JPH0818914B2 - Superconductor device and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to a superconductor device and a method for manufacturing the same.

(Prior Art) It is said that the superconductivity phenomenon is the most peculiar property among various electromagnetic properties exhibited by a substance. It is expected to be utilized and further development in the future.

As an electronic device utilizing such a superconducting phenomenon, a wide range of applications including high-speed switches, high-sensitivity detectors, and high-sensitivity magnetometers are expected.

As a superconductor often used in conventional superconducting devices, for example, Nb ₃ G on the substrate by plasma sputtering is used.
There is a thin film. This critical temperature is 23 ° K at most, and can be used only at the liquid helium temperature. However, the use of liquid helium increases the cooling cost and technical burden accompanying the need for liquefaction / cooling incidental equipment, and further, because the helium resource is extremely small,
It has been a big problem to prevent the practical use of superconductors in the industrial and consumer fields.

Therefore, various attempts have been made to obtain superconductors with a high critical temperature. In particular, recent research on oxide superconducting thin films has been remarkable, and the superconducting critical temperature exceeds 77 ° K, making it an inexpensive liquid. It became possible to operate nitrogen as a refrigerant.

Conventionally, such oxide superconducting thin films have been produced by heating MgO heated to a high temperature mainly by a sputtering method or an evaporation method.
A method of forming on a single crystal substrate or a SrTiO ₃ single crystal substrate is adopted.

Other single crystals for substrates include sapphire and YS.
Z, silicon, gallium arsenide, LiNbO ₃ , GGG, LaGaO ₃ , LaAlO
Attention has been paid to ₃ mag.

However, in the conventional thin film forming method using the MgO single crystal substrate or the SrTiO ₃ single crystal substrate as the substrate, (10
It was difficult to obtain good quality oxide superconducting thin films with (0) and (110) orientations.

In addition, as a common feature of oxide superconductors, (00
1) The surface has a strong orientation. Therefore, (0
It is not only difficult to control the (100) plane (110) orientation other than the 01) plane, but there is a problem that even if the orientation is successful, sufficient superconductivity cannot be obtained.

For these reasons, currently, the development of thin film devices using (001) plane oriented superconducting thin films is the main focus.

However, SIS (superconductor-insulator-superconductor)
When forming a laminated device having a structure, it is necessary to form a thin film having a (001) plane, that is, a thin film having a (100) plane or a (110) plane.

(Problems to be Solved by the Invention) As described above, in the case of forming a stacked device having a SIS structure, a thin film having a (100) plane or a (110) orientation is required, whereas a conventional oxide Conductor thin film (001)
There is a problem that it is extremely difficult to obtain an oxide superconductor thin film having a strong (100) plane or (110) orientation because the orientation is strong in the plane.

The present invention has been made in view of the above circumstances, and (10
An object is to provide an epitaxial superconducting thin film having a good (0) plane or (110) orientation.

[Structure of Invention]

(Means for Solving the Problems) Therefore, in the present invention, as a substrate material, strontium-containing composition having a K ₂ NiF ₄ type crystal structure as shown in the following formula
A (100) plane or (110) plane of a lanthanum-gallium oxide single crystal substrate is used, and a (100) -oriented or (110) oxide superconducting thin film is formed on this substrate by an epitaxial growth method. There is.

Sr _1-x La _1-y Ga _1-z O _4-w (-0.05 <x <0.05, -0.05 <y <0.05, -0.05 <z <0.
05, -0.2 <W <0.2) (Operation) By the way, in the lattice matching between the oxide superconductor and the single crystal substrate, in the case of the (001) plane orientation, the respective lattice constants of the a and b axes become a problem.

The present inventor has found that in the case of a SrLaGaO ₄ single crystal substrate, the lattice constants of the a and b axes are extremely close to those of the oxide superconductor, and the matching is excellent (Japanese Patent Application No. 63-32373).
9).

However, in the case of (100) orientation or (110) orientation, the lattice constants of the respective a and c axes become a problem.

The c-axis lattice constant of SrLaGaO ₄ is 12.681Å, but since it has a three-layer structure, the lattice constant of the smallest unit is 4.22.
It is 7Å.

This is slightly different from the lattice constant of the smallest unit of the oxide superconductor in the c-axis direction, which is 3.76 to 3.92Å. But,
It was discovered that the tetragonal property of a = 3.843Å, c = 4.227Å of SrLaGaO ₄ suppresses the (001) orientation of the oxide superconductor, and also strengthens the (100) orientation or the (110) orientation.

The present invention has been made in view of this point. SrLaGaO ₄
By forming an oxide superconducting thin film on the (100) plane or (110) plane of a single crystal, an oxide superconducting thin film having a good (100) orientation or a (110) orientation can be obtained.

(Example) Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

Example 1 First, a method for producing a SrLaGaO ₄ single crystal will be described.

As a starting material, SrCO ₃ 566.71gr (purity 99.999%), La
₂ O ₃ 677.46gr (Purity 99.999%), Ga ₂ O ₃ 374.77gr (Purity 99.
999%) powder was mixed, calcined at 1000 ° C. to perform decarbonation treatment, and then crushed and press-molded.

The compact thus formed was sintered in air at 1300 ° C. to give approximately 1450 g of Sr _0.96 La _1.04 Ga _1.00.
An O _4.02 sintered body was obtained.

This sintered body was put into an iridium crucible or a platinum crucible having an outer shape of about 80 mm, a height of about 80 mm and a wall thickness of 2 mm, and was melted by high frequency heating. When an iridium crucible was used, a nitrogen atmosphere containing 0.5 to 2% oxygen was used.
When using a platinum crucible, a nitrogen atmosphere containing 10 to 21% oxygen was used. Note that oxygen is added here to prevent decomposition and evaporation of gallium oxide.

From the SrLaGaO ₄ sintered body melted in this way,
Using a [100] -oriented seed crystal, a [100] -oriented SrLaGaO ₄ single crystal was grown by the Czochralski pulling method. The crystal pulling conditions were a pulling rate of 1 to 2 mm / Hr and a crystal rotating speed of 25 rpm, and a very good [100] axis single crystal having a diameter of 30 mm and a length of 70 mm could be obtained.

The SrLaGaO ₄ single crystal thus formed is sliced to complete the substrate for forming a superconductor thin film.

In the above example, the raw material melt was Sr _0.96 La _1.04.
Although a melted Ga _1.00 O _4.02 sintered body was used, a Sr _1.00 La _1.00 Ga _1.00 O ₄ sintered body may be used instead. However, in this case, the cell growth phase of LaSr ₂ GaO ₅ may be mixed, and the yield may be reduced. Therefore,
In the above example, Sr _0.96 whose composition was moved to the side with less Sr.
La _1.04 Ga _1.00 O _4.02 is used to improve the yield.

Further, a single crystal was formed using the method of the present invention by changing the composition ratio of the raw material melt, and in any case, if the crystal is of good quality, SrLaGaO ₄ single crystal Sr _{1- x} La _1-y Ga _1-z O _4-w (-0.05 <x <0.05, -0.05 <y <0.05, -0.05 <z <0.
05, -0.2 <W <0.2).

In such a composition, there was almost no difference in lattice constant, and no difference was observed in the film forming characteristics of the thin film in any case.

In this way, the formed SrLaGaO ₄ single crystal was sliced, and using a wafer-shaped (100) plane single crystal plate, by an RF magnetron sputtering method under an atmosphere of argon / oxygen (mixing ratio 1: 1), YBa ₂ Cu ₃ O _{7−δ with} film thickness of 1000Å
A thin film was deposited. Here, the composition ratio after film formation is YBa ₂ Cu ₃ O.
The composition of the target was adjusted so as to be _7-δ . The film forming conditions at this time were a gas pressure of 10 Pa, an electric power of 300 W, and a substrate temperature of 600 ° C.

After the deposition, annealing was performed at 900 ° C. for 1 hour in an oxygen atmosphere.

Thereafter, the YBa ₂ Cu ₃ O _7-δ film 2 other than the region to be the wiring portion 2s as shown in Figure by a method such as electron beam irradiation and the normal conductor portion 2n, YBa ₂ Cu ₃ as a wiring portion 2s An O _7-δ thin film pattern is formed. Thus (100) oriented SrLaGaO
₍₄ ) A (100) -oriented superconducting thin film pattern 2s formed on a single crystal substrate 1 can be used as a basic structure to form a device such as a superconductor memory device.

The zero resistance temperature T _c0 of the YBa ₂ Cu ₃ O _7-δ thin film thus produced was 85 ° K.

In addition, (110) is formed on a (110) -oriented SrLaGaO ₄ single crystal substrate.
The zero resistance temperature T _c0 in the case of forming a device such as a superconductor memory device was also 85 ° K when the YBa ₂ Cu ₃ O _7-δ superconducting thin film pattern of orientation was formed as a basic structure.

For comparison, Sr, which is conventionally used as a substrate
Using (100) face single crystal of TiO ₃ , under the same conditions, (001) YBa ₂
A Cu ₃ O _7-δ thin film deposited on a (110) -plane single crystal of SrTiO ₃ under the same conditions as (110) and (130) YBa ₂ Cu ₃ O
_{A 7-δ} thin film was also prepared. Table 1 shows the results of measuring the zero resistance temperature T _c0 at this time and the results of measuring the orientation and film quality of the formed superconducting film by X-ray diffraction.

As apparent from the results, it SrLaGaO ₄ of the single crystal (10
By using the (0) plane and the (110) plane, the (100) orientation and the (11) plane are compared with the case of using the SrTiO ₃ single crystal substrate.
It is understood that a YBa ₂ Cu ₃ O _7-δ superconducting thin film having a good 0) orientation can be obtained.

It is considered that this is because the SrLaGaO ₄ single crystal substrate is superior in crystallinity and uniformity of the film to the SrTiO ₃ single crystal substrate.

The crystallinity of the surface of the superconducting thin film thus prepared was observed by reflection high-energy electron diffraction.
It was found that a sharp streak-like diffraction pattern showing (100) and (110) orientations could be obtained in the superconducting thin film formed on the O ₄ single crystal substrate, and a good epitaxial growth film was formed. .

Further, the target material is LnBa ₂ Cu ₃ O _7−δ (δ = 0
~ 1, Ln: Yb, Er, Y, Ho, Gd, Eu, Dy)
On the GaO ₄ single crystal substrate, even a superconducting thin film prepared under the same conditions as above, a sharp streak-like diffraction pattern showing (100) and (110) orientations can be obtained, and a good epitaxial growth film is formed. I found out.

Example 2 Next, as a second example of the present invention, RF magnetron sputtering was performed on an SrLaGaO ₄ single crystal substrate formed by the same method as in Example 1 under an atmosphere of argon / oxygen (mixing ratio 2: 1). Method, YBa ₂ Cu ₃ O _7-δ having a film thickness of 1000 Å was deposited. Here, as the target, the composition ratio after film formation is Bi
_The one whose composition ratio was adjusted so as to be ₂ Sr ₂ Ca ₂ Cu ₃ O _x was used. In addition, the film forming conditions at this time are gas pressure 5 Pa and electric power 200
W and substrate temperature were 600 ° C.

After the deposition, annealing was performed at 900 ° C. for 1 hour in an oxygen atmosphere.

The zero resistance temperature T _c0 of the Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _x thin film thus prepared was measured, and the orientation and film quality of the formed superconducting film were measured by X-ray diffraction. The results are shown in Table 2.

As apparent from the results, it SrLaGaO ₄ of the single crystal (10
By using the (0) plane and the (110) plane, the (100) orientation and the (11) plane are compared with the case of using the SrTiO ₃ single crystal substrate.
It is found that a Bi ₂ Sr ₂ Ca ₂ Cu ₃ O _x superconducting thin film with good 0) orientation can be obtained.

Example 3 Next, as a third example of the present invention, argon / oxygen (mixing ratio 1: 1 was prepared on a (100) and (110) single crystal substrate of SrLaGaO ₄ formed by the same method as in Example 1. ) Under the atmosphere of R
Tl ₂ with a film thickness of 1000Å by F magnetron sputtering method
Ba ₂ Ca ₂ Cu ₃ O _x was deposited. The target used here was adjusted so that the composition ratio of the film after formation was Tl ₂ Ba ₂ Ca ₂ Cu ₃ O _x . The film forming conditions at this time were a gas pressure of 10 Pa, an electric power of 80 W, and a substrate temperature of 600 ° C.

After deposition, wrap with gold leaf and 905 in oxygen atmosphere
Annealing was performed at 10 ° C. for 10 minutes. The reason for wrapping with gold foil here is to prevent evaporation of thallium.

The result of measurement of the zero resistance temperature T _c0 of the Tl ₂ Ba ₂ Ca ₂ Cu ₃ O _x thin film thus prepared and the result of measurement of the orientation and film quality of the formed superconducting film by X-ray diffraction It is shown in Table 3.

Also in this case, as is clear from the results of Table 3 above,
By using the (100) and (110) planes of the SrLaGaO ₄ single crystal, compared to the case of using the SrTiO ₃ single crystal substrate,
Tl ₂ Ba ₂ Ca ₂ Cu ₃ O _x with good (100) and (110) orientation
It can be seen that a superconducting thin film can be obtained.

The present invention is not limited to these examples, and can be applied to the formation of other oxide superconducting thin films.

Moreover, not only SrLaGaO ₄ but also Ca, Nd, and
It goes without saying that those containing a slight amount of impurities such as Cr are also effective.

Furthermore, in forming the superconducting oxide thin film in the above examples, the RF magnetron sputtering method was used, but not limited to this, vacuum deposition method, multi-source deposition method, molecular beam epitaxy (MBE method), The MSD method or the like may be used.

〔The invention's effect〕

As described above, according to the present invention, in forming a superconducting thin film, as a substrate material, a strontium-lanthanum-gallium-based oxide having a K ₂ NiF ₄ type crystal structure as shown in the following formula is used. Since the (100) or (110) plane of the single crystal substrate is used, Sr _1-x La _1-y Ga _1-z O _4-w (-0.05 <x <0.05, -0.05 <y < 0.05, -0.05 <z <0.
05, -0.2 <W <0.2) A very good (100) oriented or (110) oxide superconducting thin film can be obtained.

[Brief description of drawings]

The figure shows a superconductor according to an embodiment of the present invention. 1 …… (100) SrLaGaO ₄ substrate, 2 …… YBa ₂ Cu ₃ O _7-δ thin film, 2s …… wiring part, 2n …… normal conductor part.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location H01B 12/06 ZAA 13/00 565 D H01L 39/02 ZAA B

Claims (7)

[Claims] 1. A (100) oriented strontium-lanthanum-containing compound having a K ₂ NiF ₄ type crystal structure as shown in the following formula.
A superconductor device comprising: a gallium oxide single crystal substrate; and a (100) -oriented oxide superconducting thin film formed on the substrate. Sr _1-x La _1-y Ga _1-z O _4-w (-0.05 <x <0.05, -0.05 <y <0.05, -0.05 <z <0.
05, -0.2 <W <0.2) 2. A (110) -oriented strontium-lanthanum-containing compound having a K ₂ NiF ₄ type crystal structure as shown in the following formula.
A superconductor device comprising: a gallium-based oxide single crystal substrate; and a (110) -oriented oxide superconducting thin film formed on the substrate. Sr _1-x La _1-y Ga _1-z O _4-w (-0.05 <x <0.05, -0.05 <y <0.05, -0.05 <z <0.
05, -0.2 <W <0.2) 3. A (100) -oriented strontium-lanthanum-containing compound having a K ₂ NiF ₄ type crystal structure as shown in the following formula.
A step of preparing a gallium-based oxide single crystal substrate, and a lattice constant a and b of 3.76 to 3.92Å on the single crystal substrate.
Or a superconducting thin film forming step of epitaxially growing a (100) -oriented oxide superconducting thin film in the range of 5.32 to 5.54Å. Sr _1-x La _1-y Ga _1-z O _4-w (-0.05 <x <0.05, -0.05 <y <0.05, -0.05 <z <0.
05, -0.2 <W <0.2) _4. A (110) -oriented strontium-lanthanum-containing compound having a K ₂ NiF ₄ type crystal structure represented by the following formula:
A step of preparing a gallium-based oxide single crystal substrate, and a lattice constant a and b of 3.76 to 3.92Å on the single crystal substrate.
Or a superconducting thin film forming step of epitaxially growing a (110) oriented oxide superconducting thin film in the range of 5.32 to 5.54Å. Sr _1-x La _1-y Ga _1-z O _4-w (-0.05 <x <0.05, -0.05 <y <0.05, -0.05 <z <0.
05, -0.2 <W <0.2) 5. The superconducting thin film forming step is a step of forming an oxide superconducting thin film having a composition ratio represented by the following formula. 4) A method for manufacturing a superconductor device according to the above. LnBa ₂ Cu ₃ O _7−δ (δ = 0 to 1, Ln: Yb, Er, Y, Ho, Gd, Eu, Dy) 6. The method according to claim 3, wherein the superconducting thin film forming step is a step of forming a Bi—Sr—Ca—Cu—O-based oxide thin film. Manufacturing method of superconductor device of. 7. The superconducting thin film forming step is a step of forming a Tl-Ba-Ca-Cu-O-based oxide thin film (3) or (4). Manufacturing method of superconductor device of.