JP2002168827A - Detecting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem that, when metal members are brazed to surfaces of terminal parts formed at a solid electrolyte forming a detecting element, brazed parts in the terminal parts are broken down in the tensile test in the vertical direction of the metal members. SOLUTION: The detecting element 1 is provided with a detection part which is composed by forming a pair of electrodes 3, 10 on both main faces of a zirconia solid electrolyte substrate and which detects an environmental state, the terminal parts 4a, 4b which are formed on the surface of the substrate and which are electrically connected to the electrodes 3, 10 and the metal members 13a, 13b which are brazed to the terminal parts 4a, 4b by a brazing material. The terminal parts 4a, 4b are composed of composite conductor layers which are composed of metal phases and metal oxide phases, and the maximum distance between the adjacent metal phases in a reflection electron micrograph on the surfaces of the composite conductor layers is controlled to 10 μm or less.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a detection element having a basic structure including a zirconia solid electrolyte and a detection section including a pair of electrodes, a terminal section, and a metal member brazed to the terminal section. The present invention relates to an improvement in a detection element that requires particularly heat-resistant characteristics and high reliability, such as an oxygen sensor for detecting an oxygen concentration in exhaust gas of an automobile or a NOx sensor for detecting a nitrogen oxide concentration.

[0002]

2. Description of the Related Art First, the structure of a conventional detecting element will be described with reference to FIG. FIG. 9 shows a flat heater-integrated detection element 31 for detecting the oxygen concentration. According to the detection element 31, a plate-shaped solid electrolyte 32 of oxygen ion conductivity such as zirconia is formed so as to surround the air introduction hole 37, and the measurement electrode 3 is formed on the outer surface of the solid electrolyte 32.
3. A reference electrode 34 made of Pt is formed on the side of the air introduction hole 37, and these parts form a detection unit for detecting the oxygen concentration in the surrounding atmosphere. These electrodes 33, 3
Numerals 4 are separated from each other by a solid electrolyte 32a, so that an electromotive force is generated according to the ratio of the oxygen concentration between the electrodes. These electrodes 33 and 34 are coated on a surface of a raw solid electrolyte sheet with a metal paste in which solid electrolyte powder is dispersed and fired simultaneously, or after firing a solid electrolyte plate,
It can be formed by performing electroless plating.

[0005] A heating resistor 35 sandwiched between insulating layers 36 made of aluminum oxide is built in the solid electrolyte 32 b opposed to the air inlet 37 with the air introducing hole 37 interposed therebetween. It has a heating structure.

[0004] The detecting element 31 for detecting the oxygen concentration comprises:
Pt is mainly used as a metal material for the measurement electrode 33 and the reference electrode 34 because it may be exposed to the atmosphere of 500 ° C. or more.

Regarding the electrical connection with the outside, as described in Japanese Patent Application Laid-Open No. 58-100746, as a detecting element 31 using a zirconia solid electrolyte as a base material porcelain, an electrode is provided at an end of the detecting element. There is known a terminal having a terminal structure in which an extraction portion is provided and a metal member is pressed against the metal member by a spring or the like.

In this method, the structure is complicated to connect the terminals and to ensure insulation between the metal members, and the detecting element 3
There was a problem that the reliability of (1) was reduced.

For this reason, the metal member is directly connected to the detecting element 31.
There has been proposed a method of connecting to. For example, Japanese Unexamined Patent Publication No.
No. 257,256 proposes a method in which a part of a platinum electrode of a detection element is used as a terminal portion, and a Ni wire is directly metallized to the terminal portion by baking Pt paste. JP-A-2-124456 describes that a lead wire is brazed to a terminal portion made of a platinum electrode with an Ag-Cu brazing material.

Further, a metal film is formed on the surface of the platinum electrode by a thin film forming method such as plating and brazed.

[0009]

However, when the surface of the terminal portion is made of plating, the bonding strength between the plating and the zirconia solid electrolyte is essentially low.
There has been a problem that the terminal portion peels off under a load condition with high vibration such as an automobile.

On the other hand, when the terminal portion is formed by applying and firing a metal paste, it is necessary to contain a ceramic component such as zirconia in the metal paste in order to match a difference in thermal expansion with the solid electrolyte. When a metal paste containing ceramics such as zirconia is printed on the solid electrolyte surface in a thick film and simultaneously fired, the terminal portion has a structure in which metal particles are entangled in the skeleton of the ceramic. In the portion where the metal particles such as Pt are exposed, although the Au-Pt junction with the brazing material is formed, the wettability between the zirconia and the Pt particles is essentially poor. It is difficult to secure high joining strength
There is a problem that a brazed portion of the terminal portion is broken in a vertical tensile test of the metal member.

Accordingly, an object of the present invention is to provide a detection element having a high brazing strength between a terminal portion and a metal member and having excellent durability even in a severe environment.

[0012]

Means for Solving the Problems The present inventor has made intensive studies in view of the above circumstances, and as a result, has formed a pair of electrodes on both main surfaces of a zirconia solid electrolyte substrate, and has a detecting section for detecting an environmental state. And a pair of terminal portions formed on the surface of the base body and electrically connected to the electrodes, and a metal member brazed to the terminal portions with a brazing material. Part is formed of a composite conductor layer composed of a metal phase and a metal oxide phase, and the maximum distance between adjacent metal phases in a reflection electron micrograph of the surface of the composite conductor layer is set to 10 μm or less, so that the metal phase Forms a skeleton three-dimensionally, and the metal phase and the metal oxide phase are intricately entangled. As a result, the bonding between the metal oxide phase and the zirconia solid electrolyte is ensured while securing the bonding strength between the brazing material and the metal component. Is three-dimensional Enabling lifting, it found that detector elements having a high strength terminal portions sufficiently withstand tensile test of the metal member is obtained.

[0013] In such a configuration, the composite conductor layer includes:
It is preferable that the metal phase is composed of 20 to 95% by volume and the metal oxide phase is composed of 5 to 80% by volume in order to increase the bonding strength. Further, the metal phase in the composite conductor layer forming the terminal portion is preferably used. Is made of at least one of Pt, Rh, Pd, Ru, and Au, and the metal oxide phase is Al, S
It is desirable to contain at least one selected from the group consisting of i, Zr, an alkaline earth element, and a rare earth element in order to further increase the bonding strength. Further, as the brazing material, Pd,
It is desirable to contain at least one of Ni and Au in order to increase the bonding strength between the terminal portion and the metal member, suppress occurrence of migration and the like, and increase durability and stability.

Further, when the curvature radius r of the brazing material interposed between the metal member and the terminal portion of the metal member brazed to the terminal portion is 0.05 ≦ r ≦ 4 mm, or the terminal portion is formed. The angle between the tangent to the composite conductor layer surface and the metal member connected to the composite conductor layer via a brazing material is 2
When the angle is 0 to 45 degrees, stress concentration occurring in the meniscus portion of the brazing material existing between the metal member and the terminal portion during the tensile test of the metal member can be effectively avoided.

Further, by eliminating the connection end of the terminal portion with the base in the meniscus portion, the terminal portion can be effectively prevented from being turned up or peeled off during the tensile test.

Further, a terminal portion on one surface of the solid electrolyte substrate and an electrode formed on the other surface are electrically connected to each other through an end surface of the solid electrolyte substrate, so that the metal member is formed. The brazing position can be secured with high accuracy.

The detection element of the present invention is particularly preferably employed when the zirconia solid electrolyte substrate is formed of a cylindrical tube having one end sealed.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described with reference to the drawings showing an example of a detecting element of the present invention. FIG. 1 is a schematic perspective view showing an example of the detection element. 2A is a sectional view taken along line AA of the detection element in FIG. 1, FIG. 2B is a sectional view taken along line BB, and FIG. 2C is a sectional view taken along line CC. However, FIG.
In (a), the ceramic protective layer 14 is omitted for convenience of explanation. (Overall Structure) The detection element 1 shown in FIGS. 1 and 2 is made of a zirconia ceramic solid electrolyte having oxygen ion conductivity, and a first electrode is formed on the inner surface of a cylindrical tube 2 having a sealed end, as a first electrode. A reference electrode 3 to be in contact with the reference gas is formed and adhered to the reference electrode 3 with the cylindrical tube 2 interposed therebetween. Are formed. The detection part is formed by the reference electrode 3, the cylindrical tube 2 made of a zirconia solid electrolyte, and the measurement electrode 5.

On the outer surface of the cylindrical tube 2 whose end is sealed, a ceramic insulating layer 6 of Al ₂ O ₃ or the like is adhered and formed. The opening 11 is formed so that a part or the whole is exposed.

The above-mentioned ceramic insulating layer opening 11
A heating resistor 7 made of Pt or the like for heating the detection unit is embedded in the ceramic insulating layer 6 around the above. On the surface of the ceramic insulating layer 6, a ceramic heat insulating layer 9 made of Al ₂ O ₃ or the like is formed in order to increase the heating efficiency of the heating resistor 7.

The reference electrode 3 formed on the inner surface of the cylindrical tube 2 of the electrode portion is connected to a terminal portion 4 a provided on the outer surface of the cylindrical tube 2 via the open end surface of the cylindrical tube 2. On the other hand, the measurement electrode 5 formed on the outer surface of the cylindrical tube 2 is connected to a lead portion 12 formed on the surface of the ceramic heat insulating layer 9 via an end surface of an opening 11 formed in the ceramic insulating layer 6, It is connected to the terminal portion 4b formed on the surface of the ceramic heat insulating layer 9. In addition, the edge part which exists in the said end surface in the cylindrical pipe 2 is chamfered C, and the defect of the electrical connection which arises in an edge part is avoided.

A protective layer 122 made of ZrO ₂ or the like is further formed on the surface of the lead portion 12 formed on the surface of the ceramic heat insulating layer 9. The protective layer 122 can protect the lead portion 12 from physical destruction such as scratching when assembling the element or collision with foreign matter when the element falls. This ceramic protective layer 122 is preferably made of the same ZrO ₂ as the solid electrolyte in order to prevent the occurrence of stress due to the difference in thermal expansion between the ceramic electrolyte and the solid electrolyte. Further, the surface of the detection unit is covered with a porous ceramic protective layer 14.

Metal members 13 for connection to an external circuit are fixed to the terminal portions 4a and 4b formed on the surface of the ceramic heat insulating layer 9 by brazing material 17, respectively.

Thus, the detection data generated in the detection section is connected to an external circuit via the lead section 12, the terminal sections 4a and 4b, and the metal member 13.

On the other hand, the heating resistor 7 formed in the ceramic insulating layer 6 is formed so as to penetrate the lead portion 8 also formed in the ceramic insulating layer 6 and the ceramic insulating layer 6 and the ceramic heat insulating layer 9. The terminal portion 2 formed on the outer surface of the ceramic heat insulating layer 9 by the penetrating conductor 18
4 is electrically connected. A metal member 23 for connection to an external power source for heat generation is fixed on the terminal portion 24 by a brazing material 17, and an electric current is passed through the heat generation resistor 7 through these members, whereby the heat generation resistor 7 is heated and measured. The temperature of the detection unit including the electrode 5, the cylindrical tube 2, and the reference electrode 3 is rapidly increased to a predetermined temperature. (Terminal Structure) According to the present invention, the terminals 4a, 4a connected to at least the electrodes 3, 5 in the detection element 1 described above.
More preferably, it is important that the terminal portion 24 connected to the heating resistor 7 is formed of a composite conductor layer composed of a metal phase and a metal oxide phase. As shown in FIG. 3, the composite conductor layer 16 has a metal oxide phase 20
And a metal phase 19 having a complicated intricate structure.
A metal phase is formed by contact at points or more, and this forms a three-dimensional network structure, for example, a sponge-like structure, and a metal oxide phase 20 is present in the gap.

By forming the terminal portion with the composite conductor layer 16 having such a structure, the metal oxide phase 2 is formed.
0 prevents grain growth of the metal phase 19, and prevents the terminal portions 4a, 4a
It is possible to improve the bonding strength between b and the cylindrical tube 2 serving as the underlayer.

This point will be described in more detail. As shown in a reflection electron micrograph of FIG. 3B, on the surface of the composite conductor layer 16 of the terminal portions 4a and 4b, the metal phase 19 is complicated. It is observed as an island-like structure having a sharp ridge. The insular metal phases 19 are scattered innumerably while being separated by the metal oxide phases 20 serving as a matrix, and represent the vicinity of the end of the sponge-like skeleton.

For more detailed consideration, the composite conductor layer 1
In FIG. 6, only the metal phase 19 was eluted by the acid treatment, and the skeleton of the metal phase inside the composite conductor layer 16 was observed. As shown in FIG. 4, the distance between the metal phases 19 inside the sponge-like structure was It was clarified that the distance was less than or equal to the maximum distance in the metal phase between adjacent islands observed on the surface of the terminal portion 4.

At this time, when the maximum distance between the adjacent island-like structures of the metal phase 19 is 10 μm or less, the terminal portions 4a, 4
Inside b, the metal phase 19 forms a three-dimensional sponge-like skeleton, and particularly when the maximum distance is 5 μm or less, the metal phase 19 preferably forms a more dense sponge-like structure.

In such a sponge-like skeleton of the metal phase 19, the metal phase 19 is supported three-dimensionally, and the anchor effect can be effectively exerted on the metal oxide phase 20. In addition, the metal phase 19 is unevenly distributed at the interface between the metal oxide phase 20 and the solid electrolyte forming the cylindrical tube 2 and the ceramic protective layer 9 and does not become, for example, coarse massive particles. The bonding state between the solid electrolytes is good. As a result, the tensile strength of the metal member 13 brazed on the terminal portions 4a and 4b is significantly improved.

On the other hand, the maximum distance is 10 μm
Is exceeded, a free metal phase which does not participate in the sponge-like structure is present inside the composite conductor layer in a granular form. This free metal phase can be clearly observed in the reflection electron micrographs on the surfaces of the terminal portions 4a and 4b. Since these are not supported three-dimensionally, the anchor effect does not function, and the tensile strength of the metal member 13 is remarkably large. descend.
In addition, since the metal phase 19 and the solid electrolyte have essentially poor wettability as described above, the separated metal phases easily form coarse aggregated particles inside the composite conductor layer. The coarse aggregates act as defects when the metal member 13 is evaluated for tensile strength, so that the terminal portions 4a and 4b are easily broken.

According to the present invention, the metal phase 19 comprises P
It is selected from at least one of t, Rh, Pd, Ru, and Au, and Pt is particularly excellent in oxidation resistance under a high temperature environment. These metal phases are preferable because they exist stably without causing a reaction such as oxidation under a use environment of 500 ° C. The shape and particle size are not particularly limited, but as described above, for the purpose of controlling the distance between the island-like structures of adjacent metal phases, a method such as appropriate mixing of the particle size and selection of the shape of the metal component depending on the situation. May be adopted.

The metal oxide phase 20 is composed of Al, Si,
It is desirable to be made of a composite oxide containing at least one oxide selected from the group consisting of Zr, alkaline earth elements, and rare earth elements (including Y). Specifically, the composite oxide, forsterite, steatite, spinel, rare earth oxides _{-SiO 2 -Al 2 O 3, ZrO} 2 - selected (rare earth oxide, CaO, SiO ₂₎ from the group of At least one composite oxide.

More specifically, Y ₂ O ₃ —SiO ₂ —Al ₂
As an O ₃ composite system, Y ₂ O ₃ 20 to 53% by weight, Al ₂ O
₃ 10 to 34 wt%, when formed by SiO ₂ 24 to 60% by weight of the composition, preferably easily formed melting point 1500 ° C. or less glassy ceramic. In particular, Y ₂ O ₃ 3
2.3% by weight, 21.8% by weight of Al ₂ O ₃ , SiO ₂ 4
At the composition point of 5.9% by weight, the melting point of the glassy ceramic can be set to around 1400 ° C., so that the terminal portions 4a, 4
This is desirable because the grain growth of the metal phase in the composite conductor layer constituting b can be suppressed.

ZrO ₂ — (Rare earth element oxide, CaO,
In the case of SiO ₂ ), a composition in which at least one of rare earth oxides is added to ZrO ₂ stabilized with 3 to 15 mol% of rare earth element oxide, or the total amount of the metal component and the stabilized ZrO ₂ By using a composition in which CaO is added at a ratio of 50 parts by weight or less to 100 parts by weight, the adhesion between the composite conductor layer 16 and the solid electrolyte is suitably improved.

Further, a metal component, based on 100 parts by weight of stabilized ZrO _2, when the SiO ₂ is added in a proportion of 10 wt% or less, SiO ₂ enters the ZrO ₂ grain boundary of the solid electrolyte anchor effect Therefore, the adhesion between the terminal portion and the solid electrolyte can be further improved.

The rare earth used in the above composition
As an element oxide, Y_TwoO_Three, Yb _TwoO_Three, Sc_TwoO_Three, S
m_TwoO_Three, Gd_TwoO_Three, CeO_TwoAt least selected from the group of
One of them is preferably used.

The ratio of the metal phase 19 to the metal oxide phase 20 in the composite conductor layer 16 forming the terminals 4a and 4b is preferably in the range of 95: 5 to 20: 80% by volume in terms of volume. Particularly, in the range of 95: 5 to 60: 40% by volume, the resistance can be reduced while securing the bonding strength of the terminal portions 4a and 4b to the solid electrolyte, which is very preferable. Metal phase 19 is 9
If it is more than 5% by volume, the bonding between the metal oxide phase 20 and the solid electrolyte tends to be weak. If the content of the metal phase 19 is less than 20% by volume, the specific resistance increases dramatically, so that a problem that conduction with the leads 8 and 12 cannot be obtained easily occurs.

The thickness of the terminal portions 4a and 4b is preferably 3 μm or more. If the thickness is less than 3 μm, defects such as traces of the mesh of the screen are likely to occur during screen printing on the cylindrical tube 2 or the ceramic heat-insulating layer 9, and these defects tend to cause defects such as pinholes in the wax flow. The upper limit of the thickness of the terminal portions 4a and 4b is not particularly limited, but in the case of a cylindrical detection element as shown in FIG. 1, if it exceeds 100 μm, the terminal portions 4a and 4b and the cylindrical tube 2 or the ceramic heat insulating layer 9 The difference between the curvature of the bonding interface and the curvature of the surface of the terminal portions 4a and 4b becomes large and the terminal is easily broken.
It is desirable that:

As the metal member 13 to be joined to the terminal portions 4a and 4b, at least one kind of metal having heat resistance and oxidation resistance selected from the group consisting of Ni, Kovar, Inconel and Pt is selected. I just need.

Then, the metal member 13 is connected to the terminal portion 4.
Pd, N as the brazing material for connecting to a, 4b
From among the brazing materials containing at least one selected from the group consisting of i, Au, and Ag, a brazing material having a heat-resistant temperature compatible with the use environment or the like may be selected. For example, when fixing with the Au-Cu brazing material 17 having an Au content of 35 to 90% by weight, it is suitable for brazing the detecting element 1 in which the heating resistor is adjusted so that the terminal portion 4 is 500 ° C. or less. Used for However, since Ag easily causes migration, it is preferable that Ag is not contained as much as possible.

When the metal member 13 has a rod shape, as shown in FIG. 5, the curvature radius r of the meniscus portion of the brazing material 17 formed between the metal member 13 and the terminal portion 4 when viewed from the side is 0.05. When ≦ r ≦ 4 mm, the metal member 1
In the tensile evaluation of No. 3, the brazing material curvature portion (meniscus) is preferable without being a stress expansion point. Also, r <0.05 mm
In the case of (1), when the metal member 13 is pulled, the effect of increasing the stress at the curvature portion (the principle of leverage) is remarkable, and the terminal portion 4 is broken. On the other hand, when 4 mm <r, the amount of brazing material supporting the metal member 13 is significantly reduced, and brazing defects such as removal of only the metal member 13 are likely to occur.

In other words, the angle between the tangent line on the surface of the metal member joint of the terminal portion 4 and the metal member 13 connected to the terminal portion 4 through the meniscus of the brazing material 17 may be 20 to 45 degrees. desirable. In particular, when the above angle is 30 to 40 degrees, the radius of curvature r of the meniscus portion is set to 0.
5 mm ≦ r ≦ 1 mm, the amount of brazing material used can be reduced, which is very effective for cost reduction.

Also, as shown in FIG. 5, the composite conductor constituting the terminal portion 4 at the time of the tensile test is formed by using a brazing structure in which the terminal end portions of the terminal portions 4a and 4b do not exist in the meniscus portion. It is possible to effectively avoid stress expansion occurring between the layer 16 and the solid electrolyte constituting the cylindrical tube 2 or the ceramic heat insulating layer 9, and as a result, it is possible to avoid turning up and peeling of the terminal portion 4.

The terminal 4a connected to the reference electrode 3
Can be formed on either the outer surface or the inner surface of the cylindrical tube 2. However, the metal member 13 and the brazing material 17 can be formed on the outer surface of the cylindrical tube 2 using a jig. This is very preferable because the yield in the brazing step is significantly improved as compared with the case where the film is formed on the inner surface. (Other Embodiments) The present invention can be applied not only to FIG. 1 but also to any other detecting element provided with a portion for brazing a metal member to a terminal portion electrically connected to an electrode of the detecting portion. .

Therefore, another embodiment of the detecting element of the present invention will be described with reference to FIGS. FIG.
2 will be described with the same reference numerals.

First, in FIG. 1, the measuring electrode 5 and the terminal 4b
1 is formed on the surface of the ceramic heat-insulating layer 9, but as shown in FIG. 6A, which is another embodiment of the sectional view taken along the line BB in FIG. The lead portion 12 formed in the layer 6 and the terminal portion 4b formed on the surface of the ceramic heat insulating layer 9 are connected by a through conductor 18 formed through the ceramic insulating layer 6 and the ceramic heat insulating layer 9. Can be. In this case, the connection between the lead portion 12 and the terminal portion 4b is as shown in FIG.
As shown in the side sectional view of (b), the terminal portion 4b can be routed from the end surfaces of the ceramic insulating layer 6 and the ceramic heat insulating layer 9 for connection.

Further, in the detecting element of FIG. 1, one detecting portion is formed, but as shown in FIG. 7A, a schematic perspective view and FIG. Two portions are provided at locations of the cylindrical body facing each other. As described above, if a plurality of detecting portions are formed, the directivity of the detecting element 1 with respect to the exhaust gas in the assembling fitting can be eliminated. In FIG. 7 as well, at least the surface of the detecting portion is covered with the porous ceramic protective layer 14, but is omitted in FIG. 7A for convenience of explanation.

At this time, when connecting the measuring electrode 5 and the terminal portion 4b, two measuring electrodes 5 can be connected in series and connected to the terminal portion 4b via the lead portion 12. A lead portion 12 is formed for each electrode 5 and connected to the terminal portion 4b, or as shown in FIG. 7A, the lead portions 12 are connected to each other and connected to the terminal portion 4b as shown in FIG. do it. In addition, the reference electrode 3
May be formed two in accordance with each detecting part, or two cylindrical tubes 2
By forming the reference electrode 3 on the entire inner surface of the substrate, the reference electrode 3 can be shared.

The detecting element of the present invention can be applied not only to the cylindrical shape as described above, but also to the terminal structure of a flat type detecting element. FIG. 8 shows a flat detection element. (A) is a perspective view, (b) is an EE sectional view, and (c) is an FF sectional view. This detection element has a structure in which a detection unit, an air introduction hole, and a heater unit are stacked from the top of the figure. A measuring electrode 5 on the outer surface of the solid electrolyte substrate 2;
The reference electrode 3 is formed on the inner surface on the air introduction hole 25 side.

The measurement electrode 5 is connected to terminals 4a and 4b formed on the outer surface of the solid electrolyte substrate 2 via lead portions 12 formed on the outer surface of the solid electrolyte substrate 2. Further, the reference electrode 3 formed on the inner wall of the air introduction hole 25 is drawn out just below the terminal portion 4a, and
6, the metal members 13a and 13b are brazed to the terminal portions 4a and 4b by the brazing material 17 according to the present invention.

On the other hand, the air introduction hole 25 of the solid electrolyte substrate 2
A heating resistor 7 is built in a portion opposed to the detection unit with the insulating layer 6 made of ceramic such as alumina interposed therebetween. As shown in FIG. 8C, the heating resistor 7 has the lead portion 8 extended to just below the terminal portion 24 and the vertical conductor 2.
7, a metal member 23 is connected to the heater terminal 24 according to the present invention.

[0053]

(Example 1) Tensile strength of the terminal portion 4 to the ceramic insulating layer 9 made of ZrO ₂ in the structure of FIG. 5 and an island-like structure of a metal component observed at an arbitrary position on the surface of the terminal portion 4 Was examined for correlation with adjacent distance.

First, the following materials were prepared for producing evaluation samples. a) ZrO containing 5 mol% Y ₂ O ₃ prepared by a coprecipitation method
₂ powder (for tubulars, ceramic heat insulating layer) b) for the following fine Al ₂ O ₃ powder MgO content is 10 ppm (ceramic insulating layer) c) Al ₂ O ₃ 10% by volume content to Pt paste (heating resistor 7. Lead part 8) d) Pt paste containing 30% by volume of ZrO ₂ powder containing 5 mol% Y ₂ O ₃ (for reference electrode 2, measurement electrode 5, electrode or resistor lead parts 8, 12) e) Pt paste containing 40 vol% of ZrO ₂ powder containing 5 mol% Y ₂ O ₃ (terminal part 4 for electrode, terminal part 24 for resistor) Note that the ZrO ₂ powder used in the Pt paste of the above e) was used. The average secondary particle diameter (D5) is used to control the distance between adjacent metal phases 19 in the composite conductor layer of the terminal portion 4.
0) was set to 0.5 to 5.0 μm.

First, a polyvinyl alcohol solution was added to the ZrO ₂ powder of a) to prepare a clay, and a cylindrical tube 2 having an outer diameter of about 4 mm and an inner diameter of 2.3 mm was prepared by extrusion molding. Also, after a predetermined amount of an acrylic binder was added to the ZrO ₂ powder of a) to prepare a slurry, a 200 μm-thick green sheet for the ZrO ₂ ceramic protective layer 9 was formed by a doctor blade method.

After baking the slurry of the above b) Al ₂ O ₃ powder, the slurry was applied to the surface of the green sheet for the ceramic protective layer 9 so as to have a thickness of about 10 to 15 μm.
Then, on the surface of the Al ₂ O ₃ layer, the heating resistor 7 and the lead 8 for the resistor were formed by screen printing using the Pt paste of the above c). Furthermore, the resistor lead 8
A through hole is punched in a predetermined position of d.
Of Pt paste.

Next, the green sheet for the ceramic protective layer 9 is turned over, and the lead portions 12 connected to the measurement electrodes,
The terminal portion 4b connected to the measurement electrode and the terminal portion 24 of the resistor lead 8 were formed at predetermined positions by screen printing using the Pt paste of d) or e).
On the lead portion 12 connected to the measurement electrode, the same slurry as the above-mentioned a) ZrO ₂ slurry for forming a green sheet as the ceramic protective layer 122 was fired to a thickness of about 15 to 20 μm as a ceramic protective layer 122. It was screen-printed.

After that, the green sheet is again turned over,
After sintering the slurry composed of the Al ₂ O ₃ powder of the above c), so that the heating resistor is included in the Al ₂ O ₃ layer, about 10
１５15 μm.

As described above, in the green sheet (hereinafter, referred to as a sheet-like laminate) in which the respective prints are laminated, a region where the measurement electrode 5 is formed is opened by punching, and after the opening 11 is formed. On the surface of the cylindrical tube 2, an acrylic resin is added as an adhesive layer to the 5 mol% Y ₂
Winding was performed using an adhesion liquid in which O ₃ -containing ZrO ₂ powder was dispersed, to produce a cylindrical laminate.

Next, using the Pt paste of d), the reference electrode 3 was placed inside the cylindrical tube 2 in the cylindrical laminate, and
The measuring electrode 5 was placed in the opening 11 by 10 μm after firing.
Each of them was formed by a curved surface printing method so as to have a thickness of m. Thereafter, the cylindrical laminate was placed in the atmosphere at 1400 to 1400.
It was baked at 1500 ° C. for 2 hours and integrated. After firing,
In the present detection element 1, the outer diameter of the cylindrical tube 2 is 3.0 to 3.1.
mm, and the inner diameter was 1.7 to 1.8 mm.

After sintering, the metal members 13 and 23 made of a 0.6 mm-diameter Ni wire are brazed on the terminal portion at a predetermined temperature in an inert atmosphere with a brazing material 17 of Au-Cu (Au 50% by weight, Cu 50% by weight). Then, the curvature radius r of the meniscus of the brazing material was fixed to be 0.6 mm. In addition, a metal member was brazed near the top of the terminal so that the meniscus portion of the brazing material did not include the connection end of the terminal portion 4 with the base.

After that, the surface of the measuring electrode 5 is made to have a porosity of about 30
% Of the ceramic porous layer was formed so as to have a thickness of about 100 μm, whereby the detection element 1 was produced.

In the detection element 1 thus obtained, the tensile strength of the metal member 13 in the direction perpendicular to the terminal was measured, and further a reflection electron micrograph (BEM) at an arbitrary position on the surface of the terminal 4 From the above, the maximum value of the distance between the island structures 50 of the adjacent metal phases was estimated. Table 1 shows the results.

[0064]

[Table 1]

According to Table 1, no. 5 and No. 5 8 ~
As is clear from FIG. 10, in the composite metal material forming the terminal portion, those having a maximum value of the distance between the island-like structures 50 of adjacent metal phases of 10 μm or more have a tensile strength of less than 0.3 MPa. Did not. Observation of the fractured portions of these samples shows that the portion of the terminal portion where the brazing material 17 is in close contact is peeled off with the conductor immediately below it, but the peeled surface is inside the composite conductor layer in the terminal portion. Was. Also,
As a result of observing the fractured surface with an electron microscope, granular Pt coarse grains not involved in the metal skeleton were observed on the peeled surface.

On the other hand, all the samples in which the distance between the island-like structures 50 due to the metal phase was 10 μm or less had a very good tensile strength of 1.0 MPa or more. In all of these samples, the portion of the terminal portion where the brazing material 17 is in close contact is peeled off with the conductor immediately below it, but the peeled surface is at the interface between the terminal portion 4 and the ceramic protective layer 9. there were.

(Example 2) With respect to the detecting element 1 obtained by the same method as in Example 1, a metal member made of a Ni wire was fixed on a terminal part made of a composite metal material with an Au-Cu brazing material. The Ni wire is φ0.6 mm and has a bent portion that forms an angle of 15 to 50 degrees with the terminal portion. In order to analyze the structure shown in FIG. 5 for these samples,
The radius of curvature r of the meniscus portion of the brazing material formed between the terminal portion and the metal member was measured using a projector or a photograph. Thereafter, the tensile strength of the metal member 13 was measured in the same manner as in Example 1. The same evaluation was performed for the case where the end portion of the terminal portion was present in the meniscus portion formed of the brazing material and the case where the end portion was not present. Table 2 shows the results.

[0068]

[Table 2]

As shown in Table 2, the brazing material having a meniscus portion having a radius of curvature r of 0.05 mm ≦ r ≦ 4 mm was 1.0 MP
It is clear that it shows a tensile strength of a or more and is very good. From this, it can be seen that with the above-mentioned radius of curvature, stress expansion during pulling does not occur at the curvature portion.
In addition, in the case where the end portion of the terminal portion exists in the meniscus portion, No.
In the case of Nos. 20 to 21, it is found that the terminal portion was peeled off from the ceramic protective layer, and the stress was increased between the terminal portion and the ceramic protective layer 9 at the time of pulling. (Embodiment 3) Regarding a detection element 1 obtained by the same method as in Embodiment 1, a terminal portion 4 connected to a reference electrode 3 is formed inside a cylindrical tube 2 and a terminal portion 4 is formed on an outer surface of the cylindrical tube 2 A total of three lots of 30 samples each were produced, and the tensile strength of the metal member 13 was measured for all the samples in the same manner as in Example 1. Thereafter, those having a tensile strength of 1.0 MPa or more were regarded as good products, and the product yield was determined. Table 3 shows the results.

[0070]

[Table 3]

As is apparent from Table 3, the product yield is much better when the terminal portion 4 of the reference electrode 3 is provided on the outer surface of the cylindrical tube 2. A terminal part 4 is provided on the inner surface of the cylindrical tube 2.
When the brazing structures of all the rejected products were examined in detail for the samples in which was formed, the connection terminals to the base of the terminal portion were present in the meniscus arc formed of the brazing material for all of them. This is because the inner diameter of the cylindrical tube 2 is 1.7 to
Due to its extremely small size of 1.8 mm, it is very difficult to fix the Ni wire with a jig with high positional accuracy during preparation for brazing.

[0072]

As described in detail above, in the detection element of the present invention, the terminal portion to which the metal member is brazed is formed by the composite conductor layer in which the metal phase and the metal oxide phase have a predetermined structure. Thereby, the metal phase is formed into a three-dimensional network structure (sponge-like structure), and the metal network structure is embedded in the matrix portion made of the metal oxide phase, so that the so-called anchor effect can be effectively exhibited. Further, by controlling the radius of the curvature (meniscus) formed between the metal member and the composite conductor layer by the brazing material, it is possible to achieve a brazing structure in which stress concentration does not occur at the curvature portion when the metal member is pulled. . As a result, a stable and highly reliable detection signal extraction structure can be obtained, and a highly reliable detection element that can quickly and stably detect the output signal of the detection unit for a long time can be provided.

[Brief description of the drawings]

FIG. 1 is a schematic perspective view for explaining one embodiment of a detection element of the present invention.

2A is a cross-sectional view of the detection element of FIG. 1 along AA, and FIG.
It is BB sectional drawing, (c) It is CC sectional drawing.

FIGS. 3A and 3B are a schematic cross-sectional view for explaining the structure of a terminal portion in the detection element of the present invention and a schematic diagram of a reflection electron micrograph of a composite conductor layer forming the terminal portion.

FIG. 4 is a diagram showing the relationship between the distance between metal phases inside the composite conductor layer and the distance between metal phases on the surface of the composite conductor layer in the present invention.

FIG. 5 is a schematic sectional view of a connection structure between a terminal portion and a metal member according to the present invention.

FIGS. 6A and 6B are a vertical cross-sectional view and a cross-sectional view of a further alternative embodiment, respectively, for explaining a detection element according to another embodiment of the present invention.

FIGS. 7A and 7B are a vertical sectional view and a schematic perspective view taken along the line (a) of FIG. 7 for explaining another embodiment of the detection element of the present invention.

8A and 8B are a schematic perspective view, (b) a cross-sectional view taken along the line EE, and (b) a cross-sectional view taken along the line FF for explaining another embodiment of the detection element of the present invention. .

FIG. 9A is a schematic plan view of a conventional detection element, and FIG.
It is GG sectional drawing.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Detection element 2 Cylindrical tube (solid electrolyte base) 3 Reference electrode 4a, 4b Terminal part 5 Measurement electrode 6 Ceramic insulating layer 7 Heating resistor

Claims (10)

[Claims] 1. A detecting portion for detecting an environmental condition, comprising a pair of electrodes formed on both main surfaces of a zirconia solid electrolyte substrate, and a terminal portion formed on a surface of the substrate and electrically connected to the electrodes. And a metal member brazed to the terminal portion with a brazing material, wherein the terminal portion comprises a composite conductor layer composed of a metal phase and a metal oxide phase, and the composite conductor layer A detecting element wherein the maximum distance between adjacent metal phases in a reflection electron micrograph of the surface is 10 μm or less. 2. The detecting element according to claim 1, wherein the metal phase in the composite conductor layer forming the terminal portion is at least one of Pt, Rh, Pd, Ru, and Au. 3. The metal oxide phase in the composite conductor layer forming the terminal portion contains at least one selected from the group consisting of Zr, Al, Si, alkaline earth, and rare earth elements. The detection element according to claim 2. 4. The method according to claim 1, wherein the brazing material is at least Au, Pd, N
The detection element according to any one of claims 1 to 3, comprising at least one selected from the group of i. 5. The detection according to claim 1, wherein the composite conductor layer comprises a metal phase of 20 to 95% by volume and a metal oxide phase of 5 to 80% by volume. element. 6. A curvature radius r of a meniscus portion of a brazing material interposed between said metal member and said terminal portion is 0.05 mm ≦.
2. The detecting element according to claim 1, wherein r ≦ 4 mm and a brazing structure in which an end of the terminal portion does not exist in the meniscus portion. 7. An angle between a tangent to the surface of the composite conductor layer at the terminal portion and the metal member connected to the composite conductor layer via a brazing material is 20 to 45 degrees. The detection element according to claim 1 or 6. 8. The detecting element according to claim 1, wherein no connection end of the terminal portion with the base exists in a meniscus portion of the brazing material interposed between the metal member and the composite conductor layer. 9. The solid electrolyte substrate is characterized in that a terminal portion on one surface of the solid electrolyte substrate and an electrode formed on the other surface are electrically connected via an end surface of the solid electrolyte substrate. The detection element according to claim 1, wherein 10. The zirconia solid electrolyte substrate comprises a cylindrical tube having one end sealed.
The detecting element according to claim 9.