JPH0722662A - Insulation material and its manufacture, and superconductor thin film and its manufacture - Google Patents

Abstract

PURPOSE:To provide an insulation material which compensates characteristic even at a film thickness of several 10nm and a thin film manufacturing method thereof, and a structure of a stable superconductive thin film and its manufacturing method. CONSTITUTION:Bi4Srn-1 Ti2+nO3n+9 crystal (n is an integer of 1 or more) of a lamination structure whose basic structure of crystal is composed of a (Bi2O2)<2+> layer and a (Bi2Srn-1Ti2+nO3n+7)<2-> layer in a c-axial direction is close to that of an a-axis and a b-axis of a Bi superconductor, enables mutual epitaxial growth of thin films and is a stable insulation material without allowing Ti to affect Bi superconductor crystal even if laminated with a Bi superconductor thin film. Therefore, a Bi superconductor thin film and an insulation material thin film can be epitaxially formed stably through a Bi-O layer by laminating and depositing an oxide layer whose main element includes at least Bi, an oxide layer containing Cu and an alkaline earth (11a group) and an oxide layer containing Bi, Ti and alkaline earth periodically.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an insulator, a method for producing the same, and a superconductor thin film, which are useful in converting a material such as an oxide high temperature superconductor, which undergoes a relatively high generation process at 600 to 900 ° C., into a device. The present invention relates to a manufacturing method thereof.

[0002]

2. Description of the Related Art Oxide high-temperature superconductors are one of the materials whose applications are urgently required at present. This perovskite compound is expected to have a higher transition temperature than that of a metal compound superconductor, and a Ba-La-Cu-O-based high-temperature superconductor has been proposed [JG Bednorz and KAMuller, Zeitshrift Fur Physik. Physik
B) -Condensed Matter Vol.64, 189-193 (1986)]. Furthermore, it was discovered that the Bi-Sr-Ca-Cu-O-based material exhibits a transition temperature of 100 K or higher [H. Maeda, Y. Tana.
ka, M.Fukutomi and T.Asano, Japanese Journal of Applied Physics (Japanese Journal
of Applied Physics) Vol. 27, L209-L210 (1988)]. Although the details of the superconducting mechanism of this kind of material are not clear, the transition temperature may be higher than room temperature, and it is expected to be applied in the electronic device field as a high temperature superconductor rather than the conventional binary compounds. There is.

Then, together with the development of these oxide superconductors, considering the application of this material to electronic devices,
Insulators and thin films are being developed that are stable to the high temperature process that occurs during the production of oxide superconductors [Y.
Ichikawa, H.Adachi, T.Mitsuyu and K.Wasa, Japanese Journal of Applied Physics (Ja
panese Journal of Applied Physics) Vol.27, L381-L383
(1988)].

Furthermore, by alternately laminating superconductors and insulators, a higher superconducting transition temperature has been conventionally expected [MH Cohen and DHDouglass, Jr., Physical Review Letters].
Vol. 19, 118-121 (1967)].

[0005]

However, in order to obtain good superconducting properties, the material of the oxide superconductor needs to be heat-treated at a temperature of 600 ° C. or higher or heating at the time of formation, so that the crystallinity of the insulator is high. Collapse, and inter-diffusion of each element occurs between the insulator and the insulating thin film and the superconductor, resulting in deterioration of the characteristics of the superconductor and deterioration of the characteristics of the insulator. It is extremely difficult to obtain such a laminated structure, and it has been difficult to construct an integrated device using this structure, which is a typical application example of Josephson devices.

Furthermore, since an optimum insulating thin film for a high-temperature superconductor and a thin film has not been obtained, an effective laminated structure of a superconductor and an insulator cannot be achieved, so that it is expected that the superconducting transition temperature of the superconducting material itself will rise. It was the current situation.

In order to solve the above-mentioned conventional problems, the present invention provides an insulator for compensating the characteristics even with a film thickness of about 10 nm, a method for producing the same, and a structure of a stable superconducting thin film and a method for producing the same. To aim.

[0008]

In order to achieve the above-mentioned object, the insulator of the present invention has a main component of at least bismuth (Bi), alkaline earth (IIa group), titanium (Ti),
It has a constitution that it is a laminated body of thin films containing oxygen (O) (here, the alkaline earth represents at least one element or two or more elements of the group IIa elements).

Next, in the method for producing an insulator of the present invention, an oxide layer containing at least Bi and at least Bi,
It has a structure in which an alkaline earth (IIa group) and an oxide layer containing Ti are alternately laminated (wherein the alkaline earth is at least one kind or two or more kinds of the group IIa elements). Show.).

Next, the superconducting thin film of the present invention has at least Bi, Cu and alkaline earth (IIa) as main components on the substrate.
Group) and an insulator oxide layer containing at least Bi, Ti, and an alkaline earth are periodically laminated (wherein the alkaline earth is a group IIa element). Of at least one or more than two elements).

Next, in the method for producing a superconducting thin film of the present invention, an oxide layer containing at least Bi as a main component, an oxide layer containing at least Cu and an alkaline earth (group IIa), and at least Bi, are formed on a substrate. The structure is such that an oxide layer containing Ti and an alkaline earth is periodically stacked and deposited (here, the alkaline earth represents at least one kind or two or more kinds of elements of the group IIa). ).

In the above structure, the ratio of elements is B
It is preferably represented by i: A: Ti = 4: (n-1) :( 2 + n) (wherein A represents at least one kind or two or more kinds of Group IIa elements, and n is 1). Indicates the above integer.).

[0013]

According to the above-mentioned structure of the present invention, the insulator has a crystal structure covered with a Bi ₂ O ₂ oxide film layer or a layer mainly composed of the Bi ₂ O ₂ oxide film, which is extremely stable in terms of heat. Since the formation temperature is almost the same as that of the oxide superconductor, the crystallinity and characteristics of the insulator and the oxide superconductor according to the present invention are deteriorated with each other even if they are brought into contact with the oxide high-temperature superconductor or undergo a process such as high-temperature heat treatment. There is nothing to do. Further, the crystal structure of the insulator according to the present invention is the same perovskite structure as that of the oxide superconductor, and in particular, since the a and b axes are almost equal in length, stable continuous lamination of the oxide superconductor and the insulator is possible. Is.

Further, according to the constitution of the method for producing an insulator of the present invention, in order to achieve the above structure, an oxide layer containing at least Bi, at least Bi, an alkaline earth (group IIa) and Ti are formed on the substrate. By alternately laminating the oxide layers containing the same, a Bi-based superconducting thin film and an insulating film can be laminated with good reproducibility, and the interlayer insulating film having a thickness of several 10 nm or less, which is necessary for the Josephson device design, is stable. It enables formation.

Further, according to the structure of the superconducting thin film of the present invention, the Bi ₂ O ₂ oxide film layer or the layer mainly composed of the Bi ₂ O ₂ oxide film has a crystal structure covered with Bi.
The system superconducting thin film and the insulator thin film according to the first aspect of the present invention have a structure in which the superconducting thin film and the insulating film are alternately laminated, thereby enabling mutual diffusion of elements between the superconducting thin film and the insulating film.
As a result, the superconducting transition temperature in the Bi-based superconducting thin film was stably realized with good reproducibility.

Further, according to the structure of the method for producing a superconducting thin film of the present invention, in order to achieve the structure of the superconducting thin film extremely stably and on a fine scale, an oxide layer containing at least Bi as a main component on the substrate. And an oxide layer containing at least Cu and an alkaline earth (Group IIa) and an oxide layer containing at least Bi, Ti and an alkaline earth are periodically laminated to form a Bi-based material with good reproducibility. It is intended to realize lamination of a superconducting thin film and an insulating film.

[0017]

Examples Among oxide high-temperature superconductors, Bi-based superconductors are considered to be the most promising materials for practical use from the viewpoints of stability and high superconducting transition temperature. Further, when considering the use of this type of material as an element, the production of an interlayer insulating film used for Josephson junction or the like becomes a problem. First, the present inventors
Various insulating films were examined as an interlayer insulating film for the i-based superconductor thin film.

Usually, the Bi-Sr-Ca-Cu-O type oxide superconducting thin film is obtained by vapor deposition on a substrate heated to 600 to 700 ° C. After vapor deposition, the thin film shows superconducting properties as it is, but it is then heat-treated at 700 to 950 ° C to improve the superconducting properties. However, when the insulating film is laminated subsequently to the oxide superconducting thin film when the substrate temperature is high, or when heat treatment is performed after forming the insulating film, between the superconducting film and the insulating film,
It was found that the mutual diffusion of elements occurs and the superconducting properties are greatly deteriorated. To prevent mutual diffusion, the crystallinity of the superconducting film and the insulating film is excellent, the lattice matching between the superconducting film and the insulating film is excellent, and the insulating film is 700
It is considered essential to be stable to heat treatment at ~ 950 ° C.

First, the present inventors have a basic crystal structure of a Bi-based layered ferroelectric substance consisting of a Bi ₂ O ₂ oxide layer and a perovskite-like oxide layer containing Ti, which is very similar to a Bi-based superconductor. We paid attention to the fact that it is an insulating material. In addition, when a device is formed by combining a superconductor and a dielectric, a heating state in a vacuum is an unavoidable process. Therefore, evaluation was performed by growing a dielectric on a Bi-based superconducting thin film. Fig. 1 shows B on a Bi-based superconducting thin film.
4 shows changes in X-ray diffraction spectrum when an i-Ti-O dielectric thin film was grown. 1 (a), (b), and (c) show Bi-Ti-O thin film and Bi-Sr-Ca-Cu, respectively.
-O thin film, Bi-Ti-O / Bi-Sr-Ca-Cu-
The X-ray-diffraction spectrum of an O thin film is shown. SrTi for the substrate
O ₃ with (100), calcined Bi-Ti-O, Bi-
A thin film was formed by a binary high-frequency magnetron sputtering apparatus composed of Sr-Ca-Cu-O target. The temperature of the substrate was 650 ° C. Bi-Ti-O thin film, Bi-Sr-
The thickness of the Ca-Cu-O thin film is 50 nm and 150, respectively.
nm. As shown in FIGS. 1A and 1B, Bi-
Ti-O thin film, Bi-Sr-Ca-Cu -O thin film having excellent c-axis orientation in each crystalline dielectric Bi ₄ Ti ₃ O
₁₂ , it can be seen that the superconductor is Bi ₂ Sr ₂ CaCu ₂ O ₈ . However Bi-Sr-CaCu-O thin films prepared immediately after the depositing the Bi-Ti-O thin film thereon, does not appear any crystalline phase of _{Bi 4 Ti 3 O 12, Bi} 2 Sr 2 CaCu 2 O 8 , FIG. 1 (c), Bi-Sr-
It was found that a solid solution crystal of O was completed. Further, although Bi-Ti-O was originally an insulator, there was conduction. This phenomenon occurs, for example, after the Bi-Sr-Ca-Cu-O thin film is formed, the substrate temperature is lowered to room temperature, and then Bi-Ti-O is again generated.
If to produce a Bi-Ti-O thin film by increasing the temperature of the substrate to a thin film forming temperature, Bi-Sr-Ca-Cu -O thin films prepared after the oxygen gas sufficiently in an atmosphere containing Bi ₂ Sr ₂ Ca
After heat treatment for growing Cu ₂ O ₈ crystals, Bi-
Similar observation was made when a Ti—O thin film was formed thereon. The exact cause is still unknown, but it can be considered as follows. That is, at least Bi ₄ Ti ₃
O was heated in a state necessary for the crystallization of ₁₂ Bi-Sr-C
In the a-Cu-O thin film, Bi, Sr, Ca, Cu, O
Has a weak bond, and is affected by Ti, which has the highest activity among Bi, Ti, and O that has flown on it. Especially, Ti easily bonds with O, so Bi, Sr, Ca, and Cu must be in some form. It breaks the bond with O,
Element ratio of Bi-Sr-CaCu-O and Bi-Ti-O from the interface _{Bi 2 Sr 2 CaCu 2 O 8} Bi: Sr:
The present inventors have considered that the Ca: Cu = 2: 2: 1: 2 collapses and a Bi-Sr-O solid solution is formed from the interface.

Therefore, the inventors of the present invention have conducted experiments and studies for causing Ti to fly onto the Bi-Sr-Ca-Cu-O thin film in the form of particles having a low activity, and as a result, the Bi-based ferroelectric substance has been found. Among the Bi ₂ O ₂ oxide layer forming the crystal and the perovskite-like oxide layer containing Ti, when Ti and alkaline earth (group IIa) are added to the perovskite-like oxide layer, Bi-Sr- It was found that the Bi-based dielectric can grow while the crystal structure of the Ca-Cu-O thin film is maintained, and unexpectedly that it may exhibit excellent characteristics as a ferroelectric.

(Example 1) A thin film forming apparatus used in this example
A schematic view of the structure of the device is shown in FIG. In this embodiment, Bi-Sr
-Ca-Cu-O thin film and Bi-Ti-O thin film continuously
Dual target high frequency magnetron for stacking
Each film was vapor-deposited by the sputtering method. Sputtering
Baking at 900 ℃ for 5 hours in air as a target
Bi of mixed oxide₂Sr₂Ca₂Cu₃O_{10 + x}Di
Sctarget 1 and Bi_FourTi₃O _{12 + y}Disc target
Tut 2 was used. Reference numeral 5 indicates a substrate. MgO (100) substrate 5
Each target is installed so that it is tilted about 30 ° so as to connect the points.
ing. There are shutters 3 and 4 in front of the target
Bi-Sr-Ca-Cu-O thin film and Bi-Ti-O
A thin film can be continuously deposited on the substrate 5. Ar and O₂A mixture of
Combined gas (Ar: O₂= 1: 9, 0.5 Pa)
It was used as a linguistic gas. 8 for targets 1 and 2 respectively
Sputter power of 0 W and 60 W is injected to target the target.
First, Bi-S is put on the substrate 5 which is putted and heated to 650 ° C.
A 150 nm thick r-Ca-Cu-O thin film is deposited, followed by B
An i-Ti-O thin film was deposited in a stack of 50 nm.
The crystal structure of the thin film after deposition of the Bi-Ti-O thin film is shown in FIG.
As shown in (c), the outermost surface of the thin film exhibits insulating properties.
There wasn't. Therefore, the present inventors have made a Bi-Ti-O target.
Insulation increases when Bi and Sr are added to the
I found it. That is, Bi_FourTi₃O_{12 + y}disk
Target 2 is crushed and TiO₂Powder, SrCO₃powder
Is added and fired again and used as the target 2.
-Sr-Ti-O thin film with Bi-Sr-Ca-Cu-O thin
When deposited on the film, the Bi-Sr-Ti-O thin film becomes Bi-
Insulation is exhibited even on Sr-Ca-Cu-O thin film.
I found out. TiO₂Powder and SrCO₃The powder is Ti:
It was added at a ratio of Sr = 1: 1. Therefore, Bi-Sr-Ca
Directly on the Bi-Sr-Ti-O thin film on the -Cu-O thin film
Two Pt electrodes with a diameter of 0.3 mm are sputtered to about 50 nm.
It is vapor-deposited (spacing: 1.5 mm), from 100 Hz to 1 MHz
Impedance for 5V amplitude voltage with frequency
From the change, the dielectric constant, the resistivity of the Bi-Sr-Ti-O thin film,
Leakage current was measured. It has an insulating property
The parameter that is accurately expressed is the leak current.

FIG. 3 shows the Ti + added to the Bi-Ti-O thin film.
The change in leak current with respect to the amount of Sr is shown. Ti + Sr
The amount of B is because the ratio of added Ti and Sr is 1: 1.
It was represented by z of i ₄ Sr _z Ti _{3 + z} O _{12 + y} . It was found that the leak current decreased when z> 0 and increased again when z ≧ 5. In addition, the inventors of the present invention added Ti and S when z = 2.
Similarly, the change in leak current was examined for the ratio of r. Bi-Sr-C with respect to the ratio of Ti and Sr added in FIG.
The change of the leak current of the Bi-Sr-Ti-O thin film on the a-Cu-O thin film was shown. As a result, the present inventors
It was found that the leakage current is smallest and the insulation is excellent when r = 1: 1. That is, Bi-Sr-T
The ratio of elements in the i-O thin film is Bi: Sr: Ti = 4 :.
The present inventors have found that when represented by (n-1) :( 2 + n), the insulating property is most excellent. Where n
Represents an integer of 1 or more.

The reason why a good insulator is obtained is still unclear, but it can be considered as follows. That is, T
i is a unit of Sr and Sr-Ti-O in a ratio of 1: 1 and Bi-
Bi-Sr-Ca-Cu-at the time of producing the Sr-Ti-O thin film
Since it flew over O and is already energy stable,
Bi-Sr-Ca-Cu-O without affecting other elements
It is considered that no solid solution is formed at the interface with the thin film.

Note that the present inventors have replaced Cr with C
We also found that a and Ba have the same effect.
Furthermore, the inventors of the present invention showed the Bi-Sr-T shown in this example.
It was also found that the i-O thin film is excellent as a ferroelectric. That is, Bi-without addition of Ti and Sr
It has been found that the dielectric constant is higher than that of the Ti-O film. FIG. 5 shows changes in the relative permittivity of the Bi-Sr-Ti-O thin film at room temperature with respect to the amount of Ti + Sr added to the Bi-Ti-O thin film. The inventors of the present invention added Ti and Sr.
It was also found that the relative permittivity is highest when the ratio is 1: 1. Furthermore, we replace Cr with C
We also found that a and Ba have the same effect.

Further, the present inventors have found that the Bi-based layered ferroelectric substance is (Bi ₂ O ₂ ) ²⁺ (Bi ₂ Sr _{n- 1} Ti _{2 + n} O _{3n + 7} )
Paying attention to the fact that it is represented by the composition formula of ^2- , when a Bi-O layer and a pseudo-phase perovskite layer Bi-Sr-Ti-O layer are periodically laminated in atomic order, a Bi-based layered ferroelectric thin film is formed. It was found that the crystallinity and characteristics are improved, and that when this method is applied, it is possible to obtain an insulating film with much better controllability, stable film quality, and an extremely flat film surface than the manufacturing method shown in Example 1. I found it.

Bi_FourSr_n-1Ti_{2 + n}O_{3n + 9}Crystal is c-axis
Direction (Bi₂O₂)²⁺Layer and (Bi ₂Sr_n-1Ti_{2 + n}
O_{3n + 7})^2-It is considered to be a laminated structure including layers. There
Separate the different elements or unit layers that make up the layered structure.
Parallel to the substrate surface by sequentially stacking each
The surface of the substrate can be moved by simply moving the vapor deposition elements
Due to the absence of element movement in the direction perpendicular to the plane
it is conceivable that.

Surprisingly, it was also found that the temperature of the substrate and the heat treatment temperature required to obtain good superconducting properties are lower than those of the conventional ones. To prepare a Bi-Sr-Ti-O thin film, Bi-O->(Bi-Sr-Ti-O)-> Bi-O.
Lamination methods are possible. In general, periodic stacking can be achieved by controlling an opening / closing shutter in front of an evaporation source in an MBE apparatus or a multi-source EB vapor deposition apparatus, or by switching a gas type when manufacturing by a 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 have found that a good laminated film can be produced in addition to the case where different thin layers are laminated on this Bi-Ti-O thin film by sputtering.

As a method of stacking different substances by sputter deposition, there is a method of periodically controlling the discharge position of one sputtering target having a composition distribution, but it is called sputtering of a plurality of targets having different compositions. This can be achieved relatively easily using the method. 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, it is relatively easy to perform Bi-Sr sputtering by using a plurality of targets.
It becomes possible to fabricate a periodic stack of —Ti—O-based oxides.

Example 2 In this example, the apparatus used in Example 1 shown in FIG. 2 was used. That is, FIG.
At Bi Metal Disc Target 1, Bi-Sr
-Ti-O fired disk target 2 and Bi-Sr-Ca-Cu-
An O 2 superconducting thin film was used. The targets 1 and 2 have shutters 3 and 4, respectively, and the cycle and sputtering time of each target can be set. The substrate 5 was heated to 650 ° C. by the heater 6 and each target was sputtered in a gas containing 1 Pa of a mixed atmosphere of argon and oxygen (4: 1). Bi: 60W, Bi-Sr-Ti-O:
High-frequency power of 200 W is injected, and (Bi-O) → (Bi-O)
-Sr-Ti-O)-> (Bi-O) cycle
An Sr-Ti-O thin film was prepared.

Bi-Sr-Ti thus prepared
The result of measuring the leak current of the -O thin film in the same manner as in Example 1 is shown in FIG. As seen in FIG. 6, it can be seen that the leak current is reduced by about one digit by the method of forming the insulating film by the present inventors. The reason for this is that the Bi-Sr-Ti-O thin film has a (Bi-O) layer and a (Bi-Sr-Ti-O) layer so that the Bi-Sr-Ti-O thin film constitutes its crystal structure.
It is considered that the original characteristics of the layered crystal were improved because the layers were sequentially stacked.

(Embodiment 3) FIG. 7 schematically shows a cross-sectional view of the thin film produced in this embodiment. In FIG. 7, a Bi-Sr-Ca-Cu-O film and a Bi-Sr-Ti- film are formed on the substrate.
O films were alternately stacked. As a stacking method, Example 1 was used.
In the binary high-frequency magnetron sputtering method used in Example 1, a baked Bi-Sr-Ca-Cu-O is used as the target 1, and Bi-Sr-Ti-O is used as the target 2, and Bi-Sr-
The Ca-Cu-O film 100 nm and the Bi-Sr-Ti-O film were alternately sputtered for 5 cycles, the Bi-Sr-Ti-O thin film thickness was changed, and the change in the resistivity of the thin film was investigated. 8
Shown in. When the Bi-Sr-Ti-O film was 20 nm, the highest superconducting transition temperature and zero resistance temperature, that is, characteristic 8, was obtained. The superconducting transition temperature and zero resistance temperature of characteristic 8 were about 8K higher than those values originally present in the Bi-Sr-Ca-Cu-O film. Although the detailed reason for this effect is still unknown, as shown in FIG.
Bi-Sr-Ca-C is obtained by periodically stacking the Sr-Ca-Cu-O film and the Bi-Sr-Ti-O film.
The u-O film and the Bi-Sr-Ti-O film are mutually Bi ₂ O ₂
Bi-Sr, which is also excellent in crystallinity, is not affected by mutual diffusion of elements at the stacking interface because it is epitaxially grown through the layer, and Bi-Sr is also excellent in crystallinity through a thin Bi-Sr-Ti-O film having excellent crystallinity. It is considered that some changes were caused in the superconducting mechanism in the Bi-Sr-Ca-Cu-O film by stacking the -Ca-Cu-O film, but the mechanism is still unclear.

(Embodiment 4) FIG. 9 shows the three components used in this embodiment.
FIG. 10 is a schematic view of the inside of the former magnetron sputtering apparatus.
Is a Bi disk target, 11 is a sintered Sr-Ca-C
u-O disk target, 12 is fired Bi-Sr-T
i-O disk targets, 13, 14, and 15 are shutters, 16 is a substrate, and 17 is a substrate heating heater.
The target 11 has an element ratio Sr: Ca: Cu = 2: 2: 3, and the target 12 has an element ratio Bi: Sr: Ti = 2: 2: 5.
It was arranged as shown in FIG. That is, Mg O (100)
Each target is installed so as to be tilted by about 30 ° so as to focus on the substrate 16. There are shutters 13, 14, 15 in front of each target, and targets 10, 11, 1
Films can be separately deposited from 2 to the substrate 16.
By controlling the opening and closing of the shutters 13, 14, and 15, (Bi-O)->(Sr-Ca-Cu-O)-> (Bi-O)
-O) cycle and (Bi-O) → (Bi-Sr-Ti
Sputter deposition can be performed in a cycle of -O)-> (Bi-O). Although the state of stacking is conceptually shown in FIG. 7, Bi-Sr-Ca-Cu-O deposited on the substrate 16 by controlling the input power to the targets 10 and 1112 and the sputtering time of each target. Membrane, B
The film thickness of the i-Sr-Ti-O film can be changed. The substrate 16 was heated to about 700 ° C. by the heater 17 and each target was sputtered in a gas containing 0.5 Pa of an argon / oxygen (1: 1) mixed atmosphere. After forming the thin film, heat treatment was performed at 850 ° C. for 5 hours in an oxygen atmosphere.
In this embodiment, the composition ratio of elements of the Bi-Sr-Ca-Cu-O film is Bi: Sr: Ca: Cu = 2: 2: 2: 3, Bi-S.
The composition ratio of elements in the r-Ti-O film is Bi: Sr: Ti = 4 :.
The sputtering time was adjusted to a sputtering current of 2: 5. Furthermore, it seems that the limit of the film thickness that can be reduced while maintaining the crystallinity is several nm. Since it is preferable that the insulating film be as thin as possible, the present inventors have found that h · ((Bi−O) →
(Sr-Ca-Cu-O)->(Bi-O))-> i.
((Bi-O)->(Bi-Sr-Ti-O)-> (Bi-
O)) was written for 20 cycles. Note that Bi-Sr-Ti that can be produced while maintaining a good crystal structure
The film thickness of the -O film was limited to i = 2. Therefore, the present inventors investigated the temperature change of the resistivity of the thin film that was completed by changing h when i = 2. The result at that time is shown in FIG. In FIG. 10, 18 is h = 2, 19 is h = 6,
20 shows the result when h = 10. As can be seen from this figure, when h = 6, the superconducting transition temperature and the zero resistance temperature were found to be higher than those when the insulating film Bi-Sr-Ti-O was not laminated. The physical cause of this is not clear, but the Bi-Sr-Ca-Cu-O thin film and B
It is considered that both of the i-Sr-Ti-O thin films were able to be laminated with extremely good controllability.

Furthermore, the present inventors have found that Bi oxide, Sr, Ca, Cu, and T can be used without using the sputtering method.
Example 2 when the oxides of i were separately evaporated in vacuum from different evaporation sources and the same structure was periodically stacked.
It was also found that it is possible to obtain a thin film with good controllability and stable film quality as in the method of manufacturing a laminated structure using sputtering shown in Example 4. Bi-
There are several possible methods for periodically stacking O, Sr-Ca-Cu-O, and Bi-Sr-Ti-O.
In general, periodic stacking can be achieved by controlling an opening / closing shutter in front of an evaporation source in an MBE apparatus or a multi-source EB vapor deposition apparatus, or by switching a gas type when manufacturing by a 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 inventors of the present invention have found that a good laminated film can be produced in addition to the case where different thin layers are laminated on the Bi-based oxide superconductor and the insulating thin film by sputtering. Due to the high oxygen gas pressure during sputtering and sputter discharge, introduction of oxygen into the film is further promoted, reproducibility and stabilization of superconducting characteristics are achieved, and formation of a Bi-based phase having a critical temperature of 100 K or higher, This is probably because it is convenient for the formation of the insulating thin film.

As a method of laminating different substances by sputter deposition, there is a method of periodically controlling the discharge position of one sputtering target having a composition distribution, but it is called sputtering of a plurality of targets having different compositions. This can be achieved relatively easily using the method. 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. As described above, the periodic stacking of Bi-based oxides can be relatively easily manufactured by sputtering using a plurality of targets.

[0035]

INDUSTRIAL APPLICABILITY As described above, the insulator of the present invention provides the element portion which is indispensable for the device constitution of the oxide superconducting thin film. Further, the method for producing an insulating thin film of the present invention has established a process at a low temperature which is essential for application of devices and the like. Further, the superconducting thin film of the present invention realizes high performance of the oxide superconducting thin film. Further, the method for producing a superconducting thin film of the present invention has established a process at a low temperature, which is essential for application of devices and the like, and the industrial value of the present invention is great.

[Brief description of drawings]

FIG. 1 is a Bi—Ti—O thin film of one embodiment of the present invention, Bi
-Sr-Ca-Cu-O thin film, Bi-Ti-O / Bi-
The X-ray-diffraction spectrum of a Sr-Ca-Cu-O laminated thin film.

FIG. 2 is a schematic diagram of an experimental apparatus of Example 1 of the present invention.

FIG. 3 is a graph showing changes in leak current of the Bi—Sr—Ti—O thin film of Example 1 of the present invention with respect to addition of Ti / Sr.

FIG. 4 shows changes in leak current with respect to the ratio of Ti and Sr added to the Bi—Sr—Ti—O thin film of Example 1 of the present invention.

FIG. 5 shows changes in relative permittivity of Bi—Sr—Ti—O thin film of Example 1 of the present invention with addition of Ti / Sr.

FIG. 6 shows a change in leak current with respect to addition of Ti / Sr in a Bi—Sr—Ti—O thin film of Example 2 of the present invention.

FIG. 7 is a schematic diagram of a laminated structure crystal of a Bi—Sr—Ti—O ferroelectric / Bi—Sr—Ca—Cu—O superconductor according to Example 3 of the present invention.

FIG. 8 is a Bi-Sr-Ca-Cu-of Example 3 of the present invention.
Temperature change of resistivity of O thin film.

FIG. 9 is a schematic diagram of an experimental apparatus of Example 4 of the present invention.

FIG. 10: Bi-Sr-Ca-Cu of Example 4 of the present invention
-Change in resistivity of O thin film with temperature.

[Explanation of symbols]

1,2,10,11,12 Sputtering target 3,4,13,14,15 Shutter 5,16 Substrate 6,17 Substrate heating heater 7,8,9,18,19,20 Temperature change of resistivity of thin film

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical indication C04B 35/00 ZAA 35/46 C23C 14/08 K 0827-4K C30B 29/22 501 M 8216-4G H01B 12/06 ZAA 7244-5G 13/00 565 D 7244-5G H01L 39/02 ZAA D 9276-4M

Claims (5)

[Claims] 1. A main component is at least bismuth (Bi),
Alkaline earth (IIa group), titanium (Ti), oxygen (O)
An insulator which is a laminated body of thin films containing. Here, the alkaline earth refers to at least one element or two or more elements of the group IIa elements. 2. A method for producing an insulator, wherein an oxide layer containing at least Bi and an oxide layer containing at least Bi, alkaline earth (IIa group) and Ti are alternately laminated on a substrate. Here, the alkaline earth refers to at least one element or two or more elements of the group IIa elements. 3. A main component of at least Bi, Cu on a substrate.
And a superconducting thin film having a structure in which an oxide layer containing alkaline earth (group IIa) and an insulating oxide layer containing at least Bi, Ti and alkaline earth are periodically laminated. Here, the alkaline earth refers to at least one element or two or more elements of the group IIa elements. 4. An oxide layer containing at least Bi as a main component on a substrate, at least Cu and an alkaline earth (IIa
Group) and an oxide layer containing at least Bi, Ti, and an alkaline earth are periodically stacked and deposited. Here, the alkaline earth refers to at least one element or two or more elements of the group IIa elements. 5. The ratio of elements is Bi: A: Ti = 4 :.
(N-1): represented by (2 + n), the insulator according to claim 1, the method for producing the insulator according to claim 2, the superconducting thin film according to claim 3, or the claim 4. A method for producing the superconducting thin film described. Here, A represents at least one element or two or more elements of the IIa group elements, and n represents an integer of 1 or more.