention, the linear expansion coefficient in the plane direction is ^{10 × 10 -6 / K~25 × 10} -6 / K LiNbO 3 of LiTaO ₃ , Ag and
Thickness of 1000Å-10 on a substrate made of Pd
It is characterized by forming a thin film of perovskite oxide superconductor of ⁴ mm. The oxide superconductor containing a rare earth element and having a perovskite structure may be a superconducting state, and ABa ₂ Cu ₃ O _7-δ (δ is an oxygen defect and usually 1 or less,
A is a defective perovskite type having an oxygen defect such as Y, Yb, Ho, Dy, Eu, Er, Tm, Lu; a part of Ba can be replaced with Sr, etc., Sr
-An oxide having a perovskite structure in a broad sense such as a layered perovskite type such as a La-Cu-O type. Rare earth elements are also broadly defined and include Sc, Y and lanthanum. As a typical system, in addition to the Y-Ba-Cu-O system,
Sc-Ba-Cu-O system, Sr-La-Cu-O system, Sr is Ba,
And a system substituted with Ca. The oxide superconductor of the present invention can be obtained, for example, by the following manufacturing method. The constituent elements of the perovskite-type oxide superconductor such as Y, Ba, and Cu are sufficiently mixed. In this case, oxides such as Y ₂ O ₃ , BaO, and CuO can be used for each raw material. In addition to these oxides, compounds such as carbonates, nitrates, oxalates, and hydroxides that are converted into oxides after firing may be used. The elements constituting the perovskite-type oxide superconductor are basically mixed so as to have a stoichiometric composition, but may be slightly shifted depending on the production conditions and the like. For example, in the Y-Ba-Cu-O system, the standard composition is 2 mol of Ba and 3 mol of Cu with respect to 1 mol of Y.
A deviation of about 6 to 1.4 mol%, about 1.5 to 3.0 mol% of Ba, and about 2.0 to 4.0 mol% of Cu is not a problem. After mixing the above-mentioned raw materials, they are calcined and pulverized into a desired shape and then fired. Calcination is not always necessary. Firing and calcining are preferably performed at about 800 to 940 ° C. in an oxygen-containing atmosphere capable of supplying sufficient oxygen. The superconductor device of the present invention uses a block-shaped oxide superconductor, and has a linear expansion coefficient of 10
On a substrate of × 10 ^{-6 to} 25 × 10 ^-6 , sputtering, evaporation,
It is manufactured by attaching it in the form of a thin film so as to have a thickness of 1000Å10 ⁴に よ り by a method such as electron beam plating. If necessary, the components of the superconductor may be deposited on the substrate at a predetermined component ratio by a CVD method or the like, and the superconductor may be formed on the substrate. The above oxide superconductor is manufactured, for example, as follows. First, raw materials of perovskite-type oxide superconductors such as BaCO ₃ , Y ₂ O ₃ , and CuO are mixed and pulverized so as to have a stoichiometric composition with respect to the general formula described above, and then dried and powdered. As it is, it is fired at a temperature of 800 to 940 ° C. for several hours to about 3 days, reacted and crystallized. The mixing ratio of the above-mentioned raw materials can be changed somewhat depending on the production conditions and the like. For example, Y-Ba-Cu
In the -O system, the standard composition is 2 mol of Ba and 3 mol of Cu with respect to 1 mol of Y, but in practice, other components are ± 30% based on Y.
No problem occurs even if it is shifted by about the same degree. These are formed into a predetermined shape and used as a thin film target. In addition, examples of the material for the substrate used in the present invention include the following. (Substrate) (Linear expansion coefficient) LiNbO ₃ 15 × 10 ⁻⁶ / K LiTaO ₃ 16 × 10 ⁻⁶ / K Ag 19 × 10 ⁻⁶ / K Pd 12 × 10 ⁻⁶ / K Substrate wire used in the present invention the expansion coefficient, the linear expansion coefficient in the plane direction is limited to the range of ^{10 × 10 -6 / K~25 × 10} -6 / K , the difference in linear expansion coefficient between the oxide superconductor falls outside this range Is too large, and the superconductivity of the thin film is apt to deteriorate. In the present invention, the thickness of the superconducting thin film is limited to the above range, if the film thickness is less than 1000 mm, the predetermined superconducting properties cannot be obtained due to magnetic field penetration, and even if it exceeds 10 ⁴ mm, it is no more. This is because the superconductor characteristics cannot be improved and the substrate becomes brittle, and it is easy to peel off or crack. (Operation) In the superconductor device of the present invention, since the coefficient of linear expansion of the substrate and the thin film of the perovskite-type oxide superconductor formed on the substrate are substantially equal, the stress due to the thermal cycling is small, and The decrease is small and the adhesion between the superconductor and the substrate is improved. (Example) Next, an example of the present invention will be described. Example 1 BaCO ₃ powder 2 mol%, Y ₂ O ₃ powder 0.5 mol%, CuO powder 3 mol%
Was sufficiently mixed, baked at 900 ° C. for 48 hours, and then pulverized. The powdered raw material was fired at 800 ° C. in the air for 24 hours to react, and then pulverized using a ball mill and classified to obtain a perovskite-type superconductor powder having an average particle diameter of 2 μm. Next, the superconductor was compression-molded into a plate and heat-treated at 900 ° C. for 24 hours in air at 1 atm. Using the superconductor block obtained in this manner as a target, a thickness of 1 mm was formed on an Ag plate having a thickness of 0.1 mm by sputtering.
A thin film of 500 mm was formed, and this thin film was heat-treated at 850 ° C. for 12 hours in oxygen. The critical temperature of this thin film was 90K. Next, the Ag plate on which the superconducting thin film was formed was subjected to 10 cooling / heating cycles of immersion in liquid nitrogen and returning to room temperature, but no decrease in superconducting properties was observed. No crack was observed. In addition, on the substrate
When LiNbO ₃ , LiTaO ₃ , and Pd were used, the same characteristics as those of Ag were obtained. On the other hand, a superconductor manufactured under the same conditions as in the example except that a quartz glass plate (linear expansion coefficient: 0.4 × 10 ⁻⁶ / K) was used instead of the Ag plate was subjected to a thermal cycle under the same conditions as the example. At one time, fine cracks occurred and the electric resistance did not become zero. [Effects of the Invention] As is clear from the above embodiments, the superconductor device of the present invention has a thickness of 1000 mm on a substrate having a linear expansion coefficient in the plane direction of 10 × 10 ^{−6 to} 25 × 10 ^−6. Since a thin film of perovskite-type oxide superconductor of ~ 10 ⁴ mm was formed, the generation of distortion due to thermal cycling was small, and there was no danger of deterioration in superconducting characteristics, the occurrence of peeling, cracks, etc. Can be maintained.

   ────────────────────────────────────────────────── ─── Continuation of front page    (72) Inventor Hiromi Niyu               1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi Toshiba Corporation               Within the Research Institute (72) Inventor Koichiro Inomata               1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi Toshiba Corporation               Within the Research Institute                (56) References JP-A-63-239738 (JP, A)                 JP-A-63-245820 (JP, A)

Claims (1)

(57) [Claims] Li the linear expansion coefficient in the plane direction is ^{10 × 10 -6 / K~25 × 10} -6 / K
NbO _3, LiTaO _3, Ag and on a substrate made of one selected from Pd, superconductor device, characterized by comprising forming a thin film having a thickness of 1000Å~10 ⁴ Å perovskite oxide superconductor . 2. 2. The superconductor device according to claim 1, wherein the oxide superconductor is a perovskite-type oxide superconductor containing a rare earth element. 3. The oxide superconductor is an AB ₂ Cu ₃ O _7-δ- based oxide superconductor (A is an element selected from Y, Yb, Ho, Dy, Eu, Er, Tm and Lu). Claims 1
3. The superconductor device according to item 2 or 2. 4. 3. The superconductor device according to claim 1, wherein the oxide superconductor is a Y-Ba-Cu-O-based material.