JPH02109285A - Installation of electrode onto oxide crystal - Google Patents

Abstract

PURPOSE:To enable installation of an electrode without generation of cracking, distortion and the like by forming thin films on the surfaces of oxide crystal and insulation substrate, melting a connection material made of a metal or alloy having a specified melting point, sticking the connection material so as to be in contact with both the thin films, and hardening the same. CONSTITUTION:A metal or alloy thin films 2, 4 are formed respectively on the surfaces of oxide crystal 1 and insulation substrate 3, wherein the film 2 is made not to easily react to oxygen in the crystal when it is heated. A section between the film 4 and the film 2 are electrically connected by melting and hardening a connection material made of a metal or alloy having a melting poing of 450 deg.C. Then an electrode material 5 is connected and fixed to the film 4 and taken out thereafter. It is thus possible to install the electrode with electrical and mechanical stability and to install the electrode onto minute crystal.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method of attaching an electrode member to an oxide crystal,
In particular, it enables a stable electrical connection between the oxide crystal and the electrode member from room temperature to lower temperatures, and improves the handling of the oxide crystal after the electrode is attached. The present invention relates to a method for attaching an electrode to an oxide crystal.

[Prior Art] Conventionally, as a method of attaching a linear or plate-shaped electrode member to an oxide and electrically connecting the two, Pb-3n
There is a method for joining using a solder such as a ceramic solder or an In solder in which a small amount of Zn, Ti, Sb, Aj', Si, or Cu is added to an alloy. however,
Ceramics solder and In solder have a strong bonding force for large sintered bodies, but have a drawback in that they have a weak bonding force for objects with smooth surfaces such as single crystals. In particular, there is a problem in that the bond is likely to peel off at low temperatures, and soldered oxide crystals cannot be used at low temperatures. Another disadvantage is that the method of joining by soldering cannot be applied to crystals as small as splayed particles.

Therefore, in order to attach electrodes to minute oxide crystals,
A method is adopted in which a metal thin film such as Au is formed on an oxide crystal and then electrode wires are attached to this thin film by bonding.

[Problems to be Solved by the Invention] However, in the method of bonding an electrode wire to a thin film on an oxide crystal, defects such as cracks and distortions occur in the oxide single crystal due to stress during bonding. There is a problem.

In recent years, the development of oxide superconductors has progressed and various useful materials have been proposed, but as mentioned above, there is no way to stably and reliably attach electrodes to these oxide superconductors at low temperatures. has not yet been established, and this point is an obstacle to further progress in the development and research of oxide superconductors.

The present invention was made in view of such problems, and
To provide a method for attaching an electrode to an oxide crystal, which allows an electrode to be attached reliably and stably to a minute oxide single crystal without causing cracks, distortion, etc., regardless of its shape. With the goal.

[Means for Solving the Problems] The method for attaching an electrode to an oxide crystal according to the present invention includes a first step of forming a thin film of metal or alloy on the surface of an insulating substrate and an oxide crystal, and a second step of electrically connecting the thin film on the substrate and the thin film on the oxide crystal by melting and solidifying a connecting material made of a metal or alloy with a melting point of 450° C. or less; and the insulating substrate. The method is characterized by comprising a third step of connecting and fixing an electrode member to the upper thin film and taking out the electrode to the outside.

[Function] In the present invention, first, a thin film is formed on the surface of the oxide crystal and the surface of the insulating substrate, a connecting material made of a metal or alloy with a melting point of 450°C or less is melted, and this molten connecting material is bonded to both the surfaces of the oxide crystal and the insulating substrate. It is deposited in contact with the thin film and solidified. Thereby, the thin film on the oxide crystal and the thin film on the insulating substrate are electrically connected without applying any physical external force to the crystal.

In addition, for thin films on insulating substrates, even if electrode members such as lead wires are connected and fixed by bonding etc., there will be no adverse effect on the oxide crystal. The electrode members can be firmly joined by means such as bonding connection. Therefore, after the electrode member is attached, it will not peel off.

In addition, as mentioned above, electrode members such as electrode wires or electrode plates,
Since it is not bonded directly to the oxide crystal but to a thin film provided on an insulating substrate, structurally, physical and mechanical external forces are not applied to the crystal itself, and these characteristics are stable. This facilitates handling after electrode attachment.

[Example] Next, an example of the present invention will be described with reference to the accompanying drawings.

FIG. 1 is a sectional view showing the method of this embodiment, and FIG. 2 is a perspective view of the same. Note that this embodiment is an example in which one terminal is attached to the oxide crystal 1.

East-1-■ Shield.

First, as shown in FIGS. 1 and 2, metal or alloy a) thin films 2.
form 4. An oxide crystal 1 is placed in the center of the insulating substrate 3.
are arranged, and four thin films 4 are formed at the four corners of the insulating substrate 3 so as not to contact the oxide crystal 1. Further, a thin film 2 is similarly formed at one corner of the oxide crystal. This thin film 2.4 is heated when melting the low-melting point connecting material in Step 2]2, which will be described later, so it needs to be resistant to oxidation even at high temperatures.

In particular, the thin film 2 formed on the surface of the oxide crystal 1 is preferably one that does not easily react with oxygen in the oxide crystal even when heated. Such thin film materials include Au and Ag.

Further, the thin R4 formed on the insulating substrate 3 is first formed by forming a thin MK4a of Cr on the substrate 3, and then forming a MK4 of Au or A,g on the CI film 4a. 2 formed b
It is preferable to have a layered structure. The reason why this Cr#4a is used as a base is to improve the adhesion with an oxide substrate that is normally used as an insulating substrate. Note that as the insulating substrate 3, it is preferable to use a heat-resistant substrate such as a glass plate.

Note that, prior to the second step, the oxide crystal 1 is placed on an insulating substrate 3.
It is preferable to fix it on top. Thereby, the electrode formation position on the oxide crystal can be controlled with high precision. Therefore, when it is necessary to control the electrode position with high precision as in the case of micro oxide crystals, the oxide crystal 1
It is an extremely effective means to fix the insulating substrate 3 to the insulating substrate 3.

As a method of fixing this oxide crystal 1 to the insulating substrate 3, in order to avoid applying external force to the oxide crystal 1,
It is preferable to fix with adhesive 8. The adhesive 8 is an epoxy that is electrically insulating and has heat resistance that undergoes thermal deterioration in a short time near the melting point (450°C) of the low-melting point connecting material and does not lose electrical insulation and adhesive strength. It is preferable to use resin, melanin resin or phenol resin.

1st 2111- The thin film 4 on the insulating substrate 3 and the thin film 2 on the oxide crystal 1 are electrically connected by melting and solidifying the connecting material 6 made of a metal or alloy with a melting point of 450° C. or less. . That is, the connecting material 6 is melted and attached to both thin films 2.4 so as to be in contact therewith, and then solidified. As a result, both thin JII2
．． 4 are electrically connected without applying any physical external force to the oxide crystal 1.

The connecting material 6 to be melted and solidified on the thin film has a melting point of 450.
The reason why we limited it to below 450°C is because of its melting.
If heated to a high temperature exceeding 450°C, the crystal 1 will also be heated to such a temperature, and there is a risk that the quality of the crystal 1 will change. There are very few materials that are excellent in both electrical conductivity and wettability with the underlying thin film.

In this case, when melting the low melting point connecting material 6, in addition to the connecting material 6, the entire insulating substrate 3 and the crystal J are heated, or at least the parts of the insulating substrate 3 and the crystal 1 to be connected are heated. It is also preferable to heat it.

If only the low-melting point connecting material is heated with a soldering iron or the like, the low-melting point connecting material, which usually has poor wettability, cannot be sufficiently diffused into the metal or alloy thin film. 4 becomes insufficiently bonded. On the other hand,
By heating at least the contact portions of the crystal 1 and the insulating substrate 3 with the connecting material, regardless of the wettability of the connecting material 6,
Bonding can be made between the thin M2 on the crystal and the thin film 4 on the insulating substrate 3 and the low melting point connecting material 6. In addition, by heating the contact portion of the crystal and the insulating substrate with the connecting material 6, the thin film 2 on the crystal and the low melting point connecting material 6 can be bonded, and the thin M4 on the insulating substrate and the low melting point connecting material can be bonded. 6 can be joined at the same time. Therefore, it is possible to avoid a situation in which the melted low-melting point connecting material flows to either one of the bonding sections due to the difference in wettability between the two bonding sections or the surface tension of the low-melting point bonding material.

Specifically, the low melting point connecting material 6 includes In. This Iri has a low melting point of 159°C, and after melting, an oxide film is formed on its surface to enclose the melt inside. Therefore, even if there is a difference in the wettability between the thin film 2 on the crystal and the thin film 4 on the insulating substrate, it will not flow suddenly in one direction. . Therefore,
The In melt gradually and uniformly contacts and joins both the thin film 2 of the crystal 2 and the thin film 4 of the insulating substrate 2. For this reason, it is preferable to use In as the connecting material.

Third - Step - An electrode member 5 such as a lead wire is connected and fixed to the second thin film 4 of the insulating substrate, and the electrode is taken out to the outside. This may be done, for example, by fixing the wire to the thin film 4 on the insulating substrate by soldering or by bonding. That is, in the present invention, since the electrode member 5 is not directly connected to the oxide crystal 1 but is connected on the insulating substrate 3, the electrode member 5 such as a lead wire or an electrode plate is not subjected to mechanical stress. It is possible to connect and fix the thin film 4 of the insulating substrate by freely selecting any means that can provide strong bonding without considering the inconvenience caused by the application of . Therefore, peeling of the electrode members 5 such as lead wires can be effectively prevented.

Note that the oxide crystal to which the electrode wire can be attached according to the present invention is not limited by its crystal composition or surface properties, and the present invention can be applied to various oxide crystals.

[Example] Examples of the present invention will be described below in comparison with comparative examples thereof.

Fire 1 Ru - Bi, Sr, Ca, Cu and 0 respectively in the original - r - ratio of Bi
:Sr:Ca:Cu:O=l:o,8:0.5:
0.9: Oxide crystal containing only 3.5 (size 5
■X 411111X 1+n+n), 4-terminal electrode wires were attached in each step shown below. Then, the inter-terminal resistance was measured and the temperature vs. resistance characteristic was measured using a DC four-terminal method. The reason why the oxide crystal with the above composition was selected is that this crystal is a superconductor that undergoes a superconducting transition at about 80°C, and its resistance versus temperature characteristics are known. This is because it can be easily evaluated. Electrode attachment 4-) was carried out in the following steps.

■As shown in Figure 2, A thin film 2 is formed on the surface of crystal 1.
Deposit the LL film. This Au film is divided into four parts, which are electrically isolated so as not to contact each other.

■Glass plate as insulating substrate 3 (width and length is 101 mm)
1I1. A Crria film having a thickness of 0.5n+m) divided into two and four parts and arranged so as not to be in electrical contact with each other is deposited, and an Au film 4b divided into four parts is further deposited on each Cr film 4a6. An oxide crystal 1 is adhesively fixed with an epoxy adhesive 8 on a region of the glass plate (-1) where the Cr film and the A and U films are not formed, with the side on which the Au thin film 2 is formed facing upward.

■Au film 2 on the crystal and Au film 4b on the glass substrate 3
A solid In is placed 16 so as to bridge the gap.

(2) Heat the glass substrate and the entire crystal to 200°C to melt In.

■ Cool to solidify In.

(2) A lead wire as an electrode member 5 is joined to the Au film 4b on the glass substrate 3 by solder.

This lead wire was connected to an external measuring device to measure the resistance between the terminals, and the temperature vs. resistance characteristics were also measured by a direct current four terminal method.

K1 Example 1 An Ag film was formed in place of the A LJ film on the oxide crystal in Example 1, and a Cr film and an Ag film were formed in place of the Cr film and Au film on the glass plate, and the rest was as in Example 1. The electrodes were attached in the same manner as above, and the inter-terminal resistance and temperature versus resistance characteristics were similarly measured using the DC 4-terminal method.

The electrodes were attached (2) in the same manner as in Example 1, except that the resistance was reduced, and the inter-terminal resistance and temperature versus resistance characteristics were measured using the DC 4-terminal method.

Electrodes were attached in the same manner as in Example 2, except that the size of the oxide crystal was reduced to 2 x 2 x 042, and the inter-terminal resistance and temperature vs. resistance characteristics were measured using the DC 4-terminal method. .

Example 4 - 1, 3 - Using the ultrasonic soldering method, ceramic solder (Comparative Example 1) and Irr solder (Comparative Example 2) were applied to the crystal surface of the same size as in Example 1. Attach a lead wire to the crystal surface and perform a similar measurement.

Ceramics solder (Comparative example 3) and In solder (Comparative example 4) were applied to the crystal surface of the same size as in Example 3.
A similar measurement was carried out by attaching a lead wire to the crystal surface using the ultrasonic soldering method.

Le 1” [1 After depositing Au on the crystal surface, an A with a diameter of 0.25 mm was
Similar measurements were performed after ball-bonding the U-wire and attaching a four-terminal electrode. The crystal size is as in Example 1,
This is the same as case 2.

The measurement results for each of the above examples and comparative examples are shown in
Shown in the table.

In Examples 1 to 4 of Table 1, normal characteristics were measured, and I
It was possible to measure temperatures down to OK.

On the other hand, in Comparative Example 1-12, although normal characteristics could be measured, the connection state of the electrodes was maintained only to about 80%.6 Also, the interfacial area of the electrodes was Because of the small resistance between the terminals, the contact resistance at the electrode interface accounts for most of the resistance between the terminals. When used at extremely low temperatures, the heat generated from this contact resistance cannot be ignored, so the large contact resistance as described above is extremely inconvenient. In contrast, in each Example, Comparative Example 1.
2, the resistance between the 'ζ terminals is small, and the method of the present invention is extremely effective for attaching electrodes used at extremely low temperatures.

Furthermore, in Comparative Examples 3 and 4, since the electrodes were attached to minute crystals, the solder did not bond to the oxide crystal surface with the amount of heat required to solder a portion of the crystal.

On the other hand, if the ultrasonic soldering iron is heated sufficiently to create enough heat at the interface between the solder and the crystal to achieve sufficient solder wettability, the solder will adhere to the entire surface of the crystal, which is necessary for measurement. (It is impossible to accommodate the multiple terminals of The pressure during bonding may cause cracks in the oxide crystal,
Subsequent measurement and evaluation was not possible.

[Effects of the Invention] As explained above, according to the present invention, it is possible to house an electrode in a mechanically and electrically stable manner without applying any external force to the crystal. As a result, not only can electrodes be attached to minute crystals, but they can also be easily handled after being attached. Further, an excellent effect is obtained in that stable connection is ensured even at extremely low temperatures.

Therefore, the present invention can provide extremely useful technology for the development and research of superconducting oxides, and will make a significant contribution to the progress of superconducting technology.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, and FIG. 2 is a perspective view thereof. 1: Oxide crystal, 2, 4: Thin film, 3: Insulating substrate, 5;
Electrode member, 6: Low melting point connecting material, 8. glue

Claims (7)

[Claims] (1) A first step of forming a thin film of metal or alloy on the surfaces of an insulating substrate and an oxide crystal, and a melting point of 450° C. between the thin film on the insulating substrate and the thin film on the oxide crystal. a second step of melting and solidifying a connecting material made of the following metal or alloy for electrical connection; and a third step of connecting and fixing the electrode member to the thin film on the insulating substrate and taking out the electrode to the outside. 1. A method for attaching an electrode to an oxide crystal, comprising: (2) The method for attaching an electrode to an oxide crystal according to claim 1, wherein in the second step, the connecting material is heated and melted together with the insulating substrate and the entire crystal. (3) The method for attaching an electrode to an oxide crystal according to claim 1, wherein in the second step, the connecting material is heated and melted together with the insulating substrate and the connected portion of the crystal. . (4) The method for attaching an electrode to an oxide crystal according to any one of claims 1 to 3, wherein the connecting material is In. (5) The method for attaching an electrode to an oxide crystal according to any one of claims 1 to 4, wherein the thin film on the surface of the oxide crystal is made of Au or Ag. (6) The thin film on the surface of the insulating substrate includes a Cr film formed on the surface of the insulating substrate and an A film formed on the Cr film.
6. The method for attaching an electrode to an oxide crystal according to any one of claims 1 to 5, wherein the electrode has a two-layer structure with a U film or an Ag film. (7) At least before the second step, the oxide crystal is adhesively fixed to the insulating substrate with a resin selected from the group consisting of epoxy resin, melanin resin, and phenol resin. A method for attaching an electrode to an oxide crystal according to any one of claims 1 to 6.