JPH04302179A - Superconductive element - Google Patents

Abstract

PURPOSE:To provide a superconductive element which can be applicable as a Josephson element, stable in characteristics, and large in element resistance. CONSTITUTION:A superconductive element is composed of a barrier layer 2 and an A electrode 1 and a B electrode 4 which are formed of superconductor and located at the ends of the barrier layer 2, where the barrier layer 2 is formed of non-superconductor where alkaline earth metal contained in Bi oxide superconductor is partially substituted with rare earth elements.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to superconductivity application technology.
In particular, a Bi-based oxide superconductor containing an alkaline earth metal is used for the superconducting electrode, and a portion of the alkaline-earth metal element in the Bi-based oxide superconductor is replaced with Y or a lanthanide element as a barrier layer. The present invention relates to superconducting devices using non-superconducting materials.

0002

[Prior Art] Among the oxide superconductors discovered in recent years, there are some whose superconducting transition temperature exceeds the temperature of liquid nitrogen (77.3 Kelvin), which greatly expands the field of application of superconductors. It became.

One of the practical applications of superconducting devices is the Josephson device, in which an oxide superconductor is divided into two halves and then brought into slight contact again.The oxide superconductor is made into a thin film and a small constriction is formed in the Josephson device. A bridge-type Josephson element, and a Josephson element in which oxide superconductors are connected with a noble metal such as Au or Ag, have been prototyped in the past.

0004

[Problem to be solved by the invention] Among the devices that have been prototyped in the past, superconducting devices in which two halves of a superconductor are brought into contact cannot achieve reproducibility and the characteristics are extremely unstable. there were.

Furthermore, bridge-type devices in which oxide superconductors are constricted or connected with precious metals have the disadvantage of being damaged by even the slightest electrostatic shock, and the problem is that devices with high resistance have not been obtained. there were.

[0006] Furthermore, in a superconducting element having a thin film bonding type structure using an oxide superconductor, the film formation temperature of the oxide superconductor must be approximately 600°C or higher, so the superconducting electrode located at the top must be formed at a temperature of approximately 600°C or higher. Sometimes the barrier layer diffuses, or the thermal expansion coefficients of the material used for the superconducting electrode layer and the material of the barrier layer are different, so stress is applied to the film when it is returned to room temperature, causing the superconductivity of the superconducting electrode located above to There were problems such as a significant loss in performance and the presence of pinholes in the barrier layer.

[0007] Furthermore, the crystallinity of the upper superconducting electrode is poor due to a mismatch in lattice constants due to the difference in crystal structure between the material used for the superconducting electrode layer and the material for the barrier layer, and its superconductivity is Issues such as being inferior to superconducting electrodes were also pointed out.

SUMMARY OF THE INVENTION An object of the present invention is to provide a superconducting element that has stable characteristics and a large element resistance and can be used as a Josephson element. In addition to the above-mentioned objectives, the present invention also has the advantage that even if the film is deposited at 550°C or higher and then returned to room temperature, the film maintains its crystallinity at the time of deposition without stress, and has good superconductivity even at liquid nitrogen temperatures or higher. Another objective is to provide a thin film bonding type superconducting element having the following properties.

[0009]

[Means for Solving the Problems] In a superconducting element composed of a barrier layer and two electrodes A and B made of a superconductor located at both ends of the barrier layer, the A electrode and the B electrode are provided.
B containing at least an alkaline earth metal as an electrode material
Using an i-based oxide superconductor, a part of the alkaline earth metal in the Bi-based oxide superconductor containing the above-mentioned alkaline earth metal as a barrier layer material is Y or one of the lanthanide elements. A non-superconductor substituted with is used.

0010

[Operation] At least a portion of the alkaline earth metal in the Bi-based oxide superconductor containing an alkaline earth metal is added to the barrier layer, which is one of the constituent elements of the superconducting element of the present invention, by Y or a lanthanide element. A good superconductor can be obtained by using a non-superconductor substituted with one of these, and by using a Bi-based oxide superconductor containing an alkaline earth metal for the A and B electrodes, which are the constituent elements of the superconducting element. Conductive elements can be manufactured.

[0011] Here, Bi containing an alkaline earth metal
The system oxide superconductor has both A and B superconducting electrodes:
Bi-Sr-Ca-Cu-O, Bi-Sr-Ba-Cu
-O, one of Bi-Ca-Ba-Cu-O, or Bi-Sr-Ca-Cu-O containing at least Pb
, Bi-Sr-Ba-Cu-O, Bi-Ca-Ba-C
One of u-O is provided.

[0012] Also, as the material of the barrier layer, Bi-Sr-Ca-Cu-O and Bi-Sr-B used for the superconducting electrode are used.
a-Cu-O, Bi-Ca-Ba-Cu-O, or Bi-Sr-Ca-Cu-O containing at least Pb,
Bi-Sr-Ba-Cu-O, Bi-Ca-Ba-Cu
-O in which part or all of Ca, Sr, or Ba is replaced with Y or a lanthanide element is provided.

[0013] All of these materials have a similar layered perovskite structure, and the lattice constants of their a and b crystal orientations are almost the same, and their thermal expansion coefficients are also almost the same. The mechanical stress between each electrode and the barrier layer can be reduced in response to changes in the environmental temperature, and the characteristics of the superconducting element will not deteriorate.

For example, if a single crystal or sintered body of a Bi-based oxide superconductor is used as the substrate and one superconducting electrode, and a barrier layer and another superconducting electrode are formed thereon, , even if the temperature is returned to room temperature after fabrication, the crystallinity at the time of fabrication is maintained without stress, and the superconductivity of the superconducting electrode located at the top is comparable to that of the superconductor used as the substrate. You can get the following. In this case, compared to cases where other materials are used for the substrate, there is no disturbance in crystallinity due to differences in thermal expansion coefficients, and the superconducting properties of the superconducting element, particularly the critical current density, can be increased.

Furthermore, in a superconducting element constructed on a substrate, the substrate used as the base is appropriately selected, and the lattice constant and coefficient of thermal expansion of the substrate are close to those of the oxide superconductor. By doing so, the two superconducting electrodes and the barrier layer are all in the form of thin films, and even if the film is formed at a substrate temperature of 550°C or higher and returned to room temperature, no stress is applied and the crystallinity at the time of film formation is maintained. The superconductivity of the superconducting electrode located on the substrate is also comparable to that of the superconducting electrode formed on the substrate. In addition, with this configuration, the superconducting element can be formed by continuous film formation of the A electrode, barrier layer, and B electrode in the same vacuum, which prevents the formation of a contamination layer between each layer and improves the properties of the superconducting element. can improve reproducibility and controllability. This configuration also allows the use of a large-area substrate and is advantageous when a large number of elements with the same characteristics are integrated.

On the other hand, the barrier layer (non-superconductor) used in the present invention has a high resistivity of 10 Ωcm or more at around 77K, and the element resistance of the superconducting element can be increased.

Furthermore, if both the A and B electrodes are constructed using the same material, pinholes caused by slight differences in crystal lattice constants can be reduced, and the yield can be improved when integrating a large number of elements. Improve. Also, this configuration
The device configuration in the film forming process can be simplified, which is advantageous in practical use.

Furthermore, if a Bi-based oxide thin film is used in which the A electrode, B electrode, and barrier layer are all oriented along the c-axis, the crystallinity of each layer will be distorted due to the similarity of the crystal system and constituent elements. We were able to fabricate a superconducting device with good superconducting device characteristics with good reproducibility, without any interference.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The superconducting element of the present invention has a structure in which a Bi-based oxide superconductor containing an alkaline earth metal is used as a pair of electrodes, and a barrier layer is provided between the two electrodes.

[0020] In particular, the superconducting element of the present invention is a non-superconducting material in which a part of the alkaline earth metal in the Bi-based oxide superconductor is replaced with at least Y or one of the lanthanide elements as a barrier layer. By using the body, its effects are more clearly demonstrated.

[0021] Here, Bi containing an alkaline earth metal
The system oxide superconductor has both A and B superconducting electrodes:
Bi-Sr-Ca-Cu-O, Bi-Sr-Ba-Cu
-O, one of Bi-Ca-Ba-Cu-O, or Bi-Sr-Ca-Cu-O containing at least Pb
, Bi-Sr-Ba-Cu-O, Bi-Ca-Ba-C
One of u-O is provided. When this Pb is mixed,
This had the effect of expanding the crystal temperature range.

In particular, a Bi-based oxide superconductor having the following 2212 phase structure had a stable crystal structure.

(Bi1-yPby)2-Sr2-Ca1-Cu2-O
x, (however, 0≦y<0.5, x is arbitrary) In addition, in the Bi-based oxide superconductor with the following 2223 phase structure,
The ability to obtain superconductors with higher superconducting transition temperatures has expanded the operating temperature margin of superconducting devices.

(Bi1-yPby)2-Sr2-Ca2-Cu3-O
x, (however, 0≦y<0.5, x is arbitrary) In addition, as a material for the barrier layer, Bi used for the superconducting electrode
-Sr-Ca-Cu-O, Bi-Sr-Ba-Cu-O
, Bi-Ca-Ba-Cu-O, or Bi-Sr-Ca-Cu-O, Bi-Sr- containing at least Pb
In Ba-Cu-O, Bi-Ca-Ba-Cu-O,
A material in which part or all of Ca, Sr, or Ba is replaced with Y or a lanthanide element is provided. These materials have a crystal structure similar to that of the superconducting electrode and also have a coefficient of thermal expansion approximately equal to that of the superconducting electrode, making them suitable for a laminated structure with the superconducting electrode. This resulted in a barrier layer with even higher resistivity and higher device resistance.

In particular, the following Bi-based oxide mainly having a 2212 phase was most preferred as a barrier layer because it had a high resistivity and a stable crystal structure.

(Bi1-yPby)2-Sr2-Ra1-Cu2-O
x, (0≦y<0.5, x is arbitrary, Ra refers to Y, and at least one of the lanthanide elements) In particular, as a substrate, (100) SrTiO3 or (100
) Using an MgO substrate, 221 is mainly used for the A and B electrodes.
Using the following two-phase Bi-based oxide superconductor, (Bi1-y
Pby)2-Sr2-Ca1-Cu2-Ox, (but 0
≦y<0.5, x is arbitrary) The following oxide of 2212 phase is mainly used as the material of the barrier layer, or (Bi1-yPby)2-Sr2-Ra1-Cu2-O
x, (0≦y<0.5, x is arbitrary, Ra refers to Y, and at least one of the lanthanide elements) or the following Bi-based oxide superconductor mainly of 2223 phase for the A electrode and the B electrode (Bi1-yPby)2-Sr2-Ca2-Cu3-O
x, (0≦y<0.5, x is arbitrary) When the following oxide of mainly 2212 phase is used as the material of the barrier layer, (Bi1-yPby)2-Sr2-Ra1-Cu2-O
x, (0≦y<0.5, x is arbitrary, Ra refers to Y, and at least one of the lanthanide elements) When the substrate temperature is from 600℃ to 850℃, each layer is continuous with respect to the substrate. It has been found that the superconductivity of both electrodes A and B can be improved while maintaining crystallinity even when epitaxially grown and annealed in oxygen at temperatures below 700°C.

Furthermore, when a junction-type superconducting device was fabricated using these multilayer films described above, it was found that it exhibited good superconducting properties even at temperatures above liquid nitrogen temperature and exhibited the Josephson effect.

The present invention will be explained in more detail with reference to specific examples below. Specific Embodiments First Embodiment FIG. 1 is a process diagram showing a first embodiment of the present invention. First, a (100) MgO substrate was used as the substrate 3, and mainly 2212
Bi-based oxide superconductor (Bi
1-yPby)2-Sr2-Ca1-Cu2-Ox, (
(0≦y<0.5, x is arbitrary) Using an oxide powder target adjusted to deposit 0≦y<0.5, the A electrode 1 with a thickness of 300 nm was deposited. Subsequently, in the same vacuum, a mainly 2212-phase Bi-based oxide (Bi1-yPby)2-Sr2-Nd1-Cu2-O
Barrier layer 2 was deposited to a thickness of 11 nm from an oxide powder target adjusted to deposit x, (0≦y<0.5, x is arbitrary) (see FIG. 1(a)).

Furthermore, a Bi-based oxide superconductor containing a 2212-phase oxide superconductor, which becomes the B electrode 2, (Bi1-yP
by) 2-Sr2-Ca1-Cu2-Ox, (0≦
Using an oxide powder target adjusted to deposit y < 0.5, x is arbitrary), the B electrode 4 was deposited to a thickness of 200 nm, and finally Pt was deposited to a thickness of 60 nm as the surface protective layer 5 ( Figure 1 (
b)).

However, the substrate temperature was 650° C. in all cases except for the deposition of Pt in the surface protective layer 5. Surface protective layer 5
was deposited at room temperature.

Thereafter, the barrier layer 2, B electrode 4, and surface protection layer 5 were patterned into a tunnel junction shape by photolithography using a negative resist and ion milling (see FIG. 1(c)).

Thereafter, without removing the negative resist 6, 250 nanometers of CaF2 was deposited as the interelectrode separation layer 7 by vacuum evaporation (see FIG. 1(d)), followed by ultrasonic cleaning with trichloroethane and O2 gas plasma treatment. (1
The surface protective layer 5 was exposed by a lift-off method (see FIG. 1(e)). Finally, Pt150 was applied to the entire surface for the contact electrode 8.
A contact electrode 8 was formed in contact with a part of the B electrode by photolithography using a negative resist and ion milling, and a superconducting element was completed (see FIG. 1(f)).

[0033] It was confirmed that the superconducting element manufactured by this manufacturing method exhibits good superconducting characteristics and nonlinear current-voltage characteristics at liquid nitrogen temperature.

FIG. 2 shows an X-ray diffraction pattern of the multilayer film used to fabricate the present superconducting device. According to this, each layer showed c-axis orientation at a film formation temperature of 650° C., and epitaxial growth was confirmed by high-speed electron diffraction (RHEED) observation.

The current-voltage characteristics of this superconducting element showed large nonlinearity, and by applying a high frequency, a current step indicating the AC Josephson effect was observed on the current-voltage characteristics. FIG. 3 shows an example of the current-voltage characteristics. The element resistance was higher than conventionally manufactured elements of similar shape, and the probability of the existence of pinholes was also lowered.

Second Embodiment Next, a second embodiment of the present invention will be described. FIG. 4 is a process diagram explaining the second embodiment. The A electrode 1 is a 2212-phase single crystal Bi-based oxide superconductor (Bi1-yPby)2-Sr2-Ca1-Cu2-O prepared by a melting method.
x, (0≦y<0.5, x is arbitrary) was used. This single crystal was easily opened on the AB plane, and a barrier layer 2 and a B electrode 4 were deposited on the open face by sputtering. The isolation of the single crystal was carried out using adhesive tape in a vacuum chamber with the sputtering chamber evacuated, and after heating the A electrode 1 in the same vacuum and maintaining it at a predetermined temperature, mainly 2212 phase Bi-based oxide was formed. (Bi
1-yPby)2-Sr2-Er1-Cu2-Ox, (
Barrier layer 2 was deposited to a thickness of 11 nm using an oxide powder target adjusted to deposit 0≦y<0.5, x being arbitrary (see FIG. 4(a)).

Further, a Bi-based oxide superconductor containing a 2212-phase oxide superconductor, which becomes the B electrode 4, (Bi1-yP
by) 2-Sr2-Ca1-Cu2-Ox, (0≦
Using an oxide powder target adjusted to deposit y < 0.5, x is arbitrary), 200 nanometers of Bi-based oxide superconductor was deposited.Finally, heating was stopped and A electrode 1, barrier With the layer 2 and the B electrode 4 sufficiently cooled (about room temperature), 60 nm of Pt was deposited as the surface protective layer 5 (see FIG. 4(b)).

However, except for the deposition of Pt in the surface protective layer 5, the heating temperature was 650°C. Thereafter, the barrier layer 2, B electrode 4, and surface protection layer 5 were patterned into a tunnel junction shape by photolithography and ion milling using a negative resist 6 (see FIG. 4(c)).
.

Thereafter, without removing the negative resist 6, 250 nanometers of CaF2 was deposited as the interelectrode separation layer 7 by vacuum evaporation (see FIG. 4(d)), followed by ultrasonic cleaning with trichloroethane and O2 gas plasma treatment. (1
The surface protective layer 5 was exposed by a lift-off method (see FIG. 4(e)). Finally, 150 nm of Pt was deposited on the entire surface, and a contact electrode 8 was formed in contact with a part of the B electrode 4 by photolithography using a negative resist and ion milling, thereby completing a superconducting element (see FIG. 4). f
)reference).

[0040] It was confirmed that the superconducting element manufactured by this manufacturing method also exhibited good superconducting characteristics, Josephson effect, and current-voltage characteristics with nonlinearity at liquid nitrogen temperature.

Third Embodiment FIG. 5 is a process diagram showing a third embodiment of the present invention. First, using a (100) MgO substrate as the substrate 3, a Bi-based oxide (Bi1-
Barrier layer 2 was deposited to a thickness of 200 nm from an oxide powder target adjusted to deposit yPby)2-Sr2-Nd1-Cu2-Ox, (0≦y<0.5, x is arbitrary) ( (See Figure 1(a)).

Subsequently, in the same vacuum, mainly 2
212-phase Bi-based oxide superconductor (Bi1-yPby)2-Sr2-Ca1-Cu2-O
An oxide superconducting thin film 9 having a thickness of 100 nm was deposited using an oxide powder target adjusted to deposit x, (0≦y<0.5, x is arbitrary). (See Figure 5(a)).

However, the substrate temperature was 650° C. in both cases. Thereafter, grooves with a width of 100 nm were patterned by electron beam lithography using the electron beam resist 10 (see FIG. 5(b)).

After that, the superconducting thin film 9 is patterned by ion milling to form the A electrode 1 and the B electrode 4.
The electron beam resist was removed and the superconducting device was completed (see FIG. 5(c)).

[0045] It was confirmed that the superconducting element manufactured by this manufacturing method also exhibited good superconducting characteristics and nonlinear current-voltage characteristics at liquid nitrogen temperature.

In a specific embodiment of the present invention, the A and B electrodes of the superconducting element, which are the constituent elements of the superconducting element, mainly contain Bi containing the following oxide superconductor of 2212 phase.
Using a thin film or single crystal of an oxide superconductor, (Bi1
-yPby)2-Sr2-Ca1-Cu2-Ox, (however, 0≦y<0.5, x is arbitrary) The material of the barrier layer is mainly a 2212 phase Bi-based oxide (Bi1-yPby)2-Sr2- Nd1-Cu2-O
x, (0≦y<0.5, x is arbitrary), but a Bi-based oxide superconductor thin film containing mainly the following oxide superconductor of 2223 phase or a monolayer was used for the A and B electrodes. Crystal, (Bi1-yPby)2-Sr2-Ca2-Cu3-O
It was confirmed that even if x, (0≦y<0.5, x is arbitrary) is used, a laminated film having good crystallinity can be similarly produced, and the operating temperature can also be increased. Furthermore, although a single crystal was used in the description of the second example, it was confirmed that a superconducting element could be similarly produced using a sintered body whose surface was polished.

Furthermore, by making both the A and B electrodes and the barrier layer a c-axis oriented Bi-based oxide containing at least Bi and an alkaline earth metal, each layer has a c-axis orientation with respect to the substrate at 550° C. or higher. We confirmed that an oriented film grows and that a junction-type device fabricated using the multilayer film operates as a superconducting device.

However, the Bi-based oxide containing an alkaline earth metal referred to here means Bi-based oxide for both A and B superconducting electrodes.
-Sr-Ca-Cu-O, Bi-Sr-Ba-Cu-O
, Bi-Ca-Ba-Cu-O, or
Bi-Sr-Ca-Cu-O, B containing at least Pb
i-Sr-Ba-Cu-O, Bi-Ca-Ba-Cu-
It is any one of O.

[0049] Also, as a material for the barrier layer (Bi1-y
Pby)2-Sr2-Nd1-Cu2-Ox, (but 0
≦y<0.5, x is arbitrary) or (Bi1-yPby)2-Sr2-Er1-Cu2-O
x, (however, 0≦y<0.5, x is arbitrary), but mainly the following oxide of 2212 phase (Bi1
-yPby)2-Sr2-Ra1-Cu2-Ox, (where 0≦y<0.5, x is arbitrary, Ra refers to Y and at least one of the lanthanide elements), It was confirmed that similarly good superconducting elements could be fabricated.

Further, although Pt is used as the contact electrode, metals such as Au, Ag, Pd, and Cu may be used.

In this example, a c-axis oriented film was used as the barrier layer, and the current flowed in the direction of the c-axis, but the device could also be fabricated in the same way if both the barrier layer and the superconducting electrode had a polycrystalline structure. It was confirmed that the device could operate as a superconducting device.

[0052]

According to the present invention, both the A and B electrodes of the superconducting element, which are the constituent elements of the superconducting element, and the barrier layer are all made of Bi-based oxide containing an alkaline earth metal. Because the coefficients of thermal expansion are almost the same, the substrate temperature is 5.
Even if the film is formed at 50°C or higher and returned to room temperature, no stress occurs and the film maintains its crystallinity, and the superconductivity of the superconducting electrode located at the top is also the same as that of the superconducting electrode formed on the substrate. The same level of conductivity can be obtained.

The superconducting element according to the present invention can detect high-frequency radio waves that could not be used conventionally, so that the range of use of radio frequencies in the field of telecommunications can be expanded. Furthermore, since it is highly sensitive, it may also reduce the problem of radio wave interference.

[0054]

[Brief explanation of the figure]

[0055]

FIG. 1 is a process diagram for manufacturing a superconducting element, explaining a first embodiment of the present invention.

[0056]

FIG. 2 is an X-ray diffraction diagram of the laminated thin film used in the first example of the present invention.

[0057]

FIG. 3 is a current-voltage characteristic diagram of the superconducting element described in the first embodiment of the present invention.

[0058]

FIG. 4 is a process diagram for manufacturing a superconducting element, explaining a second embodiment of the present invention.

[0059]

FIG. 5 is a process diagram for manufacturing a superconducting element, explaining a third embodiment of the present invention.

[0060]

[Explanation of symbols]

1　A electrode 2 Barrier layer 3 Base 4 B electrode 5　Surface protective layer 6 Negative resist 7　Inter-electrode separation layer 8 Contact electrode 9 Superconducting thin film 10　Electron beam resist

Claims (8)

[Claims] 1. A superconducting element comprising a barrier layer and an A electrode and a B electrode made of a superconductor in contact with two surfaces or one surface of the barrier layer,
The material of the A electrode and the B electrode is made of a Bi-based oxide superconductor containing at least an alkaline earth metal, and the material of the barrier layer is made of a Bi-based oxide superconductor containing at least an alkaline earth metal. A superconducting element comprising a non-superconductor in which a portion of an alkaline earth metal is replaced with at least one of Y or a lanthanide element. 2. The superconducting element according to claim 1, wherein at least one of the A electrode and the B electrode is constructed using a sintered body or a single crystal. 3. The superconducting element according to claim 1, wherein the A electrode, the barrier layer, and the B electrode are all constructed using thin films fabricated on a substrate. 4. The superconducting element according to claim 3, wherein both the A electrode and the B electrode are constructed using the same material. 5. The A electrode, the B electrode, or the barrier layer,
5. The superconducting element according to claim 3, characterized in that a Bi-based oxide thin film formed entirely with c-axis orientation is used. 6. The material of the A electrode and the B electrode is at least Bi-based oxide superconductor Bi-Sr-Ca-Cu-O.
, Bi-Sr-Ba-Cu-O, Bi-Ca-Ba-C
The superconducting element according to any one of claims 2 to 5, characterized in that any one of u-O is used. 7. The superconducting element according to claim 6, wherein a Bi-based oxide superconductor containing at least Pb is used as a material for the A electrode and the B electrode. [Claim 8] The materials of the A electrode and B electrode are mainly 2
212 phase Bi-based oxide superconductor (Bi1-yPby)2-Sr2-Ca1-Cu2-O
x, (however, 0≦y<0.5, x is arbitrary), or the material of the A electrode and B electrode is the following oxide superconductor (Bi1-yPby)2-Sr2-Ca2-Cu3-O, mainly having the 2223 phase.
x, (where 0≦y<0.5, x is arbitrary), and the material of the barrier layer is mainly 2
212 phase of the following oxide (Bi1-yPby)2-Sr2-Ra1-Cu2-O
The superconducting element according to claim 6 or 7, characterized in that x, (0≦y<0.5, x is arbitrary, and Ra refers to at least one of Y and a lanthanide element). .