JP2557446B2 - Method for producing complex oxide-based superconducting thin film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a thin film made of a superconductor. In particular, the present invention relates to a method for producing a composite oxide superconducting thin film having a high critical temperature used for Josephson devices and the like. More specifically, the present invention relates to a method of producing a superconducting thin film of a K ₂ NiF ₄ type oxide such as [La, Ba] ₂ CuO ₄ or [La, Sr] ₂ CuO ₄ .

2. Description of the Related Art By utilizing the superconducting phenomenon that electric resistance becomes zero, it is possible to realize an element or a device having no power loss. Therefore, many products applying this phenomenon have been devised. However, at present, the superconducting phenomenon appears only at extremely low temperatures. For example, among the previously developed superconducting materials, A-15
A group of substances with a structure has a high T _C (superconducting critical temperature), but even the substance with the highest T _C , Nb ₃ Ge, has a T _C of 23.
It is 2K.

In any case, there is no method other than using liquid helium (boiling point 4.2K) for cooling below T _C. By the way, helium is a refrigerant which has a big problem in terms of the limited cost. Furthermore, it is predicted that helium resources will be exhausted globally in the 21st century. In addition, there is a drawback that a large-scale device is required for cooling. From the above background, the emergence of superconducting materials with high T _C has been strongly desired. However, despite various efforts, the discovery of superconducting materials that exceed the above T _C has ceased for the last 10 years. However, in 1986, led to the superconducting oxide having a high T _C is found, the possibility of high-temperature superconductivity has been wide open (Bednorz, Muller, "Z.Phys.B64 ( 1986) 189").

This oxide superconductor means [La, Ba] ₂ CuO ₄ or [L
a, Sr] ₂ CuO ₄ . This oxide superconductor is known as K ₂ NiF ₄ type oxide and has been known for a long time (eg, UP3,
The crystal structure is similar to that of perovskite type superconducting oxide. The T _{C of} these substances is 30 to 50 K, which is a dramatically higher value than the conventional value. When T _C reaches this temperature, liquid hydrogen (boiling point 20.4) is used as a refrigerant for superconductivity.
K) or liquid neon (boiling point 27.3K) can be used. Especially in the case of hydrogen, there is a danger, but unlike helium, there is no fear of resource depletion.

The method of producing a compound or alloy that is a superconducting material includes (a) a method of bulk-mixing raw materials to form a compound or alloy (powder sintering method), and (b) a method of vapor-growing an alloy or compound (vapor phase). Growth method).

FIG. 3 shows the powder sintering method (a) among the above methods.
It is a process drawing showing an example. This method comprises the following steps as shown in FIG.

(1) First, for example, BaCO ₃ , La ₂ O ₃ , CuO, or S
Powders such as rCO ₃ , La ₂ O ₃ and CuO having a particle size of several μm are uniformly mixed.

(2) Next, these powders are molded using a mold or the like.

(3) The molded product is pre-sintered at a predetermined temperature and for a predetermined time.

(4) Take out the molded product and crush it again.

(5) The powder obtained by crushing is molded again.

(6) Sinter this compact.

The vapor phase growth method (b) is used, for example, when forming a thin film of the compound Nb ₃ Ge which is a superconducting material. At this time, the target is to sputter Nb and Ge particles from a target consisting of Nb and Ge alone to form a film made of a compound of Nb ₃ Ge on the substrate on which the film is to be formed. Also JP-A-56-109,824, a method of manufacturing a thin film sputtering of BaPb _1-x Bi _x O ₃ is described.

However, regarding the above-mentioned composite oxide superconducting material,
Since it was only a few days since the discovery, it was only developed as a powdered sintered body, so the method for forming it as a thin film has not yet been established. That is, K ₂ NiF ₄
Conventionally, the type oxide has been produced by molding raw material powder and then sintering it. Therefore, it is possible to use this sintered body as a bulk superconductor, but the composite oxide superconducting material obtained by the powder sintering method is not suitable for microfabrication as well as thin film formation, and is not suitable for various electronic devices. It cannot be used for purposes such as.

Therefore, an object of the present invention is to provide a novel method for forming a K ₂ NiF ₄ type oxide as a thin film.

Means for Solving the Problems That is, according to the present invention, La and Ia of the periodic table of elements, I
In a method for producing a superconducting thin film comprising a complex oxide containing one element M selected from the elements contained in the groups Ia and IIIa, and Cu, a compound containing at least La and the above elements M and Cu. There is provided a method characterized in that sputtering is carried out using a target consisting of a mixture of

Here, according to a preferred embodiment of the present invention, the composition ratio of La in the thin film obtained by the above-mentioned sputtering, the element M and Cu, that is, the atomic ratio, is represented by the formula: (La _1-x M _x ) ₂ CuO _4-y ( Here, M is an element selected from the group included in the Ia, IIa, and IIIa groups of the periodic table, and x and y are numbers satisfying 0 <x <1 and 0 ≦ y <4, respectively. It is preferable to use a mixture in which the composition ratio of La, the element M and Cu is adjusted so that

Specific examples of the element M include Ba and Sr. Examples of the mixture include oxides, carbonates, nitrates or sulfates of the elements, La ₂ O ₃ , BaCO ₃ and Cu.
A powder mixture mixed like O can be exemplified,
Furthermore, this mixed powder contains 70-95% by weight of La ₂ O ₃ and 1-2
It can be a mixed powder of 0 wt% SrCO ₃ and 1-30 wt% CuO.

The mixture may be a sintered body obtained by sintering a mixed powder of a compound containing La, the element M and Cu. In the sintering, it is also advantageous to perform the sintering of the mixed powder by a powder hot pressing or a powder hot isostatic pressing (HIP).

Here, according to a preferred embodiment of the present invention, in the composition formula, the element M is Ba and x is 0.025 ≦ x ≦.
It may be in the range of 0.125. Further, as another preferred embodiment of the present invention, in the above composition formula, the element M is Sr and x is in the range of 0.09 ≦ x ≦ 0.25.

In the method of the present invention, the substrate temperature during vapor deposition of the thin film may be 100 to 1200 ° C. as a preferable temperature range.

Further, as a preferred embodiment of the invention, a thin film is formed after the film formation.
The heat treatment may be performed at 600 to 1200 ° C.

The film formation is advantageously performed in the presence of oxygen gas, and the partial pressure of oxygen gas can be preferably set in the range of 10 ^{−6 to} 5 × 10 ⁻² Torr. In addition, the voltage applied to the substrate during film formation may be in the range of 0 to 1500V as a preferable range.

The superconducting thin film thus obtained according to the present invention is K ₂ Ni
It is considered to mainly contain a complex oxide having an F ₄ type crystal structure.

Next, according to the present invention, La and Ia, II of the periodic table of elements are
In a method for producing a superconducting thin film composed of a complex oxide containing one element M selected from the elements included in a and IIIa groups, and Cu, La in the obtained thin film, the above elements M and Cu The composition ratio, that is, the atomic ratio, of the formula: (La _1-x M _x ) ₂ CuO _4-y (where M is an element selected from the group included in the groups I a, II a, and III a of the periodic table). And x and y are numbers satisfying 0 <x <1 and 0 ≦ y <4 respectively), and sintering after mixing powders of La, the above-mentioned elements M and Cu alone or a compound thereof A method is provided in which sputtering is performed using the sintered body obtained as a target as a target, and after the film formation by the sputtering, the thin film is heat-treated in a temperature range of 600 to 1200 ° C.

Here, according to a preferred embodiment of the present invention, the composition ratio of La in the thin film obtained by the above-mentioned sputtering, the element M and Cu, that is, the atomic ratio, is represented by the formula: (La _1-x M _x ) ₂ CuO _4-y ( Here, M is an element selected from the group included in Ia, IIa, and IIIa groups of the periodic table, and x and y are numbers satisfying 0 <x <1 and 0 ≦ y <4, respectively. It is preferable to adjust the composition ratio of La, the element M and Cu so that

Specific examples of the element M include Ba and Sr. Examples of the mixture include oxides, carbonates, nitrates or sulfates of the elements, La ₂ O ₃ , BaCO ₃ and Cu.
A powder mixture mixed like O can be exemplified,
Furthermore, this mixed powder contains 70-95% by weight of La ₂ O ₃ and 1-2
It can be a mixed powder of 0 wt% SrCO ₃ and 1-30 wt% CuO.

The mixture may be a sintered body obtained by sintering a mixed powder of a compound containing La, the element M and Cu. In the sintering, it is also advantageous to perform the sintering of the mixed powder by a powder hot pressing or a powder hot isostatic pressing (HIP).

Here, according to a preferred embodiment of the present invention, in the composition formula, the element M is Ba and x is 0.025 ≦ x ≦.
It may be in the range of 0.125. Further, as another preferred embodiment of the present invention, in the above composition, the element M is Sr and x is in the range of 0.09 ≦ x ≦ 0.25.

Further, as a preferred embodiment of the invention, a thin film is formed after the film formation.
The heat treatment may be performed at 600 to 1200 ° C.

The film formation is advantageously performed in the presence of oxygen gas, and the partial pressure of oxygen gas can be preferably set in the range of 10 ^{−6 to} 5 × 10 ⁻² Torr. In addition, the voltage applied to the substrate during film formation may be in the range of 0 to 1500V as a preferable range.

The superconducting thin film thus obtained according to the present invention is K ₂ Ni
It is considered to mainly contain a complex oxide having an F ₄ type crystal structure.

Furthermore, according to the present invention, La and Ia, II of the periodic table of elements are
In a method for producing a superconducting thin film composed of a complex oxide containing one element M selected from the elements included in a and IIIa groups, and Cu, La in the obtained thin film, the above elements M and Cu The composition ratio, that is, the atomic ratio, of the formula: (La _1-x M _x ) ₂ CuO _4-y (where M is an element selected from the group included in the groups I a, II a, and III a of the periodic table). And x and y are numbers satisfying 0 <x <1 and 0 ≦ y <4 respectively), and sintering after mixing powders of La, the above-mentioned elements M and Cu alone or a compound thereof Using the obtained sintered body as a target, sputtering is performed at a substrate temperature of 100 to 1200 ° C., and, after film formation by the sputtering, a thin film is heat treated in a temperature range of 600 to 1200 ° C. Will be provided.

Here, according to a preferred embodiment of the present invention, the composition ratio of La in the thin film obtained by the above-mentioned sputtering, the element M and Cu, that is, the atomic ratio, is represented by the formula: (La _1-x M _x ) ₂ CuO _4-y ( Here, M is an element selected from the group included in the Ia, IIa, and IIIa groups of the periodic table, and x and y are numbers satisfying 0 <x <1 and 0 ≦ y <4, respectively. It is preferable to adjust the composition ratio of La, the element M, and Cu so that

Specific examples of the element M include Ba and Sr. Examples of the mixture include oxides, carbonates, nitrates or sulfates of the elements, La ₂ O ₃ , BaCO ₃ and Cu.
A powder mixture mixed like O can be exemplified,
Furthermore, this mixed powder contains 70-95% by weight of La ₂ O ₃ and 1-2
It can be a mixed powder of 0 wt% SrCO ₃ and 1-30 wt% CuO.

The mixture may be a sintered body obtained by sintering a mixed powder of a compound containing La, the element M and Cu. In the sintering, it is also advantageous to perform the sintering of the mixed powder by a powder hot pressing or a powder hot isostatic pressing (HIP).

Here, according to a preferred embodiment of the present invention, in the composition formula, the element M is Ba and x is 0.025 ≦ x ≦.
It may be in the range of 0.125. Further, as another preferred embodiment of the present invention, in the above composition formula, the element M is Sr and x is in the range of 0.09 ≦ x ≦ 0.25.

The film formation is advantageously performed in the presence of oxygen gas, and the partial pressure of oxygen gas can be preferably set in the range of 10 ^{−6 to} 5 × 10 ⁻² Torr.

The voltage applied to the substrate during film formation is 0 to 15
00V can be mentioned as a preferable range.

The superconducting thin film thus obtained according to the present invention is K ₂ Ni
It is considered to mainly contain a complex oxide having an F ₄ type crystal structure.

Action The methods for producing a superconducting thin film provided by the present invention are all La, one element M selected from the elements included in the groups Ia, IIa and IIIa of the periodic table of elements, and Cu. Its main feature is the use of targets including and.

Here, the composition ratio of La in the thin film obtained by sputtering using the above target, the element M and Cu, that is, the atomic ratio, is represented by the formula: (La _1-x M _x ) ₂ CuO _4-y (where M is It is an element selected from the group included in Ia, IIa, and IIIa groups of the periodic table, and x and y are numbers satisfying 0 <x <1 and 0 ≦ y <4, respectively) In the target, La, the above elements M and Cu
It is advantageous that the atomic ratio of is adjusted according to the vapor deposition efficiency and the like.

In particular, Ba or Sr can be selected as the element M for forming a thin film having excellent superconducting properties.

Further, by setting the substrate temperature during film formation to 100 to 1200 ° C., excellent characteristics as a superconducting thin film can be obtained.

Further, as the substrate for forming this superconducting thin film, it can be selected from various ceramic substrate materials known in the sputtering method, as particularly advantageous, magnesia, strontium titanate, beryllia, alumina, silicon, YSZ, etc. The single crystal substrate of can be mentioned.

Further, in a particularly preferred embodiment of the present invention, after forming the superconductor thin film, the thin film is heat-treated in air at 600 to 1200 ° C.

Further, according to one embodiment of the present invention, the target mixture is a sintered body obtained by sintering a powder mixture of a compound containing La, the element M and Cu.

Also in this case, the composition ratio of La in the thin film obtained by the sputtering, the element M and Cu, that is, the atomic ratio, is represented by the formula: (La _1-x M _x ) ₂ CuO _4-y (where M is the element period). Is an element selected from the group contained in the groups Ia, IIa, and IIIa, and x and y are numbers satisfying 0 <x <1 and 0 ≦ y <4, respectively. It is preferable to use, as a target, a sintered body obtained by sintering a mixture in which the composition ratio of the elements M and Cu is adjusted.

In the above composition formula, when Ba is used as M,
When the amount of M of the mixture in the target is adjusted so that x is within the range of 0.025 ≦ x ≦ 0.125 and Sr is used as M, the target x is satisfied so that 0.09 ≦ x ≦ 0.25. It is preferred to choose the amount of M in the mixture of.

As the compound, an oxide, a carbonate, a nitrate, or a sulfate containing at least one of La, the element M, and Cu can be used.

As the mixed powder of the above compound, a mixed powder of La ₂ O ₃ powder and SrCO ₃ powder or BaCO ₃ powder and CuO powder can be exemplified. In this case, the mixed powder is 70-95% by weight.
La ₂ O ₃ and 1 to 20% by weight of SrCO ₃ or BaCO ₃ and 1 to 3
It is advantageous to mix with 0% by weight of CuO.

Sintering of the mixed powder can also be advantageously carried out by powder hot pressing or powder hot isostatic pressing (HIP).

Sputtering is preferably performed in the presence of oxygen gas, and the partial pressure of oxygen gas may be in the range of 10 ^{−6 to} 5 × 10 ⁻² Torr as an advantageous range. Also, during this sputtering, the temperature of the substrate on which the thin film is deposited should be 100-120.
It is preferable to heat to 0 ° C. Also, at the time of film formation, 0 to 1
It is preferable to perform sputtering while applying a bias voltage of 500V. Further, it is advantageous to heat-treat this superconductor thin film at 600 to 1200 ° C. after the film is formed.

It can be confirmed by electron probe microanalysis (EPMA) or X-ray diffraction that the above-mentioned superconducting thin film is a thin film containing a crystal structure of K ₂ NiF ₄ type oxide.

According to still another aspect of the present invention, a composite oxidation containing La, one element M selected from the elements included in the groups Ia, IIa and IIIa of the periodic table of the elements, and Cu. In the method for producing a superconducting thin film made of a substance by sputtering, the sputtering is performed by La, the element M and Cu are performed.
Is carried out using a target made of a sintered body obtained by sintering a mixture powder of a compound containing a compound, and La in the thin film obtained by the above sputtering and the above element M
And the composition ratio of Cu, that is, the atomic ratio is represented by the formula: (La _1-x M _x ) ₂ CuO _4-y (where M is selected from the group included in groups I a, II a, and III a of the periodic table of elements). The composition ratios of La, the elements M, Cu and oxygen are adjusted so that the composition satisfying the above conditions, x and y are numbers satisfying 0 <x <1 and 0 ≦ y <4, respectively. There is provided a method of forming a sintered body and, after forming the superconductor thin film, heat treating the thin film in air at 600 to 1200 ° C.

Here, in particular, the sputtering is performed using a target made of a sintered body obtained by sintering a mixed powder of a compound containing La, the element M and Cu, and the sintered body is
Composition ratio of La in the thin film obtained by the above sputtering, the above elements M and Cu, that is, atomic ratio Formula: (La _1-x M _x ) ₂ CuO _4-y (where M is I a, II in the periodic table) a, an element selected from the group consisting of IIIa groups, and x and y are numbers satisfying 0 <x <1 and 0 ≦ y <4, respectively, so that La has the above composition. It is composed of a sintered body in which the composition ratio of the elements M, Cu and oxygen is adjusted, the temperature of the substrate on which the thin film is vapor-deposited is 100 to 1200 ° C., and this thin film is aired after the formation of the superconductor thin film. 600 ~ 1200 ℃ in
It is advantageous to heat-treat.

In fact, when a voltage is applied during sputtering, Ar gas contained in the vacuum chamber becomes Ar ⁺ and bombards the target made of the film-forming target substance. As a result, particles ejected from the target are deposited as a thin film on the substrate. At this time, if oxygen gas is introduced during sputtering, the most stable compound is (La _1-x Ba _x ) ₂ CuO _4-y , (L
A thin film is formed on the substrate as a _1-x Sr _x ) ₂ CuO _4-y . The thin film superconducting oxide prepared by the method of the present invention is K ₂ NiF ₄
It is a type oxide (La, Ba) ₂ CuO ₄ or (La, Sr) ₂ CuO ₄ .

At this time, it is recognized that the composition of the thin film formed on the substrate is uniquely determined by the composition of the substance forming the target. The present invention is based on the findings of the present inventor. That is, the mixture that constitutes the target is selected from the group of chemical formulas: (La _1-x M _x ) ₂ Cu O _4-y (M is selected from the group contained in the Ia, IIa, and IIIa groups in the periodic table of the elements). If the mixture is a mixture of elements, x is 0 <x <1, y is a number selected so as to satisfy 0 ≦ y <4), a thin film of a superconductor showing a high critical temperature will be used. Can be formed. Therefore, first, the target is represented by the chemical formula: (La
_1-x M _x ) ₂ CuO _4-y is formed as a mixture of compounds of elements contained in CuO _4-y . Then, the composition of the thin film formed on the substrate is determined according to the mixing ratio of the compounds forming the target. Therefore, by controlling the mixing ratio of the compounds constituting this target, K _{2 of the} target composition
A thin film made of a superconducting compound having a NiF ₄ type layered perovskite structure can be formed, and a compound having a uniform composition can be obtained, which exhibits optimum characteristics according to the superconducting characteristics to be used.

In a preferred method of the present invention, as a sputtering target, La, Ba or Sr as an element constituting the K ₂ NiF ₄ type oxide superconductor, an oxide containing at least one each of Cu, a carbonate, Sputtering is performed using a sintered body of nitrate or sulfate powder to form a thin film of K ₂ NiF ₄ type oxide.

Since these oxides, carbonates, nitrates and sulfates of La, Ba or Sr, Cu are relatively stable, it is easy to form a thin film of K ₂ NiF ₄ type oxide by sputtering.

According to a particularly preferred embodiment of the present invention, La ₂ O ₃ and BaCO ₃
Alternatively, a sintered body of a powder mixture of SrCO ₃ and CaO is used. At this time, the weight mixing ratio of the above powder is 70 to 95% for La ₂ O ₃ and BaCO ₃
Alternatively, it is preferable that SrCO ₃ is 1 to 20% and CuO is 1 to 30%.

The method for adjusting the components of the thin film forming target in this case will be described below.

Each of the above raw material powders has a melting point shown in Table 1 below.

As can be seen from this table, since La ₂ O ₃ has a higher melting point than other substances, it is considered that the evaporation rate during sputtering is slow. That is, unless the element ratio of the above-mentioned sintered body is properly selected, the thin film will not have a desired element ratio. Therefore, it is advisable to add La ₂ O ₃ to the target shaped sintered body so that the ratio is higher than the desired stoichiometric ratio in the thin film. Therefore,
In a preferred embodiment of the present invention, a molded sintered body in which La ₂ O ₃ is mixed at 70 to 95%, BaCO ₃ or SrCO ₃ at 1 to 20%, and CuO at a weight ratio of 1 to 30% is used.

For example, La ₂ O ₃ and BaC whose target satisfies the above range
In the case of a mixture of O ₃ and CuO, (La _1-x Ba _x ) ₂ CuO _4-y
Thin film can be formed, and if a mixture of La ₂ O ₃ , SrCO ₃ and CuO satisfies the above composition formula, a thin film of (La _1-x Sr _x ) ₂ CuO _4-y can be formed. . Also (La _1-x Ba _x ) ₂ CuO _4-y
In the case of, the highest critical temperature can be obtained when the condition of 0.025 ≦ x ≦ 0.125 is satisfied. Also, (La _1-x S
In the case of r _x ) ₂ CuO _4-y , the highest critical temperature can be obtained when the condition of 0.09 ≦ x ≦ 0.25 is satisfied.

Further, the target is preferably obtained by a powder sintering method, but the composition of the thin film is not significantly affected by the presence of unreacted portions in the target, but rather greatly influenced by the mixing ratio of the powder composed of compound particles. It It is industrially preferable that the powder sintering method is performed by a powder hot pressing, a powder hot isostatic pressing (HIP) or the like.

According to a preferred embodiment of the present invention, the sputtering is performed in an argon atmosphere in the presence of oxygen gas, and the partial pressure of oxygen gas is 10 ^{−6 to} 5 × 10 ⁻² Torr.

According to a further preferred embodiment of the invention, the substrate on which the thin film is deposited is kept at a temperature in the range of 100 to 1200 ° C. Further, it is preferable that the substrate is biased with a voltage of 0 to 1500 V to guide the ionized oxygen toward the substrate.

Further in accordance with a preferred embodiment of the present invention, after forming the superconductor thin film, the thin film is heat-treated at a temperature in the range of 600 to 1200 ° C.

Further, in the K ₂ NiF ₄ type oxide that is the object of the present invention, it is necessary that oxygen atoms are regularly incorporated and arranged with respect to other constituent atoms. Therefore, in a preferred embodiment of the present invention, in order to optimize the amount of oxygen in the superconductor thin film to be formed, the oxygen partial pressure is set to 10 ^{−6 to} 5 × 10 ⁻² Torr during sputtering. If the oxygen partial pressure is less than 10 ⁻⁶ Torr, there is almost no oxygen, and therefore the effect of adding oxygen to the above atmosphere is not effective. On the other hand, the oxygen partial pressure is 5
When it exceeds × 10 ^-2 Torr, the degree of vacuum becomes low and sputtering itself becomes difficult. From this, it is understood that the range of oxygen partial pressure is preferably 10 ^{−6 to} 5 × 10 ⁻² Torr. The sputtering may be either high frequency sputtering or DC diode sputtering.
In particular, high frequency magnetron sputtering is preferable.
Furthermore, thin film formation by ion beam vapor deposition is also possible.

In the case of high-frequency sputtering, the high-frequency power to be applied naturally varies depending on the device, but it is preferably 5000 W or less. That is, when a large electric power exceeding 5000 W is applied, the energy of ions in a vacuum increases, and problems such as abnormal discharge and pouring of impurities from the chamber wall occur in many cases, so 5000 W or less is preferable.

Further, the ionized oxygen can be guided toward the substrate by biasing the substrate with a voltage of 0 to 500V.
Voltages over 500V are not preferable because abnormal discharge occurs due to DC voltage. Further, when the voltage is high, ions are struck in the thin film and many defects are generated, which deteriorates the film.

At a substrate temperature of less than 100 ° C, the film becomes amorphous and does not exhibit superconductivity. When the substrate is heated to a temperature higher than 1200 ° C, it becomes difficult to control the element ratio in the film. Therefore, the substrate temperature is preferably in the range of 100 to 1200 ° C.

In order to further improve the superconductivity, it is particularly advantageous to subject the superconducting thin film formed by the above-mentioned preparation method to heat treatment at 600 to 1200 ° C. The superconducting thin film produced by the above method has a much higher superconducting critical temperature than before. For this reason,
It is possible to use a refrigerant other than liquid helium to cause the superconducting transition.

Hereinafter, the present invention will be described in more detail with reference to examples, but the following is merely one example of the present invention.
The technical scope of the present invention is not limited in any way.

Example FIG. 1 is a diagram schematically showing the configuration of a high frequency sputtering apparatus that can be used when carrying out the method for producing a superconducting oxide thin film of the present invention.

This high frequency sputtering device includes a bell jar 1 and
The raw material target 2 is arranged in the bell jar 1, and the substrate 4 is provided so as to face the raw material target 2 and a thin film is formed on the surface of the raw material target 2. The bell jar 1 is connected to a vacuum pump (not shown) through an exhaust hole 7 so that the inside of the bell jar 1 can be evacuated. Further, the bell jar 1 has a gas introduction hole for introducing argon and oxygen. 8 is attached. A high frequency is applied to the target 2 from a high frequency power source 3.
On the other hand, a bias voltage is applied to the substrate 4 by using a power source 5, and a heater 6 for heating is further attached to the substrate 4 so that the substrate temperature can be set to a desired temperature.

In the illustrated apparatus, the target 2 was sputtered with Ar ions to adjust the concentration in Ar gas.
The thin film by O ₂ is formed on the substrate 4 O ₂ is replenished, the desired composite oxide is formed as a thin film.

Preparation example 1: Preparation of [La, Sr] ₂ CuO ₄ thin film As target material, La ₂ O ₃ : SrCO ₃ : CuO = 1.66; 0.34: 1
The respective powders are uniformly mixed in a molar ratio (weight ratio = 80.6: 7.5: 11.8). After that, for example, using a molding jig as shown in FIG. 2, pre-sintering is performed at a temperature of 900 ° C. for 12 hours. In FIG. 2, 20 is a target material powder and 22 is a molding jig.

Next, the molded product is taken out from the molding jig, and the molded product in this state is still very brittle, so this molded product is crushed again.
The ground product is further re-sintered at a temperature of 1100 ° C. for 2 hours.

The obtained sintered material is attached to a sputtering device as a target for sputtering. As the sputtering conditions, a voltage of 1 kV was applied by a high frequency method using a device as shown in FIG. 1, the substrate surface was kept at a temperature of about 200 ° C., and a thin film was formed.

It was confirmed by electron probe microanalysis (EPMA) that the obtained thin film was a crystalline body having a uniform composition and a K ₂ NiF ₄ type layered perovskite structure.

Furthermore, when the critical temperature of the material annealed at a temperature of 900 ° C. was measured, a high critical temperature of 30 K or higher was confirmed. Also, x
A thin film made of a compound of (La _1-x Sr _x ) ₂ CuO _4-y was obtained by varying the value of _x . At this time, when the value of x is out of the range of 0.09 ≦ x ≦ 0.25, the high critical temperature becomes high. I couldn't get it.

Preparation Example 2: Preparation of [La, Ba] ₂ CuO ₄ Thin Film A (La, Ba) ₂ CuO ₄ thin film was prepared using the high frequency sputtering apparatus shown in FIG. 1.

As the raw material target 2, a sintered body of a powder mixture of La ₂ O ₃ , BaCO ₃ , and CuO was used, and as the substrate 4, Si crystal was used.
The film forming conditions are as follows.

Sputtering gas Ar partial pressure 10 ^-3 Torr, oxygen partial pressure 10 ^-4 Torr, substrate temperature 900 ° C, high-frequency power 500 W applied to raw material target, substrate bias voltage 50V.

The film formation rate was 10Å / sec and the film was formed to a thickness of about 1 μm. For comparison, a thin film was prepared under the same conditions except that oxygen was not added.

Then, a sample as shown in FIG. 4 was prepared to measure the resistance of each of the obtained thin films.

FIG. 4 is a schematic diagram of the shape of a sample for which resistance measurement is performed. According to the method of the above-described embodiment, [La, B
a] ₂ CuO ₄ thin film is formed. As shown in FIG. 4, two pairs of Al electrodes 10 are further formed on this thin film by vacuum vapor deposition, and lead wires 11 are soldered to each Al electrode 10.

The temperature characteristics of resistance of the thin films obtained in the above Examples and Comparative Examples were measured, and the results are shown in FIG. In Figure 5,
The curve labeled 31 shows the oxygen partial pressure inside the chamber.
The temperature change of resistance of the thin film prepared at 10 ⁻⁴ Torr is shown. The curve indicated by reference numeral 32 is the temperature change curve of resistance of the thin film prepared without oxygen in the chamber.

As can be seen from the resistance curve 31, the thin film prepared by the method of the present invention has a superconducting phenomenon starting temperature of about 30K and 25K.
The following is completely superconducting. On the other hand, the resistance curve 32
The resistance starts to decrease at almost the same temperature, but the decrease is gentle, and the resistance becomes completely zero only after several K.
From a comparison of these two resistance curves, it can be seen that by introducing oxygen into the chamber during film formation, the oxygen in the thin film can be appropriately controlled to form a superconducting thin film having a desired composition.

Preparation Example 3: Preparation of [La, Sr] ₂ CuO ₄ Thin Film A thin film was prepared in the same manner as in [La, Ba] ₂ CuO _{4 of} Example 2 above. As the raw material target, a sintered body of a powder mixture of La ₂ O ₃ , SrCO ₃ , and CuO was used. Target CuO weight ratio of 20
% And 60% to form a film. Other film forming conditions are as follows.

Sputtering gas Ar partial pressure 10 ^-3 Torr, oxygen partial pressure 10 ^-4 Torr, substrate temperature 900 ° C, power applied to raw material target 500W, substrate bias voltage 50V.

The temperature characteristic of resistance of the obtained thin film is shown in FIG. The curve indicated by reference numeral 41 is the resistance curve of a thin film formed with a target CuO weight ratio of 20%, and the curve indicated by reference numeral 42 is a resistance curve of a thin film formed with a target CuO weight ratio of 60%. . When the target CuO weight ratio was 60%, the amount of Cu in the thin film was too large to show superconductivity. As shown by the resistance curve 41, the temperature at which the superconducting phenomenon of the thin film formed with the target CuO weight ratio of 20% according to the present invention starts is about 38K, and becomes completely superconducting below 27K. Thus, the thin film corresponding to the resistance curve 41 exhibited excellent characteristics as a superconductor.

Effects of the Invention As described above, according to the present invention, it becomes possible to form a thin film of a superconducting oxide having a T _C much higher than that of a conventional superconductor. Therefore, the present invention is applied to a field in which a superconductor is applied as a thin film element, for example, a switching element of Matisoo called a Josephson element, a memory element of an Anacker, and a superconducting quantum interferometer (SQUID). It is effective when used for.

The thin film obtained can be used as a superconducting wire or a superconducting disk by forming it on the surface of a wire or a disk.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration example of a sputtering apparatus for carrying out the method of the present invention, and FIG. 2 is a sectional view showing an example of a molding jig that can be used for powder molding. FIG. 3 is a process diagram for explaining the steps of the powder sintering method, and FIG. 4 is a diagram showing the structure of a sample for measuring the characteristics of the superconducting thin film produced by the method of the present invention. The figure shows (La, Ba) ₂ Cu produced in Production Example 1 of the present invention.
O ₄ thin film resistor - is a graph showing the temperature characteristics and Comparative Example, Fig. 6 was produced in Production Example 2 of the present invention (La, Sr) ₂ CuO ₄
It is a graph which shows the resistance-temperature characteristic of a thin film with a comparative example. [Main reference numbers] 1 ... Bell jar, 2 ... Raw material target, 3 ... High frequency power source, 4 ... Substrate, 5 ... Power source, 6 ... Heating heater, 7 ... Exhaust hole, 8 ... Gas Introductory hole, 10 …… Al electrode, 11 …… Lead wire

Continuation of front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display location H01B 12/00 ZAA H01B 12/00 ZAA H01L 39/24 ZAA H01L 39/24 ZAAB (56) References 63-190713 (JP, A) JP 58-21880 (JP, A) JAPANESE JOURNAL OF APPLIED PHYSIC S, Vol. 26, No. 1, January 1987, PP. L1-L2

Claims (3)

(57) [Claims] 1. La and I a, II a and III of the Periodic Table of the Elements
One element M selected from the elements included in group a
And a method for producing a superconducting thin film made of a complex oxide containing Cu, characterized in that sputtering is performed in an oxygen-containing atmosphere using a target made of a mixture of at least La, the element M and a compound containing Cu. And how to. 2. La and I a, II a and III of the Periodic Table of Elements.
One element M selected from the elements included in group a
In the method for producing a superconducting thin film made of a complex oxide containing Cu and Cu, the composition ratio, that is, the atomic ratio of La, the element M and Cu in the obtained thin film is represented by the formula: La _1-x M _x ) ₂ CuO _{4 -y} (where M is an element selected from the group included in Ia, IIa, and IIIa groups of the periodic table of the elements, and x and y are each 0
<A number satisfying <x <1 and 0 ≦ y <4), and a sintered body obtained by sintering a powder mixture of La, a simple substance of the above elements M and Cu, or a compound thereof is used as a target. ,, is formed by a sputtering method in an oxygen-containing atmosphere, and a thin film is formed at 600 to 120 after the film formation.
A method characterized by performing heat treatment in a temperature range of 0 ° C. 3. La and I a, II a and III of the Periodic Table of the Elements
One element M selected from the elements included in group a
In the method for producing a superconducting thin film made of a complex oxide containing Cu and Cu, the composition ratio, that is, the atomic ratio of La, the element M and Cu in the obtained thin film is represented by the formula: La _1-x M _x ) ₂ CuO _{4 -y} (where M is an element selected from the group included in Ia, IIa, and IIIa groups of the periodic table of the elements, and x and y are each 0
<A number satisfying <x <1 and 0 ≦ y <4), and a sintered body obtained by sintering a powder mixture of La, the above element M and Cu alone or a compound. Is used as a target at a substrate temperature of 100 to 1200 ° C. to form a film by a sputtering method in an oxygen-containing atmosphere, and after the film formation, the thin film is heat-treated in a temperature range of 600 to 1200 ° C. Method.