JP2501616B2 - Preparation method of superconducting thin film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing a superconducting thin film,
More specifically, the present invention relates to a novel method for producing a superconducting thin film having a uniform composition and a high superconducting critical temperature.

2. Description of the Related Art The superconducting phenomenon, which is said to be a phase transition of electrons, is a phenomenon in which the electric resistance of a conductor becomes zero under certain conditions and shows perfect diamagnetism.

That is, under superconductivity, there is no power loss even when a current is passed through the superconductor, and a high-density current continues to flow forever.
Therefore, for example, if superconductivity technology is applied to power transmission,
It is possible to greatly reduce the transmission loss of about 7%, which is said to be caused by the current transmission. In addition, the application as an electromagnet for generating a high magnetic field is, for example, a technology that advantageously promotes the realization of a nuclear fusion reaction that is said to consume more power than the amount of power generated in the development together with MHD power generation, electric motors, etc. Expected. It is also expected to be used as power for magnetic levitation trains, electromagnetic propulsion vessels, etc. in the fields of measurement and medical treatment, such as NMR, pion therapy, and high energy physics experiments.

Apart from the use in the large-sized apparatus as described above, another use of the superconducting material includes production of various superconducting elements. A typical example is an element utilizing the Josephson effect in which quantum effects appear macroscopically by an applied current when superconducting materials are weakly joined. Since the energy gap of the superconducting material is small, the tunnel junction type Josephson device is expected as a switching device with extremely high speed and low power consumption. In addition, since the Josephson effect on electromagnetic waves and magnetic fields appears as an accurate quantum phenomenon, it is expected that the Josephson element is used as an ultrasensitive sensor for magnetic fields, microwaves, radiation, and the like. Furthermore, as the degree of integration of electronic circuits increases, the power consumption per unit area reaches the limit of cooling capacity. Therefore, the development of superconducting elements has been demanded for ultra-high-speed computers.

On the other hand, despite various efforts, the superconducting critical temperature Tc of the superconducting material could not exceed 23K of Nb ₃ Ge for a long time, but in the future of 1986, [La, Ba] ₂ CuO ₄ or Sintered materials of K ₂ NiF ₄ type oxides such as [La, Sr] ₂ CuO ₄ have been discovered as superconducting materials with high Tc, and the possibility of realizing non-low temperature superconductivity is greatly increasing. For these substances, 30
Dramatically higher Tc of ~ 50K than before is observed, and Tc of 70K or more is also observed. However, these superconducting materials are sintered materials, and unreacted particle portions are present microscopically, and the composition and the structure tend to be nonuniform, so that they cannot be directly applied to electronic devices. Also,
In order to apply to various electronic devices, it is necessary to have a thin film structure and control the fine composition and structure. Further, it is expected that a superconducting material is produced by depositing a superconducting material on a metal or other wire or tape-like material, and a technique for depositing a superconducting material is also required for the production.

Therefore, an object of the present invention is to solve the above-mentioned problems of the prior art and to provide a method for producing a thin film of a superconducting material having a high critical temperature Tc and a uniform composition and structure. Especially.

Means for Solving the Problems That is, according to the present invention, a target of a mixture of oxides and / or complex oxides containing at least one selected from the group consisting of Er, Ba and Cu, or all contained in the element group There is provided a method for producing a superconducting thin film, which comprises performing physical vapor deposition using a target of a complex oxide containing the element to form a thin film of a perovskite type oxide or a pseudo perovskite type oxide.

Here, according to a preferred embodiment of the present invention, it is advantageous that the target includes a perovskite type oxide or a pseudo perovskite type oxide.

The target is a powder mixture of Ba oxide, carbonate, nitrate or sulfate; Er oxide, carbonate, nitrate or sulfate; Cu oxide, carbonate, nitrate or sulfate. The target may be a Ba oxide, a carbonate, a nitrate or a sulfate; and an Er oxide, a carbonate, a nitrate or a sulfuric acid. 700 after pre-sintering a powder mixture of salt and Cu oxides, carbonates, nitrates or sulphates
Advantageously, the main sintering is carried out at a temperature in the range of -1500 ° C, preferably 700-1300 ° C.

The target can also use multiple targets, in which case each target is a Ba oxide,
It may be an oxide of Er or an oxide of Cu. Also, (Ba, Er) O
Two targets of _x (where x is a real number of 1 or more) and CuO may be used.

The atomic ratio Ba / (Ba + Er) in the target is preferably in the range of 0.04 to 0.96, and more preferably 0.5 to 0.7. Also, the atomic ratio Cu / (Ba + Er) in the target
Is preferably in the range of 0.5 to 0.7. The atomic ratio of Ba, Er and Cu of the target is B of the thin film to be formed.
Ba, Er and Cu based on the atomic ratio of a, Er and Cu
It is adjusted according to the vapor deposition efficiency of.

The vapor deposition atmosphere contains Ar and O ₂ , and the Ar partial pressure is in the range of 1.2 × 10 ^-3 to 2 × 10 ^-1 Torr, preferably 5.0 × 10 ^-3 to 1 × 1.
It is advantageous to be in the range of 0 ^-1 Torr. Further, it is advantageous that the O ₂ partial pressure of the vapor deposition atmosphere is in the range of 0.5 × 10 ^-3 to 1 × 10 ^-1 Torr, preferably 1.0 × 10 ^-3 to 1 × 10 ^-1 Torr. .

The physical vapor deposition may be RF sputtering, the high frequency power during sputtering is 103 W / cm ² or less, preferably 15 W /.
Advantageously it is less than cm ² . Further, the vapor deposition can be performed by magnetron sputtering.

During sputtering, it is advantageous to heat the substrate with a heater or the like. Here, the heating temperature of the substrate is 28
Advantageously, it is in the range of 0 to 1520 ° C, preferably 280 to 980 ° C, and the distance between the substrate and the target is 4 to 210 m.
Advantageously, m, preferably in the range 15 to 210 mm.

As the substrate, glass, quartz, Si, stainless steel, ceramics or the like can be used.

Further, the physical vapor deposition may be any one of ion plating, vacuum vapor deposition, ion beam vapor deposition, and molecular beam vapor deposition.

Further, according to one embodiment of the present invention, it is advantageous to heat-treat the formed thin film. Here, it is advantageous that the heating temperature in the heat treatment is in the range of 260 to 1700 ° C, more preferably 260 to 1200 ° C. In addition, the heat treatment,
It is advantageous to carry out in an atmosphere having an oxygen partial pressure of 5 × 10 ^-1 Torr or less.

Action The method for producing a superconducting thin film provided by the present invention is a physical vapor deposition targeting an oxide mixture or complex oxide containing Er, Ba and Cu to form a thin film of a perovskite type oxide or a pseudo perovskite type oxide. It is characterized by doing.

Here, the physical vapor deposition can be any of various sputtering methods, ion plating methods, vacuum vapor deposition methods, ion beam vapor deposition methods, and molecular beam vapor deposition methods, and the details will be described later. In the method of the present invention, it is preferable to use a sintered material as a target. In this case, since it does not scatter even when irradiated with an electron beam or the like, it is advantageous for sputtering or ion plating while adjusting the components. is there.

Further, in the method of the present invention, it is advantageous that the target itself also has a perovskite type structure or a pseudo perovskite type structure. In this case, the target thin film is likely to have a desired perovskite or pseudo perovskite structure.

According to a preferred embodiment of the present invention, a mixed powder of Ba, Er, and Cu oxides, carbonates, nitrates or sulfates is calcined at 250 to 1200 ° C, more preferably 250 to 1100 ° C. It is advantageous to use, as a target, a bonded product or a product obtained by subjecting this to main sintering at a temperature in the range of 700 to 1500 ° C., more preferably 700 to 1300 ° C. The sintered body obtained through such a process easily has the above-mentioned crystal structure, and particularly when the sintering is performed in the above-described preferable range, this crystal structure is easily formed. Here, the term “temporary sintering” refers to a process of temporarily firing a powder material to form a composite oxide.

The target may be only pre-sintered or may be main-sintered. Further, a powder obtained by pulverizing the sintered body or a sintered body block may be used. In the case of sintered powder, the evaporation efficiency is good and a high film formation rate can be obtained, so the particle size is 0.02 to 2 m.
It is advantageous to use powders in the range of m.

Further, in consideration of composition control during film formation, it is also advantageous to perform physical vapor deposition using a plurality of targets.
For example, if three targets are used, Ba, Er, and Cu oxides can be used as the targets. Also, (Ba, Er) O _x (However,
x is a real number of 1 or more) and CuO.

In the target used in the method of the present invention, the atomic ratio Er / (Ba + Er) is preferably in the range of 0.04 to 0.96, and more preferably 0.5 to 0.7. The atomic ratio Cu / (Ba + Er) in the target is preferably in the range of 0.5 to 0.7. That is, when the atomic ratio of the target deviates from the above range, the superconducting critical temperature of the deposited film does not become sufficiently high. In addition, it is advantageous to determine the atomic ratio of Ba, Er and Cu of the target in consideration of the deposition efficiency of Ba, Er and Cu with reference to the atomic ratio of Ba, Er and Cu of the thin film. This is Ba, which is a constituent of the thin film of the invention,
This is because the melting points and the like of the oxides of Er and Cu are different from each other, and therefore the vapor deposition efficiencies are different from each other. That is, unless the element ratio of the target is properly selected, the thin film will not have the desired element ratio. In the case of sputtering,
The target atomic ratio can also be determined from the sputtering coefficient of each oxide.

According to still another preferred embodiment of the present invention, when the method of the present invention is carried out by sputtering, the substrate is heated to 280 to 1,520, more preferably 260 to 990 by a heater or the like.
It is advantageous to heat to a temperature in the range of ° C. The heating of the substrate causes the thin film to act in a manner similar to that of sintering, and becomes an appropriate perovskite type oxide or pseudo perovskite type oxide. However, if the substrate temperature is too high, it becomes difficult to control the composition of the deposited film, and the desired perovskite-type oxide or pseudo-perovskite-type oxide cannot be obtained.

The above physical vapor deposition can be performed by, for example, sputtering. Here, the sputtering atmosphere is Ar and O ₂
And the Ar partial pressure is 1.2 × 10 ⁻³ to 2 × 10 ⁻¹ Torr, more preferably 5.0 × 10 ⁻³ to 1 × 10 ⁻¹ Torr, and the O ₂ partial pressure is 0.5.
× 10 ^-3 to 1 × 10 ^-1 Torr, more preferably 1.0 × 10 ^-3 to
Advantageously, it is 8 × 10 ^-2 Torr. That is, when the Ar partial pressure does not reach the above range, the deposition rate is slow. On the other hand, when the Ar partial pressure exceeds the above range, glow discharge is hard to occur, and the deposition of oxide having desired superconducting properties cannot be obtained. Further, when the O ₂ partial pressure does not reach the above range, the crystallinity of the deposited film is poor, and it is difficult to obtain a perovskite type oxide or a pseudo perovskite type oxide. On the other hand, the higher the O ₂ partial pressure, the better the crystallinity, but if the O ₂ partial pressure exceeds the above range, the deposition rate will remarkably decrease.

The method of the present invention can also be carried out by radio frequency sputtering (RF sputtering).

In this case, the high frequency power applied during sputtering is
103W / cm ² or less, more preferably advantageously at 15W / cm ² or less. That is, in the case of RF sputtering, but the deposition rate as the high frequency power is high is increased, if more than 15W / cm ² without plasma is stabilized, it tends exceeds 104W / cm ² and an arc discharge or abnormal discharge.

Further, it is advantageous that the distance between the substrate and the target is in the range of 4-210 mm, more preferably 15-210 mm. That is, when the distance between the substrate and the target is small, it is difficult to generate plasma, so that a certain distance or more is required. Particularly, in the case of high frequency magnetron sputtering, the plasma on the target is converged near the magnet, so that if the distance between the substrate and the target is too small, the film formation becomes non-uniform. On the other hand, when the distance between the substrate and the target is large, the deposition rate is low and the efficiency is low.

Examples of the substrate that can be advantageously used in the method of the present invention include glass, quartz, Si, stainless steel, and ceramics such as MgO, BaTiO ₃ , SiO ₂ , sapphire, and YSZ.

Further, according to a preferred embodiment of the present invention, the thin film formed by the physical vapor deposition is further heat-treated to produce a high-quality thin film having a small difference between a superconducting start temperature and a temperature at which the resistance becomes completely zero. can do. That is, by this heat treatment, the superconducting characteristics of the deposited film can be improved by controlling the oxygen atom ratio of the deposited film. As described above, the purpose of the heat treatment is to homogenize the composition of the deposited film into a perovskite type oxide or a pseudo perovskite type oxide. Therefore, it is difficult to obtain the target perovskite type oxide or pseudo perovskite type oxide at a heating temperature that does not reach the temperature range below, and the desired superconducting critical temperature cannot be obtained. Also, the required processing time is significantly increased.
On the other hand, at a treatment temperature exceeding the following range, the target perovskite type oxide or pseudo perovskite type oxide disappears, and the superconducting critical temperature is significantly lowered. The preferred temperature range for this heat treatment is 260 to 1700 ° C, more preferably 250 to 1150 ° C. Further, it is advantageous to perform the heat treatment in an atmosphere having an oxygen partial pressure of 5 × 10 ^-1 Torr or less.

As described above, the composite oxide thin film prepared according to the method of the present invention is generally represented by the formula: Ba _A Er _B Cu _C O _D (A, B, C, and D each represent an atomic ratio). In particular, (Ba, Er) ₂ CuO _4-x (x is a number of 1 or less), (Ba, Er) CuO _3-x (x is a number of 1 or less), (Ba, Er) ₃ Cu ₂ O _It is considered to include any of the composite oxides represented by _7-y (y is a number of 1 or less) or a mixed phase thereof.

Further, it is considered that the composition further includes any one of the following compositions or a mixed phase thereof, but the present situation is not limited thereto.

Hereinafter, the present invention will be described with reference to Examples, but it is needless to say that the technical scope of the present invention is not limited to these Examples.

First, an apparatus used to carry out the method of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a schematic diagram of a high-frequency sputtering apparatus used for producing a superconducting oxide thin film of the present invention. The apparatus shown in FIG. 1 is provided in opposition to a raw material target 2, a chamber 1, a target 2 disposed in the chamber 1, a sputter power source 3 juxtaposed to sputter this target with sputter atoms. And a substrate 4 on which a thin film is to be formed on the surface.
The chamber 1 is connected to a vacuum pump (not shown) via a port 7 so that the inside can be evacuated.

A bias voltage is applied to the substrate 4 using a high-voltage power supply 5. The substrate 4 is further provided with a heater 6 for heating so that the substrate temperature can be adjusted. Furthermore, chamber 1
Is provided with a gas introduction hole 8.

FIG. 2 is a schematic view of a high frequency excitation type ion plating apparatus used for producing the superconducting oxide thin film of the present invention.

The apparatus shown in FIG. 2 includes a chamber 11, a raw material target 12 disposed in the chamber 11, an electron gun 13 juxtaposed to melt and vaporize the raw material target with an electron beam, and a raw material target 12. Provided
It mainly comprises a substrate 14 on which a thin film is formed on the surface. The chamber 11 is connected to a vacuum pump (not shown) so that the inside can be evacuated.

A bias voltage is applied to the substrate 14 using a high voltage power supply 15. The substrate 14 is further provided with a heating heater 16 so that the substrate temperature can be adjusted. In the chamber 11, a high-frequency coil 17 is further provided between the raw material target 12 and the substrate 14 so as to cover the evaporated particles. Further, the chamber 11 is provided with a gas introduction hole 18 for introducing oxygen.

Production Example 1 A superconducting thin film was produced using the sputtering apparatus shown in FIG.

As the raw material target 2, BaCO ₃ , Er ₂ (CO ₃ ) ₃ , Cu
O powder was mixed and shaped so that the atomic ratio Ba / (Ba + Er) was 0.6, pre-sintered at 840 ° C, crushed, and further molded 104
A sintered block obtained by main sintering at 0 ° C. was used, and a Si crystal was used for the substrate 4. The film forming conditions are as follows.

Oxygen partial pressure 1 × 10 ^-2 Torr, Ar partial pressure 3 × 10 ^-2 Torr, substrate temperature 910 ° C, substrate bias voltage -50V, high frequency power 12W / cm ² , distance between substrate and target 50mm, deposition rate 3Å A film having a thickness of about 1 μm was formed at a time of / sec.
For comparison, the other conditions were the same, and the same operation was performed in an atmosphere containing no O ₂ to form a thin film.

Next, a sample was prepared to measure the resistance of each of the obtained thin films. The sample for resistance measurement is the substrate 4
A pair of Al electrodes was further formed on both ends of the thin film formed thereon by vacuum evaporation, and lead wires were soldered to the Al electrodes.

The thin film produced by the method of the present invention in which the oxygen partial pressure inside the chamber is 1 × 10 ^-2 Torr has a temperature at which the superconducting phenomenon starts is about 98K, and becomes a perfect superconductor at 92K or less. In contrast, thin films made without oxygen in the chamber
At about the same temperature, the resistance began to decrease, but the decrease was gentle, and the superconductor became a complete superconductor for the first time at around several K. This indicates that the oxygen in the thin film can be appropriately controlled by introducing oxygen into the chamber during film formation, and a superconducting thin film having a desired composition can be formed.

Preparation Example 2 The sintered body of Preparation Example 1 was crushed to a grain size of 0.3 mm, and this was used as a target material for sputtering under the same conditions as in Preparation Example 1 to prepare a superconducting thin film.

It was confirmed that the film forming rate was 5 Å / sec, and that the film forming rate was significantly higher than that of the preparation example 1. The temperature at which the superconducting phenomenon of the thin film produced using the target of the sintered body powder of the present preparation example was about 96K, and at 91K or less, it became a perfect superconductor. As described above, the use of the sintered powder target enabled efficient film formation, and the obtained thin film exhibited excellent characteristics as a superconductor.

Production Example 3 The same operation as in Production Example 1 was repeated, but in this Production Example,
It was obtained by mixing the raw material powders BaCO ₃ , Er ₂ (CO ₃ ) ₃ and CuO so that the atomic ratio of Ba: Er: Cu would be 0.85: 0.90: 1 and pre-sintering at 400 ° C for 12 hours. The temporary sintered material was used as a target.

The superconducting starting temperature of the obtained thin film was 95K. From this experiment, it was confirmed that a superconducting thin film can be produced even when an oxide obtained only by preliminary sintering is used as a target.

Preparation Example 4 The thin film sample obtained in Preparation Example 1 was heat-treated at a temperature of 710 ° C. for 20 minutes in an oxygen atmosphere (oxygen partial pressure: 0.9 × 10 ⁻¹ Torr).

When the sample after the heat treatment was measured by the same method as in the previous preparation example, the resistance decrease was more rapid than in the case of preparation example 1, and the difference between the superconducting start temperature and the zero resistance zero temperature was 4 ° C. became.

Preparation Example 5 The same operations as in Preparation Example 1 were repeated, but the main sintering temperature was 98.
The temperature was changed to 0 ° C., the high frequency power was changed to 3.0 W / cm ² , and the substrate was changed to magnesia.

When measured by the same measurement method as in Preparation Example 1, the electric resistance sharply decreased from 99K.

Effects of the Invention As described above, according to the present invention, it becomes possible to obtain a superconducting oxide thin film having a Tc much higher than that of a conventional superconductor.

Therefore, the superconducting thin film obtained by the present invention is used in a field applied as a thin film element, for example, a switching element of Matisoo called a Josephson element, a memory element of Anacker, and a superconducting quantum interferometer (SQUID). Can be used advantageously.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view of an example of a sputtering apparatus that can be used to carry out the method of the present invention, and FIG. 2 is a diagram of an ion plating apparatus that can be used to carry out the method of the present invention. It is an outline sectional view of an example. [Main reference numbers] 1 ... Chamber, 2 ... Raw material target, 3 ... High frequency power source, 4 ... Substrate, 5 ... High voltage power source, 6 ... Heater, 7
...... Exhaust hole, 9 ... Superconducting thin film, 11 ... Chamber, 12 ...
… Raw material target, 13… Electron gun, 14… Substrate, 15…
… High-voltage power supply, 16… Heater, 17… High frequency coil, 18…
... Gas inlet

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location H01L 39/24 ZAA H01L 39/24 ZAAB (72) Inventor Saburo Tanaka 1 chome, Kunyokita, Itami City, Hyogo Prefecture 1-1 Sumitomo Electric Industries, Ltd. Itami Works (72) Inventor Keizo Harada 1-1-1 Kunyokita, Itami City, Hyogo Prefecture Sumitomo Electric Industries Itami Works (72) Inventor Tetsuji Ueshiro Hyogo Prefecture 1-1-1 Kunyokita, Itami-shi Sumitomo Electric Industries, Ltd. Itami Works (56) References JP-A-63-224116 (JP, A) JP-A-63-224375 (JP, A)

Claims (1)

(57) [Claims] 1. A target of a mixture of an oxide and / or a complex oxide containing at least one selected from the group consisting of Er, Ba and Cu, or a complex oxide containing all elements contained in the element group. 0.5 x 1 using the target
Physical vapor deposition was performed under an oxygen partial pressure of 0 ^-3 to 1 × 10 ^-1 Torr to obtain E
A method for producing a superconducting thin film, which comprises forming a thin film of a perovskite type oxide or a pseudo perovskite type oxide containing all of r, Ba and Cu.