JPH04144913A - Production of thin-film superconductor - Google Patents

Abstract

PURPOSE:To easily and stably produce a thin-film superconductor having good superconducting characteristics by coating a hot substrate with an oxide coating film composed of one kind of Y and lanthanide elements, one kind of element of group IIa and copper and heat-treating the coated substrate in an oxygen- containing atmosphere. CONSTITUTION:An oxide coating film composed mainly of A (at least one kind of element selected from Y and lanthanide elements), B (at least one kind of group IIa elements) and copper is deposited on a substrate having controlled temperature, crystallization nuclei are formed in the coating film and the product is heat-treated in an oxygen-containing atmosphere at a controlled temperature to effect the growth of a crystal containing (A1-xCax)1B2Cu4 (0<=x<=0.3) and obtain a thin-film surer-conductor having high crystallinity.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for producing superconductors, and in particular to a method for producing compound thin film superconductors. Niobium nitride (NbN) and germanium niobium (NbsGe)
The superconducting transition temperature of these materials was known to be at most 24, but an even higher transition temperature is expected compared to perovskite steel oxides1.・Matter, No. 64t, pp. 189-193 (1986) (J, G, Dendorz and
[, A. Muller.

Zeitschrift fur physik B-
Condensed Matter.

Although a high-temperature superconductor of the Ba-La-Cu-0 system has been proposed as described in J. M., 189-193 (1986)), Y-Ba-Cu oxide of the t-2-3 system has been proposed. (For example, Physical Review Letters Vol. 58 No. 90
8-910 (1987) (MJ, Wu, J, R
, Ashburn, C.O.J., Torng, P.H., Ho.
r.

R, Meng, L, Gao, Z, J, Huang.
, Y., Q., Wang, and C.

W, Chu, Physical Review L
etters! lL8. 908-910 (19
Although it has been proposed that the superconductor is a higher temperature superconductor, the oxide superconductor of the 1-2-3 system (which is an oxygen-deficient superconductor) is a thermally For example, Y-
1-2-4 system power of Ba-Cu oxide (Nature, Part 3
36 @ pages 660-662 (1988) (J
Jarpinski.

E, Kaldis, E, Jilek, S, Ru5i
ecki and B, Bucher.

Letters to Nature, u13.6
60-662 (1988))
Although it has been proposed that the El-2-4 series Y-Ca-Ba-Cu oxide is a stable superconductor at high temperatures, for example, Nature, No. 341fs, p. 41-4
2 pages (1989) (T, Miyatake, S.
Gotoh, N., [oshizuka and S.
Tanaka, Letters to Nature
Although it has been proposed that the 1-2-4 material is a higher temperature superconductor, the details of the superconducting mechanism of 1-2-4 materials are unknown. An unknown force (the transition temperature may be higher than room temperature, and although it is expected that it will have more promising properties as a high-temperature superconductor than conventional binary compounds, the invention aims to solve the problem 1-2- 4-based materials have no oxygen vacancies and have a regular crystal structure, so they are thermally stable.
2-4 materials and current technology! i It is mainly formed through the process of sintering, and is often obtained in the form of ceramic powder or blocks11~ For the practical application of superconducting materials, there is a strong desire to process them into thin films. Force t The problem of this invention was that it was extremely difficult to make the 1-2-4 system thin, but the present invention has good superconducting properties (A + -11Ca w
) A method for producing a thin film superconductor of the present invention is aimed at providing a method for stably and easily producing a +BsCu4-based thin film superconductor.
A is Y and a lanthanum series element (atomic number 57-71)
an oxide film consisting of at least one of the following), element B (B is at least one group IIa element), and copper is deposited on a heated substrate, and the oxide film is further deposited in an atmosphere containing oxygen. By controlling the treatment temperature, (A1-11Ca
m) Heat treatment is performed to form an oxide containing +B Cua (0≦x≦0.3).Method for producing a thin film superconductor according to the present invention ('L oxidation A major feature is that the heat treatment temperature after depositing the oxide film is controlled to crystallize the oxide film. By heat-treating at a controlled temperature in an atmosphere containing the true oxygen that formed the nuclei, oxygen is supplied to the film and crystals grow around the nuclei created during the adhesion process, creating a thin film superconductor with good crystallinity. However, this heat treatment temperature must not be higher than the temperature at which the oxide film crystallizes, but must not be so high as to destroy the nuclei in the oxide film created in the deposition process. Examples Examples of the present invention will be explained with reference to the drawings. Fig. 1 shows a conceptual cross-sectional view of the thin film superconductor of the present invention. In Fig. 1,
Ternary compound coating 12L sputtering vapor deposition & C
For the purpose of retaining the 3-element compound film 12 formed on the sumo substrate 11111 by a normal method such as the VD method, a normal material such as magnesila oxide, strontium titanate, sapphire, etc. is provided, but this film 12 does not contain the element A (
Here, iQ element A represents at least one element among Y and a lanthanum series element (atomic number 57-71).

) 1 element B (here Element B indicates at least one element among Group IIa elements), Cu, 0-based composite compound (
A: B: Cu = 1: 2: 4) or a composite compound in which a part of the element is replaced with Ca.The film 12ti does not exhibit superconducting properties as it is attached, but is heat treated in an oxygen-containing atmosphere. Although superconducting properties can be obtained by rapid cooling after heat treatment, in order to improve the superconducting properties of the film, it is necessary to supplement oxygen to improve the crystallinity and orientation. Eat to supplement the oxygen
Heat treatment is performed in an oxygen-containing atmosphere. However, it was found that the above heat treatment process alone was not sufficient to improve the superconducting properties of the film.A heat treatment process was required to generate nuclei for crystallization during film deposition and to grow crystals without crushing these nuclei. aa The present inventors investigated the relationship between the superconducting properties of the ternary compound film 12 after heat treatment, the substrate temperature during film formation, and the heat treatment temperature by examining the crystal structure of the ternary compound film 12 in detail using X-ray diffraction. When the coating 12 was deposited at a substrate temperature of less than 300°C, almost no peaks due to crystal nuclei were observed.However, weak peaks were observed in the coating deposited on a substrate heated to a temperature in the range of 300°C to 550°C. Furthermore, when the substrate temperature was in the range of 550°C to 700°C, the crystallinity was excellent (
A+-++Cam) IB*Cus The oxide structure is the main component, and by controlling the substrate temperature during the deposition process, the growth of crystal nuclei can be promoted, and by heat treatment in an oxygen-containing atmosphere after the deposition process, the nuclei can be grown. Heat treatment in an oxygen-containing atmosphere from 600℃ to 8℃
(A+-xca
x) A significant peak of the +BtCua oxide phase was obtained.
A thin film with excellent crystallinity could be obtained, but if the heat treatment temperature was increased to a temperature range of 800°C to 900°C, (A 1
- w Ca 11 ) + 82Cu The proportion of (A+-xcax)+BeCu5 oxide is larger than that of a oxide! , :, At a heat treatment temperature of 600°C or less, crystallinity is difficult to improve after heat treatment (~ On the other hand, from the viewpoint of conformity, yield (A - feces Ca feces) lB2c
It has been found that in U4 oxide, there is usually a coexistence of an a-axis oriented phase and a c-axis oriented phase.The present inventors investigated the relationship between heat treatment temperature in an oxygen-containing atmosphere and orientation, and the result was 600°C. From 80
It was also discovered that in heat treatment in the range of 0°C, the higher the temperature, the more pronounced the C-axis orientation, and the lower the temperature, the more pronounced the C-axis orientation. As explained in Example 1, as shown in Figure 1! -Magnesium oxide single crystal (10
0) surface as the substrate 11 -\ An Er-Ca-Ba-Cu-0 target is sputter-deposited on the substrate 11 by high-frequency magnetron sputtering.
-Ba-Cu-0 coating 12 is deposited and formed. However, the conditions of the deposition process Gi are: 250t, 300t
t, 500t.

Heat LAr and O! to 550t and 600℃ using heaters. The coating 12 was deposited in a mixed gas atmosphere (4:1) at a gas pressure of 0.5 Pa, and the coating 12 deposited at a substrate temperature of 9250°C was hardly crystallized. % The coating deposited at a substrate temperature of 550°C was slightly crystallized, (Ez,
Even if *cas, +) IBatCu4 oxide nuclei are formed, most of the GEL deposited film becomes A+BaCu*oxide Lx at a substrate temperature of 600°C.
(Erm, mcas, +) +Barcu4 The substrate temperature is too high to form oxide nuclei. As a result of heat treatment at 760℃ for 12 hours, the film was deposited at a substrate temperature of 250℃. Even after heat treatment, the crystallinity was not improved and the film was heated to 300t.
, 500t.

Four friends were found to have good crystallinity (Era, ・Cas,
+)+BaaCua oxide thin film was obtained and at 600℃
When the film was deposited at a substrate temperature of
, +)+300 to obtain a Bazcu4 oxide thin film.
Example 2 Even if the substrate temperature in the range of 550°C is suitable, magnesium oxide single crystal (10
0) surface as the substrate 11. An Er-Ca-Ba-Cu-0 target is sputter-deposited on the substrate 11 by high-frequency magnetron sputtering.
-Ba-Cu-0 was deposited as a coating 12. However, the conditions for the deposition process were 4. The substrate 11 was heated to a temperature of 500°C with a heater in a mixed gas atmosphere of LAr and Os (4:
1) The film 12 was deposited at a gas pressure of 0.5 Pa, and the heat treatment temperature was increased to 5 Pa in an atmosphere containing oxygen at 41 atm.
50t, 600 goose 700kan 760@c% 80
Comparing the crystallinity after heat treatment at 0t and 850℃ for 12 hours, the crystallinity was not improved in the case of heat treatment at 550℃, Boot, 700
“C1760 Otori: Those heat treated at 800℃ have good crystallinity (Erm, *ca*, +)+B
When an aecua oxide thin film is obtained and heat treated at 850°C, most of it becomes A + B 2 CU$ oxide.9 Therefore, a heat treatment temperature in the range of 600°C to 800°C is appropriate. When heat treated in the range from ℃ to 800℃,
The higher the temperature, the stronger the C-axis orientation, and the lower the temperature, the stronger the C-axis orientation.
It is heat treated at 760℃ to show strong axial orientation.
A strong C-axis orientation appears.9 An example of the X-ray diffraction pattern of the thin film is shown in the jfr2 figure.A film heat-treated at 700°C for 12 hours.
An example of the X-ray diffraction pattern of the thin film is shown in Figure 3.As shown in Figures 2 and 3, the crystal orientation of the thin film can be changed by changing the heat treatment temperature. These thin films showed excellent superconducting properties. (Erm, @cas, +) +B
For comparison with the agcu4 oxide thin film (E rs, = c
ai, +) IBa elephant Cu5fl! Comparing the properties after heat treatment at 600°C in vacuum for 1 hour, the & (Ers, 5Cas, +)+Ba5Cu4 oxide thin film showed superconducting properties ((Ers, *Cas,
+)+Ba*Cu* oxide thin film exhibits semiconductor behavior 1
The thin film obtained by the method for producing a thin film superconductor of the present invention has excellent stability and can be put to practical use as a superconducting material. In the above examples, compositions containing Ca are specified. 6t
Similar results were obtained for compositions that do not contain ea. Furthermore, A is not limited to Er, but also lanthanum series elements (atomic number 57
-71), the same result would be obtained. ,,BL
Similar results were obtained for Group IIa elements. Also, exactly the same characteristics were obtained for sapphire containing low strontium titanate, which is an example of using magnesium oxide as a substrate. At-xCax) +B
Deposit a2Cu4 oxide (0≦X≦0.3) once
This invention is a method for manufacturing thin film superconductors that controls the heat treatment temperature.It is possible to provide superconducting thin films with excellent stability and reproducibility. There are also effects that can be controlled.

[Brief explanation of drawings]

FIG. 1 shows a conceptual diagram of the cross-sectional structure of a thin film superconductor according to an embodiment of the present invention. Diagram 11...Substrate 12...Name of ternary compound trapped agent Patent attorney Haruaki Ogata and two others Diagram O 3ρ 4ρ JF Diagram tθ

Claims (3)

[Claims] (1) An oxide whose main components are element A (A is at least one of Y and lanthanum series elements (atomic numbers 57 to 71)), element B (B is at least one group IIa element), and copper. An adhesion step in which the film is adhered onto a heated substrate, and further, after the adhesion step, the oxide is treated in an oxygen-containing atmosphere by controlling the treatment temperature and (A_1_−_xCa_x
)_1B_2Cu_4 (However, 0≦x≦0.3) (2) The method for producing a thin film superconductor according to claim 1, wherein the heating of the substrate is in the range of 300°C to 550°C. (3) The method for producing a thin film superconductor according to claim 1, wherein the heat treatment temperature is in the range of 600°C to 800°C.