JPH10330193A - Production of oxide superconducting film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make at high rate an oxide superconducting film with smooth surface and uniform thickness on a simple substrate structure. SOLUTION: This oxide supreconducting film is produced by the following method: a melt 1 for liquid phase epitaxial growth to be used comprises 10 wt.% Y1 Ba2 Cu3 Ox and 90 wt.% Ba3 Cu7 O10 , while a seed crystal (substrate) 2 to be used comprises 100 wt.% MgO; a film-forming atmosphere consists of 2 at.% oxygen and 98 at.% nitrogen; film-forming temperature is set at 900-970 deg.C; the objective film, i.e., Y1 Ba2 Cu3 Ox film 3, is formed by immersing the seed crystal 2 in the melt 1; after finishing the film formation, a rotating shaft 4 supporting the seed crystal 2 is gradually pulled up from position (a) via position (b) to position (c) as shown in the figure; the appropriate angle of inclination of the substrate relative to the melt 1 is 1 to 44 degree; subsequently, the shaft 4 is revolved at a rate of as high as 300 to 3,000 rpm for 5 s to 5 min as shown in (d) in the figure to remove an excess of residual melt 5 from the substrate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing an oxide superconducting film having a smooth surface and a high uniformity of thickness. The present invention also relates to a method for producing an oxide superconducting film having excellent crystallinity and epitaxial properties and having good microwave characteristics.

[0002]

2. Description of the Related Art Research on power application and electronic device application of superconducting leads, superconducting wirings, superconducting microwave devices and the like using an oxide high-temperature superconductor is currently being conducted.
In such applications, (1) high zero resistance temperature, (2) high critical current value, and (3) large area, uniformity, and surface smoothness are required. In order to satisfy the requirement (2), it is desired that a thick film can be produced and that the film has a high critical current density value at the film thickness.

In order to satisfy these requirements, the conventional thickness of 1 μm
It has been reported that a high-temperature film is formed by a co-evaporation method and a sputtering method and subjected to a high-temperature heat treatment in an oxygen atmosphere.
The critical current density was 10 ⁵ A / cm ² , which was about 1/50 as compared with the maximum value of the still thin film.

Recently, Foltyn et al.
6 μm-thick Y ₁ Ba ₂ Cu ₃ Ox formed on the eO ₂ / YSZ (100) substrate by using the pulse laser deposition method
(YBCO) thin film with critical current density of 1 × 10 ⁶ A / cm ²
The Applied Physics Letter (Ap
Plied Physics Letters) No. 63
Volume 13 No. 1848-1850. The substrate structure itself is a multilayer structure and complicated, and as a method for forming a thick film, the film forming speed of the pulse laser vapor deposition method is 0.1 to 0.1.
2 μm / min, which is reported to be slow.

On the other hand, Kitamura et al. Prepared a 10 μm thick Y ₁ Ba ₂ Cu ₃ Ox film on a MgO (100) substrate by a liquid phase epitaxial growth method, and heat-treated at 450 ° C. for 5 hours in an oxygen atmosphere after forming the film. 1 × 10 ⁵ A / at 77K
The critical current density value of cm ² was determined by Physi
cs C) reported in Vol. 256, pp. 64-72.
This film formation technique has a high growth rate of about 2 μm / min, is high in speed, and has a high critical current value proportional to the product of the film thickness and the critical density value, and is promising as a film formation technique. However, a part of the Ba-Cu oxide of the melt adheres to the film, and there is a problem in surface smoothness and uniformity as a superconducting film (superconducting wiring, superconducting microwave line) as an electronic device.

Further, application studies of electronic devices using oxide high-temperature superconductors are currently being conducted. Among them, research and development of superconducting microwave passive elements (resonators and filters) have been actively conducted with the rapid development of the field of mobile communication.

Conventionally, pulse laser deposition, sputtering, co-deposition, and metal organic chemical vapor deposition have been known as methods for producing superconducting films constituting these devices. Shows a relatively good surface resistance value in, for example, Journal of Super Conductivity.
erconductivity) Vol. 6, No. 3, 119-1
Reported in paragraph 60. However, these films have problems that need to be solved. In general, it is known that when the intermodulation distortion increases in high-frequency devices such as a resonator and a filter, interference occurs in a communication system. Therefore, in the resonator and the filter using the superconducting film, it is necessary to suppress the intermodulation distortion.

[0008] The intermodulation distortion of an oxide superconducting film strongly depends on the manufacturing technique and manufacturing conditions, for example, eye triple-e transaction on applied superconductivity (IEEE Transa).
ctions on Applied Superco
nudity) Vol. 7, No. 2, 1911-1916
The existence of grain boundaries in the film has been pointed out as a source of the problem, but it has been reported that the reduction is difficult.

On the other hand, in the liquid phase epitaxial growth method of a Y ₁ Ba ₂ Cu ₃ Ox film, the growth conditions are close to thermal equilibrium with low supersaturation, and a high-quality single crystal film can be produced at high speed. Journal
al. Crystal Growth), Vol. 158, pp. 61-67. Furthermore, liquid phase growth Y ₁ Ba
_{The 2} Cu ₃ Ox film has very small intermodulation distortion of the surface resistance in the microwave region as described above, for example, Ext.
ended Abstracts of 6th In
international Superconductor
ve Conference No. 2 J16.

However, the surface resistance value is 7 to 8 times higher than that of the film formed by the sputtering method and the pulse laser deposition method.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to prepare an oxide superconducting film having a high critical temperature and a high critical current value on a simple substrate structure at a high deposition rate.

Further, the present invention provides a manufacturing technique for effectively preventing a part of the melt, which is particularly problematic in the liquid phase epitaxial growth method, from adhering to the substrate and producing a uniform and high quality film. .

An object of the present invention is to prepare a film having a high critical temperature and a low surface resistance in a microwave region in the production of a Y ₁ Ba ₂ Cu ₃ Ox film by a liquid phase epitaxial growth method.

Further, the present invention can produce a single crystal film having a small number of grain boundaries and a very small tilt angle, which is characteristic of a liquid phase epitaxially grown Y ₁ Ba ₂ Cu ₃ Ox film. An object of the present invention is to provide a manufacturing technique for manufacturing a film having very small intermodulation distortion of surface resistance in a region.

[0015]

According to the present invention, a liquid crystal epitaxial growth method is applied to a superconducting oxide superconducting single crystal, which is applied to a superconducting wiring, a superconducting microwave device, or the like. . By using the liquid phase epitaxial growth method, a thick film having excellent crystallinity and in-plane orientation can be formed on a substrate having a simple structure at a high film forming rate.

Further, the fact that a part of the melt, which is a problem in the liquid phase epitaxially formed film, remains in the substrate and deteriorates the uniformity and surface smoothness of the film can be obtained by tilting the substrate and utilizing the viscosity of the melt. Then, it was found that most of the problems could be solved by pulling away from the melt. After the substrate was tilted and separated from the melt, it became clear that the melt remaining in the corners of the substrate could be removed from the film surface by centrifugal force by rotating the substrate at high speed. According to the present invention, superconducting films having excellent crystallinity and superconducting properties for superconducting wiring and superconducting microwave elements, and having excellent uniformity and surface smoothness can be produced, and the ripple effect of the present invention is enormous. .

Further, in the present invention, an oxide superconducting film is produced by using a liquid phase epitaxial growth method to which a single crystal producing technique is applied, and is applied to a superconducting wiring, a superconducting microwave element and the like. By using the liquid phase epitaxial growth method, a thick film having excellent crystallinity and in-plane orientation can be formed on a substrate having a simple structure at a high film forming rate.

Further, the oxygen partial pressure during film formation and during substrate cooling is reduced to 2
% Or more, it was found that the crystallinity and the in-plane orientation were further improved. Furthermore, it became clear that the surface resistance in the microwave region could be significantly reduced by increasing the oxygen partial pressure. According to the present invention, a superconducting film having good crystallinity and superconductivity for superconducting wiring and a superconducting microwave passive element and exhibiting a low surface resistance value in a microwave region can be produced. It is.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION
The embodiment will be described in detail with reference to FIGS.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a first embodiment of the present invention will be described.

FIG. 1 is a schematic view of a liquid phase epitaxial growth method of the present invention, and for comparison, FIG. 2 is a schematic view of a conventional epitaxial growth method. As the melt 1 for the liquid crystal epitaxial growth, 10 wt. % Y ₁ Ba ₂ Cu ₃ Ox, 90w
t. % Ba ₃ Cu ₇ O ₁₀ and MgO (100) as the seed crystal (substrate) 2. Here, X is the amount of oxygen. The shape of the seed crystal (substrate) 2 is a square or a circle. Oxygen 2 at. %, Nitrogen 98
at. %, And the film formation temperature was 960 to 970 ° C. As shown in FIG. 2A, a Y ₁ Ba ₂ Cu ₃ Ox film 3 is formed by immersing a seed crystal (substrate) 2 in a melt 1.

After the film formation, the rotating shaft 4 supporting the seed crystal 2 is gradually pulled up as shown in FIG. In a normal pulling method, as shown in FIG.
A part of the melt 5 where a-Cu remains remains near the center of the substrate, and the melt 5 where Ba-Cu remains and Y ₁ Ba ₂ Cu ₃ O
Due to the difference in thermal expansion coefficient between the x film 3 and the seed crystal 2, Ba-
Y ₁ Ba ₂ Cu ₃ Ox film 3 under melt 5 with Cu remaining
Of the seed crystal 2 and cleavage of the seed crystal 2 itself.

In the present invention, by tilting the substrate as shown in FIG. 1A, when the rotating shaft 4 supporting the seed crystal 2 is gradually pulled up after the film formation, Y ₁ Ba ₂ Cu ₃
Wettability between Ox film 3 and Ba-Cu melt 1 and Ba-Cu
By optimizing the lifting speed and the inclination angle based on the viscosity of the melt 1 itself, it is possible to gradually separate the melt from the substrate and remove excess Ba-Cu melt. Further, as shown in FIG. 1C, in this method, the melt 5 in which Ba-Cu remains can be driven to the edge of the substrate. FIG. 3A shows a micrograph of the substance of the thin film produced by this method. The marker at the left end is a marker,
One scale represents 1 mm. As is clear from the figure, Y ₁ Ba ₂ Cu by the melt 5 in which Ba—Cu remains at the lower right in the figure.
It turns out that a substantially uniform thin film can be produced in a region of 20 mm × 20 mm except for the portion where the ₃ Ox film is separated. FIG. 4 shows the in-plane distribution of the superconducting characteristics of the sample. The horizontal axis indicates the distance from a certain side, and the vertical axis indicates the superconducting critical temperature. The sample was prepared at 600 ° C for 10 hours,
The heat treatment was performed in an oxygen atmosphere at 00 ° C. for 10 hours and at 400 ° C. for 60 hours. As is clear from the figure, the zero resistance temperature (Tc
end) is 90K or more in this region.
It has a good and uniform superconducting property. In addition, the superconducting start temperature (Tcons)
et) has a characteristic of 92K or more, and also has a good and uniform superconducting characteristic.

It has been experimentally confirmed that when the substrate is separated from the melt surface by about 7 mm, the melt is separated from the substrate. Therefore, if the minimum substrate size is 10 mm in diameter, about 44 degrees is the maximum inclination angle. On the other hand, when the tilt angle was 1 degree or less, the viscosity of the melt did not work well, and many residual melts were confirmed in the film after lifting. Therefore, it is considered that an appropriate inclination angle of the substrate with respect to the melt surface is 1 to 44 degrees.

The pulling speed in this experiment is 1 mm to 10 mm / min.

Next, a second embodiment of the present invention will be described.

A thin film was formed under the same manufacturing conditions as in Example 1, separated from the melt 1 by the pulling method shown in FIG. 1, and then shown in FIG. 1D at a temperature of 900 to 960 ° C. And the seed crystal 2 was rotated about the rotation axis 4 at 1000 rpm for 10 seconds. At that time, the centrifugal force acting on the melt 5 with Ba-Cu remaining on the edge of the substrate is ω ² ×
In proportion to R (ω = angular rotation speed of the pulling shaft, R = distance from the center of the pulling shaft to the melt 5 where Ba-Cu remains), a force acts to separate the substrate from the substrate. FIG. 3 (b)
Fig. 3 shows a micrograph of the substance of the thin film produced under the conditions.
Compared to FIG. 3A, the peeled portion of the Y ₁ Ba ₂ Cu ₃ Ox film due to the melt 5 in which Ba—Cu remains is eliminated, and Ba—
It turns out that the melt 5 in which Cu remained is removed by high-speed rotation. As a result, a uniform thin film was formed in an area of 23 mm × 23 mm. The in-plane distribution of the superconducting critical temperature of the film shown in FIG. 3B is similar to that in FIG. 4, and it has been found that a uniform and good thin film can be produced.

As a result of the experiment, the rotation speed of the substrate was 300 rpm
It was confirmed that m to 3000 rpm was appropriate, and that the substrate rotation time was 5 seconds to 5 minutes.

Next, a third embodiment of the present invention will be described.

The Y ₁ Ba ₂ Cu ₃ Ox film was formed by a liquid phase epitaxial growth method. As a melt for liquid phase epitaxial growth, 18 wt. % Y ₁ Ba ₂ Cu ₃ Ox, 8
2 wt. % Ba ₃ Cu ₇ O ₁₀ and MgO (100) as a seed crystal substrate. FIG. 5 shows θ- of the obtained film.
The thickness dependence of the half width of the rocking curve of the 2θ X-ray diffraction peak (005) is shown. In FIG. 5, squares indicate that the atmosphere at the time of film formation and cooling is 1.3 at. %, Nitrogen 98.7a
t. % And data of a film formed at a film formation temperature of 958 ° C. (a film formed in a low oxygen atmosphere at a low temperature). The decomposition temperature of the Y ₁ Ba ₂ Cu ₃ Ox film in air at 1 atm is 10
00 ° C. In FIG. 5, the triangle indicates that the atmosphere during film formation and cooling is 13 at. %, 87 at. %, And data of a film formed at a deposition temperature of 980 ° C. (a film formed in a high oxygen atmosphere at a high temperature) are shown. In all the films, the C-axis was strongly oriented perpendicular to the substrate. In both cases, the half width of the rocking curve tends to decrease as the film thickness increases. This corresponds to the fact that the average particle size increases as the film thickness increases. Further, it can be seen that the full width at half maximum of the rocking curve of the film formed in a high oxygen atmosphere and at a high temperature is smaller than that of the film formed in a low oxygen atmosphere and at a low temperature (square in FIG. 5). That is, it is understood that the film formed in a high oxygen atmosphere and at a high temperature has good crystallinity.

Next, a fourth embodiment of the present invention will be described.

FIG. 6 shows a spectrum of a film formed under the same two kinds of manufacturing conditions as in Example 3 evaluated by Rutherford backscattering method (RBS). The film thickness was 2 μm. FIG. 6A shows an RBS spectrum of a film manufactured in a low oxygen atmosphere and a low temperature, and FIG. 6B shows an RBS spectrum of a film manufactured in a high oxygen atmosphere and a high temperature.

It can be seen that in both samples, the aligned spectrum is lower than the random spectrum. The χmin value of FIG.
The ratio between the aligned spectrum and the random spectrum at the minimum value of the aligned spectrum near the number 860) is 3.1%, which is relatively good in epitaxial property.
It is considered that there is still some disorder in crystallinity. On the other hand, FIG.
In the sample of (b), the Δmin value was 1.9%,
Its epitaxial properties are very good and this RBS
It seems to be near the limit of the detection sensitivity of the device. As compared to a film prepared at a low oxygen atmosphere and a low temperature, a high oxygen atmosphere,
It can be seen that the film produced at a high temperature shows even better epitaxial properties.

Next, a fifth embodiment of the present invention will be described.
A film was manufactured under the same manufacturing conditions as in Example 3, a microstrip resonator as shown in FIG. 7 was manufactured, and its characteristics were examined. The dimensions of the substrate 13 are 20 mm in length and 8 mm in width, and the center length of the strip portion 11 is 5 mm and the width is 0.5 m.
m, the coupling gap was 0.5 mm, and the resonance frequency was about 10.8 GHz. The strip portion 11 uses a liquid phase epitaxial growth film, and the ground portion 1
2 is a film thickness of 1 μm prepared by a pulsed laser deposition method.
Y ₁ Ba ₂ Cu ₃ Ox film was used. In order to oxidize the liquid phase epitaxially grown Y ₁ Ba ₂ Cu ₃ Ox film, the film was formed in an oxygen atmosphere at 500 ° C. for 50 hours at 400 ° C.
Heat treatment was performed for 60 hours. The no-load Q of these resonators
FIG. 8 shows the temperature change of the (Qo) value. In FIG. 8, the square is
Data of a film manufactured in a low oxygen atmosphere and a low temperature are shown, and triangles show data of a film manufactured in a high oxygen atmosphere and a high temperature. The resonator using the film manufactured in a low oxygen atmosphere and low temperature showed a value of Qo = 3500 at 77K and a value of Qo = 11000 at 60K. On the other hand, a resonator using a film produced in a high oxygen atmosphere and at a high temperature has Qo = 14000 at 77K and Qo at 40K.
= 23000. Since the Qo value of the microstrip resonator is proportional to the reciprocal of the surface resistance of the film, it can be seen that the surface resistance in the microwave region was reduced by using the film manufactured in a high oxygen atmosphere and at a high temperature. The following items can be considered as reasons why the characteristics have been improved by changing the film forming conditions.

(1) In the as-grown state, oxygen is introduced into the film to some extent in a sample prepared in a high oxygen atmosphere (C-axis length determined by X-ray diffraction method).
80 angstrom), the sample prepared in a low oxygen atmosphere is in a state in which oxygen in the film is considerably deficient (C-axis length 11.83 to 11.85 angstrom determined by X-ray diffraction method). In a sample prepared in a low-oxygen atmosphere even in the low-temperature heat treatment, oxygen is not sufficiently introduced into the film, and a part of the semiconductor phase or 60K
As a result, a phase that transitions to superconductivity remains, leading to an increase in surface resistance.

(2) As shown in Examples 3 and 4, the films prepared in a high oxygen atmosphere and at a high temperature have a small half-width of the X-ray diffraction rocking curve and a small Δmin value in RBS. It was confirmed that the crystallinity was improved, and the surface resistance of the film was reduced.

[0037]

As is apparent from the above description, according to the present invention, a thin film having excellent crystallinity and epitaxial properties and a high critical current density can be formed on a simple substrate structure at a high film forming rate. It is possible, and development of high critical current superconducting lead, superconducting wiring, and superconducting wire becomes possible, and the industrial value is great.

Further, according to the present invention, a film having excellent crystallinity and epitaxial property and a low surface resistance can be produced by a liquid phase epitaxial method, and the development of a high-performance superconducting wiring and a superconducting microwave passive element has been developed. It is possible and industrial value is great.

[Brief description of the drawings]

FIG. 1 is a schematic view of a liquid phase epitaxial growth method of the present invention.

FIG. 2 is a schematic view of a conventional liquid phase epitaxial growth method.

FIGS. 3A and 3B are photomicrographs of a thin film entity produced according to two examples of the present invention, wherein FIG.
(B) shows that of Example 2.

FIG. 4 is a graph showing a relationship between a position on a substrate and a superconducting critical temperature of an oxide superconducting film produced according to the present invention.

FIG. 5 shows the relationship between θ− of the Y ₁ Ba ₂ Cu ₃ Ox film produced by the liquid phase epitaxial growth method in Example 3 of the present invention.
It is a graph which shows the film thickness dependence of the half value width of the rocking curve of a 2 (theta) X-ray diffraction peak (005).

FIG. 6 is a graph showing a spectrum of a film manufactured by a liquid phase epitaxial growth method in Example 4 of the present invention, which is evaluated by Rutherford backscattering method. b) shows a high oxygen atmosphere and a high temperature state, respectively.

FIG. 7 is a schematic diagram of a microstrip resonator for measuring a microwave surface resistance value of a liquid phase epitaxial growth film in Example 5 of the present invention.

FIG. 8 shows a resonance frequency of 10.8 in Embodiment 5 of the present invention.
6 is a graph showing a temperature change of an unloaded Q value of a GHz microstrip resonator.

[Explanation of symbols]

1 melt 2 seed crystal _{(substrate) 3 Y 1 Ba 2 Cu 3} Ox film 4 rotating shaft 5 remaining melt 11 strip portion 12 ground portion 13 substrate

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁶ Identification code FI H01L 39/24 ZAA H01L 39/24 ZABB (72) Inventor Tadataka Morishita 1-14-3 Shinonome, Koto-ku, Tokyo Kokusai Superconductivity Inside the Superconductivity Engineering Research Center, Industrial Technology Research Center (72) Inventor Yoichi Enomoto 1-14-3 Shinonome, Koto-ku, Tokyo Inside the Superconductivity Engineering Research Center, International Superconducting Technology Research Center

Claims (8)

[Claims] 1. ReBa ₂ C having a 123-type crystal structure
In a liquid phase epitaxial growth method in which a u ₃ Ox (Re is one of lanthanoids such as Y or Nd and X is an oxygen amount) film is formed from a melt, when the film is separated from the melt after film formation, Wherein the substrate surface is inclined by 1 to 44 degrees with respect to the melt surface. 2. ReBa ₂ C having a 123-type crystal structure
In a liquid phase epitaxial growth method in which a u ₃ Ox film is formed from a melt, the substrate is separated from the melt at a high speed of 300 to 3000 rpm for 5 seconds to 5 seconds.
2. The method for producing an oxide superconducting film according to claim 1, wherein the film is rotated by a minute. 3. The film formation atmosphere is oxygen at 2 at. %, Nitrogen 98
at. The method for producing an oxide superconducting film according to claim 1, wherein the film forming temperature is 900 to 970C. 4. The method according to claim 1, wherein the melt contains 10 wt. % Y ₁ Ba ₂ Cu
₃ Ox, 90 wt. 2. The method for producing an oxide superconducting film according to claim 1, wherein the composition is% Ba ₃ Cu ₇ O ₁₀ . 5. The method according to claim 1, wherein the substrate is made of MgO (100). 6. The method for manufacturing an oxide superconducting film according to claim 1, wherein a speed at which the substrate is pulled up from the melt is 1 mm to 10 mm / min. 7. ReBa ₂ C having a 123-type crystal structure
In a liquid phase epitaxial growth method in which a u ₃ Ox film is formed from a melt, the atmosphere during film formation and substrate cooling is oxygen 2a.
t. % Of the oxide superconducting film. 8. ReBa ₂ C having a 123-type crystal structure
In a liquid phase epitaxial growth method in which a u ₃ Ox film is formed from a melt, the film forming temperature and ReBa in air at 1 atm.
_{2. A} method for producing an oxide superconducting film, wherein the difference from the decomposition temperature of ₂ Cu ₃ Ox is 30 ° C. or less.