Patent Publication Number: US-2023165168-A1

Title: Superconducting device and method for manufacturing the same

Description:
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2021-190894, filed on Nov. 25, 2021, the disclosure of which is incorporated herein in its entirety by reference. 
     TECHNICAL FIELD 
     The present invention relates to a superconducting device and the like. 
     BACKGROUND ART 
     In order to integrate a superconducting circuit, a structure in which a superconducting circuit integrated chip on which an integrated circuit is mounted is flip-chip mounted on a circuit board is known. In this structure, it is necessary to suppress reflection, interference, and the like of signals and to secure necessary signal quality (transmission characteristics). Therefore, non-contact coupling by capacitive coupling (capacitive coupling) or inductive coupling (inductive coupling) capable of reducing wiring routing in an integrated circuit is promising. 
     As a specific structure, a required number of non-contact coupling circuits are arranged in a superconducting integrated circuit chip. As the non-contact coupling circuit, for example, a capacitive coupling circuit or an inductive coupling circuit for inputting and outputting signals is used. The non-contact coupling circuit on the superconducting integrated circuit chip side and the non-contact coupling circuit on the circuit board side may be arranged to face each other. For the two non-contact coupling circuits to form a good non-contact coupling, a technique for coupling the superconducting integrated circuit chip and the circuit board while keeping the superconducting integrated circuit chip and the circuit board at a predetermined interval is required. 
     A technique related to the above requirement is disclosed in, for example, Patent Document 1 (Japanese Patent No. 2813093). In the technique of Patent Document 1, a second metal layer made of tin or tin and lead is laminated on a superconducting wire provided on a circuit board, and an electrode of the second metal layer and an electrode of a superconducting element are connected by solder. That is, first, a second metal layer having good solder wettability is formed on the superconducting wire, and then the electrode of the superconducting element and the electrode of the second metal layer are connected by solder. As a result, the electrode of the superconducting element and the superconducting wire of the electrode circuit board are connected via the second metal layer. Therefore, a highly reliable connection between the superconducting element and the circuit board can be obtained. 
     SUMMARY 
     However, in the structure disclosed in Patent Document 1, there is a problem that the distance between the non-contact coupling circuit of the superconducting integrated circuit chip and the non-contact coupling circuit of the circuit board cannot be accurately controlled. This is because there is a possibility that a mounting position of the non-contact coupling circuit of the superconducting integrated circuit chip or the non-contact coupling circuit of the circuit board is shifted while the molten solder is solidified. 
     The present invention has been made in view of the above problems, and an object thereof is to provide a superconducting device and the like capable of more accurately arranging a non-contact coupling circuit of a superconducting integrated circuit chip and a non-contact coupling circuit of a circuit board with respect to a design value. 
     In order to solve the above problems, according to an aspect of the present invention, there is provided a superconducting device including: a superconducting integrated circuit chip having a first electrode made of a first superconducting material and a first non-contact coupling circuit on a surface thereof; and a circuit board having a second electrode made of a second superconducting material and a second non-contact coupling circuit on a surface thereof, the circuit board being arranged in such a way to face the superconducting integrated circuit chip, in which the second electrode has a protrusion having a flat upper surface and protruding toward the superconducting integrated circuit chip, the first electrode includes a flat surface and a first recess arranged inside the flat surface and having an area smaller than an area of the upper surface, 
     the first recess is arranged to face the upper surface in such a way to be located inside the upper surface, the upper surface and the flat surface are in contact with each other, and a third superconducting material connecting the upper surface and the first recess is arranged inside the first recess. 
     According to another aspect of the present invention, there is provided a method for manufacturing a superconducting device including a superconducting integrated circuit chip having a first electrode made of a first superconducting material and a first non-contact coupling circuit on a surface thereof, and a circuit board having a second electrode made of a second superconducting material and a second non-contact coupling circuit on a surface thereof, the circuit board being arranged in such a way to face the superconducting integrated circuit chip, the second electrode having a protrusion having a flat upper surface and protruding toward the superconducting integrated circuit chip, the first electrode including a flat surface and a first recess arranged inside the flat surface and having an area smaller than an area of the upper surface, the method including: arranging a third superconducting material connecting the upper surface and the first recess inside the first recess; arranging the first recess in such a way that the first recess faces the upper surface to be located inside the upper surface; and bringing the upper surface and the flat surface into contact with each other. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Exemplary features and advantages of the present invention will become apparent from the following detailed description when taken with the accompanying drawings in which: 
         FIG.  1    is a cross-sectional view illustrating a configuration of a superconducting device according to a first example embodiment; 
         FIG.  2    is a cross-sectional view illustrating a configuration of a superconducting device of a second example embodiment; 
         FIG.  3    is a plan view illustrating a configuration example of a superconducting integrated circuit chip used in the superconducting device of the second example embodiment; 
         FIG.  4    is a cross-sectional view illustrating a first configuration example of the superconducting integrated circuit chip used in the superconducting device of the second example embodiment; 
         FIG.  5    is a cross-sectional view illustrating a second configuration example of the superconducting integrated circuit chip used in the superconducting device of the second example embodiment; 
         FIG.  6    is a cross-sectional view illustrating a third configuration example of the superconducting integrated circuit chip used in the superconducting device of the second example embodiment; 
         FIG.  7    is a cross-sectional view illustrating a fourth configuration example of the superconducting integrated circuit chip used in the superconducting device of the second example embodiment; 
         FIG.  8    is a cross-sectional view illustrating a fifth configuration example of the superconducting integrated circuit chip used in the superconducting device of the second example embodiment; 
         FIG.  9    is a plan view illustrating a circuit board used in the superconducting device according to the second example embodiment; 
         FIG.  10    is a cross-sectional view illustrating a first configuration example of the circuit board used in the superconducting device of the second example embodiment; 
         FIG.  11    is a cross-sectional view illustrating a second configuration example of the circuit board used in the superconducting device of the second example embodiment; 
         FIG.  12    is a cross-sectional view illustrating a first example of arrangement of a third superconducting material on the circuit board of the superconducting device of the second example embodiment; 
         FIG.  13    is a cross-sectional view illustrating a second example of the arrangement of the third superconducting material on the circuit board of the superconducting device of the second example embodiment; 
         FIG.  14    is a cross-sectional view illustrating a third configuration example of the circuit board used in the superconducting device of the second example embodiment; 
         FIG.  15    is a cross-sectional view illustrating a fourth configuration example of the circuit board used in the superconducting device of the second example embodiment; 
         FIG.  16    is a cross-sectional view illustrating a first state in a method for manufacturing the superconducting device of the second example embodiment; 
         FIG.  17    is a cross-sectional view illustrating a second state in the method for manufacturing the superconducting device of the second example embodiment; 
         FIG.  18    is a cross-sectional view illustrating a third state in the method for manufacturing the superconducting device of the second example embodiment; 
         FIG.  19    is a cross-sectional view illustrating a modification of the superconducting device of the second example embodiment. 
     
    
    
     EXAMPLE EMBODIMENT 
     Hereinafter, example embodiments of the present invention will be described in detail with reference to the drawings. However, the example embodiments described below have technically preferable limitations for carrying out the present invention, but the scope of the invention is not limited to the following. Similar components in the drawings are denoted by the same reference numerals, and description thereof may be omitted. 
     First Example Embodiment 
       FIG.  1    is a cross-sectional view illustrating a superconducting device  1  of the present example embodiment. The superconducting device  1  includes a superconducting integrated circuit chip  10  and a circuit board  20 . The superconducting integrated circuit chip  10  has a first electrode  11  made of a first superconducting material and a first non-contact coupling circuit  12  on a surface thereof. The circuit board  20  has a second electrode  21  made of a second superconducting material and a second non-contact coupling circuit  22  on the surface, and is arranged so as to face the superconducting integrated circuit chip  10 . Here, the superconducting material refers to a substance that exhibits superconducting at a so-called cryogenic temperature close to absolute zero degree (273.15 degree Celsius below zero and can also be denoted as 0K). The material to be superconductive is roughly divided into a metal system having a relatively low temperature with a critical temperature (upper limit temperature at which the material exhibits a superconducting state) of up to about 40 K and an oxide system having a relatively high temperature around 100 K. As the metal system, for example, mercury, vanadium, lead, niobium, niobium-titanium, niobium-tin, niobium-aluminum, vanadium-gallium, magnesium-boron, or the like is used. As the oxide system, for example, oxides such as yttrium-barium-copper-oxygen and bismuth-lead-strontium-calcium-copper-oxygen are used. 
     The circuit board  20  has a second electrode  21  made of a second superconducting material and a second non-contact coupling circuit  22  on a surface thereof. The second electrode  21  includes a flat upper surface  21   b  and has a protrusion  21   a  protruding toward the superconducting integrated circuit chip  10 . 
     The superconducting integrated circuit chip  10  has the first electrode  11  made of the first superconducting material and the first non-contact coupling circuit  12  on the surface thereof. The first electrode  11  includes a flat surface  11   a  and a first recess  11   b  that is arranged inside the flat surface  11   a  and has a smaller area than the upper surface  21   b . The first recess  11   b  is arranged to face the upper surface  21   b  so as to be located inside upper surface  21   b . The upper surface  21   b  and the flat surface  11   a  are in contact with each other. A third superconducting material  23  connecting the upper surface  21   b  and the first recess  11   b  is arranged inside the first recess  11   b.    
     With this configuration, the first non-contact coupling circuit  12  and the second non-contact coupling circuit  22  are arranged to face each other. The positioning of the upper surface  21   b  and the first recess  11   b  and the positioning of the first non-contact coupling circuit  12  and the second non-contact coupling circuit  22  are designed to be performed simultaneously in a direction parallel to a main surface of the circuit board  20 . 
     In the above configuration, since the upper surface  21   b  of the protrusion  21   a  is in contact with the flat surface  11   a  of the first electrode  11 , the distance between the first non-contact coupling circuit  12  and the second non-contact coupling circuit  22  is determined to a predetermined value determined by a height of the protrusion  21   a . That is, it is possible to provide the superconducting device  1  in which the first non-contact coupling circuit  12  and the second non-contact coupling circuit  22  are arranged more accurately with respect to a design value. As a result, it is possible to obtain input/output characteristics closer to a design value by non-contact coupling. The design value is a value including a predetermined tolerance with respect to a reference value. Since the first electrode  11  and the third superconducting material  23  are joined to each other in the first recess  11   b , an area of a joint surface increases as compared with a case of joining flat surfaces to each other, and a strong joint can be formed. 
     The superconducting device  1  of the first example embodiment has been described above. 
     The superconducting device  1  of the first example embodiment includes the superconducting integrated circuit chip  10  and the circuit board  20 . The superconducting integrated circuit chip  10  has the first electrode  11  made of the first superconducting material and the first non-contact coupling circuit  12  on the surface thereof. The circuit board  20  has the second electrode  21  made of the second superconducting material and the second non-contact coupling circuit  22  on the surface thereof, and is arranged so as to face the superconducting integrated circuit chip  10 . The circuit board  20  has the second electrode  21  made of the second superconducting material and the second non-contact coupling circuit  22  on the surface thereof. The second electrode  21  includes the flat upper surface  21   b  and has the protrusion  21   a  protruding toward the superconducting integrated circuit chip  10 . The superconducting integrated circuit chip  10  has the first electrode  11  made of the first superconducting material and the first non-contact coupling circuit  12  on the surface thereof. The first electrode  11  includes the flat surface  11   a  and the first recess  11   b  that is arranged inside the flat surface  11   a  and has an area smaller than that of the upper surface  21   b . The first recess  11   b  is arranged to face the upper surface  21   b  to be located inside the upper surface  21   b . The upper surface  21   b  and the flat surface  11   a  are in contact with each other. The third superconducting material  23  connecting the upper surface  21   b  and the first recess  11   b  is arranged inside the first recess  11   b.    
     In the above configuration, since the upper surface  21   b  of the protrusion  21   a  is in contact with the flat surface  11   a  of the first electrode  11 , the distance between the first non-contact coupling circuit  12  and the second non-contact coupling circuit  22  is determined to a predetermined value determined by the height of the protrusion  21   a . That is, it is possible to provide the superconducting device  1  in which the first non-contact coupling circuit  12  and the second non-contact coupling circuit  22  are arranged more accurately with respect to a design value. As a result, it is possible to obtain input/output characteristics closer to a design value by non-contact coupling. The design value is a value including a predetermined tolerance with respect to a reference value. Since the first electrode  11  and the third superconducting material  23  are joined to each other in the first recess  11   b , an area of a joint surface increases as compared with a case of joining flat surfaces to each other, and a strong joint can be formed. 
     Second Example Embodiment 
     In the present example embodiment, a superconducting device  1000  which is a specific configuration example of the superconducting device  1  of the first example embodiment will be described. 
       FIG.  2    is a cross-sectional view illustrating a configuration of the superconducting device  1000  of the second example embodiment. The superconducting device  1000  is an example of the superconducting device  1 . 
     Referring to  FIG.  2   , the superconducting device  1000  includes a superconducting integrated circuit chip  100  and a circuit board  200 . The superconducting integrated circuit chip  100  has a first electrode  110  made of a first superconducting material and a first non-contact coupling circuit  120  on a surface thereof. The circuit board  200  has a second electrode  210  made of a second superconducting material and a second non-contact coupling circuit  220  on a surface thereof. The circuit board  200  is arranged so as to face the superconducting integrated circuit chip  100 . The second electrode  210  includes a flat upper surface  212  and has a protrusion  211  protruding toward the superconducting integrated circuit chip  10 . The first electrode  110  includes a flat surface  111  and a first recess  112  arranged inside the flat surface  111  and having an area smaller than that of the upper surface  212 . The first recess  112  is arranged to face the upper surface  212  so as to be located inside the upper surface  212 . The upper surface  212  and the flat surface  111  are in contact with each other. A third superconducting material  240  connecting the upper surface  212  and the first recess  112  is arranged inside the first recess  112 . 
     Next, a configuration example of the superconducting integrated circuit chip  100  used in the superconducting device  1000  of the second example embodiment will be described.  FIG.  3    is a plan view illustrating a configuration example of the superconducting integrated circuit chip  100  used in the superconducting device  1000  of the second example embodiment.  FIG.  4    is a cross-sectional view illustrating a first configuration example of the superconducting integrated circuit chip  100  used in the superconducting device  1000  of the second example embodiment.  FIG.  4    is a cross-sectional view taken along line A-A′ of  FIG.  3   . 
     Referring to  FIGS.  3  and  4   , the superconducting integrated circuit chip  100  has a base material  101 . The first electrode  110  made of the first superconducting material and the first non-contact coupling circuit  120  are formed on the surface of the base material  101 . The first electrode  110  has the flat surface  111  and the first recess  112  provided inside the flat surface. The superconducting integrated circuit chip  100  is an example of the superconducting integrated circuit chip  10  of the first example embodiment. The first electrode  110  is an example of the first electrode  11  of the first example embodiment, the first non-contact coupling circuit  120  is an example of the first non-contact coupling circuit  12 , the flat surface  111  is an example of the flat surface  11   a , and the first recess  112  is an example of the first recess  11   b.    
     The first electrode  110  is connected to, for example, a circuit such as a ground circuit (not illustrated). The first non-contact coupling circuit  120  is connected to, for example, a superconducting circuit (not illustrated). As the first superconducting material constituting the first electrode  110 , for example, niobium, niobium nitride, aluminum, indium, lead, tin, rhenium, palladium, titanium, titanium nitride, tantalum, or an alloy containing these materials can be used. For example, silicon can be used for the base material  101 . The first non-contact coupling circuit  120  is, for example, a capacitive coupling circuit or an inductive coupling circuit for inputting and outputting signals to and from the circuit board  200 . As the base material  101 , for example, silicon can be used. Although not illustrated, a first wiring layer may be provided below the first electrode  110 . 
     As illustrated in  FIG.  4   , a thin film  110   a  of the first superconducting material is arranged on the surface of the first electrode  110 . The thin film  110   a  of the first superconducting material has, for example, a uniform film thickness. A recess forming layer  113  is arranged below the thin film  110   a  of the first superconducting material. The recess forming layer  113  is patterned, and the patterned thin film  110   a  of the first superconducting material is laminated thereon to form the flat surface  111  and the first recess  112 . The recess forming layer  113  can be formed using, for example, a wiring layer of a superconducting integrated circuit chip. 
     Next, as a modification of the superconducting integrated circuit chip  100  used in the superconducting device  1000  of the second example embodiment, a second configuration example of the superconducting integrated circuit chip  100  will be described. 
       FIG.  5    is a cross-sectional view illustrating the second configuration example of the superconducting integrated circuit chip  100  used in the superconducting device  1000  of the second example embodiment. In the second configuration illustrated in  FIG.  5   , in addition to the configuration of  FIG.  4   , a first adhesion layer  110   b  is arranged below the thin film  110   a  of the first superconducting material. By providing the first adhesion layer  110   b , adhesion between the thin film  110   a  of the first superconducting material and the base material  101  and the recess forming layer  113  is improved. For the first adhesion layer  110   b , for example, titanium, titanium nitride, iridium, or the like can be used. 
     Next, as a modification of the superconducting integrated circuit chip  100  used in the superconducting device  1000  of the second example embodiment, a third configuration example of the superconducting integrated circuit chip  100  will be described. 
       FIG.  6    is a cross-sectional view illustrating the third configuration example of the superconducting integrated circuit chip  100  used in the superconducting device  1000  of the second example embodiment. In the third configuration example, an uneven portion  112   a  is formed at a bottom portion of the first recess  112 . Other configurations can be similar to the first configuration example of  FIG.  4    or the second configuration example of  FIG.  5   . Since a surface area of the first recess  112  increases by providing the uneven portion  112   a , when the first recess  112  is filled with a joining material, a joining force between the joining material and the thin film  110   a  of the first superconducting material in the first recess  112  can increase. The uneven portion  112   a  can be formed, for example, by roughening the bottom surface of the first recess  112  by physical etching or chemical etching, or by patterning the recess forming layer  113 , but is not limited thereto. 
     Next, as a modification of the superconducting integrated circuit chip  100  used in the superconducting device  1000  of the second example embodiment, a fourth configuration example of the superconducting integrated circuit chip  100  will be described. 
       FIG.  7    is a cross-sectional view illustrating the fourth configuration example of the superconducting integrated circuit chip used in the superconducting device of the second example embodiment. As illustrated in  FIG.  7   , in the fourth configuration example, the second recess  102  is arranged below the first electrode  110  in the first recess  112 . For example, as illustrated in  FIG.  7   , the second recess  102  can be formed by digging the base material  101 . The base material  101  can be, for example, silicon, but various methods of performing three-dimensional processing with high accuracy have been developed for silicon, and these methods can be used to form the second recess  102  with high accuracy. In the above configuration, for example, it is easier to form the deep first recess  112  than the method of forming the first recess  112  using the recess forming layer  113  in the first configuration example. Since the surface area of the first recess  112  increases by making the first recess  112  deep, when the first recess  112  is filled with a joining material, the joining force between the joining material and the thin film  110   a  of the first superconducting material in the first recess  112  can increase. 
     Next, as a modification of the superconducting integrated circuit chip  100  used in the superconducting device  1000  of the second example embodiment, a fifth configuration example of the superconducting integrated circuit chip  100  will be described. 
       FIG.  8    is a cross-sectional view illustrating the fifth configuration example of the superconducting integrated circuit chip used in the superconducting device of the second example embodiment. In the fifth configuration example, a through hole  103  is formed in the base material  101  at a position corresponding to the first recess  112 , and the through hole  103  is filled to a predetermined depth with a filler  104 , thereby forming the second recess  102 . In this way, it is easy to form the deep first recess  112 . Therefore, similarly to the fourth configuration example, since the surface area of the first recess  112  increases, when the first recess  112  is filled with the joining material, the joining force between the joining material and the thin film  110   a  of the first superconducting material in the first recess  112  can be increased. 
     In the above description, an example in which the shape of the first recess  112  is a cylindrical shape has been described, but the shape of the first recess  112  is not limited thereto, and may be, for example, a polygonal prism, a cone, a polygonal cone, a truncated cone, a polygonal truncated cone, or the like. 
     Next, a configuration of the circuit board  200  used in the superconducting device  1000  of the second example embodiment will be described.  FIG.  9    is a plan view illustrating the circuit board  200  used in the superconducting device  1000  of the second example embodiment.  FIG.  10    is a cross-sectional view illustrating a first configuration example of the circuit board  200  used in the superconducting device of the second example embodiment.  FIG.  11    is a cross-sectional view illustrating a second configuration example of the circuit board  200  used in the superconducting device of the second example embodiment. 
     As illustrated in  FIGS.  9  and  10   , the circuit board  200  includes a substrate  201 . A second electrode  210  made of a second superconducting material and a second non-contact coupling circuit  220  are formed on the surface of the substrate  201 . The second electrode  210  has a protrusion  211  having a flat upper surface  212  and a predetermined height. Here, the circuit board  200  is an example of the circuit board  20  of the first example embodiment. The second electrode  210  is an example of the second electrode  21 , the second non-contact coupling circuit  220  is an example of the second non-contact coupling circuit  22 , the protrusion  211  is an example of the protrusion  21   a , and the upper surface  212  is an example of the upper surface  21   b.    
     The substrate  201  of the circuit board  200  is, for example, silicon. As the second superconducting material, for example, niobium, niobium nitride, aluminum, indium, lead, tin, rhenium, palladium, titanium, titanium nitride, tantalum, or an alloy containing these can be used. The second electrode  210  is connected to, for example, a ground circuit (not illustrated). The second non-contact coupling circuit  220  is connected to, for example, an electronic circuit (not illustrated). Although not illustrated, a second wiring layer may be provided below the second electrode  210 . 
       FIG.  10    is a cross-sectional view illustrating the circuit board  200  used in the superconducting device of the second example embodiment.  FIG.  10    is a cross-sectional view taken along line B-B′ in  FIG.  9   . As illustrated in  FIG.  10   , a protruding portion  230  having a flat upper surface and a predetermined height is formed on the substrate  201 . The second electrode  210  is formed by covering the protruding portion  230  with a thin film  210   a  of the second superconducting material. The thin film  210   a  of the second superconducting material has, for example, a uniform film thickness. The thin film  210   a  of the second superconducting material can be formed of, for example, niobium, niobium nitride, aluminum, lead, tin, rhenium, palladium, titanium, titanium nitride, tantalum, or an alloy containing these. The protruding portion  230  can be formed using a material different from the thin film  210   a  of the second superconducting material, for example, a metal such as copper, silver, gold, platinum, or an alloy containing these. 
     Some superconducting materials such as niobium have poor workability, and it is difficult to form a three-dimensional structure such as the protruding portion  230 . Therefore, the protruding portion  230  can be easily formed by using a material that is easy to process. By using a material having good workability, the height of the protruding portion  230  can be accurately controlled, and the upper surface can be made flat. Then, by stacking the thin film  210   a  of the second superconducting material whose film thickness is accurately controlled on the protruding portion  230 , the height of the protrusion  211  can be accurately controlled and the upper surface  212  can be made flat. The second electrode  210  and the protrusion  211  can be easily formed by performing processing such as photolithography and etching on the laminated film. 
     Next, as a modification of the circuit board  200  used in the superconducting device of the second example embodiment, a second configuration example of the circuit board  200  will be described. 
       FIG.  11    is a cross-sectional view illustrating the second configuration example of the circuit board  200  used in the superconducting device of the second example embodiment. In the second configuration example of the circuit board  200 , in addition to the first configuration example of  FIG.  10   , a second adhesion layer  213  is laminated below the thin film  210   a  of the second superconducting material. By providing the second adhesion layer  213 , adhesion between the thin film  210   a  of the second superconducting material and the substrate  201  and the protruding portion  230  is improved. For the second adhesion layer  213 , for example, titanium, titanium nitride, iridium, or the like can be used. 
     Next, as a modification of the arrangement of a third superconducting material  240  on the circuit board  200  used in the superconducting device of the second example embodiment, a first example of the arrangement of the third superconducting material  240  on the circuit board  200  will be described. 
       FIG.  12    is a cross-sectional view illustrating the first example of arrangement of the third superconducting material  240  on the circuit board  200  of the superconducting device  1000  according to the second example embodiment. The third superconducting material  240  connects the upper surface  212  of the protrusion  211  and the first recess  112  of the superconducting integrated circuit chip  100 . In the case of manufacturing the superconducting device  1000 , a circuit formation surface of the superconducting integrated circuit chip  100  and a circuit formation surface of the circuit board  200  face each other and brought close to each other, and the upper surface  212  of the protrusion  211  and the flat surface  111  of the first electrode  110  are brought into contact with each other. In this case, alignment is performed such that the first recess  112  is accommodated inside the upper surface  212 . Then, the third superconducting material  240  is joined to the thin film  110   a  of the first superconducting material of the first recess  112  and the thin film  210   a  of the second superconducting material of the upper surface  212 . 
     In the above configuration, a volume of the third superconducting material  240  is desirably close to a volume of the first recess  112  so that the third superconducting material  240  is in contact with the entire inner surface of the first recess  112 . Meanwhile, it is desirable that the third superconducting material  240  does not protrude from a contact portion between the upper surface  212  of the protrusion  211  and the flat surface  111  of the first electrode  110 . Therefore, for example, the volume of the third superconducting material  240  can be set to a size smaller than the volume of the first recess  112  by a predetermined margin. After such setting, the third superconducting material  240  is arranged in a bump shape on the upper surface  212 . 
     The third superconducting material  240  is crushed inside the first recess  112  to connect the thin film  110   a  of the first superconducting material and the thin film  210   a  of the second superconducting material. Therefore, as the third superconducting material  240 , it is desirable to use a material having higher spreadability than the thin film  110   a  of the first superconducting material and the thin film  210   a  of the second superconducting material. To meet this condition, it is desirable to select the third superconducting material  240  according to the material used for the thin film  110   a  of the first superconducting material and the thin film  210   a  of the second superconducting material. For example, when both the thin film  110   a  of the first superconducting material and the thin film  210   a  of the second superconducting material are niobium, the third superconducting material  240  can be indium. 
     Next, as a modification of the arrangement of the third superconducting material on the circuit board  200  used in the superconducting device of the second example embodiment, a second example of the arrangement of the third superconducting material on the circuit board  200  will be described. 
       FIG.  13    is a cross-sectional view illustrating the second example of the arrangement of the third superconducting material on the circuit board of the superconducting device according to the second example embodiment. In the second example of  FIG.  13   , in addition to the configuration of the first example of  FIG.  12   , a third adhesion layer  241  is provided between the third superconducting material  240  and the upper surface  212 . The third adhesion layer  241  can be formed of, for example, titanium, titanium nitride, or iridium. By providing the third adhesion layer  241 , adhesion between the third superconducting material  240  and the upper surface  212  can be enhanced. 
     Next, as a modification of the circuit board  200  used in the superconducting device of the second example embodiment, a third configuration example of the circuit board  200  will be described. 
       FIG.  14    is a cross-sectional view illustrating the third configuration example of the circuit board  200  used in the superconducting device of the second example embodiment. In the example of  FIG.  14   , an opening  214  in which the thin film  210   a  of the second superconducting material has the opening  214  inside the upper surface  212  can be formed by, for example, photolithography. For example, when the adhesion between the third superconducting material  240  and the thin film  210   a  of the second superconducting material is poor and the adhesion between the third superconducting material  240  and the protruding portion  230  is good, the adhesion can be enhanced by providing the opening  214 . 
     Next, as a modification of the circuit board  200  used in the superconducting device of the second example embodiment, a fourth configuration example of the circuit board  200  will be described. 
       FIG.  15    is a cross-sectional view illustrating the fourth configuration example of the circuit board used in the superconducting device of the second example embodiment. In the fourth configuration example of  FIG.  15   , in addition to the third configuration example of  FIG.  14   , a fourth adhesion layer  242  is provided between the third superconducting material  240  and the protruding portion  230 . By providing the fourth adhesion layer  242 , adhesion of the third superconducting material  240  to the protrusion  211  can be enhanced. For example, titanium, titanium nitride, or iridium can be used for the fourth adhesion layer  242 . 
     Next, a method for manufacturing a superconducting device according to the second example embodiment will be described.  FIG.  16    is a cross-sectional view illustrating a first state in the method for manufacturing the superconducting device of the second example embodiment.  FIG.  17    is a cross-sectional view illustrating a second state in the method for manufacturing the superconducting device of the second example embodiment.  FIG.  18    is a cross-sectional view illustrating a third state in the method for manufacturing the superconducting device of the second example embodiment. 
     First, as illustrated in  FIG.  16   , the superconducting integrated circuit chip  100  and the circuit board  200  are arranged in a vacuum chamber (not illustrated) in a direction in which circuit formation surfaces thereof face each other, and vacuuming is performed. In this case, the superconducting integrated circuit chip  100  is fixed by a chip fixing jig (not illustrated), and the circuit board  200  is also fixed by a board fixing jig (not illustrated). As a fixing method, for example, a clamp method, an electrostatic chuck method, or the like can be applied. A degree of vacuum in the chamber is preferably, for example, about 10 −6  Pa. 
     Next, as illustrated in  FIG.  17   , using an activation device  300 , adsorbents and oxides on the flat surface  111  of the first electrode  110  and the surface of the first recess  112 , which are to be a joint of the superconducting integrated circuit chip  100 , are removed to activate the joint. As the activation device  300  that performs activation, for example, a device that emits an ion, a neutral atom beam, or the like can be used. Similarly, using the activation device  300 , an adsorbent and an oxide on the surface of the protrusion  211  and the third superconducting material  240 , which become the joint of the circuit board  200 , are removed to activate the joint. 
     Next, as illustrated in  FIG.  18   , the superconducting integrated circuit chip  100  and the circuit board  200  are aligned such that the first non-contact coupling circuit  120  and the second non-contact coupling circuit  220  face each other. In this case, the third superconducting material  240  arranged in a bump shape on the upper surface  212  is positioned so as to face the inside of the first recess  112 . Then, in a state where the degree of vacuum is maintained, the superconducting integrated circuit chip  100  and the circuit board  200  are brought close to each other, and the flat surface  111  of the first electrode  110  and the upper surface  212  of the protrusion  211  are brought into contact with each other. The superconducting integrated circuit chip  100  and the circuit board  200  are brought close to each other so that the flat surface  111  of the first electrode  110  and the upper surface  212  of the protrusion  211  are in close contact with each other. A force in a direction in which both the superconducting integrated circuit chip  100  and the circuit board  200  approach each other is applied, and a contact portion between both is pressurized with a predetermined force. In this case, a temperature of the first recess  112  and a temperature of the third superconducting material  240  are controlled to, for example, a range of 25 to 100 degree Celsius, which is a normal temperature. By joining at a low temperature of equal to or lower than 100 degree Celsius, it is possible to reduce a positional deviation at the time of joining due to a state change of the superconducting element due to heating or thermal expansion of the member, and to perform accurately positioned joining. 
     By the above pressurization, the third superconducting material  240  having spreadability is inserted into the first recess  112  and joined following a surface roughness of the inner surface of the first recess  112 . A part of the flat surface  111  of the first electrode  110  and an outer periphery of the upper surface  212  of the protrusion  211  are also joined. In these junctions, the thin film  110   a  of the first superconducting material and the third superconducting material  240  form an amorphous layer at a junction interface, and both are firmly bonded. Similarly, the thin film  110   a  of the first superconducting material and the thin film  210   a  of the second superconducting material also form an amorphous layer at the joining interface, and both are firmly bonded. Although not illustrated, for example, alignment of the superconducting integrated circuit chip  100  and the circuit board  200  can be performed by providing alignment marks on the superconducting integrated circuit chip  100  and the circuit board  200  and adjusting the positions using a transmission image by an infrared camera. 
     Next, a modification of the superconducting device  1000  will be described.  FIG.  19    is a cross-sectional view illustrating a modification of the superconducting device  1000  described in  FIG.  18   . In this modification, as the superconducting integrated circuit chip  100 , the superconducting integrated circuit chip  100  having the uneven portion  112   a  at the bottom portion of the first recess  112  illustrated in  FIG.  6    is used. By using the superconducting integrated circuit chip  100 , the area of contact between the third superconducting material  240  filling the first recess  112  and the first recess  112  increases, and thus, the superconducting integrated circuit chip  100  and the circuit board  200  can be firmly joined. 
     The superconducting device and the like of the second example embodiment of the present invention have been described above. 
     The superconducting device  1000  of the second example embodiment includes the superconducting integrated circuit chip  100  and the circuit board  200 . The superconducting integrated circuit chip  100  has the first electrode  110  made of the first superconducting material and the first non-contact coupling circuit  120  on the surface thereof. The circuit board  200  has the second electrode  210  made of the second superconducting material and the second non-contact coupling circuit  220  on the surface thereof, and is arranged so as to face the superconducting integrated circuit chip  10 . The second electrode  210  includes the flat upper surface  212  and has the protrusion  211  protruding toward the superconducting integrated circuit chip  100 . The first electrode  110  includes the flat surface  111  and the first recess  112  arranged inside the flat surface  111  and having an area smaller than that of the upper surface  212 . Then, the first recess  112  is arranged to face the upper surface  212  to be located inside the upper surface  212 , and the upper surface  212  and the flat surface  111  are in contact with each other, and the third superconducting material  240  connecting the upper surface  212  and the first recess  112  is arranged inside the first recess  112 . 
     In the above configuration, since the upper surface  212  of the protrusion  211  is in contact with the flat surface  111  of the first electrode  110 , the distance between the first non-contact coupling circuit  120  and the second non-contact coupling circuit  220  is determined to a predetermined value determined by the height of the protrusion  211 . That is, it is possible to provide the superconducting device  1000  capable of more accurately arranging the first non-contact coupling circuit  120  and the second non-contact coupling circuit  220  with respect to the design value. As a result, it is possible to obtain input/output characteristics closer to a design value by non-contact coupling. Since the first electrode  110  and the third superconducting material  240  are joined to each other in the first recess  112 , the area of the joint surface increases as compared with the case of joining flat surfaces to each other, and a strong joint can be formed. 
     According to one aspect, in the superconducting device  1000 , the thin film  110   a  of the first superconducting material is arranged on the surface of the first electrode  110 . In this configuration, by arranging the thin film  110   a  of the first superconducting material having a uniform film thickness, the first recess  112  can be formed along the shape formed by the underlying recess forming layer  113 . 
     According to one aspect, in the superconducting device  1000 , at least one first adhesion layer  110   b  is arranged below the thin film  110   a  of the first superconducting material. By providing the first adhesion layer  110   b , adhesion between the thin film  110   a  of the first superconducting material and a base such as the base material  101  can be improved. 
     According to one aspect, in the superconducting device  1000 , the second recess  102  is arranged below the first electrode  110  at a position corresponding to the first recess  112 . By providing the second recess  102 , the first recess  112  can be formed using the thin film  110   a  of the first superconducting material having a uniform film thickness. 
     According to one aspect, in the superconducting device  1000 , the second recess  102  is provided in the base material  101  of the superconducting integrated circuit chip  100 . Providing the second recess  102  in the base material  101  facilitates forming a deeper first recess  112 . 
     According to one aspect, in the superconducting device  1000 , the second recess  102  is formed by filling the through hole  103  provided in the base material  101  of the superconducting integrated circuit chip  100  with a first material different from the base material  101  to a predetermined depth. With this configuration, it is easy to form the deeper second recess  102 , and it is easy to form the deeper first recess  112  corresponding thereto. 
     According to one aspect, in the superconducting device  1000 , the surface of the second electrode  210  is formed of the thin film  210   a  of the second superconducting material. By using the thin film  210   a  of the second superconducting material, the second electrode  210  having excellent characteristics and workability can be obtained. 
     According to one aspect, in the superconducting device  1000 , at least one second adhesion layer  213  is arranged below the thin film  210   a  of the second superconducting material. By providing the second adhesion layer  213 , adhesion between the thin film  210   a  of the second superconducting material and a base such as the substrate  201  can be improved. 
     According to one aspect, in the superconducting device  1000 , the protruding portion  230  made of a second material different from the second superconducting material is arranged in the thin film  210   a  of the second superconducting material in the protrusion  211 . By forming the protruding portion  230  using a material having good workability different from the second superconducting material, it is easy to form the protruding portion  230  having a desired shape and to form the protrusion  211  having a desired shape. 
     According to one aspect, in the superconducting device  1000 , the thin film  210   a  of the second superconducting material has the opening  214  inside the upper surface  212 , and the third superconducting material  240  is arranged at a position corresponding to the opening  214 . With such a configuration, when the adhesion between the third superconducting material  240  and the thin film  210   a  of the second superconducting material is inferior to the adhesion between the third superconducting material  240  and the material of the protruding portion  230 , the adhesion can be improved. 
     According to one aspect, in the superconducting device  1000 , the fourth adhesion layer  242  for enhancing adhesion between the second material and the third superconducting material  240  is formed in the opening  214 . By the effect of the fourth adhesion layer  242 , adhesion between the third superconducting material  240  and the protruding portion  230  can be improved. 
     According to one aspect, the third adhesion layer  241  is arranged in the superconducting device  1000 . The third adhesion layer  241  enhances adhesion between the third superconducting material  240  and at least a part of the upper surface  212 . In this configuration, the adhesion between the third superconducting material  240  and the upper surface  212  can be improved by the effect of the third adhesion layer  241 . 
     According to one aspect, in the superconducting device  1000 , at least a part of a portion where the flat surface  111  and the upper surface  212  are in contact with each other has the first joint where the flat surface  111  and the upper surface  212  are directly joined to each other. By joining the flat surface  111  and the upper surface  212 , the superconducting integrated circuit chip  100  and the circuit board can be more firmly bonded. 
     According to one aspect, in the superconducting device  1000 , the first joint has an amorphous layer including a first superconducting material and a second superconducting material. By forming the amorphous layer, the thin film  110   a  of the first superconducting material and the thin film  210   a  of the second superconducting material can be more firmly bonded. 
     According to one aspect, the superconducting device  1000  has the second joint in which the thin film  110   a  of the first superconducting material located in the first recess  112  and the third superconducting material  240  are directly joined. In this configuration, since the thin film  110   a  of the first superconducting material and the third superconducting material  240  in the first recess  112  are joined, the joining becomes stronger. 
     According to one aspect, in the superconducting device  1000 , the second joint has the amorphous layer including the first superconducting material and the third superconducting material  240 . According to this configuration, the thin film  110   a  of the first superconducting material and the third superconducting material  240  can be joined more firmly. 
     According to one aspect, in the superconducting device  1000 , the uneven portion  112   a  is formed on the bottom surface of the first recess  112 . The uneven portion  112   a  increases the contact area between the thin film  110   a  of the first superconducting material and the third superconducting material  240 , and thus, the joining can be further strengthened. 
     According to one aspect, in the superconducting device  1000 , the third superconducting material  240  is a material having higher spreadability than the first superconducting material. With this configuration, it is possible to perform joining with high strength even when the first recess  112  is miniaturized. 
     In the method for manufacturing the superconducting device  1000  of the second example embodiment, the superconducting integrated circuit chip  100  and the circuit board  200  are joined. The superconducting integrated circuit chip  100  has the first electrode  110  made of the first superconducting material and the first non-contact coupling circuit  120  on the surface thereof. The circuit board  200  has the second electrode  210  made of the second superconducting material and the second non-contact coupling circuit  220  on the surface thereof, and is arranged so as to face the superconducting integrated circuit chip  100 . Here, the second electrode  210  includes the flat upper surface  212  and has the protrusion  211  protruding toward the superconducting integrated circuit chip  100 . The first electrode  110  includes the flat surface  111  and the first recess  112  that is arranged inside the flat surface  111  and has an area smaller than that of the upper surface  212 . In the method for manufacturing the superconducting device  1000  according to the second example embodiment, the third superconducting material  240  connecting the upper surface  212  and the first recess  112  is arranged inside the first recess  112 . The first recesses  112  are arranged opposite to each other so as to be located inside the upper surface  212 , and the upper surface  212  and the flat surface  111  are brought into contact with each other. 
     According to another aspect, in the method for manufacturing the superconducting device  1000 , the superconducting integrated circuit chip  100  and the circuit board  200  are joined in a vacuum chamber. With this configuration, the flat surface  111  and the upper surface  212  can be joined, and the first recess  112  and the third superconducting material  240  can be joined. 
     According to one aspect, in the method for manufacturing the superconducting device  1000 , before the flat surface  111  and the upper surface  212  are brought into contact with each other, the surface of the first recess  112  and the surface of the third superconducting material  240  are activated to bring the flat surface  111  and the upper surface  212  into contact with each other. With this configuration, the joining between the flat surface  111  and the upper surface  212  and the joining between the first recess  112  and the third superconducting material  240  can be further strengthened. 
     According to one aspect, in the method for manufacturing the superconducting device  1000 , the temperature of the first recess  112  and the temperature of the third superconducting material  240  are controlled to fall within the range of 25 to 100 degree Celsius, which is the normal temperature, and the flat surface and the upper surface are brought into contact with each other. When the joining is performed at a low temperature of equal to or lower than 100 degree Celsius, a positional deviation at the time of joining due to a change in the state of the superconducting element due to heating or thermal expansion of the member is small, and accurately positioned joining can be performed. 
     According to one aspect, in the method for manufacturing the superconducting device  1000 , the arithmetic average roughness of the flat surface  111  and the arithmetic average roughness of the upper surface  212  are set to equal to or less than 1 nm. With this configuration, the flat surface  111  and the upper surface  212  can be more firmly joined. 
     The whole or part of the example embodiments disclosed above can be described as, but not limited to, the following supplementary notes. 
     (Supplementary Note 1) 
     A superconducting device including: 
     a superconducting integrated circuit chip having a first electrode made of a first superconducting material and a first non-contact coupling circuit on a surface thereof; and 
     a circuit board having a second electrode made of a second superconducting material and a second non-contact coupling circuit on a surface thereof, the circuit board being arranged in such a way to face the first non-contact coupling circuit, 
     wherein the second electrode has a protrusion having a flat upper surface and protruding toward the superconducting integrated circuit chip, 
     the first electrode includes a flat surface and a first recess arranged inside the flat surface and having an area smaller than an area of the upper surface, 
     the first recess is arranged to face the upper surface in such a way to be located inside the upper surface, 
     the upper surface and the flat surface are in contact with each other, and 
     a third superconducting material connecting the upper surface and the first recess is arranged inside the first recess. 
     (Supplementary Note 2) 
     The superconducting device according to Supplementary Note 1, 
     wherein a thin film of the first superconducting material is arranged on a surface of the first electrode. 
     (Supplementary Note 3) 
     The superconducting device according to Supplementary Note 2, 
     wherein at least one first adhesion layer is arranged below the thin film of the first superconducting material. 
     (Supplementary Note 4) 
     The superconducting device according to Supplementary Note 2 or 3, 
     wherein a second recess is arranged below the first electrode at a position corresponding to the first recess. 
     (Supplementary Note 5) 
     The superconducting device according to Supplementary Note 4, 
     wherein the second recess is provided in a base material of the superconducting integrated circuit chip. 
     (Supplementary Note 6) 
     The superconducting device according to Supplementary Note 4, 
     wherein the second recess is formed by filling a through hole provided in the base material of the superconducting integrated circuit chip with a first material different from the base material to a predetermined depth. 
     (Supplementary Note 7) 
     The superconducting device according to any one of Supplementary Notes 1 to 6, 
     wherein a surface of the second electrode is formed of a thin film of the second superconducting material. 
     (Supplementary Note 8) 
     The superconducting device according to Supplementary Note 7, 
     wherein at least one second adhesion layer is arranged below the thin film of the second superconducting material. 
     The superconducting device according to Supplementary Note 6 or 7, wherein a protruding portion made of a second material different from the second superconducting material is arranged inside a thin film of the second superconducting material in the protrusion. 
     (Supplementary Note 9) 
     The superconducting device according to Supplementary Note 8, 
     wherein the thin film of the second superconducting material has an opening inside the upper surface, and the third superconducting material is arranged at a position corresponding to the opening. 
     (Supplementary Note 10) 
     The superconducting device according to Supplementary Note 9, 
     wherein a third adhesion layer for enhancing adhesion between the second material and the third superconducting material is formed in the opening. 
     (Supplementary Note 11) 
     The superconducting device according to any one of Supplementary Notes 1 to 10, 
     wherein a fourth adhesion layer for enhancing adhesion between the third superconducting material and the upper surface is arranged between the third superconducting material and at least a part of the upper surface. 
     (Supplementary Note 12) 
     The superconducting device according to any one of Supplementary Note 1 to 11, 
     wherein a first joint for directly joining the flat surface and the upper surface is provided in at least a part of a portion where the flat surface and the upper surface are in contact with each other. 
     (Supplementary Note 13) 
     The superconducting device according to Supplementary Note 12, 
     wherein the first joint includes an amorphous layer including the first superconducting material and the second superconducting material. 
     (Supplementary Note 14) 
     The superconducting device according to any one of Supplementary Notes 1 to 13, further including a second joint for directly joining the first superconducting material and the third superconducting material located in the first recess. 
     (Supplementary Note 15) 
     The superconducting device according to Supplementary Note 14, 
     wherein the second joint has an amorphous layer including the first superconducting material and the third superconducting material. 
     (Supplementary Note 16) 
     The superconducting device according to any one of Supplementary Notes 1 to 15, 
     wherein an uneven portion is formed on a bottom surface of the first recess. 
     (Supplementary Note 17) 
     The superconducting device according to any one of Supplementary Notes 1 to 16, 
     wherein the third superconducting material is a material having higher spreadability than the first superconducting material. 
     (Supplementary Note 18) 
     A method for manufacturing a superconducting device including a superconducting integrated circuit chip having a first electrode made of a first superconducting material and a first non-contact coupling circuit on a surface thereof, and a circuit board having a second electrode made of a second superconducting material and a second non-contact coupling circuit on a surface thereof, the circuit board being arranged in such a way to face the first non-contact coupling circuit, the second electrode having a protrusion having a flat upper surface and protruding toward the superconducting integrated circuit chip, the first electrode including a flat surface and a first recess arranged inside the flat surface and having an area smaller than an area of the upper surface, the method including: 
     arranging a third superconducting material connecting the upper surface and the first recess inside the first recess; 
     arranging the first recess in such a way that the first recess faces the upper surface to be located inside the upper surface; and 
     bringing the upper surface and the flat surface into contact with each other. 
     (Supplementary Note 19) 
     The method for manufacturing a superconducting device according to Supplementary Note 18, further including joining the superconducting integrated circuit chip and the circuit board in a vacuum chamber. 
     (Supplementary Note 20) 
     The method for manufacturing a superconducting device according to Supplementary Note 19, further including: 
     activating a surface of the first recess and a surface of the third superconducting material before bringing the flat surface and the upper surface into contact with each other; 
     and 
     bringing the flat surface and the upper surface into contact with each other. 
     (Supplementary Note 21) 
     The method for manufacturing a superconducting device according to Supplementary Note 20, further including controlling a temperature of the first recess and a temperature of the third superconducting material to fall within a range of 25 to 100 degree Celsius to bring the flat surface and the upper surface into contact with each other. 
     (Supplementary Note 22) 
     The method for manufacturing a superconducting device according to any one of Supplementary Notes 17 to 21, 
     wherein an arithmetic average roughness of the flat surface and an arithmetic average roughness of the upper surface are set to equal to or less than 1 nm. 
     The previous description of embodiments is provided to enable a person skilled in the art to make and use the present invention. Moreover, various modifications to these example embodiments will be readily apparent to those skilled in the art, and the generic principles and specific examples defined herein may be applied to other embodiments without the use of inventive faculty. Therefore, the present invention is not intended to be limited to the example embodiments described herein but is to be accorded the widest scope as defined by the limitations of the claims and equivalents. 
     Further, it is noted that the inventor&#39;s intent is to retain all equivalents of the claimed invention even if the claims are amended during prosecution.