JP2645730B2 - Superconducting thin film - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a superconducting thin film and a method for producing the same. More specifically, the present invention relates to a novel superconducting thin film having a high superconducting critical temperature and exhibiting its high performance stably for a long period of time, and a method for producing the superconducting thin film.

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 electrical resistance of a conductor becomes zero under specific conditions, indicating complete diamagnetism. That is, under the superconductivity, even if a current flows through the superconductor, there is no power loss, and a high-density current continues to flow forever. Therefore, for example, if superconductivity is applied to the power transmission technology, about 7
% Inevitable transmission loss can be significantly reduced. In addition, the application as an electromagnet for generating a high magnetic field is MH in the field of power generation technology.
It is expected to be a technology that advantageously promotes the realization of nuclear fusion reactions, which are said to consume more power than the amount of power generated for startup, together with D power generation and electric motors. In addition, as power for magnetic levitation trains, electromagnetic propulsion ships, etc.
It is expected to be used for NMR, pion therapy, high energy physics experiment equipment, etc.

Further, apart from the use in the large-sized apparatus as described above, application of the superconducting material to various electronic elements has been proposed. A typical example is an element using the Josephson effect in which a quantum effect appears macroscopically due to an applied current when weakly joining superconducting materials. 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 an electromagnetic field or a magnetic field appears as an accurate quantum phenomenon, it is expected that the Josephson element is used as an ultra-sensitive sensor for a magnetic field, a microwave, radiation, or the like. Further, as the degree of integration of electronic circuits increases, the power consumption per unit area is expected to reach the limit of the cooling capacity. Therefore, the development of superconducting elements has been demanded for ultra-high-speed computers.

Conventionally, despite various efforts, the superconducting critical temperature Tc of a superconducting material has not been able to exceed 23 K of Nb ₃ Ge for a long time. By contrast, in 1986, Bednotes and Mueller et al. Discovered that composite oxide-based superconducting materials have a high Tc, opening up the possibility of high-temperature superconductivity (Bednorz, Mller, “ Z.
Phys. B64, 1986, 189 ").

It has been known that composite oxide ceramic materials exhibit superconducting properties. For example, U.S. Pat. No. 3,932,315 describes that a Ba-Pb-Bi-based composite oxide exhibits superconducting properties. Also,
JP-A-60-173,885 describes that a Ba-Bi-based composite oxide exhibits superconducting properties. However, heretofore known have a composite oxide superconducting material of the superconducting critical temperature T _c (hereinafter, simply referred to as Tc) is less than the overall very low 10K, expensive and rare to obtain superconductivity The use of liquid helium (boiling point 4.2K) was inevitable.

The oxide superconductor discovered by Bednauts and Mueller has a composition of (La, Ba) ₂ CuO ₄ and K ₂ Ni
It is seen as having an F ₄ type crystal structure. The composite oxide superconducting material, which had been known perovskite type oxide superconductor material crystal structure is similar, T _c is dramatically higher about 30K than the conventional superconductive material
Was the value.

In February 1987, a Ba-Y-Cu-based composite oxide exhibiting a critical temperature of 90K class was discovered by Chu et al. It is considered that the composite oxide commonly called YBCO has a composition represented by Y ₁ Ba ₂ Cu ₃ O _7-x .

Furthermore, the subsequently discovered Bi-Sr-Ca-Cu system and Tl-
The Ba-Ca-Cu-based composite oxide has a Tc exceeding 100 K and is chemically stable, and the superconducting characteristics such as YBCO are hardly deteriorated with time. Nevertheless, it is expected that it may be more practical.

With the discovery of these new composite oxide-based superconducting materials, the momentum for realizing high-temperature superconductors is rapidly increasing.

Problems to be Solved by the Invention However, it is known that, in these oxide superconductors, oxygen or oxygen vacancies in the crystal is generally reduced due to a change with time, and the superconductivity is largely deteriorated. That is,
Characteristics such as superconducting critical temperature and critical current tend to be best immediately after fabrication, and then tend to gradually deteriorate thereafter. This tendency was particularly remarkable in a thin film having a large surface area as compared with the deposition of the entire superconducting material.

The superconducting properties of the new composite oxide superconductor described above are
Oxygen vacancies in the crystal are deeply involved, so that heat treatment must be performed in an atmosphere having a high oxygen partial pressure in the final stage of the production, and the superconducting properties of the oxide superconductor which does not undergo this process are extremely poor.

Further, even in an oxide superconductor that has undergone such a treatment, oxygen in the crystal is lost with time in the air, and the superconductivity is gradually deteriorated. This may be because the composite oxide superconductor reacts with the moisture in the air, or the oxygen in the crystal is lost with the passage of time, and the contained oxygen deficiency becomes inappropriate. It is thought that this is because the oxide superconductor having excellent superconducting properties is a metastable phase and changes into another substance or another phase by reacting with moisture in the air. For this reason, at present, it is difficult to stably utilize the excellent superconducting characteristics of the composite oxide-based superconductor for a long period of time, and this is a major problem when attempting to use an oxide superconductor.

Therefore, an object of the present invention is to provide a novel composite oxide-based superconducting thin film with little change over time. Also, a novel method for producing the novel composite oxide-based superconducting thin film is within the scope of the present invention.

Means for Solving the Problems That is, according to the present invention, a composite oxide superconducting material formed as a thin film on a substrate and a polyimide resin or diallyl phthalate resin covering the surface of the composite oxide superconducting material thin film A composite oxide-based superconducting thin film provided with a high molecular compound layer that does not allow oxygen to pass therethrough.

According to another aspect of the present invention, there is provided, according to the present invention, a compound represented by the following general formula: (α _1-x β _x ) Cu _y O _{z wherein} α is an element selected from Group IIa of the periodic table, Is an element selected from Group IIIa of the periodic table III, x is an atomic ratio of β to α + β in the range of 0.1 ≦ x ≦ 0.9, and y and z are (α _1−x β _x ) being 1 And if
The atomic ratio satisfies 0.4 ≦ y ≦ 3.0 and 1 ≦ z ≦ 5. And a composite oxide superconducting material formed mainly as a thin film on a substrate, and a high oxygen impregnated with an alkyd resin formed on the surface of the composite oxide superconducting material thin film. A composite oxide-based superconducting thin film comprising a molecular compound layer is provided.

The main feature of the composite oxide superconducting thin film according to the present invention is that the surface of the composite oxide superconducting thin film formed on the substrate is covered with a polymer compound.

Here, as the above-mentioned polymer compound, a silicon resin-based polymer compound, an epoxy resin-based polymer compound or a polyimide resin-based polymer compound, which is used for a passivation film of an integrated circuit, can be exemplified as a preferable example. Further, as other high molecular compounds, for example,
Resins used for IC packaging, such as diallyl phthalate resin, alkyd resin, and UV curable resin, and thermosetting resins can also be used.

These polymer compounds have a dense structure, can suppress release of oxygen from the superconducting thin film crystal, and can maintain good characteristics at the beginning of the production of the superconducting thin film for a long period of time. Furthermore, these polymer compounds are extremely stable chemically and have no adverse effect on the superconducting thin film when used as a coating, and can be formed at a relatively low temperature. It does not hurt.

The above polymer compound layer can be formed on the superconducting thin film by a coating method using an appropriate solvent. In addition, a film can be directly formed on a superconducting thin film in a molten state without using a solvent. Further, in some cases, it can be formed directly on the superconducting thin film by transfer molding.

The substrate temperature when forming the polymer compound coating is
It is preferable to limit the temperature to 500 ° C. or lower. That is, when the above-mentioned superconducting thin film is heated to a temperature exceeding 500 ° C. after formation, oxygen in the crystal is lost, and the superconducting properties are remarkably deteriorated. Therefore, it is advantageous to set the substrate temperature to 500 ° C. or less when forming the polymer compound layer or during thermosetting after the formation.

Further, the above-mentioned polymer compound layer is not limited to a single layer, and it is also effective to laminate two or more layers having different compositions or constituent elements.

In order to manufacture the superconducting thin film of the present invention, a superconducting thin film is generally formed on the substrate by sputtering or the like using a superconducting raw material oxide prepared by sintering or the like as a target, and heat treatment is performed in an oxygen-containing atmosphere as necessary. After that, the above polymer compound is coated.

The thin film composed of the above composite oxide-based superconducting material has a periodic table
At least one element α selected from group IIa elements;
Complex of at least one element β selected from Group IIIa elements of the periodic table and at least one element γ selected from Group Ib, IIb, IIIb, IVb, and VIIIa elements of the Periodic Table It can be a thin film of oxide. Generally, the element γ is Cu.

More specifically, the following general formula: (α _1-x β _x ) Cu _y O _z [where α and β are elements as defined above, and x is α
The atomic ratio of β to + β is a number satisfying 0.1 ≦ x ≦ 0.9, and y and z are 0.4 ≦ y ≦ 3.0 and 1 ≦ z ≦, respectively, when (α _1−x β _x ) is 1. The atomic ratio satisfies the formula 5).
In the above range, the element α is Ba or Sr (10 to 80% of the element α can be replaced with one or two elements selected from Mg, Ca, and Sr), Preferred specific examples include a composite oxide film thin film in which the element β is at least one element selected from the group consisting of Y, La, Gd, Dy, Ho, Er, Tm, Yb, and Lu. . In addition to the above elements, Al, Fe, Co, N
It is also possible to include at least one element selected from the group consisting of i, Zn, Ag and Ti.

The ratio between the elements α and β can be appropriately selected depending on the types of α and β. For example, in the case of Ba-Y, Ba-La, and Sr-La, it is preferable that the following ratios are respectively satisfied.

Y / (Y + Ba): 0.06 to 0.94, preferably 0.1 to 0.4 Ba / (La + Ba): 0.04 to 0.96, preferably 0.08 to 0.45 If the atomic ratio of the oxide is out of the above range, any of the oxides Since the crystal structure, oxygen vacancy and the like are different from desired ones, Tc becomes low.

Among the combinations of the above-mentioned elements, particularly, as a composite oxide thin film to which the present invention can be particularly preferably applied, for example, Y-
Ba-Cu-O system, La-Ba-Cu-O system and La-Sr-Cu-O
-Based composite oxide thin films. Specifically, Y ₁ Ba ₂ Cu ₃ O _7-x , Ho ₁ Ba ₂ Cu ₃ O _7-x Lu ₁ Ba ₂ Cu ₃ O _7-x , Sm ₁ Ba ₂ Cu ₃ O _7-x , Nd ₁ Ba ₂ Cu ₃ O _7-x , Gd ₁ Ba ₂ Cu ₃ O _7-x , Eu ₁ Ba ₂ Cu ₃ O _7-x , Er ₁ Ba ₂ Cu ₃ O _7-x , Dy ₁ Ba ₂ Cu ₃ O _{7 -x} , Tm ₁ Ba ₂ Cu ₃ O _7-x Yb ₁ Ba ₂ Cu ₃ O _7-x La ₁ Ba ₂ Cu ₃ O _7-x [where x is a number satisfying 0 <x <1] There is a composite oxide superconducting thin film.

The oxide is preferably a perovskite oxide or a pseudo perovskite oxide. The pseudo perovskite has a structure similar to the perovskite, and includes, for example, an oxygen-deficient perovskite type, an orthorombic type, and the like.

In addition to the above system, the present invention further provides the following general formula: D ₄ (E _1-q , Ca _q ) _m Cu _h O _{p + r} [where D is Bi or Tl; M is a number satisfying 6 ≦ m ≦ 10, n is a number satisfying 4 ≦ n ≦ 8, p, q and r Can be applied to a composite oxide superconducting thin film mainly containing a composition represented by p = (6 + 2m + 2n) / 2 0 <q <1-2 ≦ r ≦ 2.

The substrate is generally made of glass, quartz, Si, sapphire, stainless steel and ceramics.
In particular, the substrate is preferably a MgO single crystal or a SrTiO ₃ single crystal. The deposition surface of these single crystal substrates can be a {001} plane or a {110} plane. Thereby, the crystal constituting the superconductor becomes a crystal having uniform c-axis orientation, and particularly the critical current density Jc is increased.

The superconducting thin film is formed by various methods such as physical vapor deposition (PVD) such as low-pressure evaporation, sputtering, and ion plating, reactive evaporation, and photo-CVD, and furthermore, such as molecular beam epitaxy. Can be used. Generally, a sputtering method is often used.

The atomic ratio of each metal element in the evaporation source used in the physical vapor deposition method is adjusted according to the evaporation efficiency of these metal elements and the probability of adsorption on the substrate. The following are specific ratios of α and β for typical composite oxide systems.

Y / (Y + Ba): 0.06 to 0.94, preferably 0.1 to 0.4 Ba / (La + Ba): 0.04 to 0.96, preferably 0.08 to 0.45 These deposition sources are oxides, carbonates, nitrates or sulfates of each metal element. Mixed powder (if necessary, mixed oxide of at least one element selected from the group consisting of Al, Fe, Co, Ni, Zn, Ag and Ti,
(A powder of carbonate, nitrate or nitrate can also be added). For example, a sintered body of a mixed powder of Y ₂ O ₃ , CuO and BaCuO ₂ can be used.

The sintering temperature in the case of the above system can be in the following range.

Y + Ba series 220 ~ 1230 ℃ La + Ba series 234 ~ 1260 ℃ The evaporation source is divided into multiple parts.
+ Y) two with a deposition source comprising a composite oxide, or
Y, Ba, and Cu can be divided into three simple substances.

In order to improve the superconducting properties of the oxide superconducting thin film,
After film formation, heat treatment is preferably performed in an oxygen-containing atmosphere. This heat treatment is performed at an oxygen partial pressure of 0.1 to 150 atm for 300 to 1500
Heat to 100 ° C and maintain the temperature for at least 1 hour, then 100 ° C
It is preferable to go through a process of gradually cooling at a cooling rate of not more than 10 ° C./min, preferably not more than 10 ° C./min. In any case, if the temperature is outside this range, the effect of heat treatment will not be exhibited, especially if the temperature exceeds 1500 ° C, the adverse effect on the oxide superconductor will be greater, and the oxide superconductor treated at such high temperature May lose superconductivity.

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. The superconducting thin films of the following examples were all manufactured using a magnetron sputtering apparatus. For comparison, a sample provided with a polymer compound layer and a sample without the same were prepared under the same other conditions for each example.

Example 1 After mounting a substrate and a raw material target in a chamber,
The chamber is evacuated to a vacuum, and 5.0 × 10 ^-2 Torr Ar gas is exhausted.
1.0 × 10 ^-2 Torr O ₂ gas was introduced. The temperature of the substrate was set to 670 ° C., and vapor deposition was performed. A high frequency power of 3 W / cm ² was applied to the magnetron electrode. As the oxide superconducting thin film material target, Y, the molar ratio of Ba is 1: at 2 by mixing a Y ₂ O ₃ and BaCO _3, further, Y, Ba, a molar ratio of Cu 1: 2: 3 A YBa ₂ Cu ₃ O ₇ sintered block (300 mmφ) obtained by sintering at 950 ° C. a mixture obtained by mixing CuO in an excess of 10% by weight as compared with the amount described below was used.
An MgO single crystal was used for the substrate, and the {001} plane was used as a film forming surface.
The film is formed at a film forming rate of about 0.50Å / sec until the film thickness becomes 1 μm.
After maintaining the temperature at 650 ° C. for 15 hours, it was cooled at 7 ° C./min.

Next, after this heat treatment, a polyimide resin layer (manufactured by DuPont) having a thickness of 5 μm was formed on the surface of the thin film by spin coating. The curing temperature after coating is 300 ℃ × 30
Minutes. That is, the obtained superconducting thin film has a polyimide resin coating on its surface. Further, as described above, a comparative sample using only the superconducting thin film without forming the polyimide resin coating layer was also prepared.

A sample was prepared for measuring the resistance of the obtained sample. In the sample for performing the resistance measurement, a pair of Al electrodes was further formed on both ends of the thin film formed on the substrate by vacuum evaporation, and a lead wire was soldered to the Al electrode.

The critical temperatures Tc and Tcf were measured by immersing the sample in liquid helium in a cryostat, cooling it to 8K, and then confirming that the sample showed superconductivity. And the temperature (Tc) at which the superconductivity of the sample disappears and exhibits the same electrical resistance as in the normal state was measured. The measurement of Tc and Tcf was performed twice, immediately after the production of the superconducting thin film and one month later, to evaluate changes over time in characteristics.

 Table 1 shows the main film forming conditions and Tc and Tcf.

Example 2 As a raw material target, La ₂ O ₃ and BaCO ₃ were mixed at a molar ratio of La and Ba of 1: 2, and CuO was mixed with a molar ratio of La, Ba and Cu of 1: 2: 3 by more than 10%. L obtained by mixing in excess by weight% and sintering at 970 ° C
An aBa ₂ Cu ₃ O ₇ sintered block was used, and a {001} plane of MgO single crystal was used as a film formation surface for a substrate.

The procedure of film formation and the method of measuring Tc and Tcf were the same as in Example 1. Table 1 shows the main film forming conditions and Tc and Tcf.

Example 3 An oxide superconducting thin film produced using the same raw materials as in Example 1 under the same conditions was coated with an epoxy resin (manufactured by Shin-Etsu Chemical Co., Ltd.) of about 1 mm in the same manner as in Example 1.

The procedure of film formation and the method of measuring Tc and Tcf were the same as in Example 1. Table 2 shows the main film forming conditions and Tc and Tcf.

Example 4 An oxide superconducting thin film produced using the same raw materials as in Example 2 and under the same conditions was coated with the same epoxy resin as in Example 4 in the same manner as in Example 1.

The procedure of film formation and the method of measuring Tc and Tcf were the same as in Example 1. Table 2 shows the main film forming conditions and Tc and Tcf.

Although the Tc and Tcf of each superconducting thin film prepared according to the method of the present invention were substantially the same as those immediately after preparation even after one month, the superconducting thin film without coating was obtained.
Tc and Tcf dropped significantly after one month.

As a result of these examples, the superconducting thin film coated with the polymer compound of the present invention can appropriately control oxygen defects in the crystal, maintain the state for a long time, and have excellent characteristics stably. Proven.

Effect of the Invention As described above, the present invention provides an oxide superconducting thin film having superconducting properties much more stable than conventional superconductors.

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 or an Anker (Anacke).
r) memory element, and superconducting quantum interferometer (SQUID)
It is effective when used for such purposes.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shuji Yazu 1-1-1, Koyokita, Itami City, Hyogo Prefecture, Japan Itami Works, Sumitomo Electric Industries, Ltd. No. 1-1, Itami Works, Sumitomo Electric Industries, Ltd. (56) References JP-A-63-303813 (JP, A) JP-A-64-7414 (JP, A) JP-A-1-282175 (JP, A) JP-A-1-305880 (JP, A) Appl. Phys. Lett. 51 (7), 17 Aug. 1987, p. 532-534

Claims (2)

(57) [Claims] 1. A composite oxide superconducting material formed as a thin film on a substrate, and a polymer impermeable to oxygen formed by a polyimide resin or diallyl phthalate resin coating the surface of the composite oxide superconducting material thin film A composite oxide-based superconducting thin film comprising a compound layer. 2. The following general formula: (α _{1 -x} β _x ) Cu _y O _{z wherein} α is an element selected from Group IIa of the periodic table and β is selected from Group IIIa of the periodic table X is an atomic ratio of β to α + β in the range of 0.1 ≦ x ≦ 0.9, and y and z are each obtained when (α _1−x β _x ) is set to 1.
The atomic ratio satisfies 0.4 ≦ y ≦ 3.0 and 1 ≦ z ≦ 5. And a composite oxide superconducting material formed mainly as a thin film on a substrate, and a high oxygen impregnated with an alkyd resin formed on the surface of the composite oxide superconducting material thin film. A composite oxide-based superconducting thin film comprising a molecular compound layer.