WO2004038816A1

WO2004038816A1 - Oxide superconductor thin film element

Info

Publication number: WO2004038816A1
Application number: PCT/JP2003/011954
Authority: WO
Inventors: Ryusuke Kita; Yutaka Yoshida
Original assignee: Hamamatsu Foundation For Science And Technology Promotion
Priority date: 2002-10-23
Filing date: 2003-09-19
Publication date: 2004-05-06
Also published as: JPWO2004038816A1; AU2003268648A1

Abstract

An oxide superconductor thin film element which comprises a substrate and an oxide superconductor thin film, wherein the oxide superconductor thin film has a composition represented by Yb1-xNdxBa2Cu3O7-y where x is 0.01 to 0.30 and y is 0.00 to 0.20, and c axes of crystal grains thereof are oriented in a direction perpendicular to the substrate. The oxide superconductor thin film element has allowed the preparation of a thin film element which is free from problems associated with conventional superconductor thin film elements, mentioned in the specification, and exhibits excellent performance capabilities, with a low temperature of a substrate.

Description

Akira Itoda Oxide superconductor thin film device Technical field

The present invention relates to a thin film device using an oxide superconductor. More specifically,

The present invention relates to a thin-film device using an oxide superconductor containing Yb and Nd. Background art

Oxide superconductor (RB a ₂ Cu ₃ 0 ₇ _ _y ; where R is Y, Gd, Eu, Nd, Ho, Yb, Tb, Sm, Pr, Dy, Lu, Er and Tm (One or more elements selected from the group) has a high critical temperature and can use inexpensive liquid nitrogen refrigerants instead of the conventionally used expensive liquid nitrogen refrigerants. It is expected to be applied to transportation wires and ultra-high-speed computing elements. However, in order to exhibit excellent properties (high critical temperature, high critical current density) even when the oxide superconductor is thinned, the crystal grains of these oxide superconductor materials having an orthorhombic structure must be used. It is necessary that the c-axis is oriented perpendicular to the substrate (hereinafter referred to as c-axis orientation).

For example, for high current devices

a ₂ Cu ₃ 0 ₇ - Use of the _y-based materials have been studied (for example, see JP Hei 9 one 03/87094.). However, in the case of Japanese Patent Application Laid-Open No. Hei 9-187094, the wire is manufactured by using a melt processing method, and the crystal grains are randomly oriented in the current transmission direction. Therefore, a sufficient current density cannot be obtained in the oxide superconducting material described in JP-A-9-187094.

In addition, in order to apply these oxide superconducting materials to thin-film devices, a multi-layer stacking process is conventionally required. Must be kept as low as possible.

However, in oxide superconductors, it has not been possible to simultaneously achieve the two tasks of (1) aligning the crystal grains along the C axis and (2) keeping the substrate temperature at the time of thin film production as low as possible.

For example, in the process for forming a YbBa ₂ Cu ₃ 0 ₇ _ _y based oxide superconductor thin film, the following low substrate temperature 700 to 750 ° C, the crystal grains may become the a-axis orientation, or the a-axis Since a considerable amount of oriented crystal grains coexist, c-axis orientation cannot be fully achieved. On the other hand, although the c-axis orientation is more easily performed as the substrate temperature is higher, when the temperature exceeds 750 ° C, diffusion of Ba into the underlying buffer layer becomes remarkable, and there is a problem that the properties of the underlying buffer layer deteriorate. Furthermore, when applied to wires for high-current transport, the total current that can flow as wires (ie, current density x film thickness) must be as large as possible. However, in conventional _{_{_{YbB a 2 Cu 3 0 7 _}}} y thin film, and decreases the critical current density rapidly with increasing film thickness, there is a problem that a sufficient total current can not be obtained. Disclosure of the invention

An object of the present invention is to solve the above-mentioned conventional problems and to provide an oxide superconductor thin film element in which an oxide superconductor exhibiting excellent performance is formed at a low substrate temperature.

That is, the present invention is composed of at least a substrate and an oxide superconductor thin film, the oxide superconductor thin _{_{film, Υ ^ _ χ Νο1 χ Β}} & 2 ( a Iotaiota ₃ 〇 _{7 y,} X is 0 An oxide superconductor thin film element having a composition of 0.01 to 0.30 and y of 0.00 to 20 and having a crystal grain c-axis oriented perpendicular to the substrate. 0.15 m to: preferably 10.0 m The film thickness of the thin film is more preferably 0.15 m to 1.0 // m. More preferably, the thin film has a thickness of 0.25 / m to 1.0 m.

In the present invention, X is 0.01 to 0.30, and y is 0.00 to 0.20.

in the step of depositing on a substrate a sintered body having a composition of a ₂ Cu ₃ 0 _{7 y} as targeting Tsu bets, preparation of the oxide superconductor thin film element temperature of the substrate is 650 ° C~ 850 ° C About.

The temperature of the substrate is preferably 750 ° C to 850 ° C.

Further, the present invention provides an oxide superconductor comprising at least a substrate and an oxide superconductor thin film, wherein the oxide superconductor thin film contains two kinds of rare earth elements, and each of the rare earth elements alone. When the difference in melting point is 10 ° C. or more and the thickness of the oxide superconductor thin film is in the range of 0.25 to 0.75, ⁵ × 10 ^{5 to} 13 × 10 ⁵ AZcm ² A critical current density, or a critical current density of 2 × 10 ^{5 to} ⁴ × 10 ⁵ A / cm ^{2 when} the thickness of the oxide superconductor thin film is in the range of 0.25 to 1 m; The present invention relates to an oxide superconductor thin film element whose axis is oriented perpendicular to a substrate.

Conventionally, there has been disclosed a composition in which a part of Yb is substituted with Nd (Japanese Patent Application Laid-Open No. 9-87094), but no thinning has been performed. According to the present invention, the _{_{Yb i-xNdxB a 2 Cu 3}} 0 7 y system, x = 0. 01~0. 30, preferably a further x = 0. 05~0. 25, also y = 0. 00 In the composition range of y = 0.20, and more preferably, y = 0.00 to 0.05, even at a low film formation temperature, a high critical current density of ⁵ × 10 ⁵ to 13 × 10 ⁵ AZ cm ² An oxide superconductor thin film having the following characteristics is obtained. BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram showing a configuration of an oxide superconducting thin film element of the present invention.

FIG. 2 shows (Yb ^ xNdx) B a ₂ Cu ₃ 〇 ₇ _ _y in the embodiment of the present invention. 5 is a graph showing the mixture ratio of impurity phases in a pulse laser vapor deposition system.

3 in an embodiment of the present invention, is a graph illustrating the _{(Yb -xNdx) B a 2 Cu} 3 0 7 _ y system, the superconducting transition in the pulsed laser deposition target temperature (Tc).

Figure 4 is a graph showing the film thickness dependency of the (Yb Ndu) the critical current density at B a ₂ Cu ₃ 0 ₇ in _{the y} thin film, the temperature 77 ° K (J c).

Figure 5 is a graph showing the film thickness dependency of the (YbQ.gNdo ^) the critical current density at B a ₂ Cu ₃ 0 ₇ in _{the y} thin film, the temperature 77 ° K (J c). BEST MODE FOR CARRYING OUT THE INVENTION

The oxide superconductor thin film element of the present invention will be described below in detail with reference to the accompanying drawings.

The present invention is composed of at least a substrate and an oxide superconductor thin film, oxide superconductor thin film, a _{_{_{Ybi- x Nd x B a 2 Cu}}} 3 0 7 y, x is from 0.01 to 0 30. An oxide superconductor thin film element having a composition in which y is 0.00 to 0.20 and the c-axis of crystal grains is oriented perpendicular to the substrate.

X is preferably from 0.05 to 0.25, more preferably from 0.1 to 0.2. Further, y is preferably from 0.00 to 0.05, more preferably from 0.00 to 0.03. X is from 0.01 to 0.30, y is out of the range of 0.00 to 0.20, the proportion of an impurity phase BaCu_〇 ₂ and Yb ₂ B ACu_〇 ₅ (hereinafter 21 1 phase) Increase or decrease the superconducting transition temperature.

The thin film has a thickness of 0.15 m to 10.0 m. The film thickness is preferably 0.15 to 1.0 im, more preferably 0.25 to 1.0 m. If the thickness of the thin film is smaller than 0.15 m, it is easily affected by the substrate and the buffer layer, and a sufficient critical current density can be obtained by forming a reaction layer. Tend not to be.

Here, that the C axis of the crystal grains is oriented perpendicular to the substrate means that the c axis is perpendicular to the substrate in most (90% or more) of the crystal grains constituting the thin film. It means that.

Further, the present invention, X is 0. from 01 to 0 30, y is 0. 00-0 20 Yb Bok _{_x} Nd _x B a ₂ Cu ₃ 0 ₇ -.. A composition of _y sintered body The present invention relates to a method for producing an oxide superconductor thin film element in which the temperature of the substrate is 650 ° C to 850 ° C in the step of vapor-depositing the target on a substrate.

The temperature of the substrate is preferably from 750 to 850 ° C, more preferably from 750 to 800 ° C. If the temperature of the substrate is lower than 650 ° C, the crystallinity of the superconductor thin film decreases, and the c-axis of the force and the crystal grains becomes difficult to be oriented perpendicular to the substrate. Since the reaction between the thin film and the substrate or the buffer layer proceeds, the orientation of crystal grains is disturbed.

It is composed of at least a substrate and an oxide superconductor thin film. The oxide superconductor thin film contains two kinds of rare earth elements, and the difference in melting point between the oxide superconductors containing each rare earth element alone is A critical current density of ⁵ × 10 ^{5 to} 13 × 10 ⁵ A / cm ^{2 when} the temperature is 10 ° C. or more and the thickness of the oxide superconductor thin film is in a range of 0.25 to 0.75 m, or When the thickness of the oxide superconductor thin film is in the range of 0.25 to 1 m, a critical current density of ² × 10 ⁵ to 4 × 10 ⁵ A / cm ² is exhibited, and the c-axis of the crystal grains is perpendicular to the substrate. The present invention relates to an oxide superconductor thin film element which is oriented in a direction.

The difference in melting point between oxide superconductors containing each rare earth element alone is preferably 10 to 160 ° C, more preferably 40 ° (: to 160.C. The melting point difference is 10 °. If it is less than C, a sufficient critical current density cannot be obtained because the pinning center is not introduced.

The thickness of the oxide superconductor thin film is in the range of 0.25 to 75 μιη. In particular, it is preferable to exhibit a critical current density of ⁵ × 10 ⁵ A / cm ² or more. If the critical current density is ⁵ XI 0 5 A / cm ² less than, it is difficult to apply this device to the power transportation and high magnetic field generation.

When the thickness of the oxide superconductor thin film is in the range of 0.25 to 1 m, it is preferable to exhibit a critical current density of ² × 10 ⁵ A / cm ² or more.

If the critical current density is ² XI 0 ⁵ A / cm 2 less than, not enough power transportation characteristics.

FIG. 1 is a cross-sectional view of the oxide superconductor thin film element of the present invention, and FIG. 2 shows the Nd concentration dependency of the impurity phase mixture ratio in the target sintered body for forming an oxide superconductor thin film of the present invention. FIG. 3 is a graph showing the dependence of the critical temperature on the Nd concentration in the target sintered body for forming an oxide superconductor thin film of the present invention. FIGS. 4 and 5 are graphs showing the oxide superconductivity of the present invention and the comparative example. 4 is a graph showing the film thickness dependence of the critical current density in a body thin film.

An oxide superconductor thin film 2 is provided on a substrate 1 (see (a) of FIG. 1). The substrate 1 is made of a Ni-based alloy such as Hastelloy, and MgO single crystal is also used. When the substrate is N i based alloy, there to prevent reaction of the substrate 1 and the oxide superconductor thin film 2, also inserted child oxide buffer layer 3, such as C e 0 ₂ (shown in FIG. 1 (b) See).

In this case, when forming the oxide superconductor thin film 2, the higher the substrate temperature, the more easily the crystal grains are oriented with the c-axis perpendicular to the substrate, and excellent characteristics (high critical temperature, high critical current density) are obtained. On the other hand, the reaction between the substrate and the oxide superconductor thin film, or the reaction between the oxide buffer layer and the oxide superconductor thin film, becomes more remarkable as the substrate temperature increases, and in many cases, the reaction between the oxide superconductor and the oxide superconductor thin film. Due to the diffusion of Ba, the characteristics of the oxide buffer layer deteriorate.

Embodiment 1

The oxide superconductor thin film 2 is formed by using a pulse laser deposition method or the like. First, an oxide superconductor target for pulsed laser deposition is fabricated as follows.

Oxide, carbonate, etc. of each metal element is used as a starting material and ground and mixed.

A)

The powder obtained in step A is sintered in air or oxygen atmosphere at 880 to 910 ° C for 12 to 48 hours. In some cases, this process is repeated several times (process B).

The sintered body obtained in step B is pulverized, mixed, formed into a predetermined shape, and then further heated to a temperature of about 900 to 930 ° C in an air or oxygen atmosphere and sintered for 12 to 96 hours ( Step C).

The sintered body obtained in step C is further pulverized, mixed and formed into a predetermined shape, and then heated in an oxygen gas flow at 880 to 910 ° C for 12 to 96 hours to perform oxygen annealing. Thereafter, it is cooled under predetermined conditions (step D).

(Yb ^ Ndx) B a ₂ Cu ₃ 〇 ₇ obtained through steps A, B, C and D — In the _y- based target, X is 0.01 to 0.30, and y is 0.00.0 to by selecting 0.10 a composition, declined the proportion of impure phase as seen B a CuO ₂ Ya丫b ₂ B aC uO _s (hereinafter 211 phase) in FIG. 2, a single crystal Phase will be included. As can be seen from FIG. 3, in this composition range, a good target having a high critical temperature can be obtained.

This sintered body is used as a target during pulsed laser deposition to produce a superconductor thin film. The laser is formed using an excimer laser such as ArF, KrF, and XeC1.

Using this target, a thin film is formed by a pulsed laser deposition method. At that time, the substrate temperature is 650 ° C to 850 ° C. Fig. 4 shows the critical current density of the oxide superconductor thin film when the substrate temperature was set at 750 to 85 Ot, and Fig. 5 shows the critical current density when the substrate temperature was set at 650 to 750. ing. In the figure, the example shows an example containing Nd, and the comparative example shows an example containing no Nd.

Despite this perform film formation at a low substrate temperature, (Y b E _{_{_{_ x Nd x) B a 2}}} Cu 3 0 7 _ y thin film was found to be oriented in the c-axis. As shown in Fig. 4, when Nd is not added (x = 0), a critical current density of 10 ⁵ to 10 ⁶ A / cm ² can be obtained with a film thickness of 0.2 m, but the increase in film thickness As a result, the critical current density is remarkably reduced, and is reduced to 2 × 10 ⁴ AZcm ² at a film thickness of 0.5 / xm. On the other hand, when Yb is replaced with Nd for x = 0.10, the critical current density hardly decreases with an increase in film thickness. As a result, a high critical current density of 5 × 10 ⁵ to 13 × 10 ⁵ A / cm ² was obtained in the thickness range of 0.25 to 0.75 m, and the film thickness was further increased to 1 zm. It was also found that the critical current density was 2 × 10 ^{5 to} ⁴ × 10 ⁵ A / cm ² , which is 30 to 60 times higher than that of the same thickness without addition of Nd. 4). Even if the film thickness is reduced to 0.25 m, the same critical current density can be obtained.

Embodiment 2

As the second embodiment, two kinds of oxide superconductor containing a rare earth element _{_{(R _ X R! 'X}} B a 2 Cu 3 〇 ₇ one _y; where R and R' are Y, Gd, Eu, Nd, Ho, Yb, Tb, Sm, Pr, Dy, Lu, Er, and Tm), and the melting point of the oxide superconductor containing each rare earth element alone. The difference is 1 o ° c or more. In general, in order to improve the critical current density of oxide superconductors, it is necessary not only to improve the quality of the superconducting phase but also to introduce a pinning center so that the penetrated magnetic flux does not move. When two types of oxide superconductors with different melting points coexist, the portion of the oxide superconductor phase on the high melting point side acts as an effective pinning center, and the superconducting state can be maintained up to a high magnetic field. Conceivable. For example, NdB a ₂ Cu ₃ 〇 _{7 y} system melting point of about 100 higher than that of Yb B a ₂ Cu ₃ 〇 ₇ _ _y system melting point. In this case, the Nd side, which is mixed in a small amount, acts as the pinning center. In the system containing Yb and Nd, the difference in melting point is about 10 o ° c.However, from the viewpoint of forming a pinning center, it is only necessary to form a region in which the orientation is different. Should be 1 o ° c or more.

Example

Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

Yb _₂ 0 _3, Nd ₂ 〇 _{_3,} B _{aC0 3,} a starting material (or B aO-) and Cu_〇 powder, Yb: Nd: Ba: Cu is 1- x: x: 2: 3 (x = 0 It was weighed so that the molar ratios became 0.05, 0.1, 0.15, 0.2, and 0.3), and sufficiently crushed and mixed (process A).

The powder obtained in step A was fired in an electric furnace at 900 ° C for 12 hours in air. The powder thus obtained was sufficiently pulverized and mixed. This step was repeated twice (step B).

The powder obtained in step B was sufficiently ground and mixed, then pelletized by applying pressure, and calcined in air at 910 ° C for 48 hours (step C).

After the pellet obtained in Step C is sufficiently ground and mixed, it is again pelletized, the pellet is heated to 910 ° C in an oxygen gas flow, held for 12 hours, and then cooled to 500. After holding for a while, oxygen annealing was performed by cooling the furnace (Step D).

The sintered body sample obtained through the above steps A, B, C and D was examined for impurity phases contained in the sample by powder X-ray diffraction method. The results are shown in FIG. 2. The vertical axis of the figure shows the relative intensity of the 211 phase to the 123 phase. As the amount of Nd substitution X increases, the proportion of the impurity phase in the sample decreases. However, at x = 0.1 or more, only the superconducting phase was detected, and no impurity phase was detected.

In addition, the samples obtained through these steps A, B, C, and D were measured for changes in electrical resistivity with temperature, and the superconducting transition temperature Tc was examined. As a result, when the Nd substitution amount X increased, Tc increased, and when x = 0.1, Tc exhibited a maximum value of 95 ° K (see Fig. 3).

As described above, the sintered body obtained through the steps A, B, C and D was used as a target, and a thin film was formed by a pulsed laser deposition method. The laser used was an ArF excimer laser and the substrate used was MgO (100) single crystal. Substrate temperatures of 600 to 850 ° C and film thicknesses of 0.2 m to 1 m were obtained, and the crystal grains were c-axis oriented in each case.

The critical current densities of these thin films at 77 ° K were measured.When the substrate temperature was 750 to 850 ° C, 5 X 10 ⁵ to 13 X in the 0.25 to 0.75 m film thickness region A high critical current density of 10 ⁵ AZcm ² was obtained, and the critical current density hardly decreased even when the force and the film thickness increased. As a result, even when the film thickness was increased to 1 / m, the critical current density was still as high as ² to 4 × 10 ⁵ A / cm ² (see Fig. 4).

On the other hand, when the substrate temperature is set to 600 to 750 ° C, the value of the critical current density is slightly reduced compared to when the substrate temperature is set to 750 to 850, but the tendency with respect to the film thickness is almost the same. (See Figure 5).

Comparative example

In the same manner as in the example, a thin film containing no Nd was produced.

If a thin film containing no Nd, as apparent from FIGS. 4 and 5, the critical current density, the film thickness that also is by 2 m in 10 ⁵ ~10 ⁶ AZcm ² about 0.1, the film thickness increases With a film thickness of 0.25 m or more, it decreases to 10 ⁴ AZcm ² or less. Therefore, in the comparative example, At a film thickness of 0.5 to 0.75 zm, only the critical current density of about 1Z50 of the example could be obtained.

According to the oxide superconductor thin film element of the present invention, the cooling efficiency is increased by several hundred times because a liquid vapor refrigerant is not required. In addition, even with the same size as conventional power cable lines using copper wires, it is possible to achieve a power transmission capacity 10 times or more. When this oxide superconducting thin film element is applied to a magnet, for example, in the case of a Bi-based oxide high-temperature superconductor, due to the inherent properties of the material, the critical current density drops sharply in a magnetic field, the temperature rises at 77 ° K. Although a magnetic field of only about 1T can be generated, a magnetic field several times larger than that can be generated, and it is expected that an ultra-strong magnet will be obtained. As a result, for example, the separation efficiency of the magnetic separation device can be increased by a factor of 10 or more. In addition, the increase in critical current density not only reduces the size of the superconducting generator to less than 1/2, but also increases the stability against load fluctuations, so that the transmission capacity can be increased by 50% even with the existing transmission equipment. For applications in the medical field, the signal intensity of a magnetic resonance imaging device (MRI) is expected to increase by a factor of 40, resulting in higher resolution.

According to the method for manufacturing an oxide superconductor thin film element of the present invention, since a film is formed at a low substrate temperature, other elements of the element do not undergo reaction deterioration during formation of the oxide superconductor thin film, In addition, since the c-axis of the crystal grains is oriented perpendicular to the substrate, the critical current density of 5 × 10 ⁵ to L 3 × 10 ⁵ A / cm ² in the range of 0.25 to 0.75 m Even when the film thickness was increased to 1, a critical current density of ² × 10 ^{5 to} ⁴ × 10 ⁵ AZ cm ² was obtained. Even with such a large film thickness, a critical current density several tens of times higher than that of a conventional oxide superconductor thin film can be obtained, so that an extremely high-performance oxide superconductor thin film element can be realized. In many applications, such as power and medical technology, significant technical and economic improvements are possible. Industrial applicability

According to production method of an oxide superconductor thin film element of the present invention, (Yb ^ Nd ^ in B a ₂ Cu ₃ 0 _{7 y} system, X is from 0.01 to 0.30, and is 0. 00 0.20, and the c-axis of the crystal grains of the thin film was oriented perpendicular to the substrate, and the other elements of the element reacted because the film was formed at a substrate temperature of 650 to 850 ° C during film formation. without degradation, and a wide range of film thickness, an oxide superconductor thin film element exhibiting the critical current density and excellent ^{^{5X 10 5 ~13 X 10 5 AZ}} cm 2 is obtained.

Claims

Scope of Word

1. At least a substrate and an oxide superconductor thin film, wherein the oxide superconductor thin film is Yb

A _{_{_{_{a 2 Cu 3 0 7 _ y}}}} , x has a composition 0. 01~ 0. 30, y is 0. 00~0. 20, c-axis of the crystal grains are oriented perpendicular to the substrate Oxide superconductor thin film element.

2. The oxide superconductor thin film element according to claim 1, wherein said thin film has a thickness of 0.15 / im to 10.0 m.

3. The oxide superconductor thin film element according to claim 2, wherein the thin film has a thickness of 0.15 to 1.0 im.

4. The oxide superconductor thin film element according to claim 3, wherein the thin film has a thickness of 0.25 / m to 1.0 im.

. 5. X is from 0.01 to 0 is 30, y is from 0.00 to 0 20 a is Yb丄_{_{_{-. X Nd x B a 2}}} Cu 3 0 7 - a a composition of _y sintered body as the target A method for producing an oxide superconductor thin film element, wherein the temperature of the substrate is 650 to 850 ° C. in the step of vapor deposition on the substrate.

6. The method for producing an oxide superconductor thin film device according to claim 5, wherein the temperature of the substrate is 750 ° (: to 850).

7. At least a substrate and an oxide superconductor thin film, wherein the oxide superconductor thin film contains two kinds of rare earth elements, and the melting point between the oxide superconductors containing each rare earth element alone. Is 5 ° C. or more and the thickness of the oxide superconductor thin film is in the range of 0.25 to 0.75 m, and 5 × 10 ⁵ to: L 3 × 10 ⁵ A / cm ² Critical current density, or a critical current density of ² × 10 ⁵ to 4 × 10 SAZcm ^{2 when} the thickness of the oxide superconductor thin film is in the range of 0.25 to ¹ , and the c-axis of the crystal grain is Oxide superconductor thin film element oriented vertically.