JP5294579B2 - Ceramic sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ceramic sensor in which there is little risk of exfoliation of a metal electrode even if the sensor is subjected to heating and cooling cycles. <P>SOLUTION: The ceramic sensor is equipped with a ceramic plate and a metal electrode joined to at least one surface of the ceramic plate, wherein the metal electrode satisfies at least one of following conditions: (1) The whole or a portion of the outer circumference of the metal electrode is lacked and the whole or a portion of the ceramic plate is exposed. (2) At least a portion of the outer circumference of the metal electrode is thinner than a central part. <P>COPYRIGHT: (C)2009,JPO&amp;INPIT

Description

  The present invention relates to a ceramic sensor, and more particularly to a ceramic sensor using ceramics having electromagnetic characteristics such as electrical conductivity, ion conductivity, piezoelectricity, strain-electric resistance characteristics, dielectric properties, and nonmagnetic properties.

Metal / ceramic bonded bodies can be used for various structural parts that require mechanical properties such as high-temperature strength, wear resistance, heat resistance, thermal shock resistance, and corrosion resistance, or electrical conductivity, ionic conductivity, piezoelectricity, and strain. -Used for various functional parts that require electromagnetic characteristics such as electrical resistance characteristics, dielectric properties and non-magnetic properties, and heat conduction characteristics.
As a method of joining a metal material and a ceramic material,
(1) Mechanical joining methods such as bolting, fitting, cast-in, etc.
(2) Adhesive method using organic or inorganic adhesives,
(3) A metallized brazing method in which a metal thin film is formed (metallized) on the surface of a ceramic material and brazed to the metal material via the metal thin film,
(4) A plating method in which a metal thin film is formed on the surface of a ceramic material by electroless plating,
(5) A diffusion bonding method in which a metal material and a ceramic material are directly or directly brought into contact with each other via an appropriate brazing material, intermediate layer, etc., and heated to a high temperature to diffuse constituent elements at the interface,
(6) Physical film formation method by CVD, electron beam, sputtering, laser ablation, PLD, ALD, vapor deposition, etc.
(7) A method of forming a paste thin film by screen printing of a conductive paste,
(8) Ultrasonic bonding method,
(9) Ceramic frit method (joining method using low melting point ceramic frit),
(10) Laser method (melt bonding method),
(11) Thermal spraying method,
(12) Metalizing method,
Etc. are known. As a diffusion bonding method, a Field-Assisted Bonding method (a method of applying an electric field) is also known in which diffusion bonding is performed by forcibly causing an interface reaction using the ionicity of an element.

  These joining methods are properly used depending on the use of the metal / ceramic bonding body, the type of ceramic material and the required film thickness, etc., but for applications that require high reliability, the metallization method, diffusion welding is generally used. Chemical bonding methods such as a combination method, a friction welding method, a gas / metal eutectic method, and a reactive bonding method are used. However, since the joining of the metal material and the ceramic material is a joining between different materials, various problems may occur when the chemical joining method (solid phase joining method) is used.

  For example, in order to join a metal material and a ceramic material using a chemical joining method, it is generally necessary to heat both to a high temperature. The thermal expansion coefficient of ceramic materials is generally smaller than the thermal expansion coefficient of metal materials. When both are heated to high temperatures and joined, and then cooled to room temperature, the ceramic materials are caused by the difference in thermal expansion coefficients from the metal materials. Thermal stress (tensile stress) is generated. When this thermal stress exceeds the mechanical strength of the ceramic material, there is a problem that the ceramic material is damaged.

As a method of solving this problem, for example,
(1) A method of interposing a material having a thermal expansion coefficient intermediate between a metal material and a ceramic material (for example, W, Mo, Zr, Nb, etc.) at the interface;
(2) A method of interposing a soft metal (for example, Al, Au, Cu, etc.) at the interface between the metal material and the ceramic material,
(3) A method of continuously changing (inclining) the thermal expansion coefficient from the ceramic side to the metal side,
Etc. have been proposed.

  In addition, various functional ceramics are often bonded with a relatively thin metal electrode on the surface thereof. Even in such a metal electrode / ceramic bonded body, various problems may occur due to the difference in thermal expansion between them, oxidation of the metal electrode during high temperature use, heat conduction through the bonded metal, and the like. There are several methods for solving this problem.

For example, in Patent Document 1, electrodes are formed on the entire upper and lower surfaces of a flat plate thermistor element (metal oxide sintered body), a lead wire is joined to the electrode surface, and the thermistor element and lead wire thermistor element connection are disclosed. On the end side, the raw materials are SiO ₂ , CaO, SrO, BaO, Al ₂ O ₃ , and SnO ₂ , and the average linear expansion coefficient in the temperature range from 30 ° C. to 700 ° C. is 8.5 × 10 ⁻⁶ / A thermistor for high temperature melted and sealed with a sealing glass having a glass transition point of 720 ° C. or higher at a temperature of 720 ° C. is disclosed.
The document describes that by adopting such a configuration, cracking of the sealing glass can be suppressed.

Further, Patent Document 2, forming an intermediate layer comprising a mixture of Pt and ZrO ₂ on the surface of the ZrO ₂ to form a bonding metal layer made of electroluminescent Ni plating layer on the intermediate layer, the bonding metal An oxygen sensor element in which a metal terminal made of Ni is bonded on a layer is disclosed.
In this document, when a bonding metal layer is directly bonded to the surface of a ceramic substrate, a large thermal stress is generated at the interface due to the difference in linear expansion coefficient between the two. It is described that the thermal stress generated at the interface can be reduced by providing an intermediate layer having an intermediate linear expansion coefficient between them.

JP 2005-294653 A JP-A-10-241753

In general, various ceramic sensors using ceramics having electromagnetic characteristics are extremely small in size. Therefore, a metal electrode having a relatively large thermal expansion coefficient can be directly bonded to the entire surface of the ceramic surface. However, when a thermal cycle is applied to the sensor in which the metal electrode is directly bonded to the entire surface of the ceramic plate, the metal electrode may be peeled off from the stress concentration portion.
In order to solve this problem, an intermediate layer may be provided between the ceramic plate and the metal electrode as disclosed in Patent Document 2. However, the method of providing the intermediate layer has a problem that the number of steps increases and the cost increases. Further, when such a ceramic sensor is used at a high temperature for a long time, a reaction or element diffusion occurs at the metal electrode / intermediate layer interface, and the composition of the metal electrode and the intermediate layer may change over time.

The problem to be solved by the present invention is to provide a ceramic sensor in which a metal electrode is less likely to be peeled off even when a cooling cycle is applied.
In addition, another problem to be solved by the present invention is to provide a ceramic sensor that is low in cost and that hardly changes over time in the composition of the metal electrode even when used at a high temperature for a long period of time. is there.

In order to solve the above problems, the ceramic sensor according to the present invention is:
Ceramic plates,
A metal electrode joined to at least one surface of the ceramic plate,
The planar shape of the ceramic plate is a quadrangle,
The planar shape of the metal electrode is the quadrangle, and the corners of the quadrangle are not cut off,
The gist of the metal electrode is that a taper is provided only at the corner.

  When joining a ceramic plate and a metal electrode, the thermal stress resulting from the difference in thermal expansion coefficient is highest at the outer peripheral portion of the metal electrode. On the other hand, if all or a part of the outer periphery of the metal electrode is missing and / or if the thickness of at least a part of the outer periphery of the metal electrode is made thinner than the central portion, the thermal stress generated in the outer periphery of the metal electrode is significantly increased. Can be reduced. Therefore, even if a cooling cycle is applied to such a ceramic sensor, the metal electrode is less likely to peel off. Further, since it is not always necessary to interpose an intermediate layer in order to reduce thermal stress, the cost is low and the metal electrode composition does not easily change with time.

Hereinafter, an embodiment of the present invention will be described in detail.
The ceramic sensor according to the present invention includes a ceramic plate and a metal electrode bonded to at least one surface of the ceramic plate.

[1. Ceramic plate]
In the present invention, the ceramic plate is made of any material that has electromagnetic properties such as electrical conductivity, ionic conductivity, piezoelectricity, strain-electric resistance properties, dielectric properties, non-magnetic properties, and heat conduction properties and functions as a sensor. Can be used.
Specifically, as a ceramic material,
(1) nitrides such as silicon nitride (Si ₃ N ₄ ), aluminum nitride (AlN), sialon (SiAlON), gallium nitride (GaN), titanium nitride (TiN), zirconium nitride (ZrN),
(2) carbides such as silicon carbide (SiC), titanium carbide (TiC), zirconium carbide (ZrC), boron carbide (B ₄ C),
(3) Alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ), molybdenum oxide (MoO _x ), ceria (CeO ₂ ), yttria (Y ₂ O ₃ ), bismuth oxide (Bi ₂ O ₃ ), barium titanate (BaTiO ₃ ), titania (TiO ₂ ), zinc oxide (ZnO), magnesia (MgO), calcia (CaO), spinel (Al ₂ MgO ₄ ), barium titanate (BaTiO ₃ ), La ₆ WO ₃ , LaBO ₃ , Oxides such as LaPO ₄ ,
(4) Borides such as titanium boride (TiB ₂ ) and zirconium boride (ZrB ₂ ),
(5) silicides such as titanium silicide (TiSi ₂ ) and zirconium silicide (ZrSi ₂ ),
(6) Pichlor type oxides such as La ₂ Zr ₂ O ₇ , Sm ₂ Zr ₂ O ₇ , Gd ₂ Zr ₂ O ₇ ,
(7) SrCeO ₃ , SrCe _1-x M _x O ₃ (M = Sc, Zn, Y, Mn, In, Nd, Sm, Dy, Yb), La _1-x CaCrO ₃ , La _1-x SrCrO ₃ , _{YMnO 3, La 1-x Co} x MnO 3, LaSrMnO 3, LaFeO 3, La 1-x Ca x CoO 3, La 1-x Sr x CoO 3, SrCeO 3, CaZrO 3, SrZrO 3, SrTiO 4, SrTi 2 Perovskite oxides such as O ₇ , BeZrO ₃ , BaCeO ₃ , BaCe _1-x Gd _x O ₃ , CaHfO ₃ , KTaO ₃ ,
and so on. These ceramic materials may be used as the ceramic material.

Many ceramic sensors are extremely small. In general, a small ceramic plate is produced by first producing a sintered body having a relatively large area and then cutting it into an appropriate size. For this reason, the planar shape of a small ceramic plate is often a quadrangle. However, the shape of the ceramic plate is not particularly limited, and can be arbitrarily selected according to the manufacturing method of the ceramic plate, the application of the sensor, and the like. That is, the planar shape of the ceramic plate may be a polygon such as a rectangle or a triangle, or a shape having a curve such as a circle or an ellipse.
The thickness of the ceramic plate is not particularly limited, and can be arbitrarily selected according to the purpose.

[2. Metal electrode]
[2.1 Metal electrode composition]
In the present invention, the composition of the metal electrode is not particularly limited, and various materials can be used according to the composition of the ceramic material, the application of the ceramic sensor, the required characteristics, and the like. In addition, as basic selection criteria,
(1) Use a metal / ceramic combination with the smallest possible thermal expansion coefficient.
(2) Use metal with low elastic modulus, or
(3) A combination that can suppress thermal stress caused by bonding, such as using high-strength ceramics, or destruction of ceramics due to thermal stress is preferable. However, in order to obtain a ceramic sensor excellent in heat resistance and / or oxidation resistance and durability, the metal electrode is preferably made of a material having high heat resistance and high oxidation resistance.

Here, "high heat resistance and high oxidation resistance material"
(1) An element that is excellent in heat resistance and / or oxidation resistance, has high peel resistance and oxidation resistance, and can form a stable and dense oxide layer on the surface of the material (hereinafter referred to as this) A metal material containing an oxide film forming element), or
(2) A metal material that has excellent heat resistance and is less likely to cause aggressive oxidation at the operating temperature.
Say.

When a ceramic sensor is used in a high-temperature oxidizing atmosphere, an oxide film is generally generated on the surface of the metal electrode. If the oxide film is peeled off or the oxide film easily diffuses oxygen, oxidation of the metal electrode proceeds during use, and the electrical resistance of the metal electrode increases in a relatively short period of time.
On the other hand, when a metal material containing a predetermined oxide film forming element is used as the metal electrode, a dense oxide film that is difficult to peel off is formed on the surface of the metal electrode. Even when a part of the oxide film is peeled off, the oxide film forming element diffuses to the metal surface, and a new oxide film is formed. Therefore, the diffusion of oxygen into the metal electrode is suppressed, and deterioration of the heat resistance and oxidation resistance of the metal electrode can be suppressed.
The same applies to the case where a metal material that does not easily cause aggressive oxidation at the operating temperature is used as the metal electrode, and the deterioration of the characteristics of the metal electrode due to the diffusion of oxygen into the material can be suppressed.

Specific examples of the oxide film forming element include Al, Cr, Si, Ni, Mg, Zr, Ti, Zn, and Ta. Any one of these oxide film forming elements may be contained in the metal electrode, or two or more of them may be contained.
The amount of the oxide film forming element contained in the metal electrode can suppress the diffusion of oxygen into the metal electrode, and the metal electrode composition and the type of oxide film forming element so as not to reduce the workability of the metal electrode. The optimum amount is selected according to the above.
Specifically, the amount of the oxide film forming element contained in the metal electrode is preferably more than the amount necessary for forming the oxide film for 100 hours or more under high temperature use conditions of 1000 ° C. or more. Further, the amount of the oxide film forming element contained in the metal electrode is preferably 1 wt% or more. In particular, a material having an Al content of 1 wt% or more is suitable as a metal electrode.

The metal electrode preferably contains an oxide film stabilizing element in addition to or instead of the oxide film forming element described above. Here, the “oxide film stabilizing element” refers to an element having a function of stabilizing the oxide film formed on the surface of the metal electrode.
In general, it is known that oxide films formed on the surface of a metal material include those having good adhesion to the underlying metal material and those having poor adhesion. If the oxide film has poor adhesion to the underlying metal material, the addition of a certain element (oxide stabilizing element) to the metal material improves the adhesion between the oxide film and the underlying film, Peeling can be suppressed. In the present invention, an oxide film stabilizing element is not necessarily required. However, when a metal electrode containing an oxide film stabilizing element is used, even if it is used for a long time in a high-temperature oxidizing atmosphere, A ceramic sensor capable of maintaining oxidation resistance is obtained.

Specific examples of such oxide film stabilizing elements include rare earth elements such as Y, Yb, La, Ce, Ta, and Th. The oxide film stabilizing element may be contained in a metal state in a metal electrode, or may be contained in an oxide or double oxide state. Further, the metal electrode may contain any one of these oxide film stabilizing elements, or may contain two or more kinds. In particular, a material containing both one kind of oxide film forming elements such as Al, Cr, and Si and a rare earth element is suitable as a metal electrode.
The amount of the oxide film stabilizing element contained in the metal electrode can increase the adhesion of the oxide film and the composition of the metal electrode, the oxide film stabilizing element so as not to deteriorate the workability of the metal electrode. Select the optimal amount according to the type.

Specifically, as a material of the metal electrode,
(1) Fe-Cr-Al alloy, Fe-Cr-Al-La alloy, Fe-Cr-Si alloy, Fe-Cr-Si-Y alloy, Fe-Cr-Y alloy, Fe-Cr-La alloy, etc. Fe-based high heat resistance and high oxidation resistance material,
(2) Ni-based high heat resistance / high oxidation resistance material such as Ni—Cr—Al alloy, Ni—Cr—Mo—Fe alloy, Ni—Cr—Fe alloy, or Ni—Cr—Mo—W alloy Ni-Cr-Mo-Nb alloy, Ni-Fe-Ce alloy, Ni-Cr-Ti-Al alloy, Ni-Al-Ti alloy, etc. Al, Mo, Fe, Cr, Cu, Nb, W, Ti, Ni alloy composed of elements such as Co, Si, Y and La,
(3) Cr-based high oxidation resistance / high heat resistance materials such as Cr—Fe—Al—Ni alloy, Cr—Fe alloy, Cr—Ni—Fe alloy, Cr—Al—Fe—Y alloy,
(4) Al, W, Nb, Zr, Ta, Ti, Ni, Pt, La, Pd, Au, Sm, Sn, Fe, Cu, Gd, Si, Co, Fe, Sc, Ru, Ti, Th, Cr , Zn, Ag, Mo, Re, etc., or a heat-resistant material made of an alloy thereof,
and so on.

The combination of the metal electrode and the ceramic material is not particularly limited, and can be arbitrarily selected according to the application of the ceramic sensor.
However, in order to obtain a ceramic sensor with excellent heat resistance, the combination of the metal electrode and the ceramic material is selected so that a diffusion layer having a melting point higher than the melting point of the metal electrode is formed at the interface after bonding. Is preferred.
For example, it is known that silicides of Pt and Ni have a lower melting point than Pt and Ni. Therefore, when either one of the metal electrode and the ceramic material contains Pt and / or Ni, it is preferable to use one containing no Si so that these silicides are not generated at the interface.

[2.2. Metal electrode thickness]
The metal electrode is for taking out a physical change generated in the ceramic plate as an electrical output. The thickness of the metal electrode affects the durability of the ceramic sensor. For example, when the ceramic sensor is used at a high temperature, when the thickness of the metal electrode is relatively thin, the metal electrode is oxidized in a short time, and it is difficult to extract the electrical output. In addition, the lead wire is joined to the metal electrode using laser welding or the like, but if the thickness of the metal electrode is too thin, the lead wire has insufficient joint strength. However, when the maximum use temperature is lower than the oxidation resistance temperature of the metal electrode, it is not limited to this and may be made thin.
In order to obtain a durability of 1000 ° C. × 100 hours or more and a practically sufficient lead wire bonding strength, the thickness of the central portion of the metal electrode is preferably 5 μm or more.

[2.3. Thermal expansion coefficients of metal electrodes and ceramic plates]
In general, when a metal electrode is directly bonded to the surface of a ceramic plate, the metal electrode peels off as the difference between the thermal expansion coefficient (α _S ) of the ceramic plate and the thermal expansion coefficient (α _M ) of the metal electrode increases. It becomes easy. On the other hand, when the shape of the metal electrode is optimized as will be described later, peeling of the metal electrode can be suppressed even when the difference in thermal expansion coefficient between the two is relatively large.
Specifically, the ratio (Δα × 100/100) of the difference between the thermal expansion coefficient (α _M ) of the metal electrode and the thermal expansion coefficient of the ceramic (Δα = α _M −α _S ) with respect to the thermal expansion coefficient (α _S ) of the ceramic plate. Even when a metal electrode having α _S ) of 10% or more is used, peeling of the metal electrode can be suppressed by optimizing the shape of the metal electrode.

[2.4. Metal electrode shape]
In the present invention, the metal electrode is made of a material that satisfies at least one of the following conditions.
(1) All or part of the outer periphery of the metal electrode is missing, and all or part of the end of the ceramic plate is exposed.
(2) The thickness of at least a part of the outer periphery of the metal electrode is thinner than the central portion.
Moreover, when a metal electrode has a corner | angular part, it is preferable that a metal electrode satisfy | fills the following conditions further.
(3) The corner of the metal electrode having the corner is missing, and the ceramic plate is exposed.

“The entire outer periphery of the metal electrode is missing” means that the area of the metal electrode is smaller than the area of the ceramic plate and the end of the ceramic plate is exposed with a predetermined width over the entire circumference of the metal electrode. The state that is.
“A part of the outer periphery of the metal electrode is missing” means that the area of the metal electrode is smaller than the area of the ceramic plate and a part of the end portion of the ceramic plate (for example, only a corner portion or only one side faces). It means a state where only two sides are exposed.
“The thickness of at least a part of the outer periphery of the metal electrode is thinner than the central part”
(A) A state in which the cross-sectional shape of the entire metal electrode is trapezoidal when the metal electrode is cut from one direction,
(B) A state in which the cross-sectional shape of the entire metal electrode is arcuate when the metal electrode is cut from a certain direction,
(C) A state in which the cross-sectional shape of the end portion of the metal electrode is an arc shape or a step shape,
And so on.
The ceramic sensor according to the present invention may satisfy any one of the above-described conditions, or may satisfy two or more simultaneously.

[3. Specific example of ceramic sensor]
[3.1. First Specific Example]
FIG. 1 shows a first specific example of a ceramic sensor according to the present invention. In FIG. 1, a ceramic sensor 10a includes a ceramic plate 12a and metal electrodes 14a and 14a bonded to both surfaces of the ceramic plate 12a.
The ceramic plate 12a and the metal electrodes 14a and 14a each have a quadrangular planar shape. In addition, the metal electrodes 14a and 14a are provided with a taper at a corner (including a case where the corner of the metal electrode 14a and 14a is cut off vertically with a width w).
In FIG. 1, “L ₁ ” and “L ₂ ” represent the lengths of the respective sides of the ceramic plate 12a (and the metal electrodes 14a and 14a), respectively. “Θ” represents an angle (taper angle) formed by the surface of the ceramic plate 12a and the inclined upper end surfaces of the metal electrodes 14a and 14a. “W” represents the distance (corner notch width) from the taper base point to the end of the ceramic plate 12a when viewed from the direction perpendicular to the side of the ceramic plate 12a. “A” represents the thickness (remaining thickness) of the extreme ends of the metal electrodes 14a, 14a.

In general, the greater the corner chip width (w), the greater the effect of suppressing the peeling of the metal electrodes 14a, 14a. In order to obtain the ceramic sensor 10a having excellent durability, the ratio (w × 100 / L) of the corner chip width (w) to the width (L) of one side of the metal electrodes 14a, 14a is preferably 5% or more. When L ₁ and L ₂ are different, the “width of one side (L)” means the width of the short side.
The taper angle (θ) can be arbitrarily selected within the range of 0 ° <θ ≦ 90 °. Depending on the taper angle (θ) and the corner chip width (w), the remaining thickness (a) may be greater than zero. If the corner chip width (w) is set to a certain value and the taper angle (θ) is increased, the remaining thickness (a) will eventually become zero, and if the taper angle (θ) is further increased, the ceramic plate The corners of 12a are exposed. Whether the remaining thickness (a) is greater than zero, the remaining thickness (a) is zero, or the end of the ceramic plate 12a is exposed, the metal electrodes 14a and 14a are peeled off. There is an effect to suppress.
When the taper angle (θ) exceeds a certain value and the corners of the ceramic plate 12a are exposed, the planar shape of the metal electrodes 14a and 14a is a polygon with square corners cut off. The corner chip width (w) is preferably 0 <w ≦ L / 2.

[3.2. Second specific example]
FIG. 2 shows a second specific example of the ceramic sensor according to the present invention. In FIG. 2, the ceramic sensor 10b includes a ceramic plate 12b and metal electrodes 14b and 14b bonded to both surfaces of the ceramic plate 12b.
The ceramic plate 12b and the metal electrodes 14b and 14b have a quadrangular planar shape. The area of the metal electrodes 14b and 14b is smaller than that of the ceramic plate 12b, and the ceramic plate 12b is exposed with a predetermined width over the entire circumference of the metal electrodes 14b and 14b. That is, the metal electrodes 14b and 14b are in a state where the entire outer periphery is missing.
In FIG. 2, “L ₁ ” and “L ₂ ” represent the lengths of the sides of the metal electrodes 14b and 14b, respectively. “B” represents the width (exposed width) of the ceramic plate 12b exposed around the metal electrodes 14b and 14b. “R” represents the radius of curvature of the corners of the metal electrodes 14b and 14b. “Θ” represents an angle (taper angle) formed by the surface of the ceramic plate 12b and the end surfaces of the metal electrodes 14b and 14b. In FIG. 2, the taper angle (θ) is 90 °, but this is merely an example, and the taper angle (θ) may be less than 90 °.

Generally, the effect of suppressing peeling of the metal electrodes 14b and 14b increases as the exposed width (b) increases. In order to obtain the ceramic sensor 10b having excellent durability, the ratio (b × 100 / L) of the exposed width (b) to the width (L) of one side of the metal electrodes 14b, 14b is preferably 1% or more. When L ₁ and L ₂ are different, the “width of one side (L)” means the width of the short side.
When the exposed width (b) having a certain width is provided around the metal electrodes 14b and 14b, the radius of curvature of the corners of the metal electrodes 14b and 14b may be zero. However, when the exposed width (b) having a certain width is provided and the corners of the metal electrodes 14b and 14b are rounded, the effect of suppressing the peeling of the metal electrodes 14b and 14b is further increased. In order to obtain the ceramic sensor 10b having excellent durability, the radius of curvature of the corners of the metal electrodes 14b and 14b with respect to the width (L (= min (L ₁ , L ₂ )) of one side of the metal electrodes 14b and 14b ( The ratio of R) (R × 100 / L) is preferably 5% or more.
If the taper angle (θ) is arbitrarily selected within the range of 0 <θ ≦ 90 °, or if the ridge lines on the outer periphery of the metal electrodes 14b and 14b are annealed, a further stress relaxation effect can be expected.

[3.3. Third specific example]
FIG. 3 shows a third specific example of the ceramic sensor according to the present invention. In FIG. 3, the ceramic sensor 10c includes a ceramic plate 12c and metal electrodes 14c and 14c bonded to both surfaces of the ceramic plate 12c.
Both the ceramic plate 12c and the metal electrodes 14c and 14c have a quadrangular planar shape. The area of the metal electrodes 14c, 14c is smaller than that of the ceramic plate 12c, and the left and right sides of the metal electrodes 14c, 14c are exposed with a predetermined width. That is, the metal electrodes 14c and 14c are in a state where a part of the outer periphery is missing. In FIG. 3, only one set of opposing sides of the metal electrodes 14c and 14c is missing, but both sides of another opposing set of sides may be missing. Furthermore, the thickness of the metal electrodes 14c and 14c in the vicinity of the boundary line where the end portion of the ceramic plate 12c is exposed is smaller than the thickness of the central portion of the metal electrodes 14c and 14c.
Here, “in the vicinity of the boundary line” refers to a region from the boundary line to a point where the thickness of the metal electrodes 14c and 14c starts to decrease.
In FIG. 3, “L ₁ ” represents the length of the metal electrodes 14 c and 14 c when viewed from the direction perpendicular to the boundary line where the ceramic plate 12 c is exposed. “L ₂ ” represents the length of the metal electrodes 14 c and 14 c when viewed from a direction parallel to the boundary line where the ceramic plate 12 c is exposed. “B” represents the width (exposed width) of the ceramic plate 12c exposed to the outside of the metal electrodes 14c, 14c. “Θ” represents an angle (taper angle) formed by the surface of the ceramic plate 12c and the inclined upper end surfaces of the metal electrodes 14c and 14c. “W” represents the distance (corner-missing width) from the taper base point to the ends (boundary lines) of the metal electrodes 14c and 14c when viewed from the direction perpendicular to the side of the ceramic plate 12c. “A” represents the thickness (remaining thickness) of the extreme ends of the metal electrodes 14c and 14c.

In general, the greater the exposure width (b), the greater the effect of suppressing the peeling of the metal electrodes 14c, 14c. In order to obtain the ceramic sensor 10c having excellent durability, the ratio (b × 100 / L) of the exposed width (b) to the width (L = L ₂ ) of one side of the metal electrodes 14c, 14c is 1% or more. preferable.
In general, the greater the corner chip width (w), the greater the effect of suppressing the peeling of the metal electrodes 14a, 14a. In order to obtain the ceramic sensor 10a having excellent durability, the ratio (w × 100 / L) of the corner chip width (w) to the width (L = L ₂ ) of one side of the metal electrodes 14a, 14a is 1% or more. Is preferred.
The taper angle (θ) can be arbitrarily selected within the range of 0 ° <θ ≦ 90 °. The taper angle (θ) is more preferably 10 ° ≦ θ ≦ 60 °. Depending on the taper angle (θ) and the corner chip width (w), the remaining thickness (a) may be greater than zero. When the corner chip width (w) is set to a certain value and the taper angle (θ) is increased, the remaining thickness (a) eventually becomes zero. Even if the remaining thickness (a) is greater than zero and the remaining thickness (a) is zero, there is an effect of suppressing peeling of the metal electrodes 14c and 14c.
Further, further stress relaxation effect can be expected by performing chamfering or R machining on the angle portion of the metal electrode as described above.

[3.4. Fourth Specific Example]
FIG. 4 shows a fourth specific example of the ceramic sensor according to the present invention. In FIG. 4, the ceramic sensor 10d includes a ceramic plate 12d and metal electrodes 14d and 14d bonded to both surfaces of the ceramic plate 12d.
The ceramic plate 12d has a quadrangular planar shape. On the other hand, the metal electrodes 14d and 14d have a circular planar shape. The diameters of the metal electrodes 14d and 14d are shorter than the length of one side of the ceramic plate 12d, and the ends of the ceramic plate 12d are exposed around the metal electrodes 14d and 14d.
In FIG. 4, “L ₁ ” and “L ₂ ” represent the widths (diameters) of the metal electrodes 14 d and 14 d viewed from the direction perpendicular to one side of the ceramic plate 12 d and the side intersecting with this, respectively. . “B” represents the shortest distance (exposed width) from the ends of the metal electrodes 14d and 14d to the end of the ceramic plate 12d. “Θ” represents an angle (taper angle) formed by the surface of the ceramic plate 12d and the end surfaces of the metal electrodes 14d and 14d. In FIG. 4, the taper angle (θ) is 90 °, but this is merely an example, and the taper angle (θ) may be less than 90 °.

In general, the greater the exposure width (b), the greater the effect of suppressing peeling of the metal electrodes 14d, 14d. In order to obtain the ceramic sensor 10d having excellent durability, the ratio (b × 100 / L) of the exposed width (b) to the width (L (= L ₁ = L ₂ )) of the metal electrodes 14d, 14d is 1 % Or more is preferable. However, when the value exceeds a certain value, the stress relaxation effect is hardly changed (see FIG. 9).
In the example shown in FIG. 4, the ceramic plate 12d has a square planar shape, but the planar shape of the ceramic plate 12d may be a shape other than a square (for example, a triangle, a circle, etc.). The electrodes 14d and 14d may be ellipses (L ₁ ≠ L ₂ ).

[3.5. Fifth Specific Example]
FIG. 5 shows a fifth specific example of the ceramic sensor according to the present invention. In FIG. 5, the ceramic sensor 10e includes a ceramic plate 12e and metal electrodes 14e and 14e bonded to both surfaces of the ceramic plate 12e.
The ceramic plate 12e has a quadrangular planar shape. On the other hand, the metal electrodes 14e and 14e have a circular planar shape. The diameters of the metal electrodes 14e and 14e are shorter than the length of one side of the ceramic plate 12e, and the ends of the ceramic plate 12e are exposed around the metal electrodes 14e and 14e. Furthermore, the cross-sectional shape of the metal electrodes 14e, 14e is arcuate (hemispheric).
In FIG. 5, “L ₁ ” and “L ₂ ” represent the widths (diameters) of the metal electrodes 14 d and 14 d viewed from the direction perpendicular to one side of the ceramic plate 12 d and the side intersecting with the one side, respectively. . “B” represents the shortest distance (exposure width) from the end of the metal electrodes 14e, 14e to the end of the ceramic plate 12e.

In general, the greater the exposure width (b), the greater the effect of suppressing peeling of the metal electrodes 14e, 14e. In order to obtain the ceramic sensor 10e having excellent durability, the ratio (b × 100 / L) of the exposed width (b) to the diameter (L (= L ₁ = L ₂ )) of the metal electrodes 14e, 14e is 1 % Or more is preferable.
In the example shown in FIG. 5, the ceramic plate 12e has a quadrangular planar shape, but the planar shape of the ceramic plate 12e may be a shape other than a square (for example, a triangle, a circle, etc.).

Next, a method for manufacturing a ceramic sensor according to the present invention will be described.
The ceramic sensor according to the present invention is:
(1) A sintered body having a relatively large area is produced,
(2) A metal foil having a predetermined thickness is bonded to the entire surface of the sintered body,
(3) Remove unnecessary parts of the metal foil by etching, machining, etc.
(4) cutting the sintered body into a predetermined size;
Can be manufactured.
In the ceramic sensor thus obtained, lead wires are usually bonded or bonded to both surfaces of the metal electrode.

The metal foil and the ceramic may be joined by directly superimposing the two, or a suitable brazing material, intermediate layer, conductive paste, conductive adhesive between the metal foil and the ceramic. Etc. may be used for the joining.
The joining temperature and time are selected optimally depending on the composition of the metal foil and ceramics, the intermediate layer, etc., the composition thereof, a combination thereof, and the like. In general, when the bonding temperature is too low as compared to the melting point of the metal foil, the intermediate layer, and / or when the bonding time is too short, sufficient bonding strength cannot be obtained. On the other hand, if the joining temperature is too high compared to the melting point of the metal foil, intermediate layer, etc. and / or if the joining time is too long, the metal foil melts, deteriorates, decomposes, or is generated on the ceramic side. Since the thickness of the diffusion layer to be increased is not preferable.

  The joining is preferably performed while pressurizing the metal foil / ceramic interface. The optimum pressure varies depending on the composition of the metal foil and the ceramic material, the composition of the intermediate layer, etc., the combination thereof, the bonding temperature, and the like. In general, when the pressure at the time of bonding is too small, a non-contact portion is likely to be generated at the metal foil and ceramic interface, so that uneven diffusion of constituent elements occurs, and sufficient bonding strength cannot be obtained. On the other hand, when the pressure at the time of joining becomes too large, the metal foil and / or the ceramic material may be deformed and broken, which is not preferable. Specifically, the applied pressure at the time of joining is preferably 0.1 MPa or more and 100 MPa or less.

For example, when joining the Fe-Cr-Al, Ni- Cr-Al metal foil and _Si 3 _{N 4} consisting of Fe-based or Ni-based heat resistant steel such as, junction temperature, 0.4 of the melting point of the metal foil material The temperature is preferably from 500 ° C. to 1200 ° C. Optimum conditions are selected for the bonding time and bonding pressure depending on the bonding temperature.

  Further, the bonding may be performed simply by heating while applying pressure, but a so-called Field-Assisted Bonding method in which an electric field or an electric field is applied at the time of bonding may be used. When an electric field is applied at the time of bonding, an interface reaction is forcibly caused, so that a good bonded body can be obtained. Alternatively, it is preferable to simply apply a voltage to the laminate of the metal foil and the ceramic and join them by Joule heat.

In general, a carbon jig coated with a release material such as a carbon jig or BN is used for pressurization during bonding. When a metal foil / ceramic laminate is pressed using such a jig, carbon and / or nitrogen diffuses from the surface of the carbon jig into the metal foil, and a carbon and / or nitrogen diffusion layer on the metal electrode surface, In addition, a carbide layer and / or a nitride layer may be generated. When such a diffusion layer or the like is generated on the surface of the metal electrode, it causes a reduction in oxidation resistance and heat resistance of the metal electrode. Moreover, when joining or welding a lead wire, there exists a possibility of reducing joinability and weldability.
In such a case, it is preferable that the metal foil is previously subjected to a treatment for suppressing the diffusion of carbon and / or nitrogen. Specifically, as such processing,
(1) A method of forming a thin oxide film on the surface of a metal foil by oxidizing a metal foil containing an oxide film forming element before joining,
(2) A method of forming a metal layer having a low affinity for carbon (for example, a noble metal layer such as platinum or rhodium) on the surface of the metal foil,
(3) A method of forming a metal layer having a higher content of oxide film forming elements than the metal foil on the surface of the metal foil,
(4) A method of forming a release layer having low reactivity such as BN and Al ₂ O ₃ between a carbon punch and a thin metal,
(5) High melting point such as Mo and W and low reactivity with the metal foil, or even if a solid solution is formed, the characteristics of the metal foil such as melting point, oxidation resistance and conductivity are not deteriorated. A method of joining a metal foil or a metal plate between a metal foil for electrodes and a carbon die,
and so on.
In (5), a release coating layer such as BN may be formed between the metal foil or metal plate and the electrode metal foil.

Next, the operation of the ceramic sensor according to the present invention will be described.
A metal having heat resistance and oxidation resistance usually has a larger coefficient of thermal expansion than ceramics. Therefore, when an electrode made of such a metal and a ceramic plate are joined, thermal stress due to a difference in thermal expansion coefficient between the two is generated at the interface. This thermal stress is highest at the outer periphery of the metal electrode. Moreover, when the shape of the ceramic plate is a polygon such as a quadrangle, the thermal stress generated at the corner is the highest.
On the other hand, if all or a part of the outer periphery of the metal electrode is missing and / or if the thickness of at least a part of the outer periphery of the metal electrode is made thinner than the central portion, the thermal stress generated in the outer periphery of the metal electrode is remarkably increased. Can be reduced. Therefore, even if a cooling cycle is applied to such a ceramic sensor, the metal electrode is less likely to peel off. In addition, this makes it possible to suppress a long-term change in resistance value resulting from the generation of cracks or peeling at the electrode / ceramic interface.
Furthermore, since it is not always necessary to interpose an intermediate layer in order to reduce thermal stress, the cost is low and the metal electrode composition hardly changes over time.

(Example 1, Reference Examples 2-3, Example 4, Reference Example 5-9, the specific Comparative Examples 1)
[1. Preparation of sample]
□ Both sides of a 10 mm × 1 mm SiC ceramic were sandwiched between two stainless steel foils (thickness 30 μm). This was heat-treated under conditions of 1000 ° C. × 10 minutes × 30 MPa, and diffusion bonded. After removing a part of the stainless steel foil by etching, the ceramic was cut into squares or rectangles of a predetermined size.
The shape of the metal electrode is
(1) Polygons with tapered corners ( Example 1, Reference Examples 2-3, Example 4 , FIG. 1),
(2) A quadrilateral with the entire circumference removed and R added to the corners ( Reference Example 5 , FIG. 2),
(3) A quadrangle ( reference examples 6 to 7 and FIG. 3) with two opposite sides removed and tapered at the corners,
(4) Cylindrical shape ( Reference Example 8 , FIG. 4), or
(5) Hemisphere ( Reference Example 9 , Fig. 5),
It was.
For comparison, as shown in FIG. 6, a non-processed ceramic sensor 10f (Comparative Example 1) in which square metal electrodes 14f and 14f were joined to the entire surface of both sides of a square ceramic plate 12f was also produced.

[2. Test method (1)]
About the obtained ceramic sensor, the thermal cycle test which makes 1000 degreeC * 50h 1 cycle in air | atmosphere was performed for 50-500h. In the thermal cycle test, the peeling state of the metal electrode was evaluated with a stereomicroscope every cycle.

[3. Result (1) ]
Table 1 shows the peel evaluation results. Table 1 also shows details of the electrode shape. In Table 1, L ₁ represents the width of the metal electrode when viewed from the direction perpendicular to one side (a ′) of the rectangular ceramic plate. L ₂ represents the width of the metal electrode when viewed from the direction perpendicular to the side (b ′) intersecting with one side (a ′). In Reference Examples 6 and 7 , the metal electrode is a 3 × 1 mm rectangle, and b represents the exposed width of the metal electrode when viewed from the direction perpendicular to the short side (L ₂ = 1 mm).
In Comparative Example 1, peeling of the metal electrode occurred within 50 hours. On the other hand, Example 1, Reference Examples 2-3, Example 4, and Reference Examples 5-9 were all 100 h, and no metal electrode peeling was observed. In particular, in Reference Examples 6 , 7 , and 9 , peeling of the metal electrode was not observed even after the heat treatment for 500 hours.

[4. Test method (2)]
The ceramic sensors obtained in Reference Example 7 and Comparative Example 1 were subjected to a cooling / heating cycle test in a vacuum at room temperature ⇔ 1050 ° C./day. Each time one cycle was completed, the sensor resistance value was measured and the peeled state was evaluated.

[5. Result (2)]
FIG. 7 shows the results of the cooling / heating cycle test. In the case of Comparative Example 1, the resistance value before the test was relatively high, and the resistance value increased rapidly after the second cycle. When observed with a stereomicroscope at the end of two cycles, peeling of the metal electrode was observed.
On the other hand, in the case of Reference Example 7 , the resistance value before the test was relatively low, and no increase in the resistance value was observed after the end of 12 cycles. Further, even when observed with a stereomicroscope, peeling of the metal electrode was not observed.

( Reference Example 10 )
[1. experimental method]
The effect of electrode area and electrode corner R processing was analyzed by FEM. The material of the ceramic plate was SiC ceramic, and the size was 8 mm square. The material of the metal electrode was Fe-Cr-Al-La, and the thickness was 30 μm. The bonding temperature was 1000 ° C.

[2. result]
FIG. 8 shows the stress relaxation effect by reducing the electrode area in an 8 mm square metal foil / ceramic plate bonding sample. In the calculation model in which the ceramic plate thickness is 1 mm and the metal foil thickness is 30 μm, when the temperature is lowered to 20 ° C. after bonding at 1000 ° C., when the exposed width (b) is zero, the maximum principal stress is metal It was found to occur at the corners of the electrode. The maximum principal stress was 2170 N / mm ² (2170 MPa). In contrast, when the entire circumference of the metal electrode was removed with a constant exposure width (b), the maximum principal stress was 1460 N / mm ² and the stress relaxation rate was −33%.
The left diagram in FIG. 9 shows the relationship between the exposure width (b) and the maximum principal stress when the angular curvature radius (R) is 0 mm. Moreover, the right figure of FIG. 9 shows the relationship between the angular curvature radius (R) and the maximum principal stress when the exposure width (b) is 0 mm. FIG. 9 shows that the maximum principal stress decreases as the exposed width (b) increases and the angular curvature radius increases.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention.

  The ceramic sensor according to the present invention can be used as various sensors used in a high-temperature oxidizing atmosphere of 600 ° C. or higher.

It is the top view (upper figure) and front view (lower figure) of the ceramic sensor which concerns on the 1st Embodiment of this invention. It is the top view (upper figure) and front view (lower figure) of the ceramic sensor which concerns on the 2nd Embodiment of this invention. It is the top view (upper left figure), front view (lower left figure), and right side view (upper right figure) of the ceramic sensor which concerns on the 3rd Embodiment of this invention. It is the top view (upper figure) and front view (lower figure) of the ceramic sensor which concerns on the 4th Embodiment of this invention. It is the top view (upper figure) and front view (lower figure) of the ceramic sensor which concerns on the 5th Embodiment of this invention. It is a top view (upper left figure), a front view (lower left figure), and a right side view (upper right figure) of a conventional ceramic sensor. It is a cooling-heat cycle test result of the ceramic sensor of the reference example 7 and the comparative example 1. It is a FEM analysis result which shows the stress relaxation effect by electrode area reduction. The left figure in FIG. 9 shows the FEM analysis result showing the relationship between the exposure width (b) and the maximum principal stress, and the right figure in FIG. 9 shows the FEM analysis result showing the relation between the angular curvature radius (R) and the maximum principal stress. It is.

Claims (3)

Ceramic plates,
A metal electrode joined to at least one surface of the ceramic plate,
The planar shape of the ceramic plate is a quadrangle,
The planar shape of the metal electrode is the quadrangle, and the corners of the quadrangle are not cut off,
The metal electrode is a ceramic sensor in which a taper is provided only at the corner. The thickness of the central portion of the metal electrode, the ceramic sensor according to claim 1 Ru der least 5 [mu] m. The metal electrode, the ceramic sensor according to claim 1 or 2 ing from the high heat resistance and high oxidation resistant material of Fe-based or Ni-based.

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