JPH04280691A - superconducting substrate - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a superconducting substrate. More specifically, the present invention relates to the structure of a novel superconducting substrate, which is a Si wafer on which an oxide superconducting thin film is mounted, and which serves as a base material for manufacturing various circuits or elements.

0002

2. Description of the Related Art Superconductivity was once thought to be a unique phenomenon at extremely low temperatures that require cooling with liquid helium. However, in 1986, Bednotes, Muller et al. showed a superconducting state at 30K (
Since the discovery of La,Ba)2CuO4 in 1987
In 2012, Chu et al. reported that the superconducting critical temperature T
In 1988, Maeda et al. discovered a so-called Bi-based composite oxide superconducting material that exhibits a critical temperature of 100 K or more. These series of composite oxide-based superconducting materials can achieve superconducting phenomena by cooling with inexpensive liquid nitrogen, and the possibility of practical application of superconducting technology has suddenly begun to be discussed.

Initially, these composite oxide-based superconducting materials were synthesized as sintered bodies using a solid-state reaction method, but as a result of subsequent research progress, today they can be fabricated as thin films with extremely high quality. It has become possible to obtain expensive things. However, each of these composite oxides has a complex crystal structure and forms a phase that exhibits effective superconducting properties only when it is formed on a specific substrate under specific conditions. That is, as the base substrate for the oxide superconducting thin film, M
A gO single crystal substrate, a SrTiO3 single crystal substrate, etc. are used.

0004

[Problems to be Solved by the Invention] However, the above-mentioned oxide single crystal substrates are generally expensive and in short supply, and their use is extremely disadvantageous when considering the practical use of oxide superconductors. It is considered to be one of the In addition, it is difficult to obtain large-diameter oxide substrates, and it is difficult to consider this material to be an appropriate material considering that oxide superconducting thin films will become larger in area in the future.

[0005] Therefore, it has been proposed to fabricate an oxide superconducting thin film using a Si wafer, which is currently most stably supplied as a low-cost and high-quality substrate material, as a base substrate. However, there is a very large difference in thermal expansion coefficient between the Si wafer and the oxide superconductor. That is, the thermal expansion coefficient of Si single crystal is 2
．． 4, whereas the coefficient of thermal expansion of Y-based composite oxide, which is a typical oxide superconductor, is 14 or more. For this reason, when an oxide superconducting thin film is formed on a Si wafer, cracks occur due to thermal mismatch. Therefore, even if a large-area Si wafer is used to form an oxide superconducting thin film, there is a problem in that the area of the oxide superconducting thin film that can be effectively utilized is limited.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a new superconducting substrate configuration that can solve the problems of the prior art described above and make more effective use of the materials used.

[0007]

[Means for Solving the Problems] That is, according to the present invention,
A superconducting substrate comprising a Si wafer and an oxide superconducting thin film mounted on the Si wafer, the oxide superconducting thin film being mounted avoiding a region near the center and a region near the periphery of the Si wafer. There is provided a superconducting substrate characterized in that the film-forming surface of the Si wafer is exposed in a region where the oxide superconducting thin film is not mounted.

[0008]

[Operation] One of the main features of the superconducting substrate according to the present invention is that it includes an oxide superconducting thin film mounted only on a specific region on a Si wafer.

That is, as a result of a detailed study of the occurrence of cracks when a large-area oxide superconducting thin film is formed on a Si wafer, it was found that the occurrence of cracks is particularly noticeable at the center and edges of the Si wafer. It turns out that there is something. Therefore, in the superconducting substrate according to the present invention, the occurrence of cracks is substantially prevented by mounting the oxide superconducting thin film avoiding the center and edges of the Si wafer.

[0010] Furthermore, one of the characteristic structures of the superconducting substrate according to the present invention is that the Si wafer is exposed on the surface in the region where the oxide superconducting thin film is not mounted. Such a configuration, as described below,
Achieving new uses for superconducting substrates.

That is, there is actually no electronic device in which the entire system from input to output is formed entirely from superconducting circuits or superconducting elements. In other words, an electronic circuit using a superconducting element or a superconducting circuit is always connected to an electronic circuit composed of a normal conducting element.

Therefore, if the superconducting substrate according to the present invention is used, a semiconductor circuit based on a Si wafer and a superconducting circuit based on an oxide superconducting thin film can be simultaneously fabricated within one substrate. It becomes possible to enter.

[0013] The oxide superconducting thin film can be patterned by wet etching using hydrochloric acid or the like as an etchant, and by processing it according to an appropriate process, it can be made into a circuit or element in the same way as a semiconductor circuit. Can be done.

[0014] Hereinafter, the present invention will be explained in more detail with reference to Examples, but the following disclosure is merely an example of the present invention and is not intended to limit the technical scope of the present invention in any way.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing an example of the structure of a superconducting substrate according to the present invention.

As shown in the figure, this superconducting substrate is constructed by mounting an oxide superconducting thin film 2 formed in an annular pattern on a substantially circular Si wafer 1. In fact, an appropriate buffer layer is formed directly above the Si wafer 1, and the oxide superconducting thin film 2 is formed on this buffer layer.

As already mentioned, the pattern of the oxide superconducting thin film 2 as described above is for preventing cracks that occur when the oxide superconducting thin film 2 is formed on the Si wafer 1. Therefore, its specific shape is closely related to the substrate temperature when forming the oxide superconducting thin film 2, the dimensions of the Si wafer 1, and the thickness of the oxide superconducting thin film 2.

Now, assuming that the substrate temperature at the time of forming the oxide superconducting thin film 2 is 580° C., the relationship between the dimensions of the Si wafer 1 and the pattern size of the oxide superconducting thin film 2 is as follows.
The range is as shown in Table 1 below.

[0019]

[Table 1]

The superconducting substrate according to the present invention as shown in FIG. 1 is ultimately used by cutting it into several pieces by dicing. In this case, as shown in Figure 2,
By cutting the Si wafer 1 in the radial direction, it is possible to obtain a section having the same shape, which includes both an exposed region of the Si wafer 1 and a region in which the oxide superconducting thin film 2 is mounted. Therefore, a predetermined integrated circuit including semiconductor circuits and superconducting circuits can be repeatedly patterned on one superconducting substrate.

[Production example] On a Si wafer with a diameter of 4 inches, M
A buffer layer of gO was formed. The film forming method was the MBE method, and the film forming conditions were as shown in Table 2 below. Further, patterning of the buffer layer was performed by an ion milling method.

[0022]

[Table 2]

[0023] Subsequently, an oxide superconducting thin film was formed on the buffer layer produced as described above in the same pattern as the buffer layer. The thin film material was Y-Ba-Cu oxide, and the film was formed using a reactive vapor deposition method under the film forming conditions shown in Table 3 below.

[0024]

[Table 3]

In the superconducting substrate produced as described above, the surface of the oxide superconducting thin film was observed using an optical microscope, but no cracks were observed.

[0026]

As explained above, the superconducting substrate according to the present invention can be used simultaneously as a base material for a superconducting circuit made of an oxide superconducting thin film and as a base material for a normal conducting circuit made of a Si semiconductor, and can be put to practical use. It can be widely used in various superconducting circuit applications.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a configuration example of a superconducting substrate according to the present invention.

FIG. 2 is a diagram showing an example of use of the superconducting substrate shown in FIG. 1.

[Explanation of symbols]

1 Si wafer, 2 Oxide superconducting thin film

Claims (1)

[Claims] 1. A superconducting substrate comprising a Si wafer and an oxide superconducting thin film mounted on the Si wafer, wherein the oxide superconducting thin film covers a region near the center and a region near the periphery of the Si wafer. A superconducting substrate characterized in that the Si wafer is mounted so as to avoid the oxide superconducting thin film, and the film-forming surface of the Si wafer is exposed in a region where the oxide superconducting thin film is not mounted.