JPS6399583A - Manufacture of josephson element - Google Patents

Abstract

PURPOSE:To enable mass production of Josephson elements having uniform quality with high precision, by bundling a plurality of superconducting metal wires with a high-resistance wire, drawing them, cutting them vertically to the axes of the wires and removing a part of high resistance matrix located near the cut face. CONSTITUTION:A Josephson element is produced by using, for example, Nb as a superconducting metal, a normally conducting metal Cu as high resistance lines, and resin 7 as a filling material while defining a distance of about 1000 Angstrom between superconducting filaments 5 which has been drawn. The Josephson element is dipped in an etching solution of CuNi, whereby a part of the CuNi constituting a high-resistance matrix 6 in the vicinity of the cut face is removed and the ends of the superconducting filaments are projected from the matrix. When the Josephson element is dipped in an etching solution of Nb, the ends of the superconducting filaments 5 are etched and pointed as needles. Liquid enamel available on the market is applied on the surface to provide a transparent insulation film 8. According to this method, Josephson elements can be produced in mass through a single manufacturing process without causing variance in the quality of the products.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing a Josephson element used in the field of cryoelectronics and the like.

[Prior Art] Conventionally, a tunnel junction type Josephson device is produced by forming a thin superconducting layer on a substrate by a method such as vapor deposition or sputtering, and then forming a high resistance barrier layer thereon.
Furthermore, superconducting layers are stacked and manufactured by methods such as vapor deposition and sputtering.

[Problems to be Solved by the Invention] However, such conventional manufacturing methods have a problem in that high-resistance barrier layers having a constant thickness cannot be manufactured in large quantities. Furthermore, when placed in a heat cycle environment between extremely low temperatures and room temperature, the difference in thermal expansion coefficient between the substrate and the thin film may cause the thin film to separate from the substrate or deteriorate. There was also a problem.

These problems can be solved by a novel method for manufacturing a Josephson device that has been filed by the present inventor. In order to explain this manufacturing method, FIGS. 4 and 5 are shown.

FIG. 4 shows a cross section of the composite wire before wire drawing. The fitting filament 1 is constructed by covering a superconducting metal wire 2 with a normal conducting wire 3. A plurality of such fitting filaments 1 are fitted into the normally conducting vibrator 4. FIG. 5 shows a state in which such a composite wire is wire-drawn.

In FIG. 5, reference numeral 6 indicates a high resistance matrix, which is formed by integrating the normal conductive wire and the normal conductive vibrator in FIG. 4 by wire drawing. Reference numeral 5 indicates a superconducting filament, which is formed by drawing the superconducting metal wire 2 in FIG. 4. The distance d between the superconducting filaments is shortened by wire drawing until the high resistance matrix located therebetween has a thickness that exhibits the Josephson effect. This distance d varies depending on the material of the superconducting metal or normal conducting metal used, but is set to about 1000λ, for example.

Next, the drawn composite wire is cut to an appropriate size, embedded in an embedding material such as resin, and then cut into circular slices in a direction perpendicular to the axis of the wire. At this time, the cut layer' is polished to prevent the superconducting filaments from coming into contact with each other due to pars, etc. A lead wire is attached to the Josephson element manufactured as described above and used.

One of the applications of the Josephson element is as a photodetector element. When the Josephson element manufactured by the above-mentioned novel manufacturing method is used as such a photodetector element, as shown in FIG. will be installed. In Fig. 6, 5 is a superconducting filament, 6 is a high resistance matrix,
7 indicates the embedded material. The light emitted from the optical fiber 8 excites the Cooper pair in the superconducting Frasoft 5,
Generate quasiparticles. Due to the generation of such quasiparticles,
Light is detected.

However, if the Josephson device manufactured by the above-mentioned manufacturing method is used as is, most of the light emitted from the optical fiber is reflected by the plasma vibration of electrons on the surface of the superconducting filament, and the quasi-particles are effectively generated. There was a problem in that it could not be generated and the detection efficiency was poor.

Therefore, the present invention is an improved invention that solves the problems in the above-mentioned Josephson element manufacturing method, and, like the above-mentioned invention, can manufacture a large quantity of highly accurate and homogeneous Josephson elements. It is an object of the present invention to provide a manufacturing method for manufacturing a Josephson element with improved photodetectability.

[Means for Solving the Problems] In the method for manufacturing a Josephson element of the present invention, a plurality of superconducting metal wires are bundled via a high resistance wire, drawn, and then cut into rounds in a direction perpendicular to the axis of the wire. The superconducting filament is exposed by cutting it into pieces and removing the high-resistance matrix portion near the cut surface.

Materials for the high resistance wire used in the present invention include insulators such as oxides and normal conductive metals, but since the high resistance wire is drawn in the present invention, it is a normal conductive material that is easy to draw. Metals are particularly preferred.

Furthermore, the material of the superconducting metal wire used in the present invention is not particularly limited, and metals, alloys, and the like conventionally known as superconductors can be used.

[Function] In the present invention, the drawn wire is cut into slices perpendicular to the axis of the wire and taken out, so a large amount of Josephson elements with the same barrier layer thickness can be produced in one manufacturing process. Manufactured.

Further, in the manufacturing method of the present invention, after cutting into slices and taking them out, the high resistance matrix portion near the cut surface is removed to expose the superconducting filaments. therefore,
Light incident from the outside between such superconducting filaments is confined between the superconducting filaments, and the amount of light reflected to the outside is reduced. Therefore, it becomes possible to efficiently excite a large amount of Cooperbears in the superconducting filament with light and generate a large amount of quasiparticles.

[Example] A Josephson device was manufactured using the manufacturing method previously described by the present inventor. Nb was used as the superconducting metal, and CuNi, a normal conducting metal, was used as the high resistance wire. The distance between superconducting filaments after wire drawing is approximately 100
It was set to 0A. In addition, resin was used as the embedding material.

The thus obtained Josephson device was made of CuNi
Etching solution (HCl1jlO for 5g of FeCa)
cc and H2O mixed at a ratio of 100 cc)
immersed in it. As a result of this immersion, the high-resistance matrix portion of CuNi near the cut surface was removed, leaving the ends of the superconducting filaments protruding. This state is the first
The figure shows a partial sectional view. In FIG. 1, 5 is a superconducting filament made of Nb, 6 is a high-resistance matrix made of CuNi, and 7 is a embedding material made of resin.

This was further added to the Nb etchant (HFloCC%H2SO
410CC, H2010CC mixed liquid)
immersed in. As a result, as shown in FIG. 2, the tip of the superconducting filament 5 was corroded and formed into a needle shape with a sharp tip. Further, a commercially available enamel liquid was applied to this surface as a transparent insulating film 8.

Au wires were attached to the thus obtained Josephson element as 4-terminal lead wires at four locations using a wire bonder device, and 1 μm infrared rays were applied to the Josephson element through an optical fiber. Detectability was measured. The measurement results are shown in Figure 3. In addition, the third
For comparison, the figure also shows a Josephson element manufactured by the manufacturing method according to the present inventor's previous application, that is, a Josephson element in which the superconducting filament is not exposed. B. is produced by the manufacturing method of the existing application, and B.
2 is produced by the manufacturing method of the present invention.

In the Josephson device according to the present invention, a critical current value I is obtained before irradiation with light. What was point A, which exceeded the above, moved to point B2 after light irradiation, and the current-voltage characteristics changed. On the other hand, in the Josephson device in which the superconducting filament was not exposed, the temperature shifted from point A to point B5 after light irradiation.

As is clear from FIG. 3, the Josephson device of the present invention exhibits a higher voltage than one without exposed superconducting filaments, resulting in increased detection sensitivity.

In the example, the superconducting filament is corroded to form a needle-like shape with a sharp tip, but it is not necessary to form it into this shape; the superconducting filament is simply exposed by removing the high-resistance matrix portion. The effects of the present invention can be exhibited even in this state.

Furthermore, in the examples, the exposed surface of the superconducting filament is covered with a transparent insulating film, but such a transparent insulating film is provided to protect the surface of the superconducting filament, and is essential to the present invention. Needless to say, it doesn't belong to me.

[Effects of the Invention] As explained above, according to the manufacturing method of the present invention, Josephson elements of constant quality can be produced in large quantities in one manufacturing process. In addition, even under a heat cycle environment between room temperature and extremely low temperature, the Josephson element according to the present invention has superconducting filaments embedded in the matrix, so it can be used in a heat cycle environment like a conventional Josephson element using thin film lamination. The thin film will not deteriorate.

Further, in the Josephson element manufactured by the manufacturing method of the present invention, since the superconducting filaments are exposed, light incident between the superconducting filaments can be detected with high efficiency. Conventional semiconductors (Hg, Cd.

Compared to a detection element based on Te), the Josephson element according to the present invention can detect even weak light with low noise. Therefore, the Josephson element according to the present invention is particularly useful as a photodetection element, such as a terminal of an image fiber for in-vivo observation, a sensor for detecting abnormal body temperature distribution for breast cancer or uterine cancer, or an optical fiber cable for long-distance optical communication. It can be effectively used as a terminal, etc. Naturally, it can also be applied to infrared detectors for astronomical observations.

Furthermore, since the Josephson device according to the present invention has a faster optical response speed than conventional semiconductor devices, it is possible to increase the signal frequency of a communication optical fiber. therefore,
By using the Josephson device according to the present invention, a large amount of information can be transported.

[Brief explanation of the drawing]

FIG. 1 is a partial sectional view showing the state after the high resistance matrix portion is removed in one embodiment of the present invention. Second
The figure is a partial cross-sectional view showing the state of a superconducting filament after it has been corroded in an embodiment of the present invention. FIG. 3 is a diagram showing the results of measuring the photodetectability of a Josephson element obtained according to an embodiment of the present invention. FIG. 4 is a sectional view showing the state of the composite wire before wire drawing in the present invention. FIG. 5 is a sectional view showing the state of the composite wire after wire drawing in the present invention. FIG. 6 is a perspective view schematically showing an installation state when a Josephson element is used as a photodetecting element. In the figure, 1 is a fitting filament, 2 is a superconducting metal wire, 3 is a normal conducting wire, 4 is a normal conducting pipe, 5 is a superconducting filament, 6 is a high resistance matrix, 7 is an embedding material, and 8 is a transparent insulating film. shows. Figure 3 Figure 4

Claims (3)

[Claims] (1) After bundling multiple superconducting metal wires through high resistance wires and drawing them, cut them into circular slices perpendicular to the axis of the wires and take them out, and remove the high resistance matrix portion near the cut surface. A method for manufacturing a Josephson device, comprising: exposing a superconducting filament formed from the superconducting metal wire. (2) The method for manufacturing a Josephson device according to claim 1, characterized in that the exposed portion of the superconducting filament is formed into a needle shape with a pointed tip. (3) The method for manufacturing a Josephson device according to claim 1 or 2, characterized in that the exposed surface of the superconducting filament is coated with a transparent insulating film.