JP4732390B2 - Manufacturing method of high-temperature superconducting device - Google Patents

Description

  The present invention relates to a method for manufacturing a high-temperature superconducting device having an electrode that is well adhered to a superconducting film.

Usually, a high-temperature superconducting device has an MgO substrate (room temperature to 77 [K], thermal shrinkage ratio 1.3 × 10 ⁻³ ) or a LaAlO ₃ substrate (room temperature to 77 [K], thermal shrinkage rate). 1.0 × 10 ⁻³ ) or the like.

Since these substrates have a small heat shrinkage rate, invar (heat shrinkage rate: 0.5 to 1.0 × 10 ⁻³ ), which is a material having a similar heat shrinkage rate, is often used for a package that accommodates a device. However, since Invar is an alloy of iron and nickel, its mass is large and the heat load on the refrigerator is also large.

  When the cooling temperature is about 50 [K] to 80 [K], the power consumption of the refrigerator and the cooling capacity are almost proportional, and when a device with a large heat load is mounted on the refrigerator, If the power consumption must be increased and the refrigeration capacity cannot keep up, the cooling temperature rises, becomes a critical state, loses the superconducting state, and does not function as a device.

  For this reason, it is important to construct a high-temperature superconducting device using a package made of a material with a small thermal load. Therefore, aluminum, aluminum alloy, magnesium, magnesium alloy, etc. are used as package materials with a small mass. Can be considered.

However, the material has a large thermal shrinkage between room temperature and 77 [K], for example, about 4 × 10 ^{−3 to} 5 × 10 ⁻³ for aluminum or aluminum alloy, and a high temperature superconducting film is formed. The stress caused by the difference in thermal shrinkage between the MgO substrate and the like is applied to the joint between the device electrode and the coaxial connector, and the electrode is peeled off due to the thermal shrinkage between the substrate and the electrode. Since the general connection is lost, the adhesion between the device electrode and the substrate or the high-temperature superconducting film is important.

  Usually, the device electrode used for bonding is formed on a high-temperature superconducting film. In this case, Ag and Au are known as electrode materials with little deterioration of superconducting characteristics. Alternatively, when the electrode is formed by applying a sputtering method or the like, the adhesion between the electrode and the substrate or the superconducting film is poor.

  In addition, in order to ensure the connection between the electrode and the high-temperature superconducting film, when connecting by soldering, a so-called solder erosion phenomenon occurs in which the electrode material diffuses into the solder.

  To counter the solder erosion phenomenon, it may be possible to increase the film thickness of the electrode, but the amount of electrode material diffusion in the solder increases, changing the mechanical properties of the solder itself and destroying the joint. May cause this.

  FIGS. 6A and 6B are explanatory views of main parts for explaining electrode peeling and solder erosion in a high-temperature superconducting device. FIG. 6A shows a high-temperature superconducting device at room temperature, and FIG. (C) shows the solder erosion phenomenon.

  In the figure, 1 is a substrate, 2 is a high-temperature superconducting film, 3 is an electrode made of Au or Ag, 4 is solder, and 5 is an electrode material taken into the solder.

  As seen in (A), even if the electrode 3 is well connected to the high temperature superconducting film 2 at room temperature, as seen in (B), the high temperature superconducting film 2 and the electrode are used at the liquid nitrogen temperature. Peeling occurs due to the difference in thermal shrinkage from 3.

  As seen in (C), when the solder 4 is used to connect the high temperature superconducting film 2 and the electrode 3, the electrode 3 diffuses into the solder 4 as the electrode material 5, and the superconducting junction is destroyed. End up.

  By the way, a technique in which an electrically conductive oxide film is formed between a high-temperature superconducting film and an electrode and Au, Ag, Pd, Pt or the like is used as an electrode is known (see, for example, Patent Document 1). In the present invention, it is similar in that a film such as an electrically conductive oxide film or a dielectric film is interposed between the high-temperature superconducting film and the electrode. Therefore, it is necessary to clarify the difference here. It seems beneficial.

In the known technology, when a coaxial connector is connected to an electrode with solder, for example, when Au or Ag is used, peeling of the electrode or solder erosion occurs, and when Pd or Pt is used, soldering is performed. Poor bonding occurs due to poor bonding.
Japanese Patent Laid-Open No. 7-2111950

  In the present invention, when the high-temperature superconducting film and the electrode are connected, the connection of the high-temperature superconducting device is prevented so that the connection is not peeled off at room temperature and low temperature, and the solder is not eroded. Try to improve the sex.

  In the method for manufacturing a high-temperature superconducting device according to the present invention, a step of forming a high-temperature superconducting film on a substrate, a step of forming a line pattern of the high-temperature superconducting film, and an end of the line pattern A step of forming an electrode on the electrode, a step of forming a solder on the electrode by heat treatment at a first temperature, a coaxial connector penetrating the package after the substrate is accommodated in the package, and the electrode And the step of heating the solder at a second temperature higher than the first temperature.

  By adopting the above means, the connection between the high temperature superconducting film and the electrode is not peeled off at room temperature and low temperature, and the soldering of the electrode material does not occur. Improve sexiness.

  In addition, since the prepared electrode has good adhesion and is less likely to be eroded by solder, there are a wide range of options for connecting the electrode and the coaxial connector, not to mention solder connection, wire bonding method. TAB (tape automated bonding) method can be introduced and the adhesion between the superconducting film and the electrode is good, so that the superconducting device has a large thermal shrinkage difference like aluminum alloy or magnesium alloy. Even if it is mounted on a package, it can be soldered.

  Furthermore, by interposing a dielectric titanium compound at the interface between the high-temperature superconducting film and the electrode, the adhesion between the two can be improved, and as the electrode, a material with low diffusivity such as Pd, Pt, Ni is formed. On the uppermost layer, a material such as Ag or Au having excellent solder bonding properties can be deposited to eliminate all the problems of the conventional techniques.

  Furthermore, the contact resistance at room temperature with direct current is 200 [Ω] to 300 [Ω] or more with an electrode area of 0.5 [mm] □, but at 2 [GHz], the coaxial connector The transmission loss at an operating temperature of 70 [K] including the junction between the electrode and the electrode can be about 0.1 [dB].

  1 and 2 are side sectional views of the main part of the high-temperature superconducting device for explaining the first embodiment of the present invention, and the manufacturing process thereof will be described below. In the figure, the left half of the high temperature superconducting device is shown, and the right half is omitted.

Refer to FIG. 1 (A) 1- (1)
High temperature superconductivity consisting of YBCO (YBa ₂ Cu ₃ O _7-x ) having a thickness of 100 [nm] to 2000 [nm] on both front and back surfaces of the substrate 11 made of single crystal MgO by applying the laser deposition method. Films 12A and 12B are formed.

As the film forming technique used here, it is possible to adopt a sputtering method in addition to the laser vapor deposition method. Also, as a high-temperature superconducting material, instead of YBCO, RBCO (R element is Y, La, Nd, Any of Sm, Eu, Gd, Dy, Ho, Er, Yb, R-Ba-Cu-O system, BSCCO (Bi-Sr-Ca-Cu-O system), PBSCCO (Pb-Bi-Sr-Ca system) -cu-O _{system), CBCCO (CuBa p Ca q} Cu r O x, 1. 5 <p <2.5,2.5 <Ca <3.5,3.5 <r <4.5) , etc. When these are used, the same effect as YBCO can be obtained.

1- (2)
The high temperature superconducting film 12A is etched into a line pattern by applying a resist process in lithography technology and a wet etching method in which an etchant is an aqueous solution diluted with phosphoric acid or hydrochloric acid. When etching a high temperature superconducting film, a dry etching method using Ar ions as an etching gas can be applied.

1- (3)
A metal mask having openings is positioned at the electrode formation scheduled portions at both ends of the line pattern, and milling using Ar ions is performed to improve the surface of the high-temperature superconducting film 12A.

    The ion milling conditions are, for example, an ion acceleration voltage of 200 [V], a beam current of 5 [mA], and a time of 10 [minutes], and this modification generates roughness on the surface of the high-temperature superconducting film 12A. .

1- (4)
By aligning metal masks with openings in the electrode formation planned portions at both ends of the high-temperature superconducting film 12A and applying the vacuum evaporation method, the substrate 11 side is contacted with the high-temperature superconducting film 12A. In this order, a titanium film 13A having a thickness of 1000 [パ ラ ジ ウ ム], a palladium film 13B having a thickness of 3000 [Å], and a silver film 13C having a thickness of 2000 [Å] are laminated to form an electrode 13 and high-temperature superconductivity. The same metal layer is deposited on the entire surface on the film 12B side to form the ground electrode 14.

See Fig. 1 (B) 1- (5)
Preliminary solder is formed on a hot plate at a temperature of 200 ° C. using an indium solder ball having a diameter of 100 μm and a melting point of 156 ° C. for the electrode 13, and then an aluminum alloy package (not shown here, FIG. 2). Set to Reference).

    By applying a heat treatment of 200 [° C.] to apply the preliminary solder described above, the titanium film 13A and the high-temperature superconducting film 12A react with each other, and a titanium compound 20 such as barium titanate is generated. Thus, the adhesion between the electrode 13 and the high-temperature superconducting film 12A is dramatically improved.

See Fig. 2- (1)
After the substrate 11 processed as described above is set in the aluminum alloy package 15, the tip of the central conductor 16 made of Au / Be-Cu in the coaxial connector is dip coated with indium solder, which is also an aluminum alloy. Set in the package 15. Reference numeral 17 denotes an insulator showing a required impedance between the center conductor 16 and the aluminum alloy package 15.

2- (2)
The aluminum alloy package 15 is placed on a hot plate having a temperature of 100 [° C.] and preheated. The soldering iron heated to a temperature of 350 [° C.] is applied to the connecting portion to perform main heating, and depends on indium solder. Thus, the electrode 13 of the superconducting device and the central conductor 16 of the coaxial connector are connected. The aluminum alloy package can be replaced with a magnesium alloy package. The magnesium alloy has a specific gravity smaller than that of an aluminum-based material (pure magnesium: 1.7 [Mg / m ³ ], pure aluminum: 2. 7 [Mg / m ³ ]), the heat load on the refrigerator can be reduced.

  The transmission characteristics in the connection body between the electrode 13 and the central conductor 16 obtained as described above were measured at 70 [K]. No change in transmission characteristics was observed even when 70 [K] and room temperature were repeated.

  In order to connect the electrode 13 and the central conductor 16, pure indium solder is supplied to both, and when mounting on the package, the indium on the electrode 13 and the indium on the central conductor 16 are brought into contact with each other. It can easily be electrically connected by indium, etc., and its electrical characteristics can be set to a value that does not change compared to the case of fusion bonding. realizable.

  FIG. 3 is a cutaway side view of the main part of the high-temperature superconducting device for explaining the second embodiment of the present invention. The same reference numerals as those used in FIGS. 1 and 2 represent the same or the same parts. It shall have meaning.

  The difference between the second embodiment and the first embodiment described above is that when the center conductor 16 of the coaxial connector is connected to the electrode 13, the tip of the center conductor 16 is bent and vertically stands on the electrode 13. With such a configuration, the stress concentration at the connection portion can be absorbed by the spring property of the central conductor 16.

  FIG. 4 is a cutaway side view of the main part of the high-temperature superconducting device for explaining the third embodiment of the present invention. The symbols used in FIGS. 1 to 3 represent the same parts or have the same meaning.

  The third embodiment is different from the other embodiments in that the electrode 13 is made of a titanium film having a thickness of 100 nm, a palladium film having a thickness of 300 nm, and a gold film having a thickness of 200 nm. The electrode 13 and the central conductor 16 of the coaxial connector are connected using an aluminum tape 18 having a width of 250 [μm] and a thickness of 30 [μm] and a purity of 4N.

  For the connection, ultrasonic bonding using conditions of a load of 100 [gforce], an output of 1.4 [W], and a time of 100 [msec] is applied and performed at room temperature.

  When the connection portion was evaluated by pulling the aluminum tape 18 after the connection, the aluminum tape 18 was broken at the portion, and no peeling occurred at the bonding portion or the connection portion between the electrode 13 and the superconductive film 12A. It was confirmed that a good connection was made.

  FIG. 5 is a cutaway side view of the main part of the high temperature superconducting device for explaining the fourth embodiment of the present invention. The symbols used in FIGS. 1 to 4 represent the same parts or have the same meaning.

  The fourth embodiment is different from the third embodiment in that a gold wire 19 having a diameter of 25 [μm] is used instead of the aluminum tape 18 in which the electrode 13 and the central conductor 16 are connected in the third embodiment. In the same manner as in the third embodiment, ultrasonic bonding is performed on both the electrode 13 and the central conductor 16.

  When the connecting portion was evaluated by pulling the gold wire 19 after the connection, breakage occurred at the portion of the gold wire 19, and no peeling occurred at the bonding portion or the connecting portion between the electrode 13 and the superconductive film 12A. I was able to confirm that the connection was made.

  Since the present invention can be implemented in many forms including the above-described embodiment, it will be exemplified below as an additional note.

(Appendix 1)
Forming a high temperature superconducting film on the substrate;
Forming a line pattern of the high temperature superconducting film;
Stacking electrodes on the end of the line pattern;
Forming a solder on the electrode by heat treatment at a first temperature;
And a step of heating the solder at a second temperature higher than the first temperature to connect the coaxial connector penetrating the package and the electrode after the substrate is accommodated in the package. A method for manufacturing a high-temperature superconducting device.

(Appendix 2)
A titanium compound generated by a heating reaction between a constituent material of the high temperature superconducting film and titanium constituting a part of the electrode is interposed at an interface between the high temperature superconducting film and the electrode. (Appendix 1) A method for producing a high-temperature superconducting device according to (1).

(Appendix 3)
The method for producing a high-temperature superconducting device according to (Appendix 2), wherein the titanium compound is formed during the heat treatment at the first temperature.

(Appendix 4)
The material of the high-temperature superconducting film is RBCO (R element is Y, La, Nd, Sm, Eu, Gd, Dy, Ho, Er, or Yb, R-Ba-Cu-O system), BSCCO (Bi- Sr-Ca-Cu-O system), PBSCCO (Pb-Bi- Sr-Ca-Cu-O _{system), CBCCO (CuBa p Ca q} Cu r O x, 1.5 <p <2.5,2.5 <Ca <3.5, 3.5 <r <4.5) The method for producing a high-temperature superconducting device according to any one of (Appendix 1) to (Appendix 3).

(Appendix 5)
The surface of both ends of the high-temperature superconducting film having the line pattern is modified by any one of an ion milling method, a reverse sputtering method, and a reactive ion etching method (Appendix 1) to (Appendix 4) The manufacturing method of the high-temperature superconducting device any one of.

(Appendix 6)
The high-temperature superconductivity according to any one of (Appendix 1) to (Appendix 5), wherein the solder is any one of indium-based metals such as pure indium, indium-tin, indium-lead, and indium-silver. Device manufacturing method.

(Appendix 7)
The method for producing a high-temperature superconducting device according to any one of (Appendix 1) to (Appendix 6), wherein the surface of the central conductor of the coaxial connector is coated with indium.

It is a principal part cutting side view of the high temperature superconducting device for demonstrating Embodiment 1 of this invention. It is a principal part cutting side view of the high temperature superconducting device for demonstrating Embodiment 1 of this invention. It is a principal part cutting side view of the high temperature superconducting device for demonstrating Embodiment 2 of this invention. It is a principal part cutting side view of the high temperature superconducting device for demonstrating Embodiment 3 of this invention. It is a principal part cutting side view of the high-temperature superconducting device for demonstrating Embodiment 4 of this invention. It is principal part explanatory drawing explaining peeling of an electrode and solder erosion in a high temperature superconducting device.

Explanation of symbols

11 Substrate 12A, 12B High-temperature superconducting film 13 Electrode 13A Titanium film 13B Palladium film 13C Silver film 14 Ground electrode 15 Aluminum alloy package 16 Central conductor 17 Insulator 18 Aluminum tape 19 Gold wire 20 Titanium compound

Claims (4)

Forming a superconducting film on a substrate,
Forming a line pattern of superconducting film,
A step of laminating an electrode containing titanium in a layer in contact with the line pattern at an end of the line pattern ;
Forming a titanium compound between the superconducting film and the electrode by forming a solder on the electrode by performing a heat treatment at a first temperature ;
After receiving the substrate in the package, have a heating the solder to connect the coaxial connector and the electrode penetrating the package at a second temperature higher than said first temperature,
Ultra material conductive film manufacturing method of the superconducting devices that wherein <br/> be YBCO. The electrode in which the layer in contact with the line pattern contains titanium is:
The electrode layer includes at least one material of Pd, Pt, and Ni;
The top layer is either Ag or Au
The method of manufacturing a superconducting device according to claim 1. Ion milling the ends surface of the superconducting film of the line pattern, the reverse sputtering, according to claim 1 or claim 2, wherein the modified with any of the methods of the reactive ion etching method A method of manufacturing a superconducting device. Claim 1 any one method of manufacturing a superconducting device according to claim 3, characterized by comprising coating the indium on the surface of the center conductor of the coaxial connector.

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