JP5739726B2 - Superconducting thin film substrate manufacturing method, superconducting thin film substrate, and superconducting thin film - Google Patents

Description

  The present invention relates to a method of manufacturing a base material for a superconducting thin film used for superconducting equipment such as a superconducting cable and a superconducting magnet, a base material for a superconducting thin film, and a superconducting thin film. Regarding technology.

Conventionally, RE-based superconductors (RE: rare earth elements) are known as a type of high-temperature superconductor exhibiting superconductivity at a liquid nitrogen temperature (77 K) or higher. In particular, an yttrium-based superconductor represented by the chemical formula YBa ₂ Cu ₃ O _7-y (hereinafter, Y-based superconductor or YBCO) is representative. Note that the Y-based superconductor includes a superconductor in which a part of yttria is replaced with gadolinium (Gd) (for example, expressed as (Y + Gd) BCO).
A superconducting thin film using a Y-based superconductor (hereinafter referred to as a Y-based superconducting thin film) is generally formed by sequentially forming an intermediate layer, a layer composed of a Y-based superconductor (hereinafter referred to as a Y-based superconducting layer), and a protective layer on a metal substrate. Have a laminated structure.
This Y-based superconducting thin film forms, for example, an intermediate layer including an alignment layer on a low-magnetic non-oriented metal substrate (for example, Hastelloy (registered trademark, manufactured by Haynes) which is a nickel-based heat-resistant and corrosion-resistant alloy) On the alignment layer, a Y-based superconducting layer is formed by pulsed laser deposition (PLD), metal organic chemical vapor deposition (MOCVD), or the like.

  It is known that the critical current characteristic (Ic characteristic) in such a high-temperature superconducting thin film greatly depends on the crystal orientation of the superconductor, particularly biaxial orientation. Therefore, in order to obtain a superconducting layer having high biaxial orientation, it is necessary to improve the crystallinity of the intermediate layer serving as a base. As one of the methods, there is an ion beam assisted deposition (IBAD) (for example, Patent Document 1). The IBAD method is a method in which an alignment layer is formed by depositing vapor deposition particles from a vapor deposition source on a film formation surface while irradiating an ion beam from an oblique direction with respect to the film formation surface. In the IBAD method, since high biaxial orientation is obtained with a thin film, MgO, which is a rock salt type, is used as a vapor deposition source and has become the mainstream of development. Hereinafter, the MgO layer formed by the IBAD method is referred to as an IBAD-MgO layer.

Further, a technique has been proposed in which a cap layer made of CeO _{2 is formed} on an IBAD-MgO layer, and the in-plane orientation is further improved by the self-alignment effect of CeO ₂ (for example, Patent Document 2 and Non-Patent Document 1). ). Patent Document 2 and Non-Patent Document 1 disclose a technique in which a CeO ₂ cap layer is formed by a PLD method on an alignment layer formed by an IBAD method, and a superconducting layer is formed thereon.

JP 2003-96563 A JP 2009-70926 A

Fujikura Technical Review No. 116, July 2009, p38-42

However, when the CeO ₂ cap layer is formed by the PLD method, since toxic F ₂ gas is used, care is required for safe handling. Further, since expensive noble gases such as Kr and Ne are used, it is difficult to reduce the cost. Furthermore, when forming a CeO ₂ cap layer by PLD, about the diameter on the surface of CeO ₂ cap layer 1 [mu] m, projections are likely to occur called droplets height of about 20 to 40 nm. These protrusions are not oriented because they are formed independently of the surrounding crystal. When a superconducting layer is formed on such a CeO ₂ cap layer, a crystal that inhibits the current path of the superconducting current is formed in the superconducting layer, so that the superconducting characteristics (eg, Ic characteristics) of the superconducting thin film are reduced. End up.

The present invention has been made in order to solve the above-mentioned problems, and it is possible to improve the safety of the CeO ₂ cap layer in the film formation process, and to reduce the cost of the superconducting thin film and improve the current-carrying characteristics. The purpose is to provide.

The invention described in claim 1
Forming a bed layer on a metal substrate;
Forming an alignment layer on the bed layer by ion beam assisted deposition;
Forming a cap layer made of CeO ₂ by sputtering on the alignment layer in a mixed gas atmosphere of an inert gas and oxygen;
Equipped with a,
In the method for producing a substrate for a superconducting thin film , the mixed gas atmosphere in the step of forming the cap layer has an oxygen partial pressure of 4.0 × 10 ^{−2 to} 1.8 × 10 ⁻¹ Pa. is there.

Invention of Claim 2 in the manufacturing method of the base material for superconducting thin films of Claim 1 ,
The method includes a step of forming a lattice matching layer made of LaMnO ₃ on the alignment layer.

Invention of Claim 3 in the manufacturing method of the base material for superconducting thin films of Claim 2 ,
The mixed gas atmosphere in the step of forming the cap layer has an oxygen partial pressure of 2.0 × 10 ^{−2 to} 1.3 × 10 ⁻¹ Pa.

Invention of Claim 4 in the manufacturing method of the base material for superconducting thin films as described in any one of Claims 1-3 ,
The mixed gas atmosphere in the step of forming the cap layer is characterized in that the total pressure is 3 × 10 ^{−1 to} 7 × 10 ⁻¹ Pa.

Invention of Claim 5 in the manufacturing method of the base material for superconducting thin films as described in any one of Claims 1-4 ,
The bed layer is made of GZO.

Invention of Claim 6 in the manufacturing method of the base material for superconducting thin films as described in any one of Claims 1-4 ,
The bed layer is composed of two layers of Y ₂ O ₃ / Al ₂ O ₃ .

The invention of claim 7 is a superconducting thin film forming substrate obtained by the production method according to any one of claim 1 to 6
The peak position of CeO ₂ (200) by X-ray diffraction of the cap layer is 32.93 ° or more.

According to an eighth aspect of the present invention, there is provided a superconducting layer on the surface of the superconducting thin film substrate obtained by the manufacturing method according to any one of the first to sixth aspects or the superconducting thin film substrate according to the seventh aspect. Is a superconducting thin film.

Below, the background that led to the completion of the present invention will be described.
The inventor of the present invention paid attention to a sputtering method that does not require the use of an expensive noble gas such as F ₂ that is a toxic gas, Kr, or Ne as a method for forming a CeO ₂ cap layer. In general, the sputtering method is performed in an Ar atmosphere, and Ar ions generated by plasma discharge collide with a vapor deposition source, thereby depositing vapor deposition particles ejected from the vapor deposition source on the film formation surface.
However, when depositing the CeO ₂ cap layer in a typical Ar atmosphere, good in-plane orientation in the CeO ₂ cap layer was not obtained. In addition, in the CeO ₂ cap layer formed by sputtering using a general Ar, not only the crystal in which the c-axis is oriented in the vertical direction of the substrate (c-axis oriented crystal), but also the c-axis is perpendicular to the substrate. It was found that there was a crystal tilted from the direction (different orientation crystal). When a different orientation crystal is present in the CeO ₂ cap layer, when the superconducting layer is formed on the CeO ₂ cap layer, a crystal that obstructs the current path of the superconducting current is formed, so that the Ic characteristic of the superconducting thin film is deteriorated. .

We investigated the deposition conditions for forming the CeO ₂ cap layer by sputtering. When the CeO ₂ cap layer is formed by sputtering, the in-plane orientation degree Δφ of the CeO ₂ cap layer is minimized at a certain value when the oxygen partial pressure is gradually increased. It was found that the degree of orientation Δφ increases. Thus, forming a CeO ₂ cap layer in a mixed gas atmosphere of argon and oxygen in which the oxygen partial pressure is controlled to an appropriate range has a good in-plane orientation and a cap layer with few different orientation crystals. We obtained the knowledge that it is very effective in realizing.

The present invention has been completed based on the above findings, and further experiments define the range of the oxygen partial pressure when the CeO ₂ cap layer is formed by sputtering.

According to the present invention, since the CeO ₂ cap layer is formed by sputtering, it is not necessary to use a toxic gas such as F ₂ gas. Therefore, the safety in the CeO ₂ cap layer deposition process is improved. In addition, since no expensive rare gas such as Kr or Ne is used, the cost can be reduced.
Furthermore, since no droplet is generated on the surface of the CeO ₂ cap layer, a cap layer having good surface flatness and in-plane orientation can be realized. Therefore, crystals that inhibit the current path of the superconducting current are not formed in the superconducting layer, and the current-carrying characteristics of the superconducting thin film can be improved.

It is a figure which shows the laminated structure of the superconducting thin film which concerns on embodiment. It is a figure which shows the structure of the base material for superconducting thin films which concerns on embodiment. It is a figure which shows the manufacturing process of the base material for superconducting thin films which concerns on embodiment. It is a figure which shows the structure of the base material for superconducting thin films which has the lattice matching layer which concerns on embodiment. It is a figure which shows the manufacturing process of the base material for superconducting thin films which has the lattice matching layer which concerns on embodiment. It is a figure which shows the relationship between the in-plane orientation degree of a cap layer, and oxygen partial pressure. It is a diagram showing the relationship between the peak position and the oxygen partial pressure of the X-ray diffraction for the cap layer CeO 2 ₍₂₀₀₎ when the measured theta-2 [Theta] by (K [alpha line of copper). It is a figure which shows the relationship between the in-plane orientation degree of the cap layer of the base material for superconducting thin films which has a lattice matching layer, and oxygen partial pressure.

Hereinafter, embodiments of the present invention will be described in detail.
FIG. 1 is a view showing a laminated structure of a superconducting thin film 1 according to this embodiment.
As shown in FIG. 1, the Y-based superconducting thin film 1 has a laminated structure in which an intermediate layer 20, a superconducting layer 30, and a stabilization layer 40 are formed in this order on a metal substrate 10. The metal substrate 10 and the intermediate layer 20 in FIG. 1 constitute the superconducting thin film substrate 2 according to the present invention.

  In the present embodiment, the metal substrate 10 is a low-magnetic non-oriented metal substrate (for example, Hastelloy C276 (registered trademark)). The intermediate layer 20 has a bed layer and an alignment layer, and is formed in order to achieve high in-plane alignment in the superconducting layer 30. The superconducting layer 30 is a Y-based superconducting layer made of a Y-based superconductor, and is formed by, for example, the MOCVD method. On the upper surface of the superconducting layer 30, a stabilizing layer 40 made of silver is formed by sputtering, for example.

FIG. 2 is a view showing the structure of the superconducting thin film substrate 2 according to this embodiment. Moreover, the film-forming process of the base material 2 for superconducting thin films is shown in FIG.
As shown in FIG. 2, the intermediate layer 20 includes a bed layer 21, an alignment layer 22, and a cap layer 23.

The bed layer 21 is a layer made of GZO (Gd ₂ Zr ₂ O ₇ ) for promoting the orientation of the orientation layer 22 and preventing the constituent elements of the metal substrate 10 from diffusing, and has a thickness of 20 to 200 nm. It is.
The bed layer 21 is formed, for example, by RF sputtering in an argon atmosphere (step S101 in FIG. 3). In the RF sputtering method, an inert gas ion (for example, Ar ⁺ ) generated by plasma discharge is caused to collide with a vapor deposition source (GZO), and the ejected vapor deposition particles are deposited on a film formation surface to form a film. The film formation conditions at this time are appropriately set depending on the film thickness of the bed layer 21 and the like. For example, RF sputtering output: 100 to 500 W, transfer speed: 10 to 100 m / h, film formation temperature: 20 to 500 ° C. Is done.
The bed layer 21 can be formed by ion beam sputtering in which ions generated by an ion generator (ion gun) collide with a vapor deposition source.

The alignment layer 22 is a polycrystalline thin film made of MgO for aligning the crystals of the superconducting layer 30 in a certain direction, and has a film thickness of 1 to 20 nm. The alignment layer 22 is formed by the IBAD method in an atmosphere of argon, oxygen, or a mixed gas of argon and oxygen (step S102 in FIG. 3). In the IBAD method, an assist ion beam is irradiated from an oblique direction with respect to a film formation surface, and vapor deposition particles ejected from a vapor deposition source (MgO) by RF sputtering (or ion beam sputtering) are deposited on the film formation surface. Film. The film formation conditions at this time are appropriately set depending on the film thickness of the alignment layer 22 and the like. For example, assist ion beam voltage: 800 to 1500 V, assist ion beam current: 80 to 350 mA, assist ion beam acceleration voltage: 200 V, RF sputtering output: 800 to 1500 W, transport speed: 80 to 500 m / h, film forming temperature: 5 to 250 ° C.
The alignment layer 22 is formed by reactive sputtering, in which Mg is formed by reacting the Mg and oxygen that is sputtered out by sputtering in a mixed gas atmosphere of argon and oxygen with the deposition source being Mg. It can also be used.

The cap layer 23 is a layer made of CeO ₂ for protecting the alignment layer 22 and improving the lattice matching with the superconducting layer 30 and has a film thickness of 200 to 400 nm. The cap layer 23 is formed by RF sputtering (step S103 in FIG. 3). The film formation conditions at this time are set as appropriate depending on the film thickness of the cap layer 23 and the like. For example, RF sputtering output: 400 to 1000 W, transfer speed: 2 to 50 m / h, film formation temperature: 450 to 800 ° C. Is done.
In the present embodiment, the cap layer 23 is formed in a mixed gas atmosphere of argon and oxygen having an oxygen partial pressure of 2.0 × 10 ^{−2 to} 2.9 × 10 ⁻¹ Pa. Thereby, the cap layer 23 having good surface flatness and in-plane orientation can be realized.

FIG. 4 is a view showing the structure of the superconducting thin film substrate 3 according to this embodiment. Moreover, the film-forming process of the base material 3 for superconducting thin films is shown in FIG.
As shown in FIG. 4, the intermediate layer 20 includes a bed layer 21, an alignment layer 22, a lattice matching layer 24, and a cap layer 23.

The bed layer 21, the alignment layer 22, and the cap layer 23 have the same configuration as in FIG. 2, and are formed by the same film forming process as in FIG.
The lattice matching layer 24 is a layer made of LMO (LaMnO ₃ ) for relaxing the mismatch between the alignment layer 22 made of MgO and the cap layer 23 made of CeO ₂ , and has a film thickness of 20 to 80 nm.
The lattice matching layer 24 is formed by RF sputtering (step S104 in FIG. 5). The film formation conditions at this time are appropriately set depending on the film thickness of the cap layer 23 and the like. For example, RF sputtering output: 100 to 300 W, transfer speed: 20 to 90 m / h, film formation temperature: 550 ° C. to 950 ° C. It is said.

[Example 1]
In Example 1, the Hastelloy substrate 10 was introduced into an RF sputtering film forming apparatus and evacuated to 1 × 10 ⁻³ Pa. Then, the bed layer 21 made of GZO was formed at room temperature at a film thickness of 100 nm and a conveyance speed of 30 m / h by RF sputtering using GZO as an evaporation source.

Next, the base material on which the bed layer 21 was formed was introduced into an IBAD apparatus and evacuated to 1 × 10 ⁻⁴ Pa. Then, the alignment layer 22 made of MgO was deposited at room temperature at a film thickness of 5 nm and a transport speed of 80 m / h by using the IBAD method using MgO as a deposition source.

Next, the base material on which the alignment layer 22 was formed was introduced into an RF sputtering film forming apparatus and evacuated to 1 × 10 ⁻³ Pa. And it heated up until base-material temperature (film-forming temperature) became 500 degreeC, Then, it vacuumed to 3.0 * 10 < ^-3 > Pa.
Thereafter, a mixed gas of argon and oxygen was introduced to make the total pressure 4.4 × 10 ⁻¹ Pa. Then, the CeO ₂ as an evaporation source, a cap layer 23 made of CeO ₂ by RF sputtering, was formed in a thickness of 400 nm. The film formation conditions were RF sputter output: 800 W and transfer speed: 4 m / h. At this time, the oxygen partial pressure was changed in the range of ⁰ to 2.9 × 10 ⁻¹ Pa in order to examine the change in the properties of the cap layer 23 due to the oxygen partial pressure.
And the superconducting layer 30 and the stabilization layer 40 were formed into the film | membrane 2 for obtained superconducting thin films, and the superconducting thin film 1 was produced.

[Example 2]
In Example 2, in the film forming process of the cap layer 23, the cap layer 23 made of CeO ₂ was formed with a film thickness of 200 nm at a conveyance speed of 8 m / h. At this time, the oxygen partial pressure was changed in the range of ⁰ to 2.9 × 10 ⁻¹ Pa in order to examine the properties of the cap layer 23 due to the oxygen partial pressure. Other film forming conditions were the same as in Example 1.
And the superconducting layer 30 and the stabilization layer 40 were formed into the film | membrane 2 for obtained superconducting thin films, and the superconducting thin film 1 was produced.

FIG. 6 is a graph showing the relationship between the in-plane orientation degree of the cap layer 23 of the superconducting thin film substrate 2 obtained in Examples 1 and 2 and the oxygen partial pressure. FIG. 7 shows CeO ₂ (200) when θ-2θ is measured by X-ray diffraction (copper Kα ray) for the cap layer 23 of the superconducting thin film substrate 2 obtained in Examples 1 and 2. It is a figure which shows the relationship between the peak position of and oxygen partial pressure.

[Example 3]
In Example 3, the Hastelloy substrate 10 was introduced into an RF sputtering film forming apparatus and evacuated to 1 × 10 ⁻³ Pa. Then, the bed layer 21 made of GZO was formed at room temperature at a film thickness of 100 nm and a conveyance speed of 30 m / h by RF sputtering using GZO as an evaporation source.

Next, the base material on which the bed layer 21 was formed was introduced into an IBAD apparatus and evacuated to 1 × 10 ⁻⁴ Pa. Then, the alignment layer 22 made of MgO was deposited at room temperature at a film thickness of 5 nm and a transport speed of 80 m / h by using the IBAD method using MgO as a deposition source.

Next, the base material on which the alignment layer 22 was formed was introduced into an RF sputtering film forming apparatus and evacuated to 1 × 10 ⁻³ Pa. And it heated up until the substrate temperature (film-forming temperature) became 800 degreeC, Then, it vacuumed to 3.0 * 10 < ^-3 > Pa. Then, using LaMnO ₃ as an evaporation source, the lattice matching layer 24 made of LaMnO ₃ was formed by RF sputtering at a film thickness of 30 nm and a conveyance speed of 60 m / h.

Next, the base material on which the lattice matching layer 24 was formed was introduced into an RF sputtering film forming apparatus and evacuated to 1 × 10 ⁻³ Pa. And it heated up until the substrate temperature (film-forming temperature) became 700 degreeC, Then, it vacuumed to 3.0 * 10 < ^-3 > Pa.
Thereafter, a mixed gas of argon and oxygen was introduced to make the total pressure 4.4 × 10 ⁻¹ Pa. Then, the CeO ₂ as an evaporation source, a cap layer 23 made of CeO ₂ by RF sputtering, was formed in a thickness of 200 nm. The film formation conditions were RF sputter output: 800 W and transfer speed: 4 m / h. At this time, the oxygen partial pressure was changed in the range of ⁰ to 2.9 × 10 ⁻¹ Pa in order to examine the change in the properties of the cap layer 23 due to the oxygen partial pressure.
And the superconducting layer 30 and the stabilization layer 40 were formed into the film | membrane 3 for obtained superconducting thin films, and the superconducting thin film 1 was produced.
FIG. 8 is a graph showing the relationship between the in-plane orientation degree of the cap layer 23 of the superconducting thin film substrate 3 obtained in Example 3 and the oxygen partial pressure.

In the case of Example 1 (the thickness of the cap layer 23 is 400 nm), as shown in FIG. 6, when the oxygen partial pressure is 2.0 × 10 ^{−2 to} 2.9 × 10 ⁻¹ Pa, the cap layer The in-plane orientation degree Δφ of No. 23 was 6 ° or less, and it was confirmed that the film had good in-plane orientation. Further, when the oxygen partial pressure is 4.0 × 10 ^{−2 to} 1.8 × 10 ⁻¹ Pa, the in-plane orientation degree Δφ of the cap layer 23 is 5 ° or less, and it has a better in-plane orientation. Was confirmed. Further, when the oxygen partial pressure is 5.5 × 10 ^{−2 to} 1.4 × 10 ⁻¹ Pa, the in-plane orientation degree Δφ of the cap layer 23 is 4.5 ° or less, and a better in-plane orientation is obtained. It was confirmed to have.

When the oxygen partial pressure is as low as less than 2.0 × 10 ⁻² Pa, CeO ₂ is in an oxygen-deficient state, and the crystal structure of the cubic crystal of CeO ₂ is distorted, shifting from a cubic structure that is a complete crystal structure to a crystal structure. Occurs. For this reason, it is considered that the variation in crystal orientation is large and Δφ has increased.
On the other hand, when the oxygen partial pressure is increased, the crystal structure of CeO ₂ approaches a cube having a complete crystal structure, so that the crystal orientation is likely to be aligned and Δφ is considered to have decreased.

Further, as shown in FIG. 7, when the oxygen partial pressure was 2.0 × 10 ⁻² Pa or more, the peak position of CeO ₂ (200) was 32.93 ° to 32.96 °. Since the CeO ₂ (200) peak position is high, the lattice constant of the CeO ₂ cap layer 23 is small and the degree of lattice mismatch with the MgO orientation layer 22 is small, so that the in-plane orientation degree Δφ is 6 ° or less. It is thought.
On the other hand, when the oxygen partial pressure is less than 2.0 × 10 ⁻² Pa, since the peak position of CeO ₂ (200) is low, the lattice constant of the CeO ₂ cap layer 23 is large, and the lattice with the MgO alignment layer 22 is large. It is considered that the in-plane orientation degree Δφ is larger than 6 ° due to the large degree of mismatch.
Further, when the oxygen partial pressure is larger than 2.9 × 10 ⁻¹ Pa, since the peak position of CeO ₂ (200) is high, it is considered that the degree of lattice mismatch with the MgO alignment layer 22 is small. It is considered that the in-plane orientation degree Δφ is larger than 6 ° because the amount of oxygen ions sputtering the deposition source is increased and the energy of Ce ejected from the deposition source is reduced.
Since the peak position of CeO ₂ (200) is 33.10 ° at the maximum due to the composition of CeO ₂ , the peak position of CeO ₂ (200) is 32.93 ° or more, and The angle is preferably 10 ° or less.

In the case of Example 2 (the thickness of the cap layer 23 is 200 nm), as shown in FIG. 6, when the oxygen partial pressure is 3.0 × 10 ^{−2 to} 1.8 × 10 ⁻¹ Pa, the cap layer The in-plane orientation degree Δφ of No. 23 was 6 ° or less, and it was confirmed that the film had good in-plane orientation.

As in Example 1, when the oxygen partial pressure is as low as less than 3.0 × 10 ⁻² Pa, CeO ₂ is in an oxygen deficient state, and the cubic crystal structure of CeO ₂ is distorted, resulting in a complete crystal structure. A crystal structure shifts from a certain cube. For this reason, it is considered that the variation in crystal orientation is large and Δφ has increased.
On the other hand, when the oxygen partial pressure is increased, the crystal structure of CeO ₂ approaches a cube having a complete crystal structure, so that the crystal orientation is likely to be aligned and Δφ is considered to have decreased.

Further, as shown in FIG. 7, when the oxygen partial pressure was 3.0 × 10 ⁻² Pa or more, the peak position of CeO ₂ (200) was 32.95 ° or more. Since the CeO ₂ (200) peak position is high, the lattice constant of the CeO ₂ cap layer 23 is small and the degree of lattice mismatch with the MgO orientation layer 22 is small, so that the in-plane orientation degree Δφ is 6 ° or less. It is thought.
On the other hand, when the oxygen partial pressure is less than 3.0 × 10 ⁻² Pa, since the peak position of CeO ₂ (200) is low, the lattice constant of the CeO ₂ cap layer 23 is large, and the lattice with the MgO alignment layer 22 is large. It is considered that the in-plane orientation degree Δφ is larger than 6 ° due to the large degree of mismatch.
Further, when the oxygen partial pressure is larger than 1.8 × 10 ⁻¹ Pa, since the peak position of CeO ₂ (200) is high, it is considered that the degree of lattice mismatch with the MgO alignment layer 22 is small. It is considered that the in-plane orientation degree Δφ is larger than 6 ° because the amount of oxygen ions sputtering the deposition source is increased and the energy of Ce ejected from the deposition source is reduced.

In the case of Example 3 (when the LaMnO ₃ layer (lattice matching layer 24) is introduced between the cap layer 23 and the alignment layer 22, the thickness of the cap layer 23 is 200 nm), as shown in FIG. When the pressure is 2.0 × 10 ^{−2 to} 1.3 × 10 ⁻¹ Pa, the in-plane orientation degree Δφ of the cap layer 23 is 6.5 ° or less, and it is confirmed that the in-plane orientation is good. It was done.

As in Examples 1 and 2, when the oxygen partial pressure is as low as less than 2.0 × 10 ⁻² Pa, CeO ₂ is in an oxygen deficient state, and the crystal structure of the cubic crystal of CeO ₂ is distorted, resulting in a complete crystal The crystal structure is deviated from the cubic structure. For this reason, it is considered that the variation in crystal orientation is large and Δφ has increased.
On the other hand, when the oxygen partial pressure is increased, the crystal structure of CeO ₂ approaches a cube having a complete crystal structure, so that the crystal orientation is likely to be aligned and Δφ is considered to have decreased.
Further, when the oxygen partial pressure is larger than 1.3 × 10 ⁻¹ Pa, since the peak position of CeO ₂ (200) is high, the degree of lattice mismatch with the MgO alignment layer 22 is considered to be small. It is considered that the in-plane orientation degree Δφ is larger than 6.5 ° because the amount of oxygen ions that sputter the deposition source increases and the energy of Ce ejected from the deposition source decreases.

  Among the protrusions on the surface of the cap layer 23 in Examples 1 to 3, it was confirmed that those having a diameter of 3 μm or less had a height smaller than 20 nm.

  Moreover, when the critical current in liquid nitrogen was measured as a voltage definition of 1 μV / cm by the four-terminal method for the superconducting thin films (width 1 cm) obtained in Examples 1 to 3, the in-plane orientation degree Δφ of the cap layer 23 was measured. There was a tendency for Ic characteristics to be better as the value was smaller. Specifically, when the in-plane orientation degree Δφ of the cap layer 23 is 6.5 ° or less, the critical current value is 150 A or more, when it is 6 ° or less, 200 A or more, and when it is 5 ° or less, 250 A or more. In the case of 5 degrees or less, it was 300 A or more.

Thus, in this embodiment, the bed layer 21 is formed on the metal substrate 10 (step S101 in FIGS. 3 and 5), and the alignment layer 22 is formed on the bed layer 21 by ion beam assisted deposition ( step S102 in FIG. 3 and 5), forming a cap layer 23 made of CeO ₂ by sputtering on the alignment layer 22 in a mixed gas atmosphere of argon and oxygen (the step S103 in FIG. 3 and 5). Further, the step of forming a cap layer 23 made of CeO _2, carried out at an oxygen partial pressure of ^{2.0 × 10 -2 ~2.9 × 10 -1} Pa at a argon and oxygen mixed gas atmosphere of.

Thereby, since it is not necessary to use a toxic gas such as F ₂ gas as in the PLD method, safety in the film forming process of the CeO ₂ cap layer 23 is improved. In addition, since no expensive rare gas such as Kr or Ne is used, the cost can be reduced.
Further, since no droplets are generated on the surface of the CeO ₂ cap layer 23, a cap layer having good surface flatness and in-plane orientation can be realized (for example, when the film thickness is 400 μm, the in-plane orientation degree Δφ is 6). .5 ° or less). Therefore, crystals that inhibit the current path of the superconducting current are not formed in the superconducting layer, and the current-carrying characteristics of the superconducting thin film can be improved.
Further, by optimizing the range of oxygen partial pressure, further increase the plane orientation of the CeO ₂ cap layer 23 can be thinned in the CeO ₂ cap layer 23.
Note that when the CeO ₂ cap layer 23 is thinned, it is desired that the in-plane orientation degree Δφ is 6.5 ° or less, and therefore the thickness of the cap layer 23 is preferably 150 nm or more. Further, the in-plane orientation degree is improved by increasing the thickness of the cap layer 23. However, since the improvement in the in-plane orientation degree is saturated when the thickness exceeds 800 nm, the film thickness of the cap layer 23 is preferably 800 nm or less. is there.

The mixed gas atmosphere preferably has a total pressure of 3 × 10 ^{−1 to} 7 × 10 ⁻¹ Pa. When the total pressure exceeds 7 × 10 ⁻¹ Pa, the amount of inert gas increases, so the density of inert gas ions increases, the energy of each inert gas ion decreases, and the inert gas Since ions are sputtered to reduce evaporation, the energy of Ce ejected from the evaporation source is reduced, which is not preferable. In addition, when the total pressure is less than 3 × 10 ⁻¹ Pa, the amount of inert gas is small, so the amount of sputtering to reduce the deposition is reduced, and the amount of Ce ejected from the deposition source is reduced, which is not preferable. .

As mentioned above, although the invention made by this inventor was concretely demonstrated based on embodiment, this invention is not limited to the said embodiment, It can change in the range which does not deviate from the summary.
For example, although the case where the bed layer 21 is made of GZO has been described in the above embodiment, the bed layer 21 may be made up of two layers of Y ₂ O ₃ / Al ₂ O ₃ . In this case, the Y ₂ O ₃ layer promotes the orientation of the alignment layer 22, and the Al ₂ O ₃ layer suppresses cation diffusion from the metal substrate 10.
Further, for example, a non-oriented metal substrate other than Hastelloy, such as SUS304, can be applied to the metal substrate 10.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

DESCRIPTION OF SYMBOLS 1 Superconducting thin film 2 Base material for superconducting thin film 3 Base material for superconducting thin film 10 Metal substrate (Hastelloy)
20 Intermediate layer 21 Bed layer (GZO)
22 Biaxial orientation layer (IBAD-MgO)
23 Cap layer (CeO ₂ )
24 Lattice matching layer (LaMnO ₃ )
30 Superconducting layer (YBCO)
40 Stabilization layer

Claims (8)

Forming a bed layer on a metal substrate;
Forming an alignment layer on the bed layer by ion beam assisted deposition;
Forming a cap layer made of CeO ₂ by sputtering on the alignment layer in a mixed gas atmosphere of an inert gas and oxygen;
Equipped with a,
The mixed gas atmosphere in the step of forming the cap layer has an oxygen partial pressure of 4.0 × 10 ^{−2 to} 1.8 × 10 ⁻¹ Pa . The method for producing a substrate for a superconducting thin film according to claim 1 , further comprising a step of forming a lattice matching layer made of LaMnO ₃ on the alignment layer. 3. The superconducting thin film according to claim 2 , wherein the mixed gas atmosphere in the step of forming the cap layer has an oxygen partial pressure of 2.0 × 10 ^{−2 to} 1.3 × 10 ⁻¹ Pa. A method for producing a substrate. The mixed gas atmosphere in the step of forming said cap layer, a superconducting according to any one of claim 1 to 3, wherein the total pressure is ^{3 × 10 -1 ~7 × 10 -1} Pa A method for producing a thin film substrate. The said bed layer is comprised with GZO, The manufacturing method of the base material for superconducting thin films as described in any one of Claims 1-4 characterized by the above-mentioned. The bed layer is, Y 2 _O 3 _/ Al ₂ superconducting method of manufacturing the thin-film base material according to any one of claim 1 to 4, characterized in that O ₃ of which is composed of two layers. A substrate for a superconducting thin film obtained by the production method according to any one of claims 1 to 6 ,
A base material for a superconducting thin film, wherein a peak position of CeO ₂ (200) by X-ray diffraction of the cap layer is 32.93 ° or more. A superconducting thin film obtained by forming a superconducting layer on the surface of the superconducting thin film substrate obtained by the production method according to any one of claims 1 to 6 or the superconducting thin film substrate according to claim 7 .

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