JPS6356969A - Manufacture of josephson device - Google Patents

Abstract

PURPOSE:To prevent the peeling due to the heat cycle between the superconducting layer and the high-resistance barrier layer by bundling superconducting metal wires and high- resistance wires so that the high-resistance wires are positioned between the superconducting metal wires, applying the composite wire drawing process until the high-resistance barrier layer formed by the high-resistance wires have a thickness of exhibiting the tunnel effect, and then cutting it in the width direction and taking out it in the shape of a round slice, thereby strongly integrating the superconducting layer and the high-resistance barrier layer. CONSTITUTION:The Josephson device has superconducting metal wires 1 composed of Nb and a high-resistance barrier layer 2 composed of CuNi. Such Josephason device is formed by disposing high-resistance wires around a pair of superconducting metal wires, bundling them so that the high-resistance wires are positioned between the pair of superconducting metal wires, subjecting this to the wire drawing process, then cutting it in the width direction and taking out it in the shape of a round slice, and burying and fixing this in a material for burying 5. Then both surface of the material for burying are abraded to expose both end faces of the Josephson device, and further an etching process is applied. Stop welding is performed to attach current terminals 4 and voltage terminals 6 to this. Since the superconducting layer and the high-resistance barrier layer are strongly integrated together by this, the peeling or degradation is not caused even by the heat cycle between an extremely low temperature and a normal temperature.

Description

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

[Prior art] Josephson device structures include a tunnel junction type in which an insulating layer such as an oxide film or a normal conducting layer is provided as a high-resistance barrier layer between two superconducting layers, and a type in which the boundary between the two superconducting layers is narrowed. There are bridge junction types and point contact junction types, which have minute current paths.

The present invention relates to the former tunnel junction type Josephson device. Conventionally, tunnel junction type Josephson devices have been produced by forming a thin superconducting layer on a substrate by vapor deposition or sputtering, forming a high-resistance barrier layer thereon, and then forming a superconducting layer by vapor deposition, sputtering, etc. It is manufactured by stacking and forming by the method of

[Problems to be Solved by the Invention] However, with such conventional manufacturing methods, it is difficult to form a film that is a high-resistance barrier layer with a uniform thickness. There was a problem that it was not possible to produce large quantities of. Furthermore, when an oxide film is used as the high-resistance barrier layer, the film thickness is very thin, which may cause electrical conduction between the superconducting layers. When conduction occurs between the superconducting layers, the phase difference becomes zero, causing the problem that the superconducting layer does not function as a Josephson device.

Moreover, even if such conduction does not occur between superconducting layers,
When an excessive current was input from the outside, the high-resistance barrier layer was burned out.

Furthermore, since the Josephson element is generally used by being immersed in liquid helium, it is placed under a heat cycle environment between extremely low temperatures and room temperature. In this case, the conventional Josephson element has a problem in that the thin film may peel off from the substrate or the thin film may deteriorate because there is a difference in coefficient of thermal expansion between the substrate and the thin film.

Therefore, an object of the present invention is to provide a method for manufacturing a Josephson device in which the thickness of the high-resistance barrier layer is uniform and the thin film does not easily peel off even during heat cycles between cryogenic temperatures and room temperature. be.

[Means for Solving the Problems] The Josephson device manufacturing method of the present invention includes bundling a pair of superconducting metal wires such that a high resistance wire is located between them, and It is characterized in that the barrier layer is subjected to vertical wire drawing until it reaches a thickness that exhibits a tunnel effect, and then cut in the width direction and taken out in round slices to form Josephson elements.

[Function] In the manufacturing method of the present invention, the thickness of the high-resistance barrier layer formed by the high-resistance wire is reduced by wire drawing to a thickness that exhibits a tunnel effect as a Josephson element.

Since the Josephson element produced by the manufacturing method of the present invention is used by cutting a composite wire-drawn wire material in the width direction and taking it out into slices, the high-resistance barrier layer has a uniform thickness.

In addition, since it is not formed on a substrate as in the past,
There is no problem of peeling off from the substrate.

Furthermore, in the manufacturing method of the present invention, since the superconducting metal wire and the high-resistance wire are wire-drawn, the superconducting layer and the high-resistance barrier layer are firmly integrated, and separation between them due to heat cycles does not occur.

[Example] FIG. 1 is a sectional view showing a state after wire drawing according to the manufacturing method of the present invention. In FIG. 1, 1 indicates a superconducting metal wire, and 2 indicates a high-resistance barrier layer. In the example shown in FIG. 1, the high resistance wire is arranged not only between the pair of superconducting metal wires 1 but also around the superconducting metal wire 1, and the high resistance wire covers the periphery of the superconducting metal wire. has been in a state. However, in the present invention, it is sufficient that the high resistance wire is disposed at least between the superconducting metal wires, and the periphery of the superconducting metal wires may be coated with another material.

In FIG. 1, numerals indicate the thickness of the high-resistance barrier layer, which has been made thinner by wire drawing to a thickness that exhibits the l·nner effect as a Josephson element. This thickness is
Although it differs depending on the material of the superconducting metal wire and the high-resistance barrier layer, it is usually about 1000 A and the thickness is 10 μm or less.

FIG. 2 is a perspective view showing a Josephson element according to an embodiment of the present invention. In FIG. 2, numeral 1 indicates a superconducting metal wire made of Nb, and numeral 2 indicates a high-resistance barrier layer made of CuNi. On the end faces of the superconducting metal wires 1, gold spot welds 3 are made by ultrasonic crimping to form ohmic connections, and a current terminal 4 and a voltage terminal 6 are attached to the spot welds 3, respectively. The entire Josephson element is made of an embedding material 5 made of resin, for example.
embedded in.

The Josephson device shown in FIG. 2 is manufactured as follows. A high-resistance wire is arranged around a pair of superconducting metal wires, and the high-resistance wire is bundled so that the high-resistance wire is positioned between the pair of superconducting metal wires. Cut it and take it out into slices, and embed and fix it in the embedding material. Next, both sides of the embedding material are polished to expose both end faces of the Josephson element, and then etched. A current terminal and a voltage terminal are attached to this by spot welding as described above.

In the example of the Josephson device shown in Figure 2, the distance α between the superconducting metal wires is 0.1 μm, and the diameter d of the superconducting gold wire is 0.
．． It is 5 μm. Note that the length h of the Josephson element is 1 mm.

The Josephson element shown in FIG. 2 was mounted on a fixture and cooled by immersing it in a liquid helium container. A current was passed through this Josephson device, and the current-voltage characteristics of the Josephson device were measured using a four-terminal method. The obtained current-voltage characteristics are shown in FIG.

As shown in FIG. 3, the current value is I when the voltage is 0.

When the current value exceeded Io, there was a jump in B corresponding to the superconducting energy gap, and the state transitioned to a normal conductive resistance state. When the current was lowered from this resistance state, it returned to the state of zero voltage through path C. From such current-voltage characteristics, it was confirmed that the device manufactured by the manufacturing method of the present invention has the Josephson effect.

In the examples, Nb was illustrated as the material of the superconducting metal wire, but in this invention, without being limited to this,
Metals and alloys conventionally known as superconductors can be used.

[Effects of the Invention] As explained above, according to the manufacturing method of the present invention, the thickness of the high-resistance barrier layer of the Josephson element can be kept constant with high precision. In addition, in the manufacturing method of the present invention, a drawn wire material is cut in the width direction to take out a large number of sliced Josephson elements, so a large number of Josephson elements can be produced in one manufacturing process. It can be manufactured and therefore cheaply manufactured.

The superconducting layer and high-resistance barrier layer of the Josephson device manufactured by the manufacturing method of this invention are strongly integrated with each other, so they will not peel off or deteriorate even during heat cycles between cryogenic temperatures and room temperature. do not have. In addition, in the Josephson device manufactured by the manufacturing method of the present invention, only the end faces of the superconducting layer are exposed to the atmosphere, so the superconducting layer is less likely to be oxidized or corroded by the atmosphere than in conventional thin-film Josephson devices. There's not much to do.

Furthermore, as shown in the examples, when a normal conductive metal such as CuNi is used as the high resistance barrier layer,
Even if excessive current flows and heat is generated in the high-resistance barrier layer, the barrier layer is surrounded by a normal conductive metal with good thermal conductivity, so
The high resistance barrier layer will not burn out.

As mentioned above, the Josephson element manufactured by the manufacturing method of the present invention has excellent characteristics, so it has the highest sensitivity magnetic flux 7 using 5QUID, which is the conventional application of Josephson element.
! p1 constant meter and magnetic flux gradient! 1. It can be applied to high-sensitivity voltmeters, etc. These are used in a wide variety of fields, including magnetic exploration, medical magnetic needles, and thermal noise thermometers (on the order of μ). Furthermore, the Josephson element alone can be used as a highly sensitive photodetector, and can be effectively used in the range from millimeter waves to infrared rays. Furthermore, it can be applied not only to detection, but also to parametric amplifiers, mixers, etc., and can also be used for optical communications, infrared astronomy, etc. Furthermore, it can be used as a computer element in the same way as a conventional Josephson element.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the state after wire drawing according to the manufacturing method of the present invention. FIG. 2 is a perspective view showing a Josephson element according to an embodiment of the present invention. FIG. 3 is a diagram showing the current-voltage characteristics of the Josephson element shown in FIG. 2. In the figure, 1 is a superconducting metal wire, 2 is a high-resistance barrier layer,
3 is a spot weld, 4 is a current terminal, 5 is an embedded material, and 6 is a voltage terminal. Figure 7 Figure 3 Figure 2

Claims (2)

[Claims] (1) A pair of superconducting metal wires is bundled so that a high resistance wire is located between them, and a composite wire drawing process is performed until a high resistance barrier layer formed by the high resistance wire has a thickness that exhibits a tunnel effect,
A method for manufacturing a Josephson element, which comprises: then cutting in the width direction and taking out slices to obtain a Josephson element. (2) The method for manufacturing a Josephson element according to claim 1, wherein the high resistance wire is made of a normally conducting metal.