JPH03297178A - Squid device - Google Patents

Abstract

PURPOSE:To prevent any noise and self heating from being produced by forming a metal film manifesting a proximity effect at the upper and lower stage sides putting a step provided on a substrate therebetween and further forming a high temperature superconductor thin film on the former, and constructing a Josephson junction part by joinning mutually weakly said films thorugh the stepped part. CONSTITUTION:A step part 1a is provided on the surface of a substrate 10 by etching using a resist film 11 as a mask, and an Au thin film is formed by sputtering, etc., from the upper portion. At this time, as the substrate 10 is slanted in the direction of the advance of sputtering particles, a stepped part 1a produces a shadow, and hence the Au thin film is not partly formed and the Au thin films separated mutually are formed. Then, a YBCO thin film 12 is uniformly formed by sputtering from the upper portion of the films 2, 3, and is weakly coupled on the upper and lower stage sides at the stepped part 1a. Then, there is formed a pattern by a resist 13 where the films 12 on the upper and lower stage sides are joinned at two portions along the stepped part 1a, which is used as a mask to etch the film 12 and hence a DC- SQUID device is yielded. Hereby, the noise is reduced and self heat production can be restricted.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention is a SQUID used for detecting extremely small magnetic fields in the medical field, including the measurement of biomagnetism in the brain, and in the military industry field, such as anti-submarine patrol. Regarding elements.

<Prior Art> SQUID (superconducting flux quantum interferometer) is a device that measures minute magnetic fields using the quantum effect of superconductors.

The SQUID element, which is the detection element in this SQUID, has one or two Josephson junctions in a superconductor ring, and currently contains Nb, which has a superconducting transition temperature of 9.23. The one used has been put into practical use.

On the other hand, high-temperature superconductors (oxide superconductors) that have been discovered and studied in recent years, especially YB az Cu30
．． 4 and other substances with critical temperatures higher than liquid nitrogen temperature have been in the spotlight for their applications, but SQUID devices made from such high-temperature superconductors have yet to be put into practical use. not present.

<Problem to be solved by the invention> By the way, Y B at C030? High-temperature superconductors such as -8 have a short coherence length, so thin films made using them may have non-uniform areas, or the thinner the film is, the easier it is for magnetic flux to pass through. .

Generally, in a SQUID element, there are parts (junction parts) where it is better for the magnetic flux to pass through, and parts (electrode parts, etc.) where it is inconvenient for the magnetic flux to pass through.

Transmission of magnetic flux to the electrode portion or movement of the transmitted magnetic flux causes noise. Therefore, in order to obtain a SQUID device using a high-temperature superconductor, it is a challenge to prevent magnetic flux from penetrating except for the junction portion.

The present invention has been made to solve these problems and to put into practical use a SQUID device using a high-temperature superconductor.The present invention uses a high-temperature superconductor thin film that has a structure that prevents magnetic flux from penetrating into areas other than junctions. The purpose is to provide SQUID devices.

<Means for Solving the Problems> A configuration for achieving the above object will be described with reference to FIG. 1 corresponding to the embodiment. Metal thin films 2 and 3 having a proximity effect with respect to the high-temperature superconductor thin film are formed on each of the upper and lower planes with the stepped portion 1a in between, and above the metal thin films 2 and 3 on both stages. A high-temperature superconductor thin film 4 is formed, and the upper and lower high-temperature superconductor thin films 4a and 4b are joined to each other at the step 1a by narrowed portions 5a and 5b of the high-temperature superconductor thin film.

<Function> Constriction portions 5a and 5b that become Josephson junction portions
The metal thin films 2 and 3 in contact with the high-temperature superconductor thin films 4a and 4b except for the portions thereof become superconductive due to the proximity effect. Metals that exhibit this proximity effect include Au, A
There are I, Pt, etc., but their coherence length is generally much longer than that of high-temperature superconductors, so the coherence length of this electrode portion is longer, and the penetration of magnetic flux is reduced accordingly.

<Embodiment> FIG. 1 is a perspective view of an embodiment of the present invention, showing an example in which the present invention is applied to a DC-3QUID.

A step is provided on the surface of the substrate 1 made of a material having good compatibility with a high temperature superconductor, such as MgO or YSZ.
Au films 2 and 3 are formed on the upper and lower planes of the step portion 1a, respectively.

Above the Au thin films 2 and 3 on both stages, YBCO thin films 4a and 4b, which are high-temperature superconductors, are formed, respectively, and these are two constrictions of the same YBCO3 film formed across the step 1a. They are joined to each other by portions 5a and 5b.

According to the above-described embodiments of the present invention, the Au thin films 2 and 3 formed below the YBCO thin films 4a and 4b forming the electrode portions of the DC-3QUID are made superconducting by the proximity effect, and the coherent length of the electrode portions is Approximately 1,000 people accumulate. As a result, it becomes difficult for magnetic flux to enter this electrode portion by the length of the coherent length.

On the other hand, since the portions of the narrowed portions 5a and 5b, which serve as junction portions, are in direct contact with the substrate 1 at the step portion 1a, the coherent length remains unchanged, and therefore, these portions are weakly joined.

Next, the manufacturing method of the above embodiment of the present invention will be described.

FIG. 2 is an explanatory diagram of the manufacturing procedure.

First, as shown in FIG. 2(a), a flat substrate 10 of an appropriate thickness is prepared, and a resist is uniformly applied to the surface of the substrate. One side is left and the other side is removed with approximately the center as the border.

Next, by etching the surface of the substrate 10 by Ar ion milling using the remaining resist film 11 as a mask, the substrate 10 having the stepped portion 1a as shown in FIG. 2(C) is etched.
get.

Then, an Au thin film is formed by sputtering or the like from above the substrate 1 having such a stepped portion 1a. At this time, as shown in FIG. 3, the substrate 1 is tilted with respect to the traveling direction of sputtered particles from the target 31. This results in
As shown in FIG. 2(d), the stepped portion 1a becomes a shadow and the Au
A portion of the thin film is not formed at this step portion 1a, and Au thin films 2 and 3 are formed on the substrate 1 at the upper and lower planar portions in a state where they are separated from each other.

In this state, a YBCO thin film 12 is uniformly formed on the Auf3it films 2 and 3 by sputtering or the like as shown in FIG. 2(e). At this time, as shown in FIG. 4, an enlarged view of the main part in this state, the obtained YBCOF4 film 1
Reference numeral 2 denotes a step portion 1a where the upper and lower membranes are weakly connected.

Next, as shown in the plan view in FIG. 2(f), a C-3QUID pattern is formed using the resist 13 so that the upper and lower YBCOfl films 12 are bonded at two places at the step portion 1a. Using this as a mask, the YBCOFII film is etched by Ar ion milling. As a result, the DC-3QUID device shown in FIG. 1 is obtained.

In addition, in the above examples, the high temperature superconductor thin film 2.3
Of course, it is possible to use not only the YBCo thin film but also other high temperature superconductor thin films, and the material of the substrate 1 may be any material as long as it has good compatibility with the high temperature superconductor used. whatever. In addition to Au, there are other metals that exhibit the proximity effect, such as AI and Pt, and it goes without saying that these may also be used.

Furthermore, the present invention provides an RF-3 with one junction section.
Of course, it can be applied to QUID in exactly the same way.

<Effects of the Invention> As explained above, according to the present invention, a metal thin film that exerts a proximity effect is formed on the upper and lower sides by sandwiching the stepped portion, and a high-temperature superconductor thin film is formed above the metal thin film. The high-temperature superconductor thin films on the upper and lower sides were weakly bonded to each other at the step part to form a Josephson junction, so that the coherent length of the high-temperature superconductor thin film in the electrode part was determined by using Au as the metal thin film. If there were, about 1,000 people would accumulate and it would be long.

As a result, the penetration of magnetic flux into the film of the electrode portion is reduced, eliminating hysteresis as in the conventional case, and reducing noise due to fluctuations in the magnetic flux trapped within the film.

In addition, heat generated by magnetic flux movement, contact resistance, etc.
It also has the effect of suppressing self-heating because it quickly diffuses through thin metal films such as.

Note that since the high temperature superconductor thin film is formed after forming the metal thin film having the proximity effect, there is no particular deterioration in its performance.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of an embodiment of the present invention, FIG. 2 is an explanatory diagram of its manufacturing procedure, and FIGS. 3 and 4 are supplementary explanatory diagrams of steps in the manufacturing procedure. 1...Substrate 1a...Stepped portion 2.3...Au thin film 4a, 4b, ---YBCO thin film 5a, 5b...Narrowed portion Fig. 3 Fig. 4

Claims (1)

[Claims] A metal thin film having a proximity effect with respect to the high-temperature superconductor thin film is formed on each of the upper and lower planes of the substrate surface with the step sandwiching the step. A SQUID element in which a high-temperature superconductor thin film is formed above, and the high-temperature superconductor thin films on the upper and lower sides are joined to each other at the stepped portion by a constricted portion of the high-temperature superconductor thin film.