JPS63313876A - Support structure of superconductor thin-film - Google Patents

Abstract

PURPOSE:To reduce various constraint at the time when a superconductor thin- film is annealed by bringing a section used as an element constitution section in the superconductor thin-film to the state in which it is floated from a support section for a substrate, etc. CONSTITUTION:A first superconductor thin-film 15 consisting of an oxide such as Y-Ba-Cu-O one and a second superconductor thin-film 17 are formed onto an insulating substrate 11 and a surface shaping section 13 (a support section). When the whole is dipped into an etchant, into which the superconductor thin- films are not dissolved and glass is dissolved, glass existing on a window section in a resist mask is removed and a hole section 41 is acquired, and the superconductor thin-films existing on the hole section 41 are brought to the state in which they are floated from the support section (glass) 13. Accordingly, a direct effect on element constitution section itself of the stress of the support section is reduced.

Description

Detailed Description of the Invention (Field of Industrial Application) This invention provides a superconductor suitable for improving the characteristics of a Josephson device when a superconductor thin film is used to form the device. This invention relates to a thin film support structure.

(Prior Art) Superconductors are applied to various fields because of their special physical properties. One such application example is
There is a Josephson junction element, which makes it possible to put computers capable of high-speed calculations, ultra-high sensitivity magnetometers, ultra-weak electromagnetic wave detectors, and other useful snowmaking devices into practical use. Therefore, research on Josephson junction elements has been energetically conducted.

As a conventional Josephson junction element, there is one disclosed, for example, in Japanese Patent Application Laid-Open No. 179584/1984 filed by the applicant of this application. FIG. 7 is a perspective view schematically showing the structure of one example of the Josephson junction element described in this publication. In FIG. 7, reference numeral 11 indicates an insulating substrate as a support portion. In this case, this insulating substrate 11 has two surfaces with different levels, and furthermore, this insulating substrate 1
A surface shaping section indicated by 13 and also functioning as a support section is provided on the lower surface of the two surfaces of 1.

This surface shaping part 13 has a shape in which the thickness thereof gradually increases, and therefore, this surface shaping part 1
The surface of No. 3 continues from the low surface of the base mentioned above to a position roughly higher than the high surface of this base. Then, a first superconductor thin film 15 is provided over the lower surface of the base 11 and the surface of the surface shaping portion 13, and
A second superconductor thin film 17 is provided on the higher surface of the superconductor. According to such a structure 1, the first superconductor thin film 15 and the second superconductor thin film 17 are connected collectively at a certain angle to each other at a point P in FIG. They will come into contact with each other, and a weak coupling portion will be formed at this portion. As a result, the weak coupling portion is shortened to the utmost, and the characteristics of this element are favorable.

Further, another example of the conventional Josephson junction element is disclosed in Japanese Patent Application Laid-Open No. 179585/1985, filed by the applicant of this application. FIG. 8 is a perspective view schematically showing the structure of the Josephson junction device described in this publication. In FIG. 8, 21 indicates an insulating substrate as a support portion. In some areas above, 2
A laminate 23 is provided, which is a laminate indicated by 3 and is constituted by a first insulating film 25, a first superconductor thin film 27, and a second insulating film 29. It is being Further, in a region near the laminate 23 on the insulating substrate 21, a second superconductor thin film indicated by 31 has a part of the end surface of the laminate 21 including the first superconductor thin film 27. It is provided so as to be in contact with the section. In such a structure, the area indicated by Q in FIG. 8 and marked with diagonal lines is the region where the weak bond is formed, and in this structure as well, the bonding area of the weak bond that causes the Josephon effect must be significantly narrowed. was possible.

In addition to Nb, NbN, etc., superconductors for forming the superconductor thin film as described above include, for example, Y-Ba-Cu-0 based compounds that exhibit superconducting properties at relatively high temperatures. Alternatively, La-Ba-Cu-0 type compounds are known.

This Y-Ba-Cu-○ type compound or La-Ba
A -Cu-○-based compound is known as a substance that exhibits superconductivity even though it is an oxide. Regarding such oxide superconductors, for example, the literature (Nikkei New Material [2
7] P, 76 (1987)).

Such oxides are generally produced by baking the constituent elements and their oxides at a temperature of around 1000°C, and the resulting oxides are relatively stable even in the atmosphere. be. In addition, in order to apply such an oxide as an element, it is necessary to make it into a thin film by a suitable method such as sputtering or vapor deposition. By annealing at a temperature of around 800° C., the temperature (TC) at which this thin film exhibits superconductivity increases. Roughly speaking, even if a thin film does not exhibit superconductivity as it is, by annealing it at a high temperature, the thin film will exhibit superconductivity.

Also, although it is slightly different from the heat treatment described above, the temperature of the substrate is set to a sufficiently high temperature (approximately 800°C) during the formation of the oxide film described above.
It is known that a thin film formed on the substrate exhibits superconductivity if the substrate is kept at a temperature of about 100 nm.However, Tc in this case is low.

As described above, when attempting to fabricate a device using a superconductor thin film, the thin film must be heat-treated at a high temperature in any case.

(Problems to be Solved by the Invention) However, in the conventional structure explained using FIG. 7 and FIG. That is, since it is formed on the support part, problems as described below arise.

If the superconductor thin film is heat-treated while it is formed on the support, the same temperature will be applied to the support, and therefore,
There was a problem in that the support part itself was also required to have heat resistance.

Additionally, there was a risk that the support portion and the superconductor thin film would react at high temperatures.

In general, there is a problem in that when the temperature is returned to room temperature after high-temperature heat treatment, cracks occur in the superconductor thin film due to the difference in the thermal expansion coefficients of the support portion and the superconductor thin film. The occurrence of rack in this way is caused by the element % T c
It also occurs due to the temperature difference between the temperature below and room temperature.

The above-mentioned problem is that the material and time (and even the plane orientation) of the support part used to form a superconductor thin film are restricted, which significantly limits the degree of freedom in selecting the support part.
Moreover, the heat treatment temperature for the superconductor thin film by 1 also imposes a significant restriction, which is not at all desirable.

This invention has been made in view of the above points, and therefore, an object of the invention is to provide a support structure for a superconductor thin film that can alleviate various restrictions when annealing a superconductor thin film. I have one thing to offer.

(Means for solving the problem) In order to achieve this object, according to the superconductor thin film support structure of the present invention, at least a portion of the superconductor thin film used as an element component is in a floating state. The present invention is characterized in that the above-mentioned superconductor thin film is provided on the support portion.

(Function) According to such a configuration, it is possible to make the element component using the superconductor thin film floating from the support part. Therefore, even if the support portion and the superconductor thin film are heat-treated together, the influence of stress caused by the difference in their thermal expansion coefficients is reduced.

Further, it is also possible to perform annealing using, for example, a laser or the like only on this element component.

(Embodiments) Hereinafter, embodiments of the superconductor thin film support structure of the present invention will be described with reference to the drawings. Note that each drawing used in the following explanation is only a schematic illustration to the extent that the present invention can be understood, and therefore, the dimensions, shapes, and arrangement relationships of each component are shown only in the illustrated example (this is not limited to It should be understood that the same components as in the prior art are designated by the same reference numerals in the drawings used for the explanation, and some explanations thereof are omitted.

The present invention is characterized in that the above-mentioned superconductor thin film is provided on a support portion so that at least a portion of the superconductor thin film used as an element component is in a floating state. The element referred to herein may include various elements such as a Josephson junction element, or even an inductance element, and the following embodiments will be explained using an example in which this element is a Josephson junction element. Furthermore, the element constituent part referred to here may be the whole or a part of the element, but in the case of this embodiment, the weak coupling part of the Josephson junction element and its vicinity are referred to as the element constituent part. This will be explained using an example.

First, the support structure of the first embodiment of the present invention will be explained with reference to FIG.

<Description of Support Structure> This first embodiment is basically an example in which the support structure of the present invention is applied to the Josephson junction element described using FIG. 7. In order to explain this support structure, FIG.
FIG. 2 is a perspective view schematically showing a weak coupling portion and its surrounding area of a Josephson junction element with this support structure.

In FIG. 1, reference numeral 11 indicates an insulating substrate, and reference numeral 13 indicates a surface shaping section. In the case of this embodiment, the insulating substrate 11 and the surface shaping section are called the supporting section. This insulating substrate has a hole 41 in a predetermined area. Further, from a part of the periphery of the hole 41 of this insulating substrate 11, the first superconductor thin film 1 as already explained using FIG. 7 is formed on this hole 41.
5 extends, and from other parts around the hole 41 of the completely rounded substrate 11, there is a second superconductor on this hole 41 (as already explained using FIG. 7). The superconductor thin films 15 and 17 are in contact with each other at a certain angle at a certain angle, as described above with reference to FIG. A weak coupling portion is formed in the region (position indicated by P in FIG. 1). In addition, in FIG.
The first electrode 45 is deposited on the second superconductor thin film 17, and the second electrode 45 is deposited on the second superconductor thin film 17. Examples of the constituent material of these electrodes 43 and 45 include gold (
Au)7& can be listed. According to the structure shown in FIG. 1, the portions of the superconductor thin film forming the weak coupling portion and the surrounding portions thereof, that is, the first superconductor thin film 15 and the second superconductor thin film 17, respectively. Since the end portion is provided just above the hole portion 41 in the form of a bridge, at least the portion of the superconductor thin film that constitutes the weak coupling portion is in a state floating from the support portion. According to such a structure, the weak connection part is not directly subjected to stress when the support part deforms due to temperature change. Further, it is also possible to shorten the weak coupling portion to the utmost limit in the same way as in the conventional case.

<Method of forming the support structure of the first embodiment> In order to deepen the understanding of the support structure of the first embodiment, a method of forming the support structure of the first embodiment will be explained with reference to FIGS. 7 and 1.

The insulating substrate 11 and the surface shaping section 13 are made of glass, for example. Then, by a suitable method, e.g. Y-8
First superconductor thin film 15 made of a-Cu-○ based oxide
Then, a second superconductor thin film 17 is formed on the insulating substrate 11 and the surface shaping portion 13 (hereinafter also referred to as a support portion) in a predetermined manner. Next, a resist mask having a window that exposes the peripheral region including the weak bond is formed on the support including the superconductor thin film by a suitable method. Next, the sample having such a resist mask is immersed for an appropriate time in an etching solution (for example, a hydrofluoric acid-based etching solution may be used) that does not dissolve the superconductor thin film but dissolves the glass. As a result, the glass present in the window portion of the resist mask is removed and the hole 41 is obtained. Further, since the glass that was in contact with the superconductor thin film existing in the hole 41 is removed, the superconductor thin film is floating from the support (glass). In this way, a Josephson device having the superconductor thin film support structure of the present invention as shown in FIG. 1 is obtained.

Further, the first electrode 43 and the second electrode 45 are formed by forming the first and second superconductor thin films 15, for example, before forming a resist mask.
and 17, respectively. Note that these electrodes 43 and 45 are connected to the first and second superconductor films 15 and 1.
This is provided for the purpose of reinforcing the circuit 7 and facilitating connection with an external circuit, and is not necessarily required. Further, the thickness of the first and second superconductor thin films is generally 1 μm or less, and the thickness of the first and second electrodes is generally about Ium, but these can be changed according to the design.

Breast; Top L Next, a second embodiment of the present invention will be described with reference to FIGS. 2 and 3. These figures, like FIG. 1, are perspective views schematically showing the weak coupling portion of the Joseph Soci junction element and its surrounding area.

Description of Support Structure> In FIG. 2, 11 indicates an insulating substrate, and on this insulating substrate 11, a first electrode indicated by 51 and a second electrode indicated by 53 are provided spaced apart from each other. be. Note that these electrodes 51 and 53 have the following functions in addition to their function as electrodes. A portion of the first electrode indicated by 51a in FIG. 2 also has the function of the waveform shaping section 13 shown in FIG. The surface of the portion indicated by 51b is the lower surface described using FIG. 7, and the second electrode 53
The surface corresponds to the high surface described using FIG. Further, the first superconductor thin film 15 and the second superconductor thin film 17 are provided on the first electrode 51 and the second electrode 53, respectively, as already explained using FIG. The superconductor thin film 15 and the superconductor thin film 15 extend from each other in the direction between the first electrode 51 and the second electrode 53, and as already explained using FIG. Parts of the end surfaces are in contact with each other, and the contact point (P in Figure 1)
The region 3) shown in 3) constitutes a weak coupling part.

FIG. 2 (With the structure shown in this figure, at least the portion of the superconductor thin film forming a weak bond is in a state floating from the support portion between both electrodes 51 and 53.

In addition, in the description of the second embodiment, the first electrode 51 is 51
Although the first electrode 51 has been described as an example composed of two parts indicated by a and 51b, it is clear that the first electrode 51 may be composed of an integral part.

<Method for forming the support structure of the second embodiment> Next, in order to deepen the understanding of the support structure of the second embodiment, the third
An example of a method for forming the support structure of the second embodiment shown in FIG. 2 will be explained with reference to the drawings.

First, on the insulating substrate 11, a pedestal portion 55 having two uneven surfaces is formed using, for example, Au (gold). Furthermore, a part of the lower surface of this trapezoidal portion 55 has a shape similar to that of the surface shaping portion 13 shown in FIG.
A surface shaping portion 57 made of a material similar to the above is formed. Next, a first superconductor thin film 15 is formed on the lower surface of the trapezoidal portion 55 and the surface of the surface shaping portion 57, and a second superconductor thin film 17 is formed on the higher surface of the trapezoidal portion 55 (75). In this way, a structure similar to that of the Josephson junction element shown in FIG. 7 is obtained, although the base of the superconductor thin films 15 and 17 is gold. , a resist mask is formed that has a window that exposes the weak bonding part (the part indicated by P in FIG. 3) and its surroundings, for example, the part 59 surrounded by a dotted line in FIG. The Au portion exposed through the window is removed using an etching solution that selectively removes only the Au portion.

By such a method, the support structure for the superconductor thin film of the second embodiment shown in FIG. 2 can be obtained.

Next, a support structure according to a third embodiment of the present invention will be described with reference to FIG. 4. This third embodiment is basically an example in which the support structure of the present invention is applied to the Josephson junction element already described using FIG. 8. FIG. 4 illustrates this support structure. FIG. 1 is a perspective view schematically showing a weak coupling portion and its surrounding area of a Josephson junction element provided with this support structure.

In FIG. 4, 21 indicates an insulating substrate. On this insulating substrate 11, a first electrode 61 and a second electrode 63 made of Au or the like are provided spaced apart from each other. The first superconductor thin film 27 and the second superconductor thin film 31 are provided on the second electrode 53, respectively. and the second electrode 63, and as already explained with reference to FIG. The shaded area indicated by Q) constitutes a weak coupling part.

If the structure is as shown in FIG.
3 is in a state where it is floating from the support portion such as the insulating substrate 11 or the electrode.

One possible method for forming the support structure shown in FIG. 4 is as follows.

Instead of the first insulating film 25 and the second insulating film 29 shown in FIG.
Insert. Furthermore, the Au layer used in place of the first insulating film 25 is provided to extend to the region of the insulating substrate 11 where the second superconductor thin film is to be formed, and the second superconductor thin film of this Au layer is The layer thickness of the formed portion is set to be thinner than that of the portion in contact with the first superconductor thin film. Next, a second superconductor thin film 31 is formed on this thinned portion of the Au layer.

Next, a resist mask having a window that exposes the weak coupling part (the part indicated by Q in FIG. 4) between the first and second superconductor thin films 27 and 31 and its surrounding area is applied to the superconductor thin films 27 and 31. It is formed on an insulating substrate 21 having a. Next, by etching the area inside the window using an etching solution that dissolves Au but not the superconductor thin film, the △uV present in the window is removed and a superconductor as shown in Figure 4 is formed. Obtain a thin film support structure.

Next, a support structure according to a fourth embodiment of the present invention will be explained with reference to FIG. 5. This embodiment is an example of a three-terminal electrode structure, and in order to explain this support structure, FIG. 5 shows a weak coupling part of a Josephson junction element equipped with this support structure,
FIG. 2 is a perspective view schematically showing the surrounding area.

FIG. 5 (here, 71 indicates an insulating substrate. On this insulating substrate 71, a first electrode 73 and a third electrode 75 made of Au or the like are spaced apart from each other. Furthermore, a first superconductor thin film indicated by 77 is provided on the first electrode 73 so that its end protrudes toward the third electrode 75. A second electrode 79 is provided on the upper side of the superconductor thin film 77 and is insulated from the first superconductor thin film 77. A second superconductor electrode 81 is provided on the second electrode 79. The conductor thin film is provided so that its ends protrude toward the second electrode 75. On the other hand, on the third electrode 75, a third superconductor thin film indicated by 83 is provided with its ends extending toward the second electrode 75 side. However, the end surfaces 83a of the third superconductor thin film 83 are the end surfaces 77a and 81a of the second and second superconductor thin films 77 and 81 so as to protrude toward the two electrodes.
They are arranged so that they are in contact with each other. In this case, the end face 8
A weak coupling portion is formed at a portion where the end surface 3a and the end surface 77a contact, and at a portion where the end surface 83a and the end surface 81a contact.

According to the structure shown in FIG. 5, at least a portion of the superconductor thin film forming a weak bond floats from the insulating substrate 11 or the supporting portion such as the electrode between the first electrode 73 and the third electrode 75. state.

Incidentally, the present invention is not limited to each of the embodiments described above.

For example, the superconductor that can be used may be a material other than those described in the examples as long as it can be made into a thin film.

Furthermore, the first, second and third electrodes may be made of other suitable materials other than Au that can be selectively etched with the superconductor thin film.

In addition, as already explained, the present invention claims that the superconductor thin film is provided on the support portion so that at least the portion of the superconductor thin film used as the element component is in a floating state, The present invention is not limited to making the weak joint of the Josephson junction floating. Various applications of this invention can be considered, and for example, an example of application as shown in FIG. 6 can be considered.

FIG. 6 is a diagram for explaining a fifth embodiment of the present invention, in which an inductance element is constructed using a superconductor thin film, and the superconductor thin film is supported so that the element part is in a floating state. FIG. 3 is a perspective view schematically showing an example provided in the section.

In FIG. 6, reference numeral 91 indicates an insulating substrate as a support portion. In this embodiment, the insulating substrate 91 is provided with a hole 93. Further, on this insulating substrate 91, an insulating substrate 91
A superconductor thin film 95 is provided from a part of the periphery of the hole 93 to extend over the hole 93 to other surrounding parts, and the part 95 of the superconductor thin film 95 corresponding to the hole 93
The inductance element is constructed by setting a to be Ω-shaped.

If you support the inductance element in this way,
The stress of the support portion no longer directly affects the Ω-shaped portion 95a.

Note that the inductance element as described above can be formed, for example, by a method as described below.

A superconductor thin film is formed on an insulating substrate 91. Next, this superconductor thin film is patterned into a predetermined shape including the above-mentioned Ω shape 95a. Next, a hole 93 is formed by selectively etching a portion of the insulating substrate 11 corresponding to the region including the Ω shape 65a.

In this way, the support structure shown in FIG. 6 can be obtained.

It goes without saying that the present invention also includes a structure in which the superconductor thin film is cantilevered from the support and the overhang is supported by the support.

(Effects of the Invention) As is clear from the above explanation, according to the superconductor thin film support structure of the present invention, at least the portion of the superconductor thin film used as an element component is lifted from the support portion such as the substrate. It can be put into a state of Therefore, it is possible to prevent various problems caused by, for example, differences in the thermal expansion coefficients of the substrate and the superconductor thin film. Further, reaction between the substrate and the superconductor thin film can also be prevented.

For this reason, it can be said that the degree of freedom in selecting the substrate increases.

In general, according to the present invention, it becomes possible to sufficiently anneal the substrate and the superconductor thin film, thereby making it possible to obtain good superconductivity.

In addition, during annealing, the floating parts of the superconductor thin film are likely to receive more effective heat treatment than the supporting parts, so for example, the connection state of the weak coupling part of a Josephson junction element is We can expect it to be more stable.

[BRIEF DESCRIPTION OF THE DRAWINGS] FIG. 1 is a perspective view showing a first embodiment of the support structure for a superconductor thin film of the present invention, and FIG. 2 is a perspective view showing a second embodiment of the support structure for a superconductor thin film of the present invention. FIG. 3 is a perspective view showing a superconductor thin film support structure according to the present invention; FIG. FIG. 5 is a perspective view showing a fourth embodiment of the superconductor thin film support structure of the present invention; FIG. 6 is a perspective view of the superconductor thin film support structure of the present invention. A perspective view showing a fifth embodiment of a thin film support structure, and FIGS. 7 and 8 are views for explaining the prior art. 11.2L71.91--Insulating substrate (support part) 13,
57...Surface shaping part (supporting part) +5.27.77...
・First superconductor thin film 17, 31, 8 +-...Second superconductor thin film P, Q...Weak coupling part 4L93-...Hole part, 43.61.73...
First electrode 45.63.79...Second electrode, 55-.
・Platelet portion 59...Exposed portion, 75...Third electrode 77a...End face 81a of first superconductor thin film...End face 83a of second superconductor thin film...Third superconductor End face 95 of body thin film: superconductor thin film, 95a: Ω-shaped portion.

Claims (1)

[Claims] (1) A support structure for a superconductor thin film, characterized in that the superconductor thin film is provided on a support portion so that at least a portion of the superconductor thin film used as an element component is in a floating state.