JPH0687696A - Method for manufacturing superconducting thin film - Google Patents

Abstract

(57) [Abstract] [Purpose] To eliminate cracks in the superconducting thin film caused by tensile thermal stress during the cooling process during film formation. [Structure] An oxide superconductor having a crystal orientation other than the (001) axis and a substrate having a coefficient of thermal expansion larger than that of the oxide superconductor are used to form a thin film of the oxide superconductor on the substrate. Therefore, in the process of cooling from high temperature during the film formation to room temperature, the substrate shrinks more than the superconducting thin film, so that compressive stress acts on the superconducting thin film and it is possible to prevent cracks from occurring in the superconducting thin film. it can.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an oxide superconducting thin film.

[0002]

2. Description of the Related Art In order to use an oxide superconductor in electronic devices such as Josephson devices, it is necessary to make the superconductor thin. In particular, when manufacturing a laminated Josephson junction, a superconducting thin film having a crystal orientation other than the (001) axis with a short coherence length must be used. To form a thin film of oxide superconductor, a physical vapor deposition method such as a sputtering method, an electron beam vapor deposition method or a laser ablation method, or a chemical vapor deposition method such as MOCVD is usually used to deposit a film on a substrate. There is. In these film forming methods, the substrate is heated to a high temperature of several hundreds of degrees Celsius or more in order to epitaxially grow the superconducting thin film. , Stress is generated in the superconducting thin film, which causes cracks. In particular, when the crystal orientation of the superconducting thin film is other than (001), the coefficient of thermal expansion of MgO or SrTiO ₃ is smaller than that of the oxide superconductor.
When a substrate made of such a material is used, a tensile stress is generated in the superconducting thin film during the cooling process, and minute cracks are formed.
Detailed examination shows that this crack is prone to cracking (0
01) It was found that it occurred in the plane. The state of this crack is shown in the schematic perspective view of the oxide superconducting element of FIG. FIG. 2 shows that, for example, the thermal expansion coefficient is 9.4, which is often used conventionally.
Substrate 1 of SrTiO ₃ (110) having × 10 ⁻⁶ / ° C.
The coefficient of thermal expansion along the c-axis is 18.46 × 10 ^-6 / ° C.
When the oxide superconducting thin film 2 of 1 is formed, the substrate 1 has a smaller thermal expansion coefficient than the superconducting thin film 2.
It shows that cracks 3 occur in the.

[0003]

The problem is that the crack 3 as shown in FIG. 2 is inconvenient for using the superconducting thin film 2 as an electronic device, and therefore, the crack 3 during the film formation process.
That is, it is necessary to form a superconducting thin film 2 which does not enter. An object of the present invention is to provide a method for producing a superconducting thin film in which cracks due to tensile thermal stress do not occur in the cooling process during film formation.

[0004]

[Means for Solving the Problems]
For this reason, the method of the present invention uses (00
1) LnBa having crystal orientation other than the axis₂Cu₃O_7-X
(Ln is Y, La, Sm, Eu, Gd, Dy, Ho, E
Any one element of r, Tm, Yb, and Ln, x
Is the oxygen deficiency) and the thermal expansion from these oxide superconductors
Large expansion coefficient, thermal expansion coefficient 18.5 × 10^-6/ ° C or less
On LaSrGaO_Four, VO₂, GaCO ₃Substrate such as
To form a thin film of oxide superconductor on this substrate.
It is something.

[0005]

By forming the superconducting thin film on the substrate as described above, the substrate shrinks more than the superconducting thin film in the process of cooling from several 100 ° C. or higher during the film formation to room temperature. It is possible to prevent the generation of cracks in the superconducting thin film due to the action of compressive stress.

[0006]

EXAMPLES The present invention will be described below based on examples. The present invention resides in using a substrate having a coefficient of thermal expansion larger than that of the oxide superconductor. A schematic perspective view of the obtained oxide superconducting element is shown in FIG. In the device shown in FIG. 1, the generation of the crack 3 as shown in FIG. 2 is not recognized.

In order to obtain such a device, in the present invention, YBa ₂ Cu ₃ O _7-X (x is an oxygen deficiency amount) [hereinafter abbreviated as YBCO] is used as the oxide superconductor, and LaSrGaO is used as the substrate 1. ₄ (110) is used. The linear expansion coefficient of YBCO in the c-axis direction is 18.46 × 10 ⁻⁶ / ° C., and the linear expansion coefficient of LaSrGaO _{4 in} the (001) direction is 18.9 × 10 ⁻⁶ / ° C. RF magnetron sputtering is used as the film forming method, and the substrate temperature is 650 ° C. and the thickness is 300 nm.
The YBCO thin film 2a was formed to a film thickness of. After the film formation, the YBCO thin film 2a obtained by cooling to room temperature has a (110) orientation, and as shown in FIG. 1, no cracks occur.

Next, using YBCO for the oxide superconductor,
VO ₂ (110) was used for the substrate 1. VO ₂ (00
The coefficient of linear expansion in the 1) direction is 21.4 × 10 ^-6 / ° C.
The film forming method and the film thickness were the same as in the above case, and the YBCO thin film 2a obtained by cooling to room temperature after the film formation had a (013) orientation, and at this time, as in the case shown in FIG. There were no cracks at all.

Further, YBCO was used for the oxide superconductor, and GaCO ₃ (110) was used for the substrate 1 to form a YBCO thin film 2a. The linear expansion coefficient of GaCO _{3 in} the (001) direction is 26.3 × 10 ^-6 / ° C. The YBCO thin film 2a obtained by cooling to room temperature after the film formation has the (013) orientation by the film formation method and the film thickness similar to the above two cases,
In this case as well, the occurrence of cracks was not recognized as in the above two cases.

The case where three different kinds of substrates 1 are used has been described above. From these examples, the coefficient of thermal expansion of the substrate should be at least 18.5 × 10 ⁻⁶ / ° C., and
In addition to the above, oxide superconductors include LnBa ₂ Cu ₃ O _7-X
(Ln is La, Sm, Eu, Gd, Dy, Ho, Er,
The same effect can be obtained by using any one element of Tm, Yb, and Ln and x is an oxygen deficiency amount.

As described above, according to the present invention, an oxide superconductor having a crystal orientation other than the (001) axis (having an inclination in the c axis) and a substrate having a thermal expansion coefficient larger than that of the oxide superconductor are used. As a result, in the process of cooling from a high temperature during film formation to room temperature, the substrate shrinks more than the superconducting thin film, and compressive stress acts on the superconducting thin film, so that cracking can be prevented.

[0012]

According to the method of the present invention, an oxide superconductor having a crystal orientation other than the (001) axis and a substrate having a thermal expansion coefficient larger than that of the oxide superconductor are used. Since the superconducting thin film was formed on the surface of
Since the substrate shrinks more than the superconducting thin film, and the compressive stress acts on the superconducting thin film, cracks do not occur in the superconducting thin film. By applying
It is possible to manufacture a Josephson device having good characteristics.

[Brief description of drawings]

FIG. 1 is a schematic perspective view of an oxide superconducting element obtained by the present invention.

FIG. 2 is a schematic perspective view showing a state of cracks generated in an oxide superconducting element.

[Explanation of symbols]

 1 substrate 2 superconducting thin film 2a YBCO thin film 3 crack

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Kimura 1-1 Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd. No. 1 in Fuji Electric Co., Ltd. (72) Inventor Koichi Tsuda 1-1 No. 1 Tanabe Nitta, Kawasaki-ku, Kawasaki City, Kanagawa Prefecture Fuji Electric Co., Ltd.

Claims (3)

[Claims] 1. An oxide superconductor having LnBa ₂ Cu ₃ O _7-X (Ln is Y, L having crystal orientation other than the (001) axis.
a, Sm, Eu, Gd, Dy, Ho, Er, Tm, Y
Any one element of b and Ln, x is an oxygen deficiency amount), a substrate of a material having a larger thermal expansion coefficient than these oxide superconductors is used, and a thin film of the oxide superconductor is formed on the substrate. Forming a superconducting thin film. 2. The method for producing a superconducting thin film according to claim 1, wherein the substrate has a thermal expansion coefficient of 18.5 × 10 ⁻⁶ / ° C. or more. 3. The method according to claim 1 or 2, wherein
The plate is LaSrGaO _Four, VO₂, GaCO₃Out of
Manufacturing method of superconducting thin film characterized by using a gap
Law.