JPH0680419A - Production of oxide superconductor thin film and superconducting tunnel junction and superconducting element - Google Patents

Abstract

PURPOSE:To provide a method for producing an oxide superconductor thin film having an infinite layer structure of good quality without using a high- pressure process and a method for producing a superconducting tunnel junction of good quality in a simple production process. CONSTITUTION:Atoms or molecules in an amount of a nearly one atomic layer expressed by the formula A1-xRExOz [A denotes alkaline earth element; RE denotes rare earth element; (x) denote 0<=(x)<1; (z) denotes the amount of oxygen] and atoms or molecules in an amount of one atomic layer of Cuz are alternately deposited by a method for forming a thin film satisfying conditions of T>=500, 0.1<=P<1 and P>=0.005T-2.9 when the substrate temperature in forming the film is T ( deg.C) and the oxygen partial pressure in an atmospheric gas in forming the film is P (Pa). Thereby, the objective oxide superconductor layer having an infinite layer structure is formed. A nonsuperconductor layer composed of the elements of the same construction is formed according to a method for forming the thin film satisfying the conditions of T>=500, P<0.1 and P<0.005T-2.9.

Description

Detailed Description of the Invention

[0001]

The present invention relates to ACuO having a simple crystal structure.
_{The present} invention relates to a method for producing a _2- type oxide superconductor thin film, a method for producing a superconducting tunnel junction using the thin film, and a superconducting element.

[0002]

2. Description of the Related Art A superconducting tunnel junction known as a Josephson junction is generally a thin non-superconducting layer (tunnel layer) with a film thickness of about 10 nm to 100 nm between two layers of superconductors.
Has a structure in which is interposed. This junction is expected to be applied as an ultra-high-speed and low-power-consumption switching element, an ultra-sensitive sensor for magnetic fields, microwaves, radiation, etc.

Conventionally, a metallic material such as Nb ₃ Sn has been used as the superconductor. However, since the metallic superconductor has a low critical temperature, it is necessary to use liquid helium as a refrigerant, which is costly. Had the problem of being expensive. On the other hand, since the discovery of the copper oxide superconductor, a superconducting material having a critical temperature higher than the temperature of liquid nitrogen has been realized, and the possibility of application to the electronics field has greatly expanded.

As an oxide superconductor whose critical temperature exceeds the liquid nitrogen temperature as described above, the critical temperature T _{c of} superconductivity is
Y-based superconductor (Y ₁ Ba ₂ Cu ₃ O _7-α (0 <α <
1)), about 110K of Bi-based oxide superconductor (Bi ₂ Sr ₂ Ca ₂ Cu
₃ O _z ), etc. are known. However, the crystal structure of these oxide superconductors is complicated. For example, in the case of Y-based superconductors, the unit crystals are BaO layer, CuO layer, BaO layer, CuO ₂ layer, YO
It consists of 6 layers, CuO ₂ layer, and more layers in Bi-based superconductors.

By the way, in order to apply an oxide superconductor to an electronic device, it is necessary to make it thin. But,
In Y-based and Bi-based oxide superconductors, since the crystal structure is complicated as described above, it is difficult to produce a good quality thin film, crystal defects are likely to occur in the film, and the film surface is It had a drawback that it became coarse. Such drawbacks are
It is a big obstacle when applied to electronic devices.

On the other hand, it has a simple crystal structure in which CuO ₂ layers and (A _1-x RE _x ) layers (A is an alkaline earth element and RE is a rare earth element) are alternately stacked. , ACuO ₂
An oxide superconductor ((A _1-x RE _x ) Cu ₁ O _y ) of a type (hereinafter referred to as an infinite layer structure) is known. However, the oxide superconductor having the above crystal structure is synthesized only under high pressure such as 25000 atm, and even if the composition is (A _1-x RE _x ) Cu ₁ O _y , it is infinite. For example, it has a crystal structure with a double CuO chain different from the layer structure and does not become a superconductor, or the above non-superconducting phase is mixed in a superconductor with an infinite layer structure and sufficient superconducting properties are obtained. There was a problem that I could not get it.

On the other hand, when forming a superconducting tunnel junction, an insulator such as MgO or a normal conductor such as Ag can be used as the tunnel layer. However, in order to form a high-quality superconductor layer on the tunnel layer, it is preferable to perform epitaxial growth. For this reason, for example, for Y-based oxide superconductors, Pr ₁ Ba ₂ Cu ₃ O _7-α is used as a non-superconductor whose crystal structure and lattice constant are similar. However, using films made of different constituent elements for the superconducting layer and the non-superconducting layer as described above has a problem that the manufacturing process is complicated.

[0008]

As described above, the ACuO ₂ type oxide superconductor having an infinite layer structure is considered to be advantageous for application to electronic devices in terms of crystal structure, but the conventional manufacturing method. Has been synthesized only in a high pressure of tens of thousands of atmospheres, and there is a problem that it is difficult to obtain a high-quality superconductor except for high pressure synthesis.

On the other hand, when forming a superconducting tunnel junction, it is necessary to epitaxially grow an oxide superconductor layer on the tunnel layer in order to obtain a good quality superconductor layer. There is a problem in that the manufacturing process becomes complicated in the combination of the non-superconductor with the above because the constituent elements are different.

The present invention has been made in view of the above problems, and it is possible to manufacture an oxide superconductor thin film having a good infinite layer structure without using a high-pressure process. Another object of the present invention is to provide a simple manufacturing process.
It is an object of the present invention to provide a method of manufacturing a superconducting tunnel junction in which a superconductor layer and a tunnel layer which are epitaxially grown can be obtained. Furthermore, it is an object of the present invention to provide a superconducting element in which each layer has a high crystallinity and is highly reliable, for example, a tunnel junction can be stably obtained.

[0011]

The method for producing an oxide superconductor thin film according to the present invention comprises: (A _1-x RE _x ) _1-δ Cu ₁ O _y
(However, A represents at least one element selected from alkaline earth elements, RE represents at least one element selected from rare earth elements, and x represents an A element of RE element satisfying 0 ≦ x <1. The amount of substitution, δ is the amount of A site ion deficiency satisfying 0 ≦ δ ≦ 0.3, and y is the amount of oxygen of about 2. The same shall apply hereinafter) when forming an oxide superconductor thin film. When the substrate temperature during film formation is T (° C.) and the oxygen partial pressure in the atmosphere gas during film formation is P (Pa), T ≧
Approximately 1 atomic layer of A _1-x RE _x O _z (z represents the amount of oxygen. The same applies hereinafter) by a thin film forming method satisfying the conditions of 500, 0.1 ≦ P <1, and P ≧ 0.005T-2.9. It is characterized by alternately depositing a minute atom or molecule and one atomic layer or molecule of CuO _z .

In the method for manufacturing a superconducting tunnel junction according to the present invention, the substrate temperature during film formation is T (° C.) on the substrate,
When the oxygen partial pressure in the atmosphere gas at the time of film formation is P (Pa), A _{1 is} formed by a thin film forming method that satisfies the conditions of T ≧ 500, 0.1 ≦ P <1, and P ≧ 0.005T-2.9. _-x RE _x O _{z About} one atomic layer of atoms or molecules and CuO _z of one atomic layer of atoms or molecules are alternately deposited, and (A _1-x R
E _x ) _1-δ Cu ₁ O _y The first step of forming an oxide superconductor layer represented by: and T ≧ 50 on the oxide superconductor layer.
The orthorhombic (A _1-x RE _x ) _1-δ Cu was formed by the thin film formation method satisfying the conditions of 0 and P <0.1 or P <0.005T-2.9.
A second step of forming a non-superconductor layer made of ₁ O _y or (A _1-x RE _x ) ₂ Cu ₁ O _3, and on the non-superconductor layer,
Similar to the first step, (A _1-x RE _x ) _1-δ Cu ₁ O
and a third step of forming an oxide superconductor layer represented by _y .

Furthermore, the superconducting element of the present invention is a tetragonal crystal.
(A _1-x RE _x ) _1-δ Cu ₁ O _y Superconductor layer and orthorhombic (A _1-x RE _x ) _1-δ Cu ₁ O _y or (A _1-x RE _x ) ₂ Cu
It is characterized by having a laminated structure with a non-superconductor layer made of ₁ O ₃ .

[0014]

In the method for producing an oxide superconductor thin film of the present invention, when the substrate temperature during film formation is T (° C.) and the oxygen partial pressure in the atmosphere gas during film formation is P (Pa), Area A of 1
As shown in the shaded area, T ≧ 500, 0.1 ≦ P <1,
A thin film forming method such as a sputtering method or a vapor deposition method satisfying the condition of P ≧ 0.005T-2.9 and the atoms or molecules of about 1 atomic layer of A _1-x RE _x O _z and 1 atom of CuO _z . Layers of atoms or molecules are deposited alternately. By satisfying the above-mentioned film forming conditions, the two adjacent oxide layers react well with each other, and the (A _1-x RE _x ) _1-δ layer and the CuO layer are perpendicular to the substrate surface. _An infinite layer structure (A _1-x RE _x ) _1-δ Cu ₁ O _y thin film in which _two layers are alternately arranged is formed, and an oxide superconductor thin film in which the c-axis is oriented perpendicular to the film surface is formed.

Here, when the substrate temperature T during film formation is less than 500 ° C., the film after film formation becomes amorphous. Also, the oxygen partial pressure P is
Below 0.1 Pa (region C in Figure 1), it is an insulator (A _1-x
RE _x ) ₂ Cu ₁ O ₃ and an oxygen partial pressure P of 1.0 Pa or more results in an infinite layer structure, but only substances exhibiting semiconductor-like electrical characteristics can be obtained. Furthermore, if the relationship between the substrate temperature T and the oxygen partial pressure P during film formation is P <0.005T-2.9 (region B in FIG. 1), the non-superconductor orthorhombic (A _1-x RE _x ) _1-δ
Cu ₁ O _y is mixed or orthorhombic (A _1-x RE _x )
Only _1-δ Cu ₁ O _y can be obtained. That is, T ≧ 50
For the first time, a non-superconducting phase (A _1-x RE _x ) _1-δ Cu with a double CuO chain will be produced by a thin film formation method satisfying the conditions of 0, 0.1 ≦ P <1, and P ≧ 0.005T-2.9. ₁ O _y or (A
It is possible to obtain a high-quality (A _1-x RE _x ) _1-δ Cu ₁ O _y superconducting thin film having no infinite layer structure without mixing _1-x RE _x ) ₂ Cu ₁ O ₃ .

As described above, the conditions for film formation are
≧ 500 and P <0.1, or T ≧ 500 and P <0.005T-
2.9, the other conditions are the same as those of the above oxide superconductor thin film production, and the lattice constants are almost equal to (A _1-x RE _x ) _1-δ Cu ₁ O _{y of} infinite layer structure. , Orthorhombic (A _1-x RE _x ) _1-δ Cu ₁ O _{y of} the non-superconducting phase,
(A _1-x RE _x ) ₂ Cu ₁ O ₃ can be formed. Therefore, following the manufacturing process of the oxide superconductor layer described above, if the non-superconductor layer is formed and an oxide superconductor layer having an infinite layer structure is formed thereon again, the film formation parameters are changed. The crystallinity of each layer is excellent and each layer is epitaxially grown by a simple process.
A highly reliable superconducting tunnel junction can be manufactured.

Further, a superconductor layer made of tetragonal (A _1-x RE _x ) _1-δ Cu ₁ O _{y having} the above-mentioned infinite layer structure and an orthorhombic (A _1-x RE _x ) _1-δ Cu ₁ O _y or (A _1-x RE _x ) ₂ Cu
_{Since the} superconducting element having a laminated structure with the non-superconducting layer made of ₁ O ₃ has excellent crystallinity of each layer as described above, it is possible to obtain highly reliable, for example, tunnel junction with good reproducibility. Become.

[0018]

EXAMPLES Next, examples of the present invention will be described.

FIG. 2 is a diagram showing an example of the construction of a sputtering apparatus for carrying out the method for producing an oxide superconductor thin film of the present invention. In the figure, 1 is a film forming chamber, and in this film forming chamber 1, a substrate holder 3 for holding a substrate 2
Disc targets 4, 5 and 6 for magnetron sputtering are arranged to face each other. The substrate holder 3 has a heater 7, and shutters 8, 9, and 10 are installed in front of the disk targets 4, 5, and 6, respectively. Each of the disk targets 4, 5 and 6 has a power supply 1 for sputtering.
1, 12, 13 are connected. Note that reference numerals 14 and 1
Reference numeral 5 is a gas supply system, and 16 is an exhaust system.

Example 1 Using the sputtering apparatus shown in FIG. 1, as an oxide superconductor thin film having an infinite layer structure with x = 0, Sr _1-δ
A thin film of Cu ₁ O _y was prepared. As the substrate 2, 20 mmφ ×
A 0.3 mmt SrTiO ₃ (100) plane was used. This substrate 2 is set on the substrate holder 3 and the substrate temperature is set to 500 by the heater 7.
After the temperature is set to ℃ ~ 620 ℃, the purity from the gas supply system 14, 15
The same amount of 9.999% Ar gas and O ₂ gas are supplied, and the film formation chamber 1
The gas pressure inside was 0.9 Pa (oxygen partial pressure: 0.45 Pa). As the targets 4 and 6, a SrCO ₃ sintered body and Cu metal were used, and RF power and DC power were supplied from the power supplies 11 and 13, respectively, and a film was formed by the following procedure.

First, the shutter 8 of the SrCO ₃ target 4 was opened, and 0.9 atomic layer of SrO _z was deposited on the SrTiO ₃ (100) substrate 2. Next, after closing the shutter 8 of the SrCO ₃ target 4, the shutter 10 on the Cu target 6 is closed.
Opened and deposited CuO _z for one atomic layer. The above operation 1
This was repeated 00 times to form a thin film with a thickness of about 35 nm.

As an example of the sputtering conditions for depositing one atomic layer at a time, an RF power of 110 W is applied to the SrCO ₃ target 4.
The shutter 8 was opened for 110 seconds while being supplied, and the shutter 10 was opened for 13 seconds while supplying DC power of 51 W to the Cu target 6.

The crystal structure of the thin film thus obtained was evaluated by X-ray diffraction, and the surface condition of the film was evaluated by SEM.
The temperature dependence of electrical resistance was measured by the usual four-terminal method. As an example, FIG. 3 shows an X-ray diffraction pattern immediately after film formation of a thin film formed at a substrate temperature of 580 ° C. and an oxygen partial pressure of 0.45 Pa. Except for the diffraction peak of SrTiO _{3, only} the diffraction peaks of (001) and (002) of the infinite layer structure were observed. The thin film prepared in this example had an infinite layer whose c-axis was oriented perpendicular to the substrate surface. It was found that the structure was a single-phase film of Sr _0.9 Cu ₁ O _y . In addition, the film surface was a mirror surface, and no precipitate or unevenness was observed on the surface even in a SEM image of 20,000 times.
The critical temperature _Tc of this thin film was 103K onset and 92K zero resistance.

The substrate temperature is 500 at an oxygen partial pressure of 0.45 Pa.
When the temperature was from ℃ to 620 ℃, all of the above-mentioned single-phase infinite layer structure thin films were obtained.

Example 2 Instead of the SrO _z layer deposited in Example 1, shutters 8 and 9 on the SrCO ₃ target 4 and the Nd target 5 were simultaneously opened, and Sr _0.9 Nd _0.1 O 2 was formed by a binary co-sputtering method.
_{As in} Example 1, except that the _z layer is deposited, (Sr
_{A 0.9} Nd _0.1 ) Cu ₁ O _y thin film was formed. The thin film thus obtained is also a single-phase film having an infinite layer structure in which the c-axis is oriented perpendicular to the substrate surface, and T _c has an onset of 4
At 0K, the zero resistance was 26K. In addition, the film surface is also as in Example
Similarly to the above, no precipitate or unevenness was observed on the surface even in a SEM image of 20,000 times.

Comparative Example 1 Sr-Cu-O was prepared in the same manner as in Example 1 except that the oxygen partial pressure during film formation was 0.25 Pa (total pressure 0.5 Pa) and the substrate temperature was changed.
A system thin film was formed. As a result, the substrate temperature is 640 ℃ ~ 680
At 700 ° C, b-axis oriented non-superconductor orthorhombic Sr ₁ Cu ₁ O ₂ is mixed, and at 700 ° C or higher, it becomes a single-phase film of b-axis oriented non-superconductor orthorhombic Sr ₁ Cu ₁ O _2. It was The lattice constants a and c of this phase are 0.39 nm and 0.36 nm, respectively. The temperature dependence of the electric resistance of these films was semiconductor-like and did not result in superconductivity, but the surface properties were good. Comparative Example 2 Sr-Cu-O was used in the same manner as in Example 1 except that the oxygen partial pressure during film formation was 0.02 Pa (total pressure 0.9 Pa) and the substrate temperature was 580 ° C.
A system thin film was formed. The X-ray diffraction pattern of this film is shown in FIG. No diffraction peak of the infinite layer structure was observed, and the film was a single-phase film of Sr ₂ Cu ₁ O ₃ that was an a-axis oriented insulator. The lattice constants b and c of this phase are 0.39 nm and 0.35 nm, respectively.
Is. The surface property of this film was also good.

Comparative Example 3 Sr-Cu-O was used in the same manner as in Example 1 except that the oxygen partial pressure during film formation was 1.5 Pa (total pressure 3.0 Pa) and the substrate temperature was 580 ° C.
A system thin film was formed. The X-ray diffraction pattern of this film is shown in FIG.
Although it had an infinite layer structure as well, the electric resistance increased semiconductingly as the temperature decreased, and it did not become superconducting up to 10K.

Example 3 Next, an example of forming a superconducting element having a superconducting-insulator-superconductor (SIS) type superconducting tunnel junction will be described with reference to FIG.

As the substrate 21, a (100) plane of SrTiO ₃ was used, which was heated to 580 ° C. and then the oxygen gas partial pressure was 0.45 Pa.
(Total pressure 0.9 Pa), in the same manner as in Example 1, Sr _0.9 Cu ₁
The O _y superconductor layer 22 was formed with a thickness of 35 nm. Subsequently, the Sr _0.9 Cu ₁ O _y superconducting layer 22 shown in Comparative Example 2 was formed in the same manner as the Sr _0.9 Cu ₁ O _y superconducting layer 22 except that the oxygen gas partial pressure was set to 0.02 Pa on the lower superconducting layer 22. A 5 unit cell layer 23 of ₂ Cu ₁ O ₃ insulator was formed. The lattice constants b and c of this phase are 0.39 nm and 0.35 nm, respectively.
Since it substantially coincides with the lattice constant (a = b = 0.39 nm) of Sr _0.9 Cu ₁ O _y as ₂ , the Sr ₂ Cu ₁ O ₃ insulator layer 23 is epitaxially grown with the a-axis oriented. Even after laminating the layers, the surface thereof had a mirror surface. The oxygen gas partial pressure can be controlled without taking out the film thus laminated from the film formation chamber.
After returning to 0.45 Pa, a Sr _0.9 Cu ₁ O _y superconductor layer 24, which was c-axis oriented like the lower superconductor layer 22, was further laminated with a thickness of 35 nm. Sr _0.9 Cu ₁ O _y superconductor layer 24 on this
The surface property was good even after the lamination. Further, the electrodes 2 are formed on the lower superconducting layer 22 and the upper superconducting layer 24, respectively.
When Nos. 5 and 26 were provided and the electrical characteristics were measured, Josephson characteristics were observed in the temperature range of 80K or lower.

In each of the above-mentioned embodiments, an example in which the manufacturing method of the present invention is carried out by the sputtering method has been described, but the present invention is not limited to this, and the vapor deposition method, cluster ion beam method, Various thin film forming methods such as the CVD method can be applied.

[0031]

As described above, according to the present invention, an infinite layered oxide superconductor thin film having excellent superconducting properties and film surface smoothness can be reproduced without using a high pressure process of tens of thousands of atmospheric pressure or more. It is possible to manufacture with good performance.
In addition, it is possible to obtain a highly reliable superconducting tunnel junction in which each layer has excellent crystallinity by a simple process of changing the film forming process. Further, according to the superconducting element of the present invention, since the crystallinity of each layer is excellent, it becomes possible to stably obtain a highly reliable superconductor / non-superconductor junction, for example, a tunnel junction. Therefore, the superconducting element of the present invention is suitable for an element having the above-described junction, such as a Josephson element or a superconducting transistor.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a substrate temperature and an oxygen partial pressure and a phase to be formed in the method for producing an oxide superconductor thin film of the present invention.

FIG. 2 is a diagram schematically showing a configuration of a sputtering apparatus used in an example of the present invention.

FIG. 3 is a diagram showing an X-ray diffraction pattern of an oxide superconductor thin film obtained in one example of the present invention.

FIG. 4 is a diagram showing an X-ray diffraction pattern of a non-superconductor thin film produced as a comparison with the present invention.

FIG. 5 is a cross-sectional view schematically showing the configuration of a superconducting element having a superconducting tunnel junction according to an example of the present invention.

[Explanation of symbols]

 21 ... Substrate 22 ... Superconductor layer 23 ... Insulator layer 24 ... Superconductor layer

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H01L 39/24 ZAA J 9276-4M

Claims (3)

[Claims] 1. An (A _1-x RE _x ) _1-δ Cu ₁ O film is formed on a substrate.
_y (However, A is at least one element selected from alkaline earth elements, RE is at least one element selected from rare earth elements, and x is an element of the RE element satisfying 0 ≦ x <1. , Δ is the amount of A-site ion deficiency that satisfies 0 ≦ δ ≦ 0.3, and y is the oxygen content of about 2). When the substrate temperature at the time is T (° C.) and the oxygen partial pressure in the atmosphere gas at the time of film formation is P (Pa), T ≧ 500, 0.1 ≦
Abbreviation of A _1-x RE _x O _z (z represents the oxygen amount) by the thin film forming method satisfying the conditions of P <1 and P ≧ 0.005T-2.9.
A method for producing an oxide superconductor thin film, which comprises alternately depositing one atomic layer of atoms or molecules and one atomic layer of CuO _z (z represents the amount of oxygen). 2. The temperature of the substrate during film formation is set to T on the substrate.
(° C.), where P (Pa) is the oxygen partial pressure in the atmosphere gas during film formation, T ≧ 500, 0.1 ≦ P <1, and P ≧ 0.005T-
By the thin film formation method that satisfies the condition of 2.9, A _1-x RE _x O
_z (provided that A is at least one element selected from alkaline earth elements, RE is at least one element selected from rare earth elements, and x is an RE element satisfying 0 ≦ x <1) , Z is the amount of oxygen) 1
Atomic layers of atoms or molecules and CuO _z of one atomic layer of atoms or molecules are alternately deposited, and (A _1-x RE _x )
_1-δ Cu ₁ O _y (δ represents the amount of A-site ion deficiency satisfying 0 ≦ δ ≦ 0.3, and y represents the amount of oxygen of about 2) First forming the oxide superconductor layer And a thin film formation method on the oxide superconductor layer satisfying the conditions of T ≧ 500 and P <0.1 or P <0.005T-2.9, the orthorhombic (A _1-x RE _x ) _1-δ Cu ₁ O _y or (A _1-x
RE _x ) ₂ Cu ₁ O _{3 second} layer forming non-superconductor layer
On the non-superconductor layer, in the same manner as the first step,
(A _1-x RE _x ) _1-δ Cu ₁ O _{y A} third step of forming an oxide superconductor layer, the method for producing a superconducting tunnel junction. 3. A tetragonal (A _1-x RE _x ) _1-δ Cu ₁ O _y (where A is at least 1 selected from alkaline earth elements).
RE is at least 1 selected from rare earth elements
X represents the element of the species, x is the substitution amount of A element by RE element satisfying 0 ≦ x <1, δ is the amount of A site ion deficiency satisfying 0 ≦ δ ≦ 0.3, and y is about 2 oxygen. (A _1-x RE _x ) _1-δ Cu ₁ O
A superconducting element having a laminated structure with a non-superconducting layer made of _y or (A _1-x RE _x ) ₂ Cu ₁ O ₃ .