JP2006222008A - Ceramic heater and heater-built-in electronic component - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a ceramic heater excellent in durability at high temperature, restrained from generation of crack at the periphery of lead wiring, and to provide a heater-built-in electronic component provided with the ceramic heater. <P>SOLUTION: The ceramic heater is excellent in durability at high temperature, and capable of restraining generation of crack at the periphery of the lead wiring because stress generated by a volume expansion reaction of alkali metal like Na accumulated at a specific temperature area of the lead wiring is lowered by arranging an expansion relieving layer on the ceramic layer using direct current. Namely, the expansion relieving layer is arranged at least at a part of the surface of the lead wiring at the neighboring area of the boundary between the heater and the lead wiring, on the ceramic heater formed by embedding a heater circuit composed of the pair of lead wiring arranged in parallel with each other, and the heater integrally connected to the lead wiring so as to electrically connect the pair of lead wiring. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a ceramic heater excellent in durability and suitably used for heating a semiconductor substrate heater, a petroleum fan heater, and an oxygen gas sensor for a vehicle.

  Conventionally, a ceramic heater in which a heating element is embedded in an insulating substrate made of an insulating ceramic such as alumina is known (see, for example, Patent Document 1). In addition to a heater for a semiconductor substrate, a hot water heater or an oil fan is known. It is used as a heater.

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 amount of air and fuel 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 NO _x is employed.

  As this detection element, a solid electrolyte type oxygen sensor is used in which a pair of electrode layers are respectively formed on the outer surface and the inner surface of a solid electrolyte substrate mainly composed of zirconia having oxygen ion conductivity.

  A typical oxygen sensor includes a ceramic heater in which a reference electrode and a measurement electrode are provided on the outer and inner surfaces of a flat solid electrolyte substrate, and at the same time a platinum heating element is embedded in the ceramic insulator. An integrated oxygen sensor has been proposed (see, for example, Patent Documents 2 and 3).

The oxygen sensor in which the above ceramic heater is integrated has an advantage that the detection part is rapidly heated to a high temperature of 800 to 1000 ° C. by being directly heated by the ceramic heater.
JP-A-3-149971 JP 2002-540399 A JP 2002-236104 A

  However, when the ceramic heater is used in a high temperature environment exceeding 1000 ° C. using DC current, or when the heater is heated rapidly, the lead wiring near the heating element of the lead wiring that becomes negative voltage is compared. There was a problem that cracks occurred around the lead wiring held at a low temperature (600 to 900 ° C.), and the ceramic heater was damaged in the worst case.

For example, the ceramic heater shown in FIG. 8 includes a heater circuit 105 including a pair of lead wirings 105a and a heating element 105b connected to connect the pair of lead wirings 105a inside the ceramic base 1. When the heater circuit 105 is heated by applying a direct current to the heater circuit 105, a crack 110 is gradually generated in the vicinity of the boundary with the heating element 105b of the negative lead wiring. Therefore, the present invention is excellent in durability at high temperatures. At the same time, it is an object of the present invention to provide a ceramic heater in which cracks are unlikely to occur from around the lead wiring and a heater built-in electronic component including the ceramic heater.

  The present invention reduces the stress caused by the volume expansion reaction of alkali metals such as Na accumulated in a specific temperature region of the lead wiring by providing an expansion relaxation layer in the ceramic heater using a direct current. A ceramic heater that is excellent in durability, does not generate cracks from the periphery of the lead wiring, and has a small change in the resistance value of the lead wiring, and a heater built-in electronic component including the ceramic heater can be realized.

  That is, the ceramic heater of the present invention is integrally connected to the lead wiring so as to electrically connect the pair of lead wirings and the pair of lead wirings arranged in parallel in the ceramic layer. In a ceramic heater in which a heater circuit comprising a heating element is embedded, an expansion relaxation layer is provided on at least a part of the surface of the lead wiring near the boundary with the heating element.

  In particular, the expansion relaxation layer is preferably composed of a porous layer.

  The expansion relaxation layer is preferably a void.

  It is preferable that the gap is formed in a slit shape between the heater circuit and the ceramic layer.

  The maximum width of the slit-shaped gap is preferably 10 nm or more.

  It is preferable that the gap is formed at a side end portion of the lead wiring.

  The gap is preferably formed within 200 μm from the lead wiring.

  After energizing the heater circuit for 100 hours or more and heating the heating element to a temperature of 1000 ° C. or more, the Na content is preferably 10 to 300 ppm in terms of oxide in the vicinity of the boundary of the lead wiring.

  The ceramic layer preferably contains at least one of alumina, aluminum nitride, silicon nitride, zirconia, and forsterite as a main component.

  It is preferable that the heating element and the lead wiring are mainly composed of at least one of tungsten, gold, silver, and platinum.

  The distance between the pair of lead wires is preferably 0.5 mm or more.

From the boundary between the lead wires and the heating element, to the maximum distance d _h to the end of the heating side of the expansion buffer layer, and the maximum distance d _L to the end of the lead wire side of the expansion buffer layer the ratio _d L / _{d h} of is preferably 0.5 to 8.

  Further, the electronic component with built-in heater according to the present invention is characterized in that the ceramic heater is built in and an electric element is mounted on a portion heated by a heating element of the ceramic heater.

  The electrical element is preferably a sensor.

  In general, ceramic powder for industrial use contains several tens to several hundred ppm of Na, and an additive such as a binder or platinum powder contains an alkali metal and an alkaline earth metal such as Na. In the ceramic heater manufacturing process, alkali metals such as Na and Ca and alkaline earth metals are mixed in the ceramic as sweat and other impurities.

  The inevitable metal contained in the ceramic porcelain moves to the negative electrode along the electric field existing in the ceramic porcelain as ions, and the ions that have reached the negative electrode and the inevitable metal contained in the heater circuit become ions in the electric field of the heater circuit. And move from the positive electrode to the negative electrode and reach the negative lead wiring. In particular, the moving speed of the region heated by the heating element is high. However, since it becomes difficult to move ions at a low temperature, the ions are accumulated in a specific temperature region of 600 to 900 ° C. of the lead wiring.

  In this way, Na ions are concentrated in the specific temperature region of the negative lead wiring, and at the same time, Na ions cause a chemical reaction accompanied by volume expansion such as oxidation. This volume expansion is considered to cause cracks in the conventional ceramic heater. According to the present invention, the expansion relaxation layer provided on the surface of the lead wiring can relieve the stress generated by the above volume expansion, and as a result, the breakage of the lead wiring can be effectively performed at a rapid temperature rise. Can be prevented.

  As described above, the expansion relaxation layer in the present invention can absorb the volume expansion of the lead wiring and can relieve the generated stress. Specifically, it indicates a void, a porous layer, and the like. It is.

  According to the present invention, Na is surprisingly expected to have the same effect on cations such as alkali metals such as Mg and alkaline earth metals.

  A ceramic heater according to an embodiment of the present invention will be described as an example.

  FIG. 1 is a transparent perspective view of a ceramic heater of the present invention, and also shows a heater circuit formed therein. FIG. 2 is a cross-sectional view taken along line X-X ′ in FIG. 1.

  In the ceramic heater of the present invention, a heater circuit 5 comprising a heating element 2 and a lead wire 3 electrically connected to the heating element 2 and supplying a current to the heating element 2 is embedded in a ceramic substrate 1. ing. A pair of electrode pads 6 for connecting to external wiring are provided on the surface of the ceramic substrate 1, and each is connected to each lead wiring 3 through a through-hole conductor 7.

  According to the present invention, it is important to provide the expansion relaxation layer 4 on at least a part of the surface of the lead wiring 3. As shown in FIG. 2, the expansion relaxation layer 4 may be an inclusion-type expansion relaxation layer 4 a formed so as to cover the lead wiring 3, or may be formed on a part of the surface of the lead wiring 3. The partial formation type expansion relaxation layer 4b may be used.

  In the expansion relaxation layer 4, at least one of alkali metal and alkaline earth metal is accumulated in a portion corresponding to a specific temperature region of the lead wiring 3, and causes a chemical reaction accompanied by volume expansion. It is important to have an absorbing structure.

  For example, as the expansion relaxation layer 4, a void, a porous layer, and a combination thereof can be used. The specific example is shown in FIG. According to FIG. 3A, a slit-like gap 4 c is provided as the expansion relaxation layer 4 between the ceramic substrate 1 and the lead wiring 3. The slit-shaped gap 4 c is preferably formed on at least one surface of the lead wiring 3.

In particular, by setting the maximum width L _p to 10 nm or more, particularly 20 nm or more, 50 nm or more, even if the lead wiring 3 expands, the volume corresponding to the expansion can be easily ensured. The stress can be further reduced to effectively suppress the generation of cracks. Further, as shown in FIG. 3B, the same effect can be expected even when a plurality of gaps 4d are formed discontinuously on the surface of the lead wiring 3.

  In particular, as shown in FIG. 3 (c), when the corners of the lead wire 3 are formed at the side ends in the major axis direction, the extension in the major axis direction due to volume expansion is large, which is very effective. Cracks can be suppressed. Further, as shown in FIG. 3D, the lead wiring 3 and the part 1a of the ceramic base may be in close contact, and a gap 4f may be formed between the part 1a of the ceramic base and the ceramic base 1. . In particular, it is preferable that the gap 4f is formed within 200 μm, particularly within 150 μm, and further within 100 μm from the lead wiring 3.

The length L _c of the gap 4e formed on the side end portion of the lead wire 3, 200 [mu] m or less for the gap 4e is less likely to be a starting point of fracture, especially 150μm or less, and more preferably to 100μm or less. Also, since to achieve the above effect of the air gap 4e effectively, or 1μm length _{L c} of the gap 4e, particularly 2μm or more, more preferably at least 5 [mu] m. As the width _{L w} of the gap 4c, usually becomes maximum in the vicinity of the end of the lead wire, 0.1 to 10 [mu] m or less, desirably in particular is 1 to 5 [mu] m.

When only the gap 4e at the side end portion in the major axis direction of the lead wiring 3 is used as the expansion relaxation layer 4,
Preferably, setting the length _{L c} of the gap 4e to 20 to 100 [mu] m. In the present invention, the length Lc of the air gap is defined as the maximum length of the air gap 4e existing on the side end face of the lead wiring at four locations in the cross section.

  In the cross-sectional view as shown in FIG. 3, the ratio β of the total cross-sectional area of the expansion relaxation layer 4 to the cross-sectional area of each lead wiring 3 is 0.01 to 10%, particularly 0.1 to 5%, and further 0.5. It is preferably ˜2%. The area ratio is appropriately set within the above range depending on the content of alkali metal and alkaline earth metal contained in the ceramic heater, whereby the stress generated by volume expansion can be reduced.

  For example, when a plurality of gaps 4d are provided on the surface of the lead wiring 3 as shown in FIG. 3B, the section is cut in a direction perpendicular to the longitudinal direction of the ceramic heater, and the cross section is polished into a mirror surface. The polished surface can be photographed with a manipulation electron microscope (SEM), and the cross-sectional area of each gap can be calculated by image analysis, and the sum can be set as the area ratio β. In the case where a combination of a porous layer and voids is used as the expansion relaxation layer 4, the total ratio of the total area of the porous layer and the total area of the voids can be set as the ratio β.

  Further, in the case where the thermal expansion coefficient difference of the lead wiring 3 is larger than that of the ceramic substrate 1, the temperature of the lead wiring 3 rises before the ceramic substrate 1 when a temperature cycle with rapid temperature rise is given. Since the volume change of the lead wiring 3 is larger than the volume change of the base body 1, the difference in the volume change can be absorbed, and the effect of preventing the generation of cracks in the lead wiring 3 and the breakage of the ceramic heater can be achieved. it can.

  The cross-sectional shape of the lead wiring 3 is not limited to an elliptical shape, and may be a semi-elliptical shape obtained by cutting an ellipse in half from the center, a circular shape, a semicircular shape, a rectangular shape, or a shape made of another curved surface. Also good.

  FIG. 4 is a partial plan view of the ceramic heater of the present invention, and shows the heater circuit 5 formed inside. Alkali metals and alkaline earth metals, particularly Na, in the porcelain reach the negative electrode along the electric field along the negative electrode direction (see arrow in the figure). When it reaches the negative electrode, it reaches the lead wiring from the heating element along the electric field of the heater circuit (refer to the arrow in the figure), and further moves along the electric field in the lead wiring. Since it becomes extremely low, ions are concentrated in the temperature region of 600 to 900 ° C. of the lead wiring.

  Therefore, the expansion relaxation layer 4 formed on a part of the surface of the lead wiring 3 corresponding to the negative electrode is set at a portion heated to 600 to 900 ° C. where alkali metal such as Na or alkaline earth metal is concentrated. Good to do. Specifically, although it depends on the shape of the heater circuit 5, the cross-sectional area ratio between the heating element 2 and the lead wiring 3, the material, etc., in general, the boundary with the heating element 2 as shown in FIG. It is preferable to set in the vicinity.

Moreover, in order to improve symmetry or to suppress warping during sintering, it can be formed other than the surface of the lead wiring 3 serving as a negative electrode. For example, as shown in FIG. 4B, the heater circuit can be formed between the lead wire 3a serving as the negative electrode and the lead wire 3b serving as the positive electrode and in the vicinity thereof. Further, in addition to the side surface of the lead wiring 3, it can be formed around the heating element as long as it does not depart from the gist of the present invention. In that case, the width _{d H} of the heating side from the boundary between the heat generating element 2 and the lead wire 3 is, the range where the ratio of the width _{d L} of the lead wire side _d H / _{d L} does not exceed 1.0, particularly 0.8 or less Further, it is preferably 0.5 or less.

  Furthermore, the formation region of the expansion relaxation layer 4 may be formed on the entire lead wiring, or may be expanded around the heating element pattern. For example, it may extend from the boundary between the lead wiring and the heating element to a range of about 2 to 5 mm toward the heating element.

  In FIG. 5B in which the vicinity T of the boundary in FIG. 5A is enlarged, there is a tapered portion at the boundary portion between the heating element 2 and the lead wiring 3, but in view of the gist of the present invention, the tapered portion. Since the temperature is lower because the resistance is lower than the temperature of the heating element 2, the tapered portion can be regarded as a part of the lead wiring 3. That is, the part indicated by the arrow in FIG. 5B can be regarded as the boundary Bo.

  According to the present invention, when the heater circuit 5 is energized and heated for a total of 100 hours or more so that the temperature of the heating element portion 2a composed of a region having a substantially uniform resistance value is 1000 ° C. or higher. The Na content in the concentrated portion Ct near the boundary of the lead wiring 3a is preferably set to 10 to 300 ppm in terms of oxide, particularly the upper limit is set to 100 ppm or less, and more preferably 50 ppm or less. Thereby, the volume expansion amount can be reduced, the generated stress can be further reduced, and the region of the expansion relaxation layer can be reduced.

  The ceramic substrate 1 is preferably made of a ceramic mainly composed of at least one of alumina, silicon nitride, aluminum nitride, zirconia, silicon carbide, titania, cordierite, spinel, and forsterite. In particular, alumina is preferable in terms of low cost and excellent oxidation resistance, silicon nitride is preferable in terms of high strength, aluminum nitride is preferable in terms of high thermal conductivity, and zirconia is highly insulating in terms of high toughness. Forsterite is preferred in terms of sex.

  As the heating element 2 and the lead wiring 3, one or more metals, alloys, or compounds selected from platinum, gold, silver, tungsten, molybdenum, rhodium, ruthenium, and palladium can be used as appropriate. Among these, platinum and gold are preferable in terms of inertness, and tungsten is preferable in terms of a high melting point and a thermal expansion coefficient close to that of ceramics.

Moreover, insulating ceramics, such as an alumina, can be contained as a co-material.

  Further, the heating element and the lead wiring are each composed mainly of platinum, and further contains alumina. The contained alumina has a role of preventing the resistance from changing due to sintering of platinum at a high temperature during sintering or energization. Although it depends on the use of the ceramic heater, both the heating element and the lead wiring have excellent alumina contents of 5 to 45% by volume, particularly 20 to 40% by volume.

  In addition, the shape (pattern) of the heating element is not particularly limited. From the viewpoint of uniformly printing the thickness of the heating element and the ability to form the heating element 5 at a high density, the viewpoint of excellent temperature rise performance. Therefore, the heating element is preferably a folded heating element pattern with respect to the longitudinal direction of the ceramic heater, as shown in FIG.

  From the viewpoint of preventing heat generation in the lead wiring, it is preferable to increase the resistance value by adding ceramics in the heating element. For example, in the heating element, at least the same amount as the alumina content of the lead wiring, preferably It is desirable to increase the resistance of the heating element by increasing the alumina content in the heating element.

  When the alumina content of the heating element is different from that of the lead wiring, the alumina content of the heating element is 30 to 40% by volume and the lead wiring is 20 to 25% by volume. Adjust the resistance ratio between the heating element and the lead wiring. It is preferable from the viewpoint of easy.

  According to the present invention, the distance between adjacent lead wires is preferably 0.5 mm or more, particularly 1 mm or more, and more preferably 1.5 mm or more from the viewpoint of suppressing the diffusion of Na. Below that, there is little effect of weakening the electric field between adjacent lead wires, and it becomes difficult to suppress the diffusion of Na.

  The ceramic heater shown in FIG. 1 is capable of rapid temperature rise and is not easily damaged by rapid temperature rise. The outer dimensions are preferably a width of 2 to 3.5 mm and a thickness of 0.5 to 2 mm. Among them, a width of 2.5 to 3.2 mm and a thickness of 1 to 1.5 mm show particularly excellent performance.

Further, the heater pattern formed by heating elements symmetric (e.g., see the center line Z ₁ in FIG. 5) be in the laminated surface of the heating element is formed, the heat distribution is symmetrical, Since the temperature distribution of the ceramic heater element can be made symmetric and thermal stress can be prevented from being biased, it can be suitably used.

  Next, a method for producing the ceramic heater of the present invention will be described.

  Next, a manufacturing method of the ceramic heater 1 of the present invention shown in FIG. 1 at the interface between the lead wiring and the ceramic insulating layer will be described in detail below.

  First, a ceramic green sheet is produced. As the ceramic raw material powder, for example, when preparing an alumina green sheet, for the alumina raw material powder having an average particle size of 0.2 to 3 μm, an organic binder for molding and a doctor blade method by adding a solvent, It is produced by a known method such as extrusion molding, isostatic pressing (rubber press) or press formation.

  A binder is added to a mixed powder of a conductive powder such as platinum and a ceramic material such as alumina powder on the surface of the obtained ceramic green sheet to produce a printing paste, and a lead wiring pattern to be a heating element pattern and a lead wiring is formed. Form.

  Next, a void forming layer or a porous forming layer serving as an expansion relaxation layer is formed on at least a part of the surface of the lead wiring. As a method for forming the porous forming layer, a paste obtained by adding alumina or spinel powder to an acrylic resin, polyvinyl butyral resin, or the like, or a paste using an organic binder containing a pore forming agent such as fine powder carbon is preferably used. be able to. These can form a porous layer after firing.

  As a method for forming the void forming layer, a pore forming material that is thermally decomposed during degreasing or firing can be used. Thereby, voids can be formed after degreasing or after firing. If desired, a predetermined amount of these pore forming materials can be printed and applied to at least a part of the surface of the lead wiring pattern to be a lead wiring near the heating element to form an expansion relaxation layer.

  As another method for forming the gap forming layer, a recess is formed in the green sheet in advance, and the recess is laminated so as to contact the lead wiring pattern, and a gap is formed between the green sheet and the wiring pattern. You can also.

  Furthermore, as a method of forming the voids as shown in FIG. 3 (c), when obtaining the green sheet, by adjusting the binder and the plasticizer, for example, the Young's modulus is increased to 500 to 800 MPa and the deformation is performed. If a sheet that is difficult to fabricate is produced, a heater pattern is printed using the sheet, and lamination is performed at a weak pressure (for example, 50 to 200 MPa) in a later-described lamination process, a corner-like void is formed at the side edge of the lead wiring. Is possible.

  Next, on the green sheet formed with the heating element pattern, the lead wiring pattern, and the expansion relaxation layer formed in this manner, another green sheet provided with a molded body to be a through conductor or an extraction electrode is laminated as desired. To do.

  In forming the through conductor, first, a through hole having a desired size is formed in the green sheet. Next, the through hole is filled with a conductive paste made of a mixed powder of platinum and alumina and a binder to form a through conductor molded body having a through conductor.

  Next, the conductor paste is printed so as to cover the through conductor molded body, and the extraction electrode molded body to be the extraction electrode is produced. These conductor pastes can be formed by printing by screen printing, pad printing, or roll transfer.

  Thereafter, a green sheet having a lead wiring pattern to be a lead wiring, and a green sheet having a through conductor molded body to be a through conductor and a takeout electrode molded body to be a takeout electrode are laminated, and the obtained laminate is obtained. By firing, the ceramic heater element of the present invention can be produced.

  In order to suppress deformation of the green sheet during lamination, the thickness of the heating element pattern, lead wiring pattern, and extraction electrode molded body is preferably 20 μm or less and 15 μm or less as measured by a grind gauge.

  The shape of the ceramic heater may be long and flat, as well as cylindrical or elliptical. For example, FIG. 6 shows the structure of a cylindrical ceramic heater, FIG. 6 (a) is a perspective view, and FIG. 6 (b) is a cross-sectional view taken along line Y-Y 'in FIG. 6 (a). According to FIG. 6, a plurality of green sheets are wound around the surface of the cylindrical insulator 21a to form an insulating layer 21b, and a heater circuit including a heating element and a lead wiring 23 is formed inside the insulating layer 21b. The circuit is electrically connected to the electrode pad 26. An expansion absorption layer 24 is formed around the lead wiring 23.

  The electronic component with a built-in heater according to the present invention includes the above-described ceramic heater and has an electronic element mounted on a portion heated by a heating element of the ceramic heater. Next, an oxygen sensor with a built-in ceramic heater will be described as an example of an electronic component with a built-in heater.

FIG. 7 shows the structure of the oxygen sensor. As shown in FIG. 7A, the electronic element B is integrally formed on the ceramic heater A. Ceramic heater A is made from the heater of Figure 5 is intended FIG. 7 (a) corresponds to a cross-sectional view of the distal end near the Z ₂ of the heating element, FIG. 7 (b) is a sectional view in the Lead wires Z ₃ It is equivalent to.

  According to FIG. 7, the electronic component with built-in heater according to the present invention includes the ceramic heater A therein, the heating element 32 is embedded in the base 31, and the electronic element is positioned at a position heated by the heating element 32. B is installed.

  The electronic element B is rapidly provided by providing an oxygen sensor unit composed of a solid electrolyte substrate 36 and a pair of platinum-based electrodes 37a and 37b disposed so as to sandwich the solid electrolyte substrate 36. The oxygen gas sensor is excellent in reliability and capable of raising the temperature.

  The oxygen gas sensor includes a lead wire for a heating element embedded in a ceramic insulating layer, and a flat plate-like ceramic heater A having an air introduction hole 35 with a sealed tip, and a flat plate-like ceramic heater A. A solid electrolyte substrate 36 made of zirconia and having oxygen ion conductivity, a reference lead wiring of a reference electrode 37a in contact with air formed on both opposing surfaces of the solid electrolyte substrate 36, and, for example, an oxygen concentration of exhaust gas A detection lead wiring of the measurement electrode 37b in contact with the measurement gas is formed.

  According to the present invention, as described above, it is important to form the expansion relaxation layer around the lead wiring where the alkali metal such as Na or the alkaline earth metal is concentrated.

  In addition, the expansion | swelling relaxation layer shown in FIG.7 (b) can use a space | gap or a porous layer, and the shape is any of (a), (b), (c) and (d) of FIG. It goes without saying that can be adopted.

  A reference lead wire and a detection lead wire (both not shown) are connected to the reference electrode 37a and the measurement electrode 37b, and oxygen is measured by measuring an electromotive force generated between the reference electrode 37a and the measurement electrode 37b. The function as a gas sensor can be expressed. That is, oxygen molecules become oxygen ions on the surface of the zirconia ceramic on the oxygen concentration side (reference gas side) and move toward the oxygen concentration side (exhaust gas side). On the other hand, on the surface of the zirconia ceramic on the side with a low oxygen concentration (exhaust gas side), a reaction that tends to change from oxygen ions to oxygen molecules occurs. At this time, electrons are required to become ions on the high concentration side, and conversely, on the low concentration side, the oxygen gas is used, so electrons are unnecessary, and electrons tend to flow from the exhaust gas side toward the reference gas side. Potential is generated. By capturing this potential, it is possible to sense whether there is a difference between the oxygen concentrations on both sides.

  The oxygen gas sensor includes a heating element 32 embedded in a ceramic base 31 and a flat plate-shaped hollow ceramic heater A having an air introduction hole 35 whose tip is sealed, and is made of flat plate zirconia. The solid electrolyte substrate 36 having oxygen ion conductivity, the reference electrode 37a that is in contact with air, and the measurement electrode 37b formed on both opposing surfaces of the solid electrolyte substrate 36, and the function of detecting the oxygen concentration. The sensor part which it has is integrated.

  Further, as shown in FIG. 7A, a ceramic porous layer 38 for protecting the measurement electrode 37b can be formed on the measurement electrode 37b.

  Next, the ceramic base 31 constituting the ceramic heater A and the electronic element B of the present invention may be composed of a dense ceramic made of alumina ceramic having a relative density of 90% or more, particularly 95% or more. desirable.

  In addition, by setting the relative density within the above range, the strength of the insulating base 1 and the ceramic heater element 9 is increased, so that the mechanical strength of the oxygen gas sensor itself can be increased.

Moreover, in the oxygen gas sensor which is an electronic component with a built-in heater according to the present invention, the solid electrolyte 31 is made of a ceramic containing ZrO ₂ , and Y ₂ O _3, 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 of, preferably partially stabilized ZrO ₂ or stabilized ZrO ₂ containing 3 to 15 mol% It is used. Further, by using ZrO ₂ in which 1 to 20 atomic% of Zr in ZrO ₂ is substituted with Ce, there is an effect that the ionic conductivity is increased and the responsiveness is further improved. Furthermore, for the purpose of improving the sinterability, Al ₂ O ₃ and SiO ₂ can be added to ZrO ₂ , but if it is contained in a large amount, the creep properties at high temperatures deteriorate, The total amount of Al ₂ O ₃ and SiO ₂ added is preferably 5% by mass or less, particularly 2% by mass or less.

  The reference electrode 37a and the measurement electrode 37b deposited on the surface of the solid electrolyte substrate 36 are both platinum alone or an alloy of platinum and one selected from the group of rhodium, palladium, ruthenium and gold. It is desirable to form using. Further, for the purpose of preventing the growth of metal grains in the electrode during the operation of the oxygen gas sensor and the purpose of increasing the contact at the so-called three-phase interface between platinum particles, solid electrolyte, and gas related to responsiveness, The electrolyte component may be mixed in the electrode at a ratio of 1 to 50% by volume, particularly 10 to 30% by volume. Further, the electrode shape may be a quadrangle or an ellipse. The thickness of the electrode is preferably 3 to 20 μm, particularly preferably 5 to 10 μm.

  The porous ceramic layer 38 formed on the surface of the measuring electrode 37b is made of zirconia, alumina, γ-alumina, titania and spinel having a thickness of 10 to 1500 μm, particularly 100 to 500 μm and a porosity of 10 to 50%. It is desirable to be formed of a ceramic containing at least one selected from the group. As a result, the electrode poisoning substances P, Pb, Si and the like are difficult to reach the electrode, so that the electrode performance is stable and the gas responsiveness can be maintained.

  In addition, regarding the integration of the ceramic heater and the sensor portion, the sintered body may be bonded with glass or the like after being manufactured by sintering the ceramic heater and the sensor portion. It is also possible to produce a sintered body in which the ceramic heater and the sensor unit are integrated by simultaneous firing after forming a molded body including the ceramic heater and the sensor unit in advance.

  Next, a method for manufacturing the above oxygen gas sensor will be described.

  First, a solid electrolyte green sheet is prepared. This green sheet is prepared by adding a forming organic binder, as appropriate, to a ceramic solid electrolyte powder having oxygen ion conductivity of zirconia, for example, by a doctor blade method, extrusion molding, isostatic pressing (rubber press) or It is produced by a known method such as press forming.

  The obtained green sheet is cut into a desired size, and a pattern serving as a measurement electrode and a reference electrode, a lead wiring pattern serving as a lead wiring connected to the measurement electrode and the reference electrode, and an electrode pad on both sides of the green sheet, respectively. A through hole or the like is printed and formed by screen printing, pad printing or roll transfer using, for example, a conductive paste containing platinum, and a sensor unit is manufactured.

  On the other hand, a green sheet made of an insulating ceramic material is produced. The obtained green sheet is cut into a desired size, and a pattern that becomes a heating element and a lead wiring, an extraction electrode pad, a through hole, etc. are used on both sides of the green sheet, for example, using a conductive paste containing platinum. Then, printing is performed by screen printing, pad printing, and roll transfer, and a heater portion is manufactured.

  Then, a void forming layer or a porous forming layer serving as an expansion relaxation layer is formed on at least a part of the lead wiring pattern. Specifically, the method is the same as the method for manufacturing the expansion relaxation layer of the ceramic heater. For example, an organic binder (polyvinyl butyral resin or the like) is applied as the void forming layer, and resin beads are used as the porous forming layer. A porous slurry made of a ceramic material can be formed by printing.

  The ceramic heater portion is manufactured according to the above-described ceramic heater manufacturing method. However, in the oxygen gas sensor, it is necessary to form an air introduction hole for supplying air to the reference electrode. The air introduction hole may be mechanically bonded to an alumina green sheet previously punched or the like, with an adhesive such as an acrylic resin or an organic solvent interposed therebetween, or with pressure applied by a roller or the like. .

  After this, the laminated body of the sensor unit and the ceramic heater unit is bonded and integrated by interposing an adhesive such as an acrylic resin or an organic solvent, or by mechanically bonding the two while applying pressure with a roller or the like, These are fired. Firing is performed in the air or in an inert gas atmosphere at a temperature range of 1300 ° C. to 1700 ° C. for 1 to 10 hours. Note that, during firing, the amount of warpage can be reduced by placing a substrate of high-purity smooth alumina or the like as a weight on the laminate in order to suppress warping of the sensor portion during firing.

  Further, when the sensor unit and the laminated body of the ceramic heater unit are simultaneously fired and integrated, in order to reduce the generation of stress due to the difference in thermal expansion coefficient between them, for example, the solid electrolyte component forming the sensor unit It is desirable to interpose a composite material of an insulating component forming a ceramic insulating layer of the ceramic heater portion.

  Thereafter, if desired, the surface of the measurement electrode after firing may be a porous ceramic material containing at least one ceramic selected from the group consisting of alumina, zirconia, and spinel by plasma spraying, dipping, printing, tape attaching, or the like. By forming the mass layer 38, an oxygen gas sensor in which the ceramic heater portion A is integrated can be formed.

  In the above method, the case where the ceramic heater A and the electronic element B are formed by simultaneous firing has been described. However, after the ceramic heater A and the electronic element B are fired separately from each other, an appropriate inorganic material such as glass is used. It is also possible to integrate by bonding with a bonding material.

  The ceramic heater of the present invention can also be suitably used as an oxygen gas sensor, for example, an oxygen gas sensor such as a NOx sensor and a CO sensor in addition to an oxygen sensor.

  A ceramic heater using the slit-shaped gap of FIG. 3A as an expansion relaxation layer was produced.

  A slurry is prepared by adding an acrylic binder and toluene to an alumina powder (containing 0.1% by mass of silica) having a purity of 99.9% and an average particle diameter of 0.2 μm. The thickness is 0 by a doctor blade method. An alumina green sheet having a thickness of 2 mm was prepared.

  Next, a through hole was formed at a predetermined position of the green sheet with a punch die.

  Next, a mixed powder containing 60% by volume of platinum powder having an average particle diameter of 1 μm and 20% by volume of alumina powder having an average particle diameter of 0.5 μm in this through-hole is mixed with an acrylic binder and terpineol (hereinafter simply referred to as “pure powder”). A conductive paste prepared by mixing three rolls of TPO) was filled by screen printing.

Next, an acrylic binder and TPO are mixed with three rolls into a mixed powder containing 60% by volume of platinum powder having an average particle diameter of 1 μm and 40% by volume of alumina powder having an average particle diameter of 0.5 μm. A conductive paste for a heating element was produced. On the other hand, mixed lead powder containing 65% by volume of platinum powder having an average particle diameter of 1 μm and 35% by volume of alumina powder having an average particle diameter of 0.5 μm is mixed with an acrylic binder and TPO by three rolls. A conductive paste for wiring was prepared. Using these two types of conductive paste, a conductive paste for a heating element was first formed on the surface of an alumina green sheet so that the resistance value at room temperature after firing was about 8Ω. The heating element was screen printed using the conductive paste for lead wiring, and the lead wiring was screen printed so as to overlap the heating element pattern to form a ceramic heater pattern. The ceramic heater pattern was ideally formed after firing as shown in FIG.

  Next, a pattern to be a lead wiring and a pattern to be a take-out electrode were formed on the front and back surfaces of a green sheet provided with a ceramic heater pattern and a molded body to be a through conductor using the conductive paste.

  Next, sample No. The expansion relaxation layer was formed about 2-19. Sample No. In Nos. 2 to 7 and 16 to 19, an organic binder (polyvinyl butyral resin) is placed on the lead wiring pattern so that the shape of the void formed around the lead wiring after firing is as shown in FIG. Printed by screen printing. At this time, slurries with different binder solid contents were printed by screen printing so as to be in the range of FIG.

  Sample No. 8 to 10 are the same as the ceramic sheet serving as the ceramic substrate and 20% by volume of acrylic beads (particle size: 5 μm) as a pore-forming agent in the organic binder in order to form a void whose void shape is as shown in FIG. A paste having a composition mixed powder of 80% by volume was prepared with three rolls, and the paste was printed on the pattern of the lead wiring by screen printing.

  Furthermore, sample no. In Nos. 11 to 14, an organic binder (acrylic resin) was printed by screen printing on the end portion of the lead wiring pattern in order to form a void in which the shape of the void was as shown in FIG.

  Furthermore, sample no. 15, a slurry for forming a ceramic sheet to be a ceramic base is printed on the lead wiring in order to form a void in which the shape of the void is as shown in FIG. 3D, and an organic binder ( (Polyvinyl butyral resin) was printed on the pattern of the lead wiring by screen printing.

  And the laminated body used as a ceramic heater element was produced by laminating | stacking five sheets of the alumina green sheets on the upper surface of these ceramic heater element patterns using the allyl binder.

  Next, this laminate was fired in the atmosphere at 1500 ° C. for 2 hours.

  After this firing step, the sintered body was cut so that the external dimensions were 3 mm wide and 40 mm long.

  In this way, a fold test was performed on the manufactured ceramic heater element so that a load was applied to the portion where the thermal cycle test and the void were formed.

  In addition, the size of the lead wiring gap is mirrored on the lead wiring cross section of the ceramic heater, photographed with a scanning electron microscope, the top five of the largest gaps are selected, and the average value is the maximum gap. The size of The void shapes were classified into FIGS. 3A to 3D and simply indicated by (a), (b), (c), and (d), respectively.

In addition, while measuring the maximum width L _p of the gaps in FIGS. 3A and 3D, the area ratio β in FIG. 3B, the gap length L _c and the gap width L _w in FIG. for the maximum distance d _h to the end of the heating side of the expansion buffer layer was measured ratio d _{L /} d _h and the lead wiring distance K between the maximum distance d _L to the end of the lead wire side of the expansion buffer layer .

  In the ceramic heater element thermal cycle test, a voltage of about 25 V was applied between the ceramic heater elements, the temperature was raised from room temperature to 1100 ° C. in about 20 seconds, held at this temperature for 1 minute, and then the applied voltage was turned off. The temperature cycle of air-cooling the ceramic heater element to room temperature was taken as one cycle, and the breakage rate of the ceramic heater element when this was repeated 100,000 times was determined. At this time, 50 samples were used. The bending strength was measured by measuring the load at which the ceramic heater element was damaged in a three-point bending test at a span of 20 mm and a crosshead speed of 0.5 mm / min.

  Further, after energizing for 100 hours and heating the heating element to a temperature of 1000 ° C. or higher, the Na content was measured by ICP analysis near the boundary of the lead wiring.

  As a comparative example, a conventional ceramic heater having no gap around the lead wire was also produced. However, the conventional ceramic heater having no gap around the lead wire contains a pore forming agent to form the gap. Except for the step of applying an organic binder, it was prepared in the same manner as in the examples.

The results are shown in Table 1.

  Sample No. of the present invention. Nos. 2 to 19 had breakage rates of 30% or less in the high-speed temperature rise durability test.

  On the other hand, Sample No. No. 1 had a high breakage rate of 80%.

  Therefore, it was found that the ceramic heater of the present invention has a remarkably high high-speed temperature rise property, reliability, mechanical strength, and handleability.

  An oxygen gas sensor was fabricated as an electronic component with a built-in heater.

  First, a slurry is prepared by adding an acrylic binder and toluene to an alumina powder (containing 0.1% by mass of silica) having a commercial purity of 99.9% and an average particle size of 0.2 μm. An alumina green sheet having a sheet thickness of 0.2 mm was prepared.

  Next, a through hole was formed at a predetermined position of the green sheet with a punch die.

  Next, a mixed powder containing 60% by volume of platinum powder having an average particle diameter of 1 μm and 40% by volume of alumina powder having an average particle diameter of 0.5 μm in this through hole, three acrylic binders and TPO. The conductive paste produced by roll mixing was filled by screen printing.

  Next, an acrylic binder and TPO are mixed with three rolls into a mixed powder containing 60% by volume of platinum powder having an average particle diameter of 1 μm and 40% by volume of alumina powder having an average particle diameter of 0.5 μm. A conductive paste was prepared, and a ceramic heater element pattern having a resistance value of about 8Ω at room temperature after firing was printed on the surface of an alumina green sheet by screen printing.

  Next, a pattern to be a lead wiring and a pattern to be a take-out electrode were formed on the front and back surfaces of a green sheet provided with a ceramic heater element pattern and a molded body to be a through conductor using the conductive paste.

  Next, sample No. An expansion relaxation layer was formed for 20-38. Sample No. 21-26 and 35-38 are screened with an organic binder (polyvinyl butyral resin) on the pattern of the lead wiring so that the shape of the void formed around the lead wiring after firing is as shown in FIG. Printed by printing. At this time, slurries with different binder solid contents were printed by screen printing so as to be in the range of FIG.

  Sample No. Nos. 27 to 29 are the same as the ceramic sheet as the ceramic base, and 20% by volume of acrylic beads (particle size: 5 μm) as a pore forming agent in the organic binder in order to form a void whose void shape is as shown in FIG. A paste having a composition mixed powder of 80% by volume was prepared with three rolls, and the paste was printed on the pattern of the lead wiring by screen printing.

  Furthermore, sample no. In Nos. 30 to 33, an organic binder (acrylic resin) was printed on the end portions of the lead wiring pattern by screen printing in order to form a void having a void shape as shown in FIG.

  Furthermore, sample no. 34, a slurry for forming a ceramic sheet to be a ceramic substrate is printed on the lead wiring in order to form a void in which the shape of the void is as shown in FIG. 3D, and an organic binder ( (Polyvinyl butyral resin) was printed on the pattern of the lead wiring by screen printing.

  A punched green sheet was also prepared by punching a portion corresponding to an air introduction hole having a width of 1.4 mm and a height of 0.5 mm after firing with a die punch.

  Then, 5 layers of the alumina green sheet and 3 punched green sheets are laminated on the upper surface of the green sheet on which the ceramic heater element pattern and the organic binder are printed, using an allyl binder, to obtain a ceramic heater element. Was made.

  On the other hand, a slurry is prepared by adding an acrylic binder and toluene to partially stabilized zirconia (yttria 5 mol) having an average particle size of 0.2 μm, and the sheet thickness is reduced to 0.25 mm by the doctor blade method. A solid electrolyte green sheet was prepared.

  A conductive paste prepared by mixing 20% by volume of the above zirconia powder and 80% by volume of platinum powder having an average particle diameter of 1 μm with three rolls of an acrylic binder and TPO was prepared. A detection electrode, a reference electrode, and a lead wiring pattern were printed on the front and back surfaces of the green sheet by screen printing.

  Further, an alumina paste containing 50% by volume of the pore forming agent having an average particle diameter of 5 μm was applied to the surface of the detection electrode to form a protective layer. Thereafter, an allyl binder was applied between the surface of the zirconia green sheet on which the pattern serving as the reference electrode was provided and the surface on which the space serving as the air introduction hole of the ceramic heater element was formed. And an oxygen gas sensor laminate was obtained.

  Next, this laminate was fired in the atmosphere at 1500 ° C. for 2 hours.

  After the firing step, the sintered body was cut so that the outer dimensions were 3 mm wide and 40 mm long, and the edge portion was processed.

  Thus, the thermal cycle test and the bending load were measured with respect to the produced oxygen gas sensor.

  The ratio of the cross-sectional area S2 of the air gap to the cross-sectional area S1 of the heating element was calculated by image processing by taking a mirror image of the cross section of the heating element of the oxygen gas sensor and taking a photograph with a scanning electron microscope.

  In the thermal cycle test of the oxygen gas sensor, a voltage of about 25 V was applied to the heating element, the temperature was raised from room temperature to 1100 ° C. in about 20 seconds, and held at this temperature for 1 minute. The temperature cycle in which the element was air-cooled to room temperature was defined as one cycle, and the breakage rate of the ceramic heater element was determined when this was repeated 100,000 times. At that time, the number of samples was 50.

  The bending load was measured by measuring the load at which the oxygen gas sensor was damaged in a three-point bending test at a span of 20 mm and a crosshead speed of 0.5 mm / min.

  As a comparative example, a conventional oxygen gas sensor having no gap around the lead wiring was produced.

  A conventional oxygen gas sensor having no void around the lead wiring was prepared in the same manner as in Example 4 except that the step of applying an organic binder containing a pore forming agent was removed to form the void.

  The same evaluation as the case of the ceramic heater element was performed about the produced sample.

The results are shown in Table 2.

  Sample No. of the present invention. Nos. 21 to 38 had breakage rates of 30% or less in the high-speed temperature rise durability test.

  On the other hand, Sample No. No. 20 had a high breakage rate of 80%.

  Therefore, it was found that the oxygen gas sensor of the present invention is remarkably excellent in high-speed temperature rise performance, reliability, mechanical strength, and handleability.

(A) It is a permeation | transmission perspective view of the ceramic heater of this invention. It is an expanded sectional view in X-X 'of the ceramic heater of FIG. It is another expanded sectional view in X-X 'of the ceramic heater of FIG. It is a schematic plan view of the ceramic heater of this invention. It is explanatory drawing which shows the heater circuit of the ceramic heater of this invention. The structure of the other ceramic heater of this invention is shown, (a) is a perspective view, (b) is sectional drawing in Y-Y 'of Fig.6 (a). 1 shows a structure of an oxygen gas sensor which is an example of an electronic component with a built-in heater according to the present invention, in which FIG. It is a top view of the conventional ceramic heater.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 31 ... Ceramic base | substrate 2, 32 ... Heat generating body 2a ... Heat generating body part 3, 33 ... Lead wiring 4, 34 ... Expansion relaxation layer 4a ... Inclusion type expansion relaxation layer 4b: Partially formed expansion relaxation layer 4c to 4f ... Air gap 5 ... Heater circuit 6 ... Electrode pad 7 ... Through-hole conductor 35 ... Air introduction hole 36 ... Solid electrolyte Substrate 37a ... Reference electrode 37b ... Measurement electrode 38 ... Ceramic porous layer A ... Ceramic heater B ... Electronic element T ... Boundary Bo ... Boundary Ct ... Concentration part

Claims (14)

A heater circuit comprising a pair of lead wires arranged in parallel on the ceramic layer, and a heating element integrally connected to the lead wires so as to electrically connect the pair of lead wires. In the embedded ceramic heater, an expansion relaxation layer is provided on at least a part of the surface of the lead wiring in the vicinity of the boundary with the heating element. The ceramic heater according to claim 1, wherein the expansion relaxation layer is made of a porous layer. The ceramic heater according to claim 1, wherein the expansion relaxation layer is a void. 4. The ceramic heater according to claim 3, wherein the gap is formed in a slit shape between the heater circuit and the ceramic layer. The ceramic heater according to claim 4, wherein a maximum width of the slit-shaped gap is 10 nm or more. 4. The ceramic heater according to claim 3, wherein the gap is formed at a side end portion of the lead wiring. The ceramic heater according to claim 6, wherein the gap is formed within 200 μm from the lead wiring. The heater circuit is energized for 100 hours or more, and after heating the heating element to a temperature of 1000 ° C. or more, the Na content is 10 to 300 ppm in terms of oxides in the vicinity of the boundary of the lead wiring. The ceramic heater according to claim 1. The ceramic heater according to any one of claims 1 to 8, wherein the ceramic layer is mainly composed of at least one of alumina, aluminum nitride, silicon nitride, zirconia, and forsterite. The ceramic heater according to any one of claims 1 to 9, wherein the heating element and the lead wiring are mainly composed of at least one of tungsten, gold, silver, and platinum. The distance between said pair of lead wiring is 0.5 mm or more, The ceramic heater in any one of Claims 1-10 characterized by the above-mentioned. From the boundary between the lead wires and the heating element, to the maximum distance d _h to the end of the heating side of the expansion buffer layer, and the maximum distance d _L to the end of the lead wire side of the expansion buffer layer The ceramic heater according to claim 1, wherein the ratio d _L / d _h is 0.5 to 8. An electronic component with a built-in heater, wherein the ceramic heater according to any one of claims 1 to 12 is built in and an electric element is mounted on a portion heated by a heating element of the ceramic heater. The heater built-in electronic component according to claim 13, wherein the electric element is a sensor.

Images