JP2006190675A - Ceramic heating element, method of manufacturing heating element and method of using heating element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a ceramic heating element for heating a sensor element, especially, for measuring concentration of gas component in mixed gas, which has at least one resistive conductor path enclosed by electrically insulating ceramic material at least in a wide area, the resistive conductor path of which is improved so that the heating element has a long useful life and also is manufactured with ease at low cost. <P>SOLUTION: The resistive conductor path 24 has a cross section at least partially different from a rectangular. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The invention relates to a ceramic heating element, in particular for heating a sensor element for measuring the concentration of a gas component in a mixed gas, provided with at least one resistance conductor path, said resistance conductor path Relates to a type which is at least extensively surrounded by an electrically insulating material of ceramic, and to a method of manufacturing such a heating element and to the use of the heating element.

  Ceramic sensor elements for measuring the oxygen concentration in the exhaust gas of an internal combustion engine are known, these sensor elements are composed of a planar solid electrolyte body and are equipped with electromechanical pumps and / or Nernst cells. You may have.

  Since the ceramic solid electrolyte material has sufficient ionic conductivity only at high temperatures, the sensor element further comprises a ceramic heating element in the form of a resistive conductor path formed between the ceramic insulating layers. This heating element is used to heat the sensor element to an operating temperature of 750 to 800 ° C.

  For example, in order to obtain a rapid operational readiness of the sensor element during a cold start, it is required to achieve a short heating time. However, this is associated with a large heater current flowing through the resistive conductor track. If the resistive conductor track has a constriction due to manufacture, local overheating is caused there due to the increased electrical resistance of the resistive conductor track. Since the material used for the resistive conductor track usually has a positive temperature coefficient, the temperature in this region rises extremely. This can lead to cracks in the ceramic insulation surrounding the resistive conductor track. However, the ceramic insulation has an electrical breakdown resistance that is approximately 50 times higher than air, which can lead to sensor element failure due to crack formation. A similar effect can occur if the resistive conductor track has a local protrusion or tip. This is because the high electric field region is similarly overheated.

  In order to solve this problem, German Patent Publication No. 199446343 already discloses that when a heating element of a ceramic oxygen sensor is manufactured, a conductor layer forming a resistance conductor path is a layer of an insulating material. After the deposition, a rolling step is performed, and the rolling step pushes the conductor layer into the material of the insulating layer. In this manner, dispersion is prevented with respect to the electrical resistance of the resistance conductor path, and leakage current inside the oxygen sensor is suppressed.

Furthermore, as can be seen in German Patent No. 19716173, in order to check the functional suitability of the heating element, a leakage current test is carried out on the sensor element with the heating element, so that a defective heating element is detected. Removed.
German Patent Publication No. 19944633 Federal Republic of Germany Patent No. 19716173

  SUMMARY OF THE INVENTION An object of the present invention is to provide a heating element that exhibits a high service life and can be manufactured simply and inexpensively.

  In order to form a heating element according to the invention, or a resistive conductor track, in which the resistive conductor track has a cross section that differs at least partly from a square, on the substrate, with respect to the surface spread of the precursor material of the resistive conductor track The method according to the invention in which a plurality of different layers are deposited and the resulting layer composite is heat treated solves the problem underlying the invention in an advantageous manner.

  In this case, the heating element has a resistive conductor path with as few edges, corners or tips as possible. This is because the large electric field generated at these locations creates a risk of local overheating, which can damage the surrounding insulation. It is particularly advantageous if the resistive conductor track has a cross section that differs at least partially from the normal quadrangular cross section. In this manner, the formation of sharp edges is effectively prevented.

  By means of the dependent claims, advantageous developments and improvements of the sensor elements or methods according to the independent claims are possible.

  According to this, it is advantageous if the resistance conductor track has a circular or elliptical cross section over a wide area at least in a partial region, for example in the heating region, or at least partially chamfered. is there. This is because such a cross section is simple to implement and does not have sharp edges.

  In a particularly advantageous configuration of the invention, any platinum group metal other than platinum, for example rhodium, is added at least in the region of the resistance conductor track of the insulating part of the heating element. In this case, a concentration of 2 to 10 percent by weight is advantageously chosen, so that no significant increase in the electrical conductivity of the insulating material is observed. During heat treatment within the framework of the production of the heating element, the added platinum group metal diffuses into the structure of the pointed protrusions that occur, especially in the resistive conductor path, where the protrusions melt due to the eutectic point drop, As a result, it is flattened.

  In the production of the heating element, the substrate is advantageously coated with a plurality of layers of the precursor material of the resistance conductor track, which differ in terms of surface spread, and the resulting layer composite is subjected to a heat treatment. In this case, it is advantageous if the precursor material layer is formed differently with respect to the width extension in the direction perpendicular to the extension of the resistance conductor track to be formed. In this manufacturing method, an existing apparatus concept can be used.

  In an alternative form of manufacturing method, a resistive conductor track precursor material layer is deposited on a substrate to form a resistive conductor track, this layer is photostructured, and the optical structure of the applied layer The unstructured areas are etched away, in which case the remaining layer edges are side-edged and destroyed, and the resulting layer composite is then subjected to a heat treatment.

  Two embodiments of the invention will now be described in detail with reference to the drawings.

FIG. 1 shows the basic configuration of a heating element, for example as incorporated in a sensor element known from DE 199019556. The sensor element 10 includes, for example, a plurality of solid electrolyte layers 11a, 11b, and 11c having oxygen ion conductivity. In this case, the solid electrolyte layers 11a and 11c are formed in the form of a ceramic sheet, and form a planar ceramic body. The ceramic sheet is made of ZrO ₂ stabilized or partially stabilized by an oxygen ion conductive solid electrolyte material such as Y ₂ O ₃ .

  The solid electrolyte layer 11b is advantageously formed, for example, on the solid electrolyte layer 11a by screen printing of a paste-like ceramic material. In this case, the same solid electrolyte material as that constituting the solid electrolyte layers 11a and 11c is preferably used as the ceramic component of the paste-like material.

  An embedded form of the ceramic heating element 10 is produced by laminating a solid electrolyte layer 11b and a ceramic sheet printed with a functional layer and then sintering the laminated structure in a known manner. .

Furthermore, the heating element 10 has a resistance conductor path 24, which is incorporated in the solid electrolyte layer 11 b and is surrounded by an electrical insulating portion 26 made of Al ₂ O ₃ .

  During manufacture of the heating element 10, protrusions, tips 28, constrictions, or other geometric deviations may occur based on the manufacture. When a current flows through the resistance conductor path 24, local overheating is caused by the high electric field generated at the tips and the protrusions based on the electrical resistance increased at the narrow portion or at the point. Since the material used for the resistive conductor track 24 usually has a positive temperature coefficient, the temperature in this region rises extremely. This can lead to cracks in the ceramic insulation 26 surrounding the resistive conductor track 24 and the negative consequences mentioned at the outset.

  In order to prevent this problem, in the present invention, the resistance conductor path 24 does not have as sharp edges, corners or tips as possible. This means that the resistive conductor track 24 has at least partly a cross section that differs from a normal rectangular cross section, in particular in the region of high heating power of the heating element. In this manner, the formation of sharp edges is effectively avoided.

  A first embodiment of a heating element having this type of resistive conductor track is shown in FIG. In this case, the same reference numerals denote the same components as in FIG. The heating element shown in FIG. 2 has a resistance conductor track 24, which has a circular or elliptical cross section, for example rounded in the heating region of the heating element. Yes. In this case, the cross-section of the resistance conductor path 24 is selected as follows, that is, in the horizontal edge region, all surface areas of the resistance conductor path 24 are adjacent to the solid electrolyte layers 11a, 11b, 11c. Are selected to have as large a spacing as possible.

  Generally speaking, the cross section of the resistance conductor path 24 is selected as follows, that is, the virtual tangent line at two points located on the circumference of the cross section with a slight interval of less than 10 μm is Is selected to make an angle greater than 90 ° in any case.

  The extension of the resistance conductor track in the heating element is usually selected as follows, i.e. the resistance conductor track is selected in a meandering manner in the heating region of the heating element. In this case, an extension that is meandered but does not have corners or bends is selected.

  The stability and service life of the heating element described above is as follows. As shown schematically in FIG. When it is added, it can be further improved. In this case, a concentration of 2 to 10 percent by weight is preferably selected, so that no significant increase in the electrical conductivity of the insulating material is observed. Since this heating element is subjected to a heat treatment during the manufacture of the heating element, the added platinum group metal diffuses into the structure of the resistance conductor path 24 and the sharp protrusion that may occur in some cases. It melts there. The addition of the platinum group metal to the insulating portion 26a is performed, for example, by adding to the printing paste at the time of manufacturing the heating element, and the insulating portion 26a is formed from the paste by a plurality of printing steps. In this case, the addition of the platinum group metal is advantageously performed on the same paste as that forming the region near the resistance conductor path of the insulating portion 26a. Alternatively, a suspension containing a platinum group metal is printed on the solid electrolyte layers 11a, 11c or the insulating part 26a, or the insulating part 26a is soaked or impregnated with such a suspension. Is done.

  3b, 3c, 3d and 3e show a variation of the heating element shown in FIG. 3a in a cross-sectional view. In this case, FIGS. 3b and 3c show a cross section of the rounded resistance conductor path 24, and FIGS. 3d and 3e show the resistance conductor path 24 having at least one chamfer.

  In the manufacture of the heating element, the solid electrolyte layer 11c or 11a is preferably coated with different layers of the precursor material of the resistance conductor path 24 on top and bottom of each other and the resulting layer composite is subjected to a heat treatment. Is done. This procedure is clarified in FIG. 3e. In this case, first, the first layer 24a of the precursor compound of the resistance conductor path 24 is applied to the solid electrolyte layer 11a, and then the second layer 24b is applied. In this case, the second layer 24b is provided with a resistance In the vertical direction in the horizontal direction with respect to the extending direction of the conductor path 24, the surface area is larger than that of the first layer 24a. Next, the third layer 24 is provided in the second layer 24b, and this third layer 24c again exhibits a larger surface area than the second layer 24b. As soon as one or more layers (here 11c, 11d) with the largest surface spread are applied, the layer structure of the further layers 24e, 24f tapers down to the cover layer 24f. In the case of this manufacturing method, the existing apparatus concept can be used.

  In this case, the layers 24a, 24b, 24c, 24d, 24e, relative to each other between the first layer 24a or the last layer 24f to be deposited and the larger surface spreading layers 24c, 24d, The difference in the surface spread of 24f is selected in the range of 25 to 75 μm.

  According to an alternative form of the manufacturing method, at least one insulating layer 26 is first printed on the solid electrolyte layer 11a or 11c, and then the extension and shape of the resistance conductor path 24 are preliminarily formed in the insulating layer 26 by a stamping die. The concave portions formed in the insulating layer 26 are stamped and filled with the material of the resistance conductor path 24.

  According to another manufacturing option, in order to form a resistive conductor track, a solid electrolyte layer 11c or 11a is coated with a layer of a precursor material for the resistive conductor track, which is photostructured and applied. The unstructured regions of the layer are etched away, in which case the remaining layer edges are side-etched and destroyed, and the resulting layer composite is then subjected to a heat treatment.

  The manufacturing methods described above can be arbitrarily combined with each other within the framework of the present invention.

  While the heating element according to the invention and the method of manufacturing the heating element can be used in electrochemical sensor elements used for measuring gases, for example oxygen, nitric oxide, sulfur oxides, ammonia, hydrocarbons. However, it can also be used in other heatable devices of the ceramic type, for example glow plugs or particulate filters. For this purpose, the layer structure shown in FIGS. 2 and 3a may have another solid electrolyte layer, insulating layer or functional layer.

1 is a cross section of a heating element according to the prior art. 1 is a cross-sectional view of a sensor element according to a first embodiment of the present invention. 3a is a cross-sectional view of a sensor element according to a second embodiment of the present invention, and FIGS. 3b, 3c, 3d, and 3e are cross-sectional views showing variations of the heating element shown in FIG. 3a. .

Explanation of symbols

  10 heating element, 11a, 11b, 11c solid electrolyte layer, 24 resistance conductor path, 24a, 24b, 24c, 24d, 24e, 24f layer, 26, 26a insulation, 28 point

Claims (11)

  In particular, it is a ceramic heating element for heating a sensor element for measuring the concentration of a gas component in a mixed gas, and is provided with at least one resistance conductor path (24). 24), in which the resistive conductor track (24) is at least partly different from a quadrangle in the form of being at least extensively surrounded by a ceramic electrically insulating material (26, 26a) A ceramic heating element characterized by comprising:   Heating according to claim 1, wherein the cross section of the resistive conductor track (24) is configured in a broad circle or ellipse, or the resistive conductor track (24) has at least partially chamfers. element.   The cross-section of the resistance conductor track (24) is constructed as follows: the tangents at two points located on the circumference of the cross-section at a distance slightly smaller than 10 μm are independent of the point selection. 3. A heating element according to claim 1 or 2, wherein in any case, the angle is greater than 90 [deg.].   4. A heating element as claimed in claim 1, wherein the resistance conductor track (24) has a non-angular extension at least in the heating region of the heating element.   The heating element according to any one of claims 1 to 4, wherein the insulating material (26a) contains a platinum group metal other than platinum at least in the region of the resistance conductor path (24).   6. A heating element according to claim 5, wherein the platinum group metal content is up to 2 to 10 weight percent.   A method for manufacturing a ceramic heating element according to any one of claims 1 to 6, wherein the heating element is provided with at least one resistance conductor path (24), the resistance conductor path (24). ) Is at least extensively surrounded by a ceramic electrically insulating material (26, 26a) in order to form a resistive conductor track (24), the substrate (11a, 11c) A plurality of layers (24a, 24b, 24c, 24d, 24f) of the precursor material of the resistance conductor path (24), which are different in terms of surface spread, are attached to each other, and the resulting layer composite is subjected to heat treatment. A method for manufacturing a ceramic heating element according to any one of claims 1 to 6.   8. The method according to claim 7, wherein the layers (24a-24f) of precursor material are formed differently with respect to the width extension perpendicular to the extension of the resistive conductor track (24) to be formed.   The first and last deposited layers (24a, 24f) of the precursor material are more perpendicular to the extension of the resistive conductor track (24) to be formed than the intermediate layers (24c, 24d) of the layer composite to be formed. 9. A method according to claim 7 or 8, wherein the direction has a width spread which is smaller by 25 to 75 [mu] m.   10. A method of manufacturing a ceramic heating element according to claim 1, wherein the heating element is provided with at least one resistance conductor path (24), the resistance conductor path (24). ) Is at least extensively surrounded by a ceramic electrically insulating material (26, 26a) in order to form a resistive conductor track (24), the substrate (11a, 11c) Deposit a layer of precursor material for resistive conductors, photostructure the layer, etch away uncoated areas of the applied layer, side etch the remaining layer edges, and destroy 10. A method for producing a ceramic heating element according to claim 1, characterized in that the resulting layer composite is then subjected to a heat treatment.   7. The method of using a heating element according to claim 1, wherein the heating element is used in a sensor for measuring oxygen in exhaust gas from an internal combustion engine. Use of the heating element according to claim 1.

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