JPH0350122A - Insulating composition - Google Patents

Abstract

PURPOSE:To improve the matchability of an insulating compsn. with a crystal face of an oxide superconductor compsn. by substituting a rare earth element such as Nd or Sm for Ca in the superconductor compsn. contg. Bi, Br, Ca and Cu so that the resulting insulating compsn. is made similar to the superconductor compsn. in crystal structure. CONSTITUTION:A rare earth element (RE) selected among Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y is substd. for Ca in an oxide superconductor compsn. consisting of Bi, Sr, Ca, Cu and O or Tl, Ba, Ca, Cu and O to form an insulating compsn. contg. Bi, Sr, RE and Cu or Tl, Ba, RE and Cu in 2:(1.5-2.5):(0.5-1.5):(1.8-2.5) ratio. This insulating compsn. is similar to the superconductor compsn. in crystal structure and has satisfactory matchability with a crystal face of the superconductor compsn.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Field of Industrial Application) The present invention relates to an insulating composition used in a superconducting element.

(Prior Art) In recent years, it has been announced that layered perovskite-type oxides based on Ba-La-Cu-0 may have a high critical temperature, and since then, research on oxide superconductors has been carried out in various places. (Z, Phys, B Condensed Mat
ter64.189-193 (1986)), among which defective perovskite-type oxide superconductors with excess oxygen, represented by the Y-Ba-Cu-0 system, have a critical temperature of 90 or higher, which is higher than that of liquid nitrogen. It has been confirmed that it has a temperature (Phys, Rev, Lett, Vo
1, 58, No. 9.908-910).

Furthermore, in 1988, the critical temperature increased to 105 13j
-Sr-Ca-Cu-0 system superconducting oxide has been discovered (Nihon Keizai Shimbun January 22, 1988, etc.).

This Bi-3r-Ca-Cu-0 based superconducting oxide is
Compared to Ba-La-Cu-0 and Y-Ba-Cu-0 type superconducting oxides, not only do they have a higher critical temperature, they do not require expensive rare earth elements, and they are chemically stable against moisture, etc. It is a superior oxide superconductor material because of its advantages such as high

By the way, since superconducting elements that utilize the tunnel effect are capable of ultra-high-speed operation and consume little power, their application to digital devices such as computer logic elements and memory elements is progressing. And Nb/^Ioxidc
4-bit multipliers and gate arrays using Nb/Nb junctions, NbN/MgO/NbN junctions, etc. have been prototyped. In addition, superconducting three-terminal devices have been prototyped as superconductor-semiconductor devices, but these devices are all made of superconductors with low critical temperatures and use liquid helium as a coolant, so it is difficult to develop peripheral technology and improve economic efficiency. Due to problems, it has not been put into practical use.

For this reason, it is being considered to apply an oxide superconductor having a high critical temperature to the superconducting water T mentioned above.

However, when obtaining the above-mentioned superconducting element using an oxide superconductor and an insulating composition, the mismatch between the crystal planes of the oxide superconductor layer and the insulating composition causes new electron degrees to be generated and charges are generated. There is a problem in that it is difficult to obtain desired characteristics because the Josephson element is trapped and its function as a Josephson element is impaired.

However, when obtaining the above-mentioned superconducting element using an oxide superconductor and an insulating composition, a new electron level is generated here due to poor alignment between the crystal planes of the oxide superconductor layer and the insulating composition. There was a problem in that it was difficult to obtain new characteristics because charges were trapped and the function as a Josephson element was impaired.

Furthermore, the Bi-based superconductors are Bi25r2Ca2Cu301o, whose transition temperature is around 110K, and Bi25r2Ca2Cu301o, whose transition temperature is around 80K.
Bi25r2CaCu208 is known to be nearby.

However, Bi25r2Ca2Cu with higher Tc
There was a problem that it was not easy to synthesize a O and o.

This is considered to be due to the modulation structure existing in the b-axis direction of the crystal of the old thread superconductor or the internal stress that is the cause thereof.

(Problems to be Solved by the Invention) As described above, when fabricating a superconducting element using a conventional insulating composition, there is a problem that the crystal planes of the oxide superconductor layer and the insulating composition have poor alignment. was there. Furthermore, there was a problem in that it was not easy to synthesize old 2S "2Ca2Cu3010" which had a higher transition temperature.

The present invention has been made in view of these problems, and its purpose is to provide an insulating composition that has good consistency with the crystal plane of an oxide superconductor. Furthermore, another object of the present invention is to provide an insulating composition in which the modulation structure is relaxed or eliminated.

[Structure of the invention] (Means for solving problems) In order to achieve the above object, the present invention provides Bi, Sr.

Ca, Cu, O or Ti, Bas Ca, C
Ca of the oxide superconductor composition consisting of u10 is RE (however, RE is Nd.

5II1% Eu5Gds Tbs Dys Jio,
Element selected from Er, Ta+, Yb, Lu and Y. ) is an insulating composition characterized by being substituted with

Note that there is no problem even if some amount of Ca remains.

Here, Bi5Sr, I? E, Cu or T1.1
3a, RIE.

The atomic ratio of Cu is basically 2:2:1:2, but a deviation of about 2:X:Y:Z is acceptable.

However, 1.5≦X≦2.5 0.5≦Y≦1.5 1.8≦Z≦2.5 Moreover, in the insulating composition of the present invention, a part of Bi is replaced with Pb. You can.

Here, the substitution amount of Bi for Pb is preferably 1.5 or less, since the crystal structure will be different if it exceeds 1.5. Furthermore, 0
．． 2 to 1.0 is particularly preferred.

The insulating composition of the present invention can be used as an insulating material for an insulating layer, a substrate, etc. in a superconductor element.

A case where the insulating composition of the present invention is used as an insulating layer of a superconductor element will be explained.

Insulating compositions include old carbonates such as Srs RESCu,
Mix oxides, organic acid salts, etc. in a stoichiometric ratio,
It can be obtained by firing at a temperature of 00°C.

Note that the blending ratio of the raw materials does not need to be strictly stoichiometric, and there may be a difference of about IO%. Also,
It is also possible to lower the reaction temperature by using trace amounts of alkali metal compounds.

For example, tunnel junction type Josephson devices can be manufactured using physical vapor deposition methods such as vacuum evaporation, magnetron sputtering, ion beam sputtering, cluster ion beam, and molecular beam epitaxy, and chemical vapor deposition methods such as CVD and plasma CVD. This can be obtained by sequentially stacking an oxide superconductor layer, an insulating layer, and an oxide superelectric layer on a substrate.

Moreover, it is also possible to form by multi-component vapor deposition or multi-component sputtering using each metal element constituting the oxide superconductor and the insulating composition as a vapor source or a target. Oxide superconductors include Bi1Sr, Ca, Cu,
0, and the insulating layer is Bi. Sr, I? E.

In the case of Cu and O, workability is good because only one element needs to be replaced to switch between forming the oxide superconductor layer and forming the insulating layer.

The thickness of the oxide superconductor layer is preferably a thickness that exhibits superconducting properties, that is, approximately 100 Å or more, and the thickness of the insulating layer is preferably a thickness that does not inhibit the tunneling effect, that is, 50 to 200 Å.

Further, after forming each material layer, heat treatment is performed at 400 to 900° C. in an oxygen-containing atmosphere as necessary to introduce oxygen into the oxygen vacancies of the oxide superconductor to improve superconducting properties.

Note that it is also possible to obtain a super-Fuhi conductive three-terminal element, a highly sensitive magnetic sensor, etc. in the same manner.

When the insulating composition of the present invention is used as a substrate for a superconductor element, the single crystal substrate can be prepared by a conventional flux method, FZ
(F!oatlng Zone) method or the Kilobros method.

When growing an insulating composition made of old Srs R1ZSCU% O by a flux method, a flux containing both Bi2O3 and CuO may be used as the flux.

Furthermore, when growing an insulating composite acid consisting of Bi, Sr, RIE, Cu, 0 by the flux method, the composition of each raw material cation is in molar percentage (β, γ, ε), βB
i2O3+7 t (Sr, RE) Ol +ε
CuOHowever, the following relationships may be satisfied: 5≦β≦25 20≦γ≦60 10≦ε≦60 2β+γ+ε=100.

(Function) The insulating composition of the present invention has the same or similar crystal structure as the oxide superconductor, and the lattice constant is also very close to that of the oxide superconductor. As a result, deterioration of characteristics due to charge trapping is suppressed.

In particular, when the insulating composition of the present invention is used as a substrate, since the crystal structures are the same or similar, an oxide superconducting thin film single crystal can be epitaxially grown on the substrate.

Furthermore, the insulating composition of the present invention is stable even during high-temperature heat treatment and does not react with the crystal planes of the oxide superconductor.

Therefore, by using a superconducting element using the insulating composition of the present invention as an insulating material, it becomes possible to manufacture ICs, h-transistors, high-sensitivity magnetic sensors, etc. that operate at ultra-high speed and consume low power.

Furthermore, by replacing a part of the old insulating composition of the present invention with Pb, the lattice constant becomes closer to that of the 81-series superconductor. Moreover, the modulated structure of the insulating composition of the present invention is relaxed or disappears.

When an old thread superconductor thin film is grown on the single crystal of the insulating composition of the present invention, it is easy to grow old 2 Srz with a high Tc.
A Ca2Cu30 to layer is obtained. This is thought to be because the modulation structure is relaxed or eliminated in the insulating composition of the present invention, and the modulation structure is also relaxed or eliminated in the superconductor thin film epitaxially grown thereon.

Furthermore, in the superconductor thin film obtained in this way, a sharp superconducting transition is obtained for the same reason.
As a result, it was found that, for example, an improvement in the critical current at 77 was also observed.

That is, by using the insulating composition of the present invention as an insulating material in a superconductor element, a good superconductor element that exhibits a sharp transition at 10K can be easily obtained.

Although the Bi system has been described above, it goes without saying that the TI system has a crystal 11M structure similar to the Bl system and the same can be said.

(Example) Hereinafter, an example of the present invention will be described based on the drawings.

Example 1 FIG. 1 shows a cross section of a tunnel junction type oxide superconducting device using the insulating composition of the present invention as an insulating layer. On top, Bi0 Sr2 Ca1Cu20 layer α 3, Bi0 Sr2 Y 1Cu20 layer 4, [li
2 Sr2 Ca+ Cuα 20 layers 5 are sequentially stacked.

α [Bi0 Sr2 Ca+ Cu20 Target production α First, +31203 powder 33.5o+o1%, 5rC (
h powder 33.5IIo1%, CaC03 powder 33.5m
01%, CuO powder IG, 7mo 1% were placed in a monopot together with zirconia balls and wet-pulverized, then dehydrated and dried, heated and calcined.85
0° C. to 900° C., 24 h), and then placed in a monopot again for wet pulverization, followed by dehydration and drying to obtain a powder (superconductor) with a particle size of 5 μm or less.

Next, polyvinyl alcohol is added to the raw material powder and granulated to prepare a granule, which is then filled into each granule mold,
Molded under pressure of 1000kg/c-, diameter 154mm
A disk with a thickness of 6.5 fins was prepared.

Further, these were fired at 840° C. for 24 hours in an oxygen-containing atmosphere to obtain a target material having a sintered density of 98% and consisting of an acid alpha oxide superconductor represented by Bi2 Sr2 Ca1Cu20.

[Manufacture of Bi2 Sr2 Y I Cu20 target] α A non-metallic target represented by 8128r2 Y + Cu20 in the form of a disc with a diameter of 154 m + * and a thickness of 6.5 mm was prepared using the same method as above except that the CaC03 powder described above was replaced with Y2O3. A target with a sintered density of 98% made of conductive acid alpha oxide was manufactured.

[Manufacture of oxide superconducting elements (Josephson elements) Bi
2 Sr2 CalCu20 target,
95α 7Pa consisting of mo1% argon and 5mo1% oxygen
by high frequency magnetron sputtering in a mixed gas of
IOX with substrate temperature of 700℃ IOX l mm 5rT
103 substrate with a thickness of 1.0 μn+ Bi2 Sr2
A Ca1Cu20 layer was formed.

Next, a BI2 Sr2 Y + Cu20 layer having a thickness of IO was formed on the old 2 Sr2 Ca1 Cu20 layer using a Bi2 Sr2 Y + Cu20 target.

α Finally, on this old 2 Sr2 Y + Cu20 a layer, a 1.0 μI thick layer of Bi was added under the same conditions as described above.
A 25r2 Ca1Cu20 layer was formed to obtain a tunnel junction type α oxide superconducting element.

The critical temperature of the oxide superconducting element thus obtained was 77, and it was confirmed that current flows through each layer due to the tunnel effect at this temperature.

As an insulating layer, TI2 Ba2 Y + Cu20
The α When a conductive element was formed, operation was confirmed at a critical temperature of 100°C.

Example 2 Instead of the 812 Sr2 CaI Cu20 target, α Bi2 Sr2 Ca2 Cu30 target was used, and instead of the old 2α Sr2 Ca1 Cu20 layer 3.5, BI2
An oxide superconducting element was manufactured in the same manner as in Example 1 except that the Sr2α Ca2 Cu30 layer was formed.

The critical temperature of this oxide superconducting element is 70°C, and it was confirmed that current flows through each layer due to the tunnel effect at this temperature.

Comparative Example 1 BI2 Srz Y I Cuz O in Example 1
An oxide superconducting element having the same structure as in Example 1 was formed except that an Al103 layer of the same thickness was formed in place of the a-layer 4, but this element did not operate even at a critical temperature of 77°C. .

In addition, in the above embodiment, Bi25r2 is used as the insulating layer.
An example using a non-conductive oxide consisting of Y + Cu20 has been described, but in the above formula, Y is replaced by Nd.

Sin, Eu5GdSTbSDy, 1loSEr,
Oxides substituted for Tm, Yb, or Lu have similar crystal structures, so similar effects can be obtained.

Example 3 BisSr, Y, Cu in atomic ratio of 3:2:1:
The raw material Bl 20 ], SrCO3,
Y 20 ], a total of 100 g of CuO was weighed and mixed,
It was placed in an aluminum crucible and kept at 1150°C in the atmosphere for 24 hours, then gradually cooled to 800°C over 100 hours, and then cooled in the furnace to room temperature to form a B of 201QII x 20III1 x 211H.
An i2 Sr2 YCu 20 It product was obtained. The α result of X-ray diffraction confirmed that it was a single crystal and had (001) facets.

13i25r2C was deposited on this substrate by RF sputtering.
When an aCu20 film was formed at a substrate temperature of 550°C, an oxide superconducting single crystal film with the same orientation as the α substrate was obtained.

Further, when a cross section of this film was analyzed by EPMA, the reaction between the substrate and the film was within the fixed limit of 111J.

Figure 2 shows the temperature characteristics of the electrical resistivity of this film.

Excellent superconducting properties with Tc -84K and ΔTc~IK were obtained.

Comparative Example 2 A film was formed under the same conditions as in Example 3 except that an MgO single crystal was used as the substrate. Although a C-plane oriented film was obtained, the film surface was a polycrystalline film with an orientation degree of about 70%. The unevenness of the film is large, and EPLiA analysis of the cross section of the film reveals that there is MgO in the film.
ion detected.

Example 4 BISSr and Nd5Cu were weighed in an atomic ratio of 4:2:2:5, a single crystal was grown in the same manner as in Example 3, and I
OXmX 1OavX 1ms Bi2 Sr2 Nd
A 2CulO single crystal was obtained, and as a result of X-ray diffraction, it was confirmed that it was a single crystal and had a (001) facet. BI2 Sr2 Ca2Cu30 was deposited on this substrate by cluster ion beam method.
When the film was formed at a substrate temperature of 450°C, an oxide superconducting single crystal film with the same orientation as the α substrate was obtained.

Example 5 BI O1,-PbO,5rCOa as starting materials,
3 Y O and CuO powders are prepared, and the atomic ratio of cations is old: Pb: Sr: Y: Cu=
Weigh out a predetermined amount so that the ratio is 1:l:2:1:2, and then add Bi2O3 and CuO as a flux so that the atomic ratio of Bi and Cu is 1 each. Mixed.

Next, this mixed powder was put into an aluminum crucible, heated in air to 1.150°C, held at this temperature for 24 hours to uniformly melt, and then slowly cooled to 800°C over 100 hours. Then, the mixture was cooled in the oven to room temperature.

In the obtained cooled and solidified product, 1OmmX 20nvX 2
mn+ and a large single crystal emitted U'r, and X-ray analysis of this single crystal revealed that BIPbSr2YCu2
It was confirmed that the single crystal had a composition of 08+δ (δ is excess oxygen) and was C-axis oriented with respect to the single crystal plate surface.

Further, the specific resistance was 104 Ω·cm at -100°C, and it was confirmed that it functions as an electrical insulator.

Next, old 0, PbO1SrCO1CaCO3 and CuO
Using 233 as a sputtering target, a Bi-based oxide superconductor thin film was deposited to a thickness of 200 mm by multi-source sputtering using high-frequency magnetron sputtering in a 7 Pa gas mixture consisting of 95 mo1% argon and 51101% oxygen. Ta. The input power ratio for each target is based on the composition of the formed thin film: S r : Ca : C
The ratio was adjusted to u-2:2:2:3.

When the obtained Bi-based oxide superconductor thin film was subjected to X-ray diffraction, it was confirmed that it was an epitaxially grown film in a high critical temperature phase with the same orientation as the insulating single crystal substrate.

This is because the insulating single crystal substrate of this example has a lattice constant similar to that of the Bi-based oxide superconductor, and the lattice mismatch at the interface is reduced as much as possible, so that the Bi-based oxide superconductor thin film can be formed well. This is because it becomes possible to form.

Furthermore, the reason why it is difficult to form a high critical temperature phase in a Bi-based oxide superconductor is considered to be due to the modulation 11,7 structure inside the crystal and the internal stress of the crystal that causes it. Incidentally, the insulating single crystal substrate of this example has a lattice constant similar to that of the Bi-based oxide superconductor, and the modulation structure has almost disappeared due to the substitution of Pb. For this purpose, the Bi
It is presumed that the oxide superconductor thin film also disappears or relaxes, resulting in a single high-critical-temperature phase.

Furthermore, Bi2O3, PbO
BIPbS “2Ycu208+,
A thin film was formed to a thickness of 50 mm, and a Bi-based oxide superconductor thin film was further formed thereon to a thickness of 200 mm under the same conditions as the oxide superconductor thin film, to produce a Josephson device.

The upper layer Bi-based oxide superconductor thin film is also a good oxide superconductor thin film composed of a high critical temperature phase, like the lower-phase Bi-based oxide superconductor thin film. The reaction at the interface between the insulating phase and the insulating phase was also intolerable. It was confirmed that this Josephson element exhibits superconducting characteristics at 110K, and that a good Josephson effect can be obtained at this temperature.

Comparative Example 3 Using SrT10aO as a substrate, Bi was deposited on it.
25r2Ca2Cu30□. . 200 δ superconductors,
50 layers of MgO as an insulating layer, and then Bi25r2Ca2
A Josephson device was fabricated by stacking 200 Cu30 to+ superconductors.

However, in this state, it did not exhibit superconducting properties. Therefore, in order to improve the crystallinity, we performed heat treatment at 600℃ and evaluated the superconducting properties, and found that the transition temperature was 6.
Although a superconducting state was exhibited at 0, good Josephson characteristics were not obtained.

Example 6 By a similar method as described in Example 5, Bi2. Pb1. Sr 2Y
A single crystal of Cu20g+(5) was created.

Bi Pb Sr Y Cu 208 of the present invention
+, lattice constant of crystal and super 2-V W 2 conductor Bi Sr CaCu O;
The modulated +11S structure of the 2 2 2 8 + δ and BI Pb Sr YCu O crystals is shown in 2-w 522g+6 in FIG.

In the figure, the horizontal axis indicates W. In other words, as W becomes larger, the ratio of substitution with B-th 'iPb increases. The upper vertical axis on the left shows the lattice constant of the C axis, and the lower vertical axis on the right shows a
, denotes the b-axis lattice constant. The vertical axis on the right shows the modulation structure.

O is Bi Pb Sr YCu O crystal a
2-WW228+δ lattice constant of the axis, * indicates the lattice constant of the b-axis, and times indicate the lattice constant of the C-axis.

◎ indicates the 22 28 + δ lattice constant of the a-axis and b-axis of BI Sr CaCu O, and the opening indicates the lattice constant of the C-axis.

△ indicates the modulation groove 2-VW22g+δ structure of the old Pb Sr YCu O crystal.

In the Bi Pb Sr YCu O crystal, the lattice constant of the b2-W ν 2 28+δ axis is as follows when about GO% of Bi is replaced with Pb.
The lattice 22 28 + δ constant of the C axis, which is closest to old Sr CaCu O, becomes as the ratio of Bl being replaced by Pb increases,
It can be seen that it is close to the old 2Sr2CaCu208+δ.

Furthermore, it can be seen that the modulation structure disappears as the ratio of Bl being replaced by Pb increases.

Examples 7 to 16 Insulating single crystals were produced using the flux method using the compositions shown in Tables 1 and 2.

Table 1 Table 2 [Effects of the Invention] As explained above, the insulating composition of the present invention has the same or similar crystal structure as that of the oxide superconductor, so it has poor consistency with the crystal plane of the oxide superconductor. A good insulating composition can be provided. Furthermore, by replacing a portion of Bi in the insulating composition of the present invention with Pb, it is possible to provide an insulating composition in which the modulation structure is relaxed or eliminated.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an oxide superconducting element whose insulating layer is the insulating composition of the present invention, and FIG. 2 is the electrical resistivity of a single crystal oxide superconducting thin film formed on a single crystal substrate according to the present invention. FIG. 3 is a diagram showing the temperature characteristics of 81 of the present invention.
It is a figure which shows the characteristic of the insulation composition substituted with. 1... Oxide superconducting element, 2... Substrate, 3.5...
・Bi25r2 CalCu20 a layer, 4-1312
Sr2Y) Cu2Oa layer

Claims (1)

[Claims] (1) Bi, Sr, Ca, Cu, O or Ti, Ba
, Ca of the oxide superconductor composition consisting of Ca, Cu, and O
is RE (however, RE is Nd, Sm, Eu, Gd, Tb
, Dy, Ho, Er, Tm, Yb, Lu and Y. ) An insulating composition characterized by being substituted with (2) Bi, Sr, RE, Cu or Ti, Ba, R
The insulating composition according to claim 1, wherein the atomic ratio of E and Cu is 2:X:Y:Z. However, 1.5≦X≦2.5 0.5≦Y≦1.5 1.8≦Z≦2.5 (3) The atomic ratio of Bi, Sr, RE, and Cu is 2:X:Y:
An insulating composition that is an oxide of Z, however, 1.5≦X≦2.5 0.5≦Y≦1.5 1.8≦Z≦2.5 As a flux when growing by flux method Bi_2
A method for growing an insulating composition, characterized by using a flux containing O_3 and CuO at the same time. (4) The atomic ratio of Bi, Sr, RE, and Cu is 2:X:Y:
The insulating composition, which is an oxide of Z, is prepared using the following conditions: 1.5≦X≦2.5 0.5≦Y≦1.5 1.8≦Z≦2.5 Each raw material when growing by flux method The composition of the cations is
In molar ratio % (β, γ, ε), βBi_2O_3+γ{(Sr,RE)O}+εCuO
However, the method for growing an insulating composition is characterized by satisfying the following relationships: 5≦β≦25 20≦γ≦60 10≦ε≦60 2β+γ+ε=100. (5) The insulating composition according to claim 1, wherein a part of Bi is replaced with Pb. (6) The atomic ratio of Bi, Pb, Sr, RE, Cu, and O is 2
-W:W:2:1:2:8+δ, the insulating composition according to claim 5. The insulating composition according to claim 6, wherein 0<W≦1.5 δ is excess oxygen (7)W, and 0.2≦W≦1.0. (8) The atomic ratio of Bi, Pb, Sr, RE, Cu, and O is 2
The insulating composition according to claim 5, characterized in that -WW:2:2:3:10+δ. The insulating composition according to claim 8, wherein 0<W≦1.5 δ is excess oxygen (9)W, and 0.2≦W≦1.0. (10) A superconducting element characterized in that the insulating composition according to claim 1 is formed as an insulating layer on an oxide superconductor. (11) A superconducting element characterized in that the insulating composition according to claim 1 is used as a substrate, and an oxide superconductor is formed on this substrate.