JPH07102974B2 - Method of manufacturing thin film superconductor - Google Patents

Description

TECHNICAL FIELD 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 K or higher.

Conventional technology As high-temperature superconductors, niobium nitride (NbN) and germanium niobium (Nb ₃ Ge) were known as A15 type binary compounds, but the superconducting transition temperature of these materials is at most
It was 24 ° K.

On the other hand, perovskite ternary compounds are expected to have even higher transition temperatures, and Ba-La-Cu-O high-temperature superconductors have been proposed [JGBendorz and KAMuller, Zetshrift Furphysik.
B) -Condensed Matter 64,189-193 (1986)].

Further, it was discovered that the Bi-Sr-Ca-Cu-O-based material exhibits a transition temperature of 100K or higher. 〔H.Maeda, Y. Tanaka, MF
ukutomi and T. Asano, Japanese Journal of Applied Physics
plied Physics) Vol.27, L209-L210 (1988)] Although the details of the superconducting mechanism of this kind of material are not clear,
Since the transition temperature may be higher than room temperature, more promising properties are expected as a high temperature superconductor than conventional binary compounds.

However, Bi-Sr-Ca-Cu-O-based materials can be formed only in the form of ceramic powder or blocks, because they can be formed mainly in the process of sintering in the present technology. On the other hand, when putting this type of material into practical use, it is strongly demanded to process it into a thin film, but it has been difficult to produce a thin film having good superconducting properties by the conventional techniques.

That is, it is known that the Bi-Sr-Ca-Cu-O system has several phases with different superconducting critical temperatures. In particular, a phase having a critical temperature of 100 K or higher is achieved in the form of a thin film. Was said to be very difficult.

Means for Solving the Problems The method for producing a thin film superconductor of the present invention comprises: a substrate heated in a range of 550 ° C. to 900 ° C .; a layer containing bismuth as a main component; and copper and an alkaline earth element as main components. And one or more layers are periodically laminated.

Several methods have been attempted for metal thin films and oxide thin films to form new thin films by periodically stacking different substances.
It was common knowledge that when the substrate temperature was raised, the periodic structure disappeared due to interlayer diffusion. For this reason, when forming a periodic structure, the substrate may be cooled. The inventors of the present invention have obtained a combination of an oxide layer of bismuth and an oxide layer of copper and alkaline earth by sputtering, for example, using two different targets with respect to the oxide superconductor containing Bi. The relationship between temperature and crystal structure of the thin film was investigated in detail.

At this time, it was found that a critical temperature of 100 K or higher was obtained, and the crystallinity was good and the reproducibility was excellent. According to the present invention, it is possible to obtain a high-quality and high-performance thin film superconductor with good reproducibility.

Example First, a study example by the present inventors will be described first.

That is, a Bi target and a Sr ₂ Ca ₂ Cu ₃ target were alternately sputtered in a mixed gas of argon and oxygen, and they were periodically laminated on a MaO (100) substrate at various temperatures. First
The figure is the X-ray diffraction pattern of the obtained thin film. When the substrate temperature is 400 ° C. or lower, a peak (∇) corresponding to the laminated periodic structure is observed, but when it is as high as 400 ° C. to 550 ° C., the periodic structure becomes weak and the appearance of another phase (×) is observed. However, it was discovered that when the temperature is further increased, a phase (○) having a critical temperature of 100 K or higher can be unexpectedly produced at a substrate temperature in the range of 550 ° C to 900 ° C. In this case, it was found that if the sputtering rates of Bi and Sr ₂ Ca ₂ Cu ₃ were appropriately adjusted within the above temperature range, a phase of 100 K or more appeared in correspondence with the stacking period. In addition, when the stacking was not performed periodically but simultaneously, only the phase having the critical temperature of 80K could be produced. 100K when the substrate temperature is 650 ℃ to 850 ℃
It was also found that it is possible to produce a crystal having a very good crystallinity in the above-mentioned phase at the critical temperature. When the substrate temperature was 900 ° C or higher, the thin film evaporated and did not deposit. The thin film prepared at 550 ℃ to 850 ℃ shows a superconducting transition in the intact state, but it is more reliable at 100K when heat-treated at about 850 ℃ in oxygen.
The above critical temperatures are shown. It was also found that the thin films laminated at 650 ° C to 850 ° C have excellent reproducibility.

There are several possible methods for periodically stacking a Bi-containing substance and a Cu- and IIa-group element-containing substance.
Periodic stacking can be achieved by controlling the opening and closing shutters in front of the vapor deposition source with a general MBE device or multi-source EB vapor deposition device, and by switching the gas type during the vapor phase growth method. it can. However, sputtering deposition has hitherto been unsuitable for stacking very thin layers of this type. The reason for this is considered to be contamination of impurities due to high gas pressure during film formation and damage by particles having high energy. However, the present inventors
When different thin layers were stacked on a Bi-based oxide superconductor by sputtering, it was discovered that a surprisingly good laminated film could be produced. It is considered that the high oxygen gas pressure during sputtering and the sputter discharge favor the formation of the Bi-based phase having a critical temperature of 100 K or higher.

As a method of stacking different substances by sputter deposition,
There is a method of periodically controlling the discharge position of one sputtering target provided with a composition distribution, but this can be achieved relatively easily by using a method of sputtering a plurality of targets having different compositions. In this case, the sputtering amount of each of the plurality of targets can be periodically controlled, or a shutter can be provided in front of the target to periodically open and close the target to form a periodic laminated film. It can also be manufactured by a method in which the substrate is moved cyclically and moved over each target. When laser sputtering or ion beam sputtering is used, a periodic laminated film is realized by periodically moving a plurality of targets to periodically change the targets irradiated by the beams. In this way, a periodic stacking film of Bi-based oxide can be prepared relatively easily by sputtering using a plurality of targets.

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

(Example 1) Bi, CaCu, the Sr ₂ Cu @ 2 pieces of a total of four targets used were arranged as shown in Figure 2. That is, the respective targets are set so as to be tilted by about 30 ° so as to focus on the MgO substrate 21. There is a rotating shutter 22 in front of the target, and by rotating the slit 23 provided therein, Bi →
Sputter deposition is performed in a cycle of Sr ₂ Cu → CaCu → Sr ₂ Cu → Bi. The substrate 21 was heated to about 700 ° C. by the heater 24, and each target was sputtered in a gas of argon / oxygen (5: 1) mixed atmosphere 3 Pa. Sputtering current of each target was set to Bi: 30mA, Sr ₂ Cu: 50mA, CaCu: 250mA, and the periodical stacking was performed with the shutter rotation period of 10 minutes to produce a phase with a critical temperature of 100K or higher. Was completed. A thin film of about 1000Å was produced by vapor deposition for about 10 hours, and the composition was Bi: Sr: Ca: Cu = 2: 2: 2: 3. Even in this state, the thin film showed a superconducting transition above 100K, but when it was further heat-treated in oxygen at 855 ℃ for 1 hour, the critical temperature above 100K could be achieved with excellent reproducibility. The crystal structure of the phase of Bi-based materials having a critical temperature of 100 K or higher is not well understood, but the metallic element is Bi-Sr-
It is also said to consist of oxide layers arranged in the order of Cu-Ca-Cu-Ca-Cu-Sr-Bi, and the production method of the present invention is very useful for producing this structure. It is thought to be.

(Example 2) Bi, Sr2 pieces, Ca2 pieces, Cu3 pieces A total of eight targets were arranged around the inside of the vacuum container 31 as shown in FIG. MgO substrate 2
It is a mechanism that can rotate around the center 32 of the container of 1 and the heater 24. When sputter deposition is performed while rotating the substrate in this way, Bi-Sr-Cu-Ca-Cu-Ca-Cu-Sr
The laminated structure is manufactured in the order of -Bi. Sputtering was performed in a gas of argon / oxygen (5: 1) 3 Pa, and the evaporation amount of each target was set appropriately.
A phase with a critical temperature of 100K or higher was produced with good reproducibility between ℃ and 850 ℃. This method can increase the number of substrates on the circumference, and is considered to be very effective for producing a large number of thin film superconductors.

As described above, the manufacturing method of the thin film superconductor of the present invention is 100K.
The present invention provides a method for producing a Bi-based oxide superconducting thin film having the above superconducting critical temperature with good reproducibility, and the industrial value of the present invention is high.

[Brief description of drawings]

FIG. 1 shows the substrate temperature and the X of the thin film which were the basis of the present invention.
FIGS. 2 and 3 showing the relationship of the line diffraction patterns are schematic views of the production of the thin film in the embodiment of the present invention. 21 …… MgO substrate, 22 …… Shutter, 23 …… Slit, 2
4 ... heater.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Reference number in the agency FI Technical display location H01B 12/06 ZAA 13/00 565 D H01L 39/24 ZAA D (72) Inventor Kiyotaka Wasa Osaka Prefecture 1006 Kadoma, Kadoma-shi, Matsushita Electric Industrial Co., Ltd. (56) Reference JP-A-63-169375 (JP, A) Nikkei Superconductivity No. 14 (July 25, 1988) 4-5 Jpn. J. Appl. Phys. , Vol. 27, No. 10 (1988) P. L1887- L1889

Claims (4)

[Claims] 1. A layer containing bismuth as a main component and one or more layers containing copper and an alkaline earth (Group IIa) as main components on a substrate heated to a temperature of 550 ° C. to 900 ° C. A method for manufacturing a thin film superconductor, characterized by being obtained by periodically stacking. Here, alkaline earth refers to at least one element or two or more elements of the IIa group elements. 2. The method for producing a thin film superconductor according to claim 1, which is obtained by laminating on a substrate heated to a temperature of 650 ° C. to 850 ° C. 3. The method for producing a thin film superconductor according to claim 1, wherein the evaporation of the laminated material is performed by sputtering. 4. The method for producing a thin film superconductor according to claim 1, wherein the evaporation of the laminated material is performed by sputtering a plurality of targets having at least two kinds of compositions.