KR100416755B1 - Ramp-edge high-temperature superconducting josephson junction structure using gallium doping ybco and fabricating method thereof - Google Patents

Abstract

PURPOSE: A ramp-edge high-temperature superconducting Josephson junction structure using gallium doping YBCO(YBa2Cu3Oy) is provided to epitaxially grow a multilayered superconducting thin film without a mismatch by forming a clean interface at a process temperature of YBCO and by having the same thermal expansion coefficient and crystal structure as YBCO. CONSTITUTION: An isolation wall is interposed between the first and second superconducting electrodes(12a,12b) of a Josephson junction structure. The edge of the junction surface of the first superconducting electrode is a tilt surface tilted as a predetermined angle. The tilt surface is covered with YBa2Cu3-xGaxOy wherein x is a rational number except zero. The isolation wall on the tilt surface is covered with the second superconducting electrode.

Description

Slope Structure High Temperature Superconducting Josephson Junction Structure Using Gallium Doped YBCO Bulkhead and Its Manufacturing Method

The present invention relates to a ramp-edge Josephson junction structure using a Ga-doped YBCO (YBa ₂ Cu ₃ O _y ) barrier (GaB) barrier and a method of manufacturing the same.

A YBCO high temperature superconducting thin film and an insulating layer deposited on a single crystal substrate were formed by a semiconductor ion photolithography to form a ramp-edge type, and then a very thin barrier on the inclined surface. A Ga-doped YBCO film as a barrier layer and a YBCO-coated structure as the final top electrode form a very stable Josephson junction.

In general, the Josephson junction structure is an element that is the basis for most superconducting electronic devices using high temperature superconductors. Application examples include superconducting quantum interference devices (SQUID), superconducting logic devices (Logic circuits), radiation detectors, supercomputers, and microwave devices for communication.

As described above, there are many ways to fabricate the Josephson junction structure, which is the basis for superconducting electronic devices, but most of them have low reproducibility, and they do not have characteristic values for practical application.

A recently developed Josephson junction structure is a ramp-edge junction structure having a four-sided structure as shown in FIG. 1. As shown in this sloped structure, the Josephson junction structure includes a YBCO first superconductor electrode 2a and an insulating layer 3 which are sequentially stacked on the LaAlO ₃ single crystal substrate 1 such that the edges have an inclined surface. The structure is joined to the second superconductor electrode 2b with the gap therebetween.

Such a structure uses a method of flowing superconducting electrons through an inclined surface, and can be considered to be the most practical form of the conventional artificial bonding fabrication method. However, PrBaCuO, CaRuO, NdGaO, SrTiO _3, etc., which are used as barrier (4) materials, are not stable at YBCO's processing temperature, ie, above 760 ° C, and have a mismatch in crystal structure, resulting in a clean interface. The problem is that it does not form. Therefore, there is a difficulty in forming a Josephson junction having excellent reliability and reproducibility.

The present invention has been made to improve the above problems, by using a material stable at 760 ℃ or more as a barrier material to form a barrier rib to form a clean interface between the high temperature superconducting material, gallium doping excellent in reliability and reproducibility It is an object of the present invention to provide a sloped high temperature superconducting Josephson bonded structure using a YBCO partition and a manufacturing method thereof.

1 is a vertical cross-sectional view of a conventional multilayered film Josephson junction structure,

2 is a schematic perspective view of a sloped high temperature superconducting Josephson junction structure using Ga-doped YBCO barrier according to the present invention;

3 to 8 are vertical cross-sectional views illustrating a method of manufacturing a sloped high temperature superconducting Josephson junction using Ga-doped YBCO barrier of FIG.

3 is a vertical cross-sectional view showing a process of depositing a high temperature superconducting thin film and an insulating layer on a single crystal substrate,

4 is a vertical cross-sectional view showing a process of forming a ramp-edge structure using an ion etching method,

5 is a vertical cross-sectional view showing a process of cleaning the inclined surface by ion milling (Ion milling),

6 is a vertical sectional view showing a process of forming a barrier on an inclined surface;

7 is a vertical sectional view showing a step of forming a superconducting upper electrode layer on an inclined surface;

8 is a vertical sectional view showing a process of patterning an upper electrode layer by ion etching;

9 is a resistivity-temperature characteristic curve of a sloped high temperature superconducting Josephson junction structure using Ga-doped YBCO barrier of FIG.

FIG. 10 is a current-voltage characteristic curve of a sloped high temperature superconducting Josephson junction structure using Ga-doped YBCO barrier of FIG. 2.

<Description of the symbols for the main parts of the drawings>

1. LaAlO ₃ single crystal substrate 2a. YBCO First Electrode

2b. YBCO 2nd electrode 3. Insulation layer

4. Bulkhead

11. LaAlO ₃ single crystal substrate 12a. YBCO First Electrode

12b. YBCO 2nd Electrode 13. Insulation Layer

14. Ga-doped bulkhead 15. Photoresist

16. Photoresist

In order to achieve the above object, the sloped structure high temperature superconducting Josephson junction structure using the gallium doped YBCO partition according to the present invention is a Josephson junction structure in which a first superconductor electrode and a second superconductor electrode are joined via a partition wall. The edge of the junction surface of the first superconductor electrode has an inclined surface inclined at a predetermined angle, and the partition wall is formed to cover the inclined surface with YBa ₂ Cu _3-x Ga _x O _y when x is a nonzero rational number. The second superconductor electrode is formed to cover the partition wall on the inclined surface.

In the present invention, the slope of the inclined surface of the first superconductor is 30 degrees or less, the x value representing the doping level of the Ga is within the range of 0.15 <x <0.45, the thickness of the partition is 10Å ~ 900Å, the slope The SrTiO ₃ insulating layer is further formed between the upper surface of the barrier rib and the second superconducting electrode, and the width of the microbridge in which the second superconductor electrode covers the barrier rib is 5 μm or less.

In addition, in order to achieve the above object, a method of manufacturing a sloped high temperature superconducting Josephson junction structure using a gallium doped YBCO partition according to the present invention, the step of sequentially depositing a first superconductor layer and an insulating layer on a substrate; Etching edges of the first superconductor layer and the insulating layer to form a first superconducting electrode having an inclined surface at a predetermined angle; Cleaning the inclined surface; forming a barrier rib on the inclined surface and the insulating layer with YBa ₂ Cu _3-x Ga _x O _y when _x is a rational number representing a doping concentration of Ga; And depositing a second superconductor layer on the substrate and the barrier rib, and etching the second superconductor layer to form a second superconductor electrode having a microbridge having a predetermined width covering the inclined surface. do.

In the present invention, the substrate is made of LaAlO ₃ single crystal, the temperature for depositing the first superconductor layer, the insulating layer and the second superconductor layer is at least 760 ℃, the insulating layer is made of SrTiO ₃ , The forming of the first superconductor electrode is etched by an ion etching method in which Ar ⁺ ions are projected at an angle of 30 ° to 60 ° on the edges of the insulating layer and the first superconductor layer, and the cleaning of the inclined surface is performed by the first superconductor. In the forming of the electrode, etching is performed by an ion etching method of projecting Ar ⁺ ions having a relatively low voltage-low current at an angle of 30 ° to 60 °, wherein the x value is within a range of 0.15 <x <0.45, and the partition wall Is formed in a thickness of 10 kV to 900 kV, and the forming of the second superconductor electrode is performed by etching an ion etching method of projecting Ar ⁺ ions onto the second superconductor layer, and forming the second superconductor electrode. In the microbridge is preferably formed so that the width is 5 ㎛ or less.

Hereinafter, a high-temperature superconducting Josephson junction structure and a manufacturing method thereof using a gallium doped YBCO partition according to the present invention will be described in detail with reference to the accompanying drawings.

The sloped high temperature superconducting Josephson junction structure using gallium doped YBCO barrier ribs according to the present invention is manufactured by using a Ga-doped YBCO superconducting material in the barrier rib which plays the most important role in the bonding of the slope structure. Solve the problem and get the characteristics close to practical use.

2 is a schematic perspective view of a sloped high temperature superconducting Josephson junction structure using Ga-doped YBCO barrier according to the present invention. As shown, the tetrahedral high-temperature superconducting Josephson junction structure using the Ga-doped YBCO barrier according to the present invention is a YBCO first superconductor electrode 12a sequentially stacked on the LaAlO ₃ single crystal substrate 11 so as to have an inclined surface. ) And an insulating layer 13 are formed in a structure bonded to the second superconductor electrode 12b with the partition 14 therebetween. Here, the partition wall 14 is formed of YBCO doped with Ga, that is, YBa ₂ Cu _3-x Ga _x O _y . Gallium doped (Ga-doped) YBCO is thermally stable, so there is no problem in the processing temperatures of the first and second high temperature superconductor electrodes 12a and 12b made of YBCO, and the coefficient of thermal expansion and crystal structure are also consistent with YBCO so that the high temperature superconductor Very easy for epitaxial growth of layers. The slope of the inclined surface of the first superconductor 12a is preferably 30 ° or less, and the x value representing the doping level of Ga in YBa ₂ Cu _3-x Ga _x O _y, which is the material of the partition 14, is 0.15 <x < 0.45 range I am suitable. The thickness of the bulkhead is 10Å ~ 900Å. The insulating layer 13 is formed of SrTiO ₃ , and the width of the microbridge in which the second superconductor electrode 12b covers the inclined surface of the partition 14 is preferably 5 μm or less.

On the other hand, the method for producing a Josephson junction sphere of the above structure is as follows.

First, as shown in FIG. 3, the YBCO first superconductor layer 12 ′ and the SrTiO ₃ insulating layer 13 ′ are sequentially deposited on the LaAlO ₃ single crystal substrate 11. All thin films are manufactured by vapor deposition using a pulsed laser. The temperature of the thin film is 760 ° C. or higher and the oxygen pressure is performed at several hundred mTorr or more. The same applies to the following deposition processes.

Next, as shown in FIG. 4, edges of the first superconductor layer 12 ′ and the insulating layer 13 are etched to form a first superconductor electrode 12a having an inclined surface of 30 ° or less. In order to produce a slope having an inclination angle of 30 ° or less, Ar ⁺ ion etching is performed in which the incidence angle of the Ar ⁺ ion beam is 35 ° to 60 ° using an ion etching method.

Next, as shown in FIG. 5, the inclined surface of the first superconductor electrode 12a is cleaned. This projects and cleans a very weak energy Ar ⁺ ion beam to clean the interface with the barrier 14 material to be deposited next.

Next, as illustrated in FIG. 6, YBa ₂ Cu _3-x Ga _x O _y is deposited on the inclined surface of the first superconductor electrode 12a and the insulating layer 13 and the insulating layer 13 to form the partition wall 14. ). Here, x is a rational number representing the relative content which is an index of the doping concentration of Ga. The partition 14 is formed with a very thin thickness of several tens to hundreds of micrometers (about 10 micrometers-900 micrometers).

Next, as shown in FIG. 7, the YBCO second superconductor layer 12 ″ is deposited on the exposed portion and the partition 14 of the substrate 11, and then the second superconductor layer 12 ″ is deposited. As shown in FIG. 8, the second superconductor electrode 12b is formed by patterning by ion etching to form a microbridge having a very small width of 5 μm or less (w in FIG. 2) on an inclined surface. This completes the Josephson junction.

The slope structure Josephson junction structure of FIG. 2 produced through the above process is a DC superconducting quantum interference element (DC SQUID) having two junctions in parallel. This can be used to create a magnetic field sensor that can detect very fine magnetic fields.

In the four-sided Josephson junction structure using the gallium doped YBCO barrier rib fabricated as described above, the superconducting electron pair flowing through the barrier rib has a coherence length of the ab axis (the direction parallel to the substrate) compared to the c axis (the direction perpendicular to the substrate). The large coherence length makes it easier to flow along the ab axis. Using this principle, the ramp-edge junction using the inclined plane in the ab axis direction is utilized. In order to obtain the characteristic value of the junction required for practical use, the characteristic voltage Vc which is the product of the critical current Ic and the phase resistance Rn is used. ) Should be high. Therefore, in order to obtain a high value of Vc, it is necessary to form a barrier rib having a clear interface, and a condition that the resistance of the barrier rib must be in the metal-insulator transition range. Here, the critical current refers to the current value at the moment when the superconducting property is broken when the current is applied to the superconductor, and the phase resistance is the resistance value when the superconducting property is broken. The characteristic voltage is a measure of how large a small signal can be. In other words, the practical value depends on how large this value is when applied to electronic devices.

The Ga-doped YBCO barrier used in the present invention forms a very clean interface as described above, and since the resistance value also satisfies the above conditions, a high value of Vc can be obtained. In addition, the existing barriers are very sensitive to the characteristics of the junction depending on the thickness, whereas Ga-doped YBCO barriers are insensitive to the change in thickness, it is easy to manufacture a relatively reliable device.

9 and 10 respectively show resistivity-temperature characteristic curves and current-voltage characteristic curves of a four-sided high temperature superconducting Josephson junction structure using Ga-doped YBCO barrier fabricated as shown in FIG. 2. . Here, the measured high-temperature superconducting Josephson junction structure was a multi-layer thin film using a pulsed laser (Pulsed Laser), the temperature at the time of manufacturing was at least 760 ℃ and the oxygen pressure was 400 mTorr or more. Ar ⁺ ion etching was performed to make the incidence angle of the Ar ⁺ ion beam 45 ° to produce a slope having an inclination angle of 30 ° or less, and cleaned with a very weak energy beam to clean the interface with the partition wall. I did it. The bulkhead was coated with a very thin thickness of about 200 mm 3, and a YBCO superconducting thin film was coated on top of it. Once again, the ion etching method was used to form a very wide 5 µm microbridge, completing the Josephson junction. In the characteristic curve of the Josephson junction manufactured as described above, the resistance value decreases as the temperature decreases, and the resistance value is completely zero at a specific temperature (threshold temperature Tc), which shows superconducting properties. 9 shows that about 80 ° K is the critical temperature. 10 shows a voltage rising sharply at a certain point and then slowly becoming a straight line. This indicates that a Josephson junction was formed. The shape of this curve is called a RSJ (resistively shunted junction) curve.

As described above, the slope structure high temperature superconducting Josephson junction structure using the gallium doped YBCO partition according to the present invention has the following advantages.

First, Ga-doped YBCO barriers are thermally stable to form a clean interface even at YBCO's treatment temperature, and the thermal expansion coefficient and crystal structure are also consistent with YBCO, making it easy to epitaxy grow multilayer superconducting thin films without mismatch. .

Secondly, it is possible to form a barrier rib with a definite interface and to obtain a junction having a high value of Vc in the resistance range of the barrier rib in the metal-insulator transition range region.

Third, Ga-doped YBCO bulkhead is very easy to fabricate due to the insensitive nature of the junction due to the change in thickness.

Claims (16)

In the Josephson junction structure in which a first superconductor electrode and a second superconductor electrode are joined with a partition wall interposed therebetween, The junction surface edge of the first superconductor electrode has an inclined surface inclined at a predetermined angle, and the partition wall is formed to cover the inclined surface with YBa ₂ Cu _3-x Ga _x O _y when x is a nonzero rational number. And the second superconductor electrode is formed to cover the partition wall on the inclined surface. The high-temperature superconducting Josephson junction structure using the gallium doped YBCO partition wall structure. The method of claim 1, The slope of the first superconductor inclined surface is 30 ° or less, the slope structure high temperature superconducting Josephson junction structure using a gallium doped YBCO partition. The method of claim 1, The x value representing the doping level of Ga is in the range 0.15 <x <0.45 Slope structure high temperature superconducting Josephson junction structure using a gallium doped YBCO partition wall. The method of claim 1, 4. The sloped high temperature superconducting Josephson junction structure using gallium-doped YBCO barrier ribs having a thickness of 10 μm to 900 μm. The method of claim 1, Slope structure high temperature superconducting Josephson junction structure using a gallium doped YBCO partition, characterized in that the SrTiO ₃ insulating layer is further formed between the upper surface of the partition and the second superconducting electrode rather than the inclined surface. The method of claim 1, 4. The sloped high-temperature superconducting Josephson junction structure using gallium-doped YBCO barrier ribs having a width of 5 μm or less in which the second superconductor electrode covers the partition wall is 5 μm or less. Sequentially depositing a first superconductor layer and an insulating layer on the substrate; Etching edges of the first superconductor layer and the insulating layer to form a first superconducting electrode having an inclined surface at a predetermined angle; Cleaning the inclined surface; forming a barrier rib on the inclined surface and the insulating layer with YBa ₂ Cu _3-x Ga _x O _y when _x is a rational number representing a doping concentration of Ga; And Depositing a second superconductor layer on the substrate and the partition wall, and etching the second superconductor layer to form a second superconductor electrode having a microbridge having a predetermined width covering the inclined surface; Method for producing a four-sided high-temperature superconducting Josephson junction structure using gallium doped YBCO partition wall comprising a. The method of claim 7, wherein The substrate is a method of manufacturing a _four- sided high-temperature superconducting Josephson junction structure using gallium doped YBCO partition wall, characterized in that the LaAlO ₃ single crystal. The method of claim 7, wherein The temperature for depositing the first superconductor layer, the insulating layer and the second superconductor layer is 760 ℃ or more, characterized in that the manufacturing method of the four-sided high temperature superconducting Josephson junction structure using gallium doped YBCO partition. The method of claim 7, wherein The insulating layer is SrTiO _{3 The} method of manufacturing a _four- sided high-temperature superconducting Josephson junction structure using a gallium doped YBCO partition wall. The method of claim 7, wherein The forming of the first superconductor electrode using gallium doped YBCO barrier ribs is performed by ion etching to project Ar ⁺ ions at an angle of 30 ° to 60 ° on the edges of the insulating layer and the first superconductor layer. Method for producing a sloped high temperature superconducting Josephson junction structure. The method of claim 7, wherein In the cleaning of the inclined surface, gallium doping may be performed by an ion etching method of projecting Ar ⁺ ions having a relatively low voltage and low current at an angle of 30 ° to 60 ° in a step of forming the first superconductor electrode. Method for producing a sloped high temperature superconducting Josephson bonded structure using YBCO partition wall. The method of claim 7, wherein The x value is present in the range 0.15 <x <0.45 method for producing a four-sided high temperature superconducting Josephson junction structure using gallium doped YBCO partition wall. The method of claim 7, wherein The partition is a slope structure high temperature superconducting Josephson junction structure using gallium-doped YBCO partition wall, characterized in that formed to a thickness of 10 ~ 900Å. The method of claim 7, wherein The forming of the second superconductor electrode is a method of manufacturing a sloped high temperature superconducting Josephson junction structure using a gallium doped YBCO partition, characterized in that the etching by the ion etching method for projecting Ar ⁺ ions on the second superconductor layer. The method of claim 7, wherein And forming the second superconductor electrode such that the microbridge is formed to have a width of 5 μm or less. 4. A method of manufacturing a sloped high temperature superconducting Josephson junction structure using gallium-doped YBCO barrier ribs.

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