JP2704625B2 - Method for producing LnA lower 2 Cu lower 3 O-low 7-x single crystal thin film and LnA lower 2 Cu lower 3 O lower 7-x thin film having three-layer perovskite structure - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to LnA ₂ Cu ₃ O _7-x having a three-layer perovskite structure, which is attracting attention as exhibiting superconductivity near 90 K ( Where Ln is Y, Nd, Sm, Eu, Gd, D
A means a rare earth metal element selected from y, Ho, Er, Tm and Yb, and A means an alkaline earth metal element selected from Ba, Sr and Ca. ).

More specifically, the present invention relates to a single crystal thin film of the above substance and a method suitable for producing the same.

LnA ₂ Cu ₃ O _7-x film having a three-layer perovskite structure showing superconductivity near 90K is considered for new applications as LSI wiring, SQUID, Josephson tunnel type device, etc.

For this use, the film has a Tc of 85K or more and a Jc of 10 ⁵ A / cm
It is necessary that the thin film having a current density of ² or more and having a thickness of 5000 ° or less have the above characteristics, and the formation temperature of these films be low.

As a material for LSI wiring, a high current density is required, so a single crystal film with a specific surface parallel to the film surface such that a current flows through the (001), (110), and (103) planes is required. is necessary.

On the other hand, the Josephson tunnel-type element has an ultra-thin insulating film for a tunnel junction of 30 mm or less, and in order to form such a junction, a superconductive film having excellent surface smoothness or a It is necessary to make an ultra-thin layer. The thickness of the insulating ultra-thin film used for bonding is limited by the length of coherence of the superconductor. The coherence length in the direction perpendicular to the (001) plane is about 4 to 7 mm, and that in the parallel direction is 15 to
It is said to be 30Å.

Therefore, the thickness of the ultra-thin insulating film used for bonding differs depending on the type of superconductor to be bonded, and the direction perpendicular to the (001) plane of the superconductor is In relation to the thickness direction of the ultra-thin insulating film, the thickness of the ultra-thin insulating film must be 10 mm or less. On the other hand, if the direction parallel to the (001) plane of the superconductor is the direction of the insulating ultrathin film, the thickness of the insulating ultrathin film may be several tens of millimeters. Is convenient.

Therefore, a single crystal film grown on the (110) plane is advantageous for the tunnel junction.

As described above, a single crystal film whose (110) plane is parallel to the film surface is required for application, but a single crystal film whose other specific surface is parallel to the film surface can also achieve a high current density. For,
It is convenient when making a superconducting magnet by making it linear.

[Conventional technology]

The LnA ₂ Cu ₃ O _7-x single crystal film is overwhelmingly produced by a sputtering method. This sputtering method
A target of an Ln-A-Cu-based composite oxide is manufactured, and then this target is set in a vacuum chamber, and O ₂
Or / and irradiation with Ar plasma, placed in the same tank
LnA ₂ Cu ₃ O _7-x is produced by depositing an injection metal or the like from a target on a substrate such as a SrTiO single crystal. In order to make LnA ₂ Cu ₃ O _7-x a film exhibiting high quality superconductivity of 77K or more, heat treatment at 800 ° C. or more is required.

On the other hand, at the IBM Watson Laboratory and Stanford University in the United States, thin films are synthesized by electron beam evaporation, but the film after evaporation is amorphous and does not show superconductivity as it is. This deposited film is then
Only after heat treatment at a high temperature of 0 ° C. and crystallization into a three-layered perovskite, superconductivity above 77K is exhibited.

[Problems to be solved by the invention]

The conventional sputtering method and electron beam evaporation method described above do not yet provide a film that can be said to be a substantially single crystal in which the (001) plane, the (110) plane, or the (103) plane is parallel to the film plane. , And both have problems in method.

For example, with a conventional sputtering method, it is not easy to manufacture a target used for sputtering. Also,
Because the method of attacking the target with plasma is exclusively used for manufacturing the target, not only the properties of the target change subtly depending on the conditions of the plasma atmosphere and the quality of the target, but also The target object is likely to change due to the attack of the target object or the like during generation, and there is a problem in reproducibility as a manufacturing method.

The further problem is that the epitaxial growth
In order to make the superconducting transition point of the LnA ₂ Cu ₃ O _7-x oxide film 77K or more, preferably 85K or more, heat treatment at a temperature of 800 ° C or more is necessary. Due to this heat treatment, the surface of the film becomes uneven, and a film having a smooth surface cannot be obtained. In addition, a reaction occurs between the substrate and LnA ₂ Cu ₃ O _7-x due to the high-temperature heat treatment, and 5000
超 Superconductivity cannot be obtained with the following ultrathin films.

The example obtained at the lowest temperature by the conventional sputtering method is 550
2000 fabricated on sapphire substrate heated to ~ 650 ° C
A thin film of YBa ₂ Cu ₃ O _7-x with a thickness of ~ 3000Å is oriented in the (001) plane and is heat-treated at 550-650 ° C to 80K
It is a report that the electrical resistance has become zero.

However, 80 K is still insufficient, and it is considered that the film is non-uniform from the temperature change of X-rays and electric resistance.

On the other hand, in the case of the conventional electron beam evaporation method, a high-temperature heat treatment is required for the deposited film, and therefore, the material of the substrate that can be used is limited. The chemical change causes a problem that a part or all of the deposited film becomes different from the intended purpose.

In addition, the quality of the film is poor in surface smoothness,
In addition, the film thickness is 5000
が あ る There is a problem that it is difficult to make it below.

In view of the above-described circumstances, the present invention has repeatedly studied a deposition method capable of directly forming LnA ₂ Cu ₃ O _7-x having a layered provskite structure on a deposition substrate with good reproducibility. The present invention has been completed.

[Means for Solving the Problems] and [Operation] That is, the present invention firstly provides the following (1), (2), and (3)
The present invention relates to a single-crystal LnA ₂ Cu ₃ O _7-x thin film shown in FIG.

(1) A LnA ₂ Cu ₃ O _7-x thin film having a three-layer perovskite structure, in which the (001) plane of the crystal is parallel to the film surface and the thin film is a single crystal as a whole A single-crystal LnA ₂ Cu ₃ O _7-x thin film having a three-layer perovskite structure, characterized by:

(2) A LnA ₂ Cu ₃ O _7-x thin film having a three-layer perovskite structure, in which the (110) plane of the crystal is parallel to the film surface, and the thin film is a single crystal as a whole. LnA ₂ Cu ₃ O _7-x single crystal thin film with characteristic three-layer perovskite structure.

(3) A LnA ₂ Cu ₃ O _7-x thin film having a three-layer perovskite structure, in which the (103) plane of the crystal is parallel to the film plane and the thin film as a whole is a single crystal A single-crystal LnA ₂ Cu ₃ O _7-x thin film having a three-layer perovskite structure, characterized by:

Secondly, the present invention relates to the following methods (4) and (5) which are suitable for producing the above-mentioned single crystal thin film of LnA ₂ Cu ₃ O _7-x .

(4) Oxygen gas is injected from the vicinity of the surface of the deposition substrate in the vacuum deposition tank from the vicinity thereof, and the oxygen gas pressure is set to 10 ^-2 to 10 ^-1 Torr only near the surface of the deposition substrate, and the vicinity of the substrate is removed. The oxygen gas pressure in the vacuum deposition tank is 10 ^-5 to 10 ^-3 Torr,
A three-layer perovskite characterized by simultaneous vaporization of Ln, A, and Cu metals from separate evaporation sources onto a substrate while controlling the Ln: A: Cu atomic ratio to approximately 1: 2: 3 Manufacturing method of LnA ₂ Cu ₃ O _7-x thin film with structure.

(5) Oxygen gas is sprayed from the vicinity of the surface of the deposition substrate in the vacuum deposition method tank, the oxygen gas pressure is set to 10 ^-2 to 10 ^-1 Torr only near the surface of the deposition substrate, and the vicinity of the substrate is reduced. Oxygen pressure in the vacuum evaporation tank was set to 10 ^-5 to 10 ^-3 Torr while plasma was generated in the vacuum evaporation tank, and Ln, A, and Cu were separated from separate evaporation sources by Ln: A: Cu. Atomic ratio of about 1: 2: 3
LnA ₂ Cu ₃ O with a three-layer perovskite structure characterized by simultaneous evaporation on the substrate while controlling
Manufacturing method of _7-x thin film.

LnA ₂ Cu ₃ O produced by the above-mentioned processes (4) and (5)
Whether the _7-x thin film becomes polycrystalline or single crystal, or what kind of single crystal, whether the substance used as the deposition substrate is polycrystalline, single crystal, or even It depends on what kind of single crystal it is.

That is, Ln having the three-layer perovskite structure of (1) described above.
In order to obtain a single crystal thin film of A ₂ Cu ₃ O _7-x by the method (4) or (5), it is necessary to use SrTiO ₃ , MgO, CoO, N
A single crystal such as iO may be used and the following method (6) may be used.

(6). In the method according to (4) or (5), a single crystal is used as a deposition substrate, and the single crystal is used as the (001)
LnA ₂ Cu ₃ O having a three-layer perovskite structure according to (1), wherein the surface is used so that the surface becomes the substrate surface.
Manufacturing method of _7-x single crystal thin film.

Similarly, in order to obtain the single crystal thin film of the above (2), the following method (7) may be used.

(7). In the method according to (4) or (5), a single crystal is used as a deposition substrate, and the single crystal is used as the (110)
LnA ₂ Cu ₃ O having a three-layer perovskite structure according to (2), wherein the surface is used so that the surface becomes the substrate surface.
Manufacturing method of _7-x single crystal thin film.

Furthermore, the production method (4) or (5) can also be used for producing a polycrystalline thin film of LnA ₂ Cu ₃ O _7-x having a three-layer perovskite structure, in which case the deposition substrate is not particularly limited.

As described above, in order to obtain a single crystal of LnA ₂ Cu ₃ O _7-x as having a specific crystal plane parallel to the surface of the deposition substrate,
It is necessary to use at least a single crystal whose surface is a specific crystal plane as a deposition substrate.

However, the conditions required for the above-mentioned vapor deposition substrate are, of course, the necessary conditions for obtaining a single crystal of LnA ₂ Cu ₃ O _7-x as a crystal having a specific crystal plane parallel to the surface of the vapor deposition substrate. However, this is not a sufficient condition.

That is, appropriate manufacturing conditions are different between the case where the above-mentioned target (1) is manufactured and the case where the above-mentioned target (2) is manufactured.

(8). (6) The method according to (1), wherein the metal is evaporated on a deposition substrate heated to 500 ° C. or higher, wherein LnA ₂ Cu ₃ O having a three-layer perovskite structure according to (1).
Manufacturing method of _7-x single crystal thin film.

(9). In the method described in (7), the metal is evaporated on a deposition substrate heated to 500 ° C. or more and less than 550 ° C., and LnA ₂ Cu ₃ O having a three-layer perovskite structure described in (2) on the surface layer first.
_{A 7-x} single crystal thin film is grown, and then the material obtained here is
LnA ₂ Cu having a three-layer perovskite structure according to (2), wherein the metal is evaporated after heating to 50 ° C. or more.
Manufacturing method of ₃ O _7-x single crystal thin film.

That is, when the object described in (1) is obtained, the above (8)
As described above, a temperature condition of 500 ° C. or more, and more preferably 520 ° C. or more and a temperature that does not adversely affect the deposition substrate and a relatively moderate condition is sufficient, thereby forming a thin film having a very good crystal structure. it can. However,
In the case of obtaining the object described in (2), the temperature in the first step is set at 500 ° C. or higher and lower than 550 ° C., more preferably around 530 ° C., as described in (9) above, on the vapor deposition substrate. Create a condition under which products are easily formed, and in the second stage, further increase the temperature to 550 ° C.
As described above, unless the temperature is preferably set to 600 ° C. or higher, a thin film having good superconducting properties cannot be formed.

In other words, both the thin film obtained in the first step and the thin film obtained in the second step are the objects described in the above (2), but the thin film obtained in the first step is a deposition substrate in the second step. It is the thin film obtained in the second stage that is used as a surface and exhibits good superconducting properties. Therefore, the first-stage operation and the second-stage operation do not always need to be performed continuously, as can be seen in the embodiments described later.

As described above, the crystal plane of the surface of the deposition substrate must be determined and the temperature condition must be determined at the same time, depending on what kind of desired single crystal of LnA ₂ Cu ₃ O _7-x is obtained. Depending on how to determine the temperature conditions, the target material described in (3) as shown in (10) below is used, although the same crystal plane as that in the above-mentioned manufacturing method (9) is used as the substrate surface of the deposition substrate. Can be manufactured.

(Ten). (7) The method according to (3), wherein the metal is evaporated on a deposition substrate heated to 550 ° C. or higher, more preferably 600 ° C. or higher, wherein the LnA ₂ Cu ₃ O has a three-layer perovskite structure. Manufacturing method of _7-x single crystal thin film.

Hereinafter, the production method of the present invention will be described more specifically together with the operation.

First, the vacuum deposition tank initially sets a high vacuum of, for example, about 10 ^-6 Torr, and then continuously injects a small amount of oxygen gas from the vicinity of the deposition substrate toward the surface of the substrate to form a vacuum. While increasing the oxygen gas pressure to 10 ^-2 to 10 ^-1 Torr only in the vicinity of the surface, the gas in the vacuum evaporation tank is continuously evacuated from an appropriate place in the vacuum evaporation tank, and most of the vacuum evaporation except for the vicinity of the evaporation substrate is performed. The oxygen gas pressure in the tank is set to 10 ^-5 to 10 ^-3 Torr.

The reason why the upper limit of the oxygen gas pressure in the portion other than the vicinity of the deposition substrate in the vacuum deposition tank is set to 10 ⁻³ Torr by the first means is that Ln, A, and Cu in the evaporation source in the same tank are deteriorated. Without letting
This is to make the evaporation smooth. On the other hand, the lower limit of 10 ^-5 Torr is the lower limit of the gas pressure required when generating plasma, and when plasma is not used,
There is no technical significance.

Further, the reason why the oxygen gas pressure was increased only in the vicinity of the deposition substrate by the first means is that Cu was reduced at an oxygen gas pressure of 10 ⁻³ Torr or less.
This is because it cannot be oxidized to Cu ^{2+ to} Cu ³⁺ .

The plasma can be generated by placing a high-frequency coil between the evaporation source and the deposition substrate and oscillating the high-frequency between the wall of the vacuum deposition tank. While desirable in the sense of improving the reaction activity, if its generation is strong, it will cause harm, such as attacking the target being generated, so the power used for plasma generation should be 50 W to 500 W, preferably around 100 W .

Secondly, for the evaporation of Ln, a, and Cu, electron beams may be used for Ln and A, and electric resistance heating may be used for Cu.

And at the time of metal evaporation by these evaporating means, by the power determined by preliminary experiments in the vacuum evaporation tank performed prior to the implementation, the evaporation amount of Ln.A.Cu, about 1: 2: 3 Should be set to.

In other words, Ln,
The amount of each metal, A and Cu, evaporating per unit time under the condition of the electric power applied to the evaporation source and forming a deposited film of Ln ₂ O ₃ , AO, CuO was determined by evaporation in a vacuum evaporation tank. Measured for each metal with a film thickness meter installed near the substrate, and Ln,
The evaporation rate of A, Cu may be grasped, and the evaporation amount of Ln, A, Cu at the time of execution may be determined by the amount of electric power applied to the evaporation source.

As described above, the details of the production method have been described, but this production method is particularly evident in comparison with the conventional sputtering method,
Since it can be carried out under operating conditions in which there is no room for impurities and which can be easily controlled, it is suitable for obtaining a target product with good reproducibility.

The present invention is based on the production and structural results of oxide single crystal thin films and artificial superlattice thin films that the inventors have studied for many years. Although the preparation of the oxide thin film of the present invention is based on reactive vapor deposition, it has been found that this method is most suitable for obtaining the object of the present invention in which perfection is required in the crystal structure.

Reactive deposition in the case of forming an oxide refers to a method in which an oxygen gas is introduced into a vacuum chamber, metal atoms are irradiated on a substrate, and an oxide film is formed while reacting on the substrate.

The main reason why this reactive deposition is appropriate is that (a) the amount of oxygen in the oxide can be controlled. (B) A good quality single crystal is produced. The factors that determine the amount of oxygen in (a) are the oxygen pressure, the substrate temperature, the metal deposition rate, and the substrate material, and each can be independently changed, so that the amount of oxygen can be freely controlled. Regarding (b), it has been found that when the deposition substrate is a single crystal, a very good single crystal can be produced. For example, when NiO is formed on the sapphire C surface under the conditions of an oxygen pressure of 4 × 10 ⁻⁴ Torr, a deposition rate of 1 ° / S, and a substrate temperature of 200 ° C., the (111) plane grows parallel to the deposition substrate.
An iO single crystal is produced, and the half-width of the rocking curve of this crystal by X-rays is 0.5 °. When the oxygen plasma is generated by RF excitation, the half width of the rocking curve becomes 0.06 °, and the crystallinity is improved.

In an artificial superlattice in which NiO and CoO are alternately stacked, the rocking curve becomes sharper as the thickness of each layer is reduced, and becomes almost the same as that of the sapphire substrate.

As described above, the reactive vapor deposition method basically has conditions capable of forming a high-quality single crystal, which is considered as follows.

The phenomenon in which the crystal grows while forming a smooth surface is called monolayer growth. Conditions for such growth are (1) growth under thermodynamically close equilibrium conditions (2) Assuming that the latent heat associated with crystallization is L, L / RT is greater than 2.

Regarding (1), (i) the crystal growth rate is slow, and (ii) the conditions are such that atoms are adsorbed in preference to high energy positions on the surface, for example, vacancies, kinks, and steps. (2) can be easily achieved if the growth temperature is low.

In the reactive evaporation method, the condition satisfying (1) is as follows.

Since oxygen molecules are adsorbed only on metal atoms, adsorption-desorption is always performed on the crystal surface, and an equilibrium relationship is established. On the other hand, once adsorbed metal atoms generally do not desorb.
However, the metal atoms having a high energy of the evaporation source can sufficiently diffuse on the surface and can be adsorbed at the high energy position on the crystal surface. The condition (1) is satisfied if the energy distribution of the reached metal atoms is small and the number of reached metal atoms is small enough that the reached atoms do not collide with each other. The vacuum (oxygen pressure) must be reduced to the order of 10 ⁻⁴ Torr or less and the mean free path must be lengthened so that the energy of the metal atoms does not change halfway. Also, metals with low evaporation temperatures, such as Zn
In the case of, the quality of the ZnO single crystal is not good, and it is necessary to excite by RF.

The inventors have found that the reactive evaporation method is the most excellent method that can freely control the conditions of the crystal growth of the oxide, and thus the basic training for such basic training was conducted. The results were applied to the production of oxide superconductors such as LnA ₂ Cu ₃ O _7-x .

〔Example〕

Example 1 A vacuum chamber (750φ × 1000h) was evacuated to 10 ⁻⁶ Torr by an oil diffusion pump. Sapphire deposition substrate (single crystal α-Al ₂ O _3), its surface (0 1 12) surface (10 ^mm × 10 ^mm)
It is used in such a way that
Heat to and maintain at this temperature. Oxygen gas jet nozzles are arranged at two places at both ends of the deposition substrate, and the oxygen gas is directly blown onto the deposition substrate. At this time, the gas pressure is only near the deposition substrate
It rises to 10 ^-2 to 10 ^-1 Torr, but only up to 10 ^-4 Torr near the deposition source far from the deposition substrate. metal
Y, Ba, and Cu are evaporated from independent evaporation sources on an evaporation substrate at an atomic ratio of 1: 2: 3 on an evaporation substrate (for example, Y ... 1
(Å / sec, Ba: 2.3Å / sec, Cu: 1.7Å / sec). Furthermore, a high-frequency coil is placed between the evaporation source and the deposition substrate to oscillate at a high frequency of 100 W to generate oxygen plasma to activate the evaporated metal and promote a reaction on the deposition substrate.

FIG. 1 shows the results of X-ray diffraction measurement of a thin film having a thickness of 1000 ° synthesized by such a method. YBa ₂ Cu ₃ O _7-x
The (013), (103), and (110) peaks characteristic of the structure are clearly observed, indicating that a crystalline film has been obtained.

The evaporation source was electron beam evaporation for Y and Ba,
For Cu, resistance heating evaporation was used. Next, the evaporation method will be described for each.

Y: A 50 g metal ingot (99.9%) was used, placed in a water-cooled crucible, and an electron beam was evaporated on the metal at an acceleration voltage of 5 KV and a filament current of 400 mA.

Evaporation was performed using a 50 g metal ingot (99.9%) as in the case of Ba: Y, with an acceleration voltage of 5 KV and a filament current of 100 mA.

Cu: Alumina crucible wound with tungsten filament is used as a resistance heating evaporation source, and 10 g of metal Cu particles (2 to 3 mm) (99.9999%) are put in the alumina crucible and a current of 10 V, 30 A is passed through the filament. Evaporated.

Example 2 The vacuum chamber (750φ × 1000h) was evacuated to 10 ⁻⁶ Torr by an oil diffusion pump. A single crystal of SrTiO _{3 is used} as a deposition substrate so that its surface becomes a (001) plane (10 ^mm × 10 ^mm ), which is heated to 650 ° by a W-line heater and maintained at this temperature. Oxygen gas jet nozzles are arranged at two places at both ends of the deposition substrate, and the oxygen gas is directly blown onto the deposition substrate. At this time, the gas pressure rises to 10 ^-2 to 10 ^-1 Torr only in the vicinity of the deposition substrate.
Only up to ^-4 Torr. Metal Y, Ba, Cu are evaporated from independent evaporation sources on an evaporation substrate at an atomic ratio of 1: 2: 3 (for example, Y ... 1Å / sec, Ba ... 2.3
(Å / sec, Cu ... 1.7Å / sec). Furthermore, a high-frequency coil is placed between the evaporation source and the deposition substrate to oscillate at a high frequency of 100 W to generate oxygen plasma to activate the evaporated metal and promote a reaction on the deposition substrate.

FIG. 2 shows the result of X-ray diffraction measurement of a thin film having a thickness of 1000 ° synthesized by such a method.
1, × 4, × 30 are magnifications indicating how many times the strength is multiplied in the drawing. ). As shown in the figure, no peak other than (00n) was observed, and it was confirmed that the film was a single crystal.

Also, after heating the thin film obtained above at 650 ° C. for 30 minutes,
When the critical current density at a liquid nitrogen temperature of 77 K was measured by a conventional method, a measured value of 4 million A / cm ² was obtained. This value is
This can be said to be much better than 1.8 million A / cm ² of the conventional YBa ₂ Cu ₃ O _7-x superconductor.

Example 3 In the same manner as in Example 2, a single crystal thin film of YBa ₂ Cu ₃ O _7-x having a three-layered perovskite structure having a thickness of 3000 mm was obtained.
The relationship between the absolute temperature and the specific resistance was measured 10 days after the production of the thin film, and the result shown in FIG. 3 was obtained.

As is apparent from FIG. 3, this thin film showed superconductivity at a little less than 50 K, which is a characteristic that appears when the degree of oxidation (X) is low. This is apparent from FIG. As a precautionary measure, when the thin film was heated in oxygen at 500 ° C for 30 minutes, it showed zero electrical resistance at 90K.

From the above, it can be seen that the single crystal thin film of the present invention is different from the conventional single crystal thin film in that the prepared thin film itself is a material having a characteristic of superconductivity.

Example 4 In producing a single crystal thin film of YBa ₂ Cu ₃ O _{7-x in} the same manner as in Example 2, the following operation was performed to check the properties of the formed thin film.

Sr with polished surface as a deposition substrate for growing thin films
Two types of TiO ₃ single crystals and those obtained by chemically etching them with hydrofluoric nitric acid were used. Scanning electron microscope (SEM) was used to examine three types of the substrate itself, which had not been etched, and a film in which a film was deposited at 300 ° and 1000 °. As a result, it was found that the SrTiO ₃ polished surface was very smooth, and the film deposited on the SrTiO ₃ became a smooth film with good continuity from a very thin film thickness of 300 °. Further, it was found that the film was similarly smooth even when the film thickness reached 1000 mm.

Further, when two types of the etched substrate and the one deposited at 1000 ° on the substrate were examined by SEM, etch pits of several μm appeared on the surface of the etched substrate. The SEM image was almost the same even when the film was deposited at 1000 ° on this, and it was found that the film was grown faithfully covering the substrate surface. This indicates that the surface of the film synthesized according to the present invention has extremely excellent smoothness.

FIG. 4 shows the result of the temperature change of the electric resistance measured after performing the oxygen treatment by the method of Example 5 on the sample deposited at 2000 ° on the polished surface. The temperature at which the electric resistance becomes zero is 90.2K, and the temperature range of the resistance change is also a very narrow value of 1.7K, which indicates that an extremely good-quality superconducting thin film is formed. FIG. 5 shows the temperature change of the AC susceptibility measured for the same sample. The real part (−x ′) of the magnetic susceptibility starts to increase sharply near the temperature where the electric resistance becomes zero, and an imaginary part (x ″) of the magnetic susceptibility also appears. This result indicates that a minor effect was observed where the electric resistance became zero.

From the above facts, it is desirable to use a polished surface with a flat surface as the substrate on which the film is grown, and in that case, the film grown thereon becomes a very good quality superconducting film with a smooth surface. Therefore, it can be said that it is particularly effective when used for electronic devices such as SQUID devices and Josephson devices in the future.

Example 5 Since a thin film after vapor deposition does not always show good superconducting properties, treatment in an oxygen atmosphere is necessary. Therefore, Embodiment 2
A single crystal thin film of YBa ₂ Cu ₃ O _7-x was manufactured in the same manner as in Example _{1 and} the effect of the treatment in an oxygen atmosphere after the deposition was confirmed. After the vapor deposition is completed, wait for the evaporation source to cool down (30 minutes), and then introduce oxygen gas into the vacuum chamber until the pressure becomes 1 atm. At this time, the temperature of the deposition substrate was lowered to 500 ° C., and the film was held at this temperature in 1 atm of oxygen for 1 hour to adjust the oxygen amount of the film. The lattice constant Co in the [001] direction obtained from the X-ray diffraction measurement of the film not subjected to the oxygen treatment was 11.749 °, and that of the film subjected to the oxygen treatment was 11.686 °. The value of the lattice constant after this treatment is almost the same as the lattice constant of a bulk crystal having a superconducting transition temperature of 90K class. The superconducting properties of the film subjected to this treatment are as shown in Example 4.

Example 6 SrTiO ₃ single crystal was used as a deposition substrate, and the surface was (110).
A YBa ₂ Cu ₃ O _7-x single crystal thin film having a thickness of 2000 mm was prepared in the same manner as in Example 2 except that the deposition substrate temperature was set to 520 ° C.

In the above operation, a reflection electron diffraction image of the substrate itself and a reflection electron diffraction image of a single crystal thin film of YBa ₂ Cu ₃ O _7-x having a thickness of 2000 mm were taken, and a three-layer perovskite structure was formed on the (110) plane of the substrate. It was confirmed that the (110) plane of YBa ₂ Cu ₃ O _7-x was epitaxially grown.

In addition, for the single crystal thin film, take further SEM pictures,
The smoothness of the surface was confirmed.

Example 7 In the same manner as in Example 1, a thin film was synthesized on a SrTiO ₃ (001) substrate kept at 640 ° C. by evaporating metal Y and Sr by electron beam heating and evaporating metal Cu by resistance heating. FIG. 6 is an X-ray diffraction pattern measured on a sample having a thickness of 1000 °, and a diffraction peak corresponding to the (005) peak of a three-layer perovskite structure similar to that of YBa ₂ Cu ₃ O _7-x is observed.

Example 8 FIGS. 7 and 8 show X-ray diffraction patterns measured on a film synthesized by changing Ln to Dy and Er in the same manner as in Example 2. FIG. Since no peaks other than (00n) were observed as shown in each figure, it was confirmed that the film was a single crystal. What is characteristic in comparison with the case where Ln is Y is that the (001) peak has the highest intensity in these systems. This is because the plane spacing corresponding to the (001) peak is the spacing between rare earth metal ions, and since Dy and Er have large atomic numbers, the scattering factor for the X-ray becomes large.
This is because diffraction by the repetition becomes strong.

Example 9 An oxygen gas ejection nozzle is inserted into a donut-shaped oxygen diffusion chamber surrounding an outer peripheral edge of a deposition substrate, and oxygen ejected from the oxygen nozzle is once diffused in the oxygen diffusion chamber. A thin film having a thickness of 100 mm was obtained in the same manner as in Example 2 except that a thin layer was ejected from the gap provided on the surface along the surface of the deposition substrate.

The result of X-ray diffraction measurement of the thin film having a thickness of 100 ° obtained as above is as shown in ninth, and since no peak other than (00n) was observed, it was confirmed that the film was a single crystal.

FIG. 10 shows the temperature change of the electrical resistance measured after the thin film was subjected to the oxygen treatment according to the method of the fifth embodiment.
The figure shows the temperature change of the AC susceptibility measured for the same thin film.

From these results, it is clear that even an ultrathin film
It can be seen that a superconducting thin film having zero electrical resistance at 2K was obtained.

Example 10 SrTiO ₃ single crystal was used as a deposition substrate, and the surface was (110)
530 ° C, 550 ° C
A temperature of 580 ° C. or 630 ° C. was obtained in the same manner as in Example 9 to obtain a thin film having a thickness of 500 ° for each of the above temperature conditions.

The thin film 4 kinds obtained here was confirmed by SrTiO ₃ single crystal substrate [001] direction or [1 1 0] reflects the crystal structure of the thin film by irradiating an electron beam from a direction electron diffraction image.

The results are as shown in 12a view, second 15a view ([001] direction from the electron beam irradiation) and the 12b view, second 15b Diagram ([1 1 0] direction from the electron beam irradiation), at 530 ° C. First
As shown in FIGS. 2a and 12b, YBa ₂ Cu having a (110) plane parallel to the (110) plane of the surface of the SrTiO ₃ single crystal as a deposition substrate
A single-crystal thin film of ₃ O _7-x is formed, and at 630 ° C, FIG.
As shown in FIG. 15b, the surface of the SrTiO ₃ single crystal (11
It was found that a single crystal thin film of YBa ₂ Cu ₃ O _7-x having a (103) plane parallel to the (0) plane was formed.

On the other hand, 550 ℃ and 580 ℃ located between 530 ℃ and 630 ℃
In FIG. 13a, FIG. 13b, FIG. 14a, and FIG. 14b, a single crystal thin film of YBa ₂ Cu ₃ O _7-x obtained at 530 ° C.
It was found that a single crystal thin film of YBa ₂ Cu ₃ O _7-x obtained at 0 ° C. was formed in which both crystals coexist.

Next, the single crystal thin film of YBa ₂ Cu ₃ O _7-x having a thickness of 500 ° obtained at 630 ° C. was subjected to oxygen treatment by the method of Example 5, and the temperature change of the electric resistance was measured. The results are as shown in FIG. 16, and it was found that the material exhibited superconductivity at around 80K.

Example 11 Except that _Er was used instead of Y as the evaporation metal, the vapor deposition substrate temperature was 530 ° C., 580 ° C., 63 in the same manner as in Example 10.
At every 0 ° C., a thin film having a thickness of 500 ° was obtained.

The three types obtained here were irradiated with electron beams from two directions in the same manner as in Example 10, and the crystal structure of each thin film was confirmed by a reflected electron diffraction image.

The results are as shown in 17a view, second 19a view ([001] direction from the electron beam irradiation) and 17b view, second 19b Diagram ([1 1 0] direction from the electron beam irradiation), at 530 ° C. The 17a
As shown in FIG. 17B, ErBa having a (110) plane parallel to the (110) plane of the surface of the SrTiO ₃ single crystal as a deposition substrate.
₂ Cu ₃ O _7-x single crystal thin film is formed, and at 630 ° C, FIG.
As shown in FIG. 19b, the surface of the SrTiO ₃ single crystal (11
It was found that a single crystal thin film of ErBa ₂ Cu ₃ O _7-x having a (103) plane parallel to the (0) plane was formed.

On the other hand, at 580 ° C., as seen in FIGS. 18a and 18b, 5
It turns out that a single crystal thin film of ErBa ₂ Cu ₃ O _7-x obtained at 30 ° C and a single crystal thin film of ErBa ₂ Cu ₃ O _7-x obtained at 630 ° C are mixed. did.

Example 12 SrTiO ₃ single crystal was used as a deposition substrate, and the surface was (110)
520 ° C heating temperature of the deposition substrate
First, a thin film having a thickness of 150 ° was obtained in the same manner as in Example 9.

Next, a vapor deposition substrate having a thin film of 150 ° on the surface layer obtained above was directly used as a vapor deposition substrate, and a new film thickness of 850 μm was formed in the same manner as in Example 9 except that the heating temperature of the vapor deposition substrate was changed to 630 ° C. Was obtained.

The thin film having a thickness of 850Å obtained above was confirmed by SrTiO ₃ single crystal of [001] direction or [1 1 0] by irradiating an electron beam from a reflecting direction of the crystal structure of the thin-film electron diffraction image.

The results are as shown in FIGS. 20a and 20b,
It was found that a high-quality single crystal thin film of YBa ₂ Cu ₃ O _7-x having a (110) plane parallel to the (110) plane of the surface of the SrTiO ₃ single crystal was formed.

Next, the single crystal thin film of YBa ₂ Cu ₃ O _7-x having a thickness of 850 mm obtained above was subjected to oxygen treatment according to the method of Example 5, and the temperature change of electric resistance was measured. The result is number 21
As shown in the figure, it was found that superconductivity was exhibited at around 80K.

〔The invention's effect〕

The single-crystal thin film of LnA ₂ Cu ₃ O _7-x having a three-layer perovskite structure of (1), (2) and (3) of the present invention is a single-crystal (0
The (01) plane, the (110) plane, or the (103) plane are crystal growths parallel to the film plane.

Therefore, it has an optimal crystal structure for obtaining a high current density required when used as a film-like superconducting material.

More importantly, when configuring as an element, Ln
If A ₂ Cu ₃ O _7-x is a single crystal, an insulating single crystal such as MgO or a semiconductor single crystal such as silicon oxide can be stacked thereon. This is because when a Josephson device is formed or when superconducting LnA ₂ Cu ₃ O _7-x is used in a semiconductor device, if LnA ₂ Cu ₃ O _7-x is a single crystal, This means that the constituent crystals can be single-crystallized by epitaxial growth. In particular, in the case of a Josephson device, the insulating layer is required to be uniform to several tens of degrees or less.
If the superconductor is a single crystal having a smooth surface such as the thin film according to the present invention, a single crystal insulating layer of MgO or the like can be uniformly laminated to several tens of degrees or less.

Further, according to the present inventions (4) and (5), the perovskite is directly deposited on a vapor deposition substrate at a relatively low temperature of 500 to 800 ° C. under operating conditions in which there is no room for impurities and which is easily controlled. An LnA ₂ Cu ₃ O _7-x thin film having a structure can be formed.

Moreover, in the present invention, it is possible to form a thin film having a small thickness such as 100 ° which is not seen in the conventional proposal.

In particular, the invention (5) has high reproducibility and high utility as a method capable of providing an object even when the temperature of the deposition substrate is around 500 ° C.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction diagram of the thin film of YBa ₂ Cu ₃ O _7-x obtained in Example 1, and FIG. 2 is a diagram of the thin film of YBa ₂ Cu ₃ O _7-x obtained in Example 2. FIG. 3 is an X-ray diffraction pattern. FIG. 3 shows the YBa ₂ obtained in Example 3.
FIG. 4 is a graph showing the electrical resistance-temperature relationship of a thin film of Cu ₃ O _7-x . Further, FIG. 4 is an electric resistance-temperature correlation diagram of a 2000-Å-thick YBa ₂ Cu ₃ O _7-x thin film formed on an unetched SrTiO ₃ single crystal substrate in Example 4, and FIG. FIG. 3 is a graph showing an AC magnetic susceptibility-temperature relationship of the present invention. FIG. 6 is an X-ray diffraction diagram of the YSr ₂ Cu ₃ O _7-x thin film obtained in Example 7. FIG. 7 is an X-ray diffraction diagram of the DyBa ₂ Cu ₃ O _7-x thin film obtained in Example 8, and FIG. 8 is an X-ray diffraction of the ErBa ₂ Cu ₃ O _7-x thin film obtained in Example 8. It is a diffraction diagram. FIG. 9 is an X-ray diffraction diagram of the YBa ₂ Cu ₃ O _7-x thin film obtained in Example 9, FIG. 10 is an electric resistance-temperature correlation diagram of the thin film, and FIG. FIG. 3 is a graph showing an AC magnetic susceptibility-temperature relationship of the present invention. 12a, 13a, 14a, 15a and 12b, 1
3b, 14b and 15b show the YBa ₂ Cu ₃ O obtained in Example 10.
FIG. 16 is a photograph of a backscattered electron diffraction image showing the crystal structure of the _7-x thin film, and FIG. 16 is an electric resistance-temperature correlation diagram of the thin film obtained in Example 10. 17a, 18a, 19a and 17b, 18b, 1
FIG. 9b is a photograph of a backscattered electron diffraction image showing the crystal structure of the ErBa ₂ Cu ₃ O _7-x thin film obtained in Example 11. 20a and 2b are photographs of a reflection electron diffraction image showing the crystal structure of the YBa ₂ Cu ₃ O _7-x thin film obtained in Example 12, and FIG. 21 is a photograph of the thin film obtained in Example 12. It is an electric resistance-temperature correlation diagram.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical indication H01L 39/24 ZAA H01L 39/24 ZAAB (31) Claimed priority number Japanese Patent Application No. 63-33630 (32) ) Priority date February 15, 1988 (1988) February 33 (33) Priority claiming country Japan (JP) (31) Priority claim number Japanese Patent Application No. 63-57207 (32) Priority date March 10, 1988 (1988) (33) Priority claiming country Japan (JP) (56) References JP-A-63-307614 (JP, A) JP-A-1-100021 (JP, A) JP-A-63-248018 (JP, A) JP-A-64-74775 (JP, A) JP-A-63-274697 (JP, A) JP-A-63-315572 (JP, A)

Claims (10)

(57) [Claims] 1. LnA ₂ Cu ₃ O having a three-layer perovskite structure
_7-x thin film at a, LnA ₂ Cu ₃ having a three-layer perovskite structure, characterized in that (001) planes of the crystal forms a parallel to the film surface, and has a single crystal as a whole thin film O _7-x single crystal thin film. Where Ln is Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, T
m means a rare earth metal element selected from Yb, A is Ba,
It means an alkaline earth metal element selected from Sr and Ca. 2. LnA ₂ Cu ₃ O having a three-layer perovskite structure
_7-x thin film at a, LnA ₂ Cu ₃ having a three-layer perovskite structure, characterized in that (110) planes of the crystal forms a parallel to the film surface, and has a single crystal as a whole thin film O _7-x single crystal thin film. Where Ln is Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, T
m means a rare earth metal element selected from Yb, A is Ba,
It means an alkaline earth metal element selected from Sr and Ca. 3. LnA ₂ Cu ₃ O having a three-layer perovskite structure
LnA ₂ Cu ₃ having a three-layer perovskite structure, wherein the (103) plane of the _7-x thin film is parallel to the film surface, and the thin film is a single crystal as a whole. O _7-x single crystal thin film. Where Ln is Y, Nd, Sm, Eu, Gd, Dy, Ho, Er, T
m means a rare earth metal element selected from Yb, A is Ba,
It means an alkaline earth metal element selected from Sr and Ca. 4. An oxygen gas is injected from the vicinity of the surface of a deposition substrate in a vacuum deposition tank from the vicinity thereof, and the oxygen gas pressure is set to 10 ^-2 to 10 ^-1 Torr only in the vicinity of the surface of the deposition substrate. The oxygen gas pressure in the vacuum evaporation tank excluding 10 ^-5 ~ 10 ^-3 Torr, Ln, A, each metal of Cu from a separate evaporation source Ln: A: Cu atomic ratio of about 1: 2: 3 A method for producing an LnA ₂ Cu ₃ O _7-x thin film having a three-layer perovskite structure, characterized in that the thin film is simultaneously evaporated on a substrate while controlling such that Where Ln is Y, N
d means a rare earth metal element selected from Sm, Eu, Gd, Dy, Ho, Er, Tm and Yb, and A means an alkaline earth metal element selected from Ba, Sr and Ca. 5. An oxygen gas is injected from the vicinity of the surface of a deposition substrate in a vacuum deposition tank from the vicinity thereof, and the oxygen gas pressure is set to 10 ^-2 to 10 ^-1 Torr only in the vicinity of the surface of the deposition substrate. The oxygen pressure in the vacuum evaporation tank except for the above was set to 10 ^-5 to 10 ^-3 Torr, while plasma was generated in the vacuum evaporation tank, and each metal of Ln, A, and Cu was separated from a separate evaporation source by Ln: A: The atomic ratio of Cu is about 1: 2: 3
LnA ₂ Cu ₃ O with a three-layer perovskite structure characterized by simultaneous evaporation on the substrate while controlling
Manufacturing method of _7-x thin film. Where Ln is Y, Nd, Sm, Eu, Gd, Dy,
Ho, Er, means a rare earth metal element selected from Tm and Yb,
A means an alkaline earth metal element selected from Ba, Sr and Ca. 6. The method according to claim 4, wherein a single crystal is used as the deposition substrate, and the single crystal is used so that its (001) plane is the substrate surface. The method for producing a single-crystal thin film of LnA ₂ Cu ₃ O _7-x having a three-layer perovskite structure according to claim (1). 7. The method according to claim 4, wherein a single crystal is used as the deposition substrate, and the single crystal is used so that the (110) plane becomes the substrate surface. The method for producing a single-crystal thin film of LnA ₂ Cu ₃ O _7-x having a three-layer perovskite structure according to claim (2). 8. The method according to claim 6, wherein the temperature is 500 ° C.
LnA ₂ Cu ₃ O _7-x preparation of single crystal thin film having a three-layered perovskite structure as claimed in claim 1, wherein the evaporating metal on the deposition substrate heated to above. 9. The method according to claim 7, wherein the temperature is 500 ° C.
The metal is evaporated on a deposition substrate heated to a temperature of less than 550 ° C. to grow a single-crystal thin film of LnA ₂ Cu ₃ O _7-x having a three-layer perovskite structure according to claim (2) on the surface layer. producing a single-crystal thin film of an LnA ₂ Cu ₃ O _7-x having a three-layer perovskite structure according to claim (2), wherein the evaporating metal on heating the obtained here material above 550 ° C. Law. 10. The method according to claim 7, wherein 550
The method for producing a single-crystal thin film of LnA ₂ Cu ₃ O _7-x having a three-layer perovskite structure according to claim 3, wherein the metal is evaporated on a deposition substrate heated to a temperature of not less than ° C.