JPH07223818A - Insulation material, production thereof, supreconductor thin film and production thereof - Google Patents

Abstract

PURPOSE:To obtain an insulation material compensating the characteristics even at a film thickness of about several tens nm and to provide its production process and a process for producing a stable superconductor thin film. CONSTITUTION:A Bi metal disk target and a Bi-Pb-Ti-O baked disk target are used as sputtering targets and a Bi-Sr-Ca-Cu-O superconductor thin film formed on MgO (100) beforehand is used as a substrate. Each target is sputtered in a gaseous mixture of argon and oxygen (4:1) under a pressure of 1.0 Pa by a (Bi-O) (Bi-Pb-Ti-O) (Bi-O) cycle to form a Bi-Pb-Ti-O dielectric thin film on the substrate heated at 650 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. 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. The manufacturing method is related.

[0002]

2. Description of the Related Art Oxide high-temperature superconductors are one of the materials for which application is 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 [JGBednorz and KAMuller, Zeitshrift Für-Fijik (Zeitshrift Fur Physik
B) -Condensed Matter Vol.64, 189-193 (1986)]. Further, it was also discovered that the Bi-Sr-Ca-Cu-O-based material exhibits a transition temperature of 100 Kelvin or more [H. Maeda,
Y. Tanaka, M. Fukutomi and T. Asano, Japanese Journal of Applied Physics (Japanese Jo
urnal of Applied Physics) Vol.27, L209-L210 (198
8)]. Although the details of the superconducting mechanism of this type of material are not clear, the transition temperature may rise above room temperature, and it is expected to be applied as a high-temperature superconductor in the field of electronic devices rather than conventional binary compounds. .

Considering the application of this material to an electronic device in combination with the development of these oxide superconductors, an insulator which is stable even in the high heat process that occurs during the production of oxide superconductors. And the development of insulating thin film [Y.Ichi
kawa, H.Adachi, T.Mitsuyu and K.Wasa, Japanese
Journal of Applied Physics (Japane
se Journal of Applied Physics) Vol.27, L381-L383 (198
8)].

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

[0005]

However, in order to obtain good superconducting properties, the material of the oxide superconductor requires at least 600 ° C. or higher heat treatment or heating during formation. Therefore, the crystallinity of the insulator collapses, mutual diffusion of each element occurs between the insulator and the insulating thin film, and the superconductor, and the characteristics of the superconductor and the insulator deteriorate. It is extremely difficult to obtain a periodic laminated structure of the insulating film and the insulating film, and it has been impossible to construct an integrated device using this structure, which is a typical application example of the Josephson device.

Further, since the optimum insulating thin film for the high temperature superconductor and the thin film has not been obtained, an effective laminated structure of the superconductor and the insulator has not been realized, and the superconducting transition temperature of the superconducting material itself rises. It was the current situation that I couldn't hope.

In order to solve the above-mentioned problems of the prior art, it is an object of the present invention to provide an insulator that compensates the characteristics even when the film thickness is about 10 nm, a method for manufacturing the same, and a stable superconductor thin film and a method for manufacturing the same. To do.

[0008]

In order to achieve the above object, the insulator according to the present invention is a thin film containing at least bismuth (Bi), lead (Pb), titanium (Ti) and oxygen (O) as main components. It is provided with a structure of being composed of a laminated body of.

Further, the method for manufacturing an insulator according to the present invention is
The structure is such that an oxide layer containing at least Bi and an oxide layer containing at least Bi, Pb, and Ti are alternately laminated on a substrate.

Further, the superconductor thin film according to the present invention comprises an oxide layer containing at least Bi, Cu and alkaline earth (IIa group) as main components on a substrate, and at least Bi,
It has a structure in which an insulator oxide layer containing Ti and Pb is periodically laminated (here, the alkaline earth represents at least one element or two or more elements of the group IIa elements. ).

Further, the method for producing a superconductor thin film according to the present invention comprises 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 Pb
And a structure in which an oxide layer containing is periodically stacked and deposited (here, the alkaline earth represents at least one element or two or more elements of the group IIa elements).

In the above structure, the ratio of elements is preferably expressed by Bi: Pb: Ti = 4: (n-1) :( 2 + n) (where n is an integer of 1 or more). Show.).

[0013]

According to the structure of the insulator of the present invention, the oxide superconductor has a crystal structure covered with a Bi ₂ O ₂ oxide film layer which is also extremely thermally stable or a layer mainly containing the Bi ₂ O ₂ oxide film layer. Since the formation temperature is almost equal to that of the oxide high temperature superconductor, the crystallinity and characteristics of the insulator and the superconductor thin film according to the present invention are not 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. Absent. Furthermore, the crystal structure of the insulator of the present invention is the same perovskite structure as that of the oxide superconductor, and in particular, since the lengths of the a-axis and the b-axis are almost equal, a stable continuous lamination of the oxide superconductor and the insulator is achieved. Is possible.

Further, according to the structure of the method for producing an insulator of the present invention, in order to achieve the structure of the insulator, an oxide layer containing at least Bi and at least Bi and P are formed on the substrate.
By alternately laminating the oxide layers containing b and Ti, it is possible to realize the laminated structure of the Bi-based superconductor thin film and the insulating film with good reproducibility, and it is necessary for the design of the Josephson device. It is possible to stably form an interlayer insulating film having a thickness of several 10 nm or less.

Further, according to the structure of the superconductor thin film of the present invention, the Bi-based superconductor thin film having the crystal structure covered with the Bi ₂ O ₂ oxide film layer or the layer mainly containing the Bi ₂ O ₂ oxide film layer and the first The thin film of the insulator according to the invention, by adopting a structure of alternately laminated, it is possible to realize a laminated structure without mutual diffusion of elements between the superconductor thin film and the insulating film, as a result, The superconducting transition temperature in the Bi-based superconductor thin film can be stably realized with good reproducibility.

Further, according to the structure of the method for producing a superconductor thin film of the present invention, in order to realize the superconductor thin film according to the third invention in an extremely stable manner and on a fine scale, at least as a main component on the substrate. Bi-based superconductivity is obtained by periodically stacking and depositing an oxide layer containing Bi, an oxide layer containing at least Cu and alkaline earth (group IIa), and an oxide layer containing at least Bi, Ti, and Pb. The lamination of the body thin film and the insulating film can be realized with good reproducibility.

[0017]

EXAMPLES The present invention will be described in more detail below with reference to examples. Among the oxide high-temperature superconductors, the Bi-based superconductors are considered to be the most promising materials for practical use from the viewpoint 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. Therefore, the present inventors first examined various insulating films as the interlayer insulating film for the Bi-based superconductor thin film.

The Bi-Sr-Ca-Cu-O-based oxide superconductor thin film is usually obtained by vapor deposition on a substrate heated to 600 to 700 ° C. This thin film shows superconducting properties even after vapor deposition as it is.
If the heat treatment is performed at a temperature of 950 ° C., the superconducting property can be further improved. However, when the insulating film is continuously stacked on the superconductor thin film when the substrate temperature is high, or when heat treatment is performed after the insulating film is formed, mutual diffusion of elements occurs between the superconductor thin film and the insulating film, and It was found that the characteristics were significantly deteriorated. In order to prevent mutual diffusion of elements, the crystallinity of the superconductor thin film and the insulating film is excellent, the lattice matching between the superconductor thin film and the insulating film is excellent, It is considered essential to be stable to the heat treatment at 950 ° C.

First, the inventors of the present invention 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 made by combining a superconductor and a dielectric, a heating state in a vacuum is an unavoidable process. Therefore, a dielectric thin film is grown on a Bi-based superconductor thin film for evaluation. I went.

In FIG. 1, Bi-on a Bi-based superconductor thin film,
X-ray diffraction spectrum of Ti-O dielectric thin film grown
Shows the change in tor. 1 (a), (b) and (c) are
Bi-Ti-O dielectric thin film, Bi-Sr-Ca-C, respectively
u-O superconductor thin film, Bi-Ti-O / Bi-Sr-C
It is an X-ray diffraction spectrum of an a-Cu-O thin film. Base
Then SrTiO₃(100) was used and baked Bi-
Ti-O target, Bi-Sr-Ca-Cu-O target
Dual high-frequency magnetron sputtering system consisting of a get
A thin film was prepared using. In this case, the temperature of the substrate is 65
It was set to 0 ° C. In addition, Bi-Ti-O dielectric thin film, Bi-
The film thickness of each Sr-Ca-Cu-O superconductor thin film is 5
It was set to 0 nm and 150 nm. Shown in FIGS. 1 (a) and 1 (b)
, Bi-Ti-O dielectric thin film, Bi-Sr-Ca
-Cu-O superconductor thin films are c-axis with excellent crystallinity.
Oriented dielectric Bi_FourTi₃O₁₂, Superconductor Bi₂Sr₂
CaCu₂O₈You can see that it has become. But B
After producing the i-Sr-Ca-Cu-O superconductor thin film,
If a Bi-Ti-O dielectric thin film is immediately deposited on it,
In the case of Bi_FourTi₃O₁₂, Bi₂Sr₂CaCu₂O
₈None of the crystal phases appeared, as shown in Fig. 1 (c).
In addition, Bi-Sr-O solid solution crystals may be formed.
Do you get it. Bi-Ti-O is essentially an insulator.
However, continuity was confirmed. This phenomenon is caused by, for example, Bi-S.
After producing the r-Ca-Cu-O superconductor thin film, the substrate temperature was
Temperature to room temperature, and then the temperature of the substrate is again induced by Bi-Ti-O.
Bi-Ti-O dielectric thin
When a film is deposited, or Bi-Sr-Ca-Cu-O supercurrent
After forming the conductor thin film, Bi is formed in an atmosphere containing oxygen gas.
₂Sr₂CaCu₂O₈Heat treatment to grow crystals
Fully applied, and then a Bi-Ti-O dielectric thin film is formed thereon.
Was also observed in the case of depositing. The cause is accurate
Is still unknown, but it can be thought about as follows.
it can. That is, at least Bi_FourTi₃O₁₂Crystal of
Bi-Sr-Ca-Cu- heated to the state required for
In the O superconductor thin film, Bi, Sr, Ca, C
u and O have weak bonds, and Bi, Ti and O fly over them.
Of Ti, which has the strongest activity,
Is easily bonded to O, Bi, Sr, Ca, Cu
Be sure to break the bond with O which is bound in some form
Mai, Bi-Sr-Ca-Cu-O superconductor thin film and Bi
From the interface of the -Ti-O dielectric thin film to Bi₂Sr₂CaCu
₂O ₈Element ratio of Bi: Sr: Ca: Cu = 2: 2:
It collapses from 1: 2, and Bi-Sr-O solid
It is thought that a solution crystal will be formed.

Therefore, the present inventors have conducted experiments and studies for causing Ti to fly onto the Bi-Sr-Ca-Cu-O superconductor thin film in the form of particles having low activity. As a result, by adding Ti and Pb to the perovskite-like oxide layer among the Bi ₂ O ₂ oxide layer and the perovskite-like oxide layer containing Ti constituting the Bi-based ferroelectric crystal, Bi That the Bi-based dielectric grows while maintaining the crystal structure of the —Sr—Ca—Cu—O superconductor thin film;
Further, they have found that they may exhibit excellent properties as a ferroelectric, and have made a series of inventions.

The present invention will be described in more detail below with reference to specific examples. (Embodiment 1) FIG. 2 shows a schematic view of the thin film forming apparatus used in the present embodiment 1. In the first embodiment, Bi-Sr-
In order to continuously stack the Ca-Cu-O superconductor thin film and the Bi-Ti-O dielectric thin film, the respective films were vapor-deposited by a high-frequency magnetron sputtering method using a binary target. The MgO (100) substrate 5 is used as the substrate, and the sputtering target in air is 90%.
Bi ₂ Sr _{2 of} mixed oxides calcined at 0 ° C. for 5 hours
Ca ₂ Cu ₃ O _{10 + x} disk target 1 and Bi ₄ Ti
₃ O _{12 + y} disk target 2 was used. As the sputtering gas, a mixed gas of Ar and O ₂ (Ar: O
₂ = 1: 9, 0.5 Pa) was used. Each target 1,
2 is about 3 so as to focus on the MgO (100) substrate 5.
It is installed at an angle of 0 °. Shutters 3 and 4 are provided in front of the targets 1 and 2, respectively.
The Sr-Ca-Cu-O superconductor thin film and the Bi-Ti-O dielectric thin film can be continuously laminated on the substrate 5. In FIG. 2, 6 is a heater for heating the substrate.

Targets 1 and 2 are 80 W and 40, respectively
Targets 1 and 2 are sputtered by injecting a sputtering power of W, and a Bi-Sr-Ca-Cu-O superconductor thin film is first formed on the substrate 5 heated to 650 ° C. by the heater 6.
Deposited to a film thickness of 50 nm, and then Bi-Ti-
An O dielectric thin film was laminated and deposited to a film thickness of 50 nm. Bi-
The crystal structure of the thin film after depositing the Ti—O dielectric thin film is as shown in FIG. 1 (c), and the outermost surface of the thin film did not show insulation.

The inventors of the present invention have found that the insulating property is improved by adding Bi and Pb to the Bi-Ti-O target. That is, a Bi ₄ Ti ₃ O _{12 + y} disk target was crushed, TiO ₂ powder and PbO powder were added, and the mixture was fired again.
The Pb-Ti-O dielectric thin film was Bi-Sr-Ca-Cu-
If it is deposited on the O superconductor thin film, Bi-Pb-Ti-
It has been found that the O-dielectric thin film exhibits insulating properties even on the Bi-Sr-Ca-Cu-O superconductor thin film. still,
The TiO ₂ powder and PbO powder were added at a ratio of Ti: Pb = 1: 1. On the Bi-Pb-Ti-O dielectric thin film on the Bi-Sr-Ca-Cu-O superconductor thin film, a Pt electrode having a diameter of 0.3 mm and a film thickness of about 50 nm was spaced by 1.5 mm using a sputtering method. Two vapor deposition at 100Hz to 1MHz
Of the Bi-Pb-Ti-O dielectric thin film from the impedance change with respect to the voltage of amplitude 5V having the frequency of
The resistivity and leak current were measured. The parameter that most accurately expresses the insulating property was the leak current.

FIG. 3 shows the change in leak current with respect to the amount of Ti + Pb added to the Bi-Ti-O dielectric thin film.
As for the amount of Ti + Pb, the ratio of added Ti and Pb is 1: 1.
Therefore, it is represented by z of Bi ₄ Pb _z Ti _{3 + z} O _{12 + y} . It was found that the leakage current decreased when z> 0 and increased again when z ≧ 5. Further, the present inventors also examined the change in leak current for the ratio of Ti and Pb added when z = 2. FIG. 4 shows a change in the leak current of the Bi-Pb-Ti-O dielectric thin film on the Bi-Pb-Ca-Cu-O superconductor thin film with respect to the ratio of added Ti and Pb (Pb / Ti). As is clear from FIG. 4, Ti:
It can be seen that when Pb = 1: 1, the leak current is the smallest and the insulation is excellent. That is, Bi-Pb-
The ratio of elements in the Ti—O dielectric thin film is Bi: Pb: Ti.
= 4: (n-1) :( 2 + n), it can be seen that the insulating property is the best. Here, n is an integer of 1 or more.

The reason why such a good insulator is obtained is still unclear, but it can be considered as follows. That is, Ti is Pb and Pb-T with a ratio of 1: 1.
When a Bi-Pb-Ti-O dielectric thin film is produced in units of i-O, it jumps onto the Bi-Sr-Ca-Cu-O superconductor thin film and is already in an energy stable state. Bi-Sr-
It is considered that this is because no solid solution crystal is formed at the interface with the Ca-Cu-O superconductor thin film.

Furthermore, the present inventors have also found that the Bi-Pb-Ti-O dielectric thin film shown in this Example 1 is excellent as a ferroelectric. That is, Ti, Pb
It has been found that the dielectric constant is higher than that of the Bi-Ti-O dielectric thin film in which is not added. In FIG. 5, Bi-Ti-
3 shows changes in the relative permittivity of a Bi-Pb-Ti-O dielectric thin film at room temperature with respect to the amount of Ti + Pb added to the O dielectric thin film. The inventors also found that the relative permittivity was highest when the ratio of added Ti and Pb was 1: 1.

Furthermore, the present inventors have found that the Bi-based layered ferroelectric substance is (Bi ₂ O ₂ ) ²⁺ (Bi ₂ Pb _{n- 1} Ti _{2 + n} O _{3n + 7} )
Paying attention to the fact that it is represented by a composition formula of ^2- , when a Bi-O layer and a Bi-Pb-Ti-O layer that is a temporary perovskite layer are periodically laminated in atomic order, a Bi-based layered ferroelectric It has been found that the crystallinity and characteristics of the body thin film are improved. When the insulator of the first invention is manufactured by this method, an insulating film having much better controllability, stable film quality, and extremely flat film surface than the manufacturing method shown in the first embodiment is obtained. I found that I could do it.

Bi ₄ Pb _n-1 Ti _{2 + n} O _{3n + 9} crystals are c
Axial direction of (Bi ₂ O ₂ ) ²⁺ layer and (Bi ₂ Pb _n-1 Ti)
It is considered to have a laminated structure composed of _{2 + n} O _{3n + 7} ) ²⁻ layers. This is because by sequentially laminating different elements or unit layers that respectively form a layered structure,
This is because it is considered that the deposited vapor deposition elements move only in the plane parallel to the substrate surface, and that the elements do not move in the direction perpendicular to the substrate surface.

Further, it has been found that the substrate temperature and the heat treatment temperature necessary for obtaining good superconducting properties are lower than those in the conventional case. As a method for producing a Bi-Pb-Ti-O dielectric thin film, Bi-O->(Bi-Pb-Ti-O)-> Bi-
A method of stacking in an O cycle can be considered. Generally, M
A periodic stacking structure can be realized by controlling the opening and closing shutter in front of the evaporation source with a BE apparatus or a multi-source EB vapor deposition apparatus, or by switching the type of gas when the vapor phase growth method is used. However, conventionally, sputtering deposition has been unsuitable for stacking such a very thin layer. It is considered that the reason is that there is contamination by impurities due to high gas pressure during film formation and damage by particles having high energy. However, the present inventors have found that when a different thin layer is laminated on this Bi-Ti-O dielectric thin film by sputtering vapor deposition, a good laminated film can be produced.

As a method of laminating different substances by sputtering vapor deposition, there is a method of periodically controlling the discharge position of one sputtering target having a composition distribution, but a plurality of targets having different compositions are sputtered. This can be achieved relatively easily by using this method. In this case, the periodic laminated film can be manufactured by periodically controlling the sputtering amount of each of the plurality of targets, or by providing a shutter in front of the target and periodically opening and closing it. Also, a periodic laminated film can be similarly produced by adopting a method of moving the substrate over each target by periodically moving the substrate. When laser sputtering or ion beam sputtering is used, a periodic laminated film can be realized by periodically moving a plurality of targets and periodically changing the targets for beam irradiation. By adopting sputtering deposition using a plurality of targets in this way, it becomes possible to relatively easily form a periodic laminated film of Bi—Pb—Ti—O-based oxide.

(Embodiment 2) In Embodiment 2 as well, the apparatus shown in FIG. 2 was used as in Embodiment 1. In FIG. 2, 1 is B
i metal disk target, 2 is Bi-Pb-Ti-
O burning disc target. As the substrate 5, Bi-Sr-Ca- which was already formed on MgO (100) was used.
A Cu-O superconductor thin film was used. Shutters 3 and 4 are provided in front of the targets 1 and 2, respectively, so that the cycle and sputtering time of each target 1 and 2 can be set. As the sputtering gas, a mixed gas of Ar and O ₂ (Ar: O ₂ = 4:
1, 1.0 Pa) was used.

Targets 1 and 2 are 60 W and 20 respectively
Targets 1 and 2 were sputtered by injecting 0 W of sputter power, and (Bi-
A Bi-Pb-Ti-O dielectric thin film was produced by a cycle of (O)->(Bi-Pb-Ti-O)-> (Bi-O).

Bi-Pb-Ti produced in this way
The leak current of the -O dielectric thin film was measured in the same manner as in Example 1. The result is shown in FIG. As shown in FIG. 6, it was found that the leak current is reduced by about one digit by adopting the above method as a method for forming the insulating film (see FIG. 4). The reason why the leak current is reduced is (B
It is considered that the original characteristics of the layered crystal were improved by sequentially stacking the (i-O) layer and the (Bi-Pb-Ti-O) layer.

(Embodiment 3) FIG. 7 schematically shows a cross-sectional view of the thin film produced in this Embodiment 3. As shown in FIG. 7, a Bi-Sr-Ca-Cu-O superconductor thin film and Bi were formed on the substrate.
-Pb-Ti-O dielectric thin films were alternately laminated. As a laminating method, a binary high frequency magnetron sputtering method was used as in Example 1. Firing Bi- as target 1
Sr-Ca-Cu-O, Bi-Pb as the target 2
-Ti-O, Bi-Sr-Ca-Cu-O superconductor thin film 100 nm and Bi-Pb-Ti-O dielectric thin film were alternately sputtered for 5 cycles to obtain Bi-Pb-Ti-O dielectric thin film. The change in the resistivity of the thin film was investigated by changing the film thickness of. The result is shown in FIG. As shown in FIG. 8, Bi-Pb-
It was possible to obtain the highest superconducting transition temperature and zero resistance temperature, that is, characteristic 8, when the Ti—O dielectric thin film had a thickness of 20 nm. The superconducting transition temperature and zero resistance temperature of characteristic 8 are B
It was about 8 Kelvin higher than the original values of the i-Sr-Ca-Cu-O superconductor thin film. Although the detailed reason for this effect is still unknown, as shown in FIG.
-Sr-Ca-Cu-O superconductor thin film and Bi-Pb-T
By periodically laminating an i-O dielectric thin film, B
i-Sr-Ca-Cu-O superconductor thin film and Bi-Pb-
Since the Ti—O dielectric thin film and the Ti—O dielectric thin film are epitaxially grown on each other through the Bi ₂ O ₂ layer, there is no influence of mutual diffusion of elements at the stacking interface, and the thin Bi—Pb is excellent in crystallinity.
B, which is also excellent in crystallinity via a -Ti-O dielectric thin film
It is considered that by laminating the i-Sr-Ca-Cu-O superconductor thin film, some change was caused in the superconducting mechanism in the Bi-Sr-Ca-Cu-O superconductor thin film, but the mechanism is Not clear yet.

(Embodiment 4) FIG. 9 shows a schematic view of a thin film forming apparatus used in this Embodiment 4. In the fourth embodiment,
Bi-Sr-Ca-Cu-O superconductor thin film and Bi-Pb
In order to continuously stack the —Ti—O dielectric thin film, 3
Each film was vapor-deposited by the high frequency magnetron sputtering method of the original target. MgO (10
0) The substrate 16 is used, and the sputtering target is a Bi disk target 10 or a calcined Sr-Ca-C.
u-O disk target 11 and fired Bi-Pb-T
The i-O disk target 12 was used. Here, the element ratio of the target 11 is Sr: Ca: Cu = 2: 2:
3, the element ratio of the target 12 is Bi: Pb: Ti =
It is 2: 2: 5. Each target 10, 11, 12
Approximately 30 ° to focus on the MgO (100) substrate 16.
It is installed at an angle. Shutters 13, 14 and 15 are provided in front of the targets 10, 11 and 12, respectively, so that films can be separately deposited from the targets 10, 11 and 12 onto the substrate 16. Then, by controlling opening / closing of the shutters 13, 14, 15, (Bi-O) → (Sr-Ca-Cu-
O) → (Bi−O) cycle and (Bi−O) → (Bi
Sputter deposition can be performed in the cycle of -Pb-Ti-O)-> (Bi-O). In FIG. 9, 17 is a heater for heating the substrate. The state of stacking is conceptually shown in FIG. 7, but by controlling the input power to the targets 10, 11, 12 and the sputtering time of each target 10, 11, 12 to deposit Bi on the substrate 16, Sr-C
The film thickness of the a-Cu-O superconductor thin film and the Bi-Pb-Ti-O dielectric thin film can be changed.

The substrate 16 is heated to about 700 by the heater 17.
Heated to 0 ° C. and mixed with argon / oxygen (1: 1) atmosphere of 0.
The targets 10, 11 and 12 were sputtered in a gas of 5 Pa. Then, after forming the thin film, heat treatment was performed at 850 ° C. for 5 hours in an oxygen atmosphere. In Example 4, the composition ratio of elements of the Bi-Sr-Ca-Cu-O superconductor thin film was Bi: Sr: Ca: Cu = 2 :.
The sputtering time and sputtering current were adjusted so that the composition ratio of the elements of the Bi-Pb-Ti-O dielectric thin film was 2: 2: 3, Bi: Pb: Ti = 4: 2: 5. According to the present inventors, 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-Pb-Ti-O)-> (Bi
-O)] was performed for 20 cycles. As a result, Bi-Pb that can be produced while maintaining a good crystal structure
The film thickness of the —Ti—O dielectric thin film was limited to i = 2.
Therefore, the present inventors investigated the temperature change of the resistivity of the thin films produced by changing h when i = 2. The result is shown in FIG. In FIG. 10, 18 is h = 2, 19 is h
= 6 and 20 are the results when h = 10. As is apparent from FIG. 10, it was found that when h = 6, the superconducting transition temperature and the zero resistance temperature were the highest compared with the case where the insulating film Bi-Pb-Ti-O dielectric thin film was not laminated. The physical cause of this is not clear, but Bi-Sr-Ca-
This is probably because both the Cu-O superconductor thin film and the Bi-Pb-Ti-O dielectric thin film could be laminated with extremely good controllability.

Further, the inventors of the present invention have confirmed that Bi oxide, Sr, Ca, Cu and T may be used without using the sputtering method.
When the oxides of i and Pb are separately evaporated in a vacuum from different evaporation sources and the same structure is periodically stacked, the stacked structure manufacturing method using sputtering shown in Examples 2 and 4 is performed. It was also found that it is possible to obtain a thin film with good controllability and stable film quality. Bi-O, Sr
There are several possible methods for periodically stacking -Ca-Cu-O and Bi-Pb-Ti-O. In general, a periodic stacking structure can be realized by controlling the opening and closing shutter in front of the evaporation source with an MBE apparatus or a multi-source EB vapor deposition apparatus, or by switching the gas type when manufacturing by the vapor phase growth method. it can. However, conventionally, sputtering deposition has been unsuitable for stacking such a very thin layer. It is considered that the reason is that there is contamination by 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 by laminating different thin layers on the Bi-based oxide superconductor or the insulating thin film by sputtering deposition. Due to the high oxygen gas pressure during sputtering and sputter discharge, introduction of oxygen into the film is promoted, reproducibility and stabilization of superconducting characteristics are achieved, and formation and insulation of a Bi-based phase having a critical temperature of 100 Kelvin or higher. This is probably because it is convenient for forming a thin film.

As a method of laminating different substances by sputtering vapor deposition, there is a method of periodically controlling the discharge position of one sputtering target having a composition distribution, but a plurality of targets having different compositions are sputtered. This can be achieved relatively easily by using this method. In this case, the periodic laminated film can be manufactured by periodically controlling the sputtering amount of each of the plurality of targets, or by providing a shutter in front of the target and periodically opening and closing it. Further, even if a method of moving the substrate periodically to move it over each target is adopted, the periodic laminated film can be similarly produced. When laser sputtering or ion beam sputtering is used, a periodic laminated film can be realized by periodically moving a plurality of targets and periodically changing the targets for beam irradiation. By adopting the sputtering deposition using a plurality of targets in this way, it becomes possible to relatively easily form the periodic stacking film of the Bi-based oxide.

[0040]

As described above, the insulator according to the present invention has a crystal structure covered with a Bi ₂ O ₂ oxide film layer which is extremely stable in terms of heat or a layer mainly containing the Bi ₂ O ₂ oxide film layer. However, since the formation temperature is almost the same as that of the oxide superconductor, the crystallinity and characteristics of the insulator and the superconductor thin film according to the present invention are maintained even if the oxide high temperature superconductor is brought into contact with the oxide superconductor and the high temperature heat treatment is performed. Do not deteriorate each other. Furthermore, the crystal structure of the insulator of the present invention is the same perovskite structure as that of the oxide superconductor, and in particular, since the lengths of the a-axis and the b-axis are almost equal, a stable continuous lamination of the oxide superconductor and the insulator is achieved. Is possible.

Further, according to the method for producing an insulator of the present invention, in order to achieve the above-mentioned constitution of the insulator, an oxide layer containing at least Bi and at least Bi and Pb are formed on the substrate.
By alternately stacking Ti and an oxide layer containing Ti, a stacked structure of a Bi-based superconductor thin film and an insulating film can be realized with good reproducibility, and it is necessary for the design of Josephson devices. It is possible to stably form an interlayer insulating film having a thickness of several 10 nm or less.

According to the superconducting thin film of the present invention, the Bi-based superconducting thin film having the crystal structure covered with the Bi ₂ O ₂ oxide film layer or the layer mainly composed of the Bi ₂ O ₂ oxide film layer and the first superconducting thin film. By adopting a structure in which the thin film of the insulator according to the invention is alternately laminated, it is possible to realize a laminated structure without mutual diffusion of elements between the superconductor thin film and the insulating film, and as a result, Bi The superconducting transition temperature in the system superconductor thin film can be stably realized with good reproducibility.

According to the method for producing a superconductor thin film according to the present invention, in order to realize the superconductor thin film according to the third invention extremely stably and on a fine scale, 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 Pb are periodically laminated and deposited. It is possible to realize the lamination of the superconducting system thin film and the insulating film with good reproducibility.

[Brief description of drawings]

FIG. 1 is a Bi-Ti-O dielectric thin film, a Bi-Sr-Ca-Cu-O superconductor thin film, and a Bi-Ti-O dielectric thin film according to an embodiment of the present invention.
It is a figure which shows the X-ray-diffraction spectrum of a Ti-O / Bi-Sr-Ca-Cu-O laminated thin film.

FIG. 2 is a schematic view of a thin film forming apparatus used in Example 1 of the present invention.

FIG. 3 is a diagram showing changes in leak current with respect to the amount of Ti + Pb added to the Bi—Ti—O dielectric thin film of Example 1 of the present invention.

FIG. 4 is a graph showing changes in leak current with respect to the ratio of added Ti and Pb in the Bi-Pb-Ti-O dielectric thin film of Example 1 of the present invention.

FIG. 5: Bi-Pb at room temperature with respect to the amount of Ti + Pb added to the Bi-Ti-O dielectric thin film of Example 1 of the present invention.
It is a figure which shows the change of the relative dielectric constant of a -Ti-O dielectric thin film.

FIG. 6 is a diagram showing changes in leak current with respect to the amount of Ti + Pb added to the Bi—Pb—Ti—O dielectric thin film of Example 2 of the present invention.

FIG. 7: Bi-Pb-Ti produced in Example 3 of the present invention
It is a schematic diagram showing a laminated structure crystal of a -O ferroelectric / Bi-Sr-Ca-Cu-O superconductor.

FIG. 8: Bi-Sr-Ca produced in Example 3 of the present invention
It is a figure which shows the temperature change of the resistivity of a -Cu-O superconductor thin film.

FIG. 9 is a schematic view of a thin film forming apparatus used in Example 4 of the present invention.

FIG. 10: Bi-Sr-Ca-Cu of Example 4 of the present invention
It is a figure which shows the temperature change of the resistivity of a -O superconductor thin film.

[Explanation of symbols]

 1, 2, 10, 11, 12 Sputtering target 3, 4, 13, 14, 15 Shutter 5, 16 Substrate 6, 17 Heater for heating the substrate

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location H01B 12/06 ZAA 13/00 565 D H01L 39/24 ZAA D

Claims (5)

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