JP2004296142A - Ceramic heater and detecting element using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ceramic heater capable of prolonging the service life thereof and rapidly elevating the temperature by solving problems such as durability of the heater at a high temperature and destruction caused by a thermal shock at the time of rapid elevation of the temperature. <P>SOLUTION: In the heater, a heating element mainly made of platinum is embedded in an insulating ceramic substrate 26 mainly made of aluminum, aluminum of 30-60 volume% is contained in the heating element, the aluminum existed as particles with the average crystal particle diameter of 0.2-1.0 μm and a thermal expansion coefficient of the heating element in a range at room temperature-800°C is greater than that of the ceramic substrate 26 by 0.8-1.4×10<SP>-6</SP>/°C. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【００５１】
表１より、発熱体と絶縁性セラミック基体の熱膨張係数の差が１．４×１０^−６／℃を超える試料Ｎｏ．１と試料Ｎｏ．２では破損率が高いことがわかる。
【００５２】
また、その差が０．８×１０^−６／℃より小さい試料Ｎｏ．６と試料Ｎｏ．７では、アルミナの含有率が６０体積％を超え、発熱体の抵抗値が高くヒータとしては不適当であった。一方、本発明品はいずれも破損率が５０％以下と低く、耐久性に優れたセラミックヒータであった。
【００５３】
【発明の効果】
以上詳述したとおり、本発明によれば、発熱体の高温度におけるヒータの耐久性や急速昇温の際の熱衝撃による破壊等の問題を解決し、ヒータ寿命を長期化した急速昇温が可能なセラミックヒータを提供する事ができる。
【図面の簡単な説明】
【図１】セラミックヒータの構造を説明するための概略断面図である。
【図２】本発明のセラミックヒータの一例を説明するための概略断面図である。
【図３】図２のセラミックヒータの製造方法を説明するための分解斜視図である。
【符号の説明】
１、２７ａ ・・・発熱体
２ ・・・パット
３ ・・・スルホール
４、２６ ・・・絶縁性セラミック基体
２２ ・・・固体電解質基盤
２２ａ ・・・大気導入孔
２３ａ ・・・基準電極
２４ａ ・・・測定電極
２５ ・・・セラミック多孔質層
２０ ・・・センサ部
２１ ・・・ヒータ部[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a ceramic heater excellent in durability, specifically, used for a heater for heating a semiconductor substrate, a petroleum fan heater, and the like, and particularly suitable for a heater for a detection element such as a gas sensor for a vehicle. What is used.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a ceramic heater in which a heating element is embedded in an insulating substrate made of an insulating ceramic such as alumina (see Patent Document 1) is known. In addition to a heater for a semiconductor substrate, a hot water heater or an oil fan heater is known. It is used as
[0003]
On the other hand, in an internal combustion engine such as an automobile, by detecting the oxygen concentration in the exhaust gas and controlling the air and fuel supply amounts to be supplied to the internal combustion engine based on the detected value, harmful substances from the internal combustion engine, For example, a method of reducing CO, HC, and NOx has been adopted.
[0004]
As this detection element, a solid electrolyte type oxygen sensor in which a pair of electrode layers are formed on an outer surface and an inner surface of a solid electrolyte substrate mainly composed of zirconia having oxygen ion conductivity as a main component is used.
[0005]
As a typical example of this oxygen sensor, as shown in FIG. 6, a reference electrode 32 and a measurement electrode 33 are provided on the outer surface and the inner surface of a flat solid electrolyte substrate 31, respectively, and at the same time, inside a ceramic insulator 34. An oxygen sensor has been proposed in which a ceramic heater in which a heating element 35 made of platinum is embedded is integrated (for example, Patent Documents 2 and 3). The oxygen sensor in which the ceramic heater is integrated has an advantage that the temperature of the detecting portion is rapidly raised to a high temperature of 800 to 1000 ° C. by being directly heated by the ceramic heater.
[0006]
[Patent Document 1]
JP-A-3-149791
[Patent Document 2]
JP-A-2002-540399
[Patent Document 3]
JP, 2002-236104, A
[Problems to be solved by the invention]
With respect to these ceramic heaters as described in Patent Documents 1 to 3, the performance is improved by shortening the operation time or leading to the use of the ceramic heater at a high temperature, which leads to exhibiting the respective functions for the above-mentioned applications. In order to stabilize the temperature of the ceramic heater, there has been an increasing demand for the ceramic heater itself to have a rapid temperature rising property and a high heating temperature.
[0010]
However, when the ceramic heater is used in the above-mentioned applications, when it is used in a high temperature environment exceeding 1000 ° C., or when the heater is rapidly heated, the heater may be damaged, or the resistance of the heating element may be reduced. There was a problem that it increased rapidly. Therefore, these ceramic heaters are currently used at a temperature of 1000 ° C. or less, often 700 ° C. or less, and avoiding rapid rapid temperature rise.
[0011]
The present invention solves the above-mentioned problems, such as the durability of the heater at high temperatures and the destruction due to thermal shock at the time of rapid temperature rise, and provides a ceramic heater capable of rapid temperature rise with a longer heater life. It is an object of the present invention to provide a detection element using the same.
[0012]
[Means for Solving the Problems]
The present inventor has studied the above problem, and as a result, a ceramic heater in which a heating element containing platinum as a main component is embedded in an insulating ceramic base containing alumina as a main component. It contains 30 to 60% by volume of alumina, and the alumina is present as particles having an average crystal particle diameter of 0.2 to 1.0 μm, and the coefficient of thermal expansion of the heating element in the range of room temperature to 800 ° C. Was found to be 0.8 to 1.4 × 10 ⁻⁶ / ° C. larger than that of the insulating ceramic substrate to solve the above problem, and the present invention was achieved.
[0013]
Further, it is desirable that the content of Na in the alumina is 50 ppm or less in order to enhance durability.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the basic structure of the ceramic heater of the present invention will be described. In the ceramic heater of the present invention, as shown in FIG. 1, a heating element 2 mainly composed of platinum is embedded in an insulating ceramic base 1 mainly composed of alumina. The heating element 2 is electrically connected to an electrode 5 formed on one surface of the insulating ceramic base 1 via a lead 3 and a through-hole conductor 4.
[0015]
In the present invention, in such a ceramic heater, the thermal expansion coefficient of the heating element 2 in the range of room temperature to 800 ° C. is larger than the thermal expansion coefficient of the insulating ceramic substrate 1 by 0.8 to 1.4 × 10 ⁻⁶ / ° C. This is very important. If the difference in thermal expansion is larger than 1.4 × 10 ⁻⁶ / ° C., the thermal expansion between the heating element 2 and the insulating ceramic base 1 may be caused when the heater is rapidly heated or when the heater is heated to a high temperature. Cracks develop due to thermal stress caused by the difference in the coefficients, and as a result, the element is broken. On the other hand, if the temperature is set to 0.8 × 10 ⁻⁶ / ° C. or less, it is difficult to control the conductor paste when forming the heating element, the mass productivity is deteriorated, and as a result, the cost is increased. This difference in thermal expansion is particularly preferably 0.9 to 1.2 × 10 ⁻⁶ / ° C.
[0016]
The heating element 2 in the present invention contains platinum as a main component. More specifically, an alloy of platinum alone or platinum and one of platinum selected from the group consisting of rhodium, palladium and ruthenium is used.
[0017]
It is important that the heating element 2 contains 30 to 60% by volume of alumina in addition to the above metal component. If the alumina content is less than 30% by volume, the difference in thermal expansion coefficient between the insulating ceramic substrate and the heating element becomes greater than 1.4 × 10 ⁻⁶ , so that the heating element is liable to break during heating of the heater. Conversely, when the alumina content exceeds 60% by volume, the electric resistance of the heating element 2 increases, and the thickness of the heating element 2 needs to be increased. Cracks easily occur. The alumina content of the heating element 2 is particularly preferably in the range of 35 to 45% by volume.
[0018]
It is important that the average crystal particle diameter of alumina in the heating element 2 be 0.2 to 1.0 μm, particularly 0.3 to 0.5 μm. This is because if the average particle diameter is larger than 1.0 μm, unevenness is formed on the heating element, and characteristics are varied, and stress is concentrated on the uneven portion, so that the heating element 2 is easily broken. On the other hand, when the diameter is smaller than 0.2 μm, the alumina aggregates to cause a variation in the secondary particle diameter, which causes a temperature variation in the heating element, and the disconnection or the like easily occurs.
[0019]
In the present invention, the alumina ceramic constituting the insulating ceramic substrate 1 is a ceramic containing 3% by mass or less, particularly 0.5 to 1.5% by mass of silica, calcia and magnesia as sintering aid components. It is desirable that From the viewpoint of preventing Na and K from moving to the negative electrode side and increasing the resistance, the contents of Na and K in the ceramic substrate 1 are desirably 50 ppm or less, and particularly preferably 30 ppm or less.
[0020]
As a method of manufacturing such a ceramic heater, first, a heating element paste for printing is prepared by weighing and mixing a metal powder such as platinum and alumina powder in the above range, and a heating element pattern is formed on the surface of the alumina green sheet. It is preferable to print and form the leads, electrode patterns, and through holes, and then fire them all at the same time.
[0021]
At this time, it is important from the viewpoint of the durability of the heating element that the paste for producing the heating element is controlled to 20 μm or less, particularly 15 μm or less as measured by a grind gauge. The grind gauge is a device for measuring the particle size of the paste, and is a parameter representing the maximum particle size. That is, when the grind gauge is larger than 20 μm, the heating element has irregularities, which causes a decrease in reliability of the characteristics. The grind gauge can be controlled by adjusting the diameter of the alumina particles and the diameter of the platinum particles in the paste.
[0022]
The pattern of the heating element of the ceramic heater according to the present invention may be a structure that extends in the longitudinal direction of the element and is folded at an end in the longitudinal direction, or a waveform (meander) structure that is folded at an end in a direction perpendicular to the longitudinal direction. May be.
[0023]
The ceramic heater of the present invention has no problem even if it has a cylindrical shape in addition to the flat shape as shown in FIG. Furthermore, gas sensors such as an oxygen sensor element, a NOx sensor, and a CO sensor having the ceramic heater of the present invention are also included in the present invention.
[0024]
As an application example of the present invention, FIG. 2 shows a case where the ceramic heater of the present invention is applied to heating of an oxygen sensor element.
[0025]
This is generally called a stoichiometric sensor element. In the example of FIG. 2, the sensor section 20 and the heater section 21 are integrally formed.
[0026]
In the oxygen sensor element of FIG. 2, a solid electrolyte substrate 22 made of zirconia and having oxygen ion conductivity, a reference electrode 23a in contact with air, and a measurement electrode in contact with exhaust gas are provided on both opposite surfaces of the solid electrolyte substrate 22. 24a are formed to form a sensor section 20 having a function of detecting oxygen concentration.
[0027]
On the other hand, the heater section 21 composed of the insulating ceramic base 26 in which the heating element 27a is embedded has a flat hollow shape with a sealed end, and this hollow section forms an air introduction hole 22a. A reference electrode 23a that is in contact with a reference gas such as air is formed on the hollow inner wall, and a measurement that contacts a measurement gas such as exhaust gas is formed on the outer surface of the solid electrolyte substrate 22 facing the reference electrode 23a. An electrode 24a is formed.
[0028]
Further, from the viewpoint of preventing the electrode from being poisoned by exhaust gas, a ceramic porous layer 25 is formed on the surface of the measurement electrode 24a as an electrode protection layer.
[0029]
The solid electrolyte used in the oxygen sensor element of the present invention is made of a ceramic containing ZrO ₂ , and as stabilizers Y ₂ O ₃ and Yb ₂ O ₃ , Sc ₂ O ₃ , Sm ₂ O ₃ , Nd ₂ O _{3, Dy} 2 _{O 3} or the like 1 to 30 mol% of rare earth oxide in terms of oxide, preferably the partially stabilized ZrO ₂ or stabilized ZrO ₂ containing 3 to 15 mol% are used.
[0030]
Also, by using ZrO ₂ in which Zr in ZrO ₂ is substituted with 1 to 20 atomic% of Ce for Ce, there is an effect that ionic conductivity is increased and responsiveness is further improved.
[0031]
Further, for the purpose of improving the sinterability, Al ₂ O ₃ or SiO ₂ can be added to the above-mentioned ZrO ₂ , but if it is contained in a large amount, the creep characteristics at high temperatures become poor. The total amount of Al ₂ O ₃ and SiO ₂ is preferably 5% by weight or less, particularly preferably 2% by weight or less.
[0032]
The reference electrode 23a and the measurement electrode 24a formed on the surface of the solid electrolyte substrate 22 are each made of platinum or an alloy of platinum and one selected from the group consisting of rhodium, palladium, ruthenium and gold.
[0033]
In addition, the above-mentioned ceramic solid electrolyte component is used for the purpose of preventing the grain growth of the metal in the electrode during the operation and to increase the contact point at the so-called three-phase interface between the platinum particles, the solid electrolyte, and the gas related to the response. May be mixed in the electrode at a ratio of 1 to 50% by volume, particularly 10 to 30% by volume.
[0034]
Further, the shape of the electrodes 23a and 24a may be square or elliptical. Further, the thickness of the electrode is preferably 3 to 20 μm, particularly preferably 5 to 10 μm.
[0035]
On the other hand, the insulating ceramic substrate 26 in which the heating element 27a is embedded is preferably made of dense ceramics made of alumina ceramics with a relative density of 80% or more and an open porosity of 5% or less.
[0036]
At this time, Mg, Ca, and Si may be contained in a total amount of 1 to 10% by mass for the purpose of improving the sinterability. In order to deteriorate the electrical insulation property of No. 2, it is desirable to control it to 50 ppm or less in terms of oxide. Further, by setting the relative density within the above range, the strength of the substrate is increased, so that the mechanical strength of the oxygen sensor itself can be increased.
[0037]
The heating element 27a buried in the insulating ceramic base 26 in the heater section 21 is mainly composed of platinum, and has a thermal expansion coefficient of 0% lower than that of the insulating ceramic base 26 in the range of room temperature to 800 ° C. It is preferable to contain 30 to 60% by volume of alumina in order to increase the density by 0.8 to 1.4 × 10 −6 / ° C. Further, in order to enhance the reliability of the heating element 27a, it is desirable that the average crystal particle diameter of the alumina is 0.2 to 1.0 μm.
[0038]
The heating pattern of the heating element 27a in the heater section 21 may have a meandering structure as well as a structure extending in the longitudinal direction and folded at an end in the longitudinal direction.
[0039]
The ceramic porous layer 25 formed on the surface of the measurement electrode 24a has a thickness of 10 to 800 μm and a porosity of 10 to 50% and is at least one selected from the group consisting of zirconia, alumina, γ-alumina, and spinel. Is desirably formed.
[0040]
Further, the detection element such as the ceramic heater or the oxygen sensor of the present invention has a total element thickness of 0.8 to 1.5 mm, particularly 1.0 to 1.2 mm, and an element length of 45 to 55 mm. In particular, 45 to 50 mm is preferable in view of the relationship between the rapid temperature rise and the degree of attachment of the element to the engine.
[0041]
Next, a method for manufacturing the ceramic heater structure of the present invention will be described with reference to the exploded perspective view of FIG. 3 using the method of manufacturing the ceramic heater structure of FIG. 2 as an example.
[0042]
First, a green sheet 41 of a solid electrolyte is prepared. The green sheet 41 is formed, for example, by adding an organic binder for molding to a ceramic solid electrolyte powder having oxygen ion conductivity of zirconia as appropriate, for example, by a doctor blade method, extrusion molding, or hydrostatic molding (rubber press). Alternatively, it is manufactured by a known method such as press forming.
[0043]
Next, on both surfaces of the green sheet 41, patterns 42a and 42c, lead patterns 42b and 42d, pads 43a, through holes 43b, and the like that become the measurement electrode 24 and the reference electrode 23, respectively, are formed of, for example, a conductive paste containing platinum. The sensor part A is manufactured by printing using a slurry dipping method, or screen printing, pad printing, or roll transfer using the above method.
[0044]
Further, as the conductive paste containing platinum used at this time, platinum particles containing 1 to 50% by volume, particularly 10 to 30% by volume of zirconia composed of the above-mentioned ceramic solid electrolyte component are used. In addition, those containing an organic resin component such as ethyl cellulose are desirable.
[0045]
Next, a mixed powder of platinum having an average particle size of 0.5 to 2.0 μm, alumina having an average particle size of 0.1 to 1.2 μm, and a binder were formed on the surface of the green sheet 47 made of an insulating ceramic substrate. The heating element pattern 49, the lead pattern 50, the electrode pattern 51, the through hole 52, and the like are formed by screen printing, pad printing, and roll transfer using a printing paste of a heating element made of. The green sheets 45 and 46 made of an insulating ceramic substrate having the air introduction holes 44 formed thereon are further formed by interposing an alumina green sheet with an adhesive such as an acrylic resin or an organic solvent or applying pressure with a roller or the like. By mechanically bonding, a laminate B for the heater unit 21 is manufactured. At this time, the printing paste of the heating element is desirably 20 μm or less as measured by a grind gauge. In order to control the grind gauge within the above range, it may be adjusted by grinding platinum or alumina with a rotary mill or the like.
[0046]
Thereafter, the laminate A of the sensor unit 20 and the laminate B of the heater unit 21 are mechanically adhered to each other by interposing an adhesive such as an acrylic resin or an organic solvent, or by applying pressure using a roller or the like. After bonding and integration, they are fired. The firing is performed in the air or in an inert gas atmosphere at a temperature in the range of 1300 ° C. to 1700 ° C. for 1 to 10 hours. At the time of firing, in order to suppress the warpage of the sensor portion A at the time of firing, the amount of warpage can be reduced by placing a smooth substrate such as alumina as a weight on the laminate.
[0047]
【Example】
The ceramic heater shown in FIG. 1 was manufactured. Commercially available 99.9% pure alumina powder having an average particle diameter of 0.5 μm (containing 0.1% by weight of silica) and platinum powder containing 1 to 50% by volume of an alumina powder having an average particle diameter of 0.2 μm Was prepared. A slurry was prepared by adding an acrylic binder and toluene to the alumina powder, and a green sheet of alumina having a sheet thickness of 0.3 mm was prepared by a doctor blade method.
[0048]
A paste made of platinum powder in which the amount of alumina powder added was changed to 20 to 80% by volume and the coefficient of thermal expansion of the heating element was changed as shown in Table 1 (alumina average crystal particle diameter was 0.1 to 1. (Change to 2 μm) (grind gauge: 5 to 25 μm) was prepared, and a heater pattern was printed on the surface of the green sheet of alumina by screen printing so that the resistance value was about 8Ω at room temperature after firing. Then, three green sheets of alumina were laminated on the surface of these heater patterns using an allyl binder to produce a laminated body of heaters. The firing was performed at 1500 ° C. for 2 hours in the air. Thereafter, the outer periphery was machined so that the width of the heater was 4 mm and the length was 5 mm, and then the edge portion was chamfered by 0.2 mm.
[0049]
The durability of the heater is as follows. A voltage of about 25 V is applied between the heaters, the temperature is raised from room temperature to 1100 ° C. in about 20 seconds, and after maintaining at this temperature for 1 minute, the applied voltage is turned off and the heater is cooled to room temperature. Air cooled. With this temperature cycle as one cycle, the rate of breakage of the heater when this was repeated 100,000 times was determined. At this time, the number of samples was 10, respectively. Table 1 shows the results.
[0050]
[Table 1]

[0051]
From Table 1, it can be seen that the difference between the coefficient of thermal expansion of the heating element and the coefficient of thermal expansion of the insulating ceramic substrate exceeds 1.4 × 10 ⁻⁶ / ° C. 1 and sample no. 2 shows that the breakage rate is high.
[0052]
The sample No. whose difference was smaller than 0.8 × 10 ⁻⁶ / ° C. 6 and sample no. In No. 7, the alumina content exceeded 60% by volume, and the resistance of the heating element was so high that it was unsuitable as a heater. On the other hand, all of the products of the present invention were ceramic heaters having a low breakage rate of 50% or less and excellent durability.
[0053]
【The invention's effect】
As described in detail above, according to the present invention, it is possible to solve problems such as durability of a heater at a high temperature of a heating element and destruction due to thermal shock at the time of rapid temperature rise, and to achieve rapid temperature rise with a longer heater life. A possible ceramic heater can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic sectional view for explaining the structure of a ceramic heater.
FIG. 2 is a schematic sectional view for explaining an example of a ceramic heater of the present invention.
FIG. 3 is an exploded perspective view for explaining a method of manufacturing the ceramic heater of FIG. 2;
[Explanation of symbols]
1, 27a ... heating element 2 ... pad 3 ... through hole 4, 26 ... insulating ceramic substrate 22 ... solid electrolyte substrate 22a ... atmosphere introduction hole 23a ... reference electrode 24a ..Measurement electrode 25... Ceramic porous layer 20... Sensor part 21... Heater part

Claims (3)

A ceramic heater in which a heating element containing platinum as a main component is embedded in an insulating ceramic base containing alumina as a main component, wherein the heating element contains 30 to 60% by volume of alumina. Alumina is present as particles having an average crystal particle diameter of 0.2 to 1.0 μm, and the coefficient of thermal expansion of the heating element in the range of room temperature to 800 ° C. is 0.8 to 1 higher than that of the insulating ceramic substrate. A ceramic heater characterized in that it is larger by 4 × 10 ⁻⁶ / ° C. The ceramic heater according to claim 1, wherein the content of Na in the alumina is 50 ppm or less. A detection element comprising the ceramic heater according to claim 1.

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