JP2931779B2 - Superconducting element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a superconducting element having a non-superconducting oxide layer as a buffer layer or a barrier layer.

[0002]

2. Description of the Related Art High-temperature oxide superconductors are expected to be applied to Josephson devices, superconducting transistors, LSI wiring and the like. In any of these applications, it is necessary to reduce the thickness of the high-temperature oxide superconductor. But,
The conventional thin film technology for high-temperature oxide superconductors has various problems as described below.

For example, conventional high-temperature oxide superconductors include Y-Ba-Cu-0, Bi-Sr-Ca-Cu-O, Tl-Ba-Ca-Cu
-O system, Hg-Ba-Ca-Cu-O system and the like are used. Further, as a substrate for forming these oxide superconductors, SrTiO ₃ , MgO, LaAlO ₃ , NdGaO _{3 and the} like are usually frequently used, but a sputtering method, a laser ablation method, a CVD method, Irrespective of the film forming method such as the vacuum deposition method, due to lattice mismatch or residual stress at the interface between the substrate and the oxide superconductor, a layer with disordered orientation or a layer with severe irregularities due to precipitates is likely to be generated. There was such a problem. For this reason,
Morphology was disturbed at the interface with the buffer layer and at the oxide superconductor layer, leading to deterioration of superconducting characteristics and device operating characteristics. Furthermore, the stress at the interface may remain without being mitigated by the thin film growth process, it has been a big problem towards device characteristics improvement by the residual stress electrical characteristics such as the superconducting transition temperature T _c decreases .

[0004] In particular, regarding the characteristics of a Josephson device having a three-layer laminated structure of an oxide superconductor / barrier layer / oxide superconductor, when a thin film having the above-mentioned problems is used, the Josephson device is manufactured. With the decrease in the electrical characteristics described above, unevenness at the interface between the electrode layer and the barrier layer, such as leakage current, flux flow, and magnetic flux trap, and the presence of impurities,
Very frequently, phenomena considered to be caused by non-uniform film thickness, lowering of the coverage of the barrier layer, and the like were observed, and the characteristics of the device were deteriorated.

[0005]

As described above, in the conventional superconducting element, the oxide mismatch caused by the lattice mismatch at the interface between the substrate and the oxide superconductor layer and the mutual diffusion of metal elements. Problems such as disorder in the morphology of the superconductor layer and residual stress have occurred. In order to solve such a problem, various oxide materials have been studied as a buffer layer and a barrier layer.However, a high-quality material that completely solves the above-mentioned problems has not yet been developed, and a stacked type material has not been developed. Superconducting elements typified by Josephson elements have not yet achieved sufficient high performance.

Accordingly, in order to improve the superconducting characteristics and device characteristics, the lattice matching with the base such as the buffer layer and the barrier layer during the initial growth of the oxide superconductor is improved, and the buffer layer and Increasing the number of elements shared by the barrier layer and the oxide superconductor and having a film structure that does not adversely affect the crystallinity or electrical characteristics even if interdiffusion occurs is the biggest challenge in conventional superconducting elements. ing.

SUMMARY OF THE INVENTION The present invention has been made to address such a problem, and reduces the effects of lattice mismatch and interdiffusion between an underlayer and an oxide superconductor layer to reduce the influence of the oxide superconductor layer. It is an object of the present invention to provide a superconducting element capable of improving the orientation, increasing the flatness at the interface to the atomic level, and further reducing the residual stress. It is another object of the present invention to provide a superconducting element whose properties are improved to a practical level by improving these properties.

[0008]

According to a first aspect of the present invention, there is provided a first superconducting element, comprising: a substrate; an oxide superconductor layer provided on the substrate; and the oxide superconductor. In a superconducting element having a non-superconducting layer provided as a base of a layer, the non-superconducting layer has a composition formula: A _x AE _y MO _w (1) (where A is selected from Y and a rare earth element) AE represents at least one element selected from Ca, Sr and Ba, M represents at least one element selected from Ga, Fe, Co, Ni and Cu, x, y And w
Is substantially a composition satisfying 0 ≦ x ≦ 1, 0 ≦ y ≦ 1 (where x and y are not simultaneously 0), 0.8 ≦ x + y <1, 2 ≦ w ≦ 4) Is characterized by having an oxide layer represented by

Further, the second superconducting element is provided as a substrate, an oxide superconductor layer provided on the substrate, and a base for the oxide superconductor layer. a superconducting device comprising a non-superconducting layer, the non-superconducting layer, the composition _{formula: (A1 a AE y) MO} w ...... (2) ( wherein, A1 is La, Ce, Pr, Nd, Pm, Sm And AE is at least one element selected from Ca, Sr and Ba, and M is Ga, Fe, Co, Ni
And at least one element selected from Cu and
a, y and u are 0 <a ≦ 1, 0 ≦ y ≦ 1, 0.8 ≦ a + y ≦
1.2, which is a number that satisfies 2 ≦ w ≦ 4), the first oxide layer formed on the substrate side, and a composition formula: (A2 _b AE _y ) MO _w ... … (3) (where A2 is Y, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu
AE is at least one element selected from Ca, Sr and Ba, M is Ga, F
e, shows at least one element selected from Co, Ni and Cu, b, y and u are 0 <b ≦ 1, 0 ≦ y ≦ 1,
0.8 ≦ b + y ≦ 1.2, a number that satisfies 2 ≦ w ≦ 4) and has a second oxide layer formed on the oxide superconductor layer side. It is characterized by.

In the first superconducting element of the present invention, the superconducting element has a perovskite crystal structure common to the oxide superconductor and has many constituent metal elements common to the oxide superconductor. An oxide layer whose composition is represented by
It is used as a buffer layer between a substrate and an oxide superconductor layer or as a barrier layer between oxide superconductor layers. By sharing the constituent metal elements of the oxide superconductor with the buffer layer and the barrier layer, it is possible to prevent crystallinity and orientation from being disturbed due to their mutual diffusion and deteriorating electrical characteristics. Accordingly, the electrical characteristics particularly at the interface between the buffer layer and the oxide superconductor layer and at the interface between the barrier layer and the oxide superconductor layer are improved, and a high-quality superconducting element can be obtained.

Further, in the first superconducting element, the effective ionic radius of the metal element at the A site of the above-described oxide having a perovskite structure is controlled so as to approach the lattice constant of the oxide superconductor by controlling the A site composition. , The lattice matching between the oxide layer serving as the buffer layer and the barrier layer and the oxide superconductor layer can be greatly improved.

Since the oxide superconductor is a material having orthorhombic symmetry and having structural anisotropy, it has lattice matching with any of the a-axis, b-axis and c-axis. It is very difficult to produce excellent substrates and intermediate layers. In order to solve this, in the first superconducting element, by changing the effective ionic radius of the A site of the perovskite structure by controlling the composition of the A site, the first superconducting element is significantly different from various oxide superconductors formed thereon. A buffer layer and a barrier layer with good lattice matching can be obtained.

More specifically, a part of the AE element (alkaline earth metal) having a large ionic radius or an intermediate element A (Y and a rare earth metal) which usually occupies the A site, such as Cu having a smaller ionic radius, is used. By substituting the M element (transition metal) of the above, in other words, by making the A site into a solid solution system of the AE element, the A element and the M element, the lattice constant of the oxide serving as the intermediate layer becomes the oxide superconductivity. This makes it possible to approach the lattice constant of the body, and further to make the lattice mismatch value at the interface between the oxide layer and the oxide superconductor layer substantially 0%.

That is, the oxide layer constituting the buffer layer or the barrier layer has a large ionic radius in the above formula (1).
It has a composition of 0.8 ≦ x + y <1, where the M element with a small ionic radius is excessive with respect to the AE element and the A element. It is a solid solution system. Further, in the present invention, it is more preferable that the composition in the above formula (1) satisfies 0.8 ≦ x + y ≦ 0.95. That is, if the value of x + y exceeds 0.95, the above-described effects may not be sufficiently obtained,
On the other hand, if it is less than 0.8, it is difficult to form a perovskite structure, and excessive M elements form precipitates to deteriorate the film quality. As for the value of w indicating the composition of oxygen, w = 3 in the stoichiometric composition, but a slight variation from this value is allowed. However, it is difficult to obtain a composition far out of w = 3, and usually 2 ≦ w ≦ 4.

As described above, by improving the lattice matching between the oxide layer serving as the buffer layer or the barrier layer and the oxide superconductor layer, the disorder of the orientation at the interface, the generation of precipitates and residual stress, etc. it can be suppressed, and since it is possible to greatly improve the flatness, it is possible to improve the superconducting properties and device properties such as T _c.

In the oxide layer represented by the above formula (1), the specific types and ratios of the element A and the AE element are appropriately selected according to the oxide superconductor layer in contact therewith. is there.

Further, the second superconducting element of the present invention has a common perovskite-type crystal structure with the oxide superconductor and has the same structure as the oxide superconductor, similarly to the above-mentioned first superconducting element. Abundant metal elements, above (2)
A non-superconducting layer having a first oxide layer whose composition is substantially represented by the formula and a second oxide layer whose composition is substantially represented by the formula (3) is formed on a substrate and an oxide superconductor. Since the oxide superconductor layer and the buffer layer are used as a buffer layer or the like between the layers, crystallinity and orientation are not disturbed due to mutual diffusion between the oxide superconductor layer and the buffer layer or the like, and electric characteristics are prevented from being deteriorated.

Then, in the second superconducting element,
A first oxide layer having a composition substantially represented by the formula (2) is formed on the substrate side, and a second oxide layer having a composition substantially represented by the formula (3) is formed by oxide superconductivity. It is formed on the body layer side.
Here, the first oxide layer is made of La, Ce, Pr, Nd, Pm, or Sm having a relatively large ionic radius as a rare earth element (A1 element).
And at least one element selected from Eu, and has a cubic perovskite structure in high-temperature film formation,
SrTiO ₃ , LaAlO ₃ , NdGaO ₃ , MgO, YSZ (Y-stabilized Z
It has excellent lattice matching with substrate materials such as rO ₂ ), YAG, sapphire, and Y ₂ O ₃ , and has excellent flatness and orientation.
Although it has the feature that the precipitate density is very low, it has poor lattice matching with the oxide superconductor. For example,
(Pr _0.3 Ba _0.7 ) CuO _w and high temperature tetragonal YBa ₂ Cu ₃ O _z (6 ≦
The lattice mismatch value with z ≦ 7) is about 4%.

On the other hand, the second oxide layer is made of a rare earth element (A2
Y), Gd, Tb,
At least one selected from Dy, Ho, Er, Tm, Yb and Lu
It uses the same kind of elements and has the same crystal structure as the oxide superconductor, so it has excellent lattice matching with the oxide superconductor, and has excellent flatness and orientation. Since it is necessary to form a film at a low temperature, it has a property of having a very high impurity density when formed directly on a substrate. However, when formed over the first oxide layer having many common elements and common structures, the density of precipitates can be extremely low.

Therefore, in the non-superconducting layer having the first oxide layer formed on the substrate side and the second oxide layer formed on the oxide superconductor layer side, the lattice matching with the oxide superconductor In addition, excellent properties are obtained in addition to excellent flatness and orientation at the interface, and very low precipitate density. And the oxide superconductor layer formed on such a non-superconducting layer can greatly reduce the precipitate density, increase the flatness of the interface, and furthermore, due to lattice mismatch at the interface. for unstressed, it is possible to improve the superconducting properties and device properties such as T _c.

However, if the amount of A-site element (a + y / b + y) in the expressions (2) and (3) is less than 0.8, the amount of lattice defects of the A-site that can maintain a perovskite-like structure is exceeded.
The perovskite structure cannot be maintained,
On the other hand, if it exceeds 1.2, the excess A-site metal forms a precipitate, so that the values of a + y and b + y are both 0.8 to
The range is 1.2. In order to sufficiently obtain the effect of the second invention, it is preferable that 0.2 ≦ a ≦ 1 and 0.2 ≦ b ≦ 1.

[0022]

Embodiments of the present invention will be described below.

FIG. 1 is a sectional view showing an embodiment of the first superconducting element of the present invention. In the figure, 1 is SrTiO
₃ , a substrate composed of LaAlO ₃ , NdGaO ₃ , MgO, YSZ, YAG, sapphire, Y ₂ O _3, etc. On this substrate 1, a non-superconducting material whose composition is substantially represented by the above-mentioned formula (1) The oxide layer 2 is formed as a buffer layer. An oxide superconductor layer 3 is formed on the non-superconducting oxide layer 2 as a buffer layer. Note that the specific composition of the non-superconducting oxide layer 2 is appropriately set according to the oxide superconducting layer 3.

As described above, the non-superconducting oxide layer 2
Usually, the AE element occupying the A site of the perovskite structure and a part of the A element are replaced with the M element, and the A site is replaced with the AE element,
Since it is a solid solution of the three elements A and M, it has excellent lattice matching with the oxide superconductor layer 3.
The lattice mismatch value at the interface between the non-superconducting oxide layer 2 and the oxide superconducting layer 3 can be made substantially 0% by selecting the composition.

For example, YBa is directly deposited on a SrTiO ₃ (100) substrate.
_When (100) and (001) oriented films of ₂ Cu ₃ O _z are formed, the lattice mismatch value is about 2%, but (Pr _0.3 Ba _0.6 ) Cu
_{1.1 When} O _{w ′} is adopted as the buffer layer,
₂ Cu ₃ O _z (100) and (001) lattice mismatch value at the interface between the alignment film can be substantially 0%. Furthermore, even when a substrate having poor lattice matching with YBa ₂ Cu ₃ O _z is used, the lattice mismatch value can be made substantially 0% by interposing the buffer layer.

Therefore, the flatness of the interface between the non-superconducting oxide layer 2 and the oxide superconductor layer 3 is greatly improved, and the heterogeneous phase, hetero-oriented grains and precipitates in the interface and in the oxide superconductor layer 3 are greatly improved. Can be prevented and the orientation disorder can be prevented.
An oxide superconductor layer 3 having excellent surface flatness and electrical characteristics can be obtained. Further, it is possible to suppress the crystallinity and orientation from being disturbed by the mutual diffusion between the non-superconducting oxide layer 2 and the oxide superconducting layer 3 and to prevent the electric characteristics from deteriorating. RSJ (Resistively Shunted Junction) eliminates adverse effects such as leakage current and magnetic flux traps.
A high-quality Josephson device or the like having characteristics of the type or SIS type (including the SNS type; the same applies hereinafter) can be realized.

The non-superconducting oxide layer 2 is preferably formed with a thickness of about 0.3 to 100 nm. The non-superconducting oxide layer 2 has a unit lattice of about 0.38 nm, so it is difficult to form a film with a thickness of less than 0.3 nm. No longer suitable for layers. When used as a buffer layer, the thickness is preferably about 10 to 50 nm, which allows complete coating and has good flatness. In order to obtain SIS type characteristics, it is desirable to control the thickness of the barrier layer in the range of 0.3 to 100 nm and to control the resistance value and critical current of the device. The method for forming the film is not particularly limited, and may be a sputtering method, a CVD method, a vacuum evaporation method,
Various film formation methods such as a laser ablation method can be applied.

The non-superconducting oxide layer 2 whose composition is substantially represented by the formula (1) is not limited to the buffer layer shown in FIG. 1, but may be, for example, as shown in FIG. Layer 4
It can also be used as a barrier layer between the oxide superconductor layer 5 and the upper oxide superconductor layer 5. In this case, the coverage by the barrier layer, the flatness of the interface between the lower oxide superconductor layer 4 and the upper oxide superconductor layer 5, and the upper oxide superconductor layer 5
, Crystallinity, orientation, surface flatness, electrical characteristics and the like can be improved. As a result, it is possible to improve not only the electrical characteristics but also the leakage current, the flux flow, the magnetic flux trap and the like, and similarly, it is possible to realize a high-quality Josephson device having the characteristics of the RSJ type or the SIS type. In addition, since the control of the electronic state at the interface between the oxide superconductor layers 4 and 5 and the barrier layer can be performed with good reproducibility, when applied to a Josephson device, a device with significantly improved characteristics is obtained. be able to.

The above-described non-superconducting oxide layer 2 used as a buffer layer, a barrier layer, or the like can provide the above-described effects even when used as a simple single-layer structure film. , The characteristics can be further improved by changing the lattice constant continuously or intermittently in the film thickness direction or by forming a multilayer laminated structure film. For example, on the substrate 1 side, while reducing the composition of the M element, which has a small ionic radius,
On the oxide superconductor layer 3 side, M
By increasing the composition of the elements, the lattice matching with the substrate 1 and the oxide superconductor layer 3 can be improved. The non-superconducting oxide layer 2 in which the composition of the A site is continuously or intermittently changed is also effective as a barrier layer between different oxide superconducting layers 4 and 5.

When the thickness of the oxide thin film is equal to or less than a certain thickness determined by the material, the oxide thin film receives strain from the lower layer and the upper layer due to lattice mismatch, and the lattice length changes so as to reduce the lattice mismatch. By utilizing such properties and stacking the non-superconducting oxide layers 2 having different compositions in multiple layers, the lattice matching with the substrate 1 and the oxide superconducting layer 3 can be respectively improved.

Further, when a buffer layer or a barrier layer of a multi-layered structure film is used, for example, as shown in FIG.
FIG. 4 shows a multi-layer structure film in which a non-superconducting oxide layer 2 substantially represented by the formula (1) and an oxide layer 3 'having the same composition as the oxide superconductor layer 3 are alternately laminated. As shown
The oxide layer 3 'and the substrate 1 having the same composition as the non-superconducting oxide layer 2 and the oxide superconductor layer 3 substantially represented by the formula (1)
It is also possible to use, as the buffer layer 6 and the like, a multi-layered structure film or the like in which an oxide layer 1 ′ having the same composition as the above is laminated in order. Also in such a case, the lattice matching with the substrate 1 and the oxide superconductor layer 3 can be respectively improved. Note that the preferable thickness of the multi-layer structure film as described above may be such that each layer is set within the range of 0.3 to 100 nm as described above.

The non-superconducting oxide layer 2 substantially represented by the formula (1) is not limited to the buffer layer and the barrier layer shown in FIGS. 1 to 4, but may be, for example, as shown in FIG. It can also be used for a multiple Josephson element or the like in which the material layer 2 and the oxide superconductor layer 3 are alternately stacked. Also in such an element structure, the lattice matching at each interface between the non-superconducting oxide layer 2 and the oxide superconducting layer 3 can be improved, so that the element characteristics can be improved.

FIG. 6 is a view showing an embodiment of the second superconducting element of the present invention. Reference numeral 1 denotes a substrate similar to that of the above-described embodiment, and a non-superconducting A layer is formed, and the oxide superconductor layer 3 is formed on the buffer layer 7. The composition of the buffer layer 7 is substantially represented by the above-described formula (2), and substantially equal to the first non-superconducting oxide layer 8 formed on the substrate 1 side by the above-described formula (3). The composition of the oxide superconductor layer 3
And a second non-superconducting oxide layer 9 formed on the side. Note that the specific composition of the first and second non-superconducting oxide layers 8 and 9 is appropriately set according to the substrate 1 and the oxide superconducting layer 3.

Here, the first non-superconducting oxide layer 8 is excellent in lattice matching with the constituent material of the substrate 1 and is also excellent in flatness and orientation. The second non-superconducting oxide layer 9 formed thereon can have a very low precipitate density while maintaining the feature of being excellent in lattice matching with the oxide superconducting layer 3. As a result, the flatness of the interface between the buffer layer 7 and the oxide superconductor layer 3 can be greatly improved, and the generation of heterophases, hetero-oriented grains, precipitates, and the like at the interface and within the oxide superconductor layer 3 can be achieved. And disorder of orientation can be prevented. Due to these, the oxide superconductor layer 3 having excellent crystallinity, orientation, surface flatness, and electric properties
Can be obtained. In addition, it is possible to suppress the crystallinity and orientation from being disturbed due to the interdiffusion between the buffer layer 7 and the oxide superconductor layer 3 and the electrical characteristics from deteriorating. Therefore, a high-quality Josephson device having RSJ type or SIS type characteristics can be realized.

In this case, a preferable thickness of the buffer layer is such that the thickness of each of the first non-superconducting oxide layer 8 and the second non-superconducting oxide layer 9 is in the range of 0.3 to 100 nm. . In addition, the above-mentioned first non-superconducting oxide layer 8
The second non-superconducting oxide layer 9 can also be used as a multi-layer structure film in which these are multi-layered.

[0036]

Embodiments of the present invention will be described below.

Example 1 A (Pr _0.3 Ba _0.6 ) Cu _1.1 O _{w ′} layer having a thickness of 30 nm was formed as a buffer layer on a substrate, and an oxide superconductor layer having a YBa ₂ Cu ₃ O _z composition was formed thereon. A film was formed. The substrate is SrT
iO ₃ (100), MgO (100), NdGdO ₃ (110), YSZ, LaAlO
₃ (100), r-plane of sapphire was used. All film formation was performed using RF magnetron sputtering with a multi-metal target attached. The target is metal Y, B
a / Cu alloy, metal Cu, and metal Pr were used. In particular, SrTiO ₃ (10
0) Table 1 shows film forming conditions when a substrate was used. Also,
Table 1 also shows the characteristics of the c-axis oriented film of YBa ₂ Cu ₃ O _z formed on the buffer layer.

(Pr _0.3 Ba _0.6 ) Cu as buffer layer
_{1.1 The} O _{w '} layer is composed of Pr, Ba, Cu
Was randomly solid-dissolved and oxygen deficiency was present, confirming that the compound had a cubic perovskite structure having oxygen deficiency. The lattice constant of this phase is 0.3860nm at room temperature, lattice mismatch values of YBa ₂ Cu ₃ O _z with more than 870K of the temperature dependence of the measurement of the lattice constant
It was less than 0.1%. Further, it was confirmed by resistance measurement that the buffer layer had an electrically semiconductive property.
Further, as shown in Table 1, the c-axis oriented film of YBa ₂ Cu ₃ O _z formed on the buffer layer was (Pr _0.3 Ba _0.7 ) CuO
It was confirmed that the orientation, the flatness, and the electrical characteristics were remarkably excellent as compared with the case where _w was formed as a buffer layer.

[0039]

[Table 1] Example 2 In Example 1, except that the composition of the oxide layer serving as the buffer layer was changed to the oxide composition shown in Table 2, the substrate temperature was changed by RF sputtering using a multimetal target. A buffer layer was formed on each of the substrates at 893K. Table 2 also shows the composition, structure, and lattice constant of each oxide layer at room temperature. All oxide layers shown in Table 2 had a lattice mismatch value with tetragonal YBa ₂ Cu ₃ O _z of 0.1% or less at a high temperature of 923 K or more. When a c-axis oriented film of YBa ₂ Cu ₃ O _z was formed on each of these oxide layers in the same manner as in Example 1, an oxide superconductor layer having remarkably excellent orientation, flatness, and electric properties was obtained. was gotten.

[0040]

[Table 2] Example 3 As shown in FIG. 3, (Pr _0.3 Ba _0.6 ) Cu _1.1
O _{w 'film} and YBa ₂ Cu ₃ O _z and a-axis oriented film of the substrate temperature 8
At 43K, 100 unit lattices (approximately 40 nm) were alternately stacked in layers of 10 layers each. This multi-layer structure film was used as a buffer layer. Table 3 shows the film forming conditions at this time. Further, an a-axis oriented film of YBa ₂ Cu ₃ O _z was formed at the same substrate temperature on the buffer layer having the multi-layer structure. Table 3 also shows the characteristics of the YBa ₂ Cu ₃ O _z film formed on the buffer layer.

From a structural analysis by an electron microscope or the like, in the buffer layer having the multi-layer structure, the lattice mismatch value of the two layers decreases in both the b-axis and the c-axis as the film thickness increases in the laminating direction. At the interface between the formed YBa ₂ Cu ₃ O _{z and} the a-axis oriented film, the lattice mismatch value was 0.1% or less. As shown in Table 3, it was formed on top of the buffer layer.
The characteristics of the a-axis oriented film of YBa ₂ Cu ₃ O _z were significantly improved as compared with the case where no buffer layer was used.

[0042]

[Table 3] Example 4 As shown in FIG. 4, SrTiO ₃ (100)
₃ film, (Pr _0.3 Ba _0.6 ) Cu _1.1 O _{w ′} film and YBa ₂ Cu
_{A 3 Oz} c-axis oriented film is multi-layered in order of three layers each of 100 unit lattice, 100 unit lattice and 10 unit lattice respectively, and this multi-layer structure film is used as a buffer layer, and furthermore, on top of it.
A c-axis oriented film of YBa ₂ Cu ₃ O _z was formed. Table 4 shows the film forming conditions and characteristic measurement results at this time. By using the buffer layer having the multi-layer structure described above, the lattice mismatch value at the interface with the c-axis oriented film of YBa ₂ Cu ₃ O _z formed thereon is 0.1% or less, and the flatness, orientation, and electric An oxide superconductor layer having extremely excellent characteristics was obtained.

[0043]

[Table 4] As shown in Example 5 FIG. 7, on a SrTiO ₃ (100) substrate 1, a non-superconducting oxide layer in the thickness direction changing the metal composition of the A site (Pr _x Ba _y CuO _3-layer) 2 buffer A 100 unit lattice was formed as a layer, and an a-axis oriented film of YBa ₂ Cu ₃ O _z was further formed thereon as an oxide superconductor layer 3. This buffer layer is composed of the substrate 1 and the b-axis of the a-axis oriented film of YBa ₂ Cu ₃ O _z ,
All lattice mismatch values with the c-axis are 0.1% or less, and as a result, the flatness, orientation, and the a-axis orientation film of YBa ₂ Cu ₃ O _z
The electrical properties were all significantly improved.

Example 6 As shown in FIG. 6, a first non-superconducting oxide layer 8 was formed on a SrTiO ₃ (100) substrate 1 at a substrate temperature of 893 K (Pr _0.3 Ba).
_0.7 ) Form a 100-unit lattice of CuO _w layer, followed by a substrate temperature of 82
(Y _0.3 Ba _0.7 ) CuO as the second non-superconducting oxide layer 9 at 3K
_A double layer was formed as a buffer layer 7 by forming a _w layer. YBa ₂ Cu ₃ on the buffer layer 7 at a substrate temperature of 843K
An _Oz a-axis alignment film was formed as the oxide superconductor layer 3. Table 5 shows the film forming conditions and characteristic evaluation results at that time.

The lower (Pr _0.3 Ba _0.7 ) CuO _w layer has the characteristics of being excellent in flatness and orientation and having a very low precipitate density, but has a lattice with high temperature tetragonal YBa ₂ Cu ₃ O _z. The mismatch value is bad at about 4%. On the other hand, the upper (Y _0.3 Ba _0.7 ) CuO
_{The w} layer has a lattice mismatch value with high-temperature tetragonal YBa ₂ Cu ₃ O _z of almost 0%, and is excellent in orientation and flatness. There is a property of having a very high impurity density when formed directly on the film. However, the lower (Pr _0.3 B
a _0.7 ) When formed on a CuO _w layer, the density of precipitates is extremely low, and a buffer layer 7 with extremely excellent lattice matching can be obtained. The a-axis oriented film of YBa ₂ Cu ₃ O _z formed on such a buffer layer 7 has a very low precipitate density and does not receive stress due to lattice mismatch, so that it has a low normal conduction resistance and a T _{c now} has 90K zero resistance with good reproducibility.

[0046]

[Table 5] Example 7 As shown in FIG. 8, first, at a substrate temperature of 843 K, SrTiO
_{3 A} (Pr _0.3 Ba _0.6 ) Cu _1.1 O _{w ′} layer is formed as a buffer layer 12 on a (100) substrate 11 as a 100 unit lattice, and an a-axis oriented film of YBa ₂ Cu ₃ O _z is formed thereon as a lower superconducting electrode 13. Is formed to a thickness of 240 nm, and a 10 nm-thick PrBa ₂ Cu
An a-axis oriented film of YBa ₂ Cu ₃ O _z having a thickness of 120 nm was formed as an upper superconducting electrode 15 via a barrier layer 14 composed of a ₃ O _{z ′} (6 ≦ z ′ ≦ 7) film. Compared to the case where the buffer layer 12 was not used, the lamination type thin film had much improved flatness at the interface and surface, and contained almost no voids or impurities.

Next, a Josephson element having the structure shown in FIG. 8 was manufactured by processing the above-mentioned laminated thin film using photolithography. The stacked Josephson element is patterned so that the junction area is 20 × 20 μm. A gold wiring 17 is provided on the upper superconducting electrode 15 via an insulating interlayer film 16. And gold wiring layer 17 and gold contact 18
Connected through.

By using the buffer layer 12 described above, typical Fraunhofer characteristics can be obtained.
Short-circuiting between electrodes frequently seen in conventional superconducting elements,
High quality and uniform Josephson characteristics were observed in which no flux flow characteristics were observed. FIG. 9 shows typical IV characteristics of this device. The obtained device shows RSJ-like characteristics, and from the experimental results of magnetic field application shown in FIG.
It can be seen that a higher quality Josephson device is formed than before. In this device, since the thickness of the barrier layer 14 is as thin as about 1/5 to 1/10, the I _c · R _n product has increased about 10 times. Example 8 As in Example 7, SrTiO ₃ (1
After a buffer layer and a lower superconducting electrode having the same composition as in Example 7 were formed on the substrate, a (Pr _0.3 Ba _0.6 ) Cu _1.1 O _{w ′} layer having the same composition as the buffer layer as a barrier layer was formed to a thickness of 50 nm.
The laminated Josephson element formed by the above was manufactured. The resistivity of the barrier layer is about 1/10 compared to PrBa ₂ Cu ₃ O _{z ',} characteristic of the device becomes a typical RSJ characteristics, I _c
· R _n product rose to about 10 times compared to devices using conventional PrBa ₂ Cu ₃ O _{z 'layer} as a barrier layer.

Embodiment 9 As shown in FIG. 5, a 50 nm thick (Pr _0.3 Ba _0.6 ) Cu was formed on the SrTiO ₃ (100) substrate 11 as the non-superconducting oxide layer 2.
_1.1 O _{w '} layer and oxide superconductor layer 3 having a thickness of 50 nm
A device in which YBa ₂ Cu ₃ O _z layers were alternately stacked in layers of 10 layers each was manufactured. This device maintained a flatness of about 0.4 nm unit lattice at each layer interface, and showed the characteristics of a multiple Josephson device from the evaluation of electrical characteristics.

It should be noted that the present invention is not limited to the above-described embodiments. Even when other rare earth elements, alkaline earth elements, and transition metal elements are used in the buffer layer and the barrier layer, the present invention is not limited to the above embodiments. Similar effects were obtained even when the composition ratio of each metal element at the site was changed, and when the oxide superconductor layer formed further on the top was an oxide superconductor other than YBa ₂ Cu ₃ O _z . The substrate is S
Not only rTiO ₃ (100), but also MgO, La AlO ₃ , NdGaO ₃ , Y
The present invention is similarly effective when a substrate that is usually frequently used such as SZ or Y ₂ O ₃ is used. Actually, when Bi-based, Tl-based, Hg-based, etc. are used as a part of the buffer layer or the oxide superconductor layer on these oxide substrates, similarly excellent crystallinity and device characteristics are obtained. Was.

[0051]

As described above, according to the superconducting element of the present invention, the orientation of the oxide superconductor layer can be improved, and the flatness of the interface with the buffer layer and the barrier layer can be greatly improved. The residual stress can be further reduced. Therefore, it is possible to provide a superconducting element whose characteristics are improved to a practical level.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an embodiment of a first superconducting element of the present invention.

FIG. 2 is a sectional view showing another embodiment of the first superconducting element of the present invention.

FIG. 3 is a sectional view showing a modification of the superconducting element shown in FIG.

FIG. 4 is a sectional view showing another modified example of the superconducting element shown in FIG.

FIG. 5 is a sectional view showing still another embodiment of the first superconducting element of the present invention.

FIG. 6 is a sectional view showing an embodiment of the second superconducting element of the present invention.

FIG. 7 is a diagram showing the structure of a superconducting element according to Example 5 of the present invention, and the A-site composition and lattice constant of a barrier layer.

FIG. 8 is a sectional view showing a structure of a Josephson device according to a seventh embodiment of the present invention.

9 is a diagram showing current-voltage characteristics of the Josephson device shown in FIG.

10 is a diagram showing the magnetic field dependence of the critical current value of the Josephson device shown in FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Non-superconducting oxide layer 3 ... Oxide superconducting layer 4 ... Lower oxide superconducting layer 5 ... Upper oxide superconducting layer 8 ... First non-superconducting oxide layer 9 ... Second non-superconducting oxide layer

Continuation of the front page (51) Int.Cl. ⁶ Identification code FI C01G 53/00 C01G 53/00 A C30B 29/22 501 C30B 29/22 501N H01L 39/02 ZAA H01L 39/02 ZAAB (58) (Int.Cl. ⁶ , DB name) H01L 39/24 C30B 29/22 H01L 39/02 H01L 39/22 H01L 39/00

Claims (2)

(57) [Claims] 1. A superconducting element comprising a substrate, an oxide superconductor layer provided on the substrate, and a non-superconducting layer provided as a base of the oxide superconductor layer, wherein the non-superconducting layer is , Composition formula: A _x AE _y MO _w (where A is at least one element selected from Y and rare earth elements, AE is at least one element selected from Ca, Sr and Ba, and M is Ga , Fe, Co, Ni and Cu represent at least one element selected from x, y and w
Is substantially a composition satisfying 0 ≦ x ≦ 1, 0 ≦ y ≦ 1 (where x and y are not simultaneously 0), 0.8 ≦ x + y <1, 2 ≦ w ≦ 4) A superconducting element comprising an oxide layer represented by the formula: 2. A superconducting element comprising a substrate, an oxide superconductor layer provided on the substrate, and a non-superconducting layer provided as a base of the oxide superconductor layer, wherein the non-superconducting layer is , Composition formula: (A1 _a AE _y ) MO _w (where A1 is at least one element selected from La, Ce, Pr, Nd, Pm, Sm and Eu, and AE is selected from Ca, Sr and Ba M is Ga, Fe, Co, Ni
And at least one element selected from Cu and
a, y and u are 0 <a ≦ 1, 0 ≦ y ≦ 1, 0.8 ≦ a + y ≦
1.2, which is a number that satisfies 2 ≦ w ≦ 4), the first oxide layer formed on the substrate side, and a composition formula: (A2 _b AE _y ) MO _w ( Wherein A2 is Y, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu
AE is at least one element selected from Ca, Sr and Ba, M is Ga, F
e, shows at least one element selected from Co, Ni and Cu, b, y and u are 0 <b ≦ 1, 0 ≦ y ≦ 1,
0.8 ≦ b + y ≦ 1.2, a number that satisfies 2 ≦ w ≦ 4) and has a second oxide layer formed on the oxide superconductor layer side. A superconducting element characterized by the following.