JPH05251778A - Manufacture of josephson element - Google Patents

Abstract

PURPOSE:To provide the novel manufacture of a Josephson element, in which the problem of conductive anisotropy and the problem of the mutual diffusion of a superconducting layer and a normal conductive layer are solved, regarding the manufacture of the Josephson element using a C60 superconducting film. CONSTITUTION:The manufacture of a Josephson element has a process, in which the first film of a C60 superconductor material 2 is formed onto the surface of a substrate 1, a process, in which the first film is irradiated with light, the C60 superconductor material 2 is isomerized constantly by the energy of light and the first film is changed into a normal conductor, and a process, in which the second films 3, 14 of the C60 superconductor material are shaped onto the isomerized first film while keeping the temperature of the substrate at 100 deg.C or lower.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a Josephson device, and more particularly to a method for manufacturing a Josephson device using a C ₆₀ superconducting thin film.

Since the Josephson element utilizing the Josephson effect has excellent characteristics, it is expected that its application field will be further developed in the future. Applications of Josephson devices include voltage standards, magnetic sensors, ultrafast switching devices, and submillimeter wave detectors. For example, as a magnetic sensor using a Josephson element, SQU
ID (Superconducting Quantu
m Interface Device) is expected.

[0003]

2. Description of the Related Art A Josephson device basically has a thin insulating film disposed between two electrodes of a superconductor to generate a voltage-current characteristic peculiar to the Josephson device between the superconducting electrodes. However, SNS (Super-Normal-S)
The upper) Josephson device has a structure in which a normal conductor is sandwiched between a pair of superconductors. As a superconducting electrode, an oxide superconductor having a relatively high superconducting dislocation temperature is about to be used in place of the metal superconductor used conventionally.

[0004]

Although an oxide superconductor has the advantage of having a high superconducting dislocation temperature, it is not so easy to use it as a Josephson device.

For example, when comparing a metal superconductor and an oxide superconductor, the problem is that the oxide superconductor has a remarkably shorter coherence length. Moreover, there is a problem that the oxide superconductor has a large anisotropy of coherence length and a particularly small coherence length in the C-axis direction. This is a significant disadvantage in the manufacture of tunnel type Josephson devices.

Further, in a so-called SNS type Josephson element in which a normal conductor is sandwiched between superconducting electrodes, mutual diffusion of constituent elements at the junction between the superconducting electrode and the normal conductive layer is also a problem. This occurs because the temperature of the substrate when forming the superconducting layer on the normal conducting layer is high.

It is an object of the present invention to provide a novel method for manufacturing a Josephson device which can solve the problem of conduction anisotropy and the problem of mutual diffusion between a superconducting layer and a normal conducting layer.

[0008]

In the method for manufacturing a Josephson device according to the present invention, a step of forming a first film of a C ₆₀ superconductor material on the surface of a substrate, and a step of forming an optical film on the first film. Irradiating the C ₆₀ superconductor material with the energy of the light to permanently isomerize the C ₆₀ superconductor material to make the first film a normal conductor, and isomerize while maintaining the temperature of the substrate at 100 ° C or lower. Forming a second film of a C ₆₀ superconductor material on the first film that has been turned into a film.

[0009]

By using C ₆₀ as the superconducting electrode, conduction anisotropy can be eliminated and the growth temperature can be made sufficiently low. Moreover, since the C ₆₀ is irradiated with light to cause phase transition to a normal conductive phase under a low substrate temperature condition to form a normal conductive layer, the problem of mutual diffusion of constituent elements can be solved.

[0010]

1 is an external view for explaining the structure of a Josephson device manufactured by a manufacturing method according to an embodiment of the present invention.

[0011] The Rb to C ₆₀ carbon alone using doping materials as superconductors. C ₆₀ has ₆₀ carbon atoms bonded in a cluster like a soccer ball, and becomes a superconducting substance by doping Rb. Further, when light energy is applied to the superconducting C ₆₀ , the carbon bond is decomposed to become a normal conductor.

In FIG. 1, a normal conductive layer 2 which is a normal conductor obtained by photoisomerizing a C ₆₀ superconductor by laser irradiation on a (100) cleaved surface of an insulating substrate 1 made of a MoSe ₂ material is used.
The film is formed with a thickness of 0Å.

Furthermore, about 10 C ₆₀ superconductors are further formed thereon.
The superconducting electrode layer is formed with a thickness of 00Å. The central part is cut into a groove with a width of about 1000Å and a depth of about 2000Å to leave the normal conductive layer with a thickness of about 2000Å. The electrodes 3 and 4 and the tunnel barrier portion 5 are formed. Then, current extraction terminals 31 and 41 and voltage extraction terminals 32 and 42 are formed on the surfaces of the superconducting electrodes 3 and 4, respectively.

Next, a method of manufacturing the Josephson device shown in FIG. 1 will be described with reference to FIG. FIG. 2 shows a cross-sectional view of an MBE apparatus for manufacturing Josephson devices. The vacuum container 20 is evacuated from the exhaust path 21 to a high vacuum of the order of 10 ⁻⁷ Torr.

Inside the container, Knuds
en Cell) 22 is arranged, Rb to C ₆₀ therein
A vapor deposition material doped with is added and heated to 200 to 250 ° C.

Further, the MoSe ₂ substrate 1 is arranged at the position where the beam emitted from the Knudsen cell inside the container hits, and the vapor of superconducting C ₆₀ is (10) of the MoSe ₂ substrate 1.
0) Vapor deposition is performed on the cleavage plane. Deposition of superconducting C ₆₀ is performed at a substrate temperature of about 100 ° C or lower,
The film is formed to a thickness of 0Å.

With the superconducting C ₆₀ film formed on the MoSe ₂ substrate 1, ArF (argon fluoride) excimer laser light (not shown) is applied to the entire surface of the superconducting C ₆₀ film to form C.
₆₀ Membrane isomerization is performed. As a result, the C ₆₀ film becomes the normal conductive layer 2 shown in FIG. This ArF excimer laser light irradiation can be performed in the same apparatus by providing the ultraviolet ray transmission window 24 in the vacuum container 20 and introducing the excimer laser light from the outside.

Using the same evaporation source in the same MBE apparatus,
Rb-doped superconducting C ₆₀ is further vapor-deposited on the photoisomerized C ₆₀ normal conducting layer 2 to form a superconducting electrode layer of about 1000
Deposition to a thickness of Å.

Substrate on which a superconducting electrode layer is formed After forming a mask having a predetermined opening on the superconducting electrode layer, the mask is placed in a focused ion beam (FIB) etching apparatus and a focused ion of Ar is used. Ion beam etching with a beam is performed to etch the width of about 1000 Å and the depth of about 2000 Å to divide the superconducting electrode layer, and further cut off the normal conductive layer 2 thereunder (to leave about 2000 Å thickness). In this way, the superconducting electrodes 3 and 4 and the tunnel barrier portion 5 are formed, and the Josephson element as shown in FIG. 1 is manufactured.

The current and voltage take-out terminals 31, 32, 41 and 42 are formed on this Josephson element and the current-voltage characteristics of the element are measured. As a result, the characteristics of the Josephson element as shown in FIG. 3 are obtained. It was That is, the SNS type Josephson device was manufactured using C ₆₀ by the above process.

[0021] Besides Josephson device of FIG 1, according to the present invention, the superconducting layer of C ₆₀ on the substrate, normal conducting layer of C _60, were laminated sequentially longitudinally superconducting layer C ₆₀ It is also possible to manufacture a Josephson device with a structure. Even in this case, the normal conductive layer can be produced by irradiating superconducting C ₆₀ with laser to make it anisotropic.

[0022] Further, in the above-mentioned embodiment, the Knudsen cell 2
C doped with Rb 2₆₀I put the ingredients, but C₆₀And Rb
Put and in different Knudsen cells to perform vapor deposition
May be.

The present invention has been described above with reference to the embodiments.
It will be apparent to those skilled in the art that the present invention is not limited to the above-described embodiments, and various improvements, changes and combinations can be made.

[0024]

According to the present invention, C _{60 is used} as a superconducting electrode.
By using, the conductive anisotropy is eliminated and the film can be formed at a low temperature. In addition, since C ₆₀ is irradiated with light to cause normal dislocations under low substrate temperature conditions to form a normal conductive layer, a Josephson device without mutual diffusion of constituent elements can be manufactured.

Further, there is an advantage that the superconducting layer and the normal conducting layer can be continuously manufactured from the same material source in the same manufacturing apparatus.

[Brief description of drawings]

FIG. 1 is an external view for explaining a structural example of a Josephson device manufactured by a manufacturing method according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view of an MBE device used in a method for manufacturing a Josephson device according to an embodiment of the present invention.

FIG. 3 is a current-voltage characteristic diagram of a configuration example of a Josephson device manufactured by a manufacturing method according to an example of the present invention.

[Explanation of symbols]

1 MoSe ₂ Substrate 2 C ₆₀ Normal Conductive Layer 3, 4 C ₆₀ Superconducting Electrode 5 Tunnel Barrier 20 Vacuum Container 21 Exhaust Path 22 Knudsen Cell 31, 41 Current Extraction Terminal 32, 42 Voltage Extraction Terminal

Claims (3)

[Claims] 1. A step of forming a first film (2) of a C ₆₀ superconductor material on a surface of a substrate (1), the method comprising: irradiating the first film (2) with light; The C ₆₀ superconducting material is permanently isomerized by energy to generate the first
The step of making the film of No. 2 as a normal conductor, and the second film of C ₆₀ superconductor material on the isomerized first film (2) while maintaining the temperature of the substrate (1) at 100 ° C. or less. And a step of forming films (3, 4). 2. The method for manufacturing a Josephson device according to claim 1, wherein the light is ArF excimer laser light. 3. The surface of the substrate is made of MoSe ₂ (10
(3) The method for manufacturing a Josephson device according to claim 1, wherein the cleavage plane is 0).