JPH0465320A - Superconducting thin film and its production - Google Patents

Abstract

PURPOSE:To improve superconductivity and to lower the production temp. by alternately laminating a layer oxide superconducting thin film consisting essentially of Bi, Cu and alkaline-earth elements (group IIa) and a layer oxide thin film consisting of the above-mentioned elements and rare-earth elements. CONSTITUTION:The rare-earth elements are the lanthanides except Pm and group IIIa Sc and Y. The Bi-Sr-Ca-Cu-O target 11 and Bi-Sr-Y-Cu-O target 12 obtained by press-forming the sintered body are obliquely arranged so that their focuses are positioned on an MgO(100) substrate 15. The rotation of a shutter 13 in front of the target is controlled, and sputtering vapor deposition is carried out in the cycle of Bi-Sr-Ca-Cu-O, Bi-Sr-Y-Cu-O and Bi-Sr-Ca-Cu-O. Consequently, a Bi-Sr-Y-Cu-O layer oxide thin film 21 and a Bi-Sr-Ca-Cu-O layer oxide superconducting thin film 22 are alternately laminated on the substrate 15 to obtain the superconducting thin film.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a superconducting thin film containing bismuth, which is expected to have a high critical temperature of 80 or higher, and a method for producing the same.

Conventional technology As high-temperature superconductors, A15 type binary compounds such as niobium nitride (NbN) and germanium niobium (NbsGe) are known. The superconducting transition temperature of these materials is at most 23°C. -Human perovskite compounds (
A higher transition temperature is expected for Ba-La-Cu
−○-based high-temperature superconductors have been proposed [J, G, Bedn
orz and K, Al Muller, Zetshrift 7 Your Fish
Fur Physik B)-Condense
dMatter Vol, 64, 189-193
(1986) It was also discovered that materials of the B1-3r-Ca-Cu-0 series exhibit a transition temperature of 80°C or higher [H, Maeda, Y, Tanaka, M, Fukut
Omi and T, Asano, Shiyabanisu゛・Shiyanal・Off・Apply・Fish? 7kus Dapanese Journal of App
Lied Physics) Vol, 27. L20
9-210 (1988) L The details of the superconducting mechanism of this type of material are not clear.
More promising properties are expected than the original compounds.

Furthermore, by alternately laminating superconductors and non-superconductors, higher critical current density and higher critical magnetic field have been expected, but the problem that the invention attempts to solve is B i-3r -Ca-Cu-0 With current technology, this type of material can only be formed mainly through the process of sintering.When this kind of material is put into practical use, it can only be obtained in the form of ceramic powder or blocks.
It is difficult to fabricate a thin film with good superconducting properties using conventional techniques.
It is known that the Cu-0 system has several phases with different superconducting transition temperatures (especially those with a transition temperature of 100
It was considered very difficult to achieve a phase of K or higher in the form of a thin film.In addition, conventionally, in order to form a thin film that exhibits good superconducting properties in this Bi system, heat treatment at at least 700°C or higher or heating during formation is required. Therefore, it is considered extremely difficult to obtain a periodic laminated structure with non-superconducting thin films that is expected to have a high critical current density and a high critical magnetic field, and it is difficult to construct an integrated device using this structure. In addition, when producing a laminated structure film of a Bi-based superconducting thin film with excellent superconducting properties and a non-superconducting thin film, the consistency of atomic diffusion at the interface between the two has become a major issue. The present invention is intended to solve these conventional problems, and aims to provide a B1-based superconducting thin film having excellent superconductivity and a method for manufacturing the same.

Means for Solving the Problems In order to achieve the above objects, the superconducting thin film i&B of the present invention
A layered oxide superconducting thin film mainly composed of i, Cu and alkaline earth (group IIa), and a layered oxide superconducting thin film mainly composed of bi, Cu and alkaline earth (group IIa)
It has a structure in which layered oxide thin films mainly composed of group IIa) and rare earth elements are laminated alternately.9 Here, alkaline earths are one or more of the group IIa elements, and rare earths are lanthanoid elements other than Pm and group IIIa elements. 4. Furthermore, the method for producing a superconducting thin film of the present invention (Table 1)
A layered oxide superconducting thin film is formed by periodically stacking oxides mainly composed of B1, Cu, and alkaline earth elements (group IIa);
A layered oxide thin film formed by periodically stacking layered oxide thin films mainly composed of rare earth metals and rare earth elements is alternately stacked by an evaporation method using two or more evaporation sources. Alkaline earth 1 One or more elements of group IIa elements Rare earths are one or more elements of lanthanide elements other than Pm and Sc and Y of group IIIa.

Effect The present invention has the above-described structure, and the Bi-based superconducting thin film and B
Since the i-based oxide thin film becomes stable and has a crystal structure covered with a 1203 oxide film layer or a layer mainly composed of this, it becomes possible to stack layers with less mutual diffusion between superconducting thin films and non-superconducting thin films. .

Furthermore, in the present invention, superconducting thin films having the above structure are alternately laminated by a sputtering method using two or more types of evaporation sources, and the thin films are manufactured by control at the molecular level.
A laminated thin film of an i-based superconducting thin film and a Bi-based oxide thin film can be manufactured with good reproducibility.ExampleThe following describes an example of the present invention. To achieve a periodic laminated structure with a non-superconducting thin film, we studied the interaction at the interface between a Bi-based superconducting thin film and various non-superconducting thin films.The B1-based superconducting thin film was prepared on a substrate heated to 500 to 700°C. Obtained by vapor deposition on top. After deposition, the thin film exhibits superconducting properties even as it is (afterwards, heat treatment at 800 to 950°C may improve the superconducting properties). Or, if heat treatment is performed after forming a non-superconducting thin film,
It has been found that mutual diffusion of elements occurs between superconducting thin films and non-superconducting thin films, which significantly deteriorates the superconducting properties. It is considered essential that the crystal lattice matching between the superconducting thin film and the non-superconducting thin film be excellent, and that the non-superconducting thin film be stable against heat treatment at 800 to 950°C.

As a result of various studies, the present inventors found that B1-8 r-
We found that Ln-Cu-0 thin films are suitable as non-superconducting thin films, where Ln is a rare earth element. The reason for this is thought to be that the main constituent elements are the same and the crystal structures are similar; however, the crystal lattice matching with the &Bi-based superconductor is extremely excellent.2 Also, even during high-temperature heat treatment, B It is thought that the interface with the system superconductor is very stable.

Example 1 A specific example will be described using FIG.

FIG. 1 is a diagram showing the internal structure of the high-frequency binary magnetron sputtering apparatus used in this example, and 11 is a B1-3r
-Ca-Cu-0 target, l2 is B1-3r
-Y-Cu-0 target, 13 is shutter 14
15 is an aperture, 15 is a substrate, and 16 is a heater for heating the substrate. 2 made by press molding a sintered body
Targets 11 and 12 are arranged as shown in FIG. 1, and each target is set at an angle of about 30'' so that the target is focused on a substrate 15 made of Mg0 (100). In front of the target is a rotating shutter 13, in which an aperture 14 is provided.The rotation of the shutter 13 is controlled by a pulse motor.
By controlling the aperture 14 with B1-3r
-Ca-Cu-0 target or B1-3r-Y-C
It can be stopped on the u-0 target. In this way, B1-3r-Ca-Cu-0-+ B1-
3r-YCu-0-B i -3r-Ca-Cu-0-
*B1-3r-Y-Cu-0-+ B1-3r-C
Sputter deposition can be performed with aCu-0 cycle. B1-3r-Ca-Cu-Oll B1-3r
FIG. 2 conceptually shows how the -Y-Cu-0 films are stacked. In FIG. 2, 21 indicates a B1-3r-Y-Cu-0 layered oxide thin trap, and 22 indicates a B1-3r-Ca-Cu-0 layered oxide superconducting thin film. B1-8r is deposited on the substrate 15 by controlling the input power to the targets 11 and 12 and the sputtering time of each target.
The film thicknesses of the -Y-Cu-0 film and the B1-3r-CaCu-0 film can be changed. Heat the substrate 15 with the heater 16 for about 7
Sputtering was performed on each target in an argon/oxygen (1:1) mixed atmosphere at 0.5 Pa. After thin film production, sputtering was performed in an oxygen atmosphere at 8
In this example, the sputtering power of each target was changed to B1-3r-Ca-Cu-
0: 150 W, B1-8r-YCu-0: 1
00 W and controlled the sputtering time of targets 11 and 12.The elemental composition ratio of the B1-8r-Ca-Cu-0 film was Bi:Sr:Ca:Cu=2:2:l:2.
The elemental composition ratio of the B1-3r-Y-Cu-0 film is Bi:
The composition ratio of the elements of targets 11 and 12 was adjusted so that Sr:Y:Cu=2:2:1:2.
-3r-Ca-Cu-0 film to B1-3r-Y-Cu-0
When formed on the substrate 15 without being laminated with a film, that is, B
1-3 Characteristics of the r-CaCu-0 film itself +1 It seems that superconducting transition occurs at 80 and the resistance becomes zero at L 78. Also, when only Bi25r2YCu20* film was formed and the electrical properties were measured, 4 In bulk Is it an insulator similar to what has been reported? , :, BB1
25r2YCu20 film and Bj2SraCaCu20
It is known that when a V film is formed alone, it changes to a crystalline thin film when the film thickness is 60 Å or more.Therefore, we investigated the relationship between film thickness and electrical properties for Bi25rpCaCu20v films, as shown in Figure 3. The film thickness is 30 people,
100 people, 200 people, 300 people,
This film shows the temperature dependence of resistivity when 1000 people are used, and when the film thickness is 300 Å or more, Thick Bi25r2YCu20s
The superconducting transition temperature does not change even if 200 people are stacked on top of each other.1. As is clear from Figure 3, the superconductivity deteriorates as the film thickness decreases, and when the film thickness was 30, no superconducting transition was observed even when the temperature was lowered to 4.2K.Bi25r2
The temperature dependence of electrical resistance when the thickness of the YCua Os layered oxide thin film 21 is 60, the thickness of the Bi25r2YaCu20V layered oxide superconducting thin film 22 is 60, 120, and 240, and the number of repetitions is 20. This is shown in FIG.

In characteristics 41 and 42, the zero resistance temperature is as low as 5 and 25, respectively. In characteristic 43! ;L Bi
BiaSr2CaCu20.25ra when deposited on substrate 15 without periodic stacking with YCuaOs film. Figure 5 shows the temperature dependence of the electrical resistance when a magnetic field is applied.

Compared to a film in which Bi25r2YCu20ep is not laminated, the spread of the superconducting transition temperature region due to the magnetic field is smaller in the laminated film. Even if this means improving the upper critical magnetic field, the upper critical magnetic field it Bi25ra
Approximately 20% improvement over the original cacu20ν film9 4
．． At 2K, the value when applying a magnetic field parallel to the C axis was 20 Tesla, and the value perpendicular to the C axis was 400 Tesla. Also, the critical current density was Bi25r2Ycu
We found that the ZOA film was improved by about 30% compared to a film without lamination, and reached 3.2 million people/cm2 in 77cm.Currently, the detailed reason for these effects is still unknown. It is considered that some change was caused in the superconducting mechanism in the Bj2Sr2CaCu20y film 22 by stacking the plurality of B1-3r-Ca-Cu-0 films 21 via the film 22.

When the present inventors performed sputtering by adding lead (Pb) to targets II or 12, the temperature of the substrate 15 was approximately 100°C lower than in the above embodiments, and results equivalent to those in the above embodiments were obtained. Furthermore, the present inventors found that oxides of i & Bi and Sr, Ca, C
The oxides of u were evaporated separately in vacuum from different evaporation sources, and B1-0-*5r-Cu-0-+Ca-Cu
When laminated periodically in the order of O → 5r-Cu-0 → B1-0, and further evaporated and laminated in a vacuum using a Y-Cu target, the laminated structure shown in Example 1 is obtained. An example in which it was found that a 1-3r-Ca-Cu-0 superconducting thin film and a B1-3r-Y-Cu-0 thin film with extremely good controllability, stable film quality α, and extremely flat film surface could be obtained using the manufacturing method. 2 Furthermore, the present inventors i4 B1-0.5r-Cu-0,
Ca-Cu-0 and B1-3r-Y-Cu-0 were evaporated from separate evaporation sources, and the B1-3rCa-Cu-0 superconducting thin film and the B1-3r-Y-Cu-0 thin film were periodically stacked. Very good controllability (Bi-3r-Ca-Cu
-0) -n (Bi-3r-Y-Cu-0) It was discovered that a thin film having a periodic structure can be formed.9 Here, m and n each represent a positive integer of 1 or more. This m (Bi-3r-Ca-Cu-0) ・n (B
i-3r-Y-Cu-0) thin film was B1 shown in Example 1.
Compared to a thin film obtained by periodically laminating a superconducting thin film obtained by simultaneously depositing -3r-Ca-Cu-0 and an oxide thin film obtained by simultaneously depositing B1-3r-Y-Cu-0. Furthermore, the present inventors (above) also found that B1-3r-
We found that both the Ca-Cu-0 superconducting thin film and the B15r-Y-Cu-0 thin film have extremely flat thin film surfaces. On the other hand, this is thought to be due to the fact that the stacked evaporated elements only move in parallel planes and there is no movement of the elements in the direction perpendicular to the substrate surface.

Furthermore, the temperature of the substrate required to obtain good superconducting properties,
Heat treatment temperature B1-0.5r-Cu-0, Ca-Cu-0, B1-3 found to be lower than conventional
There are several possible ways to periodically stack r-Y-Cu-0.

By controlling the opening/closing shutter in front of the evaporation source in a general E, MBE device or multi-source EB evaporation device, or by switching the type of gas during production using the vapor phase growth method,
Although it is possible to achieve periodic stacking, sputtering deposition has traditionally been considered unsuitable for this type of stacking of very thin layers. However, the inventors of the present invention discovered that by sputtering different thin layers of this Bl-based oxide superconducting thin film, the laminated film was surprisingly good. We have discovered that it is possible to produce B
This may be because it is convenient for forming a thin film of B1-3r-Y-Cu-0 due to the phase shape of the i-based material, which has a critical temperature of 100 or higher.
This can be achieved relatively easily by using a method of periodically controlling the discharge position of one sputtering target with a composition distribution, or by using a method of sputtering multiple targets with different compositions. In this case, a periodic laminated film can be manufactured 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 periodically opening and closing it. It is also possible to manufacture the substrate by periodically moving the substrate over each target.

When laser sputtering or ion beam sputtering is used, the targets irradiated by the beam can be changed periodically by moving multiple targets periodically. By using the sputtering method used, a periodic stack of Bl-based oxides can be produced relatively easily.

Example 3 Next, another example will be explained using FIG. This figure shows a configuration diagram of a quaternary magnetron sputtering apparatus.

In the same figure, 61 is the B1 target, 62 is S r
Cu alloy target, 63 is CaCu alloy target,
64 is Y-Cu target, 65 is shutter 6
6 is the aperture, 67 is Mg0 (100) is the substrate,
68 indicates a heater for heating the substrate. A total of four targets 61, 62, 63, and 64 were arranged in the same manner as shown in Fig. 1. Each target was set at an angle of about 30° so that the focus was on the instant jaw MgO (l o o) substrate 67. has been done. In front of the targets is a rotating shutter 65, which is driven by a pulse motor to control the rotation of an aperture 66 provided therein, thereby making it possible to set the cycle and sputtering time for each target. M
The g0 (100) substrate 67 is heated to approximately 600°C with a heater 68, and the argon/oxygen (5:1) mixed atmosphere 3P
Sputtering was performed on each target in the gas of 9. The sputtering current for each target was Bi: 30 mA, Bi: 30 mA,
5rCu: 80 mA, CaCu: 300 mA,
YCu: Film formation was performed at 300 mA.

Bi-+ 5rCu-+ CaCu-+ 5rCu-+
Sputtering 1, B1-3r-C with Bi cycle
The composition ratio of the elements of the a-Cu-0 film is Bi:Sr:Ca:
The sputtering time of each target was adjusted so that Cu-2:2:1:2, and the above cycle was repeated 20 times.
It is possible to produce a phase with a critical temperature of lloK or higher.9 Even in this state, this B1-3rCa-Cu-0
The thin film showed a superconducting transition of 80°C or higher.Furthermore, heat treatment in oxygen for 600t for 1 hour resulted in very good reproducibility; the superconducting transition temperature was 82K, and the temperature at which resistance became zero was 79K. Island superconducting transition temperature is 100
In the phase exceeding K, the metal element is BISr-Cu-Ca-Cu-
It is also said that the structure consists of layers of oxides arranged in the order Ca-Cu-3r-Bi, and it is thought that the manufacturing method of the present invention is very useful in creating this structure.

In addition, the present inventors found that when B1-8r-Y-Cu-0 was formed alone, it had a crystal structure when the film thickness was at least 30 Å or more. 5rCu is laminated for n periods as one period, and then B1-3r-
Each target was sputtered with Y-Cu-0 to a film thickness of d (included) n (Bi-3r-Ca-Cu-0).
d (Bi-3r-Y-Cu-0) thin film with MgO(1
00) Manufactured on the substrate 67 9 Here, n represents a positive integer of 1 or more. The present inventors found that when n10, B1-3r-
Investigate the superconducting properties of the films obtained by stacking Y-Cu-0 thin films with varying thicknesses d. At this time, B1-3r-Ca-C
The number of repetitions of stacking the u-0 thin film/B1-3r-Y-Cu-0 thin film was 10.1. In Figure 7, d = 60 people,
The temperature changes in the resistance of the multilayer film obtained when 120 and 240 people were tested are shown in characteristics 71, 72, and 73, respectively. In Figure 7, when d=60, the highest superconducting transition temperature and zero resistance temperature are obtained.9 The superconducting transition temperature and zero resistance temperature are equivalent to those values of the original B1-3r-Ca-Cu-0 film At 9, the critical current density is at 77K.
3.6 million A/cm2, B i2s r2Y
The value was 45% higher than that of the thin film without stacking Cu20g film. Also, the upper critical magnetic field is B1-8r-Ca-Cu
At 4.2K, which is about 30% better than the original -0 film, the value when a magnetic field is applied in a direction parallel to the C axis is 23
tesla, and in the direction perpendicular to C#I, it was 440 tesla.The detailed reason for this effect is still unknown.B1-3r-Ca-Cu-
By periodically stacking the 0 film and the B1-8r-Y-Cu-0 film, B1-3r-Ca-Cu-Op and B1
-3r-Y-Cu-0 film is grown epitaxially, so there is no influence of interdiffusion of elements at the lamination interface,
And B1-3r-Ca-Cu- which also has excellent crystallinity is passed through a thin B1-3r-Y-Cu-0 film which also has excellent crystallinity.
By stacking 0 films, B1-3r-Ca-Cu-0
It is conceivable that some change was caused in the superconducting mechanism in the film.
0) It was found that the temperature of the substrate 67 was about 100°C lower than in the above example, and results equivalent to those in the above example could be obtained. The same effect can be obtained by using the method.

Effects of the Invention As described above, the superconducting thin film of the present invention has superior superconductivity such as critical current density and critical Fa field compared to conventional Bi-based superconducting thin films, and its manufacturing method allows it to be manufactured at lower temperatures than conventional ones, and it is suitable for devices. Since the present invention can be applied to the production of products such as

[Brief explanation of drawings]

FIG. 1 shows the schematic structure of an apparatus for carrying out the method for producing a superconducting thin film in an embodiment of the present invention. FIG. 2 shows the structural concept of a superconducting thin film of the present invention. Figure 5 shows the temperature characteristics of the resistance of the superconducting thin film produced by the apparatus shown in Figure 1 under an external magnetic field. 7 is a temperature characteristic diagram of the resistance of the superconducting thin film manufactured by the apparatus shown in FIG. 6. 11...Bi-3r-Ca-Cu-0 target, 12...Bi-3r-Y-Cu-0 target, 15--...substrate, 2
1 ... B i-8r -Y -
Cu-0 layered oxide thin yIL 22...B1-5
Name of r-Ca-Cu-0 layered oxide superconducting thin wind agent Patent attorney Shigetaka Awano @l@r f3i-5r-Ca-Cu-0 Terke Soto Diagram Kiden R/R ) Kunidenki A-zume 2 R/R (3oor,) R/R (to 300) No. R/ (to 300)

Claims (2)

[Claims] (1) A layered oxide superconducting thin film whose main components are bismuth (Bi), copper (Cu), and alkaline earth (group IIa), and a layered oxide superconducting thin film whose main components are Bi, Cu, alkaline earth (group IIa), and rare earth. A superconducting thin film consisting of alternating layered oxide thin films. Here, the alkaline earths are one or more elements of group IIa elements, and the rare earths are one or more elements of lanthanide elements except promethium (Pm) and scandium (Sc) and yttrium (Y) of group IIIa. (2) Bi, Cu and alkaline earth (II) on the substrate.
A layered oxide superconducting thin film formed by periodically depositing oxides whose main components are Bi, Cu, alkaline earths (group IIa), and rare earths. A method for producing a superconducting thin film in which layered oxide thin films formed by stacking layers are alternately stacked by an evaporation method using two or more evaporation sources. Here, the alkaline earth is one or more of the group IIa elements. The rare earth element is one or more of the lanthanide elements except Pm and Sc and Y of Group IIIa.