JPH02145761A - Manufacture of thin superconductor film - Google Patents

Abstract

PURPOSE:To form a thin film of oxide superconductor having superconducting critical temp. at low temp. by periodically laminating a Bi-containing material and a material containing Cu and alkaline earth elements on a base material by a sputtering method by using a gas containing nitrous oxide. CONSTITUTION:A base material is heated up to <=850 deg.C. A material containing at least Bi and a material containing at least Cu and alkaline earth elements (group IIa) are periodically laminated on the above base material by using a sputtering gas consisting of gaseous nitrous oxide, argon, etc. For example, the above periodical lamination is carried out by exerting sputtering by using plural targets with two or more kinds of compositions. By this method, the thin film of Bi oxide superconductor having >= about 100K superconducting critical temp. can be manufactured at low temp. with superior reproducibility.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for producing a thin film of an oxide superconductor containing bismuth, which is expected to have a high critical temperature of 100 or higher.

Conventional technology As high-temperature superconductors7, niobium nitride (NbN) and germanium niobium (Nb3Ge) are used as A15 type binary compounds.
), but the superconducting transition temperature of these materials was at most 24°.

On the other hand, perovskite-based ternary compounds are expected to have even higher transition temperatures, and Ba-La-Cu-0-based high-temperature superconductors have been proposed (J, G, Bendorz
and K, A, Mulle Otzeit Schrift
Fair Physique (Zetshrift, Fur
physik B)-Condensed Mat
ter 64.189-193 (1986)).

Furthermore, B 1-5r-Ca-Cu-0 type material is 10
It has also been discovered that they exhibit transition temperatures above 0. (H,
Maeda, Y., Tanaka, M., Fuku.
toa+i andT, Asano, Japanese・
Journal of Applied Physics (Jap
anese Journey cfApplied
Physics) Vol, 27. L, 209-L
21.0 The details of the superconducting mechanism of this type of material are not clear, but the transition temperature may be higher than room temperature, and it is expected to have more promising properties as a high-temperature superconductor than conventional binary compounds. Ru.

Problems to be Solved by the Invention When putting this type of material into practical use, there is a strong demand for processing it into a thin film. Conventionally, film thinning has been carried out by sputtering or the like, but there is a problem in practical use because the substrate temperature during production is high.

Therefore, it is desired to reduce the substrate temperature.

Means for Solving the Problems The method for producing a thin film superconductor of the present invention involves sputtering at least bismuth onto a substrate heated to 850° C. or lower using a gas containing at least nitrous oxide gas as a sputtering gas. It is produced by periodically laminating a substance containing copper and a substance containing at least copper and alkaline earth metals.

Action Nitrous oxide has a lower dissociation energy than oxygen, and active oxygen radicals and ions are easily obtained, so the kinetic energy and combination energy necessary for crystal growth are supplied, and oxygen is easily incorporated into the film. Therefore, by using nitrous oxide as a sputtering gas,
It becomes possible to lower the substrate temperature during formation.

The superconducting properties of oxide superconductors such as the Y-Ba-Cu-0 system are very sensitive to oxygen concentration, and the introduction of oxygen into the film is a very important factor in the formation of these thin films. be. For this reason, when producing a thin film by sputtering, a mixed gas of argon and oxygen has been used as the sputtering gas.

This time, the present inventors produced a B i -8r-Ca-Cu-0 superconducting thin film using various sputtering gases. Argon gas (Ar
) and a gas containing oxygen atoms, Bi target and S r2Ca2Cu3 target were alternately sputtered in oxygen, and Mg0(100) at various temperatures were sputtered.
It is layered periodically on the substrate. As a result, it is better to use a mixed gas of Ar and nitrous oxide (N20) as a sputtering gas than to use a mixture of Ar (!1-02) to achieve a critical temperature of 100K or more at a lower substrate temperature. This phase was observed by X-ray diffraction pattern.

FIG. 1 is an X-ray diffraction pattern of a thin film produced using a mixed gas of Ar and N20. When the substrate temperature is 300° C. or less, a peak corresponding to the laminated periodic structure is observed, but when the temperature is increased to 300° C. to 500° C., the periodic structure becomes weaker and the appearance of another phase (x) is observed. However, when the temperature is raised further (when the substrate temperature is in the range of 500°C to 850°C, a phase with a critical temperature of 100 or more (○)
We discovered that it is possible to create In this case, it has been found that if the sputtering rate of Bi and 5r2Ca2Cu3 is adjusted appropriately in the temperature range F, more than 100 phases appear depending on the lamination period. Furthermore, when the lamination was carried out simultaneously rather than periodically, only a phase having a critical temperature of 80°C could be produced. Especially when the substrate temperature is 550℃~8
It has also been discovered that when the temperature is 50° C., a phase with a critical temperature of 100° C. or more with very good crystallinity can be produced. When the substrate temperature was 900° C. or higher, the thin film evaporated and was not deposited. The thin film produced at 500°C to 850°C is
Although it exhibits superconducting transition even in its original state, 850
When the heat treatment was performed at a temperature of about 100° C., the critical temperature of 100° C. or more was more reliably shown.

It has also been discovered that thin films laminated at temperatures between 550°C and 850°C have particularly good reproducibility.

In this way, when a mixed gas of argon and nitrous oxide is used as a sputtering gas, the substrate temperature can be lowered by 50°C to 100°C compared to when a mixed gas of argon and oxygen is used.
Bi has a critical temperature of 100 K or more even at low temperatures.
system superconducting film can be obtained. Using nitrous oxide gas makes it possible to lower the temperature because nitrous oxide has a lower dissociation energy than oxygen, making it easier to obtain active oxygen radicals and ions, which are necessary to obtain superconducting thin films. This is because sufficient active oxygen can be obtained. Zunawachi,
In the present invention, superconducting properties can be obtained even at low substrate temperatures.

Nitrogen in the film was examined using secondary ion mass spectrometry, but no nitrogen was observed in the film.

There is a method of layering different materials using sputter deposition.
There is a method of periodically controlling the discharge position of one sputtering target with a composition distribution, but this can be achieved relatively easily by using a method of sputtering multiple targets with different compositions. In this case, a periodic laminated film can be produced by periodically controlling the amount of sputtering for each of a plurality of targets, or by providing a shutter in front of the target and opening and closing it periodically. It can also be manufactured by a method in which the substrate is moved periodically and moved over each target. When laser sputtering or ion beam sputtering is used, periodic laminated films can be realized by periodically moving a plurality of targets and periodically changing the targets irradiated with the beam. In this manner, by sputtering using a plurality of targets, a periodic laminated film of Bi-based oxide can be produced in the comparison section #LI.

In order to further understand the content of the present invention, some specific examples will be shown below.

(Example 1) A total of one target 1-4, consisting of Bi, CaCu, and two Sr2Cu, was used and arranged as shown in FIG. 2.

That is, each target is installed at an angle of approximately 30° so as to focus on the MgO substrate 21.

There is a rotating shutter 22 in front of the target,
By rotating the slit 23 provided therein, B i
→S r2Cu → CaCu-8r2(::u-"Bi) Sputter deposition is performed in a cycle. The substrate 21 is heated to about 650°C with a heater 24, and a mixed atmosphere of albo]/nitrous oxide (5:1) is applied. Target sputtering was performed in a gas of 3 Pa. The sputtering current for each target was Bi: 30 mA, S r2 Cu: 50 mA.
, CaCu: When periodic lamination was carried out at 250 mA and a shutter rotation period of 10 minutes, 100
We were able to create a phase with a critical temperature higher than .

A thin film of about 100 OA was produced by vapor deposition for about 10 hours, and the composition was Bi:Sr:Ca:Cu=2:2:2;3
It became. Even in this state, this thin film has a 100%
It showed a superconducting transition of K or more, but in addition, 8
Very good reproducibility <1 after heat treatment at 55℃ for 1 hour
It was possible to achieve a critical temperature of 00K or higher. Bi
The crystal structure of a phase with a critical temperature of 100°C or higher in a system material is still unknown (although it is not understood,
It is also said that it consists of layers of oxides arranged in the order r-Cu-Ca-Cu-Ca-Cu-3r-Bi], and the manufacturing method of the present invention is very useful for creating this structure. It is thought that this may be the case.

(Example 2) A total of eight targets, including two targets of Bi, two Sr targets, two targets of Ca, and three targets of Cu, were arranged around the inside of a vacuum vessel 31 as shown in FIG. λ□1 g O base 21 and heater 24 are
It has a mechanism that allows it to rotate around the center 32 of the container.

When sputter deposition is performed while rotating the substrate in this way, B i-3r -CIJCa-Cu-Ca-Cu-8
A stacked structure is produced in the order r-B i. Argon·
Sputtering was carried out in a nitrous oxide (5:1) gas of 3 Pa, and the amount of evaporation of each target was set appropriately.
We were able to create a phase with a critical temperature higher than .

This method allows the number of substrates to be increased around the circumference and is considered to be very effective for producing a large amount of thin film superconductors.

Effects of the Invention As described above, the method for producing a thin film superconductor of the present invention has a
The present invention provides a method for producing a Bi-based oxide superconducting thin film having a superconducting critical temperature of 0 K or more at low temperatures with good reproducibility, and the present invention has high industrial value such as application to electronic devices and the like.

[Brief explanation of the drawing]

Figure 1 shows the substrate temperature and the X of the thin film, which led to the discovery of the present invention.
1, 2, and 3 are schematic diagrams of the preparation of the l1 olfactory in an example of the present invention. 21...MgO substrate, 22...Shutter 23...Slit, 24...Name of heater agent Patent attorney Shigetaka Awano 1 person lol
JO 2θ

Claims (2)

[Claims] (1) Sputtering a substance containing at least bismuth and at least copper and alkaline earth (group IIa) onto a substrate set at 850°C or lower using a sputtering gas containing at least nitrous oxide gas. 1. A method for producing a thin film superconductor, the method comprising periodically stacking a superconducting material and a superconducting thin film. Here, alkaline earth refers to at least one or two or more elements of group IIa elements. (2) The method for producing a thin film superconductor according to claim 1, wherein the laminated superconducting thin film is formed by sputtering a plurality of targets having at least two types of compositions.