JP2516122B2 - Method of joining metal and solid electrolyte - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for joining a metal and a solid electrolyte, and is particularly suitable for application to the manufacture of thin film type sensors such as oxygen sensors manufactured by using thin film technology such as sputtering and vapor deposition. The present invention relates to a method for joining a metal and a solid electrolyte.

[0002]

2. Description of the Related Art Conventionally, when manufacturing a thin film sensor such as an oxygen sensor, a solid electrolyte such as zirconia (substrate,
The metal to be an electrode such as platinum is sputtered or vapor-deposited on the (layer) to bond the metal to the solid electrolyte. In addition, after the metal paste is applied on the solid electrolyte, firing may be performed in an atmosphere of a very high temperature to cause a reaction at the interface between the solid electrolyte and the metal to bond them.

[0003]

However, the conventional method for joining a metal and a solid electrolyte has a problem that the joining strength is generally weak. In particular, when the metal layer is formed on the solid electrolyte simply by sputtering, the contact strength is very poor, so that the electric resistance is increased and the ability as an electrode is extremely reduced. This phenomenon is prominent in the presence of thermal cycling. As a solution in this case, it may be considered that the surface of the solid electrolyte on the side to be sputtered is made rough and the resulting unevenness of the surface is utilized, but it cannot be said to be a fundamental solution.

Further, in the method of joining the solid electrolyte and the metal by causing a reaction at the interface between them by heating and firing, it is necessary to raise the atmosphere to a very high temperature, which is difficult from the viewpoint of heat resistance of other materials. In some cases, there is a cost disadvantage. Further, there is a risk that the surface of the metal layer or the solid electrolyte itself may be modified.

In view of the above, it is an object of the present invention to provide a method for joining a metal and a solid electrolyte capable of increasing the joining strength between the solid electrolyte and the metal without the need for a high temperature atmosphere. .

[0006]

In order to achieve the above object, in the method of joining a metal and a solid electrolyte according to the present invention, a zirconium-yttrium-based solid electrolyte is coated with copper.
Ru or bismuth is included, and then the solid electrolyte and the metal are joined, and the joined body is placed in a high temperature atmosphere to oxidize the copper or bismuth in the solid electrolyte in the high temperature atmosphere. The oxide layer is formed as a buffer layer at the interface between the solid electrolyte and the metal, so that the metal and the solid electrolyte can be separated from each other without being exposed to an atmosphere of a high temperature. The joint strength between the two can be increased. As a result, the electrical contact property of the metal to the solid electrolyte is also improved.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings. In this embodiment, the oxygen sensor is manufactured by applying the bonding method of the present invention.
First, as shown in FIG. 1, a porous substrate 1 having a thickness of 0.1 mm, such as alumina, zirconia, or porous crystallized glass, is prepared, and a porous metal layer serving as an electrode is formed on this surface as shown in FIG. Form 2. Here, the porous metal layer 2 having a thickness of 1 μm and containing platinum (Pt) as a main component was formed by sputtering. As shown in FIG. 3, a solid electrolyte layer (specifically, stabilized zirconia: Zr-8Y) 3 having a thickness of 2 μm was formed thereon by sputtering as well. The solid electrolyte layer 3 contains zirconium (Zr) and yttrium (Y) as main components, and contains copper (Cu) and bismuth (Bi) at 3% by weight. Further, as shown in FIG. 4, a platinum porous metal layer 4 having a thickness of 0.1 μm was formed on the solid electrolyte layer 3 by sputtering similarly to the metal layer 2 described above.

Thereafter, the porous substrate 1 on which the metal layer 2, the solid electrolyte layer 3 and the metal layer 4 are laminated in this manner is
Firing was performed by exposing it to an atmosphere of 000 ° C. for 8 hours. Then, by this firing step, zirconium such as Zr → ZrO ₂ Y → Y ₂ O ₃ Cu → CuO Bi → BiO (Bi ₂ O ₃ ) is formed near the interface of the solid electrolyte layer 3 in contact with the metal layers 2 and 4. , Yttrium, copper, and bismuth are oxidized to form the oxide layer 5 thereof.
The oxide layer 5 is present at the interface between the metal layer 2 and the solid electrolyte layer 3 and at the interface between the metal layer 4 and the solid electrolyte layer 3 and functions as a buffer layer between them. The bonding strength between the layers 2 and 4 and the solid electrolyte layer 3 is increased. That is, CuO and Bi are provided between ZrO ₂ —Y ₂ O ₃ and Pt.
O (Bi ₂ O ₃ ) is formed, and CuO, BiO (Bi
It seems that ₂ O ₃ ) and the like contribute to the buffer layer of Zr-8Y and Pt.

In the oxygen sensor thus manufactured, the solid electrolyte layer 3 is formed by the oxide layer (buffer layer) 5 as described above.
Although the bonding strength between the metal layers 2 and 4 is increased, the bonding strength can be confirmed by a peeling test performed by peeling after the adhesive tape is attached. That is,
10 samples prepared as described above are prepared, a 2 mm × 2 mm square cut is made in the metal layer 4 on the surface thereof, an adhesive tape is attached to the surface including the portion, and then the adhesive tape is peeled off. . Then, if the bonding strength is weak, the metal layer 4 in the square portion peels off together with the adhesive tape, but none of the samples made in this example peeled off. By the way, in the conventional oxygen sensor made without containing copper or bismuth in the solid electrolyte layer 3, the peeling test was similarly performed on 10 samples, and as a result, some peeling occurred in all 10 samples.

In this oxygen sensor, the oxygen concentration is measured by utilizing the ionic conductivity of the solid electrolyte layer 3. This oxygen sensor is also called a limiting current type oxygen sensor.
A negative voltage is applied to the metal layer 4, and a positive voltage is applied to the metal layer 4 to cause a current having oxygen ions as carriers to flow in the solid electrolyte layer 3 from the metal layer 2 side to the metal layer 4 side. As a result, oxygen flows upward from the lower surface of the porous substrate 1 through the substrate 1, the porous metal layer 2, the solid electrolyte layer 3 and the porous metal layer 4. The amount of oxygen passing through the porous substrate 1 is limited to a constant amount by the air resistance determined by the porosity and the pore diameter of the porous substrate 1 itself. Therefore, the metal layers 4, 2
The current value flowing during that time converges to a constant value corresponding to the oxygen concentration of the inflowing air. This current characteristic is called the limiting current characteristic. When the lower surface side of the porous substrate 1 is used as an oxygen concentration measurement atmosphere, the oxygen concentration in the atmosphere can be measured.

As described above, the solid electrolyte layer 3 and the metal layer 2,
4 has good bonding strength, the electric contact between the solid electrolyte layer 3 and the metal layers 2 and 4 has also been good, and the limiting current characteristics when operating as an oxygen sensor have been good. That is, the limiting current characteristics of the limiting current type oxygen sensor manufactured in this example are as shown in FIG.

Although both copper and bismuth are added to the solid electrolyte layer 3 in the above, the same effect can be obtained by including only one of copper and bismuth, for example, about 3% by weight. Can be obtained. Although sputtering is adopted in the above, the metal layers 2 and 4 and the solid electrolyte layer 3 can also be formed by another dry process such as vapor deposition.

[0013]

As described in the above embodiments, according to the method for joining a metal and a solid electrolyte of the present invention, several percent of copper and / or bismuth is added to the solid electrolyte, followed by firing in the subsequent step. It is possible to greatly improve the bonding strength at the interface between the solid electrolyte and the metal layer by a simple process such as oxidation. By improving the bonding strength, mechanical reliability is improved, and problems such as peeling can be solved especially when a heat cycle is repeated. By improving the bonding strength at the interface between the solid electrolyte and the metal layer, the electrical contact property at the interface is improved and the electrical resistance is lowered, and very good electrical characteristics can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing a first manufacturing step in a method for joining a metal and a solid electrolyte according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a second manufacturing process in the example.

FIG. 3 is a sectional view showing a third manufacturing step in the same example.

FIG. 4 is a sectional view showing a fourth manufacturing process in the embodiment.

FIG. 5 is a sectional view showing a fifth manufacturing step in the same example.

FIG. 6 is a graph showing current characteristics of the oxygen sensor manufactured in the same example.

[Explanation of symbols]

 1 Porous Substrate 2, 4 Porous Metal Layer 3 Solid Electrolyte Layer 5 Oxide Layer

 ─────────────────────────────────────────────────── ─── Continued front page (72) Inventor Issei Ishibashi 1-5-1, Kiba, Koto-ku, Tokyo Within Fujikura Electric Wire Co., Ltd. (72) Yoshinori Kato 1-1-5, Kiba, Koto-ku, Tokyo Fujikura Electric Wire Co., Ltd. (56) Reference JP-A-3-140860 (JP, A) JP-A-56-100353 (JP, A) JP-A-49-60310 (JP, A) JP-A-2-252682 (JP, A)

Claims (2)

(57) [Claims] 1. A step of joining a metal and a solid electrolyte containing copper, and a step of placing a joined body of the metal and the solid electrolyte in a high temperature atmosphere to oxidize the copper in the solid electrolyte. A method for joining a metal and a solid electrolyte, comprising: 2. A step of joining a metal and a solid electrolyte containing bismuth, and a step of placing the joined body of the metal and the solid electrolyte in a high temperature atmosphere to oxidize the bismuth in the solid electrolyte. A method for joining a metal and a solid electrolyte, comprising: