JPH042182A - Thin film superconductor and manufacture thereof - Google Patents

Abstract

PURPOSE:To improve a critical current density, a critical magnetic field by alternately laminating a layer oxide superconducting thin films each including bismuth, copper and alkaline earth element and magnetic thin films made of perovskite type oxide. CONSTITUTION:Bi-O, Sr-Cu-0, Ca-Cu-O, Bi-Mn-O are evaporated from separate evaporation sources. When Bi-Sr-Ca-Cu-O superconducting thin films and Bi-Mn- O magnetic thin films are periodically laminated, a thin film having a periodic structure of m(Bi-Sr-Ca-Cu-O).n(Bi-Mn-O) can be formed with extremely high controllability. The thin film has far excellent crystallinity as compared with the thin film obtained by periodically laminating a superconducting thin film obtained by simultaneously depositing Bi-Sr-Ca-Cu-O and an oxide magnetic thin film obtained by simultaneously depositing Bi-Mn-O, and has superior critical current density and upper critical magnetic field characteristics. Further, the temperature of a base necessary to obtain excellent superconducting characteristic and heat treatment temperature can be lowered as compared with that of prior art.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) 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 more.

(Prior art) Niobium nitride (NbN) and germanium niobium (Nb3Ge) are used as A15 type binary compounds as high-temperature superconductors.
were known, but the superconducting transition temperature of these materials was at most 23'. On the other hand, perovskite compounds are expected to have even higher transition temperatures, and Ba-La
-Cu-0-based high-temperature superconductors were proposed [J,G
, Bednorz and K., A., Muller.

Zeitschrift Fuyur Physique (Zetsh)
rift Fur Physik B)-Conden
sedMatter, Vol. 64.189-193
(1986)].

Furthermore, B i-S r-Ca-Cu-0 type material is 1
It was also discovered that [H
+Maed0. Y, Tanak0. M, Fukutom
i andT, A 5ano, Japanese
Journal of Applied Physics (J a
Panese Journal of Applied
Physics) Vol, 27. L209-210
(1988)].

Although the details of the superconducting mechanism of this type of material are not clear,
The transition temperature can be higher than room temperature, and it is expected to have more promising properties as a high-temperature superconductor than conventional binary compounds.

Furthermore, higher critical current density and higher critical magnetic field have been conventionally expected by alternately stacking superconductors and magnetic materials.

(Problem to be solved by the invention) However, B1-5r-Ca-Cu-〇-based materials can only be formed mainly through the process of sintering with current technology, so they can only be obtained in the form of ceramic powder or blocks. I can't. On the other hand, when this type of material is to be put to practical use, there is a strong demand for processing it into a thin film, but it has been difficult to fabricate a thin film with good superconducting properties using conventional techniques.

In other words, it is known that there are several phases with different superconducting transition temperatures in the B1-5r-Ca-Cu-○ system, but it is particularly difficult to achieve a phase with a transition temperature of too ' or higher in the form of a thin film. It was considered extremely difficult to do so.

In addition, conventionally, in order to form a thin film exhibiting good superconducting properties in this Bi system, heat treatment at least 700°C or higher or heating during formation is required. It was thought to be extremely difficult to obtain a periodic layered structure with thin films, and it was also considered to be extremely difficult to construct an integrated device using this structure.

An object of the present invention is to eliminate the conventional drawbacks and provide a bismuth-containing oxide superconducting thin film that is expected to have a high critical temperature of 100' or more, and a method for manufacturing the same.

(Means for solving problems) The thin film superconductor of the first invention by the present inventors is as follows.

The main components are at least bismuth (Bi) and copper (Cu).

It has a structure in which layered oxide superconducting thin films containing alkaline earth elements (group IIa) and magnetic thin films whose main component is a perovskite oxide are laminated alternately.

Furthermore, the method for producing a thin film superconductor according to the second invention includes an oxide film formed by periodically stacking an oxide containing at least Bi and an oxide containing at least copper and alkaline earth (group IIa) on a substrate. This is a method for manufacturing a thin film superconductor obtained by alternately stacking a magnetic thin film made of a perovskite type oxide and a magnetic thin film made of a perovskite type oxide.

Here, the alkaline earth refers to at least one or two or more elements of the lla group elements. In addition, perovskite oxide is RFeO3 (R=Yt Sm, E
u, Gdv Tbt Dy, H0. Er, Tm
.

Yb, Lu) or MMnO3 (M=BieL
a0.7Cao, sp L0. ,? S ro ,
z e L0. , t B ao, a *L0. ,,,
pb,,4. La0. tCdo, 3)y or
A Mn O@ (A = G d2 Cot B ax
It is an oxide magnetic material made of F ev Ca2F e).

(Function) In the first invention, the film is composed of a Bi-based superconducting thin film and a perovskite-type oxide, which have a crystalline structure covered with a stable 1202 oxide film layer or a layer mainly composed of this. By adopting a structure in which the magnetic thin films are alternately stacked, it is possible to stack the superconducting thin films and the magnetic thin films with less mutual diffusion. Furthermore, the critical current density and critical magnetic field in the Bi-based superconducting thin film have been improved due to the interaction between the magnetic moment or spin of the magnetic thin film and the superconductor.

Furthermore, in the second invention, in order to achieve the above structure,
This can be reproduced by periodically stacking an oxide containing at least Bi and an oxide or perovskite oxide containing at least copper and alkaline earth (group IIa) to create a thin film through control at the molecular level. Good character
A laminated layer of a Bi-based superconducting thin film and a magnetic thin film is obtained.

(Example) First, in order to realize a periodic stacked structure of a Bi-based superconducting thin film and a magnetic thin film, the interaction at the interface between a Bi-based superconducting thin film and various magnetic thin films was studied.

Usually, a Bi-based superconducting thin film is obtained by vapor deposition on a substrate heated to 500 to 700°C. After vapor deposition, the thin film exhibits superconducting properties as it is, but it is then subjected to heat treatment at 800 to 950°C to improve its superconducting properties.

However, when a magnetic thin film is laminated next to a Bi-based superconducting thin film when the substrate temperature is high, or when heat treatment is performed after forming the magnetic thin film, mutual diffusion of one element occurs between the superconducting thin film and the magnetic thin film, resulting in superconducting It was found that the characteristics were significantly deteriorated. In order to prevent mutual diffusion, the crystallinity of the superconducting thin film and the magnetic thin film must be excellent, the lattice matching between the superconducting thin film and the magnetic thin film must be excellent, and the magnetic thin film must be heat-treated at 800 to 950°C. It is considered essential to be stable against

As a result of various studies, we found that perovskite-type oxide thin films are suitable as magnetic thin films. The reason for this is not clear, but perovskite oxides are
It has extremely good lattice matching with i-based superconductors,
It is also believed that the interface with the Bi-based superconductor is very stable even during high-temperature heat treatment.

Furthermore, it has been found that when a Bi-based superconducting thin film and a perovskite-type oxide thin film are stacked periodically, the critical current density and critical magnetic field inherent to the Bi-based superconducting thin film are improved.

In order to understand the contents of the first invention more deeply, please refer to the first invention.
A specific example will be shown using figures.

(Example 1) FIG. 1 is a schematic diagram of the inside of the high-frequency binary magnetron sputtering apparatus used in this example, and 11 is a B1-5r-C
12 is a B1-Mn-0 target, 13 is a shutter, 14 is an aperture 15 is a substrate, and 16 is a heater for heating the substrate. Two targets 11 and 12 produced by press forming a sintered body were used and arranged as shown in FIG.

That is, each target is installed at an angle of approximately 30° so as to focus on the Mg0 (100) substrate 15. In front of the target is a rotating shutter 13 in which an aperture 14 is provided. By controlling the rotation of the shutter I3 with a pulse motor, the aperture 14 can be stopped on the B1-8r-Ca-Cu-0 target or the B1-Mn-0 target. In this way, B i-S r-Ca-C
u-○-+Bf-Mn-0-)Bi-8r-Ca-Cu
-0-*B1-Mn-0-+B1-8r-Ca-Cu-
Sputter deposition can be performed with zero cycles. B1
FIG. 2 conceptually shows how the -5r-Ca-Cu-0 film and the B1-Mn-0 film are stacked. In the same figure, 21 is B
1-Mn-0 film, 22 indicates B1-5r-Ca-Cu-0 film, are deposited on the substrate 15 by controlling the input power to the targets 11 and 12 and the sputtering time of each target. B1-Mn-011 [21,
The thickness of the B1-8r-Ca-Cu-0 film 22 can be changed. The substrate 15 is heated to about 700° C. with a heater 16 and placed in an argon/oxygen (1:l) mixed atmosphere of 0.5 Pa.
Each target was sputtered in the following gas.

In this example, the sputtering power for each target was 150 W for B1-5r-Ca-Cu-〇.
, B1-Mn-0: 100w, target 11
．． 12 sputtering times were controlled. B1-5r-Ca
-Cu-○ The composition ratio of the elements of the film 22 is Bi: Sr:
Ca: Cu=2:2:2:3. B1-M
The composition ratio of the elements of the n-0 film 21 is Bi:Mn:○=1:
The composition ratio of the elements in the target 11.12 was adjusted to be 1:3* B1-8r-Ca-Cu-0 film 22
is formed on the substrate 15 without being laminated with the B1-Mn-0 film 21, that is, the B1-8r-Ca-Cu-0 film 22
Its characteristics were that it underwent a superconducting transition at 110'K and its resistance value became zero at 100'K.Furthermore, when only the B1MnO3 film was formed and the magnetization was measured, it was the same as the bulk value. The thickness of the B1Mn0. film and the Bi, Sr, C0.Cu, O, film was 50%, respectively.
The layers were stacked one layer at a time with 0 people. FIG. 3 shows the temperature characteristics of the resistance value of this film. The superconducting transition temperature C (onset temperature) was 110' and was not different from the case where no B i M n O film was laminated. External magnetic field 10kOe
FIG. 4 shows the temperature dependence of the critical current density, which was measured when the magnetic material film was magnetized by applying it perpendicularly to the film surface of the laminated film, and then the external magnetic field was removed. The critical current density is approximately 30% larger at each temperature than the value before applying the magnetic field. FIG. 5 shows the temperature characteristics of electrical resistance when an external magnetic field is applied. When compared with the results of the B1-5r-Ca-Cu-0 film itself, which is not laminated with a B1MnO3 film, it was found that in the laminated film, the spread of the superconducting transition temperature region due to the magnetic field becomes smaller. This means an improvement in the upper critical magnetic field. The reason for these improvements in critical current density and upper critical magnetic field is not clear, but the magnetization or spin of the B i M n O3 film is
This is considered to be a result of affecting the superconducting mechanism of the S r-Ca-Cu-0 film. It was also found that when the B1MnO3 film and the B1-8r-Ca-Cu-0 film were formed alone, a crystalline thin film was obtained when the film thickness was 100 Å or more and 50 Å or more, respectively. In Figure 2,
B1-Mn-〇The film thickness of film 21 is 100 people.
The thickness of the 8r-Ca-Cu-0 film 22 is 100 and 300.
The characteristics when the number of people is 500 and the number of repetitions is 20 are shown in characteristics 61, 62, and 53 in FIG. 6, respectively. In characteristic 61, the zero resistance temperature is about 30 balls and B
It was found that the characteristics of the i-S r-Ca-Cu-0 film 22 deteriorated. The reason for this is that B i-S r-Ca
It is considered that the crystallinity of the films 21 and 22 is destroyed due to mutual diffusion of elements between the -Cu-0 film 22 and the B1 to Mn-0 film 21. Furthermore, in characteristic 63, B1-Mn-0 film 2
B when applied on the substrate 15 without periodic lamination with 1
The superconducting properties were almost the same as those of the 1-5r-Ca-Cu-0 film 22, and no stacking effect with the magnetic thin film B1-Mn-0 film 21 was observed. However, in characteristic 62, the critical current density was improved by about 30% compared to the film without laminated magnetic film, reaching 3.2 million A10 at 77'. The critical magnetic field was improved by about 20% compared to the original B i-S r-Ca-Cu-0 film. 4. At 2'K,
When a magnetic field is applied in a direction parallel to the C axis, the value is 30 Tesla,
Moreover, in the direction perpendicular to the C axis, it was 450 Tesla. the current,
Although the detailed reasons for these effects are still unknown, they may be due to the influence of the magnetic moment or spin of the B1-Mn-0 film 21, or the influence of the magnetic moment or spin of the B1-Mn-0 film 21, or the It is considered that some change was caused in the superconducting mechanism in the B1-5r-Ca-Cu-0 film 22 by laminating the -Ca-Cu-◯ film 22.

It has been found that when sputtering is performed by adding lead (PB) to target 11 or 12, results equivalent to those of the above embodiment can be obtained even if the temperature of the base 15 is about 100° C. lower than that of the above embodiment. Ta.

Furthermore, Bi oxide, Sr, C0. The oxides of Cu were evaporated separately in vacuum from different evaporation sources.

B1-0-+5r-Cu-0-+Ca-Cu- on the substrate
When laminated periodically in the order of 0-*5r-Cu-0 → B1-0, and further laminated by evaporation in vacuum using a Mn target, the laminated structure shown in (Example 1) can be produced. It has been found that an i-S r-Ca-Cu-〇 superconducting thin film and a B1-Mn-0 magnetic thin film can be obtained using this method with extremely good controllability, stable film quality, and an extremely flat film surface.

Furthermore, B1-0.5r-Cu-○, Ca-Cu-0,
B1-Mn-0 is evaporated from separate sources, Bi-5
When r-Ca-Cu-〇 superconducting thin films and B1-Mn-0 magnetic thin films are laminated periodically, extremely controlled Sumira<m(Bi
-5r-Ca-Cu-○) ・n (B 1-Mn-0
) was found to be able to form a thin film with a periodic structure. Here, m and n each represent a positive integer of at least 1 or more. Furthermore, this m(Bi-Sr-Ca-Cu-0
) ・n(Bi-Mn-〇) thin film is obtained by simultaneously depositing the superconducting thin film of B1-5r-Ca-Cu-0 shown in (Example 1) and B1-Mn-0. Compared to the thin film obtained by periodically laminating the obtained oxide magnetic thin film,
It was also found that the crystallinity was far superior, and the properties of critical current density and upper critical magnetic field were superior. Furthermore, B1-5 r-Ca- produced by the above method
It was found that both the Cu-0 superconducting thin film and the B1-Mn-0 magnetic thin film have extremely flat thin film surfaces.

These things are possible because by stacking different elements separately and sequentially, the deposited elements move only in the plane parallel to the substrate surface, but the elements do not move in the direction perpendicular to the substrate surface. This is thought to be due to the fact that there is no such thing.

Furthermore, the temperature of the substrate required to obtain good superconducting properties,
It was also found that the heat treatment temperature was lower than conventional ones.

B1-0.5r-Cu-0, Ca-Cu-0, B1-M
There are several possible methods for periodically stacking n-0 layers. In general, periodic stacking can be achieved by controlling an opening/closing shutter in front of the evaporation source in an MBE device or multi-source EB evaporation device, or by switching the type of gas during production using the vapor phase growth method. can. However, sputtering deposition has traditionally been considered unsuitable for this type of extremely thin layer stacking. The reason for this is thought to be the incorporation of impurities due to the high gas pressure during film formation and damage caused by high energy particles. However, this B
We have discovered that it is possible to produce a good laminated film by laminating different thin layers on an i-based oxide superconductor by sputtering. This is probably because the high oxygen gas pressure and sputter discharge during sputtering are convenient for the formation of a Bi-based phase having a critical temperature of 100' or more and for the formation of a B1-Mn-〇 insulating film.

The method of layering different materials using sputter deposition is as follows:
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 one-period layered 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 way, by sputtering using a plurality of targets, a periodic stack of Bl-based oxides can be produced relatively easily.

In order to further understand the content of the invention in Section 2 below, specific examples will be shown.

(Example 2) FIG. 7 shows a schematic diagram of a four-element magnetron sputtering apparatus used in this example. In Fig. 7, 71 is Bi
72 is a 5rCu alloy target, 73 is Ca C
74 is a Mn target, 75 is a shutter, 76 is an aperture, 77 is a substrate, and 78 is a heater for heating the substrate. Total of 4 targets 71.72
．． 73 and 74 were arranged in the same manner as shown in FIG. That is, each target is installed at an angle of about 30° so as to focus on the MgO (100) substrate 77. In front of the targets is a rotating shutter 75, which is driven by a pulse motor to control the rotation of an aperture 76 provided therein, thereby making it possible to set the cycle and sputtering time for each target. Base body 77
was heated to about 600° C. with a heater 78, and each target was sputtered in a mixed atmosphere of argon and oxygen (5:1) at 3 Pa. The sputtering current of each target was Bi: 30 mA, 5rCu: 80
mA, CaCu: 300mA, Mn:
The experiment was conducted at 80+*A. Bi-+5rCu-+
Sputtering is performed with a cycle of CaCu-+5rCu-+Bi, and the elemental composition ratio of the B1-5r-Ca-Cu-〇 film is B.
i: Sr: Ca: Cu=2: 2: 2:
By setting the sputtering time of each target to 3 and performing the above cycle 20 times, it is possible to produce a phase having a critical temperature of 110' or more. Even in this state, this B1-5r-Ca-Cu-0 film exhibits a superconducting transition of 110'K or more, but it also exhibits a superconducting transition of 600'C1 in oxygen.
After 1 hour of heat treatment, the reproducibility was very good, and the superconducting transition temperature was 115'K, and the temperature at which the resistance value became zero was 100'K.The phase whose superconducting transition temperature exceeds 100'K is metal. Element is B1-8r-Cu-Ca-Cu-C
It is said that it is made up of oxide layers arranged in the order a-Cu-8r-Bi, and it is thought that the manufacturing method of the present invention is extremely useful in creating this structure. .

Furthermore, it has been found that when a film of B1-Mn-〇 is formed alone, a perovskite crystal structure is obtained when the film thickness is at least 70 Å or more.

Bi−+5rCu−+CaCc+−)SrCu is stacked in one period, and each target is sputtered to have a film thickness of d (layers).
(Bi-3r-Ca-Cu-0) ・d(Bi-Mn-
0) A thin film was produced on the substrate 77. Here, n represents a positive integer of 1 or more. When n=10, the superconducting properties of films obtained by stacking B1-Mn-〇 thin films with varying film thicknesses d were investigated. At this time, B1-5r-Ca-Cu-0 thin film/B1
The number of repetitions of stacking the -Mn-0 thin film was 10 times. Figure 8 shows the temperature changes in the resistance of the multilayer film obtained when d = 70, 200, and 1000 people, respectively.
Shown below.

In FIG. 8, when d=200 people, the highest superconducting transition temperature and zero resistance temperature, ie, characteristic 82, were obtained. The superconducting transition temperature and zero resistance temperature of characteristic 82 are B1
-5r-Ca-Cu-0 film original values. The critical current density is 3.6 million A1 at 77'K
0, which is 4 compared to the value of a thin film that is not laminated with a magnetic thin film.
5% higher. Also, the upper critical magnetic field is B1-5r-C
a-C; improved by about 30% over the original value of the u-○ film. 4
．． At 2'K, the value when a magnetic field was applied in the direction parallel to the C axis was 33 Tesla, and the value was 490 Tesla in the direction perpendicular to the C axis. Although the detailed reason for this effect is still unknown, the method shown in this example allows B i-S r-
By periodically stacking the Ca-Cu-0 film and the B1-Mn-○ film, the B i-S r-Ca-Cu-○ film and the B1-Mn-○ film are epitaxially grown. Layering a B i-S r-Ca-Cu-0 film, which also has excellent crystallinity, through a thin B1-Mn-0 film, which has no effect of mutual diffusion of elements at the interface and has excellent crystallinity. It is considered that some change was caused in the superconducting mechanism in the B1-8r-C, a-Cu-0 film.

Furthermore, target 71. Alternatively, it has been found that when lead (pb) is added to 74 and sputtered, results equivalent to those of the above example can be obtained even if the temperature of the base 77 is about 100° C. lower than that of the above example.

(Effects of the Invention) The thin film superconductor of the first invention provides a structure that improves the critical current density and critical magnetic field of the Bi-based thin film superconductor, and the method for manufacturing a thin film superconductor of the second invention is the first
This invention more effectively realizes the invention described above, and establishes a low-temperature process that is essential for applications such as devices, and the present invention has great industrial value.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a thin film manufacturing apparatus according to an embodiment of the first invention, FIG. 2 is a structural conceptual diagram of the first invention, and FIGS. 3 and 6 are thin films obtained by the apparatus of FIG. 1. Figure 4 shows the temperature dependence of the critical current density in the thin film obtained with the apparatus shown in Figure 1. Figure 5 shows the temperature dependence of the critical current density in the thin film obtained with the apparatus shown in Figure 1 under an external magnetic field. 7 is a schematic diagram of the thin film manufacturing apparatus in the embodiment of the second invention, and FIG. 8 is a temperature characteristic diagram of the resistance value of the thin film obtained by the apparatus of FIG. 7. . 11, 12.71.72.73.74... Sputtering target, 13.75... Shutter 14, 7
6...Aperture, 15.77Mg○ base, 16
．． 78... Heater, 21- B1-Mn-0 film, 22- B1-5r-Ca-Cu-〇 film, 61.62
．． 63.81.82.83--Temperature characteristics of thin film resistance. Patent applicant Matsushita Electric Industrial Co., Ltd. Matsushita Electric Works Co., Ltd. Agent Koji Hoshino No. 1

Claims (4)

[Claims] (1) The main components are at least bismuth (Bi) and copper (C).
u), and a thin film superconductor having a structure in which layered oxide superconducting thin films containing alkaline earth elements (group IIa) and magnetic thin films consisting of at least one type of perovskite oxide are alternately laminated. . Here, alkaline earth refers to at least one or two or more elements of Group IIa elements, and perovskite oxide refers to RFeO_3 (R=Y, Sm, Eu, Gd, T
b, Dy, Ho, Er, Tm, Yb, Lu) or
MMnO_3(M=Bi, La_0_._7Ca_0_
．． _3, La_0_. _7Sr_0_. _3, La_0
＿． _7Ba_0_. _3, La_0_. ＿６、Pb＿
0__. _4, La_0_. _7Cd_0_. _3), or AMnO_6 (A=Gd_2Co, Ba_2F
The figure shows an oxide magnetic material represented by (e, Ca_2Fe) and a composite oxide magnetic material containing at least two or more of these. (2) An oxide thin film formed by periodically stacking an oxide containing at least Bi and an oxide containing at least copper and alkaline earth (group IIa) on a substrate, and a magnetic material made of a perovskite oxide. 1. A method for producing a thin film superconductor, characterized in that the thin film superconductor is obtained by alternately laminating thin films. Here, alkaline earth refers to at least one or two or more elements of Group IIa elements, and perovskite oxide refers to RFeO_3 (R=Y, Sm, Eu, Gd,
Tb, Dy, Ho, Er, Tm, Yb, Lu) or MMnO_3 (M=Bi, La_0_._7Ca_0
＿． _3, La_0_. _7Sr_0_. ＿３、La＿
0__. _7Ba_0_. _3, La_0_. 6, Pb_
0__. _4, La_0_. _7Cd_0_. _3), or AMnO_6 (A=Gd_2Co, Ba_2F
This shows an oxide magnetic material represented by e, Ca_2Fe). (3) The method for manufacturing a thin film superconductor according to claim (2), characterized in that the evaporation of the laminated material is performed using at least two types of evaporation sources. (4) The method for manufacturing a thin film superconductor according to claim (2), wherein the evaporation of the laminated material is performed by sputtering.